Articles de revues : « B cell lymphoma, Chronic Lymphocytic Leukemia, B lymphocytes, mouse models »

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Collins, Ryan, Prabhjot Kaur, Olga Danilova, James Direnzo et Alexey V. Danilov. « p53 Homolog TAp63 elicits apoptosis in Chronic Lymphocytic Leukemia (CLL) B-Cells »,. Blood 118, n^o 21 (18 novembre 2011) : 3894. http://dx.doi.org/10.1182/blood.v118.21.3894.3894.

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Abstract Abstract 3894 p63 is a p53 homolog whose function depends on the cellular context. The full-length TAp63 variant may carry an anti-oncogenic potential in solid tumor models, where it mediates Ras-induced cellular senescence, antagonizes tumorigenesis and suppresses the development of metastases. In hepatoma cells TAp63 is involved in activation of both extrinsic and intrinsic apoptosis pathways. By contrast, ΔNp63, an amino-terminally truncated p63 variant, is oncogenic in tumors of squamous cell origin. TAp63 is the predominantly expressed p63 isoform in lymphoid malignancies. Increased expression of TAp63 in diffuse large B-cell lymphoma confers an unfavorable prognosis. In CLL TAp63 was shown to mediate B-cell homing to the bone marrow, thus possibly contributing to apoptosis evasion. We studied expression of p63 in CLL and determined whether p63 plays a role in CLL B-cell survival and sensitivity to chemotherapy. We enrolled 25 previously untreated subjects with B-CLL at the Norris Cotton Cancer Center (Lebanon, NH). CLL B-cells were isolated from peripheral blood with standard Ficoll-Hypaque technique and purified using a B-cell (CLL) Isolation Kit. Small interfering RNA against p63 were delivered using Lonza Nucleofector with transfection efficiency of 20–50% and viability of 60–80% at 24 h. Viability was enhanced when cells were cocultured with “feeder cells”. To test sensitivity to chemotherapy, cells were treated with 10 μM chlorambucil and 5 μM fludarabine for 48–72 h. For apoptosis analysis cells were stained with Annexin V and 7-AAD and assayed by flow cytometry. Five lymph node tissues were analyzed for p63 expression by immunohistochemistry using a mouse monoclonal p63 antibody (clone 4A4). Of 25 CLL patients 15 were males (60%). Median age was 61 years. Median follow up was 3 years. Most patients presented in Rai stage 0–1 (92%). TAp63 mRNA transcripts were expressed in all CLL samples, while ΔNp63 variant was not detected. TAp63α was the predominantly expressed splicing variant. A C-terminally truncated TAp63γ variant was detected at a low level. TAp63 mRNA transcript levels were higher in CLL B-cells than in normal B-cells, but 10- to 100-fold lower than in high-grade lymphoma cell lines. Of five lymph nodes analyzed, weak nuclear p63 staining was detected in one. In this small cohort, p63 expression in the peripheral blood CLL B-cells did not correlate with ZAP-70 expression. CD38-positive (>30%) CLL samples expressed higher TAp63 mRNA transcript levels (p<0.05). siRNA knockdown of p63 in CLL cells resulted in protection from spontaneous apoptosis at 24–48 h, which persisted when cells were cultured on a “feeder layer”. Furthermore, p63 knockdown conferred protection against chlorambucil and fludarabine. B-cell receptor crosslinking with IgM resulted in a 2.5-fold repression of TAp63 transcription, consistent with the pro-survival role of a B-cell receptor in CLL. Thus, TAp63α is the predominantly expressed p63 variant in the peripheral blood CLL cells. TAp63a contributes to the intrinsic apoptosis program in CLL and may play a role in sensitizing CLL B-cells to standard chemotherapy drugs. Disclosures: No relevant conflicts of interest to declare.

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Byrd, John C. « Therapeutic Targeting of B-Cell Receptor Signaling Pathways ». Blood 120, n^o 21 (16 novembre 2012) : SCI—27—SCI—27. http://dx.doi.org/10.1182/blood.v120.21.sci-27.sci-27.

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Abstract Abstract SCI-27 Targeted therapy in hematologic malignancies has achieved significant therapeutic success when relatively selective inhibition is attainable to a target dispensable to the majority of normal cells. The best appreciated example of this is imatinib in chronic myeloid leukemia (CML), in which a single translocation forms a fusion protein involving the tyrosine kinase ABL that molecularly defines the disease. Kinase inhibition of ABL in this setting by imatinib (or other second- and third-generation kinase inhibitors) promotes durable, long-term remission in CML patients. The great majority of B-cell malignancies lack a characteristic translocation, activating mutation, or other aberration that facilitates such targeted therapy as employed in CML. Nonetheless, a common global signaling pathway involving the B-cell receptor (BCR) pathway has emerged as one that might be important to the control of these diseases. Furthermore, mouse models of select kinase targets (phosphoinositide-3 kinase p110 isoform-delta and Bruton's tyrosine kinase [BTK]) have shown that these are dispensable relative to long-term survival. Indeed, knockout or mutation of BTK and p110 delta each have a modest phenotype outside of diminished B-cell development and function. Based upon these preclinical observations, several molecules targeting BCR signaling have come forward to the clinic with exciting results across a wide range of B-cell malignancies. GS-1101 is a selective phosphoinositide-3 kinase p100 delta inhibitor with a very favorable toxicity profile that has shown promising clinical activity in low-grade lymphoma and chronic lymphocytic leukemia (CLL). The toxicity of this orally administered agent is quite modest in the majority of patients and allows sustained continuous dosing. Similarly, ibrutinib is an irreversible inhibitor of BTK and has shown promising clinical potential in an even broader range of B-cell malignancies, including diffuse large B-cell lymphoma, mantle cell lymphoma, low-grade lymphoma, and CLL. Toxicity with ibrutinib has also been modest, allowing long-term continuous dosing. Notably, each of these agents also produces an atypical mobilization of malignant lymphocytes into the blood soon after treatment. This treatment lymphocytosis is BCR-target-related due to diminished CXCR4/SDF-1 interface between tumor cells and stromal cells in the bone marrow, with egress of these cells to the blood. GS-1101 and ibrutinib are now entering phase III studies for regulatory approval and offer great potential to change the treatment paradigm of both CLL and B-cell non-Hodgkin lymphoma (NHL). Questions moving forward with these agents will include molecular predictors of response, feasibility and efficacy of combining with other effective therapies, and mechanisms of resistance. The scientific session presentation will provide an overview of the most promising BCR signaling agents in CLL and NHL clinical trials. Disclosures: No relevant conflicts of interest to declare.

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Paoluzzi, Luca, Mithat Gonen, Govind Bhagat, Richard R. Furman, Jeffrey R. Gardner, Luigi Scotto, Volodia D. Gueorguiev, Mark L. Heaney, Katia Manova et Owen A. O'Connor. « The BH3-only mimetic ABT-737 synergizes the antineoplastic activity of proteasome inhibitors in lymphoid malignancies ». Blood 112, n^o 7 (1 octobre 2008) : 2906–16. http://dx.doi.org/10.1182/blood-2007-12-130781.

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Abstract Overexpression of antiapoptotic members of the Bcl-2 family is observed in approximately 80% of B-cell lymphomas, contributing to intrinsic and acquired drug resistance. Nullifying the antiapoptotic influence of these proteins can potentially overcome this resistance, and may complement conventional chemotherapy. ABT-737 is a BH3-only mimetic and potent inhibitor of the antiapoptotic Bcl-2 family members Bcl-2, Bcl-XL, and Bcl-w. In vitro, ABT-737 exhibited concentration-dependent cytotoxicity against a broad panel of lymphoma cell lines including mantle cell lymphoma (MCL) and diffuse large B-cell lymphoma (DLBCL). ABT-737 showed synergism when combined with the proteasome inhibitors bortezomib or carfilzomib in select lymphoma cell lines and induced potent mitochondrial membrane depolarization and apoptosis when combined with either. ABT-737 plus bortezomib also induced significant apoptosis in primary samples of MCL, DLBCL, and chronic lymphocytic leukemia (CLL) but no significant cytotoxic effect was observed in peripheral blood mononuclear cells from healthy donors. In severe combined immunodeficient beige mouse models of MCL, the addition of ABT-737 to bortezomib enhanced efficacy compared with either drug alone and with the control. Collectively, these data suggest that ABT-737 alone or in combination with a proteasome inhibitor represents a novel and potentially important platform for the treatment of B-cell malignancies.

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Walker, Janek S., Casey B. Cempre, Jordan N. Skinner, Brandi R. Walker, John C. Byrd et Rosa Lapalombella. « Simultaneous Disruption of XPO1 and A20 in Murine B Cells Influences Both B and T Cell Repertoire ». Blood 138, Supplement 1 (5 novembre 2021) : 1542. http://dx.doi.org/10.1182/blood-2021-152777.

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Abstract Introduction & Objectives: Efforts to characterize the heterogeneity of advanced hematologic malignancies using large-scale genomic studies have identified recurrent monoallelic mutations affecting the E571 residue of the essential nuclear exporter, Exportin-1 (XPO1; E571K in ~80% of cases, E571G in ~15% of cases). E571-XPO1 mutations alter the charge and structural basis of the cargo-binding region, disrupting critical biophysical interactions between XPO1 and its' cargos. Enriched in hematologic malignancies, E571-XPO1 mutations are predominantly reported in chronic lymphocytic leukemia (CLL; 5-10% of cases), classical Hodgkin's lymphoma (~25% of cases), and primary mediastinal B cell lymphoma (PMBCL; 25-30% of cases). The subsequent change in XPO1-cargo localization alters the transcriptional profile and overall phenotype of the leukemic cell, with evidence suggesting hyper-active NF-κB and NFAT signaling pathways as leading leukemogenic mechanisms. Moreover, while overall immune dysfunction in CLL leads to infections as a major cause of morbidity and mortality, CLL patients with E571-XPO1 mutations are more susceptible to death by infection, suggesting these mutations may exacerbate the leukemia-induced immunosuppressive phenotype. Similarly, inactivating mutations/deletions to A20 (TNFAIP3 gene), the master regulator of NF-κB, are recurrently reported in several B cell malignancies but most frequently observed in PMBCL (~30% of cases). E571-XPO1 mutations and TNFAIP3 deletions/mutations have been found as co-occurring genetic abnormalities in PMBCL, and while TNFAIP3 mutations in CLL are rare, functional convergence on NF-κB and immune signaling suggests altered XPO1 and A20 activity may have unreported pathogenic significance in CLL. Thus, we aimed to explore the oncogenic and immunologic consequence of co-occurring XPO1 and A20 abnormalities by evaluating a novel in-vivo model recapitulating this scenario. Methods: To explore concurrent aberrations to XPO1 and A20, we developed a novel mouse model to recapitulate this event (Eµ-XPO1xA20 KO). This model was generated by crossing the Eµ-XPO1 transgenic mouse - which overexpresses wildtype (WT), E571K, or E571G-XPO1 under control of a VH promoter-IgH-Eµ enhancer to target transgene expression to immature and mature B cells - with a B cell-specific A20 inactivation mouse (A20 KO) - which lacks functional A20 as a result of Cre recombinase-mediated excision of TNFAIP3 exon 3 via loxP recombination sites flanking this region and Cre recombinase expressed under CD19 promoter/enhancer elements. Eµ-XPO1 and Eµ-XPO1xA20 KO mice were aged and followed, and their B and T cell repertoire was assessed via flow cytometry. Results & Conclusion: We previously demonstrated Eµ-XPO1 mice develop a CLL-like disease (CD19+/CD5+/B220dim B lymphocytes), but leukemia development is significantly delayed - evident between 20-30 months of age. Preliminary analysis in adolescent animals revealed irregular lymphocyte populations as early as 6 months of age in the blood and spleen of Eµ-XPO1xA20 KO mice when compared to non-transgenic and Eµ-XPO1 mice; highlighted by elevated populations of CD93+/CD23+ transitional B cells and CD3+ T cells, and reduced populations of CD21+/IgM+ marginal zone B cells. Moreover, development of a circulating CLL-like disease accompanied by palpable lymphadenopathy and splenomegaly was observed in Eµ-XPO1xA20 KO mice as early as 17-20 months of age, again presenting a distinct immunophenotype inconsistent with that observed in Eµ-XPO1 mice. Additionally, progressive accumulation of CD3+/CD19- T cell leukemia-like populations were observed in a subset of Eµ-XPO1xA20 KO and A20 KO mice, indicating these aberrations may further disrupt and stimulate uncontrolled proliferation affecting the overall immune repertoire. Significance: We report that simultaneous disruption of essential regulators XPO1 and A20 in murine B cells encourages development of irregular B and T cell populations, and can stimulate a progressive CLL-like or T cell leukemia-like expansion. Continued investigation with these models can further our understanding of the relationship between overall immune function and these critical regulatory molecules, and can provide considerable insight to identifying pathways for selective targeting as a personalized therapy in several high-risk cancer types. Disclosures Byrd: AstraZeneca: Consultancy; Takada: Consultancy; Novartis: Consultancy; Pharmacyclics: Consultancy; Syndex: Consultancy; Trillium: Consultancy; Vincera Pharmaceuticals: Current equity holder in publicly-traded company.

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ElGamal, Dalia, Yiming Zhong, Katie Williams, Chia-Hsien Wu, Ching-Shih Chen, Rosa Lapalombella et John C. Byrd. « PKC Inhibitor AEB071 Demonstrates Pre-Clinical Activity In Chronic Lymphocytic Leukemia ». Blood 122, n^o 21 (15 novembre 2013) : 4187. http://dx.doi.org/10.1182/blood.v122.21.4187.4187.

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Abstract Targeting B-cell receptor (BCR) downstream pathways is of therapeutic importance in eradicating chronic lymphocytic leukemia (CLL) cells. Members of the protein kinase C (PKC) family play an important role in B-cell activation. PKC-β has recently been shown to be over-expressed in CLL and essential to CLL development in the TCL1 mouse model. Mice deficient in PKC-β exhibit a survival defect in response to BCR stimulation, correlating with an inability to induce the NF-κB-dependent anti-apoptotic proteins as Bcl-xL and A1. Moreover, PKC-β-dependent activation of NF-κB in stromal cells is pivotal for the survival of B-CLL cells in vivo; wherein PKC-β inhibition was shown to prevent microenvironment protection of CLL. Additionally, PKC-β lies downstream of PLC-γ2 where activating mutations have been noted in BTK (ibrutinib) resistant patients, which conveys a potential mechanism to target resistance related to mutations in this target protein. Therefore exploration of a PCK-β inhibitor in CLL is highly justified and innovative. Sotrastaurin (AEB071) is an orally administered potent inhibitor of classical and novel PKC isotypes; with strong and specific activity on PKC-α, PKC-β and PKC-θ and lesser activity on PKC-δ, PKC-ε, and PKC-η. Pre-clinically, AEB071 has demonstrated in vivo pre-clinical activity in activated B-cell diffuse large B-cell lymphoma (DLBCL) models and is currently being tested for efficacy in CD79b mutated DLBCL. Since PKC-β is indispensable for BCR-induced NF-κB activation and B-cell survival, herein we evaluate the impact of AEB071 on CLL cell survival as a promising therapeutic to target this pathway. Our preliminary work demonstrated that AEB071 was markedly cytotoxic to CLL cells in a dose-dependent (≤6.25uM, p<0.001) and time-dependent manner (p=0.011) as measured by MTS analysis. In a whole blood assay, AEB071 exhibits a retained selective cytotoxicity against tumor cells with a modest reduction in B-CLL cells whereas no effect on T-cells or natural killer cells was detected in CLL patient samples. Notably, upon treatment of blood from healthy subjects, AEB071 showed no toxic effects on normal B-cells, T-cells and natural killer cells. AEB071 inhibits CPG-induced survival of CLL cells in vitro (p<0.01), and effectively blocks the protection induced by soluble factors such as CD40L, IL-4, and TNF (p<0.01), which are known to reduce the spontaneous apoptosis associated with CLL cells. Similar effects were observed with stromal cell contact; wherein AEB071 showed enhanced cytotoxic potency on CLL cells under co-culture conditions with stromal cells compared to CLL alone (p<0.05). Additionally, AEB071 attenuated anti-IgM-induced survival of CLL cells with a modest induction of apoptosis (p<0.001). Furthermore, treatment of PMA- or BCR-activated CLL cells with AEB071 could effectively abrogate downstream survival pathways including ERK1/2, p38MAPK, AKT, GSK3β, and NF-κB as revealed by immunoblot analysis. Collectively, this data indicate that therapeutic strategies to inhibit PKC-β have the potential to disrupt signaling from the microenvironment that lead to in vivo CLL cell survival and potentially drug resistance. Current studies are ongoing to evaluate the in vivo tolerability and therapeutic efficacy of AEB071 in the Eμ-TCL1 transgenic mouse model of CLL. In conclusion, PKC-β represents an innovative target for CLL and therefore, future efforts targeting PKC with the PKC inhibitor AEB071 as monotherapy in clinical trials of relapsed and refractory CLL patients may be warranted. Disclosures: No relevant conflicts of interest to declare.

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Ghia, Paolo, Maria TS Bertilaccio, Cristina Scielzo, Giorgia Simonetti, Benedetta Apollonio, Claudia Fazi, Marta Muzio, Maurilio Ponzoni et Federico Caligaris-Cappio. « Novel Mouse Models of Chronic Lymphocytic Leukemia (CLL) Unravel the Molecular Mechanisms Controlling Bone Marrow Involvement by Leukemic B Cells. » Blood 114, n^o 22 (20 novembre 2009) : 360. http://dx.doi.org/10.1182/blood.v114.22.360.360.

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Abstract Abstract 360 In CLL, the bone marrow (BM) represents a typical site of involvement and relapse, suggesting a preferential homing of leukemic cells to this anatomical site compared to other lymphoid organs, though the mechanisms controlling CLL cell migration and accumulation within the BM are unclear. In order to define the rules driving in vivo CLL cell re-circulation between the blood and tissutal compartments, we specifically generated two different mouse models and investigated the role played by HS1; this molecule, other than being a putative prognostic factor in CLL, is also involved in cytoskeleton reorganization of lymphocytes, and, potentially, in the control of cellular shape, migration and homing. First, we established a novel transplantable xenograft murine model of CLL by engrafting the cell line MEC1 into RAG2-/-γc-/- mice, at a variance with previous studies in nude mice where MEC cells failed to engraft. Likely due to the lack of B, T and NK cells (while nude mice retain NK cells), RAG2-/-γc-/- animals were successfully transplanted with the CLL cell line through either subcutaneous or intravenous routes, resulting in a systemic blood and tissutal involvement. When subcutaneous MEC1 cells silenced for HS1 expression were injected in these animals, we observed a preferential localization in the tumor draining axillary and inguinal lymph nodes and especially in the BM, when compared to controls. As we have previously demonstrated that CLL cases with hyper-phosphorylated HS1 show a worse clinical outcome, we took advantage of this mouse model to investigate the in vivo homing ability of primary CLL cells from patients showing different HS1 phosphorylation patterns. Purified leukemic cells from 4 patients with hyper-phosphorylated HS1 were labeled with high concentration of the dye CSFE, and each sample was paired and admixed with purified CLL cells obtained from patients with low levels of HS1 phosphorylation and separately labeled with low CSFE concentration. Each pair of samples was injected i.v. into RAG2-/-γc-/- mice recipients. When we analyzed the different organs of the animals by flow-cytometry, the differential expression of CFSE fluorescence (CFSE-high vs CFSE-low) allowed us to distinguish between the two leukemic cell populations with opposite HS1 phosphorylation status. In 3/4 experiments, CLL cells with hyper-phosphorylated HS1 revealed a preferential homing to the BM. Based on these results and on the in vitro evidence that B lymphocytes from HS1-/- mice have an impaired spontaneous migration, we have crossed HS1-/- (H-/-) mice with the Eμ-TCL1 transgenic (Ttg) mouse, an animal model that between 13 and 18 months of age develops a disease resembling human CLL. In the H-/-/Ttg mice, monoclonal CD19+CD5+ cells became evident earlier (at 7-13 months of age) and in significantly higher proportion as compared to Eμ-TCL1 transgenic mice. Cells preferentially localized in the BM where leukemic cells are usually observed at low frequencies in the Eμ-TCL1 mouse (mean value: 28%±16 vs 5%±2, respectively, p=0,008). These findings suggest that HS1 may have a relevant role in both normal and leukemic B-cells and in particular is crucial for cell migration, through its involvement in cytoskeleton organization. Accordingly, we also provide evidence that, in the absence of HS1, cells fail to form actin-myosin complexes, leading to an instability of the cell signalling complex. Our findings suggest a relationship between the expression of HS1 and the development and progression of CLL, most notably in terms of BM involvement, indicating that specific abnormalities in the cytoskeleton organization may be pivotal in regulating leukemic migration and infiltration in selected anatomical sites. This points at HS1 as a target for development of novel cancer treatments, aiming at interfering with the lymphoid tissue infiltration and invasion which is characteristic of the disease. In addition, these animal models could become very useful for evaluating the biological basis of CLL growth and dissemination as well as the efficacy of new therapeutic agents. Disclosures: No relevant conflicts of interest to declare.

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Kuo, Hsu-Ping, Sidney Hsieh, Jennifer Whang, Yujun Huang, Mint Sirisawad et Betty Y. Chang. « Ibrutinib Potentiated NK Cell-Mediated Cytotoxicity in Mouse Models of B-Cell Lymphomas ». Blood 128, n^o 22 (2 décembre 2016) : 4140. http://dx.doi.org/10.1182/blood.v128.22.4140.4140.

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Abstract Background: Ibrutinib, a first-in-class, once-daily oral inhibitor of Bruton's tyrosine kinase (BTK), is indicated by the US FDA for the treatment of patients with chronic lymphocytic leukemia/small lymphocytic lymphoma, including patients with deletion 17p, patients with mantle cell lymphoma who have received at least 1 prior therapy, and patients with Waldenström's macroglobulinemia. In addition to blocking B-cell activation via inhibition of BTK signaling, ibrutinib was reported to modulate immune function by driving TH1 response through IL-2-inducible T-cell kinase (Dubovsky, Blood 2013). Ibrutinib was also shown to reprogram macrophages toward a TH1 phenotype that fostered CD8+ T-cell cytotoxicity in pancreas ductal adenocarcinoma-bearing mice (Gunderson, Cancer Discov 2016). Both the direct and indirect effects on TH1 response may play a role in the therapeutic efficacy of ibrutinib in models of lymphoma and solid tumors (Sagiv-Barfi, PNAS 2015). Another essential component of the immune system with a role against cancer is natural killer (NK) cells involved in the recognition and elimination of tumor cells. In this study, we evaluated the effects of ibrutinib on NK cell-mediated cytotoxicity in mouse models of B-cell lymphoma. Methods: Experiments in TMD8 xenograft models were performed in CB17.SCID and NSG mice, and experiments in an A20 syngeneic model were performed in BALB/c mice. Mice were orally administered ibrutinib (once daily) for a total duration of 2 weeks starting from the time tumors reached a volume of 100-150 mm3. Tumor BTK occupancy was determined by a gel-based probe assay 4 hours after the last dose of ibrutinib, and was normalized to the total BTK level. NK cell-mediated cytotoxicity was also evaluated in mice carrying X-linked spontaneous mutation in BTK, Btk(xid) mice (009361; Jackson Laboratory). For the NK cell cytotoxicity assay, mouse splenocytes were added to PKH67-labeled YAC-1 cells at different effector-to-target ratios and incubated at 37°C for 4 hours. Propidium iodide was added and flow cytometry was performed to determine target cell viability. Human or mouse cytokines/chemokines were quantified using MILLIPLEX® MAP Kit (HCYTMAG-60K-PX38 and MCYTMAG-70K-PX32). Results: In TMD8 ABC-DLBCL models, tumor suppression after ibrutinib treatment was only observed in CB17.SCID mice but not in NSG mice despite tumor BTK occupancy of >90% in both models. As these 2 strains of mice differ in their NK cell profile (NSG mice lack mature T, B, and NK cells whereas CB17.SCID mice are severely deficient in T and B cells), we were interested in studying the immune modulation function of ibrutinib on NK cells. Interestingly, elevated NK cell cytotoxicity was seen in Btk(xid) mice compared to Btk wild-type mice, suggesting a potential role of BTK depletion in NK cell function. Treatment with ibrutinib increased NK cell-mediated cytotoxicity in both syngeneic A20 B-cell lymphoma and TMD8 xenograft models (Figure 1), but did not affect NK cell population (% of NKp46+ or CD3-CD49b+). A20 tumor-bearing mice had lower NK cell cytotoxicity compared to non-tumor-bearing mice, suggesting suppression of NK cell function by tumors. In addition, ibrutinib reduced tumor-derived cytokines IL-6 and IL-10, which are negative regulators of NK cells. IFN-gamma secreted by nontumor cells was increased in the sera of CB17.SCID but not in NSG mice after ibrutinib treatment, providing further evidence of the increased NK function with ibrutinib. The detailed mechanisms of modulation of NK cell function by ibrutinib is currently under investigation. Conclusions: We report herein that ibrutinib enhanced NK cell-mediated cytotoxicity in mouse models of B-cell lymphomas. In addition to its direct effect on BTK inhibition in tumor cells, these data provide further evidence of the immune modulation function of ibrutinib. The role of ibrutinib in NK cell activation as observed in the current study may further expand the potential application of ibrutinib therapy. Disclosures Kuo: Pharmacyclics, LLC, an AbbVie Company: Employment, Other: Travel, Accommodations, and Expenses, Patents & Royalties: Pharmacyclics, LLC, an AbbVie Company; AbbVie: Equity Ownership. Hsieh:Pharmacyclics, LLC, an AbbVie Company: Employment. Whang:Pharmacyclics, LLC, an AbbVie Company: Employment; AbbVie: Equity Ownership. Huang:Juno: Equity Ownership; Pharmacyclics, LLC, an AbbVie Company: Employment; Five Prime: Equity Ownership; Merrimack: Equity Ownership. Sirisawad:AbbVie: Equity Ownership; Pharmacyclics, LLC, an AbbVie Company: Employment. Chang:AbbVie: Equity Ownership; Pharmacyclics, LLC, an AbbVie Company: Employment, Patents & Royalties: Pharmacyclics, LLC, an AbbVie Company.

