Pigs have long been seen as possible incubators of human organs to use in transplants. Experiments at California’s Altos Labs have moved science closer to that goal.

Researchers there grew human kidney cells in pig embryos, the first time human organ cells have been grown in another kind of animal.

Other scientists have grown human muscle and blood vessel cells in pigs but never organ tissue.

Pigs’ biology is similar enough to humans to make them candidates for organ swaps. In trials, pig hearts and kidneys have been transplanted into brain-dead and terminally ill people. The replanted organs functioned but recipients would have required lifetime treatment with drugs to suppress organ rejection.

In contrast, human organs such as kidneys could be seeded in pigs with a person’s stem cells. Once grown, the organs could be transplanted into the person with no worries about rejection—the person’s body would see the new organ as one of its own.

Before implanting the human cells in pig embryos’ kidneys, the researchers genetically altered the human stem cells to outcompete the pigs’ cells so the kidney tissue would establish itself and not be overwhelmed by the pigs’ biological systems.

The experiments lasted only a month to prove that human organ cells could be grown in pigs.

Now new tests will be needed to see if human kidneys can be grown to maturity in pigs and to see if the human kidneys might contain pigs’ cells that would trigger rejection.

TRENDPOST: Ethical issues abound in this work, beyond the concern of raising pigs for the purpose of killing them if someone needs a kidney. 

Just as pigs’ cells could be incorporated into human kidneys, the scientists found some human cells had migrated into the pig embryos’ brains and spinal cords. That could alter their sensory or mental functions. No human genetic material was found in the embryos’ developing reproductive systems, but that doesn’t mean it couldn’t happen.

Human stem cells would have to undergo additional editing to ensure that pigs and humans aren’t able to swap cells and genetic material, the researchers said. 

In parallel with this work, others are looking for ways to grow organs from stem cells in laboratory containers resembling artificial wombs. That approach presents both fewer ethical challenges and genetic dangers than enlisting pigs to grow humans’ replacement organs.