Development and validation of a fourfold multiplexed opsonization assay (MOPA4) for pneumococcal antibodies

Genome sequences of 36 Streptococcus pneumoniae strains optimized for the multiplexed opsonophagocytosis killing assay

A multiplexed opsonophagocytosis assay (MOPA) was developed as a cost-effective, high-throughput biological assay to evaluate the efficacy of pneumococcal vaccines by in vitro measurement of opsonophagocytic activity of anti-capsular antibodies. Here, we report draft genomes of the 36 strains of Streptococcus pneumoniae developed for use in the reference pneumococcal MOPA.

Implications of Cross-Reactivity and Cross-Protection for Pneumococcal Vaccine Development

Pneumococcal vaccines are a cornerstone for the prevention of pneumococcal diseases, reducing morbidity and mortality in children and adults worldwide. Pneumococcal vaccine composition is based on the polysaccharide capsule of Streptococcus pneumoniae, which is one of the most important identified contributors to the pathogen's virulence. Similarities in the structural composition of polysaccharides included in licensed pneumococcal vaccines may result in cross-reactivity of immune response against closely related serotypes, including serotypes not included in the vaccine. Therefore, it is important to understand whether cross-reactive antibodies offer clinical protection against pneumococcal disease. This review explores available evidence of cross-reactivity and cross-protection associated with pneumococcal vaccines, the challenges associated with the assessment of cross-reactivity and cross-protection, and implications for vaccine design and development.

Clonal Expansion of a Streptococcus pneumoniae Serotype 3 Capsule Variant Sequence Type 700 With Enhanced Vaccine Escape Potential After 13-Valent Pneumococcal Conjugate Vaccine Introduction

BACKGROUND

Streptococcus pneumoniae serotype 3 remains a problem globally. Malawi introduced 13-valent pneumococcal conjugate vaccine (PCV13) in 2011, but there has been no direct protection against serotype 3 carriage. We explored whether vaccine escape by serotype 3 is due to clonal expansion of a lineage with a competitive advantage.

METHODS

The distribution of serotype 3 Global Pneumococcal Sequence Clusters (GPSCs) and sequence types (STs) globally was assessed using sequences from the Global Pneumococcal Sequencing Project. Whole-genome sequences of 135 serotype 3 carriage isolates from Blantyre, Malawi (2015-2019) were analyzed. Comparative analysis of the capsule locus, entire genomes, antimicrobial resistance, and phylogenetic reconstructions were undertaken. Opsonophagocytosis was evaluated using serum samples from vaccinated adults and children.

RESULTS

Serotype 3 GPSC10-ST700 isolates were most prominent in Malawi. Compared with the prototypical serotype 3 capsular polysaccharide locus sequence, 6 genes are absent, with retention of capsule polysaccharide biosynthesis. This lineage is characterized by increased antimicrobial resistance and lower susceptibility to opsonophagocytic killing.

CONCLUSIONS

A serotype 3 variant in Malawi has genotypic and phenotypic characteristics that could enhance vaccine escape and clonal expansion after post-PCV13 introduction. Genomic surveillance among high-burden populations is essential to improve the effectiveness of next-generation pneumococcal vaccines.

Biological puzzles solved by using Streptococcus pneumoniae: a historical review of the pneumococcal studies that have impacted medicine and shaped molecular bacteriology

The major human pathogen Streptococcus pneumoniae has been the subject of intensive clinical and basic scientific study for over 140 years. In multiple instances, these efforts have resulted in major breakthroughs in our understanding of basic biological principles as well as fundamental tenets of bacterial pathogenesis, immunology, vaccinology, and genetics. Discoveries made with S. pneumoniae have led to multiple major public health victories that have saved the lives of millions. Studies on S. pneumoniae continue today, where this bacterium is being used to dissect the impact of the host on disease processes, as a powerful cell biology model, and to better understand the consequence of human actions on commensal bacteria at the population level. Herein we review the major findings, i.e., puzzle pieces, made with S. pneumoniae and how, over the years, they have come together to shape our understanding of this bacterium's biology and the practice of medicine and modern molecular biology.

Streptococcus agalactiae glycolipids promote virulence by thwarting immune cell clearance

Streptococcus agalactiae [group B Streptococcus (GBS)] is a leading cause of neonatal meningitis, with late-onset disease (LOD) occurring after gastrointestinal tract colonization in infants. Bacterial membrane lipids are essential for host-pathogen interactions, and the functions of glycolipids are yet to be fully elucidated. GBS synthesizes three major glycolipids: glucosyl-diacylglycerol (Glc-DAG), diglucosyl-DAG (Glc2-DAG), and lysyl-Glc-DAG (Lys-Glc-DAG). Here, we identify the enzyme, IagB, as responsible for biosynthesis of Glc-DAG, the precursor for the two other glycolipids in GBS. To examine the collective role of glycolipids to GBS virulence, we adapted a murine model of neonatal meningitis to simulate LOD. The GBS∆iagB mutant traversed the gut-epithelial barrier comparable to wild type but was severely attenuated in bloodstream survival, resulting in decreased bacterial loads in the brain. The GBS∆iagB mutant was more susceptible to neutrophil killing and membrane targeting by host antimicrobial peptides. This work reveals an unexplored function of GBS glycolipids with their ability to protect the bacterial cell from host antimicrobial killing.

Safety, tolerability and immunogenicity of a novel 24-valent pneumococcal vaccine in toddlers: A phase 1 randomized controlled trial

BACKGROUND

Pneumococcal conjugate vaccines (PCVs) significantly reduced pneumococcal disease burden. Nevertheless, alternative approaches for controlling more serotypes are needed. Here, the safety, tolerability, and immunogenicity of a 24-valent (1/2/3/4/5/6A/6B/7F/8/9N/9V/10A/11A/12F/14/15B/17F/18C/19A/19F/20B/22F/23F/33F) pneumococcal vaccine based on Multiple Antigen-Presenting System (MAPS) technology (Pn-MAPS24v) was assessed in toddlers.

METHODS

In this phase 1, blinded, dose-escalation, active-controlled multicenter study conducted in the United States (September/2020-April/2022), 12-15-month-old toddlers primed with three doses of 13-valent PCV (PCV13) were randomized 3:2 to receive a single dose of one of three Pn-MAPS24v dose levels (1 μg/2 μg/5 μg per polysaccharide) or PCV13 intramuscularly. Reactogenicity (within 7 days), treatment-emergent adverse events (TEAEs, within 180 days), serious/medically attended adverse events (SAEs/MAAEs, within 180 days), and immunogenicity (serotype-specific anti-capsular polysaccharide immunoglobulin G [IgG] and opsonophagocytic activity [OPA] responses at 30 days post-vaccination) were assessed.

RESULTS

Of 75 toddlers enrolled, 74 completed the study (Pn-MAPS24v 1 μg/2 μg/5 μg: 15/14/16, PCV13: 29). Frequencies of local (60 %/67 %/31 %) and systemic events (67 %/67 %/75 %) in the Pn-MAPS24v 1 μg/2 μg/5 μg and the PCV13 (55 %, 79 %) groups were in similar ranges. TEAEs were reported by 47 %/40 %/63 % of Pn-MAPS24v 1 μg/2 μg/5 μg recipients and 52 % of PCV13 recipients. No vaccine-related SAE was reported. At 30 days post-vaccination, for each of the 13 common serotypes, ≥93 % of participants in each group had IgG concentrations ≥0.35 μg/mL; >92 % had OPA titers ≥lower limit of quantitation (LLOQ), except for serotype 1 (79 %). For 7/11 unique serotypes (2/8/9N/11A/17F/22F/33F), at all dose levels, ≥78 % of Pn-MAPS24v recipients in each group had IgG concentrations ≥0.35 μg/mL and 80 %-100 % had OPA titers ≥LLOQ.

CONCLUSIONS

In 12-15-month-old toddlers, a single dose of Pn-MAPS24v showed an acceptable safety profile, regardless of dose level; AEs were reported at similar frequencies by Pn-MAPS24v and PCV13 recipients. Pn-MAPS24v elicited IgG and OPA responses to all common and most unique serotypes. These results support further clinical evaluation in infants.

Distinct baseline immune characteristics associated with responses to conjugated and unconjugated pneumococcal polysaccharide vaccines in older adults

Pneumococcal infections cause serious illness and death among older adults. The capsular polysaccharide vaccine PPSV23 and conjugated alternative PCV13 can prevent these infections; yet, underlying immunological responses and baseline predictors remain unknown. We vaccinated 39 older adults (>60 years) with PPSV23 or PCV13 and observed comparable antibody responses (day 28) and plasmablast transcriptional responses (day 10); however, the baseline predictors were distinct. Analyses of baseline flow cytometry and bulk and single-cell RNA-sequencing data revealed a baseline phenotype specifically associated with weaker PCV13 responses, which was characterized by increased expression of cytotoxicity-associated genes, increased frequencies of CD16+ natural killer cells and interleukin-17-producing helper T cells and a decreased frequency of type 1 helper T cells. Men displayed this phenotype more robustly and mounted weaker PCV13 responses than women. Baseline expression levels of a distinct gene set predicted PPSV23 responses. This pneumococcal precision vaccinology study in older adults uncovered distinct baseline predictors that might transform vaccination strategies and initiate novel interventions.

PCV15, a pneumococcal conjugate vaccine, for the prevention of invasive pneumococcal disease in infants and children

INTRODUCTION

Streptococcus pneumoniae is a causative agent of pneumonia and acute otitis media (AOM), as well as invasive diseases such as meningitis and bacteremia. PCV15 (V114) is a new 15-valent pneumococcal conjugate vaccine (PCV) approved for use in individuals ≥6 weeks of age for the prevention of pneumonia, AOM, and invasive pneumococcal disease.

AREAS COVERED

This review summarizes the V114 Phase 3 development program leading to approval in infants and children, including pivotal studies, interchangeability and catch-up vaccination studies, and studies in at-risk populations. An integrated safety summary is presented in addition to immunogenicity and concomitant use of V114 with other routine pediatric vaccines.

