Academic literature on the topic 'Acute Myeloid Leukemia, immunotherapy, chimeric antigen receptor'

Several immune checkpoint molecules and immune targets in leukemic cells have been investigated. Recent studies have suggested the potential clinical benefits of immuno-oncology (IO) therapy against acute myeloid leukemia (AML), especially targeting CD33, CD123, and CLL-1, as well as immune checkpoint inhibitors (e.g., anti-PD (programmed cell death)-1 and anti-CTLA4 (cytotoxic T-lymphocyte-associated protein 4) antibodies) with or without conventional chemotherapy. Early-phase clinical trials of chimeric antigen receptor (CAR)-T or natural killer (NK) cells for relapsed/refractory AML showed complete remission (CR) or marked reduction of marrow blasts in a few enrolled patients. Bi-/tri-specific antibodies (e.g., bispecific T-cell engager (BiTE) and dual-affinity retargeting (DART)) exhibited 11–67% CR rates with 13–78% risk of cytokine-releasing syndrome (CRS). Conventional chemotherapy in combination with anti-PD-1/anti-CTLA4 antibody for relapsed/refractory AML showed 10–36% CR rates with 7–24 month-long median survival. The current advantages of IO therapy in the field of AML are summarized herein. However, although cancer vaccination should be included in the concept of IO therapy, it is not mentioned in this review because of the paucity of relevant evidence.

Abstract Abstract 2618 Adoptive transfer of antigen-specific T cells emerged as an attractive strategy to provide cancer patients with immune cells of a desired specificity. The efficacy of such adoptive transfers has been demonstrated in clinical studies. However, enrichment and expansion of tumor-specific T cells are time-consuming and often ineffective, due to the low frequency of tumor-specific precursors in vivo. Alternatively, polyclonal T cells can be genetically modified with chimeric antigen receptors (CARs) to provide these cells with new antigen specificities. CARs consist of a binding moiety specifically recognizing a tumor cell surface antigen fused to a signaling chain derived from a lymphocyte activating receptor. The chimeric receptor approach is able to bypass many of the mechanisms by which tumors avoid immunorecognition, such as MHC down-regulation, lack of expression of costimulatory molecules, and induction of T cell suppression. Acute myeloid leukemia (AML) is an intrinsically resistant disease and even though the majority of the patients initially respond to chemotherapy, the 3-year survival rate is still low. A promising target for immunotherapy of AML is CD33, which is absent on normal pluripotent hematopoietic stem cells and normal tissues, but is present on leukemic blasts in 85–90 % of adult and pediatric AML cases independent of the subtype of AML. Novel human CD33-specific CARs were constructed by fusing a CD33 specific scFv in series with CD3ζ chain plus an additional costimulatory sequence derived from CD28 (Fig. 1A). Both native human CD8+ and CD4+ T cells engrafted with CD33-specific CARs exhibited antigen-specific cytokine secretion, proliferation and target cell lysis (Fig. 1B, C). Moreover, AML blast derived from patients were efficiently killed by allogeneic CAR-engrafted T cells (Fig. 1D). Next, the CD33-specific scFv was fully humanized and afterwards incorporated into the CAR constructs. With this humanized CAR engrafted T cells from AML patients could be redirected against CD33+ cell lines and autologous AML blasts. Upon antigen-recognition, the modified T cells secreted high amount of inflammatory cytokines and efficiently killed the target cells.Fig. 1:Human CAR-engrafted T cells mediate effector functions against CD33+ target cells.A. Schematic representation of the CD33-specific CARs. VL: variable light chain; VH: variable heavy chain; E-Tag: linker epitope in between the VL and the VH chain.Fig. 1:. Human CAR-engrafted T cells mediate effector functions against CD33+ target cells. / A. Schematic representation of the CD33-specific CARs. VL: variable light chain; VH: variable heavy chain; E-Tag: linker epitope in between the VL and the VH chain.B. Cytotoxic effector functions of CAR engrafted human CD8+ and CD4+ T cells against the CD33+ blast line U937 were measured in a standard chromium release assay after 6h of co-incubation.B. Cytotoxic effector functions of CAR engrafted human CD8+ and CD4+ T cells against the CD33+ blast line U937 were measured in a standard chromium release assay after 6h of co-incubation.C. Killing of patient-derived AML blast by allogeneic CAR engrafted T cells was measured in a flow cytometer by exact cell count after 48h of co-cultivation. Three independent donor/patient pairings are shown.C. Killing of patient-derived AML blast by allogeneic CAR engrafted T cells was measured in a flow cytometer by exact cell count after 48h of co-cultivation. Three independent donor/patient pairings are shown. Until now, one major obstacle for an adoptive therapy of genetically modified T cells is the limited amount of T cells that can be isolated from AML patients and modified in vitro. For an efficient in vitro expansion restricted to CAR modified T cells from patients we developed a new method based on a novel CAR-mediated strategy. For this purpose, magnetic beads were coated with an antibody recognizing an epitope (Fig. 1A, E-Tag) which we included in the linker domain between the heavy and the light chain of the scFv portion of the CAR. Adding such magnetic beads to cultures of CAR modified T cells, the CAR engrafted T cells were expanded to similar extends as polyclonal T cell populations with anti-CD3/anti-CD28 coated beads. Furthermore, the antibody-coated beads can be used to isolate the CAR engrafted T cells after expansion and get rid of any contaminating non-modified cells. It may also be useful for elimination of CAR expressing T cells in vivo if necessary. The feasibility of the described method was not limited to CD33 specific CARs but was also functional for CARs equipped with scFvs of other specificities. Therefore, it might be universally applicable for the expansion and preparation of CAR modified T cell grafts in vitro before adoptive transfer back in patients. Taken together, we describe novel humanized CD33-specific CARs that (I) can be specifically expanded, (II) specifically eliminated, if necessary, and (III) may therefore become a novel potent treatment option for a cellular therapy of AML patients. Disclosures: No relevant conflicts of interest to declare.

