They have inoculated human stem cells into pig embryos to produce human-pig embryos known as chimeras.
The embryos are part of study aimed at prevailing over the worldwide shortage of transplant organs.
The team from California University, Davis says they should look and act like normal pigs except that one organ will be composed of human cells.
The chimeric embryos from human-pig combination are being permitted to develop in the sows for 28 days before the pregnancies are brought to an end and the tissue removed for analysis.
Creating a chimera
Creating the chimeric embryos takes two stages. First, a technique called CRISPR gene editing is utilized to remove DNA from a newly fertilised pig embryo that would allow the resulting foetus to grow a pancreas.
This creates a genetic "niche" or void. Then, human induced pluripotent (iPS) stem cells are inoculated into the embryo. The iPS cells were derived from adult cells and "dialled back" to become stem cells having the ability to develop into any tissue in the body.
The team at UC Davis hopes the human stem cells will use the genetic niche in the pig embryo and the resulting foetus will grow a human pancreas.
Gene editing method could change future
A reproductive biologist, Pablo Ross, who is leading the research said that their hope is that this pig embryo will develop normally but the pancreas will be made nearly exclusively out of human cells and could be well matched with a patient for transplantation."
Although the work is arguable. Last year, the National Institutes of Health, the main US medical research agency enforced a moratorium on funding such experiments.
So, the major concern is that the human cells might relocate to the developing pig's brain and make it, in some way, more human.
The reproductive biologist, Pablo Ross says that this is improbable although is a key reason why the research is proceeding with such caution: and they think there is very low potential for a human brain to grow, although this is something they will be investigating."
Biological incubator
His team has previously inoculated human stem cells into pig embryos although without first creating the genetic niche. Prof Ross said although they later found human cells in some parts of the developing foetus, they "struggled to compete" with the pig cells. By removing an important gene involved in the creation of the pig pancreas, they hope the human cells will have more success creating a pancreas resembling that of a human being.
Other teams in the United States have created human-pig chimeric embryos but none has permitted the foetuses to be born.
Professor in the department of neurosurgery, University of Minnesota, Walter Low said pigs were an perfect biological incubator for growing human organs, and could potentially be used to create not just a pancreas but lungs, corneas, hearts, kidneys and livers.
He said if the iPS cells were taken from a patient who requires a transplant, then these could be inoculated in a pig embryo which had the major genes removed for creating the required organ like the liver: He also said that the organ would be an exact genetic duplicate of your liver although a much healthier and younger version and you would not require to take immunosuppressive drugs which carry side-effects.
Although Prof Low stressed that the research, using another form of gene editing known as TALENs, was up to this time at the preliminary stages, trying to identify the target genes which must be deleted for the sake of preventing the pig from developing a particular organ.
His team is also trying to form human neurons that produces dopamine from chimeric embryos to treat patients with Parkinson's disease.
These embryos have been permitted to develop for likely 62 days - the normal gestation period is around 114 days.
Like the team in California, Prof Low said they were keeping under observation the effects on the pig brain: He said with every organ they will look at what's taking place in the brain and if they find that it's too human like, then they won't let those foetuses be born.
Animal viruses
Gene editing has quickened research into xenotransplantation, and the idea of using animal organs for human beings.
In the mid-90s there were expectations that genetically modified pigs might provide an endless supply of organs for patients, and also the cross-species transplants were not far off.
Although clinical trials stalled because of fears that human beings might be infected with animal viruses.
Some time last year, a team at Harvard Medical School utilized CRISPR gene editing to delete at least 60 copies of a pig retrovirus.
Prof George Church, who led the research said it opens up the likelihood of not just transplantation from pigs to humans but the whole concept that a pig organ is perfectible.
He said gene editing could make sure the organs are very clean, available on demand and healthy, so that they could surpass human donor organs.
Animal suffering
Although organisations lobbying for an end to factory farming are disturbed at the thought of organ farms.
Peter Stevenson, from Compassion in World Farming said he’s nervous about opening up a new source of animal suffering; Let's first get many more people to give organs. He also said if there is still a shortage after that,they can consider using pigs, but on the basis that they eat less meat so that there is no general increase in the number of pigs being utilized for human purposes.
In Greek mythology, chimeras were fire-breathing monsters made up of several animals - part lion, goat and snake. The scientific teams believe chimeras from human-pig combination should look and act like normal pigs except that one organ will be composed of human cells.
Scott Fahrenkrug, whose Recombinetics company is based in Minnesota is teaming up on the chimera research with Prof Low said may be the term chimera is going to take on a new meaning and it will be one that's much more friendly: chimeras will be seen to be called a liberator, given that they will provide, life-saving, sustaining organs for our patients.
People in the UK numbering seven thousand are on the transplant waiting list and hundreds die yearly before a donor can be found.
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