Regulation gone wrong: a subset of Sézary patients have malignant regulatory T cells.

Cutaneous T-cell lymphomas (CTCLs) are non-Hodgkin's lymphomas derived from T cells that home to and inhabit the skin. There are conflicting reports as to whether CTCLs represent a malignancy of regulatory T cells (Tregs), a T-cell subset that can suppress local immune reactions. In this issue, Heid et al. present convincing evidence that the malignant T cells in a subgroup of Sézary patients are FOXP3(+) regulatory T cells. Clonal malignant T cells showed increased expression of the Treg-associated transcription factor FOXP3 and demethylation of the FOXP3 gene locus, and T cells from at least some of these patients suppressed T-cell proliferation in vitro.