Pediatric bone marrow microenvironment before and after allogeneic hematopoietic stem cell transplantation: a multicenter retrospective study comparing donors and recipients.

To compare the bone marrow microenvironment between healthy children and adults and investigate the association between the posttransplant bone marrow microenvironment and PGF in pediatric HSCT recipients. This retrospective study involved pediatric patients who underwent allogeneic-HSCT at Beijing Children's Hospital and Baoding Children's Hospital between January 2021 and June 2024. Bone marrow samples were collected before HSCT and between Days 14 and 90 post-HSCT to measure the percentages of endothelial progenitor cells (EPCs) and hematopoietic stem cells (CD34 + HSCs), as well as reactive oxygen species (ROS) levels. Selected donors were enrolled as controls, and their bone marrow samples were similarly assessed for those parameters. One hundred forty pediatric patients and 48 bone marrow donors were included in this study. Subsequent analysis revealed that adult donors had a significantly lower proportion of HSCs compared with the 0-6-year donors subgroup (0.865% (0.03, 2.21) vs. 3.38% (1.38, 5.23); U = 3.93, P < 0.001) and significantly higher HSC-ROS levels (1,979 (1,039, 5,166) vs. 977 (453, 1,597); U = 3.11, P = 0.002). The good graft function (GGF) group had a significantly greater proportion of EPCs compared with the poor graft function (PGF) group (0.106% (0.03-0.69) vs. 0.047%(0.015-0.09), U = 3.184, P = 0.001). Receiver operating characteristic (ROC) analysis revealed that an EPC proportion threshold > 0.071% in the bone marrow at 14-90 days post-transplantation predicted GGF outcomes (AUC = 0.874; 95% CI: 0.743-1.000). These findings suggest that compared with their adult counterparts, pediatric bone marrow niches possess superior hematopoietic regenerative capacity and reduced oxidative stress and that a lower proportion of EPCs is responsible for defective hematopoiesis in PGF pediatric patients.