A single, low dose oral antigen exposure in newborn piglets primes mucosal immunity if administered with CpG oligodeoxynucleotides and polyphosphazene adjuvants

Oral vaccination of piglets against Mycoplasma hyopneumoniae using silica SBA-15 as an adjuvant effectively reduced consolidation lung lesions at slaughter

Mycoplasma (M.) hyopneumoniae is the main pathogen of porcine enzootic pneumonia (PEP). Its controlling is challenging, and requires alternative strategies. This study aimed to develop an oral vaccine against M. hyopneumoniae using a nanostructured mesoporous silica (SBA-15) as an adjuvant, and compare its effect with an intramuscular (IM) commercial vaccine (CV). Fifty 24 day-old M. hyopneumoniae-free piglets composed five equal groups for different immunization protocols, consisting of a CV and/or oral immunization (OI). Control piglets did not receive any form of immunization. All piglets were challenged with M. hyopneumoniae strain 232 on D49 by tracheal route. IgA antibody response in the respiratory tract, bacterial shedding and serum IgG were evaluated. The piglets were euthanized on 28 (D77) and 56 (D105) days post-infection. Lung lesions were macroscopically evaluated; lung fragments and bronchoalveolar fluid (BALF) were collected for estimation of bacterial loads by qPCR and/or histopathology examination. All immunization protocols induced reduction on Mycoplasma-like macroscopic lung lesions. IgA Ab responses anti-M. hyopneumoniae, the expression of IL-4 cytokine and a lower expression of IL-8 were induced by CV and OI vaccines, while IgG was induced only by CV. Oral immunization using silica as a carrier-adjuvant can be viable in controlling M. hyopneumoniae infection.

Polyphosphazenes as Adjuvants for Animal Vaccines and Other Medical Applications

Polyphosphazenes are a class of experimental adjuvants that have shown great versatility as vaccine adjuvants in many animal species ranging from laboratory rodents to large animal species. Their adjuvant activity has shown promising results with numerous viral and bacterial antigens, as well as with crude and purified antigens. Vaccines adjuvanted with polyphosphazenes can be delivered via systemic and mucosal administration including respiratory, oral, rectal, and intravaginal routes. Polyphosphazenes can be used in combination with other adjuvants, further enhancing immune responses to antigens. The mechanisms of action of polyphosphazenes have not fully been defined, but several systematic studies have suggested that they act primarily by activating innate immunity. In the present review, we will highlight progress in the development of polyphosphazenes as adjuvants in animals and their other medical applications.

Polyphosphazene immunoadjuvants: Historical perspective and recent advances

The development of successful vaccines has been increasingly reliant on the use of immunoadjuvants - additives, which can enhance and modulate immune responses to vaccine antigens. Immunoadjuvants of the polyphosphazene family encompass synthetic biodegradable macromolecules, which attain in vivo activity via antigen delivery and immunostimulation mechanisms. Over the last decades, the technology has witnessed evolvement of next generation members, expansion to include various antigens and routes of administration, and progression to clinical phase. This was accompanied by gaining important insights into the mechanism of action and the development of a novel class of virus-mimicking nano-assemblies for antigen delivery. The present review evaluates in vitro and in vivo data generated to date in the context of latest advances in understanding the primary function and biophysical behavior of these macromolecules. It also provides an overview of relevant synthetic and characterization methods, macromolecular biodegradation pathways, and polyphosphazene-based multi-component, nanoparticulate, and microfabricated formulations.

