Neisseria gonorrhoeae vaccine development: hope on the horizon?

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.

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.

Epidemiology of gonorrhoea: systematic review, meta-analyses, and meta-regressions, World Health Organization European Region, 1949 to 2021

BackgroundEpidemiology of Neisseria gonorrhoeae (NG) infection remains inadequately understood.AimWe aimed to characterise NG epidemiology in Europe.MethodsWe used Cochrane and PRISMA guidelines to systematically review, report, synthesise and analyse NG prevalence data from 1949 to 30 September 2021. Random-effects meta-analyses estimated pooled prevalence. Meta-regression analyses investigated associations and sources of heterogeneity.ResultsThe 844 included publications yielded 1,573 prevalence measures. Pooled prevalence of current urogenital infection was 1.0% (95% CI: 0.7-1.2%) among general populations, 3.2% (95% CI: 1.8-4.8%) among female sex workers, 4.9% (95% CI: 4.2-5.6%) among sexually transmitted infection clinic attendees and 12.1% (95% CI: 8.8-15.8%) among symptomatic men. Among men who have sex with men, pooled prevalence was 0.9% (95% CI: 0.5-1.4%), 5.6% (95% CI: 3.6-8.1%), and 3.8% (95% CI: 2.5-5.4%), respectively, for current urogenital, anorectal or oropharyngeal infection. Current urogenital, anorectal or oropharyngeal infection was 1.45-fold (95% CI: 1.19-1.77%), 2.75-fold (95% CI: 1.89-4.02%) and 2.64-fold (95% CI: 1.77-3.93%) higher among men than women. Current urogenital infection declined 0.97-fold (95% CI: 0.96-0.98%) yearly, but anorectal and oropharyngeal infection increased (1.02-fold; 95% CI: 1.01-1.04% and 1.02-fold; 95% CI: 1.00-1.04%), respectively.ConclusionsNeisseria gonorrhoeae epidemiology in Europe has distinct and contrasting epidemiologies for vaginal sex transmission in heterosexual sex networks vs anal and oral sex transmission in MSM sexual networks. Increased transmission may facilitate drug-resistant strain emergence. Europe is far from achieving the World Health Organization target of 90% incidence reduction by 2030.

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.

The potential for bacteriophages and prophage elements in fighting and preventing the gonorrhea

Bacteriophages are the most numerous entities on earth and are found everywhere their bacterial hosts live. As natural bacteria killers, phages are extensively investigated as a potential cure for bacterial infections. Neisseria gonorrhoeae (the gonococcus) is the etiologic agent of a sexually transmitted disease: gonorrhea. The rapid increase of resistance of N. gonorrhoeae to antibiotics urges scientists to look for alternative treatments to combat gonococcal infections. Phage therapy has not been tested as an anti-gonococcal therapy so far. To date, no lytic phage has been discovered against N. gonorrhoeae. Nevertheless, gonococcal genomes contain both dsDNA and ssDNA prophages, and viral particle induction has been documented. In this review, we consider literature data about the attempts of hunting for a bacteriophage specific for gonococci - the gonophage. We also discuss the potential application of prophage elements in the fight against N. gonorrhoeae. Temperate phages may be useful in preventing and treating gonorrhea as a scaffold for anti-gonococcal vaccine development and as a source of lytic enzymes with anti-gonococcal activity.

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.

Strategies for successful designing of immunocontraceptive vaccines and recent updates in vaccine development against sexually transmitted infections - A Review

Background

Objective

Methods

Results

Conclusion

Complete Genome Sequences of Seven Neisseria gonorrhoeae Clinical Isolates from Mucosal and Disseminated Gonococcal Infections

Neisseria gonorrhoeae is a Gram-negative bacterium that causes the sexually transmitted infection gonorrhea. N. gonorrhoeae has progressively developed resistance to all currently prescribed antibiotics, and no vaccine is available. Here, we report the closed, completed, annotated genome sequences for seven N. gonorrhoeae strains obtained by single-molecule real-time (SMRT) long-read genome sequencing.

