Intranasal immunization with influenza antigens conjugated with cholera toxin subunit B stimulates broad spectrum immunity against influenza viruses

Development of transgenic algae strain expressing CTB-M2e fusion gene an approach towards the development of a universal edible vaccine in algae

Avian Influenza, the most studied virus, is of high concern due to its zoonotic pandemic potential. In recent years, several influenza vaccines have been used with the broad goal of managing and in certain cases, eliminating the disease. The matrix 2 extracellular domain (M2e), is one of the key targets of the universal influenza vaccine, a liner peptide that is conserved throughout all influenza A subtypes virus. Many recombinant influenza proteins have been expressed in yeast and plants for vaccine development. A remarkable development has been made in the field of biotechnology to explore the potential of microalga as an expression host. In this study, we designed a fusion gene code for M2e peptide and CTB protein as M2e's natural form has a low level of immunogenicity. The fusion gene was cloned in the Chloroplast transformation vector pSRSapI and expressed in the TN72 mutant strain of Chlamydomonas reinhardii. The expression of the targeted protein was confirmed by ECL western blot analysis. A GM1-ELISA was carried out to detect the affinity of fusion protein for GM1 monosialoganglioside and the significant P-value is lower than 0.05. Immunogenicity assay on chicken detected the anti-M2e bodies in chicken serum. This study gives evidence of therapeutic protein production through algae chloroplast and a stable, selection free and low cost oral delivery for universal vaccine against influenza A virus.

Non-Invasive Vaccines: Challenges in Formulation and Vaccine Adjuvants

Given the limitations of conventional invasive vaccines, such as the requirement for a cold chain system and trained personnel, needle-based injuries, and limited immunogenicity, non-invasive vaccines have gained significant attention. Although numerous approaches for formulating and administrating non-invasive vaccines have emerged, each of them faces its own challenges associated with vaccine bioavailability, toxicity, and other issues. To overcome such limitations, researchers have created novel supplementary materials and delivery systems. The goal of this review article is to provide vaccine formulation researchers with the most up-to-date information on vaccine formulation and the immunological mechanisms available, to identify the technical challenges associated with the commercialization of non-invasive vaccines, and to guide future research and development efforts.

Developments in Vaccine Adjuvants

Vaccines, including subunit, recombinant, and conjugate vaccines, require the use of an immunostimulator/adjuvant for maximum efficacy. Adjuvants not only enhance the strength and longevity of immune responses but may also influence the type of response. In this chapter, we review the adjuvants that are available for use in human vaccines, such as alum, MF59, AS03, and AS01. We extensively discuss their composition, characteristics, mechanism of action, and effects on the immune system. Additionally, we summarize recent trends in adjuvant discovery, providing a brief overview of saponins, TLRs agonists, polysaccharides, nanoparticles, cytokines, and mucosal adjuvants.

Attenuation Methods for Live Vaccines

Vaccination was developed by Edward Jenner in 1796. Since then, vaccination and vaccine development research has been a hotspot of research in the scientific community. Various ways of vaccine development are successfully employed in mass production of vaccines. One of the most successful ways to generate vaccines is the method of virulence attenuation in pathogens. The attenuated strains of viruses, bacteria, and parasites are used as vaccines which elicit robust immune response and confers protection against virulent pathogens. This chapter brings together the most common and efficient ways of generating live attenuated vaccine strains in viruses, bacteria, and parasites.

Immunogenicity of Antigen Adjuvanted with AS04 and Its Deposition in the Upper Respiratory Tract after Intranasal Administration

Adjuvant system 04 (AS04) is in injectable human vaccines. AS04 contains two known adjuvants, 3-O-desacyl-4'-monophosphoryl lipid A (MPL) and insoluble aluminum salts. Data from previous studies showed that both MPL and insoluble aluminum salts have nasal mucosal vaccine adjuvant activity. The present study was designed to test the feasibility of using AS04 as an adjuvant to help nasally administered antigens to induce specific mucosal and systemic immunity as well as to evaluate the deposition of antigens in the upper respiratory tract when adjuvanted with AS04. Alhydrogel, an aluminum (oxy)hydroxide suspension, was mixed with MPL to form AS04, which was then mixed with ovalbumin (OVA) or 3× M2e-HA2, a synthetic influenza virus hemagglutinin fusion protein, as an antigen to prepare OVA/AS04 and 3× M2e-HA2/AS04 vaccines, respectively. In mice, AS04 enabled antigens, when given intranasally, to induce specific IgA response in nasal and lung mucosal secretions as well as specific IgG response in the serum samples of the immunized mice, whereas subcutaneous injection of the same vaccine induced specific antibody responses only in the serum samples but not in the mucosal secretions. Splenocytes isolated from mice intranasally immunized with the OVA/AS04 also proliferated and released cytokines (i.e., IL-4 and IFN-γ) after in vitro stimulation with the antigen. In the immunogenicity test, intranasal OVA/AS04 was not more effective than intranasal OVA/MPL at the dosing regimens tested. However, when compared to OVA/MPL, OVA/AS04 showed a different atomized droplet size distribution and more importantly a more favorable OVA deposition profile when atomized into a nasal cast that was 3-D printed based on the computer tomography scan of the nose of a child. It is concluded that AS04 has mucosal adjuvant activity when given intranasally. In addition, there is a reason to be optimistic about using AS04 as an adjuvant to target an antigen of interest to the right region of the nasal cavity in humans for immune response induction.

