Avoiding Unintended Consequences in Genetic Editing

The pig cells multiplying in this embryo contain a carefully introduced genetic alteration. By the time this story airs, this University of Missouri swine embryo will have become a piglet in the school’s growing herd of genetically edited pigs.

This herd’s original purposes varied from growing organs for human transplant to studying transmission of diseases in humans and livestock. The herd’s existence helped Mizzou researcher Kiho Lee secure a $3 million grant from the National Institutes of Health. Lee’s study, which also involves USDA research scientists, is designed to pinpoint any unintended consequences of genetic editing. His work will be shared with other geneticists to help them do the same.

Kiho Lee, University of Missouri: “I thought: We need to invest on developing systems to be able to quickly and accurately identify these unintended genetic modifications and develop a strategy to reduce these side effects if any.”

Although he spent much of his life in the U.S., Lee was a high school student in South Korea when a news item about the world’s first mammal cloned from an adult cell – a sheep in Scotland named Dolly - caught his attention.

Kiho Lee, University of Missouri: “I really didn't know what to do as a career or even picking a major in a university. But then that year, Dolly the sheep was born and that got me really intrigued. And I thought as a teenager I wanted to do something unique and special.”

His dad wanted him to become a lawyer, but Lee stuck with his plan to find his way into livestock genetics.

Kiho Lee, University of Missouri: “And so he was not happy that I went into animal science. Because as a businessman, he always thought, I'm just chasing pigs. But then now that he sees more papers’ news on a xenotransplantation and how we can use pig organs to help a patient, he's very proud of me. And whenever he sees the articles, he sends me a text.”

Lately, Lee is focused on improving detection of and reducing any off-targeting events, which refers to those unintended consequences of using modern technology to knock out and replace a portion of DNA.

Kiho Lee, University of Missouri: We may not want to talk about these side effects, but then, as a scientist, we also want to be accurate. So if we, say, introduce a targeted modification, we want that statement to be true. So my interest was to really figure out, okay, so if there is a side effect, what is the side effect? That’s not something we want to hide about. We want to further study that and to develop a system that can minimize or even reduce these side effects.”

The University of Missouri’s initial study involved 15 of their genetically altered pigs. Many of the pigs had no off-target consequences, others showed naturally occurring genetic changes, but five had off-target genetic modifications associated with the editing. While the off-target events didn’t appear to create any problems for the pigs, Lee says it’s always best to reduce or eliminate the risk entirely.

Kiho Lee, University of Missouri: “So these off-targeting events, many scientists tend to neglect or ignore because, in theory, the type of modifications we introduce won’t impact the phenotype… However, as a scientist, we really wanted to see then: what is the level, what is the frequency of these side effects? And then how do we mitigate it?”

While the FDA has approved a couple genetically modified animals for human consumption, including salmon, monitoring of off-target events is also important as the nation moves toward the use of genetic modification in human medicine. In a historic move in December 2023, the FDA for the first time, approved a genome-editing therapy for treating humans, in this case those with sickle cell disease. Sickle cell disease is an inherited and debilitating blood disorder affected 100,000 in the U.S., particularly African Americans.

The therapy, proposed to the FDA by two Massachusetts companies, will be used to modify the patients’ blood stem cells using genome editing technology called CRISPR/Cas9, the same technology used by the University of Missouri with their genetically edited pigs.

Lee is also working on another study looking at Alzheimer’s in pigs, with hopes of finding a genetic answer for humans.

University of Missouri researchers will also continue to work on genetic solutions for livestock illnesses like porcine reproductive and respiratory syndrome, or PRSS, a viral disease in hogs. Researchers there have already made progress toward building hogs’ resistance to the disease.

Kiho Lee, University of Missouri: “If we can enhance these animals, make sure that they don't get sick and it's related to animal welfare, if they don't have to suffer from these deadly viruses and it will really help producers to protect their investment. And if I could help on achieving those goals, that will be my goal.”

By Colleen Bradford Krantz, colleen.krantz@iowapbs.org