A direct comparison of human papillomavirus type 16 L1 particles reveals a lower immunogenicity of capsomeres than viruslike particles with respect to the induced antibody response

Bacterial production of recombinant contraceptive vaccine antigen from CatSper displayed on a human papilloma virus-like particle

CatSper is a voltage dependent calcium ion channel present in the principal piece of sperm tail. It plays a crucial role in sperm hyperactivated motility and so in fertilization. Extracellular loops of mouse sperm CatSper were used to develop a vaccine to achieve protection from pregnancy. These loops were inserted at one of the three hypervariable regions of Human Papilloma Virus (HPV) capsid protein (L1). Recombinant vaccines were expressed in E.coli as inclusion body (IB), purified, refolded and assembled into virus-like particles (VLP) in vitro, and adsorbed on alum. Four vaccine candidates were tested in Balb/C mice. All the constructs proved immunogenic, one showed contraceptive efficacy. This recombinant contraceptive vaccine is a non-hormonal intervention and is expected to give long-acting protection from undesired pregnancies.

Identifying Active Progeny Virus Particles in Formalin-Fixed, Paraffin-Embedded Sections Using Correlative Light and Scanning Electron Microscopy

Immunohistochemical analysis of formalin-fixed paraffin-embedded (FFPE) tissue blocks is routinely used to identify virus-infected cells. However, detecting virus particles in FFPE sections using light microscopy is difficult because of the light diffraction resolution limitations of an optical microscope. In this study, light microscopy and field emission scanning electron microscopy were performed to observe 3-dimensional virus particles in FFPE sections in a nondestructive manner using NanoSuit or osmium conductive treatment methods. The virus particles in FFPE sections were immunostained with specific antibodies against the surface antigens of the viral particles and stained with 3,3'-diaminobenzidine. A metal solution (0.2% gold chloride or 2% osmium tetroxide) was applied to enhance the 3,3'-diaminobenzidine-stained area. This procedure is nondestructive for FFPE sections and is a simpler method than transmission electron microscopy. To validate the applicability of this technique, we performed 3-dimensional imaging of the virus particles of different sizes, such as human papillomavirus, cytomegalovirus, and varicella-zoster virus. Furthermore, ultrathin sections from the FFPE sections that were observed to harbor viral particles using field emission scanning electron microscopy were prepared and assessed using transmission electron microscopy. In the correlative areas, transmission electron microscopy confirmed the presence of large numbers of virus particles. These results indicated that the combination of marking viral particles with 3,3'-diaminobenzidine/metal staining and conductive treatment can identify active progeny virus particles in FFPE sections using scanning electron microscopy. This easy correlative imaging of field emission scanning electron microscopy of the identical area of FFPE in light microscopy may help elucidate new pathological mechanisms of virus-related diseases.

Combined truncations at both N- and C-terminus of human papillomavirus type 58 L1 enhanced the yield of virus-like particles produced in a baculovirus system

Human papillomavirus (HPV) major capsid protein L1 virus-like particles (VLPs) produced in baculovirus system are highly immunogenic, but the relatively high production cost limits its application in the development of broad-spectrum vaccines. Here we report a novel method for enhancing VLP production in this system. We incorporated respectively 4, 8 or 13 residues truncation mutations in the N-terminus of L1ΔC, a C-terminal 25-residue-deleted L1 of HPV58, to construct three mutants. After expression in Sf9 cells, L1ΔN4C exhibited 2.3-fold higher protein production, 2.0-fold mRNA expression and lower rate of mRNA decay, compared to L1ΔC. More importantly, L1ΔN4C protein was easily purified by two-step chromatography with a VLP yield of up to 60 mg/L (purity > 99 %), 5-fold that of L1ΔC, whereas L1ΔN8C and L1ΔN13C behaved similarly to L1ΔC either in protein or mRNA expression. Moreover, L1ΔN4C VLPs showed similar binding activities with six HPV58 neutralizing monoclonal antibodies and induced comparable level of neutralizing antibody in mice to that of L1ΔC VLPs. Our results demonstrate that certain N- and C-terminal truncations of HPV58 L1 can enhance VLP yield. This method may be used to reduce production costs of other L1VLPs or chimeric VLPs to developing pan-HPV vaccines using baculovirus system.

Thermostability of a trivalent, capsomere-based vaccine for human papillomavirus infection

Currently licensed vaccines require a cold-chain to maintain efficacy. This cold-chain requirement reduces the availability of vaccines in resource-poor areas of the world. Commercially available human papillomavirus (HPV) vaccines protect against the most common HPV types related to cervical cancer; however, their impact is limited in many regions due to cold-chain requirements. The goal of this study was to test the thermostability of an adjuvanted, trivalent HPV L1 capsomere-based vaccine (containing HPV types 16, 18, and 31) that was formulated by using lyophilization to embed the antigens within a solid, glassy matrix. Thermal stabilities were determined by storing the vaccine formulations for 3 months at 50 °C, followed by immunization of BALB/c mice and measurement of antibody responses. Antibody responses to capsomere vaccines formulated with alum were unchanged after storage for 3 months at 50 °C. Neutralizing responses to these vaccines were unchanged by high-temperature storage, and were equivalent to those generated after administration of the commercially available liquid HPV vaccine Gardasil®9.

Head-to-Head Comparison of Modular Vaccines Developed Using Different Capsid Virus-Like Particle Backbones and Antigen Conjugation Systems

Capsid virus-like particles (cVLPs) are used as molecular scaffolds to increase the immunogenicity of displayed antigens. Modular platforms have been developed whereby antigens are attached to the surface of pre-assembled cVLPs. However, it remains unknown to what extent the employed cVLP backbone and conjugation system may influence the immune response elicited against the displayed antigen. Here, we performed a head-to-head comparison of antigen-specific IgG responses elicited by modular cVLP-vaccines differing by their employed cVLP backbone or conjugation system, respectively. Covalent antigen conjugation (i.e., employing the SpyTag/SpyCatcher system) resulted in significantly higher antigen-specific IgG titers compared to when using affinity-based conjugation (i.e., using biotin/streptavidin). The cVLP backbone also influenced the antigen-specific IgG response. Specifically, vaccines based on the bacteriophage AP205 cVLP elicited significantly higher antigen-specific IgG compared to corresponding vaccines using the human papillomavirus major capsid protein (HPV L1) cVLP. In addition, the AP205 cVLP platform mediated induction of antigen-specific IgG with a different subclass profile (i.e., higher IgG2a and IgG2b) compared to HPV L1 cVLP. These results demonstrate that the cVLP backbone and conjugation system can individually affect the IgG response elicited against a displayed antigen. These data will aid the understanding and process of tailoring modular cVLP vaccines to achieve improved immune responses.

