Immunological analyses of human papillomavirus capsids

Global evaluation of lineage-specific human papillomavirus capsid antigenicity using antibodies elicited by natural infection

Human Papillomavirus (HPV) type variants have been classified into lineages and sublineages based upon their whole genome sequence. Here we have examined the specificity of antibodies generated following natural infection with lineage variants of oncogenic types (HPV16, 18, 31, 33, 45, 52 and 58) by testing serum samples assembled from existing archives from women residing in Africa, The Americas, Asia or Europe against representative lineage-specific pseudoviruses for each genotype. We have subjected the resulting neutralizing antibody data to antigenic clustering methods and created relational antigenic profiles for each genotype to inform the delineation of lineage-specific serotypes. For most genotypes, there was evidence of differential recognition of lineage-specific antigens and in some cases of a sufficient magnitude to suggest that some lineages should be considered antigenically distinct within their respective genotypes. These data provide compelling evidence for a degree of lineage specificity within the humoral immune response following natural infection with oncogenic HPV.

Exploring the utility of FTS as a bonafide binding partner for EGFR: A potential drug target for cervical cancer

Establishment of human papilloma virus (HPV) infection and its progression to cervical cancer (CC) requires the participation of epidermal growth factor (EGF) receptor (EGFR) and fused toes homolog (FTS). This review is an attempt to understand the structure-function relationship between FTS and EGFR as a tool for the development of newer CC drugs. Motif analysis was performed using national center for biotechnology information (NCBI), kyoto encyclopedia of genes and genomes (KEGG), simple modular architecture research tool (SMART) and multiple expectation maximizations for motif elicitation (MEME) database. The secondary and tertiary structure prediction of FTS was performed using DISOPRED3 and threading assembly, respectively. A positive correlation was found between the transcript levels of FTS and EGFR. Amino acids responsible for interaction between EGFR and FTS were determined. The nine micro-RNAs (miRNAs) that regulates the expression of FTS were predicted using Network Analyst 3.0 database. hsa-miR-629-5p and hsa-miR-615-3p are identified as significant positive and negative regulators of FTS gene expression. This review opens up new avenues for the development of CC drugs which interfere with the interaction between FTS and EGFR.

Induction of cross-neutralizing antibodies by sequential immunization with heterologous papillomavirus L1VLPs and its implications for HPV prophylactic vaccines

Sequential immunization with antigens from different strains of HIV-1, influenza viruses or dengue viruses induced cross-neutralizing antibodies and enhanced the antibody responses against previous antigens. The characteristics of neutralizing antibodies induced by sequential immunization with different types of human papillomavirus (HPV) L1 virus-like particles (L1VLPs) are unclear. In this study, mice were primed with one or two types (HPV-16 or HPV16/18) of L1VLPs, then boosted sequentially with HPV6/18/45/11/31/58 or HPV6/45/11/31/58 L1VLPs, and sera were analyzed with HPV pseudovirus-based neutralization assay. The results showed that neutralizing activities against earlier immunized vaccine types were enhanced gradually by subsequent immunizations, and low levels of neutralizing activities against nonvaccine types (HPV33/35/52/59/68) were also observed. After absorbing the immune sera with vaccine-type (HPV16/18/45) L1VLPs, neutralizing activities against tested priming and boosting types (HPV16/18/58) decreased significantly, and that against nonvaccine type (HPV-33) was also partially eliminated. Moreover, neutralizing activities against vaccine types (HPV16/58) were significantly reduced after absorbing with nonvaccine-type VLPs (HPV33/52). These data suggest that cross-neutralizing epitopes exist among different HPV L1VLPs. The cross-neutralizing activities against nonvaccine types and the enhanced neutralizing activities against earlier immunized vaccine types may result from sequential boosting with these cross-neutralizing epitopes. These observations support early vaccination with more types of L1VLPs derived from HPVs that cause a serious threat to the population.

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.

Production and characterization of virus-like particles of grapevine fanleaf virus presenting L2 epitope of human papillomavirus minor capsid protein

Background

Virus-like particle (VLP) platform represents a promising approach for the generation of efficient and immunogenic subunit vaccines. Here, the feasibility of using grapevine fanleaf virus (GFLV) VLPs as a new carrier for the presentation of human papillomavirus (HPV) L2 epitope was studied. To achieve this goal, a model of the HPV L2 epitope secondary structure was predicted and its insertion within 5 external loops in the GFLV capsid protein (CP) was evaluated.

Results

The epitope sequence was genetically inserted in the αB-αB^” domain C of the GFLV CP, which was then over-expressed in Pichia pastoris and Escherichia coli. The highest expression yield was obtained in E. coli. Using this system, VLP formation requires a denaturation-refolding step, whereas VLPs with lower production yield were directly formed using P. pastoris, as confirmed by electron microscopy and immunostaining electron microscopy. Since the GFLV L2 VLPs were found to interact with the HPV L2 antibody under native conditions in capillary electrophoresis and in ELISA, it can be assumed that the inserted epitope is located at the VLP surface with its proper ternary structure.

Conclusions

The results demonstrate that GFLV VLPs constitute a potential scaffold for surface display of the epitope of interest.

Development and characterization of an HPV18 detection kit using two novel HPV18 type-specific monoclonal antibodies

Background

HPV 18 is one of the most prevalent oncogenic types, only second to HPV 16, and included in the licensed vaccines on the market. In this study, we describe the production and characterization of a panel of monoclonal antibodies (mAb) to HPV18.

Methods

The immunocompetence of 1B1 and 4C2 mAbs for HPV L1 protein was evaluated by SDS-PAGE analysis, neutralization assays, affinity identification, and ELISA. The 1B1 and 4C2 genes were sequenced and analyzed. Finally, the detection kit with the two mAbs was assessed for linearity, repeatability and specificity.

Results

Both mAbs specifically recognized HPV18 L1 and virus-like particles (VLPs). These mAbs are conformation-neutralizing antibodies that have high affinity and type specificity. Based on these characteristics of these mAbs, we developed an ELISA kit for specifically detecting HPV 18 antigen. We showed that this kit displayed good linearity, repeatability and sensitivity for detecting HPV18 L1 pentamer and HPV18 VLP.

Conclusions

We characterized two monoclonal neutralizing antibodies for HPV L1 protein, and developed an ELISA kit for specifically detecting HPV 18 antigen. This newly developed kit can be used to monitor the potency of HPV vaccines throughout the entire production process as well as preliminary analysis of HPV18 infections.

Eradicating HPV-Associated Cancer Through Immunization: A Glass Half Full…

The human papillomavirus (HPV) is an important causal agent of premalignant cervical epithelial changes and cervical cancers. These cancers account for ∼5% of all cancers globally and kill more than a quarter million women annually. HPV infections also associate with certain anogenital and oropharyngeal cancers. Events leading to the development of HPV vaccines to prevent associated cancers are described, with a further discussion of goals that must be met to achieve full virus eradication.

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.

