TMED10 inhibition suppresses cell-surface PD-1 expression and overcomes T cell dysfunction

PD-1 immune checkpoint blockade (ICB) is revolutionizing cancer therapy, but little is known about the mechanisms governing its expression. In a whole-genome, dual- marker FACS-based CRISPR-Cas9 screen in primary murine CD8 T cells, we found that inactivation of the EMP24/GP25L/p24 protein family, most prominently TMED10, reduced PD-1 cell-surface stability, thereby augmenting T cell activity. Treatment with TMED inhibitor AGN192403 led to lysosomal degradation of the TMED-PD-1 complex and reduced PD-1 expression in intratumoral CD8 T cells in mice, thus reversing T cell dysfunction. Clinically corroborating these findings, single-cell RNA analyses revealed a positive correlation between TMED expression in tumor-infiltrating CD8 T cells (TIL), and both a T cell dysfunction signature and lack of ICB response. Similarly, patients receiving a TIL product with high TMED expression had a shorter overall survival. Our results uncover a novel mechanism of PD-1 regulation, and provide a possible opportunity for PD-1 small molecule inhibition