G-CSF Priming of Haploidentical Bone Marrow: Effects on Cell Yield, Collection Efficiency, and Tolerogenic Graft Composition

BACKGROUND Allogeneic hematopoietic stem cell transplantation (HSCT) from haploidentical donors is a well-established treatment for patients without related or matched unrelated donors. Peripheral blood stem cells are preferred over bone marrow stem cells because of easier collection, faster engraftment, lower relapse rates, and improved progression-free survival, despite higher rates of graft-versus-host disease (GVHD). Previous studies have primarily compared granulocyte colony-stimulating factor (G-CSF)-primed peripheral blood stem cells with steady-state bone marrow grafts, rather than G-CSF-primed bone marrow grafts. MATERIAL AND METHODS This ambispective study included a retrospective analysis conducted at the University Hospital Centre Zagreb, Croatia, involving 61 patients who underwent bone marrow HSCT from haploidentical donors. Hospital records were reviewed to collect donor and recipient demographics, transplant details, and outcomes. Participants were consenting adults who received bone marrow transplantation from haploidentical donors. The prospective dataset comprised information regarding graft composition and collection times from 17 G-CSF-primed donors and 9 non-primed donors (controls). RESULTS G-CSF priming improved bone marrow collection efficiency and altered graft composition, increasing regulatory T-cell and dendritic cell content in accordance with a tolerogenic immune profile. These findings suggest a mechanism for reducing GVHD risk while maintaining engraftment efficacy. CONCLUSIONS G-CSF priming may enhance bone marrow collection efficiency and modify graft composition to reduce GVHD risk. The retrospective design and absence of a control group limit causal inference. Future studies should prospectively investigate the relationship between these immunological changes and clinical outcomes, refine priming regimens, and evaluate applicability according to donor type and conditioning protocol.