ANALYSIS OF VIRAL RESERVOIRS IN CHRONICALLY SIV-INFECTED SOOTY MANGABEYS TREATED WITH COMBINATION ANTIRETROVIRAL THERAPY (CART)

Background: Human Immunodeficiency Virus (HIV), the causative pathogen of Acquired Immunodeficiency Syndrome (AIDS), continues to be a major global public health issue. Although, potent antiretroviral therapy (ART) has dramatically reduced the morbidity and mortality in HIV-infected individuals, one of the most consistent obstacles to HIV eradication is the presence of stable viral reservoirs of latently infected cells. The aim of the present study is to understand the mechanisms of the complex virus-host interactions that lead to persistent infection, and to achieve the ideal combination of therapies to eliminate HIV virus in an non human primate model, Sooty Mangabeys (SMs), that preserves CD4+ T cells homeostasis, avoiding the AIDS progression which occurs in Rhesus Macaque (RM) and humans. Materials and Methods: Twelve experimental chronically SIV-infected SMs, not homozygous for CCR5-null alleles and with viral load of 103-105 viral RNA copies/ml, were treated with combination antiretroviral therapy (cART) regimen consisting of Tenofovir, Emtricitabine, Raltegravir and Darunavir. The selected SMs were divided in four-treatment interruption groups receiving cART up to 2, 6, 9 and 12 months. Plasma viral loads were detected by RT PCR, while CD4+ T subsets dynamics and their proliferation and activation status were analyzed by flow cytometry in different anatomical compartments and prior to the treatment initiation and during the cART in all SMs. cART-induced variations in CD4+ T cell subsets susceptibility to SIV infection were evaluated through FACS procedure and cell-associated SIV-DNA assay. Results: No severe cART-related side effects, in terms of body weight and renal function indices were observed. Eleven out of twelve treated animals experienced a 2-3 log decline of plasma viremia at the earliest time points, below the level of detection. Although, analysis of total circulating CD4+ population showed minor changes in terms of frequency and absolute number, a significant recovery of CD4+ T cells in the mucosal compartment was observed. Interestingly, the study of CD4+ T cells subsets in the blood, highlighted a rapid and marked reduction of frequency and absolute count of effector memory (EM) and an expansion of central memory (CM) and memory stem cells (SCM) at early time point after ART initiation in SMs. cART resulted to be efficient in reducing immune activation levels on CD8+ T cells both in blood and mucosal compartments. In response to cART, a generalized reduction in SIV-infected CD4+ T cell subsets was observed and specifically in the fraction that represented the main virus source, i.e, EM and transitional memory T cells (TM). Analysis of cART interruption revealed that although, the group receiving cART for 2 months, experienced a rapid viral rebound after therapy interruption, interestingly, a control in viremia was observed after 6 months of cART in the treated animals. Conclusion: The four-drugs regimen proved to be safe, well tolerated with no discernible side effects and effective in suppressing viral replication in treated SMs. cART induced immunological changes and specifically a significant reduction of immune activation in both blood and mucosal compartments. A redistribution of CD4+ T cell subsets and a generalized decrease of CD4+ cellular subsets harboring virus in the early phases of treatment is a favorable scenario at promoting further reduction of SIV reservoirs or their clearance for prolonged cART periods (9-12 months).