Oral immunization with different assembly forms of the HPV 16 major capsid protein L1 induces neutralizing antibodies and cytotoxic T-lymphocytes

Mammalian cells-based platforms for the generation of SARS-CoV-2 virus-like particles

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of COVID-19. Though many COVID-19 vaccines have been developed, most of them are delivered via intramuscular injection and thus confer relatively weak mucosal immunity against the natural infection. Virus-Like Particles (VLPs) are self-assembled nanostructures composed of key viral structural proteins, that mimic the wild-type virus structure but are non-infectious and non-replicating due to the lack of viral genetic material. In this study, we efficiently generated SARS-CoV-2 VLPs by co-expressing the four SARS-CoV-2 structural proteins, specifically the membrane (M), small envelope (E), spike (S) and nucleocapsid (N) proteins. We show that these proteins are essential and sufficient for the efficient formation and release of SARS-CoV-2 VLPs. Moreover, we used lentiviral vectors to generate human cell lines that stably produce VLPs. Because VLPs can bind to the virus natural receptors, hence leading to entry into cells and viral antigen presentation, this platform could be used to develop novel vaccine candidates that are delivered intranasally.

Exploring the Molecular Pathogenesis, Pathogen Association, and Therapeutic Strategies against HPV Infection

The human papillomavirus (HPV), commonly documented as the cause of warts, has gained much interest recently due to its possible links to several types of cancer. HPV infection is discussed in this review from multiple angles, including its virology, epidemiology, etiology, immunology, clinical symptoms, and treatment. Recent breakthroughs in molecular biology have led to the development of new methods for detecting and treating HPV in tissue. There is no cure for HPV, and although vaccines are available to prevent infection with the most common HPV viruses, their utilization is limited. Destruction and excision are the primary treatment modalities. This review sheds light on the epidemiology, molecular pathogenesis, the association of several other pathogens with HPV, the latest treatment strategies available to treat the same, and an overview of the progress made and the obstacles still to be overcome in the fight against HPV infection.

Towards novel nano-based vaccine platforms for SARS-CoV-2 and its variants of concern: Advances, challenges and limitations

Vaccination is the most effective tool available for fighting the spread of COVID-19. Recently, emerging variants of SARS-CoV-2 have led to growing concerns about increased transmissibility and decreased vaccine effectiveness. Currently, many vaccines are approved for emergency use and more are under development. This review highlights the ongoing advances in the design and development of different nano-based vaccine platforms. The challenges, limitations, and ethical consideration imposed by these nanocarriers are also discussed. Further, the effectiveness of the leading vaccine candidates against all SARS-CoV-2 variants of concern are highlighted. The review also focuses on the possibility of using an alternative non-invasive routes of vaccine administration using micro and nanotechnologies to enhance vaccination compliance and coverage.

Inducible expression of human papillomavirus-16 L1 capsomeres in the plastomes of Nicotiana tabacum: Transplastomic plants develop normal flowers and pollen

Human papillomavirus type-16 (HPV-16) is the major HPV type involved in causing cervical cancer among women. The disease burden is high in developing and underdeveloped countries. Previously, the constitutive expression of HPV-16 L1 protein led to male sterility in transplastomic tobacco plants. Here, the HPV-16 L1 gene was expressed in chloroplasts of Nicotiana tabacum under the control of an ethanol-inducible promoter, trans-activated by nucleus-derived signal peptide. Plants containing nuclear component were transformed with transformation vector pEXP-T7-L1 by biolistic gun. The transformation and homoplasmic status of transformed plants was verified by polymerase chain reaction and Southern blotting, respectively. Protein was induced by spraying 5% ethanol for 7 consecutive days. The correct folding of L1 protein was confirmed by antigen-capture ELISA using a conformation-specific antibody. The L1 protein accumulated up to 3 μg/g of fresh plant material. The L1 protein was further purified using affinity chromatography. All transplastomic plants developed normal flowers and produced viable seeds upon self-pollination. Pollens also showed completely normal structure under light microscope and scanning electron microscopy. These data confirm the use of the inducible expression as plant-safe approach for expressing transgenes in plants, especially those genes that cause detrimental effects on plant growth and morphology.

