DP T cells, similarly to CD8+ SP T cells, contained a higher frequency of CD69+CD137+ cells in hPVL groups, and CD4dimCD8+ DP T cells from patients with HAM expressed significantly higher levels of CD69+CD137+ than AC hPVL (Figure 4H and Supplemental Figure 4A). Here, TNFRSF9 is linked to tropical spastic paraparesis.