Interleukin‐17 is associated with expression of programmed cell death 1 ligand 1 in ovarian carcinoma

The programmed cell death 1/programmed cell death 1 ligand 1 pathway was successfully targeted in cancer immunotherapy. Elevated interleukin‐17 (IL‐17), which is known in autoimmune diseases, has recently been recognized in cancer patients. We investigated the role of IL‐17 in the regulation of expression of programmed cell death 1 ligand 1 in ovarian cancer by evaluating changes in the number of IL‐17‐producing cluster of differentiation 4 helper T cells (Th17) and γδT cells (γδT17) in PBMC of 52 gynecological cancer patients (including 30 ovarian cancer patients) and 18 healthy controls. The occupancy ratio of Th17 and γδT17 was higher in ovarian cancer and endometrial cancer patients than in controls, determined by multi‐color flow cytometry (Th17: P < 0.0001 and P = 0.0002, respectively; γδT17: P = 0.0020 and P = 0.0084, respectively). IL‐17 mRNA level was elevated in PBMC of ovarian cancer patients (P = 0.0029), as measured by RT‐PCR. The neutrophil‐to‐lymphocyte ratio, which is a prognostic biomarker of ovarian cancer, correlated with Th17 occupancy ratio in patients (P = 0.0068). We found that programmed cell death 1 ligand 1 expression and its associated factors (IL‐6 and phospho‐signal transducer and activator of transcription 3) were induced by IL‐17 in an ovarian cancer cell line. These results suggest that increased Th17 counts and IL‐17 level, which correlated with high neutrophil‐to‐lymphocyte ratio and programmed cell death 1 ligand 1 expression, are potential biomarkers for poor prognosis in ovarian cancer and likely indications for application of programmed cell death 1 ligand 1 pathway inhibitors.