Hematopoietic stem cell therapy with gene modification to treat sickle cell disease.

Hematopoietic stem cells (HSCs) reconstitute blood cells throughout life. DNA-level correction of HSCs allows for a one-time cure of genetic diseases, including sickle cell disease (SCD). Sickle cell disease is one of the most common single-gene disorders; therefore, SCD is a prime candidate for gene therapy. Several drug therapies are available for SCD, including hydroxyurea, which is the first-line choice despite requiring lifelong administration. Allogeneic HSC transplantation is a one-time, curative treatment for SCD with limited availability of histocompatible donors. Therefore, autologous HSC gene therapy was developed using patients' own HSCs with lentiviral gene addition/silencing and clustered regularly interspaced short palindromic repeats gene editing, making gene therapy applicable to most patients. However, the established method of HSC gene therapy requires costly and complex ex vivo HSC culture. Therefore, in vivo HSC gene therapy is being developed to treat SCD, envisioning a single-injection HSC-targeted gene delivery system. This review discusses various therapeutic methods to treat SCD, the development of HSC gene therapy, and clinical gene therapy trials in SCD, ranging from FDA-approved to novel in vivo gene therapy.