Transforming genes of neoplasms induced by avian lymphoid leukosis viruses

Abstract

Oncogenic avian retroviruses can be classified into 3 groups: sarcoma viruses, acute leukemia viruses and lymphoid leukosis viruses (LLV). Sarcoma and acute leukemia viruses transform fibroblasts and/or hematopoietic cells in culture and induce tumors with short latent periods in infected birds. LLV do not transform cells in vitro and require long latent periods before formation of neoplasms in vivo. The most frequent neoplasm induced by LLV is malignant lymphoma of the bursa of Fabricius, but LLV also induce other neoplasms, including sarcomas, nephroblastomas and erythroblastosis. The genomes of sarcoma and acute leukemia viruses contain specific genes responsible for viral oncogenicity, whereas the genome of LLV aparently includes only genes required for virus replication. The genetic basis for the low oncogenic potential of LLV is obscure. LLV-induced tumors contain transforming genes that can be detected by transfection of NIH 3T3 mouse cells. These transforming genes are not linked to LLV DNA sequences, suggesting that oncogenesis by LLV may result from indirect activation of cellular transforming genes.