Biological effects of stroma-derived factor-1α on normal and CML CD34+ haemopoietic cells

We compared the biological effects of the CXC chemokine SDF-1 alpha on immunomagnetically purified CD34(+) cells isolated from human normal bone marrow (NBM), leukapheresis products (LP) and patients with chronic myeloid leukaemia (CML). LP CD34(+) cells showed a significantly stronger migration response to SDF-1 alpha (100 ng/ml) than CD34(+) cells isolated from the peripheral blood (PB) of CML patients (P < 0.05). The chemotactic response to SDF-1 alpha was also reduced in CML BM CD34+ cells in comparison to NBM CD34+ cells but the observed differences were not statistically significant. In analogy to normal CD34+ cells circulating CML PB CD34(+) cells were less responsive to SDF-1 alpha than their BM counterparts (P : 0.05). Furthermore, SDF-1 alpha elicited similar concentration-dependent growth suppressive effects on normal and CML CD34(+) cells (P > 0.05) in colony-forming cell assays. We then demonstrated that SDF-1 alpha triggers intracellular calcium increases in CD34+ cells and there were no differences in the time course and dose response characteristics of normal and CML CD34(+) cells. The reduced migration response to SDF-1 alpha in CML CD34+ cells was not due to a down-regulation of the SDF-1 alpha receptor CXCR-4 as flow cytometric analysis revealed similar CXCR-4 expression levels on NBM, LP, CML PB and CML BM CD34(+) cells (P > 0.05). Finally, no differences in the modulation of CXCR-4 levels in response to SDF-1 alpha and serum were observed in CML and normal CD34(+) cells. Our data suggest that the impaired chemotactic response of CML CD34(+) cells to SDF-1 alpha is not caused by a lack or complete uncoupling of CXCR-4, but may be due to an intracellular signalling defect downstream of the receptor.