The Membrane Phenotype of T‐Prolymphocytic Leukaemia

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Abstract
Cells from 13 cases of T‐prolymphocytic leukaemia (T‐PLL) were studied with a battery of immunological techniques in order to define their membrane phenotype. All cases were E‐rosette positive and were negative with OKT6, anti‐HLA‐DR, anti‐Ig and M‐rosettes; in 3, 20–30% of the cells had receptors for C3b. 7 cases had predominantly a ‘helper/inducer’ T‐subset phenotype, (OKT4+, OKT8‐) and 4 had a ‘suppressor/cytotoxic’ phenotype (OKT8+, OKT4‐). Cells in 2 cases coexpressed OKT4 and OKT8 in 48% and 95% of prolymphocytes and in another, both OKT4 and OKT8 were negative. Terminal transferase (TdT) was negative by IF in all the cases, but a low positive level was detected biochemically in one. Although T‐PLL appears to be heterogenous in respect of membrane phenotype, the observation of unexpected features in 8 of the cases raises the possibility that it may originate in a cell of intermediate maturation between late thymocytes and mature T‐lymphocytes. These features plus the clinical manifestation of the disease — typical morphology, splenomegaly, lymphadenopathy, skin lesions, high WBC and aggressive clinical course — help define T‐PLL as a distinct clinicopathological entity.