Universal Gene Correction Approaches for β-hemoglobinopathies Using CRISPR-Cas9 and Adeno-Associated Virus Serotype 6 Donor Templates

Mutations in the human beta-globin gene are the cause of beta-hemoglobinopathies, one of the most common inherited single-gene blood disorders in the world. Novel therapeutic approaches are based on lentiviral vectors (LVs) or CRISPR-Cas9-mediated gene disruption to express adult hemoglobin (HbA), or to reactivate the completely functional fetal hemoglobin, respectively. Nonetheless, LVs present a risk of insertional mutagenesis, while gene-disrupting transcription factors (BCL11A, KLF1) involved in the fetal-to-adult hemoglobin switch might generate dysregulation of other cellular processes. Therefore, universal gene addition/correction approaches combining CRISPR-Cas9 and homology directed repair (HDR) by delivering a DNA repair template through adeno-associated virus could mitigate the limitations of both lentiviral gene transfer and gene disruption strategies, ensuring targeted integration and controlled transgene expression. In this study, we attained high rates of gene addition (up to 12%) and gene correction (up to 38%) in hematopoietic stem and progenitor cells from healthy donors without any cell sorting/enrichment or the application of HDR enhancers. Furthermore, these approaches were tested in heterozygous (beta(0)/beta(+)) and homozygous (beta(0)/beta(0), beta(+)/beta(+)) beta-thalassemia patients, achieving a significant increase in HbA and demonstrating the universal therapeutic potential of this study for the treatment of beta-hemoglobinopathies.