Profiling IgG and IgA antibody responses during vaccination and infection in a high-risk gonorrhoea population.

Development of a vaccine against gonorrhoea is a global priority, driven by the rise in antibiotic resistance. Although Neisseria gonorrhoeae (Ng) infection does not induce substantial protective immunity, highly exposed individuals may develop immunity against re-infection with the same strain. Retrospective epidemiological studies have shown that vaccines containing Neisseria meningitidis (Nm) outer membrane vesicles (OMVs) provide a degree of cross-protection against Ng infection. We conducted a clinical trial (NCT04297436) of 4CMenB (Bexsero, GSK), a licensed Nm vaccine containing OMVs and recombinant antigens, comprising a single arm, open label study of two doses with 50 adults in coastal Kenya who have high exposure to Ng. Data from a Ng antigen microarray established that serum IgG and IgA reactivities against the gonococcal homologs of the recombinant antigens in the vaccine peaked at 10 but had declined by 24 weeks. For most reactive OMV-derived antigens, the reverse was the case. A cohort of similar individuals with laboratory-confirmed gonococcal infection were compared before, during, and after infection: their reactivities were weaker and differed from the vaccinated cohort. We conclude that the cross-protection of the 4CMenB vaccine against gonorrhoea could be explained by cross-reaction against a diverse selection of antigens derived from the OMV component.

Dual species transcriptomics reveals conserved metabolic and immunologic processes in interactions between human neutrophils and Neisseria gonorrhoeae.

Neisseria gonorrhoeae (the gonococcus, Gc) causes the sexually transmitted infection gonorrhea. Gc is a prominent threat to human health by causing severe lifelong sequelae, including infertility and chronic pelvic pain, which is amplified by the emergence of "superbug" strains resistant to all current antibiotics. Gc is highly adapted to colonize human mucosal surfaces, where it survives despite initiating a robust inflammatory response and influx of polymorphonuclear leukocytes (PMNs, neutrophils) that typically clear bacteria. Here, dual-species RNA-sequencing was used to define Gc and PMN transcriptional profiles alone and after infection. Core host and bacterial responses were assessed for two strains of Gc and three human donors' PMNs. Comparative analysis of Gc transcripts revealed overlap between Gc responses to PMNs, iron, and hydrogen peroxide; 98 transcripts were differentially expressed across both Gc strains in response to PMN co-culture, including iron-responsive and oxidative stress response genes. We experimentally determined that the iron-dependent TbpB is suppressed by PMN co-culture, and iron-limited Gc have a survival advantage when cultured with PMNs. Analysis of PMN transcripts modulated by Gc infection revealed differential expression of genes driving cell adhesion, migration, inflammatory responses, and inflammation resolution pathways. Production of pro-inflammatory cytokines, including IL1B and IL8, the adhesion factor ICAM1, and prostaglandin PGE2 were induced in PMNs in response to Gc. Together, this study represents a comprehensive and experimentally validated dual-species transcriptomic analysis of two isolates of Gc and primary human PMNs that gives insight into how this bacterium survives innate immune onslaught to cause disease.

4CMenB journey to the 10-year anniversary and beyond.

The 4-component meningococcal serogroup B (MenB) vaccine, 4CMenB, the first broadly protective, protein-based MenB vaccine to be licensed, is now registered in more than 50 countries worldwide. Real-world evidence (RWE) from the last decade confirms its effectiveness and impact, with infant immunization programs showing vaccine effectiveness of 71-95% against invasive MenB disease and cross-protection against non-B serogroups, including a 69% decrease in serogroup W cases in 4CMenB-eligible cohorts in England. RWE from different countries also demonstrates the potential for additional moderate protection against gonorrhea in adolescents. The real-world safety profile of 4CMenB is consistent with prelicensure reports. Use of the endogenous complement human serum bactericidal antibody (enc-hSBA) assay against 110 MenB strains may enable assessment of the immunological effectiveness of multicomponent MenB vaccines in clinical trial settings. Equitable access to 4CMenB vaccination is required to better protect all age groups, including older adults, and vulnerable groups through comprehensive immunization policies.