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Qin, Hong, Guowei Wei, Ippei Sakamaki, Zhenyuan Dong, Diane Lynne Smith, Feng Wen, Han Sun, Wesley A. Cheng et Larry W. Kwak. « Novel BAFF-Receptor Antibody to Natively Folded and Glycosylated Recombinant Protein Eliminates Drug Resistant B Cell Malignancies In Vivo ». Blood 128, n^o 22 (2 décembre 2016) : 468. http://dx.doi.org/10.1182/blood.v128.22.468.468.

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Abstract Background: Targeted monoclonal antibodies (mAbs) such as the anti-CD20 rituximab, are proven therapies in lymphoma, yet these diseases remain incurable because of primary or acquired resistance. Using a eukaryotic expression system to produce antigen closely representing endogenous protein, we developed a new therapeutic antibody against an alternative lymphoma target. B cell activating factor receptor (BAFF-R/TNFRSF13C) is a tumor-necrosis factor receptor superfamily member specifically involved in B lymphocyte development and mature B cell survival. Although earlier attempts to target the BAFF/BAFF-R axis therapeutically for B cell tumors yielded limited success, BAFF-R remains an attractive target for B cell lymphoma therapeutic antibody development, particularly for rituximab-resistant tumors. Methods and Results: We generated 2 mAbs to human BAFF-R expressed as a natively folded, eukaryotically glycosylated cell-surface immunogen on engineered mouse fibroblast (L) cells. Both mAbs specifically bound BAFF-R-expressing L cells, but not the parental counterparts. Each of the complementarity determining regions (CDRs) of the 2 mAbs are unique, suggesting different binding epitopes. Both mAbs bound with high affinity to the human B cell lymphoma cell lines JeKo-1 (mantle cell lymphoma; MCL), SU-DHL6 (diffuse large B cell lymphoma; DLBCL), Raji (Burkitt's lymphoma) and RL (follicular lymphoma). Because our goal is to develop antibodies for clinical use, we substituted in human IgG1 Fc to generate the chimeric mAbs C55 and C90. The chimeric mAbs retained the binding specificity and affinity of the mouse antibodies to their target cells. By immunohistochemistry C55 and C90 staining was specific to the B cell-containing organs tonsil and spleen. No detectable staining was observed in heart, lung, brain, liver, and kidney. Using primary human natural killer (NK) cells as effectors, we demonstrated the chimeric antibodies induced potent antibody-dependent cellular cytotoxicity (ADCC) against BAFF-R-expressing L cells and the JeKo-1, SU-DHL6, Raji and RL human lymphoma cell lines. C55 and C90 were also able to elicit ADCC in primary human lymphomas; they efficiently killed tumor cells from patients with MCL, DLBCL, follicular lymphoma and chronic lymphocytic leukemia (CLL) (n=8). Notably, 5 of these primary lymphomas were from patients who had relapsed after rituximab treatment (2 MCL, 3 CLL). We next determined the activity of C55 and C90 in models of drug-resistant lymphoma. Both ibrutinib and rituximab are effective anti-lymphoma agents, however, primary or acquired resistance to these drugs is common. We derived a rituximab-resistant JeKo-1 variant (JeKo-1 CD20KO) using the CRISPR/HDR system to knock-out CD20 gene expression, and also used the naturally ibrutinib-resistant (Z-138) lymphoma cell line. We confirmed that the C55 and C90 anti-BAFF-R antibodies induced ADCC in both drug-resistant cell lines in vitro. Using xenogenic tumor models in NOD scid gamma (NSG) mice we observed remarkable in vivo anti-tumor effects of both the C55 and C90 chimeric antibodies. We found our antibodies significantly inhibited growth of implanted Z-138 and JeKo-1 CD20KO lymphomas (P<0.001; Figure). Conclusion: In contrast to previously reported BAFF-R antibodies, our in vitro and in vivo results strongly support the translational development of our novel BAFF-R-specific monoclonal antibodies, especially as an alternative immunotherapy against ribuximab- or ibrunitib-resisitant B cell maglinancies. Other preliminary data also suggest BAFF-R may be an effective target of CAR T cells. Figure Figure. Disclosures No relevant conflicts of interest to declare.

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Rogers, Kerry A., Dalia El-Gamal, Harrington K. Bonnie, Hing A. Zachary, Goettl M. Virginia, Mantel Rose, Lisa L. Smith et al. « The Eµ-Myc/TCL1 Transgenic Mouse As a New Aggressive B-Cell Malignancy Model Suitable for Preclinical Therapeutics Testing ». Blood 126, n^o 23 (3 décembre 2015) : 2752. http://dx.doi.org/10.1182/blood.v126.23.2752.2752.

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Abstract Background: Aggressive B-cell lymphomas occurring in the setting of Chronic Lymphocytic Leukemia (CLL) as a large cell transformation are an important clinical problem, and improved mouse models to test novel and targeted therapeutics are needed. The Eµ-Myc mouse overexpresses c-Myc gene which is placed under control of the Myc promoter and lymphoid-specific IgH enhancer (Eµ), resulting in c-Myc overexpression and spontaneous B-cell lymphoma development. The Eµ-Myc mice have been used in drug development, however malignancy develops at variable ages and with differing genetics and response to therapeutic agents, making drug studies difficult. The Eµ-TCL1 transgenic mouse overexpresses the human TCL1 oncogene, under the control of the B-cell specific IgVH promoter and Eµ enhancer. Mice develop a spontaneous mature B-cell leukemia after a long latency period and represent a well-established model of human CLL. We crossed the Eµ-Myc and TCL1 mice to create a new model of aggressive B-cell lymphoma to test novel therapeutics that would be more homogeneous than the Eµ-Myc model. Methods: Eµ-Myc and TCL1 mice on C57BL/6 background strain were crossed and resulting genotypes were verified by PCR. All mice were kept in standard pathogen-free housing until death or removal from study. All mice born within a 24 month time period were followed for survival. At the time of death, spleen, lymph nodes, bone marrow, and liver were fixed in 10% neutral buffered formalin, embedded in paraffin, sectioned at 4uM, and stained with hematoxylin and eosin for histologic evaluation. For engraftment studies, adoptive cell transfer was done by injecting fresh splenic white blood cells (1e7 cells, >75% CD5+/CD19+) into the tail vein of C57BL/6 wild type recipient mice. In the drug treatment experiments ibrutinib (~30mg/kg/day) was administered in drinking water and KPT-8602 (15mg/kg) by daily oral gavage. Survival was shown using Kaplan-Meier curves and survival curves compared statistically using a log-rank test. Results: The Eµ-Myc/TCL1 mice had significantly worse survival (median 45.5, range 29-74 days) compared to Eµ-Myc (median 118, range 42-520 days) or TCL1 (median 359.5, range 188-531 days) mice (p=<0.0001). Survival curves are show in Figure 1. Pathologic examination revealed aggressive B-cell histology similar to Burkitt lymphoma in both the Eµ-Myc mice and Eµ-Myc/TCL1 mice, whereas the TCL1 mice showed mature B-cell morphology. Infiltration of the bone marrow of Eµ-Myc and Eµ-Myc/TCL1 mice was extensive in comparison with TCL1 mice. In all three mouse genotypes the normal architecture in the spleen was effaced by neoplastic cells. Adoptive transfer of Eµ-Myc/TCL1 splenic lymphocytes produced similar pathologic findings to the Eµ-Myc/TCL1 transgenic mice with less severe splenic enlargement in the engrafted mice. Median survival of the engrafted mice was short (38 days). There was a differential response to targeted therapeutics between the groups. Ibrutinib, an irreversible inhibitor of Bruton tyrosine kinase (BTK) previously demonstrated to improve survival in TCL1 mice, had no survival advantage over vehicle treatment in either Eµ-Myc or Eµ-Myc/TCL1 mice (p=0.876 and P=0.83 respectively). KPT-8602, a second generation selective inhibitor of exportin 1 (XPO1) was tested in Eµ-Myc/TCL1 engrafted mice, and demonstrated a significant improvement in survival compared to vehicle alone (p=<0.0001). A first generation agent (selinexor) targeting XPO1 is currently in human clinical trials for aggressive lymphomas, including large cell transformation of CLL. Conclusions: Mice with both c-Myc and TCL1 transgenes develop an aggressive B-cell malignancy and have decreased survival compared to Eµ-Myc or TCL1 mice. The histology of the disease is similar to that of Eµ-Myc mice, but with shorter survival with less variability. The resulting mouse model has differential responses to targeted therapeutics, with a poor response to ibrutinib more similar to aggressive lymphoma than CLL. The malignant B cells can be adoptively transferred into immunocompetent mice for experimental drug treatment studies. These qualities make Eµ-Myc/TCL1 mice a useful tool to test new therapies for aggressive lymphoma where there is an unmet clinical need. Work is currently underway to further define the genetic characteristics of this mouse in comparison to human lymphoma sub-types and responsiveness to targeted agents. Disclosures Byrd: Acerta Pharma BV: Research Funding.

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Schrage, Matthew I., David Kim, Jeffrey Calimlim, Evelena Ontiveros, Michael A. Teitell, Jonathan W. Said et Sven de Vos. « The PIM1 Oncogene Accelerates TCL1 Driven Lymphomagenesis in a Double-Transgenic Murine Model. » Blood 112, n^o 11 (16 novembre 2008) : 1806. http://dx.doi.org/10.1182/blood.v112.11.1806.1806.

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Abstract Previously, we identified and validated PIM-1 as a differentially expressed gene in mantle cell lymphoma (MCL) patient samples. Further, we have shown PIM-1 to be a significant prognostic biomarker in MCL. PIM-1 is an oncogenic serine/threonine kinase that is transcriptionally regulated by cytokines, mitogens, and numerous growth factors. It cooperates with other oncogenes in tumorigenesis and has been implicated in the development of leukemias, lymphomas, late progression events, and most recently in prostate cancer. PIM-1 is overexpressed in aggressive lymphomas, such as the blastoid variant of MCL, and the ABC-type of DLBCL. Here we tested the in vivo cooperation of PIM-1 with TCL1 in murine lymphomagenesis by producing double transgenic murine strains. PIM-1 transgenic mice overexpress murine PIM-1 under the control of the immunoglobulin enhancer Eμ. TCL1 transgenic mice (pEμ -B29-TCL1) fail to downregulate TCL1 expression in mature B and T cells and provide a unique model for mature B-cell malignancies, including Burkitt-like lymphoma (BLL), DLBCL, marginal zone lymphoma, and B-cell chronic lymphocytic leukemia. We hypothesized that PIM-1 would either accelerate TCL1-driven lymphomagenesis, result in the development of immature lymphomas, or both. Lymphoid malignancies were examined by immunohistochemistry and flow cytometry and classified according to the mouse models of human cancer consortium (MMHCC) ‘Bethesda’ classification scheme. Forty double transgenic mice (PIM-1/TCL1) have been generated and observed for a median follow-up of 9 months. To date, 8/40 (20 %) of the PIM-1/TCL1 mice developed lymphomas, in contrast to 9/88 (10%) PIM-1 and 11/49 (22%) TCL1 transgenic mice, with a median follow-up of 7 and 15 months, respectively. A Kaplan-Meyer plot demonstrated statistically significant acceleration of lymphomagenesis in the PIM-1/TCL1 transgenic mice when compared with single TCL1 transgenic mice (p=0.037). PIM-1 transgenic mice developed early (< 7 months of age) T-cell lymphoblastic lymphomas and late (> 20 months of age) DLBCL. TCL1 transgenic mice developed DLBCL, with single occurrences of lymphoblastic, lymphocytic and Burkitt lymphomas. PIM-1/TCL1 transgenic mice developed DLBCL, frequently with extranodal involvement (spleen, liver and lung). A single case of follicular lymphoma was seen. In addition, endogenous expression of PIM kinase family members was investigated in a human lymphoma cell line bank (n=40) by quantitative real-time PCR. PIM-1, PIM-2, and also PIM-3 were found to be overexpressed in cell lines derived from human lymphoid malignancies of multiple histologies. In summary, aberrant PIM-1 overexpression in TCL1 transgenic mice accelerated the development of mature B-cell lymphomas. To date, the classification of lymphomas in PIM-1/TCL1 mice revealed similar histologies as in TCL1 single transgenic mice, mainly DLBCL. The expression of all 3 PIM kinase family members in lymphomas implies that pan-PIM kinase inhibitors should be developed as a potential mechanism of resistance to more restricted PIM inhibitors could be compensatory overexpression of the non-targeted family members.

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ten Hacken, Elisa. « Abstract IA26 : Understanding CLL and Richter’s syndrome biology through mouse models of human genetics ». Blood Cancer Discovery 3, n^o 5_Supplement (6 septembre 2022) : IA26. http://dx.doi.org/10.1158/2643-3249.lymphoma22-ia26.

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Abstract Large-scale human next generation sequencing studies have progressively defined the complex genetic landscape of chronic lymphocytic leukemia (CLL) and Richter’s syndrome (RS), yet the difficulties in rapid manipulation of primary CLL cells and the limited availability of cell lines have challenged studies aimed at interrogating the function of the so-called disease “drivers”, defined in human studies through statistical inference. Mouse models represent powerful tools to study mechanisms of normal and malignant B cell biology. Conditional knock-in/knock-out systems have allowed B-cell restricted modeling of CLL genetic lesions, with MDR mice being the first example of a genetically-faithful CLL model, recapitulating the most common genomic aberration of human disease, del(13q). Since then, a series of models generated by our group and others have allowed to uncover key functional changes underlying disease onset and transformation, including in the context of combined mutation in the splicing factor Sf3b1 and the DNA damage response gene Atm, sole mutation in the B cell developmental factor Ikzf3, the nuclear export receptor Xpo1, the ribosomal protein Rps15, and the DNA methyltransferase Dnmt3a (the latter not a CLL lesion per se, but recapitulating disordered methylation patterns typical of CLL). The CRISPR-Cas9 gene editing technology has further enabled B-cell restricted introduction of multiple combinatorial loss-of-function lesions, allowing the generation of faithful models not only of CLL but, importantly, of transformation into RS. In this presentation, I will describe the application of mouse models to studies of CLL and RS pathogenesis and treatment, with a focus on key aspects uncovered through the characterization of genetically- inspired mouse lines of recurrent disease drivers. I will provide a perspective on how these novel models combined with new technology allowed the dissection of mechanisms of disease evolution and response to therapy with greater depth than previously possible, representing valuable platforms for functional genomic analyses. Citation Format: Elisa ten Hacken. Understanding CLL and Richter’s syndrome biology through mouse models of human genetics [abstract]. In: Proceedings of the Third AACR International Meeting: Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2022 Jun 23-26; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2022;3(5_Suppl):Abstract nr IA26.

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He, Li-Zhen, Larry Thomas, Jeffery Weidlick, Laura Vitale, Tom O'Neill, Naseem Prostak, Karuna Sundarapandiyan et al. « Development of a Human Anti-CD27 Antibody with Efficacy in Lymphoma and Leukemia Models by Two Distinct Mechanisms ». Blood 118, n^o 21 (18 novembre 2011) : 2861. http://dx.doi.org/10.1182/blood.v118.21.2861.2861.

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Abstract Abstract 2861 CD27, a lymphoid cell-specific TNFR superfamily member, is constitutively expressed on the majority of T cells, some NK cells and memory B cells. Through interaction with its ligand CD70, CD27 transduces a co-stimulatory signal promoting T cell and NK cell activation and cytotoxicity. In addition, CD27 is also expressed on many lymphoid-originated hematological neoplastic cells, such as chronic lymphocytic leukemia, mantle cell lymphoma, and Waldenstrom macroglobulinemia, thus being a potential direct target for antibody therapy. To generate potential antibodies for clinical development, we immunized human Ig transgenic mice and developed a panel of CD27 specific human mAbs. Clone 1F5 was identified as a lead based on its high affinity to both human and monkey CD27, enhanced co-stimulation of T cells, and ADCC of CD27-expressing lymphoblastic cell lines. Using SCID mice challenged with CD27-expressing human lymphoid cell lines, we demonstrated that 1F5 mediates conventional antibody effector function. Compared to human IgG1 isotype control (huIgG1), 1F5 at doses ranging 33 μg – 500 μg (x 6) significantly delayed the growth of Burkitt's lymphoma Raji even when administration was initiated 1 week after tumor inoculation. Similar anti-tumor activity was observed against other CD27-expressing tumor lines including, Daudi and T-originated acute lymphoblastic leukemia CCRF-CEM. In order to investigate 1F5 in vivo agonistic activities and T cell-mediated tumor eradication, a human CD27 transgenic mouse model (hCD27-Tg) was generated and backcrossed onto C57BL/6 and BALB/c backgrounds. The expression profile and regulation of the human CD27 transgene driven by its own promoter were similar to that observed with endogenous mouse CD27. In addition to enhancing T cell responses when combined with vaccination, 1F5 treatment was highly effective against syngeneic mouse tumors including lymphoma BCL1 (BALB/c) and thymoma EL4-derived E.G7 (C57BL/6). For the BCL1 model, various dose levels of 1F5 mAb were delivered to mice intraperitoneally on days 3, 5, 7, 9 and 11 after i.v. administration of 107 BCL1 cells to huCD27 Tg and control animals. Controls including hCD27-Tg mice treated with saline or isotype control, or WT mice treated with 1F5 all performed consistently, leading to 50% survival approximately 23 days after tumor challenge. Treatment of mice with mAb, 1F5 substantially improved the 50% survival in a dose dependent fashion to >70 days post tumor challenge at the higher dose levels. Based on the promising efficacy data with anti-CD27 mAb 1F5 in immunocompromised and immunocompetent lymphoma models, a clinical grade product, referred to as CDX-1127 was manufactured and tested for safety. To assess the potential for 1F5 to mediate lymphocyte activation, we investigated its ability to induce proliferation and cytokine release from human PBMC or purified T cell cultures. Consistent with the known biology of CD27 we demonstrated the 1F5 mAb does not lead to direct activation of lymphocytes in the absence of additional signals. However, combining 1F5 with suboptimal levels of T cell receptor stimulation using anti-CD3 mAb (OKT3) was shown to enhance proliferation of human T cells. Two studies were performed using cynomolgus macaques. There were no CDX-1127 related mortalities or changes noted in the clinical condition, food appetence, body weights and body temperature, ophthalmic, electrocardiographic and clinical pathology assessments, organ weights and bone marrow assessments. In addition, there were no major differences in the percentage of lymphocyte populations between control and CDX-1127 treated animals at the end of the study demonstrating that the antibody did not significantly deplete normal CD27-expresssing cells. Based on the pre-clinical studies we are planning a Phase 1 clinical trial of CDX-1127 in patients with hematological malignancies and selected solid tumors. The trial is designed with separate arms to independently assess the safety and activity of CDX-1127 in hematologic malignancies, in which the antibody may act through multiple mechanisms, and in solid tumors where it would be fully dependent on indirect immune mechanisms. Disclosures: He: Celldex Therapeutics, Inc.: Employment. Thomas:Celldex Therapeutics, Inc.: Employment. Weidlick:Celldex Therapeutics, Inc.: Employment. Vitale:Celldex Therapeutics, Inc.: Employment. O'Neill:Celldex Therapeutics, Inc.: Employment. Prostak:Celldex Therapeutics, Inc.: Employment. Sundarapandiyan:Celldex Therapeutics, Inc.: Employment. Marsh:Celldex Therapeutics, Inc.: Employment. Yellin:Celldex Therapeutics, Inc.: Employment. Davis:Celldex Therapeutics, Inc.: Employment. Keler:Celldex Therapeutics, Inc.: Employment.

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Bellone, Matteo, Paolo Dellabona, Arianna Calcinotto, Giulia Casorati, Alessandra Rovida, Maria Teresa Sabrina Bertilaccio, Elena Cattaneo, Matteo Grioni, Federico caligaris-Cappio et Paolo Ghia. « CD4+ T Cells Sustain Aggressive Chronic Lymphocytic Leukemia through a CD40L-Independent Mechanism ». Blood 134, Supplement_1 (13 novembre 2019) : 683. http://dx.doi.org/10.1182/blood-2019-128246.

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In Chronic Lymphocytic Leukemia (CLL), mature CD5+ B cells accumulate in lymphoid organs such as bone marrow and lymph nodes where they proliferate and expand within localized proliferation centers. In vitro and in vivo data suggest that survival and proliferation of CLL cells within proliferation centers may be also dependent on microenvironmental interactions originating from the surrounding cellular elements (e.g. monocyte-derived nurse-like cells, mesenchymal stromal cells, or CD4+ T lymphocytes), that deliver both membrane-bound and soluble signals to CLL cells. In particular, the role of CD4+ T cells in vivo is less defined and data in animal models are conflicting as they appear to sustain CLL clone expansion and survival through CD40L-CD40 interactions, though in approximately 40% of patients with CLL, aggressive leukemic clones appear to be independent of CD40 stimulation. We aimed at clarifying the role of CD4+ T lymphocytes taking advantage of the Eμ-TCL1 mouse model, which develops a disease that mimics aggressive, human CLL. To this aim, we generated genetically modified Eμ-TCL1 mice lacking either CD4+ T cells (TCL1+/+AB0), CD40 (TCL1+/+CD40-/-), or CD8+ T cells (TCL1+/+TAP-/-). In these mice, disease appearance and progression were monitored in lymphoid organs and blood by flow cytometry and immunohistochemistry analyses. Findings were confirmed by adoptive transfer of leukemic clones into mice either lacking CD4+ T cells, or CD40L, or treated with monoclonal antibodies depleting selected T cell populations, or blocking CD40L-CD40 interactions. Interestingly, we observed that CLL clones did not expand in mice either lacking or depleted of CD4+ T cells, thus confirming that CD4+ T cells are essential for CLL development in Eμ-TCL1 mice. On the contrary, in TCL1+/+TAP-/- mice, lacking CD8+ T cells, disease progression was accelerated, suggesting an anti-tumor activity exerted by this subset of T cells. Specificity of CD4+ T cells was marginal for CLL development, as leukemic clones developed regularly in transgenic mice whose CD4+ T cells had TCR with CLL-unrelated specificities. Similarly, TCL1+/+CD40-/- mice developed frank CLL with no differences compared to controls, as well as leukemic clones expanded when transferred into wild type mice treated with monoclonal antibodies blocking CD40, or into CD40L-/- mice, suggesting a dispensable role for CD40/CD40L stimulation in the development of murine CLL. Analysis of peritoneal fluid, spleen, lymph nodes and bone marrow showed similar CLL development in Eμ-TCL1 and TCL1+/+CD40-/- mice. In conclusion, our data demonstrates that CD8+ and CD4+ T cells exert opposite roles in CLL: CD8+ T cells restrain CLL progression, whereas CD4+ T cells support the expansion of CLL clones in Eμ-TCL1 mice through CD40-indipendent, and apparently non-cognate mechanisms. Further studies are warranted to dissect the nature of the molecules, either soluble or membrane-bound, responsible for the interactions occurring between CD4+ T cells and CLL B cells fueling the onset and expansion of CLL cells. Disclosures Ghia: AbbVie: Consultancy, Honoraria, Research Funding; Acerta/AstraZeneca: Consultancy, Honoraria; ArQule: Consultancy, Honoraria; BeiGene: Consultancy, Honoraria; Dynamo: Consultancy, Honoraria; Gilead: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Juno/Celgene: Consultancy, Honoraria; Sunesis: Consultancy, Honoraria, Research Funding; Novartis: Research Funding; Pharmacyclics LLC, an AbbVie Company: Consultancy.

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Smith, Audrey L., Alexandria P. Eiken, Sydney A. Skupa, Dalia Y. Moore, Avyakta Kallam, Christopher D'Angelo, Gregory R. Bociek et al. « BET Inhibition As a Targeted Epigenetic Approach to Reverse T Cell Dysfunction in Chronic Lymphocytic Leukemia ». Blood 138, Supplement 1 (5 novembre 2021) : 3715. http://dx.doi.org/10.1182/blood-2021-153921.

