CRISPR-based therapeutic genome editing for inherited blood disorders

Therapeutic genome editing promises to transform medicine. Pivotal discoveries have provided a diverse and versatile set of tools to correct pathogenic mutations or produce protective alleles using CRISPR-based technologies. These innovative therapies are especially adaptable for blood and immune disorders, where clinical methods allow haematopoietic stem cells (HSCs) to be mobilized, harvested, engineered ex vivo and transplanted back into a patient to permanently replace their blood system. This paradigm has been exemplified with the first US Food and Drug Administration (FDA)-approved CRISPR-Cas9 therapy for sickle cell disease and β-thalassaemia, exa-cel (Casgevy). Although promising, efficient delivery of gene edits involves complicated ex vivo manipulation and toxic myeloablative conditioning. The quiescent and elusive nature of HSCs also brings associated challenges. In this Review, we explore the state-of-the-art genome editing technologies of nucleases, base editors and prime editors, which hold promise to address unmet clinical needs for patients with inherited haematological disorders. We highlight the progress made for several disorders and discuss the challenges that remain for ex vivo and in vivo targeting of HSCs for next-generation gene therapies.