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Suppression of Exosomal PD-L1 Induces Systemic Anti-tumor Immunity and Memory.

  • Author(s): Poggio, Mauro;
  • Hu, Tianyi;
  • Pai, Chien-Chun;
  • Chu, Brandon;
  • Belair, Cassandra D;
  • Chang, Anthony;
  • Montabana, Elizabeth;
  • Lang, Ursula E;
  • Fu, Qi;
  • Fong, Lawrence;
  • Blelloch, Robert
  • et al.
Abstract

PD-L1 on the surface of tumor cells binds its receptor PD-1 on effector T cells, thereby suppressing their activity. Antibody blockade of PD-L1 can activate an anti-tumor immune response leading to durable remissions in a subset of cancer patients. Here, we describe an alternative mechanism of PD-L1 activity involving its secretion in tumor-derived exosomes. Removal of exosomal PD-L1 inhibits tumor growth, even in models resistant to anti-PD-L1 antibodies. Exosomal PD-L1 from the tumor suppresses T cell activation in the draining lymph node. Systemically introduced exosomal PD-L1 rescues growth of tumors unable to secrete their own. Exposure to exosomal PD-L1-deficient tumor cells suppresses growth of wild-type tumor cells injected at a distant site, simultaneously or months later. Anti-PD-L1 antibodies work additively, not redundantly, with exosomal PD-L1 blockade to suppress tumor growth. Together, these findings show that exosomal PD-L1 represents an unexplored therapeutic target, which could overcome resistance to current antibody approaches.

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