Immunological study of two stocks of Moloney sarcoma virus producing regressor and progressor tumors in C57BL/6 mice.

The immune response to progressor murine sarcoma virus (P-MuSV)2 and regressor murine sarcoma virus (R-MuSV) was analyzed by the radioisotopic footpad assay (FPA) for delayed hypersensitivity (DH) and by the membrane immunofluorescence assay for anti-tumor antibodies. In mice injected with P-MuSV, the footpad response remained at a low level for 7 weeks, while membrane immunofluorescence antibody titers reached their maximum levels after 5 weeks. By contrast, in mice injected with R-MuSV, the footpad response rose to a maximum by 4 weeks and membrane immunofluorescence antibody titers reached a maximum after 4 weeks. The adoptive footpad response reached its highest level in 2 weeks. A most striking difference between the P-MuSV and the R-MuSV systems was the lower immunogenicity of tumor cells induced by the P-MuSV as measured by the FPA. Considerable differences between the two stocks were also observed in oncogenic activity and tumor growth patterns. The P-MuSV contained one-tenth the amount of helper Moloney leukemia virus found in R-MuSV. Addition of more helper Moloney leukemia virus to the P-MuSV did not produce regressor tumors.