Cross-protective efficacy of dendritic cells targeting conserved influenza virus antigen expressed by Lactobacillus plantarum

Recombinant probiotic Escherichia coli delivers the polymeric protein of swine influenza virus for protection

Swine influenza virus invades the host through the respiratory mucosa, which severely restricts the development of the pig breeding industry. To construct monomeric and trimeric vaccines, we developed recombinant Escherichia coli Nissle 1917 (EcN) strains that express the receptor binding site (RBS) of the hemagglutinin (HA) antigen from H1N1 swine influenza virus. After the mucosal immunization of mice, we found that probiotics activated CD40 and CD86 in DCs and increased the levels of IL-4 and IFN-γ secretion by T cells. Furthermore, the probiotics improved the function of the mucosal immune system, increased the level of SIgA, level of IgG and number of B220+IgA+, and activated germinal center B cells. The challenge experiment revealed that the probiotics alleviated weight loss, reduced pathological injury to the lungs, and protected the mice from virus infection. We also observed that the serum neutralizing antibodies of immunized piglets significantly increased, which reduced the shedding frequency of swine influenza virus in the nose of the piglets and reduced the pathological damage by activating the T cell immune response in infected piglets. Thus, the constructed probiotics are promising candidates for effective non-traditional swine influenza vaccines.

Live Attenuated Bacterial Vectors as Vehicles for DNA Vaccine Delivery: A Mini Review

DNA vaccines are third-generation vaccines composed of plasmids that encode vaccine antigens. Their advantages include fast development, safety, stability, and cost effectiveness, which make them an attractive vaccine platform for genetic and infectious diseases. However, the low transfection efficiency of DNA vaccines results in poor performance in both larger animals and humans, thereby limiting their clinical use. To overcome this issue, live attenuated bacterial vector (LABV) has been proposed as a DNA delivery vehicle. LABV is known to improve DNA vaccine transfection efficiency, thus enhancing the immune response. This article highlights recent advancements in the development of LABV DNA vaccines, the design of shuttle plasmids and adjuvants, and the potential applications of LABV candidates.

The Immunomodulatory Effects and Applications of Probiotic Lactiplantibacillus plantarum in Vaccine Development

Lactiplantibacillus plantarum (previously known as Lactobacillus plantarum) is a lactic acid bacterium that exists in various niches. L. plantarum is a food-grade microorganism that is commonly considered a safe and beneficial microorganism. It is widely used in food fermentation, agricultural enhancement, and environmental protection. L. plantarum is also part of the normal flora that can regulate the intestinal microflora and promote intestinal health. Some strains of L. plantarum are powerful probiotics that induce and modulate the innate and adaptive immune responses. Due to its outstanding immunoregulatory capacities, an increasing number of studies have examined the use of probiotic L. plantarum strains as natural immune adjuvants or alternative live vaccine carriers. The present review summarizes the main immunomodulatory characteristics of L. plantarum and discusses the preliminary immunological effects of L. plantarum as a vaccine adjuvant and delivery carrier. Different methods for improving the immune capacities of recombinant vector vaccines are also discussed.

TLR3/TRIF and MAVS Signaling Is Essential in Regulating Mucosal T Cell Responses during Rotavirus Infection

The functions of the natural dsRNA sensors TLR3 (TRIF) and RIG-I (MAVS) are crucial during viral challenge and have not been accurately clarified in adaptive immune responses to rotavirus (RV) infection. In this study, we found that RV infection caused severe pathological damage to the small intestine of TLR3-/- and TRIF-/- mice. Our data found that dendritic cells from TLR3-/- and TRIF-/- mice had impaired Ag presentation to the RV and attenuated initiation of T cells upon viral infection. These attenuated functions resulted in impaired CD4+ T and CD8+ T function in mice lacking TLR3-TRIF signaling postinfection. Additionally, attenuated proliferative capacity of T cells from TLR3-/- and TRIF-/- mice was observed. Subsequently, we observed a significant reduction in the absolute number of memory T cells in the spleen and mesenteric lymph node (MLN) of TRIF-/- recipient mice following RV infection in a bone marrow chimeric model. Furthermore, there was reduced migration of type 2 classical dendritic cells from the intestine to MLNs after RV infection in TLR3-/- and TRIF-/- mice. Notably, RV infection resulted in attenuated killing of spleen and MLN tissues in TRIF-/- and MAVS-/- mice. Finally, we demonstrated that RV infection promoted apoptosis of CD8+ T cells in TRIF-/- and TLR3-/-MAVS-/- mice. Taken together, our findings highlight an important mechanism of TLR3 signaling through TRIF in mucosal T cell responses to RV and lay the foundation for the development of a novel vaccine.