Outcomes for pediatric patients with acute myeloid leukemia (AML) remain poor, highlighting the need for improved targeted therapies. Building on the success of CD19-directed immune therapy for acute lymphocytic leukemia (ALL), efforts are ongoing to develop similar strategies for AML. Identifying target antigens for AML is challenging because of the high expression overlap in hematopoietic cells and normal tissues. Despite this, CD123 and CD33 antigen targeted therapies, among others, have emerged as promising candidates. In this review we focus on AML-specific T cell engaging bispecific antibodies and chimeric antigen receptor (CAR) T cells. We review antigens being explored for T cell-based immunotherapy in AML, describe the landscape of clinical trials upcoming for bispecific antibodies and CAR T cells, and highlight strategies to overcome additional challenges facing translation of T cell-based immunotherapy for AML.

Acute myeloid leukemia (AML) is a heterogeneous disease associated with various alterations in T cell phenotype and function leading to an abnormal cell population, ultimately leading to immune exhaustion. However, restoration of T cell function allows for the execution of cytotoxic mechanisms against leukemic cells in AML patients. Therefore, long-term disease control, which requires multiple therapeutic approaches, includes those aimed at the re-establishment of cytotoxic T cell activity. AML treatments that harness the power of T lymphocytes against tumor cells have rapidly evolved over the last 3 to 5 years through various stages of preclinical and clinical development. These include tissue-infiltrated lymphocytes (TILs), bispecific antibodies, immune checkpoint inhibitors (ICIs), chimeric antigen receptor T (CAR-T) cell therapy, and tumor-specific T cell receptor gene-transduced T (TCR-T) cells. In this review, these T cell-based immunotherapies and the potential of TILs as a novel antileukemic therapy will be discussed.

Acute leukemia is a constellation of rapidly progressing diseases that affect a wide range of patients regardless of age or gender. Traditional treatment options for patients with acute leukemia include chemotherapy and hematopoietic cell transplantation. The advent of cancer immunotherapy has had a significant impact on acute leukemia treatment. Novel immunotherapeutic agents including antibody-drug conjugates, bispecific T cell engagers, and chimeric antigen receptor T cell therapies have efficacy and have recently been approved by the US Food and Drug Administration (FDA) for the treatment of patients with acute leukemia. The Society for Immunotherapy of Cancer (SITC) convened a panel of experts to develop a clinical practice guideline composed of consensus recommendations on immunotherapy for the treatment of acute lymphoblastic leukemia and acute myeloid leukemia.

Chemotherapy resistance and relapse remain significant sources of mortality for children and adults with acute myeloid leukemia (AML). Further intensification of conventional cytotoxic chemotherapy is likely not feasible due to the severity of acute and long-term side effects upon normal tissues commonly induced by these drugs. Successful development and implementation of new precision medicine treatment approaches for patients with AML, which may improve leukemia remission and diminish toxicity, is thus a major priority. Tumor antigen-redirected chimeric antigen receptor (CAR) T-cell immunotherapies have induced remarkable responses in patients with relapsed or chemorefractory B-lymphoblastic leukemia, and similar strategies are now under early clinical study in adults with relapsed/refractory AML. However, potential on target/off tumor toxicity of AML CAR T-cell immunotherapies, notably aplasia of normal myeloid cells, may limit broader implementation of such approaches. Careful selection of optimal target antigens, consideration of toxicity mitigation strategies, and development of methodologies to circumvent potential CAR T-cell resistance are essential for successful implementation of cellular immunotherapies for patients with high-risk AML.

