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Building a Human Being, Cell By Cell

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A stunning new advance.Photograph by Getty Images

Homer called it “a thing of immortal make.” The Chimera (have your pick of spellings) was a hideous hybrid: “lion-fronted and snake behind, a goat in the middle, and snorting out the breath of the terrible flame of bright fire.”

So, natch, the biomed fandom has been all goat-in-the-middle over a report in the current issue of Cell that conjures up this monstrous mash-up once more. Scientists at the Salk Institute for Biological Studies, led by Juan Carlos Izpisua Belmonte, revealed that they’d created their own viable chimeras—or, in polite company, “interspecies blastocyst complementations.” Using the gene-editing tool CRISPR-Cas9 to turn off certain genes in a mouse zygote as well as other new techniques to enrich the pluripotent stem cells of a rat, the group managed to grow various rat organs (a pancreas, heart, and eyes) in a mouse embryo.

“Once implanted in surrogate mouse mothers, the embryos developed normally—except for the fact that each mouse was growing a rat pancreas” [or heart, or eyes], said the Salk Institute’s own news analysis—which, incidentally, called the Salk team’s paper a “tour de force.”

The group also reported—and I guess I’m burying the sci-fi lede here—growing human cells and tissues in pig and cattle embryos. Oh yeah…that.

Now, why is this important, beyond making Hollywood screenwriters salivate? Because, as Belmonte rightly explains, the new “precisely targeted” tools can help us “study species evolution, biology and disease, and may lead ultimately to the ability to grow human organs for transplant.”

As cool as the Salk experiments are, though, they overshadowed several other important reports on the stem cell front over the past few weeks. A research group at Cincinnati Children’s Hospital Medical Center used human pluripotent stem cells (hPSCs) to grow human stomach tissue (paywall)—and, notably, the part of the organ that produces digestive enzymes.

Another group whipped up self-renewing epicardial cells (cells that form a layer of connective tissue that surrounds the heart).

And, perhaps most strikingly, a team at a gaggle of New York research institutions published a paper showing how they’d used hPSCs to cook up—in just days, rather than several months—cortical neurons (critical central nervous system cells) that had normal electrophysiological signaling properties. That noteworthy advance could have huge implications for those with brain and other CNS disorders one day.

In sum, it’s been a great few weeks for blind Greek poets and science.