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Abstract Introduction : Chronic Lymphocytic Leukemia (CLL) is characterized by the clonal expansion of mature CD19+/CD5+ lymphocytes in the peripheral blood and secondary lymphoid organs. The accumulation of B-CLL cells yields profound immune defects in the CLL tumor microenvironment (TME), promoting evasion of immune surveillance that contributes to tumor persistence and thus relapsed/refractory disease. The bromodomain and extra-terminal domain (BET) family of proteins are epigenetic readers that bind acetylated histone residues to regulate transcription of numerous genes involved in critical CLL protumor pathways. Of the BET family proteins, BRD4 is overexpressed in CLL and highly enriched at super-enhancers of genes that regulate CLL-TME interactions such as B cell receptor pathway components, chemokine/cytokine receptors, and immune checkpoint molecules. Pan BET inhibitors (BET-i), such as PLX51107 (Plexxikon Inc.) significantly improve survival in aggressive CLL murine models. Here we demonstrate that blocking BRD4 function with PLX51107 (PLX5) can alleviate the inherent immune defects observed in CLL, hence reducing B-CLL induced T cell dysfunction and allowing for robust B-CLL cell elimination. This therapeutic strategy may be vital in overcoming frequent drug resistance and/or bolstering the anti-tumor effect of current CLL therapies. Methods : Primary leukemic B cells were isolated from the peripheral blood of CLL patients and co-cultured with healthy donor T cells to evaluate the effect of PLX5 (0.1-0.5μM) on CLL-induced T cell immunosuppression ex vivo via an array of flow cytometry assays. T cell proliferation was assessed using CFSE after 96 h co-culture with α-CD3/α-CD28 stimulation. Effector cytokine production was evaluated after 48 h co-culture in the presence of PMA/ionomycin (final 6 h) and brefeldin A (final 5 h). Immune inhibitory molecule surface expression was measured following 48 h co-culture with α-CD3/α-CD28 stimulation. To further validate our ex vivo findings, the E μ-TCL1 adoptive transfer model was used. Once disease onset was confirmed in recipient WT B6 mice (>10% CD45+/CD19+/CD5+ peripheral blood lymphocytes), mice were randomized to receive either PLX5 (20 mg/kg) or vehicle (VEH) equivalent daily by oral gavage for 4 weeks. Following treatment, mouse spleens were processed to evaluate exhaustion marker expression, T cell proliferation (CellTrace™ Violet, 72 h a-CD3/α-CD28 stimulation ex-vivo), and T-cell effector function (ex-vivo mitogenic stimulation, 6 h). Results : T cell proliferation indices were reduced following ex vivo co-culture with primary B-CLL cells (mean ± SEM for T cells vs. co-culture, 2.0 ± 0.13 vs. 1.57 ± 0.05; P<0.01). This suppression was significantly alleviated in 0.5μM PLX5-treated co-cultures (1.84 ± 0.08; P<0.01). In a similar fashion, the percentage of polyfunctional TNF-α+/IFN-γ+ CD4+ T cells markedly increased in PLX5-treated co-cultures (VEH vs. 0.5μM PLX5, 10.0% ± 0.76% vs. 15.2% ± 0.92%; P<0.01). Notably, BET inhibition with PLX5 also bolstered T cell inflammatory function (%TNF-α+/IFN-γ+) in the absence of B-CLL cells (VEH vs. PLX5, 12.9% ± 1.0% vs. 15.3% ± 0.69%; P<0.05). Remarkably, the expression of numerous immune inhibitory molecules (e.g., PDL1, PD1, CTLA4, LAG3) was consistently reduced between 1.8- and 3-fold in PLX5-treated co-cultures (0.1μM). In the adoptive transfer E μ-TCL1 model, mice receiving PLX5 displayed reduced expansion of B-CLL cells and increased T cell infiltration in the spleen (Fig. 1A). Splenic CD4+ T cells from PLX5-treated mice had significantly greater proliferative capacity (Fig. 1B) and pro-inflammatory functionality (Fig. 1C). Finally, PLX5 treatment markedly reduced the surface expression of immune inhibitory molecules (e.g., PDL1, LAG3, VISTA) on CD4+ and CD8+ T cells in the spleen (Fig. 1D). Studies to evaluate the effects of PLX5 on malignant B-CLL and T cells within the bone marrow niche and soluble factors in the plasma are ongoing. Collectively, our data indicate that the novel BET-i, PLX5, exerts beneficial immunomodulatory effects on T cells within the CLL TME. Conclusion : Epigenetic-targeted therapies such as BET-i have the potential to alleviate CLL-induced T cell dysfunction while eliminating B-CLL cells and preventing tumor expansion. Future profiling studies are pending to further illuminate how BET proteins regulate immune function in CLL. Figure 1 Figure 1. Disclosures Lunning: AstraZeneca: Consultancy; Legend: Consultancy; Acrotech: Consultancy; ADC Therapeutics: Consultancy; Kyowa Kirin: Consultancy; Myeloid Therapeutics: Consultancy; Beigene: Consultancy; Celgene, a Bristol Myers Squibb Co.: Consultancy; Verastem: Consultancy; Janssen: Consultancy; Daiichi-Sankyo: Consultancy; Morphosys: Consultancy; TG Therapeutics: Consultancy; Novartis: Consultancy; Karyopharm: Consultancy; AbbVie: Consultancy; Spectrum: Consultancy; Kite, a Gilead Company: Consultancy. Vose: Kite, a Gilead Company: Honoraria, Research Funding. Powell: Plexxikon Inc.: Current Employment.

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El-Gamal, Dalia, Zachary A. Hing, Shaneice Mitchell, Taylor D. LaFollette, Paul J. Brennan, Joseph M. Flynn, Jeffrey A. Jones et al. « A Novel Inhibitor of BET Family Bromodomains Demonstrates In Vivo and I n Vi tro Potency in B-Cell Malignancies ». Blood 126, n^o 23 (3 décembre 2015) : 318. http://dx.doi.org/10.1182/blood.v126.23.318.318.

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Abstract Chronic Lymphocytic Leukemia (CLL) is a B-cell malignancy with aberrant activation of the B-cell receptor (BCR) pathway. Despite durable remissions with targeted therapies (e.g., ibrutinib) in CLL, it remains an incurable disease. Epigenetic modifications, including DNA methylation and dysregulation of chromatin regulators have been shown to contribute to the neoplastic phenotype and the differential biologic behavior of tumor cells, including leukemia. An additional layer of epigenetic complexity in cancer cells is the acquisition of super-enhancer regions enriched at genes with known oncogenic function including MYC and BCL2. Super-enhancers in multiple myeloma cells and other tumors have been found strongly enriched for binding of BRD4, a member of the human bromodomain and extraterminal (BET) domain family of proteins which includes BRD2, BRD3, BRD4, and the testis-specific member BRDT. BRD4 binds to acetylated lysines on histones and regulates the expression of important oncogenes (e.g., MYC and BCL2). We investigated the therapeutic benefit of BET inhibition in cell culture and in vivo disease models of leukemia/lymphoma using PLX51107, a novel BRD4 inhibitor with unique binding mode. Results: We report that BRD4 is significantly overexpressed in CLL patient-derived B-cells compared to B-cells from healthy donors on both transcript and protein level (p < .001). RNA-seq analysis of 55 CLL patients revealed expression of various BRD4 isoforms with marked abundance of BRD4-long and BRD4-short. Next we sought to investigate the anti-tumor activity of PLX51107 in multiple malignant B-cell lines and patient-derived CLL cells. PLX51107 inhibited cell growth in MEC1, OCI-Ly2 and OCI-Ly6 (p < .001) dose-dependently with IC50 of 1.0 ± 0.09, 1.2 ± 0.05, 1.8 ± 0.05 μM, respectively. Notably, PLX51107 antagonized CpG-induced increase in cell proliferation of primary CLL cells (p < .01) which was consistent with the downmodulation of MYC and MCL1 along with the accumulation of the cyclin-dependent kinase inhibitor p21 and IκBα (p < .005). Furthermore, the efficacy of PLX51107 to disrupt survival signaling from the microenvironment was investigated under co-culture conditions with two different bone marrow stroma cell lines, wherein PLX51107 treatment significantly induced cytotoxicity in B-CLL cells (p < .01) without affecting stromal cell viability. By employing microarray analysis we identified possible novel targets of BRD4 in CLL. Validation of those targets is currently ongoing. Particularly, Bruton's tyrosine kinase (BTK) and phospholipase C gamma 2 (PLCG2) were markedly decreased with PLX51107 treatment (p < .005), thereby signifying potential therapeutic effect(s) for dual targeting of BRD4 and BCR-associated kinases to achieve deeper and durable responses in relapsed/refractory B-cell malignancies. Lastly, anti-tumor effects of BRD4 inhibition were evaluated in vivo using Eμ-TCL1 and cMYC/TCL1 adoptive transfer models of leukemia and lymphoma, respectively. In the Eμ-TCL1 engraftment model of aggressive CLL, PLX51107 treatment resulted in prolonged survival (p < .001) accompanied with decreased disease burden, lymphocyte infiltration and proliferation when compared to vehicle-treated mice. Next, the cMYC/TCL1 adoptive transfer mouse model was used to evaluate BRD4 inhibition in a highly penetrant, malignant leukemia/lymphoma phenotype analogous to high grade lymphoma wherein PLX51107 prolonged survival (p < .0001), decreased peripheral lymphocyte counts and neoplastic cell infiltration and proliferation in both spleen and lymph nodes. Conclusion: Collectively our findings reveal BRD4 as a valid and novel target for epigenetic therapy directed against core transcriptional programs in malignant/proliferating B-cells and provide support for use of PLX51107 as an effective treatment in clinical trials for relapsed/refractory CLL patients and related aggressive forms of B-cell malignancies, with the ultimate goal of improving the outcome of these patients. Disclosures Byrd: Acerta Pharma BV: Research Funding.

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Klein, Ulf, Marie Lia, Qiong Shen, Paula M. Smith, Hongyan Tang, Tongwei Mo, Marta Crespo, Rachael Siegel, Govind Bhagat et Riccardo Dalla-Favera. « The DLEU2/Mir-15a/Mir-16-1 Locus, Commonly Deleted in B-Cell Chronic Lymphocytic Leukemia (CLL), Controls B-Cell Compartment Expansion and Its Deletion Leads to CLL in Mice ». Blood 112, n^o 11 (16 novembre 2008) : 25. http://dx.doi.org/10.1182/blood.v112.11.25.25.

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Abstract B-cell chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) is derived by the malignant transformation of mature B cells. Approximately 50% of CLL cases have monoallelic or biallelic deletions of the chromosomal region 13q14, suggesting the presence of a tumor suppressor involved in CLL pathogenesis. Similar deletions are associated with lymphoproliferative disorders, such as CD5+ monoclonal B-cell lymphocytosis (MBL), that may predispose to CLL, B-cell non-Hodgkin lymphoma (NHL) and multiple myeloma. We and others previously identified a minimal deleted region (MDR) at 13q14 which contains: the DLEU2 gene, encoding a long (1.2 Kb) non-coding RNA that is necessary for miR-15a/miR-16-1 production and forms a processed mRNA that is stable in the cytoplasm suggestive of an independent function; and the microRNAs miR-15a/miR-16-1, located within the intronic region of DLEU2. Although miR-15a/miR-16-1 have been proposed as the culprit of the deletion, no conclusive proof of the respective roles of the DLEU2 or miR-15a/miR-16-1 genes in tumor suppression has been obtained. We therefore investigated the consequences of eliminating these genetic elements in vivo by establishing two transgenic mouse lines that carry deletions of either the ~120 kb large MDR, including dLeu2 and miR-15a/miR-16-1, or of miR-15a/miR-16-1 alone. Young MDR−/− and miR-15a/miR-16-1−/− mice did not display phenotypic abnormalities, and showed normal lymphoid development. However, between 12–18 months, both MDR−/− and miR-15a/miR-16-1−/− mice developed MBL (~15% of cases), CLL/SLL with multiorgan involvement (~20%), or CD5− NHL subtypes (~5%). Analogous lymphoproliferations were observed, albeit at lower frequencies in heterozygous mice, suggesting a haploinsufficient role for the 13q14 locus. Both MDR−/− and miR-15a/miR-16-1−/− mice succumbed to their disease earlier than their heterozygous or wild-type littermates. To ascertain whether the observed lymphoproliferative disorders were B-cell autonomous, we generated B-cell conditional deletions by crossing “floxed” MDR and miR-15a/miR-16-1 alleles with Cd19-Cre. These mice developed pathologies comparable in frequency and type to the constitutional knock-out mice, indicating that the B-cell proliferative disorders were not dependent on other cell types. In conclusion, these results indicate that the 13q14 region contains a locus controlling the expansion of the B-cell compartment that includes both CD5+ and CD5− B cells. Deletion of the locus leads to B cell-autonomous lymphoproliferative disorders, indicating a tumor suppressor function for which the miR-15a/miR-16-1 cluster but not the mature DLEU2 RNA, is required. The development of indolent lymphoproliferative disorders in mice with 13q14 deletions, such as MBL, CLL, and other NHL recapitulates the spectrum of CLL-associated phenotypes, suggesting that these mice are representative of the natural history of this disease. As such, these mice represent genotypically and phenotypically faithful models of the human disease uniquely suited for studies of mechanisms underlying disease progression and for testing novel anti-CLL therapeutic modalities.

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Matas-Céspedes, Alba, Anna Vidal-Crespo, Vanina Rodriguez, Gael Roue, Elias Campo, Dolors Colomer, Jeroen Lammerts van Bueren et al. « Daratumumab, a Novel Human Anti-CD38 Monoclonal Antibody for the Treatment of Chronic Lymphocytic Leukemia and B-Cell Non–Hodgkin Lymphoma ». Blood 120, n^o 21 (16 novembre 2012) : 3935. http://dx.doi.org/10.1182/blood.v120.21.3935.3935.

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Abstract Abstract 3935 Daratumumab (DARA) is a human CD38 antibody with broad-spectrum killing activity. DARA induces killing of tumor cells, mainly via complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC) (de Weers M, J Immunol 2011). DARA is currently being evaluated in phase I/II clinical trials in patients with multiple myeloma. In these clinical studies the adverse events have been manageable and marked reductions in paraprotein and bone marrow plasma cells have been observed. In the present study, we have analyzed the potential of targeting CD38 using DARA in two types of B-cell non-Hodgkin lymphoma (B-NHL) (follicular lymphoma (FL) and mantle cell lymphoma (MCL)), and in chronic lymphocytic leukemia (CLL). Flow cytometry analysis demonstrated that MCL and CLL tumor cells show heterogeneous expression of CD38, while FL cells showed invariable high CD38 levels. CD38 has attracted special attention in CLL where high CD38 expression is a marker of bad prognosis (Hamblin et al, Blood 1999 and 2002) and is expressed preferentially in the proliferating fraction of the tumor (Damle RN, Blood 2007). In addition, we have recently shown that high CD38 expression in MCL was associated with resistance to the proteasome inhibitor bortezomib (Pérez-Galán P, Blood 2011). Here, we tested the cytotoxic activity of DARA in tumor cell lines and in fresh tumor cells obtained from patients. DARA did not induce CDC in MCL cell lines (MINO, REC, HBL2, JEKO), irrespective of CD38 expression levels. Also, FL cell lines (WSU-FSCCL, RL) expressing relatively high CD38 levels were insensitive to DARA-induced CDC. This low CDC was associated with high expression of the complement inhibitors CD55 and CD59. In addition, the number of CD38 molecules per cell in these MCL and FL cell lines was lower than that found on the CDC-sensitive Daudi Burkitt lymphoma cell line, suggesting a threshold for CD38-targeted CDC lysis. In the presence of PBMC effector cells obtained from healthy donors, DARA showed significant levels of ADCC in cells from MCL, FL and CLL. In CLL primary cases (n=8) tested, DARA (14–43% lysis) was generally superior or at least equally effective (mean+/−SD=28,78 +/− 9,78) in inducing ADCC as compared to the anti-CD20 antibodies ofatumumab (mean+/−SD=21,35 +/− 15,71) and rituximab (mean+/−SD=29,30 +/− 15,90). The immunomodulatory agent lenalidomide shows considerable single agent activity in MCL, FL and CLL. Interestingly, it has been shown that lenalidomide may be able to increase ADCC, probably via activation of NK cells. We therefore tested whether the combination of lenalidomide and DARA could enhance ADCC. Noteworthy, DARA-induced ADCC in MCL, FL cell lines and primary CLL cells was significantly (p<0,05) enhanced when effector cells were pretreated with the immunomodulatory agent lenalidomide (3 μM, 72 h) with DARA doses ranging from 0,01–1 μg/ml. Finally, CD38 is important for cell migration and adhesion, especially for CXCR4-CXCL12-induced migration of tumor cells (Vaisitti et al, Leukemia 2010). Our preliminary results suggest that in the CLL subtype with high CD38 and more migratory capacity DARA (10–30 μg/ml) inhibits CXCL12/SDF1α mediated migration up to 70%. These results are of high importance because inhibition of tumor cell trafficking to tissue sites as bone marrow and lymph nodes, may be clinically relevant, as increasing evidence indicates that tumor–microenvironment interactions may play an important role in drug resistance and contribute to clinical failures. We are currently validating this in vitro results in a CLL mouse model. Taken together, these results suggest that DARA may be a promising therapeutic agent both for MCL, FL and CLL, in which DARA exerts its effects mainly via ADCC and for CLL also via inhibition of migration of tumor cells. Interestingly, the cytotoxic activity of DARA by ADCC could be further augmented by addition of lenalidomide in these three models. Disclosures: Lammerts van Bueren: Genmab: Employment. Bakker:genmab: Employment. Parren:genmab: Employment. Perez-Galan:Genmab: Research Funding.

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Beckwith, Kyle A., Frank W. Frissora, Matthew R. Stefanovski, Jutta Deckert, Carlo M. Croce, Xiaokui Mo, David Jarjoura, John C. Byrd et Natarajan Muthusamy. « A Transgenic Mouse Model of Aggressive B-Cell Malignancy for Evaluating Anti-Human CD37 Therapeutics ». Blood 120, n^o 21 (16 novembre 2012) : 188. http://dx.doi.org/10.1182/blood.v120.21.188.188.

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Abstract Abstract 188 BACKGROUND: Introduction of the anti-CD20 antibody rituximab has led to remarkable progress in the development of targeted therapies for CLL and other B-cell malignancies. Despite prolonging patient survival, therapies targeting CD20 have not been curative. In recent years, alternative targets for therapeutic antibodies have emerged. One of the most promising targets has been CD37, which is highly expressed on malignant B-cells in chronic lymphocytic leukemia (CLL) and non-Hodgkin's lymphoma. The recent interest in this target has led to the generation of novel anti-CD37 therapeutics that could benefit from more extensive preclinical evaluation. However, preclinical development of these agents has been limited by the absence of appropriate leukemia animal models that provide targets expressing human CD37 (hCD37). Here we describe the development and characterization of a transgenic mouse where CLL-like leukemic B-cells express hCD37 and aggressively transplant into syngenic hosts. We demonstrate the utility of this unique mouse model by evaluating the in vivo efficacy of IMGN529, a novel antibody-drug conjugate targeting hCD37 that consists of the CD37-targeting K7153A antibody linked to the maytansinoid DM1 via the thioether SMCC linker. METHODS: The hCD37 transgenic mouse (hCD37-Tg) founder lines were generated by conventional methodology at the OSU Transgenic Facility. B-cell specific expression of hCD37 is driven by immunoglobulin heavy chain promoter and Ig-μ enhancer elements. Founder lines were evaluated by RT-PCR and flow cytometry to confirm RNA and protein expression, respectively. These lines were then crossed with the EμTCL1 mouse model of CLL to generate hCD37xTCL1 mice that develop CD5+CD19+hCD37+ leukemia. For in vivo studies, splenocytes from a leukemic hCD37xTCL1 donor were injected i.v. into healthy hCD37-Tg mice. Mice were randomly assigned to the following treatment groups (n=8–10 per group): IMGN529 conjugate, its K7153A antibody component, or negative controls (isotype antibody-DM1 conjugate or trastuzumab). Upon diagnosis of leukemia, a 10 mg/kg dose was administered i.p. and repeat doses were given 2 times per week for 3 weeks (70 mg/kg total). Peripheral blood disease was monitored by flow cytometry, using counting beads to obtain the absolute number of leukemic CD5+CD19+ B-cells. CD37 expression levels were determined by quantitative flow cytometry. In vitro cytotoxicity was evaluated after 24 hour incubation by flow cytometry with Annexin V and propidium iodide staining. RESULTS: IMGN529 and its K7153A antibody component demonstrated comparable in vitro activity against freshly isolated human CLL cells even in the absence of cross-linking agents (mean IMGN529 cytotoxicity=50.04% vs. 48.85% for K7153A; p=0.175; n=9). Both compounds also demonstrated cytotoxicity against hCD37 Tg B-cells ex vivo in a cross-linking dependent manner, and while expression of hCD37 in hCD37-Tg animals was B-cell specific, the expression levels were substantially lower than those observed in human CLL cells. In vivo studies with transferred hCD37xTCL1 splenocytes demonstrated rapid and complete depletion of CD5+CD19+ leukemic B-cells in response to IMGN529 conjugate, but not K7153A antibody treatment. After 1 week of IMGN529 treatment, peripheral blood leukemia was nearly undetectable and previously detected massive splenomegaly was no longer palpable. In contrast, leukemic counts and spleen sizes continued to increase in control cohorts. CONCLUSIONS: In summary, our group has generated a mouse model that develops a transplantable CD5+CD19+ leukemia expressing hCD37. We demonstrate the utility of this model for both in vitro and in vivo testing of therapeutics targeting hCD37. In addition, preclinical mouse studies expose the robust anti-leukemic effects of IMGN529 in this in vivo model of aggressive B-cell malignancy, despite the relatively low expression of hCD37 on the leukemic B-cells. Our engraftment model shows that IMGN529 is capable of eliminating widespread and highly proliferative mouse leukemia by a mechanism that is both CD37 antigen and conjugate dependent. Therefore, we propose that this novel therapeutic may also exhibit substantial efficacy in a wide range of human B-cell malignancies, even those with relatively low CD37 expression. [This work was supported by NIH (NM, JCB), LLS (NM, JCB) and Pelotonia (KAB)]. Disclosures: Deckert: ImmunoGen Inc.: Employment.

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Yin, Shanye, Anat Biran, Helene Kretzmer, Elisa Ten Hacken, Salma Parvin, Fabienne Lucas, Mohamed Uduman et al. « B Cell-Restricted Depletion of Dnmt3a Activates Notch Signaling and Causes Chronic Lymphocytic Leukemia ». Blood 138, Supplement 1 (5 novembre 2021) : 249. http://dx.doi.org/10.1182/blood-2021-150789.

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Abstract Previous studies have revealed a critical role of methylation deregulation in the onset and progression of chronic lymphocytic leukemia (CLL). In mammalian cells, DNA methylation is dynamically established by the DNA methyltransferase 3 (DNMT3) family of de novo methyltransferases DNMT3A. Although mutations of DNMT3A are rarely observed in CLL, our RNA-sequencing (RNA-seq) analysis of 107 human CLLs show that low DNMT3A expression is associated with more aggressive disease, and supports a driving role of DNMT3A loss in CLL. To test this hypothesis, we generated a conditional knock-out mouse model with B cell-restricted deletion of Dnmt3a. Homozygous Dnmt3a depletion in B cells resulted in the development of CD5+ B cell leukemia mimicking human CLL with 100% penetrance at a median age of onset of 5.3 months, and heterozygous Dnmt3a depletion yielded a disease penetrance of 89% with a median onset at 18.5 months, confirming its role as a haplo-insufficient tumor suppressor. Given the known role of Dnmt3a as a de novo methyltransferase, we first evaluated the impact of Dnmt3a depletion on global DNA methylation in non-leukemic CD5+ B cells isolated from the peritoneal cavity by cell sorting (i.e. B1a cells) using reduced representation bisulfite sequencing (RRBS). We identified a set of differentially methylated regions (DMRs) (difference>0.2), mostly hypomethylated, in Dnmt3afl/fl versus WT B1a cells (473 hypomethylated, 19 hypermethylated). Genes with dysregulated methylation were highly enriched in pathways involved in immune response (e.g., Interferon-α signaling, JAK/STAT3 signaling) and proliferation (Wnt Signaling and Notch signaling). Given the prominent hypomethylation changes observed in Dnmt3a depleted B1a cells, we investigated whether these would lead to altered gene transcript expression. Using RNA-seq, we detected 460 downregulated and 168 upregulated genes in the Dnmt3afl/fl B1a cells compared to WT B1a cells (FDR<0.05, fold change >2). Consistent with the methylation data, differentially expressed genes were likewise enriched for JAK/STAT3 signaling, Wnt Signaling and Notch signaling, supporting a direct influence of dysregulated methylation on downstream signaling cascades. We investigated the changes in methylomes of the CLL cells arising from the Dnmt3afl/fl animals. Compared to WT B1a cells, Dnmt3afl/fl CLL cells generated 1335 hypomethylated and 2369 hypermethylated DMRs in. Focusing on genes that were hypomethylated in CLL compared to WT B1a cells, we found that these were highly enriched for several oncogenic signaling pathways including Notch signaling and Wnt Signaling, consistent with the pre-leukemia findings. RNA-seq analysis identified more upregulated (n=2801) than downregulated (n=1244) genes in CLL cells compared to WT B1a cells (FDR<0.05, FC>2), supporting a role of Dnmt3a depletion in transcriptional activation. We observed a general upregulation of Notch signaling genes and the downstream Notch targets, implicating Notch activation in this CLL mouse model. Of note, we showed Dnmt3a-depleted CLL cells to be highly sensitive to Notch inhibitor DAPT both in vitro and in a transplantable mouse model. Consistently, primary human CLL cells with low DNMT3A expression were more sensitive to DAPT than those with higher DNMT3A expression (P=0.005, Spearman correlation), despite similar sensitivity to ibrutinib and venetoclax. Together, our results have confirmed the causal role of Dnmt3a downregulation in CLL generation. We provide evidence in support of the interaction between Dnmt3a-dependent methylation changes and hyperactivation of Notch signaling in transcriptional reprogramming and transformation of B1a cells into CLL. Furthermore, we demonstrate differential sensitivity of DNMT3A high and low expressing primary CLLs to Notch inhibition, indicative of consistent dependencies of human and murine CLLs. Thus, the Dnmt3a models provides a unique opportunity for the study of non-mutational Notch activation, and a useful platform for the study of Notch-signaling targeted therapeutics. Disclosures Kipps: Abbott Laboratories: Consultancy, Research Funding; Celgene Corporation: Consultancy, Honoraria, Research Funding; Pharmacyclics LLC, an Abbvie Company: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses, Research Funding, Speakers Bureau; Genentech, Inc.: Honoraria, Research Funding, Speakers Bureau; Gilead Sciences, Inc.: Honoraria, Research Funding; GlaxoSmithKline: Research Funding; MedImmune Inc: Research Funding; Moores Cancer Center: Current Employment; Oncternal Therapeutics, Inc.: Current holder of stock options in a privately-held company, Other: Stock or other ownership, Patents & Royalties: Cirmtuzumab was developed by Thomas J. Kipps in the Thomas J. Kipps laboratory and licensed by the University of California to Oncternal Therapeutics, Inc., which provided stock options and research funding to the Thomas J. Kipps laboratory., Research Funding; AbbVie: Consultancy, Honoraria, Other, Speakers Bureau; DAVAOncology: Consultancy, Honoraria, Other; DAVA Pharmaceuticals: Speakers Bureau; Bionest Partner: Other; Celgene: Consultancy, Honoraria, Other, Research Funding; Genetech: Honoraria, Other; Genentech-Roche: Consultancy; Gilead Sciences: Consultancy, Honoraria, Other, Speakers Bureau; Janssen: Consultancy, Honoraria, Other, Research Funding, Speakers Bureau; Roche: Honoraria, Other; MD Anderson Cancer Center: Research Funding; Velos: Research Funding; CRIM: Research Funding; Indy Hematology Review: Other; TG Therapeutics: Other; Verstem: Other, Speakers Bureau; University of California, San Diego: Current Employment; Pharmacyclics/AbbVie: Honoraria, Research Funding; Breast Cancer Research Foundation: Research Funding; SCOR - The Leukemia and Lymphoma Society: Research Funding; National Cancer Institute/NIH: Honoraria, Research Funding; Genentech/Roche: Honoraria; European Research Initiative on CLL (ERIC): Honoraria. Neuberg: Madrigal Pharmaceuticals: Other: Stock ownership; Pharmacyclics: Research Funding. Letai: Flash Therapeutics: Other: equity holding member of the scientific advisory board; Dialectic Therapeutics: Other: equity holding member of the scientific advisory board; Zentalis Pharmaceuticals: Other: equity holding member of the scientific advisory board. Wu: BioNTech: Current equity holder in publicly-traded company; Pharmacyclics: Research Funding.

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Yin, Wu, Nie Zhe, Andrew Placzek, Michael Trzoss, Goran Krilov, Shulu Feng, Morgan Lawrenz et al. « Identification of Potent Paracaspase MALT1 Inhibitors for Hematological Malignancies ». Blood 136, Supplement 1 (5 novembre 2020) : 30. http://dx.doi.org/10.1182/blood-2020-141146.

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Introduction: MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1), was identified as a translocation protein fused with cIAP2 in mucosa-associated lymphoid tissue (MALT) B cell lymphomas. MALT1, a key mediator of NF-κB signaling and the main driver of a subset of B-cell lymphomas, functions via formation of a complex with CARMA1 and BCL10 to mediate antigen receptor-induced lymphocyte activation. MALT1 has been considered as a potential therapeutic target for several non-Hodgkin B cell lymphomas as well as chronic lymphocytic leukemia (CLL). Here, we describe the discovery of novel, potent MALT1 inhibitors that result in antiproliferative effects in non-Hodgkin B-cell lymphoma cells. Results: We have identified novel small molecule MALT1 inhibitors using our proprietary physics-based Free Energy Perturbation (FEP+) modeling technology. Our compounds show potent (sub nM) inhibition of MALT1 enzymatic activity, as well as high binding affinity (sub nM) to MALT1 protein measured by Surface Plasmon Resonance (SPR). BCL10 is a binding partner of MALT1 that is cleaved by MALT1 at the C-terminus. Our inhibitors were efficacious in a target engagement assay showing prevention of BCL10 cleavage in Activated B-cell (ABC) subtype of diffuse large B cell lymphoma (DLBCL) cell lines OCI-LY3 and OCI-LY10, which are Bruton tyrosine kinase (BTK) inhibitor ibrutinib-resistant and -responsive respectively. Our compounds are potent inhibitors of IL10 secretion in both OCI-LY3 and OCI-LY10 cells, which is consistent with the inhibition of NF-κB signaling. We also examined the effect of our MALT1 inhibitors on ABC-DLBCL cell proliferation. Our inhibitors demonstrated potent anti-proliferative effects in both OCI-LY3 and OCI-LY10 cell lines, as well as synergistic effects with ibrutinib in a BTKi sensitive ABC-DLBCL cell panel. Examinations of a protease panel and off-target safety screening panel, as well as in vivo high dose tolerability study showed our compound had excellent selectivity and significant safety margin. Plasma IL10 and tumor BCL10 have been identified as robust PD markers in PK/PD studies in both OCI-LY3 and OCI-LY10 tumor bearing mice. Dose-dependent tumor growth inhibition was observed after 3 weeks of treatment in OCI-LY3 xenograft model, with efficacy also observed in combination with venetoclax. Ongoing work: We are continuing to explore the synergistic effects of our compounds with BTK inhibitors in B-cell lymphoma mouse models. Preliminary data showed potent inhibition of IL-2 secretion in Jurkat cells from our compound treatment. Additional studies are ongoing to elucidate the role of MALT1 inhibition in Treg as well as Teffector cells in vitro and in vivo. Refinement of the current inhibitor series, using co-crystal structures, is in progress in preparation for further development of optimized molecules. Conclusion and Future Plans: We have identified novel potent MALT1 protease small molecule inhibitors that are efficacious in the in vitro B-cell lymphoma cell proliferation assays and in the in vivo B-cell lymphoma xenograft model. Our data suggest that targeting MALT1 may expand therapy options for patients with selected B-cell lymphomas, such as ABC-DLBCL. Our work provided insight into the anti-tumor efficacy of our inhibitors in B-cell lymphomas as single agent, and ongoing work will continue to assess the potential combination with BTKi to overcome drug-induced resistance in patients with relapsed/refractory B-cell lymphoma. Disclosures Yin: Schrodinger: Current Employment, Current equity holder in publicly-traded company. Zhe:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Placzek:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Trzoss:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Krilov:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Feng:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Lawrenz:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Pelletier:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Lai:Triplet Therapeutics: Current Employment, Current equity holder in private company. Bell:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Calkins:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Grimes:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Tang:Schrodinger: Current Employment, Current equity holder in publicly-traded company. McRobb:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Gerasyuto:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Feher:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Mondal:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Jensen:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Wright:Schrodinger: Current Employment, Current equity holder in publicly-traded company. Akinsanya:Schrodinger: Current Employment, Current equity holder in publicly-traded company.

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Owusu-Ansah, Frank, Jumana Afaghani, Stanley Lee et Justin Taylor. « Inhibiting the Nuclear Exporter XPO1 and the Antiapoptotic Factor BCL2 Is Synergistic in XPO1 Mutant and Wildtype Lymphoma ». Blood 136, Supplement 1 (5 novembre 2020) : 17–18. http://dx.doi.org/10.1182/blood-2020-134807.

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We have recently shown that XPO1 mutations are drivers of lymphomagenesis and occur across B-cell lymphomas, specifically in chronic lymphocytic leukemia (CLL), classical Hodgkin lymphoma and primary mediastinal B-cell lymphoma. The co-occurrence of other oncogenic events cooperating with XPO1 provides an opportunity for combined targeted therapy. Increased expression of the anti-apoptotic factor BCL2 has long been known to be a critical part of the pathophysiology of B-cell lymphomas. Recently, the oral BCL2 inhibitor, venetoclax, was approved in CLL and is currently being evaluated in clinical trials for other B-cell lymphomas. Selinexor is a potent, oral XPO1 inhibitor that was recently approved in multiple myeloma and diffuse large B-cell lymphoma. XPO1 inhibition exerts its antineoplastic effects by blocking key lymphomagenic pathways, such as NFκB, and decreasing the anti-apoptotic protein survivin. We therefore hypothesized that combining selinexor and venetoclax would have potential synergy and provide an oral precision combination therapy for relapsed, refractory lymphoma. We first set out to determine whether XPO1 mutant lymphoma cell lines showed differential response to either selinexor or venetoclax monotherapy. Five lymphoma cell lines; 3 diffuse large B-cell lymphoma (SU-DHL-6, SU-DHL-16, FARAGE) and 2 classical Hodgkin lymphoma (L428 and SUP-HD1), were subjected to next-generation sequencing (NGS) to assess for the presence or absence of XPO1 mutations. SUDHL-16 and SUP-HD1 were heterozygous for the XPO1 E571K hotspot mutation while SUDHL-6, FARAGE and SUP-HD1 were wildtype at the XPO1 locus. These 5 cell lines were used to assess sensitivity to Selinexor and/or Venetoclax. The CellTiter Glo assay was used to assess cell viability after 72 hours of treatment. Assays were performed in triplicate on 96-well plates that were read using a Spectramax plate reader. The XPO1 mutant cells showed increased sensitivity to selinexor (XPO1 mutant IC50 = 16-35nM; XPO1 WT IC50 = 41-231nM) as previously seen in conditional knockin mouse models of XPO1 mutant CLL (Figure A). Additionally, the XPO1 mutant cell lines showed increased sensitivity to single-agent venetoclax (XPO1 mutant IC50 = 2-13nM; XPO1 WT IC50 = 5-2853nM), an observation that has not previously been made (Figure B). Next, we tested the synergy of the combination of selinexor and venetoclax in the XPO1 mutant and wildtype cell lines. Increasing concentrations of the individual drugs were applied to each individual cell line in a 6x6 matrix. The cell viability percentage for each concentration was then entered into a synergy finder (www. synergyfinder.fimm.fi). The Bliss Independence model was used to calculate synergy of the Selinexor-Venetoclax combinations. As hypothesized, the combination of selinexor and venetoclax indeed showed synergy in both the wildtype and mutant XPO1 cell lines. Furthermore, the XPO1 mutant cell lines showed a higher degree of synergy compared to the wildtype cells (Figure C). Finally, a remarkable patient allowed us to test this combination ex vivo. This patient with CLL had undergone multiple therapies including chemoimmunotherapy, ibrutinib and venetoclax monotherapies. This patient had a founder XPO1 E571K mutation and also had acquired a BTK C481S ibrutinib resistance mutation and MYC amplification. These cells were unique in that they were easily able to be tested in ex-vivo culture to test sensitivity to different therapies. When tested with chemotherapy or ibrutinib they were completely resistant, and even with venetoclax they were fairly resistant; however, they remained sensitive to XPO1 inhibition with Selinexor. Selinexor and venetoclax showed remarkable synergy measured by a BLISS delta score of 18.78 (Figure D). In conclusion, inhibiting the nuclear exporter XPO1 and the anti-apoptotic factor BCL2 is synergistic in both XPO1 wildtype and mutant lymphoma. XPO1 mutant lymphomas show increased sensitivity to both selinexor and venetoclax. Additionally, selinexor and venetoclax showed a higher degree of synergism in XPO1 mutant lymphoma cell lines and were highly synergistic in primary XPO1 mutant CLL patient cells ex vivo. This combination is highly promising as an all oral alternative for relapsed, refractory lymphoma. Next steps include preclinical testing in mouse models in vivo using XPO1 mutant and wildtype mice crossed with mice overexpressing BCL2. Figure Disclosures No relevant conflicts of interest to declare.

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Pozzato, Gabriele, Nelly Mezzaroba, Sonia Zorzet, Erika Secco, Stefania Biffi, Claudio Tripodo, Marco Calvaruso et al. « New Therapeutic Approach for the Treatment of B-Cell Disorders Using Chlorambucil/Hydroxychloroquine-Loaded AntiCD20 Nanoparticles ». Blood 120, n^o 21 (16 novembre 2012) : 158. http://dx.doi.org/10.1182/blood.v120.21.158.158.

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Abstract Abstract 158 B-cell disorders show highly variable clinical courses, ranging between indolent diseases like the chronic lymphocytic leukemia (CLL) and highly aggressive lymphoproliferative disorders like Burkitt Lymphoma. The treatments of these disorders have been characterized by the development of new approaches, including dose-intensive chemotherapy regimens and immunotherapy via monoclonal antibodies (Ab). Despite the promising survival rates, these multi-agent treatments are flawed by a high degree of toxicity and a significant fraction of patients do not respond. The use of core shell nanoparticles design with specific Ab-coating represents a new strategy to target only tumor cells with high-dose chemotherapy. We characterized, both in vitro and in vivo, the effects of a new kind of biodegradable nanoparticles (BNP) coated with an anti-CD20 antibody and loaded with Chlorambucil (CLB) and Hydroxychloroquine (HCQ). BJAB and MEC1 are two well characterized Burkitt lymphoma and CLL cell line, respectively; both are mutated in P53, express different amount of CD20 and result quite resistant to CLB, but more susceptible to HCQ. HCQ/CLB-loaded antiCD20 BNP can release enough amounts of drugs inside the cancer cells and overcome multi-drug resistance mechanisms, which are over-expressed in many B-cell disorders. The presence of antiCD20 antibody targets BNP on cells expressing this antigen, inducing a selective penetration in these cells, as demonstrated by electron microscopy studies; the cytotoxic effect was evident analyzing apoptosis and after 24–48 hours all the cancer B-cells resulted destroyed. Data indicate that BNP were able to kill also cells expressing very low amount of CD20, where Rituximab was almost ineffective. These results were confirmed using primary cells isolated from more than 40 patients with untreated chronic lymphocytic leukemia. These data were obtained incubating fresh isolated blood with HCQ/CLB-loaded antiCD20 BNP and analyzing residual viable or apoptotic cells. Endovenous or intraperitoneal injection of HCQ/CLB-loaded antiCD20 BNP in mice did not induced tissue damages, weight loss or death, while the same amount of free cytotoxic agent cause death of all the animals. Biodistribution analysis demonstrated a selective targeting of the antiCD20 BNP to tumor cells, with a peak 48 hours after injection; BNP elimination was mainly documented in liver and intestine but not by spleen, kidney, lungs or other organs. The intraperitoneal injection of BJAB cells in SCID mice determined the formation of a tumor mass visible at the site of injection followed by early multi-organ involvement and death of all animals. Eight injections of antiCD20 BNP containing CLB/HCQ (400 micrograms each) in 17 days were able to increase survival in 100% of mice and 90% of animals were cured. The same amount of CLB+HCQ cannot be used as free drugs because of their toxicity able to kill all the animals in about a week. The intravenous injection of MEC1 cells in SCID mice allowed the development a new human/mouse model of leukemia. The treatment with antiCD20 BNP containing CLB/HCQ showed comparable therapeutic efficacy, while free drugs were almost uneffective. In conclusion, the results of the present study demonstrate that antiCD20 BNP containing HCQ/CLB can be effective as a single agent in controlling both aggressive and indolent models of disseminated B-cell disorders and provide a rationale for adopting this new therapeutic approach in clinical trials. Furthermore, the results demonstrate that nanoparticles are effective via different administration methods. Disclosures: No relevant conflicts of interest to declare.

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Deckert, Jutta, Jose F. Ponte, Jennifer A. Coccia, Leanne Lanieri, Sharon Chicklas, Yong Yi, Krystal Watkins, Rodrigo Ruiz-Soto, Angela Romanelli et Robert J. Lutz. « Preclinical Mechanistic Studies Investigating Neutrophil and Lymphoid Cell Depletion By IMGN529, a CD37-Targeting Antibody-Drug Conjugate (ADC) ». Blood 124, n^o 21 (6 décembre 2014) : 3119. http://dx.doi.org/10.1182/blood.v124.21.3119.3119.

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Abstract CD37 is a surface antigen widely expressed on malignant B cells in non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia (CLL). In normal tissues, CD37 expression is restricted to lymphoid tissues and blood cells, with high levels of expression on B lymphocytes and low levels on non-B lymphoid and myeloid cells. IMGN529 is a CD37-targeting ADC currently in a Phase I clinical study in adult patients with relapsed or refractory NHL (NCT01534715). This ADC uniquely combines the intrinsic pro-apoptotic and immune effector activities of its anti-CD37 antibody component with the potent cytotoxic mechanism provided by targeted delivery of its maytansinoid payload, DM1. In the Phase I study, IMGN529 has demonstrated early evidence of clinical activity. A reduction in lymphocyte counts was also observed in the majority of patients after dosing, consistent with the proposed mechanism of action of a CD37-targeted therapy. However, in the initial dose-escalation phase, some patients experienced transient, early-onset neutropenia. To investigate the potential mechanisms of this transient neutropenia observed in patients, different pre-clinical models were considered and utilized to recapitulate clinical findings. In vitro studies with peripheral blood cells from normal human donors demonstrated that incubation with IMGN529 for 1 hour or 24 hours resulted in significant B-cell depletion with no apparent neutrophil depletion detected, similar to observations after rituximab treatment. In contrast, alemtuzumab treatment in vitro resulted in both B-cell and neutrophil depletion. This is consistent with the high level of CD37 expression on target B cells and the relatively low CD37 expression level on other blood cells. Analysis of cytokine release by normal human donor peripheral blood cells incubated with IMGN529 revealed increased levels of IL-8, CCL2 (MCP-1) and CCL4 (MIP-1β), but not IL-6 or TNF, to a similar extent as rituximab but less pronounced than alemtuzumab. An anti-murine CD37 antibody was identified to enable in vivo studies in a murine model and characterize CD37 expression on murine blood cells. Similar to the expression profile of CD37 in human peripheral blood cells, CD37 expression on murine peripheral blood cells was highest in B cells, with much lower expression seen on T cells and granulocytes. In vivo activity of the anti-muCD37 antibody and the corresponding ADC, with the same SMCC-DM1 linker-payload combination as IMGN529, was evaluated to discern antibody and payload-mediated events in comparison to the classic cytotoxic cyclophosphamide (CPA). Treatment of C57/B6 mice with 1-10 mg/kg of anti-muCD37 antibody or anti-muCD37 ADC resulted in a significant decrease in absolute lymphocyte counts (ALC) lasting greater than 7 days and a transient decrease in absolute neutrophil counts (ANC) lasting 1-2 days. A non-targeted control SMCC-DM1 ADC had no effect on ALC or ANC counts, suggesting the decrease is a CD37-mediated effect. In contrast, treatment with CPA resulted in an ALC decrease with similar kinetics but a more pronounced ANC decline. No impact on bone marrow lymphocyte, myeloid or erythroid precursor cell counts was observed in response to the anti-muCD37 antibody or anti-muCD37 ADC, whereas CPA treatment caused reduced cellularity with a decrease in the percentage of mature myeloid precursors and neutrophils in bone marrow. Elevated levels of CCL2 and CCL4 chemokines were detected in mouse plasma after anti-muCD37 ADC treatment, which may contribute to a redistribution of circulating neutrophils into peripheral tissues. Studies are currently underway to assess neutrophil distribution in murine tissues post anti-muCD37 ADC treatment. Current preclinical studies provide no clear evidence for direct IMGN529-mediated depletion of normal human neutrophils in the context of B-cell depletion in vitro. In vivo studies with an anti-muCD37 ADC recapitulate transient peripheral lymphopenia and neutropenia with no impact on bone marrow precursors observed, indicative of a different mechanism than classic chemotherapy-induced bone marrow myelosuppression. These preliminary results suggest a role for chemokine-mediated neutrophil redistribution following CD37 engagement, which is the subject of further studies. Disclosures Deckert: ImmunoGen, Inc.: Employment, Equity Ownership. Ponte:ImmunoGen, Inc.: Employment, Equity Ownership. Coccia:ImmunoGen, Inc.: Employment, Equity Ownership. Lanieri:ImmunoGen, Inc.: Employment, Equity Ownership. Chicklas:ImmunoGen, Inc.: Employment, Equity Ownership. Yi:ImmunoGen, Inc.: Employment, Equity Ownership. Watkins:ImmunoGen, Inc.: Employment, Equity Ownership. Ruiz-Soto:ImmunoGen, Inc.: Employment, Equity Ownership; sanofi: Employment. Romanelli:ImmunoGen, Inc.: Employment, Equity Ownership; sanofi: Employment. Lutz:ImmunoGen, Inc.: Employment, Equity Ownership.

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Schutt, Steven D., Chih-Hang Anthony Tang, Yongxia Wu, David A. Bastian, Juan Del Valle, Chih-Chi Andrew Hu et Xue-Zhong Yu. « Prevention of Chronic Gvhd By Targeting Xbp-1 Genetically or Pharmacologically in Mice ». Blood 128, n^o 22 (2 décembre 2016) : 4541. http://dx.doi.org/10.1182/blood.v128.22.4541.4541.

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Abstract Inhibition of the endoplasmic reticulum (ER) stress response via blockade of inositol-requiring enzyme-1α (IRE-1α) is currently a promising therapeutic strategy to treat B-cell leukemia, lymphoma, and myeloma. Because B cells play an important role in the development of chronic graft-versus-host disease (cGVHD), we hypothesize that the ER stress response contributes to B-cell function and pathogenicity in cGVHD. Here, we report that the ER stress response mediated by IRE-1α and its target X-box binding protein-1 (XBP-1) plays a critical role in cGVHD pathophysiology and represents a potential therapeutic target to prevent cGVHD. We tested the role of XBP-1 specifically in B cells by testing XBP-1 conditional knockout B cell grafts (XBP1fl/flCD19Cre+) in two mouse models of cGVHD. In the first model (B6 to BALB/c), recipients given XBP-1-deficient donor grafts showed significantly reduced cGVHD clinical scores, which were associated with reduced frequencies of donor-derived CD4 helper T cells within the lungs compared to the recipients of XBP-1fl/flCD19Cre- littermate donor grafts. XBP-1-deficient B cells produced significantly higher levels of IL-10 compared to WT control B cells after activation ex vivo. In the second model (B6 to B10.BR), the conversion of donor B cells to plasma cells (B220+CD38+CD138+) was reduced in both the spleens and lungs of recipients transplanted with XBP1fl/flCD19Cre+ grafts compared to those of the recipients given XBP1fl/flCD19Cre- grafts. Recipients given XBP1fl/flCD19Cre+ grafts also showed significantly higher total splenocytes and vastly increased splenic B-cell populations when compared with the recipients of XBP1fl/flCD19Cre- grafts. To expand on these findings, we tested if systemic XBP-1 blockade via a novel IRE-1α inhibitor, B-I09, would attenuate cGVHD. In a cutaneous model of cGVHD (B10.D2 to BALB/c), we found that prophylactic administration of B-I09 significantly reduced clinical features of cGVHD compared to vehicle controls (Fig. 1A). Validating these findings, hematoxylin and eosin stained skin sections of B-I09-treated mice had significantly lower pathology scores compared to vehicle controls (Fig. 1B). Isolated skin lymphocytes from recipients treated with B-I09 showed significant reductions in donor derived T cells and DCs compared to those treated with vehicle controls (Fig. 1C and D). Taken together, our findings reveal a novel role of the IRE-1α/XBP-1 pathway of the ER stress response in cGVHD pathophysiology and provide a readily translatable strategy to prevent the development of cGVHD in the clinic. Disclosures No relevant conflicts of interest to declare.

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Tedder, Thomas F. « Regulatory B Cells (B10 Cells) in Human Disease ». Blood 122, n^o 21 (15 novembre 2013) : SCI—2—SCI—2. http://dx.doi.org/10.1182/blood.v122.21.sci-2.sci-2.

