Professor Katsuhiko Hayashi, a leading expert in developmental genetics at Osaka University, stated that scientists are approaching a breakthrough in creating human sex cells in the laboratory. In a conversation with The Guardian, Hayashi indicated that researchers are making swift progress toward converting adult cells, such as those from skin or blood, into viable eggs and sperm—a technique known as in-vitro gametogenesis (IVG).
Hayashi estimated that his own research group could reach this milestone within approximately seven years. He also acknowledged that other institutions are advancing in the same direction, including a prominent team at Kyoto University and the California-based startup Conception Biosciences.
The startup, which counts OpenAI founder Sam Altman among its Silicon Valley investors, sees IVG as a potential solution to falling birth rates. Its CEO suggested that producing lab-grown eggs could not only help counter population decline but also open the door to future possibilities in human gene editing, the Guardian reported.
He acknowledged feeling some pressure, likening his work in in-vitro gametogenesis (IVG) to being part of a competitive race. Speaking ahead of his presentation at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) in Paris, he said he tries to stay grounded by reminding himself to adhere to scientific values.
Hayashi noted that, if proven safe, IVG could potentially allow anyone—regardless of age or fertility status—to have biological children. He also pointed out that his lab has previously succeeded in creating mice with two biological fathers, suggesting that this technology could one day be extended to same-sex couples.
He mentioned receiving regular messages from fertility patients—sometimes weekly—including some expressing willingness to travel to Japan for treatment, which he sees as a clear indicator of public interest.
Meanwhile, Matt Krisiloff, CEO of Conception Biosciences, emphasised the potential scale of the breakthrough, suggesting that the ability to grow human eggs in a lab could have a transformative impact on reproductive technology in the future.
He pointed out that the ability to extend women’s reproductive years could be a game-changing aspect of in-vitro gametogenesis (IVG). He suggested that, beyond its societal implications, the technology may become one of the most effective tools for addressing population decline by dramatically widening the timeframe in which people can plan families.
Meanwhile, at the ESHRE conference, Professor Katsuhiko Hayashi presented recent progress from his lab. Among the developments, his team has successfully generated early-stage mouse sperm within a lab-grown testicular organoid. They have also made strides toward creating human eggs by developing a human ovary organoid—an important step in enabling egg cultivation outside the body.
In-vitro gametogenesis (IVG) involves a multi-step scientific process that begins by reprogramming adult skin or blood cells into stem cells, which are capable of becoming any type of cell in the human body. Scientists then guide these stem cells to develop into primordial germ cells, the early-stage precursors of sperm and eggs. These germ cells are placed into lab-created organoids—artificial structures made from stem cells—that replicate the intricate biological environment needed to direct their development into mature reproductive cells.
Professor Katsuhiko Hayashi’s team has made headway using this approach in mice. In their experiments, they managed to grow spermatocytes—immature sperm cells—within artificial testes that are only about a millimetre in size. However, the cells failed to fully mature and eventually died. Hayashi believes the issue may be linked to insufficient oxygen within the organoids, and he hopes that future versions with improved oxygen delivery could help the cells reach full development.
Looking ahead, Hayashi predicted that producing viable human sperm in the lab could be achievable within the next seven years. While creating sperm from female cells remains a more complex challenge, he did not rule out the possibility.
Experts in the field largely support Professor Hayashi’s projection regarding the timeline for lab-grown human sex cells. Professor Rod Mitchell, a specialist in male fertility preservation at the University of Edinburgh, emphasised how rapidly the field is progressing. He noted that while the public may not fully grasp the pace of developments, it's now quite feasible to expect that sperm or eggs derived from immature reproductive cells could become a reality within five to ten years. He described this as a more credible forecast than the cautious estimates typically offered.
Professor Allan Pacey of the University of Manchester echoed this view, expressing confidence that a breakthrough is imminent. He said he feels prepared for the scientific leap but questioned whether society is equally aware or ready for such a development.
In the competitive pursuit of in-vitro gametogenesis (IVG), Professor Katsuhiko Hayashi acknowledged that others may be edging ahead. Hayashi noted that Conception operates with a high level of secrecy, making it difficult to assess their progress.
Matt Krisiloff, CEO of Conception, did not disclose detailed updates but indicated that the company is advancing steadily toward establishing a complete IVG protocol. He said that, in an optimistic scenario, the technology might reach clinical use within five years, though he acknowledged it could take longer.
There are serious concerns about the risk of genetic abnormalities being introduced during the IVG process, potentially affecting embryos and future generations. As a result, years of rigorous validation would likely be needed before human applications could be safely approved.
Professor Katsuhiko Hayashi emphasised the critical need to demonstrate that lab-grown reproductive cells are safe before any clinical use, calling it a major responsibility for scientists working in the field.
In the United Kingdom, current legislation prohibits the use of lab-generated sperm or eggs in fertility treatments. The Human Fertilisation and Embryology Authority (HFEA) is already considering the complex regulatory and scientific questions that would need to be resolved before such technologies could move toward human application. This includes determining which tests would be necessary to ensure safety.
There are also ethical and societal questions surrounding how in-vitro gametogenesis (IVG) might ultimately be used. While helping people struggling with infertility remains a key motivation, Professor Katsuhiko Hayashi expressed mixed feelings about extending the technology to enable much older women or same-sex couples to have biological children. His concerns stem largely from the increased safety risks that might accompany such applications. However, he stated that he would not oppose these uses if society at large supported them.
Reflecting on his own research—such as the creation of a mouse using two male parents—Hayashi acknowledged that such outcomes fall outside the boundaries of what is considered natural. Because of that, he cautioned that any scientific breakthrough that deviates from natural processes should be approached with extreme care.
Some observers are already considering the more controversial potentials of in-vitro gametogenesis (IVG), including large-scale embryo screening or genetic editing of stem cells prior to creating embryos.
Matt Krisiloff, CEO of Conception Biosciences, acknowledged that such outcomes are technically feasible with this emerging technology. He emphasised, however, that any movement in that direction would require careful regulation and strong ethical oversight. Krisiloff expressed support for using IVG to help prevent certain genetic diseases in future generations, but also warned against letting scientific enthusiasm outpace responsible practice.