SCIENTISTS say they have successfully made immature sperm cells from human bone marrow samples.
If these can be grown into fully developed sperm, which the researchers hope to do within five years, they may be useful in fertility treatments.
But experts have warned the findings from the German study should be interpreted with caution at this very early stage.
The researchers from the universities of GÃ¶ttingen and MÃ¼nster and the Medical School of Hannover isolated adult stem cells â€“â€“ cells that have the ability to become many types of tissue in the body â€“â€“ from bone marrow samples taken from male volunteers.
Normally these stem cells from the bone marrow would develop into the different cell types in muscle tissue.
But the researchers induced a small number of them to develop into what appeared to be spermatagonial cells â€“â€“ cells found in the testes which would normally develop into mature sperm cells.
This is the first time human spermatagonial cells have been made artificially in this way.
And lead researcher Professor Karim Nayernia, now at the North-east England Stem Cell Institute based at the Centre for Life in Newcastle upon Tyne, said he hopes his investigations will mean he might one day be able to treat young men rendered infertile by chemotherapy.
He said: â€œWe are very excited about this discovery. Our next goal is to see if we can get the spermatagonial cells to progress to mature sperm in the laboratory and this should take around three to five years of experiments.â€
Sperm made from human bone marrow