Washington ? Scientists mimicked a powerful immune-system disease in creating a pill that may block the rejection of transplanted organs without as many of the side effects that patients now face, researchers reported Thursday.

The experimental drug helped monkeys that had been given kidney transplants — a crucial hurdle, the researchers said. Although much more research is needed, human safety studies are beginning.

If it works, the drug, created by Pfizer Inc., could mark a more sophisticated way to prevent transplant rejection. Unlike today’s anti-rejection drugs, it was specially engineered to inhibit a molecule called JAK3 that is key to marshaling the immune cells that attack and destroy newly implanted organs.

Ironically, the new compound was inspired by the deadly “bubble boy disease,” in which children are born without a functioning immune system. A complete lack of JAK3 is at the root of the genetic disease, also called SCID or severe combined immunodeficiency. With the new compound, Pfizer scientists hope to harness JAK3’s immune suppression powers enough to help transplant recipients without overwhelming the body’s defenses.

“It’s a brand new concept,” said Dr. Dominic Borie, transplant immunologist at Stanford University school of medicine.

The results are reported in the journal Science.