A genetically engineered protein that kills transplant-attacking cells in mice should be tested soon on humans, and researchers hope it will reduce or eliminate the need for anti-rejection drugs.

"It's the promise for the future that's very exciting," said Dr. Jack Murphy, chief of biomolecular medicine at Boston University Medical Center.Researchers expect the protein to be introduced for some leukemia patients this fall and for transplant patients in about a year. The leukemia patients suffer from a form of the disease marked by an excess of the transplant-attacking blood cells.

"There's no question that if everything works out the way we'd like it to, it will be a whole new way" of treating transplant patients and victims of certain immune diseases, said Dr. Robert Kirkman, a transplant surgeon at Brigham and Women's Hospital in Boston.

Kirkman said this week at the annual meeting of the American Society of Transplant Physicians that the new fusion protein has succeeded in prolonging the lives of mice after heart transplantation. Nine of the 10 mice in the experiment appeared to retain their new hearts permanently without need for continual therapy.