ABSTRACT: Background: Tumor specific ectopic expression of the immunomodulatory molecule, HLA-G is known to mediate immune tolerance and promote carcinogenesis. Viruses too employ strategies to evade immune surveillance. Considering the role of both HLA-G and HPV in tumor growth and progression, it is pertinent to investigate the relationship between HLA-G and HPV in context of immune modulation in HNSCC. Method: A hospital based case-control study was conducted in histopathologically confirmed HNSCC tissues. HLA-G isoform expression and HPV association studies were carried out and mRNA levels of HLA-G, markers of proliferation and differentiation (ki-67, keratin 18, cyclin D1), immune checkpoint molecules (IL-10, PD-1. TGF-?), SOCS (SOCS1 and SOCS3) and pro-inflammatory cytokine IFN-? were determined. Results: Higher expression of HLA-G was noted in HPV positive tumors (5.14 fold, p = 0.002). HLA-G7 was the most frequent isoform (29/80) found in HNSCC particularly in HPV positive tumors (13/16). In HPV negative tumors, all the checkpoint molecules were upregulated along with pro-inflammatory IFN-?. In contrast, in HPV positive tumors, IFN-? expression was higher (2.12 fold) but levels of IL-10, PD-1, TGF-?, SOCS1 and SOCS3 were markedly lower (fold change of IL-10 = 0.37, PD1 = 0.41, TGF-? = 0.17, SOCS1 = 0.055, SOCS3 = 0.027). HPV positive tumors were more proliferative and differentiated with higher expression of ki-67 and keratin18 (6.25 fold, p = 0.079 and 10.62 fold, p = 0.009). Decreased expression of cyclin D1 was noted in HPV positive tumors (6.94 fold, p = 0.006) than HPV negative tumors (17.69 fold). Also, HLA-G7 expressing HPV positive tumors showed lowest expression of cyclin D1. Interestingly, SOCS showed normal expression in HLA-G7 expressing HPV negative tumors (1.2 and 1.4 fold). IFN-? was downregulated in HPV positive tumors without HLA-G7 (0.31 fold). Conclusion: Our data suggests that SOCS were downregulated irrespective of HLA-G positivity and IFN- ? expression appeared to be mediated by HLA-G. SOCS are reported to have anti-tumor activity and also SOCS and soluble HLA-G are known to interfere with cell cycle progression. Hence, through regulating HLA-G expression, HPV positive tumors could mediate immune suppression by manipulating SOCS, IFN-?, IL-10 and cyclin D1 pathways which needs further exploration.
