The surgery re-opened the ethical question of potential recipients fathering someone else's children.
A 36-year-old man born without testicles now has one — thanks to his twin brother, and an international team of surgeons.
The identical siblings went under the knife to share the wealth in a six-hour operation performed in Belgrade, Serbia, last week.
In an interview with the New York Times, Dr. Dicken Ko said the aim of the surgery was to provide the recipient more stable levels of testosterone, to make his genitals look and feel more natural, and to allow him to potentially have children — even though technically, they'd be his brother's.
Because the recipient (who wished to remain anonymous) was missing the vas deferens — the duct which conveys sperm from the testicle to the urethra via ejaculation — he can not (yet) impregnate someone in the traditional way.
However, he can via IVF; or he could opt to use his brother's sperm, which would produce the same results. Otherwise, the operation — only the third known transplant of its type — was a complete success.
Because the pair were twin brothers, they didn't even need the immunosuppression drugs most transplant patients take to prevent their bodies from rejecting the foreign organs. "He's good, he looks good, his brother looks good," Dr. Ko told the publication, adding that the fertility of the donor brother, who already has children, will not be affected should he want more.
Dr. Branko Bojovic, who was also part of the team, said that once the donor testicle was removed they were up against the clock, as it will only remain viable for 4-6 hours without a blood supply.
The team had to stitch together two arteries and two veins less than 2 millimeters wide each, which can take up to an hour a piece; however the team managed to suture all four in less than two hours.
Dr. Bojovic and Dr Ko were also part of the surgical team that performed the first penis transplant in the United States in 2016. Their achievements are of particular interest to those seeking gender re-assignment surgery.
Female-to-male procedures currently involve phalloplasty, which builds a visual penis from grafted tissue, or metoidioplasty, which creates a penis from the patient's clitoris. Concurrently, male-to female procedures usually dump otherwise healthy male organs after removal.
According to lead surgeon Dr Miroslav Djordjevic, it's a supply and demand issue that answers itself.
"We have to do this as soon as possible, to stop putting healthy organs in the garbage," he said.
However in potential future cases, Dr Djordjevic agrees that testicles should not be part of those transplants, as it raises the ethical issue of the recipient being able to father someone else's children "Then the offspring is technically whose child?" Dr. Ko questioned. "It raises much debate in the literature of medical ethics."
The first two successful testicle transplants were done by Dr. Sherman J. Silber in 1978 and 1979, both on identical twin brothers. Dr Silber, who learned his craft of microsurgery by performing kidney transplants on more than 2,000 rats, said the first ever recipient went on to have five kids.