Broad Cross-Protection Is Induced in Preclinical Models by a Human Papillomavirus Vaccine Composed of L1/L2 Chimeric Virus-Like Particles

The h4 coil surface region of human papillomavirus type 58 L1 virus-like particle serves as a potential location for presenting the RG1 epitope peptide

The licensed prophylactic human papillomavirus (HPV) vaccines, based on L1 virus-like particles (VLPs), effectively prevent infection and HPV-associated cancers caused by the vaccine types but offer limited protection against non-vaccine types. L2 N-terminal peptides, such as the RG1 epitope peptide, contain conserved cross-neutralizing epitopes, and their immunogenicity could be enhanced via display on the surface of L1VLPs. To our knowledge, there have been no reports on the construction and immunogenicity research of chimeric L1-L2 proteins based on HPV58 L1VLP, the third most prevalent high-risk type in Asia. Here, we inserted the RG1 epitope peptides at two sites of the highly expressed HPV58 L1 - the h4 coil region or the DE loop (with linkers) - to construct seven chimeras. These chimeras were expressed in insect cells, self-assembled into chimeric VLPs (cVLPs), and their immunogenicity was assessed in a mouse model. Notably, three cVLPs with h4 coil insertions elicited comparable levels of L1-specific antibody response in mice to the L1VLP control and induced cross-neutralizing antibody responses against fourteen pseudoviruses. Conversely, four cVLPs with DE loop insertions induced significantly lower L1-specific antibody titers compared with the L1VLP control (p < .001). This might be attributed to the disruption or obstruction of neutralizing epitope(s) targeted by HPV58-specific conformation-dependent monoclonal antibodies, caused by the sequence insertions. Our findings suggest that the h4 coil region of HPV58 L1VLP might be a potential location for RG1 epitope display, guiding the presentation of heterologous epitopes to develop chimeric HPV58 L1VLP-based vaccines.

Nanotechnology-based strategies for vaccine development: accelerating innovation and delivery

The key role and impact of nanotechnology in vaccine development became particularly prominent following the outbreak of the coronavirus disease 2019 (COVID-19) pandemic in 2019. Especially in the process of designing and optimising COVID-19 vaccines, the application of nanomaterials significantly accelerated vaccine development and efficient delivery. In this review, we categorised and evaluated conventional vaccines, including attenuated live vaccines, inactivated vaccines, and subunit vaccines, highlighting their advantages and limitations. We summarised the development history, mechanisms, and latest technologies of vaccine adjuvants, emphasising their critical role in immune responses. Furthermore, we focused on the application of nanotechnology in the vaccine field, detailing the characteristics of nanoparticle vaccines, including virus-like particles, lipid-based carriers, inorganic nanoparticles, and polymer-based carriers. We emphasised their potential advantages in enhancing vaccine stability and immunogenicity, as well as their ability to deliver vaccines and present antigens through various routes. Despite facing challenges such as low drug loading efficiency, issues with long-term storage, high costs, and difficulties in large-scale production, nano-vaccines hold promise for the future. This review underscores the pivotal role and prospects of nanotechnology in vaccine development, offering new pathways and strategies to address current and future disease challenges.

Tailored Viral-like Particles as Drivers of Medical Breakthroughs

Despite the recognized potential of nanoparticles, only a few formulations have progressed to clinical trials, and an even smaller number have been approved by the regulatory authorities and marketed. Virus-like particles (VLPs) have emerged as promising alternatives to conventional nanoparticles due to their safety, biocompatibility, immunogenicity, structural stability, scalability, and versatility. Furthermore, VLPs can be surface-functionalized with small molecules to improve circulation half-life and target specificity. Through the functionalization and coating of VLPs, it is possible to optimize the response properties to a given stimulus, such as heat, pH, an alternating magnetic field, or even enzymes. Surface functionalization can also modulate other properties, such as biocompatibility, stability, and specificity, deeming VLPs as potential vaccine candidates or delivery systems. This review aims to address the different types of surface functionalization of VLPs, highlighting the more recent cutting-edge technologies that have been explored for the design of tailored VLPs, their importance, and their consequent applicability in the medical field.

