When Tax and HBZ expression was examined in CD4+ T cells expressing CD25 and CD39 of HAM/TSP patients, HBZ mRNA expression was significantly correlated with CD39+CD4+ T cells while Tax expression was restricted to CD25-expressing CD4+ T cells regardless of CD39 expression (Leal et al., 2013). Here, ENTPD1 is linked to tropical spastic paraparesis.