The therapeutic potential of genome editing for β-thalassemia

Abstract

The rapid advances in the field of genome editing using targeted endonucleases have called considerable attention to the potential of this technology for human gene therapy. Targeted correction of disease-causing mutations could ensure lifelong, tissue-specific expression of the relevant gene, thereby alleviating or resolving a specific disease phenotype. In this review, we aim to explore the potential of this technology for the therapy of β-thalassemia. This blood disorder is caused by mutations in the gene encoding the β-globin chain of hemoglobin, leading to severe anemia in affected patients. Curative allogeneic bone marrow transplantation is available only to a small subset of patients, leaving the majority of patients dependent on regular blood transfusions and iron chelation therapy. The transfer of gene-corrected autologous hematopoietic stem cells could provide a therapeutic alternative, as recent results from gene therapy trials using a lentiviral gene addition approach have demonstrated. Genome editing has the potential to further advance this approach as it eliminates the need for semi-randomly integrating viral vectors and their associated risk of insertional mutagenesis. In the following pages we will highlight the advantages and risks of genome editing compared to standard therapy for β-thalassemia and elaborate on lessons learned from recent gene therapy trials.

Keywords: gene therapy; genome; thalassemia.

Figure 1.. Genome editing technologies.

ZFNs, TALENs, and CRISPR/Cas9 are used to introduce site-specific DSBs into a target genome. Subsequently, cellular repair mechanisms can be harnessed to introduce precise genetic modifications. Small insertions and deletions generated by NHEJ can be used for gene knockout. In the presence of a homologous repair template, new sequences can be incorporated via HDR, allowing for gene repair, transgene insertion, and gene replacement.

Figure 2.. Publications on genome editing between 2005 and 2014.

Data obtained from Medline trend using the search terms “CRISPR Cas9”, “Zinc-finger nuclease”, and “TALEN” show an increase in the use of programmable endonucleases during this period .