Watch Dr. John Tisdale of the National Institute of Diabetes and Digestive and Kidney Diseases at the National Institutes of Health brief the Congressional Biomedical Research Caucus on Stem Cells in Gene Therapy. Dr. Tisdale describes a new method of bone marrow transplantation that has effectively reversed sickle cell disease. In trials, nearly 200 children with severe sickle cell disease were cured with complete bone marrow transplants after undergoing a regimen in which their own marrow was completely destroyed with chemotherapy. That regimen, however, proved too toxic for adults, who have years of accumulated organ damage from the disease and are less able to tolerate complete marrow transplantation. In a separate trial, Dr. Tisdale and others sought to only partially replace the patients’ bone marrow–believing that the healthy cells would outlast and completely replace the disease-causing cells. After 2 1/2 years of follow-up, all 10 recipients were alive and sickle cell disease was eliminated in nine.