EXPRESSION OF MHC CLASS-I AND CLASS-II ANTIGENS IN PANCREATIC ADENOCARCINOMAS

The antigens encoded by the major histocompatibility complex (MHC) are cell surface glycoproteins that play a fundamental role in the regula tion of the immune response. Anomalous MHC expression in tumor cells h as been viewed as an important feature to escape tumor recognition by immune cells. Low or absent MHC class I expression as well as ectopic MHC class II expression have been often observed to correlate with hig h grade malignancy and metastatic potential in a variety of human canc ers. To date, very little investigation of MHC (HLA in man) class I an d class II expression in human pancreatic cancer has been reported. We investigated this aspect on frozen sections of 8 pancreatic adenocarc inomas and 18 established in vitro cell Lines. HLA class I was express ed in all but two cancers whereas ne novo HLA class II expression was detected in 3 of 8 cancers. Interestingly, a hierarchy in the expressi on of the various subsets of HLA class II was found with HLA-DR>-DP>-D Q. Results on cell lines strongly resembled the ones obtained in cance r tissues. However, a peculiar feature was observed in certain cell li nes. HLA class II antigens were expressed in only a few cell lines and in some of them a mixed population of positive and negative cells was found. Sorting and cloning of the two populations confirmed the exist ence of tumor cell clones with stable and distinct HLA class II phenot ype. Taken together, these results indicate the cellular heterogeneity of pancreatic cancer cells with regard to the qualitative and quantit ative expression of major histocompatibility complex genes, and may pr ovide new insights for a better understanding of the tumor-host relati onships in this extremely severe form of neoplasia.