Experimental vaccine induces Th1-driven immune responses and resistance to Neisseria gonorrhoeae infection in a murine model

Meningococcal vaccine 4CMenB elicits a robust cellular immune response that targets but is not consistently protective against Neisseria gonorrhoeae during murine vaginal infection

Retrospective epidemiological studies suggest that the licensed serogroup B meningococcal vaccine 4CMenB (Bexsero) provides some protection against the closely related pathogen Neisseria gonorrhoeae in humans. This result has been replicated in murine models of gonococcal colonization, with a gonococci-reactive humoral response and more rapid clearance of vaginal infection. However, immunization with 4CMenB consistently elicits a robust humoral response but does not protect all individuals; hence, the correlates of protection remain undefined. Herein, we exploit the fact that 4CMenB promotes gonococcal clearance in only a subset of immunized mice to perform a broad analysis of the adaptive response in animals that are or are not protected. We observe that 4CMenB vaccination induces high levels of anti-neisserial antibodies in both serum and the vaginal lumen, and a robust cellular response highlighted by an increase in both conventional naïve and memory populations as well as unconventional lymphocyte subsets. Multiplex and flow cytometry results show that 4CMenB vaccination generates a robust, multi-faceted cytokine response that spans numerous T cell subsets (TH1, TH2, Treg, and TH17) and that non-T non-B lymphocytes play an important role in this response, as indicated by an unbiased principal component analysis. Together, this work provides the first comprehensive analysis of the robust humoral and complex cellular response to 4CMenB so as to reveal the effector mechanisms that may contribute to immunity against vaginal gonococcal infection.IMPORTANCEGonorrhea, a sexually transmitted infection caused by the human-specific pathogen Neisseria gonorrhoeae (Ngo), is a growing public health concern due to its rise in prevalence and increasing antibiotic resistance against first-line agents. There is currently no vaccine available for this important bacterium due, in part, to our lack of understanding of immune correlates of protection. Interestingly, a human-approved vaccine (4CMenB; Bexsero) against a related pathogen (N. meningitidis; a cause of meningitis) has demonstrated some protection against gonorrhea in epidemiologic studies. Herein, we provide the first detailed analysis of cellular and antibody-mediated immune responses to this vaccine in animals protected against gonococcal colonization. These findings provide new understanding regarding immune correlates of protection against N. gonorrhoeae, providing new insight into immune protection and helping guide the development of a much-needed vaccine.

Protection against N. gonorrhoeae induced by OMV-based meningococcal vaccines are associated with cross-species directed humoral and cellular immune responses

Introduction

Limited protective immunologic responses to natural N. gonorrhoeae infection and a lack of knowledge about mechanisms of protection have hampered development of an effective vaccine. Recent studies in humans and mice have found meningococcal outer membrane vesicle-containing vaccines (OMV) induce cross species immune responses against gonococci and are associated with protection. The exact mechanisms or how humoral and cellular immunity are related to protection, remain unclear.

Methods

To study this, we immunized mice with two meningococcal OMV-containing vaccines known to accelerate clearance of N. gonorrhoeae, 4CMenB and OMV from an engineered N. meningitidis strain lacking major surface antigens PorA, PorB, and Rmp (MC58 ΔABR). We assessed serologic and cellular immune signatures associated with these immunizations and assessed bacterial clearance in the mice using a vaginal/cervical gonococcal infection model.

Results

Mice immunized with 4CMenB or MC58 ΔABR demonstrated shortened courses of recovery of vaginal N. gonorrhoeae compared to control mice immunized with alum alone. Vaccination with 4CMenB or MC58ΔABR OMV elicited serum and vaginal cross-reactive anti-Ng-OMV antibody responses that were augmented after vaginal challenge with N. gonorrhoeae. Further, splenocytes in 4CMenB and MC58 ΔABR immunized mice exhibited elevated cytokine production after restimulation with heterologous N. gonorrhoeae OMV when compared to splenocytes from Alum immunized mice. We further tested for correlations between bacterial burden and the measured anti-gonococcal immune responses within each vaccination group and found different immunologic parameters associated with reduced bacterial burden for each vaccine.

Discussion

Our findings suggest the cross-protection against gonococcal infection induced by different meningococcal OMV vaccines is likely multifactorial and mediated by different humoral and cellular immune responses induced by these two vaccines.

Immunogenic evaluation of LptD + LtgC as a bivalent vaccine candidate against Neisseria gonorrhoeae

BACKGROUND

Neisseria gonorrhoeae is an escalating global health threat due to increasing antimicrobial resistance. The emergence of multidrug-resistant (MDR) strains necessitates alternative prevention strategies. This study focused on the development of a bivalent vaccine formulation to address this challenge. Lipopolysaccharide transport protein D (LptD) and lytic transglycosylase C (LtgC) as two promising immunogenic targets were considered in this study.

METHODS

The ltgC and lptD genes of N. gonorrhoeae ATCC 19424 were amplified, then cloned into the pET-28a (+) vector, expressed in Escherichia coli BL21 (DE3), and purified using Ni-NTA affinity chromatography. Antigen-specific total IgG levels in serum of patients with gonorrhea were assessed using enzyme-linked immunosorbent assay (ELISA). Proteins were formulated with monophosphoryl lipid A (MPLA) adjuvant in three groups: LptD, LtgC, and a bivalent LptD + LtgC. One additional group received LptD with liposomal MPLA, along with control groups. Vaccine formulations were administered to BALB/c mice in three doses at two-week intervals. Total IgG, IgG1, IgG2a, and IgA levels in sera and vaginal samples were measured using ELISA. Moreover, serum bactericidal (SBA) and opsonophagocytic (OPA) assays were conducted.

RESULTS

The total IgG levels against both proteins were considerably higher in the patients' sera compared to healthy individuals. All vaccine formulations significantly increased total IgG levels in animal model. The LptD + liposomal MPLA group exhibited the highest specific IgG level, whereas the bivalent formulation group exhibited the highest long-term IgG level until the day 112, which also yielded the strongest total IgG response in the whole-cell ELISA. The IgG2a/ IgG1 ratio was greater than 1 in all vaccine regimens, indicating a Th1-polarized response. The LptD + liposomal MPLA formulation elicited the highest serum IgA levels, followed by the LptD + LtgC combination. In addition, the bivalent formulation achieved the highest SBA and OPA titers.

CONCLUSION

This study successfully developed and evaluated a recombinant bivalent vaccine against N. gonorrhoeae. This formulation exhibited the most potent immunogenicity, as evidenced by higher antibody levels and SBA and OPA titers than single-antigen formulations. The Th1-polarized immune response further highlights the vaccine's potential to elicit a protective immune profile. These findings suggest that this multi-antigen formulation can be a promising vaccine candidate against gonorrhea. However, more investigations are required to confirm the vaccine efficacy.

IFN-γ licenses normal and pathogenic ALPK1/TIFA pathway in human monocytes

Alpha-kinase 1 (ALPK1) is an immune receptor sensing the bacterial nucleotide sugar ADP-heptose. ALPK1 phosphorylates TIFA leading to its oligomerization and downstream NF-κB activation. Specific mutations in ALPK1 are associated with an autoinflammatory syndrome termed ROSAH and with spiradenoma (skin cancers with sweat gland differentiation). This study investigated ALPK1 responses in human mononuclear cells and demonstrates that human mononuclear cells have distinct abilities to respond to ADP-heptose. Notably, IFN-γ is required to license the ALPK1/TIFA pathway in monocytes, while it was dispensable for the responsiveness of B cells. IFN-γ induced TIFA upregulation in monocytes, and TIFA induction was sufficient to recapitulate the licensing effect of IFN-γ. IFN-γ treatment promoted the phenotypic expression of pathogenic ALPK1 mutations. The licensing effect of IFN-γ in monocytes was blocked by JAK inhibitors. These findings underscore the critical role of IFN-γ in ALPK1 function and suggest JAK inhibitors as potential therapies for ALPK1-related inflammatory conditions.

