Novel expansion platforms enhance HSC gene editing

Due to their potency, hematopoietic stem cells (HSCs) are a particularly attractive target for gene therapy. Indeed, the rapid adoption of genetic precision tools, such as CRISPR/Cas9, has put HSCs on center stage of therapeutic genome editing applications. However, due to the low frequency of functional HSCs, protocols for their ex vivo expansion are crucial for the generation of gene edited HSC grafts. Unfortunately, attempts to induce proliferation of HSCs outside of their physiologic niche often result in the loss of self-renewal. Over the past years, our group has focused on establishing culture conditions permissive to bone fide HSC expansion. Recently, we have reported that serum replacement by synthetic polymers combined with all-recombinant cytokine supplementation greatly enhances ex vivo HSC proliferation while maintaining their self-renewal properties. We succeeded in applying our culture system to gene editing, demonstrating that Cas9-edited, expanded HSCs corrected the immunodeficient phenotype in a murine SCID model. Further work has established a novel polymer-based system which supports the expansion of edited HSCs to the single cell level, allowing for marker-free selection strategies. This talk will highlight the encouraging potential of our defined HSC expansion platform and demonstrate its utility to gene editing and other HSC-centric therapeutic strategies.