Although CCR4 is known to be selectively expressed on Th2, Th17, and Treg cells [23], [26] in healthy individuals, the expression levels of Foxp3, a hallmark of Treg cells [17], [18], has been reported to be reduced in HAM/TSP patients [20], [27]–[29]. The gene discussed is CCR4; the disease is tropical spastic paraparesis.