Chimeric Virus-Like Particles and Capsomeres Induce Similar CD8+ T Cell Responses but Differ in Capacity to Induce CD4+ T Cell Responses and Antibody Responses

Despite extensive research, the development of an effective malaria vaccine remains elusive. The induction of robust and sustained T cell and antibody response by vaccination is an urgent unmet need. Chimeric virus-like particles (VLPs) are a promising vaccine platform. VLPs are composed of multiple subunit capsomeres which can be rapidly produced in a cost-effective manner, but the ability of capsomeres to induce antigen-specific cellular immune responses has not been thoroughly investigated. Accordingly, we have compared chimeric VLPs and their sub-unit capsomeres for capacity to induce CD8⁺ and CD4⁺ T cell and antibody responses. We produced chimeric murine polyomavirus VLPs and capsomeres each incorporating defined CD8⁺ T cell, CD4⁺ T cell or B cell repeat epitopes derived from Plasmodium yoelii CSP. VLPs and capsomeres were evaluated using both homologous or heterologous DNA prime/boost immunization regimens for T cell and antibody immunogenicity. Chimeric VLP and capsomere vaccine platforms induced robust CD8⁺ T cell responses at similar levels which was enhanced by a heterologous DNA prime. The capsomere platform was, however, more efficient at inducing CD4⁺ T cell responses and less efficient at inducing antigen-specific antibody responses. Our data suggest that capsomeres, which have significant manufacturing advantages over VLPs, should be considered for diseases where a T cell response is the desired outcome.

Advantages and Prospects of Tag/Catcher Mediated Antigen Display on Capsid-Like Particle-Based Vaccines

Capsid-like particles (CLPs) are multimeric, repetitive assemblies of recombinant viral capsid proteins, which are highly immunogenic due to their structural similarity to wild-type viruses. CLPs can be used as molecular scaffolds to enable the presentation of soluble vaccine antigens in a similar structural format, which can significantly increase the immunogenicity of the antigen. CLP-based antigen display can be obtained by various genetic and modular conjugation methods. However, these vary in their versatility as well as efficiency in achieving an immunogenic antigen display. Here, we make a comparative review of the major CLP-based antigen display technologies. The Tag/Catcher-AP205 platform is highlighted as a particularly versatile and efficient technology that offers new qualitative and practical advantages in designing modular CLP vaccines. Finally, we discuss how split-protein Tag/Catcher conjugation systems can help to further propagate and enhance modular CLP vaccine designs.

Functional epitopes on hepatitis E virions and recombinant capsids are highly conformation-dependent

Hepatitis E virus (HEV) is responsible for epidemic and sporadic acute hepatitis cases, especially in developing countries. Hepatitis E has become a vaccine-preventable disease in recent years with the development of a licensed vaccine. Most functional and neutralizing monoclonal antibodies (mAbs) are known to be highly sensitive to antigen conformation. In this study, a similar approach was used to characterize the conformational sensitivity of antibodies in human or mouse serum samples. Interestingly, comparative binding analysis using different antigen forms showed that the antibodies in the sera of naturally infected individuals, of human vaccinees and from mice immunized with the HEV p239 vaccine all exhibited a strong preference to particulate antigens over the monomeric form of the truncated capsid protein. The degree of discriminating the two test antigens is similar for serum samples to that for the well-characterized murine mAbs. A functional assay for assessing the inhibition of subviral particle cell entry by antibodies was used to determine the functional titers of anti-HEV antibodies in mouse sera. A good correlation was observed between the functional and binding titers in mouse sera determined using two different methods. This result supports the continued use of the enzyme-linked immunosorbent assay as the primary serological assay assuming that the coating antigen contains conformational and native-like epitopes, as in the case for HEV p239.

Chimeric Murine Polyomavirus Virus-Like Particles Induce Plasmodium Antigen-Specific CD8+ T Cell and Antibody Responses

An effective vaccine against the Plasmodium parasite is likely to require the induction of robust antibody and T cell responses. Chimeric virus-like particles are an effective vaccine platform for induction of antibody responses, but their capacity to induce robust cellular responses and cell-mediated protection against pathogen challenge has not been established. To evaluate this, we produced chimeric constructs using the murine polyomavirus structural protein with surface-exposed CD8+ or CD4+ T cell or B cell repeat epitopes derived from the Plasmodium yoelii circumsporozoite protein, and assessed immunogenicity and protective capacity in a murine model. Robust CD8+ T cell responses were induced by immunization with the chimeric CD8+ T cell epitope virus-like particles, however CD4+ T cell responses were very low. The B cell chimeric construct induced robust antibody responses but there was no apparent synergy when T cell and B cell constructs were administered as a pool. A heterologous prime/boost regimen using plasmid DNA priming followed by a VLP boost was more effective than homologous VLP immunization for cellular immunity and protection. These data show that chimeric murine polyomavirus virus-like particles are a good platform for induction of CD8+ T cell responses as well as antibody responses.

N-terminal truncations on L1 proteins of human papillomaviruses promote their soluble expression in Escherichia coli and self-assembly in vitro

Human papillomavirus (HPV) is the causative agent in genital warts and nearly all cervical, anogenital, and oropharyngeal cancers. Nine HPV types (6, 11, 16, 18, 31, 33, 45, 52, and 58) are associated with about 90% of cervical cancers and 90% of genital warts. HPV neutralization by vaccine-elicited neutralizing antibodies can block viral infection and prevent HPV-associated diseases. However, there is only one commercially available HPV vaccine, Gardasil 9, produced from Saccharomyces cerevisiae that covers all nine types, raising the need for microbial production of broad-spectrum HPV vaccines. Here, we investigated whether N-terminal truncations of the major HPV capsid proteins L1, improve their soluble expression in Escherichia coli. We found that N-terminal truncations promoted the soluble expression of HPV 33 (truncated by 10 amino acids [aa]), 52 (15 aa), and 58 (10 aa). The resultant HPV L1 proteins were purified in pentamer form and extensively characterized with biochemical, biophysical, and immunochemical methods. The pentamers self-assembled into virus-like particles (VLPs) in vitro, and 3D cryo-EM reconstructions revealed that all formed T = 7 icosahedral particles having 50–60-nm diameters. Moreover, we formulated a nine-valent HPV vaccine candidate with aluminum adjuvant and L1 VLPs from four genotypes used in this study and five from previous work. Immunogenicity assays in mice and non-human primates indicated that this HPV nine-valent vaccine candidate elicits neutralizing antibody titers comparable to those induced by Gardasil 9. Our study provides a method for producing a nine-valent HPV vaccine in E. coli and may inform strategies for the soluble expression of other vaccine candidates.

