Use of Gene Editing in Animals

Written By Saachi Jain

Since its fruition in the late 1900s, gene editing has taken a front seat in scientific research as scientists seek cures for harmful medical conditions. Genetically modified animals have become integral to testing various treatments and drugs. Despite advancements in gene editing technologies like CRISPR-Cas9, significant ethical concerns and practical limitations persist. In addition to the profound ethical drawbacks of using genetically modified animals in research, this practice is further exacerbated by the reduced efficacy of animal models in a lab setting compared to a human’s actual response. 

Use of gene editing in animal models

In 1974, German biologist Rudolf Jaenisch successfully transplanted one mouse’s genes into another without causing tumors in the recipient mouse, marking the first instance of genetically modified animals. Today, 50% of the 115 million animals used in science are genetically modified. These animals are typically used to test the function of particular genes in humans in hopes of advancing cures or treatments for genetic diseases and conditions. 

Mice are the most commonly modified animals because a large database of their genome already exists, and they are cheap to use in testing. The most common method for genetic modification is via injection, which induces knockout or insertion mutations in embryonic mice. This targets a particular gene sequence in the mouse’s genome, modifying or replacing it to create symptoms that mimic conditions like HIV, Parkinson’s Disease, or cancer. In some situations, “humanized mice,” or mice modified to have human organs, are also used for further testing of treatments. These mice are often injected with a sample from a human, such as a small strand of DNA or tissue. The mice then synthesize proteins using the human’s genetic code. Through this procedure, humanized mice become an in-vivo model of a human.

Larger animals are more anatomically and physiologically similar to humans, making them preferable for some disease testing. For example, experiments studying Huntington’s Disease can induce neurodegeneration in pigs’ brains. Recent studies have also illustrated the potential of transplanting genetically edited pig organs into humans, saving the need for human donors. Another example is using monkeys to create a realistic model of Autism Spectrum Disorder—typically done by simulating environmental conditions such as maternal infection—and testing the possible biological origins of the disorder. 

Detrimental effects of gene editing in animals

Despite the benefits of genetically modified animals for research purposes, there are significant drawbacks and ethical concerns. For example, treatments on genetically modified animal models may not perfectly replicate the same effects that would occur in human systems. By testing with animal models, time, money, and animal lives are used on treatments that, over 50% of the time, do not work the same in humans. 

In addition, gene editing technology such as CRISPR-Cas9 allows researchers to efficiently and easily create genetically modified animals, but sometimes these edits can become excessive. Gene editing in animals also greatly harms the animals themselves. Without a comprehensive knowledge of an animal’s genome, non-target, accidental gene mutations can lead to unnecessary waste. Many animals develop cancer, others die from adverse effects, and some are killed for their lost use. The genetically modified animals can also develop skeletal abnormalities, seizures, and other terminal diseases. 

To introduce new genes and mutations, researchers modify the animals at the embryonic level and allow the organism to mature to adulthood with the edited genome. In the pursuit of conducting a thorough study, many researchers use drug-induced superovulation for greater embryo output, which forces females to produce up to three eggs per menstrual cycle as opposed to the typical one egg. After using females for their eggs, scientists often kill them via neck dislocation or carbon dioxide poisoning, both of which are torturous processes for the organisms to endure. The embryos themselves are modified and transplanted into a surrogate mother. However, only a small fraction of the transplanted embryos survive. Moreover, only a quarter of surviving embryos, or about 7% of all harvested embryos, are successfully genetically modified. These animals are also usually single-use; in 2015, around 2 million animals used in science in the UK were genetically modified but used only once and killed after experimentation. 

Although gene editing has developed monumentally since its first use and continues to be invaluable for simulating human diseases and testing potential cures, it is unrefined, unethical, and costly—in terms of both resources and animal lives. Looking to the future, alternatives to gene editing must be considered to allow scientific innovation while minimizing ethical implications. 

Saachi Jain
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