CD4 and glioblastoma: The proportion of CD4+CD25+FoxP3+ T cells (Treg cell) in orthotopic drug-resistant GBM tissue in normal saline, Fe3O4-siPD-L1, Fe3O4-siPD-L1@M-BV2 (0.3 mg/kg) and Fe3O4-siPD-L1@M-BV2 (1 mg/kg) treatment group was 18.76%, 11.05%, 7.24% and 5.29%, respectively.