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Abstract B cells have been historically characterized as positive regulators of immune responses, but can also influence immune responses through numerous mechanisms other than antibody production. In one example, we and others have functionally identified a rare but specific subset of IL-10-competent regulatory B cells in humans and mice by their ability to secrete IL-10. We have labeled these B cells as “B10 cells” to identify them as the exclusive source of B-cell IL-10. The capacity of B10 cells to produce IL-10 is central to their ability to negatively regulate inflammation and autoimmune disease, as well as adaptive and innate immune responses. Rare B10 cell numbers often increase during inflammation and autoimmunity, particularly in some patients with active disease and autoimmune-prone mice. Nonetheless, the in vivo expansion of B10 cells in mice and patients responding to inflammation is inadequate to effectively control disease. However, the adoptive transfer of 1-2x105 spleen B10 cells from naïve or antigen-primed mice significantly inhibits disease initiation in mouse models of inflammation, autoimmune disease, and contact hypersensitivity. B10 cells are not overtly immunosuppressive, but instead have antigen-specific regulatory functions. Appropriate B-cell antigen receptor specificity and signals are required to drive B10 cell development and acquisition of IL-10 competence under physiological conditions in vivo. Following antigen-specific B10 cell development, their maturation into functional IL-10-secreting effector cells in vivo requires IL-21 and CD40-dependent cognate interactions with antigen-specific T cells. These critical checkpoints are likely to direct localized B10 cell IL-10 production to blunt antigen-specific T-cell responses during cognate B10:T cell interactions. These findings likely explain how antigen-specific B10 cell-effector function can exert such potent in vivo effects and selectively inhibit antigen-specific T-cell function during inflammation and autoimmunity without untoward immunosuppression. Human B10 cells are likely to have similar in vivo regulatory activities. In support of this, collaborative studies with Brice Weinberg and others have shown that human blood B10 cells and malignant cells from 90 percent of patients with chronic lymphocytic leukemia (CLL) share similar cell surface phenotypes and the capacity to express IL-10. Mouse B10 cells and malignant cells in the Tcl-1 transgenic mouse model of CLL also share similar phenotypes and the capacity to express IL-10. Of importance, CLL cell production of IL-10 appears to be dynamically regulated in mice and CLL patients are frequently immunosuppressed with abnormalities in both humoral and cellular immunity. Thus, B10 cells and CLL cells share regulatory properties. Insights into the molecular pathways that regulate antigen-specific B10 cell function in vivo have led to the development of an in vitro culture system that expands functionally-active mouse B10 cells (B10 effector cells) ex vivo by 4 million-fold. B10 effector cells resulting from this culture system secrete IL-10, retain their antigen-specific regulatory functions, and have demonstrated potent anti-inflammatory effects that effectively treat mice with established autoimmune disease. In mice, this culture system allows the generation of sufficient B10 effector cells from one mouse to treat 21,000 syngeneic mice with established disease. Thus, autologous B10 effector cells may eventually provide a new therapy that successfully treats patients with severe and refractory autoimmune disease, particularly those individuals for whom effective drugs have not been identified, as well as those who experience transplant rejection. Disclosures: Tedder: Angelica Therapeutics, Inc.: Consultancy, Equity Ownership; National Institutes of Health grants AI56363 and AI057157: Research Funding; Lymphoma Research Foundation: Research Funding.

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Mato, Anthony, Alexey Valeryevich Danilov, Manish R. Patel, Michael Timothy Tees, Ian W. Flinn, Weiyun Z. Ai, Krish Patel et al. « A first-in-human phase 1 trial of NX-2127, a first-in-class oral BTK degrader with IMiD-like activity, in patients with relapsed and refractory B-cell malignancies. » Journal of Clinical Oncology 40, n^o 16_suppl (1 juin 2022) : TPS7581. http://dx.doi.org/10.1200/jco.2022.40.16_suppl.tps7581.

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TPS7581 Background: Bruton’s tyrosine kinase inhibitors (BTKi) have received regulatory approvals and are standard of care for patients with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), mantle cell lymphoma (MCL), marginal zone lymphoma (MZL), and WaldenstrÖm macroglobulinemia (WM). However, BTKi-resistant disease remains a clinical challenge with limited options for subsequent therapy. Immunomodulatory drugs (IMiDs, e.g., lenalidomide) are approved as monotherapy for follicular lymphoma (FL), MZL, and MCL, in combination with other therapies for diffuse large B-cell lymphoma (DLBCL) and have shown synergy with BTK-targeted therapy. Dual activity of BTK protein degradation with IMiD-like activity offers a unique approach to overcome known resistance to BTKi. NX-2127 is an oral small molecule that induces BTK degradation via recruitment of cereblon, an adaptor protein of the E3 ubiquitin ligase complex. NX-2127 has shown preclinical activity similar to IMiDs by catalyzing the ubiquitination of Ikaros (IKZF1) and Aiolos (IKZF3), ultimately leading to increased T-cell activation. NX-2127 was shown to degrade both wild-type (WT) and C481-mutated (ibrutinib-resistant) BTK protein in vitro. Robust BTK degradation was also shown in non-human primate studies. Further, NX-2127 demonstrates potent tumor growth inhibition in BTK-dependent mouse xenograft tumor models expressing either WT or ibrutinib-resistant C481S BTK-mutant protein. This dual activity of BTK degradation and IMiD-like activity offers a promising treatment for patients who have failed prior therapy. Methods: NX-2127-001 is a first-in-human, dose escalation (Phase 1a) and cohort expansion (Phase 1b) study designed to evaluate the safety, tolerability, and preliminary efficacy of NX-2127 in adult patients with relapsed/refractory B-cell malignancies with once daily oral dosing. Dose escalation will proceed using a modified Fibonacci design with 1 patient per cohort, proceeding to a standard 3 + 3 design based on protocol specified criteria. There will be up to 5 expansion cohorts in Phase 1b enrolling patients with CLL/SLL, DLBCL, FL, MCL, MZL, and WM. Key eligibility criteria include >2 two prior lines of therapy (>1 prior for WM); measurable disease; and an Eastern Cooperative Oncology Group performance status of 0 or 1. Approximately 130 patients (30 in Phase 1a, 100 in Phase 1b) will be enrolled and treated until disease progression or unacceptable toxicity. The primary objectives are to evaluate safety and tolerability and to determine the maximum tolerated dose (Phase 1a), and to evaluate the early clinical activity of NX-2127 in expansion cohorts (Phase 1b). The Phase 1a part of this study is currently enrolling in the United States. Clinical trial information: NCT04830137.

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Vire, Berengere, Alexandre David, Joshua D. Thomas, Terrence R. Burke, Christoph Rader et Adrian Wiestner. « Fcμ-Receptor (FcμR ; TOSO/FAIM3) Mediated Internalization of Antibody-Drug Conjugates : A Novel Approach to Selectively Target Chronic Lymphocytic Leukemia Cells ». Blood 118, n^o 21 (18 novembre 2011) : 734. http://dx.doi.org/10.1182/blood.v118.21.734.734.

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Abstract Abstract 734 The therapeutic principle of antibody-drug conjugates (ADCs) in cancer relies on an antibody to deliver a cytotoxic agent into malignant cells that express a tumor-associated antigen. Recent progress in the field has shown that the use of such conjugates can increase drug activity and reduce cytotoxicity through selective targeting. Recently, TOSO/FAIM3 was identified as the long sought FcR for IgM (FcμR). FcμR is a transmembrane protein expressed on CD19+ B cells, on some CD4+/CD8+ T cells, and weakly on CD56+/CD3− NK cells. We and others have shown that FcμR is consistently overexpressed on chronic lymphocytic leukemia (CLL) cells compared to normal B-cells. In addition, we detected FcμR expression in the mantle cell lymphoma cell line Mino. Using immunofluorescence staining, we found that FcμR can rapidly internalize IgM and transport it through the endocytic pathway to the lysosome. Interestingly, aggregation of FcμR with IgM lead to rapid internalization (>80% internalized within 5 minutes, n=5) whereas mAb bound FcμR was not internalized (n=3). Because of its restricted expression on CLL cells, its cell surface localization and its rapid internalization, FcμR represents an excellent target to deliver a cytotoxic drug into CLL cells using an ADC. To make use of the rapid internalization of FcμR when bound by the Fc-portion of IgM, we engineered a protein scaffold derived from the CH3-CH4 IgM constant region, and inserted a C-terminal selenocysteine, that allows site specific and covalent conjugation of drugs to the protein scaffold. Using gel filtration, we found that purified CH3-CH4 exists mostly as a multimer including pentameric and hexameric forms, similar to native IgM. First, we verified that the CH3-CH4 protein scaffold also binds FcμR, is internalized and addressed to the lysosomes. Next, we conjugated the CH3-CH4 protein scaffold to cemadotin, a synthetic anti-mitotic agent that inhibits tubulin polymerization. This CH3-CH4-cemadotin conjugate was designed to specifically release the drug inside the cell by inserting a peptide linker that can by cleaved by cathepsin B in the lysosomal compartment. In vitro cell killing showed that this CH3-CH4-cemadotin conjugate potently and selectively killed FcμR expressing cells (IC(50) <0.16 μM) while it was about 200-fold less efficient for cells with undetectable FcμR (IC(50) >31 μM). Control experiments showed equal, i.e. non-selective cytotoxicity of free cemadotin against FcμR expressing and non-expressing cells and absence of cell killing with the unconjugated CH3-CH4 protein scaffold. Taken together, these data identify FcμR as a promising therapeutic target in CLL and possibly select other malignanices. IgM-derived scaffolds constitute ideal carriers for drugs or toxins as they are rapidly internalized. In addition, trafficking of IgM scaffolds to the lysosome provides an additional layer of selectivity as a precursor inactive drug can be activated through lysosomal peptidases. Ongoing efforts aim to test modifications of the scaffold and evaluate additional cytotoxic drugs. Furthermore, we are scaling up production of the lead scaffold drug conjugate in order to test its efficacy in xenograft mouse models. This work was supported by the Intramural Research Program of the National, Heart, Lung and Blood Institute. Disclosures: No relevant conflicts of interest to declare.

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Rafiq, Sarwish, Jonathan P. Butchar, Carolyn Cheney, Xiaokui Mo, David Jarjoura, Susheela Tridandapani, Natarajan Muthusamy et John C. Byrd. « Comparative Assessment of Different Clinically Utilized CD20 Directed Antibodies in Chronic Lymphocytic Leukemia (CLL) Cells Reveals Divergent NK-Cell, Monocyte and Macrophage Properties »,. Blood 118, n^o 21 (18 novembre 2011) : 3717. http://dx.doi.org/10.1182/blood.v118.21.3717.3717.

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Abstract Abstract 3717 The anti-CD20 antibody rituximab represents the first therapy to contribute to prolongation of survival in CLL yet controversy exists as to how it promotes tumor elimination. Pre-clinical studies in CLL have suggested that innate immune cells, complement, and direct antibody killing might contribute to anti-CD20 antibody efficacy. Murine models of B-cell depletion by CD20 antibodies have shown monocytes to be the most important effector cell, although significant controversy around this point exists. Given the success of rituximab, second generation anti-CD20 antibodies (Ofatumumab and GA101 are now in phase III testing in CLL with reported improved direct (GA101), complement (Ofatumumab), or NK cell effector cell killing (GA101). To date, direct comparison of these three antibodies for direct, complement, and effector cell engagement has not been performed. Additionally, the impact of afucosylation engineering of GA101 on monocyte and macrophage function has not been reported. As a Type II anti-CD20 antibody, GA101 mediated significantly increased cell death (∼25%) without Fc crosslinking when compared to Ofatumumab or rituximab (5–8%). Direct cytotoxicity assessment of 19 pts with cross-linking demonstrated GA101 (25%) to mediate significantly greater (p=0.0003) killing than rituximab (15%) but not Ofatumumab (20%). Complement mediated killing was significantly increased over media with Ofatumumab (∼30%), whereas an average of only 5–10% killing was observed with rituximab or GA101. Immobilized GA101 significantly increased NK cell activation as detected by IFNg production and CD107a induction (p=0.005) more than rituximab or Ofatumumab. In addition, GA101 mediates 2 to 3 fold greater NK cell-mediated Antibody Dependent Cellular Cytotoxicity (ADCC) compared to Ofatumumab or rituximab at higher antibody concentrations, but not at concentrations less than 0.05 mg/ml. This enhanced ADCC with GA101 is seen with normal NK cells as well as NK cells from CLL patients. Ofatumumab mediated significantly greater (p=0.0001) NK cell ADCC than rituximab. Given the importance of macrophages in depletion of anti-CD20 tumors in mouse models of lymphoma, we next focused on this. The three anti-CD20 antibodies show Antibody Dependent Cellular Phagocytosis (ADCP) capability with Monocyte Derived Macrophages (MDM) against CLL B cells, with Ofatumumab exhibiting the greatest ADCP compared to GA101 (60% vs 40%; p=0.0036). In addition, primary monocytes stimulated with immobilized GA101 show less TNFa release, when compared to rituximab or Ofatumumab. To investigate this mechanistically, monocytes were stimulated with plate bound rituximab, Ofatumumab or GA101. Compared to the non Fc engineered antibodies (rituximab and Ofatumumab) Fc engineered GA101 induces reduced pan tyrosine phosphorylation and phosphorylation of ERK. No differences in phosphorylation of FcgRIIa or FcgRIIb was observed between the engineered and non-engineered antibodies. Further mechanistic studies to elucidate these differences in monocytes based upon antibody afucosylation changes, or differential phosphorylation of FcgR are ongoing. Collectively, our data indicate that GA101 and Ofatumumab are both superior to rituximab against CLL cells and have differential properties with respect to apoptosis, CDC, and effector cell-mediated killing. GA-101 mediates the most potent NK cell mediated killing at high concentrations whereas Ofatumumab has the greatest monocyte activation and phagocytosis despite absence of any engineering. These findings have relevance in the choice of the optimal CD20 antibody for treatment of CLL and combination strategies used. Disclosures: No relevant conflicts of interest to declare.

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Chen, Shih-Shih, Jacqueline Barrientos, Xiao-Jie Yan, Uwe Wirtz, Edith Szafer-Glusman, Kanti R. Rai et Nicholas Chiorazzi. « Efficacy of Ibrutinib Monotherapy in Pre-Clinical Mouse Models of Richter Transformation : Ibrutinib Effectively Reduces the Incidence of Richter Transformation but Fails in Treating Transformed Lymphoma, Especially in Primary Lymphoid Tissue ». Blood 138, Supplement 1 (5 novembre 2021) : 3708. http://dx.doi.org/10.1182/blood-2021-153685.

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Abstract Richter's transformation (RT) is a complication of chronic lymphocytic leukemia (CLL) characterized by the development of an aggressive lymphoma, typically diffuse large B cell lymphoma (DLBCL). RT is associated with high expression of activation-induced cytidine deaminase (AID) and aberrant somatic hypermutation of non-immunoglobulin genes. Current frontline therapy of CLL, ibrutinib, eliminates AID + CLL cells and alters tissue microenvironment to Th1-biased niches; however approximately 10-20% of CLL patients develop RT upon ibrutinib treatment. In addition, ibrutinib leads to a clinical response in only ~40% of RT patients. Thus, RT remains an important unmet challenge for CLL patients and the mechanism of RT development during ibrutinib treatment is poorly understood. To determine the contributions of AID and T cells in RT development, and to understand the efficacy of ibrutinib in the treatment of RT, we first created patient-derived xenografts (PDXs) with samples from three RT patients who were refractory to (immuno)chemotherapy but had not previously received ibrutinib. In each case, the B-lymphocytes were larger in size and expressed lower levels of CD5 but higher levels of activation markers compared with the CLL cell counterpart. In PDXs, ibrutinib treatment led to significantly less RT cells in spleen with percentage of inhibition ranging from 28-60% for all three cases. Notably, AID levels were similar in RT cells residing in spleen of ibrutinib-treated and control mice. The numbers of T cells were also similar, although Th1:Th2 ratios were significantly increased by ibrutinib (control vs ibrutinib group: 33% vs 42%, P=0.01). Interestingly, the growth and survival of RT cells located in bone marrow (BM) were not affected by ibrutinib. We then investigated the efficacy of ibrutinib in the prevention and treatment of RT in a novel strain of TCL-1 mice, TCL1/Igκ-AID mice, that have AID overexpressed solely in B lymphocytes. These mice develop accelerated CLL disease, have shorter overall survival (OS), and bear increased numbers of AID signature mutations in genes that are drivers in CLL and DLBCL. First we injected primary splenocytes from a TCL1/Igκ-AID mouse (A-31) into wild-type C57BL/6 mice. A week later, mice were treated with vehicle or ibrutinib continuously for 3 weeks (N=5 per group, duplicated experiments). At the end of treatment, RT cells were found in 25% of recipients in the control group and only in 10% of ibrutinib-treated recipients. Ibrutinib-treated animals had overall smaller spleens and lymph nodes (LNs) filled with significantly less CLL or RT cells. Importantly, the balance of Th1/Th2 cytokines was also significantly changed by ibrutinib (Th1/Th2 in control vs ibrutinib: 25% vs 47%, P=0.01). However, again RT cells in BMs of treated and control animals were similar. We then repeated the experiment to determine overall survival by giving the mice vehicle or ibrutinib continuously. Compared to the TCL1/Igκ-AID (A-31) donors, recipients treated with control vehicle developed more aggressive CLL with shorter OS. However, Ibrutinib did not change the OS; both control and ibrutinib treated recipients had similar OS with all the mice developed and died from RT eventually. Finally, to determine the efficacy of ibrutinib in the treatment of RT in TCL1/Igκ-AID mice, we sorted A-31-derived RT cells collected from LNs, and injected these into C57BL/6 mice. Mice then received treatment for 3 weeks. Notably, ibrutinib did not change the numbers or sizes of LNs or spleens. The numbers of RT cells at all sites, including BM, remained the same. In both groups, the number of T cells and the Th1:Th2 were not altered by ibrutinib. In summary, our data suggest that ibrutinib is somewhat effective against primary RT cells in the spleen in PDX models but not at all in the aggressive TCL1/IgK-AID mouse model. This might be because ibrutinib does not reduce AID levels in tissue-resident RT cells. Notably, although RT cells in spleens and LNs respond to ibrutinib, those residing in BM are resistant in both PDX and TCL1/IgK-AID models. This suggests different clones or different ibrutinib-responsiveness of RT cells in primary versus secondary lymphoid tissues. Overall, these results suggest that ibrutinib does not prevent or cure RT. Additionally, TCL1/Igκ-AID mice might provide a model to study the development, prevention, and treatment of RT without the influence of prior chemo- or other therapies. Disclosures Wirtz: Abbvie: Current Employment. Szafer-Glusman: AbbVie: Current Employment, Other: Stock or other ownership.

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Li, Lingxiao, Praechompoo Pongtornpipat, Timothy Tiutan, Samantha L. Kendrick, Soyoung Park, Daniel O. Persky, Lisa M. Rimsza, Soham D. Puvvada et Jonathan H. Schatz. « Potent Efficacy of BCL2 Inhibition with ABT-199 in High-Risk Aggressive B-Lymphoma Models When Combined with Knockdown of MCL1 ». Blood 124, n^o 21 (6 décembre 2014) : 506. http://dx.doi.org/10.1182/blood.v124.21.506.506.

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Abstract Avoiding apoptosis is a hallmark of cancer. Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoma and carries a poor prognosis in cases at high-risk of failing up-front R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone). Frequent expression of the anti-apoptotic protein BCL2 is well-described in DLBCL in numerous studies and is clear a negative prognostic marker when co-expressed with the oncogenic transcription factor c-MYC. Expression of the anti-apoptotic protein MCL1 also is found in about half of cases. BCL2 and MCL1 have redundant function in protecting cells from apoptosis. Direct inhibitors of MCL1 are not clinically available, but its short half-life permits knock-down through inhibition of cyclin-dependent kinase 9 (CDK9), which regulates transcriptional elongation. Older multi-CDK inhibitors have anti-tumor activity from loss of MCL1 but are not approved clinically due to off-target toxicities. Dinaciclib is a more potent and specific multi-CDK inhibitor with activity against CDK9. We tested dinaciclib against a panel of >20 DLBCL cell lines and found high potency, with IC50 < 20 nM in most lines. Both in vitro and in vivo, dinaciclib results in rapid loss of MCL1 protein and corresponding induction of apoptosis. Interestingly, both sensitive and resistant lines show loss of MCL1 in response to the compound. Thus, we hypothesized BCL2 activity compensates for loss of MCL1 in resistant lines. Correspondingly, over-expression of BCL2 in sensitive cells renders them completely insensitive to dinaciclib without effecting MCL1 knockdown. In 59 DLBCL cases with known BCL2 status, we assessed MCL1 protein by immunohistochemistry and found no significant difference in MCL1 expression between BCL2 positive (66%, 10/15) and negative (57%, 25/44) cases (p=0.5576). Expression of MCL1, BCL2, or both in DLBCL and the proteins’ redundant function led to the hypothesis that knockdown of MCL1 combined with direct BCL2 inhibition would synergize in the killing of high-risk DLBCL tumors. ABT-199 is a third-generation BH3 mimetic direct inhibitor of BCL2, which has shown remarkable clinical activity in chronic lymphocytic leukemia but less activity in DLBCL and other more aggressive lymphomas. We found ABT-199 combines potently and synergistically with dinaciclib in DLBCL cell lines with none of 23 lines resistant to the combination. We confirmed this in vivo using the line U2932, which is resistant in vitro to both drugs as single agents. U2932 xenografts showed dramatic reduction of tumor burden in response to the combination, a response far superior to either drug alone. We next evaluated a genetically defined immunocompetent mouse model of MYC-BCL2 double-hit lymphoma, based on MYC expression in the VavP-Bcl2 transgenic model, replicating the genetics, pathology, and aggressive clinical behavior of the human disease. Tumors from this model in vitro, interestingly, show little response to single-agent ABT-199, but the combination with dinaciclib is again synergistic. Treatment of tumor-bearing mice in vivo showed animals treated with either drug alone had no significant survival difference from vehicle-treated controls, while those treated with the combination had dramatically improved survival by Kaplan-Meier analysis (p<0.0001). Finally, we assessed the effect of combining ABT-199 with standard lymphoma chemotherapy drugs that are thought to affect MCL1 protein levels due to global effects on transcription. Doxorubicin, etoposide, and cytarabine all result in loss of MCL1 at peak in vivo attainable concentrations and synergize with ABT-199 to kill DLBCL cells otherwise resistant to the single agents. In sum, we propose therapeutic strategies combining direct inhibition of BCL2 with knockdown of MCL1 expression will be effective and tolerable for poor-prognosis lymphomas such as high-risk DLBCL and double-hit lymphoma. Disclosures No relevant conflicts of interest to declare.

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Galan, Patricia Perez, Colby M. Chapman, Federica Gibellini, Poching Liu, Nalini Raghavachari, Mark Roschewski et Adrian Wiestner. « The PI3K Inhibitor ON 01910.Na Inhibits Critical Survival Pathways and Induces Apoptosis in CLL Cells through Induction of NOXA and BIM. » Blood 114, n^o 22 (20 novembre 2009) : 412. http://dx.doi.org/10.1182/blood.v114.22.412.412.

