A tandem repeat of MUC1 core protein induces a weak in vitro immune response in human B cells

We have recently described an efficient method to study the human humoral i mmune response in vitro and to generate isotype-switched, antigen-specific human B cells, which has allowed us to produce high-affinity IgG antibodies against different peptides. In an attempt to study the in vitro immune res ponse against self-antigens, such as tumour-associated antigens, this proto col was used to immunise resting human peripheral blood B cells with a pept ide epitope from the human-adenocarcinoma-associated antigen, MUC1. After t he two-step in vitro immunisation, the secondary immunised cultures were te sted for MUC-1-specific antibodies by enzyme-linked immunosorbent assay (EL ISA). Phage I;molecular libraries were subsequently constructed, using the variable parts of IE genes derived from cells taken from ELISA-positive wel ls. The libraries were selected on the MUC1 core peptide. Antigen-specific Fab fragments, specific for the self antigen MUC1, were found in the librar y of secondary immunised IgG(+) B cells and these antibodies were evaluated by BIAcore analysis. The specific Fab fragments exhibited an unusually rap id dissociation rate constant and the overall response frequency was lower, as compared to other antibodies generated by this protocol, which might be explained by the repetitive nature of the core peptide used for immunisati on.