An international team of scientists has successfully injected human stem cells into pig embryos to create a human-pig hybrid with a goal toward eventually growing human-compatible organs in animals.1 The team was led by Dr. Juan Carlos Izpisua Belmonte from the Salk Institute in California. Photo Credit: Juan Carlos Izpisua Belmonte, pig embryo with human cells.
The work hopes to address the shortage of life-saving organs available for transplant. Right now, there are almost 115,000 people on the national organ transplant waiting list and every ten minutes another person is added.2 On average, 20 people die each day waiting for a transplant.3
An article in National Geographic describing the research asks, “What if, rather than relying on a generous donor, you could grow a custom organ inside an animal instead?”4 The research is considered proof of the concept that one day there could be a ready supply of human organs thanks to “chimeras,” the term for human-animal hybrids.
The name “chimera” is taken from a mythical Greek monster with the head of a lion, the body of a goat, and a serpent’s tail.5 The National Geographic article quoted Dr. Jun Wu, one of the study authors at the Salk Institute: “In ancient civilizations, chimeras were associated with God, and our ancestors thought ‘the chimeric form can guard humans.’ In a sense, that’s what the team hopes human-animal hybrids will one day do.”4
The human-pig chimera was created by injecting human stem cells into early pig embryos that were then transferred into surrogate pigs where they were allowed to develop for 28 days before they were removed and analyzed. The pig experiments were conducted at two commercial pig farms in Murcia, Spain, the pig experimental unit of the University of Murcia, and the animal facilities at the University of California Davis.1
The work is considered so promising in addressing the organ shortage that Time magazine named its lead author as of the “50 Most Influential People in Health Care” for 2018. In recognizing Dr. Izpisua Belmonte’s work in “closing the organ deficit,” Time senior writer, Alice Park, wrote, that the team has developed a “scientifically innovative—albeit ethically controversial—solution: growing human cells in animal embryos to produce, say, human liver tissue inside a living pig or nonhuman primate, which can then be transplanted into people. It’s the first step toward growing enough human organs without relying on human donors.”6
As far as the ethical controversy goes, the MIT Technology Review described it this way: “The worry is that the animals might turn out to be a little too human for comfort, say ending up with human reproductive cells, patches of people hair, or just higher intelligence. ‘We are not near the island of Dr. Moreau, but science moves fast,’ NIH ethicist David Resnik said during the agency’s November meeting. ‘The specter of an intelligent mouse stuck in a laboratory somewhere screaming ‘I want to get out’ would be very troubling to people.’”7
1Wu J, Platero-Luengo A, Sakurai M, et al. Interspecies Chimerism with Mammalian Pluripotent Stem Cells. Cell. 2017;168(3):473-486.e15.
2U.S. Department of Health & Human Services. Organ Procurement and Transplantation Network. 5 December 2018.
3U.S. Department of Health & Human Services. Organ Procurement and Transplantation Network, Professional Education. n.d.
4Blakemore E. Human-Pig Hybrid Created in the Lab—Here Are the Facts. 26 January 2017. National Geographic.
5Merriam-Webster. Chimera Definition.
6Time. “50 Most Influential People in Health Care.” 2018. Time.
7Regalado A. Human-Animal Chimeras Are Gestating on U.S. Research Farms. MIT Technology Review. 6 January 2016.
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