Pig organs are similar to their human equivalents
Chinese scientists have given cells from adult pigs the ability to turn into any tissue in the body, just like embryonic stem cells.
They hope the breakthrough could aid research into human disease, and the breeding of animals for organ transplants for humans.
It may also enable the development of pigs that are resistant to diseases such as swine flu.
The study appears online in the Journal of Molecular Cell Biology.
Lead researcher Dr Lei Xiao, of the Shanghai Institute of Biochemistry and Cell Biology, said many other attempts had been made to transform adult cells from animals such as pigs into "pluripotent" stem cells, but they had failed.
He said: "Therefore, it is entirely new, very important and has a number of applications for both human and animal health."
Dr Xiao's team reprogrammed cells taken from a pig's ear and bone marrow, using a cocktail of chemicals introduced into the cells via a virus.
Tests showed that the reprogrammed cells were capable of becoming any of the cell types that make up the three layers in a developing embryo.
Dr Xiao said pigs were a potentially ideal source of organs for transplant, as their organs were similar in function and size to those found in humans.
He said reprogrammed stem cells could potentially be used to make a pig organ compatible to the human immune system, minimising the risk of rejection.
The cells could also be used to mimic human disease in pigs, allowing scientists to test new therapies without requiring human volunteers.
In addition to medical applications, Dr Xiao said his discovery could be used to improve animal farming, by making the animals healthier, and regulating the way they grow.
However, he warned it could take several years before some of the potential medical applications of his research could be used in the clinic.
Professor Chris Mason, an expert in regenerative medicine at University College London, said: "This breakthrough to produce pig stem cells potentially reinvigorates the quest to grow humanised pig organs such as pancreases for diabetics and kidneys for chronic renal failure.
"The clinical use of humanised porcine tissues and organs (xenografts) has moved a long way forward in recent months with successful small-scale clinical trials.
"Whilst the xenograft approach may not necessarily be the long-term solution, it may represent a major step change in the treatment of organ failure, which potentially could deliver real benefit to millions of patients within a decade."
Dr Sebastien Farnaud, science director of the Dr Hadwen Trust for Humane Research, said: "Persisting with highly speculative research that would see us use sentient animals as little more that living organ grow-bags, is not only ethically unsupportable but also scientifically dubious.
"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."