There is now a pressing need to discuss the already described and newly emerging mechanisms to see how they can be put together in more or less cohesive structure and how they can help to improve immune response to tumors. This monograph will, for the first time, present a comprehensive overview of different mechanisms of immune dysfunction in cancer as well as therapeutic approaches to their correction. It will discuss a number of new mechanisms that have never been discussed in a monograph before: T-cell inhibitory molecules, regulatory tolerogenic DCs, and signaling pathways in antigen-presenting cells involved in T-cell tolerance.