This report provides an overview of gene therapy use of stem cell for the treatment of primary immunodeficiencies (PIDs). Human stem cells are non-specialized cells, able to differentiate, starting from the embryo and for the whole duration of the life of each individual, into different cell types, through two types of cell division: symmetrical creating two stem cells and asymmetric differentiating to any cell lineage. These cells represented the ideal target for gene correction to guarantee production of engineered multi-lineage progeny. Their use in gene therapy led to the development of an effective treatment for PIDs, such as ADA deficiency, SCID-X1, WAS, CGD, and providing potential long-term clinical benefit for affected patients. © 2018, Accademia Nazionale dei Lincei.