Two sperm before grafting, one after
A Brussels team returned 11 fragments of prepubertal testicular tissue frozen in 2008, before treatment for sickle cell disease, to the same patient in December 2024. The sequence of the counts matters: on the transplant day, two immotile, abnormally shaped sperm were found in the patient's native testicular tissue before grafting. One year later, enzymatic digestion recovered a single sperm from one intratesticular graft.[1], [2]
Two of four intratesticular grafts showed evidence of active spermatogenesis, while no germ cells were found at the four subcutaneous sites. The patient's azoospermia persisted, with no significant improvement in semen or hormone measures during follow-up. The result is therefore proof that frozen human tissue can regain function, not evidence of fertilization, pregnancy or routine clinical benefit.[2]
The gap between a first and a treatment
The intended population is people who banked tissue before receiving gonadotoxic treatment and before they could produce sperm. But this case did not yield enough sperm for unassisted fertilization; the literature anticipates that ICSI may be needed because sperm made in a graft may not connect to the normal outflow tract. Safety also depends on the original disease, because stored tissue from some cancer patients could reintroduce malignant cells.[2]
The study is a medRxiv preprint describing a single patient. Tissue stored for sixteen years produced signs of active spermatogenesis and one sperm, while the patient remained azoospermic and no fertilization was demonstrated. The path to clinical use runs through replication in other patients, more mature and motile sperm, genetic integrity, fertilization and healthy births. The present milestone is biological feasibility, not an established treatment outcome.[2]