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Étude de l'effet de l'expression de la protéine virale Nef du virus de l'immunodéficience humaine sur la lymphopoïèse T

HIV-1 infection is characterized by a progressive loss of CD4 T cell leading to a severe immune deficiency. More than 20 years after the identification of HIV, the exact mechanisms by which HIV leads to the depletion of CD4 T cells are not completely understood and remain a matter of cntroversy. The purpose of this work has been to explore out of the viral context, the effect of the HIV-1 Nef protein on the T cell differentiation. The HIV-1Nef gene is essential for AIDS pathogenesis. HIV-1Nef protein is a 27-kDa protein that is expressed early during cell infection. Nef increases viral replication in vivo and enhances viral infectivity. Nef interferes with the expression of crucial molecules at the surface of lymphocytes such as CD4, MHC class I and II, CD28, DC-SIGN, and chemokine receptors. Nef also alters T-cell signaling pathways and immunological synapse formation. During this work, we found that Nef expression in hematopoietic precursors interfere by an apoptotic pathway in the differentiation of a T/NK progenitor. In order to study the differenciation, we used a recent model of murine stromal cells engineered to express the Notch ligand delta 1 (OP9-DL1 system). This system allows the differentiation of hematopoietic progenitors to a DP CD4+CD8+ stage and led us to examine the effects of Nef expression on T-cell development. For this, Nef was expressed in hematopoietic CD34+ precursors using lentiviral vectors. In this study, we demonstrate that HIV-1Nef expression in the absence of other viral genes hampers the T and NK cell potential of human hematopoietic progenitors. We show that the generation of T cells from CD34+ progenitors is affected at a CD3e+CD5+CD1a+ precursor stage that has initiated a DJB rearrangement of the TCRB locus. Subsequent stages of T cell development were also affected with a quantitative reduction of CD4 ISP and DP CD4+CD8+ TCRas cells. Nef also decreased the generation of CD56+NK cells whereas B cell production was not affected. Limiting dilution analyses demonstrated a significant reduction in the frequency of T/NK progenitors among Nef-expressing CD34+ cells. Collectively, these data indicate that Nef interferes with the differentiation of a primitive lymphoid precursor with a T/NK potential. This interference was caused by the triggering of an apoptotic pathway which triggered the mitochondrial depolarization. This study allows a better knowledge of the interference mechanisms used by HIV on the T cell hematopoiesis, more accurately on the effect of Nef on human T cell differentiation