French scientists claim to have grown mature sperm cells for the first time in the laboratory, dubbed a breakthrough in infertility treatments among both young and adult men.

French biotechnology startup Kallistem, conducting collaborative research led by its scientific director Philippe Durand with researchers from the French national center for scientific research (CNRS), announced in a press release that it has produced mature human sperm in vitro using immature cells from the testes of six infertile males.

“We have completed spermatogenesis – the production of mature sperm cells – in vitro using a bioreactor. We have done it in three different species, rat, monkey and human, which has never been done before,” Dr. Durand said. 

Created in an artificial “bioreactor,” the sperm cells appear identical to naturally produced ones and are targeted to help infertile men – including those whose reproductive potential are affected by cancer treatments such as chemotherapy – conceive their own biological children.

CNRS senior researcher Marie-Helene Perrard said that the technology could assist in issues affecting 15,000 young cancer patients and 120,000 men worldwide, where their fertility could be preserved by developing and freezing mature sperm from their own immature cells.

The process done at a top government lab in Lyon, France took 72 hours and involved recreating the fluid in which seminiferous tubules, the tiny structures where sperm cells are formed, can live outside the human body. The fluid helped researchers coax rat, monkey, and human sperm cells from the immature cells that will become sperm.

The next step entails giving life to rats with rat sperm using the same process, and then a battery of tests with the lab-manufactured human sperm for clinical testing.

However, experts have expressed doubts that the findings cannot be verified until the study is published in a peer-reviewed journal. The research was submitted for publication in September.

Sheffield University professor Allan Pacey told the Independent that he is “deeply skeptical” until he is able to see the published research.

“The only decent thing for the science and for the public is for them to show us all the evidence,” Pacey said, adding that the picture of the sperm does not look appear to him as a mature sperm but instead an elongated cell.

A 2009 study published in Stem Cells and Development was retracted within weeks due to doubts about its veracity and plagiarism charges.

However, in August 2011, scientists in Kyoto, Japan announced they had successfully coaxed sperm cells from the embryonic stem cells of mice.