Purpose: To identify the presence of membrane-bound regulators of complement activation (m-RCA) on uveal melanomas and uveal melanoma cell lines and to examine their role in the inhibition of complement-mediated lysis in vitro.
Methods: Immunohistochemistry and flow cytometric analysis with monoclonal antibodies directed against m-RCA CD46, CD55, and CD59 were applied to tissue sections of 10 uveal melanomas, three primary uveal melanoma cell lines, and one uveal melanoma metastatic cell line. A microcytotoxicity test was used for measuring antibody-dependent complement-mediated lysis.
Results: The tissue sections and all four uveal melanoma cell lines expressed CD46, CD55, and CD59. Complement-mediated lysis in the presence of human complement was increased after partial removal of the m-RCA CD55 and CD59 with phosphatidylinositol-specific phospholipase C from the uveal melanoma cell line 92-1.
Conclusions: These results demonstrate that CD46, CD55, and CD59 are expressed in uveal melanomas and that CD55 or CD59, or both, plays a role in resistance to complement-mediated cytotoxicity. The finding that m-RCA are expressed in uveal melanomas may have implications for the effectiveness of the anti-tumor response and in the therapeutic application of monoclonal antibodies directed against tumor-associated antigens.