How well can an idiotope peptide mimic replace its parent idiotype in a synthetic peptide vaccine?

Generation of anti-idiotypic antibodies mimicking Cry2Aa toxin from an immunized mouse phage display library as potential insecticidal agents against Plutella xylostella

This study tried to generate anti-idiotypic antibodies (Ab2s) which mimic Cry2Aa toxin using a phage-display antibody library (2.8 × 107 CFU/mL). The latter was constructed from a mouse immunized with F (ab')2 fragments digested from anti-Cry2Aa polyclonal antibodies. The F (ab')2 fragments and Plutella xylostella (P. xylostella) brush border membrane vesicles (BBMV) were utilized as targets for selection. Eight mouse phage-display single-chain variable fragments (scFvs) were isolated and identified by enzyme-linked immunoassay (ELISA), PCR and DNA sequencing after four rounds of biopanning. Among them, M3 exhibited the highest binding affinity with F (ab')2, while M4 bound the best with the toxin binding region of cadherin of P. xylostella (PxCad-TBR). Both of these two fragments were chosen for prokaryotic expression. The expressed M3 and M4 proteins with molecular weights of 30 kDa were purified. The M4 showed a binding affinity of 29.9 ± 2.4 nM with the PxCad-TBR and resulted in 27.8 ± 4.3 % larvae mortality against P. xylostella. Computer-assisted molecular modeling and docking analysis showed that mouse scFv M4 mimicked some Cry2Aa toxin binding sites when interacting with PxCad-TBR. Therefore, anti-idiotypic antibodies generated by BBMV-based screening could be useful for the development of new bio-insecticides as an alternative to Cry2Aa toxin for pest control.

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.