Characterization of simian retrovirus genome related to human T-cell leukemia virus type I.

Human T-cell leukemia virus type I (HTLV-I) is exogenous for human transmission by viral infection and was shown to be a causative agent of adult T-cell leukemia (ATL) in man. Monkeys of several species were found to have antibodies reactive with HTLV-I antigens and thus infection with HTLV-I like retroviruses was suspected. The retroviruses in several species of monkeys were characterized by Southern hybridization, molecular cloning and sequencing. These monkey retroviruses, tentatively called simian T-cell leukemia viruses (STLV), have a genome structure of LTR-gag-pol-env-pX-LTR and are highly homologous with HTLV-I in all regions. A DNA clone of the STLV was isolated from a pig-tailed monkey and the nucleotide sequence was determined. The STLV showed 90% homology in the nucleotide sequence with that of HTLV-I in env-pX-LTR region. This highly homologous sequence indicates that the STLV is a member of the HTLV family but apparently different from HTLV-I. This result excluded the possibility of recent interspecies viral transmission from monkeys to humans, and suggested that STLV can be useful as an animal model in studies on HTLV-I transmission and leukemogenesis in humans. Supporting this suggestion, an African green monkey which was naturally infected with STLV was found to have developed T-cell leukemia that was very similar to human ATL.