An approach to the influenza chimeric subunit vaccine (3M2e-HA2-NP) provides efficient protection against lethal virus challenge

OBJECTIVES

Vaccination is the most effective preventive strategy for influenza disease. As the virus undergoes high antigenic drift, it requires a constant reformulation to obtain high protection.

RESULTS

Immunogenicity of a purified chimeric protein containing conserved regions of influenza A/H1N1 viruses including the Hemagglutinin stalk domain, Nucleoprotein, and Matrix protein produced in a prokaryotic system was assessed in vitro and in vivo, alone or in combination with adjuvants by evaluating antibody responses, cytokine production, lymphocyte proliferative assay, and mortality rate after challenge. The animals that received the chimeric protein had specific antibody responses, elicited memory CD4 cells, cytokines of Th1 and Th2 cells and showed 75% protection against influenza virus lethal challenge. The animals injected with the chimeric protein supplemented with Alum showed improved immune responses, but they had 67% protection. In other words, although Alum adjuvant enriched the chimera specific immune responses potently, it could not enhance its protectivity.

CONCLUSION

Regarding the immunogenicity and protectivity of the chimeric protein construct against influenza, findings of the study suggested that the chimeric protein could be considered as a promising influenza vaccine candidate.

Intranasally administered protein coated chitosan nanoparticles encapsulating influenza H9N2 HA2 and M2e mRNA molecules elicit protective immunity against avian influenza viruses in chickens

Chitosan nanoparticles (CNPs) represent an efficient vaccination tool to deliver immunogenic antigens to the antigen-presenting cells (APCs), which subsequently stimulate protective immune responses against infectious diseases. Herein, we prepared CNPs encapsulating mRNA molecules followed by surface coating with conserved H9N2 HA2 and M2e influenza proteins. We demonstrated that CNPs efficiently delivered mRNA molecules into APCs and had effectively penetrated the mucosal barrier to reach to the immune initiation sites. To investigate the potential of CNPs delivering influenza antigens to stimulate protective immunity, we intranasally vaccinated chickens with empty CNPs, CNPs delivering HA2 and M2e in both mRNA and protein formats (CNPs + RNA + Pr) or CNPs delivering antigens in protein format only (CNPs + Pr). Our results demonstrated that chickens vaccinated with CNPs + RNA + Pr elicited significantly (p < 0.05) higher systemic IgG, mucosal IgA antibody responses and cellular immune responses compared to the CNPs + Pr vaccinated group. Consequently, upon challenge with either H7N9 or H9N2 avian influenza viruses (AIVs), efficient protection, in the context of viral load and lung pathology, was observed in chickens vaccinated with CNPs + RNA + Pr than CNPs + Pr vaccinated group. In conclusion, we show that HA2 and M2e antigens elicited a broad spectrum of protection against AIVs and incorporation of mRNAs in vaccine formulation is an effective strategy to induce superior immune responses.

