Progress towards embryo stem cell therapies

One of the key obstacles to getting human embryonic stem cell (ES cell) therapies 'from the bench to the bedside' has been overcome, according to UK researcher Roger Pedersen of the University of Cambridge. Speaking at the Human Fertilisation and Embryology Authority (HFEA)'s annual research conference, Professor Pederson said that his group has successfully developed the 'pristine' culture conditions necessary for any future clinical application of this technology. The work also sheds light on the biological mechanisms that enable human ES cells to retain their pluripotency - their ability to grow into almost any body tissue.

While existing human ES cell-lines appear to be genetically stable, most will never be suitable for clinical use because they have been grown on a layer of mouse 'feeder' cells. The problem with this approach is that it introduces the potential for contamination, for example by viruses, said Pedersen, and also adds an 'uncontrolled' element to any experiments, since feeder cell-lines vary from batch to batch. So the Cambridge group, long with other ES cell researchers around the world, has been trying to develop synthetic culture media that contains everything necessary to keep ES cells growing in a pluripotent state.

The 'chemically defined' medium (CDM) developed by Pedersen and his colleagues contains no animal products, and has added 'growth factors' known as Activin and FGF (fibroblast growth factor). It seems that these two proteins together enable human ES cells to grow in the laboratory indefinitely, without growing into other types of body tissue - a process known as differentiation. The work suggests that the biological pathway responsible for maintaining pluripotency in human ES cells - which involves Activin, FGF and another key protein called Nodal - is completely different to that found in mouse ES cells.

The next big challenge is to find out which proteins trigger the transformation of human ES cells into different inner tissue layers, says Pedersen - research which he estimates will take 'another one or two years'. He added that UK scientists have a 'remarkable opportunity' to carry out ES cell research, due to the country's regulatory framework. There are currently 13 ongoing human ES cell studies licensed by the HFEA, representing 40 per cent of all human embryo research projects. The remaining 20 relate to either embryology or genetic testing of embryos.

Also speaking at the conference was Professor Andre Van Steirteghem, of the Dutch-speaking Brussels Free University. He called for more clinical follow-up studies of babies born using IVF and ICSI of which there are now an estimated 2 million worldwide. He also said that more work was needed to investigate the effectiveness of PGS (preimplantation genetic screening), also known as aneuploidy screening, in which IVF embryos are tested for chromosome abnormalities before being transferred back into patients. Professor Van Steirteghem said that although PGS appears to increase embryo implantation rates, there is currently 'no evidence' that it increases the rate of pregnancies per treatment cycle.

Finally, Professor Van Steirteghem called for more countries to adopt measures aimed at reducing the numbers of multiple births associated with IVF treatment, since an estimated 50 per cent of such children born so far are not the result of singleton pregnancies. In Belgium, he said, new rules limiting the number of embryos transferred to one or two had cut the rate of IVF multiple births from 28 to ten per cent. Belgian patients under the age of 43 are now entitled to a maximum of six funded cycles of treatment, he added.