Pelvic inflammatory disease in the adolescent and young adult: An update

Pelvic inflammatory disease (PID) is an infection of the female upper genital tract that is typically polymicrobial with classic core involvement of Neisseria gonorrhoeae and/or Chlamydia trachomatis, though other endogenous flora from the vagino-cervical areas can be involved as well. It is often a sexually transmitted disease but other etiologic routes are also noted. A variety of risk factors have been identified including adolescence, young adulthood, adolescent cervical ectropion, multiple sexual partners, immature immune system, history of previous PID, risky contraceptive practices and others. An early diagnosis and prompt treatment are necessary to reduce risks of PID complications such as chronic pelvic pain, ectopic pregnancy and infertility. Current management principles of PID are also reviewed. It is important for clinicians to screen sexually active females for common sexually transmitted infections such as Chlamydia trachomatis and provide safer sex education to their adolescent and young adult patients. Clinicians should provide comprehensive management to persons with PID and utilize established guidelines such as those from the US Centers for Disease Control and Prevention (CDC).

A Screen of Natural Product Extracts Identifies Moenomycin as a Potent Antigonococcal Agent

Increasing multidrug resistance in Neisseria gonorrheae is a growing public health crisis. Resistance to the last line therapies, cephalosporins and azithromycin, are of particular concern, fueling the need to discover new treatments. Here, we identified the phosphoglycolipid moenomycin from a screen of microbial natural products against drug-resistant N. gonorrheae as a potent antigonococcal agent. Moenomycin demonstrates excellent activity (MIC = 0.004-0.03 μg/mL) against a variety of multidrug-resistant N. gonorrheae. Importantly, moenomycin, thought to be a Gram-positive specific antibiotic, penetrates the Gram-negative gonococcal outer membrane. Moenomycin causes intracellular accumulation of peptidoglycan precursors, cell blebbing, and rupture of the cell envelope, all consistent with cell wall biosynthesis inhibition. Serial bacterial exposure to moenomycin for 14 days revealed slow development of resistance (MIC_Day14 = 0.03-0.06 μg/mL), unlike the clinically used drug azithromycin. Our results offer the potential utility of moenomycin as a lead for antigonococcal therapeutic candidates and warrant further investigation.

The role of vaccines in combatting antimicrobial resistance

The use of antibiotics has enabled the successful treatment of bacterial infections, saving the lives and improving the health of many patients worldwide. However, the emergence and spread of antimicrobial resistance (AMR) has been highlighted as a global threat by different health organizations, and pathogens resistant to antimicrobials cause substantial morbidity and death. As resistance to multiple drugs increases, novel and effective therapies as well as prevention strategies are needed. In this Review, we discuss evidence that vaccines can have a major role in fighting AMR. Vaccines are used prophylactically, decreasing the number of infectious disease cases, and thus antibiotic use and the emergence and spread of AMR. We also describe the current state of development of vaccines against resistant bacterial pathogens that cause a substantial disease burden both in high-income countries and in low- and medium-income countries, discuss possible obstacles that hinder progress in vaccine development and speculate on the impact of next-generation vaccines against bacterial infectious diseases on AMR.

Assessment of the Potential of Vaccination to Combat Antibiotic Resistance in Gonorrhea: A Modeling Analysis to Determine Preferred Product Characteristics

BACKGROUND

Gonorrhea incidence is increasing rapidly in many countries, while antibiotic resistance is making treatment more difficult. Combined with evidence that two meningococcal vaccines are likely partially protective against gonorrhea, this has renewed interest in a gonococcal vaccine, and several candidates are in development. Key questions are how protective and long-lasting a vaccine needs to be, and how to target it. We assessed vaccination's potential impact and the feasibility of achieving the World Health Organization's (WHO) target of reducing gonorrhea incidence by 90% during 2018-2030, by comparing realistic vaccination strategies under a range of scenarios of vaccine efficacy and duration of protection, and emergence of extensively-resistant gonorrhea.

METHODS

We developed a stochastic transmission-dynamic model, incorporating asymptomatic and symptomatic infection and heterogeneous sexual behavior in men who have sex with men (MSM). We used data from England, which has a comprehensive, consistent nationwide surveillance system. Using particle Markov chain Monte Carlo methods, we fitted to gonorrhea incidence in 2008-2017, then used Bayesian forecasting to examine an extensive range of scenarios.

RESULTS

Even in the worst-case scenario of untreatable infection emerging, the WHO target is achievable if all MSM attending sexual health clinics receive a vaccine offering ≥ 52% protection for ≥ 6 years. A vaccine conferring 31% protection (as estimated for MeNZB) for 2-4 years could reduce incidence in 2030 by 45% in the worst-case scenario, and by 75% if > 70% of resistant gonorrhea remains treatable.

CONCLUSIONS

Even a partially-protective vaccine, delivered through a realistic targeting strategy, could substantially reduce gonorrhea incidence, despite antibiotic resistance.

