The immune checkpoint LAG-3 is expressed by melanoma cells and correlates with clinical progression of the melanoma.

Immune checkpoint blockers have substantially improved prognosis of melanoma patients, nevertheless, resistance remains a significant problem. Here, intrinsic and extrinsic factors in the tumor microenvironment are discussed, including the expression of alternative immune checkpoints such as lymphocyte activation gene 3 (LAG-3) and T-cell immunoglobulin and mucin domain-containing protein 3 (TIM-3). While most studies focus on immune cell expression of these proteins, we investigated their melanoma cell intrinsic expression by immunohistochemistry in melanoma metastases of 60 patients treated with anti-programmed cell death protein 1 (PD-1) and/or anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) therapy, and correlated it with the expression of potential ligands, RNA sequencing data and clinical outcome. LAG-3 and TIM-3 were commonly expressed in melanoma cells. In the stage IV cohort, expression of LAG-3 was associated with M1 stage (p < 0.001) and previous exposure to immune checkpoint inhibitors (p = 0.029). Moreover, in the anti-PD-1 monotherapy treatment group patients with high LAG-3 expression by tumor cells tended to have a shorter progression-free survival (p = 0.088), whereas high expression of TIM-3 was associated with a significantly longer overall survival (p = 0.007). In conclusion, we provide a systematic analysis of melanoma cell intrinsic LAG-3 and TIM-3 expression, highlighting potential implications of their expression on patient survival.