Papillomavirus virus-like particles can deliver defined CTL epitopes to the MHC class I pathway

Therapeutic Role of HPV Vaccination on Benign HPV-induced Epithelial Proliferations in Immunocompetent and Immunocompromised Patients: Case Study and Review of the Literature

Human papillomavirus (HPV) vaccination represents a milestone in primary prevention of sexually transmitted infections. However, little is known about its possible effects on already established HPV infections. We report the case of a 9-year-old immunosuppressed girl with refractory warts, successfully treated with the nonavalent-HPV vaccine and review the literature about the therapeutic effects of HPV vaccination on benign HPV-induced epithelial proliferations in immunocompetent and immunosuppressed patients. In the literature, promising results were shown on cutaneous warts after HPV vaccination, especially in children and young adults, also in immunosuppressed patients, whereas controverse results were found on anogenital warts. These findings suggest a critical need for randomized clinical trials to assess the efficacy of HPV vaccination in the treatment of benign HPV-induced epithelial proliferations.

A tetravalent nanovaccine that inhibits growth of HPV-associated head and neck carcinoma via dendritic and T cell activation

The global incidence of human papillomavirus (HPV) associated head and neck carcinoma is on the rise, in response to this a tetravalent therapeutic vaccine named Qβ-HPVag was developed. This vaccine, utilizing virus-like particles (VLPs) loaded with toll-like receptor ligands and chemically coupled to four HPV16-derived peptides, demonstrated strong anti-tumor effects in a murine head and neck cancer model. Qβ-HPVag impeded tumor progression, increased infiltration of HPV-specific T cells, and significantly improved survival. The vaccine`s efficacy was associated with immune repolarization in the tumor microenvironment, characterized by expanded activated dendritic cell subsets (cDC1, cDC2, DC3). Notably, mice responding to treatment exhibited a higher percentage of migratory DC3 cells expressing CCR7. These findings suggest promising prospects for optimized VLP-based vaccines in treating HPV-associated head and neck cancer.

Bioengineered Bovine Papillomavirus L1 Protein Virus-like Particle (VLP) Vaccines for Enhanced Induction of CD8 T Cell Responses through Cross-Priming

Safe and effective T cell vaccines are needed for the treatment or prevention of cancers as well as infectious agents where vaccines for neutralizing antibodies have performed poorly. Recent research highlights an important role for tissue-resident memory T cells (T_RM cells) in protective immunity and the role of a subset of dendritic cells that are capable of cross-priming for the induction of T_RM cells. However, efficient vaccine technologies that operate through cross-priming and induce robust CD8+ T cell responses are lacking. We developed a platform technology by genetically engineering the bovine papillomavirus L1 major capsid protein to insert a polyglutamic acid/cysteine motif in place of wild-type amino acids in the HI loop. Virus-like particles (VLPs) are formed by self-assembly in insect cells infected with a recombinant baculovirus. Polyarginine/cysteine-tagged antigens are linked to the VLP by a reversible disulfide bond. The VLP possesses self-adjuvanting properties due to the immunostimulatory activity of papillomavirus VLPs. Polyionic VLP vaccines induce robust CD8+ T cell responses in peripheral blood and tumor tissues. A prostate cancer polyionic VLP vaccine was more efficacious than other vaccines and immunotherapies for the treatment of prostate cancer in a physiologically relevant murine model and successfully treated more advanced diseases than the less efficacious technologies. The immunogenicity of polyionic VLP vaccines is dependent on particle size, reversible linkage of the antigen to the VLP, and an interferon type 1 and Toll-like receptor (TLR)3/7-dependent mechanism.

Chimeric Human Papillomavirus-16 Virus-like Particles Presenting HIV-1 P18I10 Peptide: Expression, Purification, Bio-Physical Properties and Immunogenicity in BALB/c Mice

Human papillomavirus (HPV) vaccines based on HPV L1 virus-like particles (VLPs) are already licensed but not accessible worldwide. About 38.0 million people were living with HIV in 2020 and there is no HIV vaccine yet. Therefore, safe, effective, and affordable vaccines against both viruses are an urgent need. In this study, the HIV-1 P18I10 CTL peptide from the V3 loop of HIV-1 gp120 glycoprotein was inserted into the HPV16 L1 protein to construct chimeric HPV:HIV (L1:P18I10) VLPs. Instead of the traditional baculovirus expression vector/insect cell (BEVS/IC) system, we established an alternative mammalian 293F cell-based expression system using cost-effective polyethylenimine-mediated transfection for L1:P18I10 protein production. Compared with conventional ultracentrifugation, we optimized a novel chromatographic purification method which could significantly increase L1:P18I10 VLP recovery (~56%). Chimeric L1:P18I10 VLPs purified from both methods were capable of self-assembling to integral particles and shared similar biophysical and morphological properties. After BALB/c mice immunization with 293F cell-derived and chromatography-purified L1:P18I10 VLPs, almost the same titer of anti-L1 IgG (p = 0.6409) was observed as Gardasil anti-HPV vaccine-immunized mice. Significant titers of anti-P18I10 binding antibodies (p < 0.01%) and P18I10-specific IFN-γ secreting splenocytes (p = 0.0002) were detected in L1:P18I10 VLP-immunized mice in comparison with licensed Gardasil-9 HPV vaccine. Furthermore, we demonstrated that insertion of HIV-1 P18I10 peptide into HPV16 L1 capsid protein did not affect the induction in anti-L1 antibodies. All in all, we expected that the mammalian cell expression system and chromatographic purification methods could be time-saving, cost-effective, scalable platforms to engineer bivalent VLP-based vaccines against HPV and HIV-1.

Chimeric Human Papillomavirus-16 Virus-like Particles Presenting P18I10 and T20 Peptides from HIV-1 Envelope Induce HPV16 and HIV-1-Specific Humoral and T Cell-Mediated Immunity in BALB/c Mice

In this study, the HIV-1 P18I10 CTL peptide derived from the V3 loop of HIV-1 gp120 and the T20 anti-fusion peptide of HIV-1 gp41 were inserted into the HPV16 L1 capsid protein to construct chimeric HPV:HIV (L1:P18I10 and L1:T20) VLPs by using the mammalian cell expression system. The HPV:HIV VLPs were purified by chromatography. We demonstrated that the insertion of P18I10 or T20 peptides into the DE loop of HPV16 L1 capsid proteins did not affect in vitro stability, self-assembly and morphology of chimeric HPV:HIV VLPs. Importantly, it did not interfere either with the HIV-1 antibody reactivity targeting sequential and conformational P18I10 and T20 peptides presented on chimeric HPV:HIV VLPs or with the induction of HPV16 L1-specific antibodies in vivo. We observed that chimeric L1:P18I10/L1:T20 VLPs vaccines could induce HPV16- but weak HIV-1-specific antibody responses and elicited HPV16- and HIV-1-specific T-cell responses in BALB/c mice. Moreover, could be a potential booster to increase HIV-specific cellular responses in the heterologous immunization after priming with rBCG.HIVA vaccine. This research work would contribute a step towards the development of the novel chimeric HPV:HIV VLP-based vaccine platform for controlling HPV16 and HIV-1 infection, which is urgently needed in developing and industrialized countries.

