Duke University doctors report that a baby is doing well after a heart transplant. The procedure included a bonus technique to prevent rejection.

The immune system is built largely by the thymus. Doctors wonder if thymus tissue from a donor organ could be implanted to help it survive, without the recipient needing to take toxic anti-rejection drugs.

Easton Sinnamon, a North Carolina boy, had his unique transplant last summer at the age of six months. Duke didn’t announce the news until Monday, after doctors discovered that the specially-processed thymus implant was working as expected — producing immune cells which don’t treat Easton’s new heart like it’s foreign tissue.

According to Dr. Joseph Turek of Duke, the chief of pediatric cardiac surgery, doctors will eventually try to wean Easton off immuno-suppressing medications after a transplant.

Researchers are still in the early stages of this research and only one method is being tested by scientists to induce what’s known as immune tolerance to a transplant.

Turek said that if the transplant works, it can be done with other organs as well, and not just the heart.

Easton was eligible for experimental transplants because he had two different health issues. Easton was born with a number of heart defects which surgery failed to correct. He also had recurrent infections, which doctors later discovered meant that his thymus was not working correctly.

A few babies are born with no thymus. This stimulates the development of T cells, which is part of the immune system. Enzyvant Therapeutics, a Duke research group, has been developing lab-grown implants from donated thymus tissue. This rare condition is being treated by Duke researchers.

Easton had a combination of both procedures. While the donor thymus was being sent to a laboratory, Easton’s new heart was implanted by his first surgeons. Two weeks later, he underwent a second operation to place the thymus tissue. To make way for new immune cells, his own partially functioning thymus was taken out.

Turek said that six months later, tests showed that the thymus tissue was building Easton-functioning T cells.