Coordinated β-globin expression and α2-globin reduction in a multiplex lentiviral gene therapy vector for β-thalassemia.

Abstract A primary challenge in lentiviral gene therapy of β-hemoglobinopathies is to maintain low vector copy numbers to avoid genotoxicity, while becoming reliably therapeutic for all genotypes. We have thus designed a high-titer lentiviral vector, LVβ-shα2, which allows for coordinated expression of the therapeutic βA-T87Q-globin gene and of an intron-embedded miR-30-based shRNA selectively targeting the α2-globin mRNA. Our approach was guided by the knowledge that moderate reduction of α-globin chain synthesis ameliorates disease severity in β-thalassemia. We demonstrate that LVβ-shα2 reduces α2-globin mRNA expression in erythroid cells, while keeping α1-globin mRNA levels unchanged and βA-T87Q-globin gene expression identical to the parent vector. Compared to the first βA-T87Q-globin lentiviral vector having received conditional marketing authorization, BB305, LVβ-shα2 shows 1.7-fold greater potency to improve α/β ratios. It may thus result in greater therapeutic efficacy and reliability for the most severe types of β-thalassemia and provide an improved benefit/risk ratio regardless of the β-thalassemia genotype.