Intranasally administered polyethylenimine adjuvanted influenza M2 ectodomain induces partial protection against H9N2 influenza A virus infection in chickens

This study aimed to investigate whether intranasally coadministered four tandem copies of extracellular domains of M2 (M2e) and polyethyleneimine (PEI), a mucosal adjuvant, can protect chickens against H9N2 influenza A virus infection. Groups of chickens were intranasally vaccinated with M2e plus PEI adjuvant, M2e alone or PEI adjuvant, and antibody (serum IgG and mucosal IgA) and cellular (CD4⁺ T cells and IFN-γ levels) immune responses were measured post-vaccination. We demonstrated that the chickens vaccinated with M2e plus PEI adjuvant showed significantly (p < 0.05) higher M2e-specific systemic IgG and mucosal IgA responses compared to the chickens that received either M2e alone or PEI adjuvant. The IgA responses measured in lungs were almost comparable to that of the serum IgG levels. Upon restimulation of the vaccinated peripheral blood mononuclear cells (PBMCs) with M2e antigen, significantly (p < 0.05) higher IFN-γ levels were observed only in M2e plus PEI adjuvant vaccinated group. Lymphoproliferative and CD4⁺ T cell responses, as measured by MTT-based assay and flow cytometry, respectively, were also observed significantly (p < 0.05) higher in M2e plus PEI adjuvant vaccinated chickens. On challenge with the H9N2 virus (10⁴TCID₅₀) at 28^th day post-vaccination, M2e plus PEI adjuvant vaccinated group exhibited lower lung inflammation and viral load compared to the chickens treated with either M2e alone or PEI adjuvant. In summary, we show that intranasally coadministered M2e and PEI adjuvant can elicit humoral and cell-mediated immune responses and can reduce viremia levels in chickens post H9N2 infection in chickens.

Intranasal Vaccination With Lipoproteins Confers Protection Against Pneumococcal Colonisation

Streptococcus pneumoniae is endowed with a variety of surface-exposed proteins representing putative vaccine candidates. Lipoproteins are covalently anchored to the cell membrane and highly conserved among pneumococcal serotypes. Here, we evaluated these lipoproteins for their immunogenicity and protective potential against pneumococcal colonisation. A multiplex-based immunoproteomics approach revealed the immunogenicity of selected lipoproteins. High antibody titres were measured in sera from mice immunised with the lipoproteins MetQ, PnrA, PsaA, and DacB. An analysis of convalescent patient sera confirmed the immunogenicity of these lipoproteins. Examining the surface localisation and accessibility of the lipoproteins using flow cytometry indicated that PnrA and DacB were highly abundant on the surface of the bacteria. Mice were immunised intranasally with PnrA, DacB, and MetQ using cholera toxin subunit B (CTB) as an adjuvant, followed by an intranasal challenge with S. pneumoniae D39. PnrA protected the mice from pneumococcal colonisation. For the immunisation with DacB and MetQ, a trend in reducing the bacterial load could be observed, although this effect was not statistically significant. The reduction in bacterial colonisation was correlated with the increased production of antigen-specific IL-17A in the nasal cavity. Immunisation induced high systemic IgG levels with a predominance for the IgG1 isotype, except for DacB, where IgG levels were substantially lower compared to MetQ and PnrA. Our results indicate that lipoproteins are interesting targets for future vaccine strategies as they are highly conserved, abundant, and immunogenic.

The Nontoxic Cholera B Subunit Is a Potent Adjuvant for Intradermal DC-Targeted Vaccination

CD4⁺ T cells are major players in the immune response against several diseases; including AIDS, leishmaniasis, tuberculosis, influenza and cancer. Their activation has been successfully achieved by administering antigen coupled with antibodies, against DC-specific receptors in combination with adjuvants. Unfortunately, most of the adjuvants used so far in experimental models are unsuitable for human use. Therefore, human DC-targeted vaccination awaits the description of potent, yet nontoxic adjuvants. The nontoxic cholera B subunit (CTB) can be safely used in humans and it has the potential to activate CD4⁺ T cell responses. However, it remains unclear whether CTB can promote DC activation and can act as an adjuvant for DC-targeted antigens. Here, we evaluated the CTB's capacity to activate DCs and CD4⁺ T cell responses, and to generate long-lasting protective immunity. Intradermal (i.d.) administration of CTB promoted late and prolonged activation and accumulation of skin and lymphoid-resident DCs. When CTB was co-administered with anti-DEC205-OVA, it promoted CD4⁺ T cell expansion, differentiation, and infiltration to peripheral nonlymphoid tissues, i.e., the skin, lungs and intestine. Indeed, CTB promoted a polyfunctional CD4⁺ T cell response, including the priming of Th1 and Th17 cells, as well as resident memory T (RM) cell differentiation in peripheral nonlymphoid tissues. It is worth noting that CTB together with a DC-targeted antigen promoted local and systemic protection against experimental melanoma and murine rotavirus. We conclude that CTB administered i.d. can be used as an adjuvant to DC-targeted antigens for the induction of broad CD4⁺ T cell responses as well as for promoting long-lasting protective immunity.

