The presence of T_HS cells in blood correlates with skin disease severity. (A) Peripheral blood T cells were drawn from patient 099 (stage IV L-CTCL) over a 4-year period during which the extent of her skin disease fluctuated. The presence of T_HS cells (red) correlated with the severity of skin disease. At all time points, T_HS cells were clonal CD4⁺ T cells expressing the previously identified malignant TCR Vβ17 clonotype. The absolute CD4 T-cell count and CD4/CD8 ratio are also shown. (B-D) Successful clearing of skin lesions on ECP is associated with loss of the high-scatter malignant T-cell clone in patients with L-CTCL. (B) Three T-cell populations were typically evident in patients with CTCL with blood involvement on ECP. The lowest-scatter T-cell population, shown in green, had high levels of caspase 6 activation, consistent with apoptosis (data not shown). Two patients with stage IV L-CTCL with identifiable malignant clones and extensive skin involvement were studied. (C) Patient 099 had worsening of skin disease on ECP and had large numbers of clonal T_HS cells demonstrable in the blood. (D) Patient 119 experienced complete clearing of skin lesions on ECP, and study of her blood at the time of skin clearing showed very few high-scatter clonal T cells. Both patients also had some cells expressing the malignant Vβ subunit in the low-scatter T-cell population. SSC-A indicates side-scatter area; FSC-H, forward-scatter height; PE, phycoerythrin; APC, allophycocyanin; and FITC, fluorescein isothiocyanate. In gated histograms, the % total cells in each quadrant are shown.