Published: 08:05 AM, 06 July 2025
Lab-grown sperm and eggs just a few years away, scientists say
Scientists are just a few years from creating viable human sex cells in the lab, according to an internationally renowned pioneer of the field, who says the advance could open up biology-defying possibilities for reproduction.
Speaking to the Guardian, Prof Katsuhiko Hayashi, a developmental geneticist at the University of Osaka, said rapid progress is being made towards being able to transform adult skin or blood cells into eggs and sperm, a feat of genetic conjury known as in-vitro gametogenesis (IVG).
His own lab is about seven years away from the milestone, he predicts. Other frontrunners include a team at the University of Kyoto and a California-based startup, Conception Biosciences, whose Silicon Valley backers include the OpenAI founder, Sam Altman and whose CEO told the Guardian that growing eggs in the lab "might be the best tool we have to reverse population decline" and could pave the way for human gene editing.
"I feel a bit of pressure. It feels like being in a race," said Hayashi, speaking before his talk at the European Society of Human Reproduction and Embryology's (ESHRE) annual meeting in Paris this week. "On the other hand, I always try to persuade myself to keep to a scientific sense of value."
If shown to be safe, IVG could pave the way for anyone - regardless of fertility or age - to have biological children. And given that Hayashi's lab previously created mice with two biological fathers, theoretically this could extend to same-sex couples.
"We get emails from [fertility] patients, maybe once a week," said Hayashi. "Some people say": 'I can come to Japan.' So I feel the demand from people."
Matt Krisiloff, Conception's CEO, told the Guardian that lab-grown eggs "could be massive in the future".
"Just the aspect alone of pushing the fertility clock … to potentially allow women to have children at a much older age would be huge," he said. "Outside of social policy, in the long term this technology might be the best tool we have to reverse population decline dynamics due to its potential to significantly expand that family planning window."
In a presentation at the ESHRE conference, Hayashi outlined his team's latest advances, including creating primitive mouse sperm cells inside a lab-grown testicle organoid and developing an human ovary organoid, a step on the path to being able to cultivate human eggs.
IVG typically begins with genetically reprogramming adult skin or blood cells into stem cells, which have the potential to become any cell type in the body. The stem cells are then coaxed into becoming primordial germ cells, the precursors to eggs and sperm. These are then placed into a lab-grown organoid (itself cultured from stem cells) designed to give out the complex sequence of biological signals required to steer the germ cells on to the developmental path to becoming mature eggs or sperm.
Inside the artificial mouse testes, measuring only about 1mm across, Hayashi's team were able to grow spermatocytes, the precursors of sperm cells, at which point the cells died. It is hoped that an updated testicle organoid, with a better oxygen supply, will bring them closer to mature sperm.
Hayashi estimated that viable lab-grown human sperm could be about seven years away. Sperm cultivated from female cells would be "technically challenging, but I don't say it is impossible", he added.
Others agreed with Hayashi's predicted timescale. "People might not realise how quickly the science is moving," said Prof Rod Mitchell, research lead for male fertility preservation in children with cancer at the University of Edinburgh. "It's now realistic that we will be looking at eggs or sperm generated from immature cells in the testicle or ovary in five or 10 years' time. I think that is a realistic estimate rather than the standard answer to questions about timescale."
