An attenuated Salmonella-vectored vaccine elicits protective immunity against Mycobacterium tuberculosis

Lactococcus lactis FNBPA+ (pValac:e6ag85a) Induces Cellular and Humoral Immune Responses After Oral Immunization of Mice

The development of a new vaccine strategy against tuberculosis is urgently needed and has been greatly encouraged by the scientific community worldwide. In this work, we constructed a lactococcal DNA vaccine based on the fusion of two Mycobacterium tuberculosis antigens, ESAT-6 and Ag85A, and examined its immunogenicity. The coding sequences of the ESAT-6 and Ag85A genes were fused and cloned into the eukaryotic expression pValac vector, and the functionality of the vector was confirmed in vitro. Then, L. lactis FnBPA⁺ (pValac:e6ag85a) was obtained and used for oral immunization of mice. This strain induced significant increases in IFN-γ, TNF-α, and IL-17 cytokines in stimulated splenocyte cultures, and significant production of antigen-specific sIgA was observed in the colonic tissues of immunized mice. We demonstrated that L. lactis FnBPA⁺ (pValac:e6ag85a) generated a cellular and humoral immune response after oral immunization of mice. The strategy developed in this work may represent an interesting DNA mucosal vaccine candidate against tuberculosis, using the fusion of two highly immunogenic antigens delivered by safe lactic acid bacteria.

Live-Attenuated Bacterial Vectors for Delivery of Mucosal Vaccines, DNA Vaccines, and Cancer Immunotherapy

Vaccines save millions of lives each year from various life-threatening infectious diseases, and there are more than 20 vaccines currently licensed for human use worldwide. Moreover, in recent decades immunotherapy has become the mainstream therapy, which highlights the tremendous potential of immune response mediators, including vaccines for prevention and treatment of various forms of cancer. However, despite the tremendous advances in microbiology and immunology, there are several vaccine preventable diseases which still lack effective vaccines. Classically, weakened forms (attenuated) of pathogenic microbes were used as vaccines. Although the attenuated microbes induce effective immune response, a significant risk of reversion to pathogenic forms remains. While in the twenty-first century, with the advent of genetic engineering, microbes can be tailored with desired properties.

In this review, I have focused on the use of genetically modified bacteria for the delivery of vaccine antigens. More specifically, the live-attenuated bacteria, derived from pathogenic bacteria, possess many features that make them highly suitable vectors for the delivery of vaccine antigens. Bacteria can theoretically express any heterologous gene or can deliver mammalian expression vectors harboring vaccine antigens (DNA vaccines). These properties of live-attenuated microbes are being harnessed to make vaccines against several infectious and noninfectious diseases. In this regard, I have described the desired features of live-attenuated bacterial vectors and the mechanisms of immune responses manifested by live-attenuated bacterial vectors. Interestingly anaerobic bacteria are naturally attracted to tumors, which make them suitable vehicles to deliver tumor-associated antigens thus I have discussed important studies investigating the role of bacterial vectors in immunotherapy. Finally, I have provided important discussion on novel approaches for improvement and tailoring of live-attenuated bacterial vectors for the generation of desired immune responses.

Ficolin-2 triggers antitumor effect by activating macrophages and CD8+ T cells

Ficolin-2 is an important serum complement lectin. Here, we describe novel findings indicating that serum ficolin-2 concentrations in multiple tumor patients are significantly lower than those in healthy donors. Administration of exogenous ficolin-2 or ficolin-A (a ficolin-2-like molecule in mouse), with only once, could remarkably inhibit the tumor cells growth in murine tumor models via early macrophages, dendritic cells (DCs) and CD8+ T cells, but not CD4+ T cells. Ficolin-A (FCN-A) knockout (KO) mice exhibits significantly increased tumor cell growth. Ficolin-2 induces macrophage activation, promotes M1 polarization and facilitates proliferation and antigen-specific cytotoxicity of CD8+ T cells. Ficolin-2 binds to Toll-like receptor 4 (TLR4) on macrophages and DCs and promotes their antigen-presenting abilities to CD8+ T cells. Our findings provide a new therapeutic strategy for tumors based on the triggering of immune-mediated antitumor effect by ficolin-2.

