For couples who can’t seem to get pregnant, one of the more common causes is egg or sperm quality: sperm that never make it to the egg or that can’t fertilize it once they’re there, and eggs that resist fertilization or implantation in the uterine wall. Now, for the first time, scientists have turned adult cells into egg- and sperm-cell precursors, an achievement that could one day help infertile couples conceive a child that shares their DNA.
Amander Clark, a developmental biologist at the University of California, Los Angeles, created the egg and sperm precursors using an existing line of induced pluripotent stem (iPS) cells, so named for their ability to turn into just about any tissue type and lauded for their potential in regenerative medicine. Until now, however, no one had shown that it was possible to prod iPS cells to rewind their internal clocks all the way back to the gamete, or “germ cell,” stage.
Researchers had previously shown that embryonic stem cells could produce egg- and sperm-cell precursors. But infertile couples would need to use donor eggs or sperm obtained from infertility clinics. “The benefit of using an iPS cell is that it has the donor’s own genetics,” Clark says. “Our research is many, many, many years awayam from generating a cell type that would be capable of fertilization and, therefore, making a healthy child. But this is one of the first steps.”
The study also highlights the differences between embryonic stem cells and iPS cells, which have been under study for a much shorter time period. When Clark compared the developmental potential of iPS cells to that of embryonic stem cells, she found that the latter resulted in egg and sperm precursors that were substantially healthier, with fewer chromosomal abnormalities. (This difference could be a major obstacle on the path toward using iPS cells in the infertility clinic.) “Because the [desired] outcome of using these cells is producing a healthy baby, the quality of a germ cell is essential in order to ensure that you have the birth of a healthy child,” Clark says. As a result, she notes, it will be essential to establish tests that can determine the quality of a germ cell before it gets anywhere near the clinic.