Mechanisms of cellular and humoral immunity through the lens of VLP-based vaccines

INTRODUCTION

Vaccination can be effective defense against many infectious agents and the corresponding diseases. Discoveries elucidating the mechanisms of the immune system have given hopes to developing vaccines against diseases recalcitrant to current treatment/prevention strategies. One such finding is the ability of immunogenic biological nanoparticles to powerfully boost the immunogenicity of poorer antigens conjugated to them with virus-like particle (VLP)-based vaccines as a key example. VLPs take advantage of the well-defined molecular structures associated with sub-unit vaccines and the immunostimulatory nature of conjugate vaccines.

AREAS COVERED

In this review, we will discuss how advances in understanding the immune system can inform VLP-based vaccine design and how VLP-based vaccines have uncovered underlying mechanisms in the immune system.

EXPERT OPINION

As our understanding of mechanisms underlying the immune system increases, that knowledge should inform our vaccine design. Testing of proof-of-concept vaccines in the lab should seek to elucidate the underlying mechanisms of immune responses. The integration of these approaches will allow for VLP-based vaccines to live up to their promise as a powerful plug-and-play platform for next generation vaccine development.

A Comparative Study on Delivery of Externally Attached DNA by Papillomavirus VLPs and Pseudoviruses

Human papillomavirus (HPV) 16 capsids have been chosen as a DNA delivery vehicle in many studies. Our preliminary studies suggest that HPV58 capsids could be better vehicles than HPV16 capsids to deliver encapsidated DNA in vitro and in vivo. In the current study, we compared HPV16, HPV58, and the cottontail rabbit papillomavirus (CRPV) capsids either as L1/L2 VLPs or pseudoviruses (PSVs) to deliver externally attached GFP-expressing DNA. Both rabbit and human cells were used to test whether there was a species-specific effect. DNA delivery efficiency was determined by quantifying either GFP-expressing cell populations or mean fluorescent intensities (MFI) by flow cytometry. Interestingly, CRPV and 58-VLPs and PSVs were significantly more efficient at delivering attached DNA when compared to 16-VLPs and PSVs. A capsid/DNA ratio of 2:1 showed the highest efficiency for delivering external DNA. The PSVs with papillomavirus DNA genomes also showed higher efficiency than those with irrelevant plasmid DNA. HPV16L1/58L2 hybrid VLPs displayed increased efficiency compared to HPV58L1/16L2 VLPs, suggesting that L2 may play a critical role in the delivery of attached DNA. Additionally, we demonstrated that VLPs increased in vivo infectivity of CRPV DNA in rabbits. We conclude that choosing CRPV or 58 capsids to deliver external DNA could improve DNA uptake in in vitro and in vivo models.

Association Between BoLA-DRB3.2 Polymorphism and Bovine Papillomavirus Infection for Bladder Tumor Risk in Podolica Cattle

Blood samples from 260 unrelated cattle (132 animals affected by papillomavirus-associated bladder tumors and 128 healthy) were genotyped using the classic polymerase chain reaction/restriction fragment length polymorphism method to screen MHC class II bovine leukocyte antigen-DRB3. 2 polymorphism. The DRB3^*22 allele was significantly (p ≤ 0.01) detected in healthy cattle, thus appearing to have a negative association (protective effect) with virus infection of the urinary bladder known to represent a bladder tumor risk for cattle living free at pasture. Considering the two sequence alleles identified in animals carrying DRB3^*22, DRB3^*011:01 allele from samples of animals harboring the unexpressed bovine papillomaviruses (BPV)-2 E5 gene was characterized by amino acid residues believed to have a protective effect against BPV infection such as arginine at position 71 (R⁷¹) in pocket 4, histidine at position 11 (H¹¹) in pocket 6, and both glutamine at position 9 (Q⁹) and serine at position 57 (S⁵⁷) in pocket 9 of the antigen-binding groove. The DRB3^*011:02v allele from affected animals was characterized by amino acids believed to be susceptibility residues such as lysine (K⁷¹), tyrosine (Y¹¹), glutamic acid (E⁹), and aspartic acid (D⁵⁷) in these pockets. These results suggest that animals harboring the DRB3^*011:01 allele may have a lower risk of BPV infection and, consequently, a reduced risk of bladder tumors.

Immunogenicity in Rabbits of Virus-Like Particles from a Contemporary Rabbit Haemorrhagic Disease Virus Type 2 (GI.2/RHDV2/b) Isolated in The Netherlands

Rabbit haemorrhagic disease virus (RHDV) type 2 (GI.2/RHDV2/b) is an emerging pathogen in wild rabbits and in domestic rabbits vaccinated against RHDV (GI.1). Here we report the genome sequence of a contemporary RHDV2 isolate from the Netherlands and investigate the immunogenicity of virus-like particles (VLPs) produced in insect cells. RHDV2 RNA was isolated from the liver of a naturally infected wild rabbit and the complete viral genome sequence was assembled from sequenced RT-PCR products. Phylogenetic analysis based on the VP60 capsid gene demonstrated that the RHDV2 NL2016 isolate clustered with other contemporary RHDV2 strains. The VP60 gene was cloned in a baculovirus expression vector to produce VLPs in Sf9 insect cells. Density-gradient purified RHDV2 VLPs were visualized by transmission electron microscopy as spherical particles of around 30 nm in diameter with a morphology resembling authentic RHDV. Immunization of rabbits with RHDV2 VLPs resulted in high production of serum antibodies against VP60, and the production of cytokines (IFN-γ and IL-4) was significantly elevated in the immunized rabbits compared to the control group. The results demonstrate that the recombinant RHDV2 VLPs are highly immunogenic and may find applications in serological detection assays and might be further developed as a vaccine candidate to protect domestic rabbits against RHDV2 infection.

Safety and Immunogenicity of a Nonadjuvant Human Papillomavirus Type 6 Virus-like Particle Vaccine in Recurrent Respiratory Papillomatosis

OBJECTIVES

To assess the safety and immunogenicity of a nonadjuvant human papillomavirus (HPV) type 6 L1 virus-like particle (VLP) vaccine in recurrent respiratory papillomatosis (RRP) in local Chinese patients.

METHODS

Patients with RRP who had undergone surgical treatment before intramuscular administration of an escalating dose of HPV type 6 L1 VLPs (1, 5, and 25 µg at 4 weekly intervals) as part of their treatment were followed up for more than 10 years. Efficacy was assessed by detecting the vaccine-induced type-specific antibody titer, calculating the intersurgical interval, and observing recurrence or remission of papillomas after receiving the vaccine.

