CRISPR/Cas9-Mediated Gene Knockout Reveals a Nonredundant Role for p16INK4A in Controlling TCR-Dependent and Independent CD8 T Cell Expansion.

The possibility of enhancing T cell function by deleting specific genes represents a long-sought goal in preclinical studies and ultimately for clinical applications. Using CRISPR/Cas9 genome editing, we report that, in human cytotoxic CD8 T cell clones, the cell cycle checkpoint gene CDKN2A, encoding p16INK4A, plays a nonredundant role in controlling T cell receptor (TCR)-dependent and independent cell expansion. Deletion of CDKN2A dramatically enhanced antigen-driven and homeostatic proliferation, while preserving effector functions. In contrast, the deletion of other cell cycle inhibitors (CDKN1B, CDKN2C, and CDKN2D), alone or in combination, had no impact on T cell proliferation. We also report that mediator complex subunit 12 (MED12) and the E3 ubiquitin ligase CBL-B deletions did not affect proliferative capacity of CD8 T cell clones. Interestingly, deletion of the negative regulator of Ras signaling, RASA2, increased antigen sensitivity and cytotoxic activity, while not improving in vitro expansion. Collectively, these findings reveal a unique and critical nonredundant role for p16INK4A in regulating CD8 T cells. Deletion of CDKN2A offers a promising strategy to enhance CD8 T cell expansion ex vivo, thereby improving TCR discovery pipelines and, potentially, therapeutic applications.