Efficacy of polymeric encapsulated C5a peptidase-based group B streptococcus vaccines in a murine model

Current research update on group B streptococcal infection related to obstetrics and gynecology

Group B streptococcal (GBS) is a Gram-positive bacterium that is commonly found in the gastrointestinal tract and urogenital tract. GBS infestation during pregnancy is a significant contributor to maternal and neonatal morbidity and mortality globally. This article aims to discuss the infectious diseases caused by GBS in the field of obstetrics and gynecology, as well as the challenges associated with the detection, treatment, and prevention of GBS.

Vaccines for Streptococcus agalactiae: current status and future perspectives

A maternal vaccine to protect newborns against invasive Streptococcus agalactiae infection is a developing medical need. The vaccine should be offered during the third trimester of pregnancy and induce strong immune responses and placental transfer of protective antibodies. Polysaccharide vaccines against S. agalactiae conjugated to protein carriers are in advanced stages of development. Additionally, protein-based vaccines are also in development, showing great promise as they can provide protection regardless of serotype. Furthermore, safety concerns regarding a new vaccine are the main barriers identified. Here, we present vaccines in development and identified safety, cost, and efficacy concerns, especially in high-need, low-income countries.

Immunization with Multiple Virulence Factors Provides Maternal and Neonatal Protection against Group B Streptococcus Serotypes

Group B streptococcus (GBS) commonly colonizes the vaginal tract and is a leading cause of life-threatening neonatal infections and adverse pregnancy outcomes. No effective vaccine is clinically available. Conserved bacterial virulence factors, including those of GBS, have been employed as vaccine components. We investigated serotype-independent protection against GBS by intranasal immunization with six conserved GBS virulence factors (GBSV6). GBSV6 induced systemic and vaginal antibodies and T cell responses in mice. The immunity reduced mouse mortality and vaginal colonization by various GBS serotypes and protected newborn mice of immunized dams against GBS challenge. Intranasal GBSV6 immunization also provided long-lasting protective immunity and had advantages over intramuscular GBSV6 immunization regarding restricting vaginal GBS colonization. Our findings indicate that intranasal immunization targeting multiple conserved GBS virulence factors induces serotype-independent immunity, which protects against GBS infection systemically and vaginally in dams and prevents newborn death. The study presents valuable strategies for GBS vaccine development.

Streptococcal bacterial components in cancer therapy

The incidence rate of cancer is steadily increasing all around the world, and there is an urgent need to develop novel and more effective treatment strategies. Recently, bacterial therapy has been investigated as a new approach to target cancer, and is becoming a serious option. Streptococcus strains are among the most common and well-studied virulent bacteria that cause a variety of human infections. Everyone has experienced a sore throat during their lifetime, or has been asymptomatically colonized by streptococci. The ability of Streptococcus bacteria to fight cancer was discovered more than 100 years ago, and over the years has undergone clinical trials, but the mechanism is not yet completely understood. Recently, several animal models and human clinical trials have been reported. Streptococcal strains can have an intrinsic anti-tumor activity, or can activate the host immune system to fight the tumor. Bacteria can selectively accumulate and proliferate in the hypoxic regions of solid tumors. Moreover, the bacteria can be genetically engineered to secrete toxins or enzymes that can specifically attack the tumors.

The Role of Streptococcal Cell-Envelope Proteases in Bacterial Evasion of the Innate Immune System

Bacteria possess the ability to evolve varied and ingenious strategies to outwit the host immune system, instigating an evolutionary arms race. Proteases are amongst the many weapons employed by bacteria, which specifically cleave and neutralize key signalling molecules required for a coordinated immune response. In this article, we focus on a family of S8 subtilisin-like serine proteases expressed as cell-envelope proteases (CEPs) by group A and group B streptococci. Two of these proteases known as Streptococcus pyogenes CEP (SpyCEP) and C5a peptidase cleave the chemokine CXCL8 and the complement fragment C5a, respectively. Both CXCL8 and C5a are potent neutrophil-recruiting chemokines, and by neutralizing their activity, streptococci evade a key defence mechanism of innate immunity. We review the mechanisms by which CXCL8 and C5a recruit neutrophils and the characterization of SpyCEP and C5a peptidase, including both in vitro and in vivo studies. Recently described structural insights into the function of this CEP family are also discussed. We conclude by examining the progress of prototypic vaccines incorporating SpyCEP and C5a peptidase in their preparation. Since streptococci-producing SpyCEP and C5a peptidase are responsible for a considerable global disease burden, targeting these proteases by vaccination strategies or by small-molecule antagonists should provide protection from and promote the resolution of streptococcal infections.

