Nasal immunization of mice with human papillomavirus type 16 virus-like particles elicits neutralizing antibodies in mucosal secretions

Viral-vectored respiratory mucosal vaccine strategies

Increasing global concerns of pandemic respiratory viruses highlight the importance of developing optimal vaccination strategies that encompass vaccine platform, delivery route, and regimens. The decades-long effort to develop vaccines to combat respiratory infections such as influenza, respiratory syncytial virus, and tuberculosis has met with challenges, including the inability of systemically administered vaccines to induce respiratory mucosal (RM) immunity. In this regard, ample preclinical and available clinical studies have demonstrated the superiority of RM vaccination to induce RM immunity over parenteral route of vaccination. A great stride has been made in developing vaccines for RM delivery against respiratory pathogens, including M. tuberculosis and SARS-CoV-2. In particular, inhaled aerosol delivery of adenoviral-vectored vaccines has shown significant promise.

Viral protein nanoparticles (Part 1): Pharmaceutical characteristics

Viral protein nanoparticles fill the gap between viruses and synthetic nanoparticles. Combining advantageous properties of both systems, they have revolutionized pharmaceutical research. Virus-like particles are characterized by a structure identical to viruses but lacking genetic material. Another type of viral protein nanoparticles, virosomes, are similar to liposomes but include viral spike proteins. Both systems are effective and safe vaccine candidates capable of overcoming the disadvantages of both traditional and subunit vaccines. Besides, their particulate structure, biocompatibility, and biodegradability make them good candidates as vectors for drug and gene delivery, and for diagnostic applications. In this review, we analyze viral protein nanoparticles from a pharmaceutical perspective and examine current research focused on their development process, from production to administration. Advances in synthesis, modification and formulation of viral protein nanoparticles are critical so that large-scale production of viral protein nanoparticle products becomes viable and affordable, which ultimately will increase their market penetration in the future. We will discuss their expression systems, modification strategies, formulation, biopharmaceutical properties, and biocompatibility.

Nonclinical safety evaluation of oral recombinant anti-human papilloma virus vaccine (RHPV 16 & 18): Regulatory toxicology studies in mice, rats and rabbits - An innovative approach

AIM

The human papilloma virus (HPV) type 16 and 18 causes nearly 70% of uterine cervical cancers. Oral administration of live Salmonella typhi Ty21a, expressing major capsid proteins (L1) of HPV 16 and 18 is a potential choice for immunization in adolescent girls under low resource settings. Present study aimed to assess the nonclinical safety of recombinant S. typhi expressing HPV 16 and 18 (rStHPV) proteins.

METHODOLOGY

The acute toxicity of rStHPV was tested by intranasal single dose administration, of 10 and 50 folds higher than clinical prophylactic dose, in mice and rat followed by monitoring their survival for 14 days. Sub-chronic toxicity was evaluated in rats and rabbits with prophylactic and 5 times (average) to clinical prophylactic dosages on scheduled days (1st, 3rd & 5th day) through oral and intranasal routes. The immune/allergic response of rStHPV was assessed in mice through intranasal and intra-peritoneal routes. Experimental animals were daily monitored for live phase, and clinical chemistry, haematology, immunotoxicology, immunogenic response and histopathological examination of vital organs on 15th, 29th and 93rd days.

RESULTS

No abnormal changes were noticed in live phase activity, clinical chemistry and haematology profile. The gross necropsy, organ weights and histopathology were found to be normal. No immunotoxicity was recorded as evaluated by tier I tests. Allergic immune response, as evaluated with IgE levels was also negative irrespective of test routes. On the other hand, a significant (P < 0.01) increase of anti-HPV IgG levels was noted in mice exposed through intranasal route. Though the pre-terminal mortality was noted in mice (6-15%), rats (10%) and rabbits (15%), the autopsy revealed no signs of toxicity related to rStHPV, as the changes neither significant nor dose dependent; and even noted in vehicle control also.

CONCLUSION

The study results suggested 'no observable adverse effects' of rStHPV even at higher dosages (5, 10 & 50 folds) than intended clinical dose. A significant increase of anti-HPV specific IgG suggests the immunogenicity of vaccine. The innovative approach of current study is nonclinical toxicology evaluation of vaccine through intra-nasal route, an alternate route apart from stipulated regulatory guidelines.

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

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

Different types of adjuvants in prophylactic and therapeutic human papillomavirus vaccines in laboratory animals: a systematic review

Human papillomavirus (HPV) causes cervical carcinoma, which and is the third most common cancer, accounting for 275,000 deaths annually worldwide. Adjuvants have a key role in promotion of vaccine efficacy; therefore, using prophylactic and therapeutic vaccines combined with adjuvant could be of great benefit in prevention and treatment of cervical cancer. There are different types of adjuvants, including MF59^TM adjuvants, RNA-based, JY (interleukin2/chitosan), cholera toxin (CT), heat-labile enterotoxin (LT), Freund's adjuvant, alum, SA-4-1BBL, λ-carrageenan (λ-CGN), heat shock proteins (HSPs), juzen-taiho-to (JTT) and hochu-ekki-to (HET), ISCOM and ISCOMATRIX™, very small size proteoliposomes (VSSPs), granulocyte macrophage colony-stimulating factor (GM-CSF), and Toll-like receptors (TLRs). Adjuvants have various functions, especially in therapeutic vaccines, and they lead to an increase in cytotoxic T lymphocytes (CTLs), so they are important in the design of vaccines. Here, we review the currently used adjuvants and their combinations with HPV protein vaccines in order to introduce an appropriate adjuvant for HPV vaccines.

Infection and vaccine-induced HPV-specific antibodies in cervicovaginal secretions. A review of the literature

Background

Human papillomavirus (HPV) infects and propagates in the cervical mucosal epithelium. Hence, in addition to assessing systemic immunity, the accurate measurement of cervical immunity is important to evaluate local immune responses to HPV infection and vaccination. This review discusses studies that investigated the presence of infection and vaccine-induced HPV-specific antibodies in cervicovaginal secretions (CVS).

Methods

We searched the two main health sciences databases, PubMed and the ISI Web of Science, from the earliest dates available to March 2019. From the eligible publications, information was extracted regarding: (i) study design, (ii) the reported HPV-specific antibody concentrations in CVS (and the associated serum levels, when provided), (iii) the CVS collection method, and (iv) the immunoassays used.