Recombinant ClearColi™-derived outer membrane vesicles as an effective carrier for development of neoepitope-based vaccine candidate against colon carcinoma

BACKGROUND

Colorectal carcinoma (CRC) is the third most common cancer worldwide, with high clonal heterogeneity due to somatic mutations. Poly neoepitope vaccines can inhibit the tumor's escape from the immune system. However, they have rapid clearance and low immunogenicity. Bacteria-derived recombinant outer membrane vesicles (OMVs) have gained increased attention as ideal cancer vaccine candidates due to their unique adjuvant properties and ability to carry antigens. Herein, the benefits of OMV-based and polyneoepitope-based vaccines were combined to obtain a functional individualized cancer vaccine.

METHODS

OMVs and rOMVs displaying CT26 polytopes were isolated from ClearColi™ and recombinant ClearColi™ containing pET-22b (ClyA-CT26 polytope) by the AS (70 %) + UDF method. BALB/c mice were immunized with OMVs (40 µg) and rOMVs (20 and 40 µg) and subcutaneously challenged with CT26 cells. Then, IgG1 and IgG2a antibodies specific for CT26 M90 and CT26 polytope, the stimulated IFN-γ, TNF-α, and IL-10 cytokines and the stimulated CTL responses by measuring granzyme B were evaluated. To investigate whether pooled sera and pooled splenocytes are indicators of individual responses, pooled and individual methods for determining the elicited immunity were compared. Additionally, the ability of OMVs and rOMVs (20 and 40 µg) to prevent tumor growth against the CT26 challenge was investigated.

RESULTS

Immunization with rOMVs displaying CT26 polytopes induced a higher titer of CT26 polytope- and CT26 M90 peptide-specific IgG2a than IgG1 antibodies in a dose-dependent manner, thus directing immunity to Th1. The antibody responses determined by pooled sera can be used as indicators of individual responses. In addition, both OMVs and rOMVs displaying CT26 polytopes could induce tumor-suppressing cytokines (IFN-γ and TNF-α). The ability of rOMVs displaying CT26 polytopes to induce these cytokines was higher than OMVs in a dose-dependent way. The results of the granzyme B assay were also in agreement with the cytokine assay. The survival of mice after the CT26 challenge was 100 % in the OMVs and rOMVs groups, and inhibition of tumor growth was significantly higher by rOMVs (40 µg) compared to OMVs.

CONCLUSION

The bioengineered OMVs displaying CT26 neoepitopes have the potential for the development of personalized tumor vaccines. Our results can provide new insights for developing rOMV-based vaccines displaying polytopes against diseases containing highly variable antigens.

Protection against N. gonorrhoeae induced by OMV-based Meningococcal Vaccines are associated with cross-species directed humoral and cellular immune responses

Limited protective immunologic responses to natural N. gonorrhoeae infection and a lack of knowledge about mechanisms of protection have hampered development of an effective vaccine. Recent studies in humans and mice have found meningococcal outer membrane vesicle-containing vaccines (OMV) induce cross species immune responses against gonococci and are associated with protection. The exact mechanisms or how humoral and cellular immunity are related to protection, remain unclear. To study this, we immunized mice with two meningococcal OMV-containing vaccines known to accelerate clearance of N. gonorrhoeae , 4CMenB and OMV from an engineered N. meningitidis strain lacking major surface antigens PorA, PorB, and Rmp (MC58 ΔABR). We assessed serologic and cellular immune signatures associated with these immunizations and assessed bacterial clearance in the mice using a vaginal/cervical gonococcal infection model. Mice immunized with 4CMenB or MC58 ΔABR demonstrated shortened courses of recovery of vaginal N. gonorrhoeae compared to control mice immunized with alum alone. Vaccination with 4CMenB or MC58ΔABR OMV elicited serum and vaginal cross-reactive anti-Ng-OMV antibody responses that were augmented after vaginal challenge with N. gonorrhoeae . Further, splenocytes in 4CMenB and MC58 ΔABR immunized mice exhibited elevated cytokine production after restimulation with heterologous N. gonorrhoeae OMV when compared to splenocytes from Alum immunized mice. We further tested for correlations between bacterial burden and the measured anti-gonococcal immune responses within each vaccination group and found different immunologic parameters associated with reduced bacterial burden for each vaccine. Our findings suggest the cross-protection against gonococcal infection induced by different meningococcal OMV vaccines is likely multifactorial and mediated by different humoral and cellular immune responses induced by these two vaccines.

Intranasal trivalent candidate vaccine induces strong mucosal and systemic immune responses against Neisseria gonorrhoeae

The spread of multidrug-resistant strains of Neisseria gonorrhoeae poses a great challenge in gonorrhea treatment. At present, vaccination is the best strategy for gonorrhea control. However, given the extensive antigenic variability of N. gonorrhoeae, the effectiveness of monovalent vaccines is limited. Therefore, increasing the coverage of vaccination by using a multivalent vaccine may be more effective. In this study, a trivalent vaccine comprising three conserved antigens, namely, the App passenger domain, MetQ, and neisserial heparin binding antigen (NHBA), was constructed, and its protective effect was evaluated. Trivalent vaccines induced stronger circulating IgG and IgA antibody responses in mice than monovalent vaccines, in addition to eliciting Th1, Th2, and Th17 immune responses. Antiserum generated by the trivalent vaccine killed N. gonorrhoeae strains (homologous FA1090 and heterologous FA19), exhibiting superior bactericidal capacity than NHBA and MetQ vaccine antisera against N. gonorrhoeae, but similar capacities to those of the App vaccine antiserum. In addition, the trivalent vaccine antiserum achieved greater inhibition of N. gonorrhoeae FA1090 strain adherence to ME-180 cells compared to that elicited by the monovalent vaccine antiserum. In a mouse vaginal infection model, the trivalent vaccine was modestly effective (9.2% decrease in mean area under curve compared to the pCold-TF control mice), which was somewhat better than the protection seen with the monovalent vaccines. Our findings suggest that recombinant multivalent vaccines targeting N. gonorrhoeae exhibit advantages in protective efficacy compared to monovalent vaccines, and future research on multivalent vaccines should focus on optimizing different antigen combinations.

Tackling immunosuppression by Neisseria gonorrhoeae to facilitate vaccine design

Gonorrhoea, caused by Neisseria gonorrhoeae, is a common sexually transmitted infection. Increasing multi-drug resistance and the impact of asymptomatic infections on sexual and reproductive health underline the need for an effective gonococcal vaccine. Outer membrane vesicles (OMVs) from Neisseria meningitidis induce modest cross-protection against gonococcal infection. However, the presence of proteins in OMVs derived from N. gonorrhoeae that manipulate immune responses could hamper their success as a vaccine. Here we modified two key immunomodulatory proteins of the gonococcus; RmpM, which can elicit 'blocking antibodies', and PorB, an outer membrane porin which contributes to immunosuppression. As meningococcal PorB has adjuvant properties, we replaced gonococcal PorB with a meningococcal PorB. Immunisation with OMVs from N. gonorrhoeae lacking rmpM and expressing meningococcal porB elicited higher antibody titres against model antigens in mice compared to OMVs with native PorB. Further, a gonococcal protein microarray revealed stronger IgG antibody responses to a more diverse range of antigens in the Nm PorB OMV immunised group. Finally, meningococcal PorB OMVs resulted in a Th1-skewed response, exemplified by increased serum IgG2a antibody responses and increased IFNɣ production by splenocytes from immunised mice. In summary, we demonstrate that the replacement of PorB in gonococcal OMVs enhances immune responses and offers a strategy for gonococcal vaccine development.

Intradermal administration of novel particulate Chlamydia trachomatis vaccine candidates drives protective immune responses

Chlamydia trachomatis causes the most prevalent bacterial sexually transmitted infection worldwide. Its complex lifecycle and the lack of appropriate antigen delivery vehicles make it difficult to develop an effective C. trachomatis vaccine. Recently, bacterial protein bodies (PBs) have emerged as promising bioparticles for vaccine antigen delivery. By developing a PB-tag for translational fusion, we were able to induce the aggregation of recombinant antigens expressed in Escherichia coli into PBs. Here, we investigated the immunogenicity and efficacy of PBs containing either the C. trachomatis MOMP-derived CTH522-SP or HtrA antigen in mice. Intradermal administration of c-di-AMP-adjuvanted PB-CTH522-SP and PB-HtrA vaccines, produced in an LPS-detoxified E. coli strain, induced antigen-specific cellular immunity, as measured by significant release of IFN-γ and IL17a in draining cervical lymph node and splenic cell cultures. Moreover, significant induction of HtrA-specific IFN-γ expressing CD4+ and CD8+ T cells was detected in the spleens. While immunization with the two PB vaccines led to prominent levels of specific antibodies in both serum and vaginal compartments, only antiserum against PB-CTH522-SP exhibited C. trachomatis-specific neutralization activity. Importantly, intradermal immunization with PB-CTH522-SP significantly reduced bacterial counts following C. trachomatis genital challenge. These data highlight the potential of the PB-based platform for the development of C. trachomatis vaccines.

