Victoria Towne

Disassembly and reassembly of human papillomavirus virus-like particles produces more virion-like antibody reactivity

BackgroundHuman papillomavirus (HPV) vaccines based on major capsid protein L1 are licensed in over 100 countries to prevent HPV infections. The yeast-derived recombinant quadrivalent HPV L1 vaccine, GARDASIL(R), has played an important role in reducing cancer and genital warts since its introduction in 2006. The L1 proteins self-assemble into virus-like particles (VLPs).ResultsVLPs were subjected to post-purification disassembly and reassembly (D/R) treatment during bioprocessing to improve VLP immunoreactivity and stability. The post-D/R HPV16 VLPs and their complex with H16.V5 neutralizing antibody Fab fragments were visualized by cryo electron microscopy, showing VLPs densely decorated with antibody. Along with structural improvements, post-D/R VLPs showed markedly higher antigenicity to conformational and neutralizing monoclonal antibodies (mAbs) H16.V5, H16.E70 and H263.A2, whereas binding to mAbs recognizing linear epitopes (H16.J4, H16.O7, and H16.H5) was greatly reduced.Strikingly, post-D/R VLPs showed no detectable binding to H16.H5, indicating that the H16.H5 epitope is not accessible in fully assembled VLPs. An atomic homology model of the entireHPV16 VLP was generated based on previously determined high-resolution structures of bovine papillomavirus and HPV16 L1 pentameric capsomeres.ConclusionsD/R treatment of HPV16 L1 VLPs produces more homogeneous VLPs with more virion-like antibody reactivity. These effects can be attributed to a combination of more complete and regular assembly of the VLPs, better folding of L1, reduced non-specific disulfide-mediated aggregation and increased stability of the VLPs. Markedly different antigenicity of HPV16 VLPs was observed upon D/R treatment with a panel of monoclonal antibodies targeting neutralization sensitive epitopes. Multiple epitope-specific assays with a panel of mAbs with different properties and epitopes are required to gain a better understanding of the immunochemical properties of VLPs and to correlate the observed changes at the molecular level. Mapping of known antibody epitopes to the homology model explains the changes in antibody reactivity upon D/R. In particular, the H16.H5 epitope is partially occluded by intercapsomeric interactions involving the L1 C-terminal arm. The homology model allows a more precise mapping of antibody epitopes. This work provides a better understanding of VLPs in current vaccines and could guide the design of improved vaccines or therapeutics.

A fully human monoclonal antibody to Staphylococcus aureus iron regulated surface determinant B (IsdB) with functional activity in vitro and in vivo.

A fully human monoclonal antibody (CS-D7, IgG1) specific for the iron regulated surface determinant B (IsdB) of Staphylococcus aureus was isolated from the Cambridge Antibody Technology (CAT) scFv antibody library. As compared to previously described IsdB specific murine monoclonals, CS-D7 has a unique, non-overlapping binding site on IsdB, and exhibits increased in vivo activity. The antibody recognizes a conformational epitope spanning amino acids 50 to 285 and has a binding affinity of 340 (± 75) pM for IsdB. CS-D7 bound to a wide variety of S. aureus strains, but not to an isdB deletion mutant. The antibody mediated opsonophagocytic (OP) killing in vitro and mediated significant protection in vivo. In a murine lethal sepsis model, the antibody conferred protection from death when dosed prior to challenge, but not when dosed after challenge. Importantly, in a central venous catheter (CVC) model in rats, the antibody reduced bacteremia and prevented colonization of indwelling catheters. Protection was observed when rats were dosed with CS-D7 prior to challenge as well as post challenge. IsdB is currently being investigated for clinical efficacy against S. aureus infection, and the activity of this human IsdB specific antibody supplements the growing body of evidence to support targeting this antigen for vaccine development.

Selection and Characterization of Murine Monoclonal Antibodies to Staphylococcus aureus Iron-Regulated Surface Determinant B with Functional Activity In Vitro and In Vivo

