Benign clonally expanded T cells are found in the low-scatter T-cell population and can be discriminated from malignant T-cell clones. (A) Spectratype analysis of blood T cells showed a clonal T-cell population expressing TCR Vβ16.1 in a patient with long-standing stable stage IB MF and no other evidence of peripheral blood involvement. (B) Spectratype analysis of T cells isolated from skin lesions showed a diverse T-cell population expressing TCR Vβ16.1. (C) Further analysis of peripheral blood showed a lack of T_HS cells and showed that the expanded TCR Vβ16.1⁺ T-cell population was CD8⁺, lacked expression of CCR4, and produced effector cytokines, including interferon γ (IFNγ) and tumor necrosis factor-α (TNFα), suggesting that these cells represented a benign expanded CD8 clonal T-cell population. SSC-A indicates side-scatter area; FSC-H, forward-scatter height; and IL-4, interleukin-4.