Sézary cells with an unusual phenotype, their modulation with 12-O-tetradecanoyl phorbol-13-acetate (TPA) in vitro, and their relationship to T-cell development.

Leukemic cells from a patient with Sézary syndrome were studied with a panel of monoclonal antibodies. Despite their typical morphology, the cells expressed an unusual surface phenotype. They simultaneously expressed OKT4 and OKT8 reactivity, indicating a more immature origin of the neoplastic cells than what has previously been observed in Sézary syndrome, but they were OKT6 negative. In response to 12-O-tetradecanoyl phorbol-13-acetate (TPA) the cells underwent phenotypic alterations, as the OKT4 reactivity was significantly reduced and the OKT8 expression was retained. Thus, following TPA, the cells expressed a surface phenotype consistent with the cytotoxic/suppressor T-cell subset in normal peripheral blood. The findings are discussed in relation to normal T-cell maturation and differentiation processes.