LAUSR

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.