Membrane receptors for interleukin 2 on hematopoietic precursors in chronic myeloid leukemia

In this report we present data on the expression of IL2 receptors on chronic phase CML cells. Using an anti IL2 receptor monoclonal antibody (McAb aIL2r) in indirect immunofluorescence we found significant proportions (42.2% +/- 19.7 SD) of the CML cells (previously depleted of E rosetting T cells) to be IL2 receptor positive following incubation in suspension for 18 hours at 37 degrees C. Noninduced cells did not express IL2 receptors. After induction the aIL2r positive and negative cell subpopulations were sorted and analyzed separately for morphology, lineage specific cell surface markers, and clonogenic cell numbers. The IL2 receptor positive CML subpopulations mainly contained blast cells and monocytes and revealed reactivity with myeloid McAbs but not with T cell, B cell, platelet, or erythroid markers. Clonogenic cells (CFU-GEMM, BFUe, and CFU-GM) were selectively recovered from aIL2r positive CML cells and thus were IL2 receptor positive. The addition of recombinant IL2 (rIL2) to CFU-GM and BFUe cultures, in concentrations from 50 to 500 U/mL, did not influence the efficiency of colony formation. Binding of a radiolabeled IL2 preparation to the in vitro activated CML cells indicated the presence of low affinity receptors for IL2. In contrast to CML, normal human marrow cells were consistently aIL2r nonreactive. Thus, IL2 receptor inducibility is a characteristic feature of CML clonogenic cells, which they share with AML, but not with normal marrow progenitors. The role of IL2 receptors in the regulation of proliferation of CML cells requires further investigation.