Modified Hypoxia-Inducible Factor Expression in CD8+ T Cells Increases Antitumor Efficacy

Abstract

Adoptive transfer of antitumor cytotoxic T cells is an emerging form of cancer immunotherapy. A key challenge to expanding the utility of adoptive-cell therapies is how to enhance the survival and function of the transferred T cells. Immune-cell survival requires adaptation to different microenvironments, and particularly to the hypoxic milieu of solid tumors. The hypoxia-inducible factor (HIF) transcription factors are an essential aspect of this adaptation. In this study, we undertook experiments to define structural determinants of HIF that potentiate antitumor efficacy in cytotoxic T cells. We first created retroviral vectors to deliver ectopic expression of HIF1ɑ and HIF2ɑ in mouse CD8+ T cells, together or individually, and with or without sensitivity to the oxygen-dependent HIFɑ inhibitors Von Hippel-Lindau (VHL) and Factor Inhibiting HIF (FIH). HIF2ɑ, but not HIF1ɑ, drove broad transcriptional changes in CD8+ T cells, resulting in increased cytotoxic differentiation and cytolytic function against tumor targets. A specific mutation replacing the hydroxyl group-acceptor site for FIH in HIF2ɑ gave rise to the most effective antitumor T cells after adoptive transfer in vivo. In addition, co-delivering an FIH-insensitive form of HIF2ɑ with an anti-CD19 chimeric antigen receptor greatly enhanced cytolytic function of human CD8+ T cells against lymphoma cells both in vitro and in a xenograft adoptive transfer model. These experiments point to a means to increase the antitumor efficacy of therapeutic CD8+ T cells via ectopic expression of the HIF transcription factor.