• N-terminal truncations promote the soluble expression of HPV L1 proteins in E. coli and their self-assembly of T = 7 icosahedral particle in vitro

• An HPV 9-valent vaccine candidate was formulated with E. coli-derived HPV 6, 11, 16, 18, 31, 33, 45, 52, and 58 VLPs, and conferred comparable immunogenicity with Gardasil 9

Opportunities and challenges for human papillomavirus vaccination in cancer

The discovery of genotype 16 as the prototype oncogenic human papillomavirus (HPV) initiated a quarter century of laboratory and epidemiological studies that demonstrated their necessary, but not sufficient, aetiological role in cervical and several other anogenital and oropharyngeal cancers. Early virus-induced immune deviation can lead to persistent subclinical infection that brings the risk of progression to cancer. Effective secondary prevention of cervical cancer through cytological and/or HPV screening depends on regular and widespread use in the general population, but coverage is inadequate in low-resource settings. The discovery that the major capsid antigen L1 could self-assemble into empty virus-like particles (VLPs) that are both highly immunogenic and protective led to the licensure of several prophylactic VLP-based HPV vaccines for the prevention of cervical cancer. The implementation of vaccination programmes in adolescent females is underway in many countries, but their impact critically depends on the population coverage and is improved by herd immunity. This Review considers how our expanding knowledge of the virology and immunology of HPV infection can be exploited to improve vaccine technologies and delivery of such preventive strategies to maximize reductions in HPV-associated disease, including incorporation of an HPV vaccine covering oncogenic types within a standard multitarget paediatric vaccine.

Oral immunization with cell-free self-assembly virus-like particles against orange-spotted grouper nervous necrosis virus in grouper larvae, Epinephelus coioides

Nervous necrosis virus (NNV) infection causes viral nervous necrosis, inflicting serious economic losses in marine fish cultivation. Vaccination is the most effective choice for controlling and preventing viral infection. Virus-like particles (VLPs) are considered a novel vaccine platform because they are not infectious and they induce neutralizing antibodies efficiently. In the present study, we investigated the effect of the recombinant orange-spotted grouper NNV (OSGNNV) capsid proteins produced in Escherichia coli and cell-free self-assembled into VLPs on protective immune responses in orange-spotted grouper following immersion, intramuscular injection and oral immunization. We found the OSGNNV VLPs elicited neutralizing antibody with high efficacy, and provided the fish with full protection against OSGNNV challenge. In addition, the cell-free self-assembled OSGNNV VLPs did not contain residual host cell components and was safer compared with the intracellular assembled VLPs. Thus, oral vaccination is a more convenient and preferred route for fish vaccination. Our results show that the fish fed four times with a diet supplemented with 50-200 μg/g OSGNNV VLPs at 7-day intervals have sufficient protection. These findings demonstrate that cell-free self-assembled OSGNNV VLPs have potential as oral vaccines in grouper.

Human papillomavirus first and second generation vaccines-current status and future directions

It has been more than 10 years that the first prophylactic papillomavirus vaccine became available, although distribution has been mainly limited to the more affluent countries. The first two vaccines have been a great success, hundreds of millions of women and a much smaller number of men have been vaccinated ever since. In a few countries with high vaccination coverage, in particular Australia but also parts of Great Britain and others, clinical impact of vaccination programs is already visible and there are indications for herd immunity as well. Vaccine efficacy is higher than originally estimated and the vaccines have an excellent safety profile. Gardasil9 is a second generation HPV virus-like particle vaccine that was licensed in 2015 and there are more to come in the near future. Currently, burning questions in respect to HPV vaccination are the duration of protection - especially in regard to cross-protection - reduction of the three-dose regimen and its impact on cross-protection; and duration of response, as well as protection against oropharyngeal HPV infections. Furthermore, researchers are seeking to overcome limitations of the VLP vaccines, namely low thermal stability, cost, invasive administration, limited coverage of non-vaccine HPV types, and lack of therapeutic efficacy. In this review we summarize the current status of licensed VLP vaccines and address questions related to second and third generation HPV vaccines.

Characterization of an Escherichia coli-derived human papillomavirus type 16 and 18 bivalent vaccine

Human papillomavirus (HPV) types 16 and 18 account for approximately 70% of cervical cancer worldwide. Neutralizing HPV prophylactic vaccines offer significant benefit, as they block HPV infection and prevent subsequent disease. However, the three licensed HPV vaccines that cover these two genotypes were produced in eukaryotic cells, which is expensive, particularly for low-income countries where HPV is highest. Here, we report a new HPV16 and -18 bivalent candidate vaccine produced from Escherichia coli. We used two strategies of N-terminal truncation of HPV L1 proteins and soluble non-fusion expression to generate HPV16 and HPV18 L1-only virus-like particles (VLPs) in a scalable process. Through comprehensive characterization of the bivalent candidate vaccine, we confirm lot consistency in a pilot scale-up of 30L, 100L and 500L. Using cryo-EM 3D reconstruction, we found that HPV16 and -18VLPs present in a T=7 icosahedral arrangement, similar in shape and size to that of the native virions. This HPV16/18 bivalent vaccine shares comparable immunogenicity with the licensed vaccines. Overall, we show that the production of a HPV16/18 bivalent vaccine from an E. coli expression system is robust and scalable, with potentially good accessibility worldwide as a population-based immunization strategy.

HPV vaccines: Global perspectives

The discovery of HPV as the etiological factor for HPV-associated malignancies and disease has opened up several opportunities for prevention and therapy. Current commercially available HPV vaccines (Gardasil, Gardasil 9, and Cervarix) are prophylactic in nature and derived from adjuvanted L1-based virus-like particles of HPV. Globally, through several clinical trials, they were found to be very safe and efficacious. Certain limitations such as cost-effectiveness, low coverage against all HPV types and a 3-dose schedule make these vaccines difficult to use worldwide. Approaches to address these issues involve alternate expression systems using L1 or alternate antigen (L2) as well as optimizing doses and broadening protection to provide cheap and cross-protective vaccines. Additionally, promising preclinical immunogenicity results from our own studies using alternative hosts such as Pichia and an antigen delivery system-based measles vector have potential for development as next generation HPV prophylactic vaccines. Several other therapeutic approaches are also ongoing.

Lessons learned from successful human vaccines: Delineating key epitopes by dissecting the capsid proteins

Recombinant VLP-based vaccines have been successfully used against 3 diseases caused by viral infections: Hepatitis B, cervical cancer and hepatitis E. The VLP approach is attracting increasing attention in vaccine design and development for human and veterinary use. This review summarizes the clinically relevant epitopes on the VLP antigens in successful human vaccines. These virion-like epitopes, which can be delineated with molecular biology, cryo-electron microscopy and x-ray crystallographic methods, are the prerequisites for these efficacious vaccines to elicit functional antibodies. The critical epitopes and key factors influencing these epitopes are discussed for the HEV, HPV and HBV vaccines. A pentamer (for HPV) or a dimer (for HEV and HBV), rather than a monomer, is the basic building block harboring critical epitopes for the assembly of VLP antigen. The processing and formulation of VLP-based vaccines need to be developed to promote the formation and stabilization of these epitopes in the recombinant antigens. Delineating the critical epitopes is essential for antigen design in the early phase of vaccine development and for critical quality attribute analysis in the commercial phase of vaccine manufacturing.

