Mécanismes moléculaires de permissivité à l’infection par le VIH dans les lymphocytes T CD4+

Human immunodeficiency virus type 1 (HIV-1) causes a chronic infection characterized by a progressive loss of CD4+ T-cells and an increased susceptibility to opportunistic infections in people living with HIV (PLWH). Th17-polarized CD4+ T-cells play an important role in mucosal immunity and in the maintenance of the intestinal barrier integrity. Mucosal Th17 cells are also the first and main targets of HIV infection and are rapidly depleted after infection, especially in the intestinal mucosa. Antiretroviral therapy (ART) does not restore the frequency and function of intestinal Th17 cells. The paucity of Th17 cells increases the risk of non-AIDS comorbidities in ART-treated PLWH. Thus, it is important to identify additional therapeutic strategies to restore mucosal immunity in these individuals. Previous laboratory studies have shown that HIV persists preferentially in colon- infiltrating CCR6+Th17-polarized T-cells from aviremic subjects on ART. In addition, induction of intestinal tropism via retinoic acid (RA) preferentially increases the permissiveness to HIV infection of CCR6+ T-cells. At the beginning of my Ph.D. training, molecular mechanisms underlying HIV permissiveness in gut-homing CCR6+ T-cells remained to be elucidated in view of the identification of new antiviral and immune-regulatory therapeutic strategies.The first part of this thesis demonstrated that the induction of intestinal tropism via AR activates the Akt/PI3K/mTORC1 pathway in CCR6+ T-cells. We have shown that mTORC1 (rapamycin) or mTORC1/2 (INK128) inhibitors abrogate the effects of AR on HIV replication/reactivation in CCR6+ T-cells. In addition, high levels of CCR5 and phosphorylated mTOR were observed in colon infiltrating CCR6+ T-cells from ART-treated PLWH, providing an explanation for the permissiveness and preferential persistence of HIV in these cells. This work demonstrating that HIV selectively targets gut-homing CCR6+ T-cells via mTOR-dependent mechanisms, prompted us to investigate the clinical benefits of metformin, an indirect mTOR inhibitory well-tolerated drug, in ART-treated PLWH. Thus, in the second part of this thesis, we explored the effects of metformin on the size of HIV reservoirs in the colon and on the persistent inflammation. Despite a subtle reduction in plasma markers of inflammation and alterations of the intestinal barrier, metformin significantly decreased several parameters in colon infiltrating T-cells, including a decrease of the frequency/activation of CD4+ T-cells and a decrease of the phosphorylated mTOR expression. These modulations were associated, in 68% of the participants, to a reduction of the residual HIV transcription in the colon. Finally, in an alternative strategy, we explored the possibility of restoring the effector functions of Th17 cells in order to restore mucosal immunity in ART-treated PLWH. Previous studies in the laboratory identified the expression of PPAR in Th17 cells as a negative regulation of HIV and RORC transcription. In the third part of this thesis, we explored the effects of the pharmacological inhibition of PPAR activity as a « shock and kill » strategy for the HIV eradication and amplification of Th17 effector functions. Our results demonstrated that the PPARγ antagonist T0070907 leads to an increase in IL-17A production and in HIV transcription. Unexpectedly, T0070907 inhibited virion release and HIV replication in vitro. Whole genome transcriptional profile studies revealed multiple signaling genes/pathways modulated by the PPARγ antagonist, including: i) a decrease expression of factors involved in HIV permissiveness (e.g., CCR5, furin); ii) an increase expression of HIV restriction/resistance (e.g. TRIM22, BST2, miR29) and iii) an increase of genes related to Th17 effector functions (e.g. RORγt, STAT3, BCL6, IL-17A / F, IL-21). Of major importance, PPAR antagonism significantly increases the production of IL-21, a cytokine with properties acting as immunoregulatory and antiviral shares. In conclusion the work of this thesis designates the CCR6+ T cells as being key therapeutic targets, especially in the intestine and proposes to further explore the clinical benefits of using immune-modulatory drugs such as mTOR inhibitors or PPARγ antagonists for HIV cure/remission strategies in ART-treated PLWH.

Keyphrases: Th17, CCR6, intestin, PPARg, Retinoic acid, Gut-homing, Metformin, PPARγ