Base editing of β⁰-thalassemia mutations as a therapeutic strategy for severe β-hemoglobinopathies

Gene therapy has emerged as a promising curative treatment for β-hemoglobinopathies, the most common genetic disorders worldwide. However, current approved approaches still have some limitations in terms of safety and efficacy. Here, we used highly processive adenine base editor (ABE) variants to precisely correct some of the most prevalent and severe β-thalassemia-causing mutations in the β-globin-encoding HBB gene, including CD39 and IVS2-1, using NRCH-ABE8e and SpRY-ABE8e, respectively. More than 90% of editing of hematopoietic stem and progenitor cells (HSPCs) led to improved β-globin expression in their erythroid progeny and persistent correction of both β-thalassemia and sickle cell-β-thalassemia phenotypes. The safety of this strategy was confirmed in HSPCs in vitro and in vivo through the absence of gene dysregulation and any meaningful impact on the DNA mutational burden, RNA deamination, β-globin gene locus integrity, and the clonality of the HSPC graft, as assessed by RNA sequencing, whole-exome sequencing, long-read sequencing, and human HSPC transplantation in immunodeficient mice. Overall, these preclinical studies suggest that base editing-mediated gene correction may be a safe and effective strategy for treating β-hemoglobinopathies.