Loss of heterozygosity in the HLA class I region in human pancreatic cancer.

An altered human leukocyte antigen (HLA) class I expression constitutes an important tumor-escape mechanism counteracting T-cell mediated immune responses. We utilized the technique of microsatellite analysis to characterize the loss of heterozygosity (LOH) in the HLA class I region in 24 samples of patients with human ductal pancreatic carcinoma. The expression of HLA class I and the infiltration by T cells were studied in parallel by standard immunohistochemistry. The present study demonstrates LOH in the HLA class I region in five patients with pancreatic carcinoma. Immunohistochemical analysis showed that pancreatic carcinomas were frequently characterized by a total or partial loss of expression in HLA class I antigen. The positive or negative LOH status corresponded with the expression analysis in eight cases. Reduction of HLA class I expression without LOH was found in 14 cases. Lymphocyte infiltration with CD3+, CD4+, and CD8+ T cells did not show significant differences between LOH-positive and LOH-negative tumors. In conclusion, LOH does not seem to be the only factor for the reduced expression of HLA class I antigen as well as for the T-cell infiltration in this type of tumor.