EXPERT OPINION

Across the development program, V114 demonstrated a safety profile that is comparable to PCV13 in infants and children. Immunogenicity of V114 is comparable to PCV13 for all shared serotypes except serotype 3, where V114 demonstrated superior immunogenicity. Higher immune responses were demonstrated for V114 serotypes 22F and 33F. Results of the ongoing study to evaluate V114 efficacy against vaccine-type pneumococcal AOM and anticipated real-world evidence studies will support assessment of vaccine effectiveness and impact, with an additional question of whether higher serotype 3 immunogenicity translates to better protection against serotype 3 pneumococcal disease.

Benefits of Combining Molecular Biology and Controlled Human Infection Model Methodologies in Advancing Vaccine Development

Infectious diseases continue to account for a significant portion of global deaths despite the use of vaccines for several centuries. Immunization programs around the world are a testament to the great success of multiple vaccines, yet there are still diseases without vaccines and others that require safer more effective ones. Addressing uncontrolled and emerging disease threats is restrained by the limitations and bottlenecks encountered with traditional vaccine development paradigms. Recent advances in modern molecular biology technologies have enhanced the interrogation of host pathogen interaction and deciphered complex pathways, thereby uncovering the myriad interplay of biological events that generate immune protection against foreign agents. Consequent to insights into the immune system, modern biology has been instrumental in the development and production of next generation 21st century vaccines. As these biological tools, commonly and collectively referred to as 'omics, became readily available, there has been a renewed consideration of Controlled Human Infection Models (CHIMs). Successful and reproducible CHIMs can complement modern molecular biology for the study of infectious diseases and development of effective vaccines in a regulated process that mitigates risk, cost, and time, with capacity to discern immune correlates of protection.

Establishment of a modified opsonophagocytic killing assay for anti-pneumococcal surface protein A antibody

Streptococcus pneumoniae (pneumococcus) is a pathogenic gram-positive bacterium that causes pneumonia, meningitis, and sepsis. Pneumococcal surface protein A (PspA) induces antibodies that protect against lethal infections by pneumococci. PspA is a choline-binding protein present on the cell surface of almost all pneumococcal strains and is a non-capsular polysaccharide vaccine candidate. For research and development of PspA-based vaccines, an in-vitro test system to measure the activity of functional antibodies capable of killing pneumococci is essential. The opsonophagocytic killing (OPK) assay is used to evaluate the opsonic activity of functional antibodies induced by capsular polysaccharide (CPS)-based vaccines (standard OPK assay). Despite the potential of anti-PspA antibodies to protect against lethal infections in mice, the standard OPK assay fails to evaluate anti-PspA antibodies. Using a pneumococcal surface protein C-deficient strain and extending the incubation time of opsonized bacteria, complement, and HL-60 cells reportedly results in enhanced bactericidal activity (modified OPK assay). We aimed to measure the bactericidal activity of anti-PspA antibodies in intact pneumococcal strains. We optimized the pneumococcal culture method used in the OPK assay to increase the efficiency of anti-PspA antibody-mediated phagocytosis of HL-60 cells. As thick capsules hinder phagocytosis, we attempted to obtain pneumococci with thin capsules through an improved culture method. As pneumococci attached to cells exhibit thin capsules, pneumococci cultured in Todd Hewitt yeast extract (THY) broth were spread on blood agar plates and incubated for 4 h. cpsA mRNA transcript levels in pneumococci cultured on blood agar were lower than those in pneumococci cultured in THY broth. OPK activity against pneumococci expressing PspA of clades 1-5 was reasonably well detected using pneumococci cultured on blood agar in the modified OPK assay. The modified OPK assay for anti-PspA antibody using pneumococci cultured on blood agar represents a useful assay to determine the killing activity of functional anti-PspA antibodies against pneumococci.

Novel pneumococcal capsule type 33E results from the inactivation of glycosyltransferase WciE in vaccine type 33F

The polysaccharide (PS) capsule is essential for immune evasion and virulence of Streptococcus pneumoniae. Existing pneumococcal vaccines are designed to elicit anticapsule antibodies; however, the effectiveness of these vaccines is being challenged by the emergence of new capsule types or variants. Herein, we characterize a newly discovered capsule type, 33E, that appears to have repeatedly emerged from vaccine type 33F via an inactivation mutation in the capsule glycosyltransferase gene, wciE. Structural analysis demonstrated that 33E and 33F share an identical repeat unit backbone [→5)-β-D-Galf2Ac-(1→3)-β-D-Galp-(1→3)-α-D-Galp-(1→3)-β-D-Galf-(1→3)-β-D-Glcp-(1→], except that a galactose (α-D-Galp) branch is present in 33F but not in 33E. Though the two capsule types were indistinguishable using conventional typing methods, the monoclonal antibody Hyp33FM1 selectively bound 33F but not 33E pneumococci. Further, we confirmed that wciE encodes a glycosyltransferase that catalyzes the addition of the branching α-D-Galp and that its inactivation in 33F strains results in the expression of the 33E capsule type. Though 33F and 33E share a structural and antigenic similarity, our pilot study suggested that immunization with a 23-valent pneumococcal PS vaccine containing 33F PS did not significantly elicit cross-opsonic antibodies to 33E. New conjugate vaccines that target capsule type 33F may not necessarily protect against 33E. Therefore, studies of new conjugate vaccines require knowledge of the newly identified capsule type 33E and reliable pneumococcal typing methods capable of distinguishing it from 33F.

Reduced quantity and function of pneumococcal antibodies are associated with exacerbations of COPD in SPIROMICS

While hypogammaglobulinemia is associated with COPD exacerbations, it is unknown whether frequent exacerbators have specific defects in antibody production/function. We hypothesized that reduced quantity/function of serum pneumococcal antibodies correlate with exacerbation risk in the SPIROMICS cohort. We measured total pneumococcal IgG in n = 764 previously vaccinated participants with COPD. In a propensity-matched subset of n = 200 with vaccination within five years (n = 50 without exacerbations in the previous year; n = 75 with one, n = 75 with ≥2), we measured pneumococcal IgG for 23 individual serotypes, and pneumococcal antibody function for 4 serotypes. Higher total pneumococcal IgG, serotype-specific IgG (17/23 serotypes), and antibody function (3/4 serotypes) were independently associated with fewer prior exacerbations. Higher pneumococcal IgG (5/23 serotypes) predicted lower exacerbation risk in the following year. Pneumococcal antibodies are inversely associated with exacerbations, supporting the presence of immune defects in frequent exacerbators. With further study, pneumococcal antibodies may be useful biomarkers for immune dysfunction in COPD.

Distinct baseline immune characteristics associated with responses to conjugated and unconjugated pneumococcal polysaccharide vaccines in older adults

Pneumococcal infections cause serious illness and death among older adults. A capsular polysaccharide vaccine PPSV23 (Pneumovax®) and a conjugated polysaccharide vaccine PCV13 (Prevnar®) are used to prevent these infections, yet underlying responses, and baseline predictors remain unknown. We recruited and vaccinated 39 older adults (>60 years) with PPSV23 or PCV13. Both vaccines induced strong antibody responses at day 28 and similar plasmablast transcriptional signatures at day 10, however, their baseline predictors were distinct. Analyses of baseline flow cytometry and RNA-seq data (bulk and single cell) revealed a novel baseline phenotype that is specifically associated with weaker PCV13 responses, characterized by i) increased expression of cytotoxicity-associated genes and increased CD16+ NK frequency; ii) increased Th17 and decreased Th1 cell frequency. Men were more likely to display this cytotoxic phenotype and mounted weaker responses to PCV13 than women. Baseline expression levels of a distinct gene set was predictive of PPSV23 responses. This first precision vaccinology study for pneumococcal vaccine responses of older adults uncovered novel and distinct baseline predictors that might transform vaccination strategies and initiate novel interventions.

Evaluation of cross-protection between S. Pneumoniae serotypes 35B and 29 in a mouse model

Pneumococcal conjugate vaccines (PCVs) have reduced vaccine-type pneumococcal disease but in turn have also resulted in replacement with non-vaccine serotypes. One such serotype, 35B, a multidrug resistant type, has been associated with an increase in disease. Mice were immunized intramuscularly with monovalent pneumococcal polysaccharide 35B conjugated to CRM197 containing aluminum phosphate adjuvant on days 0, 14, and 28. Pneumococcal enzyme-linked immunosorbent assay, opsonophagocytic killing assays, and competition OPA were performed for STs 35B and 29 to measure serotype-specific binding and functional antibodies. On day 52, mice were intratracheally challenged with S. pneumoniae ST29 to evaluate cross-protection. 35B-CRM197 immunized mice had binding and functional antibodies to both PnPs 35B and 29. 35B-CRM197 immunized mice were 100% protected from IT challenge with S. pneumoniae ST29 as compared to 30% survival in the naïve group. Future vaccines containing polysaccharide 35B, such as the investigational 21-valent PCV, V116, may provide cross protection against the non-vaccine serotype 29 due to structural similarity.

The Development of Immunological Assays to Evaluate the Level and Function of Antibodies Induced by Klebsiella pneumoniae O-Antigen Vaccines

Klebsiella pneumoniae, a Gram-negative bacterium, has been listed as a critical pathogen for urgent intervention by the World Health Organization. With no licensed vaccine and increasing resistance to antibiotics, Klebsiella pneumoniae causes a high incidence of hospital- and community-acquired infections. Recently, there has been progress in anti-Klebsiella pneumoniae vaccine development, which has highlighted the lack of standardized assays to measure vaccine immunogenicity. We have developed and optimized methods to measure antibody level and function after vaccination with an in-development Klebsiella pneumoniae O-antigen vaccine. We describe the qualification of a Luminex-based multiplex antibody binding assay and both an opsonophagocytic killing assay and serum bactericidal assay to measure antibody function. Serum from immunized animals were immunogenic and capable of binding to and killing specific Klebsiella serotypes. Cross-reactivity was observed but limited among serotypes sharing antigenic epitopes. In summary, these results demonstrate the standardization of assays that can be used to test new anti-Klebsiella pneumoniae vaccine candidates, which is important for moving them into clinical trials. IMPORTANCE There is no licensed vaccine for the prevention of Klebsiella pneumoniae infections, and increasing levels of antibiotic resistance make this pathogen a high priority for vaccine and therapeutic development. Standardized assays for testing vaccine immunogenicity are paramount for the development of vaccines, and so in this study, we optimized and standardized both antibody-level and function assays for evaluating in-development K. pneumoniae bioconjugate vaccine response in rabbits.

