The idea of transplanting organs from pigs into humans has been around for a long time. And for a long time, xenotransplants—or putting organs from one species into another—has come up against two seemingly insurmountable problems.
The first problem is fairly intuitive: Pig organs provoke a massive and destructive immune response in humans—far more so than an organ from another person. The second problem is less obvious: Pig genomes are rife with DNA sequences of viruses that can infect human cells. In the 1990s, the pharmaceutical giant Novartis planned to throw as much $1 billion at animal-to-human transplant research, only to shutter its research unit after several years of failed experiments.
Quite suddenly, however, solving these two problems has become much easier and much faster thanks to the gene-editing technology CRISPR. With CRISPR, scientists can knock out the pig genes that trigger the human immune response. And they can inactivate the viruses—called …