Mice have been used to make human sperm for the first time in a breakthrough that could lead to a treatment for infertile men.

The discovery shows the animals can be used as surrogate sperm producers for men who cannot produce viable sperm of their own.

The research could, however, prove controversial because it gives a separate species an intimate role in human reproduction.

“Our data indicate that the mouse can yield human sperm cells,” said Irina Kerkis of the Roger Abdelmassih clinic and research centre in Sao Paolo, Brazil.

Kerkis, whose earlier fertility research has been published in the scientific journal, Nature, will outline her findings this week at the annual meeting of the European Society of Human Reproduction and Embryology in Barcelona.

In an advance summary, Kerkis describes how she and her colleagues first extracted dental pulp from the tooth of a male donor.

The pulp, found in the soft material in the centre of teeth, is rich in stem cells. These are the precursors of almost every type of cell in the body with the power to develop into anything from heart muscle to brain cells.

Kerkis then isolated the stem cells from the dental pulp and injected them into the testes of live male mice.

The mice were killed at various intervals after the injection and their testes examined to see if the stem cells had survived.

Kerkis found the human stem cells had not only settled into the mouse’s testes but had also successfully “differentiated” into cells that were producing viable sperm.

In practice, once sperm had been extracted from the mouse’s testes they could then be used to fertilise a donated egg. This could then be transplanted into a prospective mother.

The discovery means that an infertile man could have a baby by giving up one of his teeth and agreeing to involve a mouse in the process of reproduction.

About 10-15% of men have a low sperm count, impaired sperm mobility or are unable to have children, and about 1-2% can produce no sperm at all.

Currently eggs from cows are being used by British scientists to create human stem cells that may be used to test drugs or even as treatments for multiple sclerosis and motor neurone disease.

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