When doctors at Johns Hopkins Hospital transplanted new arms onto former U.S. Army sergeant Brendan Marrocco in 2012, they used a new technique that helped limit the number of potentially dangerous anti-rejection drugs he would have to take.

The procedure, which involved an infusion of marrow derived from the donor’s lower spine, reduced the number of such drugs Marrocco needed from three to one.

That was beneficial because the anti-rejection drugs can have harmful side effects, possibly leading to infection, organ damage or cancer.

Now, a year and a half later, his doctors say the technique has been refined to where such patients might eventually need no anti-rejection drugs at all.

The goal is to “replace immunosuppression with a more sophisticated approach of immune regulation, which is what the immune system naturally does,” said Gerald Brandacher, associate professor of surgery and a member of Marrocco’s transplant team.

The body mounts “an immune response, the immune response is shut off,” he said. “We try to do the same in the setting of transplantation.”

The team has submitted a grant proposal for its first clinical trial. “We are very excited about this protocol,” Brandacher said.

In Marrocco’s case, he has been taking a single anti-rejection drug at very low levels, Brandacher said. “He’s doing very well with that,” he said. “There are no side effects that we could attest to.”

Marrocco, 27, of Staten Island in New York, lost both legs and parts of both arms in a makeshift roadside bomb explosion in Iraq in 2009.

At the time, he was the first service member from the wars in Iraq and Afghanistan to survive the loss of four limbs.

He is the first service member to receive a double arm transplant and is one of only seven people in the United States who have successfully undergone the procedure.

He is undergoing rehabilitation at Walter Reed National Military Medical Center in Bethesda.