A study that cast doubt on the usefulness of CRISPR-Cas9 “gene editing” technology to introduce genetic changes in animals has been retracted by the journal Nature Methods. Among those refuting the work were Professor Kent Lloyd, director of the UC Davis Mouse Biology Program, and colleagues from the International Mouse Phenotyping Consortium, whose letter was one of five published by the journal March 30.
CRISPR-Cas9 can be used to introduce very specific edits into DNA. In laboratory mice, the technology could be used to make edits in embryos that are then grown to adult mice. One of the attractions of CRISPR-Cas9 is that it is supposed to make these edits without affecting other genes.
But the original paper by Kellie Schaefer of Stanford University and colleagues claimed to show that gene-edited mice had large numbers of genetic changes outside the target area. These changes are called single-nucleotide variants, or SNVs, because they involve changing a single “letter” of DNA. If CRISPR-Cas9 were to produce many such off-target changes, it would be a serious setback to using the technology.
In their response, Lloyd and IMPC colleagues Lauryl Nutter, Jason Heaney, Stephen Murray, John Seavitt, William Skarnes, Lydia Teboul, Steve Brown and Mark Moore argue instead that these differences between the gene-edited and control mice in the original study were due to natural variations and genetic drift. Although technically the same strain, the test and control mice came from different breeding stocks that had been separated for several generations, providing enough time for their DNA to diverge a bit.
Other studies do not show evidence of the off-target genetic changes found by Schaefer and colleagues, they said.
The affair shows the need for standardized approaches to such gene-editing studies, Nutter, Lloyd and colleagues said.
“Only with excellent quality assurance during production and quality control of derived mouse lines can we have confidence in our ability to generate reliable and reproducible data,” they conclude.
Schaefer and colleagues recently published a preprint contradicting their earlier work.
The International Mouse Phenotyping Consortium aims to produce a complete catalog of all genes in the laboratory mouse. The consortium includes 15 research institutes and centers worldwide, including UC Davis.
Response to “Unexpected mutations after CRISPR–Cas9 editing in vivo” (Nature Methods)