Stable expression of HIV-1 MPER extended epitope on the surface of the recombinant probiotic bacteria Escherichia Coli Nissle 1917 using CRISPR/Cas9

BACKGROUND

Mucosal vaccines have the potential to induce protective immune responses at the sites of infection. Applying CRISPR/Cas9 editing, we aimed to develop a probiotic-based vaccine candidate expressing the HIV-1 envelope membrane-proximal external region (MPER) on the surface of E. coli Nissle 1917.

RESULTS

The HIV-1 MPER epitope was successfully introduced in the porin OmpF of the E. coli Nissle 1917 (EcN-MPER) and the modification was stable over 30 passages of the recombinant bacteria on the DNA and protein level. Furthermore, the introduced epitope was recognized by a human anti-HIV-1 gp41 (2F5) antibody using both live and heat-killed EcN-MPER, and this antigenicity was also retained over 30 passages. Whole-cell dot blot suggested a stronger binding of anti-HIV-1 gp41 (2F5) to heat-killed EcN-MPER than their live counterpart. An outer membrane vesicle (OMV) - rich extract from EcN-MPER culture supernatant was equally antigenic to anti-HIV-1 gp41 antibody which suggests that the MPER antigen could be harboured in EcN-MPER OMVs. Using quantitative ELISA, we determined the amount of MPER produced by the modified EcN to be 14.3 µg/108 cfu.

CONCLUSIONS

The CRISPR/Cas9 technology was an effective method for establishment of recombinant EcN-MPER bacteria that was stable over many passages. The developed EcN-MPER clone was devoid of extraneous plasmids and antibiotic resistance genes which eliminates the risk of plasmid transfer to animal hosts, should this clone be used as a vaccine. Also, the EcN-MPER clone was recognised by anti-HIV-1 gp41 (2F5) both as live and heat-killed bacteria making it suitable for pre-clinical evaluation. Expression of OmpF on bacterial surfaces and released OMVs identifies it as a compelling candidate for recombinant epitope modification, enabling surface epitope presentation on both bacteria and OMVs. By applying the methods described in this study, we present a potential platform for cost-effective and rational vaccine antigen expression and administration, offering promising prospects for further research in the field of vaccine development.

Immunogenicity of engineered probiotics expressing conserved antigens of influenza virus and FLIC flagellin against H9N2 AIVinfection in mice

Avian influenza virus (AIV)is easy to cause diseases in birds and humans.It causes great economic losses to the poultry farms and leads to public health problems. Using vaccines is the main approach to control the prevalence of AIV. In our previously published article, a recombinant Lactobacillus plantarum (L. plantarum) expressing the NP-M2 peptide ofH9N2 AIV was generated, and its protective effect was evaluated in a chicken model. In this study, the protective effect was estimated in mice model. Humoral and cellular immune response parameters were measured using flow cytometry adding to body weight loss, survival rate, virus load, and histopathological changes in the lung. The obtained results elucidated that, the recombinant L. plantarum can promote the activation of dendritic cells (DC), proliferation of T and B cells adding to eliciting protective secretory IgA (sIgA) and humeral IgG level in mice model. Accordingly, it could be used as a patent vaccine to control the AIV infection.

Dendritic cell-natural killer cell cross-talk modulates T cell activation in response to influenza A viral infection

Influenza viruses lead to substantial morbidity and mortality including ~3-5 million cases of severe illness and ~290,000-650,000 deaths annually. One of the major hurdles regarding influenza vaccine efficacy is generating a durable, robust cellular immune response. Appropriate stimulation of the innate immune system is key to generating cellular immunity. Cross-talk between innate dendritic cells (DC) and natural killer (NK) cells plays a key role in activating virus-specific T cells, yet the mechanisms used by influenza A viruses (IAV) to govern this process remain incompletely understood. Here, we used an ex vivo autologous human primary immune cell culture system to evaluate the impact of DC-NK cell cross-talk and subsequent naïve T cell activation at steady-state and after exposure to genetically distinct IAV strains-A/California/07/2009 (H1N1) and A/Victoria/361/2011 (H3N2). Using flow cytometry, we found that exposure of DCs to IAV in co-culture with NK cells led to a decreased frequency of CD83⁺ and CD86⁺ cells on DCs and an increased frequency of HLA-DR⁺ on both DCs and NK cells. We then assessed the outcome of DC-NK cell cross-talk on T cell activation. At steady-state, DC-NK cell cross-talk increased pan T cell CD69 and CD25 expression while exposure to either IAV strain reduced pan T cell CD25 expression and suppressed CD4⁺ and CD8⁺ T cell IFN-γ and TNF production, following chemical stimulation with PMA/Ionomycin. Moreover, exposure to A/Victoria/361/2011 elicited lower IFN-γ production by CD4⁺ and CD8⁺ T cells compared with A/California/07/2009. Overall, our results indicate a role for DC-NK cell cross-talk in T cell priming in the context of influenza infection, informing the immunological mechanisms that could be manipulated for the next generation of influenza vaccines or immunotherapeutics.

