Mucosal immunity and nasal influenza vaccination

Mucosally administered Lactobacillus surface-displayed influenza antigens (sM2 and HA2) with cholera toxin subunit A1 (CTA1) Induce broadly protective immune responses against divergent influenza subtypes

The development of a universal influenza vaccine that provides broad cross protection against existing and unforeseen influenza viruses is a critical challenge. In this study, we constructed and expressed conserved sM2 and HA2 influenza antigens with cholera toxin subunit A1 (CTA1) on the surface of Lactobacillus casei (pgsA-CTA1sM2HA2/L. casei). Oral and nasal administrations of recombinant L. casei into mice resulted in high levels of serum immunoglobulin G (IgG) and their isotypes (IgG1 & IgG2a) as well as mucosal IgA. The mucosal administration of pgsA-CTA1sM2HA2/L. casei may also significantly increase the levels of sM2- or HA2-specific cell-mediated immunity because increased release of both IFN-γ and IL-4 was observed. The recombinant pgsA-CTA1sM2HA2/L. casei provided better protection of BALB/c mice against 10 times the 50% mouse lethal doses (MLD50) of homologous A/EM/Korea/W149/06(H5N1) or A/Aquatic bird/Korea/W81/2005 (H5N2) and heterologous A/Puerto Rico/8/34(H1N1), or A/Chicken/Korea/116/2004(H9N2) or A/Philippines/2/08(H3N2) viruses, compared with L. casei harboring sM2HA2 and also the protection was maintained up to seven months after administration. These results indicate that recombinant L. casei expressing the highly conserved sM2, HA2 of influenza and CTA1 as a mucosal adjuvant could be a potential mucosal vaccine candidate or tool to protect against divergent influenza viruses for human and animal.

Parents' attitude toward multiple vaccinations at a single visit with alternative delivery methods

Last decades, the number of routine childhood vaccinations has increased considerably, which consequently has led to multiple vaccine injections per consultation. Implementation of additional vaccines will probably lead to more than 2 vaccine injections per consult, which might be a barrier for parents to vaccinate their child. A decrease in vaccination coverage, however, increases the risk of disease outbreaks. Less stressful alternative methods for vaccine delivery might lead to an increased acceptance of multiple childhood vaccinations by parents. The present questionnaire study was set up to explore the maximum number of vaccine injections per visit that is acceptable for parents, as well as to gauge parents’ attitude toward alternative needle-free methods for vaccine delivery. For this purpose, the parents’ opinion toward a jet injector, a patch, a microneedle system, and nasal spray device as methods for vaccine delivery was assessed. The majority of the 1154 participating parents indicated that 3 vaccine injections per visit was perceived as too much. Most participants had a positive attitude with respect to the jet injector and the patch as alternative vaccine delivery method, whereas the microneedle device and an intranasal spray device were not perceived as better than the conventional syringe by the parents. Parents indicated that both the jet injector and the patch might increase their acceptance of giving their children more than 2 vaccinations at the same time. This should encourage vaccine developers and manufacturers to put efforts in developing these delivery methods for their vaccines.

CpG DNA assists the whole inactivated H9N2 influenza virus in crossing the intestinal epithelial barriers via transepithelial uptake of dendritic cell dendrites

Intestinal mucosa remains a pivotal barrier for the oral vaccine absorption of H9N2 whole inactivated influenza virus (WIV). However, CpG DNA, as an adjuvant, can effectively improve relevant mucosal and systemic immunity. The downstream mechanism is well confirmed, yet the evidence of CpG DNA assisting H9N2 WIV in transepithelial delivery is lacking. Here, we reported both in vitro and in vivo that CpG DNA combined with H9N2 WIV was capable of recruiting additional dendritic cells (DCs) to the intestinal epithelial cells (ECs) to form transepithelial dendrites (TEDs) for luminal viral uptake. Both CD103(+) and CD103(-) DCs participated in this process. The engagement of the chemokine CCL20 from the apical ECs and the DCs drove DC recruitment and TED formation. Virus-loaded CD103(+) but not CD103(-) DCs also quickly migrated into mesenteric lymph nodes within 2 h. Moreover, the mechanism of CpG DNA was independent of epithelial transcytosis and disruption of the epithelial barriers. Finally, the subsequent phenotypic and functional maturation of DCs was also enhanced. Our findings indicated that CpG DNA improved the delivery of H9N2 WIV via TEDs of intestinal DCs, and this may be an important mechanism for downstream effective antigen-specific immune responses.