Next generation prophylactic human papillomavirus vaccines

The two licensed bivalent and quadrivalent human papillomavirus (HPV) L1 (the major papillomavirus virion protein) virus-like particle (VLP) vaccines are regarded as safe, effective, and well established prophylactic vaccines. However, they have some inherent limitations, including a fairly high production and delivery cost, virus-type restricted protection, and no reported therapeutic activity, which might be addressed with the development of alternative dosing schedules and vaccine products. A change from a three-dose to a two-dose protocol for the licensed HPV vaccines, especially in younger adolescents (aged 9-13 years), is underway in several countries and is likely to become the future norm. Preliminary evidence suggests that recipients of HPV vaccines might derive prophylactic benefits from one dose of the bivalent vaccine. Substantial interest exists in both the academic and industrial sectors in the development of second-generation L1 VLP vaccines in terms of cost reduction-eg, by production in Escherichia coli or alternative types of yeast. However, Merck's nonavalent vaccine, produced via the Saccharomyces cerevisiae production system that is also used for their quadrivalent vaccine, is the first second-generation HPV VLP vaccine to be available on the market. By contrast, other pharmaceutical companies are developing microbial vectors that deliver L1 genes. These two approaches would add an HPV component to existing live attenuated vaccines for measles and typhoid fever. Prophylactic vaccines that are based on induction of broadly cross-neutralising antibodies to L2, the minor HPV capsid protein, are also being developed both as simple monomeric fusion proteins and as virus-like display vaccines. The strong interest in developing the next generation of vaccines, particularly by manufacturers in middle-to-high income countries, increases the likelihood that vaccine production will become decentralised with the hope that effective HPV vaccines will be made increasingly available in low-resource settings where they are most needed.

Broad spectrum assessment of the epitope fluctuation--Immunogenicity hypothesis

Prediction of immunogenicity is a substantial barrier in vaccine design. Here, a molecular dynamics approach to assessing the immunogenicity of nanoparticles based on structure is presented. Molecular properties of epitopes on nonenveloped viral particles are quantified via a set of metrics. One such metric, epitope fluctuation (and implied flexibility), is shown to be inversely correlated with immunogenicity for each of a broad spectrum of nonenveloped viruses. The molecular metrics and experimentally determined immunogenicities for these viruses are archived in the open-source vaccine computer-aided design database. Results indicate the promise of computer-aided vaccine design to bring greater efficiency to traditional lab-based vaccine discovery approaches.

Development of a highly thermostable, adjuvanted human papillomavirus vaccine

A major impediment to economical, worldwide vaccine distribution is the requirement for a "cold chain" to preserve antigenicity. We addressed this problem using a model human papillomavirus (HPV) vaccine stabilized by immobilizing HPV16 L1 capsomeres, i.e., pentameric subunits of the virus capsid, within organic glasses formed by lyophilization. Lyophilized glass and liquid vaccine formulations were incubated at 50°C for 12weeks, and then analyzed for retention of capsomere conformational integrity and the ability to elicit neutralizing antibody responses after immunization of BALB/c mice. Capsomeres in glassy-state vaccines retained tertiary and quaternary structure, and critical conformational epitopes. Moreover, glassy formulations adjuvanted with aluminum hydroxide or aluminum hydroxide and glycopyranoside lipid A were not only as immunogenic as the commercially available HPV vaccine Cervarix®, but also retained complete neutralizing immunogenicity after high-temperature storage. The thermal stability of such adjuvanted vaccine powder preparations may thus eliminate the need for the cold chain.

Development of an IP-Free Biotechnology Platform for Constitutive Production of HPV16 L1 Capsid Protein Using the Pichia pastoris PGK1 Promoter

The human papillomavirus (HPV) L1 major capsid protein, which forms the basis of the currently available vaccines against cervical cancer, self-assembles into virus-like particles (VLPs) when expressed heterologously. We report the development of a biotechnology platform for HPV16 L1 protein expression based on the constitutive PGK1 promoter (P_PGK1) from the methylotrophic yeast Pichia pastoris. The L1 gene was cloned under regulation of P_PGK1 into pPGKΔ3 expression vector to achieve intracellular expression. In parallel, secretion of the L1 protein was obtained through the use of an alternative vector called pPGKΔ3α, in which a codon optimized α-factor signal sequence was inserted. We devised a work-flow based on the detection of the L1 protein by dot blot, colony blot, and western blot to classify the positive clones. Finally, intracellular HPV VLPs assembly was demonstrated for the first time in yeast cells. This study opens up perspectives for the establishment of an innovative platform for the production of HPV VLPs or other viral antigens for vaccination purposes, based on constitutive expression in P. pastoris.

The human papillomavirus type 16 L1 protein directly interacts with E2 and enhances E2-dependent replication and transcription activation

The human papillomavirus (HPV) E2 protein is a multifunctional protein essential for the control of virus gene expression, genome replication and persistence. E2 is expressed throughout the differentiation-dependent virus life cycle and is functionally regulated by association with multiple viral and cellular proteins. Here, we show for the first time to our knowledge that HPV16 E2 directly associates with the major capsid protein L1, independently of other viral or cellular proteins. We have mapped the L1 binding region within E2 and show that the α-2 helices within the E2 DNA-binding domain mediate L1 interaction. Using cell-based assays, we show that co-expression of L1 and E2 results in enhanced transcription and virus origin-dependent DNA replication. Upon co-expression in keratinocytes, L1 reduces nucleolar association of E2 protein, and when co-expressed with E1 and E2, L1 is partially recruited to viral replication factories. Furthermore, co-distribution of E2 and L1 was detected in the nuclei of upper suprabasal cells in stratified epithelia of HPV16 genome-containing primary human keratinocytes. Taken together, our findings suggest that the interaction between E2 and L1 is important for the regulation of E2 function during the late events of the HPV life cycle.

