For the 55 infected clones derived from in vivo persistent infection, i.e. from PBMCs of patients with HAM/TSP, results of cell cycle analysis paralleled and even surpassed those previously published [8], with a significant redistribution of CD4+ lymphocytes from the G0/G1 phase towards the S and G2M phases of the cell cycle (Figure 4A). The gene discussed is CD4; the disease is tropical spastic paraparesis.