Expression of H3N2 nucleoprotein in maize seeds and immunogenicity in mice

Oral administration of maize-expressed H3N2 nucleoprotein induced antibody responses in mice showing the immunogenicity of plant-derived antigen and its potential to be utilized as a universal flu vaccine. Influenza A viruses cause influenza epidemics that are devastating to humans and livestock. The vaccine for influenza needs to be reformulated every year to match the circulating strains due to virus mutation. Influenza virus nucleoprotein (NP) is a multifunctional RNA-binding protein that is highly conserved among strains, making it a potential candidate for a universal vaccine. In this study, the NP gene of H3N2 swine origin influenza virus was expressed in maize endosperm. Twelve transgenic maize lines were generated and analyzed for recombinant NP (rNP) expression. Transcript analysis showed the main accumulation of rNP in seed. Protein level of rNP in T1 transgenic maize seeds ranged from 8.0 to 35 µg of NP/g of corn seed. The level increased up to 70 µg of NP/g in T3 seeds. A mouse study was performed to test the immunogenicity of one line of maize-derived rNP (MNP). Mice were immunized with MNP in a prime-boost design. Oral gavage administration showed that a humoral immune response was elicited in the mice treated with MNP indicating the immunogenicity of MNP. NP-specific antibody responses in the MNP group showed comparable antibody titer with the groups receiving positive controls such as Vero cell-derived NP (VNP) or alphavirus replicon particle-derived NP (ANP). Cytokine analysis showed antigen-specific stimulation of IL-4 cytokine elicited in splenocytes from mice treated with MNP further confirming a TH2 humoral immune response induced by MNP administration.

The application of pseudotypes to influenza pandemic preparedness

ABSTRACT 

Human and animal populations are constantly exposed to multiple influenza strains due to zoonotic spillover and rapid viral evolution driven by intrinsic error-prone replication and immunological pressure. In this context, antibody responses directed against the hemagglutinin protein on the surface of the virus are of importance since they have been shown to correlate with protective immunity. Serological techniques, detecting these responses, play a critical role in influenza pandemic preparedness in particular with regard to the measurement of vaccine immunogenicity. As the recent human pandemics (H1N1) and avian influenza outbreaks (H5 and H7) have demonstrated, there is an urgent need to be better prepared to assess the contribution of the antibody response to protection against newly emerged viruses and to evaluate the extent of pre-existing heterosubtypic immunity in populations. This review compares pseudotype-based assays with wild-type and virus-like particle virus assays and discusses their place in the pandemic preparedness against the influenza virus. It additionally addresses the state-of-the-art developments of pseudotype-based assays (chimeric hemagglutinins, multiplex and post-attachment) including the development and future deployment of assay kits and approaches toward standardization to both preclinical and clinical endpoints. Progress toward the development of an influenza pseudotype library for the purposes of pandemic preparedness is also outlined and discussed.

