Don't Cut the Cord: Why Umbilical Cord Blood Still Deserves a Place in Transplantation

The use of umbilical cord blood (UCB) as a stem cell source in haematopoietic stem cell transplant (HSCT) has greatly declined in recent years. It has largely been replaced by mismatched unrelated and family donors, facilitated by advances in transplant technologies, including post-transplant cyclophosphamide to prevent graft-versus-host disease (GVHD). UCB remains a distinctive source of haematopoietic stem cells (HSCs) with unique immunologic and practical advantages, including for those with malignant and non-malignant diseases. Compared to other cell sources, UCB transplantation (UCBT) offers comparable survival with reduced chronic GVHD (cGVHD) and with a potent graft-versus-leukaemia (GVL) effect. These outcomes likely reflect the biology of cord-derived lymphocytes-particularly naïve, adaptable CD8⁺ T-cells capable of rapid differentiation and tumour-directed cytotoxicity without sustained alloreactivity. UCB permits greater human leukocyte antigen (HLA) mismatch tolerance, especially when transplant is performed T-cell replete and can be accessed immediately, reducing time to transplant for high-risk leukaemia. In addition, recent advances in ex vivo expansion technologies have overcome historical limitations of low cell dose and delayed engraftment, expanding UCB's applicability to older paediatric and adult recipients. This review discusses the evidence of using UCB as a preferred stem cell source in patients with relapsed/refractory haematological malignancies and how we may interrogate the properties of UCB to improve outcomes in these high-risk cohorts.