Gardnerella and vaginal health: the truth is out there

The human vagina is a dynamic ecosystem in which homeostasis depends on mutually beneficial interactions between the host and their microorganisms. However, the vaginal ecosystem can be thrown off balance by a wide variety of factors. Bacterial vaginosis (BV) is the most common vaginal infection in women of childbearing age but its etiology is not yet fully understood, with different controversial theories being raised over the years. What is generally accepted is that BV is often characterized by a shift in the composition of the normal vaginal microbiota, from a Lactobacillus species dominated microbiota to a mixture of anaerobic and facultative anaerobic bacteria. During BV, a polymicrobial biofilm develops in the vaginal microenvironment, being mainly composed of Gardnerella species. The interactions between vaginal microorganisms are thought to play a pivotal role in the shift from health to disease and might also increase the risk of sexually transmitted infections acquisition. Here, we review the current knowledge regarding the specific interactions that occur in the vaginal niche and discuss mechanisms by which these interactions might be mediated. Furthermore, we discuss the importance of novel strategies to fight chronic vaginal infections.

Machine Learning Platform to Discover Novel Growth Inhibitors of Neisseria gonorrhoeae

PURPOSE

To advance fundamental biological and translational research with the bacterium Neisseria gonorrhoeae through the prediction of novel small molecule growth inhibitors via naïve Bayesian modeling methodology.

METHODS

Inspection and curation of data from the publicly available ChEMBL web site for small molecule growth inhibition data of the bacterium Neisseria gonorrhoeae resulted in a training set for the construction of machine learning models. A naïve Bayesian model for bacterial growth inhibition was utilized in a workflow to predict novel antibacterial agents against this bacterium of global health relevance from a commercial library of >10⁵ drug-like small molecules. Follow-up efforts involved empirical assessment of the predictions and validation of the hits.

RESULTS

Specifically, two small molecules were found that exhibited promising activity profiles and represent novel chemotypes for agents against N. gonorrrhoeae.

CONCLUSIONS

This represents, to the best of our knowledge, the first machine learning approach to successfully predict novel growth inhibitors of this bacterium. To assist the chemical tool and drug discovery fields, we have made our curated training set available as part of the Supplementary Material and the Bayesian model is accessible via the web. Graphical Abstract.

Global epidemiology of Neisseria gonorrhoeae in infertile populations: systematic review, meta-analysis and metaregression

Objective

To provide an in-depth systematic assessment of the global epidemiology of gonorrhoea infection in infertile populations.

Methods

A systematic literature review was conducted up to 29 April 2019 on international databases and WHO regional databases, and reported following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. All prevalence measures of gonorrhoea infection among infertile populations, based on primary data, qualified for inclusion. Infertile populations were broadly defined to encompass women/men undergoing infertility evaluation or treatment (infertility clinic attendees and partners). Pooled mean prevalence by relevant strata was estimated using random-effects meta-analysis. Associations with prevalence and sources of heterogeneity were explored using metaregression. Risk of bias was assessed using four quality domains.

Findings

A total of 147 gonorrhoea prevalence studies were identified from 56 countries. The pooled mean prevalence of current gonorrhoea infection was estimated globally at 2.2% (95% CI 1.3% to 3.2%), with the highest prevalence in Africa at 5.0% (95% CI 1.9% to 9.3%). The mean prevalence was higher for populations with tubal factor infertility (3.6%, 95% CI 0.9%–7.7%) and mixed cause and unexplained infertility (3.6%, 95% CI 0.0% to 11.6%) compared with other diagnoses, such as ovarian and non-tubal infertility (0.1%, 95% CI 0.0% to 0.8%), and for secondary (2.5%, 95% CI 0.2% to 6.5%) compared with primary (0.5%, 95% CI 0.0% to 1.7%) infertility. Metaregression identified evidence of variations in prevalence by region and by infertility diagnosis, higher prevalence in women than men and a small-study effect. There was a trend of declining prevalence by about 3% per year over the last four decades (OR=0.97, 95% CI 0.95 to 0.99).

Conclusions

Gonorrhoea prevalence in infertile populations is several folds higher than that in the general population, with even higher prevalence in women with tubal factor infertility and in individuals with secondary infertility. These findings support the potential role of gonorrhoea in infertility and suggest that some infertility is possibly preventable by controlling gonorrhoea transmission.

PROSPERO registration number

CRD42018102934.

