Although more than twice Cooper's age, Little Mama's last physical showed her in good health with clean lungs and a strong heart.

CNN: Meet one of the oldest chimpanzees in captivity

One of these, Great Ormond Street Hospital in London, worked for more than 12 hours to separate the babies, but Hope's lungs were not sufficiently strong to support her without her twin, and she died shortly after the operation.

BBC: Twin separations: A history of risk

The team hope to have results within around four years which will give a strong pointer as to whether reconditioned organs will last as long as standard transplanted lungs.

BBC: Re-conditioning lungs for transplant