Prof. Roger Pedersen, Cambridge University
Roger - I would like to talk about the subject of human embryonic stem cells. This type of stem cell, the mother of all stem cells, has the potential to turn into every tissue in the body. It therefore is very exciting and has lots of potential for the clinic. I want to talk about why we should be interested in these cells not only as a product but also what they can tell us about ourselves and how we came into existence. It is interesting to think about what we have learnt about these cells and how they are contributing to very fundamental knowledge.
Chris - Stem cells have had lots of media coverage, but what is a stem cell?
Roger - It is a cell that can undergo specialisation to form a specialised cell, but at the same time, retain the ability to specialise. When stem cells divide, one becomes a specialised cell, while the other remains a stem cell. Specialised cells are all the different cells in our body that perform a function. They are all the cells we see on us and in us, such as lung cells, skin cells, hair cells, and kidney cells.
Chris - One egg meets one sperm and you get a single cell. Is that therefore a stem cell?
Roger - That would be a special use of the word stem cell because that is the first cell of human development. This cell has the potential to make all the cells in not only the foetus but the placenta too. What we are interested in are the cells that have made that first decision to be the embryo rather than the placenta. These are the source of stem cells, which has caused so much excitement for their clinical use.
Chris - They are controversial too because if we want to get stem cells, we need to get an embryo. To get an embryo for ourselves would require cloning ourselves.
Roger - I will split this into two parts: the embryo and cloning. The embryo that is the source of embryonic stem cells comes from the surplus embryos from in vitro fertilisation. They were donated by patients who had finished their families and want those embryos to be used for scientific research. The source is a very tiny hollow ball of cells the size of the point of a pin.
Huseyin - I'd like to add that legally, if these eggs are not donated, they must be destroyed once the people have conceived. Many people who have been helped by IVF technology say that as they are spare embryos that they can not use themselves, they want to donate them to help research. The embryos can only be saved if they are donated.
Chris - The embryonic stem cells that we want to use are in the very early stages of development. They are the cells that are going to go on to form a developing foetus.
Roger - Yes, and once they are growing in the petri dish, they maintain this very early unspecialised state. The cells themselves look very innocent. They look like very non-descript flat cells that don't appear to have this enormous capacity to grow into any cell in the body.
Chris - How can they be used?
Roger - That is the challenge of our research. We know that they can specialise but the challenge is to find out how to do it in the petri dish. For that reason, we need to find out what they are and what it is to be a stem cell at the very early stages in development. How does it know what to turn into and how does it make that decision?
Chris - Do we know any of the signals that makes a stem cell know to turn into, say, a heart cell? What are the triggers?
Roger - There's quite a lot known now from studying animal models such as frogs, fish, sea urchins and mice. We know quite a lot about what goes on in them but we don't know much about humans.
Chris - I have heard that if you inject stem cells into damaged areas, the cell knows where to go and travels to the site needing repair.
Roger - There are some early studies that suggest this. However, what is not so clear is that the damage is repaired by stem cells. They might be helping the native cells to repair themselves. When we have an injury, blood goes straight to the damaged area. This might be the reason why damaged skin goes green if Green Fluorescent Protein-labelled stem cells are injected into bone marrow.