Current issues regarding the application of recombinant lactic acid bacteria to mucosal vaccine carriers

Display of FliC131 on the Surface of Lactococcus lactis as a Strategy to Increase its Adjuvanticity for Mucosal Immunization

Research on innovative mucosal adjuvants is essential to develop new vaccines for safe mucosal application. In this work, we propose the development of a Lactococcus lactis that expresses a variant of flagellin on its surface (FliC131*), to increase the adjuvanticity of the living cell and cell wall-derived particles (CWDP). We optimized the expression of FliC131*, and confirmed its identity and localization by Western blot and flow cytometry. We also generated CWDP containing FliC131* (CDWP-FliC131*) and evaluated their storage stability. Lastly, we measured the human TLR5 stimulating activity in vitro and assessed the adjuvanticity in vivo using ovalbumin (OVA) as a model antigen. As a result, we generated L. lactis/pCWA-FliC131*, that expresses and displays FliC131* on its surface, obtained the corresponding CWDP-FliC131*, and showed that both activated hTLR5 in vitro in a dose-dependent manner. Furthermore, CWDP-FliC131* retained this biological activity after being lyophilized and stored for a year. Finally, intranasal immunization of mice with OVA plus live L. lactis/pCWA-FliC131* or CWDP-FliC131* induced OVA-specific IgG and IgA in serum, intestinal lavages, and bronchoalveolar lavages. Our work demonstrates the potential of this recombinant L. lactis with an enhanced adjuvant effect, prompting its further evaluation for the design of novel mucosal vaccines.

Genomic and transcriptomic analysis of Ligilactobacillus salivarius IBB3154-in search of new promoters for vaccine construction

IMPORTANCE

The genome of the strain Ligilactobacillus salivarius IBB3154 was sequenced, and transcriptome analysis was carried out at two different temperatures, allowing the determination of gene expression levels in response to environmental changes (temperature). Genes with higher expression at 42°C were identified. The use of a reporter gene (β- glucuronidase) did not confirm the transcriptomic results; it was found that the promoters of the genes sasA1 and sasA2 were active in the presence of bile salts. This opens up new opportunities for the overexpression of genes of other bacterial species in Ligilactobacillus cells in the intestinal environment.

Advancing Insights into Probiotics during Vegetable Fermentation

Fermented vegetables have a long history and are enjoyed worldwide for their unique flavors and health benefits. The process of fermentation improves the nutritional value, taste, and shelf life of foods. Microorganisms play a crucial role in this process through the production of metabolites. The flavors of fermented vegetables are closely related to the evaluation and succession of microbiota. Lactic acid bacteria (LABs) are typically the dominant bacteria in fermented vegetables, and they help inhibit the growth of spoilage bacteria and maintain a healthy gut microbiota in humans. However, homemade and small-scale artisanal products rely on spontaneous fermentation using bacteria naturally present on fresh vegetables or from aged brine, which may introduce external microorganisms and lead to spoilage and substandard products. Hence, understanding the role of LABs and other probiotics in maintaining the quality and safety of fermented vegetables is essential. Additionally, selecting probiotic fermentation microbiota and isolating beneficial probiotics from fermented vegetables can facilitate the use of safe and healthy starter cultures for large-scale industrial production. This review provides insights into the traditional fermentation process of making fermented vegetables, explains the mechanisms involved, and discusses the use of modern microbiome technologies to regulate fermentation microorganisms and create probiotic fermentation microbiota for the production of highly effective, wholesome, safe, and healthy fermented vegetable foods.

Oral and intranasal immunization with food-grade recombinant Lactococcus lactis expressing high conserved region of SARS-CoV-2 spike protein triggers mice's immunity responses

The COVID-19 pandemic began at the end of 2019 in Wuhan, China, and has spread throughout the world. Vaccination is still the most effective method of prevention of pathogenic infections, including viral infections. However, there is little evidence that vaccination can protect against SARS-CoV-2 virus for a long time. Thus, regular re-vaccination is necessary to control COVID-19. Vaccination by injection is invasive, and is one of the reasons people refuse to get re-vaccinated. Therefore, we developed a less invasive vaccine based on oral or nasal administration. The gene encoding the high conserved region (HCR) spike protein was inserted into pNZ8149 and expressed in L.lactis NZ3900. Mice were immunized at 3-week intervals with oral or nasal routes. Anti-SARS-CoV2 spike antibody (IgG and IgA) level were measured using ELISA method before and after treatment. Plasma cells population in lymph were analyzed using flowcytometry and the CD4 + and CD8 + cells in lymph and intestine were analyzed using immunofluorescence method. The results of nasal and oral administration in experimental animals showed that L.lactis carrying the HCR gene could induce a humoral immune response, as indicated by increased levels of IgG and IgA against SARS-CoV-2 (IgG/IgA-SARS-CoV-2). The plasma cell population after nasal and oral vaccination in mice were significantly different with control group (p < 0.05). The CD4 + and CD8 + cells in intestine were significantly higher in orally immunized group mice than control group. The CD8 + cells in lymph were significantly higher in intranasal immunized group mice than control group. Our data demonstrate L.lactis expressing spike protein can be developed into a less invasive alternative to nasal and oral vaccination.