Safety and immunogenicity of sequential administration of PCV13 followed by PPSV23 in pneumococcal vaccine-naïve adults aged ≥ 65 years: Comparison of booster effects based on intervals of 0.5 and 1.0 year

OBJECTIVE

An open-label study was conducted to compare the safety and immunogenicity of a sequential administration of 13-valent pneumococcal conjugate vaccine (PCV13) followed by 23-valent pneumococcal polysaccharide vaccine (PPSV23) between an interval of 0.5 (0.5-y) and 1 year (1.0-y) in adults aged ≥ 65 years.

METHODS

Pneumococcal vaccine-naïve adults aged ≥ 65 years (n = 129) received a sequential administration with an interval of 0.5-y or 1.0-y or received a single administration of PPSV23 (single PPSV23). We evaluated the immunogenicity before and 1 month after each vaccination and at 0.5-y intervals for 2 years. The primary endpoint was the increase in geometric mean fold rises (GMFRs) of immunoglobulin G (IgG) or opsonophagocytic activity (OPA) for eight common serotypes one month after one dose of PPSV23. The secondary endpoint was the safety profile for one dose of PPSV23.

RESULTS

One month after administration of PPSV23, the GMFRs of IgG considerably increased for five of eight serotypes in the 1.0-y interval group, whereas the GMFRs of IgG considerably increased for two serotypes in the 0.5-y interval group. Furthermore, GMFRs of OPA markedly increased for all eight serotypes in the 1.0-y interval group, while GMFRs of OPA markedly increased for four serotypes in the 0.5-y interval group. At 2 years after initial vaccination, GMFRs of IgG or OPA were higher for all serotypes, except for serotype 3, than those in the single PPSV23 group irrespective of intervals. No significant difference was found in the frequencies of local reactions of all grades between the two intervals.

CONCLUSIONS

The 1.0-y interval provided better booster effects induced by PPSV23 than those of the 0.5-y interval in a sequential administration in pneumococcal vaccine-naïve adults aged ≥ 65 years. No difference was found in the safety profile between both intervals.

A phase 3, multicenter, randomized, double-blind, active-comparator-controlled study to evaluate the safety, tolerability, and immunogenicity of a 4-dose regimen of V114, a 15-valent pneumococcal conjugate vaccine, in healthy infants (PNEU-PED)

BACKGROUND

Pneumococcal disease (PD) remains a major health concern with considerable morbidity and mortality in children. Currently licensed pneumococcal conjugate vaccines (PCVs) confer protection against PD caused by most vaccine serotypes, but non-vaccine serotypes contribute to residual disease. V114 is a 15-valent PCV containing all 13 serotypes in Prevnar 13™ (PCV13) and additional serotypes 22F and 33F. This pivotal phase 3 study compared safety and immunogenicity of V114 and PCV13.

METHODS

1720 healthy infants were randomized 1:1 to receive a 4-dose regimen of V114 or PCV13 concomitantly with other routine pediatric vaccines. Safety was evaluated after each dose as proportion of participants with adverse events (AEs). Serotype-specific anti-pneumococcal immunoglobulin G (IgG) was measured at 1-month post-dose 3 (PD3), pre-dose 4, and 1-month post-dose 4 (PD4). IgG response rates, geometric mean concentrations (GMCs), and opsonophagocytic activity (OPA) were compared between vaccination groups.

RESULTS

The proportion, maximum intensity, and duration of injection-site, systemic, and serious AEs were generally comparable between V114 and PCV13 groups. In comparison to PCV13, V114 met non-inferiority criteria for all 15 serotypes based on IgG response rates at PD3. V114 met non-inferiority criteria by IgG GMCs for all serotypes at PD3 and PD4, except for serotype 6A at PD3. V114-induced antibodies had bactericidal activity as assessed by OPA. Further, V114 met superiority criteria for shared serotype 3 and unique serotypes 22F and 33F compared to PCV13 by serotype-specific IgG GMCs at both PD3 and PD4. Immunogenicity of concomitantly administered routine pediatric vaccines was comparable in V114 and PCV13 groups.

CONCLUSIONS

In healthy infants, V114 displays acceptable safety and tolerability profiles and generates comparable immune responses to PCV13. V114 also met superiority criteria for serotypes 3, 22F, and 33F. These results support use of V114 for prevention of PD as part of routine infant vaccination schedules.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT03893448; EudraCT: 2018-004109-21.

Preclinical evaluation of an investigational 21-valent pneumococcal conjugate vaccine, V116, in adult-rhesus monkey, rabbit, and mouse models

Despite the widespread effectiveness of pneumococcal conjugate vaccines on the overall incidence of invasive pneumococcal disease, the global epidemiological landscape continues to be transformed by residual disease from non-vaccine serotypes, thus highlighting the need for vaccines with expanded disease coverage. To address these needs, we have developed V116,an investigational 21-valent non-adjuvanted pneumococcal conjugate vaccine (PCV),containingpneumococcal polysaccharides (PnPs) 3, 6A, 7F, 8, 9N, 10A, 11A,12F, 15A, 16F, 17F, 19A, 20, 22F, 23A, 23B, 24F, 31, 33F, 35B, anda de-O-acetylated 15B(deOAc15B) individually conjugated to the nontoxic diphtheria toxoid CRM197 carrier protein. Preclinical studies evaluated the immunogenicity of V116 inadult monkeys, rabbits, and mice. Following one dose, V116 was found to be immunogenic in preclinical animal species and induced functional antibodies for all serotypes included in the vaccine, in addition to cross-reactive functional antibodies to serotypes 6C and 15B. In these preclinical animal studies, the increased valency of V116 did not result in serotype-specific antibody suppression when compared to lower valent vaccines V114 or PCV13. In addition, when compared with naïve controls, splenocytes from V116 to immunized animals demonstrated significant induction of CRM197-specific T cells in both IFN-γ and IL-4 ELISPOT assays, as well as Th1 and Th2 cytokine induction through in vitro stimulation assays, thus suggesting the ability of V116 to engage T cell dependent immune response pathways to aid in development of memory B cells. V116 also demonstrated significant protection in mice from intratracheal challenge with serotype 24F, a novel serotype not contained in any currently licensed vaccine.

Potentiating pneumococcal glycoconjugate vaccine PCV13 with saponin adjuvant VSA-1

VSA-1 is a semisynthetic saponin adjuvant prepared from naturally occurring Momordica saponin and capable of stimulating antigen-specific humoral and cellular immune responses. Its immunostimulating activity in enhancing the immune responses induced by the clinical glycoconjugate pneumococcal vaccine PCV13 is compared with QS-21 in female BALB/c mice. Both VSA-1 and QS-21 boosted IgG and opsonic antibodies titers against seven selected serotypes, including serotypes 3, 14, and 19A that are involved in most PCV13 breakthroughs. Since VSA-1 is much more accessible and of lower toxicity than QS-21, it can be a practical saponin immunostimulant to be included in a new glycoconjugate pneumococcal vaccine formulation.

Quality of antibody responses by adults and young children to 13-valent pneumococcal conjugate vaccination and Streptococcus pneumoniae colonisation

Childhood pneumococcal conjugate vaccine (PCV) protects against invasive pneumococcal disease caused by vaccine-serotype (VT) Streptococcus pneumoniae by generating opsonophagocytic anti-capsular antibodies, but how vaccination protects against and reduces VT carriage is less well understood. Using serological samples from PCV-vaccinated Malawian individuals and a UK human challenge model, we explored whether antibody quality (IgG subclass, opsonophagocytic killing, and avidity) is associated with protection from carriage. Following experimental challenge of adults with S. pneumoniae serotype 6B, 3/21 PCV13-vaccinees were colonised with pneumococcus compared to 12/24 hepatitis A-vaccinated controls; PCV13-vaccination induced serotype-specific IgG, IgG1, and IgG2, and strong opsonophagocytic responses. However, there was no clear relationship between antibody quality and protection from carriage or carriage intensity after vaccination. Similarly, among PCV13-vaccinated Malawian infants there was no relationship between serotype-specific antibody titre or quality and carriage through exposure to circulating serotypes. Although opsonophagocytic responses were low in infants, antibody titre and avidity to circulating serotypes 19F and 6A were maintained or increased with age. These data suggest a complex relationship between antibody-mediated immunity and pneumococcal carriage, and that PCV13-driven antibody quality may mature with age and exposure.

Phase 1/2 study of a novel 24-valent pneumococcal vaccine in healthy adults aged 18 to 64 years and in older adults aged 65 to 85 years

BACKGROUND

Pneumococcal diseases remain prevalent despite available polysaccharide and conjugate vaccines. This phase 1/2 study evaluated safety/tolerability and immunogenicity of a novel 24-valent pneumococcal vaccine (ASP3772) based on high-affinity complexing of proteins and polysaccharides.

METHODS

Pneumococcal vaccine-naïve adults aged 18-85 years were randomized to receive either ASP3772 or PCV13 (13-valent conjugate vaccine). Participants received a single intramuscular injection of ASP3772 (1-, 2-, or 5-µg dose per polysaccharide) or PCV13. A separate, nonrandomized group of PCV13-vaccinated participants (65-85 years) received PPSV23 (23-valent polysaccharide vaccine). Assessments were obtained through Day 7 for reactogenicity, through Day 30 for safety and tolerability, and through Month 6 for serious adverse events. Immunogenicity was measured at Day 30 using assays for functional opsonophagocytic activity (OPA) and pneumococcal serotype-specific anticapsular polysaccharide immunoglobulin G for each serotype.