Enhancement of live vaccines by co-delivery of immune modulating proteins

Vaccines are very effective in providing protection against many infectious diseases. However, it has proven difficult to develop highly efficacious vaccines against some pathogens and so there is a continuing need to improve vaccine technologies. The first successful and widely used vaccines were based on attenuated pathogens (e.g., laboratory passaged Pasteurella multocida to vaccinate against fowl cholera) or closely related non-pathogenic organisms (e.g., cowpox to vaccinate against smallpox). Subsequently, live vaccines, either attenuated pathogens or non-pathogenic microorganisms modified to deliver heterologous antigens, have been successfully used to induce protective immune responses against many pathogens. Unlike conventional killed and subunit vaccines, live vaccines can deliver antigens to mucosal surfaces in a similar manner and context as the natural infection and hence can often produce a more appropriate and protective immune response. Despite these advantages, there is still a need to improve the immunogenicity of some live vaccines. The efficacy of injectable killed and subunit vaccines is usually enhanced using adjuvants such mineral salts, oils, and saponin, but such adjuvants cannot be used with live vaccines. Instead, live vaccines can be engineered to produce immunomodulatory molecules that can stimulate the immune system to induce more robust and long-lasting adaptive immune responses. This review focuses on research that has been undertaken to engineer live vaccines to produce immunomodulatory molecules that act as adjuvants to increase immunogenicity. Adjuvant strategies with varying mechanisms of action (inflammatory, antibody-mediated, cell-mediated) and delivery modes (oral, intramuscular, intranasal) have been investigated, with varying degrees of success. The goal of such research is to define adjuvant strategies that can be adapted to enhance live vaccine efficacy by triggering strong innate and adaptive immune responses and produce vaccines against a wider range of pathogens.

Human dendritic cell targeting peptide can be targeted to porcine dendritic cells to improve antigen capture efficiency to stimulate stronger immune response

Dendritic cells (DCs) play a key role in the natural recognition of pathogens and subsequent activation of adaptive immune responses due to their potent antigen-presenting ability. Dendritic cell-targeting peptide (DCpep) is strongly targeted to DCs, which often express antigens, to enhance the efficacy of vaccines. Our previous study showed that recombinant Lactobacillus expressing human DCpep could significantly induce stronger immune responses than recombinant Lactobacillus without DCpep, but the mechanism remains unclear. In this study, the mechanism by which DCpep enhances the immune response against recombinant Lactobacillus was explored. Fluorescence-labeled human DCpep was synthesized to evaluate the binding ability of human DCpep to porcine monocyte-derived dendritic cells (Mo-DCs) and DCs of the small intestine. The effects of Mo-DC function induced by recombinant Lactobacillus expressing human DCpep fused with the porcine epidemic diarrhea virus (PEDV) core neutralizing epitope (COE) antigen were also investigated. The results showed that human DCpep bind to porcine DCs, but not to porcine small intestinal epithelial cells. Human DCpep can also improve the capture efficiency of recombinant Lactobacillus by Mo-DCs, promote the maturation of dendritic cells, secrete more cytokines, and enhance the ability of porcine DCs to activate T-cell proliferation. Taken together, these results promote advanced understanding of the mechanism by which DCpep enhances immune responses. We found that some DCpeps are conserved between humans and pigs, which provides a theoretical basis for the development of a DC-targeted vaccine.

Construction of the Enterococcal Strain Expressing Immunogenic Fragment of SARS-Cov-2 Virus

Contemporary SARS-Cov-2 pandemic, besides its dramatic global influence on the human race including health care systems, economies, and political decisions, opened a window for the global experiment with human vaccination employing novel injectable vaccines providing predominantly specific IgG response with little knowledge of their impact on the mucosal immunity. However, it is widely accepted that protection against the pathogens at the gates of the infection - on mucosal surfaces—predominantly rely on an IgA response. Some genetically modified bacteria, including probiotics, represent attractive vehicles for oral or nasal mucosal delivery of therapeutic molecules. Probiotic-based vaccines for mucous membranes are easy to produce in large quantities; they have low cost, provide quite a long T-cell memory, and gut IgA response to oral vaccines is highly synchronized and strongly oligoclonal. Here we present a study demonstrating construction of the novel SARS-Cov-2 vaccine candidate employing the gene fragment of S1 SARS-Cov-2 gene. This DNA fragment was inserted in frame into major pili protein gene with d2 domain of enterococcal operon encoding for pili. The DNA sequencing proved the presence of the insert in enterococcal genome. RNA transcription, immunoprecipitation, and immune electron microscopy with human sera obtained from the SARS-Cov-2 patients demonstrated expression of SARS-Cov-2 antigens in bacteria. Taken together the data obtained allowed considering this genetically modified probiotic strain as an interesting candidate for vaccine against SARS-Cov-2.

