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.

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.

Discovery and Characterization of Pneumococcal Serogroup 36 Capsule Subtypes, Serotypes 36A and 36B

Streptococcus pneumoniae can produce a wide breadth of antigenically diverse capsule types, a fact that poses a looming threat to the success of vaccines that target pneumococcal polysaccharide (PS) capsule. Yet, many pneumococcal capsule types remain undiscovered and/or uncharacterized. Prior sequence analysis of pneumococcal capsule synthesis (cps) loci suggested the existence of capsule subtypes among isolates identified as "serotype 36" according to conventional capsule typing methods. We discovered these subtypes represent two antigenically similar but distinguishable pneumococcal capsule serotypes, 36A and 36B. Biochemical analysis of their capsule PS structure reveals that both have the shared repeat unit backbone [→5)-α-d-Galf-(1→1)-d-Rib-ol-(5→P→6)-β-d-ManpNAc-(1→4)-β-d-Glcp-(1→] with two branching structures. Both serotypes have a β-d-Galp branch to Ribitol. Serotypes 36A and 36B differ by the presence of a α-d-Glcp-(1→3)-β-d-ManpNAc or α-d-Galp-(1→3)-β-d-ManpNAc branch, respectively. Comparison of the phylogenetically distant serogroup 9 and 36 cps loci, which all encode this distinguishing glycosidic bond, revealed that the incorporation of Glcp (in types 9N and 36A) versus Galp (in types 9A, 9V, 9L, and 36B) is associated with the identity of four amino acids in the cps-encoded glycosyltransferase WcjA. Identifying functional determinants of cps-encoded enzymes and their impact on capsule PS structure is key to improving the resolution and reliability of sequencing-based capsule typing methods and discovering novel capsule variants indistinguishable by conventional serotyping methods.

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.

Whole microbe arrays accurately predict interactions and overall antimicrobial activity of galectin-8 toward distinct strains of Streptococcus pneumoniae

Microbial glycan microarrays (MGMs) populated with purified microbial glycans have been used to define the specificity of host immune factors toward microbes in a high throughput manner. However, a limitation of such arrays is that glycan presentation may not fully recapitulate the natural presentation that exists on microbes. This raises the possibility that interactions observed on the array, while often helpful in predicting actual interactions with intact microbes, may not always accurately ascertain the overall affinity of a host immune factor for a given microbe. Using galectin-8 (Gal-8) as a probe, we compared the specificity and overall affinity observed using a MGM populated with glycans harvested from various strains of Streptococcus pneumoniae to an intact microbe microarray (MMA). Our results demonstrate that while similarities in binding specificity between the MGM and MMA are apparent, Gal-8 binding toward the MMA more accurately predicted interactions with strains of S. pneumoniae, including the overall specificity of Gal-8 antimicrobial activity. Taken together, these results not only demonstrate that Gal-8 possesses antimicrobial activity against distinct strains of S. pneumoniae that utilize molecular mimicry, but that microarray platforms populated with intact microbes present an advantageous strategy when exploring host interactions with microbes.

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.

Investigation on the virulence of non-encapsulated Streptococcus pneumoniae using liquid agar pneumonia model

INTRODUCTION

Since the introduction of pneumococcal conjugate vaccine, there have been warnings of an increase in infections caused by non-vaccine type of Streptococcus pneumoniae strains. Among them, nonencapsulated Streptococcus pneumoniae (NESp) has been reported to cause invasive infections, especially in children and the elderly. Due to low virulence, however, basic experimental reports on invasive infections are limited.

METHODS

We applied a liquid-agar method to establish a mouse model of invasive NESp infection. Mice were intratracheally administered a bacterial suspension including agar. With this technique, we investigated the pathogenicity of NESp and the effect of Pneumococcal surface protein K (PspK), a specific surface protein antigen of NESp. NESp wild-type strain (MNZ11) and NESp pspK-deleted mutant strain (MNZ1131) were used in this study. The survival rate, number of bacteria, cytokine/chemokine levels in the bronchoalveolar lavage fluid, and histology of the lung tissue were evaluated.

RESULTS

Mice that were intratracheally administered MNZ11 developed lethal pneumonia with bacteremia within 48 h. Conversely, MNZ1131 showed predominantly low lethality without significant pro-inflammatory cytokine production. NESp was found to cause severe pneumonia and bacteremia upon reaching the lower respiratory tract, and PspK was a critical factor of NESp for developing invasive infections.

CONCLUSIONS

The current study demonstrated the ability of NESp to develop invasive diseases, especially in connection with PspK by use of a mouse pneumonia model.

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.

Oral streptococci expressing pneumococci-like cross-reactive capsule types can affect WHO recommended pneumococcal carriage procedure

BACKGROUND

Carriage studies are fundamental to assess the effects of pneumococcal vaccines. Since a large proportion of oral streptococci carry homologs of pneumococcal genes, nonculture-based detection and serotyping of upper respiratory tract (URT) samples can be problematic. Herein, we investigated if culture-free molecular methods could differentiate pneumococci from oral streptococci carried by adults in URT.

METHODS

Paired nasopharyngeal (NP) and oropharyngeal (OP) samples were collected from 100 older adults twice a month for one year. Extracts from the combined NP+OP samples (n=2400) were subjected to lytA real-time PCR. Positive samples were subjected to pure culture isolation followed by species confirmation using multiple approaches. Multibead assay and whole-genome sequencing were used for serotyping.

