PDCD1 and neoplasm: Other strategies are also being developed to breach the BBB in GBM patients in order to enhance drug delivery and efficacy; for example, ultrasound disruption via an intratumor-implanted device to locally compromise the BBB in the tumor bed (e.g., NCT04528680) [137] Nonetheless, recent studies demonstrate that the BBB does not preclude the activity of PD-1 blocking antibodies at the site of the tumor, as pre- and post-treatment analyses of rGBM tumor tissue revealed changes in both DCs and T cells after neoadjuvant PD-1 blockade [138].