Construction of the Enterococcal Strain Expressing Immunogenic Fragment of SARS-Cov-2 Virus

Contemporary SARS-Cov-2 pandemic, besides its dramatic global influence on the human race including health care systems, economies, and political decisions, opened a window for the global experiment with human vaccination employing novel injectable vaccines providing predominantly specific IgG response with little knowledge of their impact on the mucosal immunity. However, it is widely accepted that protection against the pathogens at the gates of the infection - on mucosal surfaces—predominantly rely on an IgA response. Some genetically modified bacteria, including probiotics, represent attractive vehicles for oral or nasal mucosal delivery of therapeutic molecules. Probiotic-based vaccines for mucous membranes are easy to produce in large quantities; they have low cost, provide quite a long T-cell memory, and gut IgA response to oral vaccines is highly synchronized and strongly oligoclonal. Here we present a study demonstrating construction of the novel SARS-Cov-2 vaccine candidate employing the gene fragment of S1 SARS-Cov-2 gene. This DNA fragment was inserted in frame into major pili protein gene with d2 domain of enterococcal operon encoding for pili. The DNA sequencing proved the presence of the insert in enterococcal genome. RNA transcription, immunoprecipitation, and immune electron microscopy with human sera obtained from the SARS-Cov-2 patients demonstrated expression of SARS-Cov-2 antigens in bacteria. Taken together the data obtained allowed considering this genetically modified probiotic strain as an interesting candidate for vaccine against SARS-Cov-2.

Immune Evaluation of Recombinant Lactobacillus plantarum With Surface Display of HA1-DCpep in Mice

Avian influenza viruses can be efficiently transmitted through mucous membranes, and conventional vaccines are not effective in protecting against mucosal infection by influenza viruses. To induce multiple immune responses in an organism, we constructed a recombinant Lactobacillus plantarum expressing the influenza virus antigen HA1 with the adjuvant dendritic cell-targeting peptide (DCpep). The recombinant L. plantarum strains NC8Δ-pWCF-HA1 and NC8Δ-pWCF-HA1-DCpep were used to immunize mice via oral administration, and the humoral, cellular and mucosal immune responses were evaluated. In addition, the serum levels of specific antibodies and hemagglutination inhibition (HI) levels were also measured. Our results showed that recombinant L. plantarum activated dendritic cells in Peyer's patches (PPs), increased the numbers of CD4⁺IFN-γ⁺ and CD8⁺IFN-γ⁺ cells in the spleen and mesenteric lymph nodes (MLNs), and affected the ability of CD4⁺ and CD8⁺ cells to proliferate in the spleen and MLNs. Additionally, recombinant L. plantarum increased the number of B220⁺IgA⁺ cells in PPs and the level of IgA in the lungs and different intestinal segments. In addition, specific IgG, IgG1 and IgG2a antibodies were induced at high levels in the mice serum, specific IgA antibodies were induced at high levels in the mice feces, and HI potency was significantly increased. Thus, the recombinant L. plantarum strains NC8Δ-pWCF-HA1 and NC8Δ-pWCF-HA1-DCpep have potential as vaccine candidates for avian influenza virus.

Recombinant lactic acid bacteria as promising vectors for mucosal vaccination

Lactic acid bacteria (LAB), a diverse family of gram-positive bacteria, has been proven effective in delivering varieties of therapeutic and prophylactic molecules such as antigens and cytokines. Featuring the properties of acid-resistant, high uptake into Peyer's patches, and superior capacity for inducing secretory IgA antibodies, LAB have good potential to be used as vaccine vectors for mucosal vaccination. Mucosal immunization enables both mucosal and systemic immune responses, which are critical for resisting pathogens that invade the host through the mucosal surfaces. With the development of genetic engineering, LAB strains, primarily Lactococcus and Lactobacillus have been exploited to express a range of heterologous antigens. Numerous studies have demonstrated that LAB mucosal vaccines can stimulate all arms of the immune system to provide adequate protection against pathogen infections. Additionally, several LAB-based human papillomavirus vaccines have entered the clinical trial studies, which suggest the great promise of LAB vaccines for new interventions in mucosal transport diseases. Herein, we will discuss the factors that influence the immunogenicity of LAB vaccines, including LAB strains, the location of antigens, and administration routes, and focus on the current strategies that have been reported for optimizing LAB vaccines.

Improved pathogenicity of H9N2 subtype of avian influenza virus induced by mutations occurred after serial adaptations in mice

