Another challenge the field needs to overcome is the starting material – no adult has embryonic stem cells.
The Chinese group believe converting skin cells into a stem-cell state, which can be done reliably, will be the solution.
Professor Robin Lovell-Badge, from the UK’s Francis Crick Institute, praised “an impressive amount of work” and “exciting” results which will be “fantastically useful for basic research”.
He said: “I expect many think it is easy to make sperm, most men just sit there and make millions of the little blighters every hour. However, as this paper clearly shows, it is much more complex than this.”
While Professor Allan Pacey, from the University of Sheffield, argued making sperm outside the body “would be a remarkable thing to be able to do, both for the advancement of science and also to be able to help infertile men”.
He added: “In spite of these encouraging results, we are still some way from immediately applying this technique as a potential cure for human male infertility.”