Studies on the growth and regression of a transplantable Moloney sarcoma.

X-irradiated (400 R) CBF (BALB/c 9 X C57BL/6 o") FI mice inoculated with BALB/c Moloney sarcoma cells developed more tumors and exhibited fewer tumor regressions than normal CBF controls. Most of the latter and only one of the former produced detectable fluorescent antibody as tested against BALB/c Moloney lymphoma cells. BALB/c Moloney sarcoma cells incubated with spleen cells from C57BL/6 mice whose pri mary Moloney-sarcoma-virus-induced tumors had regressed did not grow in X-irradiated CBF hosts. Mice inoculated with Moloney sarcoma cells after incubation with immune serum de veloped as many tumors as mice inoculated with Moloney sar coma cells incubated with normal C57BL/6 serum. However, the latency period to tumor development was longer in the former. Absorption studies showed that the tumors which developed lacked somatic isoantigens of the C57BL/6 genotype, in contrast to primary CBF Moloney sarcoma cells. The data presented are consistent with the hypothesis that tumor rejection is largely mediated by immune lymphoid cells.