Invasive meningococcal disease, caused by the bacterium Neisseria meningitidis(meningococcus), is rare but often devastating and can be deadly. Effective vaccines are available, including vaccines against meningococcal serogroup B disease. In 2013, the 4-component meningococcal serogroup B vaccine, 4CMenB, became the first broadly protective, protein-based vaccine against serogroup B to be licensed, with the second (bivalent vaccine, MenB-FHbp) licensed the following year. 4CMenB is now registered in more than 50 countries, in the majority, for infants and all age groups. In the US, it is approved for individuals aged 10­25 years. Evidence from immunization programs in the last decade, comparing vaccinated and unvaccinated individuals and the same population before and after vaccination, confirms the effectiveness and positive impact of 4CMenB against serogroup B disease. This also demonstrates that 4CMenB can provide protection against invasive diseases caused by other meningococcal serogroups. Furthermore, N. meningitidis is closely related to the bacterium that causes gonorrhea, N. gonorrhoeae, and emerging real-world evidence suggests that 4CMenB provides additional moderate protection against gonococcal disease. The safety of 4CMenB when given to large numbers of infants, children, adolescents, and adults is consistent with the 4CMenB safety profile reported before licensure.For the future, it would be beneficial to address differences among national guidelines for the recommended administration of 4CMenB, particularly where there is supportive epidemiological evidence but no equitable access to vaccination. New assays for assessing the potential effectiveness of meningococcal serogroup B vaccines in clinical trials are also required because serogroup B strains circulating in the population are extremely diverse across different countries.

IL-17C is a driver of damaging inflammation during Neisseria gonorrhoeae infection of human Fallopian tube.

The human pathogen Neisseria gonorrhoeae ascends into the upper female reproductive tract to cause damaging inflammation within the Fallopian tubes and pelvic inflammatory disease (PID), increasing the risk of infertility and ectopic pregnancy. The loss of ciliated cells from the epithelium is thought to be both a consequence of inflammation and a cause of adverse sequelae. However, the links between infection, inflammation, and ciliated cell extrusion remain unresolved. With the use of ex vivo cultures of human Fallopian tube paired with RNA sequencing we defined the tissue response to gonococcal challenge, identifying cytokine, chemokine, cell adhesion, and apoptosis related transcripts not previously recognized as potentiators of gonococcal PID. Unexpectedly, IL-17C was one of the most highly induced genes. Yet, this cytokine has no previous association with gonococcal infection nor pelvic inflammatory disease and thus it was selected for further characterization. We show that human Fallopian tubes express the IL-17C receptor on the epithelial surface and that treatment with purified IL-17C induces pro-inflammatory cytokine secretion in addition to sloughing of the epithelium and generalized tissue damage. These results demonstrate a previously unrecognized but critical role of IL-17C in the damaging inflammation induced by gonococci in a human explant model of PID.

Characterization of Neisseria gonorrhoeae colonization of macrophages under distinct polarization states and nutrients environment.

Neisseria gonorrhoeae (Ng) is a uniquely adapted human pathogen and the etiological agent of gonorrhea, a sexually transmitted disease. Ng has developed numerous mechanisms to avoid and actively suppress innate and adaptive immune responses. Ng successfully colonizes and establishes topologically distinct colonies in human macrophages and avoids phagocytic killing. During colonization, Ng manipulates the actin cytoskeleton to invade and create an intracellular niche supportive of bacterial replication. The cellular reservoir(s) supporting bacterial replication and persistence in gonorrhea infections are poorly defined. The manner in which gonococci colonize macrophages points to this innate immune phagocyte as a strong candidate for a cellular niche during natural infection. Here we investigate whether nutrients availability and immunological polarization alter macrophage colonization by Ng. Differentiation of macrophages in pro-inflammatory (M1-like) and tolerogenic (M2-like) phenotypes prior to infection reveals that Ng can invade macrophages in all activation states, albeit with lower efficiency in M1-like macrophages. These results suggest that during natural infection, bacteria could invade and grow within macrophages regardless of the nutrients availability and the macrophage immune activation status.

Neisseria gonorrhoeae scavenges host sialic acid for Siglec-mediated, complement-independent suppression of neutrophil activation.