Results

The systematic search and selection process yielded 44 articles. The evidence of HPV-specific antibodies in CVS after natural infection (26/44) and HPV vaccination (18/44) is discussed. Many studies indicate that HPV-specific antibody detection in CVS is variable but feasible with a variety of collection methods and immunoassays. Most CVS samples were collected by cervicovaginal washing or wicks, and antibody presence was mostly determined by VLP-based ELISAs. The moderate to strong correlation between vaccine-induced antibody levels in serum and in CVS indicates that HPV vaccines generate antibodies that transudate through the cervical mucosal epithelium.

Conclusion

Although HPV-specific antibodies have lower titres in CVS than in serum samples, studies have shown that their detection in CVS is feasible. Nevertheless, the high variability of published observations and the lack of a strictly uniform, well-validated method for the collection, isolation and quantification of antibodies indicates a need for specific methods to improve and standardize the detection of HPV-specific antibodies in CVS.

Modified chitosan-based nanoadjuvants enhance immunogenicity of protein antigens after mucosal vaccination

Nasal vaccination is considered to be an effective and convenient way of increasing immune responses both systemically and locally. Although various nanovaccine carriers have been introduced as potential immune adjuvants, further improvements are still needed before they can be taken to clinical usage. Chitosan-based nanovaccine carriers are one of the most widely studiedadjuvants, owing to the abilityof chitosan toopen tight junctions between nasal epithelial cells and enhance particle uptake as well as its inherent immune activating role. In present study, bovine serum albumin (BSA) loaded nanoparticles were prepared using novel aminated (aChi) and aminated plus thiolated chitosan (atChi) polymers, to further enhance mucoadhesiveness and adjuvanticity of the vaccine system by improving electrostatic interactions of polymers with negatively charged glycoproteins. Nanocarriers with optimum size and surface charge, high encapsulation efficiency of model antigen and good stability were developed. Negligible toxicity was observed in Calu-3 and A549 cell lines. In vivo studies, revealed high levels of systemic antibodies (IgG, IgG₁ and IgG_2a) throughout the study and presence of sIgA in vaginal washes showed that common mucosal system was successfully stimulated. Cytokine levels indicated a mixed Th1/Th2 immune response. A shift towards cellular immune responses was observed after nasal immunisation with antigen loaded nanoparticle formulations. These nanoparticles exhibit great potential for nasal application of vaccines.

Evaluation of the Effect of Promoter Type on the Immunogenicity of the Live Recombinant Salmonella Vaccines Expressing Escherichia Coli Heat-labile Enterotoxins (LTB)

Enterotoxigenic Escherichia coli (ETEC)-induced diarrhoea is the second most common cause of death in children in the developing countries. Heat labile toxin (LT) is responsible for ETEC-induced diarrhoea. In the present study, a novel live ETEC vaccine based on subunit B of LT (LTB) expression in attenuated PhoP^c Salmonella strain was developed. Herein, we aimed to compare the in-vitro activity of promoters including constitutive tac, IPTG inducible trc, and in-vivo-inducible (nirB and nirB78-23) in PhoP^c. Additionally, the ability of these recombinant PhoP^c/pLTBs to induce LTB-specific antibody responses in BALB/c mice after nasal immunization was evaluated. In-vitro studies demonstrated that PhoP^c has the ability to produce rLTB. Furthermore, nirB promoter directed significantly more LTB expression in PhoP^c/pnirBLTB under anaerobic condition without induction compared to the amount of rLTB secreted by PhoP^c/ptrcLTB in bacterial soup under uninduced condition (6.06 ± 0.05 vs. 1.4 ± 0.46 μg/10⁹ cfu, p < 0.01). In addition, the constitutive rLTB expression from tac promoter was more than its expression from uninduced trc promoter in bacterial soup (4.2 ± 0.92 vs. 1.4 ± 0.46 (μg/10⁹ cfu)) and pellet (27.4 ± 0.89 vs. 13.4 ± 1.42 (μg/10⁹ cfu), p < 0.0001). However, the mice immunized with PhoP^c/ptrcLTB elicited the superior anti-LTB responses among the PhoP^c containing the examined prompters, which were significantly higher than those induced by PhoP^c/pnirB78-23LTB and PhoP^c/pnirB, 6 weeks after the first immunization. Totally, it could be concluded that in-vitro analysis of promoters for LTB expression in PhoP^c may not necessarily predict the recombinant PhoP^c immunogenicity.

Gas-filled microbubbles: Novel mucosal antigen-delivery system for induction of anti-pathogen's immune responses in the gut

Despite important success in protecting individuals against many pathogenic infections, parenteral vaccination is not optimal to induce immunity at the site of pathogen entry, i.e. mucosal surfaces. Moreover, designing adequate delivery systems and safe adjuvants to overcome the inherent tolerogenic environment of the mucosal tissue is challenging, in particular in the gastrointestinal tract prone to antigen degradation. We recently demonstrated that intranasal administration of a Salmonella-derived antigen associated with gas-filled microbubbles induced specific Ab and T cell responses in the gut and was associated with a reduction in local and systemic bacterial load after oral Salmonella infection. Building on these promising data, the adequate choice of antigen(s) to be administered and how to make it suitable for possible human application are discussed. We additionally present novel data dealing with oral administration of microbubbles and describe research strategies to direct them to mucosal sampling/inductive sites.

Unique cellular and humoral immunogenicity profiles generated by aerosol, intranasal, or parenteral vaccination in rhesus macaques

Respiratory mucosa immunization is capable of eliciting both local and distal mucosal immune responses; it is a potentially powerful yet largely unused modality for vaccination against respiratory diseases. Targeting the lower versus upper airways by aerosol delivery alters the immunogenicity profile of a vaccine, although the full extent of this impact is not well characterized. We set out to define the cellular and humoral response profiles elicited by immunization via intranasal, small aerosol droplets, and large aerosol droplets. We compared responses following adenovirus-vectored vaccination by these routes in macaques, either for the generation of primary immune responses or for the boosting of previously primed systemic responses. Aerosol delivery (4 or 10μm diameter droplets, addressing lower or upper airways, respectively) generated the highest magnitude lung CD4 and CD8 T-cell responses, reaching 10-30% vaccine-specific levels in bronchoalveolar lavage cells. In contrast, intranasal delivery was less immunogenic with >10-fold lower peak lung T-cell responses. Systemic (blood) T-cell responses were only observed following 4μm aerosol (and parenteral) immunization, while all delivery routes elicited similar humoral responses. These data demonstrate distinct immune response profiles with each respiratory tract vaccination modality and suggest that small droplet aerosol offers several immunological advantages over other respiratory routes.

