The use of genetically modified (GM) animals in science is a significant cause of the year-on-year increase in the number of animals used in experiments around the world.

For example, in the UK alone, half of all experiments (around 2 million) carried out in 2017 involved the production and breeding of GM animals that were not used in further research; and 38% of actual experiments used GM animals (Ref 1). The welfare concerns for these animals are considerable, and suffering has been acknowledged at every step of the GM process (Ref. 2,3).

A new method called the CRISPR/Cas9 system, or simply CRISPR, has entered the limelight mainly because, compared to other methods, it is an inexpensive, relatively simple and quick way of producing GM animals. It has also been claimed to not only be more accurate than traditional methods but to actually help reduce animal numbers (because it is so accurate that less animals might be wasted). Unfortunately, neither claim is true.

In fact, CRISPR is only likely to exacerbate the current ethical and welfare problems associated with the production of GM animals by simply increasing the number of GM animals created. This will more than offset any potential benefits that may arise from its possible greater efficiency in the future.

While CRISPR may be more efficient and specific at generating desired genetic modifications, there is evidence that it is far from good enough. Studies have shown that the efficiency of CRISPR to insert or ‘knock-in’ a particular gene in an animal is less than 4% (Ref. 4) or less than 1% (Ref. 5), while the efficiency to delete or ‘knock-out’ a gene is around 7% (Ref. 5). Furthermore, it appears that CRISPR introduces unwanted or ‘off-target’ mutations (in addition to those that are intended). While the degree is open to question, these unintended genetic modifications can be numerous, and may well have serious consequences.

Perhaps even more troubling is the increasing use of CRISPR in larger animals. Some scientists are calling for more GM monkeys or dogs to be created, in an effort to ‘fix’ rodent models of human diseases that are increasingly acknowledged as failures (Ref. 6,7). Just last month, two experiments that involved the use of CRISPR in monkeys and dogs were published in high-profile scientific journals Nature and Science:

•  In a particularly cruel experiment on monkeys in China, researchers wanted to determine the function of a gene thought to play a significant role in ageing. This gene was ‘knocked-out’ of GM monkeys using CRISPR. To generate these monkeys, 48 embryos were transferred into 12 surrogate mothers, and of these, only 4 were successfully impregnated, with 3 completing their pregnancy and giving birth. Sadly, all 3 babies died soon after birth, and showed ‘retarded development’ that resembled that of a 2 to 4-month old foetus. Shockingly, the authors plan to continue to create these monkeys to study miscarriages and stillbirths (Ref. 8). We are writing to Nature to complain about their decision to publish this unethical study, which has little scientific merit.
• Scientists at the UK’s Royal Veterinary College have been breeding dogs with Duchenne muscular dystrophy (DMD), a rare and devastating muscle-wasting disease, in a bid to find a cure for the condition in humans. According to a journalist who visited the breeding facility, dogs with the disease were visibly weak and were seen stumbling and struggling to walk9. The scientists claim that they have managed to ‘cure’ DMD in dogs thanks to CRISPR, which they used to edit a mutated gene to once again produce dystrophin, an important muscle protein. Regardless of the hype, the study has already been widely criticised for several reasons including; its short duration (less than 2 months), the small number of dogs used (4 beagles), and uncertainty surrounding the long-term effects of the CRISPR, e.g. possibility that cancer-causing mutations may be introduced. Further, while the dogs were able to produce dystrophin, there was little evidence they regained any muscle function. Sadly, the researchers plan to conduct longer lasting experiments on a larger number of dogs (Ref. 10).

Fortunately, there are scientists who do not support the breeding and use of GM dogs and monkeys, and who warn against it for both scientific (e.g. they are difficult to successfully create) and animal welfare reasons (Ref. 11).

Animals have always been bad models for humans due to species differences, and no amount of genetic modification can remedy that, even if those techniques were perfect. Instead of trying to ‘improve’ GM processes, we should be working towards the greater adoption and use of technologically advanced and human-specific alternatives such as 3D culture of human stem cells, human organoids and tissue/body-on-a-chip technologies, which are already being used to investigate a wide range of diseases.

Next year the European Commission President’s European Group on Ethics in Science and New Technologies (EGE) will be reviewing the ethics of gene editing techniques and will be discussing whether it is ethical to produce GM monkeys. We will be ensuring our concerns are shared with them.

References:

1. UK Home Office. (2018). Statistics of Scientific Procedures on Living Animals: Great Britain 2017. [online] Available at: https://www.gov.uk/government/statistics/statistics-of-scientific-procedures-on-living-animals-great-britain-2017.
2. LASA (Laboratory Animal Science Association). (2008). Position paper: transgenics. [online] Available: http://www.lasa.co.uk/PDF/position_transgenics.pdf
3. BVAAWF/FRAME/RSPCA/UFAW Joint Working Group on Refinement (2003). Refinement and reduction in the production of genetically modified mice. Laboratory Animals ;37 Suppl 1:S1-S49.
4. Genome editing using CRISPR/Cas9-based knock-in approaches in zebrafish. (2017). Methods 121, 77-85.
5. Ultra-superovulation for the CRISPR-Cas9-mediated production of gene-knockout, single-amino-acid-substituted, and floxed mice. (2016). Biology Open 5, 1142-1148.
6. Refining strategies to translate genome editing to the clinic. (2017). Nature Medicine 23, 415-423.
7. Opportunities and challenges in modeling human brain disorders in transgenic primates. (2016). Nature Neuroscience 19, 1123-1130.
8. SIRT6 deficiency results in developmental retardation in cynomolgus monkeys. (2018). Nature, 560: 661-665.
9. Beagles bred with muscular dystrophy offer ‘hope of a human cure’. (2015). The Guardian, 14 November: http://www.theguardian.com/science/2015/nov/15/beagles-study-hope-cure-muscular-dystrophy.
10. In dogs, CRISPR fixes a muscular dystrophy. (2018). Science, 36(1): 835.
11. Every silver lining has a cloud: the scientific and animal welfare issues surrounding a new approach to the production of transgenic animals. (2014). Alternatives to Laboratory Animals 42, 137-145.