Adjuvants and delivery systems based on polymeric nanoparticles for mucosal vaccines

Most pathogens enter the body through mucosal surfaces. Therefore, vaccination through the mucosal route can greatly enhance the mucosal immune response. Vaccination via the mucosal surface is the most effective way to trigger a protective mucosal immune response, but the vast majority of vaccines used are administered by injection. Strategies to enhance the mucosal immunity have been developed by using vaccine adjuvants, delivery systems, bacterial or viral vectors, and DNA vaccines. Appropriate vaccine adjuvants and drug delivery systems can improve the immunogenicity of antigens, induce a stronger immune response, and reduce the vaccine dose and production cost. In recent years, many studies have focused on finding safe and effective vaccine adjuvants and drug delivery systems to formulate the mucosal vaccines for solving the above problems. Great progress has also been made in vaccine adjuvants and drug delivery systems based on biodegradable polymer nanoparticles. In this paper, the research progress of the mucosal vaccine and its related adjuvants and drug delivery systems in recent years was reviewed, and the application of polymers as adjuvants and drug delivery system in vaccine was prospected. This review provides a fundamental knowledge for the application of biodegradable polymer nanoparticles as adjuvants and carriers in mucosal vaccines and shows great application prospects.

Administration of Poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and Avian Beta Defensin as Adjuvants in Inactivated Inclusion Body Hepatitis Virus and its Hexon Protein-Based Experimental Vaccine Formulations in Chickens

Inclusion body hepatitis (IBH) is one of the major infectious diseases adversely affecting the poultry industry of the United States and Canada. Currently, no effective and safe vaccine is available for the control of IBH virus (IBHV) infection in chickens. However, based on the excellent safety and immunogenic profiles of experimental veterinary vaccines developed with the use of new generation adjuvants, we hypothesized that characterization of vaccine formulations containing inactivated IBHV or its capsid protein hexon as antigens, along with poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and avian beta defensin 2 (ABD2) as vaccine adjuvants, will be helpful in development of an effective and safe vaccine formulation for IBH. Our data demonstrated that experimental administration of vaccine formulations containing inactivated IBHV and a mixture of PCEP with or without ABD2 as an adjuvant induced significantly higher antibody responses compared with other vaccine formulations, while hexon protein-based vaccine formulations showed relatively lower levels of antibody responses. Thus, a vaccine formulation containing inactivated IBHV with PCEP or a mixture of PCEP and ABD2 (with a reduced dosage of PCEP) as an adjuvant may serve as a potential vaccine candidate. However, in order to overcome the risks associated with whole virus inactivated vaccines, characterization of additional viral capsid proteins, including fiber protein and penton of IBHV along with hexon protein in combination with more new generation adjuvants, will be helpful in further improvements of vaccines against IBHV infection.

Salmonella ghosts expressing enterotoxigenic Escherichia coli k88ab, k88ac, k99, and fasa fimbrial antigens induce robust immune responses in a mouse model

BACKGROUND

Bacterial ghosts can be developed as safe and effective vaccines against bacterial infectious disease such as enterotoxigenic Escherichia coli (ETEC)-induced diarrhea in neonatal piglets.

OBJECTIVE

Immune responses against a Salmonella ghost expressing ETEC K88ab, K88ac, K99, and FasA antigens with various adjuvants and inoculation routes were evaluated in mice.

ANIMALS AND METHODS

A ghost cell expressing K88ab, K88ac, K99, and FasA fimbrial antigens of ETEC on the envelope of △asd Salmonella typhimurium was constructed as a candidate vaccine against ETEC infection. To optimize the immunization strategy, 6-week-old female BALB/c mice were inoculated with the ghost and various adjuvants, and the immune responses against the individual fimbrial antigens were measured. Blood samples from caudal vein to evaluate serum IgG concentrations and fecal samples to evaluate mucosal IgA concentrations were collected up to 14 weeks post-prime immunization.

RESULTS

All groups with single, double, and triple inoculations of the ghost showed higher humoral and mucosal immune responses than the control group. In particular, the groups with intramuscular double and triple inoculations showed significantly higher immune responses. In addition, oral inoculation with a combination of the ghost and MONTANIDE IMS 1113 (MI1113) resulted in high and prolonged induction of intestinal IgA levels.

CONCLUSION

These results indicated that both systemic and mucosal immunity against ETEC fimbrial antigens expressed by the ghost are induced by intramuscular booster inoculation with the ghost, and that addition of M1113 to the ghost was found to result in prominent induction of mucosal immunity through oral inoculation.