A novel C-terminal modification method enhanced the yield of human papillomavirus L1 or chimeric L1-L2 virus-like particles in the baculovirus system

Human papillomavirus (HPV) major capsid protein L1 virus-like particles (VLPs) produced in the baculovirus system showed excellent safety and immunogenicity, but the relatively high production cost stands as a substantial barrier to extensive commercialization, especially in producing multivalent vaccines. Here, a novel method, C-terminal basic amino acid (aa) substitution, was developed for increasing VLP and chimeric VLP (cVLP) production in this system. A series of mutants of five HPV types, including three L1 VLPs (6L1, 11L1, and 52L1) and two L1-L2 cVLPs (16L1-33L2, 58L1-16L2), were constructed. We found that most mutants exhibited higher protein expression in Sf9 cells, among which the yields of the superior mutants, 6L1CS4, 11L1CS3, 52L1m4∆N13CS1, 16L1-33L2 CS1, and 58L1-16L2 CS3, were up to 40, 35, 20, 35, and 60 mg/L, which respectively increased by 4.2-, 7.3-, 5-, 2.5-, and 3.4-fold, and they also showed robust immunogenicity and great stabilities. Additionally, we found that the increased level of steady-state mRNA may play a crucial role in promoting L1 protein expression. Our results demonstrated that this novel method was cost-effective and can be used to reduce the production costs of L1 VLPs and L1-L2 cVLPs to develop broadly protective and affordable multivalent HPV vaccines.

Self-Assembling Protein Nanoparticles in the Design of Vaccines: 2022 Update

Vaccines constitute a pillar in the prevention of infectious diseases. The unprecedented emergence of novel immunization strategies due to the COVID-19 pandemic has again positioned vaccination as a pivotal measure to protect humankind and reduce the clinical impact and socioeconomic burden worldwide. Vaccination pursues the ultimate goal of eliciting a protective response in immunized individuals. To achieve this, immunogens must be efficiently delivered to prime the immune system and produce robust protection. Given their safety, immunogenicity, and flexibility to display varied and native epitopes, self-assembling protein nanoparticles represent one of the most promising immunogen delivery platforms. Currently marketed vaccines against the human papillomavirus, for instance, illustrate the potential of these nanoassemblies. This review is intended to provide novelties, since 2015, on the ground of vaccine design and self-assembling protein nanoparticles, as well as a comparison with the current emergence of mRNA-based vaccines.

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.

Improvement of RG1-VLP vaccine performance in BALB/c mice by substitution of alhydrogel with the next generation polyphosphazene adjuvant PCEP

Current human papillomavirus (HPV) vaccines provide substantial protection against the most common HPV types responsible for oral and anogenital cancers, but many circulating cancer-causing types remain for which vaccine coverage is lacking. In addition, all current HPV vaccines rely on aluminum salt-based adjuvant formulations that function through unclear mechanisms with few substitutes available. In an effort to expand the toolbox of available adjuvants suitable for HPV vaccines, we compared the immunogenicity of the RG1-VLP (virus-like particle) vaccine in BALB/c mice when formulated with either the aluminum hydroxide adjuvant Alhydrogel or the novel polyphosphazene macromolecular adjuvant poly[di (carboxylatoethylphenoxy) phosphazene] (PCEP). PCEP-formulated RG1-VLPs routinely outperformed VLP/Alhydrogel in several measurements of VLP-specific humoral immunity, including consistent improvements in the magnitude of antibody (Ab) responses to both HPV16-L1 and the L2 RG1 epitope as well as neutralizing titers to HPV16 and cross-neutralization of pseudovirion (PsV) types HPV18 and HPV39. Dose-sparing studies indicated that RG1-VLPs could be reduced in dose by 75% and the presence of PCEP ensured activity comparable to a full VLP dose adjuvanted by Alhydrogel. In addition, levels of HPV16-L1 and -L2-specific Abs were achieved after two vaccinations with PCEP as adjuvant that were equivalent to or greater than levels achieved with three vaccinations with Alhydrogel alone, indicating that the presence of PCEP resulted in accelerated immune responses that could allow for a decreased dose schedule. Given the extensive clinical track record of polyphosphazenes, these data suggest that substitution of alum-based adjuvants with PCEP for the RG1-VLP vaccine could lead to rapid seropositivity requiring fewer boosts, the dose-sparing of commercial VLP-based vaccines, and the establishment of longer-lasting humoral responses to HPV.

