A man left infertile by chemotherapy he received as a boy is now producing sperm after doctors successfully transplanted testicular tissue that had been frozen for more than 16 years — a world first that could transform fertility options for thousands of young cancer survivors.
The 27-year-old patient, who was treated for sickle cell disease in 2008, had one testicle surgically removed before undergoing high-dose chemotherapy as part of a bone marrow transplant. The removed tissue was cut into small pieces and frozen by specialists at Vrije Universiteit Brussel, whose team had pioneered reproductive tissue banking in 2002 — the first programme of its kind anywhere in the world. The man went through puberty unable to produce sperm and in 2022, wanting to start a family with his partner, contacted the clinic to ask whether a transplant might be possible.
In 2025, four fragments of the preserved tissue were grafted back into his remaining testicle and the surrounding area. After a year, the grafts were removed for analysis and found to be generating mature sperm, which has since been collected and frozen. The findings were reported by The Guardian and published as a preprint paper — meaning they have not yet been peer reviewed.
Researchers identified spermatogonial stem cells, together with evidence of active spermatogenesis, in two of the four intra-testicular grafts, while no germ cells were detected in the subcutaneous scrotal grafts. The team said the results provided essential proof of concept that fertility could be restored in individuals who had banked testicular tissue before puberty.
Prof Ellen Goossens, who led the research at Vrije University, described it as “a huge finding.” She told The Guardian: “Many more people will have hope that they can have biological children. It’s great to see for the patients for whom we already have tissue banked.”
There are important caveats. Because the implants are not connected to the sperm duct, sperm cannot enter the semen naturally, meaning IVF would be the only route to parenthood. The team also cautioned that while the sperm appeared normal under analysis, it remains unclear whether it is capable of fertilising an egg. In their preprint paper, they wrote that “close monitoring of embryo development, pregnancy progression and long-term health outcomes in any resulting offspring will be essential to ensure both safety and efficacy of this fertility restoration approach.”
The breakthrough is nonetheless significant for a group of patients who have historically had no options. Unlike adults facing cancer treatment, children are unable to store sperm or mature eggs before undergoing damaging radiotherapy or chemotherapy. Chemotherapy and radiation therapy can destroy the stem cells that produce sperm, leading to infertility later in life, and prepubescent boys do not yet produce sperm cells — meaning the only way to preserve their future fertility is to bank the tissue itself.
Clinics around the world have been freezing such tissue for several decades in the hope that techniques might eventually allow it to be used. In Britain alone, more than 1,600 children have had tissue stored. Globally, ovarian tissue banking has already resulted in around 200 live births — but until now, the male equivalent had never been successfully demonstrated in a human patient.
The Belgian team’s pioneering steps build on a clinical fertility preservation programme at UZ Brussel that began in 2002, the first of its kind worldwide to collect and store testicular tissue from young boys facing fertility-threatening treatments. Researchers are also developing an alternative approach for patients whose stored tissue may contain cancer cells — a method involving the extraction and injection of sperm-forming stem cells directly, rather than transplanting whole tissue fragments.
For now, the patient intends to pursue biological parenthood, and the medical team says it will monitor any pregnancy carefully. The work, funded by the Research Foundation Flanders and Vrije Universiteit Brussel, is expected to undergo full peer review in due course.
