Human precursor sperm cells grown using mice as incubators

A Penn team grew immature human sperm precursor cells inside mice, but no functional human sperm resulted.

A University of Pennsylvania team led by Kotaro Sasaki grew immature human sperm cells by placing human cells beneath the kidneys of immunodeficient mice, using the animal as a living incubator. The grafts stayed stable for at least six months and survived up to nine. Some cells developed into spermatogonia, the self-renewing precursors of sperm, and underwent a genome-wide epigenetic reset resembling the natural process.

The starting material came from human induced pluripotent stem cells, made from ordinary cells such as blood cells. An earlier approach, a mix called xrTestis that combined immature human cells with mouse testes support cells, collapsed after about 80 days, likely for lack of a blood supply. The team also produced immature sperm cells from monkeys, whose reproductive biology is closer to humans.

If this line of work eventually yields functional gametes, it would open new options for people who cannot produce viable sperm, addressing a form of infertility that current treatments cannot. That is why the frontier matters for reproductive care.

The crucial caveat is that no functional human sperm was made; the cells stopped at an immature stage. Rodent successes, including pups from two fathers, have not translated easily to humans because of species differences. Clinical use remains far off and would require extensive primate testing, and researchers flag bioethical concerns about designer babies and creating gametes without consent. Watch for whether these precursor cells can be matured further.

Source: Singularity Hub