Strategy used to compare in vivo and in vitro HTLV-1 infections. The materials used for in vivo infection were PBMCs derived from TSP/HAM patients with a disease duration of more than 6 to more than 26 years. In vitro infection was carried out by 28-day co-culture of normal PBMCs from blood donors with irradiated MT2 cells, as detailed in the Methods section. Both cell preparations were cloned at 0.1 cell/well and cultured during 1.5 -- 3 months in the same conditions. Then cells were assayed for HTLV-1 infection and integration, tax expression, CD4+ and CD8+ expression, cell cycling and apoptosis, as shown in Figure 1 and as detailed in the Methods section.