A Review on Current COVID-19 Vaccines and Evaluation of Particulate Vaccine Delivery Systems

First detected in Wuhan, China, a highly contagious coronavirus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), also known as COVID-19, spread globally in December of 2019. As of 19 September 2021, approximately 4.5 million people have died globally, and 215 million active cases have been reported. To date, six vaccines have been developed and approved for human use. However, current production and supply capabilities are unable to meet global demands to immunize the entire world population. Only a few countries have been able to successfully vaccinate many of their residents. Therefore, an alternative vaccine that can be prepared in an easy and cost-effective manner is urgently needed. A vaccine that could be prepared in this manner, as well as can be preserved and transported at room temperature, would be of great benefit to public health. It is possible to develop such an alternative vaccine by using nano- or microparticle platforms. These platforms address most of the existing vaccine limitations as they are stable at room temperature, are inexpensive to produce and distribute, can be administered orally, and do not require cold chain storage for transportation or preservation. Particulate vaccines can be administered as either oral solutions or in sublingual or buccal film dosage forms. Besides improved patient compliance, the major advantage of oral, sublingual, and buccal routes of administration is that they can elicit mucosal immunity. Mucosal immunity, along with systemic immunity, can be a strong defense against SARS-CoV-2 as the virus enters the system through inhalation or saliva. This review discusses the possibility to produce a particulate COVID vaccine by using nano- or microparticles as platforms for oral administration or in sublingual or buccal film dosage forms in order to accelerate global vaccination.

Progress in the use of Immunotherapy to Treat Uterine Cervical Cancer

Cervical intraepithelial neoplasia has a high incidence in many of the world's populations, and it has been hypothesized to be a precursor of uterine cervical cancer. Cervical intraepithelial neoplasia also shares similar pathological traits with human papillomavirus infections. Various surgical treatments have been proposed over the years for the treatment of cervical intraepithelial neoplasia, including conization, hysterectomy and, more recently, a loop electrosurgical excisional procedure. However, a higher recurrence rate of the disease has been observed after these procedures. Therefore, immunotherapy has been proposed as a potential treatment to be used in conjunction with surgery, or independently, as treatment for cervical intraepithelial neoplasia. Currently, immunotherapy includes the application of recombinant viral proteins, vaccines, or antibody- and dendritic cell-based therapies. In this review, we summarize the development and testing of these immunotherapy approaches, particularly in regard to their application for the treatment of cervical intraepithelial neoplasia.

Immunization with Human Papillomavirus 16 L1+E2 Chimeric Capsomers Elicits Cellular Immune Response and Antitumor Activity in a Mouse Model

Development of cervical cancer is associated with persistent infections by high-risk human papillomavirus (HPV). Although current HPV L1-based prophylactic vaccines prevent infection, they do not help to eliminate prevalent infections or lesions. Our aims were (i) to generate a vaccine combining prophylactic and therapeutic properties by producing chimeric capsomers after fusion of the L1 protein to different fragments of E2 from HPV 16, and (ii) to evaluate their capacity to generate an antitumoral cellular response, while conserving L1 neutralizing epitopes. Chimeric proteins were produced in Escherichia coli and purified by glutathione S-transferase (GST)-affinity chromatography. Their structure was characterized using size exclusion chromatography, sucrose gradient centrifugation, electron microscopy, and anti-L1 enzyme-linked immunosorbent assay. All chimeric proteins form capsomers and heterogeneous aggregates. One, containing part of the carboxy-terminal domain of E2 and its hinge region (L1Δ+E2H/NC, aa 206-307), conserved the neutralizing epitope H16.V5. We then evaluated the capacity of this chimeric protein to induce a cytotoxic T-cell response against HPV 16 E2. In (51)Cr release cytotoxicity assays, splenocytes from C57BL/6 immunized mice recognized and lysed TC-1/E2 cells, which express and present endogenously processed E2 peptides. Moreover, this E2-specific cytotoxic response inhibited the growth of tumors of TC-1/E2 cells in mice. Finally, we identified an epitope (aa 292-301) of E2 involved in this cytotoxic response. We conclude that the L1Δ+E2H/NC chimeric protein produced in bacteria can be an effective and economically interesting candidate for a combined prophylactic and therapeutic vaccine that could help eliminating HPV16-positive low-grade cervical lesions and persistent viral infections, thus preventing the development of lesions and, at the same time, the establishment of new infections.