Abstract Abstract 4225 Despite the progress in the treatment of acute myeloid leukemia (AML) achieved in the last decades, a significant number of patients are still refractory to or relapse after conventional chemotherapy regimens. Therefore it is necessary to develop novel alternative approaches. Immunotherapy with T cells genetically modified to express chimeric antigen receptors (CARs) represent a valid option in this sense. CARs are artificial T-cell receptors constituted by a specific antigen-binding domain, and a signaling region, that, upon antigen recognition, leads to T-cell activation, and lysis of the target cells. AML is a potential optimal target for CAR strategy because of the over-expression of a number of surface antigens like CD33, CD123. Since CD33 is also expressed on normal hematopoietic stem/progenitors cells (HSPCs) resulting in a potential severe impairment of normal myelopoiesis, CD123 has recently emerged as new potential attractive molecules based on its differential expression pattern, being still wildly overexpressed by AML population, and at the same time less expressed on HSPCs. Here we describe the in vivo efficacy and the safety of this approach based on Cytokine-Induced-Killers (CIK) cells genetically modified to express CAR molecules specific for the CD33 or CD123 antigen. Once injected into low-level AML engrafted NSG mice (median of hCD45+CD33+ 0.6% before treatment), genetically modify T cells had a potent antitumor effect. Indeed, the bone marrow of control untreated animals or mice treated with un-manipulated CIK cells, was infiltrated by leukemic cells (86% and 81% leukemic engraftment), while in 7/8 anti-CD33-CD28-OX40-ζ and 8/10 anti-CD123-CD28-OX40-ζ treated mice we couldn't detect any AML cells. Similar results have been obtained when the treatment via T cell injection start when high AML burden has been obtained (median of hCD45+CD33+ 70% before treatment). One week after the last CIK's injection the level of AML engraftment was 96%, 87%, 0.35% and 0.34% for untreated mice, mice treated with un-manipulated CIK cells and with anti-CD33-CD28-OX40-ζ and anti-CD123-CD28-OX40-ζ transduced CIK-cells respectively. We performed secondary transplantation on the residual AML cells present in these animals and mice were treated again with transduced CIK cells. Residual AML cells were still sensitive to CARs approach, leading once again to an almost complete eradication of the disease (median level of hCD45+CD33+ engraftment was 98%, 0.02% and 0.04% respectively for untreated mice, anti-CD33-CD28-OX40-ζ and anti-CD123-CD28-OX40-ζ transduced CIK-cells). Furthermore, a fundamental issue was to determine the safety profile of such approach against normal hematopoietic precursors. In untreated mice injected with primary cord blood derived CD34+ cells the level of engraftment of hCD45 compartment was 42% whilst in mice treated with un-manipulated, anti-CD33-CD28-OX40-ζ or anti-CD123-CD28-OX40-ζ transduced CIK-cells the levels of human compartment was 40%, 11.7% and 26.3% respectively. Moreover when we consider specifically the CD34+CD38- compartment, enriched in HSC, the level of engraftment was 1.92%, 1.02%, 0.55% and 0.83%. Secondary transplantations are now ongoing to give a more complete profile about the remaining HSC repopulating capability after treatment. To more closely mimic a physiological context, similar experiments are ongoing using mice engrafted with normal adult bone marrow instead of umbilical cord blood. These experiments should offer relevant information concerning the efficacy and safety of the proposed strategy particularly in the context of minimal residual disease in high-risk transplanted AML patients. Moreover CAR approach could be potentially used to treat patients resistant to conventional chemotherapeutic approaches or for whom high dose chemotherapy treatment could not be proposed. Disclosures: No relevant conflicts of interest to declare.

Adoptive transfer of gene-engineered chimeric antigen receptor (CAR)-T-cells has emerged as a powerful immunotherapy for combating hematologic cancers. Several target antigens that are prevalently expressed on AML cells have undergone evaluation in preclinical CAR-T-cell testing. Attributes of an ‘ideal’ target antigen for CAR-T-cell therapy in AML include high-level expression on leukemic blasts and leukemic stem cells (LSCs), and absence on healthy tissues, normal hematopoietic stem and progenitor cells (HSPCs). In contrast to other blood cancer types, where CAR-T therapies are being similarly studied, only a rather small number of AML patients has received CAR-T-cell treatment in clinical trials, resulting in limited clinical experience for this therapeutic approach in AML. For curative AML treatment, abrogation of bulk blasts and LSCs is mandatory with the need for hematopoietic recovery after CAR-T administration. Herein, we provide a critical review of the current pipeline of candidate target antigens and corresponding CAR-T-cell products in AML, assess challenges for clinical translation and implementation in routine clinical practice, as well as perspectives for overcoming them.

Despite the advent of novel therapies, acute myeloid leukemia (AML) remains associated with a grim prognosis. This is exemplified by 5-year overall survival rates not exceeding 30%. Even with frontline high-intensity chemotherapy regimens and allogeneic hematopoietic stem cell transplantation, the majority of patients with AML will relapse. For these patients, treatment options are few, and novel therapies are urgently needed. Adoptive T-cell therapies represent an attractive therapeutic avenue due to the intrinsic ability of T lymphocytes to recognize tumor cells with high specificity and efficiency. In particular, T-cell therapies focused on introducing T-cell receptors (TCRs) against tumor antigens have achieved objective clinical responses in solid tumors such as synovial sarcoma and melanoma. However, contrary to chimeric antigen receptor (CAR)-T cells with groundbreaking results in B-cell malignancies, the use of TCR-T cells for hematological malignancies is still in its infancy. In this review, we provide an overview of the status and clinical advances in adoptive TCR-T-cell therapy for the treatment of AML.

Leukemia is a malignancy of the bone marrow and blood resulting from the abnormal differentiation of hematopoietic stem cells (HSCs). There are four main types of leukemia including acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myeloid leukemia (CML), and chronic lymphocytic leukemia (CLL). While chemotherapy and radiation have been conventional forms of treatment for leukemia, these therapies increase infection susceptibility, adverse side effects and immune cell inactivation. Immunotherapies are becoming promising treatment options for leukemia, with natural killer (NK) cell-mediated therapy providing a specific direction of interest. The role of NK cells is critical for cancer cell elimination as these immune cells are the first line of defense against cancer proliferation and are involved in both recognition and cytolysis of rapidly dividing and abnormal cell populations. NK cells possess various activating and inhibitory receptors, which regulate NK cell function, signaling either inhibition and continued surveillance, or activation and subsequent cytotoxic activity. In this review, we describe NK cells and NK cell receptors, functional impairment of NK cells in leukemia, NK cell immunotherapies currently under investigation, including monoclonal antibodies (mAbs), adoptive transfer, chimeric antigen receptor-NKs (CAR-NKs), bi-specific/tri-specific killer engagers (BiKEs/TriKEs) and future potential targets of NK cell-based immunotherapy for leukemia.

