Higher human lymphocyte antigen class I expression in early‐stage cancer cells leads to high sensitivity for cytotoxic T lymphocytes

Human lymphocyte antigen (HLA) class I molecules play a central role in cytotoxic T lymphocytes (CTL)‐based antitumor immunity. However, the expression rate of HLA class I in cancer cells remains a topic of discussion. We compared HLA class I expression levels between cancer cells and surrounding non–tumorous hepatocytes in 20 early‐stage hepatocellular carcinoma (HCC) patients by immunohistochemistry using EMR 8‐5. The expression levels of HLA class I were classified as negative, incomplete positive or complete positive. Similarly, for various types of solid cancers, HLA class I expression was examined. For the HLA class I expression in cancer cells, among 20 HCC patients, 13 were complete positive, 3 were incomplete positive, and 4 were negative. In addition, 15 (75.0%) had higher expression levels of HLA class I in cancer cells compared with that in surrounding non–tumorous hepatocytes. An interferon‐γ (IFN‐γ) enzyme‐linked immunospot (ELISPOT) assay indicated that cancer cells with positive expression of HLA class I had strong sensitivity to antigen‐specific CTL. We suggested that HLA class I expression in cancer cells could be involved in the clinical prognosis of HCC patients. Similarly, 66.7%, 100.0%, 66.7% and 62.5% of patients with early‐stage pancreatic, gallbladder, esophageal and breast cancers, respectively, had higher expression levels of HLA class I in cancer cells than in surrounding normal tissue cells. We suggest that in several early‐stage solid cancers, including HCC, HLA class I expression levels in cancer cells are higher than that in surrounding normal tissue cells, which could result in the anti–tumor effect of CTL‐based cancer immunotherapy.