Man's sperm production restored with testicular tissue frozen as a boy 16 years earlier

A medical team has restored a man's ability to produce sperm by transplanting testicular tissue that was removed from him and frozen 16 years earlier, when he was still a child, Nature reports (https://www.nature.com/articles/d41586-026-02191-3). Scientists describe the procedure as a potential turning point for fertility preservation in boys facing treatments that threaten their future ability to have children.

The tissue was taken shortly before the boy underwent chemotherapy that put his fertility at risk, according to Nature (https://www.nature.com/articles/d41586-026-02191-3). Rod Mitchell, a paediatric endocrinologist at the University of Edinburgh who was not involved in the work, called it "an important breakthrough," saying it "offers hope for prepubertal boys who are facing treatments, such as chemotherapy and radiotherapy, that can affect their future fertility."

The findings were presented at the European Society of Human Reproduction and Embryology (ESHRE) annual meeting in London and released as an unreviewed preprint on bioRxiv earlier this year, Nature writes (https://www.nature.com/articles/d41586-026-02191-3). As childhood-cancer survival has improved, attention has turned to the long-term effects of aggressive therapy, including fertility loss: from 2002 to 2022, more than 3,000 boys across 16 sites in Europe, Australia and the United States chose to freeze testicular samples in hopes of later restoring their fertility.

In 2008, physicians at the University Hospital in Brussels removed a testicle from a ten-year-old boy and froze tissue from it before he received chemotherapy in preparation for a blood-stem-cell transplant to treat sickle-cell disease, per Nature (https://www.nature.com/articles/d41586-026-02191-3). More than a decade later, as an adult who wanted children, he was monitored for two years and confirmed unable to produce normal sperm on his own before clinicians grafted 11 of the frozen fragments — by then stored for 16 years — into his remaining testicle or under the skin of his scrotum.

After a year, the grafts yielded sperm-producing stem cells and signs of active sperm production, with a single mature sperm found in one sample, Ellen Goossens, a reproductive biologist at the Free University of Brussels and a co-author, told Nature (https://www.nature.com/articles/d41586-026-02191-3). The team halted analysis and preserved the remaining graft in the hope that more sperm can later be collected for in-vitro fertilisation — a result researchers say could mark the start of a new wave of fertility treatments, though the work has yet to clear peer review.

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