A Live Vector Expressing HPV16 L1 Generates an Adjuvant-Induced Antibody Response In-vivo

Background:

The association between human papillomavirus (HPV) infections and cervical cancer has suggested the design of prophylactic and therapeutic vaccines against genital warts. The HPV capsid has made of two L1 and L2 coat proteins that have produced late in viral infections. Regarding to the recent studies, two commercial prophylactic vaccines have based on L1 viral like particles (VLPs) could strongly induce antibody responses, and protect human body from HPV infections. However, the use of these HPV vaccines has hindered due to their high cost and some limitations. Currently, among various vaccination strategies, live vector-based vaccines have attracted a great attention.

Objectives:

Herein, a non-pathogenic strain of the protozoan organism known as Leishmania tarentolae has utilized to induce potent humoral immunity in mice model.

Materials and Methods:

At first, cloning of HPV16 L1 gene into Leishmania expression vector has performed and confirmed by PCR and digestion with restriction enzymes. The promastigotes of Leishmania tarentolae (L.tar) have transfected with linearized DNA construct by electroporation. Protein expression has analyzed by SDS-PAGE and western blotting. Then, the immunogenicity of leishmania expressing L1 protein (L.tar-L1) has assessed in mice model.

Results:

Our data has indicated that subcutaneous immunization of mice with the recombinant L.tar-L1 has led to enhance the levels of IgG1 and lgG2a in comparison with control groups. Furthermore, there was no significant increase in antibody levels between two and three times of immunizations.

Conclusions:

The recombinant live vector was able to induce humoral immunity in mice without need of any adjuvant. However, further studies have required to increase its efficiency.

Whole recombinant Pichia pastoris expressing HPV16 L1 antigen is superior in inducing protection against tumor growth as compared to killed transgenic Leishmania

The development of an efficient vaccine against high-risk HPV types can reduce the incidence rates of cervical cancer by generating anti-tumor protective responses. Traditionally, the majority of prophylactic viral vaccines are composed of live, attenuated or inactivated viruses. Among them, the design of an effective and low-cost vaccine is critical. Inactivated vaccines especially heat-killed yeast cells have emerged as a promising approach for generating antigen-specific immunotherapy. Recent studies have indicated that yeast cell wall components possess adjuvant activities. Moreover, a non-pathogenic protozoan, Leishmania tarentolae (L.tar) has attracted a great attention as a live candidate vaccine. In current study, immunological and protective efficacy of whole recombinant killed Pichia pastoris and Leishmania tarentolae expressing HPV16 L1 capsid protein was evaluated in tumor mice model. We found that Pichia-L1, L.tar-L1 and Gardasil groups increase the IgG2a/IgG1 ratio, indicating a relative preference for the induction of Th1 immune responses. Furthermore, subcutaneous injection of killed Pichia-L1 generated the significant L1-specific IFN-γ immune response as well as the best protective effects in vaccinated mice as compared to killed L.tar-L1, killed Pichia pastoris, killed L.tar and PBS groups. Indeed, whole recombinant Leishmania tarentolae could not protect mice against C3 tumor mice model. These data suggest that Pichia-L1 may be a candidate for the control of HPV infections.

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.

Immunoprevention of human papillomavirus-associated malignancies

Persistent infection by one of 15 high-risk human papillomavirus (hrHPV) types is a necessary but not sufficient cause of 5% of all human cancers. This provides a remarkable opportunity for cancer prevention via immunization. Since Harald zur Hausen's pioneering identification of hrHPV types 16 and 18, found in approximately 50% and 20% of cervical cancers, respectively, two prophylactic HPV vaccines containing virus-like particles (VLP) of each genotype have been widely licensed. These vaccines are beginning to affect infection and HPV-associated neoplasia rates after immunization campaigns in adolescents. Here, we review recent progress and opportunities to better prevent HPV-associated cancers, including broadening immune protection to cover all hrHPV types, reducing the cost of HPV vaccines especially for developing countries that have the highest rates of cervical cancer, and immune-based treatment of established HPV infections. Screening based upon George Papanicolaou's cervical cytology testing, and more recently detection of hrHPV DNA/RNA, followed by ablative treatment of high-grade cervical intraepithelial neoplasia (CIN2/3) have substantially reduced cervical cancer rates, and we examine their interplay with immune-based modalities for the prevention and eventual elimination of cervical cancer and other HPV-related malignancies.