Glassy-state stabilization of a dominant negative inhibitor anthrax vaccine containing aluminum hydroxide and glycopyranoside lipid A adjuvants

During transport and storage, vaccines may be exposed to temperatures outside of the range recommended for storage, potentially causing efficacy losses. To better understand and prevent such losses, dominant negative inhibitor (DNI), a recombinant protein antigen for a candidate vaccine against anthrax, was formulated as a liquid and as a glassy lyophilized powder with the adjuvants aluminum hydroxide and glycopyranoside lipid A (GLA). Freeze-thawing of the liquid vaccine caused the adjuvants to aggregate and decreased its immunogenicity in mice. Immunogenicity of liquid vaccines also decreased when stored at 40°C for 8 weeks, as measured by decreases in neutralizing antibody titers in vaccinated mice. Concomitant with efficacy losses at elevated temperatures, changes in DNI structure were detected by fluorescence spectroscopy and increased deamidation was observed by capillary isoelectric focusing (cIEF) after only 1 week of storage of the liquid formulation at 40°C. In contrast, upon lyophilization, no additional deamidation after 4 weeks at 40°C and no detectable changes in DNI structure or reduction in immunogenicity after 16 weeks at 40°C were observed. Vaccines containing aluminum hydroxide and GLA elicited higher immune responses than vaccines adjuvanted with only aluminum hydroxide, with more mice responding to a single dose.

Expression of HPV-16 L1 capsomeres with glutathione-S-transferase as a fusion protein in tobacco plastids: an approach for a capsomere-based HPV vaccine

Human Papillomavirus (HPV) is the main cause of cervical cancer, which is the second most severe cancer of women worldwide, particularly in developing countries. Although vaccines against HPV infection are commercially available, they are neither affordable nor accessible to women in low income countries e.g. Africa. Thus, alternative cost-effective vaccine production approaches need to be developed. This study uses tobacco plants to express pentameric capsomeres of HPV that have been reported to generate elevated immune responses against HPV. A modified HPV-16 L1 (L1_2xCysM) protein has been expressed as a fusion protein with glutathione-S-transferase (GST) in tobacco chloroplasts following biolistic transformation. In total 7 transplastomic lines with healthy phenotypes were generated. Site specific integration of the GST-L1_2xCysM and aadA genes was confirmed by PCR. Southern blot analysis verified homogenous transformation of all transplastomic lines. Antigen capture ELISA with the conformation-specific antibody Ritti01, showed protein expression as well as the retention of immunogenic epitopes of L1 protein. In their morphology, GST-L1 expressing tobacco plants were identical to wild type plants and yielded fertile flowers. Taken together, these data enrich knowledge for future development of cost-effective plant-made vaccines against HPV.

Evaluation of specific humoral and cellular immune responses against the major capsid L1 protein of cutaneous wart-associated alpha-Papillomaviruses in solid organ transplant recipients

BACKGROUND

Infection with different species of cutaneous human papillomaviruses (cHPV) of genus alpha (cαHPVs) and associated skin disease are highly prevalent in solid organ transplant recipients (OTR), documenting the importance of the immunological control of HPV infection.

OBJECTIVES

To investigate the natural course of cαHPV-specific cellular and humoral immune responses during systemic long-term immunosuppression.

METHODS

Integrating bead-based multiplex serology and flow cytometry we analyzed natural cαHPV-specific antibodies and T(H) cell responses against the major capsid protein L1 of HPV types 2, 27, 57 (species 4) and 3, 10 and 77 (species 2) in sera and blood of OTR before and after initiation of iatrogenic immunosuppression and in comparison to immunocompetent individuals (IC).

RESULTS

Among OTR we observed an overall 42% decrease in humoral L1-specific immune responses during the course of iatrogenic immunosuppression, comparing median values 30 d before and 30 d after initiation of immunosuppressive therapy (p < 0.05). This difference disappeared after long-term (>1 year) immunosuppression. The predominant cellular L1-specific immune response was of type T(H)1 (CD4(+)CD40L(+)IL-2(+)IFN-γ(+)). Consistent with the detected L1-specific antibody titers, L1-specific T(H)1 responses were unchanged in long-term immunosuppressed OTR compared to IC. Notably, cαHPV-L1-specific IL-2(+)/CD40L(+)CD4(+) or IFN-γ(+)/CD40L(+) CD4(+) T(H) cell responses against any of the cαHPV-L1 types were significantly higher in OTR with clinically apparent common warts.

CONCLUSION

The systemic humoral immune response against cαHPV may reflect the individual degree of iatrogenic immunosuppression indicating a higher susceptibility for cαHPV infection among OTR during the early phase after organ transplantation. Humoral cαHPV-specific immune responses may show a reconstitution to pre-transplantation levels despite continuous potent immunosuppression.

Prophylactic papillomavirus vaccines

Human papillomaviruses (HPV) are the causative agents of cervical cancer, the third most common cancer in women. The development of prophylactic HPV vaccines Gardasil® and Cervarix® targeting the major oncogenic HPV types is now the frontline of cervical cancer prevention. Both vaccines have been proven to be highly effective and safe although there are still open questions about their target population, cross-protection, and long-term efficacy. The main limitation for a worldwide implementation of Gardasil® and Cervarix® is their high cost. To develop more affordable vaccines research groups are concentrated in new formulations with different antigens including capsomeres, the minor capsid protein L2 and DNA. In this article we describe the vaccines' impact on HPV-associated disease, the main open questions about the marketed vaccines, and current efforts for the development of second-generation vaccines.

Influence of Brucella abortus lipopolysaccharide as an adjuvant on the immunogenicity of HPV-16 L1VLP vaccine in mice

Brucella abortus lipopolysaccharide (LPS) has less toxicity and no pyrogenic properties in comparison with other bacterial LPS. It is a toll-like receptor 4 agonist and has been shown to have the potential use as a vaccine adjuvant. In this study, the immunostimulatory properties of LPS from smooth and rough strains of B. abortus (S19 and RB51) as adjuvants were investigated for the human papillomavirus type 16 (HPV16) L1 virus-like particles (L1VLPs) vaccines. C57BL/6 mice were immunized subcutaneously three times either with HPV-16 L1VLPs alone, or in combination with smooth LPS (S-LPS), rough LPS (R-LPS), aluminum hydroxide or a mixture of them as adjuvant. The humoral immunity was evaluated by measuring the specific and total IgG levels, and also the T-cell immune response of mice was evaluated by measuring different cytokines such as IFN-γ, TNF-α, IL-4, IL-10 and IL-17. Results showed that serum anti-HPV16 L1VLP IgG antibody titers was significantly higher in mice immunized with a combination of VLPs and R-LPS or S-LPS compared with other immunized groups. Co-administration of HPV-16 L1VLPs with R-LPS elicited the highest levels of splenocytes cytokines (IFN-γ, IL-4, IL-17 and TNF-α) and also effectively induced improvement of a Th1-type cytokine response characterized with a high ratio of IFN-γ/IL-10. The data indicate that B. abortus LPS particularly RB51-LPS enhances the immune responses to HPV-16 L1VLPs and suggests its potential as an adjuvant for the development of a potent prophylactic HPV vaccine and other candidate vaccines.

