PDCD1 and central nervous system cancer: Our findings showed that Bifidobacterium could decrease PD-1 expression on protein level and significantly suppress the protein expression of PD-L1 (p < 0.0001, Supplementary Figures S4A–C), indicating that Bifidobacterium might synergize with anti-PD-L1 to inhibit gliomas, but needing further investigation.