RESULTS

lytA-PCR was positive in 301 combined NP+OP extracts, 20 of which grew probable pneumococcal-like colonies based on colony morphology and biochemical tests. Multiple approaches confirmed that four isolates were S. pneumoniae, three were S. psuedopneumoniae, and thirteen were S. mitis. Eight nonpneumococcal strains carried pneumococcus-like cps loci (size: ~18 to 25 kb) that showed >70% of nucleotide identity with their pneumococcal counterparts. While investigating the antigenic profile, we found some S. mitis strains (P066 and P107) reacted with both serotype-specific polyclonal (Type 39 and FS17b) and monoclonal (Hyp10AG1 and Hyp17FM1) antisera, whereas some strains (P063 and P074) reacted only with polyclonal antisera (Type 5 and FS35a).

CONCLUSION

The extensive capsular overlap suggests that pneumococcal vaccines could reduce carriage of oral streptococci expressing cross-reactive capsules. Further, direct use of culture-free PCR-based methods in URT samples has limited usefulness for carriage studies.

Assignment of opsonic values to pneumococcal reference serum 007sp and a second pneumococcal OPA calibration serum panel (Ewha QC sera panel B) for 11 serotypes

Pneumococcal conjugate vaccines (PCVs) have been effective in reducing the disease burden caused by Streptococcus pneumoniae. The first licensed PCV (PCV7) was composed of capsular polysaccharides from seven serotypes. This was followed by PCV10, then PCV13, and currently there are a number of higher valency vaccines in development. As part of licensure, new vaccine iterations require assessment of immunogenicity. Since some antibodies can be non-functional, measuring functional antibodies is desirable. To meet this need, opsonophagocytic assays (OPAs) have been developed. Previous studies have shown there can be significant variations in OPA results from different laboratories. We have previously shown that standardizing OPA data using reference serum 007sp can decrease this variation. To extend this approach to additional serotypes, a panel of sera was tested by five laboratories using a multiplexed OPA for serotypes 2, 8, 9N, 10A, 11A, 12F, 15B, 17F, 20B, 22F, and 33F. Each sample was tested in five runs with 007sp tested three times in each run. Results were analyzed using a mixed effects ANOVA model. Standardization of the results significantly decreased the inter-laboratory variation for some serotypes. For serotypes 2, 8, and 11A, the variability was reduced by 40%, 45%, and 40%, respectively. For serotypes 12F, 17F, and 20B, the reductions were more modest (14%, 19%, and 24%, respectively). Standardization had little effect for the remaining serotypes. In many cases, the impact of normalization was blunted by the results from five sera that were collected after an extended post-vaccination interval. We have previously reported consensus values for 007sp for 13 serotypes, as well as the creation of a calibration serum panel ("Ewha Panel A"). Here, we report consensus values for 11 additional serotypes for 007sp and the creation of a second serum panel ("Ewha Panel B"). These consensus values will facilitate the development of next-generation PCVs.

Phosphorylcholine esterase is critical for Dolichos biflorus and Helix pomatia agglutinin binding to pneumococcal teichoic acid

Streptococcus pneumoniae (the pneumococcus) has wall teichoic acid (WTA) and lipoteichoic acid (LTA) expressing the Forssman antigen (FA). Two lectins, Dolichos biflorus agglutinin (DBA) and Helix pomatia agglutinin (HPA), are known to bind FA. To determine the molecular structure targeted by these two lectins, different pneumococcal strains were studied for DBA/HPA binding with flow cytometry and fluorescence microscopy. Genetic experiments were used to further examine the lectins' molecular target. Twelve strains were positive for DBA binding, whereas three were negative. Super-resolution microscopy showed that DBA stained only the subcapsular area of pneumococci. The three DBA nonbinders showed no phosphorylcholine esterase (Pce) activity in vitro, whereas 10 DBA binders displayed Pce activity (the remaining two strains were DBA binders with no Pce activity in vitro). The pcegene sequence for 10 representative strains revealed two functional pce alleles, the previously recognized "allele A" and a newly discovered "allele B" (with 12 additional nucleotides). Isolates with allele B showed no Pce activity in vitro but did bind to DBA, indicating allele B Pce is functional in vivo. Genetic transfer experiments confirmed that either allele is sufficient (and necessary) for DBA binding. The three DBA nonbinders had various mutations that affected Pce function. Observations with HPA were identical to those with DBA. We show that DBA and HPA bind only to the WTA/LTA of pneumococcal isolates with a functional Pce enzyme. A newly discovered Pce variant (allele B) is functional in vivo but nonfunctional when assayed in vitro.

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.

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.

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.

2597. Dolichos biflorus Agglutinin Binds to Pneumococcal Teichoic Acid and Lipoteichoic Acid

Background

Dolichos biflorus agglutinin (DBA) is a lectin with a binding specificity toward α-linked N-acetylgalactosamine (α-GalNAc). While DBA is known to bind some, but not all, pneumococci, its target molecule has not been identified. Pneumococcus teichoic acid (TA) and lipoteichoic acid (LTA) have repeating units with α-GalNAc-(1→3)β-GalNAc decorated with phosphorylcholine (PC) at the O-6 positions. Two PC transferases, LicD1 and LicD2, mediate the attachment of PC to GalNAc residues while phosphorylcholine esterase (Pce) removes PCs attached to the terminal GalNAcs. We examined if DBA binds to the terminal α-GalNAc-(1→3)β-GalNAc created by Pce.