RESULTS

Nonadjuvant HPV vaccine was generally well tolerated, with no serious vaccine-related adverse episodes. It induced seroconversion for each vaccine-related HPV type. At week 12 (4 weeks after injecting 25 µg), the vaccine-induced type-specific antibody titer was significantly high. Analysis of all patients found a significant increase in the intersurgical interval and decrease in the scores. One patient (16.7%; female) experienced complete remission. Five patients (83.3%) (two males and three females) experienced partial remission. In total, complete or partial remission was achieved in six (100%) patients.

CONCLUSIONS

Administration of nonadjuvant HPV type 6 L1 VLPs vaccine to RRP was generally well tolerated and highly immunogenic.

Engineered outer membrane vesicle is potent to elicit HPV16E7-specific cellular immunity in a mouse model of TC-1 graft tumor

PURPOSE

Currently, therapeutic tumor vaccines under development generally lack significant effects in human clinical trials. Exploring a powerful antigen delivery system is a potential approach to improve vaccine efficacy. We sought to explore engineered bacterial outer membrane vesicles (OMVs) as a new vaccine carrier for efficiently delivering tumor antigens and provoking robust antitumor immune responses.

MATERIALS AND METHODS

First, the tumoral antigen human papillomavirus type 16 early protein E7 (HPV16E7) was presented on Escherichia coli-derived OMVs by genetic engineering methods, acquiring the recombinant OMV vaccine. Second, the ability of recombinant OMVs delivering their components and the model antigen green fluorescent protein to antigen-presenting cells was investigated in the macrophage Raw264.7 cells and in bone marrow-derived dendritic cells in vitro. Third, it was evaluated in TC-1 graft tumor model in mice that the recombinant OMVs displaying HPV16E7 stimulated specific cellular immune response and intervened the growth of established tumor.

RESULTS

E. coli DH5α-derived OMVs could be taken up rapidly by dendritic cells, for which vesicle structure has been proven to be important. OMVs significantly stimulated the expression of dendritic cellmaturation markers CD80, CD86, CD83 and CD40. The HPV16E7 was successfully embedded in engineered OMVs through gene recombinant techniques. Subcutaneous immunization with the engineered OMVs induced E7 antigen-specific cellular immune responses, as shown by the increased numbers of interferon-gamma-expressing splenocytes by enzyme-linked immunospot assay and interferon-gamma-expressing CD4⁺ and CD8⁺ cells by flow cytometry analyses. Furthermore, the growth of grafted TC-1 tumors in mice was significantly suppressed by therapeutic vaccination. The recombinant E7 proteins presented by OMVs were more potent than those mixed with wild-type OMVs or administered alone for inducing specific cellular immunity and suppressing tumor growth.

CONCLUSION

The results indicated that the nano-grade OMVs might be a useful vaccine platform for antigen delivery in cancer immunotherapy.

Enhancing antitumor immunogenicity of HPV16-E7 DNA vaccine by fusing DNA encoding E7-antigenic peptide to DNA encoding capsid protein L1 of Bovine papillomavirus

Background

Human papillomavirus (HPV) has been identified as the primary etiologic factor of cervical cancer, the fourth leading cause of cancer death in females worldwide. We have previously shown that coadministration of DNA encoding L1 capsid protein of Bovine papillomavirus (BPV) can enhance the antigen-specific immune response elicited by a therapeutic HPV16-E7 DNA vaccination. In this study, we sought to generate and evaluate the immunogenicity of a therapeutic HPV16-E7 DNA vaccine that encodes the fusion construct of HPV16-E7 and BPV-L1.

Results

We generated a therapeutic HPV16-E7 DNA vaccine construct, pcDNA3-BPVL1-E7(49-57), encoding the fusion sequence of full-length BPVL1 protein and a murine E7 antigenic epitope, aa49-57. Transfecting 293-D^b cells with pcDNA3-BPVL1-E7(49-57) demonstrated that this DNA construct can effectively lead to the presentation of E7 epitope for the activation of E7-specific CD8+ T cells in vitro. Intramuscular vaccination of pcDNA3-BPVL1-E7(49-57) with electroporation generated a stronger E7-specific CD8+ T cell-mediated immune response than coadministration of pcDNA3-BPVL1 and pcDNA3-E7(49-57) in C57BL/6 mice. Furthermore, we observed that the strong E7-specific CD8+ T cell response elicited by pcDNA3-BPVL1-E7(49-57) vaccination translated into potent protective and therapeutic antitumor effects in C57BL/6 mice against HPV16-E7 expressing TC-1 tumor cells. Finally, using antibody depletion experiment, we showed that the antitumor immune response generated by pcDNA3-BPVL1-E7(49-57) is CD8+ T cell dependent, and CD4+ T cell and NK cell independent.

Conclusion

Treatment with fusion construct of BPV-L1 and HPV16-E7 epitope can elicit effective E7-specific antitumor immune response in mice. Due to the potential ability of the fusion DNA construct to also trigger immune responses specific to the L1 protein, the current study serves to support future design of HPV DNA vaccines encoding fusion HPVL1-E6/E7 constructs for the generation of both T cell and B cell mediated immune responses against HPV infections and associated diseases.

Blocking IL-10 signalling at the time of immunization does not increase unwanted side effects in mice

BACKGROUND

Cancer therapeutic vaccine induced cytotoxic T cell (CTL) responses are pivotal for the killing of tumour cells. Blocking interleukin 10 (IL-10) signalling at the time of immunization increases vaccine induced CTL responses and improves prevention of tumour growth in animal models compared to immunization without an IL-10 signalling blockade. Therefore, this immunization strategy may have potential to curtail cancer in a clinical setting. However, IL-10 deficiency leads to autoimmune disease in the gut. Blocking IL-10 at the time of immunization may result in unwanted side effects, especially immune-pathological diseases in the intestine.

METHODS

We investigated whether blocking IL-10 at the time of immunization results in intestinal inflammation responses in a mouse TC-1 tumour model and in a NOD autoimmune disease prone mouse model.

RESULTS

We now show that blocking IL-10 at the time of immunization increases IL-10 production by CD4+ T cells in the spleen and draining lymph nodes, and does not result in blood cell infiltration to the intestines leading to intestinal pathological changes. Moreover, immunization with papillomavirus like particles combined with simultaneously blocking IL-10 signalling does not increase the incidence of autoimmune disease in Non-obese diabetic (NOD) mice.

CONCLUSIONS

Our results indicate that immunization with an IL-10 inhibitor may facilitate the generation of safe, effective therapeutic vaccines against chronic viral infection and cancer.