RG1-VLP and Other L2-Based, Broad-Spectrum HPV Vaccine Candidates

Licensed human papillomavirus (HPV) vaccines contain virus-like particles (VLPs) self-assembled from L1 major-capsid proteins that are remarkably effective prophylactic immunogens. However, the induced type-restricted immune response limits coverage to the included vaccine types, and costly multiplex formulations, restrictive storage and distribution conditions drive the need for next generation HPV vaccines. Vaccine candidates based upon the minor structural protein L2 are particularly promising because conserved N-terminal epitopes induce broadly cross-type neutralizing and protective antibodies. Several strategies to increase the immunological potency of such epitopes are being investigated, including concatemeric multimers, fusion to toll-like receptors ligands or T cell epitopes, as well as immunodominant presentation by different nanoparticle or VLP structures. Several promising L2-based vaccine candidates have reached or will soon enter first-in-man clinical studies. RG1-VLP present the HPV16L2 amino-acid 17-36 conserved neutralization epitope "RG1" repetitively and closely spaced on an immunodominant surface loop of HPV16 L1-VLP and small animal immunizations provide cross-protection against challenge with all medically-significant high-risk and several low-risk HPV types. With a successful current good manufacturing practice (cGMP) campaign and this promising breadth of activity, even encompassing cross-neutralization of several cutaneous HPV types, RG1-VLP are ready for a first-in-human clinical study. This review aims to provide a general overview of these candidates with a special focus on the RG1-VLP vaccine and its road to the clinic.

Vaccination Strategies for the Control and Treatment of HPV Infection and HPV-Associated Cancer

Human papillomavirus (HPV) is the most common sexually transmitted infection, currently affecting close to 80 million Americans. Importantly, HPV infection is recognized as the etiologic factor for numerous cancers, including cervical, vulval, vaginal, penile, anal, and a subset of oropharyngeal cancers. The prevalence of HPV infection and its associated diseases are a significant problem, affecting millions of individuals worldwide. Likewise, the incidence of HPV infection poses a significant burden on individuals and the broader healthcare system. Between 2011 and 2015, there were an estimated 42,700 new cases of HPV-associated cancers each year in the United States alone. Similarly, the global burden of HPV is high, with around 630,000 new cases of HPV-associated cancer occurring each year. In the last decade, a total of three preventive major capsid protein (L1) virus-like particle-based HPV vaccines have been licensed and brought to market as a means to prevent the spread of HPV infection. These prophylactic vaccines have been demonstrated to be safe and efficacious in preventing HPV infection. The most recent iteration of the preventive HPV vaccine, a nanovalent, L1-VLP vaccine, protects against a total of nine HPV types (seven high-risk and two low-risk HPV types), including the high-risk types HPV16 and HPV18, which are responsible for causing the majority of HPV-associated cancers. Although current prophylactic HPV vaccines have demonstrated huge success in preventing infection, existing barriers to vaccine acquisition have limited their widespread use, especially in low- and middle-income countries, where the burden of HPV-associated diseases is highest. Prophylactic vaccines are unable to provide protection to individuals with existing HPV infections or HPV-associated diseases. Instead, therapeutic HPV vaccines capable of generating T cell-mediated immunity against HPV infection and associated diseases are needed to ameliorate the burden of disease in individuals with existing HPV infection. To generate a cell-mediated immune response against HPV, most therapeutic vaccines target HPV oncoproteins E6 and E7. Several types of therapeutic HPV vaccine candidates have been developed including live-vector, protein, peptide, dendritic cell, and DNA-based vaccines. This chapter will review the commercially available prophylactic HPV vaccines and discuss the recent progress in the development of therapeutic HPV vaccines.

Broad Neutralization Responses Against Oncogenic Human Papillomaviruses Induced by a Minor Capsid L2 Polytope Genetically Incorporated Into Bacterial Ferritin Nanoparticles

Cervical cancer remains a global health burden despite the introduction of highly effective vaccines for the prophylaxis of causative human papillomavirus infection (HPV). Current efforts to eradicate cervical cancer focus on the development of broadly protective, cost-effective approaches. HPV minor capsid protein L2 is being recognized as a promising alternative to the major capsid protein L1 because of its ability to induce responses against a wider range of different HPV types. However, a major limitation of L2 as a source of cross-neutralizing epitopes is its lower immunogenicity compared to L1 when assembled into VLPs. Various approaches have been proposed to overcome this limitation, we developed and tested ferritin-based bio-nanoparticles displaying tandemly repeated L2 epitopes from eight different HPV types grafted onto the surface of Pyrococcus furiosus thioredoxin (Pf Trx). Genetic fusion of the Pf Trx-L2(8x) module to P. furiosus ferritin (Pf Fe) did not interfere with ferritin self-assembly into an octahedral structure composed by 24 protomers. In guinea pigs and mice, the ferritin super-scaffolded, L2 antigen induced a broadly neutralizing antibody response covering 14 oncogenic and two non-oncogenic HPV types. Immune-responsiveness lasted for at least one year and the resulting antibodies also conferred protection in a cervico-vaginal mouse model of HPV infection. Given the broad organism distribution of thioredoxin and ferritin, we also verified the lack of cross-reactivity of the antibodies elicited against the scaffolds with human thioredoxin or ferritin. Altogether, the results of this study point to P. furiosus ferritin nanoparticles as a robust platform for the construction of peptide-epitope-based HPV vaccines.