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.

SPECT/CT study of bronchial deposition of inhaled particles. A human aerosol vaccination model against HPV

AIMS

Vaccination by aerosol inhalation can be used to efficiently deliver antigen against HPV to mucosal tissue, which is particularly useful in developing countries (simplicity of administration, costs, no need for cold chain). For optimal immunological response, vaccine particles should preferentially be delivered to proximal bronchial airways. We aimed at quantifying the deposition of inhaled particles in central airways and peripheral lung, and to assess administration biosafety. Participants, methods: 20 healthy volunteers (13W/7M, aged 24±4y) performed a 10-min free-breathing inhalation of (99m)Tc-stannous chloride colloid aerosol (450 MBq) in a buffer solution without vaccinal particles using an ultrasonic nebulizer (mass median aerodynamic diameter 4.2 μm) and a double mask inside a biosafety cabinet dedicated to assess environmental particle release. SPECT/CT and whole-body planar scintigraphy were acquired to determine whole-body and regional C/P distribution ratio (central-to-peripheral pulmonary deposition counts). Using a phantom, SPECT sensitivity was calibrated to obtain absolute pulmonary activity deposited by inhalation.

RESULTS

All participants successfully performed the inhalation that was well tolerated (no change in pulmonary peak expiratory flow rate, p = 0.9). It was environmentally safe (no activity released in the biosafety filter.) 1.3±0.6% (range 0.4-2.6%) of the total nebulizer activity was deposited in the lungs with a C/P distribution ratio of 0.40±0.20 (range 0.15-1.14).

CONCLUSION

Quantification and regional distribution of inhaled particles in an aerosolized vaccine model is possible using radioactive particles. This will allow optimizing deposition parameters and determining the particles charge for active-particles vaccination.

Human papillomavirus infection in the oral cavity of HIV patients is not reduced by initiating antiretroviral therapy

Objective:

The incidence of human papillomavirus (HPV)-related oral malignancies is increasing among HIV-infected populations, and the prevalence of oral warts has reportedly increased among HIV patients receiving antiretroviral therapy (ART). We explored whether ART initiation among treatment-naive HIV-positive adults is followed by a change in oral HPV infection or the occurrence of oral warts.

Design:

Prospective, observational study.

Methods:

HIV-1 infected, ART-naive adults initiating ART in a clinical trial were enrolled. End points included detection of HPV DNA in throat-washes, changes in CD4⁺ T-cell count and HIV RNA, and oral wart diagnosis.

Results:

Among 388 participants, 18% had at least one HPV genotype present before initiating ART, and 24% had at least one genotype present after 12–24 weeks of ART. Among those with undetectable oral HPV DNA before ART, median change in CD4⁺ count from study entry to 4 weeks after ART initiation was larger for those with detectable HPV DNA during follow-up than those without (P =  0.003). Both prevalence and incidence of oral warts were low (3% of participants having oral warts at study entry; 2.5% acquiring oral warts during 48 weeks of follow-up).

Conclusion:

These results suggest: effective immune control of HPV in the oral cavity of HIV-infected patients is not reconstituted by 24 weeks of ART; whereas ART initiation was not followed by an increase in oral warts, we observed an increase in oral HPV DNA detection after 12–24 weeks. The prevalence of HPV-associated oral malignancies may continue to increase in the modern ART era.

Optimized Formulation of a Thermostable Spray-Dried Virus-Like Particle Vaccine against Human Papillomavirus

Existing vaccines against human papillomavirus (HPV) require continuous cold-chain storage. Previously, we developed a bacteriophage virus-like particle (VLP)-based vaccine for HPV infection, which elicits broadly neutralizing antibodies against diverse HPV types. Here, we formulated these VLPs into a thermostable dry powder using a multicomponent excipient system and by optimizing the spray-drying parameters using a half-factorial design approach. Dry-powder VLPs were stable after spray drying and after long-term storage at elevated temperatures. Immunization of mice with a single dose of reconstituted dry-powder VLPs that were stored at 37 °C for more than a year elicited high anti-L2 IgG antibody titers. Spray-dried thermostable, broadly protective L2 bacteriophage VLPs vaccine could be accessible to remote regions of the world (where ∼84% of cervical cancer patients reside) by eliminating the cold-chain requirement during transportation and storage.

Progress and prospects for L2-based human papillomavirus vaccines

Human papillomavirus (HPV) is a worldwide public health problem, particularly in resource-limited countries. Fifteen high-risk genital HPV types are sexually transmitted and cause 5% of all cancers worldwide, primarily cervical, anogenital and oropharyngeal carcinomas. Skin HPV types are generally associated with benign disease, but a subset is linked to non-melanoma skin cancer. Licensed HPV vaccines based on virus-like particles (VLPs) derived from L1 major capsid antigen of key high risk HPVs are effective at preventing these infections but do not cover cutaneous types and are not therapeutic. Vaccines targeting L2 minor capsid antigen, some using capsid display, adjuvant and fusions with early HPV antigens or Toll-like receptor agonists, are in development to fill these gaps. Progress and challenges with L2-based vaccines are summarized.

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.

