Deng et al. found that hypoxia in the tumor microenvironment induces HIF-1α to bind to a conserved hypoxia response element on the VISTA promoter, upregulating VISTA expression on leukocytes, particularly on MDSCs. VISTA expression was critical to the capacity of MDSCs to suppress T cell activity under hypoxic conditions. High expression of VISTA in patients with colon cancer was associated with poor survival. Although untested, targeting both VISTA and PD-L1, which is also regulated by hypoxia and non-redundantly contributes to the suppressive phenotype of MDSCs, would likely be synergistic.
Tumor hypoxia is a negative prognostic factor that is implicated in oncogenic signal activation, immune escape, and resistance to treatment. Identifying the mechanistic role of hypoxia in immune escape and resistance to immune checkpoint inhibitors may aid identification of therapeutic targets. We and others have shown that V-domain Ig suppressor of T-cell activation (VISTA), a negative checkpoint regulator in the B7 family, is highly expressed in the tumor microenvironment in tumor models and primary human cancers. In this study, we show that VISTA and HIF-1alpha activity are correlated in a cohort of colorectal cancer patients. High VISTA expression was associated with worse overall survival. We used the CT26 colon cancer model to investigate the regulation of VISTA by hypoxia. Compared to less hypoxic tumor regions or draining lymph nodes, regions of profound hypoxia in the tumor microenvironment were associated with increased VISTA expression on tumor-infiltrating myeloid-derived suppressor cells (MDSCs). Using chromatin immunoprecipitation and genetic silencing, we show that hypoxia-inducible factor (HIF)-1alpha binding to a conserved hypoxia response element in the VISTA promoter upregulated VISTA on myeloid cells. Further, antibody targeting or genetic ablation of VISTA under hypoxia relieved MDSC-mediated T-cell suppression, revealing VISTA as a mediator of MDSC function. Collectively, these data suggest that targeting VISTA may mitigate the deleterious effects of hypoxia on antitumor immunity.