Thymus tissue heals DiGeorge syndrome.

The rare baby born without a thymus gland can't defend itself. In the thymus, which sits atop the heart, the body's T cells learn the most important lessons of immunology: which cells to attack and which to let live. Without a thymus, a baby had no chance to live beyond a few years, until now.

Infants missing all or part of a thymus have DiGeorge syndrome. Babies with even a small thymus usually survive.

Researchers at Duke University Medical Center in Durham, N.C., have implanted thin slices of thymus tissue into the thigh muscles of 2-to-4-month-old babies with DiGeorge syndrome. The tissue had been removed from other babies during heart surgery and would otherwise have been discarded. Because the transplant recipients had no thymus to instruct T cells to attack the foreign tissue, it wasn't rejected.

T cells proliferated in four of the five recipients. Two of these patients survived and are now 1 1/2 and 6 years old. The other three died before their first birthday of infections or abnormalities associated with DiGeorge syndrome but unrelated to the transplant operation, the researchers report in the Oct. 14 NEW ENGLAND JOURNAL OF MEDICINE.

With DeGeorge syndrome, all the children were destined to get "one infection after another," particularly pneumonia, says study coauthor M. Louise Markert, a pediatric immunologist at Duke. The transplant recipients who survived are now essentially cured.

Getting the operation to work was difficult. One key to success had to do with the condition of the donated tissue. In previous thymus transplants, which had failed, researchers apparently didn't prepare the donor tissue properly, Markert says. Only extremely thin slices would stay alive in the recipients. "It took me a month just to get the tissue viable," she says.

One mystery remains: The scientists had expected the transplant recipients to be susceptible to graft-versus-host disease, a dangerous ailment in which immune cells in transplanted tissue attack their new host. Yet this didn't happen in the babies who received thymus slices.

"It's a miracle," Markert says. "It's something we don't understand." She and her colleagues speculate that the immaturity of T cells in the transplant keeps them from attacking cells in the children with DiGeorge syndrome.