Durable immunity to oncogenic human papillomaviruses elicited by adjuvanted recombinant Adeno-associated virus-like particle immunogen displaying L2 17-36 epitopes

Vaccination with the minor capsid protein L2, notably the 17-36 neutralizing epitope, induces broadly protective antibodies, although the neutralizing titers attained in serum are substantially lower than for the licensed L1 VLP vaccines. Here we examine the impact of other less reactogenic adjuvants upon the induction of durable neutralizing serum antibody responses and protective immunity after vaccination with HPV16 and HPV31 L2 amino acids 17-36 inserted at positions 587 and 453 of VP3, respectively, for surface display on Adeno-Associated Virus 2-like particles [AAVLP (HPV16/31L2)]. Mice were vaccinated three times subcutaneously with AAVLP (HPV16/31L2) at two week intervals at several doses either alone or formulated with alum, alum and MPL, RIBI adjuvant or Cervarix. The use of adjuvant with AAVLP (HPV16/31L2) was necessary in mice for the induction of L2-specific neutralizing antibody and protection against vaginal challenge with HPV16. While use of alum was sufficient to elicit durable protection (>3 months after the final immunization), antibody titers were increased by addition of MPL and RIBI adjuvants. To determine the breadth of immunity, rabbits were immunized three times with AAVLP (HPV16/31L2) either alone, formulated with alum±MPL, or RIBI adjuvants, and after serum collection, the animals were concurrently challenged with HPV16/31/35/39/45/58/59 quasivirions or cottontail rabbit papillomavirus (CRPV) at 6 or 12 months post-immunization. Strong protection against all HPV types was observed at both 6 and 12 months post-immunization, including robust protection in rabbits receiving the vaccine without adjuvant. In summary, vaccination with AAVLP presenting HPV L2 17-36 epitopes at two sites on their surface induced cross-neutralizing serum antibody, immunity against HPV16 in the genital tract, and long-term protection against skin challenge with the 7 most common oncogenic HPV types when using a clinically relevant adjuvant.

Chitosan-Poly (I:C)-PADRE Based Nanoparticles as Delivery Vehicles for Synthetic Peptide Vaccines

The safety and precision of peptide antigens has prompted the search for adjuvants capable of increasing the immune response against these intrinsically poorly immunogenic antigens. The integration of both immunostimulants and peptide antigens within nanometric delivery systems for their co-delivery to immune cells is a promising vaccination strategy. With this in mind, the potential synergistic effect of the immunostimulant poly (I:C) (pIC) and a T-Helper peptide (PADRE), integrated into a chitosan (CS) based nanostructure, was explored. The value of this nanostructured combination of materials was assessed for a peptide antigen (1338aa) derived from the HPV-16 L2 protein. These nanoparticles, produced by ionic gelation technique, exhibited a nanometric size (<300 nm), a high positive surface charge (>40 mV) and high pIC association efficiency (>96%). They also showed capacity for the association of both the 1338aa and PADRE peptides. The influence of the presence of pIC and PADRE in the nanocomposition, as well as that of the peptide presentation form (encapsulated versus surface adsorbed) on the antibody induction was evaluated in a preliminary in vivo study. The data obtained highlights the possibility to engineer nanoparticles through the rational combination of a number of adjuvant molecules together with the antigen.

Observations on the expression of human papillomavirus major capsid protein in HeLa cells

Background

The goal of this study was to identify the nature of the inclusion bodies that have been found in HeLa cells (cervical cancer immortal cell line) by electron microscope and to determine whether the major capsid protein (L1) of human papillomavirus (HPV) can be expressed in HPV-positive uterine cervix cancer cells.

Methods

HPV L1 protein expression in HeLa cells was detected with anti-HPV L1 multivalent mice monoclonal antibody and rabbit polyclonal anti-HPV L1 antibody by ELISA, light microscope immunohistochemistry, electron microscope immunocytochemistry and Western blotting assays. Reverse transcriptional PCR (RT-PCR) was performed to detect the transcription of L1 mRNA in HeLa cells. The immortalized human keratinocyte HeCat was used as the negative control.

Results

HPV L1 proteins reacted positively in the lysate of HeLa cells by ELISA assays. HRP labeled light microscope immunohistochemistry assay showed that there was a strong HPV L1 positive reaction in HeLa cells. Under the electron microscope, irregular shaped inclusion bodies, assembled by many small and uniform granules, had been observed in the cytoplasm of some HeLa cells. These granules could be labeled by the colloidal gold carried by HPV L1 antibody. The Western blotting assay showed that there was a L1 reaction strap at 80–85 kDa in the HeLa cell lysates, hence demonstrating the existence of HPV18 L1 in HeLa cells. RT-PCR assay showed that the L1 mRNA was transcribed in HeLa cells.

Conclusions

The inclusion bodies found in the cytoplasm of HeLa cells are composed of HPV18 L1 protein. Since HeLa cell line is a type of cervical cancer cells, this implies that HeLa cells have the ability to express HPV L1 proteins.

Naturally Occurring Capsid Protein Variants of Human Papillomavirus Genotype 31 Represent a Single L1 Serotype

We investigated naturally occurring variation within the major (L1) and minor (L2) capsid proteins of oncogenic human papillomavirus (HPV) genotype 31 (HPV31) to determine the impact on capsid antigenicity. L1L2 pseudoviruses (PsVs) representing the three HPV31 variant lineages, variant lineages A, B, and C, exhibited comparable particle-to-infectivity ratios and morphologies. Lineage-specific L1L2 PsVs demonstrated subtle differences in susceptibility to neutralization by antibodies elicited following vaccination or preclinical L1 virus-like particle (VLP) immunization or by monoclonal antibodies; however, these differences were generally of a low magnitude. These data indicate that the diagnostic lineage-specific single nucleotide polymorphisms within the HPV31 capsid genes have a limited effect on L1 antibody-mediated neutralization and that the three HPV31 variant lineages belong to a single L1 serotype. These data contribute to our understanding of HPV L1 variant antigenicity.

IMPORTANCE

The virus coat (capsid) of the human papillomavirus contains major (L1) and minor (L2) capsid proteins. These proteins facilitate host cell attachment and viral infectivity and are the targets for antibodies which interfere with these events. In this study, we investigated the impact of naturally occurring variation within these proteins upon susceptibility to viral neutralization by antibodies induced by L1 VLP immunization. We demonstrate that HPV31 L1 and L2 variants exhibit similar susceptibility to antibody-mediated neutralization and that for the purposes of L1 VLP-based vaccines, these variant lineages represent a single serotype.

Pre-clinical immunogenicity of human papillomavirus alpha-7 and alpha-9 major capsid proteins

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Comprehensive pre-clinical immunogenicity evaluation of HPV L1 major capsid protein.

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Majority neutralizing antibody response was genotype-specific.

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Reciprocal cross-neutralization between some Alpha-7 and Alpha-9 genotypes.

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Tetravalent formulation (HPV16/18/39/58) induced broadly neutralizing antibodies.

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These data improve our understanding of the antigenic diversity of the L1 protein.

Human papillomavirus (HPV) vaccines confer protection against the oncogenic genotypes HPV16 and HPV18 through the generation of type-specific neutralizing antibodies raised against the constituent virus-like particles (VLP) based upon the major capsid proteins (L1) of these genotypes. The vaccines also confer a degree of cross-protection against some genetically related types from the Alpha-9 (HPV16-like: HPV31, HPV33, HPV35, HPV52, HPV58) and Alpha-7 (HPV18-like: HPV39, HPV45, HPV59, HPV68) species groups. The mechanism of cross-protection is unclear but may involve antibodies capable of recognizing shared inter-genotype epitopes. The relationship(s) between the genetic and antigenic diversity of the L1 protein, particularly for non-vaccine genotypes, is poorly understood.

