Establishment of a monoclonal anti-pan HLA class I antibody suitable for immunostaining of formalin-fixed tissue: Unusually high frequency of down-regulation in breast cancer tissues

A novel monoclonal anti‐pan human leukocyte antigen (HLA) class I heavy chain antibody, EMR8‐5, was established. It could detect HLA‐A, ‐B, and ‐C antigens in formalin‐fixed paraffin embedded tissues. By immunohistochemical staining using the EMR8‐5 antibody, various cancer tissues from 246 cases were examined for HLA class I expression. It was found that HLA class I expression was decreased in 20% to 42% of the cases of lung cancer, hepatocellular carcinoma, colon cancer, renal cell carcinoma, and urothelial carcinoma. In contrast, 85% of breast cancer cases had loss of or decreased HLA class I expression. Of the 35 breast cancer cases that had decreased HLA class I heavy chain expression, 33 (94%) also had decreased beta2‐microglobulin expression detected by immunohistochemical staining. It was suggested that HLA class I down‐regulation might be a common characteristic of breast cancer mostly caused by the down‐regulation of beta2‐microglobulin expression.