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

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Abstract INTRODUCTION The expression profiles of different immune checkpoint molecules are promising for triaging personalized targeted immunotherapy. Our study was performed to determine co-expression levels of 2 major B7 immune molecules, PD-L1 and B7-H4, in gliomas where both have demonstrated to inhibit antitumor host immunity. METHODS We assessed tumor issues from primary gliomas stage II to 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 2 transcriptome datasets (TCGA and CGGA) to validate IHC expression profiles and explore properties of the glioma immune microenvironment among specific co-expression PD-L1/B7-H4 cluster groups. RESULTS PD-L1 was detected in 61% of patients whereby 23% expressed high levels. B7-H4 was expressed in 54% whereby 20% were identified as high expression. Co-expression of PD-L1 and B7-H4 in high levels was limited to 2% cases. Comparable results were seen in RNA-sequencing 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 (gliomas cluster with high mRNA expression of both PD-L1 and B7-H4 classifier genes) also verified restricted coexpression 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) was related to a cold tumor with less TILs. CONCLUSION 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.