Impact of CD34 + Bone Marrow Cell Heterogeneity and HMOX1 Promoter Polymorphism on Neutrophil Engraftment in Pediatric Patients Undergoing Hematopoietic Stem Cell Transplantation

ABSTRACT Hematopoietic stem cell transplantation (HSCT) is a therapeutic option for various pediatric diseases. In this study, we analyzed 52 pediatric patients undergoing allogeneic HSCT to determine how the content of myeloid and lymphoid CD34 + progenitor cells, as well as HMOX1 promoter polymorphisms, affects neutrophil (NE) and platelet engraftment (PE). We found that NE was significantly accelerated in patients who received a higher dose of CD34 + myeloid cells (> 4 × 10 6 /kg), while lymphoid progenitors had no impact on engraftment. PE was not affected by any CD34 + cell subtype. Moreover, in a subset of 28 patients, the presence of short HMOX1 promoter alleles in recipients, but not in donors, was associated with delayed NE, particularly during early post‐transplantation. These results highlight the importance of graft composition—specifically myeloid CD34 + cell dose—and recipient HMOX1 genotype in determining the kinetics of neutrophil recovery. This may offer a new perspective for graft optimization and potential use of HO‐1‐targeted therapies to enhance engraftment.