Gene Therapy for Sickle Cell Disease: A Lentiviral Vector Comparison Study

Sickle cell disease (SCD) is an inherited blood disorder caused by a single amino acid substitution in the -globin chain of hemoglobin. Gene therapy is a promising therapeutic alternative, particularly in patients lacking an allogeneic bone marrow (BM) donor. One of the major challenges for an effective gene therapy approach is the design of an efficient vector that combines high-level and long-term -globin expression with high infectivity in primary CD34+ cells. Two lentiviral vectors carrying an anti-sickling -globin transgene (AS3) were directly compared: the Lenti/AS3-FB, and Globe-AS3 with and without the FB insulator. The comparison was performed initially in human BM CD34+ cells derived from SCD patients in an in vitro model of erythroid differentiation. Additionally, the comparison was carried out in two in vivo models: First, an NOD SCID gamma mouse model was used to compare transduction efficiency and -globin expression in human BM CD34+ cells after transplant. Second, a sickle mouse model was used to analyze -globin expression produced from the vectors tested, as well as hematologic correction of the sickle phenotype. While minor differences were found in the vectors in the in vitro study (2.4-fold higher vector copy number in CD34+ cells when using Globe-AS3), no differences were noted in the overall correction of the SCD phenotype in the in vivo mouse model. This study provides a comprehensive in vitro and in vivo analysis of two globin lentiviral vectors, which is useful for determining the optimal candidate for SCD gene therapy.