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

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

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

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

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

Virus-like particles as a highly efficient vaccine platform: diversity of targets and production systems and advances in clinical development

Virus-like particles (VLPs) are a class of subunit vaccines that differentiate themselves from soluble recombinant antigens by stronger protective immunogenicity associated with the VLP structure. Like parental viruses, VLPs can be either non-enveloped or enveloped, and they can form following expression of one or several viral structural proteins in a recombinant heterologous system. Depending on the complexity of the VLP, it can be produced in either a prokaryotic or eukaryotic expression system using target-encoding recombinant vectors, or in some cases can be assembled in cell-free conditions. To date, a wide variety of VLP-based candidate vaccines targeting various viral, bacterial, parasitic and fungal pathogens, as well as non-infectious diseases, have been produced in different expression systems. Some VLPs have entered clinical development and a few have been licensed and commercialized. This article reviews VLP-based vaccines produced in different systems, their immunogenicity in animal models and their status in clinical development.

In planta production of a candidate vaccine against bovine papillomavirus type 1

Bovine papillomavirus type 1 (BPV-1) is an economically important virus that induces tumourigenic pathologies in horses and cows. Given that the BPV-1 L1 major coat protein can self-assemble into highly immunogenic higher-order structures, we transiently expressed it in Nicotiana benthamiana as a prelude to producing a candidate vaccine. It was found that plant codon optimization of L1 gave higher levels of expression than its non-optimized counterpart. Following protein extraction, we obtained high yields (183 mg/kg fresh weight leaf tissue) of relatively pure L1, which had self-assembled into virus-like particles (VLPs). We found that these VLPs elicited a highly specific and strong immune response, and therefore they may have utility as a potential vaccine. This is the first report demonstrating the viable production of a candidate BPV vaccine protein in plants.

New approaches to prophylactic human papillomavirus vaccines for cervical cancer prevention

The currently licensed human papillomavirus (HPV) vaccines are safe and highly effective at preventing HPV infection for a select number of papillomavirus types, thus decreasing the incidence of precursors to cervical cancer. It is expected that vaccination will also ultimately reduce the incidence of this cancer. The licensed HPV vaccines are, however, type restricted and expensive, and also require refrigeration, multiple doses and intramuscular injection. Second-generation vaccines are currently being developed to address these shortcomings. New expression systems, viral and bacterial vectors for HPV L1 capsid protein delivery, and use of the HPV L2 capsid protein will hopefully aid in decreasing cost and increasing ease of use and breadth of protection. These second-generation vaccines could also allow affordable immunization of women in developing countries, where the incidence of cervical cancer is high.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

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

Plastid expression of a double-pentameric vaccine candidate containing human papillomavirus-16 L1 antigen fused with LTB as adjuvant: transplastomic plants show pleiotropic phenotypes

Human papillomavirus (HPV) causes cervical cancer in women worldwide, which is currently prevented by vaccines based on virus-like particles (VLPs). However, these vaccines have certain limitations in their availability to developing countries, largely due to elevated costs. Concerning the highest burden of disease in resource-poor countries, development of an improved mucosal and cost-effective vaccine is a necessity. As an alternative to VLPs, capsomeres have been shown to be highly immunogenic and can be used as vaccine candidate. Furthermore, coupling of an adjuvant like Escherichia coli heat-labile enterotoxin subunit B (LTB) to an antigen can increase its immunogenicity and reduce the costs related to separate co-administration of adjuvants. Our study demonstrates the expression of two pentameric proteins: the modified HPV-16 L1 (L1_2xCysM) and LTB as a fusion protein in tobacco chloroplasts. Homoplasmy of the transplastomic plants was confirmed by Southern blotting. Western blot analysis showed that the LTB-L1 fusion protein was properly expressed in the plastids and the recombinant protein was estimated to accumulate up to 2% of total soluble protein. Proper folding and display of conformational epitopes for both LTB and L1 in the fusion protein was confirmed by GM1-ganglioside binding assay and antigen capture ELISA, respectively. However, all transplastomic lines showed chlorosis, male sterility and growth retardation, which persisted in the ensuing four generations studied. Nevertheless, plants reached maturity and produced seeds by pollination with wild-type plants. Taken together, these results pave the way for the possible development of a low-cost adjuvant-coupled vaccine with potentially improved immunogenicity against cervical cancer.