RESULTS

In both age cohorts, the most frequently reported local reactions were self-limited tenderness and pain after ASP3772 at all dose levels or after PCV13, occurring within 2-3 days. Fatigue, headache, and myalgia were the most frequently reported systemic reactions following either vaccine. Robust OPA responses for all serotypes were observed across all ASP3772 dose groups in both age cohorts. Older adults (aged 65-85 years) who received ASP3772 had significantly higher immune responses to several PCV13 serotypes and all non-PCV13 serotypes than participants who received PCV13. OPA responses to the ASP3772 5-µg dose were significantly higher for several serotypes in naïve participants than in older adults with prior exposure to PCV13 who were administered PPSV23 in this study.

CONCLUSIONS

These results demonstrate that ASP3772 is well tolerated, highly immunogenic, and in adults may offer significantly broader protection than existing pneumococcal vaccines.

CLINICALTRIALS

gov: NCT03803202.

Specific antibody deficiency: Pearls and pitfalls for diagnosis

OBJECTIVE

Specific antibody deficiency is an immune deficiency defined by the presence of normal quantitative levels of immunoglobulins but impaired antibody responses to polysaccharide antigens in patients presenting with frequent otosinopulmonary infections with pyogenic bacteria. This review summarizes the pitfalls associated with defining exactly what constitutes an "impaired" antibody response to polysaccharide antigens and the importance of documenting actual pyogenic infections before making a diagnosis of an immune deficiency.

DATA SOURCES

PubMed review using the following words: specific antibody deficiency, pneumococcal vaccination, salmonella vaccination, infectious sinusitis Study Selection: This review focused on key studies that have been utilized to define what constitutes a "normal" humoral immune response to pneumococcal and salmonella vaccination in healthy subjects as well as published papers defining current expert opinion.

RESULTS

Published studies demonstrate wide variability in response to pneumococcal vaccination in healthy individuals making it daunting to define what constitutes an abnormal response. These challenges are exacerbated by striking laboratory variability in reporting results.

CONCLUSION

Clinical evaluations in individuals with self-reported recurrent acute sinusitis or lower respiratory infections need to document an infectious etiology with pyogenic bacteria and must rule out an underlying primary airway inflammatory disorder before consideration is made regarding the presence of an immune deficiency. In addition, decision making regarding diagnosis and treatment of patients being evaluated for humoral immunodeficiency should not hinge solely on the strict application of defined cutoffs for "normal" response to a single polysaccharide vaccine, but rather a global assessment of humoral immune function in the context of the clinical presentation.

Thirteen-Valent Pneumococcal Conjugate Vaccine-Induced Immunoglobulin G (IgG) Responses in Serum Associated With Serotype-Specific IgG in the Lung

Pneumococcal conjugate vaccine (PCV) efficacy is lower for noninvasive pneumonia than invasive disease. In this study, participants were immunized with 13-valent PCV (PCV13) or hepatitis A vaccine (control). Bronchoalveolar lavage samples were taken between 2 and 6 months and serum at 4 and 7 weeks postvaccination. In the lung, anti-capsular immunoglobulin G (IgG) levels were higher in the PCV13 group compared to controls for all serotypes, except 3 and 6B. Systemically, IgG levels were elevated in the PCV13 group at 4 weeks for all serotypes, except serotype 3. IgG in bronchoalveolar lavage and serum positively correlated for nearly all serotypes. PCV13 shows poor immunogenicity to serotype 3, implying lack of protective efficacy. Clinical Trials Registration. ISRCTN 45340436.

Ficolin-2 Lectin Complement Pathway Mediates Capsule-Specific Innate Immunity Against Invasive Pneumococcal Disease

Reports conflict regarding which lectin-microbial ligand interactions elicit a protective response from the lectin pathway (LP) of complement. Using fluorescent microscopy, we demonstrate the human lectin ficolin-2 binds to Streptococcus pneumoniae serotype 11A capsule polysaccharide dependent on the O-acetyltransferase gene wcjE. This triggers complement deposition and promotes opsonophagocytosis of encapsulated pneumococci. Even partial loss of ficolin-2 ligand expression through wcjE mutation abrogated bacterial killing. Ficolin-2 did not interact with any pneumococcal non-capsule structures, including teichoic acid. We describe multiple 11A clonal derivatives expressing varying degrees of wcjE-dependent epitopes co-isolated from single blood specimens, likely representing microevolutionary shifts towards wcjE-deficient populations during invasive pneumococcal disease (IPD). We find epidemiological evidence of wcjE impairing pneumococcal invasiveness, supporting that the LP's ficolin-2 axis provides innate, serotype-specific serological protection against IPD. The fact that the LP is triggered by only a few discrete carbohydrate ligands emphasizes the need to reevaluate its impact in a glycopolymer-specific manner.

Single-Dose 13-Valent Conjugate Pneumococcal Vaccine in People Living With HIV – Immunological Response and Protection

Background

Patients living with HIV (PLHIV) are prone to invasive pneumococcal disease. The 13-valent conjugated pneumococcal vaccine (PCV13) is currently recommended for all PLHIV, followed in most guidelines by a 23-valent polysaccharide pneumococcal vaccine. Data are scarce concerning the immunological efficacy of PCV13 among PLHIV.

Objective

To assess the immunological response at one month, and the immunological protection at 1-, 6-, and 12 months in PLHIV with a CD4 cell count above 200 cells/µl after a single dose of PCV13, as measured by both ELISA and opsonophagocytic assay (OPA).

Methods

PLHIV with CD4 cell count >200 cells/µl were included. Specific IgG serum concentrations for eight serotypes by ELISA and seven serotypes by OPA were measured at baseline, 1-, 6-, and 12 months after the PCV13 vaccination. Global response was defined as a two-fold increase from baseline of specific IgG antibody levels (μg/ml) assayed by ELISA or as a four-fold increase in OPA titer from baseline, for at least five serotypes targeted by PCV13. Global protection was defined as an IgG-concentration ≥1 µg/ml by ELISA or as an opsonization titer ≥LLOQ by OPA for at least five tested serotypes targeted by PCV13. Factors associated with global response and global protection were assessed using logistic regression.

Results

Of the 38 PLHIV included, 57.9% and 63.2% were global responders, 92.1% and 78.9% were globally protected at one month, and 64.7% and 55.9% were still protected at 12 months, by ELISA and OPA respectively. A CD4/CD8 ratio of >0.8 was significantly associated with a better global response by OPA (OR=6.11, p=0.02), and a CD4 nadir <200 was significantly associated with a poorer global response by ELISA (OR=0.22, p=0.04). A CD4 cell count nadir <200 and age over 50 years were associated with poorer global protection by OPA at M1 (OR=0.18, p=0.04) and M12 (OR= 0.15, p=0.02), respectively. Plasma HIV RNA viral load <40 copies/ml was significantly associated with a better global protection at M1 by ELISA and OPA (OR=21.33, p=0.025 and OR=8.40, p=0.04)

Conclusion

Vaccination with PCV13 in these patients induced immunological response and protection at one month. At one year, more than half of patients were still immunologically protected.

Simplified 0+1 and 1+1 pneumococcal vaccine schedules in Ho Chi Minh City, Vietnam: protocol for a randomised controlled trial

INTRODUCTION

Reduced-dose schedules offer a more efficient and affordable way to use pneumococcal conjugate vaccines (PCVs). Such schedules rely primarily on the maintenance of herd protection. The Vietnam Pneumococcal Trial II (VPT-II) will evaluate reduced-dose schedules of PCV10 and PCV13 utilising an unvaccinated control group. Schedules will be compared in relation to their effect on nasopharyngeal carriage and immunogenicity.

METHODS AND ANALYSIS

VPT-II is a single-blind open-label randomised controlled trial of 2500 infants in three districts of Ho Chi Minh City, Vietnam. Eligible infants have no clinically significant maternal or perinatal history and are born at or after 36 weeks' gestation. Participants are recruited at 2 months of age and randomly assigned (4:4:4:4:9) using block randomisation, stratified by district, to one of five groups: four intervention groups that receive PCV10 in a 0+1 (at 12 months) or 1+1 (at 2 and 12 months) schedule or PCV13 in the same 0+1 or 1+1 schedule; and a control group (that receives a single dose of PCV10 at 24 months). Participants are followed up to 24 months of age. The primary outcome is vaccine-type pneumococcal carriage at 24 months of age. Secondary outcomes are carriage at 6, 12 and 18 months of age and the comparative immunogenicity of the different schedules in terms of antibody responses, functional antibody responses and memory B cell responses.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Human Research Ethics Committee of the Royal Children's Hospital Melbourne and the Vietnam Ministry of Health Ethics Committee. The results, interpretation and conclusions will be presented to parents and guardians, at national and international conferences and published in peer-reviewed open access journals.

TRIAL REGISTRATION NUMBER

NCT03098628.