Oral antigen exposure in newborn piglets circumvents induction of oral tolerance in response to intraperitoneal vaccination in later life

Background

We previously determined that newborn piglets orally gavaged with Ovalbumin (OVA) responded to systemic OVA re-exposure with tolerance; if adjuvants were included in oral vaccine, piglets responded with antibody-mediated immunity (Vet Immunol Immunopathol 161(3–4):211–21, 2014). Here, we will investigate whether newborn piglets gavaged with a vaccine comprised of OVA plus unmethylated CpG oligodeoxynucleotides (CpG; soluble component; OVA/CpG) combined with OVA plus CpG encapsulated within polyphosphazene microparticles (MP; particulate component) responded with systemic and mucosal immunity. To monitor the response to systemic antigen re-exposure, piglets were i.p.-immunized with OVA plus Incomplete Freund’s Adjuvant (IFA) one month later.

Results

Newborn piglets (n = 5/group) were gavaged with a combined soluble and particulate vaccine consisting of OVA (0.5-0.05 mg) plus 50 μg CpG and 0.5 mg OVA plus 50 μg CpG encapsulated within a polyphosphazene MP (0.5 mg) referred to as OVA/CpG + MP. Control piglets were gavaged with saline alone. Piglets were i.p. immunized with 10 mg OVA (or saline) in IFA at four weeks of age and then euthanized at eight weeks of age. We observed significantly higher titres of serum anti-OVA immunoglobulin (Ig) IgM, IgA, IgG, IgG1, IgG2 and IgG in piglets immunized with 0.05 mg OVA/CpG + MP relative to saline control animals. Thus, a single oral exposure at birth to a combined soluble and particulate OVA vaccine including adjuvants can circumvent induction of oral tolerance which impacts response to i.p. vaccination in later life. Further, piglets gavaged with 0.05 mg OVA/CpG + MP generated significant anti-OVA IgG and IgG1 titres in lung compared to saline control piglets but results were comparable to titres measured in parenteral control piglets. Peripheral blood mononuclear cells (PBMCs) ex vivo-stimulated with OVA showed markedly decreased production of IL-10 cytokine after 72 hours relative to animal-matched cells incubated with media alone. No production of IFN-γ was observed from any groups.

Conclusion

Newborn piglets gavaged with low dose soluble and particulate OVA plus CpG ODN and polyphosphazene adjuvants produced antigen-specific antibodies in serum and lung after systemic re-exposure in later life. These data indicate circumvention of oral tolerance but not induction of oral immunity.

Evidence for a common mucosal immune system in the pig

•

There is evidence that the common mucosal immune system exists in pigs.

•

Vaccination at an easily accessible mucosal site may assist in providing protection at other mucosal sites.

•

Local and distal mucosal sites should be sampled after vaccinations to define the optimal dose and formulation which promotes the common mucosal immune system in pigs.

The majority of lymphocytes activated at mucosal sites receive instructions to home back to the local mucosa, but a portion also seed distal mucosa sites. By seeding distal sites with antigen-specific effector or memory lymphocytes, the foundation is laid for the animal's mucosal immune system to respond with a secondary response should to this antigen be encountered at this site in the future. The common mucosal immune system has been studied quite extensively in rodent models but less so in large animal models such as the pig. Reasons for this paucity of reported induction of the common mucosal immune system in this species may be that distal mucosal sites were examined but no induction was observed and therefore it was not reported. However, we suspect that the majority of investigators simply did not sample distal mucosal sites and therefore there is little evidence of immune response induction in the literature. It is our hope that more pig immunologists and infectious disease experts who perform mucosal immunizations or inoculations on pigs will sample distal mucosal sites and report their findings, whether results are positive or negative. In this review, we highlight papers that show that immunization/inoculation using one route triggers mucosal immune system induction locally, systemically, and within at least one distal mucosal site. Only by understanding whether immunizations at one site triggers immunity throughout the common mucosal immune system can we rationally develop vaccines for the pig, and through these works we can gather evidence about the mucosal immune system that may be extrapolated to other livestock species or humans.