Investigation for the specific cancer immunotherapy using antigens recognized by a human natural antibody and the anti-idiotypic antibodies

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SK1 is an IgM human monoclonal antibody which recognizes a widely expressed glycoprotein antigen found on adenocarcinoma tissues. The antigen recognized by SK-1 (AgSK1) has a molecular weight of 42-46 kilodaltons and is strongly expressed on cells with high invasion capacity. We have recently identified a peptide sequence that is recognized by SK1. The antigen consisted of 54 amino acids and carboxyl terminal 20 amino acids were the antigenic epitope of SK1. The RT-PCR to determine the quantity of the AgSK1 in the panel of the human tissues revealed that the quantity of the mRNA level which encoded the AgSK1 was high in colon cancer cell lines and tissues. Whereas there was quite low or even no amount of the mRNA level found in non-epithelial tumor cell lines or in the normal colon mucosa, blood of no-cancer-bearing cases. These findings were consistent with the AgSK1 protein level in several tissues and cell lines determined by immunohistochemistry or Western blotting. We are now constructing a fibroblast cell line that had originally no AgSK1 detected but have expressed high level of AgSK1 by gene transduction. The invasion or motility capacity of the fibroblast and the inhibitory effect of this cell line by SK1 is now under investigation.