Heterogeneity of Monoclonal Antibodies

Anti-idiotypic antibodies: a new approach in prion research

Background

In certain cases, anti-idiotypic antibodies that recognize an antigen-combining site of an antibody can mimic the structure and/or function of certain nominal antigens. This feature makes them particularly useful if conventional experimental approaches fail to fulfil expectations, especially when the molecule of interest is infectious, toxic or difficult to isolate and purify. We suggest the application of an anti-idiotype concept to the field of prion biology, with the aim of evoking a humoral immune response against the pathological isoform of the prion protein (PrP^Sc). Different ways to induce anti-idiotypic responses were studied in mice and chickens using various forms of V5B2, a PrP^Sc-specific monoclonal antibody we have described previously.

Results

The preparation of anti-idiotypic monoclonal antibodies was achieved with well-defined strategies of immunization, selection and subsequent characterization. Our results demonstrate that it is possible to induce a strong anti-idiotypic immune response against the V5B2 monoclonal antibody in both xenogeneic and syngeneic experimental systems. From the competition seen between polyclonal and monoclonal anti-idiotypic antibodies and the original immunogen, the P1 peptide, and even more importantly, the ultimate target antigen, PrP^Sc, we conclude that selected antibodies bind to the antigen-combining site of the V5B2 monoclonal antibody and might even resemble the PrP^Sc-specific epitope. The involvement of both antigen-combining sites in the interaction between V5B2 and the most promising monoclonal anti-idiotypic antibody was further supported by molecular docking.

Conclusion

The results of the present study not only provide an example of the successful production of Ab2 monoclonal antibodies based on a well planned strategy for selection, but should also provide a new experimental approach that is applicable to the field of prion diseases.

Mass spectrometry analysis of photo-induced methionine oxidation of a recombinant human monoclonal antibody

Oxidation of methionine (Met) residues of a recombinant fully human monoclonal antibody after exposure to light was investigated and compared with chemically induced oxidation using tert-butyl-hydroperoxide (tBHP). Met256 and Met432 in the Fc region in the samples exposed to light or incubated with tBHP were oxidized. The Fc mass spectra of the antibody exposed to light showed mainly peaks with a molecular weight (MW) increase of 32 Da, however the sample treated with tBHP showed peaks with increase of only 16 Da. These results suggested that either oxidation of one Met residue (either Met256 or Met432) catalyzed the oxidation of the second Met residue on the same heavy chain (HC) or Met residues of one HC were preferentially oxidized when the antibody was exposed to light, while Met256 and Met432 were randomly oxidized when the antibody was incubated with tBHP.

Mass spectrometry for structural characterization of therapeutic antibodies

Antibodies, also known as immunoglobulins, have emerged as one of the most promising classes of therapeutics in the biopharmaceutical industry. The need for complete characterization of the quality attributes of these molecules requires sophisticated techniques. Mass spectrometry (MS) has become an essential analytical tool for the structural characterization of therapeutic antibodies, due to its superior resolution over other analytical techniques. It has been widely used in virtually all phases of antibody development. Structural features determined by MS include amino acid sequence, disulfide linkages, carbohydrate structure and profile, and many different post-translational, in-process, and in-storage modifications. In this review, we will discuss various MS-based techniques for the structural characterization of monoclonal antibodies. These techniques are categorized as mass determination of intact antibodies, and as middle-up, bottom-up, top-down, and middle-down structural characterizations. Each of these techniques has its advantages and disadvantages in terms of structural resolution, sequence coverage, sample consumption, and effort required for analyses. The role of MS in glycan structural characterization and profiling will also be discussed.