Methods

Fifteen pneumococcus strains expressing 14 different serotypes, including one non-encapsulated strain (R36A), were studied with flow cytometry (FC) and confocal fluorescence microscopy (CFM) for DBA binding. Pce enzyme activity was detected with a colorimetric assay using p-nitrophenyl-phosphorylcholine as the substrate. Mutant strains with pce knocked-out were constructed in R36A and D39 by replacing pce with Janus cassette. Both licD genes were sequenced for some of the strains.

Results

Ten of the 15 strains had Pce activity and all of them bound DBA (Table 1). When the pce gene was inactivated in two normally Pce-positive strains (R36A^△pce and D39^△pce), the strains did not show DBA binding by CFM (Figure 1). Thus, expression of Pce appears to be sufficient for expressing the DBA antigen. Of the five strains that had no Pce activity, two bound DBA. Sequencing of the licD genes in these two strains with positive DBA binding and negative Pce activity revealed one SNP in licD1 and four SNPs in licD2, resulting in a single amino acid difference each for LicD1 and LicD2, compared with R36A and D39.

Conclusion

DBA can bind to the terminal α-GalNAc-(1→3)β-GalNAc of pneumococcal TA and LTA, which is created by Pce. DBA binding is independent of capsule type. The unexpected binding of DBA to the two Pce-negative strains suggests that there is a Pce-independent mechanism for generating the target for DBA binding. Since LicD1 and LicD2 are involved in attaching PC to α-GalNAc-(1→3)β-GalNAc, we are now investigating their role in creating DBA targets independent of Pce.

Disclosures

All authors: No reported disclosures.

2710. Novel Analytical Models for Pneumococcal Multiplex Opsonophagocytosis Assay Results from a Healthy Older Adult Population Vaccinated with PCV13

Background

The multiplexed opsonophagocytosis assay (MOPA) measures killing of pneumococci by serum antibodies, and is the primary method for measuring pneumococcal antibodies in adults. However, pre-vaccine opsonic activity and vaccine response are highly variable among serotypes and individuals, and there are currently no criteria to define normal MOPA results.

Methods

We performed post-hoc analysis of data from n = 311 healthy, pneumococcal-vaccine naïve adults aged 55–74 who received 0.5 mL PCV13, and had MOPA performed for PCV13 serotypes (except serotype 3) at baseline, then on days 29 and 181 post-vaccine (Jackson et al. 2018, Vaccine). MOPA results (reported as opsonic index, or OI) were standardized using pneumococcal reference serum 007sp. Pairwise comparisons of proportions of undetectable baseline OI (≤ 4) between serotypes were performed using Pearson’s Chi-square. Immunogenicity (mean change in OI at day 29 post-PCV among samples with undetectable baseline OI) was compared between serotypes using one-way ANOVA. We then assigned a score based on cutoffs for pre-vaccine OI (cutoff 1, or C1) and fold-rise in OI at day 29 (cutoff 2, or C2) for each serotype, as shown in Figure 1. The sum of the scores for 12 serotypes was determined for each participant. We plotted the frequency distribution of total scores using different combinations of values for C1 and C2 to visually identify the optimal fit for the left-skewed distribution expected in a healthy population.

Results

Serotype 1 had the highest prevalence of undetectable OI at baseline (77.0%, P < 0.001), and serotype 19A had the lowest (8.8%, P < 0.001). Immunogenicity was highest for serotype 7F (mean change of 18354, P < 0.001 for all comparisons). For vaccine response analysis, C1 = 300 and C2 = 8 produced a left-skewed distribution (Figure 2). Using these cutoffs, the median total score was 7 and the 5th percentile score was −1.

Conclusion

Criteria for normal MOPA results can be developed for single-timepoint data, or using a scoring system for vaccine response data that integrates pre-vaccine OI and fold-rise in OI. Additional studies in healthy and disease populations are needed to further optimize diagnostic criteria for discriminating normal vs. abnormal results.

Disclosures

All authors: No reported disclosures.

2618. Determination of the Chemical Structure of a Novel Pneumococcal Serotype, 39X

Background

Streptococcus pneumoniae produces a diverse group of capsular polysaccharides (serotypes) that are important for the virulence of the organism and for the serotype-specific prevention of pneumococcal disease. As a consequence of widespread PCV usage and pneumococcal genome plasticity, the distribution of pneumococcal serotypes is changing with an increase in non-vaccine serotypes post-vaccine introduction, a phenomenon known as serotype replacement. Recently, a potentially novel serotype was described and was provisionally named as serotype 39X. Genetic studies suggest that this novel serotype may be a hybrid of serotypes 6C and 39/10A.

