© GEORGE RETSECKTargeted gene editing is an experimental therapeutic approach that avoids the risk of insertional mutagenesis associated with the more traditional gene-therapy method of adding a functional gene copy to cells. In gene editing, special nuclease enzymes, such as zinc finger nucleases (ZFNs), are directed to cut the mutant gene of interest, and a replacement piece of DNA—containing the desired sequence—is then integrated by means of the cell’s own homology-directed repair pathway.
While the approach has been used to correct mutations in a variety of cell lines, attempts to edit genes in human primary hematopoietic stem cells (HSCs)—important targets for treating a number of inherited blood disorders—have proved unsuccessful.
“The real hurdle was to achieve gene editing in cells relevant for [clinical] translation,” says Luigi Naldini of the San Raffaele Scientific Institute in Milan. The challenge is that homology-directed repair requires cells to be cycling, and, for the most part, HSCs are quiescent. Stimulating HSCs to divide induces differentiation, however, so the team “fine-tuned the conditions” to both expand HSCs and maintain their undifferentiated state, Naldini explains. These tweaks have now allowed his team to use ZFNs to rewrite a disease-causing mutation in HSCs from a patient ...
