Ready-made blood vessels that surgeons could take off the shelf and implant into patients may not be as far-fetched as they sound. Researchers report today in Science Translational Medicine a novel way of using human cells to generate blood vessels that may function in people without prompting an immune reaction. Unlike other engineered vessels, these can be stored for up to 12 months, which could allow hospitals to keep them on hand for immediate use in patients who need them.