CRISPR screens identify targets to rescue age-related T cell dysfunction in cancer.

Immune aging is being increasingly recognized as a critical barrier to effective cancer immunotherapy, as the aged tumor microenvironment (TME) drives T cell dysfunction and impairs immune control of cancer. However, the key molecular drivers of this process as well as potential targets to rescue T cell dysfunction in aged tumors remain incompletely understood. Therefore, we performed in vivo single-cell CRISPR screens in CD8 T cells within aged tumors and tumor-draining lymph nodes (tdLNs). We identified Dusp5 and Zfp219 as key regulators of T cell persistence and effector differentiation in aged hosts. Loss of , a negative regulator of ERK signaling, increased ERK1/2 phosphorylation and enhanced T cell proliferation in both young and aged tumors. In contrast, loss of , a transcriptional repressor, induced epigenetic reprogramming of cytotoxic gene programs, thereby increasing granzyme secretion and enhancing antitumor immunity. Moreover, expression of the human ortholog gene is increased within intratumoral CD8 T cells in older cancer patients. High expression correlates with poorer survival following immune checkpoint blockade (ICB) and reduces persistence of human intratumoral T cells. Notably, ablation synergized with anti-PD-1 blockade in mice to expand effector-like CD8 T cells, leading to significantly enhanced anti-tumor immunity and tumor clearance in aged hosts. Together, these findings highlight Dusp5 and Zfp219 as critical drivers of age-related T cell dysfunction and as potential therapeutic targets to rejuvenate T cell antitumor immunity in older cancer patients.