Despite the progress in the treatment of acute myeloid leukemia (AML) achieved in the last decades, a significant number of patients are still refractory to or relapse after standard cures. Hence, to improve cure rates of AML, it is crucial to develop novel therapeutic strategies. Immunotherapy with T cells genetically modified to express chimeric antigen receptors (CARs) represent a valid option in this sense. CARs are artificial molecules constituted by an extracellular-antigen-binding domain derived from a monoclonal antibody and an intracellular-signalling region that is immediately triggered after antigen recognition. Therefore, CARs combine the antigen binding properties of mononoclonal antibodies to T cell mediated effector functions, including the killing mechanism -that might be active against antibody resistant targets-, cytokine secretion- that might boost the anti-tumoral immune response- and capacity to efficiently home and infiltrate tumor sites. Different CARs have been generated so far, against a wide range of surface molecules expressed by many tumors and, currently, several phase I clinical trials are undergoing and the results obtained so far are very encouraging. The CARs approach can be employed to selectively target AML cells due to the overexpression of myeloid antigens, like CD33 and CD123. We recently demonstrated that expression of CD33-specific CARs in a population of ex-vivo activated T cells, called “cytokine induced killer” (CIK) cells, confers them potent in vitro anti-leukemic functions. However, since CD33 antigen is also expressed on normal haematopoietic stem/progenitors cells (HSPCs) resulting in a potential severe impairment of normal myelopoiesis, CD123 has recently been proposed as a new potential attractive molecule based on its differential expression pattern, being widely overexpressed by AML population and at the same time less expressed on HSPCs. In order to improve the safety profile against these cells we develop and test a novel CAR specific for the CD123 antigens. Here we describe the in vitro and the in vivo efficacy and the safety of this approach based on CIK cells genetically modified to express CAR molecules specific for the CD33 or CD123 antigen. The development and the optimization of the proposed strategy could be a good potential therapeutic tool in the context of minimal residual disease in high-risk transplanted AML patients. Moreover, CAR approach could be potentially used to treat patients resistant to conventional chemotherapeutic approaches or for whom high dose chemotherapy treatment could not be proposed.

