Select Committee on Science and Technology Written Evidence


Memorandum 49

Submission from Dr Stephen Minger, Director, Stem Cell Biology Laboratory, Wolfson Centre for Age-Related Disease, King's College, London

  I am writing to you in my capacity as Director of the Stem Cell Biology Laboratory at King's College London in regards to the enquiry by your committee on hydrid and chimera research. I have applied to the Human Fertilisation and Embryology Authority for permission to generate "disease-specific" human embryonic stem cell lines from individuals who carry known genetic mutations that result in a variety of neurodegenerative diseases, using non-human oocytes (eggs) as a surrogate for Somatic Cell Nuclear Transfer. I will attempt below to set out the reasons why we have proposed this research and why we think it is so important.

  Human embryonic stem (hES) cells, derived from a 6-day old preimplantation embryo, have the ability to proliferate to ad infinitum and the potential to give rise to every cell type in the human organism. Since 1998, when the first hES cell lines were derived, there has been an explosion of interest in this technology, not only for the potential application in treating a myriad of human disorders, but also as a source of cells for developing novel therapies, for devising new gene targeting strategies and for fundamental drug discovery. To date, more than 300 hES cell lines have been derived world-wide, most of these from human embryos created by in vitro fertilisation (IVF). Under license from the Human Fertilisation and Embryology Authority, the Stem Cell Biology Laboratory, together with colleagues from the Assisted Conception Unit at Kings College London, have been endeavouring to generate new hES cell lines. To date we have successfully derived a total of six new hES cell lines, and are using these cells to develop cell-based therapies for a number of devastating human clinical conditions.

  One of the unique aspects of our hES cell work, however, is the use of embryos that are at high risk of inheriting a known genetic disorder for hES cell derivation. Couples that wish to ensure that they have an unaffected child can avail themselves of IVF and subsequent screening by preimplantation genetic diagnosis (PGD), and only unaffected embryos are replaced and/or frozen for potential future use. In many cases, the affected embryos which harbour a number of different genetic disorders are donated to our research programme and are used for hES cell derivation. Since many animal models of human disease fail to replicate many of the basic pathophysiological features of human disease (eg Alzheimer's disease, Cystic Fibrosis), "disease-specific" human cell lines that contain mutations responsible for important genetic disorders thus represent an important new cellular tool for elucidating not only underlying biochemical and molecular mechanisms of disease induction, progression and pathophysiology, but such cell lines may also serve as important new targets for developing new therapies and drug candidates. To date our group has generated a well-characterised hES cell line that encodes the most common mutation resulting in Cystic Fibrosis and a more recent line currently being characterised from an embryo with 48 trinucleotide (CAG) repeats indicative of Huntington's disease. Two other research groups in the US and Belgium have also reported the generation of hES cell lines with disease-specific genetic lesions. We and others will continue to try to derive these important cell lines, but there is likely to be a limit to the number of disease-specific cell lines that can be generated from PGD embryos as this procedure is generally restricted to more common genetic disorders, particularly those that predominantly affect young children, though some late-onset disorders like Huntington's disease are allowed. Obtaining donated PGD embryos for very rare genetic disorders therefore is therefore likely to be uncommon and thus alternative means of generating stem cell lines from predominantly late onset disorders or from more rare genetic diseases are needed.

  Somatic cell nuclear transfer (SCNT) or "therapeutic cloning" is a technique that can be used to generate embryos which are genetically identical to a pre-existing mature organism. This involves the transfer of an adult cell or nuclei into an egg which has had its nucleus and hence its genetic material (DNA) removed, followed by activation (which mimics fertilisation) and subsequent progression in culture to a blastocyst stage embryo. If such embryos are implanted into surrogate mothers, cloned versions of the adult somatic cell donor can thus be created a" la Dolly, the first cloned mammal. To date a large number of cloned mammalian species have been generated including cows, pigs, dogs, cats, sheep, but this has not yet been achieved in primate species. One additional and perhaps more important use of SCNT is the generation of genetically-matched embryonic stem cell lines. Rather than the implantation of the cloned blastocyst, the inner cell mass is isolated in a manner analogous to that using IVF embryos and a cloned stem cell line can thus be obtained. Although the successful use of cloning to create cloned human embryonic stem cells has been reported by researchers in Korea and the US, these studies have subsequently been discredited and the published manuscripts retracted. So the extent to which SCNT can be used to create hES cell lines remains in doubt, although there has been a single report of successful nuclear transfer with primate oocytes and somatic cells, though no ES cell populations were derived.