ABSTRACT In an effort to characterize important epitopes of Staphylococcus aureus iron-regulated surface determinant B (IsdB), murine IsdB-specific monoclonal antibodies (MAbs) were isolated and characterized. A panel of 12 MAbs was isolated. All 12 MAbs recognized IsdB in enzyme-linked immunosorbent assays and Western blots; 10 recognized native IsdB expressed by S. aureus. The antigen epitope binding of eight of the MAbs was examined further. Three methods were used to assess binding diversity: MAb binding to IsdB muteins, pairwise binding to recombinant IsdB, and pairwise binding to IsdB-expressing bacteria. Data from these analyses indicated that MAbs could be grouped based on distinct or nonoverlapping epitope recognition. Also, MAb binding to recombinant IsdB required a significant portion of intact antigen, implying conformational epitope recognition. Four MAbs with nonoverlapping epitopes were evaluated for in vitro opsonophagocytic killing (OPK) activity and efficacy in murine challenge models. These were isotype switched from immunoglobulin G1 (IgG1) to IgG2b to potentially enhance activity; however, this isotype switch did not appear to enhance functional activity. MAb 2H2 exhibited OPK activity (≥50% killing in the in vitro OPK assay) and was protective in two lethal challenge models and a sublethal indwelling catheter model. MAb 13C7 did not exhibit OPK (<50% killing in the in vitro assay) and was protective in one lethal challenge model. Neither MAb 13G11 nor MAb 1G3 exhibited OPK activity in vitro or was active in a lethal challenge model. The data suggest that several nonoverlapping epitopes are recognized by the IsdB-specific MAbs, but not all of these epitopes induce protective antibodies.

Characterization of virus-like particles in GARDASIL® by cryo transmission electron microscopy

Cryo-transmission electron microscopy (cryoTEM) is a powerful characterization method for assessing the structural properties of biopharmaceutical nanoparticles, including Virus Like Particle-based vaccines. We demonstrate the method using the Human Papilloma Virus (HPV) VLPs in GARDASIL®. CryoTEM, coupled to automated data collection and analysis, was used to acquire images of the particles in their hydrated state, determine their morphological characteristics, and confirm the integrity of the particles when absorbed to aluminum adjuvant. In addition, we determined the three-dimensional structure of the VLPs, both alone and when interacting with neutralizing antibodies. Two modes of binding of two different neutralizing antibodies were apparent; for HPV type 11 saturated with H11.B2, 72 potential Fab binding sites were observed at the center of each capsomer, whereas for HPV 16 interacting with H16.V5, it appears that 60 pentamers (each neighboring 6 other pentamers) bind five Fabs per pentamer, for the total of 300 potential Fab binding sites per VLP.

Toolbox for Non-Intrusive Structural and Functional Analysis of Recombinant VLP Based Vaccines: A Case Study with Hepatitis B Vaccine

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. Methodology 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). Principal Findings 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. Significance 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.

In-depth process understanding of RECOMBIVAX HB® maturation and potential epitope improvements with redox treatment: multifaceted biochemical and immunochemical characterization.

Recombinant Hepatitis B surface antigen virus-like particles (VLPs) produced in yeast undergo spontaneous maturation during the vaccine production process, and the biophysical characteristics of the particles with respect to maturation were described in Zhao et al. (2006) [13]. Here we report additional biochemical and immunochemical characterization by various techniques, including the use of a panel of monoclonal antibodies (mAbs) that differ in their selectivity and conformation-sensitivity, for probing surface epitope structures. Crosslinking via interchain disulfide formation and binding of conformational specific antibodies in the mature particles were shown to be progressively enhanced. We show that redox-mediated VLP maturation is superior to heat-induced maturation in terms of generating VLPs which exhibit more complete crosslinking (>95%) and 2- to 3-fold higher antigenicity as defined by conformational antibodies. Therefore, the resulting VLPs from redox treatment resemble more closely their plasma-derived counterparts. The value of using multiple mAbs for probing surface epitopes was clearly demonstrated as different mAbs showed different degrees of sensitivity to the structural changes during HBsAg VLP maturation. The rapid, label-free technology of surface plasmon resonance performed at a single antigen concentration was shown to correlate well with a sandwich ELISA using parallel line analysis, currently implemented for product release and stability testing of RECOMBIVAX HB(®). Surface plasmon resonance offers both convenience and flexibility; multiple mAbs can be tested one at a time in the same set of experiments, providing a means to assess changes to individual epitopes. Taken together, these quantitative analytical tools enable more rapid, in-depth, and comprehensive process monitoring, process optimization, and assessment of product consistency and stability.

Real time monitoring of antigenicity development of HBsAg virus-like particles (VLPs) during heat- and redox-treatment.