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Abstract Abstract 412 Chronic Lymphocytic leukemia (CLL), the most common leukemia in Western countries, is a clinically heterogeneous disease characterized by the accumulation of mature B lymphocytes. Disease progression is driven by cell survival and proliferation signals provided by the tumor microenvironment through different receptors including the B-cell receptor, TNF, chemokine and cytokine receptors, and through other cell-cell interactions. ON 01910.Na (Onconova, Therapeutics) belongs to the family of styryl benzyl sulfones, a novel family of non-ATP competitive compounds that are currently under development as potential anticancer treatments. These compounds have shown activity in a variety of xenograft mouse models. Interestingly, it has recently been described that ON 01910.Na exerts potent antitumor activity against Mantle Cell Lymphoma (MCL) cells by inhibition of PI-3K/Akt/mTOR pathway and downregulation of Cyclin D1 translation. Here, we evaluated the cytotoxic effect of ON 01910.Na after 48 hours of in vitro exposure on PBMCs from CLL and normal donors by flow cytometry using AnnexinV-PE. We co-stained with CD3-APC and CD19-FITC to assess the effect on B and T cells separately. ON 01910.Na induced apoptosis of the leukemic cells in all CLL samples tested (n=24), without affecting T-cell viability. Notably, ON 01910.Na did not affect B and T cells from normal donors at concentrations that induced apoptosis of CLL cells. Thirteen CLL samples were highly sensitive towards ON 01910.Na (mean B-cell IC50 0.71 μM) a concentration readily achieved in phase I clinical trials, eight samples were sensitive (mean B-cell IC50 1.38 μM) and three showed moderate sensitivity (mean B-cell IC50 4.26 μM). In contrast, the IC50 of T-cells was >8 μM in all samples. No significant differences were found in ON 01910.Na cytotoxicity against CLL expressing mutated (n=9, mean B-cell IC50 1.45 μM) or unmutated (n=15, mean B-cell IC50 1.34μM) IgVH sequences. ON 01910.Na was also effective against tumor cells having 17p (n=4, mean B-cell IC50 1.45 μM) or 11q deletions (n=3, mean B-cell IC50 0.96 μM). ON 01910.Na activated the mitochondrial apoptotic pathway, as shown by flow cytometry using conformation specific antibodies to detect activation of Bax and Bak, leading to mitochondrial depolarization (measured by mitotracker) and caspase-3 activation. ON 01910.Na also induced the upregulation of the proapoptotic BH3-only proteins Noxa and Bim and decreased expression of Mcl-1 at 4 hours, well before the onset of apoptosis. Inhibition of Noxa expression by retroviral transfection reduced the sensitivity to drug by 60%. ON 01910.Na induced reactive oxygen species (ROS) that may contribute to Noxa induction. Consistently ROS blockade using N-acetyl-cysteine reduced ON 01910.Na cytotoxic activity. To further delineate the biological processes underlying ON 01910.Na induced apoptosis, we performed Gene Expression Profiling (GEP) in CLL cells treated in vitro for 4 and 10 hours with ON 01910.Na. GEP revealed the induction of Noxa and ATF3, consistent with an oxidative stress response. Noteworthy, Gene Set Enrichment Analysis (GSEA) of microarray data showed an induction of an AP-1 gene signature, (False Discovery Rate (FDR) = 0.10), validated by the nuclear accumulation of c-jun at 4 hours and a FOXO gene signature (FDR=0.13) that correlated with the upregulation of the proapoptotic BH3-only protein Bim. Strikingly, ON 01910.Na repressed B-cell receptor (FDR=0.023), NF-kB (FDR=0.084) and PI3K gene signatures. Consistent with inhibition of the BCR/PI3K/AKT axis, ON 01910.Na inhibited AKT phosphorylation by 65% after in vitro BCR activation of CLL cells. Our results identify ON 01910.Na as a promising agent in the treatment of CLL with an interesting dual mechanism of action: activation of apoptotic stress signals leading to Noxa and BIM up-regulation, combined with inhibition of the BCR/PI3K/AKT pathway that can block microenvironment-induced survival and proliferation signals. These data support the development of ON 01910.Na in CLL and a clinical trial has been initiated at our institution. Disclosures: No relevant conflicts of interest to declare.

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Chekmasova, Alena A., Holly M. Horton, Tracy E. Garrett, John W. Evans, Johanna Griecci, Amanda Hamel, Howard J. Latimer et al. « A Novel and Highly Potent CAR T Cell Drug Product for Treatment of BCMA-Expressing Hematological Malignances ». Blood 126, n^o 23 (3 décembre 2015) : 3094. http://dx.doi.org/10.1182/blood.v126.23.3094.3094.

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Abstract Recently, B cell maturation antigen (BCMA) expression has been proposed as a marker for identification of malignant plasma cells in patients with multiple myeloma (MM). Nearly all MM and some lymphoma tumor cells express BCMA, while normal tissue expression is restricted to plasma cells and a subset of mature B cells. Targeting BCMA maybe a therapeutic option for treatment of patients with MM and some lymphomas. We are developing a chimeric antigen receptor (CAR)-based therapy for the treatment of BCMA-expressing MM. Our anti-BCMA CAR consists of an extracellular single chain variable fragment (scFv) antigen recognition domain derived from an antibody specific to BCMA, fused to CD137 (4-1BB) co-stimulatory and CD3zeta chain signaling domains. Selection of our development candidate was based on the screening of four distinct anti-BCMA CARs (BCMA01-04) each comprised of unique single chain variable fragments. One candidate, BCMA02 (drug product name bb2121) was selected for further studies based on the robust frequency of CAR-positive cells, increased surface expression of the CAR molecule, and superior in vitro cytokine release and cytolytic activity against the MM cell lines. In addition to displaying specific activity against MM (U226-B1, RPMI-8226 and H929) and plasmacytoma (H929) cell lines, bb2121 was demonstrated to react to lymphoma cell lines, including Burkitt's (Raji, Daudi, Ramos), chronic lymphocytic leukemia (Mec-1), diffuse large B cell (Toledo), and a Mantle cell lymphoma (JeKo-1). Based on receptor density quantification, bb2121 can recognize tumor cells expressing less than 1000 BCMA molecules per cell. The in vivo pharmacology of bb2121 was studied in NSG mouse models of human MM and Burkitt's lymphoma. NSG mice were injected subcutaneously (SC) with 107 RPMI-8226 MM cells. After 18 days, mice received a single intravenous (IV) administration of vehicle or anti-CD19Δ (negative control, anti-CD19 CAR lacking signaling domain) or anti-BCMA CAR T cells, or repeated IV administration of bortezomib (Velcade®; 1 mg/kg twice weekly for 4 weeks). Bortezomib, which is a standard of care for MM, induced only transient reductions in tumor size and was associated with toxicity, as indicated by substantial weight loss during dosing. The vehicle and anti-CD19Δ CAR T cells failed to inhibit tumor growth. In contrast, treatment with bb2121 resulted in rapid and sustained elimination of the tumors, increased body weights, and 100% survival. Flow cytometry and immunohistochemical analysis of bb2121 T cells demonstrated trafficking of CAR+ T cells to the tumors (by Day 5) followed by significant expansion of anti-BCMA CAR+ T cells within the tumor and peripheral blood (Days 8-10), accompanied by tumor clearance and subsequent reductions in circulating CAR+ T cell numbers (Days 22-29). To further test the potency of bb2121, we used the CD19+ Daudi cell line, which has a low level of BCMA expression detectable by flow cytometry and receptor quantification analysis, but is negative by immunohistochemistry. NSG mice were injected IV with Daudi cells and allowed to accumulate a large systemic tumor burden before being treated with CAR+ T cells. Treatment with vehicle or anti-CD19Δ CAR T cells failed to prevent tumor growth. In contrast, anti-CD19 CAR T cells and anti-BCMA bb2121 demonstrated tumor clearance. Adoptive T cell immunotherapy approaches designed to modify a patient's own lymphocytes to target the BCMA antigen have clear indications as a possible therapy for MM and could be an alternative method for treatment of other chemotherapy-refractory B-cell malignancies. Based on these results, we will be initiating a phase I clinical trial of bb2121 for the treatment of patients with MM. Disclosures Chekmasova: bluebird bio, Inc: Employment, Equity Ownership. Horton:bluebird bio: Employment, Equity Ownership. Garrett:bluebird bio: Employment, Equity Ownership. Evans:bluebird bio, Inc: Employment, Equity Ownership. Griecci:bluebird bio, Inc: Employment, Equity Ownership. Hamel:bluebird bio: Employment, Equity Ownership. Latimer:bluebird bio: Employment, Equity Ownership. Seidel:bluebird bio, Inc: Employment, Equity Ownership. Ryu:bluebird bio, Inc: Employment, Equity Ownership. Kuczewski:bluebird bio: Employment, Equity Ownership. Horvath:bluebird bio: Employment, Equity Ownership. Friedman:bluebird bio: Employment, Equity Ownership. Morgan:bluebird bio: Employment, Equity Ownership.

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Oostindie, Simone C., Hilma J. Van Der Horst, Marije B. Overdijk, Kristin Strumane, Sandra Verploegen, Margaret A. Lindorfer, Erica M. Cook et al. « Duohexabody-CD37, a Novel Bispecific Antibody with a Hexamerization-Enhancing Mutation Targeting CD37, Demonstrates Superior Complement-Dependent Cytotoxicity in Preclinical B-Cell Malignancy Models ». Blood 132, Supplement 1 (29 novembre 2018) : 4170. http://dx.doi.org/10.1182/blood-2018-99-114723.

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Abstract CD37 is a tetraspanin plasma membrane protein abundantly expressed on B-cells and represents a promising therapeutic target for the treatment of B-cell malignancies. Although complement-dependent cytotoxicity (CDC) has proven to be a powerful Fc-mediated effector function for killing hematological cancer cells, CD37 antibody-based therapeutics currently in clinical development are poor inducers of CDC. Here we present DuoHexaBody-CD37, a novel humanized IgG1 bispecific antibody targeting two different CD37 epitopes, with an E430G hexamerization-enhancing mutation, for the potential treatment of B-cell malignancies. The natural process of antibody hexamer formation through intermolecular Fc-Fc interactions between IgG molecules after cell surface antigen binding can be improved by introducing a single point mutation such as E430G in the IgG Fc domain, thereby facilitating more efficient C1q binding and complement activation (Diebolder et al., Science 2014; de Jong et al., PLoS Biol 2016). The hexamerization-enhancing mutation E430G was introduced into two humanized CD37 monoclonal antibodies (mAbs) that bind non-overlapping CD37 epitopes. Different antibody formats and combinations, including the single antibodies, combinations of the mAbs and bispecific mAbs were tested for their capacity to induce CDC and antibody-dependent cellular cytotoxicity (ADCC). The bispecific hexamerization-enhanced antibody variant DuoHexaBody-CD37, showed superior CDC activity compared to the single hexamerization-enhanced mAbs and the combination thereof, both in vitro over a range of different B-cell lines, and ex vivo in tumor cell samples obtained from patients with chronic lymphocytic leukemia (CLL). In a CDC assay using tumor cells obtained from a relapsed/refractory CLL patient who received prior treatment with rituximab, ibrutinib and idelalisib, DuoHexaBody-CD37 induced almost complete lysis (84% lysis at a concentration 100 µg/mL), thereby outperforming the single HexaBody molecules (15% and 23% lysis) and the combination (57%) (Figure 1). In addition to its potent CDC activity, DuoHexaBody-CD37 was also capable of inducing potent ADCC of Daudi cells (EC50 = 12.3 ± 9.5 ng/mL), as assessed using peripheral blood mononuclear cells from 8 healthy human donors in a standard chromium release assay. In assays using whole blood from 6 healthy human donors, DuoHexaBody-CD37 showed efficient B-cell binding and potent and specific depletion of the B-cell population (98% ± 1.3% depletion at 10 µg/mL, EC50 = 0.85 ± 0.284 µg/mL). Furthermore, DuoHexaBody-CD37 induced significant inhibition of tumor growth in vivo in Daudi-luc Burkitt's lymphoma and JVM-3 CLL mouse xenograft models, at doses as low as 0.1 and 1 mg/kg (p<0.05), respectively. In summary, we present a novel therapeutic antibody that, for the first time, combines proprietary DuoBody® and HexaBody® platforms. DuoHexaBody-CD37 induced highly potent CDC and efficient ADCC in preclinical models, suggesting that DuoHexaBody-CD37 may serve as a potential therapeutic mAb for the treatment of human B-cell malignancies. Disclosures Oostindie: Genmab: Employment, Equity Ownership. Van Der Horst:Genmab: Research Funding. Overdijk:Genmab: Employment, Equity Ownership. Strumane:Genmab: Employment, Equity Ownership. Verploegen:Genmab: Employment, Equity Ownership. Lindorfer:Genmab: Research Funding. Cook:Genmab: Research Funding. Chamuleau:Gilead: Research Funding; BMS: Research Funding; celgene: Research Funding; Genmab: Research Funding. Mutis:Gilead: Research Funding; Celgene: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genmab: Research Funding; Novartis: Research Funding; OnkImmune: Research Funding. Schuurman:Genmab: Employment, Other: Warrants. Sasser:Genmab: Employment, Equity Ownership. Taylor:Genmab: Research Funding. Parren:Genmab: Equity Ownership; Lava Therapeutics: Employment. Beurskens:Genmab: Employment, Equity Ownership. Breij:Genmab: Employment, Equity Ownership.

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Robbins, Daniel W., Mark Noviski, Ryan Rountree, May Tan, Nivetha Brathaban, Timothy Ingallinera, Dane E. Karr et al. « Nx-5948, a Selective Degrader of BTK with Activity in Preclinical Models of Hematologic and Brain Malignancies ». Blood 138, Supplement 1 (5 novembre 2021) : 2251. http://dx.doi.org/10.1182/blood-2021-147473.

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Abstract Bruton's tyrosine kinase (BTK) plays a key role in cell survival in B cell malignancies, and covalent inhibitors of BTK, such as ibrutinib and acalabrutinib, have proven efficacious in chronic lymphocytic leukemia (CLL), mantle cell lymphoma (MCL), marginal zone lymphoma (MZL), and Waldenstrom's macroglobulinemia (WM). BTK inhibitors have also demonstrated clinical activity in small trials of patients with relapsed/refractory primary central nervous system lymphoma. The long-term efficacy of BTK inhibitors is limited by the emergence of resistance mutations, most commonly at C481 of BTK. These mutations preclude formation of a covalent bond with BTK and lead to diminished efficacy and disease progression. Several noncovalent BTK inhibitors, which do not require covalent binding to C481, are currently being investigated in clinical trials as potential therapies for patients with relapsed and refractory disease. However, other mutations have been shown to decrease the in vitro activity of these non-covalent BTK inhibitors, suggesting that mutations may ultimately limit the effectiveness of these compounds as well. Small molecule-induced protein degradation offers a unique approach to target BTK for the treatment of B-cell malignancies. Chimeric Targeting Molecules (CTMs) catalyze ubiquitylation and proteasomal degradation of target proteins and are comprised of a target binding element ("hook"), a linker, and ubiquitin ligase binding element ("harness"). NX-5948 is a CTM that contains a BTK hook linked to a cereblon (CRBN) harness. While some CRBN-binding drugs, such as lenalidomide and pomalidomide, promote the degradation of neo-substrate proteins, such as the transcription factors Aiolos and Ikaros, NX-5948 has been engineered to avoid Aiolos and Ikaros degradation and therefore does not possess IMiD activity. Preclinical studies have shown that NX-5948 catalyzes the degradation of 50% of cellular BTK (DC 50) at < 1 nM concentrations in lymphoma cell lines and peripheral blood mononuclear cells (PBMCs). NX-5948 impairs viability in the BTK-dependent ABC-DLBCL cell line, TMD8 (EC 50: < 10 nM after 72 hours). Importantly, NX-5948 induces degradation of the mutated BTK-C481S in cells and inhibits proliferation of BTK-C481S mutant TMD8 cells more effectively than ibrutinib (NX-5948 EC 50 values of < 10 nM versus > 1 μM for ibrutinib). NX-5948 also catalyzes selective degradation of BTK. In an unbiased proteomics experiment, NX-5948 treatment of TMD8 cells demonstrates robust BTK degradation without significant downregulation of other off-target proteins. Oral administration of NX-5948 in mice leads to dose-proportional exposure in plasma and BTK degradation to <10% of baseline levels in circulating and splenic B cells. In a TMD8 xenograft model in mice containing the BTK-C481S mutation, daily oral administration of NX-5948 resulted in superior tumor growth inhibition (TGI) as compared to ibrutinib. Following a single oral dose of NX-5948 in cynomolgus monkeys, BTK degradation to <10% of baseline levels is observed in the circulating B cells. In addition, NX-5948 penetrates the central nervous system (CNS) and demonstrates activity in a model of brain malignancies. Following oral dosing of NX-5948 to mice, NX-5948 was detectable in the cerebrospinal fluid at a comparable level to the unbound concentration of NX-5948 in mouse plasma. In an intracranial TMD8 xenograft model, treatment with NX-5948 resulted in degradation of BTK in intracranial TMD8 cells, decreased intracranial tumor burden and improved survival relative to treatment with vehicle. The potent BTK degradation activity of NX-5948 and the ability of this molecule to penetrate the CNS supports its development for the treatment of B-cell malignancies, including CNS lymphoma. Disclosures Robbins: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Noviski: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Rountree: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Tan: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Brathaban: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Ingallinera: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Karr: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Kelly: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Konst: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Ma: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Tenn-McClellan: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. McKinnell: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Perez: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Guiducci: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Hansen: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company. Sands: Nurix Therapeutics: Current Employment, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees.

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Yin, Changhong, Sanghoon Lee, Timmy O'Connell, Janet Ayello, Carmella van de Ven et Mitchell S. Cairo. « Obinutuzumab (GA101) Significantly Inhibits Cell Proliferation and Induces Programmed Cell Death in Primary Mediastinal B-Cell Lymphoma (PMBL) : Obinutuzumab May be a Future Targeted Agent for the Treatment of PMBL ». Blood 124, n^o 21 (6 décembre 2014) : 4492. http://dx.doi.org/10.1182/blood.v124.21.4492.4492.

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Abstract BACKGROUND: Primary Mediastinal large B-cell lymphoma (PMBL) is a rare form of Non Hodgkin Lymphoma (NHL) representing 2% of mature B-cell non-Hodgkin lymphoma in patients less than 18 years of age (Lones/Cairo et al, JCO 2000; Burkhardt et al, BJH 2005). PMBL has histological features somewhere between Diffuse Large B-Cell Lymphoma (DLBCL) and classical HL (cHL) (Abramson et al, Blood 2005). Gene expression studies suggested that the molecular signature of PMBL had a striking resemblance to the expression profile of cHL (Rosenwald et al, JEM 2003). We have recently reported that a significant decrease in EFS among children and adolescent PMBL patients compared with other stage III non-PMBL pediatric DLBCL patients following FAB/LMB 96 therapy, suggesting that children and adolescent with PMBL required alternative treatment strategies (Gerrard/Cairo et al, Blood 2013). PMBL has been demonstrated to have an over-activated NF-kB pathway by gene expression profiling (Rosenwald et al, JEM 2003). Since over 95% of PMBL express CD20, targeting the CD20 receptor with a CD20 antibody is of high clinical interest. Obinutuzumab (GA101) is novel glycoengineered anti-CD20 targeted monoclonal antibody recognizing a unique CD20 type II epitope and it has been demonstrated to have greater efficacy in reducing tumor size, inducing remission and improving survival in other B-NHL xenograft models (Mössner et al, Blood 2010). Obinutuzumab has been recently approved by FDA for first line treatment of chronic lymphocytic leukemia (CLL) in combination with chlorambucil. OBJECTIVES: We hypothesize that obinutuzumab may be a future potential targeted agent for the treatment of PMBL, and therefore, we investigated whether obinutuzumab treatment results in significant changes in signaling pathways, genes expression, programmed cell death and cell proliferation in PMBL. METHODS: Karpas-1106P cells (DSMZ) were treated with obinutuzumab (generously provided by Dr. Klein, Roche) at every 24 hours (1-100ug/ml). qRT-PCR, western blot, MTS, Caspase 3/7 assay (Promega) and FACS analysis were performed. The BeadChip array (Illumina, HumanHT-12) was used for gene expression profiling. RESULTS: There was a significant decrease of cell proliferation in obinutuzumab-treated Karpas cells with 10ug/ml (0.69 ± 0.025, p<0.005) vs control (1.00 ± 0.000) at 48 hours. Concomitantly, there was a significant increase in programmed cell death in 10ug/ml obinutuzumab treated Karpas (37.80 ± 10.096, p<0.05) vs control (1.19 ± 0.762) at 48 hours. We also observed a significant decrease of CD20 expression (0.74± 0.010, p<0.05) with 10ug/ml obinutuzumab treatment at 48 hours. A total of 133 differentially expressed genes were identified by gene expression profiling (>1.5-fold, 0.57%) and 77.5% of genes including apoptosis related genes (CASP2 and PAK2) and MAPK signaling pathways (RASA1 and JUN) and EGR1 were upregulated and 22.5% of genes including ID3, GRAP and RAB6B were downregulated in obinutuzumab treated Karpas vs control (Fig 1). There were significant decreases of p-STAT6 (0.72± 0.011, p=0.01), p-Akt (0.69± 0.011, p<0.05), p-ikBα (0.70± 0.017, p<0.05) and p-Erk (0.56± 0.019, p<0.05) with 10ug/ml obinutuzumab treatment at 48 hours (Fig 2). Additionally, There were significant down-regulation of mRNA expression of Bcl-xL (0.91±0.011, p<0.04) and Bax (0.66±0.022, p<0.02) vs control. CONCLUSIONS: We observed that obinutuzumab significantly inhibited cell proliferation and induced programmed cell death and downregulated downstream of PI3k/Akt and NF-kB signaling pathways. Gene expression analysis indicated obinutuzumab induced changes in the expression of genes in Karpas that were involved in apoptosis and signaling pathways including CASP2, EGR1 and ID3. Future studies 1) will investigate the efficacy of combination therapies to enhance programmed cell death, and 2) will assess the proteomic signature induced by obinutuzumab in obinutuzumab sensitive and resistant PMBL, and furthermore, 3) will focus on the in vivo effects of obinutuzumab in a NOD/SCID PMBL xenograft mouse model. Obinutuzumab may be a future potential targeted agent for the adjuvant treatment of PMBL lymphoma. Disclosures No relevant conflicts of interest to declare.

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Mani, Rajeswaran, Samon Benrashid, Sarah E. Teague, Scott C. Jaros, Hsih-Te Yang, Lawrence J. Druhan, David M. Foureau et al. « Aurora Kinase Inhibition Overcomes Primary Venetoclax Failure and Leads to Synthetic Lethality in BCL2-Positive Lymphomas Via Upregulation of P53/P21/BAX Axis ». Blood 138, Supplement 1 (5 novembre 2021) : 682. http://dx.doi.org/10.1182/blood-2021-146064.

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Abstract Venetoclax (VEN), a BCL2 specific inhibitor, has shown excellent clinical activities in various types of non-Hodgkin lymphoma, and it is FDA-approved in patients with chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL). However, its efficacy has been mostly disappointing in BCL2-positive (BCL2+) lymphomas harboring classic BCL2 rearrangements, including follicular lymphoma (FL), double-hit lymphoma (DHL), and triple-hit lymphoma (THL). The mechanism by which BCL2+ lymphomas evade BCL2 inhibition remains elusive although it has shown to be in part due to overexpression of anti-apoptotic proteins like BCLxL or MCL1. Aurora kinases (AURK) are serine threonine kinases involved in mitotic regulation and have functional role in stabilization of regulatory proteins such as MYC. Here in we investigated potential mechanisms of primary resistance to VEN and the effect of AURK inhibition in overcoming primary VEN failure in BCL2+ lymphomas. BCL2+ lymphoma cells, WSU-NHL (single hit; BCL2 only), DoHH2 (DHL; BCL2 and MYC), and VAL (THL; BCL2, MYC, and BCL6) were evaluated for cell viability (ATP quantification) and apoptosis (Annexin V/7AAD staining), after treatment with various concentrations of VEN with or without MLN8237 (AURK-A inhibitor), LY3295668 (AURK-A inhibitor), or AZD2811 (AURK-B inhibitor). Addition of an AURK-A or B inhibitor to VEN induced robust killing and displayed synergism only in BCL2+ but not in BCL2-negative Raji and Ramos Burkitt lymphoma cells (MYC only). AURK-A inhibition using MLN8237 was chosen for further in-depth functional analysis. Immunoblotting revealed increased caspase-3 cleavage in DoHH2 cells treated with VEN+MLN8237 combination than either agent alone. No significant changes in BCL2, BCLxL or MCL1 protein levels were noticed in DoHH2 and VAL cells after single or combined treatments. However, MLN8237 resulted in elevated levels of proapoptotic proteins BAX and PUMA. MYC degradation occurred later in cells after treatment with MLN8237 or combination implying that MYC degradation may be a delayed and independent effect. Furthermore, VEN+MLN8237 combination completely cleared tumors in two different BCL2+ lymphoma mouse models where mice were randomized into four groups and treated with vehicle, VEN, MLN8237, or VEN+MLN8237 combination via oral gavage for 15 days. First, in a DoHH2 DHL xenograft SCID mouse model, VEN+MLN8237 combination resulted in complete tumor regression and 100% tumor-free survival on day 100 (p < 0.0001; N=8/group) with no discernable toxicity, while all mice in other groups were euthanized due to disease progression within 45 days. Next, in a disseminated THL model using VAL cells intravenously infused into NCG mice, all animals receiving combination therapy survived with no evidence of disease on day 100 (p < 0.0001; N=6-8/group), while all except one in other groups were euthanized due to removal criteria, including hindlimb paralysis and weight loss, by day 60. To investigative the tumor response to BCL2 and AURK inhibitions, we performed transcriptome sequencing (RNA seq) of DoHH2 tumors harvested from SCID mice (N=6-7/group) treated for 3 days under the 4 conditions as described above. Comparison of VEN with VEN+MLN8237 combination identified 41 genes of which 33 increased and 8 decreased in combination therapy compared to VEN alone (Fold change >2 and FDR < 0.05). Most notably, CDKN1A (p21) level was decreased by 2-fold in VEN monotherapy compared to vehicle control while the concurrent inhibition of AURK-A by MLN8237 reversed this process by upregulating p21 by > 4-fold compared to VEN monotherapy. Ingenuity pathway analysis subsequently revealed that VEN+MLN8237 combination induced significant upregulation of p53/p21/BAX network. Additional assays confirmed an early characteristic downregulation of p53 protein levels in response to VEN treatment in BCL2+ lymphoma cells. The induction of p53, p21, PUMA, and BAX in VEN+MLN8237 combination was further confirmed by immunoblotting. In contrast, VEN reduced p21, PUMA and BAX expression levels compared to vehicle treated cells. p53 knockdown in DoHH2 cells resulted in similar resistance to VEN and combination treatment. Taken together these data suggest AURK inhibition overcomes downregulation of p53/p21/BAX axis by BCL2+ lymphomas in response to BCL2 inhibition, hence lay the groundwork for further evaluation of this combination in clinical settings. Figure 1 Figure 1. Disclosures Foureau: Cytognos: Honoraria; TeneoBio, Celgene: Research Funding. Ghosh: Pharmacyclics LLC, an AbbVie Company: Consultancy, Honoraria, Research Funding, Speakers Bureau; Seattle Genetics: Consultancy, Honoraria, Speakers Bureau; Epizyme: Honoraria, Speakers Bureau; Incyte: Consultancy, Honoraria; TG Therapeutics: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding, Speakers Bureau; AstraZeneca: Consultancy, Honoraria, Speakers Bureau; Gilead: Consultancy, Honoraria, Research Funding, Speakers Bureau; Genmab: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Speakers Bureau; ADC Therapeutics: Consultancy, Honoraria; Adaptive Biotech: Consultancy, Honoraria; AbbVie: Honoraria, Speakers Bureau; Karyopharma: Consultancy, Honoraria; Genentech: Research Funding. Copelan: Amgen: Consultancy. Durden: SignalRx Pharmaceuticals: Current holder of individual stocks in a privately-held company. Avalos: Juno Therapeutics: Membership on an entity's Board of Directors or advisory committees; BMJ Best Practice: Patents & Royalties: Royalties from a co-authored article on evaluation of neutropenia. Park: Takeda: Research Funding; Rafael Pharma: Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; Morphosys: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Research Funding, Speakers Bureau; Gilead: Speakers Bureau; G1 Therapeutics: Consultancy; BMS: Membership on an entity's Board of Directors or advisory committees, Research Funding; Teva: Consultancy, Membership on an entity's Board of Directors or advisory committees.

