Blood from umbilical cords can build new immune systems for adults with leukemia. The treatment offers a potentially lifesaving alternative for the many patients who cannot find suitable bone marrow donors. Researchers at University Hospitals of Cleveland and other sites gave 68 adults cord blood transplants from unreleated donors. Infections, bleeding and other complications killed many patients within months. But, nearly one-third survived long term, about the same as with bone marrow transplants. The new research shows that umbilical cord cells proliferate rapidly enough to treat adults. Up to that point, researchers had thought there would be too little tissue to reconstitute the immune system of an adult. The cells were immature types called stem cells, which can grow into differing types of specialized cells, including immune cells.