Recombinant interleukin 6 with M cell-targeting moiety produced in Lactococcus lactis IL1403 as a potent mucosal adjuvant for peroral immunization

Recent Advances in Oral Vaccines for Animals

Compared to traditional injected vaccines, oral vaccines offer significant advantages for the immunization of livestock and wildlife due to their ease of use, high compliance, improved safety, and potential to stimulate mucosal immune responses and induce systemic immunity against pathogens. This review provides an overview of the delivery methods for oral vaccines, and the factors that influence their immunogenicity. We also highlight the global progress and achievements in the development and use of oral vaccines for animals, shedding light on potential future applications in this field.

A novel vaccine strategy against Brucellosis using Brucella abortus multi-epitope OMPs vaccine based on Lactococcus lactis live bacterial vectors

Brucella infections typically occur in mucosal membranes, emphasizing the need for mucosal vaccinations. This study evaluated the effectiveness of orally administering Lactococcus lactis (L. lactis) for producing the Brucella abortus multi-epitope OMPs peptide. A multi-epitope plasmid was generated through a reverse vaccinology method, and mice were administered the genetically modified L. lactis orally as a vaccine. The plasmid underwent digestion, synthesizing a 39 kDa-sized protein known as OMPs by the target group. The sera of mice that were administered the pNZ8124-OMPs-L. lactis vaccine exhibited a notable presence of IgG1 antibodies specific to outer membrane proteins (OMPs), heightened levels of interferon (IFN-λ) and tumor necrosis factor alpha (TNF-α), and enhanced transcription rates of interleukin 4 (IL-4) and interleukin 10 (IL-10). The spleen sections from the pNZ8124-OMPs-L. lactis and IRIBA group had less morphological damage associated with inflammation, infiltration of lymphocytes, and lesions to the spleen. The findings present a novel approach to utilizing the food-grade, non-pathogenic L. lactis as a protein cell factory to synthesize innovative immunological candidate OMPs. This approach offers a distinctive way to evaluate experimental medicinal items' practicality, safety, affordability, and long-term sustainability.

Lactococcus lactis as an Interleukin Delivery System for Prophylaxis and Treatment of Inflammatory and Autoimmune Diseases

Target delivery of therapeutic agents with anti-inflammatory properties using probiotics as delivery and recombinant protein expression vehicles is a promising approach for the prevention and treatment of many diseases, such as cancer and intestinal immune disorders. Lactococcus lactis, a Lactic Acid Bacteria (LAB) widely used in the dairy industry, is one of the most important microorganisms with GRAS status for human consumption, for which biotechnological tools have already been developed to express and deliver recombinant biomolecules with anti-inflammatory properties. Cytokines, for  example, are immune system communication molecules present at virtually all levels of the immune response. They are essential in cellular and humoral processes, such as hampering inflammation or adjuvating in the adaptive immune response, making them good candidates for therapeutic approaches. This review discusses the advances in the development of new therapies and prophylactic approaches using LAB to deliver/express cytokines for the treatment of inflammatory and autoimmune diseases in the future.

An M cell-targeting recombinant L. lactis vaccine against four H. pylori adhesins

The acidic environment and enzyme degradation lead to oral vaccines often having little immune effect. Therefore, it is an attractive strategy to study an effective and safe oral vaccine delivery system that can promote gastrointestinal mucosal immune responses and inhibit antigen degradation. Moreover, the antigens uptake by microfold cells (M cells) is the determining step in initiating efficient immune responses. Therefore, M cell-targeting is one promising approach for enhancing oral vaccine potency. In the present study, an M cell-targeting L. lactis surface display system (plSAM) was built to favor the multivalent epitope vaccine antigen (FAdE) to achieve effective gastrointestinal mucosal immunity against Helicobacter pylori. Therefore, a recombinant Lactococcus lactic acid vaccine (LL-plSAM-FAdE) was successfully prepared, and its immunological properties and protective efficacy were analyzed. The results showed that LL-plSAM-FAdE can secretively express the recombinant proteins SAM-FAdE and display the SAM-FAdE on the bacterial cell surface. More importantly, LL-plSAM-FAdE effectively promoted the phagocytosis and transport of vaccine antigen by M cells in the gastrointestinal tract of mice, and simulated high levels of cellular and humoral immune responses against four key H. pylori adhesins (Urease, CagL, HpaA, and Lpp20) in the gastrointestinal tract, thus enabling effective prevention of H. pylori infection and to some extent eliminating H. pylori already present in the gastrointestinal tract. KEY POINTS: • M-cell-targeting L. lactis surface display system LL- plSAM was designed • This system displays H. pylori vaccine-promoted phagocytosis and transport of M cell • A promising vaccine candidate for controlling H. pylori infection was verified.

