Tumor-Intrinsic PD-L1 Signals Regulate Cell Growth, Pathogenesis, and Autophagy in Ovarian Cancer and Melanoma

Cancer Res. 2016 Dec 1;76(23):6964-6974. doi: 10.1158/0008-5472.CAN-16-0258. Epub 2016 Sep 26.


PD-L1 antibodies produce efficacious clinical responses in diverse human cancers, but the basis for their effects remains unclear, leaving a gap in the understanding of how to rationally leverage therapeutic activity. PD-L1 is widely expressed in tumor cells, but its contributions to tumor pathogenicity are incompletely understood. In this study, we evaluated the hypothesis that PD-L1 exerts tumor cell-intrinsic signals that are critical for pathogenesis. Using RNAi methodology, we attenuated PD-L1 in the murine ovarian cell line ID8agg and the melanoma cell line B16 (termed PD-L1lo cells), which express basal PD-L1. We observed that PD-L1lo cells proliferated more weakly than control cells in vitro As expected, PD-L1lo cells formed tumors in immunocompetent mice relatively more slowly, but unexpectedly, they also formed tumors more slowly in immunodeficient NSG mice. RNA sequencing analysis identified a number of genes involved in autophagy and mTOR signaling that were affected by PD-L1 expression. In support of a functional role, PD-L1 attenuation augmented autophagy and blunted the ability of autophagy inhibitors to limit proliferation in vitro and in vivo in NSG mice. PD-L1 attenuation also reduced mTORC1 activity and augmented the antiproliferative effects of the mTORC1 inhibitor rapamycin. PD-L1lo cells were also relatively deficient in metastasis to the lung, and we found that anti-PD-L1 administration could block tumor cell growth and metastasis in NSG mice. This therapeutic effect was observed with B16 cells but not ID8agg cells, illustrating tumor- or compartmental-specific effects in the therapeutic setting. Overall, our findings extend understanding of PD-L1 functions, illustrate nonimmune effects of anti-PD-L1 immunotherapy, and suggest broader uses for PD-L1 as a biomarker for assessing cancer therapeutic responses. Cancer Res; 76(23); 6964-74. ©2016 AACR.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Autophagy
  • B7-H1 Antigen / genetics*
  • B7-H1 Antigen / metabolism
  • Cell Line, Tumor
  • Cell Proliferation
  • Female
  • Humans
  • Melanoma / genetics*
  • Mice
  • Mice, Knockout
  • Ovarian Neoplasms / genetics*
  • Ovarian Neoplasms / pathology
  • Signal Transduction
  • Transfection


  • B7-H1 Antigen
  • CD274 protein, human