Directing vaccine immune responses to mucosa by nanosized particulate carriers encapsulating NOD ligands

Mucosal surfaces are a major portal of entry for many pathogens that are the cause of infectious diseases. Therefore, effective vaccines that induce a protective immune response at these sites are much needed. However, despite early success with the live attenuated oral polio vaccine over 50 years ago, only a few new mucosal vaccines have been subsequently licensed. Development of new adjuvants, comprising antigen delivery platforms and immunostimulatory molecules, are critical for the successful development of new mucosal vaccines. Among them, biodegradable nanoparticle delivery systems are promising and NOD-like receptors are considered as potential new targets for immunostimulatory molecules. In this work, different NOD1 and NOD2 ligands were encapsulated in polylactic acid (PLA) nanoparticles, coated with HIV-1 gag p24 antigen. We showed that these new formulations are able to induce proliferation of HIV-specific T cells from HIV(+) individuals as well as autophagy. In vivo, these formulations highly enhanced p24-specific systemic and mucosal immune responses in mice not only after mucosal administration but also after immunization via the parenteral route. Our results provide a rational approach for combining nanosized particulate carriers and encapsulated NOD receptor ligands as potent synergistic tools for induction of specific mucosal immunity.

Formulation and stabilization of recombinant protein based virus-like particle vaccines

Vaccine formulation development has traditionally focused on improving antigen storage stability and compatibility with conventional adjuvants. More recently, it has also provided an opportunity to modify the interaction and presentation of an antigen/adjuvant to the immune system to better stimulate the desired immune responses for maximal efficacy. In the last decade, there has been a paradigm shift in vaccine antigen and formulation design involving an improved physical understanding of antigens and a better understanding of the immune system. In addition, the discovery of novel adjuvants and delivery systems promises to further improve the design of new, more effective vaccines. Here we describe some of the fundamental aspects of formulation design applicable to virus-like-particle based vaccine antigens (VLPs). Case studies are presented for commercially approved VLP vaccines as well as some investigational VLP vaccine candidates. An emphasis is placed on the biophysical analysis of vaccines to facilitate formulation and stabilization of these particulate antigens.

Microneedle Vaccination Elicits Superior Protection and Antibody Response over Intranasal Vaccination against Swine-Origin Influenza A (H1N1) in Mice

Influenza is one of the critical infectious diseases globally and vaccination has been considered as the best way to prevent. In this study, immunogenicity and protection efficacy between intranasal (IN) and microneedle (MN) vaccination was compared using inactivated swine-origin influenza A/H1N1 virus vaccine. Mice were vaccinated by MN or IN administration with 1 μg of inactivated H1N1 virus vaccine. Antigen-specific antibody responses and hemagglutination-inhibition (HI) titers were measured in all immunized sera after immunization. Five weeks after an immunization, a lethal challenge was performed to evaluate the protective efficacy. Furthermore, mice were vaccinated by IN administration with higher dosages (> 1 μg), analyzed in the same manner, and compared with 1 μg-vaccine-coated MN. Significantly higher antigen-specific antibody responses and HI titer were measured in sera in MN group than those in IN group. While 100% protection, slight weight loss, and reduced viral replication were observed in MN group, 0% survival rate were observed in IN group. As vaccine dose for IN vaccination increased, MN-immunized sera showed much higher antigen-specific antibody responses and HI titer than other IN groups. In addition, protective immunity of 1 μg-MN group was similar to those of 20- and 40 μg-IN groups. We conclude that MN vaccination showed more potential immune response and protection than IN vaccination at the same vaccine dosage.

Mucosal Vaccines from Plant Biotechnology

The use of plants for production of recombinant proteins has evolved over the past 25 years. The first plant-based vaccines were expressed in stably transgenic plants, with the idea to conveniently deliver “edible vaccines” by ingestion of the antigen-containing plant material. These systems provided a proof of concept that oral delivery of vaccines in crude plant material could stimulate antigen-specific serum and mucosal antibodies. Transgenic grains like rice in particular provide a stable and robust vehicle for antigen delivery. However, some issues exist with stably transgenic plants, including relatively low expression levels and regulatory issues. Thus, many recent studies use transient expression with plant viral vectors to achieve rapid high expression in Nicotiana benthamiana, followed by purification of antigen and intranasal delivery for effective stimulation of mucosal immune responses.

Polymeric penetration enhancers promote humoral immune responses to mucosal vaccines

Protective mucosal immune responses are thought best induced by trans-mucosal vaccination, providing greater potential to generate potent local immune responses than conventional parenteral vaccination. However, poor trans-mucosal permeability of large macromolecular antigens limits bioavailability to local inductive immune cells. This study explores the utility of polymeric penetration enhancers to promote trans-mucosal bioavailability of insulin, as a biomarker of mucosal absorption, and two vaccine candidates: recombinant HIV-1 envelope glycoprotein (CN54gp140) and tetanus toxoid (TT). Responses to vaccinating antigens were assessed by measurement of serum and the vaginal humoral responses. Polyethyleneimine (PEI), Dimethyl-β-cyclodextrin (DM-β-CD) and Chitosan enhanced the bioavailability of insulin following intranasal (IN), sublingual (SL), intravaginal (I.Vag) and intrarectal (IR) administration. The same penetration enhancers also increased antigen-specific IgG and IgA antibody responses to the model vaccine antigens in serum and vaginal secretions following IN and SL application. Co-delivery of both antigens with PEI or Chitosan showed the highest increase in systemic IgG and IgA responses following IN or SL administration. However the highest IgA titres in vaginal secretions were achieved after IN immunisations with PEI and Chitosan. None of the penetration enhancers were able to increase antibody responses to gp140 after I.Vag immunisations, while in contrast PEI and Chitosan were able to induce TT-specific systemic IgG levels following I.Vag administration. In summary, we present supporting data that suggest appropriate co-formulation of vaccine antigens with excipients known to influence mucosal barrier functions can increase the bioavailability of mucosally applied antigens promoting the induction of mucosal and systemic antibody responses.

Vaccination strategies for the prevention of cervical cancer

Infection with high-risk human papillomaviruses (HPVs) is an essential step in the multistep process leading to cervical cancer. There are approximately 120 different types of HPV identified: of these, 18 are high-risk types associated with cervical cancer, with HPV-16 being the dominant type in most parts of the world. The major capsid protein of papillomavirus, produced in a number of expression systems, self assembles to form virus-like particles. Virus-like particles are the basis of the first generation of HPV vaccines presently being tested in clinical trials. Virus-like particles are highly immunogenic and afford protection from infection both in animal models and in Phase IIb clinical trials. A number of Phase III trials are in progress to determine if the vaccine will protect against cervical disease and, in some cases, genital warts. However, it is predicted that these vaccines will be too expensive for the developing world, where they are desperately needed. Another problem is that they will be type specific. Novel approaches to the production of virus-like particles in plants, second-generation vaccine approaches including viral and bacterial vaccine vectors and DNA vaccines, as well as different routes of immunization, are also reviewed.