Gonorrhea, caused by the bacterium Neisseria gonorrhoeae (Gc), is characterized by neutrophilic influx to infection sites. Gc has developed mechanisms to resist killing by neutrophils that include modifications to its surface lipooligosaccharide (LOS). One such LOS modification is sialylation: Gc sialylates its terminal LOS sugars with cytidine-5'-monophosphate-N-acetylneuraminic acid, which is scavenged from the host using LOS sialyltransferase (Lst) since Gc cannot make its sialic acid. Sialylation enables sensitive strains of Gc to resist complement-mediated killing in a serum-dependent manner. However, little is known about the contribution of sialylation to complement-independent, direct Gc-neutrophil interactions. In the absence of complement, we found sialylated Gc expressing opacity-associated (Opa) proteins decreased the oxidative burst and granule exocytosis from primary human neutrophils. In addition, sialylated Opa+ Gc survived better than vehicle treated or Δlst Gc when challenged with neutrophils. However, Gc sialylation did not significantly affect Opa-dependent association with or internalization of Gc by neutrophils. Previous studies have implicated sialic acid-binding immunoglobulin-type lectins (Siglecs) in modulating neutrophil interactions with sialylated Gc. Blocking neutrophil Siglecs with antibodies that bind to their extracellular domains eliminated the ability of sialylated Opa+ Gc to suppress the oxidative burst and resist neutrophil killing. These findings highlight a new role for sialylation in Gc evasion of human innate immunity, with implications for the development of vaccines and therapeutics for gonorrhea. IMPORTANCE: Neisseria gonorrhoeae, the bacterium that causes gonorrhea, is an urgent global health concern due to increasing infection rates, widespread antibiotic resistance, and its ability to thwart protective immune responses. The mechanisms by which Gc subverts protective immune responses remain poorly characterized. One way N. gonorrhoeae evades human immunity is by adding sialic acid that is scavenged from the host onto its lipooligosaccharide, using the sialyltransferase Lst. Here, we found that sialylation enhances N. gonorrhoeae survival from neutrophil assault and inhibits neutrophil activation, independently of the complement system. Our results implicate bacterial binding of sialic acid-binding lectins (Siglecs) on the neutrophil surface, which dampens neutrophil antimicrobial responses. This work identifies a new role for sialylation in protecting N. gonorrhoeae from cellular innate immunity, which can be targeted to enhance the human immune response in gonorrhea.

Review of mathematical models of Neisseria gonorrhoeae vaccine impact: Implications for vaccine development.

An effective prophylactic vaccine for prevention of Neisseria gonorrhoeae infection would have a major impact on sexual and reproductive health worldwide. Interest in developing gonorrhoea vaccines is growing due to the reported high rates of N. gonorrhoeae infections globally, and the threat of antimicrobial resistance. Several gonorrhoea vaccine candidates are currently under evaluation and various mathematical models have been used to assess the potential population-level impact a gonorrhoea vaccine may have once available. Here we review key aspects of gonorrhoea vaccine mathematical modelling studies, including model structures, populations considered, and assumptions used as well as vaccine characteristics and implementation scenarios investigated. The predicted vaccine impact varied between studies, ranging from as little as ∼17 % reduction in N. gonorrhoeae prevalence after 30 years up to 100 % reduction after 5 years. However, all studies predicted that even a partially effective gonorrhoea vaccine could have a substantial impact in reducing N. gonorrhoeae prevalence or incidence, particularly when high coverage is achieved within either important risk groups or the overall sexually active population. As expected, higher vaccine efficacy against acquisition of N. gonorrhoeae and longer duration of protection were linked to greater reductions in infections. A vaccine that alters onward transmission could also substantially reduce infections. Several gaps and research needs have been identified by researchers in the field and via this narrative literature review. For example, future modelling to inform gonorrhoea vaccine development and implementation should consider additional populations that are at high risk of N. gonorrhoeae infection, especially in low- and middle-income settings, as well as the impact of vaccination on the potential adverse sexual and reproductive health outcomes of infection. In addition, more detailed and robust epidemiological, biological, and behavioural data is needed to enable more accurate and robust modelling of gonorrhoea vaccine impact to inform future scientific and public health decision-making.

