Targeting of interleukin (IL)-17A inhibits PDL1 expression in tumor cells and induces anticancer immunity in an estrogen receptor-negative murine model of breast cancer

The expression of IL-17A and programmed death ligand 1 (PDL1) is increased in estrogen receptor-negative breast cancer. IL-17A promotes tumor cell survival and invasiveness and inhibits the antitumor immune response. The PDL1–PD1 (programmed death protein 1) signaling pathway promotes escape from immune surveillance in tumor cells. The pro-tumor properties of IL-17A and PDL1 in various cancers have been previously examined; however, the relationship and roles of IL-17A and PDL1 in ER-negative breast cancer have not been evaluated. Therefore, we assessed whether IL-17A promotes PDL1 expression in tumor cells and whether targeting of IL-17A could inhibit ER-negative breast cancer progression in a murine model. Our study revealed that IL-17A promoted PDL1 expression in human and mouse cells. In the murine cancer model, targeting of IL-17A inhibited PDL1 expression in the tumor microenvironment, decreased the percentage of Treg cells in tumor-infiltrating lymphocytes, and promoted CD4(+) and CD8(+) T cells to secrete interferon gamma. More importantly, treatment with combined anti-IL-17A and anti-PDL1 antibodies enhanced antitumor effects in favor of tumor eradication. Thus, our study established a pro-tumor role of IL-17A in promoting tumor immune escape and supports the development of a novel cytokine immunotherapy against breast cancer.