Intranasal and oral vaccination with protein-based antigens: advantages, challenges and formulation strategies

Most pathogens initiate their infections at the human mucosal surface. Therefore, mucosal vaccination, especially through oral or intranasal administration routes, is highly desired for infectious diseases. Meanwhile, protein-based antigens provide a safer alternative to the whole pathogen or DNA based ones in vaccine development. However, the unique biopharmaceutical hurdles that intranasally or orally delivered protein vaccines need to overcome before they reach the sites of targeting, the relatively low immunogenicity, as well as the low stability of the protein antigens, require thoughtful and fine-tuned mucosal vaccine formulations, including the selection of immunostimulants, the identification of the suitable vaccine delivery system, and the determination of the exact composition and manufacturing conditions. This review aims to provide an up-to-date survey of the protein antigen-based vaccine formulation development, including the usage of immunostimulants and the optimization of vaccine delivery systems for intranasal and oral administrations.

CpG Oligodeoxynucleotides Facilitate Delivery of Whole Inactivated H9N2 Influenza Virus via Transepithelial Dendrites of Dendritic Cells in Nasal Mucosa

The spread of the low-pathogenicity avian H9N2 influenza virus has seriously increased the risk of a new influenza pandemic. Although whole inactivated virus (WIV) vaccine via intranasal pathway is the effective method of blocking virus transmission, the mucosal barrier seems to be a major factor hampering its development. CpG oligodeoxynucleotides, a known adjuvant, can target downstream dendritic cells (DCs) and effectively enhance the mucosal and systemic immune responses. However, the ability of CpGs to assist H9N2 WIV in transepithelial transport remains unknown. Here, in vitro and in vivo, we showed that CpGs provided assistance for H9N2 WIV in recruiting DCs to the nasal epithelial cells (ECs) and forming transepithelial dendrites (TEDs) to capture luminal viruses. CD103(+) DCs participated in this process. Chemokine CCL20 from nasal ECs played a key role in driving DC recruitment and TED formation. Virus-loaded DCs quickly migrated into the draining cervical lymph nodes (CLNs) for antigen presentation. In addition, the competence of CpGs was independent of direct epithelial transport via the transcellular or paracellular pathway. Taken together, our data demonstrated that CpGs enhanced the transport of H9N2 WIV via TEDs of nasal DCs, which might be a novel mechanism for optimal adaptive immune responses.

IMPORTANCE

This paper demonstrates by both an in vivo and an in vitro coculture model that CpG oligodeoxynucleotides, known as an adjuvant generally targeting downstream immune responses, also are crucial for the transport of H9N2 WIV across nasal epithelial cells (ECs) via the uptake of transepithelial dendrites (TEDs). Our results prove for the first time to our knowledge that the immune-potentiating mechanism of CpGs is based on strengthening the transepithelial uptake of H9N2 WIV in nasal mucosa. These findings provide a fresh perspective for further improvement of intranasal influenza vaccines, which are urgently needed in the face of the potential threat of H9N2 influenza.

H9N2 influenza whole inactivated virus combined with polyethyleneimine strongly enhances mucosal and systemic immunity after intranasal immunization in mice

Influenza whole inactivated virus (WIV) is more immunogenic and induces protective antibody responses compared with other formulations, like split virus or subunit vaccines, after intranasal mucosal delivery. Polyethyleneimine (PEI), an organic polycation, is widely used as a reagent for gene transfection and DNA vaccine delivery. Although PEI recently has demonstrated potent mucosal adjuvant activity for viral subunit glycoprotein antigens, its immune activity with H9N2 WIV is not well demonstrated. Here, mice were immunized intranasally with H9N2 WIV combined with PEI, and the levels of local respiratory tract and systemic immune responses were measured. Compared to H9N2 WIV alone, antigen-specific IgA levels in the local nasal cavity, trachea, and lung, as well as levels of IgG and its subtypes (IgG1 and IgG2a) in the serum, were strongly enhanced with the combination. Similarly, the activation and proliferation of splenocytes were markedly increased. In addition, PEI is superior as an H9N2 WIV delivery system due to its ability to greatly increase the viral adhesion to mucosal epithelial cells and to enhance the cellular uptake and endosomal escape of antigens in dendritic cells (DCs) and further significantly activate DCs to mature. Taken together, these results provided more insights that PEI has potential as an adjuvant for H9N2 particle antigen intranasal vaccination.