La Leucemia Mieloide Acuta (LMA) è ancora associata ad alti tassi di ricaduta in seguito al trattamento con le terapie convenzionali che comprendono la chemioterapia e il trapianto di cellule staminali ematopoietiche. Da qui la necessità di identificare nuove strategie terapeutiche. L’immunoterapia con linfociti T ingegnerizzati per esprimere recettori chimerici artificiali (CARs) in grado di riconoscere specifici antigeni tumorali ha mostrato risultati sorprendenti in particolare nel contesto leucemie linfoblastiche di tipo B, suscitando un vivo interesse nell'estendere questo approccio anche ad altre neoplasie ematologiche come la LMA. Tra le molecole di superficie identificate nell’ambito della LMA, il CD33 e CD123 (la subunità α del recettore dell’IL-3), essendo ampiamente espressi sia dai blasti leucemici che dalle cellule staminali leucemiche, rappresentano dei buoni antigeni bersaglio per lo sviluppo di terapie CAR mediate. Il mio progetto di dottorato è stato dunque incentrato sulla caratterizzazione di cellule killer indotte da citochine (CIK) geneticamente modificate attraverso il sistema non virale “Sleeping Beauty” per esprimere CARs specifici per il CD123 e il CD33 quale strategia terapeutica per il trattamento della LMA. Nel contesto del targeting dell’antigene CD123, abbiamo focalizzato la nostra attenzione sull’ effetto di diverse variabili coinvolte nel CAR design, e note per la loro capacità di modulare i profili funzionali delle cellule CAR T, come l'affinità di legame e l'espressione del CAR in relazione alla densità dell'antigene bersaglio. Infatti, mentre l'effetto "off-target" associato al targeting del CD33 è per lo più limitato al compartimento ematologico, il targeting del CD123 richiede un livello più alto di cautela, a causa del potenziale riconoscimento da parte del CD123.CAR del tessuto endoteliale che esprime il CD123 a bassi livelli. Utilizzando il nostro modello in vitro siamo stati in grado di definire sia soglie di antigene "litiche" che di "attivazione" dimostrando che, mentre l'attività citotossica precoce non è influenzata né dall'espressione del CAR né dalla modifica dell’affinità del CAR, l’ espressione del CAR rappresenta la variabile principale che incide sulle funzioni effettrici. Complessivamente, la completa caratterizzazione di tutte queste variabili ha fornito ulteriori informazioni per la corretta progettazione di un CAR anti-CD123 per il trattamento della LMA che possa garantire un corretto equilibrio tra i profili di efficacia e sicurezza. In parallelo, una corretta valutazione preclinica di queste nuove terapie richiede anche un'accurata valutazione dell'efficacia, in particolare considerando le complessità intrinseca alla LMA, come l'eterogeneità e il microambiente mieloide immunosoppressivo. Pertanto, per quanto riguarda il targeting del CD33, abbiamo studiato i profili di efficacia di cellule CD33.CAR CIK da sole e in combinazione con agenti chemioterapici convenzionali, sfruttando un modello di xenotrapianto abbinato a chemioterapia per testare le cellule CD33.CAR-CIK nei confronti di cellule di LMA resistenti / residue alla chemioterapia. Abbiamo scoperto che le cellule CD33.CAR CIK da sole mostrano una potente attività anti-leucemica in vitro e in vivo, riducendo in modo significativo lo sviluppo della LMA quando somministrate come approccio di trattamento precoce, e ritardando la progressione di LMA in topi con una malattia conclamata. Inoltre, dati preliminari hanno mostrato che le cellule CD33.CAR-CIK sono ancora in grado di eliminare le cellule di LMA nei topi con recidive dopo la chemioterapia.
Acute Myeloid Leukemia (AML) is still associated with high relapse rates when treated with conventional chemotherapeutic and hematopoietic transplantation regimens. Thus, new treatment options are urgently needed. Immunotherapy adopting T cells engineered to express tumor-directed Chimeric Antigen Receptors (CARs) has shown striking results particularly in the context of B-cell malignancies, sparking a keen interest in extending this approach also to other hematological malignancies such as AML. Among the surface molecules identified, the CD33 and CD123 (IL-3 receptor α subunit) molecules have emerged as the main validated targets in AML and, being broadly expressed on both AML blasts and leukemic stem cells (LSCs), represent suitable antigens to be targeted with CAR-T cells. My PhD project has been focused on the characterization of non-viral Sleeping-Beauty engineered Cytokine-Induced Killer (CIK) cells with both anti-CD123 and CD33 CARs as a potential tool for the treatment of AML. In the context of CD123 targeting, we focused our attention on dissecting the effect of several variables involved in the CAR design, known to modulate CAR T-cell functional profiles, such as CAR binding affinity and expression in relation to the target antigen density. Indeed, while the “on target-off tumor” effect associated to the CD33 targeting is mostly limited to the hematological compartment, the CD123 targeting demands a higher level of caution, due to the potential recognition of low CD123-positive endothelial tissue. By using our model we were able to define both “lytic” and “activation” antigen thresholds showing that, while the early cytotoxic activity is not affected either by CAR expression or by CAR affinity tuning, the CAR expression represents the main variable impacting on later effector functions. Overall, the full dissection of all these variables offers additional knowledge for the proper design of a suitable anti-CD123 CAR for the treatment of AML which can grant a proper balance between efficacy and safety profiles. In parallel, a proper preclinical assessment of novel therapies also demands for accurate efficacy evaluation, particularly considering the AML disease complexity, such as the heterogeneity and the immunosuppressive myeloid microenvironment. Thus, regarding the CD33 targeting, we investigated the efficacy profiles of CD33.CAR CIK cells alone and in combination with conventional chemotherapeutic agents by exploiting a xenograft chemotherapy model to examine the CD33.CAR-CIK cell contribute in the elimination of the chemotherapy resistant/residual AML cells. We found that CD33.CAR CIK cells alone exhibited a potent anti-leukemic activity in vitro and in vivo, significantly reducing AML development when administered as an early treatment approach and delaying the progression of established disease in mice. Moreover, preliminary data showed that CD33.CAR-CIK cells were still capable to target chemotherapy resistant/residual AML cells in mice experiencing disease recurrence after chemotherapy.

Chimeric Antigen Receptors (CARs)-redirected T lymphocytes are a promising novel immunotherapeutic approach, nowadays object of accurate preclinical evaluation also for the treatment of Acute Myeloid Leukemia (AML). In this context, we recently developed a CAR against CD123, over-expressed on AML blasts and leukemic stem cells. However, the potential recognition of low CD123-positive healthy tissues, through the "on-target-off-organ" effect, limits the safe clinical employment of CAR-redirected T cells. Therefore, in search for a CAR design optimization, we here evaluated the effect of variables capable to modulate CAR T-cell functional profiles in a context-dependent manner, such as CAR binding affinity for the target antigen, CAR expression and target antigen density. To study these variables in the absence of other interfering elements we exploited computational structural biology tools to design rational mutations in the anti-CD123 CAR antigen binding domain that altered CAR expression and CAR binding affinity, without affecting the overall CAR design. We were able to define both “lytic” and “activation” antigen thresholds, showing that whereas the early T-cell cytotoxic activity is not affected either by CAR expression or CAR affinity tuning, later effector functions are impaired by low CAR expression. Moreover, a promising balance in the efficacy and safety profiles of CAR T cells was observed in the lowest affinity mutant in response to targets with different antigen densities. Overall, the full dissection of all these variables offers additional knowledge for the proper design of a suitable anti-CD123 CAR for the treatment of AML.