Methods

Three 39X strains with the distinct serological and genetic description of the cps biosynthetic loci were obtained from the Global Pneumococcal Sequencing project (www.pneumogen.net). Capsular polysaccharide from one (Camb.853/MNZ2334) of the 39X strains was purified by sequential ethanol precipitation followed by ion-exchange chromatography. To detect polysaccharide fractions during purification, an inhibition ELISA assay was developed using factor serum 10d. The chemical structure of the 39X repeating unit was determined using one-dimensional (1D) and 2D nuclear magnetic resonance (NMR).

Results

All three isolates were confirmed to have the 39X genotype by PCR amplification and sequencing of the 39X specific region (wciN_6c-wcrO-wcrC₃₉) of the cps locus. (Figure 1). The 39X capsule PS fractions were detected during purification and pooled for structural studies (Figure 2). 1D-NMR for 39X showed it to be chemically distinct (Figure 3). 2D-NMR studies revealed that five of the sugar residues in 39X PS are identical to those in 39 PS, except the acetylation (Figure 4). The remaining part of the structure is being investigated.

Conclusion

The 39X capsular PS has a distinct chemical structure in addition to its distinct serologic and genetic properties. Given that serotype 39X is a new serotype, it becomes the 100th pneumococcal serotype. The chemical structure supports the genetic depiction of serotype evolution as a result of recombination between well-characterized and unrelated serotypes. Structural elucidation of the 39X capsule PS will help facilitate our understanding of serotype replacement and vaccine development.

Disclosures

All authors: No reported disclosures.

Molecular typing, antibiotic susceptibility, and biofilm production in nonencapsulated Streptococcus pneumoniae isolated from children in Japan

The prevalence of nonencapsulated Streptococcus pneumoniae (NESp) has increased with the introduction of pneumococcal conjugate vaccines in children; however, the bacteriological characteristics of NESp have not been sufficiently clarified. In this study, NESp strains isolated from the nasopharyngeal carriage of children from four nursery schools in Japan were analyzed for molecular type, antibiotic susceptibility, and biofilm productivity. A total of 152 putative S. pneumoniae strains were identified by optochin-susceptibility analysis, of which 21 were not serotypeable by slide agglutination, quellung reaction, or multiplex PCR. Among these 21 strains, three were lytA-negative and, therefore, not S. pneumoniae. The remaining 18 strains were positive for lytA, ply, pspK, and bile solubility and were confirmed as NESp. Therefore, the isolation rate of NESp in the S. pneumoniae strains in this study was 12.0% (18/149). Molecular-typing analyses classified five strains as two existing sequence types (STs; ST7502 and ST7786), and 13 strains formed four novel STs. Horizontal spread was suspected, because strains with the same ST were often isolated from the same nursery school. The NESp isolates were generally susceptible to most antimicrobials, with the exception of macrolides; however, all isolates possessed more than one abnormal penicillin-binding protein gene. Furthermore, NESp strains were more effective than encapsulated counterparts at forming biofilms, which showed obvious differences in morphology. These data indicated that NESp strains should be continuously monitored as emerging respiratory pathogens.

Putative novel cps loci in a large global collection of pneumococci

The pneumococcus produces a polysaccharide capsule, encoded by the cps locus, that provides protection against phagocytosis and determines serotype. Nearly 100 serotypes have been identified with new serotypes still being discovered, especially in previously understudied regions. Here we present an analysis of the cps loci of more than 18  000 genomes from the Global Pneumococcal Sequencing (GPS) project with the aim of identifying novel cps loci with the potential to produce previously unrecognized capsule structures. Serotypes were assigned using whole genome sequence data and 66 of the approximately 100 known serotypes were included in the final dataset. Closer examination of each serotype’s sequences identified nine putative novel cps loci (9X, 11X, 16X, 18X1, 18X2, 18X3, 29X, 33X and 36X) found in ~2.6  % of the genomes. The large number and global distribution of GPS genomes provided an unprecedented opportunity to identify novel cps loci and consider their phylogenetic and geographical distribution. Nine putative novel cps loci were identified and examples of each will undergo subsequent structural and immunological analysis.

Measuring quantity and function of pneumococcal antibodies in immunoglobulin products

BACKGROUND

Immunoglobulin replacement therapy is a cornerstone of the treatment of primary immunodeficiencies. Preparations used for replacement therapy are processed by purifying immunoglobulins from large pools of plasma, which were obtained from healthy donors. The constituent antibodies in these products depend on the immune history of the donor pool as well as manufacturing processes that differ among manufacturers. For these reasons various methods have been proposed to examine the levels and function of antibodies to organisms such as Streptococcus pneumoniae, which frequently causes infections in patients with immunodeficiencies. Pneumococcal antibody levels or antibody function can be measured with enzyme-linked immunosorbent assay (ELISA) or multiplexed opsonophagocytosis assay (MOPA). Although these assays were developed initially to assess the immunogenicity of pneumococcal vaccines, the techniques have been adapted to evaluate immunoglobulin products as well.

STUDY DESIGN AND METHODS

This article provides a concise review of the analytic techniques for measuring pneumococcal antibodies and prior studies of immunoglobulin products utilizing these methods.

RESULTS

Studies utilizing these assays have demonstrated that antibody levels of immunoglobulin products can vary with time, location, and manufacturer.

CONCLUSIONS

We highlight current issues and future considerations concerning measurement of pneumococcal antibodies in immunoglobulin products, and the assays used for this purpose.

