Increased levels of red cell fetal hemogloblin, whether due to hereditary persistence of expression or from induction with
hydroxyurea therapy, effectively ameliorate
sickle cell disease (SCD). Therefore, we developed erythroid-specific,
gamma-globin lentiviral vectors for hematopoietic stem cell (HSC)-targeted gene therapy with the goal of permanently increasing
fetal hemoglobin (HbF) production in sickle red cells. We evaluated two different
gamma-globin lentiviral vectors for therapeutic efficacy in the BERK sickle cell mouse model. The first vector, V5, contained the
gamma-globin gene driven by 3.1 kb of
beta-globin regulatory sequences and a 130-bp
beta-globin promoter. The second vector, V5m3, was identical except that the
gamma-globin 3'-untranslated region (3'-UTR) was replaced with the
beta-globin 3'-UTR. Adult erythroid cells have
beta-globin mRNA 3'-UTR-binding
proteins that enhance
beta-globin mRNA stability and we postulated this design might enhance
gamma-globin expression. Stem cell gene transfer was efficient and nearly all red cells in transplanted mice expressed human
gamma-globin. Both vectors demonstrated efficacy in disease correction, with the V5m3 vector producing a higher level of
gamma-globin mRNA which was associated with high-level correction of
anemia and secondary organ pathology. These data support the rationale for a gene
therapy approach to SCD by permanently enhancing HbF using
a gamma-globin lentiviral vector.