Effects of irradiation on the expression of surface antigens in human ovarian cancer.

Tumor cells from four established human ovarian carcinoma cell lines were analyzed for their expression of surface antigens including MHC Class I, Class II, ICAM-1, and the tumor-associated antigens CA 125 and Her2-neu before and after exposure to high doses of gamma irradiation. All four ovarian cell IInes expressed variable levels of MHC Class I and Her2-neu. ICAM-1 antigens were expressed in only two cell lines and Class II and CA 125 surface antigens were absent in all the cell lines evaluated. Exposure to high doses of gamma irradiation (i.e., 5000 to 10,000 cGy) significantly and consistently increased the expression of all surface antigens present on the cells prior to irradiation. Importantly, the irradiation-induced upregulation was persistent and lasted until all the cells died. Irradiation was unable to induce neoexpression of antigens previously not expressed by the cells (i.e., MHC Class II or ICAM-1). These findings may partially explain the increased immunogenicity of tumor cells following irradiation and may suggest enhanced immune recognition in tumor tissue in patients receiving radiation therapy.