In a development that may someday help men facing infertility, Chinese scientists have just announced they were able to create sperm in a lab petri dish using embryonic stem cells from mice. The sperm was used to fertilize mouse eggs using in vitro fertilization (IVF), creating healthy babies that went on to have their own offspring. That's promising.
Embryonic stem cells can actually develop into any type of cell in the body and have previously been used to create sperm. However, in the past, transforming such cells into sperm required the cells to be transplanted into the testicles of mice. The new technique represents an advance as the sperm was able to develop in a lab dish containing testicle cells.
According to study results in the journal Cell Stem Cell, mouse sperm was used to fertilize mouse eggs and of 379 eggs injected, nine babies resulted. After 15 months, all mice appear healthy, and they're having their own offspring.
While the sperm developed in the lab is a primitive type, not fully mature, known as spermatids, they still contained their full genetic component and were sufficient to fertilize eggs. Spermatids have been used to create healthy human babies in Japan, while some countries have outlawed the procedure.
A number of scientists interviewed about the study results expressed excitement for how the work -- making sperm outside the body -- could aid research into basic sperm development and eventually help infertile men. Some Japanese researchers questioned the results suggesting that others have "struggled to replicate similar claims."
For all mammals, making sperm in the testes is one of the longest and most complicated processes in the body, taking more than a month. In this research, an embryonic stem cell was used and "guided towards becoming sperm with a cocktail of chemicals, hormones and testicular tissue." To accomplish this, the cell must first go through a process called meiosis that involves rearrangement of DNA. Sperm, like eggs, must lose half of their DNA so a fertilized egg has the right amount. Chinese scientists say they followed the international research gold standard established in 2014 for reproducing meiosis in the lab. Properly replicating meiosis is critical for genetically healthy offspring.
If this technique can be adapted to work for humans, doctors might be able to help infertile men by using their own skin cells or other cells to create stem cells and ultimately, sperm. For those men unable to produce sperm due to infection, cancer treatment or a physical problem, the new approach would allow a man to pass his DNA on to his children.
One major challenge to pursuing the work with humans is that embryonic stem cells are not found in adults. Chinese researchers believe this problem may be solved by converting skin cells into stem cells which can be done now.
Other issues include ethical concerns and differences in embryo and sperm development between mice and humans. According to Harvard Medical School geneticist Yi Zhang, this "may not be as straightforward as people hope." The study authors have begun research with monkeys. And, Azim Surani, a developmental biologist at the University of Cambridge, UK who finds the results encouraging, cautions that it's hard to know whether the artificial spermatids behave exactly like their natural counterparts.
Still, "the fact that the resulting cell could be injected into an egg and produce a viable animal is a stringent test," states Allan Spradling, a reproductive biologist at the Carnegie Institution for Science in Baltimore, Maryland. However, he added mice that resulted "might still contain defects or problems that do not manifest themselves until later."
Reaction to the new research is best described as excitement mixed with caution and rightly so. Using this new technique with humans is likely years away assuming the issues cited can be addressed. For infertility specialists and our patients, we continue to be encouraged by the pace of scientific discovery and its application to infertility treatment. It seems as if there's something new to report almost every week in the global search to solve infertility and create healthy babies.
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