Whole inactivated avian Influenza H9N2 viruses induce nasal submucosal dendritic cells to sample luminal viruses via transepithelial dendrites and trigger subsequent DC maturation

Nasal mucosal barrier is a key impediment for the absorption of influenza whole inactivated virus (WIV) intranasal vaccine. Yet it is still unclear how WIV cross the epithelial cells (ECs) in nasal cavity. Here, in vitro, a coculture system was well established, consisting of surrogate nasal ECs (Calu-3) and dendritic cells (DCs). After adding H9N2 WIV on the apical side of ECs, we found that submucosal DCs extended their transepithelial dendrites (TEDs) and sampled luminal viruses. However, ECs were not involved in the transepithelial transport of viruses. Subsequently, the phenotypic and functional maturation of DCs were also enhanced, whereas they were attenuated after blocking of TED formation by anti-JAM1 antibody. In vivo, we confirmed that H9N2 WIV were capable of inducing nasal submucosal DCs to sample luminal viruses via TEDs in the nasal passage but not nasal-associated lymphoid tissue (NALT). CD103(+) and CD103(-) DC subsets participated in this process. Of note, chemokine CCL20, released from the H9N2 WIV-induced ECs, played a vital role in DC recruitment and TED formation. Taken together, our findings indicated that TEDs played a critical role in facilitating viral transport across the epithelial barrier, which may guide the design of novel nasal mucosal vaccine strategies.

Reducing Campylobacter jejuni colonization of poultry via vaccination

Campylobacter jejuni is a leading bacterial cause of human gastrointestinal disease worldwide. While C. jejuni is a commensal organism in chickens, case-studies have demonstrated a link between infection with C. jejuni and the consumption of foods that have been cross-contaminated with raw or undercooked poultry. We hypothesized that vaccination of chickens with C. jejuni surface-exposed colonization proteins (SECPs) would reduce the ability of C. jejuni to colonize chickens, thereby reducing the contamination of poultry products at the retail level and potentially providing a safer food product for consumers. To test our hypothesis, we injected chickens with recombinant C. jejuni peptides from CadF, FlaA, FlpA, CmeC, and a CadF-FlaA-FlpA fusion protein. Seven days following challenge, chickens were necropsied and cecal contents were serially diluted and plated to determine the number of C. jejuni per gram of material. The sera from the chickens were also analyzed to determine the concentration and specificity of antibodies reactive against the C. jejuni SECPs. Vaccination of chickens with the CadF, FlaA, and FlpA peptides resulted in a reduction in the number of C. jejuni in the ceca compared to the non-vaccinated C. jejuni-challenged group. The greatest reduction in C. jejuni colonization was observed in chickens injected with the FlaA, FlpA, or CadF-FlaA-FlpA fusion proteins. Vaccination of chickens with different SECPs resulted in the production of C. jejuni-specific IgY antibodies. In summary, we show that the vaccination of poultry with individual C. jejuni SECPs or a combination of SECPs provides protection of chickens from C. jejuni colonization.

Intranasal delivery of influenza rNP adjuvanted with c-di-AMP induces strong humoral and cellular immune responses and provides protection against virus challenge

There is a critical need for new influenza vaccines able to protect against constantly emerging divergent virus strains. This will be sustained by the induction of vigorous cellular responses and humoral immunity capable of acting at the portal of entry of this pathogen. In this study we evaluate the protective efficacy of intranasal vaccination with recombinant influenza nucleoprotein (rNP) co-administrated with bis-(3′,5′)-cyclic dimeric adenosine monophosphate (c-di-AMP) as adjuvant. Immunization of BALB/c mice with two doses of the formulation stimulates high titers of NP-specific IgG in serum and secretory IgA at mucosal sites. This formulation also promotes a strong Th1 response characterized by high secretion of INF-γ and IL-2. The immune response elicited promotes efficient protection against virus challenge. These results suggest that c-di-AMP is a potent mucosal adjuvant which may significantly contribute towards the development of innovative mucosal vaccines against influenza.