Development of HPV Vaccines for HPV-associated Head and Neck Squamous Cell Carcinoma

High-risk genotypes of the human papillomavirus (HPV), particularly HPV type 16, are found in a distinct subset of head and neck squamous cell carcinomas (HNSCC). Thus, these HPV-associated HNSCC may be prevented or treated by vaccines designed to induce appropriate HPV virus-specific immune responses. Infection by HPV may be prevented by neutralizing antibodies specific for the viral capsid proteins. In clinical trials, vaccines comprised of HPV virus-like particles (VLPs) have shown great promise as prophylactic HPV vaccines. However, given that capsid proteins are not expressed at detectable levels by infected basal keratinocytes, vaccines with therapeutic potential must target other non-structural viral antigens. Two HPV oncogenic proteins, E6 and E7, are important in the induction and maintenance of cellular transformation and are co-expressed in the majority of HPV-containing carcinomas. Therefore, therapeutic vaccines targeting these proteins may have potential to control HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 is administered in live vectors, in peptides or protein, in nucleic acid form, as components of chimeric VLPs, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. Should they fulfill their promise, these vaccines may prevent HPV infection or control its potentially life-threatening consequences in humans.

Different applications of virus-like particles in biology and medicine: Vaccination and delivery systems

Virus-like particles (VLPs) mimic the whole construct of virus particles devoid of viral genome as used in subunit vaccine design. VLPs can elicit efficient protective immunity as direct immunogens compared to soluble antigens co-administered with adjuvants in several booster injections. Up to now, several prokaryotic and eukaryotic systems such as insect, yeast, plant, and E. coli were used to express recombinant proteins, especially for VLP production. Recent studies are also generating VLPs in plants using different transient expression vectors for edible vaccines. VLPs and viral particles have been applied for different functions such as gene therapy, vaccination, nanotechnology, and diagnostics. Herein, we describe VLP production in different systems as well as its applications in biology and medicine.

Next generation prophylactic human papillomavirus vaccines

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

Chimeric infectious bursal disease virus-like particles as potent vaccines for eradication of established HPV-16 E7-dependent tumors

Cervical cancer is caused by persistent high-risk human papillomavirus (HR-HPV) infection and represents the second most frequent gynecological malignancy in the world. The HPV-16 type accounts for up to 55% of all cervical cancers. The HPV-16 oncoproteins E6 and E7 are necessary for induction and maintenance of malignant transformation and represent tumor-specific antigens for targeted cytotoxic T lymphocyte–mediated immunotherapy. Therapeutic cancer vaccines have become a challenging area of oncology research in recent decades. Among current cancer immunotherapy strategies, virus-like particle (VLP)–based vaccines have emerged as a potent and safe approach. We generated a vaccine (VLP-E7) incorporating a long C-terminal fragment of HPV-16 E7 protein into the infectious bursal disease virus VLP and tested its therapeutic potential in HLA-A2 humanized transgenic mice grafted with TC1/A2 tumor cells. We performed a series of tumor challenge experiments demonstrating a strong immune response against already-formed tumors (complete eradication). Remarkably, therapeutic efficacy was obtained with a single dose without adjuvant and against two injections of tumor cells, indicating a potent and long-lasting immune response.

Human papillomavirus 16 L1-E7 chimeric virus like particles show prophylactic and therapeutic efficacy in murine model of cervical cancer

Cervical cancer is found to be associated with human papillomavirus (HPV) infection, with HPV16 being the most prevalent. An effective vaccine against HPV can thus, be instrumental in controlling cervical cancer. An ideal HPV vaccine should aim to generate both humoral immune response to prevent new infection as well as cell-mediated immunity to eliminate established infection. In this study, we have generated a potential preventive and therapeutic candidate vaccine against HPV16. We expressed and purified recombinant HPV16 L1(ΔN26)-E7(ΔC38) protein in E. coli which was assembled into chimeric virus like particles (CVLPs) in vitro. These CVLPs were able to induce neutralizing antibodies and trigger cell-mediated immune response, in murine model of cervical cancer, exhibiting antitumor efficacy. Hence, this study has aimed to provide a vaccine candidate possessing both, prophylactic and therapeutic efficacy against HPV16 associated cervical cancer.

A randomized trial of immunotherapy for persistent genital warts

AIM

To determine whether immunotherapy with HPV6 L1 virus like particles (VLPs) without adjuvant (VLP immunotherapy) reduces recurrence of genital warts following destructive therapy.

TRIAL DESIGN

A randomized placebo controlled blinded study of treatment of recurrent genital warts amenable to destructive therapy, conducted independently in Australia and China.

METHODS

Patients received conventional destructive therapy of all evident warts together with intramuscular administration of 1 µg, 5 µg or 25 µg of VLP immunotherapy, or of placebo immunotherapy (0.9% NaCl), as immunotherapy at week 0 and week 4. Primary outcome, assessed at week 8, was recurrence of visible warts.

RESULTS

Of 33 protocol compliant Brisbane recipients of placebo immunotherapy, 11 were disease free at two months, and a further 9 demonstrated reduction of > 50% in total wart area. Wart area reduction following destructive treatment correlated with prior duration of disease. Among 102 protocol compliant Brisbane recipients of VLP immunotherapy, disease reduction was significantly greater than among the placebo immunotherapy (50% ± s.e.m. 7%) recipients for subjects receiving 5 µg or 25 µg of VLP immunotherapy/dose (71% ± s.e.m. 7%) but not for those receiving 1 µg VLP immunotherapy/dose (42% ± 7%). Of 52 protocol compliant placebo immunotherapy recipients in Wenzhou, 37 were disease free at two months, and a further 8 had > 50% disease reduction. Prior disease duration was much shorter in Wenzhou subject (8.1 ± 1.1 mo) than in Brisbane subjects (53.7 ± 5.5 mo). No significant reduction in mean wart area was observed for the 168 Wenzhou protocol compliant subjects who also received VLP immunotherapy.

CONCLUSIONS

This study confirms the findings in a previous open label trial that administration of VLP immunotherapy may assist in clearance of recurrent genital warts in patients for whom destructive therapy is unsuccessful and that unsuccessful destructive therapy is more common with increasing prior disease duration.

Papillomavirus virus like particle-based therapeutic vaccine against human papillomavirus infection related diseases: immunological problems and future directions

Chronic infection with certain types of human papillomaviruses (HPV), especially HPV-16 and HPV-18, leads to the development of cervical cancer. Prophylactic HPV vaccines based on HPV virus like particles (VLPs) have now been developed. The commercial vaccines, Gardasil and Cervarix are clinically effective in preventing HPV infection but do not have a therapeutic effect against existing chronic HPV infections. However, papillomavirus (PV) VLPs elicit strong cytotoxic T cell (CTL) responses and PV VLPs without any adjuvant have therapeutic effects in animal PV infection model. Alum in Gardasil, Alum and 3-O-deacylated-4'-monophosphoryl lipid A (ASO4) in Cervarix may stimulate IL10 production and inhibit the Th1, CTL immune response of immunized individuals. PV VLPs also stimulate the production of IL10 by CD4(+) T cells, which prevent their CTL generation effect as a therapeutic vaccine. Neutralizing IL10 at the time of PV VLPs immunization increases cytotoxic T cell responses. PV VLPs incorporating PV early protein E2, 6 and 7, together with immune stimulator that promote strong type 1 responses, and at the same time blocking the effect of IL10 may have therapeutic effect against HPV infection related diseases and are worth further basic and clinical investigation.