Lactococcus lactis carrying a DNA vaccine coding for the ESAT-6 antigen increases IL-17 cytokine secretion and boosts the BCG vaccine immune response

AIMS

A regimen utilizing Bacille Calmette-Guerin (BCG) and another vaccine system as a booster may represent a promising strategy for the development of an efficient tuberculosis vaccine for adults. In a previous work, we confirmed the ability of Lactococcus lactis fibronectin-binding protein A (FnBPA+) (pValac:ESAT-6), a live mucosal DNA vaccine, to produce a specific immune response in mice after oral immunization. In this study, we examined the immunogenicity of this strain as a booster for the BCG vaccine in mice.

METHODS AND RESULTS

After immunization, cytokine and immunoglobulin profiles were measured. The BCG prime L. lactis FnBPA+ (pValac:ESAT-6) boost group was the most responsive group, with a significant increase in splenic pro-inflammatory cytokines IL-17, IFN-γ, IL-6 and TNF-α compared with the negative control.

CONCLUSIONS

Based on the results obtained here, we demonstrated that L. lactis FnBPA+ (pValac:ESAT-6) was able to increase the BCG vaccine general immune response.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work is of great scientific and social importance because it represents the first step towards the development of a booster to the BCG vaccine using L. lactis as a DNA delivery system.

Development of a new DNA vaccine based on mycobacterial ESAT-6 antigen delivered by recombinant invasive Lactococcus lactis FnBPA+

The use of the food-grade bacterium Lactococcus lactis as a vehicle for the oral delivery of DNA vaccine plasmids constitutes a promising strategy for vaccination. The delivery of DNA plasmids into eukaryotic cells is of critical importance for subsequent DNA expression and effectiveness of the vaccine. In this context, the use of the recombinant invasive L. lactis FnBPA+ (fibronectin-binding protein A) strain for the oral delivery of the eukaryotic expression vector vaccination using lactic acid bacteria (pValac), coding for the 6-kDa early secreted antigenic target (ESAT-6) gene of Mycobacterium tuberculosis, could represent a new DNA vaccine strategy against tuberculosis. To this end, the ESAT-6 sequence was cloned into the pValac vector; the L. lactis fibronectin-binding protein A (FnBPA)+ (pValac:ESAT-6) strain was obtained, and its immunological profile was checked in BALB/c mice. This strain was able to significantly increase interferon gamma (IFN-γ) production in spleen cells, showing a systemic T helper 1 (Th1) cell response. The mice also showed a significant increase in specific secretory immunoglobulin A (sIgA) production in colon tissue and fecal extracts. Thus, this is the first time that L. lactis has been used to deliver a plasmid DNA harboring a gene that encodes an antigen against tuberculosis through mucous membranes.

Evaluation of a Salmonella vectored vaccine expressing Mycobacterium avium subsp. paratuberculosis antigens against challenge in a goat model

