Transient EZH2 Suppression by Tazemetostat during In Vitro Expansion Maintains T-Cell Stemness and Improves Adoptive T-Cell Therapy

The histone methyltransferase enhancer of zeste homolog 2 (EZH2) plays important roles in T-cell differentiation, proliferation, and function. Previous studies have demonstrated that genetic deletion of EZH2 in CD8+ or total T cells impairs their antiviral and antitumor activities, cytokine production, and ability to expand upon rechallenge. Contrary to the detrimental role of deleting T cell-intrinsic EZH2, in this study, we demonstrated that transient inhibition of EZH2 in T cells prior to the phenotypic onset of exhaustion with a clinically approved inhibitor, tazemetostat (Taz), delayed their dysfunctional progression and preserved T-cell stemness and polyfunctionality but had no negative impact on cell proliferation. Taz-induced T-cell epigenetic reprogramming increased the expression of the self-renewal T-cell transcription factor TCF1 by reducing H3K27 methylation at its promoter preferentially in rapidly dividing T cells. In a murine melanoma model, T cells depleted of EZH2 induced poor tumor control, whereas adoptively transferred T cells pretreated with Taz exhibited superior antitumor immunity, especially when used in combination with anti-PD-1 blockade. Collectively, these data highlight the potential of transient epigenetic reprogramming by EZH2 inhibition to enhance adoptive T-cell immunotherapy.