Private Idiotypes Located on Light and Heavy Chains of Human Myeloma Proteins Characterized by Monoclonal Antibodies

Idiotypic determinant, an epitope located on the variable region of the heavy or light chain of an immunoglobulin molecule, could be classified into private and public forms. The private idiotype is a marker unique to a single clone of B cell and hence a fingerprint of an individual clone. It could therefore be exploited to monitor expansion of normal or malignant B cells and to target clonally expanded tumorous B cells specifically. In the present study, five murine monoclonal anti-idiotypic antibodies were generated against two human immunoglobulin G (IgG) myeloma proteins. These monoclonal antibodies (MAbs) are produced by hybridoma clones obtained by the fusion of myeloma cells with splenocytes from BALB/c mice immunized with either human IgG1 (three clones) or IgG2 (two clones) myeloma proteins. All MAbs reacted only with the immunizing antigens and had no reactivity with a panel of purified myeloma proteins of four IgG subclasses with different light chains, including IgG1 (n = 9), IgG2 (n = 4), IgG3 (n = 4) and IgG4 (n = 5). They reacted with the Fab, but not the Fc fraction of the immunizing antigen and displayed no reactivity with normal human serum or polyclonal IgG. Immunoblotting analysis demonstrated that two of the MAbs react with linear idiotypes on light chain, whereas the remaining three MAbs recognize heavy chain associated idiotopes, either conformational (n = 2) or linear (n = 1). Such MAbs with specificity for private idiotypes could have potential implications for monitoring and specific immunotherapy of B cell malignancies. They also are useful tools to study structural correlates of idiotypes.