Therapeutic HPV DNA vaccines

It is now well established that most cervical cancers are causally associated with HPV infection. This realization has led to efforts to control HPV-associated malignancy through prevention or treatment of HPV infection. Currently, commercially available HPV vaccines are not designed to control established HPV infection and associated premalignant and malignant lesions. To treat and eradicate pre-existing HPV infections and associated lesions which remain prevalent in the U.S. and worldwide, effective therapeutic HPV vaccines are needed. DNA vaccination has emerged as a particularly promising form of therapeutic HPV vaccines due to its safety, stability and ability to induce antigen-specific immunity. This review focuses on improving the potency of therapeutic HPV vaccines through modification of dendritic cells (DCs) by [1] increasing the number of antigen-expressing/antigen-loaded DCs, [2] improving HPV antigen expression, processing and presentation in DCs, and [3] enhancing DC and T cell interaction. Continued improvement in therapeutic HPV DNA vaccines may ultimately lead to an effective DNA vaccine for the treatment of HPV-associated malignancies.

Expression of HPV6b L1/EBV LMP2 multiepitope and immunogenicity in mice

Human papillomavirus (HPV) major capsid protein L1 is an important vehicle for the delivery of epitopes. To investigate the expression and immunogenicity of hybridized HPV6b L1 containing multiepitope of Epstein-Barr virus (EBV) latency membrane protein 2 (LMP2), a recombinant plasmid pcDNA3.1(+) containing mammalian codon-optimization HPV6b L1 gene and EBV LMP2 multiepitope was constructed. The EBV LMP2 multiepitope containing T- and B-cell epitope-rich peptides was inserted into C-terminal of HPV6b L1-coding sequence. The constructed plasmid after verified by enzyme restriction assay and DNA sequencing was transfected into COS-7 cells. Expression of the chimeric gene in COS-7 cells was confirmed by RT-PCR, western blot analysis and immunofluorescence assay. Results revealed successful expression of the chimeric HPV6b L1/EBV LMP2 multiepitope gene both at the mRNA and protein levels in transfected COS-7 cells. Intramuscular administration in mice was able to elicit not only antibodies against HPV6b L1 virus-like particle and EBV LMP2, but also cytotoxic T lymphocyte activity against the EBV LMP2 epitopes. The present results confirmed that HPV L1 protein is potential to deliver multiepitope of EBV LMP2 as immunogen to the MHC class I and class II pathways, extending the use of HPV L1 as delivery vehicles.

Therapeutic HPV DNA vaccines

Human papillomavirus (HPV) has been associated with several human cancers, including cervical cancer, vulvar cancer, vaginal and anal cancer, and a subset of head and neck cancers. The identification of HPV as an etiological factor for HPV-associated malignancies creates the opportunity for the control of these cancers through vaccination. Currently, the preventive HPV vaccine using HPV virus-like particles has been proven to be safe and highly effective. However, this preventive vaccine does not have therapeutic effects, and a significant number of people have established HPV infection and HPV-associated lesions. Therefore, it is necessary to develop therapeutic HPV vaccines to facilitate the control of HPV-associated malignancies and their precursor lesions. Among the various forms of therapeutic HPV vaccines, DNA vaccines have emerged as a potentially promising approach for vaccine development due to their safety profile, ease of preparation and stability. However, since DNA does not have the intrinsic ability to amplify or spread in transfected cells like viral vectors, DNA vaccines can have limited immunogenicity. Therefore, it is important to develop innovative strategies to improve DNA vaccine potency. Since dendritic cells (DCs) are key players in the generation of antigen-specific immune responses, it is important to develop innovative strategies to modify the properties of the DNA-transfected DCs. These strategies include increasing the number of antigen-expressing/antigen-loaded DCs, improving antigen processing and presentation in DCs, and enhancing the interaction between DCs and T cells. Many of the studies on DNA vaccines have been performed on preclinical models. Encouraging results from impressive preclinical studies have led to several clinical trials.

IFN-gamma promotes generation of IL-10 secreting CD4+ T cells that suppress generation of CD8 responses in an antigen-experienced host

Ags characterizing tumors or chronic viral infection are generally presented to the host immune system before specific immunotherapy is initiated, and consequent generation of regulatory CD4(+) T cells can inhibit induction of desired effector CD8 T cell responses. IL-10 produced in response to ongoing Ag exposure inhibits generation of CD8 T cells in an Ag-experienced host. We now show that this IL-10 is produced by Ag experienced CD4(+) glucocorticoid-induced tumor necrosis factor receptor(+) T cells that also secrete IFN-gamma upon antigenic stimulation, that IL-10 secretion by these cells is enhanced through IFN-gamma signaling, and, unexpectedly, that IFN-gamma signaling is required for inhibition of generation of Ag-specific CD8 T cell responses in an Ag-experienced host. Systemic inhibition of both IL-10 and IFN-gamma at the time of immunization may therefore facilitate induction of effective immunotherapeutic responses against tumor specific and viral Ags.

Antigen-specific immunotherapy of cervical and ovarian cancer

We contrast the efforts to treat ovarian cancer and cervical cancer through vaccination because of their different pathobiology. A plethora of approaches have been developed for therapeutic vaccination against cancer, many of which target defined tumor-associated antigens (TAAs). Persistent infection with oncogenic human papillomavirus (HPV) types causes cervical cancer. Furthermore, cervical cancer patients frequently mount both humoral and T-cell immune responses to the HPV E6 and E7 oncoproteins, whose expression is required for the transformed phenotype. Numerous vaccine studies target these viral TAAs, including recent trials that may enhance clearance of pre-malignant disease. By contrast, little is known about the etiology of epithelial ovarian cancer. Although it is clear that p53 mutation or loss is a critical early event in the development of epithelial ovarian cancer, no precursor lesion has been described for the most common serous histotype, and even the location of its origin is debated. These issues have complicated the selection of appropriate ovarian TAAs and the design of vaccines. Here we focus on mesothelin as a promising ovarian TAA, because it is overexpressed and immunogenic at high frequency in patients, is displayed on the cell surface, and potentially contributes to ovarian cancer biology.

An investigation into the use of human papillomavirus type 16 virus-like particles as a delivery vector system for foreign proteins: N- and C-terminal fusion of GFP to the L1 and L2 capsid proteins

Development of vaccine strategies against human papillomavirus (HPV), which causes cervical cancer, is a priority. We investigated the use of virus-like particles (VLPs) of the most prevalent type, HPV-16, as carriers of foreign proteins. Green fluorescent protein (GFP) was fused to the N or C terminus of both L1 and L2, with L2 chimeras being co-expressed with native L1. Purified chimaeric VLPs were comparable in size ( approximately 55 nm) to native HPV VLPs. Conformation-specific monoclonal antibodies (Mabs) bound to the VLPs, thereby indicating that they possibly retain their antigenicity. In addition, all of the VLPs encapsidated DNA in the range of 6-8 kb.