Noninvasive vaccination against infectious diseases

The development of a successful vaccine, which should elicit a combination of humoral and cellular responses to control or prevent infections, is the first step in protecting against infectious diseases. A vaccine may protect against bacterial, fungal, parasitic, or viral infections in animal models, but to be effective in humans there are some issues that should be considered, such as the adjuvant, the route of vaccination, and the antigen-carrier system. While almost all licensed vaccines are injected such that inoculation is by far the most commonly used method, injection has several potential disadvantages, including pain, cross contamination, needlestick injury, under- or overdosing, and increased cost. It is also problematic for patients from rural areas of developing countries, who must travel to a hospital for vaccine administration. Noninvasive immunizations, including oral, intranasal, and transcutaneous administration of vaccines, can reduce or eliminate pain, reduce the cost of vaccinations, and increase their safety. Several preclinical and clinical studies as well as experience with licensed vaccines have demonstrated that noninvasive vaccine immunization activates cellular and humoral immunity, which protect against pathogen infections. Here we review the development of noninvasive immunization with vaccines based on live attenuated virus, recombinant adenovirus, inactivated virus, viral subunits, virus-like particles, DNA, RNA, and antigen expression in rice in preclinical and clinical studies. We predict that noninvasive vaccine administration will be more widely applied in the clinic in the near future.

Nasal aluminum (oxy)hydroxide enables adsorbed antigens to induce specific systemic and mucosal immune responses

Some insoluble aluminum salts are commonly used in injectable vaccines as adjuvants to accelerate, prolong, or enhance the antigen-specific immune responses. Data from previous studies testing the nasal mucosal vaccine adjuvant activity of aluminum salts are conflicting. The present study is designed to further assess the feasibility of using aluminum salts in injectable vaccines as nasal mucosal vaccine adjuvants. Using Alhydrogel®, the international scientific standard of aluminum (oxy)hydroxide gels, and ovalbumin or 3 × M2e-HA2, a synthetic influenza virus fusion protein, as antigens, we showed in a mouse model that when dosed intranasally Alhydrogel® enables antigens adsorbed on it to induce stronger antigen-specific immune responses in both serum samples (e.g., specific IgG) and nasal and lung mucosal secretions (i.e., specific IgA) in all immunized mice, as compared with nasal immunization with the antigens alone. Rerouting insoluble aluminum salts in injectable vaccines may represent a viable approach for (nasal) mucosal vaccine adjuvant discovery.

A dual purpose universal influenza vaccine candidate confers protective immunity against anthrax

Preventive influenza vaccines must be reformulated annually because of antigen shift and drift of circulating influenza viral strains. However, seasonal vaccines do not always match the circulating strains, and there is the ever-present threat that avian influenza viruses may adapt to humans. Hence, a universal influenza vaccine is needed to provide protective immunity against a broad range of influenza viruses. We designed an influenza antigen consisting of three tandem M2e repeats plus HA2, in combination with a detoxified anthrax oedema toxin delivery system (EFn plus PA) to enhance immune responses. The EFn-3×M2e-HA2 plus PA vaccine formulation elicited robust, antigen-specific, IgG responses; and was protective against heterologous influenza viral challenge when intranasally delivered to mice three times. Moreover, use of the detoxified anthrax toxin system as an adjuvant had the additional benefit of generating protective immunity against anthrax. Hence, this novel vaccine strategy could potentially address two major emerging public health and biodefence threats.

Generation of a safe and effective live viral vaccine by virus self-attenuation using species-specific artificial microRNA

Vaccination with live attenuated vaccines (LAVs) is an effective way for prevention of infectious disease. While several methods are employed to create them, efficacy and safety are still a challenge. In this study, we evaluated the feasibility of creating a self-attenuated RNA virus expressing a functional species-specific artificial microRNA. Using influenza virus as a model, we produced an attenuated virus carrying a mammalian-specific miR-93 expression cassette that expresses a viral nucleoprotein (NP)-specific artificial microRNA from an insertion site within the non-structural (NS) gene segment. The resulting engineered live-attenuated influenza virus, PR8-amiR-93NP, produced mature and functional artificial microRNA against NP in mammalian cells, but not in avian cells. Furthermore, PR8-amiR-93NP was attenuated by 10(4) fold in mice compared with its wild-type counterpart. Importantly, intranasal immunization with PR8-amiR-93NP conferred cross-protective immunity against heterologous influenza virus strains. In short, this method provides a safe and effective platform for creation of live attenuated RNA viral vaccines.