AMD3100 and G-CSF Synergize To Promote Repopulating Stem Cell Mobilization in Fanca −/− and Fancc −/− Mice.

Fanconi Anemia (FA) is an autosomal recessive DNA repair disorder clinically characterized by congenital abnormalities, progressive bone marrow (BM) failure and a propensity for malignancies. It is advantageous to bank FA patients’ cells for autologous treatment of pancytopenia, transplantation following chemotherapy or future gene therapy trials. Because the amount of cells able to be collected by BM harvesting is limited and the process is often problematic in children, mobilization of stem cells into the circulation would be an ideal means of collecting repopulating hematopoietic stem and progenitor cells (HSPC). Traditional mobilization protocols utilizing granulocyte colony-stimulating factor (G-CSF) as a mobilizing agent result in poor yields of phenotypic HSPC in FA patients. We have shown that analogous to the human patients with FA, administration of recombinant G-CSF is not sufficient to effectively mobilize myeloid progenitors from the BM of Fancc −/− mice (Broxmeyer et al, JEM, 2005). Antagonists to chemokine receptors, together with G-CSF, can enhance mobilization of murine wild type (WT) HSPC. AMD3100 is a selective antagonist of CXCR4, which is thought to function in the retention of HSPC in the BM. We hypothesized that the combination of AMD3100 and G-CSF would enhance mobilization of HSPC in Fanca −/− and Fancc −/− mice. Peripheral blood was collected to assess the number of myeloid progenitors and HSPC repopulating ability. Myeloid progenitor numbers were assessed using progenitor assays. Either G-CSF or AMD3100 alone resulted in poor mobilization of hematopoietic progenitors. In contrast, administration of AMD3100 and G-CSF together increased the number of colonies of myeloid progenitors up to 18 fold above that of either G-CSF or AMD3100 alone in both Fanca −/− and Fancc −/− mice. The stem cell activity of mobilized peripheral blood cells was evaluated using competitive repopulation assays, in which a common pool of isogenic ‘competitor cells’ and ‘test cells’ from mice of different genotypes or treatment conditions are co-transplanted. Fanca −/− and Fancc −/− cells mobilized with both G-CSF and AMD3100 yielded a 3–4 fold increase in peripheral blood chimerism as compared to the cells mobilized with G-CSF or AMD3100 alone. The latter mice also had a decreased survival. Phenotypic analysis of the peripheral blood of primary recipients confirmed the engraftment of multi-lineage test cells. Transplantation of chimeric bone marrow into secondary recipients maintained the test cell chimerism, confirming that long-term repopulating cells were mobilized. Collectively, these data from two FA murine models demonstrate that the AMD3100 and G-CSF protocol is an effective strategy to mobilize FA deficient repopulating HSPC. This has potential implications for more efficient banking of FA patients’ HSPC for future use or for use in gene transfer protocols.