Efficient CRISPR-Cas9-based genome editing of β-globin gene on erythroid cells from homozygous β039-thalassemia patients

Gene editing by the CRISPR-Cas9 nuclease system technology can be considered among the most promising strategies to correct hereditary mutations in a variety of monogenic diseases. In this paper, we present for the first time the correction, by CRISPR-Cas9 gene editing, of the beta(0)39-thalassemia mutation, one of the most frequent in the Mediterranean area. The results obtained demonstrated the presence of normal beta-globin genes after CRISPR-Cas9 correction of the beta(0)39-thalassemia mutation performed on erythroid precursor cells from homozygous beta(0)39-thalassemia patients. This was demonstrated by allele-specific PCR and sequencing. Accumulation of corrected beta-globin mRNA and relevant "de novo" production of beta-globin and adult hemoglobin (HbA) were found with high efficiency. The CRISPR-Cas9-forced HbA production levels were associated with a significant reduction of the excess of free alpha-globin chains. Genomic toxicity of the editing procedure (low indels and no off-targeting) was analyzed. The protocol might be the starting point for the development of an efficient editing of CD34(+) cells derived from beta(0)39 patients and for the design of combined treatments using, together with the CRISPR-Cas9 editing of the beta-globin gene, other therapeutic approaches, such as, for instance, induction of HbA and/or fetal hemoglobin (HbF) using chemical inducers.