Phenotypic characterization of cutaneous T-cell lymphoma. Use of monoclonal antibodies to compare with other malignant T cells.

We studied the surface-antigen pattern of T cells in peripheral blood and cell lines from patients with advanced cutaneous T-cell lymphoma (CTCL) or T-cell acute lymphoblastic leukemia. The antigen patterns of cutaneous T-cell lymphoma cells from peripheral blood and established cell lines were nearly identical; the cells were negative for human thymus antigen (OKT6 and NA1/34), positive for pan-T-cell (OKT3, 17F12, 10.2, and 9.6) and helper-T-cell-subset (OKT4) antigens, and negative for T-cell-subset antigens 3A1 and OKT8. In contrast, the phenotypes of malignant T cells from patients with acute lymphoblastic leukemia were heterogeneous, with at least five patterns of reactivity. The T-cell-specific antibody 3A1 was the only monoclonal reagent that clearly distinguished the peripheral-blood T cells in CTCL (3A1-) from those in acute lymphoblastic leukemia (3A1+). Moreover, 3A1 was the most reliable T-cell marker in acute lymphoblastic leukemia. We conclude that circulating CTCL (Sézary) T cells are homogeneous in their antigen phenotype and are derived from a well-differentiated 3A1-, OKT4+, OKT8- helper-T-cell subset.