Altered pathogenicity of avian myelocytomatosis (MC29) viruses with mutations in the v-myc gene.

Avian myelocytomatosis virus MC29 inoculated into the wing web of 1-day-old Brown Leghorn chickens causes a high incidence of tumors, predominantly endotheliomas that are apparently induced directly by the action of the viral myc gene. Mutants of MC29, in which portions of the v-myc gene have been deleted and which have reduced ability to transform macrophages in vitro, induce few tumors, among which lymphomas and osteopetrosis predominate. Analysis of lymphomas from birds infected with mutant MC29 suggested that they were a result of helper virus action rather than the mutant MC29.