We carried out a comprehensive evaluation of the immunogenicity of L1 VLP derived from genotypes within the Alpha-7 and Alpha-9 species groups in New Zealand White rabbits and used L1L2 pseudoviruses as the target antigens in neutralization assays.

The majority antibody response against L1 VLP was type-specific, as expected, but several instances of robust cross-neutralization were nevertheless observed including between HPV33 and HPV58 within the Alpha-9 species and between HPV39, HPV59 and HPV68 in the Alpha-7 species. Immunization with an experimental tetravalent preparation comprising VLP based upon HPV16, HPV18, HPV39 and HPV58 was capable of generating neutralizing antibodies against all the Alpha-7 and Alpha-9 genotypes. Competition of HPV31 and HPV33 cross-neutralizing antibodies in the tetravalent sera confirmed that these antibodies originated from HPV16 and HPV58 VLP, respectively, and suggested that they represent minority specificities within the antibody repertoire generated by the immunizing antigen. These data improve our understanding of the antigenic diversity of the L1 protein per se and may inform the rational design of a next generation vaccine formulation based upon empirical data.

Antibody detection in tear samples as a surrogate to monitor host immunity against papillomavirus infections in vaccinated and naturally infected hosts

Monitoring serum antibodies against natural infections or after immunizations has been a standard clinical diagnostic procedure. However, collecting blood samples requires trained personnel, and may cause discomfort and increase the risk of complications. In this study, we investigated whether tear samples could serve as a surrogate for serum samples to measure specific antibodies. A widely used preclinical cottontail rabbit papillomavirus (CRPV)/rabbit model has been a surrogate model for high-risk human papillomavirus (HPV) infections. New Zealand white rabbits, either naturally infected with CRPV or immunized with two clinically available HPV vaccines (Gardasil and Cervarix), were examined for antibody generation in both tear and serum samples. We demonstrated that antibodies were detectable in tears from both naturally infected as well as vaccinated animals. Overall, the antibody levels in tears were ~10-fold lower than those from the corresponding serum samples, but background noise was lower in tear samples. The isotypes of antibodies in tears were predominantly IgA and IgG. These findings showed clearly that tears could be a surrogate for serum samples for monitoring antibody responses. As collecting tears causes no discomfort and poses no risk to patients, it represents a novel and promising method for monitoring future HPV epidemiological studies as well as for use in clinical practice.

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.

Fusion of HPV L1 into Shigella surface IcsA: a new approach in developing live attenuated Shigella-HPV vaccine

Despite the success of L1 virus-like particles (VLPs) vaccines in prevention of high-risk human papillomavirus (HPV) infection and cervical cancer, extraordinary high cost for the complete vaccination has impeded widespread use of the vaccine in resource-poor countries, where cervical cancers impose greater challenge. Presentation of HPV L1 protein by attenuated pathogenic bacteria through natural infection provides a promising low-cost and convenient alternative. Here, we describe the construction and characterization of attenuated L1-expressing Shigella vaccine candidate, by fusion of L1 into the autotransporter of Shigella sonnei, IcsA, an essential virulence factor responsible for actin-based motility. The functional α domain of IcsA was replaced by codon-optimized L1 gene with independent open reading frames (ORFs) facilitated by suicide vector pJCB12. The L1 gene was stabilized in the genome of recombinant S. sonnei with protein expression and assembly of VLPs in the bacterial cytoplasm. Through conjunctival route vaccination in guinea pigs, L1-containing S. sonnei was able to elicit specific immune response to HPV16 L1 VLP as well as bacterial antigens. The results demonstrated the feasibility of the novel stratagem to develop prophylactic Shigella-HPV vaccines.

Monoclonal antibodies recognizing cross-neutralization epitopes in human papillomavirus 16 minor capsid protein L2

Antisera induced by immunization of rabbits with the synthetic peptide P56/75, which has the amino acid (aa) sequence from aa56 to aa75 of HPV16 L2, neutralize pseudovirions and raft-virions of multiple high-risk HPV types, indicating that cross-neutralization epitopes are present in the aa56-75 region. We generated two mouse monoclonal antibodies (MAb): MAb13B and MAb24B recognizing the regions of aa64-73 and aa58-64, respectively. The neutralization assay using pseudovirions of HPV16, 18, 31, 33, 35, 51, 52 and 58 showed that MAb13B neutralized HPV16, 18, and 51, and MAb24B neutralized all the types tested. The mixture of MAb13B and MAb24B neutralized HPV16, 18, and 51 pseudovirions more efficiently than each of the MAbs alone. The data indicate that there are at least two cross-neutralization epitopes in the aa56-75 region and that an antigen capable of presenting the two cross-neutralization epitopes would be a good vaccine candidate for a broad-spectrum of HPVs.

Host-cell factors involved in papillomavirus entry

Papillomaviruses infect skin and mucosa where they induce warts and cancers. For entry to occur, they sequentially engage numerous host proteins, allowing them to deliver their genetic information into target cells. This multistep process starts with initial binding via its L1 major capsid protein, followed by structural changes of the capsid on the cell surface, engagement of different receptors, and endocytosis. The post-entry phase includes capsid disassembly, endosomal escape of a complex of the minor capsid protein L2 and the viral genome, its transport into the nucleus, and accumulation at nuclear substructures. This review summarizes the current knowledge of the papillomavirus entry pathway and the role of cellular proteins involved in this course of events.

Mother-infant transfer of anti-human papillomavirus (HPV) antibodies following vaccination with the quadrivalent HPV (type 6/11/16/18) virus-like particle vaccine

The exploratory immunogenicity objective of this analysis was to characterize the titer of vaccine human papillomavirus (HPV)-type immunoglobulins in both peripartum maternal blood and the cord blood of infants born to women who received blinded therapy. Data were derived from a randomized, placebo-controlled, double-blind safety, immunogenicity, and efficacy study (protocol 019; NCT00090220). This study enrolled 3,819 women between the ages of 24 and 45 years from 38 international study sites between 18 June 2004 and 30 April 2005. Data in the current analysis are from subjects enrolled in Philippines and Thailand. For each of HPV types 6, 11, 16, and 18, maternal anti-HPV was found in cord blood samples. Furthermore, HPV titers in cord blood samples were highly positively correlated with maternal HPV titers. Additionally, there were instances when anti-HPV antibodies were no longer detectable in maternal serum samples and yet were detected in matched cord blood samples. These results demonstrate that quadrivalent HPV (qHPV) vaccine-induced antibodies cross the placenta and could potentially provide some benefit against vaccine-type HPV infection and related diseases such as recurrent respiratory papillomatosis.

