The transplant recipients are injected with blood stem cells taken from donor bone marrow, protecting the transplanted organ from immune system attack, the Chicago Tribune said Thursday. The technique allows patients to live without immunosuppressant drugs that increase the risk of infections, cancer, and other serious medical problems.

The findings, published in the New England Journal of Medicine, are described as "very preliminary," the newspaper said.

Researchers at Massachusetts General Hospital said four of five patients who underwent antigen-mismatched kidney transplants have been able to discontinue immunosuppressive drugs, the hospital said in a release. Dr. David H. Sachs, director of the MGH Transplantation Biology Research Center, said the approach needs to be tested in a larger group of patients before it is ready for broad clinical use.

Stanford University School of Medicine also reported a patient who has been able to live for two years without the immunosuppressive drugs. In the Stanford case, the kidney from the patient's brother was an antigen match.