In HAM/TSP patients, CD4+CD25+ T cells contain high frequency of HTLV-1 proviral DNA, express HTLV-1 tax mRNA at significantly higher levels than in CD4+CD25- cells and induces various cytokines including IFN-γ (Yamano et al., 2004, 2009). The gene discussed is CD4; the disease is tropical spastic paraparesis.