A High-throughput Shigella-specific Bactericidal Assay

Serum bactericidal assays (SBAs) measure the functional activity of antibodies and have been used for many decades. SBAs directly measure antibody killing activity by assessing the ability of antibodies in serum to bind to bacteria and activate complement. This complement activation results in the lysis and killing of the target bacteria. These assays are valuable because they go beyond quantifying antibody production to elucidate the biological functions that these antibodies have, allowing researchers to study the role that antibodies may play in preventing infection. SBAs have been used to study immune responses for many human pathogens, but there is no widely accepted methodology for Shigella at present. Historically, SBAs have been very labor-intensive, requiring many time-consuming steps to accurately quantify surviving bacteria. This protocol describes a simple, robust, and high-throughput assay that measures functional antibodies specific for Shigella in serum in vitro. The method described here offers many advantages over traditional SBAs, including the use of frozen bacterial stocks, 96 well assay plates, a micro-culture system, and automated colony-counting. All of these modifications make this assay less labor-intensive and more high-throughput. This protocol is simpler and faster to perform than traditional SBAs while still using simple technologies and readily available reagents. The protocol has been successfully applied in multiple independent laboratories and the assay is robust and reproducible. The assay can be used to assess immune responses in pre-clinical as well as clinical studies. Quantifying shigellacidal antibody titers both before and after antigen exposure (either by immunization or infection) allows for a broader understanding of how functional antibody responses are generated and their contribution to protective immunity. The development of this standardized, well-characterized assay may greatly facilitate Shigella vaccine design.

Ficolin-2 binds to serotype 35B pneumococcus as it does to serotypes 11A and 31, and these serotypes cause more infections in older adults than in children

Among 98 serotypes of Streptococcus pneumoniae, only a small subset regularly causes invasive pneumococcal diseases (IPD). We previously demonstrated that serotype 11A binds to ficolin-2 and has low invasiveness in children. Epidemiologic data suggested, however, that serotype 11A IPD afflicts older adults, possibly indicating reduced ficolin-2-mediated immune protection. Therefore, we studied the epidemiology of ficolin-2-bound serotypes. We obtained IPD case data from the United States Centers for Disease Control and Prevention. We studied three prominent ficolin-2-bound serotypes and their acetyltransferase-deficient variants for ficolin-2 binding and ficolin-2-mediated complement deposition with flow-cytometry. We determined the age distributions of these serotypes from the obtained epidemiologic data. We discovered that the serotype 35B capsule is a novel ficolin-2 ligand due to O-acetylation via WciG. Ficolin-2-mediated complement deposition was observed on serotypes 11A and 35B but not serotype 31 or any O-acetyl transferase deficient derivatives of these serotypes. Serotypes 11A, 35B, and 31 cause more IPD among older adults than children. Studies of the three serotypes provide additional evidence for ficolin-2 providing innate immunity against IPD. The skewed age distribution of the three serotypes suggests that older adults have reduced ficolin-2-mediated immunity and are more susceptible to these serotypes.

1003. Clinical Implications of Emerging Nonvaccine-Serotype Invasive Pneumococcal Disease Among Adults in the Republic of Korea in the Era of Protein-Conjugated Pneumococcal Vaccine

Background

In the Republic of Korea (ROK), protein conjugated vaccines (PCV13 and PCV10) in replacement of PCV7 have been used in children since 2010, and then included in the childhood national immunization program (NIP) in 2014. This study investigated indirect effect of PVCs on serotypes in PCV-naïve adult invasive pneumococcal disease (IPD) and its clinical implications.

Methods

A prospective observational cohort study was conducted, through the serotype surveillance program following the NIP implementation of 23-valent pneumococcal polysaccharide vaccine (PPV23) for elderly population (≥65 years) from 2013 to 2015. Clinical data and pneumococcal isolates from adult IPD patients (≥18 years) were collected from 20 hospitals. Clinical characteristics were compared between vaccine-serotype (VT) and nonvaccine-serotype (NVT) groups.

Results

Of a total of 319 IPD patients enrolled, 189 cases (59.2%) were available for serotypes. Among them, the proportion of PCV-naïve cases was 99.5% (188/189) and 189 patients consisted of NVT (n = 64, 33.9%) and VT group (n = 125, 66.1%). Compared with the previous study in the ROK (2004–2010), the proportion of PCV13 serotypes was decreased (61.4% vs. 37.0%, P < 0.001) and PPV23 serotypes were stationary (71.5% vs. 65.6%), but NVT serotypes were increased (23.4% vs. 33.9%, P = 0.033) in our study. The most common serotype was 3 (20.8%) and 34 (23.4%) in VT and NVT group, respectively. VT group had more bacteremic pneumonia (72.0% vs. 48.4%, P = 0.002). There was no difference of the case fatality rate between NVT and VT groups (29.7% vs. 35.2%, P = 0.447). Multiple logistic regression analysis showed that chronic kidney disease (odds ratio [OR] 10.26, 95% confidence interval [CI] 1.94–54.44, P = 0.006), younger age of 18–49 years (OR 4.04, 95% CI 1.29–12.71, P = 0.017), deep-seated infection (OR 3.73, 95% CI 1.34–10.39, P = 0.012), meropenem resistance (OR 3.21, 95% CI 1.49–6.91, P = 0.003) were significantly associated with NVT-IPD cases.

