In the last decade, gene therapy for adenosine deaminase deficiency has been developed as a successful alternative strategy to allogeneic bone marrow transplant and enzyme replacement therapy. Infusion of autologous hematopoietic stem cells, corrected ex vivo by retroviral vectors and combined to low-intensity conditioning regimen, has resulted in immunologic improvement, metabolic correction, and long-term clinical benefits. These findings have opened the way to applications of gene therapy in other primary immune deficiencies using novel vector technology.