Dissecting the epigenetic regulation of the fetal hemoglobin genes to unravel a novel therapeutic approach for ß-hemoglobinopathies

Beta-hemoglobinopathies are severe genetic diseases caused by mutations affecting the production of the adult ß-globin chain. The clinical severity is mitigated by the co-inheritance of mutations that reactivate the production of the fetal ß-like ?-globin in adults. However, the epigenetic mechanisms underlying the adult-to-fetal hemoglobin (HbA-to-HbF) switching are still not fully understood. Here, we used epigenome editing technologies to dissect the molecular mechanisms underlying ?- and ß-globin gene regulation, and to develop novel potential therapeutics for ß-hemoglobinopathies. Targeted removal of DNA methylation by dCas9-Tet1 (alone or together with the deposition of histone acetylation by CBP-dCas9) at the fetal promoters led to efficient and durable ?-globin reactivation, demonstrating that DNA methylation is a driver for HbF repression. This strategy, characterized by high specificity and a good safety profile, led to a substantial correction of the pathological phenotype in erythroid cells from patients with sickle cell disease.