Urgent Need to Understand and Prevent Gonococcal Infection: From the Laboratory to Real-World Context

Neisseria gonorrhoeae is widespread globally. Primary prevention is unsuccessful and antimicrobial resistance threatens optimal management. There is no specific vaccine and natural infection studies show that N gonorrhoeae can avoid and suppress immune responses. In addition to extensive variation in expression and specificity of many gonococcal surface antigens, it induces a robust inflammatory response through the Th17 pathway with a large influx of neutrophils and inflammatory cytokines but evades macrophages. The Th1- and Th2-mediated response is suppressed, resulting in low, short-lived antibody titers. Real-world evidence suggests that gonorrhea cases are reduced among recipients of Neisseria meningitidis group B vaccines containing outer membrane vesicles (OMVs). Although the first randomized trial of an OMV-containing MenB vaccine against N gonorrhoeae infection did not show statistically significant vaccine efficacy, ongoing trials might shed further light. Several candidate vaccine antigens for a gonococcal-specific vaccine are being evaluated preclinically but only one has reached clinical trials.

Immunity to Sexually Transmitted Bacterial Infections of the Female Genital Tract: Toward Effective Vaccines

Sexually transmitted infections (STIs) caused by bacterial pathogens Chlamydia trachomatis, Neisseria gonorrhoeae, and Treponema pallidum present significant public health challenges. These infections profoundly impact reproductive health, leading to pelvic inflammatory disease, infertility, and increased susceptibility to other infections. Prevention measures, including antibiotic treatments, are limited by the often-asymptomatic nature of these infections, the need for repetitive and continual screening of sexually active persons, antibiotic resistance for gonorrhea, and shortages of penicillin for syphilis. While vaccines exist for viral STIs like human papillomavirus (HPV) and hepatitis B virus (HBV), there are no vaccines available for bacterial STIs. This review examines the immune responses in the female genital tract to these bacterial pathogens and the implications for developing effective vaccines against bacterial STIs.

Sweet complexity: O-linked protein glycosylation in pathogenic Neisseria

The genus Neisseria, which colonizes mucosal surfaces, includes both commensal and pathogenic species that are exclusive to humans. The two pathogenic Neisseria species are closely related but cause quite different diseases, meningococcal sepsis and meningitis (Neisseria meningitidis) and sexually transmitted gonorrhea (Neisseria gonorrhoeae). Although obvious differences in bacterial niches and mechanisms for transmission exists, pathogenic Neisseria have high levels of conservation at the levels of nucleotide sequences, gene content and synteny. Species of Neisseria express broad-spectrum O-linked protein glycosylation where the glycoproteins are largely transmembrane proteins or lipoproteins localized on the cell surface or in the periplasm. There are diverse functions among the identified glycoproteins, for example type IV biogenesis proteins, proteins involved in antimicrobial resistance, as well as surface proteins that have been suggested as vaccine candidates. The most abundant glycoprotein, PilE, is the major subunit of pili which are an important colonization factor. The glycans attached can vary extensively due to phase variation of protein glycosylation (pgl) genes and polymorphic pgl gene content. The exact roles of glycosylation in Neisseria remains to be determined, but increasing evidence suggests that glycan variability can be a strategy to evade the human immune system. In addition, pathogenic and commensal Neisseria appear to have significant glycosylation differences. Here, the current knowledge and implications of protein glycosylation genes, glycan diversity, glycoproteins and immunogenicity in pathogenic Neisseria are summarized and discussed.

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.

Characterization of protective immune responses against Neisseria gonorrhoeae induced by intranasal immunization with adhesion and penetration protein

Drug-resistant N. gonorrhoeae is an urgent threat to global public health, and vaccine development is the best long-term strategy for controlling gonorrhea. We have previously shown that adhesion and penetration protein (App) play a role in the adhesion, invasion, and reproductive tract colonization of N. gonorrhoeae. Here, we describe the immune response induced by intranasal immunization with passenger and translocator fragments of App. The recombinant App passenger and translocator fragments induced high titers of IgG and IgA antibodies in serum and vaginal washes. Antibodies produced by App passenger and the combination of passenger and translocator mediated the killing of N. gonorrhoeae via serum bactericidal activity and opsonophagocytic activity, whereas antisera from translocator-immunized groups had lower bactericidal activity and opsonophagocytic activity. The antisera of the App passenger and translocator, alone and in combination, inhibited the adhesion of N. gonorrhoeae to cervical epithelial cells in a concentration-dependent manner. Nasal immunization with App passenger and translocator fragments alone or in combination induced high levels of IgG1, IgG2a, and IgG2b antibodies and stimulated mouse splenocytes to secrete cytokines IFN-γ and IL-17A, suggesting that Th1 and Th17 cellular immune responses were activated. In vivo experiments have shown that immune App passenger and transporter fragments can accelerate the clearance of N. gonorrhoeae in the vagina of mice. These data suggest that the App protein is a promising N. gonorrhoeae vaccine antigen.

Bacteria-derived extracellular vesicles: endogenous roles, therapeutic potentials and their biomimetics for the treatment and prevention of sepsis

Sepsis is one of the medical conditions with a high mortality rate and lacks specific treatment despite several years of extensive research. Bacterial extracellular vesicles (bEVs) are emerging as a focal target in the pathophysiology and treatment of sepsis. Extracellular vesicles (EVs) derived from pathogenic microorganisms carry pathogenic factors such as carbohydrates, proteins, lipids, nucleic acids, and virulence factors and are regarded as "long-range weapons" to trigger an inflammatory response. In particular, the small size of bEVs can cross the blood-brain and placental barriers that are difficult for pathogens to cross, deliver pathogenic agents to host cells, activate the host immune system, and possibly accelerate the bacterial infection process and subsequent sepsis. Over the years, research into host-derived EVs has increased, leading to breakthroughs in cancer and sepsis treatments. However, related approaches to the role and use of bacterial-derived EVs are still rare in the treatment of sepsis. Herein, this review looked at the dual nature of bEVs in sepsis by highlighting their inherent functions and emphasizing their therapeutic characteristics and potential. Various biomimetics of bEVs for the treatment and prevention of sepsis have also been reviewed. Finally, the latest progress and various obstacles in the clinical application of bEVs have been highlighted.

Experimental Urethral Infection with Neisseria gonorrhoeae

Gonorrhea rates and antibiotic resistance are both increasing. Neisseria gonorrhoeae (Ng) is an exclusively human pathogen and is exquisitely adapted to its natural host. Ng can subvert immune responses and undergoes frequent antigenic variation, resulting in limited immunity and protection from reinfection. Previous gonococcal vaccine efforts have been largely unsuccessful, and the last vaccine to be tested in humans was more than 35 years ago. Advancing technologies and the threat of untreatable gonorrhea have fueled renewed pursuit of a vaccine as a long-term sustainable solution for gonorrhea control. Despite the development of a female mouse model of genital gonococcal infection two decades ago, correlates of immunity or protection remain largely unknown, making the gonococcus a challenging vaccine target. The controlled human urethral infection model of gonorrhea (Ng CHIM) has been used to study gonococcal pathogenesis and the basis of anti-gonococcal immunity. Over 200 participants have been inoculated without serious adverse events. The Ng CHIM replicates the early natural course of urethral infection. We are now at an inflexion point to pivot the use of the model for vaccine testing to address the urgency of improved gonorrhea control. Herein we discuss the need for gonorrhea vaccines, and the advantages and limitations of the Ng CHIM in accelerating the development of gonorrhea vaccines.