The concentration of carbon source in the medium affects the quality of virus-like particles of human papillomavirus type 16 produced in Saccharomyces cerevisiae

There is accumulating evidence that virus-like particles (VLPs) recombinantly produced in Saccharomyces cerevisiae (S. cerevisiae) are characterized by low structural stability, and that this is associated with reduced antigenicity and immunogenicity. However, little attention has been devoted to methods of improving the quality of the VLPs. Here, we investigated the effect of carbon source concentration in the medium on the antigenicity and immunogenicity of human papillomavirus (HPV) type 16 L1 VLPs expressed in S. cerevisiae from the galactose promoter. Media containing 2, 4, 6, and 8% carbon source, composed of both glucose and galactose in equal proportion, were used. VLP antigenicity was enhanced in cultures grown on media with 6 or 8% carbon source, compared to those from cultures with less than 6% carbon source. Moreover, the VLPs obtained from these cultures induced higher anti-HPV16 L1 IgG titers and neutralizing antibody titers in immunized mice than those purified from cultures with less than 6% carbon source. Our results indicate that the concentration of the carbon source in the medium plays a crucial role in determining the antigenicity and immunogenicity of HPV type16 L1 VLPs.

Generation and characterization of neutralizing monoclonal antibodies against baculo-expressed HPV 16 VLPs

Human papillomavirus (HPV) is the well-known second most cause of cervical cancer in women worldwide. According to the WHO survey, 70% of the total cervical cancers are associated with types HPV 16 and 18. Presently used prophylactic vaccine for HPV contains mainly capsid protein of L1 virus like particles (VLPs). Correct folding of VLPs and display of neutralizing epitopes are the major constraint for VLP-based vaccines. Further, monoclonal antibodies (mAbs) play a vital role in developing therapeutics and diagnostics. mAbs are also useful for the demonstration of VLP conformation, virus typing and product process assessment as well. In the present study, we have explored the usefulness of mAbs generated against sf-9 expressed HPV 16 VLPs demonstrated as type-specific and conformational dependent against HPV 16 VLPs by ELISA. High affinity and high pseudovirion neutralization titer of mAbs indicated their potential for the development of prophylactic vaccines for HPV. Also, the type-specific and conformational reactivity of the mAbs to HPV 16 VLPs in sf-9 cells by immunofluorescence assay proved their diagnostic potential.

Second-generation prophylactic HPV vaccines: successes and challenges

The role of HPV as the causative factor in cervical cancer has led to the development of the HPV vaccines Gardasil and Cervarix. These vaccines effectively protect against two HPV types associated with 70% of cervical cancer cases. Despite this success, researchers continue to develop second-generation HPV vaccines to protect against more HPV types and allow increased uptake in developing countries. While a reformulated vaccine based on the current technology is currently in clinical trials, another strategy consists of targeting highly conserved epitopes in the minor capsid protein of HPV, L2. Vaccines targeting L2 induce broadly neutralizing antibodies, capable of blocking infection by a wide range of HPV types. Several vaccine designs have been developed to optimize the display of L2 epitopes to the immune system and to reduce the cost of manufacture and distribution. L2-based vaccines show considerable promise as a potential next-generation HPV vaccine.

Bioengineering virus-like particles as vaccines

Virus-like particle (VLP) technology seeks to harness the optimally tuned immunostimulatory properties of natural viruses while omitting the infectious trait. VLPs that assemble from a single protein have been shown to be safe and highly efficacious in humans, and highly profitable. VLPs emerging from basic research possess varying levels of complexity and comprise single or multiple proteins, with or without a lipid membrane. Complex VLP assembly is traditionally orchestrated within cells using black-box approaches, which are appropriate when knowledge and control over assembly are limited. Recovery challenges including those of adherent and intracellular contaminants must then be addressed. Recent commercial VLPs variously incorporate steps that include VLP in vitro assembly to address these problems robustly, but at the expense of process complexity. Increasing research activity and translation opportunity necessitate bioengineering advances and new bioprocessing modalities for efficient and cost-effective production of VLPs. Emerging approaches are necessarily multi-scale and multi-disciplinary, encompassing diverse fields from computational design of molecules to new macro-scale purification materials. In this review, we highlight historical and emerging VLP vaccine approaches. We overview approaches that seek to specifically engineer a desirable immune response through modular VLP design, and those that seek to improve bioprocess efficiency through inhibition of intracellular assembly to allow optimal use of existing purification technologies prior to cell-free VLP assembly. Greater understanding of VLP assembly and increased interdisciplinary activity will see enormous progress in VLP technology over the coming decade, driven by clear translational opportunity.

Epitope fluctuations in the human papillomavirus are under dynamic allosteric control: a computational evaluation of a new vaccine design strategy

The dynamic properties of the capsid of the human papillomavirus (HPV) type 16 were examined using classical molecular dynamics simulations. By systematically comparing the structural fluctuations of the capsid protein, a strong dynamic allosteric connection between the epitope containing loops and the h4 helix located more than 50 Å away is identified, which was not recognized thus far. Computer simulations show that restricting the structural fluctuations of the h4 helix is key to rigidifying the epitopes, which is thought to be required for eliciting a proper immune response. The allostery identified in the components of the HPV is nonclassical because the mean structure of the epitope carrying loops remains unchanged, but as a result of allosteric effect the structural fluctuations are altered significantly, which in turn changes the biochemical reactivity profile of the epitopes. Exploiting this novel insight, a new vaccine design strategy is proposed wherein a relatively small virus capsid fragment is deposited on a silica nanoparticle in such a way that the fluctuations of the h4 helix are suppressed. The structural and dynamic properties of the epitope carrying loops on this hybrid nanoparticle match the characteristics of epitopes found on the full virus-like particle precisely, suggesting that these nanoparticles may serve as potent, cost-effective, and safe alternatives to traditionally developed vaccines. The structural and dynamic properties of the hybrid nanoparticle are examined in detail to establish the general concepts of the proposed new design.

Oral immunization with whole yeast producing viral capsid antigen provokes a stronger humoral immune response than purified viral capsid antigen

Weak antibody responses to protein antigens after oral immunization remain a serious problem. Yeasts have a rigid cell wall and are inherently resistant to harsh conditions, suggesting that recombinant antigens made in yeast could have a greater chance of making contact with the immune cells of the gastrointestinal (GI) tract in intact form. We compared antibody responses to oral immunization with purified recombinant antigen, used in the conventional manner, and responses to whole recombinant yeast producing the antigen intracellularly. Recombinant capsid protein (CP) of red-spotted grouper necrosis virus (RGNNV) was used as model antigen and Saccharomyces cerevisiae as host. The purified CP was obtained from the S. cerevisiae producing the RGNNV CP. Whole recombinant yeast producing RGNNV CP provoked 9-27 times higher anti-RGNNV CP IgG titres than purified RGNNV CP. Moreover, sera from mice immunized with the recombinant yeast had neutralizing activity against RGNNV, while those from mice immunized with purified CP did not. These results show that whole recombinant yeast is a promising platform for antigen delivery by oral immunization.

