PDCD1 and glioblastoma: Pembrolizumab and nivolumab are well tolerated; however, progression-free survival and immune analyses have indicated that anti-PD-1 monotherapy is insufficient to produce an antitumor response in the majority of patients with GBM due to high levels of CD68+ cells and few T cells within the tumor microenvironment (Chamberlain and Kim, 2017).