Whereas embryonic stem cells are derived from specially grown human embryos, amniotic stem cells are taken from the amniotic fluid surrounding a foetus, causing no harm to the unborn baby. In January 2007, Dr Paulo De Coppi, now of Great Ormond Street Hospital in the UK, published a paper in Nature Biotechnology that claimed amniotic stem cells could be successfully manipulated in the laboratory to differentiate into cells resembling both neural and liver tissue. To validate his research De Coppi examined chemical "markers" produced by the differentiated stem cells, claiming that they could only be expressed by differentiated stem cells exhibiting the characteristics of neural or liver tissue. And when injected into mice, it seemed the cells could thrive in a living organism, suggesting the possibility that they may one day be used to treat diseases such as Alzheimer's or Parkinson's. Now, Elena Cattaneo of the University of Milan, Mauro Toselli of the University of Pavia, Elisabetta Cerbai of the University of Florence and Ferdinando Rossi of the University of Torino, have published a response to this research in a letter to the editor of Nature Biotechnology challenging these claims. The Italian scientists' area of expertise is in stem cell research for neurobiology, so the letter centres of the neurological aspect of the research, citing a lack of decisive evidence to support the conclusion that the differentiated cells really did exhibit the characteristics of neural tissue. "A clear identification of the phenotype acquired by stem cells requires higher standards and deeper investigation", Dr Rossi told LabTechnologist.com. "We think that the conclusions drawn are not sustained by the experimental data." Whereas De Coppi claims the stem cells expressed certain genes to produce different chemicals that are characteristic of neural cells, the letter argues that the respective genes are also expressed in either endothelial cells, kidney cells or liver cells, so they do not substantially demonstrate a differentiation into neural cells. They also call into question a diagram that is meant to demonstrate the stem cells exhibiting the same structure as neural cells. "In our view the article by De Coppi et al fails to provide any convincing evidence to support the claim that AFS cells are able to generate neurons," the letter concludes.