SIGNIFICANCE AND IMPACT OF THE STUDY

Provoking sufficient antibody responses by oral immunization has been an enormous challenge because of the harsh conditions of the gastrointestinal (GI) tract. Immunization strategies using purified antigen to make oral vaccines are incapable of commercialization because excessive amount of antigen is required to provoke antibody responses. Therefore, resolving the problems concerning the cost and effectiveness of oral vaccines is a high priority. Our results suggest that recombinant yeast has great potential for inducing antigen-specific immune responses by oral immunization. We believe that oral immunization using recombinant yeast can be a breakthrough technology.

Immunogenic assessment of plant-produced human papillomavirus type 16 L1/L2 chimaeras

Cervical cancer is caused by infection with human papillomaviruses (HPV) and is a global concern, particularly in developing countries, which have ~80% of the burden. HPV L1 virus-like particle (VLP) type-restricted vaccines prevent new infections and associated disease. However, their high cost has limited their application, and cytological screening programmes are still required to detect malignant lesions associated with the nonvaccine types. Thus, there is an urgent need for cheap second-generation HPV vaccines that protect against multiple types. The objective of this study was to express novel HPV-16 L1-based chimaeras, containing cross-protective epitopes from the L2 minor capsid protein, in tobacco plants. These L1/L2 chimaeras contained epitope sequences derived from HPV-16 L2 amino acid 108-120, 56-81 or 17-36 substituted into the C-terminal helix 4 (h4) region of L1 from amino acid 414. All chimaeras were expressed in Nicotiana benthamiana via an Agrobacterium-mediated transient system and targeted to chloroplasts. The chimaeras were highly expressed with yields of ~1.2 g/kg plant tissue; however, they assembled differently, indicating that the length and nature of the L2 epitope affect VLP assembly. The chimaera containing L2 amino acids 108-120 was the most successful candidate vaccine. It assembled into small VLPs and elicited anti-L1 and anti-L2 responses in mice, and antisera neutralized homologous HPV-16 and heterologous HPV-52 pseudovirions. The other chimaeras predominantly assembled into capsomeres and other aggregates and elicited weaker humoral immune responses, demonstrating the importance of VLP assembly for the immunogenicity of candidate vaccines.

Epitope engineering and molecular metrics of immunogenicity: a computational approach to VLP-based vaccine design

Developing antiviral vaccines is increasingly challenging due to associated time and cost of production as well as emerging drug-resistant strains. A computer-aided vaccine design strategy is presented that could greatly accelerate the discovery process and yield vaccines with high immunogenicity and thermal stability. Our strategy is based on foreign viral epitopes engineered onto well-established virus-like particles (VLPs) and demonstrates that such constructs present similar affinity for antibodies as does a native virus. This binding affinity serves as one molecular metric of immunogenicity. As a demonstration, we engineered a preS1 epitope of hepatitis B virus (HBV) onto the EF loop of human papillomavirus VLP (HPV-VLP). HBV-associated HzKR127 antibody displayed binding affinity for this structure at distances and strengths similar to those for the complex of the antibody with the full HBV (PDBID: 2EH8). This antibody binding affinity assessment, along with other molecular immunogenicity metrics, could be a key component of a computer-aided vaccine design strategy.

Influence of oxidation and multimerization on the immunogenicity of a thioredoxin-l2 prophylactic papillomavirus vaccine

Current commercial prophylactic human papillomavirus (HPV) vaccines are based on virus-like particles assembled from the major capsid protein L1 and show excellent safety and efficacy profiles. Still, a major limitation is their rather narrow range of protection against different HPV types. In contrast, the minor capsid protein L2 contains a so-called major cross-neutralizing epitope that can induce broad-range protective responses against multiple HPV types. This epitope is conserved among different papillomaviruses (PV) and contains two cysteine residues that are present in the L2 proteins of all known PV types. The main challenge in developing L2-directed vaccines is to overcome the intrinsically low immunogenicity of the L2 protein. Previously, we developed a recombinant L2-based prototype vaccine by inserting peptide epitopes spanning the cross-neutralizing L2 sequence into a bacterial thioredoxin (Trx) scaffold. These antigens induced high-titer neutralizing antibodies in mice. Here, we address the question of whether Trx scaffold multimerization may further enhance the immunogenicity of the TrxL2 vaccine. We also demonstrate that the oxidation state of the conserved cysteine residues is not essential for vaccine functionality, but it contributes to immunogenicity.

Development of human papillomavirus chimaeric L1/L2 candidate vaccines

Recombinant human papillomavirus (HPV) virus-like particle (VLP) vaccines based on the L1 capsid protein have been shown to be efficient prophylactic vaccines, albeit type-specific. As a first step to investigate the feasibility of extending protection against non-vaccine types, HPV-16 L1 chimaeras were generated. The region downstream of L1 amino acid (aa) 413 was replaced with selected cross-neutralising epitopes (aa 108-120; 56-81 and 17-36) derived from the HPV-16 L2 protein, generating proteins designated SAF, L2.56 and L2.17, respectively. The chimaera L1BPV containing BPV-1 L2 peptide aa 1-88 was similarly constructed. The chimaeras were evaluated for expression in insect cells; their ability to form particles was studied by electron microscopy, and their immunogenicity was evaluated in mice. SAF, L2.56 and L2.17 proteins were expressed to high concentrations in insect cells and elicited HPV-16 pseudovirus-neutralising anti-L1 antibodies. L2.56 and L2.17 also elicited anti-L2 antibodies. L1BPV was a poor vaccine candidate due to low levels of expression with concomitant lack of immunogenicity. All chimaeras assembled into tertiary structures. The results indicate that chimaeric L1 vaccines incorporating cross-neutralising L2 peptides could be promising second-generation prophylactic HPV vaccine candidates.

