Artificial sperm made from stem cells

Scientists in Japan have successfully generated viable sperm cells from embryonic stem cells in mice. The sperm cells were able to fertilise eggs and for the first time this produced healthy, fertile offspring.

'In the future, it may be possible to treat infertile men with a reproductive technology based on our contribution, but there are still a lot — really a lot — of issues that need to be resolved for this purpose', said Professor Mitinori Saitou of Kyoto University, Japan, who led the study.

The researchers converted mouse embryonic stem cells into primordial germ cells (PGCs) using a cocktail of specific proteins. PGCs will develop into the germline cells needed to produce offspring — sperm cells in males and egg cells in females. In this study, the PGCs were injected into the testes of male mice unable to produce their own sperm.

Following transplantation, the PGCs restored the previously infertile mice's ability to produce sperm, which was then extracted and used to fertilise eggs in vitro. The fertilised eggs were subsequently transplanted into surrogate female mice and resulted in the birth of healthy offspring. Importantly, they were able to have offspring of their own.

'This is the first study to create healthy and fertile offspring from germline cells generated from embryonic stem cells. Previous studies have not demonstrated the generation of such offspring', said Professor Mitinori.

The procedure was successfully repeated using another type of embryonic cell that was manipulated into a stem cell state. These stem cells are known as iPS cells (induced pluripotent stem cells) and have previously been created from a variety of different starting cells, including skin cells.

Dr Allan Pacey, a leading researcher into male fertility at the University of Sheffield, said: 'This is quite a step forward in developing a process by which sperm could be made for infertile men, perhaps by taking as a starting point a cell from their skin or from something like bone marrow. Clearly more work needs to be done, but it's hugely exciting'.

The study was published this month in the journal Cell.