Preclinical developments in the delivery of protein antigens for vaccination

INTRODUCTION

Vaccine technology has constantly advanced since its origin. One of these advancements is where purified parts of a pathogen are used rather than the whole pathogen. Subunit vaccines have no chance of causing disease; however, alone these antigens are often poorly immunogenic. Therefore, they can be paired with immune stimulating adjuvants. Further, subunits can be combined with delivery strategies such as nano/microparticles to enrich their delivery to organs and cells of interest as well as protect them from in vivo degradation. Here, we seek to highlight some of the more promising delivery strategies for protein antigens.

AREAS COVERED

We present a brief description of the different types of vaccines, clinically relevant examples, and their disadvantages when compared to subunit vaccines. Also, specific preclinical examples of delivery strategies for protein antigens.

EXPERT OPINION

Subunit vaccines provide optimal safety given that they have no risk of causing disease; however, they are often not immunogenic enough on their own to provide protection. Advanced delivery systems are a promising avenue to increase the immunogenicity of subunit vaccines, but scalability and stability can be improved. Further, more research is warranted on systems that promote a mucosal immune response to provide better protection against infection.

Oral vaccination with recombinant Lactobacillus casei expressing Aha1 fused with CTB as an adjuvant against Aeromonas veronii in common carp (Cyprinus carpio)

Aeromonas veronii (A. veronii) is a pathogenic that can infect human, animal and aquatic organisms, in which poses a huge threat to the health of many aquatic organisms such as Cyprinus carpio. In this study, Lactobacillus casei (L. casei) strain CC16 was used as antigen deliver carrier and fused with cholera toxin B subunit (CTB) as an adjuvant to construct the recombinant L. casei pPG-Aha1/Lc CC16(surface-displayed) and pPG-Aha1-CTB/Lc CC16(surface-displayed) expressing Aha1 protein of A. veronii, respectively. And the immune responses in Cyprinus carpio by oral route was explored. Our results demonstrated that the recombinant strains could stimulate high serum specific antibody immunoglobulin M (IgM) and induce a stronger acid phosphatase (ACP), alkaline phosphatase (AKP), C3, C4, lysozyme (LZM), Lectin and superoxide dismutase (SOD) activity in Cyprinus carpio compared with control groups. Meanwhile, the expression of Interleukin-10 (IL-10), Interleukin-1β (IL-1β), Tumor Necrosis Factor-α (TNF-α), immunoglobulin Z1 (IgZ1) and immunoglobulin Z2 (IgZ2) in the tissues were significantly upregulated compared with Lc-pPG or PBS groups, indicating that humoral and cell immune response were triggered. Additionally, recombinant L. casei could survive and colonize in fish intestine. Significantly, recombinant L. casei provides immune protection against A. veronii infection, which Cyprinus carpio received pPG-Aha1-CTB/Lc CC16 (64.29%) and pPG-Aha1/Lc CC16 (53.57%) had higher survival rates compared with the controls. Thus, we demonstrated that recombinant pPG-Aha1/Lc CC16 and pPG-Aha1-CTB/Lc CC16 may be the promising strategy for the development of an oral vaccine against A. veronii.

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.

Oral Probiotic Vaccine Expressing Koi Herpesvirus (KHV) ORF81 Protein Delivered by Chitosan-Alginate Capsules Is a Promising Strategy for Mass Oral Vaccination of Carps against KHV Infection

Koi herpesvirus (KHV) is highly contagious and lethal to cyprinid fish, causing significant economic losses to the carp aquaculture industry, particularly to koi carp breeders. Vaccines delivered through intramuscular needle injection or gene gun are not suitable for mass vaccination of carp. So, the development of cost-effective oral vaccines that are easily applicable at a farm level is highly desirable. In this study, we utilized chitosan-alginate capsules as an oral delivery system for a live probiotic (Lactobacillus rhamnosus) vaccine, pYG-KHV-ORF81/LR CIQ249, expressing KHV ORF81 protein. The tolerance of the encapsulated recombinant Lactobacillus to various digestive environments and the ability of the probiotic strain to colonize the intestine of carp was tested. The immunogenicity and the protective efficacy of the encapsulated probiotic vaccine was evaluated by determining IgM levels, lymphocyte proliferation, expression of immune-related genes, and viral challenge to vaccinated fish. It was clear that the chitosan-alginate capsules protected the probiotic vaccine effectively against extreme digestive environments, and a significant level (P < 0.01) of antigen-specific IgM with KHV-neutralizing activity was detected, which provided a protection rate of ca. 85% for koi carp against KHV challenge. The strategy of using chitosan-alginate capsules to deliver probiotic vaccines is easily applicable for mass oral vaccination of fish.IMPORTANCE An oral probiotic vaccine, pYG-KHV-ORF81/LR CIQ249, encapsulated by chitosan-alginate capsules as an oral delivery system was developed for koi carp against koi herpesvirus (KHV) infection. This encapsulated probiotic vaccine can be protected from various digestive environments and maintain effectively high viability, showing a good tolerance to digestive environments. This encapsulated probiotic vaccine has a good immunogenicity in koi carp via oral vaccination, and a significant level of antigen-specific IgM was effectively induced after oral vaccination, displaying effective KHV-neutralizing activity. This encapsulated probiotic vaccine can provide effective protection for koi carp against KHV challenge, which is handling-stress free for the fish, cost effective, and suitable for the mass oral vaccination of koi carp at a farm level, suggesting a promising vaccine strategy for fish.