Johnes disease (JD), caused by Mycobacterium avium subsp paratuberculosis (MAP), occurs worldwide as chronic granulomatous enteritis of domestic and wild ruminants. To develop a cost effective vaccine, in a previous study we constructed an attenuated Salmonella strain that expressed a fusion product made up of partial fragments of MAP antigens (Ag85A, Ag85B and SOD) that imparted protection against challenge in a mouse model. In the current study we evaluated the differential immune response and protective efficacy of the Sal-Ag vaccine against challenge in a goat model as compared to the live attenuated vaccine MAP316F. PBMCs from goats vaccinated with Sal-Ag and challenged with MAP generated significantly lower levels of IFN-γ, following in vitro stimulation with either Antigen-mix or PPD jhonin, than PBMC from MAP316F vaccinated animals. Flow cytometric analysis showed the increase in IFN-γ correlated with a significantly higher level of proliferation of CD4, CD8 and γδT cells and an increased expression of CD25 and CD45R0 in MAP316F vaccinated animals as compared to control animals. Evaluation of a range of cytokines involved in Th1, Th2, Treg, and Th17 immune responses by quantitative PCR showed low levels of expression of Th1 (IFN-γ, IL-2, IL-12) and proinflammatory cytokines (IL-6, IL-8, IL-18, TNF-α) in the Sal-Ag immunized group. Significant levels of Th2 and anti-inflammatory cytokines transcripts (IL-4, IL-10, IL-13, TGF-β) were expressed but their level was low and with a pattern similar to the control group. Over all, Sal-Ag vaccine imparted partial protection that limited colonization in tissues of some animals upon challenge with wild type MAP but not to the level achieved with MAP316F. In conclusion, the data indicates that Sal-Ag vaccine induced only a low level of protective immunity that failed to limit the colonization of MAP in infected animals. Hence the Sal-Ag vaccine needs further refinement to increase its efficacy.

Immune response and protective efficacy of live attenuated Salmonella vaccine expressing antigens of Mycobacterium avium subsp. paratuberculosis against challenge in mice

Mycobacterium avium subsp. paratuberculosis (MAP) causes chronic granulomatous enteritis in ruminants that leads to diarrhea and eventually death. Existing vaccines have proven useful in limiting disease progression but have not been effective in preventing infection. To address this problem we constructed an attenuated Salmonella (ΔyejE; ΔssaV) strain harboring a plasmid that expressed a fusion protein comprised of the Salmonella Type III secretion system (T3SS) effector SopE and MAP antigens (85A, 85B, SOD, 74F) and evaluated its potential as vaccine candidate against MAP infection in mice. Of various SopE-MAP fusion proteins analyzed, only SopE104-Ag85A C-terminal(202-347)-SOD N-terminal(1-72)-Ag85B C-terminal(173-330) and SopE104-74F(1-148+669-786)were successfully expressed and secreted into culture media as revealed by western blot analysis. Mice immunized with attenuated Salmonella (ΔyejE; ΔssaV) harboring the SopE104-Ag85A C-terminal(202-347)-SOD N-terminal(1-72)-Ag85B C-terminal(173-330) and SopE104-74F(1-148+669-786)plasmid generated a potent and long lasting Th1 response characterized by production of IFN-γ. The cytokine profile varied at various time points after immunization and challenge, which showed down regulation of Th2 cytokines (IL-4, IL-10) and up-regulation of proinflammatory cytokines (IL-12 and IL-17). Further, the immune response correlated with protection as revealed by reduced bacterial load and improved histopathology of spleen and liver, which showed fewer granulomas and lower numbers of acid-fast bacilli as compared to PBS controls. Interestingly, vaccination with antigens mixed with Ribi adjuvant (Agmix+Ribi) imparted better protection than the attenuated salmonella vectored vaccine. Thus, priming with a live recombinant Salmonella strain that secretes MAP antigens represents a promising approach that could lead to development of an efficacious and cost effective vaccine for Johne's disease.

Tuberculosis vaccine research in China

It is now privately acknowledged that there may be little if any perceptible impact of the national Bacille Calmette-Guerin (BCG) vaccination program on disease prevalence, despite the extensive coverage of the newborn infant population and likely benefit in the early years of life. A better preventive vaccine than BCG is now being sought by Chinese researchers. Urgency has been added to the control problem by the emergence of multidrug-resistant tuberculosis (TB). Furthermore, expensive second-line drugs seem unlikely to be made available by the government to treat drug-resistant cases, so attention in addition has turned to the potential of immunotherapy as an adjunct to chemotherapy. Research trends are summarized here.

