Protective effect of syngeneic antitumor serum on mammary tumor in a syngeneic host.

The possibility of passive immunotherapy was examined using syngeneic antitumor serum, which could lyse tumor cells in co-operation with immune or activated macrophages. Intraperitoneal injection of syngeneic antiserum into mice soon after inoculation of MM46 tumor cells clearly suppressed peritoneal or subcutaneous tumor growth. However, the antiserum did not suppress an established tumor. The tumor-specific synantibody responsible for the protection was shown by gel filtration to be in the IgG fraction, not the IgM fraction.