Around 1% of men — roughly 1.7 million in the US — have azoospermia, a condition where no sperm is present in their ejaculate. For about half of them, sperm can be retrieved directly from the testes, but for the other half, there's currently no option for biological parenthood. A new study published in Cell Stem Cell (July 2026) is bringing that possibility closer, with researchers successfully generating spermatogonia-like cells from stem cells — cells that closely resemble the sperm stem cells naturally found in human testes.

Led by Dr. Kotaro Sasaki at the University of Pennsylvania, the team combined human germ cell precursors with mouse fetal testicular cells to form "mini testes," which were then transplanted under the kidney capsules of immunodeficient mice. This allowed the cells to survive, mature, and form 3D structures — ultimately producing spermatogonia-like cells nearly indistinguishable from natural human spermatogonia at the RNA and DNA level.

Key Takeaways:

• The next critical hurdle is getting cells through meiosis — the cell division that halves chromosomes to create sperm — which no lab has achieved in any species beyond mice
• The technology could have near-term applications in reproductive toxicology, helping study how drugs, chemicals, and environmental exposures affect human germ cell development
• Ethical questions around gene editing, "designer babies," and same-sex biological parenthood are already being discussed as guardrails for future use

Why it matters: For men with no viable sperm, this research could one day mean the difference between biological parenthood and none at all. Researchers estimate functional lab-grown sperm could exist within 5 years — but clinical use in humans is likely 10+ years away.