Pigs: A New Source for Stem Cells?

Given their unique regenerative abilities, stem cells offer new potentials for treating or curing many diseases and conditions. For example, they may help generate new, healthy tissue or valves to reverse degenerative heart disease. Scientists have discovered several sources of stem cells, the most coveted being those derived from embryos, called pluripotent stem cells, as they can differentiate into any type of cell in the body. Over the past few years, however, researchers have developed a way to successfully induce adult stem cells, which are found in many organs and tissues, into a pluripotent state; making them more versatile. And now, researchers in China say they have been able to reprogram adult cells taken from pigs so that they become pluripotent—a ground-breaking achievement that they hope could lead to new ways of treating human genetic diseases, as well as for engineering animals into organ donors for humans. 

The researchers, led by Dr. Lei Xiao, of the Shanghai Institute of Biochemistry and Cell Biology, used a virus to introduce transcription factors into cells taken from a 10-week-old pig’s ear and bone marrow. Tests on the cells showed they were capable of differentiating into the three fundamental layers of tissue in an embryo: endoderm, mesoderm and ectoderm. “The cells changed and developed in the laboratory into colonies of embryonic-like stem cells,” the researchers wrote. This is the first time scientists have been able to create pluripotent stem cells using cells from a hooved animal that weren’t derived from sperm or eggs.
 
Dr. Xiao says that because the pig is close to the human in many biological functions and some pig organs are similar in size to that of humans, pig pluripotent stem cells could be useful in a number of ways. “We could use embryonic stem cells or induced stem cells to modify the immune-related genes in the pig to make the pig organ compatible to the human immune system,” he said in a press release. “Then we could use these pigs as organ donors to provide organs for patients that won’t trigger an adverse reaction from the patient’s own immune system.”

Another possibility would be to use the cells to create models for genetic diseases. “Many human diseases, such as diabetes, are caused by a disorder of gene expression,” Dr. Xiao said. “We could modify the pig gene in the stem cells and generate pigs carrying the same gene disorder so that they would have a similar syndrome to that seen in human patients. Then it would be possible to use the pig model to develop therapies to treat the disease.”

Dr. Xiao said the new discovery could also improve pig farming by making the animals healthier and resistant to diseases such as swine flu. “We would do this by first, finding a gene that has anti-swine flu activity, or inhibits the proliferation of the swine flu virus; second, we can introduce this gene to the pig via pluripotent stem cells—a process known as gene knock-in. Alternatively, because the swine flu virus needs to bind with a receptor on the cell membrane of the pig to enter the cells and proliferate, we could knock out this receptor in the pig via gene targeting in the pig induced pluripotent stem cell. If the receptor is missing, the virus will not infect the pig.”

Professor Chris Mason, professor of Regenerative Medicine at the University College London, said this latest development could potentially deliver real benefits to millions of patients suffering from organ failure. “This breakthrough to produce pig stem cells potentially reinvigorates the quest to grow humanized pig organs such as pancreases for diabetics and kidneys for chronic renal failure,” he said.

However, Dr. Sebastien Farnaud, science director of the Dr. Hadwen Trust for Humane Research, has a different opinion. “Persisting with highly speculative research that would see us use sentient animals as little more than living organ grow-bags is not only ethically unsupportable but also scientifically dubious,” he said. “Creating pig stem cells does not necessarily remove the risk of organ rejection but even more worrying is the risk of infecting patients and the wider public with pig viruses.”