The Combination of Groβt and AMD3100 Leads to Rapid and Robust Mobilization of Hematopoietic Stem Cells in Nonhuman Primates

Mobilized peripheral blood grafts are the predominant source of hematopoietic stem cells (HSC) for both autologous and allogeneic transplantation. The most common clinical HSC mobilization protocol is five days of G-CSF. This regimen has been associated with bone pain, can result in unpredictable yields, induces flares in patients with Multiple Sclerosis and is contraindicated for patients with Sickle Cell Disease. Plerixafor, an inhibitor of CXCR4 given to patients that fail to mobilize adequate CD34+ cells in response to G-CSF, is insufficient as a stand-alone therapy, as a single injection fails to mobilize a suitable number of CD34+ cells in approximately 33% of patients. Thus, development of a rapid and robust mobilization method with predictable kinetics would be a significant improvement over the current standard of care. In mice, the human CXCR2 agonist GROβT induces rapid mobilization of HSPC 15 minutes after a single injection. When co-administered with AMD3100, a synergistic increase in mobilization results, with a graft enriched in highly engraftable HSC. Here, we present data demonstrating that combination treatment with GROβT and AMD3100 synergistically mobilizes CD34+ cells and colony forming units (CFU) in nonhuman primates. We tested the efficacy of GROβT alone or in combination with AMD3100 in Rhesus macaques. As previously published, administration of AMD3100 alone induced significant mobilization of hematopoietic stem and progenitor cells. The combination of GROβT + AMD3100 yielded 2-fold more CD34+ cells (30/µL) along with a 1.5-fold increase in CFU over that achieved with AMD3100 alone (P < .05). The increase in CD34+ number was associated with a rapid and significant increase in CD34+ frequency apparent within one hour of treatment that continued to rise for four hours post-treatment. Interestingly, the majority of CD34+ cells mobilized with GROβT + AMD3100 express CD90 + and not CD45RA, representing a highly enriched HSC fraction and suggesting that these grafts may contain increased numbers of true HSC relative to G-CSF-mobilized cells. We describe a rapid mobilization method that results in robust hematopoietic mobilization in nonhuman primates within four hours of a single treatment. The GROβT +AMD3100 regimen may allow for highly predictable, single day mobilization of HSPC for both autologous and allogeneic donors. These grafts are enriched in primitive HSCs and may be particularly useful for gene-therapy indications or where G-CSF is contraindicated.