Chronic lymphoproliferative disorder with regulatory T-cell phenotype.

We report a case of T-cell chronic lymphoproliferative disorder (CLPD) that shows neither features of T-cell prolymphocytic leukemia nor disease progression for more than 34 months. Flow cytometric analyses of the lymphocytes revealed high expression of CD4 and CD25. Up-regulation of Foxp3, a master regulatory gene for developmental differentiation of regulatory T cells (Treg), was confirmed at mRNA and protein levels. To our knowledge, this is the first case of extremely indolent CLPD with Treg phenotype.