Efficacy and Safety of Sequential Infusion of Hypoxic 3D-Cultured Umbilical Cord Mesenchymal Stem Cells in Haploidentical Hematopoietic Stem Cell Transplantation for Severe Aplastic Anemia: A Multicenter, Randomized, Phase 1 Trial

The enrolled patients with an HLA-haploidentical relative for HSCT received the fludarabine (Flu) + cyclophosphamide (Cy) + antithymocyte globulin (ATG) conditioning regimen. For the patients with acute SAA (SAA-I), intravenous administration of 30 mg/(m2 day) of Flu and 500-800 mg/(m2 day) of Cy was performed from days -5 to -2, and 5μg/(kg day) of ATG was administered from days -4 to -1. For the patients with chronic SAA (SAA-II), the same treatment of ATG and Cy was applied as above with the supplement of 0.6 mg/(kg 6 h) of busulfan (BU) from days -8 to -5 prior to transplantation. Donor selection and hematopoietic stem cell mobilization and collection were conducted based on the consensus of The Chinese Society of Hematology regarding indications, conditioning regimens, and donor selection for allogeneic hematopoietic stem cell transplantation. On day 0, HSCs were infused intravenously. Both groups received 5 × 10⁵/kg UC-MSCs at 4 h before HSC infusion. The control group was transfused with conventional 2D-cultured UC-MSCs, whereas the experimental group received 3D hypoxia-preconditioned UC-MSCs. Standard GVHD prophylaxis consisted of mycophenolate mofetil, cyclosporine A, and methotrexate (MTX).