Thèses sur le sujet « The immune response of T lymphocyte cell »

Par rapport à l’adulte, le nouveau-né présente une susceptibilité accrue aux agents infectieux et au développement d’allergies. Une polarisation de l’immunité acquise vers des réponses de type Th2, productrices d’IL-4, d’IL-5 et d’IL-13, et un défaut de réponses immunes de type Th1, sécrétant de l’IFN-γ, peuvent rendre compte de ce statut immunitaire particulier. De plus, un retard de production et de maturation des anticorps, caractéristiques de l’immunité humorale, s’observe en début de vie.

Récemment, de nouveaux lymphocytes T auxiliaires ont été décrits, les lymphocytes Th17, producteurs d’IL-17A, d’IL-17F et d’IL-22, d’une part, et les lymphocytes Tfh, sécrétant de l’IL-21 et exprimant CXCR5, ICOS et PD-1, d’autre part. La différenciation des lymphocytes Th17 dépend de la présence d’IL-6 ou d’IL-21 et de TGF-β, et est inhibée par l’IL-4 ;tandis que les lymphocytes Tfh sont induits en présence d’IL-21, d’IL-6 et du répresseur transcriptionnel Bcl6. Alors que les lymphocytes Th17 sont associés à des réponses inflammatoires par le recrutement de neutrophiles, les lymphocytes Tfh aident les lymphocytes B à produire des anticorps de haute affinité.

L’objectif principal de notre travail est l’étude du développement potentiel de réponses de type Th17 chez le nouveau-né de souris soumis à une stimulation allogénique et au manque d’IL-4. De plus, l’existence potentielle de lymphocytes Tfh induits chez le nouveau-né immunisé avec un vaccin constitué d’ovalbumine de poulet et d’Alum, sera investiguée.

Dans notre modèle de tolérance néonatale, l’immunisation de nouveau-nés BALB/c à l’aide de cellules spléniques semi-allogéniques F1 (AJAX x BALB/c) induit une polarisation de type Th2, associée à l’établissement d’un chimérisme lymphoïde et à l’acceptation d’une greffe de peau présentant les alloantigènes rencontrés à la naissance. Des nouveau-nés soumis à cette immunisation allogénique et à la privation d’IL-4, réalisée par l’utilisation d’anticorps monoclonaux ou de souris IL-4-/-, rejettent de façon aiguë les greffons de peau et présentent une proportion réduite de cellules chimériques. Cette rupture de la tolérance néonatale est associée à l’inhibition de la réponse allospécifique de type Th2 et au développement de lymphocytes Th17 alloréactifs, produisant de l’IL-17A. L’inhibition de la voie Th17 ne conduit toutefois pas à l’acceptation des allogreffes de peau. Par contre, la neutralisation de l’IL-6 ou de l’IL-17A et la réduction du nombre de neutrophiles restaurent la proportion de cellules chimériques présentes dans la rate, démontrant que la réponse de type Th17 allospécifique néonatale contrôle le chimérisme lymphoïde.

En réponse au vaccin OVA-Alum, les nouveau-nés présentent une proportion accrue de lymphocytes Tfh CXCR5+ PD-1+, bien que cette proportion lymphocytaire soit significativement diminuée par rapport aux adultes. Les lymphocytes Tfh néonataux expriment en outre des taux moindres des ARNm d’IL-21, d’IL-4 et de Bcl6, suggérant que la génération de lymphocytes Tfh est altérée en début de vie. En parallèle, les titres et la maturation des anticorps produits suite à la vaccination sont réduits chez les nouveau-nés, en comparaison avec les adultes. Cependant, qu’ils soient déficients en IL-4 ou non, des lymphocytes T CD4+ néonataux activés in vitro en présence d’IL-6 induisent une production d’anticorps par des lymphocytes B compétents, suggérant qu’il n’y a pas de défaut intrinsèque des lymphocytes T du nouveau-né à développer une capacité d’aide aux lymphocytes B.

En conclusion, nous avons montré que la polarisation de type Th2 néonatale inhibe la différenciation de lymphocytes Th17 alloréactifs contrôlant le rejet de cellules allogéniques, un mécanisme pouvant intervenir dans la relation immunitaire entre la mère et l’enfant. Nos résultats indiquent également que le nouveau-né est capable de différencier des lymphocytes Tfh, bien que le développement de ces derniers semble réduit. \
Doctorat en Sciences biomédicales et pharmaceutiques
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Summary of the work

Abdominal aortic aneurysm (AAA) is a chronic degenerative disease that usually affects men over 65 years with an estimated prevalence of 5%. Aneurysm rupture represents a catastrophic event which carries a mortality rate of almost 90%. Current therapeutic options for AAAs measuring 5.5 cm in diameter or larger are based on prophylactic surgery, including conventional open reconstruction and endovascular stent-graft insertion. For patients with small asymptomatic AAAs (4.0 up to 5.5 cm in diameter), evidence from two recent large randomized controlled trials indicates no long-term survival benefit from immediate elective surgical repair as compared to imaging surveillance until aneurysm expands to 5.5 cm. This highlights the need for development of novel medical management strategies, including selective pharmacologic approaches, directed at preventing aneurysm expansion. In this regard, it is expected that a detailed knowledge of the pathobiology of human AAA lesion and a better understanding of pathophysiological mechanisms underlying initiation and progression of aneurysmal degeneration, particularly the specific involvement of T lymphocytes, will have special relevance to this challenging issue.

Inflammatory and helper T-cell responses in abdominal aortic aneurysm :controversial issues

Innate and inflammatory responses to endovascular versus open AAA repair. The occurrence of early acute systemic inflammatory responses after conventional open AAA repair is widely recognized and is thought to lead to the development of organ dysfunction and multiple organ failure, responsible for a large proportion of morbidity and mortality associated with aortic surgery. New therapeutic strategies designed to avoid ischemia-reperfusion injury related to aortic cross-clamping and to minimize the degree of tissue damage have thus been developed recently. Specifically, the advent of endovascular techniques has radically extended management options for patients with AAA. Although the method is believed to offer a clear short-term benefit over open repair, notably as regards restricted perioperative haemodynamic parameter fluctuations, reduced blood loss, briefer duration of surgery, shorter hospital stay, and lower 30-day mortality and complication rates, conflicting data are available regarding the exact nature and extent of the inflammatory events arising after such endoluminal procedures ;while several authors have indeed reported that endovascular AAA repair can determine a less intense and extensive inflammatory response, others have unexpectedly observed that the method may elicit a strong inflammatory response, the so-called « postimplantation syndrome ».

Adaptive cellular immune responses in human aneurysmal aortic lesion.

The inflammatory nature of AAA disease has long been suggested by the presence of a great number of CD4+ T lymphocytes in the outer media and adventitia of human AAA lesion. Interestingly, such infiltrating T-cell populations may have significant implications in the process of aneurysm dilation, since cytokines produced by T cells, notably IFN-gamma, have previously been shown to modulate production of matrix-degrading enzymes by resident macrophages and to induce apoptosis of medial SMCs. Through these key pathological mechanisms, T cells could potentially contribute to orchestrate aortic wall connective tissue disordered remodeling and degradation, and promote extensive disruption of elastic media, ultimately leading to aneurysmal degeneration. Nevertheless, despite their relative abundance in human AAA wall tissues, there is limited and controversial information as regards the functional profile of lesional lymphocytes, the exact nature of aortic wall adaptive cellular responses, and the etiologic role of T cells and their cytokines in initiation and progression of the aneurysmal process. Indeed, both Th1-type and Th2-type responses have been identified in human studies and experimental animal models of AAA.

Aims of the work

The main objectives of our work were to explore the innate and adaptive cellular immune responses in human AAA. In the first part of our work, we aimed to examine prospectively innate and inflammatory responses arising in a non-randomised cohort of patients undergoing endovascular versus open AAA repair. In the second part of our work, we focused our efforts on characterizing the nature of adaptive cellular immune responses and the phenotypic and functional repertoire of T cells in human AAA wall tissues obtained from a consecutive series of patients undergoing open AAA repair. Specifically, we sought to determine whether type 1 or type 2 responses occur predominantly in advanced AAA lesion.

Main experimental findings

Limited inflammatory response after endovascular AAA repair. Serial peripheral venous blood samples were collected preoperatively, immediately after declamping or insertion of endograft, and after 1, 3, 6, 12, 24, 48, and 72 hours. We first examined the acute phase reaction and liberation of complement cascade products using turbidimetric method and nephelometry. We found that endovascular repair produced lower postoperative CRP, leucocytosis, neutrophilia, and C3d/C3 ratio as compared to open surgery. We next analyzed surface expression of activation markers on peripheral CD3+ T cells using flow cytometry. We observed a strong upregulation of CD38 after open but not endovascular repair. Analysis of CD69 and CD25 molecules revealed no perioperative fluctuations in any group. We then investigated release of various circulating soluble cell adhesion molecules, proinflammatory cytokines, and chemokines using enzyme-linked immunosorbent assays. We demonstrated that both procedures are characterized by similar increases in ICAM-1 and IL-6 levels. Finally, tendency towards high levels of TNF-alpha and IL-8 was detected in endovascular repair, but data failed to reach statistical significance.

Predominance of type 1 CD4+ T cells in human aneurysmal aortic lesion. We have developed a tissue enzymatic digestion and cell extraction procedure to isolate intact mononuclear cells from aortic wall segments. This original cell isolation protocol enabled us to examine ex vivo the presence, phenotype, and cytokine secretion profile of infiltrating T lymphocytes freshly isolated from human AAA tissues for comparison with their circulating counterparts using flow cytometry. We found that both populations of infiltrating CD4+ and CD8+ T cells display a unique activated memory phenotype, as assessed by an increased expression of CD69 and HLA-DR activation antigens, downregulation of CD62L molecule, and predominant expression of the CD45RO isoform characteristics of memory cells. In addition, we identified the presence in human aneurysmal aortic wall lesion of CD4+ T cells producing high levels of IFN-gamma but not IL-4, reflecting their type 1 nature. In an additional series of experiments, cytokine gene expression was determined in whole aneurysmal and non-diseased aortic samples using LightCycler-based quantitative real-time reverse transcription-polymerase chain reaction. The molecular basis of type 1 or type 2 dominant responses was further specified by analyzing mRNA levels of transcription factors specifically involved in Th1 or Th2 differentiation such as T-bet and GATA-3. We demonstrated that aneurysmal aortic specimens exhibit high transcript levels of IFN-gamma but not IL-4, and consistently overexpressed the IFN-g-promoting cytokine IL-12 and the type 1-restricted transcription factor T-bet, further establishing the prominent type 1 nature of aortic wall responses. Moreover, such selective tissue expression of IL-12 and T-bet in the vessel microenvironment points to a potential role for these signals in directing aortic wall responses towards a type 1 phenotype.

Conclusions

Our findings indicate that endovascular AAA repair is associated with a lesser degree of acute phase reaction, peripheral T-cell activation, and release of complement proteins as compared to conventional open surgery, suggesting that the innate and inflammatory responses to AAA repair are significantly attenuated by the endovascular approach as compared to the traditional open reconstruction. These results support the view that the endoluminal procedure represents an attractive alternative to open surgery for the treatment of large aneurysms. On the other hand, we have demonstrated that Th1 cell infiltrates predominate in human end-stage AAA lesion. These observations are relevant for helping clarify the pathobiology of human AAA tissues and defining prospects for the prevention of aneurysm expansion. Indeed, identification of such infiltrating populations of IFN-gamma-producing CD4+ T cells not only provide new insights into the pathogenesis of the disorder, but could also serve as a basis for the development of novel medical management strategies directed at preventing aneurysm formation and progression, including therapeutic approaches based on the modulation of aortic wall responses and designed to selectively target T-cell activation and cytokine production. In this respect, the present work provides experimental evidence in support of the emerging concept that, although multifactorial, aneurysm disease may be regarded as a Th1-driven immunopathological condition, and suggests that strategies targeting IFN-gamma could be a particularly exciting and fruitful avenue for further investigation. Ongoing clinical and basic research in these areas can be expected to yield design of promising pharmacologic approaches to control AAA expansion. From a clinical perspective, such efforts have the potential to dramatically influence both the outcome and management of this common and life threatening condition.

Doctorat en sciences médicales
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Thesis (Ph. D.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains xi, 288 p. : ill. Vita. Includes abstract. Includes bibliographical references.

Les til-t provenant de 20 lmnh b de type histologique/cytologique varies ont été étudiés et 174 clones t ont été générés dans 9 des cas. 4 groupes prolifératifs ont été identifiés sur la base de prolifération des til-t. Les pourcentages de clones proliférant dans ces 4 groupes sont respectivement de 63%, 70% et 56%, et 10%. Dans les lmnh de forte malignite, 25% (5/20) des clones t prolifèrent sous l'effet des bm alors que dans les lmnh de faible malignite, il y en a 55% (36/65) (p < 0,05). Il en est de même pour leurs capacités de dissémination : dans les lmnh localisés (stades i et ii), 70% (28/40) des clones t prolifèrent au contact des bm, alors que dans les lmnh disséminés (stades iii et iv), 29% (13/45) des clones t ont cette capacité. La différence apparaît encore plus significative (p < 0,01). Ces corrélations ne sont pas observées avec la stimulation par les cellules b normales autologues infectées par le virus epstein barr (b-ebv) ou les cellules b normales allogeniques (bn-allo). La réponse proliférative des clones t vis-à-vis des bm n'est pas corrélée à un phénotype préférentiel des clones t cd4 ou cd8. 46 clones t provenant de 8 ganglions malins ont été testés pour leur capacité cytotoxique contre les bm. Seuls 6 clones t ont exprimé cette propriété. La production de gm-csf, d'inf, de tnf et d'il4 sur 9 clones, et celle d'il2 sur 5 clones ont été détectées sous l'effet des bm. Des clones t sont capables de proliférer et/ou d'exprimer l'ag cd25 au contact des bm, avec une intensité proportionnelle à la quantité de cellules b utilisées. La prolifération et l'expression de l'ag cd25 des cellules t est liée à une structure membranaire des bm. 6 clones t sont incapables de proliférer au contact des b-ebv et des bn-allo, ce qui est très en faveur de l'existence d'un antigène stimulant propre aux bm. En utilisant la méthode des ac bloquants, nous avons démontré que des clones t prolifèrent au contact des bm selon deux mécanismes qui impliquent tous le tcr mais qui se différencient par l'intervention ou non du cmh des bm

Les nouveau-nés et les jeunes enfants ont une susceptibilité plus élevée aux infections par rapport aux enfants plus âgés et aux adultes. Cette caractéristique est en partie attribuée à l’immaturité de leur système immunitaire qui est associée à une capacité limitée à développer des réponses immunitaires à médiation cellulaire. L’infection par le cytomégalovirus (HCMV) est la cause la plus fréquente d’infection congénitale chez l’Homme et une cause majeure de surdité et de retard mental. En Belgique, le dépistage anténatal de l’infection primaire par le HCMV chez les femmes enceintes offre l’opportunité d’étudier les réponses immunitaires du foetus à ce virus et de les comparer à celles de leur maman.

Les lymphocytes T CD4+ Th1 et les lymphocytes T CD8+ cytotoxiques jouent un rôle crucial dans le contrôle des pathogènes intracellulaires dont le HCMV fait partie. La littérature montre une capacité limitée des enfants congénitalement infectés par le HCMV à développer des réponses T CD4+ spécifiques du HCMV. En contraste, des réponses de lymphocytes T CD8+ spécifiques du HCMV ont été rapportées chez des enfants infectés in utero, mais ces réponses n’ont pas été comparées en détails à celles de l’adulte. De plus, notre connaissance des réponses T spécifiques du HCMV durant l’infection primaire par ce virus est limitée. Des études antérieures ont rapporté un défaut de prolifération et de production d’IL-2 des lymphocytes T spécifiques du HCMV chez des adultes avec durant la phase primaire de l’infection, mais les mécanismes restent non-élucidés.

Nous avons caractérisé les réponses de lymphocytes T CD4+ et CD8+ spécifiques du HCMV provenant du sang de cordon de nouveau-nés congénitalement infectés par le HCMV, et nous avons comparé ces réponses à celles de leurs mamans diagnostiquées avec une infection primaire par le HCMV durant la grossesse. En plus, nous avons comparé les réponses T CD4+ et CD8+ de ces mamans à celles d’adultes infectés chroniquement par le virus. Chez les nouveau-nés, nous avons démontré que des lymphocytes T CD4+ de sang de cordon exprimant un phénotype de différentiation spécifique du HCMV (CD27-CD28-) ainsi qu’un phénotype Th1 similaire à celui des cellules maternelles étaient induits in utero lors de l’infection congénitale par le HCMV. De plus, la détection d’expansions oligoclonales suggérait fortement une expansion antigène-spécifique de ces cellules. Cependant, les T CD4+ de nouveau-nés présentaient une capacité fortement réduite à produire des cytokines anti-virales (IFN-γ, TNF-α et MIP-1β) en réponse à une stimulation ex vivo avec les antigènes du HCMV, par rapport aux cellules maternelles. Les lymphocytes T (CD27-CD28-) CD4+ de nouveau-nés produisaient également des niveaux plus bas de cytokines antivirales en réponse à des stimulations polyclonales avec l’anti-CD3 et la PMA/ionomycine, suggérant des altérations en amont et en aval de la voie de signalisation du TCR. Nos résultats suggèrent que ces altérations pourraient impliquer la diminution de l’expression de molécules impliquées dans cette voie de signalisation. De la même manière, nous

avons montré que chez le nouveau-né, la fonction des T CD8+ spécifiques du HCMV était altérée par rapport à celle de l’adulte. Nous avons observé des proportions similaires de T CD8+ (CD27-CD28-) chez les nouveau-nés et les adultes. De plus, l’analyse du répertoire du TCR Vβ de ces cellules par séquençage haut-débit a révélé une capacité similaire à générer un répertoire T diversifié dans les deux groupes. Comme rapporté précédemment, nous avons détecté des fréquences similaires de lymphocytes T CD8+ spécifiques pour l’antigène immunodominant pp65. Cependant, lorsque les stimulations ont été étendues à d’autres antigènes du HCMV, nous avons observé que le répertoire antigénique reconnu par ces cellules était significativement réduit chez les nouveau-nés, en association avec une diminution de la polyfonctionalité et de la production de cytokines par cellule.