Effect of Secretion Efficiency of Mutant KRAS Neoantigen by Lactococcus lactis on the Immune Response of a Mucosal Vaccine Delivery Vehicle Targeting Colorectal Cancer

Colorectal cancer (CRC) is often caused by mutations in the KRAS oncogene, making KRAS neoantigens a promising vaccine candidate for immunotherapy. Secreting KRAS antigens using live Generally Recognized as Safe (GRAS) vaccine delivery hosts such as Lactococcus lactis is deemed to be an effective strategy in inducing specific desired responses. Recently, through the engineering of a novel signal peptide SPK1 from Pediococcus pentosaceus, an optimized secretion system was developed in the L. lactis NZ9000 host. In this study, the potential of the L. lactis NZ9000 as a vaccine delivery host for the production of two KRAS oncopeptides (mutant 68V-DT and wild-type KRAS) through the use of the signal peptide SPK1 and its mutated derivative (SPKM19) was investigated. The expression and secretion efficiency analyses of KRAS peptides from L. lactis were performed in vitro and in vivo in BALB/c mice. Contradictory to our previous study using the reporter staphylococcal nuclease (NUC), the yield of secreted KRAS antigens mediated by the target mutant signal peptide SPKM19 was significantly lower (by ~1.3-folds) compared to the wild-type SPK1. Consistently, a superior elevation of IgA response against KRAS aided by SPK1 rather than mutant SPKM19 was observed. Despite the lower specific IgA response for SPKM19, a positive IgA immune response from mice intestinal washes was successfully triggered following immunization. Size and secondary conformation of the mature proteins are suggested to be the contributing factors for these discrepancies. This study proves the potential of L. lactis NZ9000 as a host for oral vaccine delivery due to its ability to evoke the desired mucosal immune response in the gastrointestinal tract of mice.

Current Progress and Challenges in the Study of Adjuvants for Oral Vaccines

Over the past 20 years, a variety of potential adjuvants have been studied to enhance the effect of oral vaccines in the intestinal mucosal immune system; however, no licensed adjuvant for clinical application in oral vaccines is available. In this review, we systematically updated the research progress of oral vaccine adjuvants over the past 2 decades, including biogenic adjuvants, non-biogenic adjuvants, and their multi-type composite adjuvant materials, and introduced their immune mechanisms of adjuvanticity, aiming at providing theoretical basis for developing feasible and effective adjuvants for oral vaccines. Based on these insights, we briefly discussed the challenges in the development of oral vaccine adjuvants and prospects for their future development.

Construction of a Lactobacillus plantarum-based claudin-3 targeting delivery system for the development of vaccines against Eimeria tenella

Avian coccidiosis causes huge economic losses to the poultry industry worldwide and currently lacks effective live vector vaccines. Achieving efficient antigen delivery to mucosa-associated lymphoid tissue (MALT) is critical for improving the effectiveness of vaccines. Here, chicken claudin-3 (CLDN3), a tight junction protein expressed in MALT, was identified as a target, and the C-terminal region of Clostridium perfringens enterotoxin (C-CPE) was proven to bind to chicken CLDN3. Then, a CLDN3-targeting Lactobacillus plantarum NC8-expressing C-CPE surface display system (NC8/GFP-C-CPE) was constructed to successfully express the heterologous protein on the surface of L. plantarum. The colonization level of NC8/GFP-C-CPE was significantly increased compared to the non-targeting strain and could persist in the intestine for at least 72 h. An oral vaccine strain expressing five EGF domains of Eimeria tenella microneme protein 8 (EtMIC8-EGF) (NC8/EtMIC8-EGF-C-CPE) was constructed to evaluate the protective efficacy against E. tenella infection. The results revealed that CLDN3-targeting L. plantarum induced stronger mucosal immunity in gut-associated lymphoid tissues (GALT) as well as humoral responses and conferred better protection in terms of parasite replication and pathology than the non-targeting strain. Overall, we successfully constructed a CLDN3-targeting L. plantarum NC8 surface display system characterized by MALT-targeting, which is an efficient antigen delivery system to confer enhanced protective efficacy in chickens against E. tenella infection.

