Brain tumor immunotherapy: seeing the brain in the body.

Brain tumor immunotherapy is often interpreted in terms of immune privilege and the blood-brain barrier (BBB), but a broader view is warranted. The delicate regulatory balance of the immune system is relevant at any site, as are the heterogeneity and plasticity of tumor growth. Criteria for tumor antigens, and often the antigens themselves, cut across tumor types. Here, this broader view, complemented by current understanding of privilege and the BBB, provides the context for review. Future success is likely to exploit simplified methods, used in combination; and similarities - more than differences - between the brain and other sites.