Shared antigens between human malignant melanoma cells and Mycobacterium bovis (BCG)

This study was undertaken to investigate the antigenic relationships between human malignant melanoma cells and Mycobacterium bovis (BCG). Rabbits were immunized with sonicates of BCG or with malignant melanoma cells from different patients and the resulting antisera were tested for their capacity to bind radiolabeled soluble extracts prepared from BCG and melanoma cells. The binding of antibodies to radiolabeled antigens was studied by precipitation of radiolabeled antigen-antibody complexes by anti-rabbit immunoglobulin. Antibodies in sera from rabbits immunized with either BCG (anti-BCG) or melanoma cells (anti-melanoma) bound both the labeled BCG and melanoma antigens. Control antisera, from rabbits immunized with human acute or chronic lymphatic leukemia cells or with normal human spleen cells, did not bind significant amounts of radiolabeled BCG. Antibodies in sera from rabbits immunized with normal spleen cells bound small but significant amounts of radiolabeled melanoma antigens. Binding by anti-BCG and anti-melanoma to the radiolabeled antigens was studied before and after absorption of antisera with cells from human melanoma, leukemia, guinea pig hepatoma, and normal human spleen cells. Inhibition studies using unlabeled BCG extracts also were carried out. The absorption and inhibition studies confirmed that the binding reactions were specific and that antigens from five melanoma patients shared antigenic determinants with BCG.