German investigators have demonstrated that sperm cells, derived from embryonic stem cells, have a reproductive potential.
From BBC News:
Professor Karim Nayernia and colleagues at the Georg-August University in Göttingen, Germany, took stem cells from a mouse embryo that was only a few days old and grew these cells in the laboratory.
Using a specialised sorting instrument they were able to isolate some stem cells that had begun to develop as sperm.
They encouraged these early-stage sperm cells, known as spermatogonial stem cells, to grow into adult sperm cells and then injected some of these into female mouse eggs.
The fertilised eggs grew and were successfully transplanted into female mice and produced seven babies.