Preclinical efficacy of a cell division protein candidate gonococcal vaccine identified by artificial intelligence

IMPORTANCE

Vaccines to curb the global spread of multidrug-resistant gonorrhea are urgently needed. Here, 26 vaccine candidates identified by an artificial intelligence-driven platform (Efficacy Discriminative Educated Network[EDEN]) were screened for efficacy in the mouse vaginal colonization model. Complement-dependent bactericidal activity of antisera and the EDEN protective scores both correlated positively with the reduction in overall bacterial colonization burden. NGO1549 (FtsN) and NGO0265, both involved in cell division, displayed the best activity and were selected for further development. Both antigens, when fused to create a chimeric protein, elicited bactericidal antibodies against a wide array of gonococcal isolates and significantly attenuated the duration and burden of gonococcal colonization of mouse vaginas. Protection was abrogated in mice that lacked complement C9, the last step in the formation of the membrane attack complex pore, suggesting complement-dependent bactericidal activity as a mechanistic correlate of protection of the vaccine. FtsN and NGO0265 represent promising vaccine candidates against gonorrhea.

In Vitro Pre-Clinical Evaluation of a Gonococcal Trivalent Candidate Vaccine Identified by Transcriptomics

Gonorrhea, a sexually transmitted disease caused by Neisseria gonorrhoeae, poses a significant global public health threat. Infection in women can be asymptomatic and may result in severe reproductive complications. Escalating antibiotic resistance underscores the need for an effective vaccine. Approaches being explored include subunit vaccines and outer membrane vesicles (OMVs), but an ideal candidate remains elusive. Meningococcal OMV-based vaccines have been associated with reduced rates of gonorrhea in retrospective epidemiologic studies, and with accelerated gonococcal clearance in mouse vaginal colonization models. Cross-protection is attributed to shared antigens and possibly cross-reactive, bactericidal antibodies. Using a Candidate Antigen Selection Strategy (CASS) based on the gonococcal transcriptome during human mucosal infection, we identified new potential vaccine targets that, when used to immunize mice, induced the production of antibodies with bactericidal activity against N. gonorrhoeae strains. The current study determined antigen recognition by human sera from N. gonorrhoeae-infected subjects, evaluated their potential as a multi-antigen (combination) vaccine in mice and examined the impact of different adjuvants (Alum or Alum+MPLA) on functional antibody responses to N. gonorrhoeae. Our results indicated that a stronger Th1 immune response component induced by Alum+MPLA led to antibodies with improved bactericidal activity. In conclusion, a combination of CASS-derived antigens may be promising for developing effective gonococcal vaccines.

Development of a Tag/Catcher-mediated capsid virus-like particle vaccine presenting the conserved Neisseria gonorrhoeae SliC antigen that blocks human lysozyme

Virus-like particles (VLPs) are promising nanotools for the development of subunit vaccines due to high immunogenicity and safety. Herein, we explored the versatile and effective Tag/Catcher-AP205 capsid VLP (cVLP) vaccine platform to address the urgent need for the development of an effective and safe vaccine against gonorrhea. The benefits of this clinically validated cVLP platform include its ability to facilitate unidirectional, high-density display of complex/full-length antigens through an effective split-protein Tag/Catcher conjugation system. To assess this modular approach for making cVLP vaccines, we used a conserved surface lipoprotein, SliC, that contributes to the Neisseria gonorrhoeae defense against human lysozyme, as a model antigen. This protein was genetically fused at the N- or C-terminus to the small peptide Tag enabling their conjugation to AP205 cVLP, displaying the complementary Catcher. We determined that SliC with the N-terminal SpyTag, N-SliC, retained lysozyme-blocking activity and could be displayed at high density on cVLPs without causing aggregation. In mice, the N-SliC-VLP vaccines, adjuvanted with AddaVax or CpG, induced significantly higher antibody titers compared to controls. In contrast, similar vaccine formulations containing monomeric SliC were non-immunogenic. Accordingly, sera from N-SliC-VLP-immunized mice also had significantly higher human complement-dependent serum bactericidal activity. Furthermore, the N-SliC-VLP vaccines administered subcutaneously with an intranasal boost elicited systemic and vaginal IgG and IgA, whereas subcutaneous delivery alone failed to induce vaginal IgA. The N-SliC-VLP with CpG (10 µg/dose) induced the most significant increase in total serum IgG and IgG3 titers, vaginal IgG and IgA, and bactericidal antibodies.

Characterization of exclusively non-commensal Neisseria gonorrhoeae pangenome to prioritize globally conserved and thermodynamically stable vaccine candidates using immune-molecular dynamic simulations

Neisseria gonorrhoeae (Ngo) has emerged as a global threat leading to one of the most common sexually transmitted diseases in the world. It has also become one of the leading antimicrobial resistant organisms, resulting in fewer treatment options and an increased morbidity. Therefore, in recent years, there has been an increased focus on the development of new treatments and preventive strategies to combat its infection. In this study, we have combined the most conserved epitopes from the completely assembled strains of Ngo to develop a universal and a thermodynamically stable vaccine candidate. For our vaccine design, the epitopes were selected for their high immunogenicity, non-allergenicity and non-cytotoxicity, making them the ideal candidates for vaccine development. For the screening process, several reverse vaccinology tools were employed to rigorously extract non-homologous and immunogenic epitopes from the selected proteins. Consequently, a total number of 3 B-cell epitopes and 6 T-cell epitopes were selected and joined by multiple immune-modulating adjuvants and linkers to generate a promiscuous immune response. Additionally, the stability and flexible nature of the vaccine construct was confirmed using various molecular dynamic simulation tools. Overall, the vaccine candidate showed promising binding affinity to various HLA alleles and TLR receptors; however, further studies are needed to assess its efficacy in-vivo. In this way, we have designed a multi-subunit vaccine candidate to potentially combat and control the spread of N. gonorrhoeae.

Th1-polarized MtrE-based gonococcal vaccines display prophylactic and therapeutic efficacy

ABSTRACTGlobal dissemination of high-level ceftriaxone-resistant Neisseria gonorrhoeae strains associated with the FC428 clone poses a threat to the efficacy ceftriaxone-based therapies. Vaccination is the best strategy to contain multidrug-resistant infections. In this study, we investigated the efficacy of MtrE and its surface Loop2 as vaccine antigens when combined with a Th1-polarizing adjuvant, which is expected to be beneficial for gonococcal vaccine development. Using in vitro dendritic cell maturation and T cell differentiation assays, CpG1826 was identified as the optimal Th1-polarizing adjuvant for MtrE and Loop2 displayed as linear epitope (Nloop2) or structural epitope (Intraloop2) on a carrier protein. Loop2-based antigens raised strongly Th1-polarized and bactericidal antibody responses in vaccinated mice. Furthermore, the vaccine formulations provided protection against a gonococcal challenge in mouse vaginal tract infection model when provided as prophylactic vaccines. Also, the vaccine formulations accelerated gonococcal clearance when provided as a single therapeutic dose to treat an already established infection, including against a strain associated with the FC428 clone. Therefore, this study demonstrated that MtrE and Loop 2 are effective gonococcal vaccine antigens when combined with the Th1-polarizing CpG1826 adjuvant.

Outer membrane vesicle-based intranasal vaccines

Delivery of vaccines via the mucosal route is regarded as the most effective mode of immunization to counteract infectious diseases that enter via mucosal tissues, including oral, nasal, pulmonary, intestinal, and urogenital surfaces. Mucosal vaccines not only induce local immune effector elements, such as secretory Immunoglobulin A (IgA) reaching the luminal site of the mucosa, but also systemic immunity. Moreover, mucosal vaccines may trigger immunity in distant mucosal tissues because of the homing of primed antigen-specific immune cells toward local and distant mucosal tissue via the common mucosal immune system. While most licensed intramuscular vaccines induce only systemic immunity, next-generation mucosal vaccines may outperform parenteral vaccination strategies by also eliciting protective mucosal immune responses that block infection and/or transmission. Especially the nasal route of vaccination, targeting the nasal-associated lymphoid tissue, is attractive for local and distant mucosal immunization. In numerous studies, bacterial outer membrane vesicles (OMVs) have proved attractive as vaccine platform for homologous bacterial strains, but also as antigen delivery platform for heterologous antigens of nonbacterial diseases, including viruses, parasites, and cancer. Their application has also been extended to mucosal delivery. Here, we will summarize the characteristics and clinical potential of (engineered) OMVs as vaccine platform for mucosal, especially intranasal delivery.

