Role of Viral Reservoirs in the Pathogenesis of HIV Disease

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Well over a decade ago, we demonstrated that the latent viral reservoir in the resting CD4+ T cell compartment persists in virtually all HIV-infected individuals receiving clinically effective ART. In addition, we demonstrated that HIV continually replicates at low levels in some chronically infected individuals who are consistently aviremic while receiving ART. Based on these findings and similar observations from other groups, the persistent viral reservoir has become a major impediment to the eradication of HIV in infected individuals receiving ART. Consequently, a major emphasis of HIV therapeutic research is the development of strategies to eliminate HIV reservoirs and to achieve ART-free virologic remission in infected individuals. Considering that the complete eradication of HIV is not currently feasible in the majority of infected individuals, new approaches aimed at containing viral replication are being considered. The goal is not necessarily to achieve complete eradication of the virus, but rather to boost HIV-specific immune responses (using therapeutic agents) in order to keep plasma viremia suppressed after discontinuation of ART. Given the vast majority of HIV-infected individuals experience plasma viral rebound upon cessation of therapy, the ultimate evaluation of the efficacy of a therapeutic agent in achieving sustained virologic suppression would require discontinuation of ART. Historical data regarding the time to viral rebound following ATI have been used to determine therapeutic efficacy in HIV cure trials. However, much of these historical data were collected from studies conducted a decade or more ago (prior to the introduction of currently available and highly potent ART regimens) and included study participants who were pre-treated with mono/dual therapies, received therapeutic interventions, were subjected to infrequent monitoring, and reinitiated ART under different criteria. Therefore, it is of great importance to conduct a clinical trial involving frequent measurements of multiple parameters to provide contemporary assessments/reference on the effect of modern ART regimens on plasma viral rebound following ATI for future curative studies. We conducted a single-arm study of 22 participants with HIV who initiated highly effective ART during the chronic phase of infection and were receiving modern drug regimens to determine 1) the kinetics of plasma viral rebound following ATI, 2) relationships between baseline virologic and immunologic parameters and timing of viral rebound, and 3) immune correlates of viral decay upon ART resumption. At baseline, the vast majority of study participants were receiving integrase strand transfer inhibitor-based regimens (90%) and suppressed plasma viremia below the limits of detection for a median of 7.7 years. All participants experienced plasma viral rebound shortly after ATI. The median time to plasma viral rebound >40 and >200 copies/ml was 1.9 and 2.6 weeks, respectively. The median time to meeting ART restart criteria was 4.9 weeks. Reasons for ART resumption included decreased CD4+ T cell counts (50%), sustained plasma viremia (35%), and thrombocytopenia (15%). We then evaluated the relationship between baseline virologic and immunologic parameters and time to plasma viral rebound following ATI. Frequencies at baseline of CD4+ T cells carrying total HIV DNA (P=0.024) but not cell-associated HIV RNA (P=0.883) nor replication-competent virus (P=0.136) correlated with time to viral rebound >200 copies/ml. Numbers or frequencies at baseline of CD4+, CD38+HLA-DR+CD8+, and CD226+TIGIT-CD8+ T cells correlated with time to plasma viral rebound >200 copies/ml (P=0.037, P=0.021, and P=0.012, respectively). Finally, we evaluated factors that may affect the decay of plasma viremia following the reinitiation of ART. When the participants were divided into early (4 weeks) versus delayed (>4 weeks) groups based on the time to reach <40 copies/ml upon reinitiation of ART, the delayed group had higher plasma viremia at the end of the ATI phase (P=0.016) and higher CD226+TIGIT-PD-1+CD8+ T cell frequencies at baseline, prior to ATI (P=0.0005), suggesting a potential role for immune exhaustion in the decay rate of antiretroviral drug-mediated plasma viremia. Our data suggest that modern ART does not alter kinetics of viral rebound when compared to previous regimens and that immunologic interventions may be necessary to achieve ART-free virologic remission. A number of bNAbs directed against HIV have recently been shown to prevent transmission of the virus, suppress viral replication, and delay plasma viral rebound following discontinuation of ART in animal models and infected humans. However, the degree and extent to which such bNAbs interact with primary lymphocytes have not been fully delineated. We evaluated the binding capacity of several bNAbs to HIV Env expressed on a chronically infected cell line as well as subsets of peripheral blood mononuclear cells (PBMCs) isolated from HIV-infected and uninfected individuals. As expected, these bNAbs exhibited high levels of binding to cell lines expressing HIV Env. However, unexpectedly, the glycan-dependent bNAbs PGT121 and PGT151 were found to bind to B, activated T, and natural killer (NK) cells of both HIV-infected and -uninfected individuals. The binding of these bNAbs to stimulated B cells and CD4+ and CD8+ T cells increased over time but significantly decreased in the presence of the glycosylation pathway inhibitor, kifunensine, suggesting that these bNAbs interacts with complex-type glycans expressed on the surface of uninfected targets. In addition, the binding of PGT121 to EBV-transformed B cell lines derived from two donors with a congenital disorder in glycosylation (type IIb) was significantly reduced compared to cell lines derived from healthy donors. Furthermore, incubation of primary NK cells with PGT151 rapidly led to auto-degranulation and cell death, suggesting that certain bNAbs can potentially mediate deleterious effector functions against immune cells ex vivo. Our data suggest that the propensity of certain bNAbs to bind uninfected/bystander cells has the potential for unexpected outcomes in passive transfer studies in humans and underscore the importance of antibody screening against uninfected and/or activated primary lymphocytes.