Virus-like particles: flexible platforms for vaccine development

Virus-like particles (VLPs) consist of viral structural proteins that, when overexpressed, spontaneously self-assemble into particles that are antigenically indistinguishable from infectious virus or subviral particles. VLPs can be considered as dense, repetitive arrays of one or more protein subunits with properties that are highly advantageous for use as stand-alone vaccines or as vaccine platforms. This review discusses the development of VLP-based platform technologies for vaccines against pathogens, as well as nontraditional targets such as self-antigens involved in chronic diseases.

Overcoming original antigenic sin to generate new CD8 T cell IFN-gamma responses in an antigen-experienced host

The failure to mount effective immunity to virus variants in a previously virus-infected host is known as original antigenic sin. We have previously shown that prior immunity to a virus capsid protein inhibits induction by immunization of an IFN-gamma CD8+ T cell response to an epitope linked to the capsid protein. We now demonstrate that capsid protein-primed CD4+ T cells secrete IL-10 in response to capsid protein presented by dendritic cells, and deviate CD8+ T cells responding to a linked MHC class I-restricted epitope to reduce IFN-gamma production. Neutralizing IL-10 while delivering further linked epitope, either in vitro or in vivo, restores induction by immunization of an Ag-specific IFN-gamma response to the epitope. This finding demonstrates a strategy for overcoming inhibition of MHC class I epitopes upon immunization of a host already primed to Ag, which may facilitate immunotherapy for chronic viral infection or cancer.

Papillomavirus virus-like particles as vehicles for the delivery of epitopes or genes

Papillomaviruses (PVs) are simple double-strand DNA viruses whose virion shells are T = 7 icosahedrons and composed of major capsid protein L1 and minor capsid protein L2.L1 alone or together with L2 can self-assemble into virus-like particles (VLPs) when expressed in eukaryotic or prokaryotic expression systems. Although the VLPs lack the virus genome DNA, their morphological and immunological characteristics are very similar to those of nature papillomaviruses. PV VLP vaccination can induce high titers of neutralizing antibodies and can effectively protect animals or humans from PV infection. Moreover, PV VLPs have been good candidates for vehicles to deliver epitopes or genes to target cells. They are widely used in the fields of vaccine development, neutralizing antibody detection, basic virologic research on papillomaviruses, and human papillomavirus (HPV) screening. Besides the structural biology and immunological basis for PV VLPs used as vehicles to deliver epitopes or genes, this review details the latest findings on chimeric papillomavirus VLPs and papillomavirus pseudoviruses, which are two important forms of PV VLPs used to transfer epitopes or genes.

Activation of dendritic cells by human papillomavirus-like particles through TLR4 and NF-kappaB-mediated signalling, moderated by TGF-beta

Human papillomavirus-like particles (HPV-VLP) are a candidate vaccine for prevention of HPV infection, and also are a candidate for an immunogenic delivery system for incorporated antigen. VLP activate in vitro generated dendritic cells (DC) but not Langerhans cells (LC); however, the mechanism of this activation is unknown. We have shown that uptake and activation of DC by VLP involves proteoglycan receptors and can be inhibited by heparin. Heparin has been shown to activate DC by signalling through Toll-like receptor 4 (TLR4) and nuclear factor (NF)-kappaB. The pathway of DC activation by VLP was further investigated in the present study. Exposure to VLP induced costimulatory molecule expression, RelB translocation and IL-10 production by DC but not by LC. The lack of LC activation was reversible when TGF-beta was removed from the LC medium. VLP-induced induction of costimulatory molecule expression, RelB activation and cytokine secretion by DC was blocked by inhibition of NF-kappaB activation, heparin or TLR4 mAb. The data provide evidence that HPV-VLP signal DC through a pathway involving proteoglycan receptors, TLR4 and NF-kappaB, and shed light on the mechanism by which VLP stimulate immunity in the absence of adjuvants in vivo. LC may resist activation in normal epithelium abundant in TGF-beta, but not in situations in which TGF-beta concentrations are reduced.

Vaccines for human papillomavirus-associated anogenital disease and cervical cancer: practical and theoretical approaches

The association of genital warts, cervical dysplasia and cervical cancer with certain human papillomavirus (HPV) types indicates that vaccine strategies that target the virus could be effective in controlling disease onset and progression. Three vaccine strategies are available. Firstly, a prophylactic approach of immunisation with HPV virus-like particles to elicit neutralising antibody would prevent infection. Secondly, vaccination targeting replicating virus in suprabasal cells of infected anogenital epithelium would be an effective therapy for infection and early dysplasias. Thirdly, immunotherapy directed to the oncoprotein products of the HPV E6 and E7 open reading frames would be effective in the control of cervical carcinoma. We examine how these strategies may be augmented by contemporary vaccine technologies, in particular through the use of live recombinant vaccine vectors, specific targeting of antigen processing pathways, dendritic cell and 'polytope' approaches, to produce 'designer' vaccines of maximum specificity and efficacy. How these approaches are being exploited by vaccine manufacturers and in clinical trials is discussed.

Heterologous papillomavirus virus-like particles and human papillomavirus virus-like particle immune complexes activate human Langerhans cells

Chimeric human papillomavirus virus-like particles (HPV cVLP) are currently being explored as a therapeutic vaccination strategy against cervical cancer. HPV cVLP are being explored as a result of their interaction with and activation of dendritic cells, a potent antigen-presenting cell. However Langerhans cells, another type of antigen-presenting cell, can interact with HPV cVLP especially during mucosal routes of vaccine administration. Langerhans cells are not activated by HPV cVLP, utilize a different endocytosis mechanism than DC for HPV cVLP uptake, do not initiate an immune response toward HPV cVLP derived antigens, and are potentially immunosuppressive after interaction with HPV cVLP. Taken together, these findings indicate that the overall effectiveness of HPV cVLP as a therapeutic vaccine may be reduced. Bovine papillomavirus (BPV) VLP, cotton-tail rabbit papillomavirus (CRPV) VLP, and HPV VLP immune complexes (IC), which are taken up via similar endocytosis mechanisms in DC and LC, activate both cell types. DC and LC incubated with these VLP upregulate surface activation markers and increase secretion of IL-12 p70. The activated cells are then able to initiate an immune response against chimeric VLP-derived antigens. These data indicate that other therapeutic vaccination strategies based on using chimeric BPV VLP, chimeric CRPV VLP, or chimeric HPV VLP immune complexes may be more effective in generating an immune response against HPV-induced diseases such as cervical cancer.