La leucemia mieloide acuta (LMA) è la neoplasia ematologica maggiormente diagnosticata nei pazienti adulti (25%) e mentre rappresenta il 15-20% dei casi nei pazienti pediatrici. La chemioterapia convenzionale, che impiega antraciclina e citarabina, rappresenta il trattamento standard per l’LMA, con tassi di remissione completa dal 60% all'80% nei bambini e dal 40% al 60% negli adulti (>60 anni). Sfortunatamente, la ricaduta dopo tale terapia è comune e la sopravvivenza dei pazienti stimata a 5 anni è ancora inferiore al 30%. Risulta quindi di primaria importanza trovare alternative terapeutiche per i pazienti recidivanti e refrattari. Il recente successo clinico, ottenuto nelle leucemie di tipo B, dell'immunoterapia con cellule CAR (chimeric antigen receptor) T ha portato allo sviluppo di nuove strategie terapeutiche nell’ambito dell’LMA. Tuttavia, lo sviluppo del trattamento con cellule CAR T nel contesto dell'LMA è ancora agli albori a causa dell'eterogeneità della malattia, della mancanza di un antigene bersaglio adatto e del ruolo protettivo del microambiente tumorale (TME). Infatti, non esiste ancora un protocollo clinico approvato per il trattamento della leucemia mieloide. Per creare le cellule CAR T abbiamo scelto di utilizzare la piattaforma non virale Sleeping-Beauty (SB) per ingegnerizzare le cellule CIK (cytokine-induced killer). In primo luogo, abbiamo scelto di utilizzare come potenziale strumento per il targeting del TME le cellule CIK ingegnerizzate con anti-CD146.CAR. Di conseguenza, abbiamo ottimizzato 6 diverse molecole CAR aventi un design differente, ottenendo un'espressione ottimale di CD146 nella variante VLVH Long. Abbiamo quindi testato le cellule CD146.CAR-CIK in vitro, ottenendo l’attivazione specifica delle funzioni effettrici (in termini di capacità di killing, produzione di citochine e proliferazione) contro cellule target CD146+. In seguito, abbiamo progettato un Tandem CAR bispecifico (CD33xCD146.CAR-CIKs) che ha mostrato una significativa attività antileucemica in vitro. È stato ampiamente dimostrato che la nicchia midollare contribuisce al supporto e alla protezione delle cellule staminali leucemiche (CSLs). Quindi, per mimare al meglio l’azione del CAR nella nicchia midollare umana, abbiamo testato le cellule CD33xCD146.CAR-CIK contro le linee cellulari stromali CD146+ e le cellule mesenchimali (MSC) primarie sane (HD-) e di derivazione mieloide (LMA-). I dati mostrano una inibizione delle funzioni effettrici delle cellule CAR-CIK e una drastica diminuzione della produzione di citochine e della proliferazione. Inoltre, l'equilibrio tra citochine pro e antinfiammatorie è risultato alterato, infatti la produzione di citochine Th1/Tc1 da parte delle cellule CD146.CAR-CIK è stata inibita dalla co-coltura con cellule stromali, mentre è stato rilevato un aumento delle citochine Th2/Tc2. Questi risultati suggeriscono un potenziale ruolo immunosoppressivo del compartimento stromale nei confronti delle cellule CAR-CIK. Sulla base dell’ effetto immunomodulatorio delle MSC sui linfociti T, abbiamo ipotizzato che la nicchia midollare possa influenzare le funzioni effettrici delle cellule CAR T. Di conseguenza, il targeting del CD146 rappresenta una "proof-of-principles" del fatto che aggredire il microambiente leucemico possa migliorare la terapia CAR T nell’ambito dell’LMA. Per ridurre al minimo la tossicità "off-target ", stiamo cercando di selezionare un antigene bersaglio specifico ed overespresso sulle cellule stromali dell'LMA, che abbia un'espressione minima nello stroma sano e che sia coinvolto nelle interazioni leucemia/nicchia. Il nuovo marker di interesse sarà accoppiato al CD33.CAR nella creazione di un CAR bispecifico, che verrà confrontato con il costrutto CD33xCD146.CAR, valutandone i profili di efficacia e sicurezza sia in vitro che in vivo.
Acute myeloid leukemia (AML) is the most frequently diagnosed leukemia in adults (25%) and accounts for 15-20% cases in pediatric patients. Conventional chemotherapy employing anthracycline and cytarabine represents the gold standard treatment for AML, with rates of complete remission from 60% to 80% in children and from 40% to 60% in adults (>60 years). Despite these high rates, relapse after conventional therapy is common and the estimated five-year survival of AML patients is still below 30%. Indeed, there is an urgency to find alternative therapeutic strategies for relapsed and refractory patients. The recent clinical success of chimeric antigen receptor (CAR) T cell immunotherapy in the context of B-cell malignancies has opened a new route of investigation also towards AML. However, the development of CAR T cell therapy in the context of AML is still in its infancy due to heterogeneity of the disease, the lack of a suitable target antigen and the leukemia protective role of the tumor microenvironment (TME) and no approved CAR T cells study exists for AML treatment yet. Non-viral Sleeping-Beauty (SB) transposon platform was employed to redirect cytokine-induce killer (CIK) cell. In this scenario, we firstly characterize non-viral SB engineered CIK cells with anti-CD146.CAR as a potential tool for the targeting of the bone marrow (BM) microenvironment. We optimized the CAR design structure by testing 6 different CAR molecules, achieving a specific and efficient CD146 expression in the VLVH Long variant. CD146.CAR-CIK cells were subsequently tested in vitro, showing an optimal activation of effector functions (in terms of killing activity, cytokines production and proliferation) when they were engaged against CD146+ target cells. Consequently, we developed a bispecific Tandem CAR (CD33xCD146.CAR-CIKs), which displayed anti-leukemic activity in vitro. It has been extensively proven that BM niche contribute to establish a sanctuary in which leukemic stem cells (LSCs) are able to acquire drug-resistant phenotype, therefore, to better mimicking the human BM niche we tested CD33xCD146.CAR-CIK cells against CD146+ stromal cell lines (HS-27A and HS-5) and primary derived healthy (HD-) and patient-derived (AML-) mesenchymal stromal cells (MSCs). Results showed inhibition of the redirected CAR-CIK cells effector functions, resulting in a drastic decrease of cytokines production and proliferation. The balance between pro- and anti- inflammatory cytokines showed that Th1/Tc1 cytokines production by CD146.CAR-CIK cells was inhibited by the co-culture with stromal cells, while increase Th2/Tc2 cytokines was detected when CD146.CAR-CIK cells were co-cultured with stromal target cells. These results suggest a potential immunosuppressive role of the stromal compartment against CAR-CIK cells. According to these results, we hypothesized that BM stromal cells can potentially exert an immunomodulatory effect on T cells, suggesting that the niche microenvironment may be involved in the regulation of CAR T cells therapy effectiveness. Indeed, the targeting of CD146 on stroma represents a “proof-of-principle” that stromal components of leukemic microenvironment may be attractive targets for CAR T based immunotherapy. To minimize “off-tumor” toxicity, we are looking for a specific surface target antigen selectively overexpressed on AML stromal cells, with minimal expression in healthy stroma and possibly involved in leukemia/niche interactions. The newly marker of interest will be coupled to the CD33.CAR and this bispecific CAR will be compared with CD33xCD146.CAR construct, evaluating their efficacy and safety profiles both in vitro and in vivo.