Nous avons également montré que, dans une moindre mesure, la fonction des lymphocytes T spécifiques du HCMV était diminuée durant l’infection primaire chez l’adulte. Comme reporté précédemment, les T CD4+ spécifiques du HCMV proliféraient moins et produisaient moins d’IL-2 par rapport à des individus dans la phase chronique de l’infection. Ce défaut de production d’IL-2 affectait à la fois les populations de cellules CD28+ et CD28-, montrant que l’accumulation de lymphocytes T CD4+ ayant perdu l’expression de la molécule CD28 (un signal de co-stimulation important pour la production d’IL-2) est seulement un des facteurs contribuant à la diminution de la production d’IL-2 par les cellules spécifiques du HCMV. En accord avec cette observation, nous avons montré une diminution de la production par cellule d’IFN-γ et de TNF-α touchant également à la fois les populations de T CD4+ CD28+ et CD28- durant la phase primaire de l’infection, un défaut associé avec une avidité fonctionnelle diminuée de ces cellules. De la même manière, la polyfonctionalité et la production de cytokines par cellule des lymphocytes T CD8+ spécifiques du HCMV étaient également diminuées chez les adultes durant la phase d’infection primaire.

En résumé, nos résultats montrent que la fonction des lymphocytes T spécifiques du HCMV de nouveau-nés et d’adultes est altérée durant l’infection primaire par rapport à des individus infectés chroniquement par le virus. Nous montrons que cette régulation fonctionnelle ressemble à l’exhaustion fonctionnelle des lymphocytes T observée durant les infections virales chroniques associées à des charges virales élevées. L’infection primaire par le HCMV est caractérisée par une réplication virale intense qui dure pendant plusieurs mois suivant l’infection. Nous émettons l’hypothèse que les hauts taux de réplication virale observés durant l’infection congénitale et chez l’adulte durant l’infection primaire par le HCMV pourraient interférer avec certaines fonctions des lymphocytes T./Neonates and young infants have a higher susceptibility to infections compared to older infants or adults. This feature is in part attributed to the immaturity of their immune system associated with a limited capacity to mount cellular-mediated immune responses. Congenital human cytomegalovirus (HCMV) infection is the most common cause of congenital infection worldwide and a major cause of hearing loss and mental retardation. In Belgium, antenatal screening of pregnant women for primary HCMV infection offers an opportunity to study neonatal immune responses to the virus and to compare them to those of their mother.

T lymphocytes are major players of the immune system. In particular, Th1 CD4+ T cells and CD8+ cytotoxic T cells play a crucial role in the control of intracellular pathogens, including HCMV infection. Previous literature has reported a limited capacity of infants born with congenital HCMV infection to mount HCMV-specific CD4+ T cell responses. In contrast, fetal antigen-specific CD8+ T cell responses have been reported following in utero HCMV infection, but these responses have not been compared in detail to those of adults with primary infection. In addition, our knowledge regarding adult HCMV-specific T cell responses during primary HCMV infection is limited. Previous studies have reported defective T cell proliferation and IL-2 production in adults with primary HCMV infection, showing that some of the T cell functions are altered during primary infection.

In this study, we have characterized neonatal HCMV-specific CD4+ and CD8+ T cell responses from the cord blood of newborns with congenital HCMV infection, and we have compared these responses to that of their mothers diagnosed with primary HCMV infection during pregnancy. Also, we compared CD4+ and CD8+ T cell responses of adults with primary HCMV infection to that of adults with chronic infection.

In newborns, it was not known if the defective CD4+ T cell responses could be attributed to the absence of HCMV-specific cells or to the induction of dysfunctional cells. We demonstrate that neonatal CD4+ T cells with a differentiation phenotype typical of HCMV infection (CD27-CD28-) and expressing a Th1 phenotype similar to that of maternal cells can differentiate in utero following HCMV infection. In addition, the detection of oligoclonal expansions by spectratyping and flow cytometry analyses strongly suggests antigen-specific responses. However, neonatal CD4+ T cells were markedly less able to produce antiviral cytokines (IFN-γ, TNF-α and MIP-1β) following ex vivo stimulation with HCMV antigens, compared to maternal cells. Also, neonatal CD27-CD28- CD4+ T cells produce lower levels of antiviral cytokines in response to polyclonal stimulations with anti-CD3 and PMA/ionomycin, suggesting alterations up-stream and down-stream of the TCR signaling pathway. Our results suggest that these alterations could involve the down-regulation of the expression of molecules that are part of the TCR signaling pathway. Similarly, we show that the function of

neonatal HCMV-specific CD8+ T cells is impaired compared to adults. Similar proportions of (CD27-CD28-) CD8+ T cells, typical of HCMV infection, were detected in newborns and adults. Analysis of the TCR Vβ repertoire of neonatal and maternal (CD27-CD28-) CD8+ T cells by high-throughput sequencing revealed a similar capacity to generate a diverse clonal repertoire. As previously reported, we detected similar frequencies of HCMV-specific CD8+ T cells specific for the immunodominant viral antigen pp65. However, when extending ex vivo stimulations to other HCMV antigens, we observed that the antigenic repertoire recognized by these cells was significantly reduced in newborns. In addition, neonatal CD8+ T cells had a reduced polyfunctionality and per cell cytokine production.

To a lower extent, the function of adult HCMV-specific T cells was also impaired during primary infection. As previously reported, maternal HCMV-specific CD4+ T cells were markedly less able to produce IL-2 and to proliferate compared to individuals in the chronic stage of the disease. Both CD28+ and CD28- T cell subsets produced decreased levels of IL-2. This observation shows that the accumulation of HCMV-specific CD4+ T cells having lost the expression of the CD28 molecule (an important co-stimulatory signal for IL-2 production) during primary infection is only one of the factors contributing to the decreased IL-2 production. Accordingly, both CD28+ and CD28- CD4+ T cell subsets had a decreased per cell production of IFN-γ and TNF-α during primary HCMV infection. This defect was associated with a lower functional avidity of these cells. Similarly, the polyfunctionality and per cell cytokine production of adult HCMV-specific CD8+ T cells was also impaired compared to adults with chronic infection.

Altogether, our results show that adult and neonatal HCMV-specific T cell responses are impaired during primary infection, compared to individuals with chronic infection. We show that this functional regulation resembles that of functional T cell exhaustion observed during chronic viral infections that are associated with high levels of viral replication. Primary HCMV infection is characterized by an intense viral replication lasting for several months post-infection. We hypothesize that the high levels of viral replication observed during congenital and adult primary HCMV infection could interfere with some of the T cell functions.
Doctorat en Sciences biomédicales et pharmaceutiques
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Marsupials and eutherians are the two principal groups of modern mammals. Mammalian immunological studies, to date, have focused on eutherian systems with little or no comprehensive work having been carried out on marsupials. This project investigates the functional and developmental aspects of T-cell responses in the marsupial, Macropus eugenii (Tammar wallaby) in both adults and pouch young at various stages of development. Determination of the age at which the Tammar wallaby immune system becomes competent has been examined through the use of cellular and molecular studies carried out on developing pouch young tissue. The capacity for generating an immunological response in adult and pouch young marsupials has been studied by following cellular proliferation in response to mitogens or mixed lymphocyte culture (MLC). After examining adult responses to mitogens and allogenic lymphocytes, optimised conditions were then used to examine the development of responsiveness in pouch young. Several further tests were conducted and findings shown. The study has shown that the earliest age at which Macropus eugenii is capable of mounting a T-cell mediated immune response is between 5 to 13 days post-partum

Cybr (Cytohesin binder and regulator) is an adaptor protein involved in the assembly and recruitment of protein complexes associated with intracellular trafficking and signaling. Cybr has attracted attention as a potential key contributor to molecular mechanisms governing cells of the immune system due to its exclusive expression in cells of hematopoietic origin. Cybr interacts with members of the ADP ribosylation factor (ARF)-activating cytohesin family, mainly cytohesin-1, and it is involved in the cytohesin-1-mediated adhesion of LFA-1 to ICAM-1. Cybr expression is highly and rapidly responsive to, and regulated by, many cytokines and other soluble effectors of the immune system suggesting a potential functional role in the vesicle formation, endocytic trafficking, regulation of TCR signalling and regulation of dendritic cell (DC)/T cell interaction during the antigen presentation. To characterize the in vivo physiological role of this molecule, a Cybr-deficient mouse strain was created. Cybr deletion does not profoundly affect the development of the immune system, but Cybr-KO mice display a reduced or delayed capacity to respond to different stimuli and in stress conditions. This project aimed at investigating the biological function of Cybr in cell-mediated immune response to tumors induced by the retroviral complex constituted by the Moloney murine sarcoma virus/Moloney murine leukemia virus (M-MSV/MuLV, hereafter indicated as M-MSV). Intramuscular injection of M-MSV in immunocompetent C57BL/6 (B6) mice causes sarcomas that spontaneously regress because of a strong immune reaction primarily mediated by cytotoxic T lymphocytes (CTL) specific for viral antigens. Conversely, Cybr-deficient mice injected with M-MSV developed larger tumors than B6 mice, which additionally regressed with a slower kinetics. To disclose the biological bases of this behavior, M-MSV-injected Cybr-deficient and wild type mice were characterized for the lymphocyte phenotype and function in tumors, lymph nodes and spleens at the peak of tumor growth (day 11 to 15). We found a reduced number of CD4+ and CD8+ T cells, as well as of antigen-specific CTL, in the tumor infiltrating cells (TIL) of Cybr-deficient mice. However, this defect was recovered after a short temporal shift. Similarly, a three-day delay was also reported in the onset of lytic activity in Cybr-deficient respect to wild type CTLs. On the contrary, wild type or Cybr-deficient memory T cells from tumor regressor mice did not show any difference in terms of lytic activity. Overall, these data indicate that Cybr deficiency has a significant impact on the activation of naive T cells and expansion of primed T cells, but do not clarify whether Cybr mostly influence priming and/or cell adhesion or trafficking and migration of immune system cells. To address this issue, we transferred naive Cybr-KO or wild type GFP T cells in tumor-bearing RAG2-/- γc-/- mice, that lack T, B and NK cells and do not spontaneously regress M-MSV-induced tumors. Despite T cell transfer, tumors continued to growth indicating that transferred naive T cells were not able to mount a fully effective immune response in this setting. This was probably due to a suboptimal recruitment and priming phase in lymph nodes, that were found to be hypoplastic. To provide a mechanistic insight, reconstitution of nu/nu athymic B6 mice with T cell-depleted bone marrow from either wild type or Cybr-KO mice, followed by adoptive transfer of naive or memory T cells from Cybr-KO/GFP or B6/GFP animals, will provide the appropriate experimental set up to assess the role of Cybr in the APC or T cell compartments. Taken together, outlined results indicate that Cybr deficiency has a significant impact on antigen-specific immune response, but further studies have to be performed to fully dissect the role played by this molecule in the priming phase and in the delayed onset of lytic activity
Cybr (cytohesin binder and regulator) è una proteina adattatrice coinvolta nell’assemblaggio e nel reclutamento di complessi proteici associati con il trafficking intracellulare e la trasduzione del segnale. Grazie alla sua esclusiva espressione in cellule di origine ematopoietica, Cybr ha attirato l’attenzione come potenziale proteina chiave nei meccanismi molecolari che controllano le cellule del sistema immunitario. Cybr interagisce con i membri della famiglia delle citoesine attivanti gli ADP ribosylation factors (ARF), specialmente con citoesina-1, e regola l’adesione citoesina-1 mediata di LFA 1 a ICAM-1. La sua espressione è rapidamente regolata da molte citochine e da altri effettori solubili del sistema immunitario. Alcuni ruoli funzionali proposti per questa molecola sono la partecipazione nella formazione delle vescicole, nel trafficking endocitico, nella regolazione del signaling del TCR e nell’interazione tra cellule dendritiche e cellule T durante la presentazione dell’antigene. Al fine di caratterizzare il ruolo fisiologico di questa molecola in vivo, è stato creato un ceppo di topi deficienti per Cybr. Questi topi, nonostante un normale sviluppo del sistema immunitario, mostrano una ridotta o ritardata capacità di rispondere a diversi stimoli e in condizioni di stress. Questo progetto di ricerca si è prefisso di investigare la funzione biologica di Cybr nella risposta immunitaria cellulo-mediata nei confronti di tumori indotti dal complesso retrovirale costituito dai virus sarcomatogeno e leucemogeno murini di Moloney (M-MSV/MuLV, in seguito indicato come M-MSV). L’inoculo intramuscolare di M-MSV in topi C57BL/6 (B6) immunocompetenti causa lo sviluppo di sarcomi che regrediscono spontaneamente grazie ad una forte risposta immunitaria mediata principalmente da linfociti T citotossici (CTL) specifici per gli antigeni virali. Al contrario, topi Cybr-deficienti inoculati con M-MSV sviluppano tumori di dimensioni maggiori e che regrediscono più lentamente rispetto ai controlli. Per comprendere i motivi di questo diverso andamento, dopo l’inoculo del complesso retrovirale in topi Cybr-deficienti e wild type, sono stati caratterizzati a livello fenotipico e funzionale i linfociti presenti nei tumori, nei linfonodi drenanti e nelle milze al momento della massima crescita tumorale (giorni 11-15). Abbiamo riscontrato un ridotto numero di linfociti T CD4+ e CD8+ e di CTL antigene specifici nella popolazione infiltrante il tumore nei topi Cybr-deficienti. Tuttavia questa differenza si è ridotta alla fine del periodo analizzato. Inoltre, un ritardo simile è stato riportato nello sviluppo dell’attività litica nei CTL provenienti da topi Cybr-KO rispetto a topi wild type. Al contrario, linfociti T memoria wild type e Cybr-KO non hanno mostrato nessuna differenza in termini di attività litica. Complessivamente, questi dati indicano che la deficienza di Cybr ha un significativo impatto nell’attivazione delle cellule T naive e nella loro espansione dopo il priming, ma non definiscono se questa proteina influenzi maggiormente la fase di priming e/o adesione cellulare o il trafficking e la migrazione delle cellule del sistema immunitario. Per chiarire questi aspetti, sono stati trasferiti linfociti T naive provenienti da topi Cybr-KO/GFP o B6/GFP in topi RAG2-/-γc-/- inoculati con il complesso retrovirale. Questi topi mancano di cellule T, B e NK e non regrediscono spontaneamente i tumori M-MSV indotti. Nonostante l’infusione di cellule T, i tumori hanno continuato a crescere, indicando che le cellule T naive non sono state in grado di montare una risposta immune pienamente efficace in questo modello, un aspetto probabilmente dovuto ad un reclutamento e priming sub ottimali nei linfonodi, che sono risultati ipoplastici. Al fine di rispondere a questi quesiti biologici, topi B6 nu/nu atimici ricostituiti con tessuto midollare depleto di linfociti T provenienti da topi wild type o Cybr-KO e successivamente infusi con linfociti T naive o memoria provenienti da topi Cybr-KO/GFP o B6/GFP, dovrebbero costituire un modello sperimentale ottimale per investigare il ruolo di Cybr sia nel comparto T che nel comparto APC. Nell’insieme, i risultati ottenuti indicano che la deficienza di Cybr ha un significativo impatto nella risposta immune antigene-specifica, ma studi addizionali devono essere condotti al fine di definire con maggior precisione il ruolo di Cybr nella fase di priming e nel ritardo dello sviluppo dell’attività litica

Stimulation of CD40 on APCs through CD40L expressed on helper CD4+ T cells activates and “licenses” the APCs to prime CD8+ T cell responses. While other stimuli, such as TLR agonists, can also activate APCs, it is unclear to what extent they can replace the signals provided by CD40-CD40L interactions. In this study, we used an adoptive transfer system to re-examine the role of CD40 in the priming of naïve CD8+ T cells. We find an approximately 50% reduction in expansion and cytokine production of TCR-transgenic T cells in the absence of CD40 on all APCs, and on dendritic cells in particular. Moreover, CD40-deficient and CD40L-deficient mice fail to develop endogenous CTL responses after immunization and are not protected from a tumor challenge. Surprisingly, the role for CD40 and CD40L are observed even in the absence of CD4+ T cells; in this situation, the CD8+T cell itself provides CD40L. Furthermore, we show that although TLR stimulation improves T cell responses, it cannot fully substitute for CD40. We also investigated whether CD40-CD40L interactions are involved in the generation, maintenance, and function of memory CD8+ T cells. Using a virus infection system as well as a dendritic cell immunization system, we show that the presence of CD40 on DCs and other host APCs influences the survival of activated effector cells and directly affects the number of memory CD8+ T cells that are formed. In addition, memory CD8+ T cell persistence is slightly impaired in the absence of CD40. However, CD40 is not required for reactivation of memory CD8+ T cells. It seems that CD40 signals during priming also contribute to memory CD8+ T cell programming but this function can be independent of CD4+T cells, similar to what we showed for primary responses. Altogether, these results reveal a direct and unique role for CD40L on CD8+ T cells interacting with CD40 on APCs that affects the magnitude and quality of primary as well as memory CD8+ T cell responses.

