A simple procedure could make life-saving bone-marrow transplants much easier on patients and increase the number of potential donors. Developed by cancer immunologist Ellen Vitetta and her colleagues at the University of Texas Southwestern Medical Center in Dallas, the process could dramatically lower the risk of a complication known as graft-versus-host disease, in which blood cells made by the donor marrow attack the recipient’s tissues. Vitetta’s solution: eliminate the donor cells that cause the complication and spare those that fight disease. Prior to transplant, doctors mix the donor marrow with the recipient’s blood to activate the “bad” cells. Once activated, these cells display a molecular marker called CD25 on their surfaces. Vitetta then adds a toxin attached to an antibody that targets CD25; the hybrid molecule selectively kills the bad marrow cells, and the rest are then infused into the patient. In an early trial in France, the procedure reduced the incidence of graft-versus-host disease from 70 percent of transplants to 25 percent. Vitetta hopes to begin U.S. clinical trials this spring.