Bacterial and Host Determinants of Group B Streptococcal Vaginal Colonization and Ascending Infection in Pregnancy

Group B streptococcus (GBS) is a gram-positive bacteria that asymptomatically colonizes the vaginal tract. However, during pregnancy maternal GBS colonization greatly predisposes the mother and baby to a wide range of adverse outcomes, including preterm birth (PTB), stillbirth, and neonatal infection. Although many mechanisms involved in GBS pathogenesis are partially elucidated, there is currently no approved GBS vaccine. The development of a safe and effective vaccine that can be administered during or prior to pregnancy remains a principal objective in the field, because current antibiotic-based therapeutic strategies do not eliminate all cases of invasive GBS infections. Herein, we review our understanding of GBS disease pathogenesis at the maternal-fetal interface with a focus on the bacterial virulence factors and host defenses that modulate the outcome of infection. We follow GBS along its path from an asymptomatic colonizer of the vagina to an invasive pathogen at the maternal-fetal interface, noting factors critical for vaginal colonization, ascending infection, and vertical transmission to the fetus. Finally, at each stage of infection we emphasize important host-pathogen interactions, which, if targeted therapeutically, may help to reduce the global burden of GBS.

Control of Streptococcal Infections: Is a Common Vaccine Target Achievable Against Streptococcus agalactiae and Streptococcus pneumoniae

Both Streptococcus agalactiae [group B streptococcus (GBS)] and Streptococcus pneumoniae (pneumococcus) remain significant pathogens as they cause life threatening infections mostly in children and the elderly. The control of diseases caused by these pathogens is dependent on antibiotics use and appropriate vaccination. The introduction of the pneumococcal conjugate vaccines (PCVs) against some serotypes has led to reduction in pneumococcal infections, however, the subsequent serotype switching, and replacement has been a serious challenge. On the other hand, no vaccine is yet licensed for use in the control of GBS diseases. In this review, we provide an overview of the history and global disease burden, disease pathophysiology and management, vaccines update, and the biology of both pathogens. Furthermore, we address recent findings regarding structural similarities that could be explored for vaccine targets across both mucosal pathogens. Finally, we conclude by proposing future genomic sequence comparison using the wealth of available sequences from both species and the possibility of identifying more related structural components that could be exploited for pan-pathogen vaccine development.

A Vaccine Against Group B Streptococcus: Recent Advances

Group B streptococcus (GBS) causes a high burden of neonatal and infant disease globally. Implementing a vaccine for pregnant women is a promising strategy to prevent neonatal and infant GBS disease and has been identified as a priority by the World Health Organisation (WHO). GBS serotype-specific polysaccharide – protein conjugate vaccines are at advanced stages of development, but a large number of participants would be required to undertake Phase III clinical efficacy trials. Efforts are therefore currently focused on establishing serocorrelates of protection in natural immunity studies as an alternative pathway for licensure of a GBS vaccine, followed by Phase IV studies to evaluate safety and effectiveness. Protein vaccines are in earlier stages of development but are highly promising as they might confer protection irrespective of serotype. Further epidemiological, immunological and health economic studies are required to enable the vaccine to reach its target population as soon as possible.

Epitopes of Immunoreactive Proteins of Streptococcus Agalactiae: Enolase, Inosine 5'-Monophosphate Dehydrogenase and Molecular Chaperone GroEL

Three Streptococcus agalactiae (group B streptococci, GBS) immunoreactive proteins: enolase (47.4 kDa), inosine 5'-monophosphate dehydrogenase (IMPDH) (53 kDa) and molecular chaperone GroEL (57 kDa) were subjected to investigation. Enolase protein was described in our previous paper, whereas IMPDH and GroEL were presented for the first time. The aim of our paper was to provide mapping of specific epitopes, highly reactive with umbilical cord blood serum. Bioinformatic analyses allowed to select 32 most likely epitopes for enolase, 36 peptides for IMPDH and 41 immunoreactive peptides for molecular chaperone GroEL, which were synthesized by PEPSCAN. Ten peptides: two in enolase, one in IMPDH and seven in molecular chaperone GroEL have been identified as potentially highly selective epitopes that can be used as markers in rapid immunological diagnostic tests or constitute a component of an innovative vaccine against GBS infections.

Progress toward a group B streptococcal vaccine

Streptococcus agalactiae (group B Streptococcus, GBS) is a leading cause of severe invasive disease in neonate, elderly, and immunocompromised patients worldwide. Despite recent advances in the diagnosis and intrapartum antibiotic prophylaxis (IAP) of GBS infections, it remains one of the most common causes of neonatal morbidity and mortality, causing serious infections. Furthermore, recent studies reported an increasing number of GBS infections in pregnant women and elderly. Although IAP is effective, it has several limitations, including increasing antimicrobial resistance and late GBS infection after negative antenatal screening. Maternal immunization is the most promising and effective countermeasure against GBS infection in neonates. However, no vaccine is available to date, but two types of vaccines, protein subunit and capsular polysaccharide conjugate vaccines, were investigated in clinical trials. Here, we provide an overview of the GBS vaccine development status and recent advances in the development of immunoassays to evaluate the GBS vaccine clinical efficacy.

