Seamless gene correction of beta-thalassemia mutations in patient-specific cells

A major hurdle in gene therapy is the efficient integration of a corrected gene into a patient's genome without mutating off-target sites.

In a paper published today in Genome Research, scientists have used CRISPR/Cas genome editing technology to seamlessly and efficiently correct disease-causing mutations in cells from patients with ?-thalassemia.

?-thalassemia results from inherited DNA mutations in the hemoglobin beta (HBB) gene, resulting in reduced HBB expression in red blood cells and, in the most severe forms, anemia.

The only established curative treatment is hematopoietic stem cell transplantation; however, this treatment requires a matched donor. Gene therapy, which delivers a corrected copy of a gene into patient cells, could bypass the need for a donor. Previous attempts using a virus to randomly insert a normal gene into the genome has been successful in one ?-thalassemia patient, but the long-term effect of viral insertion is not yet known.

To correct HBB mutations directly in a patient's genome, researchers first generated induced pluripotent stem cells, or iPSCs, from skin cells of patients. The real breakthrough came when they applied CRISPR/Cas9 to precisely engineer a double strand DNA break at the HBB locus in these cells, allowing a donor plasmid with the corrected sites to be efficiently integrated, thus replacing the mutated sites.

Importantly, the researchers could differentiate the corrected iPSCs into mature blood cells, and these blood cells showed restored expression of hemoglobin. However, much work is needed before these cells could be transplanted back into a patient for treating ?-thalassemia.