Au cours de la réponse immunitaire antitumorale, l’instabilité génétique des tumeurs combinée à la pression de sélection du système immunitaire peut conduire, via l’immunoediting, à l’émergence de variants tumoraux résistants à la lyse par les effecteurs cytotoxiques. Une meilleure compréhension de ces mécanismes potentiellement impliqués dans la susceptibilité tumorale à la lyse naturelle et/ou spécifique pourrait permettre le développement de stratégies d’immunothérapie intégratives plus efficaces. Dans ce cadre nous avons étudié un modèle de résistance à la lyse spécifique impliquant un remaniement du cytosquelette d’actine (i). Nous avons pu mettre en évidence que l’inhibition conjointe de protéines interagissant avec l’actine (caldesmone, ézrine, radixine et moésine) générait une réduction de la susceptibilité des cellules tumorales à la lyse par les lymphocytes T cytotoxiques (CTLs). Parallèlement, nous avons identifié les microARNs différentiellement exprimés entre le variant résistant et la lignée parentale et étudié leur implication dans la susceptibilité tumorale à la lyse par les CTLs. Dans le but de déterminer le rôle d’une pression de sélection par les cellules tueuses naturelles (NK pour Natural Killer), de l’immunité innée, sur les cellules tumorales et l’émergence de variants résistants, nous avons aussi établi un modèle de coculture continue de cellules tumorales de mélanomes avec des cellules NK (ii). Les cellules tumorales obtenues sont résistantes à la lyse NK (mais toujours sensibles à la lyse spécifique par un clone lymphocytaire T cytotoxique) et établissent moins de contact et de synapse immunologique avec les cellules NK que la lignée parentale. L’analyse transcriptomique a révélé la baisse d'expression de B7-H6 (ligand d'un récepteur activateur des cellules NK) qui contribue partiellement au phénomène de résistance. De nombreux gènes impliqués dans les phénomènes de migration/invasion/adhérence sont également modulés et certaines propriétés cellulaires (croissance en milieu semi-solide, adhérence, migration) semblent refléter l’acquisition d’une agressivité tumorale accrue suite à la coculture. Nous avons finalement analysé l’impact sur la réponse antitumorale de la connexine-43, impliquée dans la formation des jonctions communicantes (GJ pour Gap Junction) (iii). Nous avons montré que sa présence à la synapse entre cellules tumorales et CTL n'exerce aucun impact sur la susceptibilité à la lyse. Néanmoins, les GJs sont impliquées dans l’émergence par stimulation antigénique de lymphocyte T CD8+ spécifique hautement réactif
During antitumor immune response, cancer cells genetic instability combined with immune system selective pressure may drive to the emergence of tumor variant resistant to lysis by cytotoxic effector cells through a phenomenon called immunoediting. A better understanding of those mechanisms putatively involved in tumor susceptibility to natural and/or specific lysis would enable new integrative and more effective immunotherapeutic strategies. In this context, we studied a model of resistance to specific lysis linked to actin cytoskeleton remodeling (i). We showed that combined inhibition of actin interacting protein (caldesmone, ezrin, radixin and moesin) reduced tumor cells susceptibility to cytotoxic T lymphocytes (CTLs) lysis. Moreover, we identified microRNAs differentially expressed between parental cell line and resistant variant and are currently studying their impact on tumor susceptibility to CTLs lysis. In order to depict the role of innate immunity Natural Killer (NK) cells selective pressure, on tumor cells and on the emergence of resistant variants, we also established a maintained coculture model of melanoma cells with NK cells (ii). Selected cells obtained were resistant to NK cells-mediated lysis (but still susceptible to CTLs-mediated specific lysis) and formed less contact and immune synapse with NK cells than parental cell line. Transcriptomic analysis revealed the reduced expression of B7-H6 (ligand of an NK cells activating receptor) partially contributing to the resistance phenotype. The expression of several genes involved in migration/invasion/adhesion is also modulated and some cell characteristics (cell growth in semi-solid medium, adhesion, migration) tend to reflect the acquisition through coculture of an increased aggressiveness. Finally, we evaluated the impact of connexin-43 (Cx43), involved in the establishment of Gap Junctions (GJs), on antitumor response (iii). We showed that despite localization at the immune synapse between tumor target cell and CTL, Cx43 and GJs do not modulate susceptibility to CTL-mediated specific lysis. Nevertheless, GJs contribute to the emergence of highly reactive specific CD8+ T lymphocytes following antigen stimulation

CD4+ T cells play a central role in immunity. During virus infections, CD4+ T cells provide the necessary help for B cells to secrete anti-viral antibody and may act as effector cells themselves through the secretion of anti-viral cytokines such as IFN-γ and TNF-α. Recent studies in the lymphocytic choriomeningitis virus (LCMV) system have shown that CD4+ T cells are required to maintain the clearance of persistent viral infections as well as maintain virus-specific memory CD8+ cytotoxic T lymphocytes (CTL). Despite these important functions, surprisingly little information exists concerning the longevity, magnitude, and stability of the CD4+ T cell response following a virus infection. This thesis takes advantage of the well-studied LCMV system to address the above issues as well as to examine the role CD4+ T cells play during heterologous virus infections and to determine the fate of CD4+T cells following a high-dose LCMV infection. The cell surface phenotype of the CD4+ T cells was first examined in C57BL/6 mice acutely infected with LCMV. FACS analysis revealed the modulation of several activation markers on CD4+ T cells during an acute infection with LCMV, consistent with an activated cell phenotype. In addition, 25% of the CD4+ T cells were blast-sized by day 7 post-infection (p.i.) even though the total number of CD4+ T cells did not increase in the spleen during the acute infection. Additional studies were performed using CZ-1, a novel monoclonal antibody (mAb) previously generated in our laboratory that defines a sialic acid-dependent CD45RB-associated epitope. Examination of the expression of the CZ-1 antigen on CD4+ T cells following LCMV infection revealed that the blast-sized CD4+ T cells at day 6 p.i. were CZ-1 +. Further cell surface phenotyping showed that those blast cells activated at day 6 p.i. were CD45RB1oCD44hiCD62L-. This contrasts with the CZ-1-CD45RBhiCD441oCD62L+ resting cell population prior to infection. To determine if memory CD4+ T cells continued to express the CZ-1 epitope long after resolution of the LCMV infection, CD4+CZ-1+ and CD4+CZ-1- populations were purified by cell sorting and placed into an in vitro proliferation assay with LCMV-infected antigen-presenting cells (APC). It was found that the CD4+CZ-1+ population contained virtually all of the virus-specific memory. Thus, these studies indicate that the CZ-1 epitope defines a novel activation and memory marker for murine CD4+T cells. Examination of virus-specific cytokine production using ELISPOT assays showed a significant increase in the number of IFN-γ-secreting cells in the spleen during an acute LCMV-infection. CD8+ T cells made up the majority of the IFN-γ-producing cells, but analysis of the cell culture supernatants by ELISA revealed that the CD4+T cells produced more IFN-γ on a per cell basis. No significant increase in IL-4 levels was detected under these experimental conditions. These data suggest that LCMV infection induces primarily a virus-specific Th1 response that is characterized by increased IFN-γ production. No quantitative information was known about the frequency and longevity of the LCMV-specific CD4+ T cell response. Using limiting dilution assays (LDA), I examined the CD4+ T cell precursor (Thp) frequency in C57BL/6 mice infected with LCMV. The virus-specific CD4+ Thp frequency increased from <1/100,000 in uninfected mice to a peak of approximately 1/600 in FACS-purified splenic CD4+ T cell populations by 10 days p.i. with LCMV. After the peak of the response, the CD4+ Thp frequency decreased only about 2-fold per CD4+ T cell to approximately 1/1200 and remained stable into long-term memory. The CD4+ Thp frequency to each of the two known LCMV major histocompatibility complex (MHC) class II-restricted peptides dropped only 2- to 7-fold from the peak of the acute LCMV response into long-term memory. Thus, the CD4+T cell frequencies remain elevated after the acute infection subsides and remain extremely stable throughout long-term immunity. The above results show that LDA can account for +T cells as being virus-specific following LCMV infection. However, using newer, more sensitive assays based on intracellular cytokine production, >20% of the CD4+ T cells secreted IFN-γ after stimulation with phorbol myristic acid and ionomycin during the peak of the acute CD4+ T cell response. In addition, >10% of the CD4+ T cells secreted IFN-γ after stimulation with the LCMV MHC class II-restricted CD4 peptides. Thus, these new sensitive assays reveal a heretofore unappreciated, yet profound antigen-specific CD4+T cell response during LCMV infection. Infection of mice with a series of unrelated viruses, termed heterologous viruses, causes the reduction of memory CD8+ T cells specific to earlier infections. In order to examine the fate of CD4+ T cells under these conditions, I examined cytokine production and followed the CD4+ Thp frequency following heterologous virus infections. Challenge of LCMV-immune mice with vaccinia virus (VV) resulted in a significant increase in both the amount of IFN-γ protein and the frequency of IFN-γ-producing cells in the peritoneal cavity 3 days after infection as compared to control non-immune mice acutely infected with VV or to LCMV-immune mice alone. Intracellular IFN-γ staining revealed that both CD4+ and CD8+ T cells contributed to this increased IFN-γ production. LDA analysis of the LCMV-specific CD4+ Thp frequency following multiple heterologous virus infections or protein antigen immunizations, revealed that the CD4+ Thp frequency remains stable even under conditions that reduce the LCMV-specific CD8+ CTLp frequency. Additional studies using high-dose LCMV Clone 13 demonstrated that, like CD8+ T cells, there is a decline in detectable LCMV-specific CD4+Thp during overwhelming virus infections. The data presented in this thesis help provide a better understanding of the CD4+ T cell response during virus infections. I make several novel observations, including the demonstration that mAb CZ-1 defines a novel activation and memory marker for CD4+ T cells, that the LCMV-specific memory CD4+ Thp frequency remains extremely stable into long-term immunity, and that heterologous virus infections do not disturb the stable memory CD4+ T cell pool following a virus infection. I also provide data using new sensitive assays based on intracellular cytokine production that there is a much more profound antigen-specific CD4+ T cell response during viral infections than has previously been realized. Finally, I provide evidence that the virus-specific CD4+ T cells become unresponsive following a high-dose LCMV Clone 13 infection. Thus, the data presented in this thesis highlight some important similarities and differences between the CD4+ and CD8+ T cell responses during acute viral infections.

The generation of memory T cells following primary exposure to a pathogen is a critical feature of the vertebrate immune system which has evolved as a protective mechanism in order to defend the host against repeated assaults by the patnogen. Memory T cells are long-lived, undergo rapid proliferation upon re-activation, mediate a robust secondary response and clear the pathogen much more efficiently. These aspects have made the generation of memory T cells an attractive goal for the production of both prophylactic and therapeutic vaccines. However, the degeneracy of the T cell receptor, whereby a given T cell recognizes more than one epitope, allows the T cell to be modulated by epitope variants which could be self-ligands, ligands related to the original epitope but altered in sequence, or completely unrelated epitopes. Experiments in both mice and humans show that such cross-reactive stimulation of memory T cells results in complete, partial, or no activation of T cells, and in some cases, even alters the functional identity of the T cell (for example, T helper 1 cells start secreting IL-4, IL-5 and become part of a T helper 2 response). In the context of secondary infection of immune organisms with pathogens containing mutated or related T cell epitopes, such alterations at the cellular level translate into drastic changes in the overall clinical outcome of the infection. Thus, the presence of cross-reactive T cells in the memory population implies that the protective or pathologic nature of the secondary immune response is a consequence of the host's infection history. Although several murine models of heterologous infection resulting in altered pathological outcome have been studied, the exact immune correlates of protection versus immunopathology are still unclear. This thesis addresses this issue in dengue virus infections in humans. Dengue fever (DF) and Dengue Hemorrhagic Fever (DHF) are two disease manifestations caused by infections of humans by the dengue viruses. These are a group of 4 serologically distinct flaviviruses (D1-4) which often co-circulate among endemic populations. While primary infection with any of the four serotypes can result in the more severe clinical disease characterized by DHF, epidemiological data from several outbreaks show that 80% - 90% of DHF cases occur among individuals with secondary infection. This implies that prior immunity to dengue is actually a risk factor for developing severe disease. In these DHF cases, there are increased numbers of CD69+ CD8+ T cells in circulation, with increases observed in the frequency of epitope-specific T cells, and the serum levels of several T cell produced cytokines, chemokines, and immune receptors are highly elevated. Since the four serotypes share 65% - 75% amino acid sequence homology, the possibility that unconserved T cell epitope sequences stimulated cross-reactive responses was borne out in in vitroexaminations. In these studies, peripheral blood mononuclear cells (PBMC) and cloned T cells from both vaccinated and infected donors contained large populations of memory T cells that were cross-reactive for heterologous viral serotypes in proliferation and CTL assays. These data suggest that the severity of disease seen in DHF patients can be attributed to an immunopathologic secondary response during heterologous infection, and highlight a role for serotype cross-reactive T cells in this process. This thesis addresses the hypothesis that the recognition of the natural variants of dengue virus T cell epitopes by serotype cross-reactive CD8+ T cells of a dengue-immune donor results in an altered secondary response profile, with the changes reflected in both the quantitative and qualitative nature of the response. In order to compare the functional profile of the secondary response of dengue-immune PBMC re-activated with heterologous serotypes, we focused on a panel of 4 donors who were vaccinated with live attenuated monovalent vaccines corresponding to D1, D2, or D4 serotypes. We screened a panel of peptides predicted to bind to HLA-A*0201 for cytokine responses and identified 4 novel epitopes that were highly immunogenic in all four donors. Direct ex vivo stimulation of donor PBMC with the heterologous sequences of these epitopes also showed sizeable serotype cross-reactive T cell populations. CFSE- and intracellular staining for cytokines and chemokines showed that these cross-reactive T cells not only expanded but also produced IFNγ, TNFα, and MIP-1β. Multi-parameter staining revealed functionally diverse populations comprised of single cytokine (IFNγ+, TNFα+, MIP-1β+, double cytokine (IFNγ+TNFα+, IFNγ+MIP-1β+, TNFα+MIP-1β+, and triple cytokine (IFNγ+TNFα+MIP-1β+ secreting sub-sets. Stimulation with the epitope variants altered the magnitude of the overall response as well as the relative sizes of these sub-sets. The patterns of responses revealed the effects of epitope immunogenicity, infection history and donor-specific variability. All 4 donors showed the highest cytokine response to a -single epitope (NS4b 2353). The same two peptide variants (D2 NS4a 2148 and D3 NS4b 2343) induced the highest response in all 4 donors regardless of the serotype of primary dengue infection. Interestingly, the epitope variants which showed the highest immunogenecity in our donors corresponded to the D2 and D3 serotypes which have been documented as being more virulent as well as a viral risk factor for DHF. In one donor, the response to all peptide variants was dominated by the same cytokine sub-sets. These data suggested that the dengue-immune memory T cell repertoire was functionally diverse and underwent alterations in size after secondary stimulation. Therefore, we also investigated the effect of epitope variants on dengue-specific CD8+T cell clones isolated from vaccinated and infected donors in order to determine if epitope variants induced altered functional outcomes at the clonal level. The epitope variants functioned either as strong agonists (particularly the D2 and D3 sequences), partial agonists, or null ligands. Some variants were able to induce cytolysis but not other effector functions at low concentrations. The variant ligands also influenced the hierarchy of cytokine responses within each clone. The third part of this thesis focused on the characterization of the frequency and phenotypic profile of epitope-specific CD8+ T cells in patients with DHF and DF at different times in the disease course in order to better understand the kinetics of the response and delineate any differences between the immune profile of severe vs. moderate disease. Tetramer staining for a previously identified HLA-B*07 restricted epitope was combined with staining for activation markers (CD69, CD38, HLA-DR), homing receptors (CCR7, CD62L), and programmed death receptor 1 (PD-1). The DHF subjects had early T cell activation with higher frequencies of tetramer+CD69+ cells as compared to DF subjects, in whom T cell frequencies peaked around the time of defervescence. While each subject had a unique phenotypic profile of tetramer+ cells, there was a difference between DF and DHF subjects in terms of CCR 7 expression; all subjects expressed low levels of CCR7 during acute illness but only the DHF subjects did not show upregulation of CCR7 on tetramer+ cells during convalescence. These data suggest that there is a sustained alteration in memory phenotype in those who recovered from severe dengue disease. A majority of the tetramer+cells also expressed PD-1 during acute illness but not during convalescence. Double-staining with variant tetramers allowed us to directly visualize serotype cross-reactivity of the epitope-specific population, and showed that secondary stimulation did induce the expansion of cells with low avidity for that secondary serotype and higher avidity to the variant. Furthermore, the ratios of these sub-sets changed during the course of the response. Taken together, these studies suggest that the immune response to heterologous secondary dengue infection is mediated by a heterogeneous population of serotype-cross reactive T cells that have different functional avidities to epitope variants and is influenced by the serotype of the secondary infection as well as the prior infection history of the individual. The preferential expansion of clones which secrete IFNγ but not inflammatory MIP-1β or TNFα or a repertoire characterized by a higher ratio of cytolytic to cytokine producing clones could limit immune mediated damage while efficiently clearing the virus. This information will be useful in the design of vaccine strategies aimed at inducing protective cross-reactive responses against all 4 dengue serotypes while preventing immunopathological outcomes following secondary infection.

The early steps of activation are crucial in deciding the fate of T-cells leading to the proliferation. These steps strongly depend on the initial conditions, especially the avidity of the T-cell receptor for the specific ligand and the concentration of this ligand. The recognition induces a rapid decrease of membrane TCR-CD3 complexes inside the T-cell, then the up-regulation of CD25 and then CD25-IL2 binding which down-regulates into the T-cell. This process can be monitored by flow cytometry technique. We propose several models based on the level of complexity by using population balance modeling technique to study the dynamics of T-cells population density during the activation process. These models provide us a relation between the population of T-cells with their intracellular and extracellular components. Moreover, the hypotheses are proposed for the activation process of daughter T-cells after proliferation. The corresponding population balance equations (PBEs) include reaction term (i.e. assimilated as growth term) and activation term (i.e. assimilated as nucleation term). Further the PBEs are solved by newly developed method that is validated against analytical method wherever possible and various approximate techniques available in the literature.

Les réponses immunes contre les traitements de thérapie génique rAAV, dirigées non seulement contre la capside du vecteur, mais aussi contre le transgène, représentent un défi majeur en particulier dans le contexte d'un transfert de gènes vers le muscle pour le traitement de diverses maladies monogéniques du muscle. Cette thèse est focalisée sur la réponse dirigée contre le transgène. Celle-ci se met en place contre des éléments du transgène thérapeutique qui ne sont pas initialement présents, ou insuffisamment exprimés, chez l'hôte et peut entraîner l'élimination des cellules qui produisent le transgène. Dans ce contexte il est nécessaire de concevoir des protocoles de traitement capable d'imposer en périphérie une tolérance immunitaire spécifique du transgène. Nous avons exploré comment l'induction de l'expression d'un transgène étranger dans le foie à l'aide d'un vecteur rAAV impose une tolérance immunologique après transduction du muscle, et ceci malgré l'initiation dans le muscle d'une réponse T CD8+ et CD4+ dirigé contre le transgène. Nous avons démontré que l'expression du transgène dans le foie promeut une tolérance immunitaire envers une injection du vecteur rAAV dans le muscle et ce malgré la présence d'une réponse mémoire spécifique du transgène. Sur le plan de la réponse T CD8+, nous constatons une délétion totale ou partielle ainsi qu'une conversion des cellules vers un phénotype d'épuisement, avec l'expression du marqueur PD-1. La présence d'une réponse T CD4+ mémoire contre le transgène, ne semble pas altérer la tolérance induite par le foie. Nous discutons ensuite, en nous confrontant aux auteurs du domaine, le mécanisme global éventuellement mis en jeu : Une fois la réponse adaptative complète T CD8+ et T CD4+ initiée dans le ganglion drainant le muscle, ces cellules T doivent, avant de retourner vers le muscle, circuler par le foie. Dans le foie, elles s'y accumulent et rencontrent une seconde fois l'antigène, ce qui semble conduire à l'épuisement, suite à l'expression de PD-1, ou à la mort des cellules T CD8+ par un mécanisme décrit sous le nom d'emperipolesis suicidaire ou d'apoptose dépendant du facteur BIM. Les cellules CD4+, elle, ne subiraient pas de délétion, mais une éventuelle modification phénotypique, vers un phénotype tolérogène ou suppresseur. Ce processus serait dépendant de la rétention des cellules T dans le foie que nous avons mis en évidence, ainsi que de l'affinité de la réponse contre le transgène qui rend compte de nos résultats. Nous exposons finalement le domaine d'application de notre méthode, permettant de surmonter une réponse locale initiée dans le muscle, ce qui peut s'avérer crucial pour le traitement par thérapie génique des dystrophies musculaires monogéniques, basé sur l'emploi de transgènes potentiellement immunogènes dû au défaut d'expression chez le receveur
It is increasingly realized that immune responses to rAAV gene therapy treatments, not only to the vector capsid but also to reparative transgenes can cause adverse effects of importance in the case of muscle gene delivery in monogenic muscle disorders. These responses to "foreign" sequence elements of the reparative transgene that are not initially present or insufficiently expressed in the host represent a threat which can eliminate the transduced cells of interest. It is therefore highly desirable to design immune tolerance protocols able to impose transgene-specific immunological unresponsiveness. We explored here how liver-based recombinant adeno-associated viral vector (rAAV) mediated expression of foreign transgene imposes immune tolerance after immunogenic rAAV muscle transduction. We found that liver transgene expression driven with the hAAT hepatocyte specific promotor is effective to promote robust muscle-associated transgene expression, nullifying transgene-specific CD8+ T cell responses as well as humoral responses. Liver transgene expression equally promotes immune tolerance to subsequent rAAV muscle injections despite the presence of transgene-specific memory responses. Importantly, the CD8+ T cell tolerization process leads to partial deletion and conversion into PD-1+ CD8+ T cells, a hallmark of T cell exhaustion. Likewise, CD4+ T cell responses elicited in muscle do not compromise liver-based tolerance induction. Our results demonstrate that liver transduction with rAAV vectors using hepatocyte specific hAAT promotor imposes immune tolerance to transgene-specific T cells elicited from the naïve T cell repertoire after muscle transduction. Confronting our results with others, we suggest that CD8+ T cell depletion occurs after antigen recognition through direct capture and internalization of T cell corpses by hepatocyte in a mechanism already described and referred to as suicidal emperipolesis. Alternatively, BIM-dependent apoptotic process may also occur as a result of T cell-hepatocyte interactions. Regarding transgene-specific CD4+ T cells, we presume that they undergo phenotypic conversion such as Treg conversion as evidenced in multiple sclerosis models. Our results also suggest that the retention time and affinity of transgene-specific T cells next to transduced hepatocytes is critical for their fate. Last, considering applications for muscle gene therapies, control of local muscle immune response is of crucial importance in the treatment of several muscular dystrophies including Duchenne's muscular dystrophy. In this context our liver-based tolerance induction protocol is relevant, provided that the transgene of interest does not alter hepatocytes functions and is beneficial against adverse immune responses

Les polynucléaires neutrophiles (PN) sont des cellules essentielles au cours de la réponse immunitaire innée ; recrutés rapidement au site inflammatoire où ils participent à la phase aigüe, ils vont aussi contribuer à la résolution de l'inflammation. Ils peuvent en effet moduler la réponse adaptative par interaction avec les lymphocytes (Ly) ou les cellules dendritiques (DC) via des médiateurs solubles ou des interactions cellulaires directes. Les Neutrophil Extracellular Traps (NETs) libérés par les PN activés pourraient jouer un rôle important dans ce contexte. Les NETs sont des filaments de chromatine décondensée associés à des protéines issues principalement des granulations et du cytoplasme. Ils sont essentiels dans la réponse anti-infectieuse mais semblent également impliqués dans la physiopathologie de certaines maladies auto-immunes et inflammatoires. L'objectif de ce travail a été d'évaluer les effets des NETs sur la maturation des DC dans un contexte inflammatoire au cours duquel les PN et les DC peuvent co-exister, assurant ainsi un pont entre immunité innée et immunité adaptative. La première partie de ce travail a consisté à développer un modèle de production, isolement et caractérisation des NETs issus de PN sanguins humains. L'ionophore de calcium A23187 a été choisi pour induire les NETs et l'enzyme de restriction AluI a permis la récupération de fragments de NETs de taille hétérogène. Certains des composants de ces NETs sont quantifiables (ADN, élastase, histone 3 en particulier), et nous avons montré qu'ils conservaient leurs capacités bactéricides in vitro. Ces échantillons de NETs constituent donc un outil biologique standardisé, permettant d'évaluer leurs effets sur des cellules ou des tissus. Dans la deuxième partie de ce travail, nous avons mis en évidence que ces NETs purifiés régulaient négativement la maturation de moDC induites par le LPS (expression de HLA-DR, CD80, CD83, CD86 et production de TNFα, IL-12, IL-6, IL-23). De plus, les NETs diminuent la capacité de ces moDC à induire la prolifération des LyT, et leur polarisation est modulée en favorisant la production de cytokines de type Th2 (IL-5 et IL-13) aux dépens de cytokines de types Th1 (INFγ) et Th17 (IL-17). De manière intéressante, la capacité de migration des moDC activées par le LPS n'est pas modifiée en présence de NETs. En résumé, ces résultats suggèrent que les NETs pourraient jouer un rôle immunorégulateur sur la maturation des moDC dans des conditions inflammatoires. Les NETs produits par les PN activés pourraient ainsi participer à la régulation indispensable de la réponse inflammatoire.

L’Ins(1,3,4,5)P4 produit par l’Ins(1,4,5)P3 3-kinase de type B (Itpkb) est nécessaire au développement des thymocytes et lymphocytes T murins. Trois hypothèses sont admises quant à la fonction physiologique et au mécanisme d’action de cet inositol phosphorylé :la première postule que l’Ins(1,3,4,5)P4 module la réponse calcique intracellulaire ;la seconde, que cet inositolphosphate est un intermédiaire métabolique dans la synthèse d’inositols plus hautement phosphorylés ;la dernière, que l’Ins(1,3,4,5)P4 module la localisation subcellulaire et la fonction de protéines capables de la reconnaître par des domaines spécifiques de liaison. Afin d’investiguer cette dernière hypothèse, nous avons analysé la physiologie des lymphocytes B invalidés pour Itpkb et avons généré et analysé des souris transgéniques d’addition pour Rasa3, récepteur potentiel à l’Ins(1,3,4,5)P4.

Les lymphocytes B déficients en Itpkb présentent un défaut de survie car ils ne peuvent activer correctement les protéines kinases Erk1/2 suite à la stimulation du BCR de surface. Cela conduit à la surexpression anormale de la protéine pro-apoptotique Bim. La diminution de l’expression de Bim est suffisante dans ce modèle pour restaurer une fonction normale des lymphocytes B. In vitro, Nous avons montré que l’Ins(1,3,4,5)P4 est nécessaire à la translocation de Rasa3, protéine favorisant l’inactivation de la voie de Ras, de la membrane vers le cytoplasme. L’étude de lymphocytes invalidés pour Itpkb dans un modèle de BCR transgénique semble montrer que des anomalies de réponse calcique ne participent pas au phénotype.

En conclusion, nos résultats indiquent qu’une des voies de signalisation préférentielle de l’Ins(1,3,4,5)P4 passe par la modulation de la localisation subcellulaire de protéines possédant un domaine d’affinité pour l’Ins(1,3,4,5)P4 telle que Rasa3.

Doctorat en Sciences médicales
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T cells play a central role in cellular-mediated immunity and must become activated to participate as effector cells in the immune response. The activation process is highly intricate and involves stimulation of a number of downstream signaling pathways enabling T cells to proliferate and produce cytokines that are vital for proper effector function. This increase in protein production and protein folding activity adds to the normal physiological strain on cellular machinery. One cellular compartment that has generated a mechanism to mitigate the stress induced by increased protein production is the endoplasmic reticulum (ER). In general, an increase in cellular production of proteins that overwhelms a cell’s protein folding capability can alter ER homeostasis and lead to ER stress. To counteract this stress, an adaptive cellular mechanism known as the ER stress response (ERSR) is initiated. The ERSR allows a cell to cope with normal physiological stress within the ER caused by increased protein translation. In this dissertation, we show that in vitro and in vivoT cell activation involving T cell receptor (TCR) ligation in the presence of costimulation initiates the physiological ERSR. Interestingly, the ERSR was also activated in T cells exposed only to TCR ligation, a treatment known to induce the ‘non-responsive’ states of anergy and tolerance. We further identified a key component of the downstream TCR signaling pathway, protein kinase C (PKC), as an initiator of physiological ERSR signaling, thus revealing a previously unknown role for this serine/threonine protein kinase in T cells. Therefore, induction of the physiological ERSR through PKC signaling may be an important ‘preparatory’ mechanism initiated during the early activation phase of T cells. If ER stress is persistent and ER homeostasis is not reestablished, physiological ER stress becomes pathological and initiates cellular death pathways through ER stress-induced apoptotic signaling. We further present data demonstrating that absence of functional Gimap5, a putative GTPase implicated to play a role in TCR signaling and maintenance of overall T cell homeostasis, leads to pathological ER stress and apoptosis. Using the BioBreeding diabetes-prone (BBDP) rat, a model for type 1 diabetes (T1D), we link pathological ER stress and ER stress-induced apoptotic signaling to the observed T cell lymphopenic phenotype of the animal. By depleting the ER stress apoptotic factor CHOP with siRNA, we were able to protect Gimap5-/-BBDP rat T cells from ER stress-induced death. These findings indicate a direct relationship between Gimap5 and maintenance of ER homeostasis for T cell survival. Overall, our findings suggest that the ERSR is activated by physiological and pathological conditions that disrupt T cell homeostasis. TCR signaling that leads to PKC activation initiates a physiological ERSR, perhaps in preparation for a T cell response to antigen. In addition, we also describe an example of pathological ERSR induction in T cells. Namely, we report that the absence of functional Gimap5 protein in T cells causes CHOP-dependent ER stress-induced apoptosis, perhaps initiated by deregulation of TCR signaling. This indicates a dual role for TCR signaling and regulation in the initiation of both the physiological and pathological ERSR. Future research that provides insights into the molecular mechanisms that govern ERSR induction in TCR signaling and regulation may lead to development of therapeutic modalities for treatment of immune-mediated diseases such as T1D.

L’infection par le cytomégalovirus est le plus souvent asymptomatique chez les sujets immunocompétents mais entraine une morbidité et une mortalité importantes chez les patients immunocompromis et en cas d’infection congénitale.

Après l’infection primaire, le virus persiste tout au long de la vie à l’état latent mais peut se réactiver de manière intermittente. Ceci est associé à l’expansion de lymphocytes T CD4+ fortement différenciés ayant des fonctions auxiliaires et cytolytiques. L’infection primaire est, par contre, caractérisée par une réplication virale intense qui dure plusieurs mois. Il a été montré que l’exposition prolongée à des concentrations élevées d’antigènes entraine une perte progressive de fonction par les lymphocytes T appelée épuisement et caractérisée par l’expression de récepteurs inhibiteurs. L’impact de la réplication virale intense observée au cours de l’infection primaire par le CMV sur la fonction des lymphocytes T CD4+ n’est pas bien connu.

La fonctionnalité des lymphocytes T CD4+ a été explorée chez l’humain et le singe rhésus au cours de l’infection primaire et comparée à celle de sujets porteurs chroniques du virus.

Les résultats montrent que l’infection primaire par le CMV est associée à la détection de lymphocytes T CD4+ circulants ayant une faible capacité de prolifération et de production de cytokines et d’IL-2 en particulier.

L’impact de la différenciation sur la fonction des lymphocytes a été exploré en détail chez l’humain. Il a été observé qu’un degré de différenciation plus élevé des lymphocytes T CD4+ spécifiques du CMV joue un rôle dans la production réduite d’IL-2. Toutefois, la fraction moins différenciée (exprimant la molécule CD28) présente également une sécrétion d’IL-2 moindre au cours de l’infection primaire. Ceci fait partie d’une diminution globale de la production de cytokines au cours de l’infection primaire qui affecte également la sécrétion d’IFNγ et TNFα, entraine une polyfonctionnalité réduite et est indépendante de la différenciation. L’épuisement des lymphocytes T CD4+ spécifiques du CMV contribue à leur fonctionnalité moindre comme l’indique l’expression accrue du récepteur inhibiteur PD-1 et l’augmentation des réponses prolifératives en présence d’anticorps bloquant PD-1.

Le lien entre excrétion virale et fonction lymphocytaire a été étudié chez le macaque rhésus. L’infection par le CMV est observée chez les singes juvéniles et adultes mais pas chez les nourrissons. L’excrétion urinaire et salivaire est significativement plus fréquente et intense chez les singes juvéniles par rapport aux adultes. Comme chez l’humain au cours de l’infection primaire, les lymphocytes T CD4+ spécifiques du virus sont moins

polyfonctionnels et prolifèrent moins efficacement chez les singes juvéniles par rapport aux singes adultes. Ceci est associé à l’expression accrue du récepteur inhibiteur PD-1 chez les singes juvéniles. La réponse proliférative des lymphocytes T CD4+ est accrue en présence d’anticorps bloquant PD-1 ou d’IL-2 exogène. Enfin, une association inverse entre fonction lymphocytaire et excrétion urinaire a été mise en évidence chez les macaques adultes.

Ces résultats indiquent que l’infection par le CMV présente des caractéristiques semblables chez l’humain et le singe rhésus. L’infection primaire est associée à la détection de lymphocytes T CD4+ ayant une fonctionnalité moindre qu’au cours de l’infection chronique. L’expression du récepteur inhibiteur PD-1 typique des cellules épuisées est l’un des mécanismes impliqués et pourrait être la cible de stratégies immunomodulatrices visant à améliorer les fonctions lymphocytaires et le contrôle de la réplication virale. Les résultats présentés indiquent que l’infection naturelle chez le singe rhésus constitue un modèle potentiellement utile à l’étude de la réponse immune au CMV humain et à l’évaluation de stratégies immunomodulatrices.

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Cytomegalovirus infection is mostly asymptomatic in immunocompetent hosts but leads to severe morbidity and mortality in immunocompromised subjects and foetuses.

After primary infection, CMV establishes lifelong persistence but can reactivate intermittently. This is associated with the expansion of highly differentiated CD4+ T lymphocytes exhibiting helper functions and cytolytic activity.

Primary infection is characterised by an intense viral replication lasting several months. It has been shown that prolonged exposure to elevated antigen concentrations induces a progressive loss of function by T lymphocytes called exhaustion. This state of functional impairment is associated to the expression of inhibitory receptors. The consequence of the intense viral replication seen in primary CMV infection on CD4+ T cell function is unknown.

CD4+ T cell function has been studied in human and rhesus macaque during primary CMV infection. Chronic CMV carriers have been used as controls.

The results show that primary CMV infection is associated to the detection of circulating CD4+ T lymphocytes exhibiting weak proliferative capacities and reduced cytokine production affecting IL-2 in particular.

The impact of differentiation on lymphocyte function has been explored in detail in human. An increased proportion of terminally differentiated CD4+ T cells (CD28-) is observed during primary infection. These lymphocytes are unable to secrete IL-2 in response to CMV antigens. Interestingly, CD28+ CMV-specific CD4+ T cells also exhibit reduced IL-2 production during primary infection. This is part of a global reduction of cytokine production affecting IFNγ and TNFα as well. The impaired cytokine production is associated to reduced polyfunctionality and is independent of differentiation. Exhaustion of CMV-specific CD4+ T lymphocytes contributes to the reduced functionality as shown by an increased expression of the inhibitory receptor PD-1 and improved proliferative responses in the presence of PD-1 blocking antibodies.

The relationship between viral replication and lymphocyte function has been explored in rhesus macaques. CMV infection is observed in juvenile and adult monkeys but not in newborns. Excretion in urine and saliva is significantly more frequent and intense in juvenile monkeys than adults. As in primary infection in human, CMV-specific CD4+ T lymphocytes are less polyfunctional and have lower proliferative capacities in juveniles as compared to adults. This is associated with an increased expression of PD-1 in juvenile monkeys. CD4+ T cell proliferative responses are increased when PD-1 blocking antibodies or exogenous IL-2 are added to the culture medium. Finally, an inverse association between lymphocyte function and urinary excretion has been observed in adult macaques.

