CD4 and tropical spastic paraparesis: HAM/TSP patients are known to have a higher PVL compared with asymptomatic carriers, and this comparison is associated with increased phenotypically defined effector CD8+ T cell subsets and HTLV-1 Tax–specific CD8+ T cells (26, 29) where chronic viral antigen stimulations have been shown to drive clonal expansion in both infected CD4+ T cells and HTLV-1–specific CD8+ T cells (30).