Abstract 2163: Inhibition of HIF2A increases efficacy of immune checkpoint blockade in renal cell carcinoma

Abstract Hypoxia Inducible Factors (HIFs) are transcription factors implicated in cellular processes that are key to survival, proliferation, and function, particularly for cancer cells. In the context of clear cell renal cell carcinoma (ccRCC), HIF2A is an oncogenic driver of tumor growth via up-regulation of angiogenesis (VEGFA), cell cycling (CCND1), vascularization (EPO), and metabolism (GLUT1). HIF2A can be targeted by belzutifan (MK-6482), a first-in-class HIF2A inhibitor that is FDA-approved for VHL-associated and advanced ccRCC, significantly reducing tumor burden in patients. Both HIF1A and HIF2A are expressed by all cells in the hypoxic tumor microenvironment, including infiltrating immune cells, and HIFs have previously been implicated in T cell anti-tumor effector function. Several ongoing clinical trials are evaluating MK-6482 in combination with immune checkpoint blockade therapy for advanced ccRCC, however the potential impact that MK-6482 may directly have on the adaptive immune response remains poorly understood. Considering the functional link between HIF signaling and T cell function, we explored whether HIF-2A inhibition by MK-6482 could impact activation and/or anti-tumor action of T cells supported by anti-PD-1 and anti-CTLA-4 immune checkpoint blockade. Interrogation of primary T cell activation by mixed lymphocyte reaction revealed that MK-6482 did not induce significant changes in cytokine secretion (IFNg, IL-2) or cell proliferation with or without immune checkpoint blockade, despite evidence of HIF2A protein reduction in T cells. MK-6482 combined with immune checkpoint blockade resulted in almost complete tumor regression compared to either monotherapy in a ccRCC humanized mouse model. Histological analysis of tumors revealed a significant reduction in HIF2A protein following combined treatment, potentially driving the drastic tumor regression. By multiplexed IMC analysis, we found that tumors exhibited increased infiltration of CD4+ and CD8+ T cells with elevated markers of activation, proliferation, antigen-interaction, and cytotoxicity. mRNA sequencing of tumors also revealed increased expression of T cell activation pathways, further suggesting that the combination treatment induced greater anti-tumor activity of infiltrating T cells. Together, our data support ongoing clinical evaluation of belzutifan and checkpoint blockade combination treatment for ccRCC, and we continue to explore the potential mechanistic effects by both in vivo and in vitro follow-up studies. Citation Format: Katya Frazier, Eric Muise, Joshua Stolz, Lukas Fischer, Mark Buchanan, Charlie Schneider, Brian Pak Ho Chan, Richard Carr, Anthony Palmieri, Rodolfo Perini, Brian Long, Douglas Linn. Inhibition of HIF2A increases efficacy of immune checkpoint blockade in renal cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2163.