The immune system is a complex network of specialized cells and organs that defends the human body against attack from foreign pathogens. The major lymphocytes involved in protecting the body against potential infections are B and T cells, which also play an important role in combating tumor growth. The cells of the immune system patrol the tissues and organs through both blood and lymphatic vessels, but some organs—including cornea, testes, and brain—are usually not patrolled by these cells. The brain has been thought to be an immune-privileged site because of the tight blood–brain barrier (BBB) that protects it. Few cells migrate to the brain under normal circumstances, because the BBB permits only certain molecules to cross into brain tissue. Recently, however, studies have shown that activated T cells exposed to antigen can cross the intact BBB and migrate into brain. This finding opens the path to developing effective means of immunotherapy for lesions of the central nervous system. The authors discuss basic facets of the immune system, review the current knowledge about human neuroimmunology, and survey current strategies for developing immunotherapy-based treatments for human brain tumors.
Abbreviations used in this paper:BBB = blood–brain barrier; CAM = cell-adhesion molecule; CNS = central nervous system; Ig = immunoglobulin; MHC = major histocompatability complex.
Address reprint requests to: Anil Sehgal Ph.D., Department of Neurological Surgery, Brain Tumor Research Center, University of California at San Francisco, 1855 Folsom Street, MCB 230, San Francisco, California 94103. email: