Inclusion bodies from recombinant bacteria as a novel system for delivery of vaccine antigen by the oral route

IgYs: on her majesty's secret service

There has been an increasing interest in using Immunoglobulin Y (IgY) antibodies as an alternative to "classical" antimicrobials. Unlike traditional antibiotics, they can be utilized on a continual basis without leading to the development of resistance. The veterinary IgY antibody market is growing because of the demand for minimal antibiotic use in animal production. IgY antibodies are not as strong as antibiotics for treating infections, but they work well as preventative agents and are natural, nontoxic, and easy to produce. They can be administered orally and are well tolerated, even by young animals. Unlike antibiotics, oral IgY supplements support the microbiome that plays a vital role in maintaining overall health, including immune system function. IgY formulations can be delivered as egg yolk powder and do not require extensive purification. Lipids in IgY supplements improve antibody stability in the digestive tract. Given this, using IgY antibodies as an alternative to antimicrobials has garnered interest. In this review, we will examine their antibacterial potential.

Attacking the Intruder at the Gate: Prospects of Mucosal Anti SARS-CoV-2 Vaccines

The sudden outbreak of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic in December 2019 caused crises and health emergencies worldwide. The rapid spread of the virus created an urgent need for the development of an effective vaccine and mass immunization to achieve herd immunity. Efforts of scientific teams at universities and pharmaceutical companies around the world allowed for the development of various types of preparations and made it possible to start the vaccination process. However, it appears that the developed vaccines are not effective enough and do not guarantee long-lasting immunity, especially for new variants of SARS-CoV-2. Considering this problem, it is promising to focus on developing a Coronavirus Disease 2019 (COVID-19) mucosal vaccine. Such a preparation applied directly to the mucous membranes of the upper respiratory tract might provide an immune barrier at the primary point of virus entry into the human body while inducing systemic immunity. A number of such preparations against SARS-CoV-2 are already in various phases of preclinical and clinical trials, and several of them are very close to being accepted for general use, constituting a milestone toward pandemic containment.

Intranasal vaccination with protein bodies elicit strong protection against Streptococcus pneumoniae colonization

Protein bodies (PBs) are particles consisting of insoluble, aggregated proteins with potential as a vaccine formulation. PBs can contain high concentrations of antigen, are stable and relatively resistant to proteases, release antigen slowly and are cost-effective to manufacture. Yet, the capacity of PBs to provoke immune responses and protection in the upper respiratory tract, a major entry route of respiratory pathogens, is largely unknown. In this study, we vaccinated mice intranasally with PBs comprising antigens from Streptococcus pneumoniae and evaluated the level of protection against nasopharyngeal colonization. PBs composed of the α-helical domain of pneumococcal surface protein A (PspAα) provided superior protection against colonization with S. pneumoniae compared to soluble PspAα. Immunization with soluble protein or PBs induced differences in antibody binding to pneumococci as well as a highly distinct antigen-specific nasal cytokine profile upon in vivo stimulation with inactivated S. pneumoniae. Moreover, immunization with PBs composed of conserved putative pneumococcal antigens reduced colonization by S. pneumoniae in mice, both as a single- and as a multi-antigen formulation. In conclusion, PBs represent a vaccine formulation that elicits strong mucosal immune responses and protection. The versatility of this platform offers opportunities for development of next-generation vaccine formulations.

A Self-Assembling Ferritin Nanoplatform for Designing Classical Swine Fever Vaccine: Elicitation of Potent Neutralizing Antibody

Protein-based self-assembling nanoplatforms exhibit superior immunogenicity compared with soluble antigens. Here, we present a comprehensive vaccine strategy for displaying classical swine fever virus (CSFV) E2 glycoprotein on the surface of ferritin (fe) nanocages. An E2-specific blocking antibody assay showed that the blocking rates in pE2-fe/Gel02 (84.3%) and a half-dose cohort of E2-fe/Gel02 (81.9%) were significantly higher (p < 0.05) than that in a ferritin-free cohort of pE2/Gel02 (62.7%) at 21 days post immunization (dpi) in vivo. Furthermore, quantitation of neutralizing potency revealed that a highly significant difference (p < 0.001) was observed between the pE2-fe/Gel02 cohort (1:32, equivalent to live-attenuated strain C at 1:32) and the pE2/Gel02 cohort (1:4) at 21 dpi. Moreover, the innate immune cytokines of IL-4 and IFN-γ activated by the half-dose (20 μg) cohort of E2-fe/Gel02 were equivalent to those elicited by the full dose (40 μg) of purified E2 in the pE2/Gel02 cohort at most time points. In conclusion, we successfully obtained an antigen-displaying E2-ferritin nanoplatform and confirmed high ferritin-assisted humoral and cellular immunities. Our results provided a novel paradigm of self-assembling nanovaccine development for the defense and elimination of potentially pandemic infectious viral pathogens.