Oral administration of HPV-16 L2 displayed on Lactobacillus casei induces systematic and mucosal cross-neutralizing effects in Balb/c mice

The human papillomavirus (HPV) minor capsid protein, L2, is a good candidate for prophylactic vaccine development because L2-specific antibodies have cross-neutralizing activity against diverse HPV types. Here, we developed a HPV mucosal vaccine candidate using the poly-γ-glutamic acid synthetase A (pgsA) protein to display a partial HPV-16 L2 protein (N-terminal 1-224 amino acid) on the surface of Lactobacillus casei (L. casei). The oral immunization with L. casei-L2 induced productions of L2-specific serum IgG and vaginal IgG and IgA in Balb/c mice. To examine cross-neutralizing activity, we used a sensitive high-throughput neutralization assay based on HPV-16, -18, -45, -58, and bovine papillomavirus 1 (BPV1) pseudovirions. Our results revealed that mice vaccinated with L. casei-L2 not only generated neutralizing antibodies against HPV-16, but they also produced antibodies capable of cross-neutralizing the HPV-18, -45, and -58 pseudovirions. Consistent with previous reports, vaccination with HPV-16 L1 virus-like particles (VLPs) failed to show cross-neutralizing activity. Finally, we found that oral administration of L. casei-L2 induced significant neutralizing activities against genital infection by HPV-16, -18, -45, and -58 pseudovirions encoding a fluorescence reporter gene. These results collectively indicate that oral administration of L2 displayed on L. casei induces systemic and mucosal cross-neutralizing effects in mice.

Enterovirus type 71 neutralizing antibodies in the serum of macaque monkeys immunized with EV71 virus-like particles

Enterovirus type 71 (EV71) is a virulent form of enteroviruses causing hospitalizations for children less than three years of age. Currently there are no anti-viral therapies or vaccines available for EV71. Due to the high risk of poliomyelitis-like paralysis and fatal encephalitis, an effective vaccine to EV71 could potentially prevent virus-induced morbidity and mortality. In this study, we first tested a potential EV71 vaccine candidate based on virus-like particles (VLP). We vaccinated macaque monkeys to validate the immunogenicity of the VLP vaccine to EV71. We detected the VLP or EV71-specific antibodies, neutralization titers, ELISPOT, and T cell response to find their immune responses to EV71. When the VLP vaccine adjuvanted with alum was given to macaque monkeys, these monkeys developed both specific humoral and cellular immune responses to EV71. Despite lower neutralizing antibodies to EV71 were found in sera of VLP-immunized monkeys than monkeys vaccinated with inactivated EV71, VLP-based vaccine generated a memory immune response to EV71. Hence, VLP-based EV71 vaccine is a potential vaccine against EV71 infection.

Cross-protective efficacy of HPV-16/18 AS04-adjuvanted vaccine against cervical infection and precancer caused by non-vaccine oncogenic HPV types: 4-year end-of-study analysis of the randomised, double-blind PATRICIA trial

BACKGROUND

We evaluated the efficacy of the human papillomavirus HPV-16/18 AS04-adjuvanted vaccine against non-vaccine oncogenic HPV types in the end-of-study analysis after 4 years of follow-up in PATRICIA (PApilloma TRIal against Cancer In young Adults).

METHODS

Healthy women aged 15-25 years with no more than six lifetime sexual partners were included in PATRICIA irrespective of their baseline HPV DNA status, HPV-16 or HPV-18 serostatus, or cytology. Women were randomly assigned (1:1) to HPV-16/18 vaccine or a control hepatitis A vaccine, via an internet-based central randomisation system using a minimisation algorithm to account for age ranges and study sites. The study was double-blind. The primary endpoint of PATRICIA has been reported previously; the present analysis evaluates cross-protective vaccine efficacy against non-vaccine oncogenic HPV types in the end-of-study analysis. Analyses were done for three cohorts: the according-to-protocol cohort for efficacy (ATP-E; vaccine n=8067, control n=8047), total vaccinated HPV-naive cohort (TVC-naive; no evidence of infection with 14 oncogenic HPV types at baseline, approximating young adolescents before sexual debut; vaccine n=5824, control n=5820), and the total vaccinated cohort (TVC; all women who received at least one vaccine dose, approximating catch-up populations that include sexually active women; vaccine n=9319, control=9325). Vaccine efficacy was evaluated against 6-month persistent infection, cervical intraepithelial neoplasia grade 2 or greater (CIN2+) associated with 12 non-vaccine HPV types (individually or as composite endpoints), and CIN3+ associated with the composite of 12 non-vaccine HPV types. This study is registered with ClinicalTrials.gov, number NCT00122681.

FINDINGS

Consistent vaccine efficacy against persistent infection and CIN2+ (with or without HPV-16/18 co-infection) was seen across cohorts for HPV-33, HPV-31, HPV-45, and HPV-51. In the most conservative analysis of vaccine efficacy against CIN2+, where all cases co-infected with HPV-16/18 were removed, vaccine efficacy was noted for HPV-33 in all cohorts, and for HPV-31 in the ATP-E and TVC-naive. Vaccine efficacy against CIN2+ associated with the composite of 12 non-vaccine HPV types (31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66, and 68), with or without HPV-16/18 co-infection, was 46·8% (95% CI 30·7-59·4) in the ATP-E, 56·2% (37·2-69·9) in the TVC-naive, and 34·2% (20·4-45·8) in the TVC. Corresponding values for CIN3+ were 73·8% (48·3-87·9), 91·4% (65·0-99·0), and 47·5% (22·8-64·8).

INTERPRETATION

Data from the end-of-study analysis of PATRICIA show cross-protective efficacy of the HPV-16/18 vaccine against four oncogenic non-vaccine HPV types-HPV-33, HPV-31, HPV-45, and HPV-51-in different trial cohorts representing diverse groups of women.

FUNDING

GlaxoSmithKline Biologicals.

The preparation of human papillomavirus type 58 vaccine and exploring its biological activity and immunogenicity in vitro

OBJECTIVES

Human papillomavirus (HPV) type 58 is the second most prevalent virus infection among Chinese women. To develop an HPV58 vaccine that combines both prophylactic and therapeutic functions, we generate a chimeric virus-like particle (cVLP).

METHODS

The cVLPs contain both whole length L1 and parts of E7 peptides either from E7 amino acids (aa) 50 to aa72 or from E7 aa4 to aa12. The HPV58 L1-E7aa50-72 and L1-E7aa4-12 fusion proteins were revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and confirmed by Western blot (Supplementary Digital Content 1, http://links.lww.com/IGC/A40, which shows alignment of the protein sequence between HPV58 L1-E7aa50-72/4-12 and standard sequence). Protein folding and location of cVLPs were identified by transmission electron microscope. The immunogenicity of the fusion protein was tested by enzyme-linked immunospot assay.

RESULTS

Transmission electron microscope showed that the fusion protein formed cVLPs by self-assembly and the majority of particles located in the nucleus of the sf-9 insect cells. The cVLPs displayed a strong ability to agglutinate erythrocytes, which is distinguished from the parental VLPs. In addition, the purified HPV58 L1-E7aa50-72 or L1-E7aa4-12 fusion protein induced significant numbers of interferon γ-expressing E7aa50-72- or E7aa4-12-specific CD8 T cells.

DISCUSSION

Our results indicate that the insertion of the E7aa50-72 or E7aa4-12 peptides behind L1 did not disrupt the assembly of cVLPs and provided potent immunogenicity and bioactivity, which created a powerful basis for further preparations of HPV58 vaccines with prophylactic and therapeutic effects for the treatment of HPV58-related diseases including cervical cancer.