In vitro alternative for reactogenicity assessment of outer membrane vesicle based vaccines

Intrinsic or added immune activating molecules are key for most vaccines to provide desired immunity profiles but may increase systemic reactogenicity. Regulatory agencies require rabbit pyrogen testing (RPT) for demonstration of vaccine reactogenicity. Recently, the monocyte activation test (MAT) gained popularity as in vitro alternative, yet this assay was primarily designed to test pyrogen-free products. The aim was to adjust the MAT to enable testing of pyrogen containing vaccines in an early stage of development where no reference batch is yet available. The MAT and RPT were compared for assessing unknown safety profiles of pertussis outer membrane vesicle (OMV) vaccine candidates to those of Bexsero as surrogate reference vaccine. Pertussis OMVs with wild-type LPS predominantly activated TLR2 and TLR4 and were more reactogenic than Bexsero. However, this reactogenicity profile for pertussis OMVs could be equalized or drastically reduced compared to Bexsero or a whole-cell pertussis vaccine, respectively by dose changing, modifying the LPS, intranasal administration, or a combination of these. Importantly, except for LPS modified products, reactogenicity profiles obtained with the RPT and MAT were comparable. Overall, we demonstrated that this pertussis OMV vaccine candidate has an acceptable safety profile. Furthermore, the MAT proved its applicability to assess reactogenicity levels of pyrogen containing vaccines at multiple stages of vaccine development and could eventually replace rabbit pyrogen testing.

Vertebrate and Invertebrate Animal and New In Vitro Models for Studying Neisseria Biology

The history of Neisseria research has involved the use of a wide variety of vertebrate and invertebrate animal models, from insects to humans. In this review, we itemise these models and describe how they have made significant contributions to understanding the pathophysiology of Neisseria infections and to the development and testing of vaccines and antimicrobials. We also look ahead, briefly, to their potential replacement by complex in vitro cellular models.

Microencapsulated IL-12 Drives Genital Tract Immune Responses to Intranasal Gonococcal Outer Membrane Vesicle Vaccine and Induces Resistance to Vaginal Infection with Diverse Strains of Neisseria gonorrhoeae

An experimental gonococcal vaccine consisting of outer membrane vesicles (OMVs) and microsphere (ms)-encapsulated interleukin-12 (IL-12 ms) induces Th1-driven immunity, with circulating and genital antibodies to Neisseria gonorrhoeae, after intravaginal (i.vag.) administration in female mice, and generates resistance to vaginal challenge infection. Because i.vag. administration is inapplicable to males and may not be acceptable to women, we determined whether intranasal (i.n.) administration would generate protective immunity against N. gonorrhoeae. Female and male mice were immunized i.n. with gonococcal OMVs plus IL-12 ms or blank microspheres (blank ms). Responses to i.n. immunization were similar to those with i.vag. immunization, with serum IgG, salivary IgA, and vaginal IgG and IgA antigonococcal antibodies induced when OMVs were administered with IL-12 ms. Male mice responded with serum IgG and salivary IgA antibodies similarly to female mice. Gamma interferon (IFN-γ) production by CD4⁺ T cells from iliac lymph nodes was elevated after i.n. or i.vag. immunization with OMVs plus IL-12 ms. Female mice immunized with OMVs plus IL-12 ms by either route resisted challenge with N. gonorrhoeae to an equal extent, and resistance generated by i.n. immunization extended to heterologous strains of N. gonorrhoeae. Detergent-extracted OMVs, which have diminished lipooligosaccharide, generated protective immunity to challenge similar to native OMVs. OMVs from mutant N. gonorrhoeae, in which genes for Rmp and LpxL1 were deleted to eliminate the induction of blocking antibodies against Rmp and diminish lipooligosaccharide endotoxicity, also generated resistance to challenge infection similar to wild-type OMVs when administered i.n. with IL-12 ms. IMPORTANCE We previously demonstrated that female mice can be immunized intravaginally with gonococcal outer membrane vesicles (OMVs) plus microsphere (ms)-encapsulated interleukin-12 (IL-12 ms) to induce antigonococcal antibodies and resistance to genital tract challenge with live Neisseria gonorrhoeae. However, this route of vaccination may be impractical for human vaccine development and is inapplicable to males. Because intranasal immunization has previously been shown to induce antibody responses in both male and female genital tracts, we have evaluated this route of immunization with gonococcal OMVs plus IL-12 ms. In addition, we have refined the composition of gonococcal OMVs to reduce the endotoxicity of lipooligosaccharide and to eliminate the membrane protein Rmp, which induces countereffective blocking antibodies. The resulting vaccine may be more suitable for ultimate translation to human application against the sexually transmitted infection gonorrhea, which is becoming increasingly resistant to treatment with antibiotics.

Mechanisms of host manipulation by Neisseria gonorrhoeae

Neisseria gonorrhoeae (also known as gonococcus) has been causing gonorrhoea in humans since ancient Egyptian times. Today, global gonorrhoea infections are rising at an alarming rate, in concert with an increasing number of antimicrobial-resistant strains. The gonococcus has concurrently evolved several intricate mechanisms that promote pathogenesis by evading both host immunity and defeating common therapeutic interventions. Central to these adaptations is the ability of the gonococcus to manipulate various host microenvironments upon infection. For example, the gonococcus can survive within neutrophils through direct regulation of both the oxidative burst response and maturation of the phagosome; a concerning trait given the important role neutrophils have in defending against invading pathogens. Hence, a detailed understanding of how N. gonorrhoeae exploits the human host to establish and maintain infection is crucial for combating this pathogen. This review summarizes the mechanisms behind host manipulation, with a central focus on the exploitation of host epithelial cell signaling to promote colonization and invasion of the epithelial lining, the modulation of the host immune response to evade both innate and adaptive defenses, and the manipulation of host cell death pathways to both assist colonization and combat antimicrobial activities of innate immune cells. Collectively, these pathways act in concert to enable N. gonorrhoeae to colonize and invade a wide array of host tissues, both establishing and disseminating gonococcal infection.

The Potential Role of Vaccines in Preventing Antimicrobial Resistance (AMR): An Update and Future Perspectives

In the modern era, the consumption of antibiotics represents a revolutionary weapon against several infectious diseases, contributing to the saving of millions of lives worldwide. However, the misuse of antibiotics for human and animal purposes has fueled the process of antimicrobial resistance (AMR), considered now a global emergency by the World Health Organization (WHO), which significantly increases the mortality risk and related medical costs linked to the management of bacterial diseases. The current research aiming at developing novel efficient antibiotics is very challenging, and just a few candidates have been identified so far due to the difficulties connected with AMR. Therefore, novel therapeutic or prophylactic strategies to fight AMR are urgently needed. In this scenario, vaccines constitute a promising approach that proves to be crucial in preventing pathogen spreading in primary infections and in minimizing the usage of antibiotics following secondary bacterial infections. Unfortunately, most of the vaccines developed against the main resistant pathogens are still under preclinical and clinical evaluation due to the complexity of pathogens and technical difficulties. In this review, we describe not only the main causes of AMR and the role of vaccines in reducing the burden of infectious diseases, but we also report on specific prophylactic advancements against some of the main pathogens, focusing on new strategies that aim at improving vaccine efficiency.

Carriers and Antigens: New Developments in Glycoconjugate Vaccines

Glycoconjugate vaccines have proven their worth in the protection and prevention of infectious diseases. The introduction of the Haemophilus influenzae type b vaccine is the prime example, followed by other glycoconjugate vaccines. Glycoconjugate vaccines consist of two components: the carrier protein and the carbohydrate antigen. Current carrier proteins are tetanus toxoid, diphtheria toxoid, CRM197, Haemophilus protein D and the outer membrane protein complex of serogroup B meningococcus. Carbohydrate antigens have been produced mainly by extraction and purification from the original host. However, current efforts show great advances in the development of synthetically produced oligosaccharides and bioconjugation. This review evaluates the advances of glycoconjugate vaccines in the last five years. We focus on developments regarding both new carriers and antigens. Innovative developments regarding carriers are outer membrane vesicles, glycoengineered proteins, new carrier proteins, virus-like particles, protein nanocages and peptides. With regard to conjugated antigens, we describe recent developments in the field of antimicrobial resistance (AMR) and ESKAPE pathogens.

