CRISPR genome editing far safer than previously thought
CRISPR gene-editing technology is much safer than previously thought, according to new research published in Nature Methods. Concerns about the technique leading to unanticipated changes in the genome are addressed in the paper, which demonstrates that such off-target mutations are actually extremely rare.
The offspring of mice born from an embryo modified using CRISPR-Cas9 had their entire genomes sequenced and analysed to see if there were any signs of damage. Researchers found no significant off-target mutations that could be linked to CRISPR. This is the first time a whole-genome study of this kind has been performed using animal models.
“CRISPR technology is much safer than we have been led to believe from studies in cancer cell lines. When we used CRISPR-Cas9 in normal mouse embryos, we observed no unexpected damage. Future studies addressing CRISPR specificity and off-target mutations will need to focus on normal embryos or cells.”
Dr William Skarnes A senior author from the Wellcome Trust Sanger Institute
Previous research suggests that swapping the DNA-cutting enzyme Cas9 RNA for Cas9 nickase, a more targeted system, could make genome editing even safer. Nickases work in pairs, locating and cutting directly opposite points on the two-stranded DNA molecule. Errors are extremely unlikely to cause damage in this system because the probability of both nickases reaching the same point in the genome accidently is very low and single nickases can’t cut the DNA alone.
“There is very little difference between using wild-type Cas9 and nickases. We found only one highly-related site damaged in Cas9-treated mice, compared to no damage at all in nickase-treated animals. One drawback of the nickase approach is we’re depending on two incredibly precise events happening at the same time, so there is a greater chance that the experiment will fail. We’ve shown in this research that wild-type Cas9, which can reach more of the genome, can be just as safe.”
Dr Vivek Iyer first author from the Sanger Institute
The success of CRISPR-Cas9 in generating knock-out mice from direct modification of one-cell embryos could help to reduce the number of mice used in genetic research. Historically Methods for generating knock-out mice involve the culture and modification of embryonic stem cells, which is expensive and time consuming. The process of culturing embryonic stem cells before implantation in the mother can also introduce significant changes to the genome.
Extended breeding of embryonic stem cell-derived chimaeras is often required to transmit the genetic change to their offspring. By eliminating embryonic stem cell culture, CRISPR would significantly reduce the cost of mouse production and researchers estimate the number of mice will be reduced by a third, while simultaneously increasing accuracy and efficiency.
“This technology presents us with an incredible opportunity. If we can show, as these results begin to, that CRISPR can be used safely, we could improve the efficiency of breeding and reduce animal use dramatically while still empowering research.”
Professor Allan Bradley, Director Emeritus at the Sanger Institute and pioneer of the embryonic stem cell technology used to produce mouse mutants
Just two guide RNAs, chemicals used to direct CRISPR-Cas9 enzymes to the correct location, were tested in this piece of research. More studies like this, looking at the effect of CRISPR-Cas9 editing in different regions of the genome, will be required before CRISPR can be declared safe for use in human therapies.
“The potential of CRISPR is enormous. It is already transforming drug discovery; if we can continue to demonstrate its safety and efficiency in animal models, we can begin to think about the impact the technology could have in human medicine.”
Dr Xingxu Huang A senior author from Nanjing University currently working in ShanghaiTech University
More information
Funding
This work was supported by the 973 programme to Dr Xingxu Huang and a core grant from the Wellcome Trust to Dr William Skarnes.
Participating Centres
- Wellcome Trust Sanger Institute
- Nanjing University
- Soochow University
Publications:
Selected websites
Nanjing University
Nanjing University is one of the oldest and most prestigious institutions of higher learning in China. With the motto of ‘Sincerity with Aspiration, Perseverance and Integrity,’ this university carries the spirit of constant striving for educational and academic excellence. In the past 105 years, Nanjing University has cultivated a great number of talents, contributing greatly to the national prosperity and the revitalization of the Chinese nation. We aim to be a cradle for preparing innovative talents for the future, a frontier for activities giving insight to the unknown world, seeking truth, providing scientific grounds for solving important problems encountered by humanity; we aim to be an important source of innovation and technology transfer and a bridge for cooperation and exchange between different cultures and civilizations.
Soochow University
Soochow University is located in the ancient town of Suzhou, also called ‘Paradise on Earth’. The university is part of the national ‘211 Project’ and is a ‘2011 Plan’ university. It is also one of the Jiangsu provincial key comprehensive universities. It has grown from the former Soochow University founded in 1900. Today, Soochow University has developed into a comprehensive university with 12 major disciplines: philosophy, economics, law, education, literature, history, science, engineering, agriculture, medicine, management science, and art. It has a variety of programs and a strong foundation for students to get the education they need in almost any area.
The Wellcome Trust Sanger Institute
The Wellcome Trust Sanger Institute is one of the world’s leading genome centres. Through its ability to conduct research at scale, it is able to engage in bold and long-term exploratory projects that are designed to influence and empower medical science globally. Institute research findings, generated through its own research programmes and through its leading role in international consortia, are being used to develop new diagnostics and treatments for human disease.
The Wellcome Trust
The Wellcome Trust is a global charitable foundation dedicated to achieving extraordinary improvements in human and animal health. We support the brightest minds in biomedical research and the medical humanities. Our breadth of support includes public engagement, education and the application of research to improve health. We are independent of both political and commercial interests.
