Growth curve of HTLV T-lymphocyte immortalization assay. Human PBMCs were isolated by Ficoll/Paque and cocultivated with irradiated (10 000 rad) 729 stable cell lines (729wtHTLV-1, 729HTLVRex^-) or 729 uninfected control cells as indicated. PBMCs (2 × 10⁶) were cocultured with irradiated donor cells (1 × 10⁶) in 24-well plates. Cells were fed once per week with RPMI 1640 supplemented to contain 20% FCS. Cell viability was determined by trypan blue exclusion staining at 0, 1, 2, 3, 4, 6, and 8 weeks after cocultivation. After 4 weeks, 10 U/mL IL-2 was provided in the culture medium. The mean and standard deviation of each time point were determined from 3 independent samples.