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 helperT-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. (N Engl J Med. 1981; 304:1319–23.) THYMUS-derived (T) cells are important in all aspects of the human immune response.1 Subsets of T cells can be identified by stable cell-surface differentiation antigens that code for specific T-cell functions.2 Recently, the technology of producing monoclonal antibodies by lymphocyte hybrid lines has provided the necessary means for probing the functions of human T-cell surface molecules.3 In the past three years, several antihuman T-cell monoclonal antibodies have been produced.4 5 6 7 8 9 10 11 12 13 14 15 Mycosis fungoides and the Sézary syndrome are uncommon lymphoid malignant disorders that are part of the spectrum of cutaneous T-cell lymphoma (CTCL).16 Classic mycosis fungoides presents with a scaly eruption that.
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