Immunomodulatory action of Lactococcuslactis

Fermented foods are gaining popularity due to health-promoting properties with high levels of nutrients, phytochemicals, bioactive compounds, and probiotic microorganisms. Due to its unique fermentation process, Lactococcus lactis plays a key role in the food business, notably in the manufacturing of dairy products. The superior biological activities of L. lactis in these functional foods include anti-inflammatory and immunomodulatory capabilities. L. lactis boosted growth performance, controlled amino acid profiles, intestinal immunology, and microbiota. Besides that, the administration of L. lactis increased the rate of infection clearance. Innate and acquired immune responses would be upregulated in both local and systemic compartments, resulting in these consequences. L. lactis is often employed in the food sector and is currently being exploited as a delivery vehicle for biological research. These bacteria are being eyed as potential candidates for biotechnological applications. With this in mind, we reviewed the immunomodulatory effects of different L. lactis strains.

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.

Oral Immunization With a M Cell-Targeting Recombinant L. Lactis Vaccine LL-plSAM-FVpE Stimulate Protective Immunity Against H. Pylori in Mice

There are many virulence factors of H. pylori that contribute in diverse ways to gastric disease. Therefore, designing multivalent epitope vaccines against many key virulence factors virulence factors of H. pylori is a promising strategy to control H. pylori infection. In previous studies, we constructed a multivalent epitope vaccine FVpE against four key virulence factors of H. pylori (Urease, CagA, VacA, and NAP), and oral immunization with the FVpE vaccine plus a polysaccharide adjuvant (PA) containing lycium barbarum polysaccharide and chitosan could provide protection against H. pylori infection in the Mongolian gerbil model. Oral vaccines have many advantages over injected vaccines, such as improved safety and compliance, and easier manufacturing and administration. However, the harsh gastrointestinal (GI) environment, such as gastric acid and proteolytic enzymes, limits the development of oral vaccines to some extent. Oral vaccines need a gastrointestinal delivery system with high safety, low price and promoting vaccine antigen to stimulate immune response in the gastrointestinal mucosa. Lactic acid bacteria are gastrointestinal probiotics that have unique advantages as a delivery system for oral vaccines. In this study, a M cell-targeting surface display system for L. lactis named plSAM was designed to help vaccine antigens to stimulate effective immune responses in the gastrointestinal tract, and a M cell-targeting recombinant L. lactis vaccine LL-plSAM-FVpE was constructed by using the surface display system plSAM. recombinant L. lactis vaccine LL-plSAM-FVpE could secretively express the SAM-FVpE protein and display it on the bacterial surface. Moreover, experimental results confirmed that LL-plSAM-FVpE had an enhanced M cell-targeting property. In addition, LL-plSAM-FVpE had excellent M cell-targeting property to promote the phagocytosis and transport of the antigen SAM-FVpE by gastrointestinal M cells. More importantly, oral immunization of LL-plSAM-FVpE or SAM-FVpE plus PA can stimulate IgG and sIgA antibodies and CD4⁺ T cell immune responses against four virulence factors of H. pylori (Urease, CagA, VacA, and NAP), thus providing protective immunity against H. pylori infection in mice. The M cell-targeting recombinant L. lactis vaccine against various key H. pylori virulence factors could be a promising vaccine candidate for controlling H. pylori infection.

