because the immune response is still trying to eliminate them and there is damage in the tissue that the viruses exist in. These are the viruses we are really focusing on. Q: Can you give us an example? PK: The virus we are most keenly interested in is hepatitis C. This is an interesting virus because some people are able to clear the virus when they first encounter it - their immune response is really good. Whereas unfortunately the majority of people are unable to do so and the virus is able to set up long term infection and this is where the tissue damage, in this case to the liver, can occur. Q: What is our immune response to a hepatitis C virus infection? PK: The first few weeks of infection is the really critical time but often that is not very clinically apparent, we don't see many patients at that point. But we know what's going on is that a critical decision is being made within the immune response. Some people are able to amount a particular kind of immune response using cells called T cells, and if those cells appear to function well then the virus can be very well contained. The virus is quite tricky and unfortunately the immune response sometimes is left with a gap and the virus can sneak through. Trying to understand the differences between the responses of people who clear the virus and those who don't contain it so well has been