Anatomical site-specific carbohydrate availability impacts Streptococcus pneumoniae virulence and fitness during colonization and disease

Streptococcus pneumoniae (Spn) colonizes the nasopharynx asymptomatically but can also cause severe life-threatening disease. Importantly, stark differences in carbohydrate availability exist between the nasopharynx and invasive disease sites, such as the bloodstream, which most likely impact Spn's behavior. Herein, using chemically-defined media (CDM) supplemented with physiological levels of carbohydrates, we examined how anatomical-site specific carbohydrate availability impacted Spn physiology and virulence. Spn grown in CDM modeling the nasopharynx (CDM-N) had reduced metabolic activity, slower growth rate, demonstrated mixed acid fermentation with marked H₂O₂ production, and were in a carbon-catabolite repression (CCR)-derepressed state versus Spn grown in CDM modeling blood (CDM-B). Using RNA-seq, we determined the transcriptome for Spn WT and its isogenic CCR deficient mutant in CDM-N and CDM-B. Genes with altered expression as a result of changes in carbohydrate availability or catabolite control protein deficiency, respectively, were primarily involved in carbohydrate metabolism, but also encoded for established virulence determinants such polysaccharide capsule and surface adhesins. We confirmed that anatomical site-specific carbohydrate availability directly influenced established Spn virulence traits. Spn grown in CDM-B formed shorter chains, produced more capsule, were less adhesive, and were more resistant to macrophage killing in an opsonophagocytosis assay. Moreover, growth of Spn in CDM-N or CDM-B prior to the challenge of mice impacted relative fitness in a colonization and invasive disease model, respectively. Thus, anatomical site-specific carbohydrate availability alters Spn physiology and virulence, in turn promoting anatomical-site specific fitness.

Structural, Genetic, and Serological Elucidation of Streptococcus pneumoniae Serogroup 24 Serotypes: Discovery of a New Serotype, 24C, with a Variable Capsule Structure

Pneumococcal capsules are important in pneumococcal pathogenesis and vaccine development. Although conjugate vaccines have brought about a significant reduction in invasive pneumococcal disease (IPD) caused by vaccine serotypes, the relative serotype prevalence has shifted with the dramatic emergence of serotype 24F in some countries. Here, we describe 14 isolates (13 IPD and 1 non-IPD) expressing a new capsule type, 24C, which resembles 24F but has a novel serological profile. We also describe the antigenic, biochemical, and genetic basis of 24F and 24C and the related serotypes 24A and 24B. Structural studies show that 24B, 24C, and 24F have identical polysaccharide backbones [β-Ribf-(1→4)-α-Rhap-(1→3)-β-GlcpNAc-(1→4)-β-Rhap-(1→4)-β-Glcp] but with different side chains, as follows: 24F has arabinitol-phosphate and 24B has ribitol-phosphate. 24C has a mixture of 24F and 24B repeating units, with the ratio of ribitol to arabinitol being strain dependent. In contrast, the 24A capsule has a backbone without β-Ribf but with arabinitol-phosphate and phosphocholine side chains. These structures indicate that factor-sera 24d and 24e recognize arabinitol and ribitol, respectively, which explains the serology of serogroup 24, including those of 24C. The structures can be genetically described by the bispecificity of wcxG, which is capable of transferring arabinitol or ribitol when arabinitol is limiting. Arabinitol is likely not produced in 24B but is produced in reduced amounts in 24C due to various mutations in abpA or abpB genes. Our findings demonstrate how pneumococci modulate their capsule structure and immunologic properties with small genetic changes, thereby evading host immune responses. Our findings also suggest a potential for new capsule types within serogroup 24.

Immunogenicity of PCV24, an expanded pneumococcal conjugate vaccine, in adult monkeys and protection in mice

Invasive pneumococcal disease (IPD) is responsible for serious illnesses such as bacteremia, sepsis, meningitis, and pneumonia in young children, older adults, and persons with immunocompromising conditions and often leads to death. Although the most recent pneumococcal conjugate vaccines (PCVs) have been designed to target serotypes identified as the primary causative agents of IPD, the epidemiological landscape continues to change stressing the need to develop new PCVs. We have developed an investigational 24-valent PCV (PCV24) including serotypes 1, 2, 3, 4, 5, 6A, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19A, 19F, 20, 22F, 23F, and 33F all conjugated to CRM197 and evaluated this vaccine in adult monkeys. PCV24 was shown to be immunogenic and induced functional antibody for all vaccine serotypes. Of the serotypes common to PCV13 and V114 (PCV15), PCV24 had a similar immunogenic response with the exceptions of 23F which had higher IgG GMCs for PCV13 and V114, and 7F which had higher GMCs for PCV13. Functional antibody responses were similar for the serotypes in common between PCV24, PCV13 and V114 vaccines, with the exception of serotype 7F which was greater for PCV13. Overall, this study shows that PCV24 provided similar immunogenicity as the lower valent vaccines in adult monkeys with no apparent serotype interference. In addition, PCV24 also provided protection against pneumococcal infection in a mouse challenge model.

Sequential administration of Prevnar 13™ and PNEUMOVAX™ 23 in healthy participants 50 years of age and older

In most countries worldwide, pneumococcal conjugate vaccines have been included in the infant immunization program, resulting in a significant reduction in the burden of pneumococcal disease in children and adults. Shifting serotype distribution due to the indirect effect of infant vaccination with the 13-valent pneumococcal conjugate vaccine (PCV13) may continue to increase the gap between 23-valent pneumococcal polysaccharide vaccine (PPSV23) and PCV13 serotype coverage for older adults in the coming years. This clinical study (V110-029; NCT02225587) evaluated the safety and immunogenicity of sequential administration of PCV13 followed approximately 8 weeks later, or approximately 26 weeks later, by PPSV23 in healthy adults ≥50 years of age. Both dosing intervals were generally well tolerated as measured by the nature, frequency, and intensity of reported adverse events (AEs) in both vaccination groups. Serotype-specific opsonophagocytic activity (OPA) geometric mean titers (GMTs) measured 30 days following receipt of PPSV23 in either group and at Week 30 were generally comparable between the 2 groups for 6 serotypes unique to PPSV23 and 12 serotypes shared between PCV13 and PPSV23, regardless of the interval between receipt of PCV13 and PPSV23. In addition, administration of PPSV23 given either 8 weeks or 26 weeks following PCV13 did not negatively impact immune responses induced by PCV13. Furthermore, administration of PPSV23 given either 8 weeks or 26 weeks after PCV13 elicited serotype-specific OPA GMTs to serotypes unique to PPSV23, which could provide earlier protection against pneumococcal disease caused by these serotypes in comparison with the current Advisory Committee on Immunization Practices recommended interval of at least 12 months.

Non-clinical immunological comparison of a Next-Generation 24-valent pneumococcal conjugate vaccine (VAX-24) using site-specific carrier protein conjugation to the current standard of care (PCV13 and PPV23)

Despite widespread utilization of pneumococcal conjugate vaccines (PCVs) and the resultant disease reduction, the development of PCVs containing additional serotypes remains a public health priority due to serotype replacement and the resultant shift to non-vaccine containing serotypes. However, incorporating additional serotypes to existing PCVs using conventional technologies has proven problematic. Immune responses to individual serotypes have consistently decreased as more polysaccharide-conjugates are added due to carrier suppression. Using our proprietary cell-free protein synthesis (CFPS) platform, we have successfully produced eCRM® based on the CRM₁₉₇ sequence for use as an enhanced carrier protein to develop a 24-valent PCV. The eCRM carrier protein contains multiple non-native amino acids (nnAAs) located outside of the primary T-cell epitope regions, thereby enabling site-specific covalent conjugation of the pneumococcal polysaccharides to the nnAAs to consistently expose the critical T-cell epitopes. eCRM also serves to reduce structural heterogeneity associated with classic reductive-amination conjugation while promoting formation of the conjugate matrix structures, the hallmark of PCVs. This process serves to increase the overall polysaccharide:protein ratio, enabling the inclusion of more serotypes while minimizing carrier-mediated immunological interference. The aim of this non-clinical study was to construct a 24-valent PCV and evaluate its immunogenicity. Using the XPressCF® CFPS platform, the eCRM carrier protein was separately conjugated through nnAAs to each of the 24 pneumococcal polysaccharides through click chemistry and mixed with aluminum phosphate to produce VAX-24, Vaxcyte's proprietary PCV preclinical candidate. VAX-24, Prevnar13® and Pneumovax®23 were administered to New Zealand White rabbits to compare the resulting opsonophagocytic activity (OPA) and anti-capsular IgG antibodies. VAX-24 showed conjugate-like immune responses to all 24 serotypes based on comparable OPA and IgG responses to Prevnar13 and higher responses than Pneumovax 23. This study demonstrates the utility of site-specific conjugation technology in a preclinical setting and the potential for a PCV with improved serotype coverage.

Immunogenicity and safety of 7-valent pneumococcal conjugate vaccine (PCV7) in children aged 2-5 years in China

BACKGROUND

The widespread use of pneumococcal conjugate vaccines (PCVs) has significantly decreased pneumococcal disease worldwide. However, China has not adopted PCVs in their national immunization schedules and had only approved these vaccines for children aged 2-15 months by 2020.

METHODS

In an open-label trial, enrolled healthy children aged 2-5 years old were randomized 1:1 and divided into a 7-valent pneumococcal conjugate vaccine (PCV7) group and a Haemophilus influenzae type b conjugate vaccine (Hib) group. Children in the PCV7 group received a single dose of PCV7, and the Hib group received a single dose of Hib vaccine. Blood samples were collected before and 6 months after vaccination. Immunogenicity and safety of PCV7 were assessed at prespecified time points.

RESULTS

Six months after a single dose of PCV7, children in the PCV7 group for all 7 serotypes, IgG mean concentrations (GMCs) and opsonophagocytic geometric mean titres (GMTs) were significantly higher (P < .001) than at baseline, and the proportion of IgG ≥ 0.35 µg/mL ranged from 90.0% to 100%. Although the antibody level increased with age, preexisting antibodies did not induce hyporesponsiveness to PCV7. In the Hib group, the antibody levels were not significantly different or had changed slightly at 6 months. PCV7 was well tolerated in all age groups, and no serious adverse events (AEs) emerged during this study.

CONCLUSIONS

A single dose of PCV7 was immunogenic and safe for Chinese children aged 2-5 years, and the preexisting antibodies against the PCV7 serotypes did not change the response to vaccination. The findingssupported the effectiveness of PCV7 in this age group. PCVs with broader serotype coverage are expected to expand pneumococcal disease protection.

