Tissue Frozen at Age 10 Woke Up 16 Years Later and Made Sperm

A surgeon removed one of a 10-year-old boy's testicles in 2008, froze it, and put it in storage. Sixteen years later, the man it used to belong to got pieces of it grafted back into his body. The tissue worked.

Belgian researchers report that a 27-year-old man, left infertile after childhood treatment for sickle cell disease, produced sperm after doctors returned fragments of testicular tissue frozen when he was 10. Prepubescent children don't yet produce sperm and can't use standard preservation methods, so freezing immature tissue was the only option his family had. It was a bet on the future.

Surgeons grafted 11 of those fragments, frozen for 16 years, either into his remaining testicle or under the skin of his scrotum. The grafts sat there for a year, bathed in the hormones of an adult male body. When the team examined the tissue, they found sperm-producing stem cells and active sperm production in several grafts. In one, they found a single mature sperm. Researchers stopped and saved the rest, hoping to collect more later for IVF.

One patient. One sperm. Still a preprint. The frozen tissue held barely any sperm-producing stem cells to begin with, and even that tiny amount was enough to restart production once it went back in a body. Whether the grafts keep working past a year is unknown. Whether any of this can lead to a healthy baby is still an open question.

University Hospital Brussels pioneered this freezing method in 2002. Since then, hospitals worldwide have banked samples for more than 3,000 boys. Those samples have been waiting. Now there's a proof of concept, however early.

A frozen decade and a half. One functioning cell. Medicine just cashed in a bet nobody was sure would ever pay out.

Read the full story at Nature, July 17, 2026

Hot Take: Somewhere, an insurance actuary is trying to figure out how to price a policy on tissue that pays out on a sixteen-year delay and a sample size of one.