T_HS cells from the lesional skin of L-CTCL and advanced MF are clonal and malignant. (A) Spectratype analysis was used to identify clonal populations of T cells in the blood of patients with L-CTCL. The number of individual peaks within each Vβ subfamily is reflective of the T-cell receptor diversity within that subfamily. Patient 151 had a clonal T-cell population expressing TCR Vβ 11.1. (B) Flow cytometric studies confirmed the presence of an expanded clonal population of CD4⁺ T cells in the blood that expressed TCR Vβ 11.1. This population had high expression of CCR4 and variable CLA expression. (C) T cells isolated from the involved skin of this patient contained 2 clear T-cell populations. The T_HS cell population was composed entirely of clonal and malignant T cells. Similar findings were observed in 3 additional patients with L-CTCL. (D-E) High-scatter lesional skin T cells from patients with MF with identifiable T-cell clones were uniformly clonal and malignant. T cells were isolated from lesional skin and TCR diversity was analyzed with the use of flow cytometry. In a subset of patients, an identifiable clone was found. Selectively gating on the high-scatter population of lesional skin T cells showed that the T_HS cell population was uniformly composed of clonal malignant T cells. SSC indicates side scatter. In gated histograms, the % total cells in each quadrant are shown.