Pneumococcal Serotype-specific Opsonophagocytic Activity in Interleukin-1 Receptor-associated Kinase 4-deficient Patients

BACKGROUND

The antibody response after pneumococcal vaccines and their effectiveness against invasive pneumococcal disease (IPD) in patients with interleukin-1 receptor-associated kinase 4 (IRAK4) deficiency have not been fully evaluated. Here, we evaluated pneumococcal serotype-specific opsonophagocytic activity (OPA) in IRAK4-deficient patients along with their clinical course.

METHODS

We investigated 6 IRAK4-deficient patients in Japan, whose attending physicians could be contacted. We performed OPA measurements using stored and more recent serum samples obtained from these patients.

RESULTS

All patients had received pneumococcal vaccination. Among the 3 patients who had IPD, 2 had an episode of pneumococcal meningitis and the other developed pneumococcal bacteremia 3 years after the occurrence of pneumococcal meningitis. Only one episode of invasive bacterial infection was caused by a Streptococcus pneumoniae vaccine-type strain. An increased opsonization index was found in the sera after vaccination for all IRAK-deficient patients, including when the 23-valent pneumococcal polysaccharide vaccine was used.

CONCLUSIONS

A significant increase in levels of OPA against most of the pneumococcal vaccine antigens was observed for all IRAK4-deficient patients. However, IPD could not be prevented by pneumococcal vaccination alone. Therefore, adequate prophylaxis should be provided with antibiotics at least until 8 years of age, along with regular immunoglobulin therapy, particularly during the infantile period.

Corrected and Republished from: A Nonfunctional Opsonic Antibody Response Frequently Occurs after Pneumococcal Pneumonia and Is Associated with Invasive Disease

Numerous reports on the dynamics of antipneumococcal immunity in relation to immunization with pneumococcal vaccines and on the prevalence of naturally acquired immunity in various populations have been published. In contrast, studies on the dynamics of the humoral immune response triggered by pneumococcal infection are scarce.

Naturally acquired opsonic antipneumococcal antibodies are commonly found in nonvaccinated adults and confer protection against infection and colonization. Despite this, only limited data exist regarding the adaptive immune response after pneumococcal exposure. To investigate the dynamics of naturally acquired antipneumococcal immunity in relation to an episode of infection, opsonic antibody activity was studied with paired acute-phase and convalescent-phase sera obtained from 54 patients with pneumococcal community-acquired pneumonia (CAP) using an opsonophagocytic assay (OPA). Results were compared with clinical characteristics and anticapsular immunoglobulin (Ig) concentrations. Interestingly, a nonfunctional opsonic antibody response (characterized by a decreased convalescent-phase serum OPA titer compared to that of the acute-phase serum or undetectable titers in both sera) was observed in 19 (35%) patients. The remaining individuals exhibited either an increased convalescent-phase OPA titer (n  =  24 [44%]) or a detectable, but unchanged, titer at both time points (n = 11 [20%]). Invasive pneumococcal disease (i.e., bacteremia) was significantly more common among patients with a nonfunctional convalescent-phase response than in patients with other convalescent-phase responses. Anticapsular Ig concentrations were higher among patients with detectable convalescent-phase OPA titers (P = 0.003), and the greatest Ig concentration increase was observed among patients with an increased convalescent-phase response (P = 0.002). Our findings indicate that an episode of pneumococcal infection may act as an immunizing event. However, in some cases when patients with CAP also suffer from bacteremia, a nonfunctional opsonic antibody response may occur. Furthermore, the results suggest that factors other than anticapsular Ig concentrations determine opsonic antibody activity in serum.

IMPORTANCE Numerous reports on the dynamics of antipneumococcal immunity in relation to immunization with pneumococcal vaccines and on the prevalence of naturally acquired immunity in various populations have been published. In contrast, studies on the dynamics of the humoral immune response triggered by pneumococcal infection are scarce. This study provides valuable information that will contribute to fill this knowledge gap. Our main results indicate that a functional immune response may fail after CAP, predominantly among patients with simultaneous bacteremia.

Reduction of free polysaccharide contamination in the production of a 15-valent pneumococcal conjugate vaccine

Glycoconjugate vaccines are vaccines in which a bacterial polysaccharide antigen is conjugated to a carrier protein to enhance immunogenicity by promoting T cell-dependent immune response. However, the free (unreacted) polysaccharides remaining after the conjugation process can inhibit the immunogenicity of a conjugate vaccine. Thus, we aimed to reduce the unbound free polysaccharides in the polysaccharide-protein conjugation process for the development of a new 15-valent pneumococcal conjugate vaccine (PCV15) by varying some factors that may affect the conjugation results such as polysaccharide/protein ratio, polysaccharide size, and concentration of a coupling agent in a conjugation reaction mixture. Concentrations of a coupling agent, carbodiimide (EDAC), and a carrier protein (CRM197) used in PCV15 production, during the conjugation process, had little effect on the content of free polysaccharides. However, the size of the polysaccharide was identified as the critical factor to control the free polysaccharide content, with an inverse relationship observed between the molecular weight of the polysaccharide and the residual free polysaccharide content after conjugation. Based on these results, a new PCV15 with low free polysaccharide contamination was produced and tested for immunogenicity using a rabbit model to show that it induces similar level of immune responses in rabbits compared to a comparator vaccine Prevnar13®.

A Phase II Trial of Safety, Tolerability and Immunogenicity of V114, a 15-Valent Pneumococcal Conjugate Vaccine, Compared With 13-Valent Pneumococcal Conjugate Vaccine in Healthy Infants

BACKGROUND

Pneumococcal disease remains a public health priority worldwide. This phase 2 study (V114-008; NCT02987972; EudraCT 2016-001117-25) compared safety and immunogenicity of 2 clinical lots of V114 (investigational 15-valent pneumococcal vaccine: 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19F, 19A, 22F*, 23F, 33F*) to 13-valent pneumococcal conjugate vaccine (PCV13) in healthy infants (*serotypes unique to V114).

METHODS

Healthy infants 6-12 weeks old were randomized to receive a 4-dose regimen of V114 Lot 1, V114 Lot 2 or PCV13 at 2, 4, 6 and 12-15 months old. Adverse events were evaluated after each dose. Primary immunogenicity endpoint was to demonstrate noninferiority of V114 Lot 1 and V114 Lot 2 relative to PCV13 based on proportion of infants achieving serotype-specific IgG concentration ≥0.35 µg/mL for 13 serotypes shared with PCV13 at 1 month postdose 3 (PD3). Serotype-specific IgG geometric mean concentrations (GMCs) for all 15 V114 serotypes were measured at PD3, predose 4 and 1 month postdose 4 (PD4).

RESULTS

Overall, 1044 of 1051 randomized infants received ≥1 dose of vaccine (V114 Lot 1 [n = 350], V114 Lot 2 [n = 347] or PCV13 [n = 347]). Adverse events were generally comparable across groups. At PD3, both V114 lots met noninferiority criteria for all 13 serotypes shared with PCV13. IgG GMCs were comparable among V114 and PCV13 recipients at PD3 and PD4. Serotype 3 responses were higher following receipt of V114 than PCV13. Both V114 lots induced higher GMCs than PCV13 to the 2 unique V114 serotypes.

CONCLUSIONS

Immunogenicity of both V114 lots was noninferior to PCV13 for all 13 shared serotypes between the 2 vaccines and displayed comparable safety and tolerability profiles to PCV13.

Pneumococci Can Become Virulent by Acquiring a New Capsule From Oral Streptococci

Pneumococcal conjugate vaccines have been successful, but their use has increased infections by nonvaccine serotypes. Oral streptococci often harbor capsular polysaccharide (PS) synthesis loci (cps). Although this has not been observed in nature, if pneumococcus can replace its cps with oral streptococcal cps, it may increase its serotype repertoire. In the current study, we showed that oral Streptococcus strain SK95 and pneumococcal strain D39 both produce structurally identical capsular PS, and their genetic backgrounds influence the amount of capsule production and shielding from nonspecific killing. SK95 is avirulent in a well-established in vivo mouse model. When acapsular pneumococcus was transformed with SK95 cps, the transformant became virulent and killed all mice. Thus, cps from oral Streptococcus strains can make acapsular pneumococcus virulent, and interspecies cps transfer should be considered a potential mechanism of serotype replacement. Our findings, along with publications from the US Centers for Disease Control and Prevention, highlight potential limitations of the 2013 World Health Organization criterion for studying pneumococcal serotypes carried without isolating bacteria. We show that an oral streptococcal strain, SK95, and a pneumococcal strain, D39, both produce chemically identical capsular PS. We also show that transferring SK95 cps into noncapsulated, avirulent pneumococcus gave it the capacity for virulence in a mouse model.

Optimization and validation of a microcolony multiplexed opsonophagocytic killing assay for 15 pneumococcal serotypes

Background: To streamline and improve throughput, the agar-based multiplexed opsonophagocytic killing assay (MOPA) was optimized and validated on a microcolony platform for use in the Phase III clinical trial program for V114, an MSD 15-valent pneumococcal conjugate vaccine candidate. Results & methodology: The precision, dilutional linearity and specificity of the microcolony MOPA (mMOPA) were assessed for each serotype in validation experiments. All prespecified acceptance criteria on assay performance were satisfied. Accuracy was assessed by testing 007sp and the US FDA reference panel and comparing to consensus values. The mMOPA produced comparable results to other opsonophagocytic killing assays/MOPAs. Conclusion: The mMOPA is suitable for measuring functional antibodies in adult and pediatric samples. Benefits include throughput, reduced analyst-to-analyst variability and automation potential.

