The scientists were unable to test whether the sperm were able to fertilise mouse eggs. Nevertheless, they anticipate eventually being able to replicate their findings using human cells, giving hope to infertile men who wish to have a child using their own sperm, rather than relying on a donor.
The study, which is published in the Asian Journal of Andrology, used a nutrient-rich 'three-dimensional' medium to culture the cells rather than growing them on a flat surface, in an attempt to mimic the environment found in the testes.
The team, led by Professor Mahmoud Huleihel from the Ben-Gurion University of the Negev in Israel, developed the 3D culture, known as SACS, and inserted germ cells from seven-day-old mice into it. After 14 and 28 days of growth, they analysed the cells' DNA. The team reported that the DNA analysis showed that the relevant genes and proteins were being activated to change the germ cells into full spermatozoa.
However, as the NHS Choices website explains, 'normal-looking' sperm were only found in 11 out of the 16 samples after 30 days' growth. The researchers were also unable to isolate the live sperm produced in the laboratory to test whether they could fertilise mouse eggs. Finally, the DNA analysis did not completely reveal whether the sperm were indeed genetically 'normal'.
Previous groups' attempts to grow mammalian sperm outside of the body have failed, and the Ben-Gurion researchers believe this is largely because of the way cells have been cultured using a flat surface, as opposed to their 3D medium.
Professor Huleihel said that the study 'may open new therapeutic strategies for infertile men who cannot generate sperm and/or pre-pubertal cancer patients at risk of infertility due to aggressive chemo- or radiotherapy'. He added: 'I believe it will eventually be possible to routinely grow human male sperm to order by extracting tissue containing germ cells from a man's testicle and stimulating sperm production in the laboratory'.
Speaking to the Daily Mail, Professor Richard Sharpe of Edinburgh University, a leading fertility specialist who was not involved in the study, called the research a 'significant step towards making human sperm'.