NaV decreases CD8⁺cell antiviral function. (A) The NaV-mediated fold increase in the % Tax-expressing CD4⁺ cells was compared in whole PBMCs and CD8⁺ cell–depleted PBMCs. NaV treatment increased the % Tax⁺ CD4⁺ cells to a greater extent (*P < .02, Wilcoxon signed rank, 2-tailed) in whole PBMCs. (B) Ex vivo CD8⁺ cell lytic efficiency (the proportion of Tax-expressing CD4⁺ cells killed per CD8⁺ cell per day) was estimated in 14 HTLV-1–infected individuals with or without NaV treatment. NaV was found to significantly decrease lytic efficiency (*P = .002).