Researchers cryopreserved the mouse stem cells before launch and kept them in a deep freezer on the ISS. Once returned to Earth, the cells were thawed, expanded in vitro, and transplanted into mouse testes. Within three to four months, the mice produced offspring through natural mating. The newborn mice were healthy and showed normal gene expression.

"It is important to examine how long we can store germ cells in the ISS to better understand the limits of storage for future human spaceflight," said first author Mito Kanatsu-Shinohara.

The team initially expected space radiation to harm spermatogonial stem cells more than cryopreservation, but results showed the opposite. Hydrogen peroxide exposure during the freezing process killed some cells, whereas space exposure produced minimal differences between pre- and post-flight cells.

Despite these promising findings, the researchers stress the need for long-term assessments. While the first-generation offspring appear normal, further studies are needed to determine potential health effects across their lifespan and future generations. Additional frozen germ cells remain on the ISS for continuing experiments.

Research Report:Germline transmission of cryopreserved mouse spermatogonial stem cells maintained on the International Space Station

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