Adoptive immunotherapy using chimeric antigen receptor (CAR)-modified T cells targeting CD19 has shown remarkable therapeutic efficacy against B cell leukemia and lymphoma, and provided proof of concept for therapeutic potential in other hematologic malignancies. Acute myeloid leukemia (AML) is an entity with an unmet medical need for effective and curative treatments. Therefore, there is a strong desire for development of potentially curative CAR-T cell immunotherapy for AML treatment. FMS-like tyrosine kinase 3 (FLT3) is a homodimeric transmembrane protein expressed uniformly by AML blasts. FLT3 plays a vital role in the survival of AML blasts and is a key driver of leukemia-genesis in AML cases with internal tandem duplication (FLT3ITD) and tyrosine kinase domain (TKD) mutations. These attributes suggest that FLT3 could be an excellent target for CAR-T cell immunotherapy. Here, we engineered human CD4+ and CD8+ T cells to express FLT3-specific CARs and demonstrate that they confer potent reactivity against AML cell lines and primary AML blasts that express either wild-type FLT3 or FLT3-ITD. Further, we show that FLT3 CAR-T cells exert potent antileukemia activity in xenograft models of AML and induce complete remissions. We also demonstrate that FLT3-expression on FLT3-ITD+ AML cells can be augmented by FLT3 inhibitors, which lead to increased recognition by CARs and improved efficacy of FLT3 CAR-T cells. We confirmed this principle with three different FLT3 inhibitors which are at distinct stages of clinical development i.e. Phase II/III clinical trial (crenolanib, quizartinib) and clinically approved (midostaurin). Further, we observed the strongest anti-leukemia activity of FLT3 CAR-T cells in combination with crenolanib in vivo. FLT3 is known to be expressed by normal hematopoietic stem and progenitor cells. We evaluated FLT3-expression on normal hematopoietic stem cells (HSCs) using flow cytometry and confirmed lower level of FLT3-expression on HSCs and progenitors compared to AML cells. As anticipated, we found that FLT3 CAR-T cells recognize normal HSCs in vitro and in vivo, and compromise normal hematopoiesis, suggesting that adoptive therapy with FLT3 CAR-T cells will require successive CAR-T cell depletion and allogeneic HSC transplantation (HSCT) to reconstitute the hematopoietic system. Moreover, an FLT3 inhibitor treatment does not increase FLT3-expression on HSCs. Accordingly, we demonstrate that the depletion of FLT3 CAR-T cells is possible with inducible Caspase 9 (iCasp9) safety switch. Collectively, our data establish FLT3 as a novel CAR target in AML with particular relevance in high-risk FLT3-ITD+ AML. Our data demonstrate that FLT3 CAR-T cells act synergistically with FLT3 inhibitors in FLT3-ITD+ AML. i.e. FLT3 inhibitors-induced upregulation of FLT3 in FLT3-ITD+ AML cells enhances their recognition and elimination by FLT3 CAR-T cells. Due to recognition of normal HSCs, the clinical use of FLT3 CART cells is likely restricted to a defined therapeutic window and must be followed by CART cell depletion and allogeneic HSCT for hematopoietic reconstitution. The data provide rational to use FLT3 CAR-T cells in combination with FLT3 inhibitors to augment the anti-leukemia efficacy of FLT3 CAR-T cells in high-risk FLT3-ITD+ AML patients, and to mitigate the risk of relapse with FLT3-negative AML variants, which could otherwise develop under therapeutic pressure. The data provide proof of concept for synergistic use of CAR-T cell immunotherapy and small molecule targeted therapy and encourage the clinical evaluation of this combination treatment in high-risk patients with FLT3-ITD+ AML
