After obtaining his M.D. from the University of Leiden and a PhD on B cell receptor signaling from the University of Amsterdam, he was trained as pediatrician-immunologist at Leiden University Medical Center (LUMC). Since 2009 he is clinical director of the JACIE-accredited Pediatric Stem Cell Transplantation program which serves as the national center for stem cell therapy in patients with inherited immune disorders. In 2016 he was appointed as professor of Pediatrics and Stem Cell Transplantation at the University of Leiden. He is heading the LUMC expert center on inherited immune disorders and stem cell transplantation (SCT) which is full member of ERN-RITA. His primary research interest is to improve efficacy and safety of stem cell therapy with particular focus on optimizing conditioning regimens and immune reconstitution after SCT. He has conducted and coordinated many single and multicenter studies including investigator-initiated adoptive cellular therapy trials. He is PI of the ongoing RECOMB trial on lentiviral stem cell gene therapy in RAG1 severe combined immunodeficiency. He is co-founder of the AGORA (Access to Gene therapies fOr RAre disease) consortium, and the past chair of Inborn Errors Working Party of the European Society for Blood and Marrow Transplantation and European Society for Immune Deficiencies.