For all its well-earned fame, the gene-editing tool CRISPR is, in reality, pretty hard on the genome. It’s a pair of DNA scissors that cuts the double helix, and what’s called “editing” is actually a cell’s hasty attempt to patch things back together. That introduces errors: critics have even called these unpredictable changes a form of “genome vandalism.”
In the words of David Liu, a Harvard University biologist, the ultimate aspiration of genome engineers is “the ability to make virtually any targeted change in the genome of any living cell or organism.”
Liu is introducing “prime editing,” a molecular gadget he says can rewrite any type of genetic error without actually severing the DNA strand, as CRISPR does.
The new technology, which delivers a wider menu of edits with more finesse, is already worth untold sums of money. Even before the paper was published, a syndicate of venture capitalists, including Newpath, Google’s venture arm, and F-Prime, had formed a company, Prime Medicine, and bought rights to it from the Broad Institute, where Liu has a lab.
They say they fixed the error that causes sickle-cell disease (one wrong letter), the one that leads to Tay-Sachs disease (four extra letters), and a mutation that’s a common cause of cystic fibrosis (three missing letters).
The original CRISPR can be made to do some of these tricks too, but with low odds of accurate results, which is why for the last several years Liu’s lab had been trying to extend the technology’s abilities. An earlier invention, base editing, allowed them to transmute certain individual DNA letters into others. Yet not every type of change was possible. Prime editing, they say, could conceivably repair most inherited DNA errors found in the human species that causes genetic disease.