Enhanced B7-H4 Expression in Gliomas With Low PD-L1 Expression Identifies Cold Tumors

Abstract The expression profiles of different immune checkpoint molecules are promising for triaging personalized targeted immunotherapy. Gliomas have been shown as potential targets for immune checkpoint inhibitors. Our study was performed to determine co-expression levels of two major B7 immune molecules PD-L1 and B7-H4 in gliomas in which both have demonstrated to inhibit anti-tumor host immunity. We assessed tumor issues from primary gliomas stage II–IV(n=505) by immunohistochemistry (IHC) for protein levels of both PD-L1 and B7-H4. Gene co-expression analysis assessing clusters based on extent of PD-L1/B7-H4 classifier genes expression were investigated in two transcriptome datasets (TCGA and CGGA) to validate IHC expression profiles. Here, we found that 61% and 54% of patient samples were positive for PD-L1 and B7-H4 respectively, whereby high-expression of either protein was limited to 23% and 20% respectively. Co-expression of PD-L1 and B7-H4 in high levels was limited to 2%. Comparable results were seen in RNA-seq datasets when PD-L1 mRNA expression level corelated negatively with B7-H4. Gene co-expression modules clustered in each grade gliomas without Double-High modules (glioma cluster with high mRNA expression of both PD-L1 and B7-H4 classifier genes) also verified restricted co-expression pattern. B7-H4 mRNA expression level had negative correlation with extent of immune cell infiltration, including tumor-infiltrating lymphocytes (TILs), and High-B7-H4 module gliomas (high B7-H4 but low PD-L1 classifier genes expression) were related to a cold tumor with less TILs. The majority of gliomas express PD-L1 or B7-H4, however, co-expression of both at high levels is minimal. The High-B7-H4 module was significantly lacking in TILs, suggesting that B7-H4 might inhibit T cell trafficking into the central nervous system (CNS). This study demonstrates that PD-L1 expression alone is not fully informative in gliomas for immune targeted or active-specific immunotherapy, and PD-L1 and B7-H4 probably inhibit different aspects of the T cell functions.