CD4 and glioblastoma: Of the many immunosuppressive aspects intrinsic to GBM, CD4+CD25+FoxP3+ regulatory T cells (Treg) play a dominant role in deactivating productive anti-GBM immune responses (El Andaloussi and Lesniak, 2006; El Andaloussi et al., 2006; Fecci et al., 2006a).