A New Pneumococcal Capsule Type, 10D, is the 100th Serotype and Has a Large cps Fragment from an Oral Streptococcus

The polysaccharide capsule is essential for the pathogenicity of pneumococcus, which is responsible for millions of deaths worldwide each year. Currently available pneumococcal vaccines are designed to elicit antibodies to the capsule polysaccharides of the pneumococcal isolates commonly causing diseases, and the antibodies provide protection only against the pneumococcus expressing the vaccine-targeted capsules. Since pneumococci can produce different capsule polysaccharides and therefore reduce vaccine effectiveness, it is important to track the appearance of novel pneumococcal capsule types and how these new capsules are created. Herein, we describe a new and the 100th pneumococcal capsule type with unique chemical and serological properties. The capsule type was named 10D for its serologic similarity to 10A. Genetic studies provide strong evidence that pneumococcus created 10D capsule polysaccharide by capturing a large genetic fragment from an oral streptococcus. Such interspecies genetic exchanges could greatly increase diversity of pneumococcal capsules and complicate serotype shifts.

Streptococcus pneumoniae (pneumococcus) is a major human pathogen producing structurally diverse capsular polysaccharides. Widespread use of highly successful pneumococcal conjugate vaccines (PCVs) targeting pneumococcal capsules has greatly reduced infections by the vaccine types but increased infections by nonvaccine serotypes. Herein, we report a new and the 100th capsule type, named serotype 10D, by determining its unique chemical structure and biosynthetic roles of all capsule synthesis locus (cps) genes. The name 10D reflects its serologic cross-reaction with serotype 10A and appearance of cross-opsonic antibodies in response to immunization with 10A polysaccharide in a 23-valent pneumococcal vaccine. Genetic analysis showed that 10D cps has three large regions syntenic to and highly homologous with cps loci from serotype 6C, serotype 39, and an oral streptococcus strain (S. mitis SK145). The 10D cps region syntenic to SK145 is about 6 kb and has a short gene fragment of wciNα at the 5′ end. The presence of this nonfunctional wciNα fragment provides compelling evidence for a recent interspecies genetic transfer from oral streptococcus to pneumococcus. Since oral streptococci have a large repertoire of cps loci, widespread PCV usage could facilitate the appearance of novel serotypes through interspecies recombination.

A New Pneumococcal Capsule Type, 10D, is the 100th Serotype and Has a Large cps Fragment from an Oral Streptococcus

Streptococcus pneumoniae (pneumococcus) is a major human pathogen producing structurally diverse capsular polysaccharides. Widespread use of highly successful pneumococcal conjugate vaccines (PCVs) targeting pneumococcal capsules has greatly reduced infections by the vaccine types but increased infections by nonvaccine serotypes. Herein, we report a new and the 100th capsule type, named serotype 10D, by determining its unique chemical structure and biosynthetic roles of all capsule synthesis locus (cps) genes. The name 10D reflects its serologic cross-reaction with serotype 10A and appearance of cross-opsonic antibodies in response to immunization with 10A polysaccharide in a 23-valent pneumococcal vaccine. Genetic analysis showed that 10D cps has three large regions syntenic to and highly homologous with cps loci from serotype 6C, serotype 39, and an oral streptococcus strain (S. mitis SK145). The 10D cps region syntenic to SK145 is about 6 kb and has a short gene fragment of wciNα at the 5' end. The presence of this nonfunctional wciNα fragment provides compelling evidence for a recent interspecies genetic transfer from oral streptococcus to pneumococcus. Since oral streptococci have a large repertoire of cps loci, widespread PCV usage could facilitate the appearance of novel serotypes through interspecies recombination.IMPORTANCE The polysaccharide capsule is essential for the pathogenicity of pneumococcus, which is responsible for millions of deaths worldwide each year. Currently available pneumococcal vaccines are designed to elicit antibodies to the capsule polysaccharides of the pneumococcal isolates commonly causing diseases, and the antibodies provide protection only against the pneumococcus expressing the vaccine-targeted capsules. Since pneumococci can produce different capsule polysaccharides and therefore reduce vaccine effectiveness, it is important to track the appearance of novel pneumococcal capsule types and how these new capsules are created. Herein, we describe a new and the 100th pneumococcal capsule type with unique chemical and serological properties. The capsule type was named 10D for its serologic similarity to 10A. Genetic studies provide strong evidence that pneumococcus created 10D capsule polysaccharide by capturing a large genetic fragment from an oral streptococcus. Such interspecies genetic exchanges could greatly increase diversity of pneumococcal capsules and complicate serotype shifts.

A Common Food Glycan, Pectin, Shares an Antigen with Streptococcus pneumoniae Capsule

We are exposed daily to many glycans from bacteria and food plants. Bacterial glycans are generally antigenic and elicit antibody responses. It is unclear if food glycans' sharing of antigens with bacterial glycans influences our immune responses to bacteria. We studied 14 different plant foods for cross-reactivity with monoclonal antibodies (MAbs) against 24 pneumococcal serotypes which commonly cause infections and are included in pneumococcal vaccines. Serotype 15B-specific MAb cross-reacts with fruit peels, and serotype 10A MAb cross-reacts with many natural and processed plant foods. The serotype 10A cross-reactive epitope is terminal 1,6-linked β-galactose [βGal(1-6)], present in the rhamno-galacturonan I (RG-I) domain of pectin. Despite wide consumption of pectin, the immune response to 10A is comparable to the responses to other serotypes. An antipectin antibody can opsonize serotype 10A pneumococci, and the shared βGal(1-6) may be useful as a simple vaccine against 10A. Impact of food glycans should be considered in host-pathogen interactions and future vaccine designs.IMPORTANCE The impact of food consumption on vaccine responses is unknown. Streptococcus pneumoniae (the pneumococcus) is an important human pathogen, and its polysaccharide capsule is used as a vaccine. We show that capsule type 10A in a pneumococcal vaccine shares an antigenic epitope, βGal(1-6), with pectin, which is in many plant foods and is widely consumed. Immune response to 10A is comparable to that seen with other capsule types, and pectin ingestion may have little impact on vaccine responses. However, antibody to pectin can kill serotype 10A pneumococci and this shared epitope may be considered in pneumococcal vaccine designs.

Group A Streptococcus Cell Wall Oligosaccharide-Streptococcal C5a Peptidase Conjugates as Effective Antibacterial Vaccines

Group A streptococcus (GAS) is one of the common Gram-positive pathogenic bacteria accounting for a variety of infectious diseases. Currently, there is no commercial vaccine for GAS. To develop efficient GAS vaccines, synthetic tri-, hexa-, and nonasaccharides of a conserved group A carbohydrate (GAC) were conjugated with an inactive mutant of group A streptococcal C5a peptidase (ScpA), ScpA193, to create bivalent conjugate vaccines, which were compared with the corresponding CRM197 and TT conjugates. Systematic evaluations of these semisynthetic conjugates demonstrated that they could induce robust and comparable T-cell-dependent immune responses in mice. It was further disclosed that antibodies provoked by the ScpA193 conjugates, especially that of hexa- and nonasaccharides, could recognize and bind to GAS cells and mediate GAS opsonophagocytosis in vitro. In vivo evaluations of the hexa- and nonasaccharide-ScpA193 conjugates using a mouse model revealed that immunizing mice with especially the latter conjugate could effectively protect the animals from GAS challenges and GAS-induced pulmonary damage and significantly increase animal survival. Further in vitro studies suggested that the two ScpA193 conjugates could function through activating CD4⁺ T cells and promoting helper T cells (Th) to differentiate into antigen-specific Th1 and Th2 cells. In conclusion, the nonasaccharide-ScpA193 conjugate was identified as a particularly promising GAS vaccine candidate that is worthy of further investigation and development.

Immunogenicity and safety after the third vaccination with the 23-valent pneumococcal polysaccharide vaccine in elderly patients with chronic lung disease

An observational study to assess immunogenicity before and after the first, second, and third vaccinations with the 23-valent pneumococcal polysaccharide vaccine in a cohort of 16 elderly patients with chronic lung diseases was conducted. The safety of this vaccine was also compared between the first, second, and third vaccinations. Serotype-specific immunoglobulin G (IgG) and the opsonization index (OI) for serotypes 6B, 14, 19F, and 23F were analyzed, and adverse local and systemic reactions were compared. The levels of serotype-specific IgG and OI increased significantly 1 month after the first, second, and third vaccinations. Peak IgG levels were higher after the third vaccination than after the second vaccination, but the levels of serotypes 6B, 14, and 19F were not higher than after the first vaccination. Serotype-specific OIs did not differ after the third vaccination compared with the first and second vaccinations. The level of serotype-specific IgG required for killing 50% of bacteria decreased significantly 1 month after the second vaccination. This level was slightly elevated immediately before the third vaccination but decreased after the third vaccination. Although self-limited local and systemic reactions were more frequent after the second and third vaccinations than after the first vaccination, no serious systemic reactions were seen after any vaccination. These data suggest that sustained functional serotype-specific IgG is produced after the first, second, and third vaccinations and they confirm the safety of the second and third vaccinations in elderly people with chronic lung disease.

A Nonfunctional Opsonic Antibody Response Frequently Occurs after Pneumococcal Pneumonia and Is Associated with Invasive Disease

Numerous reports on the dynamics of antipneumococcal immunity in relation to immunization with pneumococcal vaccines and on the prevalence of naturally acquired immunity in various populations have been published. In contrast, studies on the dynamics of the humoral immune response triggered by pneumococcal infection are scarce. This study provides valuable information that will contribute to fill this knowledge gap. Our main results indicate that a functional immune response frequently fails to occur after CAP, predominantly among patients with simultaneous bacteremia.