Production and purification of bacterial membrane vesicles for biotechnology applications: Challenges and opportunities

Bacterial membrane vesicles (BMVs) are bi-layered nanostructures derived from Gram-negative and Gram-positive bacteria. Among other pathophysiological roles, BMVs are critical messengers in intercellular communication. As a result, BMVs are emerging as a promising technology for the development of numerous therapeutic applications. Despite the remarkable progress in unveiling BMV biology and functions in recent years, their successful isolation and purification have been limited. Several challenges related to vesicle purity, yield, and scalability severely hamper the further development of BMVs for biotechnology and clinical applications. This review focuses on the current technologies and methodologies used in BMV production and purification, such as ultracentrifugation, density-gradient centrifugation, size-exclusion chromatography, ultrafiltration, and precipitation. We also discuss the current challenges related to BMV isolation, large-scale production, storage, and stability that limit their application. More importantly, the present work explains the most recent strategies proposed for overcoming those challenges. Finally, we summarize the ongoing applications of BMVs in the biotechnological field.

Insight into Prevention of Neisseria Gonorrhoeae: A Short Review

Neisseria gonorrhoeae (gonococcus) and Neisseria meningitidis (meningococcus) are important global pathogens which cause the sexually transmitted diseases gonorrhea and meningitis, respectively, as well as sepsis. We prepared a review according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA), with the aims of (a) evaluating the data on the MenB vaccination as protection against sexually transmitted infections by N. gonorrhoeae and (b) to briefly comment on the data of ongoing studies of new vaccines. We evaluated existing evidence on the effect of 4CMenB, a multi-component vaccine, on invasive diseases caused by different meningococcal serogroups and on gonorrhea. Non-B meningococcal serogroups showed that the 4CMenB vaccine could potentially offer some level of protection against non-B meningococcal serogroups and N. gonorrhoeae. The assessment of the potential protection conferred by 4CMenB is further challenged by the fact that further studies are still needed to fully understand natural immune responses against gonococcal infections. A further limitation could be the potential differences between the protection mechanisms against N. gonorrhoeae, which causes local infections, and the protection mechanisms against N. meningitidis, which causes systemic infections.

The Changes in Bacterial Microbiome Associated with Immune Disorder in Allergic Respiratory Disease

Allergic respiratory disease is a worldwide and increasingly prevalent health problem. Many researchers have identified complex changes in the microbiota of the respiratory and intestinal tracts in patients with allergic respiratory diseases. These affect immune response and influence the progression of disease. However, the diversity of bacterial changes in such cases make it difficult to identify a specific microorganism to target for adjustment. Recent research evidence suggests that common bacterial variations present in allergic respiratory disease are associated with immune disorders. This finding could lead to the discovery of potential therapeutic targets in cases of allergic respiratory disease. In this review, we summarize current knowledge of bacteria changes in cases of allergic respiratory disease, to identify changes commonly associated with immune disorders, and thus provide a theoretical basis for targeting therapies of allergic respiratory disease through effective modulation of key bacteria.

Listeria monocytogenes Infection Alters the Content and Function of Extracellular Vesicles Produced by Trophoblast Stem Cells

Placental immunity is critical for fetal health during pregnancy, as invading pathogens spread from the parental blood to the fetus through this organ. However, inflammatory responses in the placenta can adversely affect both the fetus and the pregnant person, and the balance between protective placental immune response and detrimental inflammation is poorly understood. Extracellular vesicles (EVs) are membrane-enclosed vesicles that play a critical role in placental immunity. EVs produced by placental trophoblasts mediate immune tolerance to the fetus and to the placenta itself, but these EVs can also activate detrimental inflammatory responses. The regulation of these effects is not well characterized, and the role of trophoblast EVs (tEVs) in the response to infection has yet to be defined. The Gram-positive bacterial pathogen Listeria monocytogenes infects the placenta, serving as a model to study tEV function in this context. We investigated the effect of L. monocytogenes infection on the production and function of tEVs, using a trophoblast stem cell (TSC) model. We found that tEVs from infected TSCs can induce the production of the proinflammatory cytokine tumor necrosis factor alpha (TNF-α) in recipient cells. Surprisingly, this tEV treatment could confer increased susceptibility to subsequent L. monocytogenes infection, which has not been reported previously as an effect of EVs. Proteomic analysis and RNA sequencing revealed that tEVs from infected TSCs had altered cargo compared with those from uninfected TSCs. However, no L. monocytogenes proteins were detected in tEVs from infected TSCs. Together, these results suggest an immunomodulatory role for tEVs during prenatal infection.

Intramyocardial Injection for the Study of Cardiac Lymphatic Function in Zebrafish

Zebrafish have proved to be an important model for studying cardiovascular formation and function during postembryonic development and regeneration. The present protocol describes a method for injecting fluorescent tracers into the zebrafish myocardium to study interstitial fluid and debris uptake into cardiac lymphatic vessels. To do so, microspheres (200 nm diameter) and quantum dots (<10 nm diameter) are introduced into the myocardium of live zebrafish, which can be tracked using ex vivo confocal microscopy. These tracers are then tracked intermittently over several hours to follow clearance from the myocardium into cardiac lymphatic vessels. Quantum dots are transported through cardiac lymphatic vessels away from the heart, while larger microspheres remain at the injection site for over three weeks. This method of intramyocardial injection can be extended to other uses, including the injection of encapsulated MS or hydrogels to locally release cells, proteins, or compounds of interest to a targeted region of the heart.

Validation of an FFF-MALS Method to Characterize the Production and Functionalization of Outer-Membrane Vesicles for Conjugate Vaccines

With the ongoing development of conjugate vaccines battling infectious diseases, there is a need for novel carriers. Although tetanus toxoid and CRM197 belong to the traditional carrier proteins, outer-membrane vesicles (OMVs) are an excellent alternative: in addition to their size, OMVs have self-adjuvanting properties due to the presence of genetically detoxified lipopolysaccharide (LPS) and are therefore ideal as a vaccine component or antigen carrier. An essential aspect of their development for vaccine products is characterization of OMVs with respect to size and purity. We report on the development of a field-flow fractionation multiangle light-scattering (FFF-MALS) method for such characterization. Here, we introduced NIST-traceable particle-size standards and BSA as a model protein to verify the precision of the size and purity analysis of the OMVs. We executed a validation program according to the principles provided in the ICH Guidelines Q2 (R1) to assess the quality attributes of the results obtained by FFF-MALS analysis. All validation characteristics showed excellent results with coefficients of variation between 0.4 and 7.32%. Estimation of limits of detection for hydrodynamic radius and particle concentration revealed that as little as 1 μg OMV still yielded accurate results. With the validated method, we further characterized a full downstream purification process of our proprietary OMV. This was followed by the evaluation of other purified OMVs from different bacterial origin. Finally, functionalizing OMVs with N-γ-(maleimidobutyryl)oxysuccinimide-ester (GMBS), generating ready-to-conjugate OMVs, did not affect the structural integrity of the OMVs and as such, they could be evaluated with the validated FFF-MALS method.

Infection With the US Neisseria meningitidis Urethritis Clade Does Not Lower Future Risk of Urethral Gonorrhea

BACKGROUND

Cross-protective immunity between Neisseria meningitidis (Nm) and Neisseria gonorrhoeae (Ng) may inform gonococcal vaccine development. Meningococcal serogroup B (MenB) outer membrane vesicle (OMV) vaccines confer modest protection against gonorrhea. However, whether urethral Nm infection protects against gonorrhea is unknown. We examined gonorrhea risk among men with US Nm urethritis clade (US_NmUC) infections.

