Curative Therapy of Sickle Cell Disease Using Gene Editing Technologies

Sickle cell disease (SCD) is a monogenic blood disorder caused by a single nucleotide mutation in the β-globin gene that swaps the hydrophilic glutamic acid at position six with the hydrophobic valine. Haematopoietic stem cell transplantation is the only curative treatment for SCD, but has major risks and problems. Autologous gene therapy, in which "all" gene copy is put into the patient's cells, a faulty gene is fixed, or genes are deactivated, has the advantage of not requiring the patient to find a perfect donor. Gene therapy has been shown to be curative in preclinical and clinical trials. LentiGlobin, a self-inactivating lentiviral vector encoding the human antiserpentine. Haemoglobin Subunit Beta, is now being tested in clinical trials. However, lentiviral vector-based gene therapy poses potential dangers such as Replication-Competent Lentivirus and insertional mutagenesis. Gene editing technologies allow for permanent modification of disease-causing genes, and HSPCs are the therapeutic product for autologous transplantation. CRISPR/Cas9 is a versatile and efficient class of programmable nucleases that use single-stranded guide RNA sequences and the Cas9 endonuclease to attach to a specific target in the genome. Base editors are generated by pairing a nucleotide deaminase with a Cas9 protein that is catalytically suppressed. All four gene editing strategies have been evaluated in HSPCs for the treatment of SCD, including correcting the sickle cell mutation in HBB, producing enough HbF to reverse the sickle shape of the RBC, focusing on the HbF transcriptional repressors, and introducing the advantageous HPF mutations. CRISPR/Cas9 gene editing has been used to treat SCD, including correcting the sickle cell mutation, producing enough HbF to reverse the sickle shape, focusing on HbF transcriptional repressors, and introducing HPFH mutations. Future challenges for the success of CRISPR/Cas9 gene editing include off-target effects, gene repair efficiency, and in vivo transplantation of gene-edited HSPC.