Male infertility accounts for half of all cases where couples cannot conceive. To date, no approved medical treatment exists for affected men. Two research groups independently presented steps in 2026 that could change that long-term.
What Male Infertility Means
Male infertility typically manifests as too few, poorly motile, or malformed sperm. In severe cases, sperm production stops entirely, medically termed azoospermia. Causes range from genetic defects to prior cancer treatments, hormone disorders, and unknown factors.
The US Food and Drug Administration has approved no medication for these conditions. Affected men essentially have two options: donor sperm or accepting childlessness. Reproductive medicine has treated the problem as biologically too complex to address directly for decades. That is changing now.
What Penn Vet Achieved in 2026
In July 2026, the laboratory of Kotaro Sasaki at Penn Vet, the veterinary branch of the University of Pennsylvania, published a study in the journal Cell Stem Cell. The team, led by first author Eoin Whelan, converted human blood and skin cells into induced pluripotent stem cells (iPSCs) and then directed them toward spermatogonia, the earliest precursor cells of mature sperm.
The critical technical step: the stem cells were combined with reconstructed human testicular tissue and transplanted into mouse kidney tissue, which provides favorable conditions for cell growth. Six months after transplantation, human cells had developed into spermatogonia. Sasaki described the result as "the most advanced stage ever achieved for generating human sperm in the lab."
This is not yet a completed breakthrough: the cells remained at the spermatogonia stage. They did not advance to mature, fertilization-capable sperm. Precisely this next step is the open scientific question.
What Paterna Biosciences Claims
In parallel, in May 2026, a Salt Lake City company stepped forward: Paterna Biosciences announced it was the first company worldwide to produce functional human sperm entirely in the lab. CEO Alexander Pastuszak, a reproductive urologist at the University of Utah, stated the company had successfully used these lab sperm to fertilize human eggs. Early embryos formed, comparable to conventional IVF results. The sperm were structurally and genetically indistinguishable from natural sperm.
Important caveat: results have not been published in a peer-reviewed journal or replicated by independent researchers. Paterna plans clinical trials for 2027 and targets FDA approval after 2029. External scientists reacted to the announcement with cautious skepticism, since peer review is necessary for independent assessment of the method.
In Comparison: How Far Research Has Come
What works in animal models, science has already proven. Teams have generated sperm precursors from stem cells in mice and produced fertile offspring. The leap to human cells is biologically far more complex: human spermatogenesis takes months longer and is more sensitive to environmental conditions than mouse spermatogenesis.
A historical comparison provides perspective. Louise Brown, the first IVF baby, was born in 1978. More than ten years of development and clinical testing passed before IVF became routine medicine. Today, approximately twelve million people worldwide are born through IVF. In stem-cell-based sperm production, science stands at an early but comparable point: biological feasibility in animal models is proven. Proof in humans remains outstanding.
That the scientific community takes this seriously is shown by a 2026 development: the American reproductive ethics body, the ASRM Ethics Committee, published an opinion on ethical considerations for in vitro gametogenesis, the umbrella term for producing germ cells in the lab. Regulators and ethics committees are engaging because application is no longer purely theoretical.
Three Hurdles Before Clinical Use
Three technical and regulatory hurdles separate current research from clinical application. First, the complete maturation step from spermatogonia to mature sperm must succeed entirely in the lab without a mouse as a biological intermediary. This is the decisive step the Penn Vet study has not yet solved. Second, Paterna's results require independent replication and peer review. Third, clinical trials must demonstrate safety for children born from lab-grown sperm.
Early cost estimates for possible future therapy cite 5,000 to 12,000 US dollars per treatment, significantly less than many other reproductive therapies. ASRM anticipates that ethical and regulatory frameworks for approval will need to develop step by step.
For millions of couples facing male infertility, the state of research at end-2026 sends a visible signal: the scientific community no longer treats the problem as unsolvable. Two independent pathways are for the first time concretely moving toward a clinical solution.