HHLA2 is a novel prognostic predictor and potential therapeutic target in malignant glioma

Glioma is the most common and aggressive tumor type of the central nervous system and is associated with poor prognosis. To date, novel emerging immunotherapies have significantly improved outcomes for patients with various cancer types. Human endogenous retrovirus‑H long terminal repeat‑associating protein 2 (HHLA2), a newly discovered immune checkpoint molecule, has demonstrated its potential as a novel therapeutic target. Therefore, the present study aimed to investigate the clinical prognostic value of HHLA2 in gliomas and its mechanistic role. A systematic review of datasets from The Cancer Genome Atlas was performed. The RNA‑seq data of a total of 669 cases were analyzed and the biological function of HHLA2 was predicted by Gene Ontology (GO) and pathway enrichment analysis. Immunohistochemistry labelling images for HHLA2 was obtained from the Human Protein Atlas. xCell was used to comprehensively analyze the model of tumor‑infiltrating immune cell in glioma. The Cox proportional hazards regression model was used to predict outcomes for glioma patients. The results revealed that the expression levels of HHLA2 were significantly lower in high‑grade glioma, as well as glioma with wild‑type isocitrate dehydrogenase, no deletion of 1p/19q and telomerase reverse transcriptase promoter mutation. Receiver operating characteristic analysis revealed that HHLA2 was a predictor of the neural subtype. The tumor‑infiltrating immune cell model indicated that HHLA2 was negatively associated with tumor‑associated macrophages. GO analysis and pathway enrichment analysis revealed that HHLA2‑associated genes were functionally involved in inhibition of neoplasia‑associated processes. HHLA2 was significantly negatively correlated with certain genes, including interleukin‑10, transforming growth factor‑β, vascular endothelial growth factor and δ‑like canonical Notch ligand 4, and other immune checkpoint molecules, including programmed cell death 1, lymphocyte activating 3 and CD276. Survival analysis indicated that high expression of HHLA2 predicted a favorable prognosis. In conclusion, the present study revealed that upregulation of HHLA2 is significantly associated with a favorable outcome for patients with glioma. Targeting HHLA2 as an immune stimulator may become a valuable approach for the treatment of glioma in clinical practice.