High-scatter T cells from CTCL lesional skin are highly activated CD4⁺ skin homing T cells with elevated FOXP3 expression. (A) Comparison of the phenotype of high- and low-scatter T cells isolated from MF lesional skin. T_HS cells were uniformly CD4⁺ and expressed high levels of the activation markers CD69 and CD25 and the skin-homing addressins CCR4 and CLA. In contrast, low-scatter T cells contained a mixed CD4 and CD8 T cells with variable expression of activation markers and skin-homing addressins. Similar results were observed in 6 additional patients with stage I-III CTCL. (B) MF lesional skin contains a unique population of T cells with intermediate CD4 and FOXP3 expression. MF skin lesions contained both FOXP3^high regulatory T cells (Tregs), also found in normal skin, and a novel population of T cells expressing intermediate levels of both CD4 and FOXP3. (C) Selective gating on this novel population of T cells (CD4^intFOXP3^int) showed that it corresponded closely to the T_HS cell population. Reversing the gating confirmed that the high-scatter T-cell population was comprised entirely of these CD4^intFOXP3^int T cells. A second patient with stage IB disease is also shown. Similar findings were observed in 4 additional patients. (D) In a patient with CD8⁺ MF diagnosed by histopathologic studies, a clonal population of CD8⁺ T cells expressing TCR Vβ 13.2 existed in lesional skin. T_HS cells in this patient were CD8⁺. SSC-A indicates side-scatter area; FSC-H, forward-scatter height. In gated histograms, the % total cells in each quadrant are shown.