Gene therapy for primary immunodeficiencies: part 1

► Gene therapy provided a clinical benefit to most of the 60 patients affected by ADA-deficiency or SCID-X1. ► Gene therapy can be a valuable alternative to allogeneic hematopoietic stem cell transplantation. ► Insertional oncogenesis still represents the major issue to solve. ► Homologous recombination is rapidly improving to edit gene mutations.