CRISPR Gene Editing May be More Precise with New Technique

Scientists may have taken one step closer to precise genome editing. They've engineered changes to the revolutionary CRISPR-Cas9 genome editing system that significantly cut down on "off-target" editing errors.

The CRISPR-Cas9 system works by making a precisely targeted modification in a cell's DNA. The protein Cas9 alters the DNA at a location that is specified by a short RNA whose sequence matches that of the target site. While Cas9 is known to be highly efficient at cutting its target site, it can sometimes bind to and cut additional sites that are not targeted. This can produce undesired edits that can alter gene expression or knock a gene out entirely.

In this latest study, the researchers used knowledge about the structure of the Cas9 protein to decrease off-target cutting. After experimenting with various possible changes, the scientists found that mutations in three amino acids dramatically reduced off-target cuts.

The newly-engineered enzyme is called "enhanced" S. pyogenes Cas9, or eSpCas9. It will be extremely useful for genome editing applications that require a high level of specificity.

"Many of the safety concerns are related to off-target effects," said Feng Zhang, one of the researchers, in a news release. "We hope the development of eSpCas9 will help address some of those concerns, but we certainly don't see this as a magic bullet. The field is advancing at a rapid pace, and there is still a lot to learn before we can consider applying this technology for clinical use."

The findings are published in the journal Science.

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