We can’t simply grow human organs in animals for the same reason we can’t transplant animal organs into our bodies: they’ll nearly certainly be rejected by our immune system, which recognizes the tissue as foreign.
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Scientists have opened up the possibility of interspecies lung, kidney and other organ transplants after creating part-human, part-pig embryo. The researchers injected human stem cells into pig embryos, then implanted those embryos into adult pigs. They hope the method will eventually be translatable to people-and that it will prove to be more practical than implantable insulin pumps now on the market.
The study’s lead investigator Juan Carlos Izpisua Belmonte said: “Our next challenge is to improve efficiency and guide the human cells into forming a particular organ in pigs”. “We don’t have the facilities at the different labs-we needed to go to the farm”.
They successfully created mouse/rat chimeras by introducing several different types of rat pluripotent stem cells into mice embryos.
But let’s focus on the pig-human chimeras for now.
By the time the scientists harvested the embryos after four weeks, the human stem cells had established beachheads throughout the developing pigs. And he praised the new research for its execution. In the last few days, the researchers have grown cells made up with parts of little embryos. They might also prove to be a good platform for testing human drugs, they write. Izpisúa Belmonte was the senior author.
The results described in Cell are far from realizing that dream. However, the success rate in the pigs was much lower than the rat-mouse chimeras.
Researchers are getting better and better at growing these combined embryos, aka chimeras.
Added to that, the process is also inefficient. It’s also getting them closer to growing entire human organs for transplant.
But animal-human chimeras are nothing new.
“It gives us a glimmer of hope” that organs for human transplantation can be made this way someday, Wu said.
In the tissue that would soon develop into the embryonic pig’s heart, one out of every 1,000 to 10,000 cells was human. Would the pigs suddenly be more human?
Then, the human-pig embryos were transferred into the uteri of sows. And pigs bearing human organs could simply be sterilized to prevent them reproducing.
A rat-mouse chimeric fetus.
“Our rodent experiments reveal a profound secret, that a developing mouse was able to unlock a gallbladder developmental program in rat cells that is normally suppressed during rat development”, said Jun Wu, a Salk staff scientist.
Researchers have allowed these embryos to develop only four weeks, as they were required by the regulations.
But some experts say the development raises huge ethical issues, especially if any of the cells produced were from the brain or reproductive organs. For the present study, Izpisua Belmonte’s group took the experiment one step further, using CRISPR-Cas9 to delete the genes in mice that coded not only for the pancreas, but other organs, such as the heart and eyes, as well. But at least there’s a solid first step, which is that ultimately, human cells have now grow in pig embryos. “I think it’s encouraging”.
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The researchers have done only research that is legal, but they are aware of the controversy. About 30 million Americans have diabetes; more than 3 million of them rely on artificial insulin to stay alive.
