HIV infection persists despite suppressive antiretroviral therapy (ART) and treatment interruption results in rapid viral rebound. Previous studies using antibody-mediated CD8+ lymphocyte depletion in simian immunodeficiency virus (SIV)-infected rhesus macaques (RM) showed that these cells suppress viremia in ART-naïve animals. However, the role of CD8+ lymphocytes during ART-mediated virus suppression is unknown. Using in vivo CD8+ lymphocyte depletion, we sought to elucidate whether CD8+ lymphocytes are required to maintain virus suppression in ART-treated SIV-infected RM.
13 rhesus macaques were infected IV with 3000 TCID50 of SIVmac239. At 8 weeks post SIV infection animals were put on a 4 drug ART regimen consisting of Tenofovir, Emtricitabine, Raltegravir, and Darunavir for the duration of the study. Once virus was undetectable, we administered the anti-CD8 antibody MT-807R1 intravenously (50 mg/kg). Plasma viral load and quantification of cell-associated SIVmac gag DNA was determined by RT- PCR. A next-generation, ultra-sensitive RNA in situ hybridization technology, RNAscope was used to visualize SIV-RNA+ cells in lymph nodes. Multiparametric flow cytometry was performed to monitor the immunological effects of the used interventions.
We found that in SIV-infected, ART-treated RMs, depletion of CD8+ lymphocytes results in increased virus production in both plasma and lymph nodes in 100% (13 out of 13 RM) of the treated animals. We also show that repopulation of CD8+ T cells (but not CD8+ NK cells) is associated with reestablishment of virus control. In addition, we found that the level of SIV-specific CD8+ T cells pre-CD8 depletion correlate with virus production after CD8 depletion. While the levels of SIV-DNA-positive cells remained unchanged after CD8+ lymphocyte depletion and reconstitution, the frequency of SIV-infected CD4+ T-cells pre-depletion positively correlates with both peak and area-under-the-curve of viremia post-depletion.
This study is the first to examine the effects of CD8+ lymphocyte depletion on SIV-infected rhesus macaques undergoing continuous ART. Our findings reveal a previously underappreciated role of CD8+ T cells in cooperating with ART to maintain virus suppression during therapy. We believe this study provides important rationale to further explore the potential effect of therapeutic vaccinations and check-point blockade inhibitors in ART-treated HIV-infected humans.