Repurposed Drugs That Block the Gonococcus-Complement Receptor 3 Interaction Can Prevent and Cure Gonococcal Infection of Primary Human Cervical Epithelial Cells

Novel therapies that avert the problem of Neisseria gonorrhoeae with acquired antibiotic resistance are urgently needed. Gonococcal infection of the human cervix is initiated by an interaction between a galactose modification made to its surface appendages, pili, and the I-domain region of (host) complement receptor 3 (CR3). By targeting this crucial gonococcal–I-domain interaction, it may be possible to prevent cervical infection in females. To this end, we identified the I-domain galactose-binding epitope of CR3 and characterized its galactose lectin activity. Moreover, we identified two drugs, carbamazepine and methyldopa, as effective host-targeted therapies for gonorrhea treatment. At doses below those currently used for their respective existing indications, both carbamazepine and methyldopa were more effective than ceftriaxone in curing cervical infection ex vivo. This host-targeted approach would not be subject to N. gonorrhoeae drug resistance mechanisms. Thus, our data suggest a long-term solution to the growing problem of multidrug-resistant N. gonorrhoeae infections.

In the absence of a vaccine, multidrug-resistant Neisseria gonorrhoeae has emerged as a major human health threat, and new approaches to treat gonorrhea are urgently needed. N. gonorrhoeae pili are posttranslationally modified by a glycan that terminates in a galactose. The terminal galactose is critical for initial contact with the human cervical mucosa via an interaction with the I-domain of complement receptor 3 (CR3). We have now identified the I-domain galactose-binding epitope and characterized its galactose-specific lectin activity. Using surface plasmon resonance and cellular infection assays, we found that a peptide mimic of this galactose-binding region competitively inhibited the N. gonorrhoeae-CR3 interaction. A compound library was screened for potential drugs that could similarly prohibit the N. gonorrhoeae-CR3 interaction and be repurposed as novel host-targeted therapeutics for multidrug-resistant gonococcal infections in women. Two drugs, methyldopa and carbamazepine, prevented and cured cervical cell infection by multidrug-resistant gonococci by blocking the gonococcal-CR3 I-domain interaction.

Antimicrobial resistance in sexually transmitted infections

RATIONALE FOR REVIEW

International travel facilitates the spread of drug-resistant infections, including sexually transmitted infections (STIs). In 2016, the World Health Organization highlighted the global burden of 'curable' STIs, estimating 376 million new infections of gonorrhoea, chlamydia, syphilis and trichomoniasis annually, with considerable geographic variation in both the burden of disease and prevalence of resistance. Travelers' risk of contracting and transmitting drug-resistant STIs depends in part on their geographic exposure. In this review, we describe the epidemiology of antimicrobial resistance (AMR) and the management of these four common STIs and Mycoplasma genitalium, an increasingly recognized cause of non-gonococcal urethritis.

KEY FINDINGS

Multi-drug and extensively drug resistant gonorrhoea strains have been associated with international spread, particularly in travelers returning from Southeast Asia. Chlamydia is the most common bacterial STI worldwide. Although in vitro resistance has been reported, surveillance data suggest that clinically significant resistance to macrolides and tetracyclines is rare. Macrolide resistance in syphilis is now endemic in much of the world but there is no documented penicillin resistance, which remains first-line therapy. Trichomoniasis is the most common non-viral STI worldwide. Although clinical failure after treatment occurs, resistance to metronidazole is thought to be uncommon. Mycoplasma genitalium exhibits intrinsic resistance to many antibiotics, and the prevalence of resistance to both first- and second-line regimens (macrolides and fluoroquinolones) is increasing worldwide, with limited alternative therapeutic options.

RECOMMENDATIONS

International travelers are at risk for acquiring resistant STIs with limited therapeutic options. Improved diagnostics are urgently needed to improve AMR surveillance and the management of infected patients. As no vaccinations are currently available for these STIs, and pre-exposure prophylaxis is an area of active study with limited data, condom use is critical for prevention. Travel medicine providers should incorporate STI risk reduction counselling, with an emphasis on condom use, into the routine pre-travel consultation.

Neisseria gonorrhoeae Becomes Susceptible to Polymyxin B and Colistin in the Presence of PBT2

Neisseria gonorrhoeae (N. gonorrhoeae) causes the sexually transmitted disease gonorrhea, which has a global incidence of 106 million cases per year. No vaccine is available to prevent the disease, and the emergence of multidrug resistant (MDR) strains makes N. gonorrhoeae an immediate public health threat. Here, we show that an ionophore, PBT2, can reverse the intrinsic resistance of N. gonorrhoeae to polymyxin B and colistin. These antibiotics administered in combination with PBT2 may be an effective path to treat MDR gonococcal infections.

