Scientists work out number of ES cell-lines needed

UK researchers have estimated that embryonic stem cell (ES cell)-lines from just ten carefully-selected individuals could potentially provide matching tissue for around 80 per cent of the population. The team, based at Addenbrooke's Hospital in Cambridge, wanted to find out how many human ES cell-lines would be needed to establish a bank with maximum benefit in terms of matching patients' tissue type. The findings, published in the journal The Lancet, have practical, political and ethical implications for human ES cell banks, say the researchers.

In May 2004, the UK launched the world's first stem cell bank, the purpose of which is to store and grow stem cell-lines for distribution to researchers worldwide. It is hoped that human ES cell-lines stored by the bank will one day be used to treat conditions such as spinal injury and diabetes, since ES cells have the ability to grow into almost every body tissue. Creating a 'bank' of cell-lines that would be suitable for most patients is seen as a realistic alternative to growing new ES cells for each individual patient. Although cells from an unrelated person would not provide a perfect match, matching the blood groups and tissue type would lessen the chances of the transplanted tissue being rejected.

To find out how many cell-lines would be needed for such a bank, the Cambridge researchers analysed the blood group and HLA (human leukocyte antigen) tissue type of 10,000 consecutive organ donors, and compared them to that of 6577 patients registered on the UK kidney transplant waiting list. They assumed that the blood groups and tissue type of the organ donors would reflect that of potential donated 'spare' IVF embryos, and that the waiting patients would be similar to potential ES cell transplant recipients. The team found that 150 blood group-compatible donors chosen at random, or 100 blood group 'O' random donors (so-called 'universal' donors who can provide blood for people with blood group A, B or AB) would provide a 'good-enough' HLA-tissue match for 84 per cent of the recipients.

The researchers also predicted that if carefully selected for common HLA tissue types, just ten ES cell-lines would be enough to be a complete match for 38 per cent of the recipients, or a 'beneficial' match for 68 per cent. Author Roger Pederson said that 'the identification of such potentially valuable donor HLA identities within the UK population points the way for generating human ES cell-lines with broad clinical utility'. However, in an accompanying commentary, Justin St John and Jon Alderson, of the University of Birmingham, point out that the study's predictions exclude some ethnic groups. They add that these populations include those that are most likely to benefit from ES cell therapy, such as the UK Asian and African-Caribbean populations - both of which are particularly susceptible to type 2 diabetes.

The commentary also calls for a national policy to 'populate and exploit' the potential of the National Stem Cell Bank. As of January 2005, the bank contained nine different human ES cell-lines, none of which are suitable for clinical use. The authors question whether spare IVF embryos are of a high enough quality to generate ES cell-lines for clinical use, and also suggest that the Human Fertilisation and Embryology Authority (HFEA) should allow couples to donate eggs specifically for creating ES cell-lines.

Dr Glyn Stacey, director of the UK Stem Cell Bank, said that it was important that scientists were attempting to pin down how many stem cell-lines were needed. But he stressed that 'we are still a long way away in terms of establishing the basic cell culture methods', and that 'we also do not know whether all stem cell lines will give the full range of tissues'.