Mucosal immunization with integrase-defective lentiviral vectors protects against influenza virus challenge in mice

Recent reports highlight the potential for integrase-defective lentiviral vectors (IDLV) to be developed as vaccines due to their ability to elicit cell-mediated and humoral immune responses after intramuscular administration. Differently from their integrase-competent counterpart, whose utility for vaccine development is limited by the potential for insertional mutagenesis, IDLV possess a mutation in their integrase gene that prevents genomic integration. Instead, they are maintained as episomal DNA circles that retain the ability to stably express functional proteins. Despite their favorable profile, it is unknown whether IDLV elicit immune responses after intranasal administration, a route that could be advantageous in the case of infection with a respiratory agent. Using influenza as a model, we constructed IDLV expressing the influenza virus nucleoprotein (IDLV-NP), and tested their ability to generate NP-specific immune responses and protect from challenge in vivo. We found that administration of IDLV-NP elicited NP-specific T cell and antibody responses in BALB/c mice. Importantly, IDLV-NP was protective against homologous and heterosubtypic influenza virus challenge only when given by the intranasal route. This is the first report demonstrating that IDLV can induce protective immunity after intranasal administration, and suggests that IDLV may represent a promising vaccine platform against infectious agents.

Mucosal vaccines against respiratory syncytial virus

Respiratory syncytial virus (RSV) is a leading cause of severe respiratory disease in infants, young children, immune-compromised and elderly populations worldwide. Natural RSV infection in young children does not elicit long-lasting immunity and individuals remain susceptible to repeated RSV infections throughout life. Because RSV infection is restricted to the respiratory tract, an RSV vaccine should elicit mucosal immunity at upper and lower respiratory tracts in order to most effectively prevent RSV reinfection. Although there is no safe and effective RSV vaccine available, significant progress has been recently made in basic RSV research and vaccine development. This review will discuss recent advances in the identification of a new neutralizing antigenic site within the RSV fusion (F) protein, understanding the importance of mucosal immune responses against RSV infection, and the development of novel mucosal vaccination strategies.

T cell responses to viral infections - opportunities for Peptide vaccination

An effective immune response against viral infections depends on the activation of cytotoxic T cells that can clear infection by killing virus-infected cells. Proper activation of these T cells depends on professional antigen-presenting cells, such as dendritic cells (DCs). In this review, we will discuss the potential of peptide-based vaccines for prevention and treatment of viral diseases. We will describe features of an effective response against both acute and chronic infections, such as an appropriate magnitude, breadth, and quality and discuss requirements for inducing such an effective antiviral immune response. We will address modifications that affect presentation of vaccine components by DCs, including choice of antigen, adjuvants, and formulation. Furthermore, we will describe differences in design between preventive and therapeutic peptide-based vaccines. The ultimate goal in the design of preventive vaccines is to develop a universal vaccine that cross-protects against multiple strains of the virus. For therapeutic vaccines, cross-protection is of less importance, but enhancing existing T cell responses is essential. Although peptide vaccination is successful in inducing responses in human papillomavirus (HPV) infected patients, there are still several challenges such as choosing the right target epitopes, choosing safe adjuvants that improve immunogenicity of these epitopes, and steering the immune response in the desired direction. We will conclude with an overview of the current status of peptide vaccination, hurdles to overcome, and prospects for the future.

Fast vaccine design and development based on correlates of protection (COPs)

New and reemerging infectious diseases call for innovative and efficient control strategies of which fast vaccine design and development represent an important element. In emergency situations, when time is limited, identification and use of correlates of protection (COPs) may play a key role as a strategic tool for accelerated vaccine design, testing, and licensure. We propose that general rules for COP-based vaccine design can be extracted from the existing knowledge of protective immune responses against a large spectrum of relevant viral and bacterial pathogens. Herein, we focus on the applicability of this approach by reviewing the established and up-coming COPs for influenza in the context of traditional and a wide array of new vaccine concepts. The lessons learnt from this field may be applied more generally to COP-based accelerated vaccine design for emerging infections.