METHODS

We conducted a retrospective cohort study of men with urethral US_NmUC (n = 128) between January 2015 and April 2018. Using diagnosis date as the baseline visit, we examined Ng status at return visits to compute urethral Ng risk. We compared these data to 3 referent populations: men with urethral Ng (n = 253), urethral chlamydia (Ct) (n = 251), and no urethral Ng or Ct (n = 255). We conducted sensitivity analyses to assess varied approaches to censoring, missing data, and anatomical site of infection. We also compared sequences of protein antigens in the OMV-based MenB-4C vaccine, US_NmUC, and Ng.

RESULTS

Participants were primarily Black (65%) and heterosexual (82%). Over follow-up, 91 men acquired urethral Ng. Men with urethral US_NmUC had similar Ng risk to men with prior urethral Ng (adjusted hazard ratio [aHR]: 1.27; 95% CI: .65-2.48). Men with urethral US_NmUC had nonsignificantly increased Ng risk compared with men with urethral Ct (aHR: 1.51; 95% CI: .79-2.88), and significantly increased Ng risk compared with men without urethral Ng or Ct (aHR: 3.55; 95% CI: 1.27-9.91). Most of the protein antigens analyzed shared high sequence similarity.

CONCLUSIONS

Urethral US_NmUC infection did not protect against gonorrhea despite substantial sequence similarities in shared protein antigens.

Engineered bacterial membrane vesicles are promising carriers for vaccine design and tumor immunotherapy

Bacterial membrane vesicles (BMVs) have emerged as novel and promising platforms for the development of vaccines and immunotherapeutic strategies against infectious and noninfectious diseases. The rich microbe-associated molecular patterns (MAMPs) and nanoscale membrane vesicle structure of BMVs make them highly immunogenic. In addition, BMVs can be endowed with more functions via genetic and chemical modifications. This article reviews the immunological characteristics and effects of BMVs, techniques for BMV production and modification, and the applications of BMVs as vaccines or vaccine carriers. In summary, given their versatile characteristics and immunomodulatory properties, BMVs can be used for clinical vaccine or immunotherapy applications.

Auranofin exerts antibacterial activity against Neisseria gonorrhoeae in a female mouse model of genital tract infection

Neisseria gonorrhoeae has been classified by the U.S. Centers for Disease Control and Prevention as an urgent threat due to the rapid development of antibiotic resistance to currently available antibiotics. Therefore, there is an urgent need to find new antibiotics to treat gonococcal infections. In our previous study, the gold-containing drug auranofin demonstrated potent in vitro activity against clinical isolates of N. gonorrhoeae, including multidrug-resistant strains. Therefore, the aim of this study was to investigate the in vivo activity of auranofin against N. gonorrhoeae using a murine model of vaginal infection. A significant reduction in N. gonorrhoeae recovered from the vagina was observed for infected mice treated with auranofin compared to the vehicle over the course of treatment. Relative to the vehicle, after three and five days of treatment with auranofin, a 1.04 (91%) and 1.40 (96%) average log10-reduction of recovered N. gonorrhoeae was observed. In conclusion, auranofin has the potential to be further investigated as a novel, safe anti-gonococcal agent to help meet the urgent need for new antimicrobial agents for N. gonorrhoeae infection.

The Role of IL-17 During Infections in the Female Reproductive Tract

Interleukin-17 (IL-17A) is a cytokine involved in a complex array of both protective and detrimental processes. Although early biological studies focused on the pro-inflammatory function of IL-17 in the context of autoimmune and inflammatory disorders, it has become increasingly evident that the roles of IL-17 are far more nuanced. Recent work has demonstrated that the functions of IL-17 are highly context- and tissue-dependent, and there is a fine balance between the pathogenic and protective functions of IL-17. This is especially evident in mucosal tissues such as the female reproductive tract, where IL-17 has been shown to play an important role in the immune response generated during fungal, bacterial and viral infections associated with protection, but also with inflammation. In this review, we discuss the evolving landscape of IL-17 biology within the context of the vaginal mucosa, focusing on key findings that highlight the importance of this cytokine in genital mucosal immunity.

Recent Progress Towards a Gonococcal Vaccine

Gonorrhea is a global health concern. Its etiological agent, Neisseria gonorrhoeae, rapidly acquires antimicrobial resistance and does not confer protective immunity as a consequence of infection. Attempts to generate an effective vaccine for gonorrhea have thus far been unsuccessful, as many structures on the bacterial envelope have the propensity to rapidly change, thus complicating recognition by the human immune system. In response to recent efforts from global health authorities to spur the efforts towards development of a vaccine, several new and promising steps have been made towards this goal, aided by advancements in computational epitope identification and prediction methods. Here, we provide a short review of recent progress towards a viable gonococcal vaccine, with a focus on antigen identification and characterization, and discuss a few of the tools that may be important in furthering these efforts.

Looking beyond meningococcal B with the 4CMenB vaccine: the Neisseria effect

Infections with Neisseria meningitidis and Neisseria gonorrhoeae have different clinical manifestations, but the bacteria share up to 80-90% genome sequence identity. The recombinant meningococcal serogroup B (MenB) vaccine 4CMenB consists of four antigenic components that can be present in non-B meningococcal and gonococcal strains. This comprehensive review summarizes scientific evidence on the genotypic and phenotypic similarities between vaccine antigens and their homologs expressed by non-B meningococcal and gonococcal strains. It also includes immune responses of 4CMenB-vaccinated individuals and effectiveness and impact of 4CMenB against these strains. Varying degrees of strain coverage were estimated depending on the non-B meningococcal serogroup and antigenic repertoire. 4CMenB elicits immune responses against non-B meningococcal serogroups and N. gonorrhoeae. Real-world evidence showed risk reductions of 69% for meningococcal serogroup W clonal complex 11 disease and 40% for gonorrhea after 4CMenB immunization. In conclusion, functional antibody activity and real-world evidence indicate that 4CMenB has the potential to provide some protection beyond MenB disease.

The potential utility of liposomes for Neisseria vaccines

INTRODUCTION

Species of the genus Neisseria are important global pathogens. Neisseria gonorrhoeae (gonococcus) causes the sexually transmitted disease gonorrhea and Neisseria meningitidis (meningococcus) causes meningitis and sepsis. Liposomes are self-assembled spheres of phospholipid bilayers enclosing a central aqueous space, and they have attracted much interest and use as a delivery vehicle for Neisseria vaccine antigens.

AREAS COVERED

A brief background on Neisseria infections and the success of licensed meningococcal vaccines are provided. The absence of a gonococcal vaccine is highlighted. The use of liposomes for delivering Neisseria antigens and adjuvants, for the purposes of generating specific immune responses, is reviewed. The use of other lipid-based systems for antigen and adjuvant delivery is examined briefly.

EXPERT OPINION

With renewed interest in developing a gonococcal vaccine, liposomes remain an attractive option for delivering antigens. The discipline of nanotechnology provides additional nanoparticle-based options for gonococcal vaccine development. Future work would be needed to tailor the composition of liposomes and other nanoparticles to the specific vaccine antigen(s), in order to generate optimal anti-gonococcal immune responses. The potential use of liposomes and other nanoparticles to deliver anti-gonococcal compounds to treat infections also should be explored further.

Meningococcal Detoxified Outer Membrane Vesicle Vaccines Enhance Gonococcal Clearance in a Murine Infection Model

BACKGROUND

Despite decades of research efforts, development of a gonorrhea vaccine has remained elusive. Epidemiological studies suggest that detoxified outer membrane vesicle (dOMV) vaccines from Neisseria meningitidis (Nm) may protect against infection with Neisseria gonorrhoeae (Ng). We recently reported that Nm dOMVs lacking the major outer membrane proteins (OMPs) PorA, PorB, and RmpM induced greater antibody cross-reactivity against heterologous Nm strains than wild-type (WT) dOMVs and may represent an improved vaccine against gonorrhea.

METHODS

We prepared dOMV vaccines from meningococcal strains that were sufficient or deleted for PorA, PorB, and RmpM. Vaccines were tested in a murine genital tract infection model and antisera were used to identify vaccine targets.

RESULTS

Immunization with Nm dOMVs significantly and reproducibly enhanced gonococcal clearance for mice immunized with OMP-deficient dOMVs; significant clearance for WT dOMV-immunized mice was observed in one of two experiments. Clearance was associated with serum and vaginal anti-Nm dOMV IgG antibodies that cross-reacted with Ng. Serum IgG was used to identify putative Ng vaccine targets, including PilQ, MtrE, NlpD, and GuaB.

