The Possible Damage from Using CRISPR/Cas9 Are "Seriously Underestimated"

CRISPR (Credit: iStock/Meletios Verras)

Scientists have discovered that CRISPR/Cas9 gene editing can cause greater genetic damage in cells than was previously thought. These results create safety implications for gene therapies using CRISPR/Cas9 in the future as the unexpected damage could lead to dangerous changes in some cells. 

Reported Monday, in Nature Biotechnology, the study reveals that standard tests for detecting DNA changes miss finding this genetic damage, and that caution and specific testing will be required for any potential gene therapies.

The results come shortly after two studies raised a related issue, namely that the gene editing technique could induce the activation of a mechanism associated with DNA damage that leads to cell death, hindering CRISPR activity. According to that study, the world famous scissors could, in other words, inadvertently increase cancer risk in treated cells. 

Previous research had not shown many unforeseen mutations from CRISPR/Cas9 in the DNA at the genome editing target site. To investigate this further the researchers carried out a full systematic study in both mouse and human cells and discovered that CRISPR/Cas9 frequently caused extensive mutations, but at a greater distance from the target site.

What researchers found was that many of the cells had large genetic rearrangements such as DNA deletions and insertions. These could lead to important genes being switched on or off, which could have major implications for CRISPR/Cas9 use in therapies. In addition, some of these changes were too far away from the target site to be seen with standard genotyping methods.

“This is the first systematic assessment of unexpected events resulting from CRISPR/Cas9 editing in therapeutically relevant cells, and we found that changes in the DNA have been seriously underestimated before now,” said Professor Allan Bradley, corresponding author of the study from the Wellcome Sanger Institute. 

“It is important that anyone thinking of using this technology for gene therapy proceeds with caution, and looks very carefully to check for possible harmful effects,” he added. 

Unsurprisingly, the work has implications for how CRISPR/Cas9 is used therapeutically, and three publicly traded CRISPR companies lost more than $300 million in value within the first 20 minutes the study was released, reports STAT.

Reportedly, the companies, Intellia Therapeutics, Editas Medicine, and CRISPR Therapeutics questioned whether the CRISPR-caused DNA damage reported in the new study applied to the kind of cells they’re planning to CRISPR, the website writes.

Academic scientists, on the contrary, were less dismissive of the new study. 

One CRISPR developer have called it “a cautionary note to the [genome-editing] community”, “and consistent with other research showing that the DNA cuts that CRISPR makes, called double-stranded breaks, “can induce the types of genomic DNA rearrangements and deletions they report.” He asked STAT to not be identified, as he didn’t want to jeopardize business relationships with genome-editing companies.

Critics have questioned why scientists don’t see the impact of these DNA changes when they analyse the DNA of CRISPR’d cells. 

“You find what you look for”, Bradley said.   

Earlier this year, CRISPR Therapeutics’ planned to use CRISPR technology on sickle-cell patients, but the clinical trial was put on hold by U.S. regulators before it even had begun.

The biotech uses a similar approach in a clinical trial for beta-thalassemia in Europe that’s slated to begin this year, but this therapy has not been affected by the FDA’s order. 

Doctors at the University of Pennsylvania began enrolling patients for a (first) CRISPR trial in the U.S. earlier this year, where they plan on using the technology to modify human immune cells so that they become expert cancer killers.

Asked what genome analysis he plans to do, lead investigator, Dr. Edward Stadtmauer told STAT that they “are doing extensive testing of the final cellular product as well as the cells within the patient.” 

It remains to see if this paper will reignite researchers’ interest in finding alternatives to the standard CRISPR/Cas9 method for gene editing. 

As for now, further research and specific testing is vital before CRISPR/Cas9 is used in the clinic.