UT Southwestern medical school in Dallas has been running clinical studies using Cellcept in combination with Avonex.

I have a friend who has been on Cellcept now for 8 years because of a rare autoimmune blood disorder. She was on her death bed (no joke) and this was the only thing that saved her life (courtesy of European doctors who figured out what to give her to save her). Anyhow, she was recently told by the doc. in the US that she now has to go off of Cellcept because she has been on it for too long. Apparently your body can only handle so much of the drug before it is at too great a risk for lymphoma, cancers, and all sorts of other nasty things. I did not know PML was a risk. Interesting....