Oral Immunization of Mice with Cell Extracts from Recombinant Lactococcus lactis Expressing SARS-CoV-2 Spike Protein

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread all over the world and became a pandemic that named coronavirus disease-2019 (COVID-19). At present, several intramuscular vaccines have been successfully developed and mass vaccination has progressed in many countries. The aim of the study is to develop and examine an oral vaccine against COVID-19 with recombinant Lactococcus lactis IL1403, a strain of lactic acid bacteria, expressing SARS-CoV-2 spike (S) protein receptor-binding domain (RBD) S1 subunit as an immunizing antigen. PBS or cell extracts from recombinant L. lactis were orally administered into mice (control VS treatment), and formation of antigen-specific antibodies and changes in the gut microbiome were analyzed. Intracellular antigen was detected, but its secretion was not successful. After immunization, antigen-specific serum IgG and fecal IgA levels were 1.5-fold (P = 0.002) and 1.4-fold (P = 0.016) higher in the immunized mice (treatment) than control, respectively. Gut microbiome profiles were clearly separated between the two groups when analyzed for beta diversity with overall similarity. At the genus level, while Coprococcus (P = 0.036) and unclassified genus of Ruminococcaceae (P = 0.037) in treatment were more abundant than control, rc4-4 (P = 0.013) and Stenotrophomonas (P = 0.021) were less abundant. Our results indicate that cell extract containing SARS-CoV-2 antigen can induce mice to produce antigen-specific antibodies without overall changes in the gut microbiome. This strategy may be useful for the development of other oral viral vaccines.

Biotechnological Innovations and Therapeutic Application of Pediococcus and Lactic Acid Bacteria: The Next-Generation Microorganism

Lactic acid bacteria represent a worthwhile organism within the microbial consortium for the food sector, health, and biotechnological applications. They tend to offer high stability to environmental conditions, with an indicated increase in product yield, alongside their moderate antimicrobial activity. Lack of endotoxins and inclusion bodies, extracellular secretion, and surface display with other unique properties, are all winning attributes of these Gram-positive lactic acid bacteria, of which, Pediococcus is progressively becoming an attractive and promising host, as the next-generation probiotic comparable with other well-known model systems. Here, we presented the biotechnological developments in Pediococcal bacteriocin expression system, contemporary variegated models of Pediococcus and lactic acid bacteria strains as microbial cell factory, most recent applications as possible live delivery vector for use as therapeutics, as well as upsurging challenges and future perspective. With the radical introduction of artificial intelligence and neural network in Synthetic Biology, the microbial usage of lactic acid bacteria as an alternative eco-friendly strain, with safe use properties compared with the already known conventional strains is expected to see an increase in various food and biotechnological applications in years to come as it offers better hope of safety, accuracy, and higher efficiency.

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.

Intranasal immunization with O-2'-Hydroxypropyl trimethyl ammonium chloride chitosan nanoparticles loaded with Newcastle disease virus DNA vaccine enhances mucosal immune response in chickens

Background

There has been a great interest in developing strategies for enhancing antigen delivery to the mucosal immune system as well as identifying mucosal active immunostimulating agents. To elevate the potential of O-2ʹ-Hydroxypropyl trimethyl ammonium chloride chitosan (O-2ʹ-HACC) as an adjuvant and mucosal immune delivery carrier for DNA vaccine, we prepared the O-2ʹ-HACC loaded with Newcastle disease virus (NDV) F gene plasmid DNA and C3d6 molecular adjuvant (O-2ʹ-HACC/pFDNA microparticles).

Results

The O-2ʹ-HACC/pFDNA exhibited a regular spherical morphology with a particle size of 202.3 ± 0.52 nm, a zeta potential of 50.8 ± 8.21 mV, encapsulation efficiency of 90.74 ± 1.10%, and a loading capacity of 49.84 ± 1.20%. The plasmid DNA could be sustainably released from the O-2ʹ-HACC/pFDNA after an initial burst release. Intranasal vaccination of chickens immunized with O-2ʹ-HACC/pFDNA not only induced higher anti-NDV IgG and sIgA antibody titers but also significantly promoted lymphocyte proliferation and produced higher levels of IL-2, IL-4, IFN-γ, CD4+, and CD8 + T lymphocytes compared with the NDV commercial live attenuated vaccine. Intranasal delivery of the O-2ʹ-HACC/pFDNA enhanced humoral, cellular, and mucosal immune responses and protected chickens from the infection of highly virulent NDV compared with the intramuscular delivery.

Conclusions

Collectively, our findings indicated that the O-2ʹ-HACC could be used as a vaccine adjuvant and delivery system for mucosal immunity and have an immense application promise.