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Alinari, Lapo, Ryan B. Edwards, Courtney J. Prince, William H. Towns, Rajeswaran Mani, Amy Lehman, Xiaoli Zhang et al. « Targeting the Cyclin D - CDK4/6 - Rb Axis in Mantle Cell Lymphoma with the Novel Translation Inhibitor Silvestrol »,. Blood 118, n^o 21 (18 novembre 2011) : 3498. http://dx.doi.org/10.1182/blood.v118.21.3498.3498.

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Abstract Abstract 3498 During cell cycle progression, D class cyclins activate cyclin dependent kinases (CDK) 4 and 6 to phosphorylate and inactivate Rb, allowing E2F-1 mediated transcription of additional cell cycle genes including cyclin E to drive S phase entry. This critical pathway is nearly universally dysregulated in cancer, providing tumor cells a strong growth advantage and escape from normal mitotic control. Substantial research is being directed toward targeting this pathway in many cancer types, with some preliminary successes being achieved with pharmacologic inhibitors of CDK4/6. However the development of alternative strategies to block this pathway could potentially provide broad therapeutic benefit. A prime example of a tumor with a disrupted cyclin D axis is Mantle Cell Lymphoma (MCL), in which the t(11;14) translocation places CCND1, the gene for cyclin D1, under the control of an immunoglobulin promoter. This results in sustained cyclin D1 expression in tumor cells and concomitant Rb inactivation, S phase entry and cell division. MCL is a relatively uncommon subset of Non-Hodgkin Lymphoma, but accounts for a disproportionate number of deaths. Treatments are limited and relapse is nearly universal; thus, new treatment strategies are essential for this disease. Silvestrol is a structurally unique, plant-derived cyclopenta[b]benzofuran with potent in vitro and in vivo anti-tumor activity in several model systems including B-cell acute lymphoblastic leukemia (ALL) and chronic lymphocytic leukemia (CLL). Silvestrol inhibits the initiation step of translation by preventing assembly of eIF4A and capped mRNA into the eIF4F complex, leading to selective loss of short half-life proteins such as Mcl-1 and cyclin D1. We therefore hypothesized that silvestrol, through the depletion of cyclin D1, would demonstrate efficacy in MCL. Silvestrol showed low nanomolar IC50 values in the JeKo-1 (13 nM), Mino (17 nM) and SP-53 (43 nM) MCL cell lines at 48 hr (MTS assay; cell death confirmed by propidium iodide flow cytometry). This potency was similar in primary MCL tumor cells. Longer exposure times substantially improved the cytotoxicity of silvestrol assessed at 48 hr (approximately 50% effect achieved with a 16 hr exposure vs. 80% effect with a 24 hr exposure), suggesting that the cellular impacts of this agent increase with exposure time. Cyclins D1 and D3 were dramatically reduced in MCL cell lines with just 10 nM silvestrol at 16 hr (cyclin D2 was undetectable in these cells), with subsequent loss of Rb phosphorylation as well as cyclin E mRNA and protein, culminating in G1 cell cycle arrest. Similar to what we previously showed in CLL and ALL cells, silvestrol treatment under these conditions also caused loss of Mcl-1 protein with concurrent mitochondrial depolarization, although the exact mechanism of silvestrol-mediated cytotoxicity in these cells is still under investigation. In an aggressive xenograft mouse model of MCL, silvestrol produced a highly significant improvement in survival [median survival of vehicle vs. silvestrol treated mice (1.5 mg/kg every 48 hr) = 27 vs. 38 days; P<0.0001] without detectable toxicity. Together, these data demonstrate that the translation inhibitor silvestrol has promising in vitro and in vivo activity in MCL preclinical models. Furthermore, as the cyclin D/CDK/Rb axis is disrupted in most tumor types, this strategy may be broadly effective in other cancers as well. Disclosures: No relevant conflicts of interest to declare.

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Bertilaccio, Maria Teresa Sabrina, Giorgia Simonetti, Antonis Dagklis, Martina Rocchi, Tania Veliz Rodriguez, Benedetta Apollonio, Alberto Mantovani et al. « Lack of TIR8/SIGIRR triggers progression of chronic lymphocytic leukemia in mouse models ». Blood 118, n^o 3 (21 juillet 2011) : 660–69. http://dx.doi.org/10.1182/blood-2011-01-329870.

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Abstract Inflammation is involved in the initiation and progression of several chronic lymphoid malignancies of B-cell type. Toll-like receptors (TLR) are transmembrane inflammatory receptors that on recognition of pathogen-associated molecular patterns trigger an innate immune response and bridge the innate and adaptive immune response by acting as costimulatory signals for B cells. Fine tuning of TLR and IL-1R–like (ILR) activity is regulated by TIR8 (SIGIRR), a transmembrane receptor of the TLR/ILR family which inhibits other family members. To test the hypothesis that TLR and/or ILR may play a role in the natural history of chronic B-cell tumors, we crossed Eμ-TCL1 transgenic mice, a well established model of chronic lymphocytic leukemia (CLL), with mice lacking the inhibitory receptor TIR8 that allow an unabated TLR-mediated stimulation. We here report that in the absence of TIR8 the appearance of monoclonal B-cell expansions is accelerated and mouse life span is shortened. The morphology and phenotype of the mouse leukemic expansions reproduce the progression of human CLL into an aggressive and frequently terminal phase characterized by the appearance of prolymphocytes. This study reveals an important pathogenetic implication of TLR in CLL development and progression.

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Park, Jae H., Isabelle Riviere, Devanjan S. Sikder, Vladimir P. Bermudez, Brigitte Senechal, Xiuyan Wang, Thomas H. Auchincloss et al. « A Phase I Study of CD19-Targeted 19(T2)28z1xx CAR T Cells in Adult Patients with Relapsed or Refractory B-Cell Malignancies ». Blood 136, Supplement 1 (5 novembre 2020) : 43–44. http://dx.doi.org/10.1182/blood-2020-143088.

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Background: Autologous CAR T cell therapy targeting the B-cell specific surface antigen CD19 has demonstrated favorable clinical responses in relapsed or refractory (R/B) B-cell lymphomas (BCL). However, despite 40-60% initial complete response (CR) rates, only a subset of patients experience durable remissions, and there is a need to further improve the efficacy of CAR therapies by preventing relapse and attaining a deeper CR. We hypothesized that the redundancy of CD28 and CD3V signaling in a CAR design incorporating all 3 CD3Vimmunoreceptor tyrosine-based activation motifs (ITAMs) might foster counterproductive T cell differentiation and exhaustion, and therefore created a new CD19 CAR construct with calibrated CAR activation potential by mutating 2 of the 3 ITAMs, termed 1XX. In systemic ALL mouse models, 19-28z1XX CAR induced effective tumor eradication at low CAR T cell doses with improved survival compared to conventional 19-28z CAR. Further preclinical studies demonstrated that the enhanced therapeutic benefit resulted from the reduced strength of activation mediated by the 19-28z1XX CAR, achieving a favorable balance of effector and memory functions, thereby enhancing persistence of functional CAR T cells and promoting effective elimination of CD19+ leukemia at lower T cell doses than needed with 19-28z CAR T cells (Feucht J et al. Nat Med 2019). To further improve the persistence of functional CAR T cells, we screened different humanized CD19-directed scFv in the context of a 19-28z1XX CAR design and proved high specificity and functionality of 19-28z1XX CARs containing a novel humanized scFv T2 - termed 19(T2)28z1XX. Study Design and Methods: This study is a single center Phase I clinical trial of 19(T2)28z1XX in patients with R/R B-cell malignancies at Memorial Sloan Kettering Cancer Center (NCT04464200). Key disease eligibility criteria include R/R diffuse large B cell lymphoma (DLBCL), high grade BCL, primary mediastinal BCL, indolent BCL and chronic lymphocytic leukemia (CLL). Patients with prior CD19 CAR therapies are eligible as long as expression of CD19 is confirmed. Key exclusion criteria include ongoing immunosuppression such as systemic GvHD therapy and active CNS disease. The study uses a 3+3 dose-escalation design to identify the maximum tolerated dose for BCL. There are 5 planned flat-dose levels. Patients will receive conditioning chemotherapy consisting of 3 days of fludarabine and cyclophosphamide followed by a single infusion of 19(T2)28z1XX CAR T cells. In the dose-escalation phase, patients with DLBCL, high grade BCL, and primary mediastinal BCL are eligible to participate. Once the recommended phase 2 dose (RP2D) is determined, the study will open to dose expansion phase with two cohorts. Cohort 1 includes DLBCL, high grade BCL and primary mediastinal BCL (i.e. same eligibility criteria as the dose-escalation phase). Cohort 2 will include patients with indolent BCL, CLL, and Richter's transformation. The dose-expansion part of the trial is designed to further characterize the safety, efficacy, and pharmacokinetics of 19(T2)28z1XX CAR in multiple indications. The primary objective of the trial is to evaluate safety and tolerability and determine the recommended Phase 2 dose of 19(T2)28z1XX. Key secondary objectives include evaluation of 19(T2)28z1XX's efficacy and cellular kinetics. Exploratory objectives include assessment of B cell aplasia, and analysis of serum cytokines. The trial has begun enrollment in August 2020. The investigators are hopeful this study will lead to development of improved CD19 CAR T cell therapy with enhanced efficacy and favorable toxicity profiles with lower infused T cell dose. Disclosures Park: AstraZeneca: Consultancy; Servier: Consultancy, Research Funding; Autolus: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Novartis: Consultancy; Minverva: Consultancy; Artiva: Membership on an entity's Board of Directors or advisory committees; Fate Therapeutics: Research Funding; Kite: Consultancy, Research Funding; Incyte: Consultancy, Research Funding; Genentech/Roche: Research Funding; Juno Therapeutics: Research Funding; GSK: Consultancy; Intellia: Consultancy; Allogene: Consultancy. Riviere:Fate Therapeutics Inc.: Consultancy, Other: Ownership interest , Research Funding; FloDesign Sonics: Consultancy, Other: Ownership interest; Juno Therapeutics: Other: Ownership interest, Research Funding; Takeda: Research Funding; Atara: Research Funding. Palomba:Genentech: Research Funding; Juno Therapeutics, a Bristol-Meyers Squibb Company: Honoraria, Research Funding; Regeneron: Research Funding; Novartis: Honoraria; Merck: Honoraria; Celgene: Honoraria; Pharmacyclics: Honoraria. Brentjens:BMS: Research Funding; Gracell Therapeutics: Consultancy; Juno Therapeutics (a Bristol Myers Squibb company): Patents & Royalties. Sadelain:Atara: Patents & Royalties, Research Funding; Fate Therapeutics: Patents & Royalties, Research Funding; Minerva: Other: Biotechnologies , Patents & Royalties; Mnemo: Patents & Royalties; Takeda: Patents & Royalties, Research Funding. OffLabel Disclosure: Cyclophosphamide and fludarabine will be used as conditioning therapy prior to 19(T2)28z1XX CAR T cell administration.

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Gupta, Pankaj, Rosana Michel, David M. Goldenberg et Chien-Hsing Chang. « Combination Therapy with FTY720 (Fingolimod) and Bispecific Anti-CD20/CD74 Antibodies in Mantle Cell Lymphoma »,. Blood 118, n^o 21 (18 novembre 2011) : 3736. http://dx.doi.org/10.1182/blood.v118.21.3736.3736.

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Abstract Abstract 3736 Introduction: Mantle cell lymphoma (MCL) is one of the most challenging B-cell lymphomas to treat. Although the response rates with first-line conventional or high-dose chemotherapy, with or without stem-cell transplantation, are high, most patients relapse, after which their prognosis is considered poor. Thus, new therapeutic interventions in MCL are needed, among which targeted therapy with a variety of monoclonal antibodies (mAbs), either alone or in combination with other biological agents or drugs, is a major focus of ongoing clinical studies. FTY720 (fingolimod), an immunosuppressive agent approved by the FDA as a frontline treatment for relapsing multiple sclerosis, shows promising pre-clinical activity in chronic lymphocytic leukemia and MCL. More recently, FTY720 was also found to increase CD74 expression and sensitize MCL cells to milatuzumab (anti-CD74 humanized antibody)-mediated cell death (Alinari L, et al. ASH 2011 Abstract submitted). Here we report that the in vitro cytotoxicity of two novel bispecific anti-CD20-/CD74 antibodies to MCL lines can be enhanced significantly by combining with FTY720. Methods: The two bispecific, anti-CD20/CD74, hexavalent antibodies (HexAbs), designated 20-(74)-(74) and 74-(20)-(20), were generated from veltuzumab (anti-CD20 humanized mAb) and milatuzumab with the Dock-and-Lock (DNL) method. The effect of FTY720 on cell-surface expression of CD20, CD22, CD74, and HLA-DR was assessed by flow cytometry after treating JeKo-1, Granta-519 and Mino MCL cell lines with FTY720 for 18 h followed by labeling the cells with primary antibody and FITC-conjugated secondary antibody at 4°C. The in vitro cytotoxicity of the combination treatment was determined by Annexin V /PI binding assays and the data analyzed by the Chou-Talalay equation to calculate the combination index (CI). Results: In the three MCL lines tested, FTY720 at 12.5 μM induced almost 9-fold increase of CD74, a modest decrease of CD20, and no apparent change in CD22 and HLA-DR, when compared to untreated controls. Further studies in JeKo-1 incubated with varying doses of FTY720 revealed a 5-fold enhanced expression of CD74 could be achieved at 4 μM, but no notable changes were observed with FTY720 at 2.5 μM, or below. The viability of JeKo-1 cells treated with a single agent for 16 h was determined by the Annexin V/PI staining assay to be 45% for FTY720 at 4 μM and 65–70 % for either 20-(74)-(74) or 74-(20)-(20) at 33 nM. Combined treatments with FTY720 and 20-(74)-(74) at 4 μM and 33 nM, respectively, resulted in about 15% live cells (Annexin V-negative/PI-negative) with statistically significant P values (<0.01) compared to 20-(74)-(74) and FTY720 alone. For FTY720 and 74-(20)-(20), the combination treatment resulted in 21% live cells, also with statistically significant P values (<0.01) compared to each agent alone. Initial analysis of these data yielded a CI of <0.87, suggesting a synergistic effect with the combination therapy. Conclusion: The anti-MCL activity of 20-(74)-(74) and 74-(20)-(20) can be further enhanced by FTY720, as demonstrated for JeKo-1. Studies are underway to evaluate similar cytotoxic effects in xenograft mouse models of MCL and to define the signaling pathways triggered by combining FTY720 with the bispecific anti-CD20/CD74 HexAbs. Disclosures: Gupta: Immunomedics, Inc.: Employment. Michel:Immunomedics, Inc.: Employment. Goldenberg:Immunomedics, Inc.: Consultancy, Employment, Equity Ownership, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding. Chang:Immunomedcis, Inc.: Employment, Patents & Royalties, Stock Options.

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Siska, Peter J., J. Brice Weinberg, Arati V. Rao, James R. Bain, Michael J. Muehlbauer, Tingyu Liu et Jeffrey Rathmell. « Acute and Chronic Lymphocytic Leukemia Induces Exhaustion and Suppresses Metabolic Reprogramming in T Cell Activation ». Blood 124, n^o 21 (6 décembre 2014) : 4121. http://dx.doi.org/10.1182/blood.v124.21.4121.4121.

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Abstract Background. Cancer cells in both hematopoietic and non-hematopoietic malignancies can suppress anti-tumor immunity by inducing a state of T cell exhaustion and hypo-responsiveness. Indeed, T cells in patients with leukemia, such as chronic lymphocytic leukemia (CLL) and acute lymphocytic leukemia (ALL) express exhaustion markers such as PD-1 or TIM-3 and can be poorly responsive. As a result, the T cells not only fail to engage the leukemic cells, but render the host susceptible to infections. The cause of the T cell defect is not known. We have previously shown that T cell metabolism is tightly regulated and sought here to test if chronic T cell stimulation through leukemic cells in human and murine leukemia modulates T cell metabolism to suppress T cell function. Methods. We established in vitro and in vivo T cell stimulation models using syngeneic pro-B-cell BCR/ABL+ mouse lymphocytic leukemia. We also analyzed freshly collected peripheral blood from 18 CLL patients and from blood or bone marrow aspirates of 3 patients with BCR/ABL+ ALL. Using flow cytometry and radiometric assays, we measured T cell proliferation, IL-2 and IFNγ production, expression of the activation and exhaustion markers CD25, CD71 and PD-1 and changes in T cell glucose metabolism. Lastly, the role of altered glucose uptake was tested using mice with T cell-specific transgenic expression of the glucose transporter 1 (Glut1). Results . Our studies showed that murine and human lymphocytic leukemia induces chronic T cell stimulation and exhaustion as measured by increased expression of PD-1 and TIM-3. Following T cell receptor stimulation, T cells from leukemic mice and human patients had impaired up regulation of surface activation molecules. Production of IL-2 and IFNγ was reduced and proliferation of leukemia-associated T cells was impaired. Importantly, recruitment of key metabolic genes such as Glut1 was inhibited in both murine and human leukemia-associated T cells. The mechanism of T cell exhaustion was unclear, but additionally to the effects of persistent stimulation, T cells expressed inhibitory receptors and inhibitory ligands were found in the leukemic microenvironment. The nutrient profile of conditioned media from leukemia cells was markedly altered, and the conditioned media prevented mouse T cell activation and proliferation. Next we questioned whether altered glucose metabolism contributed to T cell functional defects in lymphoid leukemia. We used mice expressing transgenic Glut1 in T cells to determine the effects of chronic stimulation through leukemia cells on the phenotypes of T cells. These Glut1-transgenic T cells resisted exhaustion and partially maintained function despite the presence of leukemia. Conclusion . Results of our studies indicate that lymphocytic leukemia induces a chronic stimulation leading to T cell exhaustion and impaired T cell function in part through inhibition of glucose metabolism. Disclosures Rathmell: Novartis: Consultancy.

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Lasater, Elisabeth A., An D. Do, Luciana Burton, Yijin Li, Erin Williams, Jason Oeh, Luciana Molinero et al. « Resistance of Natural Killer and T Cells to Venetoclax Allows for Combination Treatment with Cancer Immunotherapy Agents ». Blood 132, Supplement 1 (29 novembre 2018) : 1118. http://dx.doi.org/10.1182/blood-2018-99-116405.

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Abstract Introduction: Intrinsic apoptosis is regulated by the BCL-2 family of proteins, which consists of both anti-apoptotic (BCL-2, BCL-XL, MCL-1) and pro-apoptotic (BIM, BAX, BAK, BAD) proteins. Interaction between these proteins, as well as stringent regulation of their expression, mediates cell survival and can rapidly induce cell death. A shift in balance and overexpression of anti-apoptotic proteins is a hallmark of cancer. Venetoclax (ABT-199/GDC-0199) is a potent, selective small molecule BCL-2 inhibitor that has shown preclinical and clinical activity across hematologic malignancies and is approved for the treatment of chronic lymphocytic leukemia with 17p deletion as monotherapy and in combination with rituximab. Objective: To investigate the effects of BCL-2 inhibition by venetoclax on viability and function of immune-cell subsets to inform combinability with cancer immunotherapies, such as anti-PD-L1. Methods and Results: B cells, natural killer (NK) cells, CD4+ T cells, and CD8+ T cells in peripheral blood mononuclear cells (PBMCs) from healthy donors (n=3) were exposed to increasing concentrations of venetoclax that are clinically achievable in patients, and percentage of live cells was assessed by flow-cytometry using Near-IR cell staining. B cells were more sensitive to venetoclax (IC50 of ~1nM) than CD8+ T cells (IC50 ~100nM), NK cells (IC50 ~200nM), and CD4+ T cells (IC50 ~500nM) (Figure A). CD8+ T-cell subset analysis showed that unstimulated naive, but not memory cells, were sensitive to venetoclax treatment (IC50 ~30nM and 240nM, respectively). Resistance to venetoclax frequently involves compensation by other BCL-2 family proteins (BCL-XL and MCL-1). As assessed by western blot in PBMCs isolated from healthy donors (n=6), BCL-XL expression was higher in NK cells (~8-fold) and CD4+ and CD8+ T cells (~2.5-fold) than in B cells (1X). MCL-1 protein expression was higher only in CD4+ T cells (1.8-fold) relative to B cells. To evaluate the effect of venetoclax on T-cell function, CD8+ T cells were stimulated ex vivo with CD3/CD28 beads, and cytokine production and proliferation were assessed. Venetoclax treatment with 400nM drug had minimal impact on cytokine production, including interferon gamma (IFNg), tumor necrosis factor alpha (TNFa), and IL-2, in CD8+ effector, effector memory, central memory, and naïve subsets (Figure B). CD8+ T-cell proliferation was similarly resistant to venetoclax, as subsets demonstrated an IC50 >1000nM for venetoclax. Taken together, these data suggest that survival of resting NK and T cells in not impaired by venetoclax, possibly due to increased levels of BCL-XL and MCL-1, and that T-cell activation is largely independent of BCL-2 inhibition. To evaluate dual BCL-2 inhibition and PD-L1 blockade, the syngeneic A20 murine lymphoma model that is responsive to anti-PD-L1 treatment was used. Immune-competent mice bearing A20 subcutaneous tumors were treated with clinically relevant doses of venetoclax, murine specific anti-PD-L1, or both agents. Single-agent anti-PD-L1 therapy resulted in robust tumor regression, while single-agent venetoclax had no effect. The combination of venetoclax and anti-PD-L1 resulted in efficacy comparable with single-agent anti-PD-L1 (Figure C), suggesting that BCL-2 inhibition does not impact immune-cell responses to checkpoint inhibition in vivo. These data support that venetoclax does not antagonize immune-cell function and can be combined with immunotherapy targets. Conclusions: Our data demonstrate that significant venetoclax-induced cell death at clinically relevant drug concentrations is limited to the B-cell subset and that BCL-2 inhibition is not detrimental to survival or activation of NK- or T-cell subsets. Importantly, preclinical mouse models confirm the combinability of BCL-2 and PD-L1 inhibitors. These data support the combined use of venetoclax and cancer immunotherapy agents in the treatment of patients with hematologic and solid tumor malignancies. Figure Figure. Disclosures Lasater: Genentech Inc: Employment. Do:Genentech Inc: Employment. Burton:Genentech Inc: Employment. Li:Genentech Inc: Employment. Oeh:Genentech Inc: Employment. Molinero:Genentech Inc: Employment, Equity Ownership, Patents & Royalties: Genentech Inc. Penuel:Genentech Inc: Employment. Sampath:Genentech Inc: Employment. Dail:Genentech: Employment, Equity Ownership. Belvin:CytomX Therapeutics: Equity Ownership. Sumiyoshi:Genentech Inc: Employment, Equity Ownership. Punnoose:Roche: Equity Ownership; Genentech Inc: Employment. Venstrom:Genentech Inc: Employment. Raval:Genentech Inc: Consultancy, Employment, Equity Ownership.

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Sloan, Shelby, Fiona Brown, JI Hyun Chung, Alexander Prouty, Esther Wheeler, Bonnie K. Harrington, Eric Brooks et al. « Targeting PRMT5 to Circumvent Acquired Ibrutinib Resistance in Mantle Cell Lymphoma ». Blood 134, Supplement_1 (13 novembre 2019) : 4065. http://dx.doi.org/10.1182/blood-2019-128998.