Low-affinity B cells transport viral particles from the lung to the spleen to initiate antibody responses

The lung is an important entry site for pathogens; its exposure to antigens results in systemic as well as local IgA and IgG antibodies. Here we show that intranasal administration of virus-like particles (VLPs) results in splenic B-cell responses with strong local germinal-center formation. Surprisingly, VLPs were not transported from the lung to the spleen in a free form but by B cells. The interaction between VLPs and B cells was initiated in the lung and occurred independently of complement receptor 2 and Fcγ receptors, but was dependent upon B-cell receptors. Thus, B cells passing through the lungs bind VLPs via their B-cell receptors and deliver them to local B cells within the splenic B-cell follicle. This process is fundamentally different from delivery of blood or lymph borne particulate antigens, which are transported into B cell follicles by binding to complement receptors on B cells.

Plant-derived antigens as mucosal vaccines

During the last two decades, researchers have developed robust systems for recombinant subunit vaccine production in plants. Stably and transiently transformed plants have particular advantages that enable immunization of humans and animals via mucosal delivery. The initial goal to immunize orally by ingestion of plant-derived antigens has proven difficult to attain, although many studies have demonstrated antibody production in both humans and animals, and in a few cases, protection against pathogen challenge. Substantial hurdles for this strategy are low-antigen content in crudely processed plant material and limited antigen stability in the gut. An alternative is intranasal delivery of purified plant-derived antigens expressed with robust viral vectors, especially virus-like particles. The use of pattern recognition receptor agonists as adjuvants for mucosal delivery of plant-derived antigens can substantially enhance serum and mucosal antibody responses. In this chapter, we briefly review the methods for recombinant protein expression in plants, and describe progress with human and animal vaccines that use mucosal delivery routes. We do not attempt to compile a comprehensive list, but focus on studies that progressed to clinical trials or those that showed strong indications of efficacy in animals. Finally, we discuss some regulatory concerns regarding plant-based vaccines.

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.

Cell-mediated immune response to human papillomavirus 16 E7 peptide pools in patients with cervical neoplasia

OBJECTIVE

To identify characteristics of the cell-mediated immune (CMI) response to human papillomavirus-16 (HPV) E7 viral peptide pools to help the formulation of therapeutic vaccines.

DESIGN

Prospective study. Population. Korean women.

SETTING

University hospital.

METHODS

From December 2008 to August 2010, 33 HPV-16-positive patients, seven patients exhibiting a high-risk HPV infection other than HPV-16 with grade 2/3 cervical intraepithelial neoplasm (CIN2/3), and nine healthy control donors were enrolled.

MAIN OUTCOME MEASURES

CMI response to synthetic HPV-16 E7 overlapping peptide pools using the IFN-γ ELISPOT assay.

RESULTS

The E7 sequence comprising amino acids 16-55 was a major immunogenic region. The CMI response to HPV-16 E7 is highly type-specific. The follow-up CMI response may last longer than expected after the lesion is resected.

CONCLUSIONS

We found that the E7 sequence comprising amino acids 16-55 is a major immunogenic region that is critical for the T-cell-mediated immune response with CIN2/3 or cervical cancer. The identification of CMI responses to HPV-16 E7 peptide pools may provide insight into therapeutic vaccine trials for the control of HPV-associated diseases.

A murine genital-challenge model is a sensitive measure of protective antibodies against human papillomavirus infection

The available virus-like particle (VLP)-based prophylactic vaccines against specific human papillomavirus (HPV) types afford close to 100% protection against the type-associated lesions and disease. Based on papillomavirus animal models, it is likely that protection against genital lesions in humans is mediated by HPV type-restricted neutralizing antibodies that transudate or exudate at the sites of genital infection. However, a correlate of protection was not established in the clinical trials because few disease cases occurred, and true incident infection could not be reliably distinguished from the emergence or reactivation of prevalent infection. In addition, the current assays for measuring vaccine-induced antibodies, even the gold standard HPV pseudovirion (PsV) in vitro neutralization assay, may not be sensitive enough to measure the minimum level of antibodies needed for protection. Here, we characterize the recently developed model of genital challenge with HPV PsV and determine the minimal amounts of VLP-induced neutralizing antibodies that can afford protection from genital infection in vivo after transfer into recipient mice. Our data show that serum antibody levels >100-fold lower than those detectable by in vitro PsV neutralization assays are sufficient to confer protection against an HPV PsV genital infection in this model. The results clearly demonstrate that, remarkably, the in vivo assay is substantially more sensitive than in vitro PsV neutralization and thus may be better suited for studies to establish correlates of protection.

Neisseria gonorrhoeae NspA induces specific bactericidal and opsonic antibodies in mice

Neisseria gonorrhoeae surface protein A (NspA) is a highly conserved gonococcal antigen. To explore the potential of NspA in vaccine development against gonorrhea, BALB/c mice were immunized with pcNspA containing the NspA gene from N. gonorrhoeae strain WHO-A via intramuscular (i.m.) injection, intranasal (i.n.) immunization, or intravaginal (i.vag.) immunization. Following the last DNA immunization, mice were boosted with recombinant NspA (rNspA). Enzyme-linked immunosorbent assays (ELISAs) indicated that all immunized mice generated measurable NspA-specific IgG and IgA in serum and secretory IgA (sIgA) in vaginal wash fluids. The antisera had bactericidal and opsonic activities. These data demonstrated that NspA induced antibodies with antigonococcal activity.

