The study of Grimley et al et al showed that the use of reduced-intensity melphalan conditioning instead of myeloablative busulfan in seven SCD patients undergoing autologous stem cell transplantation with CD34+ cells transduced with a lentivirus vector inducing enforced expression of γ-globin G16D decreased the duration of thrombocytopenia and neutropenia and accelerated neutrophil and platelet engraftment and reduced the time of hospitalization after transplantation compared to what observed in the studies with currently approved gene therapy products [40]. This evidence concerns the gene CD34 and neutropenia.