A genetic tweak keeps problematic plant sugars off therapeutic proteins. Growing crops is simpler and cheaper than culturing mammalian cells, which can harbour human pathogens and must be kept at precise temperatures and fed particular nutrients. But culturing mammalian cells is currently the only way to make some complex protein drugs. For example, the rare lysosomal storage disease mucopolysaccharidosis I is treated using enzyme-replacement therapy. The enzymes must be made in cells, and the high production costs mean that the drugs can cost hundreds of thousands of dollars a year. So Allison Kermode, a plant biologist at Simon Fraser University...
