Valproate increases Tax-protein expression in HTLV-1–infected CD4⁺ T cells from asymptomatic carriers and HAM/TSP patients. Rates of Tax-protein–positive cells among HTLV-1–infected CD4⁺ T cells were calculated by normalizing the percentages of Tax-positive CD4⁺ cells, determined by CD3, CD4, and Tax triple labeling (A), with the percentage of infected cells in the CD4⁺ population, as assessed by HTLV-1–proviral load (B). Estimated median (and first quartile) percentages of Tax-positive cells among HTLV-1–infected CD4⁺ cells on D0 to D2 of culture is represented for 10 ACs (●) and 10 HAM/TSP patients (♦) treated with 5mM VPA (dashed lines) or nontreated (Ctrl, solid lines), respectively.