Immortalization of human T lymphocytes by HTLV-I: Phenotypic characteristics of target cells and kinetics of virus integration and expression

In-vitro infection of normal human lymphocytes with HTLV-I (human T-cell lymphotropic retrovirus type I) has been carried out to study the target cell specificity and the kinetics of infection. Cord blood (CBL) and adult peripheral blood lymphocytes (PBL) have been co-cultivated with irradiated HTLV-I donor cells (MT2 and C91PL lines). Established ('immortalized') HTLV-I positive cell lines were obtained only from CBL: in comparison with PBL, a less mature phenotype of T-cell subsets and a lower interferon-γ production was evidenced in CBL. A progressive variation of differentiation antigen representation and of exogenous T-cell growth factor (TCGF, interleukin-2, IL-2) medium concentration was observed with increasing time from infection. The four established lines obtained showed a predominant T3+, T4+, T8-, Tac+ phenotype and a reduced TCGF requirement. Studies on kinetics of HTLV-I infection showed that p19 and p24 viral antigens became expressed after a lag phase of 5 weeks. DNA Southern blot analysis indicated that a shift from polyclonal to monoclonal pattern of proviral integration occurred with time of culture, both complete and defective copies being transmitted from donor to recipient cells.