Mechanisms of immune evasion by gliomas.

A major contributing factor to glioma development and progression is its ability to evade the immune system. This chapter will explore the mechanisms utilized by glioma to mediate immunosuppression and immune evasion. These include intrinsic mechanisms linked to its location within the brain and interactions between glioma cells and immune cells. Lack of recruitment of naïve effector immune cells perhaps accounts for most of the immune suppression mediated by these tumor cells. This is enhanced by increased recruitment of microglia which resemble immature antigen presenting cells that are unable to support T-cell mediated immunity. Furthermore, secreted factors like TGF-β, COX-2 and IL-10, altered costimulatory molecules and inhibition of STAT-3 all contribute to the recruitment and expansion of regulatory T cells, which further modulate the immunosuppressive environment of glioma. In light of these findings, multiple immunotherapeutic treatment modalities are currently being explored.