These results indicate that CMV infection shares common features in human and rhesus macaque. Primary infection is associated to the detection of CD4+ T lymphocyte displaying lower functional capacities as compared to chronic infection. Exhaustion contributes to the functional impairment and the inhibitory receptor PD-1 could be targeted by immunomodulatory strategies aiming at improving lymphocyte functions and controlling viral replication. Natural CMV infection in rhesus macaque might be useful as a model to evaluate the efficacy and safety of immunomodulatory approaches.
Doctorat en Sciences médicales
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Le cancer, l'une des principales causes de décès dans le monde, peut apparaître dans presque tout type de tissu, et est caractérisé par la prolifération anarchique de cellules et l'établissement d'une réponse immunitaire tolérogène favorisant la croissance tumorale, rendant souvent toute intervention médicamenteuse peu efficace. Les cellules dendritiques (DCs), véritables sentinelles de l'organisme, semblent jouer un rôle dans l'établissement à la fois d'une réponse anti-tumorale efficace et d'une tolérance face au cancer. Malgré tout, le rôle des différents sous-types de DCs dans le développement tumoral reste mal connu. Au cours de cette thèse, j'ai étudié différents acteurs cellulaires dendritiques et lymphocytaires, leurs relations et leur implication dans la réponse ou la tolérance immunitaire aux tumeurs. Durant la première partie de ma thèse, j'ai abordé l'effet de la modulation artificielle de l'homéostasie des DCs sur les autres cellules immunitaires ainsi que sur la réponse anti-tumorale in vivo chez la souris. J'ai montré qu'il existait un rôle paradoxal de la cytokine Flt3-L (FL) - un facteur de croissance essentiel à la différentiation et à l'homéostasie des DCs dites classiques/conventionnelles (cDCs) et des DCs plasmacytoïdes (pDCs) - sur la croissance du mélanome B16. En effet, sa surexpression ou son absence mènent à un meilleur contrôle du développement tumoral, accompagnées par une survie accrue des souris. L'absence de FL induit, en sus d'une disparition des cDCs et pDCs, une réduction drastique des lymphocytes T régulateurs (Tregs) protégeant la tumeur, ainsi qu'un renforcement général de la réponse immunitaire anti-tumorale adaptative via les lymphocytes T helpers. Sa surexpression induit une augmentation du nombre de cDCs et pDCs, et malgré une présence accrue de Tregs, un fort recrutement intra-tumoral de lymphocytes natural killer (NK) activés, un des acteurs majeurs de la réponse anti-tumorale innée. L'étude de souris déficientes en cDCs m'a également permis de démontrer l'existence d'un contrôle de l'homéostasie des NK par les DCs. De plus, la combinaison d'un traitement par FL et un anticorps déplétant les Tregs a un effet thérapeutique exacerbé chez la souris. Ensuite, par l'analyse bio-informatique de transcriptomes provenant de 35 types de cancers différents, j'ai montré que le paradoxe du FL existe également chez l'Homme, du moins pour certains cancers, et que les signatures géniques spécifiques de sous-populations de DCs peuvent être corrélées de manière paradoxale, bénéfique ou préjudiciable à la survie. En parallèle, j'ai évalué la présence de diverses cellules immunitaires dans l'infiltrat tumoral et leurs effets sur la survie des patients. Grâce aux algorithmes en langage R que j'ai développés, j'ai pu analyser pour tous les cancers étudiés les signatures géniques spécifiques de populations cellulaires immunitaires ainsi que les gènes et fonctions biologiques (pathways) les plus fortement dysrégulés ou impliqués dans le contrôle de la survie à 5 ans. Les résultats indiquent que les cellules immunitaires de l'infiltrat tumoral dans leur ensemble peuvent jouer, selon le cancer, un rôle bénéfique ou délétère. Cet infiltrat et les pathways immunitaires associés se sont révélés généralement de mauvais pronostic dans les cancers des organes dits immuno-privilégiés, mais en revanche bénéfiques dans les cancers du sein et de la peau. Pour chaque type de cancer, j'ai déterminé l'impact individuel sur la survie de différents types de cellules immunitaires et ai établi les corrélations entre les pathways impliqués et certaines de ces populations cellulaires. L'ensemble de ces résultats permet de mieux comprendre les relations complexes entre chaque cancer et son infiltrat cellulaire, et permettra à terme d'aider à développer des stratégies immuno-thérapeutiques plus adaptées à un environnement tumoral donné, en ciblant les populations immunitaires pouvant réellement impacter la survie des patients
The cancer, one of the main causes of death in the world, can appear in almost any type of tissue, and is characterized by an anarchic proliferation of cells and the establishment of a tolerogenic immune response favouring the tumour growth, leading to low efficiency of drug interventions. Dendritic cells (DCs), real sentinels of the body, seem to play a role in the establishment of both efficient anti-tumoral immune response and tolerance against cancer. Nevertheless, the role of the different DCs subtypes in the tumoral development stays poorly known. During this thesis, I studied different dendritic and lymphocytic cellular actors, their relationships and their involvement in the immune response or tolerance to tumours. During the first part of my thesis, I studied the effect of the artificial modulation of DCs homeostasis on other immune cells and also on anti-tumoral response in vivo in mice. I proved the existence of a paradoxical role of the Flt3-L (FL) cytokine - a growth factor essential to the differentiation and the homeostasis of classical/conventional dendritic cells (cDCs) and plasmacytoid dendritic cells (pDCs) - on the B16 melanoma growth. In fact, its overexpression or absence both lead to a better control of the tumoral development, accompanied by an increased survival of mice. FL deficiency induces, together with the loss of both cDCs and pDCs, a drastic reduction of regulatory T lymphocytes (Tregs) protecting the tumour, and also a global reinforcement of the anti-tumoral adaptive immune response via helper T lymphocytes. Its overexpression induces an increase of the numbers of cDCs and pDCs, and despite a raised presence of Tregs, also a strong intra-tumoral recruitment of activated natural killer (NK) cells, one of the major actors of the anti-tumoral innate response. The study of cDCs-deficient mice allowed me to demonstrate the existence of a DCs-mediated control of the NK cells homeostasis. Furthermore, the combination of both FL treatment and antibody-mediated Tregs depletion has an exacerbated therapeutic effect in mice. Next, using bioinformatic analysis of transcriptomes of 35 different cancer types, I showed that the FL paradox also exists in humans, at least for some cancers, and that gene signatures specific of DCs subsets can be correlated in a paradoxical, beneficial or detrimental manner to survival. In parallel, I evaluated the presence of several immune cells in the tumour infiltrate and their effects on patients survival. Thanks to R language algorithms I developed, I was able to analyse for each studied cancer the immune cell populations-specific gene signatures and the most involved or dysregulated genes and biological functions (pathways) in the control of the 5 years survival of patients. My results indicate that the immune cells of the tumour infiltrate can play, according to the cancer, a beneficial or deleterious role. This immune infiltrate and the associated pathways were generally of bad prognosis in cancers of immune-privileged organs, but on the other hand were beneficial in skin and breast cancers. For each cancer type, I determined the individual impact on survival of several types of immune cells and established correlations between involved pathways and some of these cell populations. Altogether, the results allow to better understand the complex relationships between each cancer and the associated immune infiltrate, and will later lead to help the development of immunotherapeutic strategies more adapted to a given tumour environment, by targeting the immune populations that could really impact the survival of patients

Patients with peritonitis or malignant obstructive jaundice (HPB⁺) have an increased morbidity and mortality due to sepsis. An altered cell-mediated immunity in the intestinal mucosa might promote gut barrier failure, increased endotoxin and cytokine release and bacterial translocation (BT) in these conditions. A clinically relevant rat model of polymicrobial peritonitis induced sepsis by cecal ligation and puncture (CLP) was used. Septic animals demonstrated a superficial injury in the small intestinal mucosa, and a significant reduction in T lymphocytes in the villi, as well as increased number of macrophages in the villi and in the MLNs as compared to sham. CLP caused increased concentration of TNF-α and IL-6 in ascitic fluid. CLP + the immunomodulator Linomide decreased the TNF-α level, reduced mucosal damage and attenuated the changes in T lymphocytes and macrophages observed following CLP. CLP + selective cyclooxygenase (COX)-2 inhibitor (SC-236) or nonselective COX inhibitor (indometacin) decreased the amount of macrophages in the mucosa and the MLNs compared to untreated CLP. CLP + indometacin decreased T lymphocytes in the villi and MLNs. SC-236 + CLP reduced mucosal injury and cytokine release as compared to indometacin. An increased rate of apoptosis in both the mucosa and MLNs was seen following CLP; COX inhibitors enhanced this phenomenon in the MLNs.

BT occurred infrequently in patients with acute peritonitis and in HPB⁺ there was no evidence of BT. Peritonitis and HPB⁺ causes significant inflammatory cellular reactions as increased endotoxin and cytokine plasma levels and an altered immune cell distribution in MLNs, in HPB⁺ a high rate of apoptosis in MLNs was observed.

An altered pattern of immunocompetent cells within the mucosa and in MLNs was found in experimental and clinical peritonitis as in HPB⁺. Lymphocyte depletion may be a result of increased apoptosis, which could reduce the ability of septic or jaundice patients to eradicate infection.

Les cellules dendritiques décrites depuis les années 60 ont instantanément capté l’intérêt des scientifiques qui ont pu mettre en évidence leur rôle indispensable dans l’initiation des réponses immunitaires adaptatives et leur ont attribué le surnom « d’adjuvant naturel ». De manière surprenante, les cellules dendritiques conventionnelles sont aussi indispensables dans le maintien de la tolérance et peuvent présenter naturellement ou acquérir une fonction suppressive. Parmi les mécanismes capables de contrôler les réponses de type Th1, l’enzyme indoléamine 2,3-dioxygénase (IDO) a particulièrement attiré notre attention. Cette enzyme initiant la première étape de dégradation du tryptophane et sa transformation en catabolites toxiques nommés kynurénines semble jouer un rôle primordial dans la tolérance envers les fœtus allogéniques et dans l’échappement des tumeurs à la réponse immunitaire.

Nous avons donc évalué le rôle de l’IDO exprimé par les cellules dendritiques conventionnelles dans la régulation de la réponse adaptative. L’ensemble des résultats in vitro révèle que l’expression d’IDO par les cellules dendritiques conventionnelles au cours de leur maturation n’influence celle-ci ni au niveau de l’expression des molécules MHCII et CD86 ni au niveau de leur capacité à induire la différenciation des lymphocytes Th1. De plus, dans des modèles d’immunisation in vivo par transfert de cellules dendritiques conventionnelles, l’expression d’IDO par ces dernières ne semble pas leur permettre de contrôler les réponses T CD4+ ou T CD8+. Cependant, nous avons constaté qu’en absence de lymphocytes T régulateurs naturels l’expression d’IDO par les cellules de l’hôte constitue un mécanisme important limitant la réponse Th1.

En cas d’inflammation ou d’infection, de profonds changements affectent le compartiment des cellules dendritiques où émerge une nouvelle sous-population qui se différencie à partir des monocytes inflammatoires du sang et qui portent le nom de cellules dendritiques inflammatoires. Alors que les cellules dendritiques conventionnelles forment une population hétérogène où chaque sous-population semble se spécialiser dans la différenciation d’un type particulier de lymphocyte T auxiliaire ou « helper », la littérature met en évidence une incroyable plasticité phénotypique des cellules dendritiques inflammatoires qui les rend capables de s’adapter au type d’infection auquel l’hôte est confronté en intervenant directement au niveau de la réponse innée mais aussi en participant à l’initiation et la régulation de la réponse T la plus adaptée.

Le modèle d’immunisation in vivo par transfert de cellules dendritiques inflammatoires présentant l’antigène OVA nous a permis de démontrer la capacité de ces cellules à promouvoir spécifiquement la différenciation de lymphocytes de type Th17. Dans le cadre d’une immunisation classique par un adjuvant, le défaut dans le recrutement des cellules dendritiques inflammatoires dans les souris CCR2-/- nous a permis de mettre en évidence le rôle indispensable des cellules dendritiques inflammatoires pour l’induction des réponses Th1 et Th17. Finalement, envisageant la possibilité d’une collaboration entre DCs conventionnelles et inflammatoires pour l’induction des réponses de type Th17, nous avons constaté que le transfert de cellules dendritiques conventionnelles présentant l’antigène KLH provoque in vivo le recrutement de cellules dendritiques inflammatoires au sein des ganglions drainant le site d’injection et que ces cellules dendritiques inflammatoires semblent nécessaires pour la différenciation des lymphocytes de type Th17.

La collaboration entre cellules dendritiques via le transfert d’informations pourrait être un évènement fréquent permettant de réguler la réponse immunitaire adaptative à trois niveaux principaux :au niveau quantitatif, en augmentant le nombre de cellules dendritiques présentant l’antigène, au niveau de la durée, en transmettant l’information aux cellules dendritiques inflammatoires colonisant les tissus desquels les cellules dendritiques conventionnelles disparaissent après activation/maturation et au niveau qualitatif, en combinant les propriétés intrinsèques des différentes sous-populations de cellules dendritiques afin de réguler la différenciation des lymphocytes T helper.

Doctorat en Sciences
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Currently, in most situations, the autologous immune system is unable to eradicate the residual leukemic burden persisting after chemo-radiotherapy, but a balance can be established between leukemic and immune cells leading to a clinical remission for several months or years. If this balance is broken, a clinical relapse can occur. The high incidence of relapses in human cancers demonstrates the frequent inefficacy of the immune system to control these residual cells. In this context, allogeneic hematopoietic stem cell transplantation (HSCT) has been proven to be the most effective way to reinforce the immune reaction against leukemia, graft-versus-leukemia (GVL) effect and, so, achieve a definitive eradication of the residual disease in a significant proportion of patients. Indeed, the whole concept of HSCT evolved from an organ transplant concept (to replace a defective ill organ with a new healthy one) to the concept of creating an extraordinary immunotherapeutic platform in which the donor immune system contributes to the eradication of the residual leukemic cells. Thus, the past and present issues remain those of finding the best immunomodulatory modalities to achieve a full engraftment, a powerful GVL effect and no or moderate graft-versus-host disease (GVHD). Different ways to reach this goal, such as post transplant cytokine modulation, specific or global cellular depletion of the graft and post transplant global or specific donor immune cell add-backs, are still extensively studied. Nevertheless, the persistent high relapse rate (RR) observed in leukemia patients after HSCT remains the most important cause of death before transplant-related toxicities. Moreover, since only about 40 to 70% (depending on the ethnic context) of patients with high-risk hematological malignancies, eligible for allogeneic HSCT, have a fully HLA-matched sibling or matched unrelated donor (MUD), a great deal of effort has been invested to make the use of an alternative haploidentical sibling donor feasible. The advantage of this procedure is the immediate availability of a donor for almost all patients.

The aim of the work described in this thesis has been to implement a strategy to transplant a patient using a HLA haploidentical donor. The strategy is to try to improve DFS that could be applied both in the autologous or allogeneic context: first, by using nonspecific immune manipulation post transplant and then, by developing specific strategies directed against leukemia antigens. Particularly in the allogeneic situation, the aim was to increase the GVL effect without inducing or aggravating the deleterious GVHD. The first part of this thesis described our own clinical results, consisting of three consecutive phase I/II studies, in which we tried to determine the feasibility of giving prophylactic donor lymphocyte infusions (DLI) post transplant and the effect of replacing granulocyte colony-stimulating factor (G-CSF), typically used to speed up neutrophil recovery, with granulocyte macrophage colony-stimulating factor (GM-CSF), which is known for its immunomodulatory properties. The slow immune reconstitution in haploidentical transplant is chiefly responsible for the high incidence of early lethal viral and fungal infections, and most probably for early relapses; therefore, we sought to accelerate and strengthen the post transplant immune reconstitution without increasing the GVHD rate. Thus, we have studied the impact of post transplant growth factor administration and of unselected DLI in haploidentical transplant. We have also implemented, in our center, anti-cytomegalovirus (CMV) specific T cell generation and infusion to improve anti-CMV immune reconstitution. Since then, our results have been pooled in a multi-center analysis performed by the European Bone Marrow Transplantation group (EBMT) allowing us to compare our results with those of the entire group. We have also participated in the design of an ongoing study aimed at selectively depleting the graft from alloreactive T cells, and improving post transplant T cell add-backs. In our attempts to generate and expand ex vivo lymphocytes (directed against pathogens (CMV) and leukemia-associated antigens, Wilms' tumor gene 1 (WT1) and to use them in vivo, we found inconsistent results (in the case of WT1) using classical clinical grade dendritic cells (DC) generated and matured in bags, as was the case for the majority of the teams worldwide. This led us to question the full functionality of these DC and we undertook a thorough comparative analysis of DC generated and differentiated in bags and in plates (typical for most pre-clinical studies). This analysis showed us that one cannot transpose pre-clinical studies (using culture plates) directly to clinical protocols (generally using clinical grade culture bags) and that DC generated in bags are functionally deficient. We learned that, if we want to use a DC vaccine to improve the GVL effect in haploidentical transplant, we will have to be careful about the technique by which they are generated. To improve immunotherapeutic approaches, the understanding of the mechanisms underlying tumor tolerance and how to manipulate them is critical in the development of new effective immunotherapeutic clinical trials. This is why we currently focus on how to obtain effective in vivo anti-leukemia immune reactions using an ex-vivo manipulated product to trigger the immunotherapeutic response. More specifically, we are analyzing the impact of regulatory T cell (Tregs) depletion and function for an adequate anti-leukemic immune response. This pre-clinical work aims at improving the outcome of leukemia patients who have relapsed and been put back into second remission and at decreasing the RR after HSCT, especially in the field of haploidentical transplantation.

In conclusion, haploidentical transplantation has become a valuable tool. The results are at least similar to those obtained using MUD when performed in the same group of patients. Specific immunomodulation post transplant can affect events such as GVHD and GVL, but clinically we are still at the level of nonspecific manipulations. It is our hope that ongoing pre-clinical work will enable us to perform specific anti-pathogen and anti-leukemia immune manipulation that will favorably influence the patient outcome.

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Dans la majorité des situations, le système immunitaire autologue est incapable d’éradiquer les cellules leucémiques résiduelles qui échappent à la radiothérapie et à la chimiothérapie, cependant un équilibre peut s’établir entre les cellules leucémiques et immunitaires aboutissant à une rémission pouvant durer plusieurs mois ou années. Si cet équilibre se rompt, une rechute clinique peut se déclarer. Dans ce contexte, il est prouvé que la greffe allogénique de cellules souches hématopoïétiques est le moyen le plus efficace de renforcer les réactions immunitaires contre la leucémie par la réaction du greffon contre la leucémie et ainsi d’obtenir une éradication définitive de la maladie résiduelle chez un nombre significatif de patients. En effet, le concept global de l’allogreffe de cellules souches hématopoïétiques a évolué du concept de transplantation d’organe (remplacement d’un organe malade par un nouvel organe sain) vers celui de créer une extraordinaire plateforme d’immunothérapie à travers laquelle le système immunitaire du donneur contribue à l’éradication des cellules leucémiques persistantes. Donc, la problématique reste celle de trouver les meilleures modalités d’immunomodulation pour achever une prise du greffon, un effet anti-leucémique puissant du greffon, et l’absence ou un minimum d’effet du greffon contre l’hôte. Différentes stratégies existent pour atteindre cet objectif, comme l’utilisation de cytokines pour moduler la reconstitution immunitaire, des déplétions cellulaires globales ou spécifiques du greffon et l’infusion de cellules immunes «globales» ou spécifiques du donneur après greffe. Ces stratégies sont encore largement à l’étude. Néanmoins, la persistance d’un taux de rechute élevé observé chez les patients leucémiques, après allogreffe reste la cause principale de décès, avant celle liée à la toxicité de la greffe. De plus, étant donné que seulement environ 40 à 70% (dépendant de l’origine ethnique) des patients avec une hémopathie à haut risque, éligibles pour une greffe allogénique, ont un donneur familial ou non familial complètement HLA compatible, des efforts importants ont été développés pour rendre faisable l’utilisation de donneurs familiaux alternatifs, haploidentiques. L’avantage de cette approche est l’accès immédiat à un donneur pour quasiment tous les patients.

