Stem cell research remains ethically controversial, but scientists are nonetheless hoping that it might be the solution to diseases of the central nervous system.
Stem-cell research involving monkeys has critics concerned
Researchers at the German Primate Center in the southern city of Göttingen propelled themselves into the headlines when they began conducting stem cell experiments on monkeys and primates as part of research into diseases such as Parkinson's. The charge was that scientists there were in fact "cross-pollinating" animal species.
But Stefan Treue, the director of the center said the experiments have nothing to do with chimaera, as human cells in monkey's brains can not release any human characteristics.
In fact, the development of chimera, organisms with two or more genetically distinct types of cells, has nothing to do with either stem cell research. Chimera are conceived through the injection of undifferentiated stem cells from the seed of one animal into the early embryo of another animal type. A new creature then develops out of different genetic characteristics.
Stem cell specialization
Researchers at the German Primate Center and the Max-Planck Institute for Biophysical Chemistry work in a completely different way. They have manipulated embryonic human stem cells in test-tubes, teaching them to specialize in the production of the nerve cells which are killed off with the onset of Parkinson's.
The question is whether these cells, which would enter the body through an injection into the human brain, can take over the function of the destroyed nerves.
Experimenting on rodents is just the first step
Experiments in which stem cells from mices' brains were implanted into rats' brains showed that the transplants in fact caused tumors. The same thing happened to a particular breed of monkey which received injections of human stem cells into its brain.
Cancer cell killers
At the moment scientists at the Max-Planck Institute for biophysical chemistry are researching what is known as a "Terminatorgen", which kills off cancer cells as they are created. Experiments are currently being performed on rats, and if they prove successful in preventing the growth of tumors in rats' brains, the experiment will be extended to monkeys.
One experimental step before humans
But getting permission to do so is not always easy.
"It has to be a very important issue to be able to justify the animal's potential suffering," Stefan Treue said. "But before we take the leap to humans, we have to take animals which are similar to us, there's no way past that."
At the end of June, Germany's ethics council will turn its attention to the issue of stem cell research, and in particular to the creation of chimera.