Scientists have taken a major step forward in the understanding and treatment of male infertility after impregnating mice with sperm grown from embryonic stem cells.
In a world first, researchers have shown that sperm generated from stem cells and developed in a laboratory can result in a live birth.
The breakthrough could lead to infertile men undergoing "sperm transplants" resulting in the birth of their own biological child rather than having to use donated samples, which are in short supply.
Experts described the work as an exciting advance and "hugely significant" for the treatment of male infertility. But some pro-life campaigners expressed concern about the use of "artificial sperm" grown from a discarded embryo rather than a man to create a life.
Professor Karim Nayernia, of Newcastle University, conducted the research - reported yesterday in the journal Developmental Cell - while working in Germany. His team first took stem cells from a mouse blastocyst - an embryo that is a cluster of cells only a few days old. Stem cells are the building blocks of the body and can develop into any type of tissue.
The cells were grown in a laboratory and a marking system was used to identify those that were developing into early-stage sperm cells, known as spermatogonial stem cells.
Scientists had already got that far in research but did not know whether the cells could really "work". The spermatogonial stem cells were monitored in laboratory conditions until they developed into gametes - sperm - a process that took 72 hours.
Professor Nayernia used a version of intracytoplasmic sperm injection (ICSI), a type of fertility treatment used in humans, in which the mouse sperm was injected directly into an egg and implanted into a female mouse.
Of the seven mice born as a result, six developed into adults. But three of the mice had abnormalities, such as being too large or small, and died.
Professor Nayernia said: "The research is particularly important in helping us to understand more about the biological process by which sperm is produced. We must know this if we are to get to the root of infertility."
He added: "If we know more about how spermatogonial stem cells turn into sperm cells, that could be translated into treatments for men whose sperm is dysfunctional. For example, we could isolate a patient's spermatogonial cells using a simple testicular biopsy, encourage them in the laboratory into becoming functional sperm and transplant them back into the patient."
Theoretically, the process also means that a baby could be created without the need for a man or a sperm donor, although current UK law prevents that.
Scientists at Sheffield University have shown human stem cells can develop into the earliest stages of sperm cells but have gone no further than that because of ethical concerns. Professor Harry Moore, an expert in reproductive biology at the University of Sheffield, said: "This latest finding is exciting as it is the first indication that cells produced in this way have the full potential to create an individual." But he warned: "We have to be very cautious about using such techniques in therapies to treat men and women who are infertile until all safety aspects are resolved. That could take years."
The breakthrough is important because scientists still know little about how sperm develops and what causes it to develop problems. Male factor infertility also appears to be on the rise, with more than half of all fertility treatments now performed using ICSI, a procedure designed to help when the problem lies with the man rather than the woman.
Other scientists raised concerns about the ethical implications of the potential to create a child without sperm from an adult man, warning that it could lead down a "slippery slope" to reproductive cloning.
Anna Smajdor, a researcher in medical ethics at Imperial College London, said: "The creation of viable sperm outside the body is a hugely significant breakthrough and offers great potential for stem cell research and fertility treatments. However, sperm and eggs play a unique role in our understanding of kinship and parenthood and being able to create these cells in a laboratory will pose a serious conceptual challenge for our society.
"Who is the father of offspring born from laboratory sperm - a collection of stem cells in a petri dish? The embryo from which these cells were derived? The answers to these questions are not clear but they go to the foundations of our sense of identity."
Josephine Quintavalle, founder of the pro-life lobby group Comment On Reproductive Ethic, said: "I do have concerns about how this would be used in humans. The mice were born with abnormalities and I know a number of scientists who have concerns about using cells like this.
"It is one thing to do this on mice but in humans you are not just using an adult as a guinea pig, you are using the unborn child in the same way too."
* About 40 per cent of fertility problems lie with the man and 20 per cent with both the man and the woman.
* More than half of all fertility treatments now involve intracytoplasmic sperm injection (ICSI), which tends to be used where the problem lies with the man.
* Up to 30 per cent of men are "sub-fertile", meaning they will have some problems conceiving and 2 per cent are totally infertile. Sperm problems account for 75 per cent of male infertility.
* Around 100 to 750 million sperm are ejaculated during orgasm but only a few hundred make it to the fallopian tube where the egg is fertilised.
* Factors affecting sperm count and movement include smoking, obesity, age, excessive heat and genetic problems.Reuse content