LAG3 and Its Ligands Show Increased Expression in High-Risk Uveal Melanoma

SIMPLE SUMMARY: Uveal melanoma (UM) is a rare type of intraocular malignancy, which often gives rise to metastases. While treatment with immune checkpoint inhibitors is often effective in the treatment of cutaneous melanoma metastases, it is hardly effective in the case of UM metastases. Lymphocyte-activation gene 3 (LAG3) is a recently recognized immune checkpoint; we determined the distribution of LAG3 expression and its ligands in three sets of primary UM. High-risk UM (epithelioid cell type, loss of chromosome 3/BAP1 staining) had a higher expression of LAG3 and its ligands, which correlated with the presence of infiltrating immune cells. We concluded that not only LAG3 but also its ligands Galectin-3 and HLA class II are especially expressed in high-risk UM and may be a target for adjuvant immunotherapy in UM. ABSTRACT: Uveal melanoma (UM) is a rare ocular malignancy which originates in the uveal tract, and often gives rise to metastases. Potential targets for immune checkpoint inhibition are lymphocyte-activation gene 3 (LAG3) and its ligands. We set out to analyse the distribution of these molecules in UM. The expression of mRNA was determined using an Illumina array in 64 primary UM from Leiden. The T lymphocyte fraction was determined by digital droplet PCR. In a second cohort of 15 cases from Leiden, mRNA expression was studied by Fluidigm qPCR, while a third cohort consisted of 80 UM from TCGA. In the first Leiden cohort, LAG3 expression was associated with the presence of epithelioid cells (p = 0.002), monosomy of chromosome 3 (p = 0.004), and loss of BAP1 staining (p = 0.001). In this Leiden cohort as well as in the TCGA cohort, LAG3 expression correlated positively with the expression of its ligands: LSECtin, Galectin-3, and the HLA class II molecules HLA-DR, HLA-DQ, and HLA-DP (all p < 0.001). Furthermore, ligands Galectin-3 and HLA class II were increased in monosomy 3 tumours and the expression of LAG3 correlated with the presence of an inflammatory phenotype (T cell fraction, macrophages, HLA-A and HLA-B expression: all p < 0.001). High expression levels of LAG3 (p = 0.01), Galectin-3 (p = 0.001), HLA-DRA1 (p = 0.002), HLA-DQA1 (p = 0.04), HLA-DQB2 (p = 0.03), and HLA-DPA1 (p = 0.007) were associated with bad survival. We conclude that expression of the LAG ligands Galectin-3 and HLA class II strongly correlates with LAG3 expression and all are increased in UM with Monosomy 3/BAP1 loss. The distribution suggests a potential benefit of monoclonal antibodies against LAG3 or Galectin-3 as adjuvant treatment in patients with high-risk UM.