HHLA2 Expression is Associated with Poor Survival in Patients with Hepatocellular Carcinoma

Background: Human endogenous retrovirus-H long terminal repeat-associating protein 2 (HHLA2) is a member of the B7 family; however, little is known regarding its expression and clinical relevance in hepatocellular carcinoma (HCC). Methods: To better characterize HHLA2 expression in HCC, we analyzed its expression by in situ staining and further investigated its correlation with immune infiltration and patient prognosis. Results: HHLA2 was primarily expressed in the peri-tumor region of HCC tissues and co-localized with CD68(+) monocytes/macrophages. In vitro analysis and multiimmunofluorescence staining showed up-regulated HHLA2 expression in tumor-activated monocytes/macrophages, and HHLA2(+) monocytes/macrophages expressed high levels of HLA-DR in HCC tissue. A correlation analysis showed that samples displaying high HHLA2 expression in the peri-tumor region had significant tumor infiltration of CD204(+) and CD11b(+) cells, and low expression of genes associated with an anti-tumor immune response. The high level of peri-tumoral HHLA2 expression was associated with a poor patient overall survival (OS; P = 0.008). A multivariate analysis revealed that HHLA2 expression in the peri-tumor region was an independent prognostic factor for OS (hazard ratio = 1.872, p = 0.003). Moreover, the expression of HHLA2 was negatively correlated with PD-L1, and patients exhibiting HHLA2 and programmed cell death-ligand 1(PD-L1) co-expression had the shortest survival time. Conclusion: HHLA2 expression represented an immunosuppressive microenvironment in HCC, and may serve as a potential target for immunotherapy.