In vivo mechanisms of vaccine-induced protection against HPV infection

Using a human papillomavirus (HPV) cervicovaginal murine challenge model, we microscopically examined the in vivo mechanisms of L1 virus-like particle (VLP) and L2 vaccine-induced inhibition of infection. In vivo HPV infection requires an initial association with the acellular basement membrane (BM) to induce conformational changes in the virion that permit its association with the keratinocyte cell surface. By passive transfer of immune serum, we determined that anti-L1 antibodies can interfere with infection at two stages. Similarly to active VLP immunization, transfer of high L1 antibody concentrations prevented BM binding. However, in the presence of low concentrations of anti-L1, virions associated with the BM, but to the epithelial cell surface was not detected. Regardless of the concentration, L2 vaccine-induced antibodies allow BM association but prevent association with the cell surface. Thus, we have revealed distinct mechanisms of vaccine-induced inhibition of virus infection in vivo.

Papillomavirus pseudovirions packaged with the L2 gene induce cross-neutralizing antibodies

BACKGROUND

Current vaccines against HPVs are constituted of L1 protein self-assembled into virus-like particles (VLPs) and they have been shown to protect against natural HPV16 and HPV18 infections and associated lesions. In addition, limited cross-protection has been observed against closely related types. Immunization with L2 protein in animal models has been shown to provide cross-protection against distant papillomavirus types, suggesting that the L2 protein contains cross-neutralizing epitopes. However, vaccination with L2 protein or L2 peptides does not induce high titers of anti-L2 antibodies. In order to develop a vaccine with the potential to protect against other high-risk HPV types, we have produced HPV58 pseudovirions encoding the HPV31 L2 protein and compared their capacity to induce cross-neutralizing antibodies with that of HPV L1 and HPV L1/L2 VLPs.

METHODS

The titers of neutralizing antibodies against HPV16, HPV18, HPV31 and HPV58 induced in Balb/c mice were compared after immunization with L2-containing vaccines.

RESULTS

Low titers of cross-neutralizing antibodies were detected in mice when immunized with L1/L2 VLPs, and the highest levels of cross-neutralizing antibodies were observed in mice immunized with HPV 58 L1/L2 pseudovirions encoding the HPV 31 L2 protein.

CONCLUSIONS

The results obtained indicate that high levels of cross-neutralizing antibodies are only observed after immunization with pseudovirions encoding the L2 protein. HPV pseudovirions thus represent a possible new strategy for the generation of a broad-spectrum vaccine to protect against high-risk HPVs and associated neoplasia.

Human cytomegalovirus reinfection is associated with intrauterine transmission in a highly cytomegalovirus-immune maternal population

OBJECTIVE

To determine contribution of reinfection with new strains of cytomegalovirus in cytomegalovirus seromimmune women to incidence of congenital cytomegalovirus infection.

STUDY DESIGN

In 7848 women studied prospectively for congenital cytomegalovirus infection from a population with near universal cytomegalovirus seroimmunity, sera from 40 mothers of congenitally infected infants and 109 mothers of uninfected newborns were analyzed for strain-specific anticytomegalovirus antibodies.

RESULTS

All women were cytomegalovirus seroimmune at first prenatal visit. Reactivity for 2 cytomegalovirus strains was found in 14 of 40 study mothers and in 17 of 109 control mothers at first prenatal visit (P = .009). Seven of 40 (17.5%) study women and 5 of 109 (4.6%) controls (P = .002) acquired antibodies reactive with new cytomegalovirus strains during pregnancy. Evidence of infection with more than 1 strain of cytomegalovirus before or during current pregnancy occurred in 21 of 40 study mothers and 22 of 109 controls (P < .0001).

CONCLUSION

Maternal reinfection by new strains of cytomegalovirus is a major source of congenital infection in this population.

Cross-protective responses to human papillomavirus infection

Human papillomavirus (HPV) infections with oncogenic types account for approximately 500,000 deaths per year worldwide, predominantly in underdeveloped countries. The major cause of death is cervical cancer in women, but some additional cancers of the head and neck and anogenital sites also have an HPV etiology. Current virus-like particle-based vaccines are in clinical trials, and show very strong, long-lasting protection against vaccine-matched HPV types. These vaccines currently contain virus-like particles for the HPV types 6, 11, 16 and 18 (Gardasil®) and HPV16 and -18 (Cervarix®). Although type-specific neutralizing antibodies develop from immunizations with these virus-like particle vaccines, promising evidence for cross-protection against related but nonvaccine HPV types is emerging. Strategies to increase cross-protection to cover all oncogenic HPV types (currently approximately 20 types) are underway. These strategies include increasing the number of HPV types in the virus-like particle vaccine, and to the development of second-generation HPV vaccines that include the minor coat protein.

Identification of neutralizing conformational epitopes on the human papillomavirus type 31 major capsid protein and functional implications

The aim of this study was to characterize the conformational neutralizing epitopes of the major capsid protein of human papillomavirus type 31. Analysis of the epitopes was performed by competitive epitope mapping using 15 anti-HPV31 and by reactivity analysis using a HPV31 mutant with an insertion of a seven-amino acid motif within the FG loop of the capsid protein. Fine mapping of neutralizing conformational epitopes on HPV L1 was analyzed by a new approach using a system displaying a combinatorial library of constrained peptides exposed on E. coli flagella. The findings demonstrate that the HPV31 FG loop is dense in neutralizing epitopes and suggest that HPV31 MAbs bind to overlapping but distinct epitopes on the central part of the FG loop, in agreement with the exposure of the FG loop on the surface of HPV VLPs, and thus confirming that neutralizing antibodies are mainly located on the tip of capsomeres. In addition, we identified a crossreacting and partially crossneutralizing conformational epitope on the relatively well conserved N-terminal part of the FG loop. Moreover, our findings support the hypothesis that there is no correlation between neutralization and the ability of MAbs to inhibit VLP binding to heparan sulfate, and confirm that the blocking of virus attachment to the extracellular matrix is an important mechanism of neutralization.

[HPV immunization for the prevention of cervical cancer]

CONTEXT

Human Papillomaviruses (HPV) infect epithelial cells of the skin and mucosae. Mucosal high-risk HPV types (mainly HPV 16 and 18) are involved in the development of cervical cancer, one of the most common cancers in young women. HPV infection is usually asymptomatic and clears spontaneously, but 10 - 15 % of high-risk HPV infections are persistent and increase the risk of precancerous and cancerous lesions of the cervix. Two HPV vaccines have been licensed to provide protection against cervical cancer.

OBJECTIVES

To report the different aspects of HPV infection in order to improve the understanding of the particular problems of HPV vaccination and to review the most recent findings related to HPV vaccines, particularly regarding the protective efficacy of vaccines and the roles of adjuvants and immune response in protection.

METHODS

Articles were selected from the PubMed database (National Library of Medicine- National Institute of Health) with the following Keywords "HPV", "Prevention", "HPV vaccines", "Immune response", "Antibody". Abstracts of oral presentations from international meetings were also selected for the more recent findings. a critical analysis of the majority of papers published was undertaken and relevant information summarized.

RESULTS

Virus-like particle production by expressing the major protein of the HPV capsid was carried out in the early 90's, leading to the recent development of two HPV vaccines. These vaccines are now licensed in many countries and have been demonstrated to be highly immunogenic. In subjects that are non-infected at the time of vaccination, HPV vaccines are highly effective in preventing persistent HPV 16 - 18 infections (90 %) and precursors lesions of cervical cancer associated with these two HPV types (close to 100 %). Clinical trials have also confirmed that HPV vaccines are well tolerated by recipients.

CONCLUSIONS

The present paper is a detailed review published in French on HPV vaccines, their efficacy in the prevention of HPV infections and unresolved questions regarding the use of HPV vaccines. This report also includes biological and immunological information to improve the understanding of HPV vaccination.