Adoptive Immuntherapie, die Chimäre- Antigenrezeptor (CAR) –modifizierte, gegen CD19 gerichtet T-Zellen verwendet, hat eine bemerkenswerte therapeutische Wirksamkeit gegen B-Zell-Leukämien und -Lymphome und großes therapeutisches Potenzial für die Behandlung anderer hämatologischer Erkrankungen gezeigt. Die Akute Myeloische Leukämie (AML) ist hierbei eine Entität, für die es bisher an wirksamen und kurativen Therapien fehlt und für die die Entwicklung einer potentiell kurativen CAR-T-Zellimmuntherapie von großer Bedeutung ist. FMS-like tyrosine kinase 3 (FLT3) ist ein homodimeres Transmembranprotein, das von AML-Blasten uniform exprimiert wird. FLT3 spielt eine wichtige Rolle beim Überleben von AML-Blasten und ist ein Schlüsselfaktor in der Leukämie-Genese bei AML-Fällen mit interner Tandem-Duplikation (FLT3-ITD) und Tyrosinkinase-Domänen (TKD)-Mutationen. Diese Eigenschaften legen die Vermutung nahe, dass FLT3 ein ausgezeichnetes Target für die CAR-T-Zell-Immuntherapie darstellen könnte. Daher setzten wir dort an und modifizierten humane CD4+ und CD8+ T-Zellen, um FLT3-spezifische CARs zu exprimieren, und konnten nachweisen, dass diese eine starke Reaktivität gegen AML-Zelllinien und primäre AML-Blasten besitzen, die entweder den FLT3-Wildtyp oder FLT3-ITD exprimieren. Weiterhin konnten wir zeigen, dass FLT3 CAR-T-Zellen in AML-Xenograft-Modellen eine starke anti-Leukämie-Aktivität besitzen und vollständige Remissionen hervorrufen können. Zudem gelang der Nachweis, dass die FLT3-Expression auf FLT3-ITD+ AML-Zellen durch FLT3-Inhibitoren verstärkt werden kann, was zu einer erhöhten Erkennung durch die CARs und einer verbesserten Wirksamkeit von FLT3-CAR-T-Zellen führt. Wir konnten dieses Prinzip mit drei verschiedenen FLT3-Inhibitoren belegen, die sich in unterschiedlichen Stadien der klinischen Entwicklung befinden, d. h. aus einer Klinischen Phase II / III-Studie (Crenolanib, Quizartinib) und einem klinisch zugelassenen Inhibitor (Midostaurin). Darüber hinaus beobachteten wir die stärkste anti-Leukämie-Aktivität von FLT3 CAR-T-Zellen in einer Kombination mit Crenolanib in vivo. Es ist bekannt, dass FLT3 von normalen hämatopoetischen Stamm- und Vorläuferzellen exprimiert wird. Wir untersuchten die FLT3-Expression in normalen hämatopoetischen Stammzellen (HSCs) mittels Durchflusszytometrie und bestätigten im Vergleich zu AML-Zellen eine niedrigere FLT3-Expression auf HSCs und Vorläuferzellen. Wie erwartet, zeigte sich, dass FLT3 CAR-T-Zellen normale HSCs in vitro und in vivo erkennen und die normale Hämatopoese beeinträchtigen, was darauf hindeutet, dass eine adoptive Therapie mit FLT3 CAR-T-Zellen eine sukzessive CAR-T-Zell-Depletion und allogene HSC-Transplantation erfordert, um das hämatopoetische System wiederaufzubauen. Darüber hinaus erhöht die Behandlung mit einem FLT3-Inhibitor nicht die FLT3-Expression auf den HSCs. Dementsprechend konnten wir aufzeigen, dass die Depletion von FLT3 CAR-T Zellen mit einer induzierbaren Caspase 9 (iCasp9) als „Sicherheitsschalter“ möglich ist. Zusammenfassend etablieren unsere Daten FLT3 als ein neuartiges CAR-Target in der Behandlung von AML mit besonderer Relevanz für die Hochrisiko-FLT3-ITD+ AML. Unsere Daten zeigen, dass FLT3 CAR-T-Zellen synergistisch mit FLT3-Inhibitoren in FLT3-ITD+ AML wirken, d.h. eine FLT3-Inhibitoren-induzierte Hochregulation von FLT3 in FLT3-ITD+ AML-Zellen bewirkt und dies die Erkennung und Eliminierung durch FLT3-CAR-T-Zellen verstärkt. Durch ihre Eigenschaft der Erkennung von normalen HSCs ist die klinische Verwendung von FLT3 CAR-T-Zellen wahrscheinlich auf ein definiertes therapeutisches Fenster beschränkt und muss durch eine anschließende CAR-T-Zell-Depletion und eine allogene HSCT zur Rekonstitution des hämatopoetischen Systems ergänzt werden. In Anbetracht der Daten scheint es sinnvoll, FLT3-CAR-T-Zellen in Kombination mit FLT3-Inhibitoren zu verwenden, um die anti-leukämische Wirksamkeit von FLT3-CAR-T-Zellen bei Hochrisiko-FLT3-ITD+ AML-Patienten zu erhöhen und das Risiko eines Rückfalls mit FLT3-negativen AML-Varianten zu verringern, die sich sonst therapiebedingt entwickeln könnten. Die Daten stellen ein Proof-of-Concept für den synergistischen Einsatz von CAR-T-Zell-Immuntherapie und niedermolekularen Inhibitoren dar, der eine klinische Evaluation dieser Kombinationsbehandlung bei Hochrisikopatienten mit FLT3-ITD+ AML erstrebenswert macht