miR-155 enhances PRC2 activity via polycomb-like protein Phf19 to sustain T cell antitumor immunity [ChIP-Seq]

The microRNA miR-155 is essential for CD8+ T cell antiviral and antitumor immunity but the mechanisms behind its activity remain unresolved. Here, we show that miR-155 increased CD8+ T cell antitumor function by restraining T cell senescence and functional exhaustion through epigenetic silencing of key drivers of effector differentiation. miR-155 enhanced the function of polycomb repressor complex 2 (PRC2) indirectly by promoting the expression of the PRC2 cofactor Phf19 via AKT signaling. Phf19 orchestrated a transcriptional program extensively shared with miR-155 to enhance T cell engraftment, polyfunctionality, and antitumor immunity. These effects were dependent on the histone-binding capacity of Phf19 which is critical for the PRC2 recruitment to chromatin. These findings establish miR-155–Phf19–PRC2 as a pivotal axis regulating CD8+ T cell differentiation. Targeting the microRNA–polycomb-group protein circuitry is a promising route to potentiate cancer immunotherapy through epigenetic reprogramming of CD8+ T cell fate.