Enhanced Functional Response to CXCL12/SDF-1 Through Retroviral Overexpression of CXCR4 on M07e Cells: Implications for Hematopoietic Stem Cell Transplantation

The chemokine CXCL12 (stromal cell derived factor-1/SDF-1) stimulates hematopoietic stem and progenitor cells (HSCs/HPCs) through the corresponding chemokine receptor CXCR4. CXCL12 is thought to be important for both proper HSC homing, retention, and engraftment into the bone marrow (BM) and mobilization out of the BM. Previous studies suggest that breaking the CXCL12–CXCR4 interaction mobilizes HPCs, blocking CXCR4 inhibits HSC homing, and overexpression increases HSC/HPC repopulation. The efficiency of mobilization and engraftment therefore appears to be dependent on the response of HSCs/HPCs to CXCL12, which is in turn dependent upon levels of CXCR4 expressed on HSCs/HPCs. However, expression of CXCR4 on the surface of HSCs/HPCs appears to be variable. To study the function of CXCR4 on HSCs/HPCs, we used the MSCV-based bicistronic (EGFP) retroviral vector MIEG3 to overexpress CXCR4 on M07e cells, an established model of human HPC. CXCR4 overexpression resulted in significant increases in CXCL12-induced chemotaxis and cell survival. Most importantly, cells overexpressing CXCR4 responded to CXCL12 at levels typically too low induce a response. These data suggest that an increased transplant efficiency resulting from CXCR4 overexpression is likely a function of increased HSC/HPC homing and increased HSC/HPC survival in the recipient's BM. These experiments also validate the ability of the MIEG3–CXCR4 retroviral construct to overexpress CXCR4 efficiently and the use of MIEG3–CXCR4 M07e cells for further study. Finally, this information may have future potential therapeutic implications for improvements in transplant efficiency.