Caractérisation des mécanismes moléculaires et virologiques contribuant à la persistance du VIH-1 chez les individus sous thérapie antirétrovirale

With nearly 35 million people infected worldwide and 60,000 in Canada, HIV remains a major public health problem. Although antiretroviral therapy (ART) has significantly improved the quality of life and lifespan of HIV-infected people, it does not completely eliminate the virus from the human body. HIV persistence is attributed to the existence of cellular and anatomical reservoirs in which the virus persists through residual replication and/or latency, and in which the virus is invisible to the host immune system and to ART. The development of new therapeutic strategies aimed at eliminating these viral reservoirs requires a thorough understanding of the nature of the cells in which the virus persists and of the molecular and virologic mechanisms contributing to viral persistence. Although the virus primarily persists in memory CD4+ T cells, the exact phenotype of the reservoir cells remains to be determined. The development of HIV-Flow, a flow cytometry-based assay allowing the detection of cells producing the viral protein p24, greatly facilitated the study of the reservoir cells’ phenotype. Our results suggest that the viral reservoir consists of a heterogeneous pool of cell subsets expressing various markers that are not specifically expressed by latently infected cells. Nevertheless, we have identified several markers preferentially expressed on the surface of p24+ cells, including PD-1, TIGIT and the a4b1 integrin. The identification of a4b1 as a marker of viral reservoirs opens the way to new therapeutic perspectives. Finally, our results show that translation-competent viruses persist in the three subsets of memory CD4 + T lymphocytes [central (TCM), transitional (TTM), and effector (TEM) memory lymphocytes], but are particularly enriched in TTM and TEM cells in ART-suppressed individuals. The three subsets of memory CD4+ T cells in which the virus persists have different properties in terms of survival and proliferation. The development of flow cytometry protocols to study various factors involved in the transcriptional expression of the proviral genome (histone acetylation, NF-kB, PTEF-b) revealed that these factors are expressed at different levels between subsets. This observation highlights the importance of taking into account the heterogeneity of viral reservoirs. We have shown that latency reversing agents have different abilities to modulate the levels of these factors between the different subsets. Finally, by using the HIV-Flow assay, we identified a combination of latency reversing agents that is highly effective to reactivate the virus in TCM cells. Further work should permit the identification of a combination that is capable of reactivating the virus very effectively in all subsets. Beyond the cellular reservoirs described above, HIV persists in a variety of anatomical sanctuaries. Since lymph nodes are a major site for HIV persistence, we studied the virologic iii mechanisms of viral persistence in this anatomical compartment. We showed that the frequency of cells producing tat/rev spontaneously is significatively higher in the lymph nodes compared to the blood. Nevertheless, we could not observe active viral production by HIV-Flow in the lymph nodes of these ART-suppressed individuals, probably due to the low number of CD4+ cells analyzed. In conclusion, the observations made in this thesis contribute to a better understanding of the phenomenon of viral persistence, which is the main obstacle to HIV eradication. These results should favor the development of new therapeutic strategies allowing the remission of HIV-infected people.

Keyphrases: éradication, HIV, AIDS, persistence, latency, reservoirs, remission, eradication