Interestingly, CD4+CD25+CCR4+ T cells become Th1-like cells in HAM/TSP patients, as evidenced by their overproduction of IFN-γ, suggesting that HTLV-1 may intracellularly induce T cell plasticity from Treg to IFN-γ+ T cells. The gene discussed is IFNG; the disease is tropical spastic paraparesis.