Immunogenicity evaluation of recombinant Lactobacillus casei W56 expressing bovine viral diarrhea virus E2 protein in conjunction with cholera toxin B subunit as an adjuvant

BACKGROUND

Bovine viral diarrhea virus (BVDV) is one of the main causes of infectious diseases in cattle and causes large financial losses to the cattle industry worldwide. In this study, Lactobacillus casei strain W56 (Lc W56) was used as antigen deliver carrier to construct a recombinant Lactobacillus vaccine pPG-E2-ctxB/Lc W56 constitutively expressing BVDV E2 protein fused with cholera toxin B subunit (ctxB) as an adjuvant, and its immunogenicity against BVDV infection in mice model by oral route was explored.

RESULTS

Our results suggested that pPG-E2-ctxB/Lc W56 can effectively activate dendritic cells (DCs) in the Peyer's patches, up-regulate the expression of Bcl-6, and promote T-follicular helper (Tfh) cells differentiation, as well as enhance B lymphocyte proliferation and promote them differentiate into specific IgA-secreting plasma cells, secreting anti-E2 mucosal sIgA antibody with BVDV-neutralizing activity. Moreover, significant levels (p < 0.01) of BVDV-neutralizing antigen-specific serum antibodies were induced in the pPG-E2-ctxB/LC W56 group post-vaccination. The recombinant Lactobacillus vaccine can induce cellular immune responses, and significant levels (p < 0.01) of Th1-associated cytokines (IL-2, IL-12, and IFN-γ), Th2-associated cytokines (IL-4, IL-10) and Th17-associated cytokine (IL-17) were determined in the serum of vaccinated mice. Significantly, the recombinant Lactobacillus vaccine provides immune protection against BVDV infection, which can be cleared effectively by the vaccine post-challenge in orally vaccinated animals.

CONCLUSIONS

The genetically engineered Lactobacillus vaccine constructed in this study is immunogenic in mice and can induce mucosal, humoral, and cellular immune responses, providing effective anti-BVDV immune protection. It thus represents a promising strategy for vaccine development against BVDV.

Recent update on lactic acid bacteria producing riboflavin and folates: application for food fortification and treatment of intestinal inflammation

Lactic acid bacteria (LAB), widely used as starter cultures for the fermentation of a large variety of food, can improve the safety, shelf life, nutritional value and overall quality of the fermented products. In this regard, the selection of strains delivering health-promoting compounds is now the main objective of many researchers. Although most LAB are auxotrophic for several vitamins, it is known that certain strains have the capability to synthesize B-group vitamins. This is an important property since humans cannot synthesize most vitamins, and these could be obtained by consuming LAB fermented foods. This review discusses the use of LAB as an alternative to fortification by the chemical synthesis to increase riboflavin and folate concentrations in food. Moreover, it provides an overview of the recent applications of vitamin-producing LAB with anti-inflammatory/antioxidant activities against gastrointestinal tract inflammation. This review shows the potential uses of riboflavin and folates producing LAB for the biofortification of food, as therapeutics against intestinal pathologies and to complement anti-inflammatory/anti-neoplastic treatments.

Twenty years of research on HPV vaccines based on genetically modified lactic acid bacteria: an overview on the gut-vagina axis

Most cervical cancer (CxCa) are related to persistent infection with high-risk human papillomavirus (HR-HPV) in the cervical mucosa, suggesting that an induction of mucosal cell-mediated immunity against HR-HPV oncoproteins can be a promising strategy to fight HPV-associated CxCa. From this perspective, many pre-clinical and clinical trials have proved the potential of lactic acid bacteria (LAB) genetically modified to deliver recombinant antigens to induce mucosal, humoral and cellular immunity in the host. Altogether, the outcomes of these studies suggest that there are several key factors to consider that may offer guidance on improvement protein yield and improving immune response. Overall, these findings showed that oral LAB-based mucosal HPV vaccines expressing inducible surface-anchored antigens display a higher potential to induce particularly specific systemic and mucosal cytotoxic cellular immune responses. In this review, we describe all LAB-based HPV vaccine investigations by reviewing databases from international studies between 2000 and 2020. Our aim is to promote the therapeutic HPV vaccines knowledge and to complete the gaps in this field to empower scientists worldwide to make proper decisions regarding the best strategies for the development of therapeutic HPV vaccines.

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.