Le but du travail décrit dans cette thèse a été l’implémentation d’une stratégie d’allogreffe utilisant un donneur haploidentique. Le travail vise également à développer de façon plus large des stratégies qui peuvent améliorer le taux de survie sans rechute, non seulement dans le contexte des greffes haploidentiques, mais également dans le cadre des greffes allogéniques en général, ainsi que dans les situations autologues :premièrement, par la manipulation immunitaire non spécifique après greffe et ensuite par le développement de stratégies spécifiques dirigées contre des antigènes leucémiques. En particulier dans la situation allogénique, le but a été d’augmenter l’effet du greffon contre la leucémie sans induire ou aggraver l’effet délétère du greffon contre l’hôte. La première partie de la thèse décrit les résultats cliniques de notre propre protocole de greffe haploidentique, qui a consisté en trois études consécutives de phase I/II. Dans ces études, nous avons voulu déterminer la faisabilité de réaliser des infusions prophylactiques de lymphocytes du donneur après transplantation, et l’impact du remplacement du « granulocyte colony-stimulating factor » (G-CSF), largement utilisé pour permettre une récupération en polynucléaires neutrophiles plus rapide, par du « granulocyte-macrophage colony-stimulating factor » (GM-CSF), lequel est connu pour ses propriétés immunomodulatrices différentes. La reconstitution immunitaire très lente après greffe haploidentique est majoritairement responsable de l’incidence élevée de décès par infections virales et fungiques précoces, et très probablement des rechutes précoces. C’est pourquoi nous avons cherché à accélérer et à renforcer la reconstitution immunitaire post-greffe sans augmenter la fréquence de réaction du greffon contre l’hôte. Nous avons donc étudié l’impact de l’administration de facteurs de croissance et l’infusion de lymphocytes non sélectionnés du donneur en post greffe haploidentique. Nous avons également implémenté dans notre centre, la génération et l’infusion de lymphocytes T spécifiques anti-cytomégalovirus (CMV) afin d’améliorer la reconstitution immunitaire anti-CMV. D’autre part, nos résultats ont été regroupés dans une étude multicentrique menée par le groupe européen de transplantation de moelle osseuse (EBMT), ce qui nous a permis de comparer nos résultats avec ceux de l’entièreté du groupe. Nous avons parallèlement participé à la conception d’une étude actuellement en cours ayant pour but d’améliorer la reconstitution immunitaire après greffe par la déplétion sélective du greffon en lymphocytes T alloréactifs et par l’infusion après greffe de lymphocytes T du donneur également sélectivement déplétés en lymphocytes T alloréactifs. Afin d’optimaliser l’effet anti-leucémique du système immunitaire, nous avons débuté un protocole de vaccination par cellules dendritiques (DCs). Ces cellules dendritiques étaient chargées en lysat de blastes leucémiques dans le cas de patients présentant au diagnostic une leucémie aigue surexprimant l’oncogène 1 de la tumeur de Wilms (WT1). Néanmoins dans nos travaux de génération et d’expansion ex-vivo de lymphocytes T spécifiques de l’antigène WT1, utilisant les DCs de grade clinique, générées et maturées en poches, nous avons rencontré des résultats inconsistants, comme c’était le cas dans la majorité des protocoles cliniques internationaux de vaccination. Nous nous sommes alors posé la question de la fonctionnalité globale de ces cellules et nous avons entrepris une analyse comparative poussée des DCs générées et différenciées en poches ou en plaques. Les DCs générées en plaques sont celles utilisées dans la plupart des travaux précliniques. Cette analyse nous a montré que l’on ne pouvait pas directement transposer les résultats précliniques basés sur des DCs générées en plaques dans des protocoles cliniques basés sur des DCs générées en poches, car ces dernières présentent des déficits fonctionnels importants. Nous avons appris que si l’on voulait utiliser un vaccin à base de cellules dendritiques pour améliorer l’effet du greffon contre la leucémie dans les greffes allogéniques, nous devions être très attentifs quant au protocole utilisé pour la génération de ces vaccins cellulaires. Pour améliorer les approches immunothérapeutiques, la connaissance des mécanismes qui établissent la tolérance tumorale et des façons de manipuler ceux-ci, est critique dans le développement de nouveaux protocoles efficaces. C’est pourquoi nous nous concentrons actuellement sur les conditions nécessaires à l’obtention in vivo d’une réaction immune anti-leucémique efficace lors de l’utilisation d’un produit cellulaire manipulé ex vivo. Plus spécifiquement, nous analysons l’impact de la déplétion en lymphocytes T régulateurs (Tregs) sur la réponse anti-leucémique. Ce travail préclinique a pour but d’améliorer le devenir de patients leucémiques qui ont rechutés et ont été mis en seconde rémission, ainsi que de diminuer le taux de rechute après allogreffe, spécifiquement après greffe haploidentique.

En conclusion, la transplantation haploidentique est actuellement un outil précieux pour de nombreux patients. Les résultats sont au minimum similaires à ceux qui sont obtenus par les greffes non-familiales HLA identiques lorsqu’elles sont pratiquées dans les mêmes groupes de patients. L’immunomodulation spécifique après greffe peut affecter des événements comme la réaction du greffon contre l’hôte et la réaction du greffon contre la leucémie, mais en pratique clinique nous en sommes encore au niveau de la manipulation aspécifique. Nous espérons que les travaux précliniques actuels vont nous permettre d’appliquer des stratégies spécifiques et d’obtenir une manipulation immune anti-leucémique qui aura une influence favorable significative sur le devenir des patients.
Doctorat en Sciences médicales
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Le purpura thrombotique thrombocytopénique (PTT) est une maladie autoimmune rare et grave caractérisée par la présence d’anticorps dirigés contre ADAMTS13 (A13), une protéase impliquée dans l’hémostase primaire. L’implication des lymphocytes T CD4⁺ spécifiques d’ADAMTS13, dans la physiopathologie de la maladie est suggérée par une restriction pour l’haplotype HLA-DRB1*11 (DR11), l’isotype IgG des anticorps. Dans ce travail, nous avons cherché à identifier les épitopes T d’A13. Tout d’abord, nous avons sélectionné in silico les peptides d’A13 susceptibles d’être présentés par les molécules HLA-DR11. Ensuite, l’étude de la liaison de ces peptides à des molécules HLA-DR11 par des tests ELISA compétitifs a permis d’identifier les peptides les plus affins. Enfin, nous avons déterminé les peptides d’ADAMTS13 reconnus par les lymphocytes T CD4⁺ de donneurs sains et de patients porteurs de l’haplotype DR11. Ces travaux ont également été reproduits pour l’haplotype HLA-DR1 et dans un modèle murin de souris transgéniques humanisées exprimant l’haplotype HLA-DR1. Les résultats de ce travail nous permettent d’envisager d’isoler des lymphocytes T CD4⁺ spécifiques d’ADAMTS13 chez les patients afin de mieux les caractériser aux différents stades de la maladie et de suivre leur évolution sous traitement dans le but de mieux anticiper les rechutes
Thrombotic thrombocytopenic purpura (TTP) is a rare and severe disease characterized by auto-antibodies directed against ADAMTS13 (A13), a plasmatic protein involved in haemostasis. The implication of CD4⁺ T cells in the pathogenesis of the disease is suggested by the existence of a restriction to particular HLA-DR alleles and by the IgG isotype of the antibodies. In this study, we wished to determine the T cell epitopes of A13. First, we selected in silico the immunodominant peptides, based on their binding capacity to HLA-DR11 molecules. Second, their binding capacity to purified HLA-DR11 molecules using a ELISA competitive assay led us to identify the best binder peptides. Finally, we determined the peptides recognized by human CD4⁺ T cells from DR11 healthy donors and patients. These results were reproduced for the HLA-DR1 haplotype and in a transgenic humanized HLA-DR1 mouse model. In a perspective point of view, our results will allow us to further isolate the specific CD4⁺ T cells in order to characterize them at different steps of the disease and during follow-up to better anticipate relapses

Bien que la plupart des études se focalisent sur les lymphocytes T CD4+ régulateurs, il a été observé que les lymphocytes T CD8+ régulateurs peuvent jouer un rôle important dans l’induction et le maintien de la tolérance immunitaire. Le transfert adoptif chez la souris et l’induction chez l’homme de lymphocytes T CD8+ régulateurs peuvent inhiber le rejet d’allogreffes et le développement de pathologies autoimmunes. Ces observations suggèrent que l’induction de ces populations peut avoir un potentiel thérapeutique. Des études supplémentaires sont encore nécessaires pour définir les conditions optimales de leur induction.

Tant les nouveaux nés humains que murins ont une plus forte capacité que l’adulte à développer des lymphocytes T CD4+ régulateurs induits par une reconnaissance antigénique. La période néonatale serait donc particulièrement appropriée à l’induction de circuits régulateurs.

Dans le cadre de ce travail, nous avons étudié le rôle des lymphocytes T CD8+, induits à la naissance, dans le contrôle de la réponse des lymphocytes T CD4+ de type Th2.

Des souris BALB/c sont immunisées à la naissance à l’aide de cellules spléniques semi-allogéniques hybrides F1 (AJAX x BALB/c). Ces cellules persistent dans l’animal, au sein des organes lymphoïdes et stimulent ainsi de manière chronique les lymphocytes T CD4+ et T CD8+ du receveur et induisent une réponse de type Th2. Suite à l’injection des cellules spléniques semi-allogéniques au nouveau né de souris, nous avons observé l’expansion d’une population de lymphocytes T CD8+CD25+, dont le phénotype se caractérise par l’expression de Foxp3 et la production conjointe d’IFN-&61543; et l’IL-10. Nous avons pu observer que ces cellules sont capables d’inhiber la production de cytokines Th2 produites par les lymphocytes T CD4+ allospécifiques activés. Par contre, ces cellules régulatrices aggravent des réponses Th2 non apparentées. En effet, suite à une sensibilisation à l’ovalbumine, à l’âge adulte, ces souris développent de plus fortes réponses asthmatiques.

D’autre part, les nouveaux nés de souris BALB/c ont été immunisés à la naissance à l’aide de cellules dendritiques semi-allogéniques hybrides F1 (AJAX x BALB/c) qui activent de manière aigüe leurs lymphocytes T. Ces souris présentent une forte réponse Th1 et Tc1/Tc2 spécifique de l’alloantigène et sont protégées contre le développement d’un asthme induit. Il a aussi été montré dans ce travail que suite à l’immunisation néonatale à l’aide de cellules dendritiques semi-allogéniques, le nombre de lymphocytes T CD8+CD44high, CD8+CD62Lhigh et CD8+CD25+ producteurs d’IFN-&61543; augmente significativement. L’IFN-&
Doctorat en Sciences biomédicales et pharmaceutiques
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L'infection par le virus d'Epstein-Barr (EBV) touche plus de 90% de la population mondiale et est dans la majorité des cas asymptomatique dans l'enfance. Certains individus, souvent à l'adolescence, développent une primo-infection symptomatique appelée mononucléose infectieuse. L'EBV peut également entraîner chez des individus immunodéprimés des désordres lymphoprolifératifs, des lymphomes ou syndromes d'activation lymphohistiocytaire. Depuis une trentaine d'années plusieurs déficits immunitaires primitifs entraînant une susceptibilité particulière à l'infection par l'EBV ont été identifiés ; parmi ceux-ci figurent les déficits en SAP, XIAP, ITK, MAGT1, CTPS1, CD27 ou CD70. Leur caractérisation a permis de mettre en évidence de nouveaux mécanismes immunitaires impliqués dans la réponse anti-EBV. L'objectif de ce travail a donc été d'identifier de nouveaux défauts génétiques entraînant une susceptibilité particulière à l'infection par l'EBV. Au sein de deux familles consanguines, trois patients ont développé des lymphomes B liés à l'EBV ainsi que des épisodes de lymphoproliférations également liées à ce virus. Deux mutations homozygotes dans RASGRP1 entraînant un stop prématuré, A638GfsStoXp16 et S314X ont été respectivement identifiées par séquençage d'exome (WES) chez ces deux familles. Sur le plan immunologique ces patients sont caractérisés par une lymphopénie CD4+, un défaut de cellules T naïves, une accumulation de cellules T effectrices mémoires et une absence de cellules MAIT et iNKT. RASGRP1 est une protéine de la famille des facteurs d'échange nucléotidiques fortement exprimée dans les lymphocytes T et NK. Elle active la petite protéine G Ras qui elle-même va activer la cascade des kinases Raf-MEK-ERK (ou cascade des MAP kinases). L'analyse des cellules du patient ou de cellules de contrôles sains dans lesquelles l'expression de RASGRP1 a été inhibée par RNA interférents a permis de mettre en évidence le rôle fondamental de RASGRP1 dans la prolifération lymphocytaire T et l'expression de gènes impliqués dans cette prolifération tels que CTPS1, PCNA ou RECQL4. A l'inverse, RASGRP1 semble être un régulateur négatif du facteur de transcription EOMES impliqué dans la différenciation des lymphocytes T. EOMES est retrouvé surexprimé dans les lymphocytes T en l'absence de RASGRP1, pouvant expliquer le phénotype effecteur mémoire et sénescent des lymphocytes des patients déficients en RASGRP1. Au sein d'une autre famille consanguine, chez deux patients ayant développé une primo-infection à l'EBV symptomatique, dont l'un a nécessité un traitement par anti-CD20 et corticoïdes, a été identifiée une mutation homozygote non-sens dans IL27RA entraînant un codon stop précoce (G96X) et une absence d'expression protéique dans les cellules T des patients. IL-27RA code pour la sous-unité alpha du récepteur à l'IL-27 impliqué dans la prolifération des lymphocytes T et le développement Th1 des lymphocytes CD4+ via la cascade des JAKs/STATs. Dans les lymphocytes T des patients, l'activation de la voie JAK/STAT par l'IL-27 est complètement abolie et l'IL-27 n'augmente pas leur prolifération en réponse à une stimulation anti-CD3 (au contraire des cellules contrôles issues de donneurs sains). De plus, un défaut fonctionnel de la voie Th1 est retrouvé chez un des deux patients. Ces résultats démontrent que la voie dépendante de l'IL-27RA est déficiente chez ces deux patients et que ce défaut génétique rend vraisemblablement compte de leur immunodéficience. La description de ces deux nouveaux déficits immunitaires caractérisés par une susceptibilité à l'EBV a permis de confirmer le rôle fondamental dans l'étape de prolifération et d'expansion des lymphocytes T au cours de la réponse immune anti-EBV, mais également de mettre en évidence de nouveaux mécanismes et facteurs impliqués dans cette étape
Epstein-Barr virus (EBV) is a gamma-herpes virus that infects 90% of humans without any symptoms in most cases. Some individuals, mostly adolescents, can develop infectious mononucleosis. In immunocompromised individuals, EBV can lead to lymphoproliferative disorders, lymphomas or virus-associated hemophagocytic syndrome. In the past 30 years, several primary immunodeficiencies associated with a high risk to develop EBV-associated disorders have been identified, including SAP, XIAP, ITK, MAGT1, CTPS1, CD27 or CD70 deficiencies. Their characterization has highlighted specific pathways required for efficient immunity to EBV. The objective of this work was to identify new genetic defects associated to a peculiar susceptibility to EBV infection. In two consanguineous families 3 patients developed EBV-associated B cell lymphomas and other EBV-associated lymphoproliferative disorders. By while exome sequencing (WES) we identified two homozygous mutations in RASGRP1 leading to a premature stop codon (A638GfsX16 and S314X). Immunologically these patients presented with CD4+ lymphopenia, low number of naïve T cells and absence of MAIT and iNKT cells. RASGRP1 codes for a diacylglycerol-regulated exchange factor preferentially expressed in T and NK cells, which acts as an activator of the small G protein RAS and the downstream RAF-MEK-ERK kinases cascade (or MAP kinases pathway). Analysis of patients' T cells or control T cells in which RASGRP1 expression was downregulated by short-hairpin RNA technique has highlighted the crucial role of RASGRP1 in T cell proliferation and in the expression of genes known to be involved in cell proliferation or replication such as CTPS1, PCNA or RECQL4. Furthermore, RASGRP1 seems to be a negative regulator of the transcription factor EOMES involved in T cell differentiation. EOMES was found overexpressed in T cells in the absence of RASGRP1. This might explain the skewed effector-memory and exhausted phenotype observed in RASGRP1-deficient patients. In another large consanguineous family two patients developed symptomatic EBV primary infection requiring for one or them anti-CD20 and corticosteroids treatment. Homozygous nonsense mutation leading to a premature stop codon in IL-27RA (G96X) was identified by exome sequencing. No protein expression could be detected in patients' cells. IL-27RA codes for the subunit of IL-27 receptor involved T cell proliferation and Th1 CD4+ development through JAKs/STATs pathway. Stimulation of patients' T cells with IL-27 led to absent JAK/STAT activation pathway and did not enhance their proliferation after anti-CD3 stimulation (contrary to healthy control T cells). Furthermore, Th1 functional defect was found in one patient. These results demonstrate that IL-27RA pathway is deficient is these two patients and that this genetic defect causes their immunodeficiency. Characterization of these two new primary immunodeficiencies associated with a high susceptibility to EBV infection has confirmed the crucial role of T cell proliferation and activation in EBV immune response but has also highlighted new pathways involved in T cell expansion

Nuclear bone morphogenetic protein 2 (nBMP2) is a nuclear variant of the secreted growth factor BMP2. Experiments in nBmp2NLStm mutant mice, which lack nBMP2 in the nucleus, have shown that nBMP2 affects intracellular calcium transport in skeletal muscle and hippocampal neurons. The objective of this study was to determine whether nBMP2 affects the immune system, since activation of lymphocytes and other immune cells depends on intracellular calcium transport. We found that spleens in nBmp2NLStm mutant mice were 24% smaller than in wild type mice. The white pulp of the spleen contains many immune cells, particularly B and T lymphocytes and reduced spleen size in the nBmp2NLStm mutant mice could be caused by a reduced number of lymphocytes migrating to the spleen. When mutants and wild types were challenged with an intravenous infection of 10^7 CFU of S. aureus, they showed similar immune responses. Samples of blood, liver, spleen, kidney and lymph nodes cultured three days after infection showed no difference in post infection bacterial load between mutant and wild type. Likewise, post-infection weight loss and percent survival were similar between mutant and wild type, suggesting that the innate immune response is functional in nBmp2NLStm mice. However, when mice were challenged with a secondary infection, immune response and spleen function were severely impaired. Mutant mice showed higher levels of bacteria remaining in the blood and had lower rate of survival to day 3 after secondary infection. In addition, CD4+ and CD8+ T-cell levels within mutant lymph nodes were significantly reduced, indicating that nBMP2 is involved in the secondary immune response.

