Scientists have now turned mice stem cells into sperm and have successfully fertilized eggs and produced offspring with those sperm. This is a very exciting step toward one day allowing an infertile man to have his own biological children.

A New Scientist article talks about the research that's being done by a team in the UK (are we shocked that it's not American research?).

Stem cells were extracted from early mouse embryos, and coaxed into becoming sperm by manipulating the environment in which they were grown in the lab. These sperm were then injected into normal mouse egg cells to fertilize them. Of 65 embryos implanted, seven mouse pups were born, six of which survived to adulthood.

So all this sounds promising, yet the end of the article reminds us that research still has a long way to go:

Problems with the procedure remain, however. The six mice that survived were all abnormally large or abnormally small, and were infertile. Many developed lung tumours and none lived for more than five months "“ well short of the typical three-year mouse lifespan.

Life doesn't sound so great for those mice. Still, it's an exciting step.