Human Fertilisation and Embryology Bill [Lords]

Let me give an example. The procedure has been used in mice since the early 1990s, and it is routinely used to make entire mice from embryonic stem cells, which are being aggregated with tetraploid embryos. When used in this way, the procedure is considered a gold standard for testing, where researchers have isolated genuine, fully functional embryonic stem cells to make every cell type in the body rather than just many cell types. Since the tetraploid cells would make tissue outside the embryo, such as placenta, the inserted embryonic stem cells would have to make every cell type in the animal. If anyone is interested, I have research papers here on that very procedure. Currently, researchers use a far less rigorous type of test for human embryonic stem cells. It is called the teratoma test, as was mentioned earlier. Teratomas are a specific type of tumour generated by embryonic stem cells, which consist of various stem cell types. However, it is a much less comprehensive test than tetraploid complementation, since relatively few cell types are generated in this way.