Human Papillomavirus Infections in Cervical Samples From HIV-Positive Women: Evaluation of the Presence of the Nonavalent HPV Genotypes and Genetic Diversity

Non-nonavalent vaccine (9v) Human papillomavirus (HPV) types have been shown to have high prevalence among HIV-positive women. Here, 1444 cervical samples were tested for HPV DNA positivity. Co-infections of the 9v HPV types with other HPV types were evaluated. The HPV81 L1 and L2 genes were used to investigate the genetic variability of antigenic epitopes. HPV-positive samples were genotyped using the HPVCLART2 assay. The L1 and L2 protein sequences were analyzed using a self-optimized prediction method to predict their secondary structure. Co-occurrence probabilities of the 9v HPV types were calculated. Non9v types represented 49% of the HPV infections; 31.2% of the non9v HPV types were among the low-grade squamous intraepithelial lesion samples, and 27.3% among the high-grade squamous intraepithelial lesion samples, and several genotypes were low risk. The co-occurrence of 9v HPV types with the other genotypes was not correlated with the filogenetic distance. HPV81 showed an amino-acid substitution within the BC loop (N75Q) and the FGb loop (T315N). In the L2 protein, all of the mutations were located outside antigenic sites. The weak cross-protection of the 9v types suggests the relevance of a sustainable and effective screening program, which should be implemented by HPV DNA testing that does not include only high-risk types.

Progress in L2-Based Prophylactic Vaccine Development for Protection against Diverse Human Papillomavirus Genotypes and Associated Diseases

The human papillomaviruses (HPVs) are a family of small DNA tumor viruses including over 200 genotypes classified by phylogeny into several genera. Different genera of HPVs cause ano-genital and oropharyngeal cancers, skin cancers, as well as benign diseases including skin and genital warts. Licensed vaccines composed of L1 virus-like particles (VLPs) confer protection generally restricted to the ≤9 HPV types targeted. Here, we examine approaches aimed at broadening the protection against diverse HPV types by targeting conserved epitopes of the minor capsid protein, L2. Compared to L1 VLP, L2 is less immunogenic. However, with appropriate presentation to the immune system, L2 can elicit durable, broadly cross-neutralizing antibody responses and protection against skin and genital challenge with diverse HPV types. Such approaches to enhance the strength and breadth of the humoral response include the display of L2 peptides on VLPs or viral capsids, bacteria, thioredoxin and other platforms for multimerization. Neither L2 nor L1 vaccinations elicit a therapeutic response. However, fusion of L2 with early viral antigens has the potential to elicit both prophylactic and therapeutic immunity. This review of cross-protective HPV vaccines based on L2 is timely as several candidates have recently entered early-phase clinical trials.

Rational design of a multi-valent human papillomavirus vaccine by capsomere-hybrid co-assembly of virus-like particles

The capsid of human papillomavirus (HPV) spontaneously arranges into a T = 7 icosahedral particle with 72 L1 pentameric capsomeres associating via disulfide bonds between Cys175 and Cys428. Here, we design a capsomere-hybrid virus-like particle (chVLP) to accommodate multiple types of L1 pentamers by the reciprocal assembly of single C175A and C428A L1 mutants, either of which alone encumbers L1 pentamer particle self-assembly. We show that co-assembly between any pair of C175A and C428A mutants across at least nine HPV genotypes occurs at a preferred equal molar stoichiometry, irrespective of the type or number of L1 sequences. A nine-valent chVLP vaccine-formed through the structural clustering of HPV epitopes-confers neutralization titers that are comparable with that of Gardasil 9 and elicits minor cross-neutralizing antibodies against some heterologous HPV types. These findings may pave the way for a new vaccine design that targets multiple pathogenic variants or cancer cells bearing diverse neoantigens.

