1. Stem Cells and Immunotherapies, National Blood Service—Oxford, NHS Blood and Transplant Authority, John Radcliffe Hospital, Headington, Oxford OX3 9BQ, UK
2. Nuffield Department of Clinical Laboratory Sciences, University of Oxford, Oxford OX3 9DU, UK
3. Department of Plastic and Reconstructive Surgery, Stoke Mandeville Hospital, Stoke Mandeville HP21 8AL, UK