Abstract

Tumor-derived exosomes carry programmed death-ligand 1 (PD-L1), which binds programmed cell death protein 1 (PD-1) on T cells, suppressing immune responses locally and systemically. However, the mechanisms governing exosomal PD-L1 sorting and secretion remain elusive. Here, we identify Munc13-4 as a crucial regulator of this process. Deletion of Munc13-4 in breast tumors enhances T cell-mediated anti-tumor immunity, suppresses tumor growth, and improves the efficacy of immune checkpoint inhibitors. Mechanistically, Munc13-4 collaborates with hepatocyte growth factor-regulated tyrosine kinase substrate (HRS), Rab27, and SNAREs to facilitate PD-L1 sorting and secretion via exosomes. Cryogenic electron microscopy (cryo-EM) analysis of the Munc13-4-Rab27a complex provide structural insights into exosome secretion. Importantly, PD-L1 sorting relies on a ternary complex composed of Munc13-4, PD-L1 and HRS, which is regulated by interferon gamma (IFNγ) signaling. A designed peptide that disrupts Munc13-4-PD-L1 interaction impedes PD-L1 sorting, enhances antitumor immunity, and suppresses tumor growth, highlighting the therapeutic potential of targeting this pathway.