H9N2 subtype, a low pathogenic avian influenza virus, is emerging as a major causative agent circulating poultry workplaces across China and other Asian countries. Increasing case number of interspecies transmissions to mammals reported recently provoked a great concern about its risks inducing global pandemics. In an attempt to understand the underlying mechanism of how the H9N2 virus disrupts the interspecies segregation to transmit to mammals. A mutant H9N2 strain was obtained by passaging the wildtype H9N2 A/chicken/Hong Kong/G9/1997 eight times from lung to lung in BALB/c mice. Our finding revealed that mice manifested severe clinical symptoms including losses of body weight, pathological damages in pulmonary sites and all died within two weeks after infected with the mutated H9N2, whereas all mice survived upon infected with wildtype strain in comparison, which suggested increased pathogenicity of the mutant strain. In addition, mice showed enhanced levels of proinflammatory cytokines in sera, including IL-6, TNF-α and IL-1β compared to those subjected to wildtype viral infections. Sequence analysis showed that five amino acid substitutions occurred at PB2₆₂₇, HA_87, HA₂₃₄, NP₃₈₇ and M₁₅₆, and a deletion mutation happened in the M gene (M₁₅₇). Of these mutations, PB2 E627K played key roles in modulating lethality in mice. Taken together, the mutant H9N2 strain obtained by serial passaging of its wildtype in mice significantly increased its virulence leading to death of mice, which might be associated the accumulated mutations occurred on its genome.

Recombinant Lactobacillus plantarum NC8 strain expressing porcine rotavirus VP7 induces specific antibodies in BALB/c mice

The major etiologic agent that causes acute gastroenteritis worldwide in young animals and children is Group A rotavirus. Currently, commercially available vaccines do not often prevent porcine rotavirus (PRV) infection. In this study, we evaluated the efficacy of oral recombinant Lactobacillus vaccine against PRV in a mouse model. Lactobacillus plantarum NC8 was used as the host strain, and bacterial vectors were constructed, because the NC8 isolated has shown the capability to survive gastric transit and to colonize the intestinal tract of humans and other mammals. To explore the immunological mechanisms, lactic acid bacterial vectors were used to express VP7 antigen from PRV. We constructed an L. plantarum strain with surface-displayed VP7, named NC8-pSIP409-pgsA-VP7-DCpep. The expressed recombinant protein had a molecular weight of ∼37 kDa. The strain was used to immunize BALB/c mice to evaluate their immunomodulatory characteristics. Mice were orally immunized with recombinant L. plantarum NC8-pSIP409-pgsA-VP7-DCpep at a dose of 2 × 109 colony forming units/200 µl. The results showed that NC8-pSIP409-pgsA-VP7-DCpep significantly stimulated the differentiation of dendritic cells (DCs) in Peyer's patches (PPs) and increased the serum levels of IL-4 and IFN-γ, as measured by enzyme-linked immunosorbent assay in mice treated with NC8-pSIP409-pgsA-VP7-DCpep. Compared to the empty vector group, NC8-pSIP409-pgsA-VP7-DCpep significantly increased the production of B220+ B cells in mesenteric lymph nodes (MLNs) and PPs and also increased the titer levels of the VP7-specific antibodies, including IgG and sIgA. The administration of NC8-pSIP409-pgsA-VP7-DCpep mediated relatively broad cellular responses. This study reveals that clear alternatives exist for PRV control strategies and provides information on PRV infection.

Probiotic-Based Vaccines May Provide Effective Protection against COVID-19 Acute Respiratory Disease

Severe acute respiratory syndrome coronavirus 2 virus (SARS-CoV-2) infection, the causative agent of COVID-19, now represents the sixth Public Health Emergency of International Concern (PHEIC)—as declared by the World Health Organization (WHO) since 2009. Considering that SARS-CoV-2 is mainly transmitted via the mucosal route, a therapy administered by this same route may represent a desirable approach to fight SARS-CoV-2 infection. It is now widely accepted that genetically modified microorganisms, including probiotics, represent attractive vehicles for oral or nasal mucosal delivery of therapeutic molecules. Previous studies have shown that the mucosal administration of therapeutic molecules is able to induce an immune response mediated by specific serum IgG and mucosal IgA antibodies along with mucosal cell-mediated immune responses, which effectively concur to neutralize and eradicate infections. Therefore, advances in the modulation of mucosal immune responses, and in particular the use of probiotics as live delivery vectors, may encourage prospective studies to assess the effectiveness of genetically modified probiotics for SARS-CoV-2 infection. Emerging trends in the ever-progressing field of vaccine development re-emphasize the contribution of adjuvants, along with optimization of codon usage (when designing a synthetic gene), expression level, and inoculation dose to elicit specific and potent protective immune responses. In this review, we will highlight the existing pre-clinical and clinical information on the use of genetically modified microorganisms in control strategies against respiratory and non-respiratory viruses. In addition, we will discuss some controversial aspects of the use of genetically modified probiotics in modulating the cross-talk between mucosal delivery of therapeutics and immune system modulation.

