Scientists have created a human-pig hybrid in a study that raises the prospect of being able to grow human organs inside animals for use in transplants, Joinfo.com reports with reference to VouxMagazine.
The scientists behind the new human-pig chimeras maintain that they understand the ethical implications of their work. To carry out this study, the Salk researchers relied on donations from private foundations and collaborated with scientists and pig farmers in Spain as well as UC Davis.
But Hiromitsu Nakauchi, a stem-cell researcher at Stanford University in California, says that the low number of human cells in the pig-human embrio means that the hybrids are still a long way from serving any useful goal, such as organ donors. Weeks later, some of the embryos showed signs that the human cells were beginning to mature and turn into “tissue precursors”.
This is one reason why the government doesn’t give out funding for chimera research right now.
The agency later proposed lifting the ban, subject to restrictions and oversight by a special committee.
The study has reignited ethical concerns that have threatened to overshadow the field’s clinical promise. “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”.
However, the contribution of human pluripotent stem cells to the formation of the developing embryo was very low. That capability – altering the genes of an embryo – raises red flags for some, Robert said. The creation of this so-called chimera – named after the cross-species beast of Greek mythology – has been hailed as a significant first step towards generating human hearts, livers and kidneys from scratch.
Other concerns are less philosophical.
Robert mentioned another issue some have raised.
Scientists created the first rat-mouse chimeras a decade ago, but until now have struggled to combine human cells with those of a large mammal.
“This has to be a slow road”, Robert said. This new research reports the results of the implantations.
“These are incredibly careful scientists trying to do good work”, Robert said.
The mouse chimeras developed gall bladders made entire of rat cells, even though evolution took rat gall bladders away. The idea was to allow the natural system of development run its course, letting the mix of genes, enzymes and proteins direct the early embryo cells to specialize into heart cells, skin cells and more.
Once the rats reached adulthood, the team removed the pancreases and implanted clusters of these pancreatic cells into mice with diabetes.
That offers a “proof-of-principle”, Wu said.
“I do think it’s going to be possible to manipulate cells and generate the right match of chimeras to get human cells to incorporate [better]”, said Janet Rossant, a developmental and stem cell biologist at the Hospital for Sick Children in Toronto, who was not involved in the study but has previously collaborated with the authors.
Experiments involving chimeras, whether they are animal to animal or animals containing human material, are subject to regulation in the United Kingdom via the Home Office and the USA researchers had to follow similar guidelines set by the International Society of Stem Cell Research.
Human-pig chimeras face the added hurdle of vastly differing development speeds. “At this point, we wanted to know whether human cells can contribute at all to address the “yes or no” question”, he says.
Similarly, the human cells could be engineered to prevent them contributing to the chimera brain.
The results might sound like a terrifying half-pig half-human monstrosity – like the freaky hybrid recently discovered in China.
Researchers are getting better and better at growing these combined embryos, aka chimeras.
But actually creating lab animals that have human tissue could prove to be a better way, Wu said.
Researchers hope the mutants will help us grow organs for transplants.
“We’re nowhere near that yet”, Wu stressed. In the case of the human-animal chimeras made in the new research, the embryos contained mostly animal cells, with a relatively small number of human cells.
Even if those scientific challenges are overcome, at least some ethical issues will persist. “Blue color (DNA) indicates both pig and human cells”.
In research that has rattled policy makers from Washington to the Vatican, scientists in California today described their controversial first attempts to create pigs with human organs inside them. But, he said, “I think most people would not strongly object to this sort of experimentation”.