Natural and vaccine-induced B cell-derived systemic and mucosal humoral immunity to human papillomavirus

Introduction: Human papillomavirus (HPV) are the causative agent of mucosal neoplasia. Both cervical, anal and oropharyngeal cancers incidence is constantly increasing, making the HPV infection, a significant worldwide concern. Together, the CD8+ T cytotoxic cell-mediated response and the HPV-specific antibody response control most of the HPV infections before the development of cancers.Areas covered: We searched the MEDLINE and EMBASE databases and identified 228 eligible studies from 1987 to 2019 which examines both naturally acquired and vaccine induced humoral immunity against HPV infection in female and male subjects from worldwide origin. Herein, we synthesize current knowledge on the features of systemic and mucosal humoral immunity against HPV. We discuss the issues of the balance between the viral clearance or the escape to the host immune response, the differences between natural and vaccine-induced HPV-specific antibodies and their neutralizing capability. We also discuss the protection afforded after natural infection or following prophylactic vaccination.Expert opinion: Understanding the antibody response induced by HPV infection has led to the design of first-generation prophylactic vaccines. Now, prophylactic vaccination induces protective and long-lasting antibody response which would also strengthened the natural moderate humoral response in people previously exposed to the virus.

Genetic engineering strategies for construction of multivalent chimeric VLPs vaccines

Introduction: Over the past two decades, virus-like particles (VLPs) have been developed as a new generation of vaccines against viral infections. Based on VLPs, chimeric VLPs (chi-VLPs) have been generated through genetic modifications or chemical couplings. For construction of multivalent chi-VLPs vaccines, multiple genetic engineering strategies are continuously being developed. Thus, it is important to provide a summary as reference for researchers in this field.Areas covered: The representative studies on the genetic engineered multivalent chi-VLPs are summarized and mainly focused on chimeric capsid VLPs and chimeric enveloped VLPs. The advantages and limitations of each strategy are also discussed at last, as well as opinions on platform choice and future directions of eVLPs vaccines.Expert opinion: The design of multivalent chi-VLPs vaccines needs to meet the following specifications: 1) the incorporated antigens are suggested to display on the exposed surface of chi-VLPs and do not have excessive adverse effects on the stability of chi-VLPs; 2) the chi-VLPs should elicit protective antibodies against the incorporated antigen as well as the source virus of VLPs. However, there is no requirement of retaining the antigenicity of VLPs when using VLPs solely as carriers for antigens display or drug delivery.

Baculovirus-Derived Vectors for Immunization and Therapeutic Applications

Baculoviruses are arthropod-specific, enveloped viruses with circular, supercoiled double-stranded deoxyribonucleic acid genomes. While many viruses are studied to seek solutions for their adverse impact on human, veterinary, and plant health, the study of baculoviruses was stimulated initially by their potential utility to control insect pests. Later, the utility of baculovirus as gene expression vectors was evidenced leading to numerous applications. Several strategies are employed to obtain recombinant viruses that express large quantities of heterologous proteins. A major step forward was the development of bacmid technology (the construction of bacterial artificial chromosomes containing the genome of the baculovirus) which allows the manipulation of the baculovirus genome in bacteria. With this technology, foreign genes can be introduced into the bacmid by homologous and site-directed recombination or by transposition. Baculoviruses have been used to explore fundamental questions in molecular biology such as the nature of programmed cell-death. Moreover, the ability of baculoviruses to transduce mammalian cells led to the consideration of their use as gene-therapy and vaccine vectors. Strategies for genetic engineering of baculoviruses have been developed to meet the requirements of new application areas. Display of foreign proteins on the surface of virions or in nucleocapsid structures, the assembly of expressed proteins to form virus-like particles or protein complexes have been explored and validated as vaccines. The aim of this chapter is to update the areas of application of the baculoviruses in protein expression, alternative vaccine designs and gene therapy of infectious diseases and genetic disorders. Finally, we review the baculovirus-derived products on the market and in the pipeline for biomedical and veterinary use.

Virus-like Particle-Based L2 Vaccines against HPVs: Where Are We Today?

Human papillomaviruses (HPVs) are the most common sexually transmitted infections worldwide. Ninety percent of infected individuals clear the infection within two years; however, in the remaining 10% of infected individuals, the infection(s) persists and ultimately leads to cancers (anogenital cancers and head and neck cancers) and genital warts. Fortunately, three prophylactic vaccines have been approved to protect against HPV infections. The most recent HPV vaccine, Gardasil-9 (a nonavalent vaccine), protects against seven HPV types associated with ~90% of cervical cancer and against two HPV types associated with ~90% genital warts with little cross-protection against non-vaccine HPV types. The current vaccines are based on virus-like particles (VLPs) derived from the major capsid protein, L1. The L1 protein is not conserved among HPV types. The minor capsid protein, L2, on the other hand, is highly conserved among HPV types and has been an alternative target antigen, for over two decades, to develop a broadly protective HPV vaccine. The L2 protein, unlike the L1, cannot form VLPs and as such, it is less immunogenic. This review summarizes current studies aimed at developing HPV L2 vaccines by multivalently displaying L2 peptides on VLPs derived from bacteriophages and eukaryotic viruses. Recent data show that a monovalent HPV L1 VLP as well as bivalent MS2 VLPs displaying HPV L2 peptides (representing amino acids 17–36 and/or consensus amino acids 69–86) elicit robust broadly protective antibodies against diverse HPV types (6/11/16/18/26/31/33/34/35/39/43/44/45/51/52/53/56/58/59/66/68/73) associated with cancers and genital warts. Thus, VLP-based L2 vaccines look promising and may be favorable, in the near future, over current L1-based HPV vaccines and should be explored further.