Spontaneous C-cleavage of a truncated intein as fusion tag to produce tag-free VP1 inclusion body nanoparticle vaccine against CVB3-induced viral myocarditis by the oral route

Background

Oral vaccine is highly desired for infectious disease which is caused by pathogens infection through the mucosal surface. The design of suitable vaccine delivery system is ongoing for the antigen protection from the harsh gastric environment and target to the Peyer’s patches to induce sufficient mucosal immune responses. Among various potential delivery systems, bacterial inclusion bodies have been widely used as delivery systems in the field of nanobiomedicine. However, a large number of heterologous complex proteins could be difficult to propagate in E. coli and fusion partners are often used to enhance target protein expression. As a safety concern the fusion protein need to be removed from the target protein to get tag-free protein, especially for the production of protein antigen in vaccinology. Until now, there is no report on how to remove fusion tag from inclusion body particles in vitro and in vivo. Coxsackievirus B3 (CVB3) is a leading causative agent of viral myocarditis and orally protein vaccine is high desired for CVB3-induced myocarditis. In this context, we explored a tag-free VP1 inclusion body nanoparticles production protocol though a truncated Ssp DnaX mini-intein spontaneous C-cleavage in vivo and also exploited the VP1 inclusion bodies as an oral protein nanoparticle vaccine to protect mice against CVB3-induced myocarditis.

Results

We successfully produced the tag-free VP1 inclusion body nanoparticle antigen of CVB3 and orally administrated to mice. The results showed that the tag-free VP1 inclusion body nanoparticles as an effective antigen delivery system targeting to the Peyer’s patches had the capacity to induce mucosal immunity as well as to efficiently protect mice from CVB3 induce myocarditis without any adjuvant. Then, we proposed the use of VP1 inclusion body nanoparticles as good candidate for oral vaccine to against CVB3-induced myocarditis.

Conclusions

Our tag-free inclusion body nanoparticles production procedure is easy and low cost and may have universal applicability to produce a variety of tag-free inclusion body nanoparticles for oral vaccine.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1115-z) contains supplementary material, which is available to authorized users.

Design and Production of a Recombinant Hybrid Toxin to Raise Protective Antibodies Against Loxosceles Spider Venom

Human accidents with spiders of the genus Loxosceles are an important health problem affecting thousands of people worldwide. Patients evolve to severe local injuries and, in many cases, to systemic disturbances as acute renal failure, in which cases antivenoms are considered to be the most effective treatment. However, for antivenom production, the extraction of the venom used in the immunization process is laborious and the yield is very low. Thus, many groups have been exploring the use of recombinant Loxosceles toxins, particularly phospholipases D (PLDs), to produce the antivenom. Nonetheless, some important venom activities are not neutralized by anti-PLD antibodies. Astacin-like metalloproteases (ALMPs) are the second most expressed toxin acting on the extracellular matrix, indicating the importance of its inclusion in the antigen’s formulation to provide a better antivenom. Here we show the construction of a hybrid recombinant immunogen, called LgRec1ALP1, composed of hydrophilic regions of the PLD and the ALMP toxins from Loxosceles gaucho. Although the LgRec1ALP1 was expressed as inclusion bodies, it resulted in good yields and it was effective to produce neutralizing antibodies in mice. The antiserum neutralized fibrinogenolytic, platelet aggregation and dermonecrotic activities elicited by L. gaucho, L. laeta, and L. intermedia venoms, indicating that the hybrid recombinant antigen may be a valuable source for the production of protective antibodies against Loxosceles ssp. venoms. In addition, the hybrid recombinant toxin approach may enrich and expand the alternative antigens for antisera production for other venoms.

