HUMAN SINGLE-CHAIN FV ANTIBODIES TO MUC1 CORE PEPTIDE SELECTED FROM PHAGE DISPLAY LIBRARIES RECOGNIZE UNIQUE EPITOPES AND PREDOMINANTLY BIND ADENOCARCINOMA

The tumor-associated antigen MUC1 is overexpressed and underglycosylat ed in human adenocarcinomas of diverse origins, such as breast, ovary, and colon, We isolated and describe five human single-chain (sc) Fv a ntibodies specific for the MUC1 variable number of tandem repeats regi on isolated by in vitro selection from a large naive phage antibody li brary containing over 6 x 10(9) different scFv antibodies, A synthetic biotinylated 100-mer peptide corresponding to five tandem repeats of the MUC1 peptide core was used for selection. Two of the antibodies me re highly specific for MUC1 as judged by; ELISA and flow cytometry. In immunohistochemistry, antibody clone 10A stained MUC1 in the cytoplas m and membrane of adenocarcinoma cells of breast and ovary, whereas in normal epithelium, only cytoplasmic or no staining was observed, With antibody clone 10B, staining was Less pronounced and was not always m embrane associated in adenocarcinoma, Determination of the Fine specif icity of 10A and 10B using a novel ''indirect epitope fingerprinting'' ELISA showed that both antibodies recognize unique epitopes that have not been described for hybridoma-derived anti-mucin antibodies of mou se origin, The selected human antibodies, like many of the murine MUC1 antibodies, recognize epitopes on the protein core of MUC1 that are a bundantly present in the underglycosylated form of cell surface mucin on adenocarcinoma, The best human scFv, clone 10A, appears to distingu ish normal cells from adenocarcinoma cells, which makes it an attracti ve candidate for use in antibody-based tumor targeting.