BCH, Boston Children’s Hospital, Boston, MA; CCHMC, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH; EFS, elongation factor 1a short; γRV, gammaretrovirus; GOSH, Great Ormond Street Hospital, London, United Kingdom; HNEM, Hopital Necker Enfants Malades, Paris, France; LV, lentivirus; NHGRI, National Human Genome Research Institute, Bethesda, MD; NIAID, National Institute of Allergy and Infectious Diseases, Bethesda, MD; OSR-TIGET, Ospedale San Raffaele–Telethon Institute for Gene Therapy, Milan, Italy; RFH, Royal Free Hospital, London, United Kingdom; SCRI, Seattle Children’s Research Institute, Seattle, WA, USA; SG-IMI, Shenzhen Geno-Immune Medical Institute, Shenzhen, People’s Republic of China; SIN, self-inactivating; SJCRH, St. Jude Childhood Research Institute, Memphis, TN; SNU, Seoul National University, Seoul, Republic of Korea; UCHZ, University Children’s Hospital Zurich, Zurich, Switzerland; UCL, University College London, London, United Kingdom; UCLA, University of California, Los Angeles, CA; UCSF, University of California, San Francisco, CA; UHF, University Hospital Frankfurt, Frankfurt, Germany.