The CD4/CD25+ cells were injected after the patients' cancer cells and immune system had been knocked out by total-body radiation and chemotherapy. Next the patients were given transplants of bone marrow containing stem cells plus mature T-cells to help the depleted immune systems fight off viral and fungal infections in the short-term.

Of all the patients who received the entire treatment, only one developed GVH. In addition, the researchers claim that the reconstitution of the hosts' immune systems appeared to occur more quickly than normal.

Study leader Massimo Martelli, head of hematology and clinical immunology at the University of Perugia, says the study shows that "T-regulatory cell-based therapy may be an innovative strategy to improve the outcome of patients who undergo bone marrow transplants."

"We hope that this new method will reduce infection-related mortality and thus improve overall survival," he adds.

Armand Keating, the director of hematology and a professor of medicine at the University of Toronto, says the new method is "an interesting and potentially important way of regulating T-cells" in stem cell transplants given to leukemia patients.

Keating adds that the method, if eventually validated, might prove particularly important for ethnic minorities who need marrow transplants. "The vast majority of donors on the registers are white people of northern European extraction. But with this method it might become possible to accept more partial matches from close family members such as siblings, or parents, if they are young enough," he says. "With these kinds of transplants you need to move fast. Sometimes a day can make all the difference, so there isn't time to find perfect matches on the register."

However, Keating stresses that bigger, longer studies are needed. "With these patients, relapse is always a concern," he says.