A microbial platform for rapid and low-cost virus-like particle and capsomere vaccines

Studies on a platform technology able to deliver low-cost viral capsomeres and virus-like particles are described. The technology involves expression of the VP1 structural protein from murine polyomavirus (MuPyV) in Escherichia coli, followed by purification using scaleable units and optional cell-free VLP assembly. Two insertion sites on the surface of MuPyV VP1 are exploited for the presentation of the M2e antigen from influenza and the J8 peptide from Group A Streptococcus (GAS). Results from testing on mice following subcutaneous administration demonstrate that VLPs are self adjuvating, that adding adjuvant to VLPs provides no significant benefit in terms of antibody titre, and that adjuvanted capsomeres induce an antibody titre comparable to VLPs but superior to unadjuvanted capsomere formulations. Antibodies raised against GAS J8 peptide following immunization with chimeric J8-VP1 VLPs are bactericidal against a GAS reference strain. E. coli is easily and widely cultivated, and well understood, and delivers unparalleled volumetric productivity in industrial bioreactors. Indeed, recent results demonstrate that MuPyV VP1 can be produced in bioreactors at multi-gram-per-litre levels. The platform technology described here therefore has the potential to deliver safe and efficacious vaccine, quickly and cost effectively, at distributed manufacturing sites including those in less developed countries. Additionally, the unique advantages of VLPs including their stability on freeze drying, and the potential for intradermal and intranasal administration, suggest this technology may be suited to numerous diseases where adequate response requires large-scale and low-cost vaccine manufacture, in a way that is rapidly adaptable to temporal or geographical variation in pathogen molecular composition.

Transplastomic expression of a modified human papillomavirus L1 protein leading to the assembly of capsomeres in tobacco: a step towards cost-effective second-generation vaccines

Certain types of human papillomaviruses (HPV) are causatively associated with cervical carcinoma, the second most common cancer in women worldwide. Due to limitations in the availability of currently used virus-like particle (VLP)-based vaccines against HPV to women of developing countries, where most cases of cervical cancer occur, the development of a cost-effective second-generation vaccine is a necessity. Capsomeres have recently been demonstrated to be highly immunogenic and to have a number of advantages as a potential cost-effective alternative to VLP-based HPV vaccines. We have expressed a mutated HPV-16 L1 (L1_2xCysM) gene that retained the ability to assemble L1 protein to capsomeres in tobacco chloroplasts. The recombinant protein yielded up to 1.5% of total soluble protein. The assembly of capsomeres was examined and verified by cesium chloride density gradient centrifugation and sucrose sedimentation analysis. An antigen capture enzyme-linked immunosorbent assay confirmed the formation of capsomeres by using a conformation-specific monoclonal antibody which recognized the conformational epitopes. Transplastomic tobacco plants exhibited normal growth and morphology, but all such lines showed male sterility in the T₀, T₁ and T₂ generations. Taken together, these results indicate the possibility of producing a low-cost capsomere-based vaccine by plastids.

Human papillomavirus type 16 E6-specific antitumor immunity is induced by oral administration of HPV16 E6-expressing Lactobacillus casei in C57BL/6 mice

Given that local cell-mediated immunity (CMI) against the human papillomavirus type 16 E6 (HPV16 E6) protein is important for eradication of HPV16 E6-expressing cancer cells in the cervical mucosa, the HPV16 E6 protein may be a target for the mucosal immunotherapy of cervical cancer. Here, we expressed the HPV16 E6 antigen on Lactobacillus casei (L. casei) and investigated E6-specific CMI following oral administration of the L. casei-PgsA-E6 to mice. Surface expression of HPV16 E6 antigens was confirmed and mice were orally inoculated with the L. casei-PgsA or the L. casei-PgsA-E6. Compared to the L. casei-PgsA-treated mice, significantly higher levels of serum IgG and mucosal IgA were observed in L. casei-PgsA-E6-immunized mice; these differences were significantly enhanced after boost. Consistent with this, systemic and local CMI were significantly increased after the boost, as shown by increased counts of IFN-γ-secreting cells in splenocytes, mesenteric lymph nodes (MLN), and vaginal samples. Furthermore, in the TC-1 tumor model, animals receiving the orally administered L. casei-PgsA-E6 showed reduced tumor size and increased survival rate versus mice receiving control (L. casei-PgsA) immunization. We also found that L. casei-PgsA-E6-induced antitumor effect was decreased by in vivo depletion of CD4⁺ or CD8⁺ T cells. Collectively, these results indicate that the oral administration of lactobacilli bearing the surface-displayed E6 protein induces T cell-mediated cellular immunity and antitumor effects in mice.