The Hepatitis B virus major surface antigen (HBsAg) is a cysteine-rich, membrane-bound protein which self-assembles into 22-nm spherical virus-like particles (VLPs). While this VLP based human vaccine has been demonstrated to be safe and efficacious since 1986, the structural and exact molecular basis for its antigenic determinants has not been elucidated. Maturation of the yeast-derived purified VLPs was characterized for the changes in 37 their biophysical properties. Using rapid and label-free surface plasmon resonance technique with a neutralizing monoclonal antibody - A1.2, the epitope evolution kinetics of purified VLPs was monitored in real time. Evidence supporting the mechanism that the correct disulfide bond pairing is the molecular basis for shaping up the native virion-like epitopes was obtained. At least 10-fold enhancement in antigenicity probed by A1.2 of the VLPs was achieved by heat-treatment (t(1/2) ∼ 6-10 h), and another 2- to 3-fold enhancement was obtained when they were treated with redox buffer. This antigenicity development, presumably via disulfide formation/isomerization, was shown to be inhibited by a free radical scavenger and facilitated in the presence of light. Relative antigenicity determination with surface plasmon resonance was shown to be a valuable tool for process characterization in the kinetic monitoring mode or for final VLP product assessment in the end point antigenicity testing mode.

Development of Neutralizing Monoclonal Antibodies for Oncogenic Human Papillomavirus Types 31, 33, 45, 52, and 58

ABSTRACT Human papillomavirus (HPV) is the etiological agent for all cervical cancers, a significant number of other anogenital cancers, and a growing number of head and neck cancers. Two licensed vaccines offer protection against the most prevalent oncogenic types, 16 and 18, responsible for approximately 70% of cervical cancer cases worldwide and one of these also offers protection against types 6 and 11, responsible for 90% of genital warts. The vaccines are comprised of recombinantly expressed major capsid proteins that self-assemble into virus-like particles (VLPs) and prevent infection by eliciting neutralizing antibodies. Adding the other frequently identified oncogenic types 31, 33, 45, 52, and 58 to a vaccine would increase the coverage against HPV-induced cancers to approximately 90%. We describe the generation and characterization of panels of monoclonal antibodies to these five additional oncogenic HPV types, and the selection of antibody pairs that were high affinity and type specific and recognized conformation-dependent neutralizing epitopes. Such characteristics make these antibodies useful tools for monitoring the production and potency of a prototype vaccine as well as monitoring vaccine-induced immune responses in the clinic.

Pairwise antibody footprinting using surface plasmon resonance technology to characterize human papillomavirus type 16 virus-like particles with direct anti-HPV antibody immobilization

This paper describes an approach to surface plasmon resonance (SPR) based epitope mapping, also referred to as pairwise antibody footprinting, involving the direct immobilization of an antigen-specific primary mAb to the surface of an SPR interface. This technique offers a more straightforward approach than indirect capture (e.g., via rabbit anti-mouse Fc) as it does not require additional steps to block the unoccupied immobilized anti-Fc to prevent non-specific antibody binding. This is also an alternative to the direct immobilization of an antigen of interest, which may cause conformational changes in the antigen or epitope degradation upon chemical immobilization, particularly in successive regeneration cycles. It is particularly suitable for highly multivalent targets such as virus-like particles (VLPs). Using this technique, we assessed a panel of eight monoclonal antibodies against HPV (human papilloma virus) L1 protein VLPs expressed by Saccharomyces cerevisiae. In the antibody epitope screening studies, HPV16 L1-directed conformational mAbs were clearly distinguished from the linear mAbs and consistent with known epitope information. Additional studies using a linear mAb and a conformational mAb demonstrate the practical application of this technique for characterizing the result of process changes and the consistency of recombinant HPV16 VLPs. The method is readily extensible to other VLPs and VLP-based vaccines.

Evaluating functional antibodies in rhesus monkeys immunized with hepatitis B virus surface antigen vaccine with novel adjuvant formulations.

Effective and safe novel adjuvants are of great interest to the vaccine research community. In this study, we describe our evaluation of adjuvant formulations containing a TLR9 agonist adjuvant (ISS1018) or ISCOMATRIX™ adjuvant for a two-dose regimen of hepatitis B virus surface antigen virus-like particle vaccine in mice and rhesus macaques. Our results show a 10-20 fold improvement in Ab binding titers determined in an antigen-sandwich assay for adjuvant formulations with ISCOMATRIX™ adjuvant, in comparison to routine aluminum formulation. Furthermore, we optimized a competition assay to evaluate a functional component of immune sera, using a conformation-dependent and protective mAb, RFHBs1, as the probe. Although good correlation was observed between Ab binding titers from the antigen-sandwich assay and functional titers from the in-solution competition against RFHBs1, the latter assessment provided a much more stringent ranking of adjuvant formulations than the former. These results indicate the importance of evaluating functional Abs when assessing and comparing novel adjuvant formulations, as it provides another angle to investigate the effects of change in adjuvant composition on antigenic integrity of the testing vaccines.