Vaccination with a low-oncogenic strain of Rous sarcoma virus prevents visceral tumors in chickens.

The oncogenic potential of different strains of Rous sarcoma virus (RSV) varies significantly in two Mhc(B) congenic chicken lines CB and CC and in their F1 hybrids with the unrelated inbred line IA. The Bryan high-titer pseudotype of RSV of antigenic subgroups D and B (BH-D, and BH-B) was highly oncogenic, eliciting mostly fatal, progressively growing tumors. Visceral tumor formation and erythroblastosis were seen after challenge with BH-B in CB and CC chickens, but not in their F1 hybrids with IA. Tumor regression induced by a low-oncogenic RSV strain PR-C elicited a protective immunity capable of preventing not only the progressive growth of challenge tumors at the site of inoculation, but also visceral tumor formation and erythroblastosis.