Vaccination with multimeric L2 fusion protein and L1 VLP or capsomeres to broaden protection against HPV infection

Immunization with L1 as pentavalent capsomeres or virus-like particles (VLPs) generates high and long-lived titers of neutralizing antibodies and protection primarily against the human papillomavirus (HPV) type from which the vaccine was derived. Conversely, vaccination with L2 minor capsid protein derived from multiple HPV types induces lower titer, but more broadly neutralizing and protective antibody responses. We combined the advantages of each protective antigen by immunization with titrated doses of multi-type L2 with either L1 capsomeres or VLP. We observed no significant interference between the L1 and L2 antibody response upon co-administration of L1 vaccines with multi-type L2 vaccines.

Combined prophylactic and therapeutic intranasal vaccination against human papillomavirus type-16 using different adeno-associated virus serotype vectors

BACKGROUND

Cervical cancer is the second most frequent cancer among woman worldwide and is considered to be caused by infection with high-risk papilloma viruses. Genetic immunization using recombinant adeno-associated virus (rAAV) vectors has shown great promise for vaccination against human papillomavirus (HPV) infections.

METHODS

rAAV5, -8 and -9 vectors expressing an HPV16 L1/E7 fusion gene were generated and applied intranasally for combined prophylactic and therapeutic vaccination of mice.

RESULTS

The rAAV5 and the rAAV9 vectors showed efficient induction of both humoral and cellular immune responses, whereas rAAV8 failed to immunize mice by the intranasal route. The L1-specific immune response evoked by expression of the L1/E7 fusion gene, however, was lower than that evoked by expression of the L1 antigen alone. This deficiency could be compensated by application of Escherichia coli heat-labile enterotoxin or monophsphoryl lipid as adjuvant upon vaccination with rAAV5-L1/E7. Coimmunization of rAAV9-L1/E7 with rAAV5-L1 or boosting of rAAV9-L1/E7 with rAAV5-L1 strongly increased L1-specific neutralizing antibody titres to levels above those achieved by vaccination with vectors expressing L1 alone. Both vectors elicited a vibrant cytotoxic T-lymphocyte response against L1 or E7. Nasal immunization with rAAV5 or rAAV9 was superior to vaccination with HPV16-L1 virus-like particles (VLPs) or HPV16-L1/E7 CVLPs with respect to humoral and cellular immune responses. Vaccination with the rAAV vectors led to a significant protection of animals against a challenge with different HPV tumour cell lines.

CONCLUSIONS

Our results show that rAAV5 and rAAV9 vectors are promising candidates for a non-invasive nasal vaccination strategy.

Virus-like particles and capsomeres are potent vaccines against cutaneous alpha HPVs

The potential as prophylactic vaccines of L1-based particles from cutaneous genus alpha human papillomavirus (HPV) types has not been assessed so far. However, there is a high medical need for such vaccines since HPV-induced skin warts represent a major burden for children and for immunocompromised adults, such as organ transplant recipients. In this study, we have examined the immunogenicity of capsomeres and virus-like particles (VLPs) from HPV types 2, 27, and 57, the most frequent causative agents of skin warts. Immunization of mice induced immune responses resembling those observed upon vaccination with HPV 16 L1-based antigens. The antibody responses were cross-reactive but type-restricted in their neutralizing capacities. Application of adjuvant led to an enhanced potential to neutralize the respective immunogen type but did not improve cross-neutralization. Vaccination with capsomeres and VLPs from all four analyzed HPV types induced robust IFNgamma-associated T-cell activation. Immunization with mixed VLPs from HPV types 2, 27, and 57 triggered an antibody response similar to that after single-type immunization and capable of efficiently neutralizing all three types. Our results imply that vaccination with combinations of VLPs from cutaneous HPV types constitutes a promising strategy to prevent HPV-induced skin lesions.

