After 20 years of trying, scientists have transformed mature cells into primordial blood cells that regenerate themselves and the components of blood. The work, described today in Nature, offers hope to people with leukaemia and other blood disorders who need bone-marrow transplants but can’t find a compatible donor. If the findings translate into the clinic, these patients could receive lab-grown versions of their own healthy cells. One team, led by stem-cell biologist George Daley of Boston Children’s Hospital in Massachusetts, created human cells that act like blood stem cells, although they are not identical to those found in nature. A second team, led by stem-cell biologist Shahin Rafii of Weill Cornell Medical College in New York City, turned mature cells from mice into fully fledged blood stem cells. “For many years, people have figured out parts of this recipe, but they’ve never quite gotten there,” says Mick Bhatia, a stem-cell researcher at McMaster University i...