Persistent productive HIV-1 infection of a CD4^- human fetal thymocyte line

Human fetal thymuses were obtained from abortuses of HIV-1 seronegative females. Thymocytes were isolated and cultured for 2 days with PHA. Thereafter, the culture was divided and half of the cells were exposed to the HIV-1 RF isolate for 4 h. After this incubation period, the HIV-1 exposed and nonexposed control cells were cultured in RPMI 1640 supplemented with IL-2 for 30 days and subsequently maintained in RPMI without the addition of growth factors. Long term culture of both HIV-1 exposed and control thymocytes has yielded two cell lines that have been maintained for more than 3 yr without the addition of growth factors. Flow cytometry using mAb that recognize T cell differentiation markers was used to analyze cell phenotypes. The HIV-1 exposed thymocyte cell line (E88/RF) was shown to be HIV-1 infected by p24 ELISA, reverse transcriptase activity, immunocytochemistry, in situ hybridization, polymerase chain reaction, electron microscopy, and to produce infectious particles by a syncytial forming assay. The non-HIV-1 exposed thymocyte cell line (T412) has remained negative by all criteria for HIV-1 infection. Flow cytometry showed the T412 cells to be positive for the T cell markers CD45, CD38, and CD4 but negative for all other markers tested. The E88/RF cells are positive for CD45 and CD38 but negative for CD4 and other markers. These data report the isolation of two human fetal thymocyte cell lines; one uninfected and susceptible to HIV-1 infection, and the other persistently and productively infected with HIV-1 with little cytopathology. These findings suggest that HIV-1 can persistently infect early T cells and may alter T cell differentiation.