Fears of Creating a Monster Animal Cross-over

"The first concern is public perception: does it violate some notion of boundaries, or the natural order of things."
"You're going to have to watch carefully what is happening during the course of development, and be ready to shut down something that looks like it's an unintentional outcome."
"Can you control where these cells go. There's less worry about growing an islet cell to help somebody with diabetes than there is finding out human cells migrated into the animal's brain and grew some structures there."
"It doesn't mean that the animal is all of a sudden going to wake up and sign up to take a bioethics course. It just means there are some human cells in there."
"But still, that bothers us more because that's where we think the mental states that identify our identity are."
"Most people don't say, well, the way I know who I am is by thinking about the cells that are in my pancreas or spleen or something. But we do when it comes to the brain."
"Forget about [the Salk researchers'] work. What if somebody said, 'I think it would be interesting or fun to see what would happen if I did try to make a pig with some element of a human brain'?"
Arthur Caplan, bioethicist, Langone Medical Center, New York University

 "...And in some of them [hybrid human-pig embryos], we observed human cells were there. They turned into the progenitors for many different tissues and organs."
"And these organs will probably function better than the organs we've already had for 30 or 40 years. We might have the ability [through harvesting chimera organs] to rejuvenate our physiology."
Jun Wu, Salk Institute scientist

"This [research succeeding in creating human-pig chimera embryos] required a tour de force. But in the end we were able to answer a key question -- can human cells grow in an animal."
"The ultimate goal is to grow functional and transplantable tissue or organs, but we are far away from that. This is an important first step." 
"It's like when you try to duplicate a key. The duplicate looks almost identical, but when you get home, it doesn't open the door. There is something we are not doing right."
"We thought growing human cells in an animal would be much more fruitful. We still have many things to learn about the early development of cells."
Juan Carlos Izpisua Belmonte, lead investigator, Salk Institute for Biological Studies, La Jolla, California

This photograph shows injection of human iPS cells into a pig blastocyst. A laser beam (green circle with a red cross inside) was used to perforate an opening to the outer membrane (Zona Pellucida) of the pig blastocyst to allow easy access of an injection needle delivering human iPS cells. Credit: Courtesy of Juan Carlos Izpisua Belmonte

But part of that goal has been achieved, according to research resulting in the successful pilot creation of a human-pig hybrid and described in a publication appearing in the scientific journal Cell, this week. Although lead researcher in this project, Juan Carlos Izpisua Belmonte modestly cautioned that there is much left to learn on how to proceed from this point, the first hurdle has been set aside. Scientists have been attempting for quite awhile to grow inter-species embryos; this is the first to date to succeed.

And the first successful 'chimera', an animal created with parts of different animals which owes its legendary presence to ancient folklore, has been developed. The goal in this development is to eventually solve the intractable problem of procuring enough body parts to be used for transplants when original body parts have failed due to disease or other functionality compromising factors. Ultimately perhaps even replacing worn out viscera in an aging human body to gain additional years of life for the recipient.

A 4-week-old pig embryo that was injected with human stem cells. The experiment was a very early step toward the possibility of growing human organs inside animals for transplantation. Salk Institute via AP

Up to now the creation of animals in their various forms has been a monopoly practised by the ultimate creatrix, Nature. It can perhaps be viewed as the last word in hubris for humans to devise biological methods by which nature can not only be emulated but manipulated in ways never meant to occur by natural means. And this dabbling about in nature's preserve raises concerns of bioethicists: "But of course the more we humanize an animal, the more we raise questions about animal ethics", pointed out Timothy Caulfield, Canada Research Chair in health law and policy.

The article published in Cell described how researchers at the Salk Institute for Biological Studies injected human stem cells into pig embryos in an experiment they hoped would result in the stem cells which have the capacity to become any other type of cell the body harbours, to mature to the point where they could eventually be harvested, and used to regenerate damaged or diseased tissue in a human subject on transplantation.

But this research is still at its dawn stage and many technical elements of the strategy are yet to be explored and refined. The researchers aspire to be able to inject human stem cells into a fertilized pig egg so that a given organ can be developed for transplantation into a waiting human whose organ has failed and requires a replacement. After the fetus is born, the animal is to be raised until the organ reaches optimum size for harvesting and transplantation.

The researchers envision pig farms reflecting a "clinical grade" of environment, to incubate the human organs. Dr. Wu points out the obvious, that any organ generated in a pig will be a 'young' organ, one that will function as a young organ, in contrast to one that has been in use in a human body for many years and whose life expectancy for usefulness has become compromised by age. Another plus would be that the body's immune response would not be called into rejection action since the organ would have been grown from the individual's own cells.

Ethicists, in a paper published in Stem Cell Research & Therapy, last year warned that a worrying worst-case scenario "would be that a pig producing human sperm could incidentally mate with a sow or vice versa". The very thought of a "humanized pig brain", sends shudders down the spines of ethicists. Though the concern of a man-pig child emerging is beyond remote, considering the "interspecies reproductive barrier is strong", concerns yet remain.