Programmed Cell Death-Ligand 1 (PD-L1) Immunohistochemical Expression in Equine Melanocytic Tumors.

Simple Summary: Programmed cell death-ligand 1 (PD-L1) is expressed by several tumors, promoting tumoral immunosuppression by binding to programmed cell death protein (PD-1). PD-1/PD-L1 blockade in human melanoma has been shown to result in tumor regression and prolonged tumor-free survival. Since there are only a few available treatments for equine melanoma, the search for new therapies is important. This work intended to study the immunolabeling of PD-L1 in equine melanocytic tumors. A total of 77 melanocytic tumors were classified as benign or malignant and evaluated by extension of labeling. A total of 59.7% of the tumors showed >50% of immunolabeled cells. Regarding malignant tumors (n = 38), 24 tumors presented >50% of labeled cells, 13 tumors presented between 25–50% and one tumor presented <10%. Regarding benign tumors (n = 39), 22 tumors presented >50% of labeled cells, nine tumors presented 25–50%, three tumors presented 10–25%, two tumors presented <10% and three tumors did not present expression. The results of this study suggest that PD-L1 may have therapeutic potential for equine melanomas. Currently available treatments for equine melanocytic tumors have limitations, mainly due to mass localization and dimension, or the presence of metastases. Therefore, a search for new therapies is necessary. Programmed cell death-ligand 1 (PD-L1) is expressed by several tumors, blocking T cell-mediated elimination of the tumor cells by binding to programmed cell death protein 1 (PD-1). A novel therapeutic approach using PD-1/PD-L1 blockade in human melanoma resulted in tumor regression and prolonged tumor-free survival. This study aimed to evaluate the immunohistochemical expression of PD-L1 in equine melanocytic tumors. A total of 77 melanocytic tumors were classified as benign or malignant and evaluated by extension of labeling. A total of 59.7% of the tumors showed >50% of immunolabeled cells. Regarding malignant tumors, 24/38 tumors presented >50% of labeled cells, 13 tumors presented between 25–50% and one tumor presented <10%. Regarding benign tumors, 22/39 tumors presented >50% of labeled cells, nine tumors presented 25–50%, three tumors presented 10–25%, two tumors presented <10% and three tumors did not present expression. Our results suggest that PD-L1 blockade may be a potential target for immunotherapy in equine melanocytic tumors and that future clinical research trials into the clinical efficacy of the anti-PD-L1 antibody are necessary. [ABSTRACT FROM AUTHOR]