Oncofetal antigen (OFA) has been defined with the use of human natural antibodies as a membrane antigen of human cancer cells that cross-reacts with human fetal brain tissues. The immunogen that elicits the antibody is unknown. The present study was undertaken to examine the immunogenicity of the OFA found on tumor cells. Postoperative melanoma patients were immunized with OFA-positive melanoma cells. Anti-OFA reactivities in the immunized sera were titrated by the immune adherence assay with the use of a known OFA-positive cultured melanoma cell line, M14, as target cell. Alloantibodies were excluded by absorption with lymphoblastoid cells autologous to M14. Anti-OFA antibody then was identified by absorption with fetal brain. In 6 months of immunization, 19 of 23 patients produced increased anti-OFA antibodies. The peak titers ranged from 1:16 to 1:2,048. Sera from 18 patients who were not immunized also were tested for 6 months postoperatively, and none had significant increases in antibody titers. The increase of anti-OFA antibody titer in response to the immunization with OFA-positive tumor cells suggests the immunogenic capability of tumor-related OFA in man.
