Scientists “Grow” Human Sperm from Stem Cells — Hosted Inside a Mouse Kidney
Imagine a person's blood cells being altered in a laboratory, transplanted into a mouse, and after several months developing into precursors of human sperm cells. It sounds like the plot of a science-fiction film, but this is what a group of researchers has just reported in the journal Cell Stem Cell, reviewed by Nature on 10 July 2026.
The team, led by Kotaro Sasaki and Eoin Whelan at the University of Pennsylvania, took human blood cells and reprogrammed them into induced pluripotent stem cells (iPS cells) — “young” cells that mimic embryonic cells and can be steered into many different body-cell types, reproductive cells included. Those cells were then mixed with non-reproductive cells from developing mouse testes, because such cells supply the nutrients and protection sperm cells need in order to grow.
The most striking step came next: the cell mixture was transplanted into a small “pocket” created in the kidney of a living mouse — an area long known to be highly supportive of transplanted tissue growth. That is where the remarkable part happened. The cells organised themselves into tubular structures, resembling the small ducts inside the testes where sperm is normally produced. Six months after transplantation, the human cells had developed into spermatogonia — cells with the potential to become mature sperm.
Not Yet the Finish Line, but a Major Step
The implanted cells did not go on to become fully mature sperm capable of fertilising an egg — the process stopped at an early stage. The researchers themselves stress that this remains pure basic research, far from clinical application. Even so, the finding opens an important route to studying the earliest stages of human sperm development, and to investigating the causes of male infertility — a condition whose cause remains unknown in roughly 40% of cases.
Making eggs and sperm from skin cells had already been achieved in mice — in one case even producing offspring from two male parents. In humans and primates, however, embryonic development is far more complex, which makes the same approach difficult to transfer directly. This breakthrough is one of the most advanced attempts yet to “translate” the rodent results into human biology.
Why This Matters for the Life Sciences
The research reaffirms what has long been the foundation of stem-cell science and regenerative biotechnology: the remarkable capacity of stem cells to be “reprogrammed” and directed into other cell types, provided they are given the right environment and biological signals. That same principle underpins the development of therapies based on stem cells and secretome — for tissue regeneration, wound healing and skincare among others — an area now under increasingly active research and development, Indonesia included.
The deeper science understands how stem cells work, the greater the opportunity to deliver health and beauty innovations that are research-based, safe and sustainable for the public.
This article is a science-news summary written for educational purposes. The findings discussed remain basic research and are not yet a clinical application.