Utility of Hybrid Transferrin Binding Protein Antigens for Protection Against Pathogenic Neisseria Species

The surface transferrin receptor proteins from Neisseria gonorrhoeae have been recognized as ideal vaccine targets due to their critical role in survival in the human male genitourinary tract. Recombinant forms of the surface lipoprotein component of the receptor, transferrin binding protein B (TbpB), can be readily produced at high levels in the Escherichia coli cytoplasm and is suitable for commercial vaccine production. In contrast, the integral outer membrane protein, transferrin binding protein A (TbpA), is produced at relatively low levels in the outer membrane and requires detergents for solubilization and stabilization, processes not favorable for commercial applications. Capitalizing on the core β-barrel structural feature common to the lipoprotein and integral outer membrane protein we engineered the lipoprotein as a scaffold for displaying conserved surface epitopes from TbpA. A stable version of the C-terminal domain of TbpB was prepared by replacing four larger exposed variable loops with short linking peptide regions. Four surface regions from the plug and barrel domains of Neisseria TbpA were transplanted onto this TbpB C-lobe scaffold, generating stable hybrid antigens. Antisera generated in mice and rabbits against the hybrid antigens recognized TbpA at the surface of Neisseria meningitidis and inhibited transferrin-dependent growth at levels comparable or better than antisera directed against the native TbpA protein. Two of the engineered hybrid antigens each elicited a TbpA-specific bactericidal antibody response comparable to that induced by TbpA. A hybrid antigen generated using a foreign scaffold (TbpB from the pig pathogen Haemophilus parasuis) displaying neisserial TbpA loop 10 was evaluated in a model of lower genital tract colonization by N. gonorrhoeae and a model of invasive infection by N. meningitidis. The loop 10 hybrid antigen was as effective as full length TbpA in eliminating N. gonorrhoeae from the lower genital tract of female mice and was protective against the low dose invasive infection by N. meningitidis. These results demonstrate that TbpB or its derivatives can serve as an effective scaffold for displaying surface epitopes of integral outer membrane antigens and these antigens can elicit protection against bacterial challenge.

Genus-Wide Comparative Genomics Analysis of Neisseria to Identify New Genes Associated with Pathogenicity and Niche Adaptation of Neisseria Pathogens

N. gonorrhoeae and N. meningitidis, the only two human pathogens of Neisseria, are closely related species. But the niches they survived in and their pathogenic characteristics are distinctly different. However, the genetic basis of these differences has not yet been fully elucidated. In this study, comparative genomics analysis was performed based on 15 N. gonorrhoeae, 75 N. meningitidis, and 7 nonpathogenic Neisseria genomes. Core-pangenome analysis found 1111 conserved gene families among them, and each of these species groups had opening pangenome. We found that 452, 78, and 319 gene families were unique in N. gonorrhoeae, N. meningitidis, and both of them, respectively. Those unique gene families were regarded as candidates that related to their pathogenicity and niche adaptation. The relationships among them have been partly verified by functional annotation analysis. But at least one-third genes for each gene set have not found the certain functional information. Simple sequence repeat (SSR), the basis of gene phase variation, was found abundant in the membrane or related genes of each unique gene set, which may facilitate their adaptation to variable host environments. Protein-protein interaction (PPI) analysis found at least five distinct PPI clusters in N. gonorrhoeae and four in N. meningitides, and 167 and 52 proteins with unknown function were contained within them, respectively.

Would immunization be the same without cross-reactivity?

"Cross-reactivity" (the observed immune response against pathogen types not specifically targeted by the vaccine antigen composition) and "cross-protection" (clinical protection against related non-vaccine microorganism types) are vaccinology concepts that are attracting renewed interest in the context of disease prevention. National health authorities are collecting mounting evidence of the importance of cross-reactivity. For some vaccines, this has been substantiated by cross-protection data from clinical studies and/or post-licensure data, where their introduction into immunization programmes has shown beneficial impacts on disease caused by related non-vaccine microorganisms. This knowledge has influenced the way new vaccines are designed, developed, and evaluated in real-life settings. Some of the new vaccines are now designed with the specific aim of having a greater breadth of protection. Ideal vaccine antigens therefore include epitopes with conserved homology across related pathogen types, because it is not always possible to include the antigens of all the individual types of a given pathogen species. The use of novel adjuvants with greater immunostimulatory properties can also contribute to improved overall vaccine cross-reactivity, as could the use of antigen delivery platforms. The growing body of evidence allows us to better understand the full impact of vaccines - beyond vaccine-type disease - which should be taken into consideration when assessing the full value of vaccination programmes.