Ex Vivo Expansion With E478 Increases The Rate Of Crispr-Mediated Homology Directed Repair Of The Beta-Globin Gene In Human Hematopoietic Stem Cells By > 10-Fold And Improves In Vivo Engraftment By > 120-Fold

Background. Site-specific gene correction of hematopoietic stem cells (HSCs) via homology directed repair (HDR) has the potential to precisely repair defective genes and provide life-long cures for a variety of blood-based diseases. It is possible to obtain high levels of HDR during in vitro HSC culture, but these cells fail to robustly engraft in vivo, suggesting that the procedure of HDR compromises HSC function or that true HSCs are not undergoing HDR. Cells need to be actively cycling in order to undergo HDR, but conditions that allow HSC replication in vitro without compromising HSC number and function remain elusive. Thus, most HDR protocols minimize time in culture, potentially limiting HDR rates and cell yield. We recently reported that ex vivo expansion of HSCs with an aryl hydrocarbon receptor (AHR) antagonist is a clinically validated method to expand HSCs. The AHR antagonist-expanded CD34+ cell therapy, MGTA-456, results in rapid and durable recovery in patients with hematologic malignancies and inherited metabolic diseases (Wagner et al Cell Stem Cell 2016; Orchard et al AAN 2019).