Synthetic DNA Delivery of an Optimized and Engineered Monoclonal Antibody Provides Rapid and Prolonged Protection against Experimental Gonococcal Infection.

Monoclonal antibody (MAb) 2C7 recognizes a lipooligosaccharide epitope expressed by most clinical Neisseria gonorrhoeae isolates and mediates complement-dependent bactericidal activity. We recently showed that a recombinant human IgG1 chimeric variant of MAb 2C7 containing an E430G Fc modification (2C7_E430G), which enhances complement activation, outperformed the parental MAb 2C7 (2C7_WT) in vivo Because natural infection with N. gonorrhoeae often does not elicit protective immunity and reinfections are common, approaches that prolong bacterial control in vivo are of great interest. Advances in DNA-based approaches have demonstrated the combined benefit of genetic engineering, formulation optimizations, and facilitated delivery via CELLECTRA-EP technology, which can induce robust in vivo expression of protective DNA-encoded monoclonal antibodies (DMAbs) with durable serum activity relative to traditional recombinant MAb therapies. Here, we created optimized 2C7-derived DMAbs encoding the parental Fc (2C7_WT) or complement-enhancing Fc variants (2C7_E430G and 2C7_E345K). 2C7 DMAbs were rapidly generated and detected throughout the 4-month study. While all complement-engaging 2C7 variants facilitated rapid clearance following primary N. gonorrhoeae challenge (day 8 after DMAb administration), the complement-enhancing 2C7_E430G variant demonstrated significantly higher potency against mice rechallenged 65 days after DMAb administration. Passive intravenous transfer of in vivo-produced, purified 2C7 DMAbs confirmed the increased potency of the complement-enhancing variants. This study highlights the ability of the DMAb platform to launch the in vivo production of antibodies engineered to promote and optimize downstream innate effector mechanisms such as complement-mediated killing, leading to hastened bacterial elimination.IMPORTANCENeisseria gonorrhoeae has become resistant to most antibiotics in clinical use. Currently, there is no safe and effective vaccine against gonorrhea. Measures to prevent the spread of gonorrhea are a global health priority. A monoclonal antibody (MAb) called 2C7, directed against a lipooligosaccharide glycan epitope expressed by most clinical isolates, displays complement-dependent bactericidal activity and hastens clearance of gonococcal vaginal colonization in mice. Fc mutations in a human IgG1 chimeric version of MAb 2C7 further enhance complement activation, and the resulting MAb displays greater activity than wild-type MAb 2C7 in vivo Here, we utilized a DNA-encoded MAb (DMAb) construct designed to launch production and assembly of "complement-enhanced" chimeric MAb 2C7 in vivo The ensuing rapid and sustained MAb 2C7 expression attenuated gonococcal colonization in mice at 8 days as well as 65 days postadministration. The DMAb system may provide an effective, economical platform to deliver MAbs for durable protection against gonorrhea.

Human endometrial MAIT cells are transiently tissue resident and respond to Neisseria gonorrhoeae.

Mucosa-associated invariant T (MAIT) cells are non-classical T cells important in the mucosal defense against microbes. Despite an increasing interest in the immunobiology of the endometrial mucosa, little is known regarding human MAIT cells in this compartment. The potential role of MAIT cells as a tissue-resident local defense against microbes in the endometrium is largely unexplored. Here, we performed a high-dimensional flow cytometry characterization of MAIT cells in endometrium from pre- and postmenopausal women, and in decidua from first-trimester pregnancies. Furthermore, we assessed MAIT cell function by stimulation with Neisseria gonorrhoeae (N. gonorrhoeae). Endometrial MAIT (eMAIT) cells represented a stable endometrial immune cell population as limited dynamic changes were observed during the menstrual cycle, post menopause, or in response to pregnancy. Furthermore, eMAIT cells exhibited an activated tissue-resident phenotype. Despite expressing CD69 and CD103, eMAIT cells were replenished over time by circulating MAIT cells, as assessed using human uterus transplantation as a model. Finally, functional experiments revealed the capability of MAIT cells to respond to the sexually transmitted and tissue-relevant pathogen, N. gonorrhoeae. In conclusion, our study provides novel insight into human MAIT cell dynamics and anti-microbial properties in the human uterus.

