Background
The anti-apoptotic molecule BCL-2 promotes the establishment, maintenance, and expansion of the CD4 T cell reservoir. In SIV-infected rhesus macaque (RMs), we found that BCL-2 inhibition at antiretroviral therapy (ART) initiation (ARTi) promotes a rapid and sustained reduction of the SIV reservoir in blood CD4 T cells. To determine mechanisms for reservoir decrease, we assess the immunological impact of a BCL-2 inhibitor, venetoclax (vtx), in SIV-infected RMs.
Methods
24 RMs were infected with barcoded SIVmac239M and initiated ART at 14 days post-infection (p.i.). 8 RMs received ART alone; 8 RMs received 10 daily doses of vtx starting at ARTi; and 8 RMs received vtx in combination with a single dose of the anti-CD8a depleting antibody MT807R1 at ARTi. RMs were followed until d294 p.i. Immunological signatures in purified CD4 T cells were assessed at the end of vtx treatment (d25 p.i.) and of the follow-up period (d294 p.i.) by flow cytometry and RNA-seq.
Results
At d25 p.i., we found a reduction of central and effector memory CD4 T cells in RMs treated with vtx alone or with MT807R1. The remaining CD4 T cells showed significant enrichment of the “Regulation of apoptosis’ gene set, consistent with BCL-2 inhibition. Additionally, pathways such as ‘inflammasomes’ and ‘NOD signaling’ were enriched, with upregulation of CARD9, PYCARD, caspase-1, and caspase-4—key mediators of pyroptosis, an alternative cell death process. Notably, there was also increased expression of anti-apoptotic molecules like clusterin, NOL-3 and BCL-2, which counteract pro-apoptotic Bax, indicating activation of pathways promoting resistance to cell death following BCL-2 inhibition in the remaining cells. Consistently, genes associated with vtx resistance in cancer patients, such as BCL-XL, CLEC7A, and CD14, were upregulated in blood CD4 T cells. At d294 p.i., gene and pathway expression had normalized, except for the T-cell receptor beta chain variable region, which remained suppressed, suggesting vtx may reduce clonotype diversity during ART.
Conclusions
BCL-2 inhibition via vtx promotes rapid changes in gene expression within CD4+ T cells, associated with reduced size of the SIV reservoirs. While key cell death mediators were upregulated, anti-apoptotic mechanisms also emerged, suggesting resistance to BCL-2 inhibition. These findings provide a rationale for targeting BCL-2 in people with HIV and identifying additional anti-apoptotic molecules to target in a combination approach to eradicate the SIV reservoir.