The current role of T cell depletion in paediatric stem cell transplantation.

Haematopoeitic stem cell transplantation (HSCT) is a curative procedure for children with malignant and non-malignant haematological disease as well as an expanding number of inherited disorders. Most patients lack a human leucocyte antigen-matched related donor, making alternative donors, such as closely matched unrelated donors, unrelated umbilical cord blood donations and haploidentical donors, necessary choices. T cell depletion (TCD) has been employed for over 30 years to reduce the risk of graft-versus-host disease (GvHD) associated with non-genoidentical HSCT. However, until recently overall survival had not improved with TCD due to increased rates of graft failure, disease relapse and delayed immune reconstitution. Recent advances in graft manipulation and reduced toxicity conditioning regimens have offered renewed hope, particularly for children undergoing haploidentical HSCT, where encouraging results have been achieved using negative depletion techniques to retain beneficial accessory cells, which speed immune reconstitution and reduce disease relapse. Translational work building on megadose CD34(+) selected grafts, including pathogen-specific immunotherapy, suicide gene therapy and other adoptive cellular immunotherapies, has also offered improved outcomes for such patients.