Uveal melanoma: no expression of HLA-G.

Purpose: To investigate whether uveal melanoma cells express HLA-G, a nonclassical HLA class I molecule that has been shown to be a critical mediator in the inhibition of natural killer (NK) cell-mediated cytolysis.

Methods: Eleven human uveal melanoma cell lines were analyzed for the expression of HLA-G by flow cytometry, immunocytochemistry, Western blot analysis, and RT-PCR followed by Southern blot analysis. Two HLA-G-specific monoclonal antibodies were used, 87G and MEM-G/1. In addition, HLA-G expression was determined on frozen tissue sections of 17 primary uveal melanomas.

Results: With all HLA-G detection methods, no evidence for HLA-G expression by uveal melanoma cells was found. In contrast, the trophoblast cell line JEG-3 clearly expressed HLA-G transcripts and protein in all cases. Furthermore, interferon-gamma did not induce HLA-G expression in the uveal melanoma cell lines. Notably, all cell lines expressed HLA-E, and this expression was significantly enhanced by interferon-gamma.

Conclusions: Because none of the uveal melanoma cell lines nor any of the primary uveal melanomas displayed expression of HLA-G, it is unlikely that HLA-G plays a role, direct or indirect, in the modulation of cellular immunity against uveal melanoma tumors.