Clonal selection of T lymphocytes infected by cell-free human T-cell leukemia/lymphoma virus type I: Parameters of virus integration and expression

We have successfully transmitted cell-free HTLV-I to normal cord blood and peripheral blood lymphocytes and have exploited this system to study the kinetics of infection and transformation of these cells. Transmission was successful in 4 out of 23 attempts. In all 4 cases, the infected cells progressed from an initial stage of polyclonality to predominantly monoclonal cells within 4-6 weeks. Both complete and defective proviruses were transmitted to the recipient cells initially, but cells with a complete provirus were preferentially maintained. The monoclonally infected cells have persisted in culture for more than 6 months and may be considered immortalized. Expression of core antigens as detected by immunoflourescence and the reverse transcriptase activity in the medium at least in one case was not observed until weeks after the cells had become monoclonal, suggesting that expression of virus or viral structural proteins is not necessary for selected growth of the infected cells in vitro.