Conclusion

Our study indicates that emerging and expanding NVT-IPD among adults, probably due to indirect herd effect of widespread use of pediatric PCV. Further changes of IPD serotypes might occur and IPD serotypes should be monitored for developing better pneumococcal vaccination policy.

Disclosures

All authors: No reported disclosures.

642. B- and T-Cell Responses to Pneumococcal Polysaccharide and Protein Vaccine Antigens in Recently Diagnosed HIV-1-Infected Patients

Backgrounds

Prevention of serious HIV-1-associated pneumococcal infections may be compromised by the limited magnitude and function of vaccine-induced antibodies. Responses to the T-independent pneumococcal capsular polysaccharide (PPS) + T-dependent diphtheria toxoid (DT) protein conjugate vaccine (PCV-13) may be influenced by CD4+ T follicular helper (TFH) cells which provide specific help for B-cell differentiation.

Methods

We immunized 22 control and 19 newly diagnosed HIV-1-infected adults (median 610 CD4+ T cells/µL (range: 139–1,408) and 69,316 plasma HIV RNA (range 232-806,936) on ART for 1–4 months with PCV13. We measured (i) PPS-specific antibody-secreting cells (ASC) by ELISPOT at Weeks 0 and 1, (ii) serum IgG to 11 PPS serotypes (ST) by multiplex ELISA and (iii) titers of opsonophagocytosis (OP) for four STs at Weeks 0 and 8, and (iv) numbers and activation (ICOS expression) of circulating TFH cells by flow cytometry at Weeks 0 and 1. Values were compared by ANOVA, paired and unpaired t and Mann–Whitney tests.

Results

The number of PPS-specific IgG, IgM and IgA ASC increased significantly from Weeks 0 to 1 post-PCV13 and to similar magnitude in both Controls and HIV+ subjects, returning to baseline by Week 8. Levels of serum PPS-specific IgG increased significantly from Weeks 0 to 8 for 10/11 vs. 7/11 ST in controls and HIV+ subjects, respectively (P = NS), and to comparable levels. Similarly, OP titers increased significantly and similarly to each of four STs in both groups from Weeks 0 to 8. In contrast, although DT-specific IgG ASC increased from Weeks 0 to 1 in HIV+ and controls, these values were lower among HIV-1+ adults (P = .001). Consistent with these limited responses, a key regulatory molecule on TFH cells, elicited largely by T-dependent antigens (DT), was upregulated on cells from Control but not HIV+ at Week 1. Moreover, levels of IL-12, which drives TFH differentiation, were also lower among HIV-1+ at Week 1.

Conclusion. Humoral responses to PPS are largely intact (ASC, serum IgG and killing function) with recently diagnosed HIV-1 infection, highlighting the importance of early HIV-1 recognition. That responses to T-dependent DT and TFH activation are more limited, even with high CD4+ counts and ART, suggests a more rapid and perhaps more recalcitrant HIV-1-associated T-cell defect.

Disclosures

All authors: No reported disclosures.

Effect of prior vaccination on carriage rates of Streptococcus pneumoniae in older adults: A longitudinal surveillance study

INTRODUCTION

Pneumococcus is a commensal of the upper respiratory tract and colonization is common in young children. Carriage studies have provided insights on vaccine effects in children and may also be useful for assessing vaccines in adults. However, culture based prevalence studies in older adults describe low colonization rates. Therefore, we assessed cumulative incidence of pneumococcal colonization in older adults using polymerase chain reaction (PCR) targeting the lytA gene and risk factors for carriage.

METHODS

100 community-dwelling adults ≥65 years were enrolled the winter of 2015 and followed biweekly for 12 months. Medical, vaccination and illness history as well as nasopharyngeal (NP) and oropharyngeal (OP) samples were collected. Combined OP and NP were incubated in enrichment broth and screened using real-time lytA PCR. Samples from new colonization events (lytA PCR+) were cultured on gentamicin blood agar plates. Isolates identified by colony morphology as S. pneumoniae were serotyped using a multiplex combined immunoassay-PCR platform which classifies 96 serotypes. Cumulative incidence of pneumococcal carriage was calculated and risk factors for carriage assessed.

RESULTS

The cumulative incidence of colonization was 41% by PCR and 14% by culture. Monthly prevalence ranged from 0 to 17% by PCR and 1 to 4% by culture with peaks in the spring and fall. Demographics were similar between colonized and never colonized subjects although colonized were younger (72.4 vs. 75.0 years, P = 0.06). Vaccination with any pneumococcal vaccine before or during study period was associated with decreased risk of becoming colonized (p < 0.001) as was vaccination with either the 13-valent conjugated pneumococcal vaccine (PCV13) or 23-valent polysaccharide vaccine (PPSV23) (p < 0.001).

CONCLUSION

Pneumococcal colonization in older adults as detected by lytA PCR is frequent and pneumococcal vaccination appears to be associated with decreased risk of carriage. Further study is needed to understand the biological significance of molecular detection of pneumococcus in adults.

