SALT LAKE CITY — The pigs rooting in the mud at Shayn Bowler’s farm in West Jordan, Utah, are destined for the dinner table, not the operating room.
But rapid advances in gene editing could change that.
The gene-editing tool known as CRISPR has allowed scientists to excise the porcine viruses that have been an obstacle to using a pig’s heart as a substitute for a human’s.
New technology also makes it possible to use pigs as incubators — “oinkubators,” one biotech company says — growing hearts composed entirely of human cells inside genetically tweaked pigs.
It may still sound like science fiction, but a long skeptical public appears to be warming to the idea, according to a new report from Pew Research Center.
But many others worry that farming animals for their parts is a troubling overreach of the biblical concept of dominion and exposes animals to suffering, not only in their premature deaths, but in the years of research that would be necessary before the practice became legal.
And some people fear the unintended consequences of putting even a few human cells into an animal embryo.
The Humane Society of the United States says xenotransplantation is neither ethical, cost-efficient or safe, even though it's been going on in U.S. laboratories for more than 50 years, and some people believe animal-enabled transplants will be part of a radical transformation in health care within a generation.
“The science around organ preservation and organ generation is rapidly evolving, and I believe that transplantation will change significantly in the coming decades,” said Dr. David Klassen, chief medical officer for the United Network for Organ Sharing.
Bowler, who, with his wife, Kristen, operates Utah Natural Meat, said he'd be open to the idea if the animals were treated humanely. But that's not the only issue that scientists have to overcome before support for their research is widespread.
In the 1960s, Dr. Keith Reemtsma transplanted kidneys from chimpanzees into 13 humans at Tulane University in New Orleans.
All the patients died within a year, and subsequent animal-to-human transplants, including a baboon heart in an infant in 1983, also failed, according to a history of cross-species transplantation written by Dr. David K.C. Cooper of the Thomas E. Starzl Transplantation Institute in Pittsburgh.
After those failures, interest began to grow in using pigs and sheep instead of primates since their organs are physiologically the closest to human organs. In fact, an adfor the United Colors of Benetton once used three pig hearts as stand-ins for human hearts, and porcine heart valves are already widely used in humans.
The current research by Cooper and his colleagues involves genetically modifying pigs so they don't carry microorganisms that could cause disease in humans, and to make it more likely that the human immune system wouldn't reject pig organs, corneas and blood cells transferred to humans.
But some scientists want to, instead, grow actual human organs in pigs.
They believe they can genetically modify pig embryos so that the embryos will develop without a certain organ, then inject pluripotent human stem cells into the embryo. (Pluripotent cells are master cells that can develop into any type of cell or tissue.) The embryo would then generate the missing organ, but it would be composed entirely of human cells.
Hiromitsu Nakauchi, a professor of genetics at Stanford University, has already used the technology to grow a rat pancreas in a mouse.
Four years ago, Nakauchi came to the United States from Japan, where such research is prohibited. It's not illegal in the U.S., but the year after Nakauchi arrived, the National Institutes of Health said it would no longer fund research that involves animals and human cells. That policy is under review. An invitation for public comment on the practice drew more than 22,000 responses, most arguing against funding for the research.
But Pew Research Center’s August report on how Americans feel about bioengineering and animals found 57 percent of respondents consider it appropriate to use technology to genetically engineer animals to grow organs or tissue for humans. Forty-one percent said this goes too far.
Of those who objected, 21 percent said they were opposed because of the potential for animal suffering, 18 percent said it would interfere with nature’s or God’s plan and 16 percent said they had concerns about human health.
“Even human-to-human organ transplants often reject, so I can only imagine the bad side effects that an animal-to-human transplant would cause,” one respondent said.
Another said, “In manufacturing organs, the existence of these animals would be miserable. I can’t ethically say that I would agree with such a practice.”
