Valproate is proapoptotic for CD4⁺ and CD8⁺ cells isolated from HAM/TSP patients. Cryopreserved peripheral blood mononuclear cells isolated from 11 HTLV-infected HAM/TSP patients (as indicated on the x-axis) were cultivated for 48 hours in the absence (open bars) or the presence (filled bars) of 2 mM VPA. After culture, apoptotic cells were identified by flow cytometry based on CD4/annexin/PI (A) or CD8/annexin/PI (B) triple labeling, and a ratio between apoptotic and live cells was calculated. (C) PVL of the 11 HAM/TSP subjects determined by real-time PCR (in number of HTLV copies per 10⁶ PBMCs).