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Early stage sperm cells have been created from the skin of men with a genetic defect that makes them infertile.
None of the men were capable of producing enough natural sperm to conceive.
Scientists believe that in the future the technique could bring new hope to men unable to generate sperm.
Scientists say they have found a way of creating early stage sperm cells from skin cells
More immediately, it offers researchers a new tool for studying sperm development and male infertility treatments.
Lead researcher Dr Reijo Pera, from the Institute for Stem Cell Biology and Regenerative Medicine at Stanford University, said: ‘Our results are the first to offer an experimental model to study sperm development.
‘Therefore, there is potential for applications to cell-based therapies in the clinic, for example, for the generation of higher quality and numbers of sperm in a dish.
‘It might even be possible to transplant stem cell-derived germ cells directly into the testes of men with problems producing sperm.’
Infertility affects 10 to 15 per cent of couples and genetic causes of the problem are surprisingly prevalent among men, say the scientists.
The most common defect is the spontaneous loss of key genes on the male Y chromosomes, but what triggers it at the molecular level is not well understood.
The discovery could eventually mean new hope for men who are infertile because they are unable to generate sperm
The three infertile men taking part in the study had missing regions of Y chromosome DNA associated with the production of few or no sperm.
Fibroblast connective tissue cells from skin samples taken from the men were genetically engineered to transform them into induced pluripotent stem (iPS) cells.
These are adult cells whose developmental clock has been turned back so they assume the properties of embryonic stem cells, including the ability to grow into virtually any kind of body tissue.
Sabotaged by the Y chromosome genetic defect, the iPS cells struggled to form sperm in a laboratory dish.
But after being transplanted into the testes of mice, they turned into sperm cell precursors - albeit fewer than the number produced by ‘healthy’ iPS cells.
The findings, published in the journal Cell Reports, indicate that Y chromosome infertility occurs relatively late in the maturing process of sperm cells.
Dr Reijo added: ‘Our studies suggest that the use of stem cells can serve as a starting material for diagnosing germ cell defects and potentially generating germ cells.
‘This approach has great potential for treatment of individuals who have genetic/idiopathic (unknown) causes for sperm loss or for cancer survivors who have lost sperm production due to gonadotoxic treatments.’
U.S. scientists from the University of Pittsburgh showed in 2012 that it was possible to generate sperm cell precursors from human iPS cells, raising the prospect of restoring a man's fertility.
However, they did not start out with adult skin cells from genetically infertile men.
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