CONCLUSIONS

Meningococcal dOMVs elicited a protective effect against experimental gonococcal infection. Recognition and identification of Ng vaccine targets by Nm dOMV-induced antibodies supports the development of a cross-protective Neisseria vaccine.

Recent advances in understanding and combatting Neisseria gonorrhoeae: a genomic perspective

The sexually transmitted infection (STI) gonorrhoea remains a major global public health concern. The World Health Organization (WHO) estimates that 87 million new cases in individuals who were 15 to 49 years of age occurred in 2016. The growing number of gonorrhoea cases is concerning given the rise in gonococci developing antimicrobial resistance (AMR). Therefore, a global action plan is needed to facilitate surveillance. Indeed, the WHO has made surveillance leading to the elimination of STIs (including gonorrhoea) a global health priority. The availability of whole genome sequence data offers new opportunities to combat gonorrhoea. This can be through (i) enhanced surveillance of the global prevalence of AMR, (ii) improved understanding of the population biology of the gonococcus, and (iii) opportunities to mine sequence data in the search for vaccine candidates. Here, we review the current status in Neisseria gonorrhoeae genomics. In particular, we explore how genomics continues to advance our understanding of this complex pathogen.

GMMA-Based Vaccines: The Known and The Unknown

Generalized Modules for Membrane Antigens (GMMA) are outer membrane vesicles derived from Gram-negative bacteria engineered to provide an over-vesiculating phenotype, which represent an attractive platform for the design of affordable vaccines. GMMA can be further genetically manipulated to modulate the risk of systemic reactogenicity and to act as delivery system for heterologous polysaccharide or protein antigens. GMMA are able to induce strong immunogenicity and protection in animal challenge models, and to be well-tolerated and immunogenic in clinical studies. The high immunogenicity could be ascribed to their particulate size, to their ability to present to the immune system multiple antigens in a natural conformation which mimics the bacterial environment, as well as to their intrinsic self-adjuvanticity. However, GMMA mechanism of action and the role in adjuvanticity are still unclear and need further investigation. In this review, we discuss progresses in the development of the GMMA vaccine platform, highlighting successful applications and identifying knowledge gaps and potential challenges.

Immune Responses to Neisseria gonorrhoeae: Challenges and Opportunities With Respect to Pelvic Inflammatory Disease

Pelvic inflammatory disease and infertility frequently develop after female genital tract infection with Neisseria gonorrhoeae, but determining their etiology from among various possibilities presents difficulties. Exploitation of serology to identify the causative agent is complicated by numerous factors, and no immunological test currently exists to determine unequivocally whether an individual currently is, or has been, infected with N. gonorrhoeae. The extensive antigenic variability of N. gonorrhoeae and its expression of antigens shared with other Neisseria species commonly carried in humans render problematic an assay that is specific for all gonococcal strains. However, novel conserved gonococcal antigens identified for potential vaccines may find additional application in diagnostic assays. N. gonorrhoeae also interferes with the adaptive immune response, and antibody responses to uncomplicated infection are usually weak. Elucidating the mechanisms whereby N. gonorrhoeae manipulates the human immune system may lead to improved understanding of the pathogenesis of pelvic inflammatory disease and infertility.

Preclinical Testing of Vaccines and Therapeutics for Gonorrhea in Female Mouse Models of Lower and Upper Reproductive Tract Infection

Murine models of Neisseria gonorrhoeae lower reproductive tract infection are valuable systems for studying N. gonorrhoeae adaptation to the female host and immune responses to infection. These models have also accelerated preclinical testing of candidate therapeutic and prophylactic products against gonorrhea. However, because N. gonorrhoeae infection is restricted to the murine cervicovaginal region, there is a need for an in vivo system for translational work on N. gonorrhoeae pelvic inflammatory disease (PID). Here we discuss the need for well-characterized preclinical upper reproductive tract infection models for developing candidate products against N. gonorrhoeae PID, and report a refinement of the gonorrhea mouse model that supports sustained upper reproductive tract infection. To establish this new model for vaccine testing, we also tested the licensed meningococcal 4CMenB vaccine, which cross-protects against murine N. gonorrhoeae lower reproductive tract infection, for efficacy against N. gonorrhoeae in the endometrium and oviducts following transcervical or vaginal challenge.

Pelvic Inflammatory Disease Due to Neisseria gonorrhoeae and Chlamydia trachomatis: Immune Evasion Mechanisms and Pathogenic Disease Pathways

Pelvic inflammatory disease (PID) results from ascension of sexually transmitted pathogens from the lower genital tract to the uterus and/or fallopian tubes in women, with potential spread to neighboring pelvic organs. Patients may present acutely with lower abdominal or pelvic pain and pelvic organ tenderness. Many have subtle symptoms or are asymptomatic and present later with tubal factor infertility, ectopic pregnancy, or chronic pelvic pain. Neisseria gonorrhoeae and Chlamydia trachomatis are the 2 most commonly recognized PID pathogens. Their ability to survive within host epithelial cells and neutrophils highlights a need for T-cell-mediated production of interferon γ in protection. Data indicate that for both pathogens, antibody can accelerate clearance by enhancing opsonophagocytosis and bacterial killing when interferon γ is present. A study of women with N. gonorrhoeae- and/or C. trachomatis-induced PID with histologic endometritis revealed activation of myeloid cell, cell death, and innate inflammatory pathways in conjunction with dampening of T-cell activation pathways. These findings are supported by multiple studies in mouse models of monoinfection with N. gonorrhoeae or Chlamydia spp. Both pathogens exert multiple mechanisms of immune evasion that benefit themselves and each other at the expense of the host. However, similarities in host immune mechanisms that defend against these 2 bacterial pathogens instill optimism for the prospects of a combined vaccine for prevention of PID and infections in both women and men.

Vaccine Candidates for the Control and Prevention of the Sexually Transmitted Disease Gonorrhea

The World Health Organization (WHO) has placed N. gonorrhoeae on the global priority list of antimicrobial resistant pathogens and is urgently seeking the development of new intervention strategies. N. gonorrhoeae causes 86.9 million cases globally per annum. The effects of gonococcal disease are seen predominantly in women and children and especially in the Australian Indigenous community. While economic modelling suggests that this infection alone may directly cost the USA health care system USD 11.0–20.6 billion, indirect costs associated with adverse disease and pregnancy outcomes, disease prevention, and productivity loss, mean that the overall effect of the disease is far greater still. In this review, we summate the current progress towards the development of a gonorrhea vaccine and describe the clinical trials being undertaken in Australia to assess the efficacy of the current formulation of Bexsero^® in controlling disease.

Planning for a Gonococcal Vaccine: A Narrative Review of Vaccine Development and Public Health Implications

ABSTRACT

Declining gonococcal susceptibility to ceftriaxone and azithromycin has raised the possibility of untreatable gonorrhea in the future and reignited interest in gonococcal vaccine development. Despite decades of research, previous gonococcal vaccine candidates have been ineffective. A growing body of data suggests that meningococcal group B outer-membrane vaccines may be cross-protective against Neisseria gonorrhoeae. Clinical trials of a licensed vaccine against Neisseria meningitidis serogroup B containing an outer-membrane vaccine component are underway to determine its efficacy against N. gonorrhoeae. Other experimental gonococcal vaccine candidates are in the preclinical phases. Population impact of future gonococcal vaccines with different levels of efficacy and duration of protection in various populations is being evaluated using modeling studies. Despite recent progress, gaps in gonococcal vaccine research remain. Research is needed to evaluate vaccine efficacy in preventing gonococcal infections acquired via various anatomic routes and among patients coinfected with other sexually transmitted infections. Studies that model the impact of a future vaccine on high-burden populations such as men who have sex with men and estimate both vaccine cost-effectiveness and the incremental cost-effectiveness ratio of vaccination to antimicrobial resistance and treatment costs are warranted. This narrative review examines the current state of gonococcal vaccine research, the possible impact of a gonococcal vaccine on gonorrhea rates based on modeling studies, gaps in the gonococcal vaccine literature, and public health implications of a future gonococcal vaccine on reducing the gonorrhea burden in the United States.