T cells were also present, although in a small amount, but both CD4+ (defined as CD3+/CD8−) and CD8+ T cells increased significantly from grade II to grade IV gliomas (Fig. 1b), paralleled by a significant expression of PD-1, increasing from grade II to grade IV (mean of 45.4% vs 73.9% vs 79.0% in grade II, III and IV for CD3+CD8− cells, and 64.8% vs 74.9% vs 80.4% in grade II, III and IV for CD3+CD8+ cells, respectively), as shown in Fig. 1c. Here, CD4 is linked to central nervous system cancer.