Principle of gene therapies ex vivo and in vivo. Gene therapy ex vivo allies the technics of gene therapy and stem cell therapy. It is a sampling of the patient's cells, that are then corrected by gene transfer (use of a viral vector), then reimplanted (autotransplantation). Gene therapy in vivo consists in injecting directly the vector bearing the therapeutic genetics into the patient's body, without going through a transplantation of cells.