Naturally acquired opsonic antipneumococcal antibodies are commonly found in nonvaccinated adults and confer protection against infection and colonization. Despite this, only limited data exist regarding the adaptive immune response after pneumococcal exposure. To investigate the dynamics of naturally acquired antipneumococcal immunity in relation to an episode of infection, opsonic antibody activity was studied with paired acute-phase and convalescent-phase sera obtained from 54 patients with pneumococcal community-acquired pneumonia (CAP) using an opsonophagocytic assay (OPA). Results were compared with clinical characteristics and anticapsular immunoglobulin (Ig) concentrations. Interestingly, a nonfunctional opsonic antibody response (characterized by a decreased convalescent-phase serum OPA titer compared to that of the acute-phase serum or undetectable titers in both sera) was observed in 19 (35%) patients. A nonfunctional convalescent-phase response was significantly more common among patients with invasive pneumococcal disease (i.e., bacteremia) than in patients without invasive disease (53%; P = 0.019). Remaining individuals exhibited either an increased convalescent-phase OPA titer (n = 24 [44%]) or a detectable, but unchanged, titer at both time points (n = 11 [20%]). No correlation was found between anticapsular Ig concentrations and OPA titers. Our findings indicate that an episode of pneumococcal infection may act as an immunizing event, leading to an improved antipneumococcal adaptive immune status. However, in some cases, when patients with CAP also suffer from bacteremia, a nonfunctional opsonic antibody response may occur. Furthermore, the results suggest that factors other than anticapsular Ig concentrations are important for opsonic antibody activity in serum.

IMPORTANCE Numerous reports on the dynamics of antipneumococcal immunity in relation to immunization with pneumococcal vaccines and on the prevalence of naturally acquired immunity in various populations have been published. In contrast, studies on the dynamics of the humoral immune response triggered by pneumococcal infection are scarce. This study provides valuable information that will contribute to fill this knowledge gap. Our main results indicate that a functional immune response frequently fails to occur after CAP, predominantly among patients with simultaneous bacteremia.

Quality Improvement of Capsular Polysaccharide in Streptococcus pneumoniae by Purification Process Optimization

Streptococcus pneumoniae is the causative agent of many diseases, most notably pneumonia. Most of the currently used vaccines to protect against this pathogen employ pneumococcal capsular polysaccharides (CPSs) as antigens, but purifying CPS of sufficient quality has been challenging. A purification process for CPS comprising conventional methods such as ultrafiltration, CTAB precipitation, and chromatography was previously established; however, this method resulted in high cell wall polysaccharide (CWPS) contamination, especially for serotype 5. Thus, a better purification method that yields CPS of a higher quality is needed for vaccine development. In this study, we significantly reduced CWPS contamination in serotype 5 CPS by improving the ultrafiltration and CTAB precipitation steps. Moreover, by applying an acid precipitation process to further remove other impurities, serotype 5 CPS was obtained with a lower impurity such as decreased nucleic acid contamination. This improved method was also successfully applied to 14 other serotypes (1, 3, 4, 6A, 6B, 7F, 9V, 11A, 14, 18C, 19A, 19F, 22F, and 23F). To assess the immunogenicity of the CPS from the 15 serotypes, two sets of 15-valent pneumococcal conjugate vaccines were prepared using the previous purification method and the improved method developed here; these vaccines were administered to a rabbit model. Enzyme-linked immunosorbent assay and opsonophagocytic assay demonstrated higher immunogenicity of the conjugate vaccine prepared using CPS produced by the improved purification process.

Peripheral CD4 T follicular cells induced by a conjugated pneumococcal vaccine correlate with enhanced opsonophagocytic antibody responses in younger individuals

BACKGROUND

PCV13 (conjugated polysaccharide) and PPSV23 (polysaccharide only) are two licensed vaccines targeting S. pneumoniae. The role of CD4 T-cell responses in pneumococcal vaccines among healthy participants and their impact on antibodies is not yet known.

METHODS

Ten adults (5 old and 5 young) received PCV13 (prime) and a year later PPSV23 (boost). Blood samples were collected prior to and multiple time points after vaccination. CD4 T cells responding to CRM₁₉₇, polysaccharide (PS), CRM₁₉₇ conjugated polysaccharide (CPS), PCV13 and PPSV23 vaccines were measured by flow cytometry. Serum antibodies were analyzed via multiplex opsonophagocytosis (MOPA) and pneumococcal IgG assays.

RESULTS

Vaccine-specific CD4 T cells were induced in all ten vaccinees post PCV13. Older vaccinees mounted higher peak responses and those specific for PCV13 and conjugated PS-1 were more polyfunctional compared to the younger group. Vaccine-elicited peripheral T follicular helper (Tfh) cells were only detected in the younger group who also exhibited a higher fold change in OPA titers post both vaccines. Importantly, Tfh cells following PCV13 correlated only with PCV13 serotype specific OPA titers after PPSV23 vaccination.

CONCLUSIONS

These findings demonstrate age related differences in immune response and the potential importance of Tfh in modulating functional antibody responses following pneumococcal vaccination.

An Opsonophagocytic Killing Assay for the Evaluation of Group A Streptococcus Vaccine Antisera

Group A Streptococcus (GAS) is a major cause of global mortality, yet there are no licensed GAS vaccines. Vaccine progress has been hampered, in part, by a lack of standardized assays able to quantify antibody function in test antisera. The most widely used assay was developed over 50 years ago by Rebecca Lancefield and relies on human whole blood as a source of complement and neutrophils. Recently, an opsonophagocytic killing (OPK) assay has been developed for GAS by adapting the OPK methods utilized in Streptococcus pneumoniae vaccine testing. This assay uses dimethylformamide (DMF)-differentiated human promyelocytic leukemia cells (HL-60 cells) as a source of neutrophils and baby rabbit complement, thus removing the major sources of variation in the Lancefield assays. This protocol outlines methods for performing a GAS OPK assay including titering test sera to generate an opsonic index. This in vitro assay could aid in selecting vaccine candidates by demonstrating whether candidate-induced antibodies lead to complement deposition and opsonophagocytic killing.

An adult case of invasive pneumococcal disease due to serotype 12F-specific polysaccharide antibody failure following a 23-valent polysaccharide vaccination

A 68-year-old Japanese man was admitted to our hospital for an acute febrile illness with shivering and impaired consciousness. He was a previous smoker and had a history of chronic obstructive pulmonary disease, for which he inhaled steroid with a long-acting bronchodilator. He had received a 23-valent pneumococcal polysaccharide vaccination 2 years previously. He was intubated and placed on a ventilator in intensive care unit because of acute respiratory failure and hypercapnia. Streptococcus pneumoniae was grown from his blood, sputum, and urine cultures, and he was diagnosed with invasive pneumococcal disease with acute renal failure. He was treated with intravenous beta-lactam and macrolide with continuous hemodiafiltration and was discharged 3 months later. The pneumococcus was identified as serotype 12F, and his serotype-specific IgG and opsonophagocytic index against serotype 12F indicating a lack of protection from IPD among PPV23 serotypes. This case highlights that some individuals may have a serotype-specific polysaccharide antibody failure that makes them susceptible to serotype 12F invasive pneumococcal disease. This case also illustrates the need for serotype-specific IgG and opsonophagocytic index titre cut-offs for each specific pneumococcal serotype in available vaccines to understand the vaccination protection for individual patients better.

Immunogenicity Comparison of a Next Generation Pneumococcal Conjugate Vaccine in Animal Models and Human Infants

BACKGROUND

Evaluation of a pneumococcal conjugate vaccine (PCV) in an animal model provides an initial assessment of the performance of the vaccine prior to evaluation in humans. Cost, availability, study duration, cross-reactivity and applicability to humans are several factors which contribute to animal model selection. PCV15 is an investigational 15-valent PCV which includes capsular polysaccharides from pneumococcal serotypes (ST) 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, 22F, 23F and 33F all individually conjugated to cross-reactive material 197 (CRM197).

METHODS

Immunogenicity of PCV15 was evaluated in infant rhesus macaques (IRM), adult New Zealand white rabbits (NZWR) and CD1 mice using multiplexed pneumococcal electrochemiluminescent (Pn ECL) assay to measure serotype-specific IgG antibodies, multiplexed opsonophagocytosis assay (MOPA) to measure serotype-specific functional antibody responses and bacterial challenge in mice to evaluate protection against a lethal dose of S. pneumoniae.

RESULTS

PCV15 was immunogenic and induced both IgG and functional antibodies to all 15 vaccine serotypes in all animal species evaluated. PCV15 also protected mice from S. pneumoniae serotype 14 intraperitoneal challenge. Opsonophagocytosis assay (OPA) titers measured from sera of human infants vaccinated with PCV15 in a Phase 2 clinical trial showed a good correlation with that observed in IRM (rs=0.69, P=0.006), a medium correlation with that of rabbits (rs=0.49, P=0.06), and no correlation with that of mice (rs=0.04, P=0.89). In contrast, there was no correlation in serum IgG levels between human infants and animal models.

CONCLUSIONS

These results demonstrate that PCV15 is immunogenic across multiple animal species, with IRM and human infants showing the best correlation for OPA responses.

Feasibility of Using a Luminescence-Based Method to Determine Serum Bactericidal Activity against Neisseria gonorrhoeae

Development of a vaccine to limit the impact of antibiotic resistant Neisseria gonorrhoeae is now a global priority. Serum bactericidal antibody (SBA) is a possible indicator of protective immunity to N. gonorrhoeae, but conventional assays measure colony forming units (CFU), which is time-consuming. A luminescent assay that quantifies ATP as a surrogate measure of bacterial viability was tested on N. gonorrhoeae strains FA1090, MS11 and P9-17 and compared to CFU-based readouts. There was a linear relationship between CFU and ATP levels for all three strains (r > 0.9). Normal human serum (NHS) is a common source of complement for SBA assays, but needs to be screened for non-specific bactericidal activity. NHS from 10 individuals were used for serum sensitivity assays-sensitivity values were significantly reduced with the ATP method for FA1090 (5/10, p < 0.05) and MS11 (10/10, p < 0.05), whereas P9-17 data were comparable for all donors. Our results suggest that measuring ATP underestimates serum sensitivity of N. gonorrhoeae and that the CFU method is a better approach. However, mouse anti-P9-17 outer membrane vesicles (OMV) SBA titres to P9-17 were comparable with both methods (r = 0.97), suggesting this assay can be used to rapidly screen sera for bactericidal antibodies to gonococci.