Increased homeostatic cytokines and stability of HIV-infected memory CD4 T-cells identify individuals with suboptimal CD4 T-cell recovery on-ART

Clinical outcomes are inferior for individuals with HIV having suboptimal CD4 T-cell recovery during antiretroviral therapy (ART). We investigated if the levels of infection and the response to homeostatic cytokines of CD4 T-cell subsets contributed to divergent CD4 T-cell recovery and HIV reservoir during ART by studying virologically-suppressed immunologic responders (IR, achieving a CD4 cell count >500 cells/μL on or before two years after ART initiation), and virologically-suppressed suboptimal responders (ISR, did not achieve a CD4 cell count >500 cells/μL in the first two years after ART initiation). Compared to IR, ISR demonstrated higher levels of HIV-DNA in naïve, central (CM), transitional (TM), and effector (EM) memory CD4 T-cells in blood, both pre- and on-ART, and specifically in CM CD4 T-cells in LN on-ART. Furthermore, ISR had higher pre-ART plasma levels of IL-7 and IL-15, cytokines regulating T-cell homeostasis. Notably, pre-ART PD-1 and TIGIT expression levels were higher in blood CM and TM CD4 T-cells for ISR; this was associated with a significantly lower fold-changes in HIV-DNA levels between pre- and on-ART time points exclusively on CM and TM T-cell subsets, but not naïve or EM T-cells. Finally, the frequency of CM CD4 T-cells expressing PD-1 or TIGIT pre-ART as well as plasma levels of IL-7 and IL-15 predicted HIV-DNA content on-ART. Our results establish the association between infection, T-cell homeostasis, and expression of PD-1 and TIGIT in long-lived CD4 T-cell subsets prior to ART with CD4 T-cell recovery and HIV persistence on-ART.
Author summary A major obstacle to curing HIV infection is our incomplete understanding of the mechanisms regulating the immunologic reconstitution of CD4 T-cells and the establishment and persistence of the latent HIV reservoir. In particular, we still do not know whether and to what extent the relative distribution of HIV infection within the various CD4 T-cell subsets influences: (i) the magnitude of the CD4 T-cell reconstitution, and (ii) the size of the persistent HIV reservoir after ART. In this study, we found that immunological suboptimal responders (ISR), people with HIV having a suboptimal CD4 T-cell recovery during ART, compared with immunological responders (IR) presented: i) higher levels of HIV-DNA in multiple CD4 T-cell subsets, and ii) higher expression of PD-1 and TIGIT exclusively on CM and TM CD4 T-cells pre-ART, indicating higher HIV reservoir maintenance. Paradoxically, we found increased plasma levels of IL-7 and IL-15 (T-cell homeostatic cytokines) be associated with suboptimal CD4 T-cell recovery during ART, which could be explained by the lack of response to these cytokines in CD4 T-cells from ISR. Altogether, these data identify a greater abundance of immune checkpoint molecules, an increased maintenance of HIV infection in long-lived CD4 T-cell subsets, and a different responsiveness to IL-7 and IL-15 as key features of and a mechanism for suboptimal CD4 T-cell recovery in ART-treated, people with HIV.