Infertile men around the world may soon find relief from the fact they aren’t naturally able to impregnate their partners, because lab-grown sperm cells will be able to do it for them. In a world first, French scientists say they’ve grown fully functioning sperm.

For nearly 15 years, scientists have been trying to grow sperm cells in the lab in order to help the tens of thousands of men who are unable to conceive on their own. But on Friday, researchers from the biotech company Kallistem announced that by the end of 2014 they had successfully grown “complete human spermatozoa in vitro” using patients’ testicular biopsies “containing only immature germ cells, or spermatogonia,” the company said in a statement, according to AFP.

“This research paves the way for innovative therapies to preserve and restore male fertility, a major issue with global impact; numbers of spermatozoa have declined by 50 percent over the last 50 years,” the company continued.

Spermatogenesis, the process by which mature, motile sperm cells are produced, is a complex process that takes up to 72 days. All of these cells grow from spermatogonia, the undifferentiated male germ cell. But while many of these germ cells develop into the mature cells we all know, others replicate to fuel that development. Kallistem claims it’s been able to do this in the lab, and that from the testicular biopsy, “it will be possible to obtain spermatozoa that will be cryopreserved until the man wishes to father a child.”

The company says the procedure, with a market value of about $2.58 billion, may help as many as 50,000 infertile men each year. Pre-clinical and clinical trials are slated to begin over the next two years. During these trials, the company will have to determine how effective the process is in humans, as it wasn’t excluded that men who suffer from a complete lack of sperm have “genetic anomalies, which would also prevent in vitro spermatogenesis,” said Nathalie Rives, manager of a fertility clinic in France, according to AFP.

Though the breakthrough research was received with optimism, experts cautioned that it hadn’t yet been published in a peer-reviewed journal, and thus should be considered with caution.

In the U.S., infertility affects 18 percent of the roughly 4.7 million men who ever visit a fertility doctor in their lifetime. While it affects more women, both men and women suffer from being unable to conceive as it takes a psychological toll on their wellbeing. This new research may alleviate some of that pain.