It is very, very early days, but it will be significant if we can replicate it in humans

Dr Mohammed Taranissi

Normally, these sertoli cells nuture sperm to maturity.

But if they carry a defective version of a particular gene they are unable to perform their usual role.

The scientists rendered mice infertile by injecting them with a virus carrying the defective version of the gene.

They then used gene therapy to restore the function of the sertoli cells so that the mice were subsequently able to father offspring.

However, the mice were not able to produce mature sperm in sufficient quantity to restore natural fertility.

IVF techniques

The scientists had to isolate the sperm that the mice did produce and use it to fertilise female eggs by employ in vitro fertilisation techniques. create embryos.

The embryos were implanted into female mice, and developed into healthy, fertile offspring.

Crucially, the new-born mice showed no sign of having inherited DNA from the virus used in the treatment.

A major obstacle to gene therapy for infertility is the danger of viral DNA becoming mixed in with sperm cell DNA and being passed on to subsequent generations.

Writing in the Proceedings of the National Academy of Sciences, the researchers wrote: "Our successful production of offspring from infertile mice has important implications for the development of gene therapy protocols to correct human male fertility."

They said that extensive further studies of the genes involved in sperm production and the safety issues were needed before a similar treatment could be tried on humans.

Dr Mohammed Taranissi, director of the Assisted Reproduction and Gynaecology Centre in London said the research was potentially significant.

He told BBC News Online: "It is very, very early days, but it will be significant if we can replicate it in humans. There is no treatment for men who have this form of infertility."

Significant problem

Male infertility accounts for about 30% of all cases. Around one in ten of these is due to defective sertoli cells.

Clare Brown, executive director of CHILD, the National Infertility Support Network, told BBC News Online: "Child finds it encouraging that scientists are always looking to improve a couples' chances of having a baby.

"Up until Intra Cytoplasmic Sperm Injection (ICSI), there have been very little treatments that could be done for couples with male factor infertility.

"Obviously, it is very early days but CHILD is awaiting the results of future research with great interest."

The research is published in the Proceedings of the National Academy of Sciences.