Schematic diagrams of lentiviral vectors expressing the human α-globin gene. Vectors differ in the inclusion and orientation of core sequences of the DNase I hypersensitive sites (HS) of the β-globin locus control region (LCR) but maintain the same short β-globin promoter, 3′ enhancer, and untranslated regions (UTRs). These vectors also use a 3′ self-inactivating LTR (sinLTR) that includes an Ankyrin insulator element and HBA2 genomic sequence. All vectors include HS2, HS3, and HS4 of the β-globin LCR. In addition, ALS19αI includes HS1 (in 3′→5′ orientation), whereas ALS20αI includes HS1 (in 3′→5′ orientation).