To determine whether CCR4 can be used as a cell surface marker to identify HTLV-1-infected T cells in HAM/TSP patients as reported in ATL cells [22], we separated peripheral blood mononuclear cells (PBMCs) from HAM/TSP patients into the following T cell subtypes by FACS sorting: CD4+CD25−CCR4−, CD4+CD25−CCR4+, CD4+CD25+CCR4−, and CD4+CD25+CCR4+ (Figure 1A). This evidence concerns the gene CCR4 and tropical spastic paraparesis.