HHLA2 predicts better survival and exhibits inhibited proliferation in epithelial ovarian cancer

PURPOSE: The role of HHLA2, a new immune checkpoint ligand, is gradually being elucidated in various solid tumours. However, its role in ovarian cancer remains unclear; thus, its expression profile and clinical significance in ovarian cancer must be examined. METHODS: We performed immunohistochemistry to examine HHLA2 expression in 64 ovarian cancer tissues and 16 normal ovarian tissues. The relationships between HHLA2 expression and clinicopathological features, prognosis, and CD8(+) tumour-infiltrating lymphocytes (TILs) in patients were analysed. Additionally, the Cancer Cell Line Encyclopedia database was used to analyse the correlation between HHLA2 expression and PD-L1 or B7x expression. Furthermore, the biological function of HHLA2 in ovarian cancer cells was initially explored. RESULTS: Only 17.2% of ovarian cancer patients showed HHLA2 expression, which was significantly associated with the differentiation of ovarian cancer cells (p = 0.027), and well-differentiated tumours expressed higher levels of HHLA2. The density of CD8(+) TIL was associated with increased HHLA2 expression (p = 0.017), and the CD8(+) TIL count was higher in the HHLA2-positive group than that in the HHLA2-negative group (p = 0.023). Moreover, multivariate analysis identified HHLA2 expression as an independent prognostic factor that predicted improved survival (p = 0.049; HR = 0.156; 95% CI = 0.025–0.992). Additionally, we also found that overexpressing HHLA2 inhibited the proliferation of ovarian cancer cells. CONCLUSION: HHLA2 is associated with tumour differentiation and high CD8(+) TIL levels; and predicts improved survival in ovarian cancer. Along with previously reported findings that HHLA2 behaves as a co-stimulatory ligand, our study suggests that the loss of HHLA2 may contribute to the immunosuppressive microenvironment and progression of ovarian cancer.