A 27-year-old man in Belgium has become the first person to produce sperm after receiving a transplant of his own testicular tissue, which had been frozen when he was 10 years old before he underwent chemotherapy for sickle cell disease. Surgeons at the Vrije Universiteit Brussel (a leading research university in Belgium's capital) re-grafted four fragments of the preserved tissue back into his body 16 years later, and analysis confirmed that two of the grafts had generated mature sperm. The breakthrough offers hope to the more than 3,000 patients worldwide who already have testicular tissue banked, as chemotherapy and radiotherapy — while life-saving — can permanently destroy fertility in boys who are too young to preserve sperm before treatment.