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Mantle cell lymphoma (MCL) is an incurable B-cell malignancy characterized by genetic dysregulation of cyclin D1 and activation of signaling pathways driving uncontrolled MCL cell proliferation and survival. Ibrutinib is an FDA-approved irreversible inhibitor of Bruton's tyrosine kinase (BTK), a downstream target of the B-cell receptor (BCR) pathway. While ibrutinib exhibits significant single-agent therapeutic activity in patients with relapsed/refractory MCL, the vast majority of MCL patients on ibrutinib progress with aggressive disease and short survival (3-8 mo). Although ~80% of chronic lymphocytic leukemia patients with acquired ibrutinib resistance have mutations in BTK and PLCγ2, this is uncommon in MCL suggesting alternative mechanisms driving this resistant phenotype. Understanding drug-resistance mechanisms and developing effective therapies for ibrutinib resistant (IR) MCL are urgently needed. The major type II protein arginine methyltransferase enzyme, PRMT5, catalyzes symmetric dimethylation of arginine residues on histone tails (H3R8 and H4R3) and other proteins. PRMT5 regulates a vast array of biologic functions including RNA processing, DNA damage response, signal transduction, and gene expression. Amplified PRMT5 activity drives the expression and activity of key oncogenes (MYC, CYCLIND1, NOTCH1) while silencing expression and activity of tumor suppressors (ST7, RBL2, and p53). Our group has shown PRMT5 is overexpressed and dysregulated in MCL and strategies aimed at selectively targeting PRMT5 show anti-tumor activity in preclinical lymphoma models. Here we describe the development of a novel patient derived xenograft (PDX) of IR-MCL and explore PRMT5 inhibition as an alternative therapeutic option to circumvent IR. Peripheral blood mononuclear cells from a 75 yo male patient diagnosed with acquired classic IR-MCL were engrafted intravenously into NSG mice. After 5 passages, all mice engrafted with 107 MCL cells developed histologically confirmed MCL infiltrating kidney, lymph nodes, bone marrow, spleen and peripheral blood. Circulating human CD5+/CD19+ cells were detectable and quantifiable by flow cytometry by day 21 post-engraftment. Karyotype analysis confirmed the hallmark t(11;14)(q13;q32) of MCL while retaining nearly all cytogenetic abnormalities present in the patient's primary tumor including a deletion of chromosome 9, associated with deletion of MTAP, a therapeutic vulnerability for PRMT5-targeted therapy. Whole exome sequencing confirmed genomic stability with successive passages. Ex vivo cytotoxicity assays and protein pathway analysis further confirmed resistance to ibrutinib (IC50 >1 µM) with maintained hyper-phosphorylation of AKT (Ser473) and ERK (Thr202/Tyr204). Western blot analysis showed elevated levels of c-MYC, CYCLIND1, BCL2, and pERK. After validation of circulating disease at day 25 post engraftment, mice were treated with either a novel small molecule inhibitor of PRMT5 (PRT382, 10 mg/kg orally 4 days on 3 days off) or ibrutinib (75 mg/kg administered in drinking water, n=5 mice per treatment group). Treatment of this PDX model with PRT382 resulted in significantly decreased disease burden and improved median survival compared to control animals from 48 to 83 days, respectively (p=0.0045). We found no significant difference in survival (p= 0.6540) or circulating disease burden with ibrutinib therapy compared to control group. The full BTK occupancy of ibrutinib treated mice was validated using fluorescence resonance energy transfer-based assay. Ex vivo PDX MCL cells from PRT382-treated mice showed loss of symmetric dimethyl arginine with preservation of asymmetric dimethyl arginine levels, reduced H4(Sme2)R3 epigenetic marks, and elevated levels of BCL2, MYC, and pAKT/pERK. We developed a cell line (SEFA) allowing for in vitro mechanistic studies. We are currently investigating potential mechanisms responsible for circumventing IR-MCL by integrating genome-wide changes to chromatin accessibility and whole transcriptome analysis. This IR-MCL PDX mouse model serves as a useful tool to investigate mechanisms of drug resistance, provides a platform to explore novel pre-clinical therapeutic strategies to circumvent IR and demonstrates the therapeutic activity of PRMT5 targeted therapy in this aggressive disease. Disclosures Byrd: Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; Ohio State University: Patents & Royalties: OSU-2S; Genentech: Research Funding; BeiGene: Research Funding; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Novartis: Other: Travel Expenses, Speakers Bureau; Genentech: Research Funding; Acerta: Research Funding; Acerta: Research Funding; Ohio State University: Patents & Royalties: OSU-2S; BeiGene: Research Funding; Genentech: Research Funding; BeiGene: Research Funding; Janssen: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; Novartis: Other: Travel Expenses, Speakers Bureau; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Gilead: Other: Travel Expenses, Research Funding, Speakers Bureau; Novartis: Other: Travel Expenses, Speakers Bureau; Pharmacyclics LLC, an AbbVie Company: Other: Travel Expenses, Research Funding, Speakers Bureau; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau; Acerta: Research Funding; Ohio State University: Patents & Royalties: OSU-2S; TG Therapeutics: Other: Travel Expenses, Research Funding, Speakers Bureau. Vaddi:Prelude Therapeutics: Employment. Scherle:Prelude Therapeutics: Employment. Baiocchi:Prelude: Consultancy.

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Bondada, Subbarao, James P. Collard, Mary Kathryn McKenna, Sunil K. Noothi, Sara S. Alhakeem, Jacqueline R. Rivas et Shelbi Broeking. « The role of the splenic microenvironment in Chronic Lymphocytic Leukemia ». Journal of Immunology 204, n^o 1_Supplement (1 mai 2020) : 163.6. http://dx.doi.org/10.4049/jimmunol.204.supp.163.6.

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Abstract Chronic Lymphocytic Leukemia (CLL), the most prevalent adult leukemia, is characterized by the clonal expansion of CD5+ CD19+ B cells within lymphoid organs and accumulation of quiescent cells in the blood. Eμ-Tcl1 transgenic mice expressing the Tcl1 oncogene in a B cell-specific manner develop CLL and adoptive transfer of CLL cells from these mice induces CLL growth in C57BL/6 mice. These models typically cause splenomegaly as the CLL burden increases, and CLL cells localize mainly in the spleen within the first 10 days post-injection. We hypothesized that the splenic microenvironment is vital for CLL expansion. Accordingly, we found that splenectomy significantly delayed and decreased CD5+ CD19+ CLL cell burden. The role of the splenic microenvironment was further explored by isolating splenic stromal cells from Eμ-Tcl1 mice and establishing stable cell lines (EMST cells). In cell culture, CLL cells divide poorly and remain mostly quiescent. The EMST cells induced proliferation in a majority of mouse and human CLL cells without the addition of any cytokines or growth factors commonly used to accomplish in vitro proliferation of CLL cells. They do not express CD40L, an important stimulatory molecule for B cell proliferation. EMST cells lack conventional immune cell markers, but they express the cytokines and chemokines BAFF, CCL2, CXCL12, and Wnt4. CCL2 levels dramatically increased upon co-culture with CLL. EMST cells also enhance IL-10 secretion by the CLL cells and thus may enhance an immunosuppressive environment to prevent anti-CLL immunity from developing. Our studies support the hypothesis that the spleen is vital for the establishment of CLL and EMST cells produce specific factors that may play a role in CLL growth.

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Luedtke, Daniel A., Yongwei Su, Holly Edwards, Lisa Polin, Juiwanna Kushner, Sijana H. Dzinic, Hai Lin, Jeffrey W. Taub et Yubin Ge. « Voruciclib, an Oral, Selective CDK9 Inhibitor, Enhances Cell Death Induced By the Bcl-2 Selective Inhibitor Venetoclax in Acute Myeloid Leukemia ». Blood 132, Supplement 1 (29 novembre 2018) : 1361. http://dx.doi.org/10.1182/blood-2018-99-118372.

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Abstract Introduction: Patients with acute myeloid leukemia (AML) face overall 5-year survival rates of 65% and 27% for children and adults, respectively, leaving significant room for improvement. Relapse remains a major contributor to such low overall survival rates, and leukemic stem cells (LSCs) that survive treatment are believed to be responsible for AML relapse. The anti-apoptotic protein Bcl-2 is overexpressed in bulk AML cells and LSCs and is associated with poor clinical outcomes. Thus, Bcl-2 represents a promising therapeutic target for the treatment of AML. Venetoclax (ABT-199) is a selective Bcl-2 inhibitor that has shown great potential for treating a number of malignancies, including AML. Venetoclax inhibits Bcl-2, preventing it from sequestering pro-apoptotic Bcl-2 family protein Bim, leading to Bim activated Bax/Bak, resulting in apoptosis. However, Mcl-1 can also sequester Bim and prevent apoptosis. We previously showed that directly targeting Mcl-1 can enhance the antileukemic activity of venetoclax (Luedtke DA, et al. Signal Transduct Target Ther. Apr 2017). Alternatively, we proposed that indirect targeting of Mcl-1 may preserve or enhance the antileukemic activity of venetoclax, and prevent resistance resulting from Mcl-1. It has been reported that inhibition of CDK9 can downregulate cell survival genes regulated by superenhancers, including Mcl-1, MYC, and Cyclin D1. One CDK9 inhibitor in clinical development, flavopiridol (alvocidib), has progressed to phase II clinical trials in AML. However, off target effects and dose-limiting toxicities remain a concern. Voruciclib is an oral, selective CDK inhibitor differentiated by its potent inhibition of CDK9 as compared to other CDK inhibitors. This selectivity may potentially circumvent toxicities resulting from inhibition of non-CDK targets like MAK and ICK that are inhibited by flavopiridol. Voruciclib has been shown in vitro to promote apoptosis and decrease Mcl-1 expression levels in chronic lymphocytic leukemia (CLL) cells (Paiva C, et al. PLOS One. Nov 2015) and inhibit tumor growth in mouse xenograft models of diffuse large B-cell lymphoma (DLBCL) in combination with venetoclax (Dey J. et al Scientific Reports. Dec 2017). Based on these data, voruciclib may downregulate Mcl-1 in AML cells and therefore synergistically enhance the antileukemic activity of venetoclax. Methods/Results: Culturing AML cell lines (THP-1, U937, MOLM-13, MV4-11, and OCI-AML3) and primary patient samples with various concentrations of voruciclib resulted in a concentration-dependent increase in Annexin V+ cells (2 μM voruciclib induced 13.8-55.8% Annexin V+ cells) along with increased levels of cleaved caspase 3 and PARP, demonstrating that voruciclib induces apoptosis in AML cells. Next, we tested the combination of voruciclib and venetoclax in AML cell lines and primary AML patient samples at clinically achievable concentrations. Annexin V/PI staining, flow cytometry analysis, and combination index calculation (using CalcuSyn software) revealed synergistic induction of apoptosis by voruciclib and venetoclax combination (combination index values for MV4-11, U937, THP-1, and MOLM-13 cells were <0.73; treatment with 2 µM voruciclib and venetoclax for 24 h resulted in >80% apoptosis). Importantly, synergy was observed in both venetoclax sensitive and resistant cell lines. This was accompanied by increased cleavage of caspase 3 and PARP. Lentiviral shRNA knockdown of Bak and Bax partially rescued AML cells from voruciclib-induced apoptosis, showing that voruciclib induces apoptosis at least partially through the intrinsic apoptosis pathway. However, Bak and Bax knockdown had little to no effect on induction of apoptosis by the combination treatment, indicating that there might be other molecular mechanisms underlying the synergistic interaction between the two agents. Treatment with the pan-caspase inhibitor Z-VAD-FMK partially rescued cells from combination treatment induced-apoptosis. Discussion: Collectively, these results demonstrate that voruciclib and venetoclax synergistically induce apoptosis in AML cells in vitro and reverse venetoclax resistance. Further studies to determine the mechanism of action and in vivo efficacy of this promising combination in AML xenografts and PDX models are underway. Disclosures Ge: MEI Pharma: Research Funding.

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Korver, Wouter, Xiaoxian Zhao, Shweta Singh, Cecile Pardoux, Ishita Barman, Gerard Aguilar, Jingsong Zhao, Eric Hsi et Arie Abo. « Potent Anti-Cancer Activity of Anti-NTB-a Monoclonal Antibodies in Preclinical Leukemia and Lymphoma Models ». Blood 112, n^o 11 (16 novembre 2008) : 4975. http://dx.doi.org/10.1182/blood.v112.11.4975.4975.

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Abstract NTB-A is a CD2-related cell surface protein expressed on lymphoid cells including B-lymphocytes from Chronic Lymphocytic Leukemia (CLL) and lymphoma patients. We have generated a series of mAbs against NTB-A and assessed their therapeutic potential in preclinical models. Selected mAbs to NTB-A were further tested in functional Complement Dependent Cytotoxicity (CDC) and Antibody Dependent Cellular Cytotoxicty (ADCC) assays in cell lines and B lymphocytes freshly isolated from CLL and lymphoma patients. Potent cytotoxic activity was demonstrated against B cells isolated from CLL patients and B lymphoma cell lines. Chimeric anti-NTB-A mAbs demonstrated anti-tumor activity equal to rituximab against CA46 human lymphoma xenografts in nude mice at a low dose. In a chimpanzee safety study, a single dose of lead anti-NTB-A mAb 994.1 resulted in near-complete depletion of peripheral lymphocytes while having a minimal effect on T cell activation. Taken together, these results demonstrate NTB-A as a promising target with an acceptable safety profile for immunotherapy of leukemia and lymphomas.

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Agee, JF, FA Garver et GB Faguet. « An antigen common to chronic lymphocytic and hairy cell leukemia cells not shared by normal lymphocytes or by other leukemic cells ». Blood 68, n^o 1 (1 juillet 1986) : 62–68. http://dx.doi.org/10.1182/blood.v68.1.62.62.

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Abstract Rabbit xenoantisera and mouse monoclonal antibodies prepared against human chronic lymphocytic leukemia (CLL) B cells were found to react against a single polypeptide chain with a mol wt of 69 kd found on leukemic cells of all CLL (N = 40) and B type hairy cell leukemia (HCL) patients (N = 9) examined. This common CLL-associated antigen (cCLLa) was not detectable on circulating T or B lymphocytes, thymocytes, lymph node and splenic lymphocytes, or bone marrow leukocytes from normal persons. In addition, the cCLLa was not detectable on cultured T or B lymphoblastoid cell lines or on malignant cells from other forms of lymphocytic or myelocytic leukemia. Non-Hodgkin's lymphoma cells also failed to express the antigen. Autologous cultured lymphoblastoid cell lines were established from residual normal B cells from a CLL patient whose cells were used to generate one of the antisera. Absorption of the antibody with these cultured polyclonal B cells did not affect the anti-CLL activity, which suggests that the cCLLa is not HLA related. Unlike the T cell differentiation complex gp65–71, the cCLLa was not expressed on fetal or cord blood lymphocytes or on mitogen-stimulated normal lymphocytes and was distinct from the antigen recognized by the LEU-1 antibody in spite of their similar mol wt. The cCLLa was also determined to be unrelated to the human T cell leukemia lymphoma virus (HTLV-1). One of the monoclonal antibodies generated against the cCLLa was a complement binding IgG which exhibited highly selective cytotoxic activity against 100% of cells bearing the cCLLa. Such an antibody might prove clinically useful in early diagnosis and treatment of CLL and HCL.

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Agee, JF, FA Garver et GB Faguet. « An antigen common to chronic lymphocytic and hairy cell leukemia cells not shared by normal lymphocytes or by other leukemic cells ». Blood 68, n^o 1 (1 juillet 1986) : 62–68. http://dx.doi.org/10.1182/blood.v68.1.62.bloodjournal68162.

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Rabbit xenoantisera and mouse monoclonal antibodies prepared against human chronic lymphocytic leukemia (CLL) B cells were found to react against a single polypeptide chain with a mol wt of 69 kd found on leukemic cells of all CLL (N = 40) and B type hairy cell leukemia (HCL) patients (N = 9) examined. This common CLL-associated antigen (cCLLa) was not detectable on circulating T or B lymphocytes, thymocytes, lymph node and splenic lymphocytes, or bone marrow leukocytes from normal persons. In addition, the cCLLa was not detectable on cultured T or B lymphoblastoid cell lines or on malignant cells from other forms of lymphocytic or myelocytic leukemia. Non-Hodgkin's lymphoma cells also failed to express the antigen. Autologous cultured lymphoblastoid cell lines were established from residual normal B cells from a CLL patient whose cells were used to generate one of the antisera. Absorption of the antibody with these cultured polyclonal B cells did not affect the anti-CLL activity, which suggests that the cCLLa is not HLA related. Unlike the T cell differentiation complex gp65–71, the cCLLa was not expressed on fetal or cord blood lymphocytes or on mitogen-stimulated normal lymphocytes and was distinct from the antigen recognized by the LEU-1 antibody in spite of their similar mol wt. The cCLLa was also determined to be unrelated to the human T cell leukemia lymphoma virus (HTLV-1). One of the monoclonal antibodies generated against the cCLLa was a complement binding IgG which exhibited highly selective cytotoxic activity against 100% of cells bearing the cCLLa. Such an antibody might prove clinically useful in early diagnosis and treatment of CLL and HCL.

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49

Zhao, Xiaoxian, Wouter Korver, Nichole Prescott, Arie Abo et Eric Hsi. « Expression of NTB-A in Normal Tissue, Non-Hodgkin Lymphomas and Investigation of Its Potential Therapeutic Impact for Chronic Lymphocytic Leukemia. » Blood 108, n^o 11 (16 novembre 2006) : 4741. http://dx.doi.org/10.1182/blood.v108.11.4741.4741.

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Abstract Introduction: Expressed on T, B, NK cells and neutrophils, NTB-A belongs to the signaling lymphocytic activation molecule (SLAM) family of immune receptors. It was reported recently that cross-linking of NTB-A induces T cell activation and Ly108 (the presumed mouse orthologue of NTB-A) controls the production of reactive oxygen species in neutrophils. To date, little is known about its expression at the protein level in normal tissues, or in hematologic malignancies. Methods: We have generated monoclonal antibodies (mAbs) to NTB-A and used tissue microarrays (TMAs) to screen normal tissues and lymphomas. Western blotting and flow cytometry were used for confirmation of selected entities. Complement dependent cytotoxicity (CDC) assays were performed using the CellTiter-Glo Luminescent Cell Viability Assay kit (Promega). Results: NTB-A was not detected in normal tissues including heart, liver, breast, kidney, brain, lung, uterus, small intestine, skin, prostate, pancreas, ovary, bladder, testis and stomach (5/5 negative cases for all above tissues) by IHC. Expression was observed in lymphocytes of normal tonsil and spleen. In lymphomas, we found NTB-A expression in diffuse large B-cell lymphoma (DLBL), follicular lymphoma, small lymphocytic lymphoma (SLL), mantle cell lymphoma and Burkitt lymphoma. Western blotting and flow cytometry of B-cell lymphoma cell lines DOHH2 (DLBL) and Raji (Burkitt) confirmed NTB-A expression in these lines. Myeloma cell lines were negative for expression. Flow cytometry of normal blood cells showed expression of NTB-A in B-cells, T-cells and NK cells (95.5 ± 6.7%, 62.6 ± 29.5% and 72.7 ± 26.5%, respectively) but not in CD66+ granulocytes. Furthermore, CD34+ progenitor cells from bone marrow were negative. Because of the expression in SLL, we focused on chronic lymphocytic leykemia (CLL) cells. All (15/15) patient samples were confirmed positive by flow cytometry. No significant differences in expression levels were observed comparing CLL B-cells vs normal B-cells (n = 10). However, anti-NTB-A antibodies were capable of inducing CDC in white blood cells from CLL patients (n=5) but not in normal white blood cells (n=5), in addition to CDC activity against Raji cells. Preliminary data also suggests that the CDC effect is greater in purified CLL B-cells than purified normal B-cells. Conclusions: These results show that NTB-A is expressed in normal lymphocytes but not in other solid tissues or in CD34+ progenitor cells. B cell malignancies, including Non-Hodgkin lymphoma cells appear to express NTB-A. In particular CLL patient cells express NTB-A, and an anti-NTB-A mouse mAb is capable of inducing CDC, suggesting NTB-A may be a potential immunotherapeutic target. Further studies examining the expression patterns in hematologic malignancies are ongoing.

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Kutlar, Abdullah, Niren Patel, Celalettin Ustun, Kavita Natarajan, Anand Jillella, Betsy Clair, Ferdane Kutlar, Rosemary Chandler, Steffen E. Meiler et Kapil N. Bhalla. « LBH589 (panobinostat) : A Potential Novel Anti-Switching Therapy. » Blood 114, n^o 22 (20 novembre 2009) : 2568. http://dx.doi.org/10.1182/blood.v114.22.2568.2568.

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Abstract Abstract 2568 Poster Board II-545 Reversing the perinatal switch from fetal to adult hemoglobin synthesis has been an attractive therapeutic goal for β-hemoglobinopathies such as sickle cell disease (SCD) and β-thalassemia. Fetal hemoglobin (Hb F) inhibits the polymerization of deoxy Hb S (anti-sickling effect) in SCD and ameliorates the globin chain imbalance by compensating for severely diminished or absent β-globin synthesis in β-thalassemia. Different classes of compounds have been used for this purpose; only hydroxyurea (HU), an S-phase specific chemotherapeutic agent, an inhibitor of ribonucleotide reductase, has been FDA approved for use in adults with SCD and is currently in phase III trials for infants and children. Despite the established efficacy of HU in many patients with SCD, there is a need for alternative Hb F inducing agents and therapies; an estimated 30% of patients do not respond to HU therapy. In addition, some patients are intolerant of HU due to a number of side effects. The development of novel, more effective anti-switching agents is hampered by a lack of a clear and complete understanding of the molecular mechanism(s) underlying the perinatal switch from fetal (γ-globin) to adult (β-globin) synthesis despite three decades of intensive research. Nevertheless, it has been established that epigenetic mechanisms such as histone deacetylation and DNA methylation do play an important role in the silencing of the γ-globin genes during the perinatal period. In vitro studies and early phase clinical trials in a small number of patients have provided the proof-of-principle for the efficacy of a number of histone deacetylase (HDAC) inhibitors and hypomethylating agents (DNA methyl transferase I inhibitors). Butyrate derivatives are an example of HDAC inhibitors whose efficacy in inducing Hb F has been proven in both SCD and β-thalassemia. More recently, other HDAC inhibitors (SAHA, Depsipeptide, Trichostatin A) have been shown to induce Hb F synthesis in erythroid cultures. DNMT-1 inhibitors, 5-Azacytidine and decitabine, have also been used in small clinical trials to enhance Hb F production and ameliorate the course of severe SCD. LBH589 (panobinostat, Novartis Pharma) is a pan-HDAC inhibitor that belongs to the hydroxamic acid class of HDAC inhibitors that is currently being investigated in Phase I/II trials in hematologic malignancies and a number of solid tumors. We monitored the Hb composition of 21 patients with relapsed/refractory hematologic malignancies enrolled into a Phase I/b trial of panobinostat conducted at the MCG Cancer Center. Hb quantification was done by a cation exchange HPLC procedure. Eight patients were on panobinostat for 2 months or longer with a starting dose of 40–60 mg PO administered thrice weekly (MWF). Three patients carried a diagnosis of Primary Myelofibrosis and one each had Chronic Lymphocytic Leukemia, Mantle Cell Lymphoma, Multiple Myeloma, Refractory Non-Hodgkins Lymphoma, and Chronic Myelogenous Leukemia-accelerated phase. Of these, 4 patients displayed an increase in Hb F over baseline values. None of the patients had an inherited hemoglobinopathy (SCD or β-thalassemia). The median Hb F was 0.33% at entry (range: 0–2.3) and increased to 1.1% (range 0–17%) at the end of the study period. The maximal response was seen in a patient with Primary Myelofibrosis whose Hb F increased from a pretreatment value of 0.2% to 17.0% over a period of 16 months. Overall, patients who were on panobinostat for longer periods of time (≥ 2 months) had a more pronounced increase in Hb F. The remaining 13 patients were on study drug for <2 months. In studies of other Hb F inducing agents, optimal response is not generally reached in less than 6 months. The slight but significant increase in Hb F in this small group of patients without an underlying hemoglobinopathy is encouraging and provides the rationale for a trial of panobinostat as an anti-switching agent in clinically significant hemoglobinopathies such as SCD and β-thalassemia. This effect will likely be enhanced in patients with hemoglobinopathies given the erythropoietic stress and the selection of RBCs containing Hb F. Studies in transgenic mouse models of SCD and a phase I study in patients with SCD who have failed or intolerant of HU are underway. Disclosures: Kutlar: Novartis Pharmaceuticals, Inc.: Research Funding; Celgene Corporation: Research Funding; HemaQuest Pharmaceuticals, Inc.: Research Funding. Meiler:Celgene Corporation: Research Funding; Novartis Pharmaceuticals, Inc.: Research Funding. Bhalla:Novartis: Honoraria, Research Funding; Merck: Honoraria.

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Articles de revues sur le sujet « B cell lymphoma, Chronic Lymphocytic Leukemia, B lymphocytes, mouse models »

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