CD4 and glioblastoma: In GBM patients, including treatment-naïve patients, it has been reported that the majority of T cells, including both CD4+ and CD8+ T cells, have been sequestered in the bone marrow due to tumour-imposed loss of S1P1,155 leading to insufficient T cell homing to secondary lymph organs or circulating in the peripheral blood, resulting in less T cell infiltration into GBM.