Parenteral is more efficient than mucosal immunization to induce regression of human papillomavirus-associated genital tumors

Cervical cancer is a public health concern as it represents the second cause of cancer death in women worldwide. High-risk human papillomaviruses (HPV) are the etiologic agents, and HPV E6 and/or E7 oncogene-specific therapeutic vaccines are under development to treat HPV-related lesions in women. Whether the use of mucosal routes of immunization may be preferable for inducing cell-mediated immune responses able to eradicate genital tumors is still debated because of the uniqueness of the female genital mucosa (GM) and the limited experimentation. Here, we compared the protective activity resulting from immunization of mice via intranasal (i.n.), intravaginal (IVAG) or subcutaneous (s.c.) routes with an adjuvanted HPV type 16 E7 polypeptide vaccine. Our data show that s.c. and i.n. immunizations elicited similar frequencies and avidity of TetE71CD81 and E7-specific Interferon-gamma-secreting cells in the GM, whereas slightly lower immune responses were induced by IVAG immunization. In a novel orthotopic murine model, both s.c. and i.n. immunizations allowed for complete long-term protection against genital E7-expressing tumor challenge. However, only s.c. immunization induced complete regression of already established genital tumors. This suggests that the higher E7-specific systemic response observed after s.c. immunization may contribute to the regression of growing genital tumors, whereas local immune responses may be sufficient to impede genital challenges. Thus, our data show that for an efficiently adjuvanted protein-based vaccine, parenteral vaccination route is superior to mucosal vaccination route for inducing regression of established genital tumors in a murine model of HPV-associated genital cancer.

Intranasal delivery of Norwalk virus-like particles formulated in an in situ gelling, dry powder vaccine

The development of a vaccine to prevent norovirus infections has been focused on immunization at a mucosal surface, but has been limited by the low immunogenicity of self-assembling Norwalk virus-like particles (NV VLPs) delivered enterically or at nasal surfaces. Nasal immunization, which offers the advantage of ease of immunization, faces obstacles imposed by the normal process of mucociliary clearance, which limits residence time of applied antigens. Herein, we describe the use of a dry powder formulation (GelVac) of an inert in situ gelling polysaccharide (GelSite) extracted from Aloe vera for nasal delivery of NV VLP antigen. Powder formulations, with or without NV VLP antigen, were similar in structure in dry form or when rehydrated in simulated nasal fluids. Immunogenicity of the dry powder VLP formulation was compared to equivalent antigen/adjuvant liquid formulations in animals. For the GelVac powder, we observed superior NV-specific serum and mucosal (aerodigestive and reproductive tracts) antibody responses relative to liquid formulations. Incorporation of the TLR7 agonist gardiquimod in dry powder formulations did not enhance antibody responses, although its inclusion in liquid formulations did enhance VLP immunogenicity irrespective of the presence or absence of GelSite. We interpret these data as showing that GelSite-based dry powder formulations (1) stabilize the immunogenic structural properties of VLPs and (2) induce systemic and mucosal antibody titers which are equal or greater than those achieved by VLPs plus adjuvant in a liquid formulation. We conclude that in situ gelation of the GelVac dry powder formulation at nasal mucosal surfaces delays mucociliary clearance and thereby prolongs VLP antigen exposure to immune effector sites.

Sublingual mucosa: A new vaccination route for systemic and mucosal immunity

Needle-free vaccine delivery has become a global priority, both to eliminate the risk of improper and unsafe needle use and to simplify vaccination procedures. In pursuit of greater ease of vaccination, a number of needle-free delivery routes have been explored, with mucosal routes being perhaps the most prominent. Since the vaccine administration route significantly affects immune responses, numerous researchers are attempting to develop alternative vaccine delivery methods including a mucosal route. My group's recent studies demonstrate the potential of the sublingual (s.l.) route for delivering vaccines capable of inducing mucosal as well as systemic immune responses. Sublingual administration conferred effective protection against a lethal challenge with influenza virus (H1N1) or genital papillomavirus. Moreover, CCR7-CCL19/CCL21-regulated dendritic cells are responsible for activation of T and B cells following s.l. administration. This review highlights current knowledge about the safety and effectiveness of s.l. vaccination and describes how s.l. vaccination can induce both systemic and mucosal immunity.

Effect of mucosal and systemic immunization with virus-like particles of severe acute respiratory syndrome coronavirus in mice

Nasal administration has emerged as a promising and attractive route for vaccination, especially for the prophylaxis of respiratory diseases. Our previous studies have shown that severe acute respiratory syndrome coronavirus (SARS-CoV) virus-like particles (VLPs) can be assembled using a recombinant baculovirus (rBV) expression system and such VLPs induce specific humoral and cellular immune responses in mice after subcutaneous injection. Here, we investigated mucosal immune responses to SARS-CoV VLPs in a mouse model. Mice were immunized in parallel, intraperitoneally or intranasally, with VLPs alone or with VLPs plus cytosine–phosphate–guanosine (CpG). Immune responses, including the production of SARS-CoV-specific serum immunoglobulin G (IgG) and secretory immunoglobulin A (sIgA), were determined in mucosal secretions and tissues. Both immunizations induced SARS-CoV-specific IgG, although the levels of IgG in groups immunized via the intraperitoneal (i.p.) route were higher. sIgA was detected in saliva in groups immunized intranasally but not in groups immunized intraperitoneally. CpG had an adjuvant effect on IgA production in genital tract washes when administered intranasally but only affected IgA production in faeces samples when administered intraperitoneally. In addition, IgA was also detected in mucosal tissues from the lung and intestine, while CpG induced an increased level of IgA in the intestine. Most importantly, neutralization antibodies were detected in sera after i.p. and intranasal (i.n.) immunizations. Secretions in genital tract washes from the i.n. group also showed neutralization activity. Furthermore, VLPs that were administered intraperitoneally elicited cellular immune responses as demonstrated by enzyme-linked immunospot (ELISPOT) assay analyses. In summary, our study indicates that mucosal immunization with rBV SARS-CoV VLPs represent an effective means for eliciting protective systemic and mucosal immune responses against SARS-CoV, providing important information for vaccine design.