Lactiplantibacillus plantarum as a Potential Adjuvant and Delivery System for the Development of SARS-CoV-2 Oral Vaccines

The most important characteristics regarding the mucosal infection and immune responses against the Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) as well as the current vaccines against coronavirus disease 2019 (COVID-19) in development or use are revised to emphasize the opportunity for lactic acid bacteria (LAB)-based vaccines to offer a valid alternative in the fight against this disease. In addition, this article revises the knowledge on: (a) the cellular and molecular mechanisms involved in the improvement of mucosal antiviral defenses by beneficial Lactiplantibacillus plantarum strains, (b) the systems for the expression of heterologous proteins in L. plantarum and (c) the successful expressions of viral antigens in L. plantarum that were capable of inducing protective immune responses in the gut and the respiratory tract after their oral administration. The ability of L. plantarum to express viral antigens, including the spike protein of SARS-CoV-2 and its capacity to differentially modulate the innate and adaptive immune responses in both the intestinal and respiratory mucosa after its oral administration, indicates the potential of this LAB to be used in the development of a mucosal COVID-19 vaccine.

Lactobacillus plantarum surface-displayed influenza antigens (NP-M2) with FliC flagellin stimulate generally protective immune responses against H9N2 influenza subtypes in chickens

The H9N2 avian influenza virus (AIV) causes serious economic losses to the poultry industry every year. Vaccines that induce a mucosal immune response may be successful against influenza virus infection because its transmission occurs primarily in the mucosa. To develop novel and potent oral vaccines based on Lactobacillus plantarum (L. plantarum) to control the spread of AIV in poultry industry, in the present study, we constructed and expressed fusions of the influenza antigens NP and M2 with the Salmonella Typhimurium flagellinprotein FliC on the surface of L. plantarum. Oral immunization of chicks was performed, and serum antibodies, mucosal antibodies, and specific cellular immunity were detected. Immunizing chicks with avian influenza virus was evaluated. The results showed high levels of IgG in addition to high levels of secretory immunoglobulin A (sIgA) in chickens orally administered recombinant L. plantarum. In addition, the fusion may significantly increase the levels of NP- and M2-specific T cell-mediated immunity in the case of mucosal administration of NC8-pSIP409-pgsA'-NP-M2-FliC. Recombinant NC8-pSIP409-pgsA'-NP-M2-FliC mediated effectively protected chickens against influenza virus and reduced virus titers in the lung. Our study outcomes indicate that the expression of influenza NP-M2 and a mucosal adjuvant (FliC), by L. plantarum could generate a mucosal vaccine candidate for animals in the future to defend against AIVs.

Dendritic Cells Targeting Lactobacillus plantarum Strain NC8 with a Surface-Displayed Single-Chain Variable Fragment of CD11c Induce an Antigen-Specific Protective Cellular Immune Response

Influenza A virus (H1N1) is an acute, highly contagious respiratory virus. The use of lactic acid bacteria (LAB) to deliver mucosal vaccines against influenza virus infection is a research hot spot. In this study, two recombinant Lactobacillus plantarum strains expressing hemagglutinin (HA) alone or coexpressing aCD11c-HA to target HA protein to dendritic cells (DCs) by fusion to an anti-CD11c single-chain antibody (aCD11c) were constructed. The activation of bone marrow dendritic cells (BMDCs) by recombinant strains and the interaction of activated BMDCs and sorted CD4⁺ or CD8⁺ T cells were evaluated through flow cytometry in vitro, and cellular supernatants were assessed by using an enzyme-linked immunosorbent assay kit. The results demonstrated that, compared to the HA strain, the aCD11c-HA strain significantly increased the activation of BMDCs and increased the production of CD4⁺ gamma interferon-positive (IFN-γ⁺) T cells, CD8⁺ IFN-γ⁺ T cells, and IFN-γ in the cell culture supernatant in vitro Consistent with these results, the aCD11c-HA strain clearly increased the activation and maturation of DCs, the HA-specific responses of CD4⁺ IFN-γ⁺ T cells, CD8⁺ IFN-γ⁺ T cells, and CD8⁺ CD107a⁺ T cells, and the proliferation of T cells in the spleen, finally increasing the levels of specific antibodies and neutralizing antibodies in mice. In addition, the protection of immunized mice was observed after viral infection, as evidenced by improved weight loss, survival, and lung pathology. The adoptive transfer of CD8⁺ T cells from the aCD11c-HA mice to NOD/Lt-SCID mice resulted in a certain level of protection after influenza virus infection, highlighting the efficacy of the aCD11c targeting strategy.

Sanguinarine has anthelmintic activity against the enteral and parenteral phases of trichinella infection in experimentally infected mice

Trichinellosis is a zoonotic parasitic disease caused by Trichinella spiralis, and it is also a widely prevalent foodborne parasitic disease. At present, albendazole and benzimidazole are the most commonly used therapeutic drugs for the clinical treatment of trichinellosis, but they have many side effects. Sanguinarine is a benzophenanthridine alkaloid that has biological activity, such as antibacterial, antitumour and antiparasitic activities. Therefore, the present study aimed to evaluate the anti-Trichinella effect of sanguinarine in vivo and in vitro. The results showed that sanguinarine had a lethal effect on muscle larvae, adults and new-borne larvae in vitro. The damage to adults treated with sanguinarine was observed by scanning electron microscopy. Sanguinarine could significantly reduce the burden of worms in mice during the pre-adult, migrating larva and encysted larva stages. The ratio of intestinal villus to crypt (V/C) in mice treated with sanguinarine was significantly higher than that in non-treated control mice. Compared with the non-treated control group, the sanguinarine-treated group exhibited a significantly increased number of small intestine goblet cells. The level of reactive oxygen species (ROS) in the serum of mice treated with sanguinarine was significantly higher than that of the control group mice in the pre-adult and encysted larva stages. This study suggests that sanguinarine is a potential drug against trichinellosis.

