Targeting DNMT1 augments anti-tumor CD8⁺ T cell function

Chronic stimulation of CD8⁺ T cells within the tumor microenvironment (TME) induces a hypofunctional state characterized by diminished cytotoxicity and functionally impaired anti-tumor function, known as exhaustion. Exhaustion is associated with epigenetic changes that remain relatively stable despite interventions like immune checkpoint inhibition (ICI). Although epigenetic changes are potentially reversible, reports of therapeutic strategies to effectively restore function in exhausted CD8⁺ T cells remain limited. Here, we report DNA methyltransferase 1 (DNMT1) inhibition (DNMT1i) in counteracting CD8 ⁺ T cell dysfunction during the anti-tumor response. We show that DNMT1i synergizes with ICI to rescue the tumor cell killing activity of chronically stimulated CD8⁺ T cells in a melanoma model. DNMT1i mitigates transcriptional features of exhaustion while inducing a divergent effector program. DNMT1i attenuates the global increase in chromatin accessibility associated with exhaustion and enables epigenetic remodeling of the exhausted chromatin landscape upon restimulation. Finally, DNMT1i enhances the effector function of melanoma patient-derived tumor infiltrating lymphocytes after prolonged ex vivo expansion. These studies establish DNMT1 targeting as a promising strategy to counteract CD8⁺ T cell exhaustion and potentiate ICI efficacy.