Sublingual immunization with nonreplicating antigens induces antibody-forming cells and cytotoxic T cells in the female genital tract mucosa and protects against genital papillomavirus infection

We have recently reported that the sublingual (s.l.) mucosa is an efficient site for inducing systemic and mucosal immune responses. In this study, the potential of s.l. immunization to induce remote Ab responses and CD8(+) cytotoxic responses in the female genital tract was examined in mice by using a nonreplicating Ag, OVA, and cholera toxin (CT) as an adjuvant. Sublingual administration of OVA and CT induced Ag-specific IgA and IgG Abs in blood and in cervicovaginal secretions. These responses were associated with large numbers of IgA Ab-secreting cells (ASCs) in the genital mucosa. Genital ASC responses were similar in magnitude and isotype distribution after s.l., intranasal, or vaginal immunization and were superior to those seen after intragastric immunization. Genital, but not blood or spleen, IgA ASC responses were inhibited by treatment with anti-CCL28 Abs, suggesting that the chemokine CCL28 plays a major role in the migration of IgA ASC progenitors to the reproductive tract mucosa. Furthermore, s.l. immunization with OVA induced OVA-specific effector CD8(+) cytolytic T cells in the genital mucosa, and these responses required coadministration of the CT adjuvant. Furthermore, s.l. administration of human papillomavirus virus-like particles with or without the CT adjuvant conferred protection against genital challenge with human papillomavirus pseudovirions. Taken together, these findings underscore the potential of s.l. immunization as an efficient vaccination strategy for inducing genital immune responses and should impact on the development of vaccines against sexually transmitted diseases.

Induction of mucosal and systemic antibody responses against the HIV coreceptor CCR5 upon intramuscular immunization and aerosol delivery of a virus-like particle based vaccine

Virus-like particles (VLPs) can be exploited as platforms to increase the immunogenicity of poorly immunogenic antigens, including self-proteins. We have developed VLP-based vaccines that target two domains of the HIV coreceptor CCR5 that are involved in HIV binding. These vaccines induce anti-CCR5 antibodies that bind to native CCR5 and inhibit SIV infection in vitro. Given the role of mucosal surfaces in HIV transmission and replication, we also asked whether an aerosolized, VLP-based pulmonary vaccine targeting CCR5 could induce a robust mucosal response in addition to a systemic response. In rats, both intramuscular and pulmonary immunization induced high-titer IgG and IgA against the vaccine in the serum, but only aerosol vaccination induced IgA antibodies at local mucosal sites. An intramuscular prime followed by an aerosol boost resulted in strong serum and mucosal antibody responses. These results show that VLP-based vaccines targeting CCR5 induce high-titer systemic antibodies, and can elicit both local and systemic mucosal response when administered via an aerosol. Vaccination against a self-molecule that is critically involved during HIV transmission and pathogenesis is an alternative to targeting the virus itself. More generally, our results provide a general method for inducing broad systemic and mucosal antibody responses using VLP-based immunogens.

Listeria monocytogenes delivery of HPV-16 major capsid protein L1 induces systemic and mucosal cell-mediated CD4+ and CD8+ T-cell responses after oral immunization

Neutralizing antibodies are thought to be required at mucosal surfaces to prevent human papillomavirus (HPV) transmission. However, the potential for cell-mediated immunity in mediating protection against HPV infection has not been well explored. We generated recombinant Listeria monocytogenes (Lm) constructs that secrete listeriolysin O (LLO) fused with overlapping N-terminal (LLO-L1(1-258)) or C-terminal (LLO-L1(238-474)) fragments of HPV type 16 major capsid protein L1 (HPV-16-L1). Oral immunization of mice with either construct induced IFN-gamma-producing CD8+ and CD4+ T cells in the spleen and in the Peyer's patches with the C-terminal construct. Oral immunization with both constructs resulted in diminished viral titers in the cervix and uterus of mice after intravaginal challenge with vaccinia virus expressing HPV-16-L1.

Rectal and vaginal immunization of mice with human papillomavirus L1 virus-like particles

Human papillomavirus (HPV) vaccines based on L1 virus-like particle (VLP) can prevent genital HPV infection and associated lesions after three intramuscular injections. Needle-free administration might facilitate vaccine implementation, especially in developing countries. Here we have investigated rectal and vaginal administration of HPV16 L1 VLPs in mice and their ability to induce anti-VLP and HPV16-neutralizing antibodies in serum and in genital, rectal and oral secretions. Rectal and vaginal immunizations were not effective in the absence of adjuvant. Cholera toxin was able to enhance systemic and mucosal anti-VLPs responses after rectal immunization, but not after vaginal immunization. Rectal immunization with Resiquimod and to a lesser extent Imiquimod, but not monophosphoryl lipid A, induced anti-HPV16 VLP antibodies in serum and secretions. Vaginal immunization was immunogenic only if administered in mice treated with nonoxynol-9, a disrupter of the cervico-vaginal epithelium. Our findings show that rectal and vaginal administration of VLPs can induce significant HPV16-neutralizing antibody levels in secretions, despite the fact that low titers are induced in serum. Imidazoquinolines, largely used to treat genital and anal warts, and nonoxonol-9, used as genital microbicide/spermicide were identified as adjuvants that could be safely used by the rectal or vaginal route, respectively.

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.

Monitoring of vaccine-specific gamma interferon induction in genital mucosa of mice by real-time reverse transcription-PCR

Monitoring of T-cell responses in genital mucosa has remained a major challenge because of the absence of lymphoid aggregates and the low abundance of T cells. Here we have adapted to genital tissue a sensitive real-time reverse transcription-PCR (TaqMan) method to measure induction of gamma interferon (IFN-gamma) mRNA transcription after 3 h of antigen-specific activation of CD8 T cells. For this purpose, we vaccinated C57BL/6 mice subcutaneously with human papillomavirus type 16 L1 virus-like particles and monitored the induction of CD8 T cells specific to the L1(165-173) H-2D(b)-restricted epitope. Comparison of the responses induced in peripheral blood mononuclear cells and lymph nodes (LN) by L1-specific IFN-gamma enzyme-linked immunospot assay and TaqMan determination of the relative increase in L1-specific IFN-gamma mRNA induction normalized to the content of CD8b mRNA showed a significant correlation, despite the difference in the readouts. Most of the cervicovaginal tissues could be analyzed by the TaqMan method if normalization to glyceraldehyde-3-phosphate dehydrogenase mRNA was used and a significant L1-specific IFN-gamma induction was found in one-third of the immunized mice. This local response did not correlate with the immune responses measured in the periphery, with the exception of the sacral LN, an LN draining the genital mucosa, where a significant correlation was found. Our data show that the TaqMan method is sensitive enough to detect antigen-specific CD8 T-cell responses in the genital mucosa of individual mice, and this may contribute to elaborate effective vaccines against genital pathogens.

