Characterisation of the differential response of normal and CML haemopoietic progenitor cells to macrophage inflammatory protein-1α

Abstract

The clonogenic cells of chronic myeloid leukaemia (CML), unlike normal haemopoietic colony forming cells (CFC), are resistant to the growth inhibitory effects of the chemokine, macrophage inflammatory protein-1α (MIP-1α). Here, we tested the hypothesis that MIP-1α protects normal, but not CML, CFC from the cytotoxic effects of the cell-cycle active drug cytosine arabinoside (Ara-C). Using a 24-h Ara-C protection assay we showed that MIP-1α confers protection to normal CFC but also sensitises CML CFC to Ara-C. The differential MIP-1α responsiveness was not due to a down-regulation of MIP-1α receptors on CML CD34⁺ cells as flow cytometric analysis showed similar binding of a biotinylated MIP-1α molecule to normal and CML CD34⁺ cells. Flow cytometric analysis of the MIP-1α receptor subtype CCR-5 revealed comparable CCR-5 expression levels on normal and CML CD34⁺ cells. Furthermore, culture of CD34⁺ cells for 10 h in the presence of TNF-α resulted in an increased MIP-1α receptor expression on both normal and CML CD34⁺ cells. Our data suggest that the unresponsiveness of CML CFC to the growth inhibitory effect of MIP-1α is not caused by a lack of MIP-1α receptor or total uncoupling of the MIP-1α responsiveness but may be due to an intracellular signalling defect downstream of the receptors.