Analysis of modified human papillomavirus type 16 L1 capsomeres: the ability to assemble into larger particles correlates with higher immunogenicity

L1 capsomeres purified from Escherichia coli represent an economic alternative to the recently launched virus-like particle (VLP)-based prophylactic vaccines against infection with human papillomavirus types 16 and 18 (HPV-16 and HPV-18), which are causative agents of cervical cancer. It was recently reported that capsomeres are much less immunogenic than VLPs. Numerous modifications of the L1 protein leading to the formation of capsomeres but preventing capsid assembly have been described, such as the replacement of the cysteine residues that form capsid-stabilizing disulfide bonds or the deletion of helix 4. So far, the influence of these modifications on immunogenicity has not been thoroughly investigated. Here, we describe the purification of eight different HPV-16 L1 proteins as capsomeres from Escherichia coli. We compared them for yield, structure, and immunogenicity in mice. All L1 proteins formed almost identical pentameric structures yet differed strongly in their immunogenicity, especially regarding the humoral immune responses. Immunization of TLR4(-/-) mice and DNA immunization by the same constructs confirmed that immunogenicity was independent of different degrees of contamination with copurifying immune-stimulatory molecules from E. coli. We hypothesize that immunogenicity correlates with the intrinsic ability of the capsomeres to assemble into larger particles, as only assembly-competent L1 proteins induced high antibody responses. One of the proteins (L1DeltaN10) proved to be the most immunogenic, inducing antibody titers equivalent to those generated in response to VLPs. However, preassembly prior to injection did not increase immunogenicity. Our data suggest that certain L1 constructs can be used to produce highly immunogenic capsomeres in bacteria as economic alternatives to VLP-based formulations.

Virus-like particle (VLP) lymphatic trafficking and immune response generation after immunization by different routes

Virus-like particles (VLPs) have gained increasing interest for their use as vaccines due to their repetitive antigenic structure that is capable of efficiently activating the immune system. The efficacy of VLP immunization may lie in its ability to traffic into draining lymph nodes while activating antigen-presenting cells to initiate the orchestration of signals required for the development of a robust immune response. Currently, there is no comprehensive study showing the correlation of different VLP vaccination routes to immune outcome. In this study, we took an optical imaging approach to directly visualize the trafficking of simian-human immunodeficiency (SHIV) VLPs after immunization by commonly used routes and analyzed the corresponding humoral and cellular immune responses generated. We found that VLPs can easily enter the subcapsular sinus of draining lymph nodes with quantitative differences in the number of lymph node involvement depending on the immunization route used. Intradermal immunization led to the largest level of lymph node involvement for the longest period of time, which correlated with the strongest humoral and cellular immune responses. Flow cytometry analysis from extracted splenocytes showed that intradermal immunization led to the largest population of germinal center and activated B cells, which translated into higher antibody levels and antigen-specific cytotoxic T lymphocyte responses. Our results indicate that VLPs traffic into lymph nodes upon immunization and can be directly visualized by optical imaging techniques. Intradermal immunization showed improved responses and might be a preferable delivery route to use for viral and cancer immunotherapeutic studies involving VLPs.

Refining HPV 16 L1 purification from E. coli: reducing endotoxin contaminations and their impact on immunogenicity

HPV 16 L1 capsomeres purified from Escherichia coli represent a promising and potentially cost-effective alternative to the recently licensed VLP-based vaccines for the prevention of cervical cancer. However, recombinant protein preparations from bacteria always bear the risk of contaminating endotoxins which are highly toxic in humans and therefore have to be eliminated from vaccine preparations. In this study, we measured the LPS concentration at various stages of the purification of HPV 16 L1 from E. coli and determined that it enhances the immunogenicity of HPV 16 VLPs and capsomeres. We confirmed the immunogenicity of the L1 capsomeres in TLR4(-/-) mice without the enhancing effect of the LPS and then elaborated a suitable protocol using Triton X-114 phase separation for the removal of LPS without any significant protein loss or influence on the structural integrity of the particles. The LPS-free capsomeres purified from E. coli induced neutralizing L1-specific antibodies. Our results demonstrate the excellent potential of capsomeres as an economically interesting alternative vaccine to prevent cervical cancer that could be made available in developing countries.

