USE OF INTEGRASE INHIBITOR TO ASSESS THE CYTOTOXIC T LYMPHOCYTE RESPONSE DURING SIMIAN IMMUNODEFICIENCY VIRUS INFECTION IN RHESUS MACAQUES
Abstract: The host immune response against human immunodeficiency virus (HIV) infection is multi-faceted, with the cytotoxic T lymphocyte (CTL) response playing a significant role in controlling the virus. However, it is uncertain what mechanism(s) these CTLs utilize to suppress virus replication. Previous research utilizing mathematical modeling and nucleoside reverse transcriptase inhibitors (NRTIs) showed that CTLs most likely have a non-cytolytic effect against infected cells, but these data are not universally accepted in the field. I hypothesized that CTLs exert the majority of their cytolytic function against infected cells containing virus that has yet to be integrated, due to minimal viral cytopathic effects at this stage. To test this hypothesis, I modeled the impact of CD8+ T cells through experimental CD8+ cell depletion on the pre- and post-integration stages of simian immunodeficiency virus (SIV) infection on both plasma viral load and 2-LTR circles. Model predictions were tested in the pathogenic SIVmac251-infected rhesus macaques (RMs) receiving the integrase inhibitor raltegravir (RAL) monotherapy with or without CD8+ T cells. CD8+ T cell depletion was profound and lasted throughout RAL therapy, with administration resulting in an immediate and sustained suppression of CD8+ cells. CD4+ cells recovered slightly during RAL treatment. The estimated efficacy of RAL in preventing integration was 97%. We next calculated the loss rate of infected cells prior to integration and determined that this loss rate was reduced by 82% in the CD8+ cell depletion with RAL treatment group compared to the RAL monotherapy group, but also that viral production increased 2.5 times in the absence of CD8+ cells. Further, we observed that CD8+ cell depletion by itself increases 2-LTR circles, RAL monotherapy does not affect 2-LTR circle levels, and combination treatment increases 2-LTR circle levels faster than CD8 depletion alone. Upon fitting an extended viral dynamics model to the 2-LTR data, we conclude that the data best matches the hypothesis that CD8+ cells exert a killing effect on infected cells prior to integration, supporting our hypothesis. We attempted to analyze the effects of RAL intensification on 2-LTR circle dynamics, but we were unable to due to the development of resistance mutations, reinforcing the fact that in suboptimally ART-treated RMs, mutations do, indeed, occur, resulting in viral rebound during treatment. The public health significance of this dissertation is that by showing CD8+ cells kill cells containing virus prior to integration, we are aiding in the hunt for an elusive vaccine and/or cure against HIV.
Advisor: Ivona Vasile-Pandrea, MD, PhD