Therapeutic vaccination with Salmonella-delivered codon-optimized outer inflammatory protein DNA vaccine enhances protection in Helicobacter pylori infected mice

Vaccination had demonstrated as an alternative way to combat Helicobacter pylori challenge. In the present study, codon-optimized outer inflammatory protein gene (oipA) for Mus species codon usage, the inclusion of optimal Kozak sequence, and modified of GC content was applied to construct a novel DNA construct. The Salmonella-delivered wild type oipA construct (SL7207/poipA) and the Salmonella-delivered codon-optimized oipA construct (SL7207/poipA-opt) were prepared and their therapeutic efficacy was evaluated in H. pylori-infected mice. The codon-optimized oipA construct (poipA-opt) expressed almost six-fold higher protein than that of wild type construct (poipA) as normalized to the β-actin expression in AGS cells. Oral therapeutic immunization with SL7207/poipA-opt significantly eliminated H. pylori colonization in the stomach; and protection was related to a robust Th1/Th2 immune response. Therefore, our results suggested that fine therapeutic efficacy was related to sufficient expression of the antigen. It is supposed that codon-optimized oipA gene improves protein expression and consequently enhances the immunogenicity of DNA vaccine, which resulted in a significant reduction of bacterial loads in H. pylori infected mice. The Salmonella-delivered codon-optimized DNA construct could be a candidate vaccine against H. pylori for the clinical application.

L-ficolin binds to the glycoproteins hemagglutinin and neuraminidase and inhibits influenza A virus infection both in vitro and in vivo

L-ficolin, one of the complement lectins found in human serum, is a novel pattern recognition molecule that can specifically bind to microbial carbohydrates, thereby activating the lectin complement pathway and mounting a protective innate immune response. However, little is known about the role of L-ficolin during viral infections in vivo. In the present study, we used a mouse model of influenza A virus infection to demonstrate that the administration of exogenous L-ficolin or ficolin A (FCNA - an L-ficolin-like molecule in the mouse) is protective against the virus. Furthermore, FCNA-null mice have a greatly increased susceptibility to infection with the influenza A virus. Moreover, we found recombinant human L-ficolin inhibited influenza A virus entry into Madin-Darby canine kidney cells. More importantly, L-ficolin can recognize and bind hemagglutinin (HA) and neuraminidase (NA) glycoproteins and different subtypes of influenza A virus, and these interactions can be competitively inhibited by N-acetyl-D-glucosamine. In addition, the binding of L-ficolin and FCNA may lead to the activation of the lectin complement pathway. To our knowledge, this is the first report demonstrating that L-ficolin can block influenza virus infections both in vitro and in vivo using FCNA-knockout mice, possibly by interacting with the carbohydrates of HA and NA. Therefore, these data may provide new immunotherapeutic strategies based on the innate immune molecule L-ficolin against the influenza A virus.

Live attenuated Salmonella vaccines against Mycobacterium tuberculosis with antigen delivery via the type III secretion system

Tuberculosis remains a global health threat, and there is dire need to develop a vaccine that is safe and efficacious and confers long-lasting protection. In this study, we constructed recombinant attenuated Salmonella vaccine (RASV) strains with plasmids expressing fusion proteins consisting of the 80 amino-terminal amino acids of the type 3 secretion system effector SopE of Salmonella and the Mycobacterium tuberculosis antigens early secreted antigenic target 6-kDa (ESAT-6) protein and culture filtrate protein 10 (CFP-10). We demonstrated that the SopE-mycobacterial antigen fusion proteins were translocated into the cytoplasm of INT-407 cells in cell culture assays. Oral immunization of mice with RASV strains synthesizing SopE-ESAT-6-CFP-10 fusion proteins resulted in significant protection of the mice against aerosol challenge with M. tuberculosis H37Rv that was similar to the protection afforded by immunization with Mycobacterium bovis bacillus Calmette-Guérin (BCG) administered subcutaneously. In addition, oral immunization with the RASV strains specifying these mycobacterial antigens elicited production of significant antibody titers to ESAT-6 and production of ESAT-6- or CFP-10-specific gamma interferon (IFN-γ)-secreting and tumor necrosis factor alpha (TNF-α)-secreting splenocytes.

