The author of a new study on changing human bone marrow stem cells into immature sperm cells is optimistic that his work will eventually allow infertile men and lesbian couples to conceive by producing their own sperm.
Karim Nayernia of Newcastle University in England expressed his excitement to ABCNEWS.com, saying that "this represents a real breakthrough from a biological and medical point of view."
Nayernia said his research suggested that "doctors may one day take a normal, adult cell -- from bone marrow or another tissue -- and coax it into becoming a sperm cell. These sperm cells could then be put into the testes of infertile men, allowing them to conceive with their partners."
Nayernia had previously worked on a similar study using bone marrow taken from mice. His team was able to coax the mouse cells to begin the process of becoming sperm cells. Invariably, however, the cells fell short of developing into useful sperm cells. The mouse cells were able to complete two of the three divisions necessary for them to become mature sperm cells.
But the fact that the third crucial division did not take place in mouse cells or in human cells has led other experts in the field to counsel caution about taking this new study's conclusions to heart.
David Smotrich, founder and medical director of the fertility institute LaJolla IVF in California, said that "although there's been tremendous excitement surrounding this study, I am skeptical about its implications. If you can't even coax these cells into becoming mature sperm cells in mice, under lab conditions, then I certainly don't see how you can make it happen in human beings."
"The hype tremendously supercedes any possibility of such trials contributing to fertility therapy," he said.
Nayernia's team took bone marrow stem cells from men who were about to undergo bone marrow transplants. The scientists then added proteins and vitamin A, which apparently promotes sperm development, to these human stem cells. As a result of this process, the stem cells began to show signs of becoming partly developed sperm cells. Unlike the sperm stem cells found in most men, they did not achieve maturity, even under lab conditions.
Nayernia believes "it is only a matter of months before lab tests show such partially formed sperm cells developing into fully functional sperm."
Not every scientist shares his hopes. Malcolm Alison, professor of stem cell biology at the Queen Mary School of Medicine and Dentistry in London, echoed Smotrich's concerns when he criticized the study and the hype surrounding its conclusions for being "excessive and premature."
Alison said that "although this isn't dubious science exactly, it's certainly preliminary science. After all, these cells never underwent the critical process of cell division -- they didn't pass the 'acid test.'"
He continued, "This is not advanced research. It's almost like a school-level biology experiment. But because anything to do with fertility and reproduction gets attention, a relatively unsophisticated experiment has captured the public's imagination."
Smotrich also cautioned against "raising false hopes on such a sensitive subject." Furthermore, he said that "there are so many ethical complexities surrounding this issue, at least in the United States, that I think too much attention to it could actually put researchers at risk."
In the United Kingdom, the experiment using lab-generated sperm to fertilize a human egg tends to be very controversial and requires authorization from the Human Fertilization and Embryology Authority. At present, such fertility treatments are not supported by the British government.
That does not deter Nayernia, who said that he hopes "in three to five years, researchers will be able to carry out clinical trials on human beings, by injecting sperm stem cells directly into the testes of infertile men."
"If we have more results in the lab," he said, "we could convince the government to allow us to run clinical trials in the future."
That does not seem likely to fertility doctors like Smotrich, who said that "the idea that this is actually going to be a viable option for single women or infertile men in the next five years is tremendously far-fetched."
For his part, when questioned as to the likelihood of such a procedure emerging in five years or even 10 years, Alison simply said: "Frankly, no one has any idea if such a day will come, and if it will come next week, next month or next year."
"Stem cell research," he said, "is a relatively new field, and while that makes it a very exciting area of research, it also means that it's prone to several false starts."
So far it would seem that this new study, although hailed as path-breaking and pioneering by British newspapers like The Independent, could well prove to be yet another such false start.
Dan Childs contributed to the reporting of this story.