The perpetual shortage of human organs for transplant has researchers turning to farm animals. Several biotech companies are genetically engineering pigs to make their organs more compatible with the human body. But some scientists are pursuing a different solution: growing fully human organs in pigs, sheep, or other animals, which could then be harvested for transplants.
The idea is biologically daunting and ethically fraught. But a few teams are chipping away at a key roadblock: getting stem cells of one species to thrive in the embryo of another. Last month, a U.S. group reported in a preprint that it had grown chimpanzee stem cells in monkey embryos. And newly loosened regulations in Japan have encouraged researchers to seek approval for experiments to boost the survival of human cells in the developing embryos of rodents and pigs.
Insoo Hyun, a bioethicist at Case Western Reserve University in Cleveland, Ohio, says the work is being done responsibly. Efforts such as the new chimp-monkey chimeras represent “baby steps forward, gathering data as you go,” he says. “And I think that’s a wise approach.”
Ultimately, the researchers envision reprogramming a person’s cells to a primitive developmental state that can form most any tissue and injecting this induced pluripotent stem (IPS) cells into another species’s embryo. The embryo would be implanted in the uterus of a surrogate, and allowed to grow to full size to serve as an organ donor.
The IPS cells could come from the person awaiting transplant or, in a potentially faster and less costly approach; human organs could be grown in advance from cells from other donors, matched for key immune signaling proteins to prevent rejection.