Male mice with genetic infertility were able to have healthy offspring after the development of a new technique to create artificial sperm. The aim is to adopt this new method for humans, but there are some hurdles yet to overcome.
As most of us probably know, our sex is determined by which sex chromosomes we possess, with women having XX and men having XY. Unfortunately, the division of cells is not a perfect art, and some boys are born instead with either an additional X chromosome making them XXY or an additional Y chromosome making them XYY.
It is thought that around 1 in 500 boys are born with Klinefelter syndrome (XXY), while roughly 1 in 1,000 are born with double Y, or Jacob’s syndrome (XYY). One of the main symptoms of both these conditions is infertility, and it was in a bid to allow these genetically infertile men to have children that the researchers decided to see if they could work around it.
They created two strains of mice, one each with either an extra X or Y chromosome. The researchers then tried to see if they could take the skin cells from the ear, and turn them into pluripotent stem cells, which in theory can then be encouraged to become any cell in the body, publishing their results in Science.
They found that, surprisingly, when they cultured the refined fibroblast cells taken from the ear tissue into stem cells, around a third of them dumped the extra chromosome that was causing infertility. They were then able to take these “cured” cells and guide them into becoming effectively pre-sperm, before they injected them back into the testes of host mice where they could then be exposed to the right conditions needed to mature into fully functioning sperm.
The matured sperm was then able to be harvested and used to fertilize eggs, with between 50 and 60 percent of pregnancies that came about resulting in live births. The researchers want to now develop the technique to achieve similar results in humans, but there is quite a major stumbling block to overcome first.
“There is currently no way to make mature sperm outside of the body,” explained senior author James Turner. “In our mouse experiments, we have to inject cells that have the potential to become sperm back into the testes to help them finish developing. But we found that this caused tumors in some of the mouse recipients.”
In fact, they found that after injecting the sperm into the testes of the host mice, between 29 and 50 percent of the subjects went on to develop tumors. This would obviously be unacceptable for use in humans, and so the researchers are now trying to figure out how to fully mature sperm in the test tube.