Evaluation of murine monoclonal antibodies targeting different epitopes of the hepatitis B virus surface antigen by using immunological as well as molecular biology and biochemical approaches

Chimeric hepatitis B surface antigen virus-like particles expressing the strep A epitope p*17 elicit a humoral immune response in mice

To optimize immunogenicity, bacterial epitopes in putative vaccine constructs can be presented to immune cells as multiple repeated structures on a defined nanoparticle. Virus-like particles (VLPs) are viral capsid proteins that self-assemble to form compact and highly ordered nanoparticles that are within the optimal size range for uptake by dendritic cells. VLPs mimic the live virus in size and form but contain no viral genetic material, are therefore noninfective and are the basis of safe and effective vaccines against hepatitis B virus (HBV) and human papillomavirus (HPV). Due to their particulate nature, molecular stability, and expression of high density and repetitive antigen displays, recombinant cell culture-derived VLPs are ideal platforms for the delivery of small molecules, including bacterial epitopes. We developed a putative vaccine by expressing a minimal epitope from the bacterium Streptococcus pyogenes (Strep A) on the surface of a recombinant VLP comprising multiple copies of HBV small envelope protein (HBsAg-S). Strep A is responsible for a wide spectrum of human infections and postinfectious diseases that disproportionately affect children and young adults living in resource-poor communities. No vaccine is currently available to offer sufficiently broad protection from the numerous and diverse strains of Strep A endemic in these at-risk populations. The Strep A antigen targeted by our vaccine construct is p*17, a cryptic epitope from a highly conserved region of the Strep A M-protein with demonstrated enhanced immunogenicity and broad protective potential against Strep A. To ensure surface expression and optimal immunogenicity, we expressed p*17 within the immunodominant "a" determinant of HBsAg-S. The recombinant VLPs (VLP-p*17) expressed in HEK293T cells spontaneously formed 22 nm particles and induced the production of high titers of p*17-specific IgG in BALB/c mice immunized with three 0.5 μg doses of VLP-p*17 formulated with adjuvant.

Monoclonal antibodies against hepatitis B viral surface antigens and epitope grouping

Monoclonal antibodies (MAbs) were generated against subtypes (ad/ad/rw) of the human hepatitis B viral surface antigen (HBsAg). Among dozens of antibodies that were generated, the majority was shown to commonly react with various ad/ay subtypes of the S protein. Epitope(s) of these antibodies were grouped by various immunoassay methods, and at least four distinct epitope regions were identified. Some of these antibodies were selected to formulate sandwich enzyme immunoassays for quantitative determinations of HBsAg in reconstituted specimens. Epitope-defined monoclonal antibodies with high affinity and specificity might be suitable for formulations as vaccines (containing a mixture of humanized monoclonal antibodies) for passive immunization in humans for immunoprophylaxis of HBV infection.

Analysis of the epitope and neutralizing capacity of human monoclonal antibodies induced by hepatitis B vaccine

Hepatitis B virus (HBV) is an infectious agent that is a significant worldwide public health issue. However, the mechanism by which vaccination-induced antibodies prevent HBV infection remains unclear. To investigate the mechanism by which antibodies induced by hepatitis B surface Ag (HBsAg)-vaccination prevent HBV infection in humans, we prepared human monoclonal antibodies (mAbs) against HBsAg using a novel cell-microarray system from peripheral blood B-lymphocytes from vaccinated individuals. We then characterized the IgG subclass, L-chain subtype, and V-gene repertoire of the H/L-chain, as well as affinities of each of these mAbs. We also determined the epitopes of the individual mAbs using synthesized peptides, and the HBV-neutralizing activities of mAbs using the hepatocyte cell line HepaRG. Consequently, IgG1 and kappa chain was mainly used as the mAbs for HBsAg. Seventy percent of the mAbs bound to the loop domain of the small-HBsAg and showed greater neutralizing activities. There were no relationships between their affinities and neutralization activities. A combination of mAbs recognizing the first loop domain showed a synergistic effect on HBV-neutralizing activity that surpassed conventional hepatitis B-Ig (HBIG) in the HepaRG cell line assay. These results may contribute to the development of effective mAb treatment against HBV infection replacing conventional HBIG administration.