Graphic Abstract

Genetic tools for the development of recombinant lactic acid bacteria

Lactic acid bacteria (LAB) are a phylogenetically diverse group with the ability to convert soluble carbohydrates into lactic acid. Many LAB have a long history of safe use in fermented foods and are recognized as food-grade microorganisms. LAB are also natural inhabitants of the human intestinal tract and have beneficial effects on health. Considering these properties, LAB have potential applications as biotherapeutic vehicles to delivery cytokines, antigens and other medicinal molecules. In this review, we summarize the development of, and advances in, genome manipulation techniques for engineering LAB and the expected future development of such genetic tools. These methods are crucial for us to maximize the value of LAB. We also discuss applications of the genome-editing tools in enhancing probiotic characteristics and therapeutic functionalities of LAB.

Cytoplasmic expression of a model antigen with M Cell-Targeting moiety in lactic acid bacteria and implication of the mechanism as a mucosal vaccine via oral route

Lactic acid bacteria (LAB) have been widely studied as mucosal vaccine delivery carriers against many infectious diseases for heterologous expression of protein antigens. There are three antigen expression strategies for LAB: cytoplasmic expression (CE), cell surface display (SD), and extracellular secretion (ES). Despite the generally higher protein expression level and many observations of antigen-specific immunogenicity in CE, its application as a mucosal vaccine has been overlooked relative to SD and ES because of the antigens enclosed by the LAB cell wall. We hypothesized that the antigens in CE could be released from the LAB into the intestinal lumen before host bacterial access to gut-associated lymphoid tissue (GALT), which could contribute to antigen-specific immune responses after oral administration. To elucidate this hypothesis, three recombinant Lactobacillus plantarum (LP) strains were constructed to produce a model antigen, BmpB, with or without an M cell-targeting moiety, and their immunogenicities were analyzed comparatively as oral vaccines in mouse model. The data indicated that the recombinant LPs producing BmpBs with different conformations could induce mucosal immunity differentially. This suggests that the cytoplasmic antigens in LAB could be released into the intestinal lumen, subsequently translocated through M cells, and stimulate the GALT to generate antigen-specific immune responses. Therefore, the CE strategy has great potential, especially in the application of oral LAB vaccines as well as SD and ES strategies. This research provides a better understanding of the mechanism for recombinant oral LAB vaccines and gives insight to the future design of LAB vaccines and oral delivery applications for useful therapeutic proteins.

Lactic acid bacteria: little helpers for many human tasks

Lactic acid bacteria (LAB) are a group of highly specialised bacteria specifically adapted to a diverse range of habitats. They are found in the gut of humans and other animals, in many food fermentations, and on plants. Their natural specialisation in close relation to human activities make them particularly interesting from an industrial point of view. They are relevant not only for traditional food fermentations, but also as probiotics, potential therapeutics and cell factories for the production of many different products. Many new tools and methods are being developed to analyse and modify these microorganisms. This review shall give an overview highlighting some of the most striking characteristics of lactic acid bacteria and our approaches to harness their potential in many respects - from home made food to industrial chemical production, from probiotic activities to the most modern cancer treatments and vaccines.

Novel Strategies for Efficient Production and Delivery of Live Biotherapeutics and Biotechnological Uses of Lactococcus lactis: The Lactic Acid Bacterium Model

Lactic acid bacteria (LAB) are traditionally used in fermentation and food preservation processes and are recognized as safe for consumption. Recently, they have attracted attention due to their health-promoting properties; many species are already widely used as probiotics for treatment or prevention of various medical conditions, including inflammatory bowel diseases, infections, and autoimmune disorders. Some LAB, especially Lactococcus lactis, have been engineered as live vehicles for delivery of DNA vaccines and for production of therapeutic biomolecules. Here, we summarize work on engineering of LAB, with emphasis on the model LAB, L. lactis. We review the various expression systems for the production of heterologous proteins in Lactococcus spp. and its use as a live delivery system of DNA vaccines and for expression of biotherapeutics using the eukaryotic cell machinery. We have included examples of molecules produced by these expression platforms and their application in clinical disorders. We also present the CRISPR-Cas approach as a novel methodology for the development and optimization of food-grade expression of useful substances, and detail methods to improve DNA delivery by LAB to the gastrointestinal tract. Finally, we discuss perspectives for the development of medical applications of recombinant LABs involving animal model studies and human clinical trials, and we touch on the main safety issues that need to be taken into account so that bioengineered versions of these generally recognized as safe organisms will be considered acceptable for medical use.