Efficient induction of mucosal and systemic immune responses by virus-like particles administered intranasally: implications for vaccine design

Intranasal (i.n.) immunization aims to induce local as well as systemic immune responses. In the present study, we assessed a vaccine platform based on virus-like particles (VLP) derived from the RNA phage Qbeta for i.n. immunization. We found that both i.n. and subcutaneous (s.c.) administration of Qbeta-VLP elicited strong and comparable specific IgG responses in serum and lung. Surprisingly, both routes also induced high levels of specific IgA in serum. In contrast, only i.n. administration of Qbeta-VLP resulted in local IgA production in the lung. Efficient induction of B cell responses by i.n. administration of VLP was further supported by the presence of large numbers of germinal centers (GC) as well as memory B cells in the spleen and plasma cells in the bone marrow. Results obtained for the VLP itself could be extended to an antigen covalently attached to it. Specifically, i.n. immunization of mice with VLP displaying the influenza virus derived ectodomain of the M2 protein resulted in strong M2-specific antibody responses as well as anti-viral protection. In contrast, i.n. immunization with VLP displaying p33 peptide, the major CTL epitope of lymphocytic choriomeningitis virus, induced relatively inefficient cytotoxic T cell responses, resulting in low numbers of specific T cells and poor effector cell differentiation. Taken together, these results suggest that effective antibody-based vaccines are achievable by i.n. administration of Qbeta-VLP displaying specific antigens.

Systemic and mucosal immunization with Candida albicans hsp90 elicits hsp90-specific humoral response in vaginal mucosa which is further enhanced during experimental vaginal candidiasis

The Candida albicans heat shock protein 90 kDa (hsp90-CA) is an important target for protective antibodies in disseminated candidiasis of experimental mice and humans. Hsp90-CA is present in the cell wall of Candida pseudohyphae or hyphae--typical pathogenic morphotypes in both mucosal and systemic Candida infections. However, the potential protective effects of hsp90-CA-specific antibodies in vaginal candidiasis has not yet been reported. In the present study we used various vaccine formulations (recombinant hsp90-CA protein and hsp90-CA-encoding DNA vaccine) and routes of administration (intradermal, intranasal, and intravenous) to induce both hsp90-CA-specific systemic and vaginal mucosa immune responses in experimental BALB/c mice. The results showed that intradermal recombinant hsp90-CA protein priming, followed by intranasal or intradermal recombinant hsp90-CA protein boosting induced significant increases in both serum and vaginal hsp90-CA-specific IgG and IgA antibodies compared to the control group, as well as enhanced hsp90-CA-specific splenocyte responses in vitro. In the intradermally boosted group, subsequent experimental vaginal Candida infection induced additional increases in the hsp90-CA specific IgG isotype, suggesting that Candida has the ability to induce a local hsp90-specific antibody (IgG) response during vulvovaginal candidiasis. Further work is required to elucidate the importance of immunity to highly conserved antigens during infection of the human female reproductive tract where a balance between immunity to and tolerance for commonly antigens such as hsp90 is necessary for the maintenance of fertility.

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

Human papillomaviruses have been recognized as the causative agent of anogenital cancer. In 2006, a commercial vaccine based on virus-like particles composed of the L1 major capsid protein of the papillomaviruses has been available. This vaccine induces virus-neutralizing antibody responses upon parenteral injection. Here we investigated the oral immunogenicity of different assembly forms of HPV 16 L1, that is: T7-VLPs, T1 particles and capsomeres. Our results show that all three assembly forms induce humoral and cellular immune responses after oral vaccination of mice. The anti-L1 antibodies were conformation-specific and showed neutralizing activity in a pseudovirion-based assay. We also investigated if adjuvants have an influence on the oral immunogenicity of the different L1 forms. For saponins we observed a significant toxicity if applied orally. Co-administration of either CpG DNA or Escherichia coli heat-labile enterotoxin LT(R192G) had no apparent enhancing effect on the production of anti-L1 antibodies. More pronounced was the effect of CpG administration on the long-term immunity as we observed a significantly stronger recall response 244 days after the first vaccination. Compared to capsomeres, VLPs induced stronger humoral immune responses while the CTL responses were induced at comparable levels. Finally, we were also able to induce neutralizing antibodies and L1-specific cytotoxic T-lymphocytes after oral administration of crude extracts of L1-expressing insect cells. In conclusion, all three assembly forms of the L1 protein are immunogenic when administered orally.

Salmonella enterica serovar Typhi Ty21a expressing human papillomavirus type 16 L1 as a potential live vaccine against cervical cancer and typhoid fever

Human papillomavirus (HPV) vaccines based on L1 virus-like particles (VLPs) can prevent HPV-induced genital neoplasias, the precursors of cervical cancer. However, most cervical cancers occur in developing countries, where the implementation of expensive vaccines requiring multiple injections will be difficult. A live Salmonella-based vaccine could be a lower-cost alternative. We previously demonstrated that high HPV type 16 (HPV16)-neutralizing titers are induced after a single oral immunization of mice with attenuated Salmonella enterica serovar Typhimurium strains expressing a codon-optimized version of HPV16 L1 (L1S). To allow the testing of this type of vaccine in women, we constructed a new L1-expressing plasmid, kanL1S, and tested kanL1S recombinants of three Salmonella enterica serovar Typhi vaccine strains shown to be safe in humans, i.e., Ty21a, the actual licensed typhoid vaccine, and two highly immunogenic typhoid vaccine candidates, Ty800 and CVD908-htrA. In an intranasal mouse model of Salmonella serovar Typhi infection, Ty21a kanL1S was unique in inducing HPV16-neutralizing antibodies in serum and genital secretions, while anti-Salmonella responses were similar to those against the parental Ty21a vaccine. Electron microscopy examination of Ty21a kanL1S lysates showed that L1 assembled in capsomers and capsomer aggregates but not well-ordered VLPs. Comparison to the neutralizing antibody response induced by purified HPV16 L1 VLP immunizations in mice suggests that Ty21a kanL1S may be an effective prophylactic HPV vaccine. Ty21a has been widely used against typhoid fever in humans with a remarkable safety record. These finds encourage clinical testing of Ty21a kanL1S as a combined typhoid fever/cervical cancer vaccine with the potential for worldwide application.