Neisserial PorB immune enhancing activity and use as a vaccine adjuvant

Neisseria gonorrhoeae vaccines: a contemporary overview

Neisseria gonorrhoeae infection is an important public health issue, with an annual global incidence of 87 million. N. gonorrhoeae infection causes significant morbidity and can have serious long-term impacts on reproductive and neonatal health and may rarely cause life-threatening disease. Global rates of N. gonorrhoeae infection have increased over the past 20 years. Importantly, rates of antimicrobial resistance to key antimicrobials also continue to increase, with the United States Centers for Disease Control and Prevention identifying drug-resistant N. gonorrhoeae as an urgent threat to public health. This review summarizes the current evidence for N. gonorrhoeae vaccines, including historical clinical trials, key N. gonorrhoeae vaccine preclinical studies, and studies of the impact of Neisseria meningitidis vaccines on N. gonorrhoeae infection. A comprehensive survey of potential vaccine antigens, including those identified through traditional vaccine immunogenicity approaches, as well as those identified using more contemporary reverse vaccinology approaches, are also described. Finally, the potential epidemiological impacts of a N. gonorrhoeae vaccine and research priorities for further vaccine development are described.

The antimicrobial peptide MetchnikowinII enhances Ptfa antigen immune responses against avian Pasteurella multocida in chickens

Immunostimulants and vaccines are the main means for controlling infectious diseases and searching highly effective and low toxic immunestimulants has always been the focus of researchers. The MetchnikowinII (MetII) had been expressed by us and exhibited both antibacterial and antifungal activities, in this study, we evaluated its potential for an adjuvant effect. In chickens, antigen-specific immunoglobulin Gs (IgGs) were increased after MetII adjuvanted vaccination using the Ptfa protein. Compared to group Ptfa + iFA, which was only adjuvanted with incomplete Freund's adjuvant (iFA), the antibody titers of the group Ptfa + iFA + Met20 μg·mL-1 (PFM20) and Ptfa + iFA + Propolis (PFP) significantly increased (P<0.05). Likewise, Interleukin-2 (IL-2) and Interferon-γ (IFN-γ) cytokines in group Ptfa + iFA + Met20 μg·mL-1 (PFM20) and Ptfa + iFA + Propolis (PFP) were significantly higher than those of the other three experimental groups (P<0.05). The stimulation index (SI) value in chickens of group PFM20 was significantly higher than that of the other four experimental groups (P<0.05). Chickens that received MetII adjuvanted vaccinations benefitted from higher protection rate (88%) when challenged with Pasteurella multocida (P. multocida), which was significantly higher than those of group PF and PFP (P<0.05). These results suggested that the antimicrobial peptide MetII may play an adjuvant role in the immune response in chickens but need a proper usage, because the higher usage of 40 μg·mL-1 and 60 μg·mL-1 resulted poor effect. Whether MetII could be a potential adjuvant or a biomolecule as part of a complex adjuvant for vaccines needs more experimental evidence, the study still provides an examples for understanding vaccine adjuvants.

Evaluation of immunogenicity of gene-deleted and subunit vaccines constructed against the emerging pseudorabies virus variants

BACKGROUND

Pseudorabies (PR) (also called Aujeszky's disease, AD) is a serious infectious disease affecting pigs and other animals worldwide. The emergence of variant strains of pseudorabies virus (PRV) since 2011 has led to PR outbreaks in China and a vaccine that antigenically more closely matches these PRV variants could represent an added value to control these infections.

METHODS

The objective of this study was to develop new live attenuated and subunit vaccines against PRV variant strains. Genomic alterations of vaccine strains were based on the highly virulent SD-2017 mutant strain and gene-deleted strains SD-2017ΔgE/gI and SD-2017ΔgE/gI/TK, which constructed using homologous recombination technology. PRV gB-DCpep (Dendritic cells targeting peptide) and PorB (the outer membrane pore proteins of N. meningitidis) proteins containing gp67 protein secretion signal peptide were expressed using the baculovirus system for the preparation of subunit vaccines. We used experimental animal rabbits to test immunogenicity to evaluate the effect of the newly constructed PR vaccines.

RESULTS

Compared with the PRV-gB subunit vaccine and SD-2017ΔgE/gI inactivated vaccines, rabbits (n = 10) that were intramuscularly vaccinated with SD-2017ΔgE/gI/TK live attenuated vaccine and PRV-gB + PorB subunit vaccine showed significantly higher anti-PRV-specific antibodies as well as neutralizing antibodies and IFN-γ levels in serum. In addition, the SD-2017ΔgE/gI/TK live attenuated vaccine and PRV-gB + PorB subunit vaccine protected (90-100%) rabbits against homologous infection by the PRV variant strain. No obvious pathological damage was observed in these vaccinated rabbits.

CONCLUSIONS

The SD-2017ΔgE/gI/TK live attenuated vaccine provided 100% protection against PRV variant challenge. Interestingly, the subunit vaccines with gB protein linked to DCpep and PorB protein as adjuvant may also be a promising and effective PRV variant vaccine candidate.