A Review of the Microbial Production of Bioactive Natural Products and Biologics

A variety of organisms, such as bacteria, fungi, and plants, produce secondary metabolites, also known as natural products. Natural products have been a prolific source and an inspiration for numerous medical agents with widely divergent chemical structures and biological activities, including antimicrobial, immunosuppressive, anticancer, and anti-inflammatory activities, many of which have been developed as treatments and have potential therapeutic applications for human diseases. Aside from natural products, the recent development of recombinant DNA technology has sparked the development of a wide array of biopharmaceutical products, such as recombinant proteins, offering significant advances in treating a broad spectrum of medical illnesses and conditions. Herein, we will introduce the structures and diverse biological activities of natural products and recombinant proteins that have been exploited as valuable molecules in medicine, agriculture and insect control. In addition, we will explore past and ongoing efforts along with achievements in the development of robust and promising microorganisms as cell factories to produce biologically active molecules. Furthermore, we will review multi-disciplinary and comprehensive engineering approaches directed at improving yields of microbial production of natural products and proteins and generating novel molecules. Throughout this article, we will suggest ways in which microbial-derived biologically active molecular entities and their analogs could continue to inspire the development of new therapeutic agents in academia and industry.

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

Over the past two decades, lactic acid bacteria (LAB) have been intensively studied as potential bacterial carriers for therapeutic materials, such as vaccine antigens, to the mucosal tissues. LAB have several attractive advantages as carriers of mucosal vaccines, and the effectiveness of LAB vaccines has been demonstrated in numerous studies. Research on LAB vaccines to date has focused on whether antigen-specific immunity, particularly antibody responses, can be induced. However, with recent developments in immunology, microbiology, and vaccinology, more detailed analyses of the underlying mechanisms, especially, of the induction of cell-mediated immunity and memory cells, have been required for vaccine development and licensure. In this mini-review, we will discuss the issues, including (i) immune responses other than antibody production, (ii) persistence of LAB vaccine immunity, (iii) comparative evaluation of LAB vaccines with any existing or reference vaccines, (iv) strategies for increasing the effectiveness of LAB vaccines, and (iv) effects of microbiota on the efficacy of LAB vaccines. Although these issues have been rarely studied or discussed to date in relation to LAB vaccine research, further understanding of them is critical for the practical application of LAB vaccine systems.

Construction of a Recombinant Lactococcus lactis Strain Expressing a Variant Porcine Epidemic Diarrhea Virus S1 Gene and Its Immunogenicity Analysis in Mice

Porcine epidemic diarrhea caused by porcine epidemic diarrhea virus (PEDV) is a highly contagious disease in newborn piglets. The spike (S) protein is the surface glycoprotein of PEDV, which can induce specific neutralization antibodies and is a candidate antigen for vaccination attempts. In our study, the S1 region of PEDV strain CH/JLDH/2016 spike gene was inserted into the Lactococcus lactis expression vector, pNZ8149, resulting in recombinant plasmid pNZ8149-S1, and the immunogenicity of recombinant L. lactis pNZ8149-S1/NZ3900 was evaluated in mice. After immunization, significantly higher levels of anti-PEDV serum IgG antibodies and mucosal sIgA antibodies were detected in mice orally administered with pNZ8149-S1/NZ3900, compared with control groups pNZ8149/NZ3900, NZ3900, and phosphate buffered saline (p < 0.01). Lymphocyte proliferation assay results showed that the recombinant L. lactis pNZ8149-S1/NZ3900 significantly stimulated the proliferation of splenic lymphocytes (p < 0.01). In addition, the recombinant L. lactis vaccine could induce high levels of IL-4 and IFN-γ in immunized mice (p < 0.01). The results of our study suggest that the recombinant L. lactis pNZ8149-S1/NZ3900 can provide a promising vaccine strategy against PEDV infection.

