Effects and long‐term follow‐up of using umbilical cord blood–derived mesenchymal stromal cells in pediatric patients with severe BK virus‐associated late‐onset hemorrhagic cystitis after unrelated cord blood transplantation

This is a retrospective study to evaluate the efficacy and safety of umbilical cord blood–derived mesenchymal stromal cells (MSCs) for the treatment of pediatric patients with severe BK virus–associated late‐onset hemorrhagic cystitis (BKV‐HC) after unrelated cord blood transplantation (UCBT). Thirteen pediatric patients with severe BKV‐HC from December 2013 to December 2015 were treated with MSCs. The number of MSCs transfused in each session was 1 × 10⁶/kg once a week until the symptoms improved. The median follow‐up time was 1432 (89‐2080) days. The median frequency of MSC infusion was 2 (1‐3), with eight cured cases and five effective cases; the total efficacy rate was 100%. The copy number of urine BKV DNA was 4.43 (0.36‐56.9) ×10⁸/mL before MSC infusion and 2.67 (0‐56.3) ×10⁸/mL after MSC infusion; the difference was not significant (P = .219). There were no significant differences in the overall survival, disease‐free survival, and the incidence of relapse and acute and chronic graft‐versus‐host disease between the MSC infusion group and non‐MSC infusion group. There was also no significant difference in the cytomegalovirus, Epstein‐Barr virus (EBV), and fungal and bacterial infection rates between the two groups. Although umbilical cord blood–derived MSCs do not reduce the number of BKV DNA copies in the urine, the cells have a high efficacy rate and minimal side effects in treating severe BKV‐HC after UCBT among pediatric patients. MSCs do not affect the rates of relapse, long‐term infection, or survival of patients with leukemia.