The CRISPR-Cas9 genome editing technique is not without risk. In two mice treated with “genetic scissors”, more than 1000 parasitic mutations were observed.
Human clinical trials are already underway in China to assess the effectiveness of CRISPR-Cas9, the gene-editing technique, in the treatment of lung cancer. But scientists who praise the safety of the method could well have gone a little too quickly, believe researchers at Columbia University (United States).
In an article published in the journal Nature Methods, they alert on the results observed in two mice. Successfully treated for genetic blindness using this “genetic scissors” technique, the two rodents exhibited, after therapy, numerous mutations throughout their genome.
Repair faults
CRISPR-Cas9 is a gene editing technology developed by the French microbiologist, geneticist and biochemist Emmanuelle Charpentier and her American colleague Jennifer Doudna. It allows DNA strands to be cut at the desired location, to remove or introduce a sequence of a gene.
It would therefore make it possible, for genetic diseases, to replace defective genes with a healthy DNA sequence. For this discovery, the two researchers have been rewarded many times, and are approached for obtaining a Nobel Prize.
It has indeed revolutionized biotechnology, and medical applications are numerous. In addition, the research carried out so far had not revealed any particular danger of unwanted genetic mutations, apart from the targeted genes.
A potential danger
But according to researchers at Columbia University, 1,500 mutations of nucleotides, the building blocks of DNA, were observed outside the intended areas of intervention in the two treated mice. Even more worrying, CRISPR-Cas9 would have caused 100 insertions or deletions of DNA sequences.
Following the editing of their genome, the mice did not seem to suffer from any particular pathologies. But these mutations are potentially dangerous, and can cause cancer or other genetic diseases.
A complex method
And if previous studies had not found these mutations, it is because the scientists were not looking in the right place. Most of them had used computer algorithms to identify areas of the genome that were most likely to be affected, then analyzed them for deletions or insertions.
Methods ill-suited to live animals, says Dr. Stephen Tsang, ophthalmologist and associate professor of pathology and cell biology at Columbia University, lead author of the study published in Nature methods.
“Researchers who don’t use whole genome sequencing to find delocalized effects are potentially missing out on important mutations,” he explains. Even a simple nucleotide change can have a significant impact. “
Reassess the risks
This discovery will undoubtedly cool a little the frenzy around the technique which, in addition to the Chinese trial, is planned in a clinical trial on several cancers, in the United States, at the instigation of the NIH, the institute of American medical research.
All therapies have side effects, and this finding does not call everything into question. But it may help calm the CRISPR-Cas9 storm a little. A calm that would allow more precautions to be taken.
“We hope that our observations will encourage other researchers to use full genome sequencing to determine the off-target effects of CRISPR techniques, and study the different versions in search of the safest, most accurate method,” concludes Dr Tsang.
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