Figure 1.

CD4⁺CD25⁺ Tregs limit the proliferation of stimulated CD4⁺CD25⁻ T cells. Studies have shown that lack of these regulatory cells can lead to lymphoproliferative disease and autoimmunity. In this issue of the JCI, Yamano et al. (2) report that CD4⁺CD25⁺ T cells infected with HTLV-I (from HAM/TSP patients) have decreased levels of FOXP3 expression and lack the ability to suppress CD4⁺CD25⁻ T cell proliferation. CD4⁺CD25⁺ T cells transfected with the HTLV-I tax gene also have decreased levels of FOXP3 expression and lack the ability to suppress the proliferation of stimulated CD4⁺CD25⁻ T cells.