For two decades now, scientists have been trying to produce human sperm in test tubes, in an effort to help infertile men. Previous attempts to grow this male cell, however, have been unsuccessful, with researchers failing to complete the complicated cycles of cell division and development.

But now researchers based at a French national research institute in Lyon are claiming that they have successfully made human sperm cells in the laboratory.

Philippe Durand, scientific director of the Kallistem biotechnology start-up who led the research team, explained that the sperm cell was made in an artificial "bioreactor."

"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," Durand said.

The research head added that the human sperm cells were produced by culturing immature cells taken from the testes of infertile men.

"The mature sperm were made by taking small biopsies from the testes of the men, and culturing these cells in the bioreactor until they developed into fully mature sperm which look identical to those produced naturally in the testes of men," Durand said.

He further said the sperm cells his team produced "could be of use clinically."

This scientific breakthrough can help adult men who cannot make their own sperm, and young boys rendered sterile by cancer treatments.

Not everyone in the scientific community, however, is convinced by the work of Durand's team. Professor Allan Pacey from the Sheffield University, for instance, said he is "deeply sceptical."

"The picture of the sperm they have published is not convincing. It doesn't look like a mature sperm to me, but an elongated cell. The only decent thing for the science and for the public is for them to show us all the evidence," Pacey said.