Translational fusion of chloroplast-expressed human papillomavirus type 16 L1 capsid protein enhances antigen accumulation in transplastomic tobacco

Human Papillomavirus (HPV) is the causal agent of cervical cancer, one of the most common causes of death for women. The major capsid L1 protein self-assembles in Virus Like Particles (VLPs), which are highly immunogenic and suitable for vaccine production. In this study, a plastid transformation approach was assessed in order to produce a plant-based HPV-16 L1 vaccine. Transplastomic plants were obtained after transformation with vectors carrying a chimeric gene encoding the L1 protein either as the native viral (L1(v) gene) or a synthetic sequence optimized for expression in plant plastids (L1(pt) gene) under control of plastid expression signals. The L1 mRNA was detected in plastids and the L1 antigen accumulated up to 1.5% total leaf proteins only when vectors included the 5'-UTR and a short N-terminal coding segment (Downstream Box) of a plastid gene. The half-life of the engineered L1 protein, determined by pulse-chase experiments, is at least 8 h. Formation of immunogenic VLPs in chloroplasts was confirmed by capture ELISA assay using antibodies recognizing conformational epitopes and by electron microscopy.

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

Capsomeres are considered to be an alternative to viruslike particle (VLP)-based vaccines as they can be produced in prokaryotic expression systems. So far, no detailed side-by-side comparison of VLPs and capsomeres has been performed. In the present study, we immunized mice with insect cell-derived human papillomavirus type 16 VLPs and capsomeres. VLPs induced consistently higher antibody titers than capsomeres but the two forms induced similar CD8 T-cell responses after subcutaneous, intranasal, and oral immunization, and at least 20 to 40 times more L1 in the form of capsomeres than in the form of VLPs was needed to achieve comparable antibody responses. These results were confirmed by DNA immunization. The lower immunogenicity of capsomeres was independent of the isotype switch, as it was also observed for the early immunoglobulin M responses. Although there were differences in the display of surface epitopes between the L1 particles, these did not contribute significantly to the differences in the immune responses. capsomeres were less immunogenic than VLPs in Toll-like receptor 4 (TLR4)-deficient mice, suggesting that the lower immunogenicity is not due to a failure of capsomeres to trigger TLR4. We observed better correlation between antibody results from enzyme-linked immunosorbent assays and neutralization assays for sera from VLP-immunized mice than for sera from capsomere-immunized mice, suggesting qualitative differences between VLPs and capsomeres. We also showed that the lower immunogenicity of capsomeres could be compensated by the use of an adjuvant system containing MPL. Taken together, these results suggest that, presumably because of the lower degree of complexity of the antigen organization, capsomeres are significantly less immunogenic than VLPs with respect to the humoral immune response and that this characteristic should be considered in the design of putative capsomere-based prophylactic vaccines.

Immunotherapy of equine sarcoid: dose-escalation trial for the use of chimeric papillomavirus-like particles

Equine sarcoids are fibrosarcoma-like skin tumours with a prevalence of approximately 1-2 %. Strong evidence exists for a causative role of bovine papillomavirus (BPV) type 1 or type 2 in the development of sarcoids. No effective treatment of equine sarcoid is available and after surgical excision relapse of the tumours is very frequent. We developed chimeric virus-like particles (CVLPs) of BPV 1 L1-E7 for the immunotherapy of equine sarcoid. In a phase I clinical trial 12 horses suffering from equine sarcoid with an average number of more than 22 tumours per animal were vaccinated in a dose-escalation setting. The animals were followed-up for 63 days, eight of the twelve horses were followed-up for more than a year and side-effects, humoral immune responses and tumour appearance were recorded. BPV DNA was detected in tumours of 11 cases. CVLPs were well tolerated in all dose groups, a robust anti-L1 antibody response was induced in all but one of the horses. Anti-E7 antibodies were detected in five of the 12 animals at low titres. Two animals showed a clear improvement of the clinical status after treatment, i.e. the number of the tumours per horse was reduced. In another horse regression of five sarcoids was observed; three of them relapsed during the study. Two animals showed tumour regression as well as growth of new sarcoids. In two horses the clinical status remained unchanged, in another two horses growth of existing tumours or growth of additional tumours was observed. The remaining three animals showed simultaneously regression and growth of existing tumours. Neither the humoral immune responses nor the observed effects on the tumours was correlated with the dose group.