Adjuvant Strategies for Lactic Acid Bacterial Mucosal Vaccines

Lactic acid bacteria (LAB) are Gram-positive, acid-tolerant bacteria that have long been used in food fermentation and are generally recognized as safe (GRAS). LAB are a part of a normal microbiome and act as probiotics, improving the gastrointestinal microbiome and health when consumed. An increasing body of research has shown the importance of the microbiome on both mucosal immune heath and immune response to pathogens and oral vaccines. Currently, there are few approved mucosal vaccines, and most are attenuated viruses or bacteria, which necessitates cold chain, carries the risk of reversion to virulence, and can have limited efficacy in individuals with poor mucosal health. On account of these limitations, new types of mucosal vaccine vectors are necessary. There has been increasing interest and success in developing recombinant LAB as next generation mucosal vaccine vectors due to their natural acid and bile resistance, stability at room temperature, endogenous activation of innate and adaptive immune responses, and the development of molecular techniques that allow for manipulation of their genomes. To enhance the immunogenicity of these LAB vaccines, numerous adjuvant strategies have been successfully employed. Here, we review these adjuvant strategies and their mechanisms of action which include: Toll-like receptor ligands, secretion of bacterial toxins, secretion of cytokines, direct delivery to antigen presenting cells, and enterocyte targeting. The ability to increase the immune response to LAB vaccines gives them the potential to be powerful mucosal vaccine vectors against mucosal pathogens.

Immune response characterization of mice immunized with Lactobacillus plantarum expressing spike antigen of transmissible gastroenteritis virus

The highly infectious porcine transmissible gastroenteritis virus (TGEV), which belongs to the coronaviruses (CoVs), causes diarrhea and high mortality rates in piglets, resulting in severe economic losses in the pork industry worldwide. In this study, we used Lactobacillus plantarum (L. plantarum) to anchor the expression of TGEV antigen (S) to dendritic cells (DCs) via dendritic cell-targeting peptides (DCpep). The results show that S antigen could be detected on the surface of L. plantarum by different detection methods. Furthermore, flow cytometry and ELISA techniques were used to measure the cellular, mucosal, and humoral immune responses of the different orally gavaged mouse groups. The obtained results demonstrated the significant effect of the constructed L. plantarum expressing S-DCpep fusion proteins in inducing high expression levels of B7 molecules on DCs, as well as high levels of IgG, secretory IgA, and IFN-γ and IL-4 cytokines compared with the other groups. Accordingly, surface expression of DC-targeted antigens successfully induced cellular, mucosal, and humoral immunity in mice and could be used as a vaccine.

Immune responses induced by recombinant Lactobacillus plantarum expressing the spike protein derived from transmissible gastroenteritis virus in piglets

Transmissible gastroenteritis coronavirus (TGEV) is one of the most severe threats to the swine industry. In this study, we constructed a suite of recombinant Lactobacillus plantarum with surface displaying the spike (S) protein coming from TGEV and fused with DC cells targeting peptides (DCpep) to develop an effective, safe, and convenient vaccine against transmissible gastroenteritis. Our research results found that the recombinant Lactobacillus plantarum (NC8-pSIP409-pgsA-S-DCpep) group expressing S fused with DCpep could not only significantly increase the percentages of MHC-II⁺CD80⁺ B cells and CD3⁺CD4⁺ T cells but also the number of IgA⁺ B cells and CD3⁺CD4⁺ T cells of ileum lamina propria, which elevated the specific secretory immunoglobulin A (SIgA) titers in feces and IgG titers in serum. Taken together, these results suggest that NC8-pSIP409-pgsA-S-DCpep expressing the S of TGEV fused with DCpep could effectively induce immune responses and provide a feasible original strategy and approach for the design of TGEV vaccines.

Lactobacillus Mucosal Vaccine Vectors: Immune Responses against Bacterial and Viral Antigens

Lactic acid bacteria (LAB) have been utilized since the 1990s for therapeutic heterologous gene expression. The ability of LAB to elicit an immune response against expressed foreign antigens has led to their exploration as potential mucosal vaccine candidates. LAB vaccine vectors offer many attractive advantages: simple, noninvasive administration (usually oral or intranasal), the acceptance and stability of genetic modifications, relatively low cost, and the highest level of safety possible. Experimentation using LAB of the genus Lactobacillus has become popular in recent years due to their ability to elicit strong systemic and mucosal immune responses. This article reviews Lactobacillus vaccine constructs, including Lactobacillus species, antigen expression, model organisms, and in vivo immune responses, with a primary focus on viral and bacterial antigens.

