From Nature:
Human embryonic stem cells have been coaxed into forming sperm-like cells, researchers report today1. The cells have some of the hallmarks of sperm — they can swim, for example — but require much more characterization before they can be embraced as an experimental model for the study of inherited diseases and infertility.
Meanwhile, the use of such cells to help infertile couples to have children remains a distant prospect; in several countries, including the UK, it would actually be illegal even if they were properly characterised. With approximately one in seven couples experiencing fertility problems, there is a strong push to develop a robust method for generating sperm and eggs for research. But researchers have struggled for years to produce reproductive cells from stem cells. The task is particularly difficult because it requires a complex form of cell division called meiosis, which reduces the number of chromosomes per cell by half.
More here.