When 9-year-old Marcus started chemotherapy for leukemia, his parents made a decision that might one day change his life: they had some of his testicular tissue frozen and stored, just in case. At the time, it felt like a hopeful guess. Now, new research from Stockholm suggests that guess might pay off in ways no one expected.
Scientists at the Karolinska Institutet have shown it is possible to create early sperm cells from frozen testicular tissue taken from young boys who underwent cancer treatment. The study, published in the journal Human Reproduction Open, offers a glimpse of what could become a way to protect and restore fertility in boys whose cancer therapy puts them at risk of never being able to have biological children.
Cancer treatments like chemotherapy can damage the cells in the testicles that would normally develop into sperm later in life. For young boys who haven't yet gone through puberty, this damage is especially tricky to handle because there are no mature sperm to save beforehand. The Karolinska team asked a different question: instead of trying to protect existing sperm-making cells, could they reprogram other cells already in the frozen tissue to step in and do that job?
To find out, researchers worked with frozen testicular tissue from two prepubertal boys who had been treated for cancer and had very few sperm-forming cells left. They isolated the remaining supporting cells from the tissue and reprogrammed them into what scientists call induced pluripotent stem cells — cells that can be guided to become almost any cell type in the body. These stem cells were then directed to become early germ cells, known as primordial germ cells, using two different methods that both worked with relatively high efficiency.
"Our results show that it is possible to generate induced pluripotent stem cells to produce early germ cells from frozen testicular tissue, even when these samples are severely affected by cancer treatment," said Tiago Macedo, the study's first author and a researcher at Karolinska's Department of Women's and Children's Health.
The team used a reprogramming method designed to be compatible with future clinical use, meaning it could eventually be adapted for actual medical treatment rather than just lab experiments. The reprogrammed stem cells passed standard quality checks and successfully turned into early germ cells.
João Pedro Alves-Lopes, the study's lead author, explained that while the findings are promising, this is still an early step. In the short term, the research helps scientists understand how cancer treatment affects sperm-forming cells. Longer term, it could open doors to new regenerative treatments that restore fertility in cancer survivors.
"In the long term, it could pave the way for new regenerative treatments to restore fertility in cancer survivors," Alves-Lopes said.
This is a proof-of-concept study, meaning it demonstrates the pipeline works in the lab, not that it is ready for hospitals tomorrow. More research is needed to make the germ cells fully mature, verify the approach is safe, and ensure the results hold up when tested more broadly. But for boys like Marcus — and the families who made the same choice his did — this research adds a reason to stay hopeful.