Oral Administration of L. Casei CRL 431 Increases Immunity in Bronchus and Mammary Glands

Lactic acid bacteria (LAB) found in numerous fermented products can interact with the gut associated lymphoid tissue increasing antibody (principally secretory IgA) production. IgA secreting cells can repopulate not only the lamina propria but also they can go to other distant sites such as bronchus, urogenital tract and mammary glands a phenomenon known as the IgA cycle. Later studies have shown that both B cells of other isotypes and T cells from Peyer's patches also exhibit gut-seeking properties. The aim of this study was to study the effect of different feeding periods of L. casei CRL 431 on the interaction with the immune cells in Peyer's patches studying the migration of not only the IgA+ cells, but also other immune cells (T lymphocytes) to other mucosal sites such as bronchus and mammary glands. BALB/c mice were fed with L. casei CRL 431 during 2, 5 or 7 days. At the end of the feeding period, the mice were killed and the small intestine, the lung and the mammary glands were removed. IgA+ cells and CD4+ and CD8+ T lymphocytes were counted in tissue slices using direct immunofluorescence. IgA+ cells increased in the intestine samples taken after 7 days of LAB feeding. In mammary gland and lung tissues, IgA+ cells increased after five days of feeding. CD4+ and CD8+ T lymphocytes were not able to migrate to sites distant from the intestine and their number did not increase in the lamina propria of the small intestine. L. casei CRL 431 was able to stimulate the IgA cycle without proliferation of T population. These results allow us to suggest that this LAB could be used as oral adjuvant to protect mucosal surfaces from intestinal and respiratory diseases, and would also be useful as an adjuvant to protect against mammary glands pathologies such as cancer.

Adjuvant-enhanced antibody and cellular responses to inclusion bodies expressing FhSAP2 correlates with protection of mice to Fasciola hepatica

Fasciola hepatica saposin-like protein-2 (FhSAP2) is a protein differentially expressed in various developmental stages of F. hepatica. Recombinant FhSAP2 has demonstrated the induction of partial protection in mice and rabbits when it is administered subcutaneously (SC) in Freund's adjuvant. Because FhSAP2 is overexpressed in bacteria in the form of inclusion bodies (IBs), we isolated IBs expressing FhSAP2 and tested their immunogenicity when administered SC in mice emulsified in two different adjuvants: QS-21 and Montanide TM ISA720. Animals received three injections containing 20 μg of protein two weeks apart and 4 weeks after the third injection, mice were infected with 10 F. hepatica metacercariae by oral route. The percentages of protection induced by FhSAP2-IBs were estimated to be between 60.0 and 62.5% when compared with adjuvant-vaccinated, infected controls. By determining the levels of IgG1 and IgG2a antibodies and IL-4 and IFNγ cytokines in the serum of experimental animals, it was found that both Th1 and Th2 immune responses were significantly increased in the FhSAP2-IBs vaccinated groups compared with the adjuvant-vaccinated, infected control groups. The adjuvant-vaccinated groups had significantly lower IgG1 to IgG2a ratios and lower IL-4 to IFNγ ratios than the FhSAP2-IBs vaccinated animals, which is indicative of higher levels of Th2 immune responses. Irrespective to the adjuvant used, animals vaccinated with FhSAP2-IBs exhibited significantly higher survival percentage and less liver damage than the adjuvant-control groups. This study suggests that FhSAP2 has potential as vaccine against F. hepatica and that the protection elicited by this molecule could be linked to a mechanism driven by the CD4-Th1 cells.

Enteric dysbiosis promotes antibiotic-resistant bacterial infection: systemic dissemination of resistant and commensal bacteria through epithelial transcytosis

Antibiotic usage promotes intestinal colonization of antibiotic-resistant bacteria. However, whether resistant bacteria gain dominance in enteric microflora or disseminate to extraintestinal viscera remains unclear. Our aim was to investigate temporal diversity changes in microbiota and transepithelial routes of bacterial translocation after antibiotic-resistant enterobacterial colonization. Mice drinking water with or without antibiotics were intragastrically gavaged with ampicillin-resistant (Amp-r) nonpathogenic Escherichia coli (E. coli) and given normal water afterward. The composition and spatial distribution of intestinal bacteria were evaluated using 16S rDNA sequencing and fluorescence in situ hybridization. Bacterial endocytosis in epithelial cells was examined using gentamicin resistance assay and transmission electromicroscopy. Paracellular permeability was assessed by tight junctional immunostaining and measured by tissue conductance and luminal-to-serosal dextran fluxes. Our results showed that antibiotic treatment enabled intestinal colonization and transient dominance of orally acquired Amp-r E. coli in mice. The colonized Amp-r E. coli peaked on day 3 postinoculation and was competed out after 1 wk, as evidenced by the recovery of commensals, such as Escherichia, Bacteroides, Lachnospiraceae, Clostridium, and Lactobacillus. Mucosal penetration and extraintestinal dissemination of exogenous and endogenous enterobacteria were correlated with abnormal epithelial transcytosis but uncoupled with paracellular tight junctional damage. In conclusion, antibiotic-induced enteric dysbiosis predisposes to exogenous infection and causes systemic dissemination of both antibiotic-resistant and commensal enterobacteria through transcytotic routes across epithelial layers. These results may help explain the susceptibility to sepsis in antibiotic-resistant enteric bacterial infection.

