Suppression of Moloney sarcoma virus immunity following sensitization with attenuated virus.

Murine sarcoma virus (Moloney strain) (MSV-M)-induced tumors are unusual in that they regularly appear less than 2 weeks after virus inoculation, progress for 1 to 2 weeks, and are rejected by normal adult BALB/c mice. Rejectio leaves the animals immune to tumor induction. In the present study, presensitization of normal adult BALB/c mice with attenuated MSV-M resulted in an altered pattern of tumor immunity. Injection of active MSV-M into the presensitized animals resulted in tumor induction and rejection similar to that observed in normal animals, but rejection failed to produce protection against the secondary inoculation with MSV-M. After the second inoculation with active MSV-M, tumors appeared and progressed but ultimately were rejected. Over 80% of the mice died, 25% after the primary challenge and the remainder after the secondary challenge. At death, all mice had histological evidence of leukemia which was the probable cause of death. The animals that died following the secondary challenge also had evidence of disseminated MSV-M. Solid tumor nodules were found in skeletal muscle distant from the original site of inoculation, and active MSV-M was isolated from spleen and lungs. The possibility that the results were produced by specific suppression of MSV-Moloney leukemia virus immunity is discussed.