Developing vaccines against minor capsid antigen L2 to prevent papillomavirus infection

A subset of human papillomavirus (HPV) genotypes is responsible for approximately 5% of all cancer deaths globally, and uterine cervical carcinoma accounts for the majority of these cases. The impact of HPV is greatest for women who do not have access to effective secondary preventive measures, and consequently over 80% of cervical cancer deaths worldwide occur in developing nations. The understanding that persistent infection by this 'oncogenic' subset of HPV genotypes is necessary for the development of cervical carcinoma has driven the development of preventive vaccines. Two preventive vaccines comprising recombinant HPV L1 virus-like particles (VLPs) have been licensed. However, the current cost of these vaccines precludes sustained global delivery, and they target only two of the approximately 15 known oncogenic HPV types, although approximately 70% of cervical cancer cases are attributed to these two types and there is evidence for some degree of cross-protection against other closely related types. A possible approach to broader immunity at lower cost is to consider vaccination against L2. L2 vaccines can be produced inexpensively and they also have the promise of conferring much broader cross-type protective immunity than that observed with L1 VLP immunization. However, L2 vaccine development lags behind L1 VLP vaccines and several technical hurdles remain.

Serological relationship between cutaneous human papillomavirus types 5, 8 and 92

Evidence of a possible association of cutaneous human papillomavirus (HPV) types, especially members of the genus Betapapillomavirus, and the development of non-melanoma skin cancer (NMSC) is accumulating. Vaccination with virus-like particles (VLPs) consisting of self-assembled L1, the major capsid protein, has been introduced to control anogenital HPV infection. This study examined the serological relationship between betapapillomavirus (beta-PV) types 5 and 8 and the new type HPV-92, which has recently been isolated from a basal cell carcinoma containing a high number of viral genomes. Following expression by recombinant baculoviruses, the L1 protein of HPV-92 self-assembled into VLPs that elicited high-titre antibodies after immunization, similar to VLPs from HPV-5 and -8. Haemagglutination inhibition (HAI) assays were used as a surrogate method for the detection of virion-neutralizing antibodies, which correlates with protection from infection. Antisera raised against HPV-5 and -8 VLPs displayed HAI activity not only against the homologous type, but also against heterologous HPV types 5, 8 and 92, whereas HAI activity of antisera against HPV-92 VLP was restricted to the homologous type. The results of neutralization assays using HPV-5 pseudovirions were consistent with those from HAI assays. Cross-neutralizing immune responses by VLP vaccination against heterologous HPV types may provide broader protection against the multiplicity of HPV types detected in NMSC. If a close link to HPV infection can be conclusively established, these results may provide a basis for further evaluation of VLPs of beta-PVs as candidates for a prophylactic skin-type HPV vaccine, aimed at reducing the incidence of NMSC.

Potent anti-HPV immune responses induced by tandem repeats of the HPV16 L2 (20 -- 38) peptide displayed on bacterial thioredoxin

The minor capsid protein L2 is a promising candidate for the construction of an anti-human papillomavirus (HPV) broadly protective vaccine for the prophylaxis of cervical cancer. However, L2-derived peptides are usually poorly immunogenic and extensive knowledge on the most relevant (cross)neutralizing epitope(s) is still needed. We systematically examined the immunogenicity and virus neutralization potential of six peptides encompassing the N-terminal (amino acids 1 -- 120) region of HPV16 L2 (20 -- 38; 28 -- 42; 56 -- 75; 64 -- 81; 96 -- 115; 108 -- 120) using bacterial thioredoxin (Trx) as a novel peptide scaffold. Mice antisera generated by 19 different Trx-L2 peptide fusions bearing one or multiple copies of each peptide were analyzed. Internal fusion to thioredoxin conferred strong immunogenicity to all the tested peptides, with a trend toward an increased immunogenicity for the multipeptide vs. the monopeptide forms of the various antigens. All Trx-L2 peptides induced HPV16 neutralizing antibodies in some of the immunized mice, but neutralization titers differed by more than two orders of magnitude. Trx-L2(20 -- 38) antisera were by far the most effective in HPV16 neutralization and did not differ significantly from those induced by a reference polypeptide covering the entire L2 (1 -- 120) region. The same antisera were also the most effective when challenged against the non-cognate HPV 18, 58, 45 and 31 pseudovirions. The data identify L2(20 -- 38) as the best (cross)neutralizing epitope among the six that were examined, and point to thioredoxin fusion derivatives of this peptide as excellent candidates for the formulation of a low-cost, broadly protective HPV vaccine.

Evolutionary and structural analyses of alpha-papillomavirus capsid proteins yields novel insights into L2 structure and interaction with L1

Background

PVs (PV) are small, non-enveloped, double-stranded DNA viruses that have been identified as the primary etiological agent for cervical cancer and their potential for malignant transformation in mucosal tissue has a large impact on public health. The PV family Papillomaviridae is organized into multiple genus based on sequential parsimony, host range, tissue tropism, and histology. We focused this analysis on the late gene products, major (L1) and minor (L2) capsid proteins from the family Papillomaviridae genus Alpha-papillomavirus. Alpha-PVs preferentially infect oral and anogenital mucosa of humans and primates with varied risk of oncogenic transformation. Development of evolutionary associations between PVs will likely provide novel information to assist in clarifying the currently elusive relationship between PV and its microenvironment (i.e., the single infected cell) and macro environment (i.e., the skin tissue). We attempt to identify the regions of the major capsid proteins as well as minor capsid proteins of alpha-papillomavirus that have been evolutionarily conserved, and define regions that are under constant selective pressure with respect to the entire family of viruses.

Results

This analysis shows the loops of L1 are in fact the most variable regions among the alpha-PVs. We also identify regions of L2, involved in interaction with L1, as evolutionarily conserved among the members of alpha- PVs. Finally, a predicted three-dimensional model was generated to further elucidate probable aspects of the L1 and L2 interaction.

Clathrin- and caveolin-independent entry of human papillomavirus type 16--involvement of tetraspanin-enriched microdomains (TEMs)

Background

Infectious entry of human papillomaviruses into their host cells is an important step in the viral life cycle. For cell binding these viruses use proteoglycans as initial attachment sites. Subsequent transfer to a secondary receptor molecule seems to be involved in virus uptake. Depending on the papillomavirus subtype, it has been reported that entry occurs by clathrin- or caveolin-mediated mechanisms. Regarding human papillomavirus type 16 (HPV16), the primary etiologic agent for development of cervical cancer, clathrin-mediated endocytosis was described as infectious entry pathway.

Methodology/Principal Findings

Using immunofluorescence and infection studies we show in contrast to published data that infectious entry of HPV16 occurs in a clathrin- and caveolin-independent manner. Inhibition of clathrin- and caveolin/raft-dependent endocytic pathways by dominant-negative mutants and siRNA-mediated knockdown, as well as inhibition of dynamin function, did not impair infection. Rather, we provide evidence for involvement of tetraspanin-enriched microdomains (TEMs) in HPV16 endocytosis. Following cell attachment, HPV16 particles colocalized with the tetraspanins CD63 and CD151 on the cell surface. Notably, tetraspanin-specific antibodies and siRNA inhibited HPV16 cell entry and infection, confirming the importance of TEMs for infectious endocytosis of HPV16.