Nanoscale size control of protein aggregates

Herein, a novel method to synthesize soluble, sub-micrometer sized protein aggregates is demonstrated by mixing native and denatured proteins without using bacteria and contaminating proteins. Ovalbumin (OVA) is employed as a model protein. The average size of the formed aggregates can be controlled by adjusting the fraction of denatured protein in the sample and it is possible to make unimodal size distributions of protein aggregates. OVA aggregates with a size of ∼95 nm are found to be more immunogenic compared to native OVA in a murine splenocyte proliferation assay. These results suggest that the novel method of engineering size specific sub-micrometer sized aggregates may constitute a potential route to increasing the efficacy of protein vaccines. The protein aggregates may also be promising for use in other applications including the surface functionalization of biomaterials and as industrial catalysis materials.

Antigenic analysis of classical swine fever virus E2 glycoprotein using pig antibodies identifies residues contributing to antigenic variation of the vaccine C-strain and group 2 strains circulating in China

Background

Glycoprotein E2, the immunodominant protein of classical swine fever virus (CSFV), can induce neutralizing antibodies and confer protective immunity in pigs. Our previous phylogenetic analysis showed that subgroup 2.1 viruses branched away from subgroup 1.1, the vaccine C-strain lineage, and became dominant in China. The E2 glycoproteins of CSFV C-strain and recent subgroup 2.1 field isolates are genetically different. However, it has not been clearly demonstrated how this diversity affects antigenicity of the protein.

Results

Antigenic variation of glycoprotein E2 was observed not only between CSFV vaccine C-strain and subgroup 2.1 strains, but also among strains of the same subgroup 2.1 as determined by ELISA-based binding assay using pig antisera to the C-strain and a representative subgroup 2.1 strain QZ-07 currently circulating in China. Antigenic incompatibility of E2 proteins markedly reduced neutralization efficiency against heterologous strains. Single amino acid substitutions of D705N, L709P, G713E, N723S, and S779A on C-strain recombinant E2 (rE2) proteins significantly increased heterologous binding to anti-QZ-07 serum, suggesting that these residues may be responsible for the antigenic variation between the C-strain and subgroup 2.1 strains. Notably, a G713E substitution caused the most dramatic enhancement of binding of the variant C-strain rE2 protein to anti-QZ-07 serum. Multiple sequence alignment revealed that the glutamic acid residue at this position is conserved within group 2 strains, while the glycine residue is invariant among the vaccine strains, highlighting the role of the residue at this position as a major determinant of antigenic variation of E2. A variant Simpson's index analysis showed that both codons and amino acids of the residues contributing to antigenic variation have undergone similar diversification.

Conclusions

These results demonstrate that CSFV vaccine C-strain and group 2 strains circulating in China differ in the antigenicity of their E2 glycoproteins. Systematic site-directed mutagenesis of the antigenic units has revealed residues that limit cross-reactivity. Our findings may be useful for the development of serological differential assays and improvement of immunogenicity of novel classical swine fever vaccines.

Transient expression of the ectodomain of matrix protein 2 (M2e) of avian influenza A virus in plants

We have previously reported an expression system based on the capsid protein gene (CP) of cucumber mosaic virus (CMV) placed under transcriptional control of a potato virus X (PVX)-based vector. PVX-expressed CMV CP formed virus-like particles, which served as carriers for heterologous antigens of the Newcastle disease virus (NDV). In this work, we applied our expression tool toward the development of plant-derived vaccine candidate against avian influenza A virus. Twenty-three amino acid-long extracellular domain of the viral M2 protein (M2e) was engineered into the internal motif 5 of CMV CP and the recombinant gene then was transiently expressed in plants through a PVX vector. Chimeric CMV capsids reacted with specific antibodies produced to synthetic M2e epitope of the H5N1 strain of the virus. In addition, CMV CP-M2e protein was expressed to high levels in Escherichia coli bacterial cells and was recognized by antibodies to both CMV and M2e. This initial study demonstrates the feasibility of using plant virus-based vectors for expression of antigenic epitopes of H5N1 avian influenza in plants.

