Since it has been demonstrated that activated HTLV-I specific CTL may play an important role in the pathogenesis of HAM/TSP and that CD244 is a crucial regulator of CTL function, we characterized the expression of CD244 on CD8+ T cells of HTLV-I-infected patients and examined their functions in patients with HAM/TSP. This evidence concerns the gene CD8A and tropical spastic paraparesis.