Transvitreal Retinochoroidal Biopsies of Primary Uveal Melanoma Reveal an Association of Low HLA Class I and High NK Cell Abundance in Low-Risk Disease

PURPOSE: Immune cells in primary uveal melanoma (PUM) have mostly been studied in enucleated tissue, thereby precluding material from thinner, low-risk PUM tumors for research purposes. Here, we investigated the feasibility of using tumor tissue acquired by transvitreal retinochoroidal (TVRC) tumor biopsies to study the tumor immune microenvironment and relation to genetic risk class.

METHODS: Collected tumor biopsies of 41 patients were tested for genetic aberrations to determine high-risk (n = 19), medium-risk (n = 12), and low-risk (n = 9) tumors and were digested for flow cytometry analysis of immune cell and tumor markers. In addition, 13 patient-matched enucleated tumors were stained using multiplex immunohistochemistry.

RESULTS: Tumor biopsies showed a high variability in the degree of immune infiltration. The tumor-specific lymphocyte infiltration pattern correlated well with the infiltration pattern in patient-matched enucleations. High-risk tumors tended to have a higher abundance of CD8 T cells, which expressed activation markers CD39, CD69, and PD-1, with reduced CD127 expression. In general, low-risk tumors exhibited decreased human leukocyte antigen (HLA) class I expression, coinciding with a higher abundance of natural killer (NK) cells (P = 0.0049), indicating a different lymphocyte infiltration pattern between low-, medium- and high-risk tumors.

CONCLUSIONS: TVRC biopsies are a suitable and valuable source of PUM tissue for research purposes. An abundance of CD8 T cells was found in high-risk PUM tumors. Further, medium- and low-risk PUM tumors are characterized by decreased HLA class I expression with a concomitant increase in NK cell infiltration as compared to high-risk PUM tumors, correlating with decreased risk of disease recurrence.