Allogeneic hematopoietic stem cell transplantation (HSCT) is an effective therapy for children with high-risk acute lymphoblastic leukemia (ALL). Human leukocyte antigen (HLA)-haploidentical HSCT (haplo-HSCT) or umbilical cord blood transplantation (UCBT) are both important alternative sources of stem cells for those without an HLA-identical sibling donor or unrelated matched donor. We aimed to compare the therapeutic effects of single UCBT and unmanipulated haplo-HSCT in high-risk ALL children (n = 129). Hematopoietic recovery was significantly faster in haplo-HSCT recipients than in UCBT recipients. The 2-year cumulative incidences of relapse in the haplo-HSCT and UCBT groups were 16.1% and 24.1%, respectively (p = 0.169). The 2-year cumulative incidences of non-relapse mortality in the haplo-HSCT and UCBT groups were 12.8% and 18.8%, respectively (p = 0.277). The 2-year probabilities of overall survival in the haplo-HSCT and UCBT groups were 82.0% and 69.6%, respectively (p = 0.071), and the 2-year probability of disease-free survival in the haplo-HSCT group was higher than in the UCBT group (71.0% vs. 57.2%, p = 0.040). However, several variables (such as leukocyte count and cytogenetics at diagnosis) were different between the groups, and a possible center effect should also be considered. In addition, only mild and moderate chronic graft-versus-host disease (GVHD) was associated with significantly improved survival compared to those without chronic GVHD in multivariate analysis. Thus, our results show that both unmanipulated haplo-HSCT and UCBT are valid for high-risk ALL children lacking a HLA matched donor, and both strategies expand the donor pool for children in need.

Umbilical cord blood transplantation (UCBT) has been performed in the clinic for over 30 years. The biological and immunological characteristics of umbilical cord blood (UCB) have been re-recognized in recent years. UCB, previously considered medical waste, is rich in hematopoietic stem cells (HSCs), which are naïve and more energetic and more easily expanded than other stem cells. UCB has been identified as a reliable source of HSCs for allogeneic hematopoietic stem cell transplantation (allo-HSCT). UCBT has several advantages over other methods, including no harm to mothers and donors, an off-the-shelf product for urgent use, less stringent HLA match, lower incidence and severity of chronic graft-vs-host disease (GVHD), and probably a stronger graft-vs-leukemia effect, especially for minimal residual disease-positive patients before transplant. Recent studies have shown that the outcome of UCBT has been improved and is comparable to other types of allo-HSCT. Currently, UCBT is widely used in malignant, nonmalignant, hematological, congenital and metabolic diseases. The number of UCB banks and transplantation procedures increased exponentially before 2013. However, the number of UCBTs increased steadily in Asia and China but decreased in the United States and Europe year-on-year from 2013 to 2019. In this review, we focus on the development of UCBT over the past 30 years, the challenges it faces and the strategies for future improvement, including increasing UCB numbers, cord blood unit selection, conditioning regimens and GVHD prophylaxis for UCBT, and management of complications of UCBT.

The aim of this report was to present a clinical comparison of unrelated cord blood transplantation (CBT) and human leukocyte antigen (HLA)-matched sibling allogeneic peripheral blood stem cell or bone marrow transplantation (allo-PBSCT/BMT) in children with high-risk or advanced acute leukemia. A total of 115 consecutive pediatric patients received unrelated CBT (n = 90) or sibling allo-PBSCT/BMT (n = 25) between 2000 and 2012. Neutrophil and platelet recovery were significantly delayed after CBT compared to allo-PBSCT/BMT. There was no difference in the incidence of acute graft-versus-host disease (GVHD) or chronic GVHD between the two groups. The cumulative incidence of transplant-related mortality (TRM) was higher in the CBT group than in the allo-PBSCT/BMT group (32.5 vs 12.8 %) (p = 0.03). The cumulative incidence of relapse was 13.1 % after CBT, which was significantly lower than that of after allo-PBSCT/BMT (45.3 %) (p = 0.015). The overall survival (OS) and leukemia-free survival (LFS) in the CBT group were similar to those of the allo-PBSCT/BMT group; however, for acute myeloid leukemia (AML) patients, the 5-year LFS in the CBT group was slightly better than the allo-PBSCT/BMT group (55.7 % for CBT and 32.7 % for allo-PBSCT/BMT) (p = 0.08). Our comparisons suggest that for high-risk or advanced childhood acute leukemia, unrelated CBT has a higher TRM and similar long-term survival, but better antileukemia effect than HLA-matched sibling PBSCT/BMT. New strategies and better supportive care are required to decrease the TRM of CBT.