An improved medium formulation for efficient <i>ex vivo</i> gene editing, expansion and engraftment of hematopoietic stem and progenitor cells.

"Declaration of interests A.J.T. is on the Scientific Advisory Board of Orchard Therapeutics and Rocket Pharmaceuticals."

"We thank Dr. Ayad Eddaoudi (Flow Cytometry Core Facility, 10.13039/501100000765University College London) for assistance with flow cytometry and cell sorting; R.R., W.V., G.S., and A.J.T. were supported by the 10.13039/100010269Wellcome Trust (104807/Z/14/Z) and the 10.13039/501100000272NIHR Biomedical Research Center at Great Ormond Street Hospital for Children NHS Foundation Trust and 10.13039/501100000765University College London. A.C., A.N., and Z.S. were supported by the GOSH Children’s Charity-LifeArc Therapeutic Accelerator Grant (VS0420), the University College London Therapeutic Acceleration Support Fund, and the 10.13039/501100000272NIHR Biomedical Research Center at Great Ormond Street Hospital for Children NHS Foundation Trust and 10.13039/501100000765University College London."