Effects of irradiation on human leukocyte antigen class I expression in human papillomavirus positive and negative base of tongue and mobile tongue squamous cell carcinoma cell lines.

Human papillomavirus (HPV) infection is a risk factor for oropharyngeal cancer, besides smoking and alcohol. Patients with HPV-positive tumors have a better prognosis than those with HPV-negative tumors. Furthermore, patients with HPV-positive tumors, with high CD8+ tumor infiltrating lymphocyte counts or absent/low human leukocyte antigen (HLA) class I expression have the best outcome. The latter is paradoxical, since HLA class I expression is important for tumor recognition. Below, the hypothesis that radiation therapy increases HLA class I expression was tested. HPV16 positive head and neck cancer cell lines UPCI-SCC-154, UPCI-SCC-090 and UM-SCC-47, and the HPV-negative cancer cell line UT-SCC-14, were treated with 2-10 Gray (Gy) and tested for HLA class I expression, cell cycle changes and apoptosis by flow cytometry. HPV16 E5, E7 and HLA-A mRNA expression was tested by quantitative PCR. A dose of 10 Gy resulted in a tendency of increased HLA class I cell surface expression for all cell lines and reached statistical significance for UPCI-SCC-154 and UPCI-SCC-090. There were, however, no significant changes in HLA-A mRNA expression in any of the cell lines, or HPV16 E5, or E7 mRNA expression for UPCI-SCC-47 and UPCI-SCC-154, while for UPCI-SCC-090 HPV16 E5 mRNA decreased. In all cell lines there was a shift towards G2/M phase and increased apoptosis after irradiation with 10 Gy. To conclude, irradiation with 10 Gy increased HLA class I expression in the HPV-positive cell lines UPCI-SCC-154 and UPCI-SCC-090. A similar tendency was observed for HPV-positive UM-SCC-47 and HPV-negative UT-SCC-14.