New embryo stem cells are step towards therapies

US researchers have reported a new method for growing human embryonic stem cells (ES cells), which does not rely on the use of 'feeder' cells. The new system, developed by scientists based at Massachusetts biotech firm Advanced Cell Technology (ACT), brings ES cell therapies a step closer. Many previously-isolated human ES cell lines, while invaluable for research, will never be suitable for therapeutic use because they were grown using mouse feeder cells, and so contain traces of animal material. And even ES cell lines grown using human feeder cells are unsafe for therapies, since they could potentially transmit infectious viruses, say the ACT team. The scientists published their results in the early online edition of the Lancet journal.

ES cells, derived from early human embryos, are the body's 'master cells', able to develop into any type of body cell. Many scientists believe that ES cell research could lead to new treatments for a range of diseases, including Parkinson's disease and diabetes. However, the first human ES cell lines were all grown on a layer of mouse feeder cells, to provide support and nourishment. Research published earlier this year found that all the human ES cells currently approved for use by state-funded scientists in the US are 'contaminated' with a non-human substance. This molecule, called Neu5Gc, would trigger an immune response leading to the destruction of any ES cells used to treat people, the study concluded. Federally-funded teams are not permitted to work on ES cell lines created after 9 August 2001.

The new method uses a supporting 'extracellular matrix', created by growing feeder cells and then washing them away to leave behind a sterile layer of vital proteins and nutrients. The  team then grew human ES cells on the matrix, under completely feeder cell and serum-free conditions. The new cells retained their ability to grow into any different tissue after six months of being grown in the laboratory. 'Our findings help solve one of the major problems associated with the use of human embryonic stem-cell therapy in the treatment of human medical conditions', said team leader Robert Lanza. He said that growing human cells together with live animal cells raised concerns over infection, with 'recognised or as yet unrecognised infectious agents'.

The new cells will not themselves be suitable for therapeutic use, as although they were not grown using live mouse cells to supply nutrients, the extracellular matrix was still derived from mouse embryo skin cells. But ACT says that making a matrix entirely free from animal components is now a formality. 'We're now working on lines which will be completely human', he told New Scientist magazine, adding: 'there's nothing in the animal layer that can't be replaced with a human equivalent'.

Although several groups have grown human ES cells using human feeder cells, Lanza says these still represent a potential source of viral infection. 'Experience with organ and tissue transplantation has shown that disease such as HIV (human immunodeficiency virus) infection and Creuzfeldt-Jakob disease, hepatitis B or C viruses and other infectious agents can be transmitted from human donor cells to recipients', he said. UK stem cell researcher Roger Pederson says the new study 'provides evidence that it is possible to derive human embryonic stem cell lines in the absence of living feeder cells'.