![]() ![]() When those just-right human cells were injected into the pig embryos, the embryos survived. Through trial and error, they learned that naïve pluripotent cells-stem cells with unlimited potential-didn’t survive as well as ones that had developed a bit more. “We tried three different types of human cells, essentially representing three different times” in the developmental process, explains Jun Wu, a Salk Institute scientist and the paper’s first author. The team discovered that, in order to introduce human cells into the pigs without killing them, they had to get the timing just right. Not that these similarities made the task any easier. Though they take less time to gestate, their organs look a lot like ours. This version failed-not surprisingly, since rats and pigs have dramatically different gestation times and evolutionary ancestors.īut pigs have a notable similarity to humans. The team then took stem cells from rats and injected them into pig blastocysts. Some even grew chimeric gall bladders made of mouse and rat cells, even though rats don’t have that particular organ. The mice that resulted managed to live into adulthood. When they introduced rat stem cells capable of producing those organs, those cells flourished. There, they deleted genes that mice need to grow certain organs. The Salk-led group took the concept one step further, using the genome editing tool called CRISPR to hack into mouse blastocysts-the precursors of embryos. On Wednesday, that team announced that mouse pancreases grown inside rats successfully treated diabetes when parts of the healthy organs were transplanted into diseased mice. Other scientists had already figured out how to grow the pancreatic tissue of a rat inside a mouse. To do so, the team piggybacked off prior chimera research conducted on mice and rats. However, it took Belmonte and more than 40 collaborators four years to figure out how to make a human-animal chimera. And often, patients must undergo painful and invasive procedures to harvest the tissues needed to kick off the process.Īt first, Juan Carlos Izpisua Belmonte, a professor in the Salk Institute’s Gene Expression Laboratory, thought the concept of using a host embryo to grow organs seemed straightforward enough. Scientists have to use scaffolds to make sure the organs grow into the right shapes. But convincing those cells to grow into the right kinds of tissues and organs is difficult.Ĭells must survive in Petri dishes. When scientists discovered stem cells, the master cells that can produce any kind of body tissue, they seemed to contain infinite scientific promise. ![]() It sounds weird, but it’s an ingenious way to eventually solve a number of vexing biological problems with lab-grown organs. The other method is to begin at the embryonic level, introducing one animal’s cells into the embryo of another and letting them grow together into a hybrid. The first is to introduce the organs of one animal into another-a risky proposition, because the host’s immune system may cause the organ to be rejected. “In ancient civilizations, chimeras were associated with God,” he says, 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. Public opinion, too, has hampered the creation of organisms that are part human, part animal.īut for lead study author Jun Wu of the Salk Institute, we need only look to mythical chimeras-like the human-bird hybrids we know as angels-for a different perspective. Such experiments are currently ineligible for public funding in the United States (so far, the Salk team has relied on private donors for the chimera project). In the past, human-animal chimeras have been beyond reach. (Read more about the DNA revolution in National Geographic magazine.) The team created what’s known scientifically as a chimera: an organism that contains cells from two different species. That’s now one step closer to reality, an international team of researchers led by the Salk Institute reports in the journal Cell. Scientists are experimenting with a technique called CRISPR to rid pig organs of viruses that harm humans. Thousands of people die every year for lack of transplantable human organs. ![]() Human blood filters through pig lungs in the lab of Lars Burdorf at the University of Maryland School of Medicine. ![]()
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