PP19128R, a Multiepitope Vaccine Designed to Prevent Latent Tuberculosis Infection, Induced Immune Responses In Silico and In Vitro Assays

Background: Latent tuberculosis infection (LTBI) is the primary source of active tuberculosis (ATB), but a preventive vaccine against LTBI is lacking. Methods: In this study, dominant helper T lymphocyte (HTL), cytotoxic T lymphocyte (CTL), and B-cell epitopes were identified from nine antigens related to LTBI and regions of difference (RDs). These epitopes were used to construct a novel multiepitope vaccine (MEV) based on their antigenicity, immunogenicity, sensitization, and toxicity. The immunological characteristics of the MEV were analyzed with immunoinformatics technology and verified by enzyme-linked immunospot assay and Th1/Th2/Th17 cytokine assay in vitro. Results: A novel MEV, designated PP19128R, containing 19 HTL epitopes, 12 CTL epitopes, 8 B-cell epitopes, toll-like receptor (TLR) agonists, and helper peptides, was successfully constructed. Bioinformatics analysis showed that the antigenicity, immunogenicity, and solubility of PP19128R were 0.8067, 9.29811, and 0.900675, respectively. The global population coverage of PP19128R in HLA class I and II alleles reached 82.24% and 93.71%, respectively. The binding energies of the PP19128R-TLR2 and PP19128R-TLR4 complexes were -1324.77 kcal/mol and -1278 kcal/mol, respectively. In vitro experiments showed that the PP19128R vaccine significantly increased the number of interferon gamma-positive (IFN-γ⁺) T lymphocytes and the levels of cytokines, such as IFN-γ, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-10. Furthermore, positive correlations were observed between PP19128R-specific cytokines in ATB patients and individuals with LTBI. Conclusions: The PP19128R vaccine is a promising MEV with excellent antigenicity and immunogenicity and no toxicity or sensitization that can induce robust immune responses in silico and in vitro. This study provides a vaccine candidate for the prevention of LTBI in the future.

CD169+ Subcapsular Macrophage Role in Antigen Adjuvant Activity

Vaccines have played a pivotal role in improving public health, however, many infectious diseases lack an effective vaccine. Controlling the spread of infectious diseases requires continuing studies to develop new and improved vaccines. Our laboratory has been investigating the immune enhancing mechanisms of Toll-like receptor (TLR) ligand-based adjuvants, including the TLR2 ligand Neisseria meningitidis outer membrane protein, PorB. Adjuvant use of PorB increases costimulatory factors on antigen presenting cells (APC), increases antigen specific antibody production, and cytokine producing T cells. We have demonstrated that macrophage expression of MyD88 (required for TLR2 signaling) is an absolute requirement for the improved antibody response induced by PorB. Here-in, we specifically investigated the role of subcapsular CD169+ marginal zone macrophages in antibody production induced by the use of TLR-ligand based adjuvants (PorB and CpG) and non-TLR-ligand adjuvants (aluminum salts). CD169 knockout mice and mice treated with low dose clodronate treated animals (which only remove marginal zone macrophages), were used to investigate the role of these macrophages in adjuvant-dependent antibody production. In both sets of mice, total antigen specific immunoglobulins (IgGs) were diminished regardless of adjuvant used. However, the greatest reduction was seen with the use of TLR ligands as adjuvants. In addition, the effect of the absence of CD169+ macrophages on adjuvant induced antigen and antigen presenting cell trafficking to the lymph nodes was examined using immunofluorescence by determining the relative extent of antigen loading on dendritic cells (DCs) and antigen deposition on follicular dendritic cells (FDC). Interestingly, only vaccine preparations containing PorB had significant decreases in antigen deposition in lymphoid follicles and germinal centers in CD169 knockout mice or mice treated with low dose clodronate as compared to wildtype controls. Mice immunized with CpG containing preparations demonstrated decreased FDC networks in the mice treated with low dose clodronate. Conversely, alum containing preparations only demonstrated significant decreases in IgG in CD169 knockout mice. These studies stress that importance of subcapsular macrophages and their unique role in adjuvant-mediated antibody production, potentially due to an effect of these adjuvants on antigen trafficking to the lymph node and deposition on follicular dendritic cells.

Sexually Transmitted Neisseria gonorrhoeae Infections-Update on Drug Treatment and Vaccine Development

Background: Sexually transmitted gonorrhea, caused by the Gram-negative diplococcus Neisseria gonorrhoeae, continues to be a serious global health challenge despite efforts to eradicate it. Multidrug resistance among clinical N. gonorrhoeae isolates has limited treatment options, and attempts to develop vaccines have not been successful. Methods: A search of published literature was conducted, and information extracted to provide an update on the status of therapeutics and vaccine development for gonorrheal infection. Results: Recommended pharmacological treatment for gonorrhea has changed multiple times due to increasing acquisition of resistance to existing antibiotics by N. gonorrhoeae. Only broad-spectrum cephalosporin-based combination therapies are currently recommended for treatment of uncomplicated urogenital and anorectal gonococcal infections. With the reported emergence of ceftriaxone resistance, successful strategies addressing the global burden of gonorrhea must include vaccination. Century-old efforts at developing an effective vaccine against gonorrhea, leading to only four clinical trials, have not yielded any successful vaccine. Conclusions: While it is important to continue to explore new drugs for the treatment of gonorrhea, the historical trend of resistance acquisition suggests that any long-term strategy should include vaccine development. Advanced technologies in proteomics and in silico approaches to vaccine target identification may provide templates for future success.

