"The field has been torn between whether this is an issue or not," says George Church, a geneticist at Harvard University and cofounder of eGenesis. "We just decided it was easier to address the issue than take a chance," he said, so they eliminated those viruses with Crispr. Compared to classic genetic engineering, which was a slow and inefficient process, Church says Crispr allows researchers to make many simultaneous edits and thus address multiple incompatibilities between pigs and humans at once. "It has certainly catalyzed the field," he says.