Creation, characterization, and assignment of opsonic values for a new pneumococcal OPA calibration serum panel (Ewha QC sera panel A) for 13 serotypes

Pneumococcal conjugate vaccines (PCVs) have been very effective in reducing the disease burden caused by Streptococcus pneumoniae serotypes covered by the current vaccine formulations. However, the incidence of disease caused by serotypes not covered by the vaccine is increasing. Consequently, there are active efforts to develop new PCVs with additional serotypes in order to provide protection against the emergent serotypes. Due to costs and ethical issues associated with performing true vaccine efficacy studies, new PCVs are being licensed based on their immunogenicity, which may be assessed with 2 in vitro assays: enzyme-linked immunosorbent assay (ELISA) for quantitating antibody level and opsonophagocytic assay (OPA) for assessing protective function. While a standardized ELISA has been developed, OPA results from different laboratories can be quite disparate, even among laboratories utilizing the same platform. In order to harmonize OPA data, a recent international collaboration assigned opsonic indices to the US Food and Drug Administration (US FDA) reference serum, 007sp, as well as a panel of US FDA calibration sera. However, due to a low number of aliquots, the availability of these calibration sera is extremely limited. Because calibration sera are critical to establish the performance characteristics of an OPA, a second calibration serum panel was created, comprised of 20 sera collected from adults immunized with the 23-valent polysaccharide vaccine, with 150 to 500 aliquots prepared for each serum. In order to establish consensus OPA values of the 20 sera for the 13 serotypes in 13-valent PCV, the sera were tested by 4 laboratories in an international collaborative OPA study. The 007sp results of 1 laboratory deviated significantly from those obtained by the other laboratories, as well as from previously assigned values. Due to these discrepancies, the consensus values for the calibration sera were determined based on the data from the remaining laboratories. Thus, we were able to create a panel of sera with consensus opsonic values that could be used by outside laboratories to calibrate pneumococcal OPAs. Our results also confirmed findings of a previous study that normalization of OPA results significantly reduces interlaboratory variation, with normalization based on 007sp reducing variation by 43% to 74%, depending on serotype.

Randomized clinical trial of a single versus a double dose of 13-valent pneumococcal conjugate vaccine in adults 55 through 74 years of age previously vaccinated with 23-valent pneumococcal polysaccharide vaccine

INTRODUCTION

In older adults, prior administration of 23-valent pneumococcal polysaccharide vaccine (PPSV23) blunts the opsonophagocytic antibody (OPA) response to subsequent administration of 13-valent pneumococcal conjugate vaccine (PCV13). To determine whether a higher dose of PCV13 could mitigate this effect in adults 55 through 74 years of age, we compared OPA responses to a double dose of PCV13 in persons previously vaccinated with PPSV23 with responses to a single dose of PCV13 in previously vaccinated persons, and with a single dose in PPSV23 naïve persons.

METHODS

Subjects previously vaccinated with PPSV23 were randomly assigned to receive either a single injection or two concurrent injections of 0.5 mL PCV13. Naïve subjects received a single injection of 0.5 mL PCV13. Serotype-specific OPA responses to 12 of the PCV13 serotypes were assessed on samples collected on Day 29 and Day 181. Comparisons of the OPA titers between study groups were based on the lower bound of the 95% confidence interval of the log geometric mean ratio to define superiority (>1) and non-inferiority (>0.5).

RESULTS

At Day 29, the OPA responses to one dose in previously vaccinated (n = 284) versus one dose in naïve subjects (n = 311) achieved the threshold for non-inferiority for only 3 of the 12 serotypes. In previously vaccinated subjects, responses to a double dose (n = 288) versus a single dose met the threshold for superiority for 7 serotypes. The responses to a double dose in previously vaccinated subjects versus a single dose in naïve subjects met the threshold for non-inferiority for 9 serotypes.

CONCLUSIONS

There is a dose response to PCV13 in older adults and the higher response to a double dose in previously vaccinated adults is non-inferior to that of a single dose in naïve adults for 9 of the 12 PCV13 serotypes evaluated.

Assignment of Opsonic Values to Pneumococcal Reference Serum 007sp for Use in Opsonophagocytic Assays for 13 Serotypes

Opsonophagocytic assays (OPAs) are routinely used for assessing the immunogenicity of pneumococcal vaccines, with OPA data often being utilized for licensure of new vaccine formulations. However, no reference serum for pneumococcal OPAs is available, making evaluation of data among different laboratories difficult. This international collaboration was initiated to (i) assign consensus opsonic indexes (OIs) to FDA pneumococcal reference serum lot 007sp (here referred to as 007sp) and a panel of serum samples used for calibration of the OPA and (ii) determine if the normalization of the OPA results obtained with test samples to those obtained with 007sp decreases the variability in OPA results among laboratories. To meet these goals, six participating laboratories tested a panel of serum samples in five runs for 13 serotypes. For each serum sample, consensus OIs were obtained using a mixed-effects analysis of variance model. For the calibration serum samples, normalized consensus values were also determined on the basis of the results obtained with 007sp. For each serotype, the overall reduction in interlaboratory variability was calculated by comparing the coefficients of variation of the unadjusted and the normalized values. Normalization of the results substantially reduced the interlaboratory variability, ranging from a 15% reduction in variability for serotype 9V to a 64% reduction for serotype 7F. Normalization also increased the proportion of data within 2-fold of the consensus value from approximately 70% (average for all serotypes) to >90%. On the basis of the data obtained in this study, pneumococcal reference standard lot 007sp will likely be a useful reagent for the normalization of pneumococcal OPA results from different laboratories. The data also support the use of the 16 FDA serum samples used for calibration of the OPA as part of the initial evaluation of new assays or periodic assessment of established assays.