Assessment of the antigen-specific antibody response induced by mucosal administration of a GnRH conjugate entrapped in lipid nanoparticles

Vaccines administered parenterally have been developed against gonadotrophin-releasing hormone (GnRH) for anti-fertility and anti-cancer purposes. The aim of this study was to demonstrate whether mucosal delivery using GnRH immunogens entrapped in lipid nanoparticles (LNP) could induce anti-GnRH antibody titers. Immunogens consisting of KLH (keyhole limpet hemocyanin) conjugated to either GnRH-I or GnRH-III analogues were entrapped in LNP. Loaded non-ionic surfactant vesicles (NISVs) were administered subcutaneously, while nasal delivery was achieved using NISV in xanthan gum and oral delivery using NISV containing deoxycholate (bilosomes). NISV and bilosomes had similar properties: they were spherical, in the nanometre size range, with a slightly negative zeta potential and surface properties that changed with protein loading and inclusion of xanthan gum. Following immunization in female BALB/c mice, systemic antibody responses were similar for both GnRH-I and GnRH-III immunization. Only nasal delivery proved to be successful in terms of producing systemic and mucosal antibodies.

FROM THE CLINICAL EDITOR

The main research question addressed in this study was whether mucosal delivery using gonadotrophin-releasing hormone immunogens entrapped in lipid nanoparticles could induce anti-GnRH antibody titers. Only nasal delivery proved to be successful in terms of producing systemic and mucosal antibodies with this approach.

Effective intranasal therapeutics and prophylactics with monoclonal antibody against lethal infection of H7N7 influenza virus

Recurrence of highly pathogenic avian influenza (HPAI) virus subtype H7 in humans and poultry continues to be a serious concern to public health. No effective prevention and treatment are currently available against H7 infection. One H7 monoclonal antibody, Mab 62 was selected and characterized. Mab 62 presented efficient neutralization activity against all six representative H7 strains tested, including the H7N9 strain from the recent outbreak in China. The epitope of 62 identified on H7 HA1 exists in all the human H7 strains, including the recent H7N9 strains from China. Mab 62 when administered passively, pre or post challenge with 5 MLD50 (50% mouse lethal dose) HPAI H7N7 influenza viruses could protect 100% of the mice from death. The efficacy of intranasal administration of the Mab was evaluated versus the intraperitoneal route. In the therapeutic study, body weight loss and virus load were reduced in intranasally inoculated mice, as compared to the intraperitoneal group. Intranasal administration results in early clearance of the virus from the lungs and completely prevents lung pathology of H7N7. The study confirmed that intranasal administration of Mab 62 is either an effective prophylactic or therapeutic means against H7 lethal infection. The results of epitope analysis suggest the potential of Mab 62 to be used for the efficacious prevention and treatment against the recent human H7N9 strains.

Evaluation of a novel immunogenic vaccine platform based on a genome replication-deficient Sendai vector

We developed a novel vaccine platform based on a paramyxoviral, genome replication-deficient Sendai virus vector that can express heterologous genes inserted into the genome. To validate the novel approach in vivo, we generated a combined vaccine candidate against human respiratory syncytial virus (RSV) and human parainfluenza virus type 3 (PIV3). The present study compares two different methods of displaying heterologous antigens: (i) the RSV fusion (F) protein, encoded as a secretable version in an additional transcription unit, serves as an antigen only after being expressed in infected cells; (ii) PIV3 fusion (F) and hemagglutinin-neuraminidase (HN) genes, replacing Sendai counterparts in the vector genome, are also expressed as structural components on the surface of vaccine particles. The efficacy of this prototype vaccine was assessed in a mouse model after mucosal administration. The vaccine candidate was able to elicit specific mucosal, humoral and T cell-mediated immune responses against RSV and PIV3. However, PIV3 antigen display on the vaccine particles' surface induced higher antibody titers than the RSV antigen, being expressed only after cell infection. Consequently, this construct induced an adequate neutralizing antibody response only to PIV3. Finally, replicating virus particles were not detected in the lungs of immunized mice, confirming the genome stability and replication deficiency of this vaccine vector in vivo. Both factors can contribute substantially to the safety profile of vaccine candidates. In conclusion, this replication-deficient Sendai vector represents an efficient platform that can be used for vaccine developments against various viral pathogens.

