CD4 and infection: For both CD4+ and CD8+ cells, the frequency of tax positive clones was significantly higher in cells derived from in vivo infection (p = 0.001 for CD4+ and CD8+ clones, Fisher exact test) and the level of tax expression in tax positive clones was significantly higher in CD4+ or CD8+ clones derived from TSP/HAM than in those generated after experimental infection (p < 10-4 for tax+-CD4+ clones, p = 0.048 for tax+-CD8+ clones, Mann Whitney test) (Figure 3).