Preventative and therapeutic vaccines for cervical cancer

"High-risk" genotypes of the human papillomavirus (HPV), most commonly HPV genotype 16, are the primary etiologic agents of cervical cancer. Indeed HPV DNA is detected in 99% of cervical carcinomas. Thus, cervical cancer and other HPV-associated malignancies might be prevented or treated by the induction of the appropriate viral-antigen-specific immune responses. Transmission of papillomavirus may be prevented by the generation of antibodies to capsid proteins L1 and L2 that neutralize viral infection. HPV L1 virus-like particles (VLPs) show great promise as prophylactic HPV vaccines in ongoing clinical trials but L2-based preventative vaccines have yet to be tested in patients. Since the capsid proteins are not expressed at detectable levels by infected basal keratinocytes or in HPV-transformed cells, therapeutic vaccines generally target the nonstructural early viral antigens. Two HPV oncogenic proteins, E6 and E7, are critical to the induction and maintenance of cellular transformation and are co-expressed in the majority of HPV-containing carcinomas. Although other early viral antigens show promise for vaccination against papillomas, therapeutic vaccines targeting E6 and E7 may provide the best opportunity to control HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, as peptides or proteins, in nucleic acid form, as components of chimeric VLPs, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. Should this new generation of HPV preventative and therapeutic vaccines function in patients as demonstrated in animal models, oncogenic HPV infection and its associated malignancies could be controlled by vaccination. Importantly, recent advances in HPV detection and continued improvements in screening further enhance our opportunities to systematically eradicate HPV-associated malignancy.

Vaccination to prevent and treat cervical cancer

Human papillomaviruses (HPVs) are the primary etiologic agents of cervical cancer. Thus, cervical cancer and other HPV-associated malignancies might be prevented or treated by HPV vaccines. Transmission of papillomavirus may be prevented by the generation of antibodies to capsid proteins L1 and L2 that neutralize viral infection. However, because the capsid proteins are not expressed at detectable levels by infected basal keratinocytes or in HPV-transformed cells, therapeutic vaccines generally target nonstructural early viral antigens. Two HPV oncogenic proteins, E6 and E7, are critical to the induction and maintenance of cellular transformation and are coexpressed in the majority of HPV-containing carcinomas. Thus, therapeutic vaccines targeting E6 and E7 may provide the best option for controlling HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, as peptides or protein, in nucleic acid form, as components of chimeric virus-like particles, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. If these preventive and therapeutic HPV vaccines prove successful in patients, as they have in animal models, then oncogenic HPV infection and its associated malignancies may be controllable by vaccination.

Despite differences between dendritic cells and Langerhans cells in the mechanism of papillomavirus-like particle antigen uptake, both cells cross-prime T cells

As human papillomavirus-like particles (HPV-VLP) represent a promising vaccine delivery vehicle, delineation of the interaction of VLP with professional APC should improve vaccine development. Differences in the capacity of VLP to signal dendritic cells (DC) and Langerhans cells (LC) have been demonstrated, and evidence has been presented for both clathrin-coated pits and proteoglycans (PG) in the uptake pathway of VLP into epithelial cells. Therefore, we compared HPV-VLP uptake mechanisms in human monocyte-derived DC and LC, and their ability to cross-present HPV VLP-associated antigen in the MHC class I pathway. DC and LC each took up virus-like particles (VLP). DC uptake of and signalling by VLP was inhibited by amiloride or cytochalasin D (CCD), but not by filipin treatment, and was blocked by several sulfated and non-sulfated polysaccharides and anti-CD16. In contrast, LC uptake was inhibited only by filipin, and VLP in LC were associated with caveolin, langerin, and CD1a. These data suggest fundamentally different routes of VLP uptake by DC and LC. Despite these differences, VLP taken up by DC and LC were each able to prime naive CD8(+) T cells and induce cytolytic effector T cells in vitro.

IL-10 mediates suppression of the CD8 T cell IFN-gamma response to a novel viral epitope in a primed host

Priming to Ag can inhibit subsequent induction of an immune response to a new epitope incorporated into that Ag, a phenomenon referred to as original antigenic sin. In this study, we show that prior immunity to a virus capsid can inhibit subsequent induction of the IFN-gamma effector T cell response to a novel CD8-restricted antigenic epitope associated with the virus capsid. Inhibition does not involve Ab to the virus capsid, as it is observed in animals lacking B cells. CD8-restricted virus-specific T cell responses are not required, as priming to virus without CTL induction is associated with inhibition. However, IL-10(-/-) mice, in contrast to IL-10(+/+) mice, generate CD8 T cell and Ab responses to novel epitopes incorporated into a virus capsid, even when priming to the capsid has resulted in high titer Ab to the capsid. Furthermore, capsid-primed mice, unable to mount a response to a novel epitope in the capsid protein, are nevertheless able to respond to the same novel epitope delivered independently of the capsid. Thus, inhibition of responsiveness to a novel epitope in a virus-primed animal is a consequence of secretion of IL-10 in response to presented Ag, which inhibits local generation of new CD8 IFN-gamma-secreting effector T cells. Induction of virus- or tumor Ag-specific CD8 effector T cells in the partially Ag-primed host may thus be facilitated by local neutralization of IL-10.

Formation of polyomavirus-like particles with different VP1 molecules that bind the urokinase plasminogen activator receptor

Icosahedral virus-like particles formed by the self-assembly of polyomavirus capsid proteins (Py-VLPs) can serve as useful nanostructures for delivering nucleic acids, proteins, and pharmaceuticals into animal cells and tissues. Four predominant surface-exposed loops in the VP1 structure offer potential sites to display sequences that might contribute new targeting specificities. Introduction into each of these loops of sequences derived from the amino-terminal fragment of urokinase plasminogen activator (uPA) or a related phage display peptide reduced the solubility of VP1 molecules when expressed in insect cells, and insertions into the EF loop reduced VP1 solubility least. Coexpression in insect cells of the uPA-VP1 molecules and VP1 containing a FLAG epitope in the HI loop permitted the formation of heterotypic Py-VLPs containing uPA-VP1 and FLAG-VP1. These heterotypic VLPs bound to uPAR on the surfaces of animal cells. Heterotypic Py-VLPs containing ligands for multiple cell surface receptors should be useful for targeting specific cells and tissues.

Construction and production of fluorescent papillomavirus-like particles

The green fluorescent protein (GFP) from the jellyfish Aequorea victoria has attracted widespread interest since it was demonstrated to be fluorescent in vivo when expressed in other organisms. In order to investigate papillomavirus life cycle which hampered by the unavailability of conventional cell culture system, we constructed a chimeric bovine papillomavirus (BPV) type 1 virus-like particles (VLPs) containing GFP. It was found that fluorescent VLPs could be assembled from L2 protein in which GFP is inserted into the N-terminal region of L2 (aa 88). The fluorescent VLPs could also be assembled from a GFP/L2 fusion protein in which part of the L2 sequence had been deleted. In vitro, fluorescent VLPs could bind to CV-1 cells, and this VLP/cell interaction could be analyzed by FACS assay. These results demonstrated that GFP could incorporate into BPV1 VLPs without disruption of the VLP structure. Fluorescent VLPs might be a useful tool for study of papillomavirus virus/cell interaction.

