Hybrid resistance to the ascites form of the murine sarcoma.

An ascites form (AA) of the methylcholanthrene-induced murine sarcoma of C3H origin was used for present experiments. The AA cells were intraperitoneally injected to syngeneic (C3H, H-2k), allogeneic (DBA, H-2d) or semisyngeneic (C3H x DBA, H-2k/d) mice at a dose 10(7) cells per animal. The DBA mice developed small amount of ascites in the peritoneal cavity followed by rejection of allogeneic tumor cells and recovery. All syngeneic and semisyngeneic animals developed tumor and died. The C3H x DBA hybrids survived significantly longer than C3H mice (mean survival times: 21.9-24.8 and 10.1-11.8 days, respectively). The hybrid mice died with voluminous ascites tumor accompanied by a sponge-like form of tumor cell aggregates dispersed in the peritoneal cavity while the syngeneic mice died with small amount of dense ascites with an accompanying massive solid tumor in the vicinity of the spleen. Therefore in the experimental system used the semisyngeneic mice were found to develop a better response against parental-strain tumor cells than the syngeneic mice. This is an example of the phenomenon referred to as "hybrid resistance" or "allogeneic inhibition".