Allogeneic Haematopoietic Stem Cell Transplantation without a Matched Sibling Donor: Current Options and Future Potential

Abstract

Allogeneic haematopoietic stem cell transplantation (HSCT) has been used to treat a variety of malignant and non-malignant diseases. For patients who do not have a matched sibling donor or a optimally matched unrelated donor (MUD) for transplantation, other graft sources have been used, including mismatched haploidentical related donors and umbilical cord blood (CB). A literature review and comparison of HSCT with MUD, haploidentical donors and CB donors was performed. The relative value of MUD and CB donor recruitment was calculated based on search-hit ratios of respective registries. The choice of haematopoietic stem cell (HSC) source for transplantation remains difficult, and is dependent on disease stage, the centre's experience, HLA-matching and cell dose. It remains a lengthy procedure to identify and procure HSC from an acceptably matched unrelated donor, which may lead to disease progression in some patients. In these cases, alternatives such as haploidentical transplants or CB transplants can offer a chance for timely treatment. Although results of haploidentical transplant have improved in some centres, this approach is less successful in many other centres embarking on this transplant technique. However, there is the prospect of availability of HSC donors for almost every patient if the challenges of haploidentical HSCT can be overcome. CB transplantation has been established as a valid alternative for patients who cannot identify a suitably matched unrelated donor quickly enough. Some centres even prefer CB as a HSC source to unrelated donor bone marrow (BM) for paediatric patients. Further increases in the size and diversity of CB inventories may realise the potential of every patient having access to at least a 5/6 matched CB unit of adequate cell dose (70-fold relative value for each CB unit banked versus each BM donor recruited). Prospective comparisons of MUD, CB, and haploidentical HSCT are needed to validate the optimal HSC source for transplant in specific diseases.