title: Toolbox for non-intrusive structural and functional analysis of recombinant VLP based vaccines: a case study with hepatitis B vaccine.
abstract: BACKGROUND
  Fundamental to vaccine development, manufacturing consistency, and product stability is an understanding of the vaccine structure-activity relationship. With the virus-like particle (VLP) approach for recombinant vaccines gaining popularity, there is growing demand for tools that define their key characteristics. We assessed a suite of non-intrusive VLP epitope structure and function characterization tools by application to the Hepatitis B surface antigen (rHBsAg) VLP-based vaccine.
  
  
  METHODS
  The epitope-specific immune reactivity of rHBsAg epitopes to a given monoclonal antibody was monitored by surface plasmon resonance (SPR) and quantitatively analyzed on rHBsAg VLPs in-solution or bound to adjuvant with a competitive enzyme-linked immunosorbent assay (ELISA). The structure of recombinant rHBsAg particles was examined by cryo transmission electron microscopy (cryoTEM) and in-solution atomic force microscopy (AFM).
  
  
  RESULTS
  SPR and competitive ELISA determined relative antigenicity in solution, in real time, with rapid turn-around, and without the need of dissolving the particulate aluminum based adjuvant. These methods demonstrated the nature of the clinically relevant epitopes of HBsAg as being responsive to heat and/or redox treatment. In-solution AFM and cryoTEM determined vaccine particle size distribution, shape, and morphology. Redox-treated rHBsAg enabled 3D reconstruction from CryoTEM images--confirming the previously proposed octahedral structure and the established lipid-to-protein ratio of HBsAg particles. Results from these non-intrusive biophysical and immunochemical analyses coalesced into a comprehensive understanding of rHBsAg vaccine epitope structure and function that was important for assuring the desired epitope formation, determinants for vaccine potency, and particle stability during vaccine design, development, and manufacturing.
  
  
  CONCLUSIONS
  Together, the methods presented here comprise a novel suite of non-intrusive VLP structural and functional characterization tools for recombinant vaccines. Key VLP structural features were defined and epitope-specific antigenicity was quantified while preserving epitope integrity and particle morphology. These tools should facilitate the development of other VLP-based vaccines.
authors.affiliation: Department of Research & Development, NanoImaging Services, La Jolla, California, United States of America. mulder@nanoimagingservices.com
authors.forename: Anke M
authors.initials: AM
authors.lastname: Mulder
authors.forename: Bridget
authors.initials: B
authors.lastname: Carragher
authors.forename: Victoria
authors.initials: V
authors.lastname: Towne
authors.forename: Yuan
authors.initials: Y
authors.lastname: Meng
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.forename: Lance
authors.initials: L
authors.lastname: Dieter
authors.forename: Clinton S
authors.initials: CS
authors.lastname: Potter
authors.forename: Michael W
authors.initials: MW
authors.lastname: Washabaugh
authors.forename: Robert D
authors.initials: RD
authors.lastname: Sitrin
authors.forename: Qinjian
authors.initials: Q
authors.lastname: Zhao
mesh_terms: D000276:Adjuvants, Immunologic; D000911:Antibodies, Monoclonal / Q000276:immunology; D020285:Cryoelectron Microscopy; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000737:chemistry / Q000276:immunology; D006509:Hepatitis B / Q000276:immunology / Q000517:prevention & control* / Q000821:virology; D006514:Hepatitis B Surface Antigens / Q000737:chemistry* / Q000276:immunology; D017325:Hepatitis B Vaccines / Q000737:chemistry* / Q000276:immunology; D006515:Hepatitis B virus / Q000737:chemistry* / Q000276:immunology / Q000648:ultrastructure; D006801:Humans; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D010316:Particle Size; D013329:Structure-Activity Relationship; D020349:Surface Plasmon Resonance; D014614:Vaccines, Synthetic; D058425:Vaccines, Virus-Like Particle / Q000737:chemistry* / Q000276:immunology / Q000648:ultrastructure
chemical_list: D000276:Adjuvants, Immunologic; D000911:Antibodies, Monoclonal; D000939:Epitopes; D006514:Hepatitis B Surface Antigens; D017325:Hepatitis B Vaccines; D014614:Vaccines, Synthetic; D058425:Vaccines, Virus-Like Particle