Many virus infections induce a transient state of immune suppression in the infected host. Virus-induced T cell suppression can be caused by T cell activation-induced cell death (AICD), dendritic cell (DC) apoptosis, DC dysfunction, and/or the enhanced expression of immune-suppressive cytokines. It has been previously demonstrated that naïve bystander CD8 T cells derived from hosts experiencing an acute virus-specific T cell response underwent AICD when polyclonally activated by anti-CD3 in vitro (Zarozinski et al., 2000). Susceptibility of naïve bystander T cells to AICD could prevent the development of a new T cell response during an ongoing immune response, and thus render infected hosts immune suppressed. Although immune suppression could result in an enhanced susceptibility to superinfections, virus-infected individuals are more commonly resistant to superinfecting pathogens. Because of these seemingly contradictory conditions, we sought to investigate how acute viral infections impact naïve bystander CD8 T cells in vivo. More specifically, we asked whether bystander CD8 T cells are susceptible to immune suppression or whether they can contribute to the resistance to superinfections. In order to address this, we examined the responses of bystander CD8 T cells activated with cognate antigen during acute viral infections in vivo. We generated several in vivomodels using P14 (LCMV glycoprotein-specific), HY (male antigen-specific), and OT-I (ovalbumin-specific) transgenic CD8 T cells, which we defined as bystander during acute infections with lymphocytic choriomeningitis virus (LCMV), Pichinde virus (PV), vaccinia virus (VV), and murine cytomegalovirus (MCMV). Consistent with the enhanced susceptibility to cell death noted in vitro, we found that bystander CD8 T cells activated with cognate antigen in vivo during acute viral infections underwent markedly reduced proliferation. Virus-induced transient T cell suppression in vivo was not exclusively mediated by Fas-FasL- or TNF-induced AICD or due to an enhanced susceptibility to apoptosis. Instead, immune suppression in vivowas associated with a delayed onset of division, which we found not to be due to a defect in antigen presentation, but rather due to a T cell intrinsic defect. Despite the suppressed proliferation of TCR-stimulated bystander CD8 T cells in vivo, we found an enhancement of the effector functions exerted by bystander CD8 T cells activated during acute viral infections. During acute viral infections or after stimulation with type 1 IFN (IFN-αβ) inducers, some bystander CD8 T cells were sensitized to immediately exert effector functions such as IFN-γ production and degranulation upon stimulation with high affinity cognate antigen. Sensitization of naïve CD8 T cells required self-MHC I and indirect effects of IFN-αβ, while IL-12, IL-18, and IFN-γ were not individually required. IL-15 was not required for the rapid expression of IFN-γ, but was required for up-regulation of granzyme B (GrzB). P14 and OT-I CD8 T cells, which are capable of homeostatic proliferation, could be sensitized by poly(I:C), but HY CD8 T cells, which are poor at homeostatic proliferation, could not, suggesting that the requirement for MHC I may be to present low affinity cryptically cross-reactive self antigens. Sensitized naive CD8 T cells up-regulated the t-box transcription factor Eomesodermin (Eomes), which can regulate these rapid effector functions. In conclusion, we demonstrate in this thesis that acute viral infections impact naïve bystander CD8 T cells such that their response to cognate antigen is altered. Prior to cognate antigen engagement, bystander CD8 T cells up-regulated Eomes, CD122, and GrzB. Following cognate antigen engagement, bystander CD8 T cells rapidly degranulated and expressed the effector cytokine IFN-γ. The ability of bystander CD8 T cells to rapidly exert effector functions may contribute to the resistance of virus-infected individuals to superinfections. Despite these rapid effector functions, the proliferation of TCR-stimulated bystander CD8 T cells was markedly inhibited. This reduced proliferation was found not to be a defect in antigen presentation, but was a T cell intrinsic defect in initiating division. Thus, bystander CD8 T cells were also susceptible to virus-induced immune suppression. It is also likely that virus-specific CD8 T cells that are not activated until later in the response, so-called latecomer CD8 T cells, may also be susceptible to immune enhancement and suppression. Thus, latecomer CD8 T cells would be able to rapidly exert effector functions at the expense of proliferation. Taken together, we propose that during an immune response, due to spatial and temporal gradients of antigen and inflammation, it is likely that a combination of heterogeneous T cells with different signal strengths and sequences of exposure from cytokines and peptide-MHC constitute the total T cell response to pathogens.

Le mélanome est un cancer de la peau dont l’incidence est en continuelle augmentation dans le monde entier. Des progrès récents dans la compréhension des mécanismes cellulaires complexes régulant l’immunité du cancer ont conduit à l’élaboration de nouvelles stratégies visant des checkpoints spécifiques de la régulation des réponses immunes. Ipilimumab est un anticorps thérapeutique dirigé contre la molécule CTLA-4. Il a permis, chez les patients atteints de mélanome métastatique, d’augmenter la survie globale et a fait l’objet d’une approbation de la FDA en 2011. Cependant cette thérapie ne semble bénéficier qu’à un nombre restreint de patients et souvent de manière retardée. L’identification de marqueurs immunologiques précoces associés à la réponse clinique et à la survie s’avère donc être nécessaire afin d’apporter des éléments d’orientation. Dans ce contexte, nous avons suivi de manière longitudinale, prospective et retrospective une cohorte de 77 patients atteints de mélanome métastatique. Nous nous sommes intéressés dans un premier temps aux molécules sériques reflétant soit l’importance de l’envahissement tumoral (LDH, S100B et MIA) soit l’implication de mécanismes d’échappement immunitaire (MICA soluble et anticorps anti-MICA). Nous montrons une association entre des faibles concentrations sériques de LDH et S100B, soutenues après première et deuxième dose d’ipilimumab, et la réponse au traitement et la survie. De plus, des niveaux élevés de MICA solubles avant le traitement sont associés à une fréquence plus faible de complications à type d’auto-immunité. Nous avons de plus suivi les populations lymphocytaires avec une attention particulière portée sur les compartiments naïf et mémoires T, les facteurs de transcription impliqués dans la différentiation des lymphocytes T mémoires, les cytokines produites et les récepteurs de chimiokines de lymphocytes T. Nos résultats montrent que le taux de lymphocytes avant l’introduction du traitement est un facteur prédictif de meilleure survie et de réponse positive à la semaine 16, indépendamment du taux de LDH et de la corticothérapie. De plus, un effet global de l'ipilimumab sur l'expansion des cellules T mémoires classiques a été observé, associé à la réponse au traitement. En revanche, les fréquences des cellules souches T mémoires (TSCM) récemment décrites diminuent malgré une augmentation de la prolifération, suggérant un processus de différenciation. L'ipilimumab induit aussi l'expansion de lymphocytes T exprimant CXCR3, CCR4 et CCR6, permettant une migration vers la peau et les tissus inflammés, avec augmentation de leur capacité à produire des cytokines effectrices. Une augmentation précoce des cellules T CD8+ exprimant le facteur de transcription Eomes s’est révélée être associée à un contrôle de la maladie. Enfin, et sur la base des résultats précédents, nous avons étudié la capacité des lymphocytes T mémoires de patients à proliférer après stimulation in vitro. Contrairement aux sujets sains, les patients présentent un défaut dans la capacité de prolifération des TSCM qui pourrait être liée à un défaut dans la régulation d’Eomes et Ki-67. Nous proposons ainsi un modèle permettant de suivre de manière précoce les étapes conduisant à la différentiation des TSCM en sous populations mémoires, associées à une réponse clinique sous ipilimumab, et impliquant le facteur de transcription Eomes
Melanoma is a skin cancer with incidence increasing at dramatic rates worldwide. Ipilimumab, an anti-CTLA-4 therapy developed in the view of counter-balancing the inhibitory role of CTLA-4 in T lymphocytes, was the first immune checkpoint inhibitor demonstrating to extend overall survival in patients with metastatic melanoma, with FDA approval in 2011. However, biomarkers allowing the identification of the subset of patients that will more likely benefit from this immunotherapy or that may allow a good monitoring of patient clinical management during treatment are lacking. The principal objective of this work was to identify potential and early predictive biomarkers of ipilimumab response and/or survival in a cohort of 77 metastatic melanoma patients. Firstly, serum levels of melanoma markers such as LDH, S100B and soluble MICA (and its counter-part anti-MICA antibody), tumour markers associated with tumour development and/or immune escape, were assessed. A correlation between lower baseline levels of LDH and S100B, sustained after the first and second doses of ipilimumab, and treatment response and survival was observed, suggesting their potential utility in treatment monitoring. In addition, higher baseline levels of soluble MICA were found to be associated with a less frequency of immune-related adverse events, which might provide important information for the management of frequent ipilimumab-related adverse events. Secondly, immune markers with a special focus on transcription factors, cytokine secretion and chemokine receptors of T lymphocytes and memory T subsets were assessed. An association between baseline absolute lymphocyte counts and extended overall survival as well as better treatment response was found. In addition, a global effect of ipilimumab on the expansion of conventional memory T cells was observed, which was associated with treatment response. By contrast, frequencies of the recently described stem-cell memory T cells were shown to decrease despite increased proliferation, suggesting a process of differentiation. Additionally, ipilimumab induced the expansion of CXCR3, CCR4 and CCR6-expressing T lymphocytes and effector cytokines secretion capacity. Early increased levels of Eomes-expressing CD8+ T cells were found to be associated with disease control. Lastly, and based on the previous results, we investigated the ability of patients’ memory T cells to proliferate under in vitro stimulation. We found that, in contrast to healthy subjects, patients possess a defect in the ability of stem-cell memory T cells expansion in vitro, that might be related to a defect in Eomes and Ki-67 regulation

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus which causes acute infectious mononucleosis and is etiologically associated with malignant lymphoproliferative disorders including Burkitt's lymphoma, nasopharyngeal carcinoma, B-cell lymphomas in immunocompromised hosts, Hodgkin's disease, T cell lymphomas, and smooth muscle tumors in allograft recipients. The medical significance of EBV is underscored by its potent growth transforming effects on human B-lymphocytes in-vitro and the potentially oncogenic consequences of infection in-vivo. The majority of EBV-associated malignancies occur in the setting of chronic infection and strong virus-specific humoral immunity, suggesting that cellular immunity is primarily responsible for preventing the outgrowth of EBV-transformed B cells in-vivo. Similarly, primary EBV infection in adolescents and adults stimulates an intense cytotoxic-T-lymphocyte (CTL) response which coincides with a marked reduction in the number of infected B cells in the peripheral blood. Evidence of previous EBV infection can be confirmed by the presence of EBV-specific, HLA-restricted memory T cells in the peripheral blood which inhibit the outgrowth of newly EBV-transformed B cells and efficiently lyse established autologous B-lymphoblastoid cell lines. Worldwide, EBV is responsible for substantial morbidity, comparable to measles, mumps and hepatitis virus, for which vaccines exists. Accordingly, the potential public health impact of an EBV vaccine has reinforced our efforts to identify the immunodominant virus-encoded T-cell epitopes which stimulate naive CTL effectors during acute infection and maintain memory CTL surveillance during convalescence. The EBV-encoded antigens against which the memory CTL response is directed have been partially defined, and include most of the EBV latent proteins (EBNA-2, 3a, 3b, 3c, LP, and LMP-l, 2a, 2b) consistently expressed by in-vitro EBV-transformed B lymphocytes (type-III latency). Importantly, all EBV-associated malignancies express EBNA-1, and as yet no EBNA-1-specific memory CTL have been convincingly demonstrated. Additionally, many EBV-specific CTL lines and clones have been described which do not recognize any of the known latent proteins or other EBV protein antigens tested thus far. Thus while much is known about CTL-mediated immunity against EBV, our knowledge of EBV-derived CTL epitopes remains incomplete. In contrast to the EBV-specific memory CTL response, very little is known about the source of viral epitopes recognized during the primary CTL response to EBV. In this regard, acute infectious mononucleosis represents an ideal model system to study virus-specific, cell-mediated immunity. Acute IM is a self-limited illness characterized by the appearance of "atypical" lymphocytes (CD3+/CD8+/HLADR+), including both virus-specific and alloreactive CTL, which undoubtedly contribute to virus elimination and provide CTL precursors for life-long immunity to EBV. Like other herpesvirus, EBV can undergo either lytic or latent cycle replication. During primary EBV infection many lytic cycle genes are expressed which are likely responsible for stimulating the intense cellular immune response associated with acute infectious mononucleosis. During convalescence a minor population of circulating B cells remain latently infected, harbor multiple EBV episomes, and express only EBNA-1 and possibly LMP-2a (type-I latency). Thus, latency type-I infected B cells in-vivo express a much more restricted spectrum of latent proteins and are therefore not subject to elimination by the same virus-specific CTL as are type-III EBV latently infected cells. Accordingly, many mechanisms have been proposed to explain EBV persistence including; restricted expression of EBV latent genes, reduced levels of cellular adhesion molecules, downregulation of MHC class-I molecules, absence of EBNA-1 T-cell-epitopes, and most recently, EBNA-1-mediated inhibition of antigen processing. While these mechanisms may contribute to ineffective T cell surveillance against latency type-I EBV- infected cells, B cells expressing the full spectrum of latent proteins (type-III) also exist transiently in vivoand maintain detectable humoral and CTL responses to most latent proteins. Our first goal was to identify the virus-encoded immunodominant antigens recognized by in-vivoactivated MHC class-I restricted CTL isolated from college students experiencing primary EBV infection, manifested as acute IM. Following a prodromal period of several weeks, newly EBV infected patients present with signs and symptoms of acute IM, including elevated numbers of activated CD8+ T cells in their peripheral blood, many of which, like memory CTL, are EBV-specific and HLA-restricted. In order to address the issue of EBV persistence and the immune control of EBV-induced lymphoproliferation, we also studied the long-term EBV-specific memory CTL response in these same individuals. Blood from acute IM patients and healthy EBV seropositive donors served as a source of peripheral blood lymphocytes to generate bulk CTL cultures and autologous target cells. The infecting strain of EBV was determined for each patient by DNA-PCR amplification of virus from saliva. Lymphocytes were isolated from whole blood by Ficoll-Paque density centrifugation and T- and B-cell enriched populations were obtained by AET-sheep red cell rosette selection. Autologous B cell blasts served as a source of target cells and recombinant vaccinia virus constructs were used to introduce individual EBV latent genes into target cells. Expression of individual EBV genes in target cells was confirmed by both western blot and immunofluorescence. Primary CTL responses to EBV were evaluated in standard 5lCr release assays using freshly isolated, T-cell enriched PBL from acute IM patients as effector cells. EBV-specific memory CTL responses were evaluated with bulk CTL culture generated by in-vitro restimulation with autologous B-LCLs. FACS analyses were routinely performed on bulk cultures of effector CTL populations in order to more clearly characterize their phenotype. Lastly, monoclonal antibody blocking studies and cold target competition assays were performed in order to accurately identify the viral antigen and MHC components responsible for target cell recognition. Our results based upon evaluation of 35 acute IM patients and 32 convalescent patients demonstrate that the virus-specific primary CTL response is broadly directed against the full spectrum of latent proteins, including EBNA1 and the viral coat glycoprotein gp350, while the memoryCTL response, which essentially lacks EBNA1 reactivity, is directed primarily against the EBNA 3 family of proteins (3A, 3B, 3C). Importantly, the immunodominant response by both primary and memory CTL was directed against the EBNA3 proteins. CTL from 7 of the 35 acute IM patients evaluated recognized EBNA1 expressing targets, and in 4 of these 7 patients, EBNA1 was an immunodominant antigen. Similarly, CTL from 7 of 35 acute IM patients recognized gp350 transfected targets, while no gp350-specific memory CTL responses were observed. While the phenotype of in-vivo primed CTL effectors were CD8+/HLA-DR+/CD11b+, the major subpopulation of memory CTL were CD8+/HLA-DR+/CD11b-. The CD11b "memory marker" reached peaked levels on the first sample day for all patients and gradually declined to baseline levels over a period of several months. In contrast, the CD11b marker was quickly shed from in vitropropogated CTL, over a period of 5-10 days. Target cell lysis by in-vivoactivated CTL was almost completely blocked by antibody directed againt [against] class-I molecules (BBM.1), whereas the effect of blocking target cell lysis by anti-CD8 mAb varied between 40-75%. These findings are consistent with an absolute need for class-I restricted antigen presentation, and imply that CD8 was variably required, likely for the lower affinity TCR/ Ag combinations. Cell lysis mediated by in-vitro-restimulated memory CTL was also largely inhibited by anti-class-I mAb, while anti-CD8 mAb was only mild/moderately effective in blocking target cell lysis, in keeping with the concept that memory CTL bear higher avidity TCR which can recognize antigen independent of CD8. Our detection of only one EBNA1-specific memory CTL response among the 32 patients tested supports the theory that latently infected B cells in-vivo, expressing only EBNA1, escape CTL recogition and thus might serve as a reservoir for viral persistence and/or reactivation. The rare ability to detect an EBNA1-specific memory CTL responses remains a relatively unexplained phenomenon and may involve a number of tolerizing mechanisms including the induction of anergy by presentation of EBNA-1 in the absence of costimulation, clonal deletion of low affinity T cells, the absence of dominant T cell epitopes within EBNA1 or a result of the recently described inhibiting properties of EBNA-1 on antigen processing and presentation. Alternatively, the absence of detectable EBNA1-specific memory CTL may be the result of insufficient or inappropriate restimulation of memory CTL in vitro. We addressed this possibility by attempting to selectively restimulate and expand EBNA1-specific CTL from acute IM patients by using EBNA1 expressing B cells blasts as a stimulus. Effector cells generated in this manner killed target cells in an MHC class-I restricted manner but were specific for an unspecified vaccinia antigen. Interestingly, the phenotype of the effector cells was predominantly CD3+/CD4-/CD8-/γδ T cells. In summary, our findings suggest that a multitude of previously unrecognized, EBV-specific CTL are present in the peripheral blood during acute IM, and include EBNA-1-specific CTL. The importance of accurately defining the in-vivo immune response to EBV is underscored by the ever-growing list of EBV associated malignancies. In addition to providing insights into the oncogenesis and potential treatment of NPC, a newly described link between precursor lesions and EBV infection raises the possibility that heightened immunity to EBV or EBV-infected cells may prevent the development of NPC. An obvious expectation would include extension of such knowledge to other EBV associated malignancies such as B and T cell lymphomas, Hodgkin's lymphomas, and smooth muscle tumors. First however, existing gaps in knowledge regarding the immune response to EBV and EBV-associated malignancies must be closed. Details about the viral gene products which are involved in stimulating a broadly protective, virus-specific immune response in a large number of individuals is fundamental to the design of an effective EBV vaccine. Since the presence of activated CD8+ T cells correlates with the rapid decline of EBV infected B cells in the peripheral blood, a concise description of the EBV-specific CTL response in the setting of acute infection will be necessary for the rational design of an effective acute IM vaccine. Increased understanding of viral escape mechanisms is also likely to contribute to therapeutic modalities to treat autoimmune disorders.

