MECHANISMS INVOLVED IN THE LACK OF IMMUNE RECONSTITUTION DURING ANTIRETROVIRAL THERAPY IN HIV-INFECTED INDIVIDUALS

Introduction: HIV infection is characterized by CD4+ T cell immunodeficiency and chronic inflammation. Antiretroviral therapy (ART) leads to the recovery of CD4+ T cells by suppressing viral replication. However 15-30% of HIV-infected ART-treated patients fail to restore CD4+ T cells despite full viral suppression and they are known as “Immunological Non-Responders (INR)”. INRs are characterized by higher risk of AIDS progression and non-AIDS-related morbidity compared to HIV-infected ART-treated immunological responder (IR) patients. Several mechanisms have been involved in immune failure, however none of them provides a full explanation for the lack of immune reconstitution observed in INRs. Inflammasomes are multimeric protein platforms involved in the regulation of inflammatory responses, Th17 activity and in a high inflammatory form of programmed cell-death called “pyroptosis”. Pyroptosis was recently shown to play a major role in CD4+ T cell loss and to contribute to immune activation in HIV infection. The possible role of inflammasomes and pyroptosis in the lack of immune reconstitution has nevertheless not been investigated. We analyzed possible associations between inflammasome and Th17 activity, caspase-1 activation, pyroptosis and immune reconstitution in HIV-infected ART treated patients. Methods: 39 HIV-infected patients on antiretroviral therapy for ≥24 months and plasma HIV-RNA<50cp/mL for ≥12 months, matched for nadir CD4+ T cell count were enrolled. Exclusion criteria: presence of actual opportunistic AIDS-related diseases, HBV or HCV co-infection, chronic inflammatory disorders, ongoing immunosuppressive therapy. Patients were classified as IRs or INRs if CD4+ T cell count was ≥500 or ≤350 cells/μL, respectively. Immune activation markers (HLA-DRII and CD38) and Th17 activity were evaluated by flow cytometry. Expression of genes involved in the inflammasome pathway and in pyroptosis were measured in unstimulated or LPS- and AT2 treated-HIV-1-stimulated cells. Pro-inflammatory cytokines, caspase-1 expression and microbial translocation markers (sCD14 and LPS) were quantified in plasma samples of all IRs and INRs. Results: INR patients were older and had a higher prevalence of past AIDS-defining illnesses. HLADRII/CD4 were significantly increased in INRs. Higher median levels of Th17 T cells (CD4/IL17A/RORγT) were also seen in INRs in unstimulated, as well as in LPS- and AT2 treated-HIV-1 stimulated conditions. LPS-stimulated inflammasome (NLRP3) and pro-inflammatory cytokines gene expression (IL-1β, IL-18, TNFα, type-I IFNs, CCL3, IL-6) were significantly increased in INR patients. AT2-HIV-1 stimulation induced NLRP3 gene expression in both IRs and INRs; NLRP3 and IL-18 expression were nevertheless significantly increased in INRs compared to IRs. Higher caspase-1gene expression was seen in both unstimulated and AT2-HIV-1 stimulated cells of INRs, whereas caspase 3, 4 and 5 expression was similar in both groups. Plasma concentration of caspase-1 and IL-1βwere higher in INR compared to IR patients. No differences in microbial translocation markers could be detected between the two groups. Conclusions: Increased immune activation levels and percentage of Th17 T cells and higher levels of inflammasome and caspase-1 expression are observed in INR patients. The upregulation of these pro-inflammatory mechanisms plausibly contributes to the persistent immune activation that characterize INRs. Notably, caspase-1 activation is likely to induce CD4+ T cell loss via pyroptosis, contributing to the unsatisfactory CD4+ T cell recovery seen in INRs.