Lactobacillus plantarum displaying conserved M2e and HA2 fusion antigens induces protection against influenza virus challenge

Avian influenza virus (AIV) can infect poultry, mammals, and other hosts and causes enormous economic losses to the global poultry industry. In this study, to develop a novel and potent oral vaccine based on Lactobacillus plantarum (L. plantarum) for controlling the spread of AIV in the poultry industry, we constructed a recombinant L. plantarum strain displaying the 3M2e-HA2 protein of the influenza virus and determined the effect of N/pgsA'-3M2e-HA2 against AIV in chicks. We first confirmed that the 3M2e-HA2 fusion protein was expressed on the surface of L. plantarum via flow cytometry and immunofluorescence experiments. Our experimental results demonstrated that chicks immunized with N/pgsA'-3M2e-HA2 could induce specific humoral, mucosal, and T cell-mediated immune responses, eliciting the host body to protect itself against AIV. Additionally, compared to oral administration, the intranasal immunization of chicks with N/pgsA'-3M2e-HA2 provided a stronger immune response, resulting in a potent protective effect that hindered the loss of body weight, decreasing pulmonary virus titers and reducing lung and throat pathological damages. Thus, our results indicate that our novel approach is an effective method of vaccine design to promote mucosal immunity.

Construction and immunogenicity analysis of Lactobacillus plantarum expressing a porcine epidemic diarrhea virus S gene fused to a DC-targeting peptide

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The S protein of PDEV was displayed on the surface of a recombinant Lactobacillus plantarum NC8 strain.

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NC8-pSIP409-pgsA'-S-DCpep promoted DC activation in the LP.

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IgG and sIgA were significant increased in mice orally administered with the NC8-pSIP409-pgsA'-S-DCpep.

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The expression of specificity cytokines IFN-γ, IL-4 and IL-17A of MLNs was enhanced in mouse treated with the NC8-pSIP409-pgsA'-S-DCpep.

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NC8-pSIP409-pgsA'-S-DCpep might mediate B cell response in mouse.

Porcine epidemic diarrhea virus (PEDV) is one of the most important causative pathogens of swine diarrhea, which is widely prevalent throughout the world and is responsible for significant economic losses in the commercial pig industry, both domestic and abroad. The spike (S) protein in the PEDV capsid structure can carry the major B lymphocyte epitope, which induces production of neutralizing antibodies and provides immunoprotective effects. Moreover, the conserved region encoded by the S gene can be considered a target for establishing a new diagnostic method and is a new candidate for vaccine design. In this study, use of anchorin pgsA' allowed the fusion protein of S-DCpep to express on the surface of recombinant Lactobacillus plantarum (NC8-pSIP409-pgsA'-S-DCpep) NC8 strain. Mice were immunized by lavage administration of the recombinant NC8-pSIP409-pgsA'-S-DCpep, which was observed to induce DC activation and high production of sIgA and IgG antibodies in experimental animals, while also eliciting production of significantly more IgA⁺B220⁺ B cells. More importantly, secretion of cytokines IFN-γ, IL-4 and IL-17 in mice that were vaccinated with NC8-pSIP409-pgsA'-S-DCpep was remarkably increased. The results of our study suggest that NC8-pSIP409-pgsA'-S-DCpep potently triggers cellular and humoral immune responses. The obtained experimental results can provide a theoretical basis that lays the foundation for production of a novel oral vaccine against PED.

Efficacy of an Adenoviral Vectored Multivalent Centralized Influenza Vaccine

Mice were immunized with Adenovirus expressing the H1-con, H2-con, H3-con and H5-con HA consensus genes in combination (multivalent) and compared to mice immunized with the traditional 2010-2011 FluZone and FluMist seasonal vaccines. Immunized mice were challenged with 10-100 MLD50 of H1N1, H3N1, H3N2 and H5N1 influenza viruses. The traditional vaccines induced robust levels of HA inhibition (HI) titers, but failed to protect against five different heterologous lethal influenza challenges. Conversely, the multivalent consensus vaccine (1 × 1010 virus particles (vp)/mouse) induced protective HI titers of ≥40 against 8 of 10 influenza viruses that represent a wide degree of divergence within the HA subtypes and protected 100% of mice from 8 of 9 lethal heterologous influenza virus challenges. The vaccine protection was dose dependent, in general, and a dose as low as 5 × 107 vp/mouse still provided 100% survival against 7 of 9 lethal heterologous influenza challenges. These data indicate that very low doses of Adenovirus-vectored consensus vaccines induce superior levels of immunity against a wide divergence of influenza subtypes as compared to traditional vaccines. These doses are scalable and translatable to humans and may provide the foundation for complete and long-lasting anti-influenza immunity.