Despite a funding prohibition from a chief health agency, several research centers in the United States continue to move ahead with their efforts to produce and grow human tissue inside animals.

Because of advances in gene-editing techniques and stem-cell biology, implanting human stem cells inside animals has become much easier for geneticists.

Once these human-animal hybrids or human-animal chimeras become fully grown, scientists hope to transfer the organs to patients without transplant rejection because the organs carry human DNA.

Animal rights activists, however, clamor against the act.

Dr. Julia Baines, a science policy adviser for People for the Ethical Treatment of Animals in the United Kingdom, called the technique "Frankenscience," an obvious reference to Mary Shelley's work.

Aside from that, some experts say it's very reminiscent of H.G. Wells' science fiction novel "The Island of Doctor Moreau" where a mad scientist creates human-animal hybrids.

"Creating human-animal hybrids is bad for people and worse for animals," said Dr. Baines. "These animals have exactly the same capacity to feel pain and suffer as any other animal, including humans."

Creating Human-Animal Chimeras

According to the American Transplant Foundation, at least 123,000 patients in the U.S. are waiting to receive an organ donation. To address the shortage of vital organs needed for transplants, scientists in universities have implanted embryos containing animal and human DNA into dozens of sheep and pigs.

Unfortunately, little is known about the effects of human stem cells on animal embryos.

Scientists are mainly concerned that the human stem cells could multiply and specialize inside the embryo. It could then begin to give the animal host human characteristics. Experts said those possible human features could range from physical disabilities to intelligence.

The Massachusetts Institute of Technology Review estimates that about 20 sheep and pigs in the U.S. and 30 more all over the world have been implanted with stem cells.

How are the human-animal chimeras created? Scientists first snip and cut the genes for a specific organ from the embryo of an animal. Then, they replace it with human stem cells.

Afterwards, the altered embryo is inserted into the womb of a pig or a sheep, and it grows containing a human organ.

Cardiologist Dr. Daniel Garry of the University of Minnesota, who worked on a human-animal chimera project, said they can create an animal that doesn't have a heart.

"We have engineered pigs that lack skeletal muscles and blood vessels," said Garry.

Meanwhile, none of the human-animal chimeras have been born yet, and it may be several years before their safety for humans is tested.

It May Be Allowed If The Benefits Outweigh The Harms

The National Institutes of Health has already said in September last year that it wouldn't fund studies concerning human-animal chimeras until it has reviewed the social and scientific implications more closely.

David Resnik, an ethicist from NIH, said scientists are nowhere close to the island of Doctor Moreau, but the new technique moves fast.

"The specter of an intelligent mouse stuck in a laboratory somewhere screaming 'I want to get out' would be very troubling to people," said Resnik.

In the UK, there is currently an organ donor shortage as the number of family members refusing to give consent is increasing. There is also concern that the number of useable organs are dropping because donors are less fit and older. About a quarter of organs are taken from obese patients now, compared with one in eight from 10 years ago, experts said.

Opposing Views

As animal rights groups oppose the act of creating human-animal hybrids, some medical experts believe the technique could save lives almost immediately.

Professor Bruce Whitelaw of the University of Edinburgh said the human-animal chimera experiment is scientifically fascinating and offers room for healthy, productive social debate.

Martin Bobrow, a former medical genetics professor at the University of Cambridge, said the work on human-animal chimeras could lead to medical advances of significant value.

"Without someone trying these experiments, we will not know whether the risks are huge, negligible or inbetween," added Bobrow.

Photo : Nick Saltmarsh | Flickr