Biomedical engineers have grown functional sperm cells from stem cells.

Chinese scientists have reported on an effort to coax mouse embryonic stem cells to turn into functional sperm-like cells, which were then injected into egg cells and produced fertile mouse offspring.

They say lab-grown sperm cells could one day be used to treat male infertility in humans.

It is not the first study to report the successful generation of sperm-precursors called ‘germ cells’ from stem cells, but previous efforts did not prove the functionality of the germ cells or provide proof for all key hallmarks of normal cell division.

Experts from Nanjing Medical University and the Institute of Zoology at the Chinese Academy of Sciences came together to develop the functional lab-grown sperm.

They first exposed mouse embryonic stem cells (ESCs) to a chemical cocktail that coaxed the ESCs to turn into primordial germ cells.

Next, the researchers mimicked the natural tissue environment of these precursor germ cells by exposing them to testicular cells as well as sex hormones such as testosterone.

Under these biologically relevant conditions, the ESC-derived primordial germ cells underwent complete meiosis, resulting in sperm-like cells with correct nuclear DNA and chromosomal content.

To provide the final gold-standard proof of meiosis, the researchers injected these sperm-like cells into mouse egg cells and transferred the embryos into female mice.

Remarkably, the embryos developed normally and gave rise to healthy, fertile offspring, which gave birth to a next generation.

In future studies, the researchers plan to test their approach in other animals such as primates, in anticipation of human studies.

But before the technique can be translated to the clinic, a large range of possible risks must be ruled out, as well as ethical concerns regarding the use of embryonic cells.

“If proven to be safe and effective in humans, our platform could potentially generate fully functional sperm for artificial insemination or in vitro fertilization techniques,” said study lead author Jiahao Sha.

“Because currently available treatments do not work for many couples, we hope that our approach could substantially improve success rates for male infertility.”

The full study is accessible here.