| My PhD was realised in the research team EA2686 at the Pole of Immunology in the Center of Biology Pathology of Lille under the direction of Doctor Myriam Labalette and in collaboration with Professor Ibrahim Yakoub-Agha from the department of Blood Diseases in the Hospital of Lille. The central line of the my work concern the implication of the different subpopulations of naive and memory T cells in the immune reconstitution and the main events post allograft of hematopoietic stem cells (HSC). 1)Study of factors controlling the homeostatic proliferation of T cells after allograft : By a prospective study, our team showed that the dynamic of reconstitution of subpopulations of naive and memory T cells during the immune reconstitution after allograft of HSC affects the occurrence of late events (Yakoub-Agha, 2009). The homeostatic proliferation of donor T cell provided by the graft and possibly also by the few residual recipient T cells is involved in the initial reconstitution of the lymphocyte compartment. Two main homeostatic cytokines are involved in this way of expansion of T cells after allograft, IL-7 and IL-15. We determined the precocious plasmatic level of these cytokines and the degree of expression of their receptor, IL-7Ralpha chain (CD127) and IL-15Rbeta chain (CD122) on the subpopulations of naive and memory T cells during the immune reconstitution post allograft. a) In 40 recipients of HSC with a myeloablative conditioning, our prospective study showed variations of IL-7 and IL-15 level during the first weeks post-graft. The plasmatic levels increased strongly to peak at day+14. Then, the concentrations return to a normal range around day+30. The increase of IL-7 and IL-15 levels observed during the first days post-graft could be due to an increase of production in response to the lymphopenia. However, at day+14 post-graft, we notice real important variations of IL-7 and IL-15 level among patients (range 3.8-30.2 and 14.3-66 pg/ml, respectively). A high level of IL-7 (≥11,9 pg/mL) at day+14 post-graft, when recipients are strongly lymphopenic, is a predictive factor of a risk of occurrence of acute GVHD (HR= 3.63 ; P= .014) compared to others factors known to favour independently this complication (reinfection to CMV, sex-mismatch). The relapse of disease is significantly associated to low level of IL-15 at day+14 (<33.3 pg/mL) (HR= 0.93; P= .035) (Thiant, 2010). b) In a prospective group of 45 recipients of HSC with a reduced conditioning inducing a lower degree of lymphopenia, the occurrence of acute GVHD is significantly associated to the plasmatic level of IL-7 and IL-15 at day+30 post-graft. This later lag is explained by the modalities of conditioning inducing a lower lymphopenia and the later occurrence of acute GVHD (median time= 42 days) compared to recipients with myeloablative conditioning (median time= 30 days). We also showed that levels of cytokines a month after the graft, affect the degree of expression of receptors, IL-7Rα and IL-15Rβ (Thiant, 2010). c) The increase of IL-7 could, in some conditions, suggest a failure of the receptivity by the IL-7Ralpha chain. We established a project of collaboration with the Professor Klaus Müller's team from the Hospital of Copenhagen, which highlighted the presence of polymorphisms located on the nucleotidic sequence encoding the IL-7R alpha chain in recipients of bone marrow (Shamim, 2006). The polymorphism +510 is correlated to the level of IL-7 and represents a factor of risk of occurrence of acute GVHD (P=.049). We know that this polymorphism induces a modification of amino acid in the sequence but the consequences on the functionality of the receptor of IL-7 are not known yet. These polymorphisms could lead in recipients some differences of capture of IL-7 by T cells and contribute indirectly to the development of an acute GVHD. The whole results indicate that the level of IL-7 and IL-15 after allograft differs in function of patients. A precocious determination of plasma level of IL-7 and IL-15 post-graft could therefore help predict subsequent occurrence of major events that complicate the allograft: acute GVHD and malignancy relapse, and help build an algorithm for their individualized prophylaxis. 2)Study of the alloreactivity of naive T cells in the allograft of HSC A high proportion of CD4+CCR7+ T cells (including naive and central memory cells) in the grafts was shown to be an independent factor of risk of the occurrence, the precocity and the severity of acute GVHD in recipients (Yakoub-Agha, 2006). Out team compared the alloreactivity of the different subsets of naive and memory CD4+ T cells against minor antigens of histocompatibility (mAH) in a sensitized model of mixed reaction. Our results demonstrate a maximal proliferative and functional response of purified naive CD4+ T cells in response to mAH (Chérel, SFHI 2009). Yet, in the case of the allograft with cord blood where the T cells are virtually all naive and where the compatibility is limited to 5/6 or 6/6 in major antigens (HLA-A, B, DR), the reactions of GVH are less frequent compared to the graft using peripheral stem cells or bone marrow. a) Thus, we evaluate, in parallel, in our sensitized model of mixed reaction, the capability of alloreactive response of naive CD4+ T cells of cord blood. Several mechanisms, sometimes controversial, were proposed to explain the relative tolerance of grafts of cord blood. We showed that the tolerance of grafts of cord blood is not linked to a higher proportion of CD4+CD25+ T cells comparing to peripheral blood. The naive T cells of cord blood are capable of a functional and proliferative response, but they present a high level of mortality, which may be prevented by the addition of IL-7 in the cultures. b) The CD4+CCR7+ T cells are involved in the acute GVHD. We propose a partial depletion of CD4+ CCR7+ T cells in rich grafts, in order to reduce the risk of occurrence of acute GVHD. The preservation of an anti-infectious immunity after reduction is necessary. We analysed the immune response of PBMC against the cytomegalovirus (CMV) after reduction of the proportion of CD4+CCR7+ T cells to less than 50% of total CD4+ T cells. The first results obtained showed that a partial depletion does not reduce significantly the functional response of T cells and that we keep sufficient anti-CMV immunity since she is mainly maintained by the contingent of memory T cells. |
