Prognostic significance of PD-1/PD-L1 expression in uveal melanoma: correlation with tumor-infiltrating lymphocytes and clinicopathological parameters.

BACKGROUND: To understand how to improve the effect of immune checkpoint inhibitors in uveal melanoma (UM), we need a better understanding of the expression of PD-1 and PD-L1, their relation with the presence of tumor-infiltrating lymphocytes (TILs), and their prognostic relevance in UM patients.
MATERIALS AND METHODS: Expression of PD-1 and PD-L1 was assessed in 71 UM tissue samples by immunohistochemistry and quantitative real-time PCR (qRT-PCR), and further validated by western blotting. The effect of interferon gamma (IFN-γ) on PD-1/PD-L1 expression was determined on four UM cell lines.
RESULTS: Immunoreactivity of PD-1 was found in 30/71 cases and of PD-L1 in 44/71 UM samples. Tumor-infiltrating lymphocytes were found in 46% of UM tissues. PD-1 was expressed on TILs while tumor cells expressed PD-L1. UM with and without TILs showed expression of PD-1 in 69% and 18% cases, respectively (p = 0.001). Similarly, PD-L1 was found in 75% of UM with TILs and in 50% of cases without TILs, respectively (p = 0.03). DFS rate were lower in patients with TILs with expression of PD-1 and PD-L1, but the rate of DFS was higher with expression of PD-L1 in patients without TILs. After treatment of UM cell lines with IFN-γ, PD-1 expression was induced in all UM cell lines whereas PD-L1 expression was found at a lower level in untreated cells, while expression also increased following treatment with IFN-γ.
CONCLUSION: Our study suggests that increased infiltration with TILs promotes the aggressive behavior and suppresses the immune response of UM cells, thereby inhibiting immunotherapy.