  One of the limiting factors to SCNT in humans is the requirement for large numbers of human eggs. Published data to date suggests that not only may hundreds or thousands of oocytes be required to derive a single cloned hES cell line, but that the most optimal source of eggs is likely to be from woman less than 30 years of age, and that the eggs should be used directly after collection from the ovary rather than the use of those which fail to fertilise. The altruistic donation of oocytes specifically for SCNT where the efficiency of hES cell derivation is completely unknown but likely to be very low raises legitimate concerns about whether it is appropriate to encourage young women to undergo an invasive and potentially harmful procedure without any direct medical benefit. Therefore, until the efficiency of successful SCNT in humans can be increased significantly (to perhaps 10-20%) alternative sources of oocytes specifically for SCNT are needed.

  One alternative to altruistic donation of eggs from young women is the generation of functional eggs from hES cell lines themselves. Since hES cell lines can generate every cell type in the adult organism, it should be possible to generate functional oocytes from existing cell lines. However, only one group has reported the derivation of "oocytes-like" structures from mouse ES cells, and to date there have been no reports that this has been replicated with human cells. Another more practical alternative to the use of donated human eggs is to rely on non-human oocytes from domesticated livestock species which are available in large numbers as by-product of farming and the food industry. There have been several reports of SCNT between different species, including at least one report of successful hES cell line derivation following somatic cell transfer of adult human fibroblasts into rabbit eggs whose genetic material had been removed. In this study, a large number of human embryos were formed and 14 hES cell lines were obtained, including four well-characterised hES cell lines that displayed numerous characteristics indicative of pluirpotent hES cell lines, thus demonstrating the potential of this protocol for generating genetically distinct hES cell lines from selected individuals. Although the status of the rabbit/human mitochondria was not addressed in this paper, the expectation would be that transferring an intact human cell into an enucleated rabbit oocyte would result in all the rabbit proteins and most of the mitochondria slowly being replaced with human versions over time.

  In our license application to the HFEA, we proposed to generate human disease-specific cell lines using intra-species SCNT and cellular fusion of human cells obtained from individuals with a variety of genetic forms of neurodegenerative disorders. For example, there are at least four different genes implicated in genetic forms of Alzheimer's (AD) and another eight genes that cause familial Parkinson's disease (PD). Although these genetic forms of the disease represent less than 5-10% of all disease sufferers, the clinical symptoms and pathophysiology of the genetic forms of the disease mirror that seen in the "sporadic" forms, although an earlier age-of-onset and more severe disease progression are often observed. Although levodopa for the treatment of PD is generally beneficial in the early stages of the disease, this ever increasingly becomes less efficacious as neurodegeneration of the dopamine system continues. Pharmacotherapy for AD is an emerging field and several new compounds have recently been licensed for patients in the mid-to-late stages of the disease, but the window of efficacy is small and the benefits seen are very marginal. For other progressive neurological disorders including Motor Neuron Disease and Spinal Muscular Atrophy there are no therapies whatsoever. Hence, the availability of hES cell-derived cell lines for AD, PD, and other progressive neurological disorders with limited or no current therapeutic options would have tremendous potential as cellular tools in furthering our understanding of each of these devastating disorders and would also stimulate the search for new drug targets and pharmacological compounds that might provide better clinical management or improvement for each of these disorders.

  I urge the Select Committee to carefully consider what the consequences of a ban on creating "hybrids" or "chimera" would entail. The commercial and academic scientific community have generated over 20,000 strains of mice and rats which contain human disease genetic material, and many of these are important research tools for developing new therapies against cancer and other important human diseases. There are strains of mice lacking a functional immune system which have been "humanised" by transplantation of human bone marrow which serve as important models for understanding human immunology and the development of new immunosuppressive drugs. Even the preclinical testing of human cells in animal disease models could be misinterpreted as the generation of a chimera, and if this was banned, we would ostensibly lose the ability to test the safety and efficacy of cell therapy prior to clinical use in man. These limited but representative examples represent technologies that are already in significant use world-wide and under regulation in the UK under the auspices of the Home Office. Cetainly all current and future hybrid and chimera work can be accommodated and regulated under current Home Office and HFEA procedures and there is no compelling reason to now restrict this research. To do so will place the UK at a competitive scientific and commercial disadvantage, will be seen by the world-wide scientific community as "anti-science" and completely at odds with pre-existing strong government support of science, and it sends a very dangerous message that the UK government can be influenced by a small number of individuals whose views on these issues do not represent mainstream opinion.

January 2007





 
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