Conclusions/Significance

Tetraspanins fulfill various roles in the life cycle of a number of important viral pathogens, including human immunodeficiency virus (HIV) and hepatitis C virus (HCV). However, their involvement in endocytosis of viral particles has not been proven. Our data indicate TEMs as a novel clathrin- and caveolin-independent invasion route for viral pathogens and especially HPV16.

Neutralizing antibodies against human papillomavirus types 16, 18, 31, 52, and 58 in serum samples from women in Japan with low-grade cervical intraepithelial neoplasia

We have very limited information on serum neutralizing antibody in women naturally infected with the human papillomaviruses (HPVs) that are causally associated with cervical cancer. In this study, serum samples collected from 217 Japanese women with low-grade cervical intraepithelial neoplasia were examined for their neutralizing activities against HPV16, -18, -31, -52, and -58 pseudovirions. Eighty-four patients (39%), 35 patients (16%), 17 patients (8%), and 1 patient were positive for neutralizing antibodies against one, two, three, and four of these types, respectively. Presence of neutralizing antibody did not always correlate with detection of HPV DNA in cervical swabs collected at the time of blood collection. The neutralizing titers of the majority of sera, ranging between 40 and 640, were found to be conserved in the second sera, collected 24 months later, independently of emergence of HPV DNA in the second cervical swabs. The data strongly suggest that HPV infection induces anti-HPV neutralizing antibody at low levels, which are maintained for a long period of time.

Modification of human papillomavirus-like particle vaccine by insertion of the cross-reactive L2-epitopes

Infection with human papillomavirus 16 (HPV16), which is one of the 15 types of HPV causally associated with cervical cancer and accounts for 50% of the cases, can be prevented in a type-specific manner by an HPV16 virus-like particle (VLP) vaccine comprised of particles of the L1 protein alone. We attempted to modify the VLP vaccine by inserting the HPV16 L2-peptides including cross-neutralization epitopes into the L1 polypeptide. The chimeric L1 had, between L1 amino acids (aa) 430 and 433, the L2 sequence of aa 18-38, 56-75, or 96-115 (with the replacements of S at aa 101 and T at aa 112 with L and S, respectively). The three chimeric L1s were each expressed from the recombinant baculovirus in insect Sf9 cells, and the resultant VLPs were characterized. The chimeric VLPs were shown to present the L2-peptides on their surface. By immunizing rabbits with the VLPs, it was shown that they retained capability to induce the antibody neutralizing HPV16 and acquired capability to elicit antibodies cross-neutralizing the infectious HPV18, 31, 52, and 58 pseudovirions. Although the cross-neutralizing titers were lower than the type-specific neutralizing titer, the results suggest that the chimeric VLPs have potential to serve as a vaccine candidate for a broad spectrum of high-risk HPVs.

Reactivity pattern of 92 monoclonal antibodies with 15 human papillomavirus types

Most anti-human papillomavirus (HPV) capsid antibody assays are based on virus-like particles (VLP). We evaluated glutathione S-transferase (GST)-L1 fusion proteins as ELISA antigens for determining type specificity and cross-reactivity of 92 VLP-specific monoclonal antibodies (mAb) generated against nine mucosal alpha papillomavirus types of species 7, 9 and 10. The antibody panel included 25 new mAb, and 24 previously published mAb are further characterized. We determined the cross-reactivity patterns with 15 different HPV types representing 6 species (alpha1, 2, 4, 7, 9 and 10) and neutralization and cross-neutralization properties with HPV types 6, 11, 16, 18 and 45. Eighty-nine (97 %) of the antibodies including 34, 71 and 14 recognizing neutralizing, conformational and linear epitopes, respectively, reacted with the GST-L1 protein of the HPV type used as immunogen, with log titres ranging from 2.0 to 7.3. Of these 89 antibodies, 52 % were monotypic, 20 % showed intra-species and 28 % inter-species cross-reactivity. Log neutralization titres to the immunogen HPV ranged from 1.7 to 5.6. A single cross-neutralizing mAb (H6.L12) was found. ELISA titres were always higher than neutralization titres. All neutralizing epitopes were conformational and mostly type-specific. Our data show that bacterially expressed, affinity-purified GST-L1 fusion proteins display a broad variety of epitopes and thus are well suited for detection of HPV antibodies. Cross-reactivity is associated with linear as well as conformational epitopes. Distantly related mucosal and skin alpha papillomaviruses share some conformational epitopes and the phylogenetic L1-based species definition may not define a serological unit since no species-specific epitope was found.

Molecular biology of cervical cancer

Cervical cancer is a virus-induced disease that is caused by the integration of high-risk infecting human papillomaviruses (HPV) in the host genome. For this reason, the carcinogenesis process of cervical cancer is associated to the expression of the viral oncogenic proteins E6 and E7. These proteins are capable of inactivating p53 and pRb, which induces a continuous cell proliferation with the increasing risk of accumulation of DNA damage that eventually leads to cancer. Moreover, cervical cancer can be prevented by prophylactic HPV vaccines; their molecular characteristics and mechanism of action are reviewed. Ultimately, new molecular targets for cervical cancer like proteasome, the EGFR family and IGF family are exposed.

Induction of mucosal and systemic immune responses following oral immunization of mice with Lactococcus lactis expressing human papillomavirus type 16 L1

Human papillomavirus type 16 L1 (HPV16 L1) has shown considerable promise as a parenteral vaccine for prevention of cervical cancers. Here, we report the possibility of oral vaccination for HPV16 L1 using Lactococcus lactis (L. lactis) as a live vector. L. lactis MG1363 was transformed with two types of HPV16 L1-encoding plasmids for intracellular expression or secretion. L. lactis transformed with HPV16 L1-encoding plasmids retained biochemical lactic acid production capability. The mucosal and systemic immune responses were affected by the cellular location of expressed HPV16 L1 proteins in L. lactis. Serum IgG responses were induced after oral immunizations of L. lactis secreting HPV16 L1. Vaginal IgA immune responses were observed following oral immunization with L. lactis expressing HPV16 L1 in an intracellular form, but not with L. lactis secreting HPV16 L1. Furthermore, induction of HPV16 L1-specific mucosal immune responses was affected by immunization frequency. Six immunizations over 5 weeks were required to induce vaginal immune responses. The levels of HPV16 L1-specific vaginal IgA were maintained until 12 weeks after the first vaccination. These results suggest the feasibility of L. lactis as an oral vaccine vehicle of HPV16 L1 and demonstrate the importance of cellular loci of expressed antigen for induction of vaginal and systemic immune responses.

