Identification of the immunoreactive peptide sequence for AgSK1, an adenocarcinoma-restricted antigen

SK1, a human immunoglobulin M (IgM) monoclonal antibody was derived from re gional nodal lymphocytes of a Dukes B colon carcinoma patient, The antigen recognized by the human monoclonal antibody (HuM-ab) SK1, termed AgSK1, was shown to be a two-chain glycoprotein with an apparent molecular weight ran ge of 42-46 kDa and preferentially expressed by human adenocarcinomas, part icularly human gastrointestinal malignancies. To identify the gene encoding the AgSK1 antigenic epitope, a cDNA expression library constructed in lamb da gt22A using mRNA from the colon carcinoma cell line HT29 was screened an d one of the isolated clones encoding a 1.5-kb cDNA, which showed strong im munoreactivity with HuMab SK1, was selected for further analysis. This clon e consisted of an amino terminal open reading frame of 54 amino acids and t he carboxyl terminal 20 amino acids of this protein coding region contained the antigenic epitope recognized by HuMab SK1.