Advances in Designing and Developing Vaccines, Drugs and Therapeutic Approaches to Counter Human Papilloma Virus

Human papillomavirus (HPV) is a viral infection with skin-to-skin based transmission mode. HPV annually caused over 500,000 cancer cases including cervical, anogenital and oropharyngeal cancer among others. HPV vaccination has become a public-health concern, worldwide, to prevent the cases of HPV infections including precancerous lesions, cervical cancers, and genital warts especially in adolescent female and male population by launching national programs with international alliances. Currently, available prophylactic and therapeutic vaccines are expensive to be used in developing countries for vaccination programs. The recent progress in immunotherapy, biotechnology, recombinant DNA technology and molecular biology along with alternative and complementary medicinal systems have paved novel ways and valuable opportunities to design and develop effective prophylactic and therapeutic vaccines, drugs and treatment approach to counter HPV effectively. Exploration and more researches on such advances could result in the gradual reduction in the incidences of HPV cases across the world. The present review presents a current global scenario and futuristic prospects of the advanced prophylactic and therapeutic approaches against HPV along with recent patents coverage of the progress and advances in drugs, vaccines and therapeutic regimens to effectively combat HPV infections and its cancerous conditions.

Displaying 31RG-1 peptide on the surface of HPV16 L1 by use of a human papillomavirus chimeric virus-like particle induces cross-neutralizing antibody responses in mice

Current available human papillomavirus (HPV) vaccines are based on the major capsid protein L1 virus-like particles (VLPs), which mainly induce type-specific neutralizing antibodies against vaccine types. Continuing to add more types of VLPs in a vaccine raises the complexity and cost of production which remains the principal impediment to achieve broad implementation of HPV vaccines, particularly in developing regions. In this study, we constructed 16L1-31L2 chimeric VLP (cVLP) by displaying HPV31 L2 aa.17-38 on the h4 coil surface region of HPV16 L1, and assessed its immunogenicity in mouse model. We found that the cVLP adjuvanted with alum plus monophosphoryl lipid A could induce cross-neutralizing antibody responses against 16 out of 17 tested HPV pseudoviruses, and the titer against HPV16 was as high as that was induced by HPV16 L1VLP (titer > 10⁵), more importantly, titers over 10³ were observed against two HR-HPVs including HPV31 (titer, 2,200) and -59 (titer, 1,013), among which HPV59 was not covered by Gardasil-9, and medium or low titers of cross-neutralizing antibodies against other 13 tested HPV pseudoviruses were also observed. Our data demonstrate that 16L1-31L2 cVLP is a promising candidate for the formulation of broader spectrum HPV vaccines.

Minor Capsid Protein L2 Polytope Induces Broad Protection against Oncogenic and Mucosal Human Papillomaviruses

