In vivo selection for corrected β-globin alleles after CRISPR/Cas9 editing in human sickle hematopoietic stem cells enhances therapeutic potential

Sickle Cell Disease (SCD), one of the world9s most common genetic disorders, causes anemia and progressive multiorgan damage that typically shortens lifespan by decades; currently there is no broadly applicable curative therapy. Here we show that Cas9 RNP-mediated gene editing with an ssDNA oligonucleotide donor yields more than 20% correction of the sickle mutation in long-term engrafting human HSCs. Using RNA-seq, we further find that in vivo erythroid differentiation markedly enriches for cells carrying corrected β-globin alleles. Adoption of a high-fidelity Cas9 variant demonstrates that this approach can yield efficient editing with almost no off-target events. These findings indicate that the sickle mutation can be corrected in human HSCs at levels that are likely to be curative if translated into a therapy.