A novel recombinant Mycobacterium bovis bacillus Calmette-Guerin strain expressing human granulocyte macrophage colony-stimulating factor and Mycobacterium tuberculosis early secretory antigenic target 6 complex augments Th1 immunity

Since Mycobacterium bovis bacillus Calmette-Guerin strain (BCG) fails to protect adults from pulmonary tuberculosis (TB), there is an urgent need for developing a new vaccine. In this study, we constructed a novel recombinant BCG strain (rBCG) expressing human granulocyte macrophage colony-stimulating factor (GM-CSF) and the 6 kDa early secretory antigenic target (ESAT6) of Mycobacterium tuberculosis, named rBCG:GE (expressing GMCSF-ESAT6 complex), and evaluated the immunogenicity of the construct in BALB/c mice. Our results indicated that the rBCG:GE was able to induce higher titer of antibody than the conventional BCG, the rBCG:G (expressing GM-CSF) and the rBCG:E (expressing ESAT6). Moreover, the rBCG:GE also elicited a longer-lasting and stronger Th1 cellular immune responses than the other groups, which was confirmed by the incremental proliferation of splenocytes, the increased percentages of CD4(+) and CD8(+) T cells of spleen, the elevated level of interferon-γ in splenocyte culture after tuberculin-purified protein derivative stimulation, and the increased concentration of GM-CSF in serum. The data presented here suggested the possibility that the recombinant BCG:GE might be a good vaccine candidate to TB.

Oral delivery of a DNA vaccine against tuberculosis using operator-repressor titration in a Salmonella enterica vector

Attenuated Salmonella enterica offers a vaccine delivery route that has the benefits of enhanced immunogenicity and oral delivery. The majority of immunization studies have been conducted to deliver recombinant proteins, expressed from a gene that is either chromosomally integrated or carried on a low- or medium-copy number plasmid. There are, however, an increasing number of reports demonstrating the delivery of DNA vaccines, but the high-copy number plasmids that are preferentially used for this application are unstable in Salmonella. Here, we use the Operator-Repressor Titration (ORT) plasmid maintenance system in Salmonella enterica serovar Typhimurium to deliver a high-copy number plasmid expressing the Mycobacterium tuberculosis gene mpt64 to mice. MPT64 expression was detected in phagocytes using immunofluorescence microscopy following Salmonella-mediated delivery of the DNA vaccine. The indicative CD8+ responses measured by antigen-specific IFN-γ were higher from the live bacterial vector than from injected plasmid DNA, and a reduction in the pulmonary bacterial load was seen following an aerogenic challenge. This illustrates the potential of live attenuated Salmonella as oral tuberculosis vaccine vectors.

Induction of Specific CD8 T Cells against Intracellular Bacteria by CD8 T-Cell-Oriented Immunization Approaches

For protection against intracellular bacteria such as Mycobacterium tuberculosis and Listeria monocytogenes, the cellular arm of adaptive immunity is necessary. A variety of immunization methods have been evaluated and are reported to induce specific CD8⁺ T cells against intracellular bacterial infection. Modified BCG vaccines have been examined to enhance CD8⁺ T-cell responses. Naked DNA vaccination is a promising strategy to induce CD8⁺ T cells. In addition to this strategy, live attenuated intracellular bacteria such as Shigella, Salmonella, and Listeria have been utilized as carriers of DNA vaccines in animal models. Vaccination with dendritic cells pulsed with antigenic peptides or the cells introduced antigen genes by virus vectors such as retroviruses is also a powerful strategy. Furthermore, vaccination with recombinant lentivirus has been attempted to induce specific CD8⁺ T cells. Combinations of these strategies (prime-boost immunization) have been studied for the efficient induction of intracellular bacteria-specific CD8⁺ T cells.