Background: Programmed cell death protein-1 (PD-1) blockade therapy is one of the most remarkable immunotherapy strategies in many solid tumors, excluding glioma. The PD-1 expression, immune characteristics, and prognosis relevance in glioma remain poorly understood.
Patients and Methods: RNA sequencing (RNA-seq) and mRNA microarray data were obtained for 325 and 301 glioma patients, respectively, from the Chinese Glioma Genome Atlas (CGGA) database. We analyzed the expression profile of PDCD1  (encoding PD-1) according to the different grade, isocitrate dehydrogenase (IDH) mutation status, and molecular subtype of glioblastoma. Gene ontology (GO) analyses were performed to explore biological processes of PD-1-related genes. Survival analysis was conducted using the Kaplan–Meier method. The findings were validated using The Cancer Genome Atlas (TCGA) RNA-seq data from 697 glioma samples. We also confirmed the PDCD1  gene expression feature and survival relevance in our own cohort of 73 glioma patients. R language was used for statistical analysis and generating figures.
Results: PDCD1  was enriched in glioblastoma (WHO, grade IV), IDH  wild-type glioma and mesenchymal glioblastoma in CGGA and TCGA datasets; similar results were validated in our own patient cohort. GO analysis revealed that PDCD1 -related genes were involved in inflammation immune responses and T cell-mediated immune responses in glioma. Circos plots indicated that PDCD1  was positively associated with CD28, ICOS , and the inhibitory checkpoint molecules CTLA4, HAVCR2, TIGIT , and LAG3 . Patients with PDCD1  upregulation had much shorter overall survival.
Conclusion: PDCD1  upregulation was found in more malignant phenotypes of glioma and indicated a worse prognosis. Immunotherapy of targeting PD-1 or combined with other checkpoint molecules (eg, TIM-3, LAG-3, or TIGIT) blockade may represent a promising treatment strategy for glioma.
Keywords: programmed cell death 1, glioma, The Cancer Genome Atlas, survival analysis, immunotherapy, costimulatory, inhibitory T-cell receptors