M cell targeting engineered biomaterials for effective vaccination

Vaccines are one of the greatest medical interventions of all time and have been successful in controlling and eliminating a myriad of diseases over the past two centuries. Among several vaccination strategies, mucosal vaccines have wide clinical applications and attract considerable interest in research, showing potential as innovative and novel therapeutics. In mucosal vaccination, targeting (microfold) M cells is a frontline prerequisite for inducing effective antigen-specific immunostimulatory effects. In this review, we primarily focus on materials engineered for use as vaccine delivery platforms to target M cells. We also describe potential M cell targeting areas, methods to overcome current challenges and limitations of the field. Furthermore, we present the potential of biomaterials engineering as well as various natural and synthetic delivery technologies to overcome the challenges of M cell targeting, all of which are absent in current literature. Finally, we briefly discuss manufacturing and regulatory processes to bring a robust perspective on the feasibility and potential of this next-generation vaccine technology.

Oral Vaccine Delivery for Intestinal Immunity-Biological Basis, Barriers, Delivery System, and M Cell Targeting

Most currently available commercial vaccines are delivered by systemic injection. However, needle-free oral vaccine delivery is currently of great interest for several reasons, including the ability to elicit mucosal immune responses, ease of administration, and the relatively improved safety. This review summarizes the biological basis, various physiological and immunological barriers, current delivery systems with delivery criteria, and suggestions for strategies to enhance the delivery of oral vaccines. In oral vaccine delivery, basic requirements are the protection of antigens from the GI environment, targeting of M cells and activation of the innate immune response. Approaches to address these requirements aim to provide new vaccines and delivery systems that mimic the pathogen's properties, which are capable of eliciting a protective mucosal immune response and a systemic immune response and that make an impact on current oral vaccine development.

A review on Lactococcus lactis: from food to factory

Lactococcus lactis has progressed a long way since its discovery and initial use in dairy product fermentation, to its present biotechnological applications in genetic engineering for the production of various recombinant proteins and metabolites that transcends the heterologous species barrier. Key desirable features of this gram-positive lactic acid non-colonizing gut bacteria include its generally recognized as safe (GRAS) status, probiotic properties, the absence of inclusion bodies and endotoxins, surface display and extracellular secretion technology, and a diverse selection of cloning and inducible expression vectors. This have made L. lactis a desirable and promising host on par with other well established model bacterial or yeast systems such as Escherichia coli, Saccharomyces [corrected] cerevisiae and Bacillus subtilis. In this article, we review recent technological advancements, challenges, future prospects and current diversified examples on the use of L. lactis as a microbial cell factory. Additionally, we will also highlight latest medical-based applications involving whole-cell L. lactis as a live delivery vector for the administration of therapeutics against both communicable and non-communicable diseases.

Capacity of lactic acid bacteria in immunity enhancement and cancer prevention

Lactic acid bacteria are associated with the human gastrointestinal tract. They are important for maintaining the balance of microflora in the human gut. An increasing number of published research reports in recent years have denoted the importance of producing interferon-gamma and IgA for treatment of disease. These agents can enhance the specific and nonspecific immune systems that are dependent on specific bacterial strains. The mechanisms of these effects were revealed in this investigation, where the cell walls of these bacteria were modulated by the cytokine pathways, while the whole bacterial cell mediated the host cell immune system and regulated the production of tumor necrosis factors and interleukins. A supplement of highly active lactic acid bacteria strains provided significant potential to enhance host's immunity, offering prevention from many diseases including some cancers. This review summarizes the current understanding of the function of lactic acid bacteria immunity enhancement and cancer prevention.

Nasal immunization with mannan-decorated mucoadhesive HPMCP microspheres containing ApxIIA toxin induces protective immunity against challenge infection with Actinobacillus pleuropneumoiae in mice

The development of subunit mucosal vaccines requires an appropriate delivery system or an immune modulator such as an adjuvant to improve antigen immunogenicity. The nasal route for vaccine delivery by microparticles has attracted considerable interest, although challenges such as the rapid mucociliary clearance in the respiratory mucosa and the low immunogenicity of subunit vaccine still remain. Here, we aimed to develop mannan-decorated mucoadhesive thiolated hydroxypropylmethyl cellulose phthalate (HPMCP) microspheres (Man-THM) that contain ApxIIA subunit vaccine - an exotoxin fragment as a candidate for a subunit nasal vaccine against Actinobacillus pleuropneumoniae. For adjuvant activity, mucoadhesive thiolated HPMCP microspheres decorated with mannan could be targeted to the PRRs (pathogen recognition receptors) and mannose receptors (MR) of antigen presenting cells (APCs) in the respiratory immune system. The potential adjuvant ability of Man-THM for intranasal immunization was confirmed by in vitro and in vivo experiments. In a mechanistic study using APCs in vitro, it was found that Man-THM enhanced receptor-mediated endocytosis by stimulating the MR of APCs. In vivo, the nasal vaccination of ApxIIA-loaded Man-THM in mice resulted in higher levels of mucosal sIgA and serum IgG than mice in the ApxIIA and ApxIIA-loaded THM groups due to the specific recognition of the mannan in the Man-THM by the MRs of the APCs. Moreover, ApxIIA-containing Man-THM protected immunized mice when challenged with strains of A. pleuropneumoniae serotype 5. These results suggest that mucoadhesive Man-THM may be a promising candidate for a nasal vaccine delivery system to elicit systemic and mucosal immunity that can protect from pathogenic bacteria infection.