The serogroup B meningococcal outer membrane vesicle-based vaccine 4CMenB induces cross-species protection against Neisseria gonorrhoeae.

There is a pressing need for a gonorrhea vaccine due to the high disease burden associated with gonococcal infections globally and the rapid evolution of antibiotic resistance in Neisseria gonorrhoeae (Ng). Current gonorrhea vaccine research is in the stages of antigen discovery and the identification of protective immune responses, and no vaccine has been tested in clinical trials in over 30 years. Recently, however, it was reported in a retrospective case-control study that vaccination of humans with a serogroup B Neisseria meningitidis (Nm) outer membrane vesicle (OMV) vaccine (MeNZB) was associated with reduced rates of gonorrhea. Here we directly tested the hypothesis that Nm OMVs induce cross-protection against gonorrhea in a well-characterized female mouse model of Ng genital tract infection. We found that immunization with the licensed Nm OMV-based vaccine 4CMenB (Bexsero) significantly accelerated clearance and reduced the Ng bacterial burden compared to administration of alum or PBS. Serum IgG and vaginal IgA and IgG that cross-reacted with Ng OMVs were induced by 4CMenB vaccination by either the subcutaneous or intraperitoneal routes. Antibodies from vaccinated mice recognized several Ng surface proteins, including PilQ, BamA, MtrE, NHBA (known to be recognized by humans), PorB, and Opa. Immune sera from both mice and humans recognized Ng PilQ and several proteins of similar apparent molecular weight, but MtrE was only recognized by mouse serum. Pooled sera from 4CMenB-immunized mice showed a 4-fold increase in serum bactericidal50 titers against the challenge strain; in contrast, no significant difference in bactericidal activity was detected when sera from 4CMenB-immunized and unimmunized subjects were compared. Our findings directly support epidemiological evidence that Nm OMVs confer cross-species protection against gonorrhea, and implicate several Ng surface antigens as potentially protective targets. Additionally, this study further defines the usefulness of murine infection model as a relevant experimental system for gonorrhea vaccine development.

Inhibition of TLR2/TLR4 alleviates the Neisseria gonorrhoeae infection damage in human endometrial epithelial cells via Nrf2 and NF-Kßsignaling.

BACKGROUND: Neisseria gonorrhoeae (N.g) is Gram-negative bacteria and can lead to endometritis in female. Toll-like receptors regulate immune response in various diseases. However, the roles of TLR2 and TLR4 in. Neisseria gonorrhoeae-induced infection damage in human endometrial epithelia were investigated. METHODS: hEECs were infected with N.g (MOI 10 and 100) and cell viability and apoptosis were measured by CCK8 and flow cytometry assays in both infected groups with the uninfected normal hEECs as negative control. TLR2/TLR4 proteins were measured by ELISA method. Pro-inflammatory markers NLRP3, PGES (PGE2) and TNF-α were assessed by RT-qPCR (mRNA expression) and Elisa (protein concentrations). Transfection assays were performed to up- or down- regulate expression of TLR2 and TLR4 so as to study the functions of TLR2/TLR4 in. N.g-infected hEECs, followed by apoptosis and inflammation assessment. Similarly, we explored the interactions between TLR2/TLR4 and Nrf2/NF-κB/p65 by knocking down TLR2/TLR4 to detect the signaling and further regulating the signaling to evaluate TLR2/ TLR4, apoptosis and inflammation in cells. RESULTS: N.g suppressed cell viabilities and induced cell apoptosis and inflammation. TLR2/TLR4 downregulation inhibited the infection damage. Nrf2 was activated while NF-κB/p65 was depleted as TLR2/ TLR4 was knocked down. Activation of Nrf2 and inhibition of NF-κB resulted in decrease of TLR2/TLR4, which could retard apoptosis and inflammation induced by N.g infection. CONCLUSION: TLR2/TLR4 depletion could alleviate the N.g-infected hEECs via Nrf2/NF-kB signaling, suggesting that TLR2/TLR4 inhibitors might serve as a treatment to reduce N.g infection in human endometrial epithelia.

Modulation of phagocytosis-induced cell death of human neutrophils by Neisseria gonorrhoeae.

