A better understanding of the mechanisms of hematopoietic stem/progenitor cell (HSPC) homing and engraftment could lead to better transplantation outcomes. Based on clinical observations that HSPC from mobilized peripheral blood (mPB) engraft faster than those derived from bone marrow (BM), we examined whether supernatants obtained from leukapheresis products (SLP) of patients mobilized with G-CSF increase the chemotactic responses of BM HSPC to SDF-1. We found that SLP alone did not induce chemotaxis of HPSC; however, it i) enhanced chemotaxis and trans-Matrigel migration to low/threshold doses of SDF-1; ii) increased matrix metalloproteinase (MMP-9, -2) secretion, iii) induced calcium flux, and iv) stimulated phosphorylation of MAPK p42/44 and AKT. In hematopoietic cells it also significantly decreased internalization of CXCR4. These effects could be reproduced with particular components of SLP such as PMV, C3a, soluble VCAM-1, soluble ICAM-1, uPAR, thrombin, hyaluronic acid, fibrinogen or fibronectin. Confocal microscopy and studies employing inhibitors of membrane raft formation (e.g., methyl-b-cyclodextrin, nystatin and amphotericin B) revealed that the priming effect of several of these molecules depends on CXCR4 incorporation into lipid rafts. Thus we postulate here that the CXCR4 receptor could be primed by various factors related to inflammation/mobilization/leukapheresis, which allows HSPC to better sense an SDF-1 gradient, and that the priming effect depends on the incorporation of CXCR4 into the lipid rafts. Finally, based on our experiments with a murine model of transplantation using primed HSPC, we suggest that some of these molecules could find clinical application for in vitro priming of human HSPC before transplantation, to accelerate engraftment and reduce the period of post-transplant neutropenia and thrombocytopenia. This novel approach would be particularly important in cord blood transplantation where the number of HSPC available for transplantation is usually limited.
Full conference title:
American Society of Hematology 45th Annual Meeting
- ASH 45th (2003)