Targeting ZMYND8 unleashes IL-2 signalling to override T cell exhaustion

CD8⁺ T cell exhaustion impedes control of chronic viral infection and cancer. This hypofunctional state is characterized by downregulation of the high-affinity IL-2 receptor (IL-2R) and STAT5 signalling, and differentiation from progenitor exhausted to terminally exhausted T cells rather than cytotoxic effector-like cells^1-3. The epigenetic mechanisms and regulatory networks that mediate IL-2R-STAT5 signal attenuation and loss of effector-like cell differentiation remain unknown. Here, using in vivo single-cell CRISPR screens of epigenetic factors and IL-2 signalling regulators, we reveal that the chromatin reader ZMYND8 antagonizes IL-2R-STAT5 signals to restrain effector-like states while promoting terminal exhaustion. ZMYND8 expression was upregulated by chronic antigen stimulation, and targeting ZMYND8 in CD8⁺ T cells promoted both intermediate exhausted T cells and killer cell lectin-like receptor-expressing exhausted T cells. Accordingly, ZMYND8-deficient CD8⁺ T cells had markedly improved antiviral and antitumour effects, especially in combination with IL-2 therapy or immune checkpoint blockade. Mechanistically, ZMYND8 bound to the active enhancer regions of the Il2ra gene locus that were co-occupied by histone acetyltransferase p300 and suppressed p300 activity. Co-deletion of p300 reversed increased IL-2R expression and effector-like cell differentiation in ZMYND8-deficient cells, suggesting that ZMYND8 represses p300-mediated transcriptional activation to curtail IL-2R-STAT5 signalling. These findings establish an epigenetic rheostat imposing 'signal 1' (chronic antigen stimulation)-induced suppression of 'signal 3' (IL-2 signalling) to enforce T cell exhaustion, with ZMYND8 deletion unleashing effector-like over terminally exhausted states and enhancing immunotherapeutic efficacy.