Wednesday, May 23, 2018 |
Column: Biohazard —
Topic: Bioethics —
They're Mixing Animal & Human Cells to Make Organs
by Paige Comstock Cunningham
How can we resolve the ever-growing worldwide shortage of organs for transplantation? Despite the best efforts of countless organ-donor networks, state agencies, and billboard ads, the number of new voluntary donors has leveled off. (There is one exception—the recent uptick in people who die of a drug overdose means that such people now comprise one of every eleven organ donors.1) In the U.S., there are about 28,000 transplants each year, with 120,000 people on a waiting list. Worldwide, organ donations meet only 10 percent of the demand.2 Many deaths could be prevented or delayed if life-saving organs were available.
Coupled with the scarcity of organs is the reality of physiology: many recipients struggle with tissue rejection, as their body identifies and assaults the "foreign" substance that has been transplanted. If they pass the critical early risks of infection and necrosis of the organ, recipients still face a lifetime regimen of anti-rejection drugs.
Enterprising biomedical researchers are investigating alternatives, using tools of regenerative medicine such as 3D printing, stem cell technologies, and tissue engineering. Successful trials began more than a decade ago, for example, with bladder transplants engineered from the patient's own cells.3
But the most recent science headline is unsettling: "Scientists take first steps to grow human organs in pigs."4
Researchers at the Salk Institute in California announced in January that they had succeeded in growing human cells inside pig embryos. Using 186 pig embryos, the researchers inserted three to ten human stem cells into each embryo. About one million human cells grew in each embryo, less than what they had hoped for, but still considered successful. The purpose of the research is to eventually grow an intact human organ, such as a liver, using the patient's own cells. The pig would be euthanized before organ retrieval and transplantation were done.
Pigs are already used in human tissue transplantation, as valves from porcine hearts have been transplanted into humans for decades. Pigs are also a preferred source for research for various other reasons, among them: non-human primates cannot be used because they are legally protected; pigs are easy to raise in large numbers; pigs come in a variety of sizes, as do human bodies; and there are fewer ethical objections to using pigs, since they are already routinely slaughtered for human consumption, as evidenced by the current bacon craze.
Xenografts and xenotransplantations—i.e., transplants of non-human tissues and organs into humans—raise significant concerns. Infection may cross from the animal species to humans. Such zoonotic diseases include anthrax, hepatitis, salmonella, tuberculosis, Lyme disease, rabies, trichinellosis/trichinosis, Ebola virus, and West Nile fever.
Moreover, the creation of human-animal chimeras and hybrids (where an egg from one species is fertilized with the sperm from another species, with the recombined DNA residing in every cell in the hybrid's body) pushes numerous ethical boundaries.
The Salk Institute's experiment with human-animal chimeras raises its own serious concerns. The ramifications of inserting otherwise ethically acceptable human pluripotent stem cells into a pig embryo are unpredictable. The goal is to create a chimera in which the only human cells are in the desired organ. But cells could migrate to the brain, affecting brain development in unknown ways. Or they could migrate to the gametes, creating human-like eggs or sperm. The effects on the animal's nervous system are unknown.
Questions of Boundaries
These unpredictable and unknowable possibilities raise questions about the boundary between human and animal. What percentage of human cells would make an animal "human-like"? The Salk Institute study succeeded in inserting one human cell per 100,000 porcine cells. As future embryos receive more and more human cells, would they gain "human-like" rights? This is not a far-fetched idea. The Nonhuman Rights Project and the Great Ape Project aim at making the notion of animal personhood respectable. In 2014, an Argentine court ruled that an ape in a zoo was a "non-human person" and therefore should be freed.5
Defining an animal's "humanness" based on its percentage of human DNA is a kind of genetic reductionism; that is, it means defining human beings simply by our DNA and nothing more. Conferring legal protection based on a DNA profile showing x percent of human cells minimizes the uniqueness of the human species.