Marker vaccine strategies and candidate CSFV marker vaccines

Classical swine fever (CSF) is an economically important highly contagious disease of swine worldwide. Classical swine fever virus (CSFV) is its etiological agent, and the only natural hosts are domestic pigs and wild boars. Although field CSFV strains vary in the virulence, they all result in serious losses in pig industry. Highly virulent field strains generally cause acute disease and high mortality; moderately virulent field strains raise subacute or chronic infections; postnatal infection by low virulent field strains produces subclinical infection and mortality in the new-born piglets. CSFV can cross the placental barrier, and this transplacental transmission usually results in mortality of fetuses and birth of congenitally infected pigs with a late-onset disease and death. Two main strategies to control CSF epidemic are systematic prophylactic vaccination with live attenuated vaccines (such as C-strain) and non-vaccination stamping-out policy. But neither of them is satisfying enough. Marker vaccine and companion serological diagnostic test is thought to be a promising strategy for future control and eradication of CSF. During the past 15 years, various candidate marker vaccines were constructed and evaluated in the animal experiments, including recombinant chimeric vaccines, recombinant deletion vaccines, DNA vaccines, subunit vaccines and peptide vaccines. Among them, two subunit vaccines entered the large scale marker vaccine trial of EU in 1999. Although they failed to fulfil all the demands of the Scientific Veterinary Committee, they successfully induced solid immunity against CSFV in the vaccinated pigs. It can be expected that new potent marker vaccines might be commercially available and used in systematic prophylactic vaccination campaign or emergency vaccination in the next 15 years. Here, we summarized current strategies and candidate CSFV marker vaccines. These strategies and methods are also helpful for the development of new-generation vaccines against other diseases.

Mucosal delivery of vaccines in domestic animals

Mucosal vaccination is proving to be one of the greatest challenges in modern vaccine development. Although highly beneficial for achieving protective immunity, the induction of mucosal immunity, especially in the gastro-intestinal tract, still remains a difficult task. As a result, only very few mucosal vaccines are commercially available for domestic animals. Here, we critically review various strategies for mucosal delivery of vaccines in domestic animals. This includes live bacterial and viral vectors, particulate delivery-systems such as polymers, alginate, polyphosphazenes, immune stimulating complex and liposomes, and receptor mediated-targeting strategies to the mucosal tissues. The most commonly used routes of immunization, strategies for delivering the antigen to the mucosal surfaces, and future prospects in the development of mucosal vaccines are discussed.

Deletion of open reading frames 9, 10 and 11 from the avian adenovirus CELO genome: effect on biodistribution and humoral responses

In this study, the in vivo effect of the 3·6 kbp deletion of the three open reading frames (ORF) 9, 10 and 11 found at the right end of the CELO genome was examined. Groups of chickens were inoculated oronasally with 105–107 p.f.u. per animal of wild-type virus and two recombinant CELO strains (rCELO) expressing luciferase and secreted alkaline phosphatase (SEAP). The tissue biodistribution, assessed by PCR, was similar for both wild-type and recombinant viruses. The infectious viral particle titre was determined by a p.f.u. counting method and the antibody responses to the CELO vector and the SEAP antigen were evaluated by ELISA. Infectious particle titres in tissues from chickens inoculated with the wild-type CELO virus increased up to 6 days post-inoculation, and declined until 11 days while titres in organs from chickens inoculated with the rCELO strain were low and only detectable at 4 days post-inoculation. Moreover, although anti-CELO antibody levels were three times lower in sera from chickens inoculated with rCELO, antibodies directed to the heterologous SEAP antigen were detected. Based on these results, no differences in tropism were observed, but the level of production of viral particles and the humoral responses appeared to decrease. Viruses replicate less efficiently with a deletion performed at the right end of the CELO genome. Nevertheless, the presence of antibodies directed to heterologous antigens makes the CELO virus an advantageous candidate for avian vaccination.

Use of a Clostridium perfringens vector to express high levels of SIV p27 protein for the development of an oral SIV vaccine

Clostridium perfringens is a normal bacterial flora of the small and large intestines of humans and other animals. The current study investigates the potential use of a noncytotoxic C. perfringens as an oral vaccine vehicle for expression and intestinal delivery of a large amount of SIV antigens. Here we report the construction of a recombinant C. perfringens vaccine vector expressing high levels of SIV p27 during sporulation. Following oral administration of this recombinant C. perfringens vaccine vector to mice, large amounts of intact p27 protein were detected in the terminal ileum where the majority of Peyer's Patches (PPs) are located. Furthermore, dendritic cells (DCs) beneath the mucosal surface in the PPs were able to capture SIV p27 antigen, when PPs were exposed to C. perfringens expressing SIV p27 antigen. In addition, uptake of C. perfringens was able to induce maturation of mouse DCs. These results support the potential use of C. perfringens as an oral SIV/HIV vaccine vector.