Heterologous boosting increases immunogenicity of chimeric papillomavirus virus-like particle vaccines

Chimeric human papillomavirus virus-like particles (HPV cVLPs), containing the HPV16 non-structural protein E7, are potent vaccines for inducing antigen-specific protective immunity against HPV-transformed tumors in animal models. Previous data demonstrated that the effectiveness of cytotoxic T lymphocyte (CTL) induction after repetitive vaccination with the same cVLP, and thus vaccine efficacy, is limited by the presence of neutralizing antibodies induced after the first application. Here, we determined if altering the route of vaccine delivery or incorporation of the target antigen into VLPs of a heterologous papillomavirus type could overcome inhibition of MHC class I antigen presentation by neutralizing antibodies, resulting in a boosting of CD8(+) T-cell responses against the incorporated antigen, HPV16 E7. Mucosal delivery of cVLPs resulted in detection of systemic E7-specific CD8(+) T cells, however, these routes were not able to bypass the inhibitory effect of circulating antibodies against homologous VLP types. In contrast, mice immunized and boosted with heterologous cVLPs containing HPV16 E7 showed a higher frequency of E7-specific T cells in vitro and displayed reduced tumor growth in a therapeutic setting compared to mice treated with homologous cVLPs. The data indicate that the use of different cVLP types for prime/boost regimens is a promising strategy to increase the efficacy and usefulness of cVLP-based vaccines for the treatment of cervical neoplasia.

Papillomavirus-like particle vaccines

Papillomavirus-like particle (VLP)-based subunit vaccines have undergone rapid development over the past 8 years. Three types are being investigated. The most basic type is composed of only the L1 major capsid protein and is designed to prevent genital human papillomavirus (HPV) infection by inducing virus-neutralizing antibodies. On the basis of positive results in animal models, clinical trials of this type of vaccine for HPV16, and other types, are currently under way. Preliminary results have been encouraging in that systemic immunization with the L1 VLPs induced high serum titers of neutralizing antibodies without substantial adverse effects. The second type of vaccine incorporates other papillomavirus polypeptides into the VLPs as L1 or L2 fusion proteins. These chimeric VLPs are designed to increase the therapeutic potential of an HPV vaccine by inducing cell-mediated responses to nonstructural viral proteins, such as E7. Studies in mice indicate that these vaccines generate potent antitumor cytotoxic lymphocyte (CTL) responses while retaining the ability to induce high-titer neutralizing antibodies. It is likely that prophylactic and therapeutic clinical trials of chimeric VLPs will be initiated in the near future. The third type of VLP-based vaccine is designed to induce autoantibodies against central self-antigens by incorporating self-peptides into the outer surface of VLPs, a process that could have therapeutic potential in various disease settings unrelated to HPV infection. In a recent proof of concept study, a peptide from an external loop of mouse CCR5 protein was inserted into a neutralizing epitope of L1. In mice, the particles generated by this chimeric L1 were able to induce high titers of CCR5 antibodies that specifically recognized the surface of CCR5-transfected cells and blocked in vitro infection of an M-tropic human immunodeficiency virus strain.

Progress in prophylactic and therapeutic vaccines for human papillomavirus infection

Virus-like particle (VLP) subunit vaccines composed of the major capsid protein L1 of the genital human papillomaviruses (HPVs) are now in Phase III clinical trials. The vaccines are immunogenic and safe and early results indicate efficacy. VLPs induce strong cell-mediated as well as humoral immune responses and chimeric VLPs including an HPV early protein may have therapeutic potential. Polynucleotide and recombinant viral vaccines encoding nonstructural viral proteins show therapeutic and prophylactic efficacy in animal models and are candidate immunotherapies for established low-grade benign genital infections. Vaccines designed to elicit cytotoxic T-lymphocytes specific for the HPV oncoproteins E6 and E7 show immunogenicity and efficacy in transplantable tumor models in rodents. In Phase I and II trials these vaccines are immunogenic and safe but show limited efficacy.

Comparison of human papillomavirus type 16 L1 chimeric virus-like particles versus L1/L2 chimeric virus-like particles in tumor prevention

Chimeric human papillomavirus (HPV) virus-like particles (cVLPs) with the HPV16 E7 antigen fused to either the major capsid protein, L1, or the minor capsid protein, L2, have been used independently to protect against the formation of HPV-induced tumors in animal models. However, the advantages and disadvantages of both types of particles with respect to production and vaccine efficacy have never been analyzed. Therefore, in this study, we compared cVLPs with the HPV16 E7 antigen fused to L1 versus cVLPs with E7 fused to L2 with respect to their ability to protect mice from tumor challenge. The first 57 amino acids of E7 were used to overcome the size limitation and limited VLP production imposed by inserting polypeptides into L1 cVLPs. C57BL/6 mice were immunized with the above cVLPs at various doses. Tumor challenge was then performed with HPV16 E7-positive TC-1 cells. HPV16 L1-E7((1-57)) was superior to HPV16 L1/L2-E7((1-57)) in eliciting tumor protection at equivalent doses, although both types of particles were able to protect mice. Both cVLPs induced a specific cytotoxic T lymphocyte (CTL) response to the H2-D(b)-restricted E7 peptide (E7(49-57)) as determined by an ELISPOT assay and tetramer staining; however, immunization with the L1-E7((1-57)) cVLPs resulted in twofold higher CTL precursor frequencies. Our results demonstrate that cVLPs with the antigen fused to L1 are a more efficient vaccine with respect to tumor prevention than cVLPs with the antigen fused to L2. At the same time, however, L1 cVLPs are limited by the size of the antigen that can be incorporated and in the amount of cVLP that can be obtained from cultures when compared to L1/L2 cVLPs. This balances out their superior ability to induce protective immunity.

Effect of vaccine delivery system on the induction of HPV16L1-specific humoral and cell-mediated immune responses in immunized rhesus macaques

There have been numerous studies to assess the immunogenicity of candidate therapeutic and prophylactic vaccines for human papillomavirus (HPV), but few of them have directly compared different vaccines in an immunologically relevant animal system. In the present study, several vaccine delivery systems (VLPs, chimeric VLPs, plasmid DNA, and a replication incompetent adenoviral vector) expressing HPV16L1 were evaluated for their ability to induce HPV16L1 VLP-specific humoral immune responses, including neutralizing antibodies, and cell-mediated immune responses in rhesus macaques. Monkeys immunized with HPV16L1 VLPs mounted a potent humoral response with strongly neutralizing antibodies and a strong L1-specific Th2 response as measured by IL-4 production by CD4+ T cells. Monkeys immunized with plasmid DNA or an adenoviral vector expressing HPV16L1 showed strong Th1/Tc1 responses as measured by IFN-gamma production by CD4+ and/or CD8+ T cells and potent humoral responses, but only weakly neutralizing antibodies. These data demonstrate that the nature of the immune response against HPV16L1 is dramatically different when it is introduced via different delivery systems. Additionally, these findings support the notion that an HPV16L1 VLP-based vaccine will induce the strongly neutralizing antibodies necessary for effective prophylaxis.