Reactivation of the embryonic ζ-globin gene ameliorates severe forms of α-thalassemia.

Hemoglobinopathies are the most common inherited anemias worldwide. While most carriers are asymptomatic or mildly affected, severe forms of α-thalassemia, including severe hemoglobin H (HbH) disease and surviving individuals with Hb Bart's hydrops fetalis syndrome (BHFS), require lifelong transfusion support or stem cell transplantation. Reactivating the silenced embryonic α-like globin (ζ-globin) gene is a promising approach for treating these diseases. Here we identify the key cis-regulatory elements responsible for silencing the ζ-globin gene in definitive erythroid cells and subsequently develop gene-editing strategies that reactivate ζ-globin expression to therapeutically relevant levels. In a preclinical mouse model of BHFS, we show that this strategy rescues the otherwise prenatal lethal condition until late in development (E17.5). Using primary erythroid cells derived from patients with HbH disease and BHFS, we show that these approaches reactivate ζ-globin expression to levels exceeding those achieved in the mouse model, producing therapeutic levels of α-like globin.