PDCD1 and neoplasm: Chimeric antigen receptor (CAR) T cells are also being investigated as a treatment for primary and metastatic brain tumors.7,8,9,10,11 Our author group has been studying locoregional delivery of interleukin-13 receptor α2−targeted and ERBB2-targeted CAR T cells in patients with recurrent high-grade gliomas, and we previously reported that CAR T cells delivered intraventricularly mediated complete tumor regression in a patient with multifocal glioblastoma.8 However, CAR T cells can be vulnerable to functional exhaustion mediated by PD-1.