The potential suffering of animals and their right to exist are the main objections of animal rights activists on the issue. Jeremy Beckham, a senior researcher with People for the Ethical Treatment of Animals, said such an ethically fraught practice is not necessary because there are other options available to solve the organ shortage. He noted that many European countries have made organ donation the default choice when people die; instead of opting-in to be an organ donor, like Americans do. People have to opt-out in countries such as Austria, France, Greece and Israel.
"We already have a solution staring us in the face," said Beckham, who is based in Salt Lake City. "It's sort of maddening that we're asking animals to suffer and give their lives because we're not willing culturally and politically to make an easy change."
Bowler, of Utah Natural Meat, said he could support using pigs, which are believed to be among the smartest mammals and have been found to learn as quickly as chimpanzees, for growing human organs, but only if they were treated humanely. "It's only duplicating the beneficial use of the pig," he said.
But the demand for pig organs wouldn't approach the demand for their meat. About 115,000 Americans are waiting for an organ transplant, according to UNOS. On average, more than 300,000 hogs and pigs are slaughtered for their meat every day, according to the U.S. Department of Agriculture.
Religion and pigs
Pigs have been used to improve human health for decades. The first insulin for diabetics was made from the pancreases of pigs, and parts from pigs slaughtered for meat are used to make blood-thinning drugs.
While the medical community has few qualms about using pigs to improve human health, there are some faith groups that must navigate this issue more carefully.
Pigs are considered unclean in the Muslim and Jewish traditions, which have ancient prohibitions about eating pork, owning pigs and, for some, even uttering the word. ("Many call the animal davar acher, 'another thing,' rather than by its proper name," the website Chabad.org says.) Some Christians, including Seventh-day Adventists, also refrain from eating pork for religious reasons, as well.
In Judaism, the prohibition stems from several Old Testament verses in the Bible, including Deuteronomy 14:8: "And the swine, because it divideth the hoof, yet cheweth not the cud, it is unclean unto you: ye shall not eat of their flesh, nor touch their dead carcass."
But Rabbi Daniel Nevins, Pearl Resnick Dean of The Rabbinical School of Jewish Theological Seminary in New York, said his faith would not necessarily prohibit the use of organs grown in pigs.
“It’s true that Jews are not supposed to eat pigs; however, we have sort of an override when it comes to life saving. There’s a rule called pikuach nefesh — saving a life — and even if you ate a pig’s flesh in order to survive, that would be allowed,” Nevins said.
Moreover, there’s no biblical law specifically against having a pig’s flesh inside your body, he said. “The Bible does not extend a prohibition like that, and neither do the rabbis," he said, adding that Judaism has no problem with the use of porcine heart valves.
Jews are, however, forbidden to cause excessive suffering to animals, and Leviticus 19:19 prohibits the mingling of species, which raises troubling questions, he said.
"Reports about new methods of growing human organs within other large mammals seem to raise concerns that human stem cells might spread to other parts of the organism, including germline cells, which would indeed trigger our concerns with the creation of chimeric creatures," he said.
For all the complexities of the debate over animal-grown organs, there are other ideas that have been suggested that are even more disturbing: for example, using brainless human bodies to grow organs, and cloning non-sentient replicas of ourselves to create "spare" organs that our bodies would not reject.
There are also options on the horizon that Americans might find easier to accept, such as using 3-D printers or a process called tissue engineering.
“There have been remarkable advances in bioengineering, stem-cell research and regenerative medicine in the last few years alone. These have created scaffolds that can be populated with human cells, which are cultured in the laboratory to create a functional organ,” said Lindsay Marshall, science communications officer for the Human Society of the United States, in an email.
Rather than being a scientific advance, Marshall said "throwing scarce research funding at the development of genetically ‘humanized’ animals for xenotransplantation is essentially a backward move."12 comments on this story
Research with animals, however, continues apace. Geneticists at Harvard University have said they believe genetically tweaked pigs can produce organs that can safely be transplanted into humans in another year and created a company toward that end.
But Beckham, the Salt Lake City researcher for PETA, said it's important to remember that optimism about xenotransplantation has ebbed and flowed for more than 50 years. "We could easily be in another period of irrational exuberance about this," he said.