If human neuronal cells migrated to a pig's brain, would they stimulate consciousness? Based on such secular markers of personhood as self-awareness, consciousness, and reasoning, a claim could be made that "thinking" pigs should be protected, and not euthanized to harvest their organs.
A similar worry would be triggered by the presence of human cells in the reproductive organs. Could a pig's ovaries or testes be the source of eggs or sperm for research? For reproduction? This is a far-fetched notion (right now), but it does suggest the horror of a human child with a porcine parent.
Answering the moral question of the human-animal chimera's status based solely on capacities (rational thought) or functions (reproduction) undermines what is distinct about human beings: our intrinsic worth grounded in our creation in God's image. Our value or moral status does not depend upon how much we possess of a particular collection of abilities.
As researchers become successful at inserting more and more human cells into embryonic animals, the lines will grow fuzzier. Will we begin to treat animals more like humans, or would we begin to treat humans more like animals? Our experience with embryonic human beings is instructive, and distressingly so. Since 1969, when Steptoe and Edwards first fertilized an egg in a petri dish, human embryos have been increasingly objectified. Their value and fate is often dependent entirely upon parental desire or the researcher's goals.
It is theoretically possible—but highly unlikely—that the ethical concerns can be alleviated, and that the placement of human cells in animal embryos can be precisely controlled. If so, this research has the potential to save many lives through creating organs that are matched to the patient's body. Despite its "weird science" quality, this would be a breakthrough to celebrate.
Meanwhile, other pathways to creating artificial human organs and tissues are showing promise. For instance, 3-D "bioprinting" of liver tissue, skin, bones, blood vessels, ears, muscles, and skin is succeeding in animal trials.6 The ultimate goal is to "print" an entire organ. Other researchers have announced early steps toward growing human hearts using the patient's own stem cells, "painting" them on a scaffold derived from a human heart that is unsuitable for transplant.7 None of these procedures cross the boundary between human and animal species. But that's a conversation for another day.
In the meantime, I will maintain a well-founded skepticism about the ability or willingness of researchers to ethically create human-animal chimeras as "organ farms" for the future. •
Notes 1. Elahe Izadi, "So many people are dying of drug overdoses that they're easing the donated organ shortage," Washington Post (May 9, 2016): washingtonpost.com/news/to-your-health/wp/2016/05/09/one-out-of-every-11-organ-donors-last-year-died-of-a-drug-overdose. 2. George Dvorsky, "How We'll Finally Put an End to Organ Donation Shortages," Gizmodo.com (Feb. 2, 2015): http://io9.gizmodo.com/how-well-finally-put-an-end-to-organ-donation-shortages-1683258349. 3. Roxanne Khamsi, "Bio-engineered bladders successful in patients," NewScientist.com (Apr. 4, 2006): newscientist.com/article/dn8939-bio-engineered-bladders-successful-in-patients. 4. "Scientists take first steps to grow human organs in pigs," CBSNews.com (Jan. 26, 2017): cbsnews.com/news/scientists-take-first-steps-to-growing-human-organs-in-pigs. 5. Richard Lough, "Captive orangutan has human right to freedom, Argentine court rules," Reuters (Dec. 21, 2014): ca.news.yahoo.com/captive-orangutan-human-freedom-argentine-court-rules-203651528.html. 6. "Printed human body parts could soon be available for transplant," Economist.com (Jan. 28, 2017): economist.com/news/science-and-technology/21715638-how-build-organs-scratch. 7. Alexandra Ossola, "Scientists Grow Full-Sized, Beating Human Hearts from Stem Cells," Popsci.com (Mar. 16, 2016): popsci.com/scientists-grow-transplantable-hearts-with-stem-cells.
Paige Comstock Cunningham is the Executive Director of The Center for Bioethics & Human Dignity in Deerfield, Illinois.
More on Bioethics from the Salvo online archives.
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They're Mixing Animal & Human Cells to Make Organs by Paige Comstock Cunningham
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