Optimal innate immune response to infection includes eradication of potential pathogens, resolution of associated inflammation, and restitution of homeostasis. Phagocytosing human polymorphonuclear leukocytes (hPMN) undergo accelerated apoptosis, a process referred to as phagocytosis-induced cell death (PICD) and an early step in their clearance from inflammatory sites. Among human pathogens that modulate hPMN apoptosis, Neisseria gonorrhoeae delays PICD, which may contribute to the exuberant neutrophilic inflammation that characterizes gonorrhea. To elucidate the mechanisms underlying delayed PICD, we compared features of hPMN cell death that followed phagocytosis of N. gonorrhoeae FA1090 wild-type (GC) or serum-opsonized zymosan (OPZ), a prototypical stimulus of PICD. Phosphatidylserine externalization required NADPH oxidase activity after ingestion of GC or OPZ, and annexin V staining and DNA fragmentation were less after phagocytosis of GC compared to OPZ. Caspase 3/7 and caspase 9 activities after phagocytosis of GC were less than that seen after ingestion of OPZ, but caspase 8 activity was the same after ingestion of GC or OPZ. When hPMN sequentially ingested GC followed by OPZ, both caspase 3/7 and 9 activities were less than that seen after OPZ alone, and the inhibition was dose dependent for GC, suggesting that ingestion of GC actively inhibited PICD. Sequential phagocytosis did not block caspase 8 activity, mitochondrial depolarization, or annexin V/propidium iodide staining compared to responses of hPMN fed OPZ alone, despite inhibition of caspases 3/7 and 9. Taken together, these data suggest that active inhibition of the intrinsic pathway of apoptosis contributes to the delay in PICD after hPMN ingestion of N. gonorrhoeae.

Complement interactions with the pathogenic Neisseriae: clinical features, deficiency states, and evasion mechanisms.

Neisseria gonorrhoeae causes the sexually transmitted infection gonorrhea, while Neisseria meningitidis is an important cause of bacterial meningitis and sepsis. Complement is a central arm of innate immune defenses and plays an important role in combating Neisserial infections. Persons with congenital and acquired defects in complement are at a significantly higher risk for invasive Neisserial infections such as invasive meningococcal disease and disseminated gonococcal infection compared to the general population. Of note, Neisseria gonorrhoeae and Neisseria meningitidis can only infect humans, which in part may be related to their ability to evade only human complement. This review summarizes the epidemiologic and clinical aspects of Neisserial infections in persons with defects in the complement system. Mechanisms used by these pathogens to subvert killing by complement and preclinical studies showing how these complement evasion strategies may be used to counteract the global threat of meningococcal and gonococcal infections are discussed.

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.

Preclinical Efficacy of a Lipooligosaccharide Peptide Mimic Candidate Gonococcal Vaccine.

The global spread of multidrug-resistant strains of Neisseria gonorrhoeae constitutes a public health emergency. With limited antibiotic treatment options, there is an urgent need for development of a safe and effective vaccine against gonorrhea. Previously, we constructed a prototype vaccine candidate comprising a peptide mimic (mimitope) of a glycan epitope on gonococcal lipooligosaccharide (LOS), recognized by monoclonal antibody 2C7. The 2C7 epitope is (i) broadly expressed as a gonococcal antigenic target in human infection, (ii) a critical requirement for gonococcal colonization in the experimental setting, and (iii) a virulence determinant that is maintained and expressed by gonococci. Here, we have synthesized to >95% purity through a relatively facile and economical process a tetrapeptide derivative of the mimitope that was cyclized through a nonreducible thioether bond, thereby rendering the compound homogeneous and stable. This vaccine candidate, called TMCP2, when administered at 0, 3, and 6 weeks to BALB/c mice at either 50, 100 or 200 µg/dose in combination with glucopyranosyl lipid A-stable oil-in-water nanoemulsion (GLA-SE; a Toll-like receptor 4 and TH1-promoting adjuvant), elicited bactericidal IgG and reduced colonization levels of gonococci in experimentally infected mice while accelerating clearance by each of two different gonococcal strains. Similarly, a 3-dose biweekly schedule (50 µg TMCP2/dose) was also effective in mice. We have developed a gonococcal vaccine candidate that can be scaled up and produced economically to a high degree of purity. The candidate elicits bactericidal antibodies and is efficacious in a preclinical experimental infection model.IMPORTANCENeisseria gonorrhoeae has become resistant to most antibiotics. The incidence of gonorrhea is also sharply increasing. A safe and effective antigonococcal vaccine is urgently needed. Lipooligosaccharide (LOS), the most abundant outer membrane molecule, is indispensable for gonococcal pathogenesis. A glycan epitope on LOS that is recognized by monoclonal antibody (MAb) 2C7 (called the 2C7 epitope) is expressed almost universally by gonococci in vivo Previously, we identified a peptide mimic (mimitope) of the 2C7 epitope, which when configured as an octamer and used as an immunogen, attenuated colonization of mice by gonococci. Here, a homogenous, stable tetrameric derivative of the mimitope, when combined with a TH1-promoting adjuvant and used as an immunogen, also effectively attenuates gonococcal colonization of mice. This candidate peptide vaccine can be produced economically, an important consideration for gonorrhea, which affects socioeconomically underprivileged populations disproportionately, and represents an important advance in the development of a gonorrhea vaccine.

