The concern about
imuran together with Remicade is for a specific type of lymphoma, a rare but just-about
-incurable form known as hepatosplenic t-cell lymphoma. It's only been reported a few times, and mostly in young adults/teens, but it's almost always fatal.
The second concern of taking imuran together with Remicade is that the combined immunosuppression greatly increases the chances of contracting an opportunistic infection, compared with just taking one or the other.
Taking imuran, Remicade, and prednisone increases the chances even higher -- much higher, in fact.