Development of experimental GBS vaccine for mucosal immunization

Streptococcus agalactiae, or group B streptococcus (GBS), is an important pathogen as it is the leading cause of neonatal deaths due to sepsis, meningitis or bacterial pneumonia. Although the development of an effective and safe GBS vaccine is on the agenda of many research labs, there is no GBS vaccine on the market yet. In the present study we attempted to engineer a live vaccine strain based on Bac, a surface protein of GBS, incorporated into a surface fimbrial protein of probiotic Enterococcus. The resulting strain induced specific systemic and local immune responses in mice and provided protection against GBS when administered via the intranasal, oral or intravaginal immunization routes.

Mucosal vaccination promotes clearance of Streptococcus agalactiae vaginal colonization

Group B Streptococcus (GBS) is a leading cause of morbidity and mortality in infants, and colonization of the maternal genital tract is the primary risk factor for newborn infection. Despite the importance of mucosal colonization in GBS pathogenesis, relevant host and bacterial factors are incompletely understood. We investigated the role of humoral immunity in clearance of vaginal colonization in vivo. B-cell-deficient mice or those lacking neonatal Fc-receptor, a mediator of IgG transport to the vaginal mucosa, exhibit prolonged GBS vaginal colonization compared to wild type animals. Intranasal but not intramuscular immunization induced systemic and mucosal immune responses and decreased GBS colonization duration without altering initial colonization density. Vaccine-induced clearance of GBS was serotype-specific, suggesting a role for anti-capsule antibodies in protection. Our results support a role for humoral immunity in GBS eradication from the female genital tract and suggest that mucosal vaccination may prime colonization clearance.

A Murine Model of Group B Streptococcus Vaginal Colonization

Streptococcus agalactiae (group B Streptococcus, GBS), is a Gram-positive, asymptomatic colonizer of the human gastrointestinal tract and vaginal tract of 10 - 30% of adults. In immune-compromised individuals, including neonates, pregnant women, and the elderly, GBS may switch to an invasive pathogen causing sepsis, arthritis, pneumonia, and meningitis. Because GBS is a leading bacterial pathogen of neonates, current prophylaxis is comprised of late gestation screening for GBS vaginal colonization and subsequent peripartum antibiotic treatment of GBS-positive mothers. Heavy GBS vaginal burden is a risk factor for both neonatal disease and colonization. Unfortunately, little is known about the host and bacterial factors that promote or permit GBS vaginal colonization. This protocol describes a technique for establishing persistent GBS vaginal colonization using a single β-estradiol pre-treatment and daily sampling to determine bacterial load. It further details methods to administer additional therapies or reagents of interest and to collect vaginal lavage fluid and reproductive tract tissues. This mouse model will further the understanding of the GBS-host interaction within the vaginal environment, which will lead to potential therapeutic targets to control maternal vaginal colonization during pregnancy and to prevent transmission to the vulnerable newborn. It will also be of interest to increase our understanding of general bacterial-host interactions in the female vaginal tract.

The essential genome of Streptococcus agalactiae

BACKGROUND

Next-generation sequencing of transposon-genome junctions from a saturated bacterial mutant library (Tn-seq) is a powerful tool that permits genome-wide determination of the contribution of genes to fitness of the organism under a wide range of experimental conditions. We report development, testing, and results from a Tn-seq system for use in Streptococcus agalactiae (group B Streptococcus; GBS), an important cause of neonatal sepsis.

METHODS

Our method uses a Himar1 mini-transposon that inserts at genomic TA dinucleotide sites, delivered to GBS on a temperature-sensitive plasmid that is subsequently cured from the bacterial population. In order to establish the GBS essential genome, we performed Tn-seq on DNA collected from three independent mutant libraries-with at least 135,000 mutants per library-at serial 24 h time points after outgrowth in rich media.

RESULTS

After statistical analysis of transposon insertion density and distribution, we identified 13.5 % of genes as essential and 1.2 % as critical, with high levels of reproducibility. Essential and critical genes are enriched for fundamental cellular housekeeping functions, such as acyl-tRNA biosynthesis, nucleotide metabolism, and glycolysis. We further validated our system by comparing fitness assignments of homologous genes in GBS and a close bacterial relative, Streptococcus pyogenes, which demonstrated 93 % concordance. Finally, we used our fitness assignments to identify signal transduction pathway components predicted to be essential or critical in GBS.

CONCLUSIONS

We believe that our baseline fitness assignments will be a valuable tool for GBS researchers and that our system has the potential to reveal key pathogenesis gene networks and potential therapeutic/preventative targets.

Biodegradable particles as vaccine antigen delivery systems for stimulating cellular immune responses

There is a need for both new and improved vaccination formulations for a range of diseases for which current vaccines are either inadequate or non-existent. Biodegradable polymer-based vaccines fulfill many of the desired properties in achieving effective long-term protection in a manner that is safe, economical, and potentially more practicable on a global scale. Here we discuss some of the work performed with micro/nanoparticles made from either synthetic (poly[lactic-co-glycolic acid] [PLGA] and polyanhydrides) or natural (chitosan) biodegradable polymers. Our attention is focused on, but not limited to, the generation of antitumor immunity where we stress the importance of particle size and co-delivery of antigen and adjuvant.