29 January, 2017
Scientists have grown human cells inside pig embryos, a very early step toward the goal of growing livers and other human organs in animals to transplant into people. A part-pig, part-human embryo has been grown for the first time in history, the Washington Post reported Thursday.
Researchers at Salk Institute for Biological Studies in La Jolla, California said they implanted the living pig-human embryos, or chimeras, in adult pigs' wombs and allowed them to grow between three and four weeks.
"We find surviving human cells, but they are not integrated and co-developing", he says.
Dr. Wu added, "The larger the evolutionary distance, the more hard for them to mix".
Or as senior author Juan Carlos Izpisua Belmonte, a professor in Salk's gene expression laboratory, sees it, "To try to imitate nature is not that easy".
It is hoped that the breakthrough could lead to the growing of human cells, tissues, and organs in animals for use in regenerative medicine in humans, though critics say it raises ethical concerns.
Previous research has produced combinations of rats and mice, which are far more closely related. And the rat cells did grow into mature organs.
The hybrid embryo was then left to develop for three to four weeks.
Dr Wu said: "When the public hears the world chimera it is always associated with Greek mythology, there is always this associated fear". It even gave the mice bonus organs like the gallbladder which are not present in rats.
Dr Wu said: "Organ generation based on this technology is in the future". However, the final aim is to generate human organs or tissues from animals. They successfully created mouse/rat chimeras by introducing several different types of rat pluripotent stem cells into mice embryos.
Then, these embryos were implanted into saws. Human cells that come to compose the reproductive tissues of an animal may also result in undesirable outcomes.
After trial and error, the researchers were able to create pig embryos with human cells. However, numerous embryos were much smaller than normal and seemed to grow more slowly, the group reports today in Cell.
He said you can imagine a pig born with a human liver being tested with pharmaceuticals before they are tested on humans. "I agree that there is this possibility, but we have ways in the lab to prevent this from happening", said Izpisua Belmonte. The unusual hybrids, known as chimeras, contain a mixture of pig and human cells.
The promising research was detailed in the journal Cell, which publishes peer-reviewed articles and reports of unusual implication in any area of investigational biology.
"There has been the use of human-animal chimeras in biomedical research for a very long time". More than 150 of the embryos developed into chimeras that were mostly pig, but with a tiny human contribution of around one in 10,000 cells. "Animal ethics activists are important and there's a place at the table for them", said Neuhaus, but "[another] important voice would be people that need organs". If too much human DNA is introduced in a pig's embryo, it could result in a pig with a "human brain".
"Furthermore, the recipient animals only needed treatment with immunosuppressive drugs for five days after transplantation, rather than the ongoing immunosuppression that would be needed for unmatched organs", said Hiromitsu Nakauchi, MD, Ph.D., a professor of genetics at Stanford, when explaining how the procedure worked in mice. The University of Wisconsin also has conducted human-animal hybrid studies.
There is wide-spread societal discomfort with the ethics of creating creatures that are part human, part animal, but it has not stopped several USA research groups from delving into the controversial experimentation anyway. "The more you can show that it stands to produce something that will actually save lives ... the more we can demonstrate that the benefit is real, tangible and probable - overall it shifts the scale of risk-benefit assessment, potentially in favor of pursing research and away from those concerns that are more philosophical and conceptual". But the study still has a long way to go. Though as a philosopher, it might be "fun" for him, it's not a wise or practical thing to do for policy.
The NIH's plans to begin funding those experiments, however, wasn't finalized before the end of the Obama administration. "The emphasis should still remain on animal welfare", he said, as it is now for any kind of animal research.