Toll-like receptor-2/7-mediated T cell activation: An innate potential to augment CD8+ T cell cytokine production

CD8⁺ T cells are critical to combat pathogens and eradicate malignantly transformed cells. To exert their effector function and kill target cells, T cells produce copious amounts of effector molecules, including the pro-inflammatory cytokines interferon γ, tumour necrosis factor α and interleukin 2. TCR triggering alone is sufficient to induce cytokine secretion by effector and memory CD8⁺ T cells. However, T cells can also be directly activated by pathogen-derived molecules, such as through the triggering of Toll-like receptors (TLRs). TLR-mediated pathogen sensing by T cells results in the production of only interferon γ. However, in particular when the antigen load on target cells is low, or when TCR affinity to the antigen is limited, antigen-experienced T cells can benefit from costimulatory signals. TLR stimulation can also function in a costimulatory fashion to enhance TCR triggering. Combined TCR and TLR triggering enhances the proliferation, memory formation and effector function of T cells, resulting in enhanced production of interferon γ, tumour necrosis factor α and interleukin 2. Therefore, TLR ligands or the exploitation of TLR signalling could provide novel opportunities for immunotherapy approaches. In fact, CD19 CAR T cells bearing an intracellular TLR2 costimulatory domain were recently employed to treat cancer patients in a clinical trial. Here, the current knowledge regarding TLR2/7 stimulation-induced cytokine production by T cells is reviewed. Specifically, the transcriptional and post-transcriptional pathways engaged upon TLR2/7 sensing and TLR2/7 signalling are discussed. Finally, the potential uses of TLRs to enhance the anti-tumor effector function of T cells are explored.

Toll-Like Receptor Ligand Based Adjuvant, PorB, Increases Antigen Deposition on Germinal Center Follicular Dendritic Cells While Enhancing the Follicular Dendritic Cells Network

Vaccines are arguably one of the greatest advancements in modern medicine. Subunit vaccines comprise the majority of current preparations and consist of two main components-antigen and adjuvant. The antigen is a small molecule against which the vaccine induces an immune response to provide protection via the immunostimulatory ability of the adjuvant. Our laboratory has investigated the adjuvant properties of Toll-like receptor (TLR) ligand-based adjuvants, especially the outer membrane protein from Neisseria mengingitidis, PorB. In this current study we used PorB, along with CpG, an intracellular TLR9 agonist, and a non-TLR adjuvant, aluminum salts (Alum), to further investigate cellular mechanisms of adjuvanticity, focusing on the fate of intact antigen in the germinal center and association with follicular dendritic cells (FDCs). FDCs are located in the B cell light zone of the germinal center and are imperative for affinity maturation. They are stromal cells that retain whole intact antigen allowing recognition by the B cell receptor of the germinal center B cells. Our studies demonstrate that TLR ligands, but not Alum, increase the FDC network, while PorB and Alum increased colocalization of FDC and the model soluble antigen, ovalbumin (OVA). As PorB is the only adjuvant tested that induces both a higher number of FDCs and increased deposition of antigen on FDCs, it has the greatest ability to increase FDC-antigen interaction, essential for induction of B cell affinity maturation. These studies demonstrate a further mechanism and potential superiority of PorB as an adjuvant and its influence on antibody production.

Progress Toward a Gonococcal Vaccine: The Way Forward

The concept of immunizing against gonorrhea has received renewed interest because of the recent emergence of strains of Neisseria gonorrhoeae that are resistant to most currently available antibiotics, an occurrence that threatens to render gonorrhea untreatable. However, despite efforts over many decades, no vaccine has yet been successfully developed for human use, leading to pessimism over whether this goal was actually attainable. Several factors have contributed to this situation, including extensive variation of the expression and specificity of many of the gonococcal surface antigens, and the ability of N. gonorrhoeae to resist destruction by complement and other innate immune defense mechanisms. The natural host restriction of N. gonorrhoeae for humans, coupled with the absence of any definable state of immunity arising from an episode of gonorrhea, have also complicated efforts to study gonococcal pathogenesis and the host's immune responses. However, recent findings have elucidated how the gonococcus exploits and manipulates the host's immune system for its own benefit, utilizing human-specific receptors for attachment to and invasion of tissues, and subverting adaptive immune responses that might otherwise be capable of eliminating it. While no single experimental model is capable of providing all the answers, experiments utilizing human cells and tissues in vitro, various in vivo animal models, including genetically modified strains of mice, and both experimental and observational human clinical studies, have combined to yield important new insight into the immuno-pathogenesis of gonococcal infection. In turn, these have now led to novel approaches for the development of a gonococcal vaccine. Ongoing investigations utilizing all available tools are now poised to make the development of an effective human vaccine against gonorrhea an achievable goal within a foreseeable time-frame.