Currently inside the United States more than 100,000 people are waiting for a solid organ transplant such as a new heart, kidney, or pancreas. With a growing disparity between the numbers of donors and recipients, last year only 28,000 people received a transplant and the vast majority of the recipients were over the age of 18 . For those under the age of 18, availability of properly sized organs is a major factor along with increased risks with the surgery. Even after the transplant surgery takes place, there is always a chance of rejection along with potentially deadly side effects of immunosuppressant medications.
In response to this issue, research scientists have begun to explore alternatives by turning to what seems an unlikely source, pigs. Though pigs are most certainly not our closest genetic relatives, we share a remarkably similar internal organ structure including every thoracic and abdominal organ with only a few variations . Pigs have long played an important role in medicine, in the past we have substituted their insulin for diabetes treatments and currently we substitute their heart valves in certain surgeries. Seemingly straight from a science fiction novel, Dr. Hiromitsu Nakauchi has elected to take this one step further in attempting to grow entire human organs inside pigs. Nakauchi’s work is currently focused on the creation of the human pancreas through creation of chimeric pigs. These pigs would be a combination of pig embryos and induced pluripotent stem cells (iPSCs) from humans that are specialized in growing the target organ . The initial pig embryos would first have to be disabled for the creation of a pancreas so that during embryonic and later development the pancreas would be fully human . These adult pigs would also then produce offspring with the target organ disabled making it much more cost effective to produce a continuous stream of human organs. And due to the use of iPSCs, the newly grown organ would contain the patient’s original DNA which would help decrease the risk of rejection.
Much of the controversy that surrounds Nakauchi’s work arises from misleading understandings of a chimera. By definition, a chimera is a single organism with a genetic composition from genetically distinct zygotes however the DNA is never mixed on a chromosomal or intracellular level. Many people are mistaking chimeras for hybrids, which include crossing two gametes to create on zygote which involves fully combining the two individual’s DNA. Nakauchi’s work does not create a half-human half-pig hybrid containing equal amounts of DNA; instead his work creates a pig that contains only a human pancreas. The main fear in regards to chimeric pigs is the potential development of “human” neurons or parts of the reproductive organs . The risks can be reduced by complimenting male cells with female donors and ongoing work is focused upon researching ways to reduce the formation of unwanted crossover cells .
However, this raises the question: where do we draw the line? In regards to our genetically closest relative, the chimpanzee, they are not accorded any standing and those deemed dangerous to the public are euthanized. If we were to change a single chimpanzee gene to make it identical to a human’s, the percent relativeness would certainly increase. With this increase would we then have to afford chimpanzees full legal rights; would it then be illegal to keep individuals locked inside a zoo? The absurdity of such a statement proves that a definitive distinction exists between being human and simply being genetically similar.
Expanding this to the chimera pigs, even with the inoculation of a small percent of human cells outside the pancreas, they would not be transformed into cognizant and self-aware human-pig hybrids. Understandably, chimera research has a tremendous ability to cross these boundaries, particularly when dealing directly with the development of humanized brains . However in the case of the pigs being created solely with pancreatic iPSCs, this risk is much reduced. Animal rights groups have also been opposed to chimera research stating “Chimeras contribution to the debasement of animals” and are a cause of pain and distress to animals being used for research . In the case of the chimera pigs used for pancreases, it has been shown that they would lead normal, healthy lives up until harvesting which in turn would differ very little from using pigs as a food supply. Another issue that may arise is what to do with the pig’s carcass with many fearing that it would find its way into our food supply. As medical waste however, it is doubtful that any carcasses would find its way out of a facility without being marked as a biohazard.
Overall, there is a need for the establishment of universal ethical boundaries in regards to chimer development to preserve animal and human genetic integrity as well as animal and human health. However, in regards to growing specific organs the gains are tremendous with little risk of creating a human-pig hybrid. The pancreases grown could be used to stop fatal and nonfatal diseases such as Type I diabetes. With further advances and the development of more organs, it would serve as a solution to the growing disparity between those needing organ transplants and the amount donated each year.
- U.S. Department of Health and Human Services. “About Donation and Transplantation.”http://organdonor.gov/about/data.html
- Miller, James S. “Fetal Pig Dissection Guide – Human/Pig Comparisons.” http://www.goshen.edu/bio/pigbook/humanpigcomparison.html
- Matsunari et al. Blastocyst complementation generates exogenic pancreas in vivo in apancreatic cloned pigs. PNAS. January 8, 2013. http://www.pnas.org/content/early/2013/02/13/1222902110.full.pdf+html
- Center for Bioethics, The University of Minnesota. “Chimeras.” http://www.ahc.umn.edu/img/assets/25857/chimeras.pdf
Image Credit: Japanese Science and Technology Agency
Quinton Bruch is a freshman at The Georgia Institute of Technology majoring in Biochemistry with an interest bioinorganics as well as research ethics. Follow The Triple Helix Online on Twitter and join us on Facebook.