Heterogeneity of the natural humoral anti-tumor immune response in mice as shown by monoclonal antibodies.

Four anti-tumor cytotoxic antibodies, namely, A6 of the IgG2 class and B3, C2, and D1 of the IgM class, were obtained in monoclonal form, from hybridization of mouse myeloma cells with spleen cells of normal untreated mice selected for high natural anti-tumor immune responses. The specificity of the four monoclonals was tested by complement-dependent cytotoxicity assay on the reference EL4 lymphoma at different days of in vivo transplant, on normal adult and fetal tissues, on the SC-1 fibroblastic cell line uninfected or infected with a murine ecotropic type-C virus, and on a panel of murine lymphomas of different origin. The four antibodies had different specificities: the A6 and B3 recognized virus-related structures, the C2 a structure expressed on fetal cells, and the D1 a normal component of fibroblasts. The different classes and specificities of the four monoclonals, as well as their in vitro-demonstrated synergistic cooperation, give support to the hypothesis that the natural humoral anti-tumor cytotoxic immune response could be the result of the cooperative activity of an array of heterogeneous antibody molecules.