Surface-exposed Amino Acid Residues of HPV16 L1 Protein Mediating Interaction with Cell Surface Heparan Sulfate

Efficient infection of cells by human papillomaviruses (HPVs) and pseudovirions requires primary interaction with cell surface proteoglycans with apparent preference for species carrying heparan sulfate (HS) side chains. To identify residues contributing to virus/cell interaction, we performed point mutational analysis of the HPV16 major capsid protein, L1, targeting surface-exposed amino acid residues. Replacement of lysine residues 278, 356, or 361 for alanine reduced cell binding and infectivity of pseudovirions. Various combinations of these amino acid exchanges further decreased cell attachment and infectivity with residual infectivity of less than 5% for the triple mutant, suggesting that these lysine residues cooperate in HS binding. Single, double, or triple exchanges for arginine did not impair infectivity, demonstrating that interaction is dependent on charge distribution rather than sequence-specific. The lysine residues are located within a pocket on the capsomere surface, which was previously proposed as the putative receptor binding site. Fab fragments of binding-neutralizing antibody H16.56E that recognize an epitope directly adjacent to lysine residues strongly reduced HS-mediated cell binding, further corroborating our findings. In contrast, mutation of basic surface residues located in the cleft between capsomeres outside this pocket did not significantly reduce interaction with HS or resulted in assembly-deficient proteins. Computer-simulated heparin docking suggested that all three lysine residues can form hydrogen bonds with 2-O-, 6-O-, and N-sulfate groups of a single HS molecule with a minimal saccharide domain length of eight monomer units. This prediction was experimentally confirmed in binding experiments using capsid protein, heparin molecules of defined length, and sulfate group modifications.

Type-specific and cross-reactive antibodies induced by human papillomavirus 31 L1/L2 virus-like particles

The aim of this study was to determine whether antibodies induced by human papillomavirus (HPV) type 31 L1/L2 virus-like particles (VLPs) could cross-react with VLPs of the closely related HPV-16 and distantly related HPV-11, and to investigate the potential role of the L2 protein in L1/L2 VLPs in inducing cross-neutralizing antibodies. Antisera were prepared from rabbits immunized with intact or denatured HPV-31 L1/L2 VLPs. Cross-reaction and cross-neutralization were analysed by Western blotting and ELISA, and by haemagglutination inhibition, respectively. Western blotting results showed that H31 L1/L2 (D) antiserum (antiserum from a rabbit immunized with denatured HPV-31 L1/L2 VLPs) could cross-react with the L1 protein of HPV-11 and -16. HPV-31 L1/L2 VLP antiserum showed strong cross-reaction with and cross-neutralization of HPV-16 VLPs, but this was significantly less with HPV-11 VLPs. In addition, the cross-neutralizing activity against HPV-16 L1/L2 VLPs was slightly higher than that against HPV-16 L1 VLPs, although the difference was not statistically significant. Epitope-blocking ELISA showed that mAb H16.V5 could partially inhibit the cross-reaction of HPV-31 L1/L2 VLP antiserum with HPV-16 L1/L2 VLPs. These results suggested that (i) H31 L1/L2 (D) antiserum could cross-react with L1 protein from both closely related and distantly related HPV types, but HPV-31 L1/L2 VLP antiserum could only cross-neutralize closely related HPV types, (ii) surface-exposed epitopes of the L2 protein in L1/L2 VLPs may induce only low titres of cross-neutralizing antibodies and (iii) certain epitopes that cross-reacted with HPV-31 L1/L2 VLP antiserum are located close to the epitopes recognized by mAb H16.V5. These findings may provide suggestions for the design of multivalent VLP vaccines.

Vaccines against human papillomavirus: perspectives for controlling cervical cancer

Prophylactic vaccines against human papillomavirus (HPV) are on the market and will certainly reduce the incidence of genital warts and the risk of developing cervical cancer. In addition, they will contribute to reducing anal as well as head and neck cancers. However, effort should be made in the short term in order for these vaccines to have a real impact in the developing world, where almost 80% of cervical cancer cases occur. Since the available vaccines include only two of the HPV types found in cancers (approximately 70%), improvements in current mass screening programs - with the use of molecular techniques - must be made, particularly in developing countries. Therapeutic vaccines have been designed to control advanced lesions and residual illness and, although success has usually been obtained in animal models, clinical studies have not yet provided the anticipated results. Finally, the next generations of prophylactic HPV vaccines will probably include subunit vaccines, transgenic bacteria and plants, among others, and could represent useful and cheaper alternatives for reducing cervical cancer, particularly in the developing world.

Efficacy of a prophylactic adjuvanted bivalent L1 virus-like-particle vaccine against infection with human papillomavirus types 16 and 18 in young women: an interim analysis of a phase III double-blind, randomised controlled trial

BACKGROUND

The aim of this interim analysis of a large, international phase III study was to assess the efficacy of an AS04 adjuvanted L1 virus-like-particle prophylactic candidate vaccine against infection with human papillomavirus (HPV) types 16 and 18 in young women.

METHODS

18,644 women aged 15-25 years were randomly assigned to receive either HPV16/18 vaccine (n=9319) or hepatitis A vaccine (n=9325) at 0, 1, and 6 months. Of these women, 88 were excluded because of high-grade cytology and 31 for missing cytology results. Thus, 9258 women received the HPV16/18 vaccine and 9267 received the control vaccine in the total vaccinated cohort for efficacy, which included women who had prevalent oncogenic HPV infections, often with several HPV types, as well as low-grade cytological abnormalities at study entry and who received at least one vaccine dose. We assessed cervical cytology and subsequent biopsy for 14 oncogenic HPV types by PCR. The primary endpoint--vaccine efficacy against cervical intraepithelial neoplasia (CIN) 2+ associated with HPV16 or HPV18--was assessed in women who were seronegative and DNA negative for the corresponding vaccine type at baseline (month 0) and allowed inclusion of lesions with several oncogenic HPV types. This interim event-defined analysis was triggered when at least 23 cases of CIN2+ with HPV16 or HPV18 DNA in the lesion were detected in the total vaccinated cohort for efficacy. Analyses were done on a modified intention-to-treat basis. This trial is registered with the US National Institutes of Health clinical trial registry, number NCT00122681.

FINDINGS

Mean length of follow-up for women in the primary analysis for efficacy at the time of the interim analysis was 14.8 (SD 4.9) months. Two cases of CIN2+ associated with HPV16 or HPV18 DNA were seen in the HPV16/18 vaccine group; 21 were recorded in the control group. Of the 23 cases, 14 (two in the HPV16/18 vaccine group, 12 in the control group) contained several oncogenic HPV types. Vaccine efficacy against CIN2+ containing HPV16/18 DNA was 90.4% (97.9% CI 53.4-99.3; p<0.0001). No clinically meaningful differences were noted in safety outcomes between the study groups.

INTERPRETATION

The adjuvanted HPV16/18 vaccine showed prophylactic efficacy against CIN2+ associated with HPV16 or HPV18 and thus could be used for cervical cancer prevention.

Recent Advances in the Search for Antiviral Agents against Human Papillomaviruses

Infection by human papillomavirus (HPV) is extremely common and associated with the development of benign warts or malignant lesions of the skin and mucosa. Infection by a high-risk (oncogenic) anogenital HPV type, most often through sexual contacts, is the starting point of virtually all cases of cervical cancers and the majority of anal cancers. The same viral types are also increasingly being linked with a subset of head-and-neck and non-melanoma skin cancers. Although prophylactic vaccines are now available to protect against the four types most commonly found in cervical and anal cancers (HPV16 and HPV18) and anogenital warts (HPV6 and HPV11), these neither protect against all genital HPVs nor are of therapeutic utility for already infected patients. Thus, the need for antiviral agents to treat HPV-associated diseases remains great, but none currently exist. This article reviews the recent progress made towards the development of antiviral agents to treat HPV infections, from target identification and validation to the discovery of lead compounds with therapeutic potential. Emphasis has been placed on novel low-molecular-weight compounds that antagonize HPV proteins or, alternatively, inhibit cellular proteins which have been usurped by papillomaviruses and are mediating their pathogenic effects.