Dear Editor, Spermatogonial stem cell transplantation (SSCT) is a potential novel fertility treatment for prepubertal cancer patients that require gonadotoxic treatment. It comprises in vitro propagation of SSCs from a cryopreserved testis biopsy followed by autotransplantation into the infertile patient’s adult testis resulting in full recovery of spermatogenesis. In this blinded preclinical study, the long-term health of SSCT-derived offspring was assessed for the first time, using a systematic blueprint testing throughout life. No major differences in health outcomes between mice born after SSCT in two consecutive generations (first generation [F1] and second generation [F2]) and control were found, thereby providing crucial evidence that SSCT is a safe procedure.

Due to its germline character, SSCT is the only adult stem cell-based transplantation therapy that can restore male fertility and may not only affect the recipient, but also the offspring. Remarkably, medically assisted reproductive (MAR) therapies have been introduced in the clinic after preclinical studies focusing mainly on its efficacy instead of safety for the offspring. 1, 2 Unfortunately, after clinical implementation, children born after some of these MARs have increased risk for congenital abnormalities and low birthweight, 3–6 developmental delays and cardiometabolic disease later in life. 3, 4, 7 To ensure the health of future generations born from fathers that have received SSCT to restore fertility, we here studied indicators of health in the offspring throughout life that can be linked to potential risk factors of developmental problems, cardiometabolic disease, and ultimately result in increased mortality and pathologies 2 (Supporting Information). Birth assessments showed that congenital abnormalities were a rare event (control n= 1/151, SSCT-F1 n= 3/125, SSCT-F2 n= 4/123; Figure 2A) with no statistically significant differences found in either SSCT generation compared to control (odds ratio [OR]: 3.78, 95% confidence