Patients with recurrent glioblastoma have lower levels of total immune effector cells, including circulating CD3+, CD4+, and CD8+ T cell subsets, B cells, and NK cells, with reductions in naïve, central memory, and effector memory subsets, activated T cells, and proliferating Ki67+ cells, than patients with newly diagnosed glioblastoma (43). Here, CD4 is linked to glioblastoma.