A STEM cell breakthrough by a scientist has raised the prospect of restoring fertility to men made infertile by medical treatment.

A team headed by Professor Karim Nayernia, of Newcastle University, has used human bone marrow to create early-stage sperm cells for the first time.

He wants to further develop the technique to restore fertility in young men who have undergone chemotherapy.

Prof Nayernia said clinical trials could be years away, but he is encouraged by his success last year in helping to create sperm cells from embryonic stem cells from mice and using them to fertilise mice eggs, resulting in seven live births.

He is also concerned that the Government's recent White Paper on human fertilisation and embryology could unintentionally outlaw attempts to restore fertility in men.

He also fears that the threat of legislation might hinder efforts to obtain funding for research.

The research was carried out while Prof Nayernia was working at Gottingen University, in Germany, and was published in the journal Reproduction: Gamete Biology.

Prof Nayernia is now based at the North-East England Stem Cell Institute at the Centre for Life, in Newcastle.

For the experiment, Prof Nayernia and his team took bone marrow from male volunteers and isolated mesenchymal stem cells, which have been found to grow into other body tissues, such as muscle.

They cultured the cells and coaxed them into becoming male reproductive cells, which are scientifically known as "germ cells".

The process did not go any further, but tests with mice suggest it might be possible in humans.

Prof Nayernia said: "We are very excited about this discovery, particularly as our earlier work in mice suggests that we could develop this work."

The next stage is to see whether it is possible to make mature sperm in the laboratory, a process that could take up to five years with the assistance of other North-East scientists from the institute.

Along with medical colleagues, Prof Nayernia wants to look at the possibility of attempting to restore fertility in young men who have undergone chemotherapy.

In theory, it could involve taking bone marrow or tissue from the testes to culture germ cells in the laboratory and implant them back into the testes.