The induction of immunity against tumor cell transplantation with a complex of tumor cell surface substance and a serum component found in the tumor-regressor animals.

Immunity against transplantation of MM2 cells, an ascites cell line of mouse mammary carcinoma, was induced in syngeneic C3H/He mice by intraperitoneal injection of a complex formed between a MM2-specific surface component isolated from the cells and a serum factor found in the serum from MM2-regressor and MM2-bearing mice. The induced immunity was transferable to other mice with the spleen cells or with the serum from the immunized animals. This cell surface component was not immunogenic by itself. A new immunogenicity was induced in the protein moiety of this substance when the serum factor was bound to the polysaccharide-containing part of the molecule. On the basis of these results, a biphasic mechanism for the induction of the humoral immunity against tumor antigens was proposed. The first phase takes place in tumor-bearing animals and gives rise to the serum factor. The second phase, which is blocked in tumor-bearing animals, consists of the induction of the humoral immunity by the complex in tumor-free animals.