Polymer nanomicelles for efficient mucus delivery and antigen-specific high mucosal immunity

Micelles for mucosal immunity: A mucosal vaccine system based on γ-PGA nanomicelles and viral antigens was synthesized. The intranasal administration of the vaccine system induces a high immune response both in the humoral and cellular immunity (see picture).

Immunogenicity of live attenuated B. pertussis BPZE1 producing the universal influenza vaccine candidate M2e

BACKGROUND

Intranasal delivery of vaccines directed against respiratory pathogens is an attractive alternative to parenteral administration. However, using this delivery route for inactivated vaccines usually requires the use of potent mucosal adjuvants, and no such adjuvant has yet been approved for human use.

METHODOLOGY/PRINCIPAL FINDINGS

We have developed a live attenuated Bordetella pertussis vaccine, called BPZE1, and show here that it can be used to present the universal influenza virus epitope M2e to the mouse respiratory tract to prime for protective immunity against viral challenge. Three copies of M2e were genetically fused to the N-terminal domain of filamentous hemagglutinin (FHA) and produced in recombinant BPZE1 derivatives in the presence or absence of endogenous full-length FHA. Only in the absence of FHA intranasal administration of the recombinant BPZE1 derivative induced antibody responses to M2e and effectively primed BALB/c mice for protection against influenza virus-induced mortality and reduced the viral load after challenge. Strong M2e-specific antibody responses and protection were observed after a single nasal administration with the recombinant BPZE1 derivative, followed by a single administration of M2e linked to a virus-like particle without adjuvant, whereas priming alone with the vaccine strain did not protect.

CONCLUSIONS/SIGNIFICANCE

Using recombinant FHA-3M2e-producing BPZE1 derivatives for priming and the universal influenza M2e peptide linked to virus-like particles for boosting may constitute a promising approach for needle-free and adjuvant-free nasal vaccination against influenza.

Evaluation of the effectiveness and safety of chitosan derivatives as adjuvants for intranasal vaccines

Intranasal immunization is currently used to deliver live virus vaccines such as influenza. However, to develop an intranasal vaccine to deliver inactivated virus, a safe and effective adjuvant is necessary to enhance the mucosal immune response. Here, we demonstrate the effectiveness of a chitosan microparticle (1-20 μm, 50 kDa, degree of deacetylation=85%) and a cationized chitosan (1000 kDa, degree of deacetylation=85%) derived from natural crab shells as adjuvants for an intranasal vaccine candidate. We examined the effectiveness of chitosan derivatives as an adjuvant by co-administering them with ovalbumin (OVA) intranasally in BALB/c mice, polymeric Ig receptor knockout (pIgR-KO) mice, and cynomolgus monkeys (Macaca fascicularis). pIgR-KO mice were used to evaluate S-IgA production on the mucosal surface without nasal swab collection. Administration of OVA with chitosan microparticles or cationized chitosan induced a high OVA-specific IgA response in the serum of pIgR-KO mice and a high IgG response in the serum of BALB/c mice and cynomolgus monkeys. We also found that administration of chitosan derivatives did not have a detrimental effect on cynomolgus monkeys as determined by complete blood count, blood chemistries, and gross pathology results. These results suggest that chitosan derivatives are safe and effective mucosal adjuvants for intranasal vaccination.