Background
Understanding the mechanisms responsible for the persistence of the virus reservoir under ART is essential to develop novel HIV cure approaches. Upregulation of the anti-apoptotic protein B cell lymphoma-2 (BCL-2) has been observed in HIV-Gag+CD4+ T cells from ART treated people living with HIV, along with an enrichment for intact proviral DNA in cells with high BCL-2 expression. These data suggest high levels of BCL-2 may help HIV-Gag+CD4+ T cells with intact provirus to evade apoptosis and enter long-term survival. Here we used BCL-2 inhibition in ART-suppressed SIV-infected Rhesus macaques (RM) to promote reservoir clearance in vivo.
Methods
29 adult RMs were infected with SIVmac239M for 8 weeks followed by daily ART for >90 weeks. To induce SIV expression under ART, we employed the previously established model of CD8a+ T cell depletion combined with IL-15 treatment. 23 RMs were given the CD8a depleting antibody MT807R1 followed by 7 doses of heterologous IL-15 across 21 days. 17 CD8a depleted RMs were administrated 10 doses of Venetoclax (300 mg) in the same period. 9 Venetoclax treated RM were given 4 SIV env protein monoclonal antibodies (RhmAbs) one day prior to CD8a depletion. All RM were followed until elective necropsy at 84 days post CD8a depletion.
Results
On day 7, following the first full cycle of Venetoclax, RM were observed to have elevated frequency (p<0.0001) of Caspase-3+CD4+ cells. We observed a significant decrease in the frequency of intact proviral DNA from this same time point (p=0.0267), followed by a further reduction 35 days after the last intervention (day 56; p<0.0001). A decline in total CD4+ T cells was observed in all MT807R1 treated RMs by day 7 post depletion concurrent with a rise in plasma viremia, however the CD4+ T cell compartment fully reconstituted in venetoclax treated RMs and even expanded by day 56. Adjusting for changes in CD4+ T cell count in whole blood showed the decreased copy number of intact proviral DNA in venetoclax treated RMs was maintained (p=0.0129).
Conclusions
In summary, BCL-2 antagonism decreased the frequency of peripheral CD4+ T cells with intact provirus in ART-treated SIV-infected RM after induction of virus expression. The reservoir reduction was maintained after CD4+ T cell re-population at day 56 post CD8 depletion, suggesting preferential loss of SIV-infected cells. These data support further exploration of BCL-2 antagonism as a tool to reduce reactivated virus reservoir under ART.