The choice of resin-bound ligand affects the structure and immunogenicity of column-purified human papillomavirus type 16 virus-like particles

Cell growth conditions and purification methods are important in determining biopharmaceutical activity. However, in studies aimed at manufacturing virus-like particles (VLPs) for the purpose of creating a prophylactic vaccine and antigen for human papillomavirus (HPV), the effects of the presence of a resin-bound ligand during purification have never been investigated. In this study, we compared the structural integrity and immunogenicity of two kinds of VLPs derived from HPV type 16 (HPV16 VLPs): one VLP was purified by heparin chromatography (hHPV16 VLP) and the other by cation-exchange chromatography (cHPV16 VLP). The reactivity of anti-HPV16 neutralizing monoclonal antibodies (H16.V5 and H16.E70) towards hHPV16 VLP were significantly higher than the observed cHPV16 VLP reactivities, implying that hHPV16 VLP possesses a greater number of neutralizing epitopes and has a greater potential to elicit anti-HPV16 neutralizing antibodies. After the application of heparin chromatography, HPV16 VLP has a higher affinity for H16.V5 and H16.E70. This result indicates that heparin chromatography is valuable in selecting functional HPV16 VLPs. In regard to VLP immunogenicity, the anti-HPV16 L1 IgG and neutralizing antibody levels elicited by immunizations of mice with hHPV16 VLPs were higher than those elicited by cHPV16 VLP with and without adjuvant. Therefore, the ability of hHPV16 VLP to elicit humoral immune responses was superior to that of cHPV16 VLP. We conclude that the specific chromatographic technique employed for the purification of HPV16 VLPs is an important factor in determining the structural characteristics and immunogenicity of column-purified VLPs.

Efficient production of chimeric human papillomavirus 16 L1 protein bearing the M2e influenza epitope in Nicotiana benthamiana plants

BACKGROUND

Human papillomavirus 16 (HPV-16) L1 protein has the capacity to self-assemble into capsomers or virus-like particles (VLPs) that are highly immunogenic, allowing their use in vaccine production. Successful expression of HPV-16 L1 protein has been reported in plants, and plant-produced VLPs have been shown to be immunogenic after administration to animals.

RESULTS

We investigated the potential of HPV-16 L1 to act as a carrier of two foreign epitopes from Influenza A virus: (i) M2e2-24, ectodomain of the M2 protein (M2e), that is highly conserved among all influenza A isolates, or (ii) M2e2-9, a shorter version of M2e containing the N-terminal highly conserved epitope, that is common for both M1 and M2 influenza proteins. A synthetic HPV-16 L1 gene optimized with human codon usage was used as a backbone gene to design four chimeric sequences containing either the M2e2-24 or the M2e2-9 epitope in two predicted surface-exposed L1 positions. All chimeric constructs were transiently expressed in plants using the Cowpea mosaic virus-derived expression vector, pEAQ-HT. Chimeras were recognized by a panel of linear and conformation-specific anti HPV-16 L1 MAbs, and two of them also reacted with the anti-influenza MAb. Electron microscopy showed that chimeric proteins made in plants spontaneously assembled in higher order structures, such as VLPs of T = 1 or T = 7 symmetry, or capsomers.

CONCLUSIONS

In this study, we report for the first time the transient expression and the self-assembly of a chimeric HPV-16 L1 bearing the M2e influenza epitope in plants, representing also the first record of a successful expression of chimeric HPV-16 L1 carrying an epitope of a heterologous virus in plants. This study further confirms the usefulness of human papillomavirus particles as carriers of exogenous epitopes and their potential relevance for the production in plants of monovalent or multivalent vaccines.

Construction and characterisation of a recombinant fowlpox virus that expresses the human papilloma virus L1 protein

BACKGROUND

Human papilloma virus (HPV)-16 is the most prevalent high-risk mucosal genotype. Virus-like-particle (VLP)-based immunogens developed recently have proven to be successful as prophylactic HPV vaccines, but are still too expensive for developing countries. Although vaccinia viruses expressing the HPV-16 L1 protein (HPV-L1) have been studied, fowlpox-based recombinants represent efficient and safer vectors for immunocompromised hosts due to their ability to elicit a complete immune response and their natural host-range restriction to avian species.

METHODS

A new fowlpox virus recombinant encoding HPV-L1 (FPL1) was engineered and evaluated for the correct expression of HPV-L1 in vitro, using RT-PCR, immunoprecipitation, Western blotting, electron microscopy, immunofluorescence, and real-time PCR assays.

RESULTS

The FPL1 recombinant correctly expresses HPV-L1 in mammalian cells, which are non-permissive for the replication of this vector.

CONCLUSION

This FPL1 recombinant represents an appropriate immunogen for expression of HPV-L1 in human cells. The final aim is to develop a safe, immunogenic, and less expensive prophylactic vaccine against HPV.

A molecular dynamics study of loop fluctuation in human papillomavirus type 16 virus-like particles: a possible indicator of immunogenicity

Immunogenicity varies between the human papillomavirus (HPV) L1 monomer assemblies of various sizes (e.g., monomers, pentamers or whole capsids). The hypothesis that this can be attributed to the intensity of fluctuations of important loops containing neutralizing epitopes for the various assemblies is proposed for HPV L1 assemblies. Molecular dynamics simulations were utilized to begin testing this hypothesis. Fluctuations of loops that contain critical neutralizing epitopes (especially FG loop) were quantified via root-mean-square fluctuation and features in the frequency spectrum of dynamic changes in loop conformation. If this fluctuation-immunogenicity hypothesis is a universal aspect of immunogenicity (i.e., immune system recognition of an epitope within a loop is more reliable when it is presented via a more stable delivery structure), then fluctuation measures can serve as one predictor of immunogenicity as part of a computer-aided vaccine design strategy.

Multiscale simulation of microbe structure and dynamics

A multiscale mathematical and computational approach is developed that captures the hierarchical organization of a microbe. It is found that a natural perspective for understanding a microbe is in terms of a hierarchy of variables at various levels of resolution. This hierarchy starts with the N -atom description and terminates with order parameters characterizing a whole microbe. This conceptual framework is used to guide the analysis of the Liouville equation for the probability density of the positions and momenta of the N atoms constituting the microbe and its environment. Using multiscale mathematical techniques, we derive equations for the co-evolution of the order parameters and the probability density of the N-atom state. This approach yields a rigorous way to transfer information between variables on different space-time scales. It elucidates the interplay between equilibrium and far-from-equilibrium processes underlying microbial behavior. It also provides framework for using coarse-grained nanocharacterization data to guide microbial simulation. It enables a methodical search for free-energy minimizing structures, many of which are typically supported by the set of macromolecules and membranes constituting a given microbe. This suite of capabilities provides a natural framework for arriving at a fundamental understanding of microbial behavior, the analysis of nanocharacterization data, and the computer-aided design of nanostructures for biotechnical and medical purposes. Selected features of the methodology are demonstrated using our multiscale bionanosystem simulator DeductiveMultiscaleSimulator. Systems used to demonstrate the approach are structural transitions in the cowpea chlorotic mosaic virus, RNA of satellite tobacco mosaic virus, virus-like particles related to human papillomavirus, and iron-binding protein lactoferrin.