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Functional p75 interleukin‐2 receptor expression on the fresh blast cells in childhood acute lymphoblastic leukemia with natural killer cell properties

Neoplastic cells of childhood acute lymphoblastic leukemia (ALL) with natural killer (NK) cell properties were studied for the expression of p75 interleukin‐2 receptors (IL‐2R) and the receptor functions. Freshly prepared blast cells from a patient with ALL had NK cell properties: (1) the phenotype such as CD56+, CD2+, E‐rosette+, CD3−, and CD19−; and (2) the presence of spontaneous cytotoxicity against NK‐sensitive K562 target cells. Although p55 Tac antigen was not detectable, there was the expression of p75 IL‐2R on the freshly prepared blast cells: 70% of the cells reacted with Mik‐β1 monoclonal antibody against p75 IL‐2R as determined by flow cytometry. Two‐color flow cytometry revealed that the blast cells expressed both p75 IL‐2R and NKH‐1. NK activity of the blast cells was augmented by their treatment with 1,000 U/ml recombinant IL‐2 (rIL‐2): the cytotoxicity level as percentage lysis increased to 38.7% from 22.0% when the normal lymphocyte value increased to 62.1% from 46.2%. Although the blast cells possessed no apparent level of proliferative capacity, the addition of 1,000 U/ml rlL‐2 yielded a 2.7‐fold increase in their thymidine uptake. These results demonstrate the expression of functional p75 IL‐2R on the patient's blast cells with NK cell properties.