Exosomal PD-L1 harbors active defense function to suppress T cell killing of breast cancer cells and promote tumor growth

Dear Editor,

The tumor-microenvironment interactions play important roles in tumor progression, metastasis, and therapeutic resistance,¹ and increasing evidence indicates that tumor cell-derived exosomes can systematically modulate or reprogram the tumor microenvironment by transferring molecules, such as microRNAs, mRNAs, and proteins from donor cells to recipient cells.² PD-L1 is a classical immune surface protein, which inhibits anti-tumor function of T cells by binding to its receptor programmed cell death-1 (PD-1) and effectively protects tumor from immune surveillance.³ Exosomes have been reported to contain certain types of proteins, including membrane proteins, e.g., EGFR and MET, that promote cancer metastasis.^4,5 As a membrane-bound protein, whether PD-L1 exists in cancer cell-derived exosomes and whether it plays a role in tumor progress are largely unknown.

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