Les phosphoantigènes (P-Ag) de P. falciparum (P.f.) induisent une forte activation et une expansion des lymphocytes T (LT) Vγ9Vδ2 par un mécanisme encore mal décrit. Les LT Vγ9Vδ2 actives inhibent le cycle sanguin de P. f. par des médiateurs cytotoxiques solubles, inhibant ainsi la capacité invasive des mérozoites. Il a été montre in vitro que des LT Vγ9Vδ2 activés par les P-Ag peuvent présenter des antigènes et activer les LT αβ, agissant ainsi comme des cellules présentatrices d’antigènes (APC). Cette fonction n’a cependant pas été démontrée dans un contexte physiopathologique. Le but de ce projet est i) d’étudier les mécanismes d’activation des LT Vγ9Vδ2 par les stades sanguins P. f. et ii) d’evaluer le potentiel APC des LT Vγ9Vδ2 stimules par P. f. Nous montrons que l’activation des LT Vγ9Vδ2 par des globules rouges parasites par P. f. (GRP) intacts ne dépend ni d’un contact cellulaire, ni de l’expression de butyrophiline par le GRP. Les LT Vγ9Vδ2 sont activés par des molécules contenues dans les surnageants de culture de GRP, ayant les caractéristiques de P-Ags et étant libérées lors de la rupture des GRP. In vitro, les LT Vγ9Vδ2 stimules par les GRP expriment des marqueurs de surface associés à un rôle d’APC et cross-présentent un antigène modèle à une lignée T CD8 spécifique. In vivo, nous montrons une expression augmentée des marqueurs APC à la surface de LT Vγ9Vδ2 de patients infectés par P. falciparum. L’ensemble de ces données suggèrent que les P-Ag libérés par les GRP dans le milieu extracellulaire pourraient activer les LT Vγ9Vδ2 à distance, et ouvrent de nouvelles perspectives quant au rôle des LT Vγ9Vδ2 dans la réponse immunitaire adaptative anti-palustre
P. falciparum derived phosphoantigens (P‐Ag) induce potent activation and expansion of Vγ9Vδ2 T-cells by a poorly described mechanism. Activated Vγ9Vδ2 T cells inhibit the Plasmodium falciparum blood cycle through soluble cytotoxic mediators, abrogating merozoite invasion capacity. In vitro, P-Ag activated Vγ9Vδ2 T lymphocytes have been shown to present antigens and induce αβ T lymphocyte responses, i.e. to act as an antigen presenting cell (APC). Whether this activity can be involved in a pathophysiological context is unknown. The aim of this PhD project is to a) investigate the mechanisms of Vγ9Vδ2 T cell activation by blood stage P. falciparum and b) assess the potential of P. falciparum activated Vγ9Vδ2 T cells to display APC functionality. We show that Vγ9Vδ2 T-cell activation by intact iRBCs is independent of iRBC contact and butyrophilin expression. Blood stage culture supernatants can potently activate Vγ9Vδ2 T-cells and bioactivity is found to be attributable to P-Ags released at the time of parasite egress from the RBC. In vitro iRBC stimulated Vγ9Vδ2 T cells up-regulate surface expression of APC associated markers and can cross-present a model antigen to specific CD8 T cell responders. In vivo we demonstrate an increase in surface expression of APC makers on Vγ9Vδ2 T cells from P. falciparum infected patients.Altogether, these data outline a framework whereby P‐Ag release by iRBC into extracellular milieu can promote activation of distant Vγ9Vδ2 T cells, and opens the door to a new aspect of Vγ9Vδ2 T cell contribution to P. falciparum adaptive immune responses

Deficiencies in immune responses can lead to increases in the rate of infections and chronic diseases, such as cancer. Critical to the adaptive immune response is the activation of the T helper (Th)/CD4+ cell, the subsequent production of interleukin 2 (IL-2), expression of IL-2 and transferrin receptors (IL-2R, TfR) and transcription of genes resulting in DNA synthesis and T cell clonal expansion. The CD4+ lymphocyte response is impaired with ageing. Recent evidence suggests that moderate, regular aerobic training may increase the responsiveness of CD4+ lymphocytes to antigenic and mitogenic challenge, and thereby improve immune function in the older individual. Large volumes of chronic endurance training, and also high intensity training, may adversely affect the immune response, leading to immunosuppression and increased risk of infections. Impaired immune function and increased rates of URTI are found in athletes who undergo large volumes of training, often at high intensity. Purpose: To investigate if long-term aerobic training improved the immune response in men and women aged 65 to 75 years and, and to investigate if long-term endurance training depressed the immune response in male athletes aged 23 to 36 years. Methods:T helper lymphocyte proliferation was assessed monthly, by inducing the expression of CD25 (IL-2R ) and CD71 (transferrin) receptors with phytohemagglutinin (PHA). Percentage of CD4+ cells positive for the receptors, and the receptor density, were measured using two colour flow cytometry. Concentrations of intracellular calcium (Ca2+) and iron (Fe3+) were also measured monthly to determine the effect of endurance training on intracellular Ca2+ ([Ca2+]i) and Fe3+ ([Fe3+]i) within the CD4+ lymphocyte signal transduction pathway. Results: After twelve months of moderate aerobic training the percentage of CD4+ lymphocytes positive for CD25 increased in males aged 65 to 75 years, but not in females. There was no training effect on the density of CD25 in either gender, nor was there a training-induced increase in [Ca2+]i, total intracellular [Ca2+] from endoplasmic reticulum stores ([Ca2+]t) or [Fe3+] in this age group. Significant month to month variations in leucocyte, erythrocyte and haemoglobin concentration, mean corpuscular haemoglobin concentration, haematocrit, platelets, CD25 expression, CD71 expression, [Ca2+] and [Fe3+] were documented for both trained and untrained male and female groups. Aerobic capacity increased significantly with training for both men and women, with increases in peak, peak power and peak ventilation (p less than 0.05). Twelve months of chronic endurance training produced significantly lower haemoglobin, mean corpuscular haemoglobin and platelet concentration for six ([Hb]) and nine months ([MCHC], platelets) of the year in Ironman-distance triathletes, compared to sedentary males aged 23 to 36 years. There was no evidence of immunosuppression in the trained group, with no significant differences between groups in the percentage of CD4+ cells positive for CD25. The trained group showed a significantly higher density of CD25 receptors in October, January and June, suggesting a better immune response during these months. Endurance training did not effect [Ca2+] or [Fe3+]. The trained group did not show a reduced leucocyte concentration, and reported significantly fewer cases of URTI in twelve months than their sedentary counterparts. The 23 to 36 years age group showed seasonal changes in haematological and immunological indices similar to older individuals, indicating that autumn, late winter and late spring are periods of reduced immuno-competency. Conclusion: Twelve months of moderate intensity training significantly increased functional capacity in older men and women, and the percentage of CD4+ lymphocytes expressing CD25 in older men, thereby improving the lymphoid immune response. Twelve months of endurance training significantly increased CD25 density in CD4+ lymphocytes in Ironman triathletes compared to sedentary young males. The monthly changes in immune variables in young and older subjects suggested that autumn, late winter and late spring might be periods where individuals were more at risk of succumbing to infections due to decreased lymphocyte responsiveness. Summer months appeared to be a period of increased lymphocyte responsiveness and proliferation.

Deficiencies in immune responses can lead to increases in the rate of infections and chronic diseases, such as cancer. Critical to the adaptive immune response is the activation of the T helper (Th)/CD4+ cell, the subsequent production of interleukin 2 (IL-2), expression of IL-2 and transferrin receptors (IL-2R, TfR) and transcription of genes resulting in DNA synthesis and T cell clonal expansion. The CD4+ lymphocyte response is impaired with ageing. Recent evidence suggests that moderate, regular aerobic training may increase the responsiveness of CD4+ lymphocytes to antigenic and mitogenic challenge, and thereby improve immune function in the older individual. Large volumes of chronic endurance training, and also high intensity training, may adversely affect the immune response, leading to immunosuppression and increased risk of infections. Impaired immune function and increased rates of URTI are found in athletes who undergo large volumes of training, often at high intensity. Purpose: To investigate if long-term aerobic training improved the immune response in men and women aged 65 to 75 years and, and to investigate if long-term endurance training depressed the immune response in male athletes aged 23 to 36 years. Methods:T helper lymphocyte proliferation was assessed monthly, by inducing the expression of CD25 (IL-2R ) and CD71 (transferrin) receptors with phytohemagglutinin (PHA). Percentage of CD4+ cells positive for the receptors, and the receptor density, were measured using two colour flow cytometry. Concentrations of intracellular calcium (Ca2+) and iron (Fe3+) were also measured monthly to determine the effect of endurance training on intracellular Ca2+ ([Ca2+]i) and Fe3+ ([Fe3+]i) within the CD4+ lymphocyte signal transduction pathway. Results: After twelve months of moderate aerobic training the percentage of CD4+ lymphocytes positive for CD25 increased in males aged 65 to 75 years, but not in females. There was no training effect on the density of CD25 in either gender, nor was there a training-induced increase in [Ca2+]i, total intracellular [Ca2+] from endoplasmic reticulum stores ([Ca2+]t) or [Fe3+] in this age group. Significant month to month variations in leucocyte, erythrocyte and haemoglobin concentration, mean corpuscular haemoglobin concentration, haematocrit, platelets, CD25 expression, CD71 expression, [Ca2+] and [Fe3+] were documented for both trained and untrained male and female groups. Aerobic capacity increased significantly with training for both men and women, with increases in peak, peak power and peak ventilation (p less than 0.05). Twelve months of chronic endurance training produced significantly lower haemoglobin, mean corpuscular haemoglobin and platelet concentration for six ([Hb]) and nine months ([MCHC], platelets) of the year in Ironman-distance triathletes, compared to sedentary males aged 23 to 36 years. There was no evidence of immunosuppression in the trained group, with no significant differences between groups in the percentage of CD4+ cells positive for CD25. The trained group showed a significantly higher density of CD25 receptors in October, January and June, suggesting a better immune response during these months. Endurance training did not effect [Ca2+] or [Fe3+]. The trained group did not show a reduced leucocyte concentration, and reported significantly fewer cases of URTI in twelve months than their sedentary counterparts. The 23 to 36 years age group showed seasonal changes in haematological and immunological indices similar to older individuals, indicating that autumn, late winter and late spring are periods of reduced immuno-competency. Conclusion: Twelve months of moderate intensity training significantly increased functional capacity in older men and women, and the percentage of CD4+ lymphocytes expressing CD25 in older men, thereby improving the lymphoid immune response. Twelve months of endurance training significantly increased CD25 density in CD4+ lymphocytes in Ironman triathletes compared to sedentary young males. The monthly changes in immune variables in young and older subjects suggested that autumn, late winter and late spring might be periods where individuals were more at risk of succumbing to infections due to decreased lymphocyte responsiveness. Summer months appeared to be a period of increased lymphocyte responsiveness and proliferation.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Physiotherapy and Exercise Science
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Thesis (Ph. D.)--West Virginia University, 2005
Title from document title page. Document formatted into pages; contains ix, 155 p. : ill. Vita. Includes abstract. Includes bibliographical references.

There are four serotypes of dengue virus designated dengue 1, 2, 3 and 4 (D1, D2, D3 and D4) and epidemiological studies indicate that a severe complication of dengue virus infection - dengue hemorrhagic fever (DHF) is more likely to occur following a secondary infection. DHF is hypothesized to be immunologically mediated and may be triggered by virus-specific T cells. It is also likely that dengue virus-specific cytotoxic T lymphocytes (CTLs) are important for recovery from dengue virus infections. An analysis of the immune response during acute illness and when the patient has recovered from the infection (immune state) is therefore important as it will provide insights into the immunopathological nature of the disease. This thesis initially examines the CD8+CTL responses in volunteers who have received live attenuated dengue vaccines and then investigates acute and immune T cell responses in children following natural infection with dengue. When this project was initiated, there was little available information on the human CD8+ T cell responses to dengue viruses. PBMC from one donor had generated memory CD8+CTL to the nonstructural protein NS3 of dengue virus. Memory CD8+CTL responses were therefore analyzed to determine the diversity of the T cell response to dengue virus and to identify immunodominant proteins using PBMC from eight healthy adult American volunteers who had received monovalent live-attenuated candidate vaccines of the 4 dengue serotypes. All the donors had specific T cell proliferation to dengue viruses and to other flaviviruses that we tested. CTLs were generated from the stimulated PBMC of all donors and in the seven donors tested, dengue virus-specific CD8+CTL activity was demonstrated. The nonstructural proteins NS3 and NS1.2a and the structural protein E were recognized by CD8+CTLs from six, five and three donors respectively. All donors recognized either NS3 or NS 1.2a. In a donor who received a dengue 4 vaccine, CTL killing was seen in bulk culture against the premembrane protein (prM). This is the first demonstration of a CTL response against the prM protein. The CTL responses using PBMC of two donors were serotype-specific whereas all other donors had serotype-cross reactive responses. For one donor, CTLs specific for E, NSl.2a and NS3 proteins were all HLA-B44 restricted. For the three other donors tested the potential restricting alleles for recognition of NS3 were HLA-B38, A24 and/or B62 and B35. These results indicate that the CD8+CTL responses of humans after immunization with a single serotype of dengue virus are diverse and directed against a variety of proteins. The nonstructural proteins NS3 and NSl.2a appear to be immunodominant and should be considered when designing subunit vaccines for dengue. Previously T cell responses had not been examined in people who have had natural infections with dengue. The HLA diversity between North American Caucasians and populations where dengue is a serious health problem, calls for the analysis of immune responses in people who have been infected with natural circulating strains of the virus. We examined the memory cytotoxic T lymphocytic (CTL) responses of peripheral blood mononuclear cells (PBMC) obtained from patients in Thailand 12 months after natural symptomatic secondary dengue infections. In all four patients analyzed, CTLs were detected in bulk culture PBMC against nonstructural dengue proteins. Numerous CD4+ and CD8+ CTL lines were generated from the bulk cultures of two patients, KPP94-037 and KPP94-024, which were specific for the NSl.2a and NS3 proteins respectively. All CTL lines derived from both patients were crossreactive with other serotypes of dengue virus. The CD8+ NS1.2a specific lines from patient KPP94-037 were HLA-B57 restricted and the CD8+ NS3 specific lines from patient KPP94-024 were HLA-B7 restricted. The CD4+ CTL lines from patient KPP94-037 were HLA-DR7 restricted. A majority of the CD8+CTLs isolated from patient KPP94-024 were found to recognize a.a. 221-232 on NS3. These results demonstrate that after symptomatic secondary natural dengue infections in Thai patients, CTLs are mainly directed against nonstructural proteins and are broadly crossreactive. The data correlate with our observations that nonstructural proteins are immunodominant proteins in volunteers who received dengue vaccines. We were interested in examining CTL responses in children during their acute illness and comparing them to memory CTLs obtained from the same children a year or more after the infection. A detailed analysis on samples from nine patients during their acute illness failed to generate any dengue virus-specific CTL responses. We therefore decided to determine if cell mediated responses are altered during acute dengue infection. Decreased proliferative responses to mitogens and recall antigens have been observed in PBMC obtained during several acute human viral infections. All responses of PBMC during acute illness were compared to the same patients PBMC obtained at least 6 months after their infection. Proliferative responses to PHA, anti-CD3, tetanus toxoid and dengue antigens were significantly decreased in PBMC obtained during the acute infection. The proliferative responses to PHA were restored by the addition of gamma-irradiated autologous immune or allogeneic PBMC. Cell contact with the irradiated PBMC was necessary to restore proliferation. Non-T cells from the acute PBMC of dengue patients did not support proliferation of T cells from control donors in response to PHA, but T cells from the PBMC of patients with acute dengue proliferated if accessory cells from a control donor were present. Addition of anti-CD28 antibodies restored anti-CD3-induced proliferation of the PBMC of some patients. The percentage of monocytes was reduced in the acute sample of PBMC of the dengue patients. Addition of IL-2 or IL-7, but not IL-4 or IL-12 also restored proliferation of acute PBMC stimulated with anti-CD3. The results demonstrate that both quantitative and qualitative defects in the accessory cell population during acute dengue illness result in a depression of in vitro T cell proliferation. The data generated from this project shed light on the nature of the immune responses during acute natural dengue infections. It strengthens the existing data on the human memory CD8+CTL responses to dengue viruses and validates the observations by examining memory CTL responses after natural dengue infection in patients from Thailand. In addition, we demonstrate a profound defect in lymphoproliferative responses during dengue illness.

T-lymphocytes (T-cells) trafficking in the lymph nodes (LNs) is key for T-cells activation and their effector functions in adaptive immune responses. T-cells enter the LNs through high endothelial venules (HEVs) and interact with dendritic cells (DCs) for cognate antigens in the T-cell zone (TCZ). After scanning the TCZ for antigens, T-cells leave the LNs through efferent lymphatic vessel. CCR7 and its ligands, CCL19 and CCL21 are involved in the recruitment and compartmentalization of T-cells in LNs. However, their specific role(s) in mediating T-cells migration in LNs sub-regions remain unclear. In addition, the mechanism behind the passage of T-cells from the TCZ to the abluminal side of medullary sinuses (for their exit through medullary sinuses) is not well understood. Here, I hypothesize that different CCL19 and CCL21 fields in LNs sub-regions, orchestrate T-cells sub-regional migration in LNs.. In this study, I examined the CCL19 and CCL21 distribution profiles in mouse LNs sub-regions by immunofluoroscence staining and confocal microscopy. Using microfluidic devices that can flexibly configure well-defined single and co-existing chemical concentration gradients, I quantitatively analyzed the migration of activated human blood T-cells in LNs relevant CCL19 and CCL21 fields. The results suggested a novel CCL19 and CCL21 based combinatorial guiding mechanism for T-cells migration in different LNs sub-regions. In particular, this mechanism operates in the TCZ periphery region to guide T-cells migration away from the TCZ. Furthermore, the CCL19 and CCL21 fields mimicking the region beyond the TCZ toward the medulla result in disturbed chemotaxis, which prevents T-cells from being attracted back to the TCZ. Taken together, this microfluidics-based in vitro study shows the coordinated T-cells migration in different single and combined CCL19 and CCL21 fields, leading to interesting new insights into the guiding mechanisms for T-cells trafficking in LNs sub-regions.