By Ludger Wess

BioWorld International Correspondent

HANOVER, Germany - Advances in tissue engineering were the focus of a Biotechnica '99 special symposium Thursday, organized jointly by the German Society for Biochemistry and Molecular Biology GBM, the Leibniz Research Laboratories for Biotechnology and Artificial Organs LEBAO, and the Society for Biotechnological Research GBF.

Anna Wobus, head of the In-vitro Differentiation Group at the Institute of Plant Genetics and Crop Plant Research, of Gatersleben, Germany, said that her group had established standardized protocols to derive differentiated cardiogenic, myogenic and neural tissue from mouse embryonic stem cells in vitro. "Using specific growth and differentiation factors, embryonic stem cells develop into selective, specialized and terminally differentiated cells, which express tissue specific genes, proteins, receptors, ion-channels, etc. We even see functional myoneural junctions in vitro." In addition, Wobus has established methods to identify and select the appropriate precursor cells during that process.

The time by which modulators such as retinoic acid (RA) or BMP-4 are added is crucial to the process, she said. "Adding retinoic acid during the first two days of stem cell development leads to neuronal cells, while adding RA at day five will result in the development of muscle cells. Even later application induces heart tissue formation."

Wobus said the method was only working in mice so far in her laboratory, but that U.S. teams had proven that similar progress could be achieved with human cells. She said there was a huge number of possible applications of human embryonic stem and germ cells, "e.g., in differentiation studies, toxicology, pharmacology, pathogenesis studies and therapy. Self- renewal of these cells makes them an unlimited resource." For autologic grafts, somatic cells could be collected and transferred into an enucleated oocyte where they could develop into a blastocyst carrying embryonic stem cells - basically the method by which Dolly was cloned two years ago.

However, Wobus expects clinical applications in 10 years, "so there is plenty of time to discuss the ethical questions arising from the possible use of human embryonic stem cells."

In Germany, removal of pluripotent cells such as embryonic stem cells from an embryo is prohibited under the Embryo Protection Law, even if the development of the embryo would not be impaired by their removal. Nuclear transfer into enucleated oocytes aimed at generating pluripotent stem cells is prohibited, too, because this technique might be employed to clone human beings. Stem cells from aborted fetuses may be used, however.

Wobus told BioWorld Today that, in accordance with a statement issued by the German Deutsche Forschungsgemeinschaft (DFG) in March, she did not see the need to change the Embryo Protection Law. Later this year, the DFG will publish a legal opinion about whether embryonic cells originating from foreign countries could legally be used for research in Germany. She added she expected that import and use of embryonic stem cells, e.g., from the U.S., will be considered legal.

However, in this very dynamic field new concepts could emerge soon in which the use of human embryonic cells could be unnecessary. Clive Svendson from the Center of Brain Repair at the University of Cambridge, UK, said that the plasticity of stem cells was enormous: "Stem cells might be much more versatile than we think. From brain to blood and from blood to brain is possible, as neuronal stem cells can become bone marrow stem cells and vice versa."

Svendsen's team, which intends to use cultivated neurons for the treatment of Parkinson's disease, isolated stem cells from human brain tissue and developed ways of keeping them alive indefinitely in the laboratory. "Growing stem cells of human brain tissue in the laboratory could make it unnecessary to transplant brain tissue from aborted fetuses," he said.

So far, his team uses stem cells from embryonic brains. "However, studies suggest that in certain zones of the adult brain stem, cells can be found that can be cultured and might be used for growing nerve cells from them. In this exciting field, we might become able to reprogram even skin cells so that they develop into oligodendrocytes, astrocytes and neurons."