High-level correction of the sickle mutation amplified <i>in vivo</i> during erythroid differentiation

Abstract

ABSTRACT Sickle Cell Disease (SCD), one of the world’s 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 markerless correction of the sickle mutation in more than 30% of long-term engrafting human hematopoietic stem cells (HSCs), using a selection-free protocol that is directly applicable to a clinical setting. We further find that in vivo erythroid differentiation markedly enriches for corrected ß-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 curative levels with a streamlined protocol that is ready to be translated into a therapy. ONE SENTENCE SUMMARY Cas9-mediated correction of the sickle mutation in human hematopoietic stem cells can be accomplished at curative levels.