LONDON: A team of British scientists claims to have created human sperm using embryonic stem cells, in a breakthrough which could ultimately lead to a cure for male infertility.

Researchers led by Professor Karim Nayernia at Newcastle University and the North East England Stem Cell Institute (NESCI) yesterday announced that they had developed a new technique allowing the creation of sperm in the laboratory.

Prof Nayernia added: 'This is an important development as it will allow researchers to study in detail how sperm forms and lead to a better understanding of infertility in men - why it happens and what is causing it.

'This understanding could help us develop new ways to help couples suffering from infertility so they can have a child which is genetically their own.'

One possible use would be to help boys made infertile by chemotherapy treatment for cancer.

The scientists stressed, however, that there were no plans to directly use the sperm, developed from stem cells with male XY chromosomes, in fertility treatment, as this is prohibited by British law.

They also ruled out the possibility of lesbian couples having children using sperm produced without the involvement of men.

The scientists said they had tried to develop cells with female XX chromosomes, but that they did not progress beyond early stage sperm, called spermatagonia.

That led them to conclude that the genes on a Y chromosome are essential for sperm maturation.

The researchers also admitted that any possible fertility treatment based on their work was still some distance away.

They say more investigation is needed to decide whether the so-called in-vitro derived sperm is suitable for such use.

But while a treatment is probably at least a decade away, Prof Nayernia says that legislation should be put in place 'sooner rather than later' to allow the technique to be licensed.

The team's work involved developing stem cells that had XY chromosomes into germline cells - cells that can pass their genetic material to future generations.

These were then prompted to complete the cruical stage of meiosis, or cell division, which produced 'fully mature, functional sperm'.

Stem cells are immature cells that can develop into different cell types.

The research, published in the journal Stem Cells And Development, could also lead to a better understanding of how genetic diseases are passed on.

However, other scientists have expressed doubt about the work.

'As a sperm biologist of 20 years' experience, I am unconvinced by the data presented in this paper that the cells produced by Professor Nayernia's group from embryonic stem cells can be accurately called 'spermatozoa',' said Dr Allen Pacey, senior lecturer in andrology at the University of Sheffield.

'While the cells produced may possess some of the distinctive genetic features and molecular markers seen in sperm, fully differentiated human spermatozoa have specific cellular morphology, behaviour and function that are not described here.'