Background
HIV reservoirs in CD4⁺ T cells may be selected for the ability to evade immune clearance, hindering HIV cure efforts. Overexpression of enhancer of zeste homolog 2 (EZH2) in HIV-infected CD4⁺ T cells that survive cytotoxic T lymphocyte (CTL) exposure suggests a putative mechanism of immune resistance. This study investigated whether inhibition of EZH2 with the FDA-approved drug tazemetostat (taz) can enhance immune-mediated elimination of HIV reservoirs.
Methods
We performed RNA sequencing on in vitro HIV-infected CD4⁺ T cells that survived CTL exposure to assess EZH2 expression. The impact of taz on MHC-I expression and CTL-mediated killing was also evaluated in vitro using primary CD4⁺ T cells from people with HIV (PWH) (n=6). Viral inhibition assays with or without taz treatment measured suppression of HIV replication over seven days. In a participant-derived xenograft (PDX) mouse model, we examined the effects of taz on MHC-I expression, reservoir seeding, and CD8⁺ T-cell phenotypes, including exhaustion markers.
Results
EZH2 was significantly overexpressed in HIV-infected CD4⁺ T cells that survived CTL exposure (p.adj. <0.05). In vitro taz treatment reduced H3K27me3 levels and increased surface MHC-I expression by 1.4-fold on CD4⁺ T cells, counteracting HIV Nef–mediated MHC-I downregulation. This enhancement improved CTL-mediated elimination of HIV-infected cells by up to 90% and significantly suppressed viral replication. In the PDX mouse model, taz increased expression of MHC-I and the pro-apoptotic protein BIM in CD4⁺ T cells, facilitating CD8⁺ T-cell–mediated reduction of HIV reservoir seeding. Mice treated with both taz and autologous CD8⁺ T cells showed a significant decrease in intact HIV proviruses compared to controls (p.adj <0.05). Additionally, taz promoted sustained skewing of CD8⁺ T cells toward less differentiated (increased TCF-1) and less exhausted (lower PD-1) phenotypes, persisting for at least 79 days post-treatment.
Conclusions
Our findings identify EZH2 overexpression as a novel mechanism of CTL-resistance in HIV-infected CD4⁺ T cells. Inhibition of EZH2 with tazemetostat enhances immune recognition and elimination of these cells by increasing MHC-I expression and modulating apoptotic pathways. The reduction in HIV reservoir formation and improvement in CD8⁺ T-cell phenotypes support tazemetostat as a therapeutic strategy to enhance clearance of HIV reservoirs. These results warrant clinical evaluation of tazemetostat in PWH towards a cure for HIV.