CARD11 Signaling Regulates CD8+ T Cell Tumoricidal Function.

Chronic stimulation in the tumor microenvironment can induce exhausted CD8+ T (Tex) cells that have limited tumoricidal activity. Here, we show an inverse correlation between signal strength and Tex cell differentiation by using patient-derived mutations in the T cell receptor (TCR)-signaling protein CARD11. Strong TCR signaling of the E134G mutant inhibits Tex cell differentiation and increases tumor growth. Conversely, reduced TCR signaling by the K215M mutant promotes Tex cell differentiation with better tumor control. These effects are a result of a restrained tumor-specific TCR clonal repertoire of Tex cells that reduces immunopathology but compromises tumoricidal activity. Mechanistically, CARD11 is a TCR signal-strength sensor, controlling the TCR repertoire of Tex cells by regulating the trafficking and homeostasis of the TCR complex. Expanding the TCR repertoire during Tex cell differentiation by fine-tuning the CARD11-mediated TCR signal strength reinvigorated antitumor function and indicates a strategy for improving cancer immunotherapy.