The amino terminus of the human papillomavirus (HPV) minor capsid protein L2 contains a major cross-neutralization epitope which provides the basis for the development of a broadly protecting HPV vaccine. A wide range of protection against different HPV types would eliminate one of the major drawbacks of the commercial, L1-based prophylactic vaccines. Previously, we have reported that insertion of the L2 epitope into a scaffold composed of bacterial thioredoxin protein generates a potent antigen inducing comprehensive protection against different animal and human papillomaviruses. We also reported, however, that although protection is broad, some oncogenic HPV types escape the neutralizing antibody response, if L2 epitopes from single HPV types are used as immunogen. We were able to compensate for this by applying a mix of thioredoxin proteins carrying L2 epitopes from HPV16, -31, and -51. As the development of a cost-efficient HPV prophylactic vaccines is one of our objectives, this approach is not feasible as it requires the development of multiple good manufacturing production processes in combination with a complex vaccine formulation. Here, we report the development of a thermostable thioredoxin-based single-peptide vaccine carrying an L2 polytope of up to 11 different HPV types. The L2 polytope antigens have excellent abilities in respect to broadness of protection and robustness of induced immune responses. To further increase immunogenicity, we fused the thioredoxin L2 polytope antigen with a heptamerization domain. In the final vaccine design, we achieve protective responses against all 14 oncogenic HPV types that we have analyzed plus the low-risk HPVs 6 and 11 and a number of cutaneous HPVs.IMPORTANCE Infections by a large number of human papillomaviruses lead to malignant and nonmalignant disease. Current commercial vaccines based on virus-like particles (VLPs) effectively protect against some HPV types but fail to do so for most others. Further, only about a third of all countries have access to the VLP vaccines. The minor capsid protein L2 has been shown to contain so-called neutralization epitopes within its N terminus. We designed polytopes comprising the L2 epitope amino acids 20 to 38 of up to 11 different mucosal HPV types and inserted them into the scaffold of thioredoxin derived from a thermophile archaebacterium. The antigen induced neutralizing antibody responses in mice and guinea pigs against 26 mucosal and cutaneous HPV types. Further, addition of a heptamerization domain significantly increased the immunogenicity. The final vaccine design comprising a heptamerized L2 8-mer thioredoxin single-peptide antigen with excellent thermal stability might overcome some of the limitations of the current VLP vaccines.

Broadly neutralizing antiviral responses induced by a single-molecule HPV vaccine based on thermostable thioredoxin-L2 multiepitope nanoparticles

Vaccines targeting the human papillomavirus (HPV) minor capsid protein L2 are emerging as chemico-physically robust and broadly protective alternatives to the current HPV (L1-VLP) vaccines. We have previously developed a trivalent L2 vaccine prototype exploiting Pyrococcus furiosus thioredoxin (PfTrx) as a thermostable scaffold for the separate presentation of three distinct HPV L2(20–38) epitopes. With the aim of achieving a highly immunogenic, yet simpler and more GMP-production affordable formulation, we report here on a novel thermostable nanoparticle vaccine relying on genetic fusion of PfTrx-L2 with the heptamerizing coiled-coil polypeptide OVX313. A prototype HPV16 monoepitope version of this nanoparticle vaccine (PfTrx-L2-OVX313; median radius: 8.6 ± 1.0 nm) proved to be approximately 10-fold more immunogenic and with a strikingly enhanced cross-neutralization capacity compared to its monomeric counterpart. Vaccine-induced (cross-)neutralizing responses were further potentiated in a multiepitope derivative displaying eight different L2(20–38) epitopes, which elicited neutralizing antibodies against 10 different HPVs including three viral types not represented in the vaccine. Considering the prospective safety of the PfTrx scaffold and of the OVX313 heptamerization module, PfTrx-OVX313 nanoparticles lend themselves as robust L2-based immunogens with a high translational potential as a 3^rd generation HPV vaccine, but also as a novel and extremely versatile peptide-antigen presentation platform.

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.

Human papillomavirus 16L1-58L2 chimeric virus-like particles elicit durable neutralizing antibody responses against a broad-spectrum of human papillomavirus types

The neutralizing antibodies elicited by human papillomavirus (HPV) major capsid protein L1 virus-like particle (VLP)-based vaccines are largely type-specific. An HPV vaccine inducing cross-neutralizing antibodies broadly will be cost-effective and of great value. To this end, we constructed HPV16L1-58L2 chimeric VLP (cVLP) by displaying HPV58 L2 aa.16-37 on the DE surface region of HPV16 L1. We found that vaccination with the HPV16L1-58L2 cVLP formulated with alum plus monophosphoryl lipid A (Alum-MPL) adjuvant elicited robust neutralizing antibodies in both mice and rabbits against all tested HPV types including HPV16/31/33/35/52/58 (genus α9), HPV18/39/45/59/68 (genus α7), HPV6/11 (genus α10), HPV2/27/57 (genus α4), and HPV5 (genus β1). Importantly, the cross-neutralizing antibody response was maintained at least 82 weeks in mice or 42 weeks in rabbits, and complete protection against HPV58 was observed at week 85 in mice. Our data demonstrate that HPV16L1-58L2 cVLP is an excellent pan-HPV vaccine candidate.

