Hematopoietic Progenitor Cell Response to SDF-1 alpha and SDF-1 alpha Production Are Impaired in Chronic Phase Chronic Myeloid Leukemia at Diagnosis.

SDF-1 alpha and its cognate receptor CXCR-4 are involved in normal Hematopoietic Progenitor Cells (HPC) regulation of adhesion, migration and survival. In Chronic Phase (CP) Chronic Myeloid leukaemia (CML), HPC exhibit a deregulation of all of those phenomena. Here, we investigated by different ways, the involvement of SDF-1 alpha in the pathogenesis of CP CML. Samples of bone marrow (BM) and peripheral blood (PB) from normal donors (ND) (n=10), CP CML (100% Ph1⁺ metaphases, all selected for Ph1⁺ LTC-IC) patients at diagnosis (n=35) and CP CML patients in Complete Cytogenetic Response (CCR) (0% Ph1⁺) (n=10) were explored. First, SDF-1 alpha concentrations were determined by ELISA assays in PB and BM samples, and showed higher yields for CP CML PB (2060±700 pg/ml) compared to CCR PB [1570±300 pg/ml (p=0.002)] and lower concentrations for CP CML BM (3080±1015 pg/ml) compared to CML in CCR BM [3990±680 pg/ml (p=0.01)] and ND BM [4060±1020 pg/ml (p=0.03)]. CCR BM and PB, and ND BM and PB SDF-1 alpha concentrations were not different. Further, we analyzed CD34⁺Lin⁻ HPC migration in a 4h-Transwell™ assay, in SFM conditions ± SDF-1 alpha or ± one of its specific inhibitors SDF-1(G2) vs control. After migration, median percentages of migrating cells were consistently higher for CML vs ND BM (32±9 vs 20±1, p=0.002) in control arm, but equivalent for CML samples with SDF-1 alpha (39±10) vs control (32±9) indicating a relative insensitivity of CML HPC to this chemokine. In addition, SDF-1(G2) significantly inhibited the migration of CML HPCs (28±7) vs SDF-1 alpha (p=0.01). The proportion of CFC and LTC-IC in the migrating fraction was equivalent in the 3 experimental arms (SDF-1 alpha vs SDF-1(G2) vs control). As assessed by FACS, CD34⁺Lin⁻ cells CXCR-4 surface expression was equivalent for CP CML (31±2.3%) and ND BM (43±2%) before migration, and there was no modification of the CXCR-4 expression after migration for CP CML. As SDF-1 alpha is involved in the regulation of the proliferation of normal HPC, we assessed CP CML CD34⁺Lin⁻ cells in ³H-Thymidine cycling assays after 14 days culture on M210B4 murine feeder cell line (producing residual concentrations of SDF-1 alpha). CP CML HPC (CFC and LTC-IC) cycling status was not modified either after SDF-1 alpha or SDF-1(G2) exposure whereas ND BM cycling was paradoxically up-regulated by SDF-1(G2) vs control, suggesting a specific functional defect of CP CML HPCs in response to SDF-1 alpha. Taken together, all these results suggest that SDF-1 alpha production by stromal cells is impaired in CP CML, and that migratory and proliferative responses of CP CML HPCs to SDF-1 alpha are likely to be perturbed. This results might illustrate some pathologic interactions between BCR-ABL and signal transduction pathways activated through CXCR-4 ligation to its sole ligand SDF-1 alpha.