Multifaceted characterization of recombinant protein-based vaccines: An immunochemical toolbox for epitope-specific analyses of the hepatitis E vaccine.

The integrity of functional epitopes is a critical quality attribute for recombinant protein based vaccines since the presence of these native-like epitopes is the structural basis for vaccines to elicit functional antibodies. To demonstrate the quality and quantity of functional epitopes on vaccine antigens, a toolbox of assessing antigen characteristics is essential. Among the physicochemical, biophysical, immunochemical and in vivo potency analyses, the epitope-specific assays are most critical assessment of the antigen functionality. In this study, we used hepatitis E virus vaccine as an example to illustrated how the monoclonal antibody (mAb) based immunochemical assays were established for in-depth and multifaceted antigen characterization. A large panel of mAbs were developed and characterized using epitope clustering analysis. A subset of these mAbs recognizing non-overlapping epitopes were chosen to be used for assay development. Orthogonal methods, including surface plasma resonance-based BIAcore, solution competitive ELISA and sandwich ELISA, were developed for the antigenicity assessment. The sandwich ELISA with a pair of mAbs, recognizing two different epitopes, was used to assess the accelerated antigen stability, showing enhanced stability with adjuvant adsorption. Such a sandwich ELISA with robust performance has the potentials to be used for in vitro potency analysis to replace animal-based potency assay as product release test. In summary, using hepatitis E vaccine as an example, we demonstrated the importance and establishment of a mAb-based immunochemical toolbox for multifaceted antigen characterization. This is particularly important to demonstrate the successful reconstruction of the native-like and functional epitopes on a recombinant antigen post expression and purification. These epitope-specific and multifaceted assays serve as critical tools for process monitoring or lot consistency tests in support of vaccine development and manufacturing.