Implications of LAG3 and CTLA4 immune checkpoints beyond PD-1/PD-L1 as a potential target in determining the prognosis of uveal melanoma patients

BackgroundResponse rate of PD-1/PD-L1 immunotherapeutic blockade agents in uveal melanoma (UM) is poor. Lymphocyte activation gene 3 (LAG3) and cytotoxic T-lymphocyte-associated protein 4 (CTLA4) are the two promising immune checkpoint targets. Therefore, our aim was to explore at how these proteins were expressed in tumour tissue and serum, as well as their prognostic implications in UM.The expression of LAG3, CTLA-4, CD3, CD4, CD8 and FOXP3 was determined by immunohistochemistry in 54 enucleated UM tissue samples. mRNA expression level of LAG3 and CTLA-4 was determined by quantitative real-time PCR and corroborated by western blotting. Furthermore, soluble form of LAG3, CTLA-4 and CCR8 expression in serum was measured in 40 UM patients using ELISA.The expression of LAG3, CTLA-4, CD3, CD4, CD8 and FOXP3 was observed in 30%, 33%, 41%, 35%, 50% and 39% of the cases, respectively. Loss of nBAP1 expression was significantly correlated with CD8+expression (p=0.012) but not with tumour infiltrating lymphocytes. LAG3 and CTLA-4 mRNA levels were higher in UM compared with normal uveal tissues. Higher LAG3 expression with CD8+expression was associated with lower metastasis-free survival (MFS) (p=0.049), but not with CTLA-4 in UM patients. MFS rate was reduced in patients having lower levels of CCR8 protein (p=0.050) and increased level of LAG3 protein (p=0.001).Our findings suggest that higher levels of LAG3 in UM with histopathologically high-risk parameters predict high metastatic potential and that it could be used as a targeted immunotherapy alone or in combination with PD-1/PD-L1 blockade agents.