C4BP-IgM protein as a therapeutic approach to treat Neisseria gonorrhoeae infections.

Gonorrhea is a sexually transmitted infection with 87 million new cases per year globally. Increasing antibiotic resistance has severely limited treatment options. A mechanism that Neisseria gonorrhoeae uses to evade complement attack is binding of the complement inhibitor C4b-binding protein (C4BP). We screened 107 porin B1a (PorB1a) and 83 PorB1b clinical isolates randomly selected from a Swedish strain collection over the last 10 years and noted that 96/107 (89.7%) PorB1a and 16/83 (19.3%) PorB1b bound C4BP; C4BP binding substantially correlated with the ability to evade complement-dependent killing (r = 0.78). We designed 2 chimeric proteins that fused C4BP domains to the backbone of IgG or IgM (C4BP-IgG; C4BP-IgM) with the aim of enhancing complement activation and killing of gonococci. Both proteins bound gonococci (KD C4BP-IgM = 2.4 nM; KD C4BP-IgG 980.7 nM), but only hexameric C4BP-IgM efficiently outcompeted heptameric C4BP from the bacterial surface, resulting in enhanced complement deposition and bacterial killing. Furthermore, C4BP-IgM substantially attenuated the duration and burden of colonization of 2 C4BP-binding gonococcal isolates but not a non-C4BP-binding strain in a mouse vaginal colonization model using human factor H/C4BP-transgenic mice. Our preclinical data present C4BP-IgM as an adjunct to conventional antimicrobials for the treatment of gonorrhea.

Advancing vaccine development for gonorrhoea and the Global STI Vaccine Roadmap.

Efforts to develop vaccines against Neisseria gonorrhoeae have become increasingly important, given the rising threat of gonococcal antimicrobial resistance (AMR). Recent data suggest vaccines for gonorrhoea are biologically feasible; in particular, epidemiological evidence shows that vaccines against a closely related pathogen, serogroup B Neisseria meningitidis outer membrane vesicle (OMV) vaccines, may reduce gonorrhoea incidence. Vaccine candidates using several approaches are currently in preclinical development, including meningococcal and gonococcal OMV vaccines, a lipooligosaccharide epitope and purified protein subunit vaccines. The Global STI Vaccine Roadmap provides action steps to build on this technical momentum and advance gonococcal vaccine development. Better quantifying the magnitude of gonorrhoea-associated disease burden, for outcomes like infertility, and modelling the predicted role of gonococcal vaccines in addressing AMR will be essential for building a full public health value proposition, which can justify investment and help with decision making about future vaccine policy and programs. Efforts are underway to gain consensus on gonorrhoea vaccine target populations, implementation strategies and other preferred product characteristics that would make these vaccines suitable for use in low- and middle-income, as well as high-income, contexts. Addressing these epidemiological, programmatic and policy considerations in parallel to advancing research and development, including direct assessment of the ability of meningococcal B OMV vaccines to prevent gonorrhoea, can help bring about the development of viable gonococcal vaccines.