HLA EXPRESSION AND TUMOR-INFILTRATING IMMUNE CELLS IN UVEAL MELANOMA

Background: In uveal melano ma, both the amount of tumor-infiltrating cells and the level of expression of HLA antigens are quite variable. We hypothesized that low levels of HLA expression lead to a lack of an tigen presentation, which might prevent proper immunologic recognition of the tumor. This lack of recognition might subsequently lead to low levels of tumor-infiltrating cells. Methods: To test this hypothesis, we determined the type and number of tumor-infiltrating cells in tumo r sections from 24 uveal melanomas. We applied monoclonal antibodies d irected against different types of immune cells and compared the resul ts with the expression of HLA class I and class II antigens on the tur ner cells. Results: Infiltrating immune cells were observed in all uve al melanomas (although in small amounts), with a predominance of T lym phocytes. Significant positive correlation:, were observed between the number of CD3+ cells (T lymphocytes) and monomorphic HLA class I expr ession, allele-specific HLA-A2 and Bw4 expression, and HLA class II ex pression. Furthermore, the number of CD4+ cells (T helper cells, monoc ytes/macrophages) and of CD11b+ cells (monocytes/macrophages) was sign ificantly correlated with the level of monomorphic HLA class I express ion. Conclusion: These data support our hypothesis that low levels of HLA expression (and therefore a lack of presentation of tumor-specific antigens) may lead to a low level of tumor infiltrate.