Chimeric L2-Based Virus-Like Particle (VLP) Vaccines Targeting Cutaneous Human Papillomaviruses (HPV)

Common cutaneous human papillomavirus (HPV) types induce skin warts, whereas species beta HPV are implicated, together with UV-radiation, in the development of non-melanoma skin cancer (NMSC) in immunosuppressed patients. Licensed HPV vaccines contain virus-like particles (VLP) self-assembled from L1 major capsid proteins that provide type-restricted protection against mucosal HPV infections causing cervical and other ano-genital and oro-pharyngeal carcinomas and warts (condylomas), but do not target heterologous HPV. Experimental papillomavirus vaccines have been designed based on L2 minor capsid proteins that contain type-common neutralization epitopes, to broaden protection to heterologous mucosal and cutaneous HPV types. Repetitive display of the HPV16 L2 cross-neutralization epitope RG1 (amino acids (aa) 17-36) on the surface of HPV16 L1 VLP has greatly enhanced immunogenicity of the L2 peptide. To more directly target cutaneous HPV, L1 fusion proteins were designed that incorporate the RG1 homolog of beta HPV17, the beta HPV5 L2 peptide aa53-72, or the common cutaneous HPV4 RG1 homolog, inserted into DE surface loops of HPV1, 5, 16 or 18 L1 VLP scaffolds. Baculovirus expressed chimeric proteins self-assembled into VLP and VLP-raised NZW rabbit immune sera were evaluated by ELISA and L1- and L2-based pseudovirion (PsV) neutralizing assays, including 12 novel beta PsV types. Chimeric VLP displaying the HPV17 RG1 epitope, but not the HPV5L2 aa53-72 epitope, induced cross-neutralizing humoral immune responses to beta HPV. In vivo cross-protection was evaluated by passive serum transfer in a murine PsV challenge model. Immune sera to HPV16L1-17RG1 VLP (cross-) protected against beta HPV5/20/24/38/96/16 (but not type 76), while antisera to HPV5L1-17RG1 VLP cross-protected against HPV20/24/96 only, and sera to HPV1L1-4RG1 VLP cross-protected against HPV4 challenge. In conclusion, RG1-based VLP are promising next generation vaccine candidates to target cutaneous HPV infections.

Recent advances in preclinical model systems for papillomaviruses

Preclinical model systems to study multiple features of the papillomavirus life cycle have greatly aided our understanding of Human Papillomavirus (HPV) biology, disease progression and treatments. The challenge to studying HPV in hosts is that HPV along with most PVs are both species and tissue restricted. Thus, fundamental properties of HPV viral proteins can be assessed in specialized cell culture systems but host responses that involve innate immunity and host restriction factors requires preclinical surrogate models. Fortunately, there are several well-characterized and new animal models of papillomavirus infections that are available to the PV research community. Old models that continue to have value include canine, bovine and rabbit PV models and new rodent models are in place to better assess host-virus interactions. Questions arise as to the strengths and weaknesses of animal PV models for HPV disease and how accurately these preclinical models predict malignant progression, vaccine efficacy and therapeutic control of HPV-associated disease. In this review, we examine current preclinical models and highlight the strengths and weaknesses of the various models as well as provide an update on new opportunities to study the numerous unknowns that persist in the HPV research field.

Developments in L2-based human papillomavirus (HPV) vaccines

Infections with sexually transmitted high-risk Human Papillomavirus (hrHPV), of which there are at least 15 genotypes, are responsible for a tremendous disease burden by causing cervical, and subsets of other ano-genital and oro-pharyngeal carcinomas, together representing 5% of all cancer cases worldwide. HPV subunit vaccines consisting of virus-like particles (VLP) self-assembled from major capsid protein L1 plus adjuvant have been licensed. Prophylactic vaccinations with the 2-valent (HPV16/18), 4-valent (HPV6/11/16/18), or 9-valent (HPV6/11/16/18/31/33/45/52/58) vaccine induce high-titer neutralizing antibodies restricted to the vaccine types that cause up to 90% of cervical carcinomas, a subset of other ano-genital and oro-pharyngeal cancers and 90% of benign ano-genital warts (condylomata). The complexity of manufacturing multivalent L1-VLP vaccines limits the number of included VLP types and thus the vaccines' spectrum of protection, leaving a panel of oncogenic mucosal HPV unaddressed. In addition, current vaccines do not protect against cutaneous HPV types causing benign skin warts, or against beta-papillomavirus (betaPV) types implicated in the development of non-melanoma skin cancer (NMSC) in immunosuppressed patients. In contrast with L1-VLP, the minor capsid protein L2 contains type-common epitopes that induce low-titer yet broadly cross-neutralizing antibodies to heterologous PV types and provide cross-protection in animal challenge models. Efforts to increase the low immunogenicity of L2 (poly)-peptides and thereby to develop broader-spectrum HPV vaccines are the focus of this review.