Juxtacrine Signaling Inhibits Antitumor Immunity by Upregulating PD-L1 Expression.

Programmed death-ligand 1 (PD-L1) is a well-known immune checkpoint protein that helps cancer cells evade immune response. Anti-PD-L1 immune therapy has been approved for the treatment of several advanced human cancers. Therefore, further understanding of the regulatory mechanisms of PD-L1 is critical to improve PD-L1-targeting immunotherapy. Recent studies indicated that contact-dependent pathways may regulate anticancer immunity, highlighting the importance of cell contact-induced signaling in cancer immunity. Here, we show that tumor cell contact upregulates PD-L1 expression and reduces T-cell-mediated cell killing through the membrane receptor tyrosine kinase ephrin receptor A10 (EphA10), which is not expressed in normal tissues except testis and is known to mediate cell contact-dependent juxtacrine signaling. Knockout of EphA10 in tumor cells increased T-cell-mediated antitumor immunity in syngeneic mouse models. EphA10 expression also correlated positively with PD-L1 in human breast tumor tissues. Together, our data reveal that in addition to paracrine/autocrine signaling, cell contact-mediated juxtacrine signaling also promotes PD-L1 expression, implying that tumor cells may escape immune surveillance via this mechanism and that targeting EphA10 to boost antitumor immunity may be a new immune checkpoint blockade strategy for female patients with breast cancer.Significance: Regulation of PD-L1 expression by cell contact-mediated signaling promotes immune escape in breast cancer and may lead to the development of an immunotherapy with less adverse effects in female patients. Cancer Res; 78(14); 3761-8. ©2018 AACR.