Effective treatment of hypertension by recombinant Lactobacillus plantarum expressing angiotensin converting enzyme inhibitory peptide

Background

Hypertension is considered the most serious risk factor for cardiovascular disease. Angiotensin-converting enzyme inhibitory peptides (ACEIPs), which are made from tuna frame protein (TFP) and yellow fin sole frame protein (YFP), have been used previously to treat hypertension. However, the production of these short peptides is usually dependent on enzymatic hydrolysis, resulting in a digested mixture that makes it difficult to purify the ACEIPs. Although it has been reported that ACEIPs could be produced in recombinant Escherichia coli strains, the use of lactic acid bacteria in the production of ACEIPs has not been demonstrated.

Results

In this study, the ACEIP coding sequences from TFP and YFP were joined through an arginine linker and expressed in the Lactobacillus plantarum (Lb. plantarum) NC8 strain by an inducible vector pSIP-409. Then, the antihypertensive effects were determined in the model of spontaneously hypertensive rats (SHRs) by measuring the blood pressure, hematology, blood biochemistry and nitric oxide (NO), endothelin (ET) and angiotensin II (Ang II) levels. The results showed that oral administration of recombinant Lb. plantarum NC8 (RLP) significantly decreased systolic blood pressure (P < 0.01) during treatment, which lasted for at least 10 days after the last dose. Furthermore, the presence of RLP resulted in an increased level of NO, as well as decreased levels of ET and Ang II in plasma, heart, and kidney. In addition, a dramatically decreased triglyceride level was also observed even though there was no significant change in hematology or blood biochemistry. Although some drawbacks were still observed, such as the presence of an antibiotic selection marker, no obvious side effects or bacterial translocation were observed in vivo, indicating the potential application of RLP in the treatment of hypertension.

Conclusion

These results demonstrated the effectiveness and safety of RLP on the treatment of hypertension.

Soluble RANKL expression in Lactococcus lactis and investigation of its potential as an oral vaccine adjuvant

BACKGROUND

To initiate mucosal immune responses, antigens in the intestinal lumen must be transported into gut-associated lymphoid tissue through M cells. Recently, it has been increasingly recognized that receptor activator of NF-kB ligand (RANKL) controls M cell differentiation by interacting with RANK expressed on the sub-epithelium of Peyer's patches. In this study, we increased the number of M cells using soluble RANKL (sRANKL) as a potent mucosal adjuvant.

RESULTS

For efficient oral delivery of sRANKL, we constructed recombinant Lactococcus lactis (L. lactis) IL1403 secreting sRANKL (sRANKL-LAB). The biological activity of recombinant sRANKL was confirmed by observing RANK-RANKL signaling in vitro. M cell development in response to oral administration of recombinant L. lactis was determined by 1.51-fold higher immunohistochemical expression of M cell marker GP-2, compared to that of non-treatment group. In addition, an adjuvant effect of sRANKL was examined by immunization of mice with M-BmpB as a model antigen after treatment with sRANKL-LAB. Compared with the wild-type L. lactis group, the sRANKL-LAB group showed significantly increased systemic and mucosal immune responses specific to M-BmpB.

CONCLUSIONS

Our results show that the M cell development by sRANKL-LAB can increase the antigen transcytotic capability of follicle-associated epithelium, and thereby enhance the mucosal immune response, which implies that oral administration of sRANKL is a promising adjuvant strategy for efficient oral vaccination.