Ficolin-2 inhibitors are present in sera after prolonged storage at -80 °C

Ficolins can activate the lectin pathway of the complement system that provides innate immune protection against pathogens, marks host cellular debris for clearance, and promotes inflammation. Baseline inflammation increases with aging in a phenomenon known as “inflammaging.” Although IL-6 and C-reactive protein are known to increase with age, contributions of many complement factors, including ficolins, to inflammaging have been little studied.

Ficolin-2 is abundant in human serum and can recognize many target structures; therefore, ficolin-2 has potential to contribute to inflammaging. We hypothesized that inflammaging would alter ficolin-2 levels among older adults and examined 360 archived sera collected from older individuals. We found that these sera had apparently reduced ficolin-2 levels and that 84.2% of archived sera exhibited ficolin-2 inhibitors, which suppressed apparent amounts of ficolin-2 detected by enzyme-linked immunosorbent assay. Fresh serum samples were obtained from donors whose archived sera showed inhibitors, but the fresh sera did not have ficolin-2 inhibitors. Ficolin-2 inhibitors were present in other long-stored sera from younger persons. Furthermore, noninhibiting samples and fresh sera from older adults had apparently normal amounts of ficolin-2. Thus, ficolin-2 inhibitors may arise as an artifact of long-term storage of serum at −80 °C.

A high throughput serum bactericidal assay for antibodies to Haemophilus influenzae type b

BACKGROUND

The protective capacities of antibodies induced with Haemophilus influenzae type b (Hib) vaccines can be directly assessed in vitro with a Hib-specific serum bactericidal assay (SBA). However, the conventional SBA requires several tedious steps including manual counting of bacterial colonies, and therefore, it is seldom used.

METHODS

To overcome these limitations, we have improved the conventional SBA by using frozen target bacteria and by developing an automated colony counting method based on agar plates with the chromogenic dye 2, 3, 5-triphenyl tetrazolium chloride (TTC).

RESULTS

These changes enabled us to analyze about 100 serum samples per day per person by SBA. When the intra- and inter-assay precisions were studied, this assay showed a coefficient of variation (CV) ranging from 1 to 38 %. To monitor the long term assay stability for assays involving different bacteria lots, complement lots, and operators, we analyzed bactericidal indices of quality control samples obtained over a 6 year period and found the CV to be about 35-50 %. Lastly, our SBA results were compared with the ELISA results obtained using 90 serum samples from children. We showed that the bactericidal index correlated with IgG anti-Hib antibody levels (r = 0.84), with a bactericidal index of 10 corresponding approximately to 0.15 μg/mL IgG, the widely accepted protective level of antibody.

CONCLUSION

We describe a simple high throughput SBA for anti-Hib antibodies that would be useful for evaluating various Hib vaccines. While additional work will be needed to standardize the assay, this SBA should greatly facilitate studies of Hib vaccines.

NOD-Like Receptors in Infection, Immunity, and Diseases

Nucleotide-binding and oligomerization domain (NOD)-like receptors (NLRs) are pattern-recognition receptors similar to toll-like receptors (TLRs). While TLRs are transmembrane receptors, NLRs are cytoplasmic receptors that play a crucial role in the innate immune response by recognizing pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Based on their N-terminal domain, NLRs are divided into four subfamilies: NLRA, NLRB, NLRC, and NLRP. NLRs can also be divided into four broad functional categories: inflammasome assembly, signaling transduction, transcription activation, and autophagy. In addition to recognizing PAMPs and DAMPs, NLRs act as a key regulator of apoptosis and early development. Therefore, there are significant associations between NLRs and various diseases related to infection and immunity. NLR studies have recently begun to unveil the roles of NLRs in diseases such as gout, cryopyrin-associated periodic fever syndromes, and Crohn's disease. As these new associations between NRLs and diseases may improve our understanding of disease pathogenesis and lead to new approaches for the prevention and treatment of such diseases, NLRs are becoming increasingly relevant to clinicians. In this review, we provide a concise overview of NLRs and their role in infection, immunity, and disease, particularly from clinical perspectives.

Indirect Effects of Pneumococcal Conjugate Vaccines in National Immunization Programs for Children on Adult Pneumococcal Disease

The pneumococcal conjugate vaccine (PCV) was developed to overcome the limitations of the pneumococcal polysaccharide vaccine, which produces poor immunogenicity in infants younger than 2 years. As many countries have included PCVs in national immunization programs for children, the incidence of invasive pneumococcal disease caused by vaccine type Streptococcus pneumoniae has declined markedly, not only among the vaccinated pediatric population, but also among unvaccinated adults. In this review, we present a concise overview of the indirect effects of mass pediatric PCV immunization on unvaccinated adults.

Rapid and efficient purification of ficolin-2 using a disposable CELLine bioreactor

The human opsonin ficolin-2 (L-ficolin) is an innate pattern-recognizing molecule that binds to acetylated moieties. Upon binding, ficolin-2 activates complement through the lectin pathway, opsonizing the target to promote phagocytic clearance. Ficolin-2 has been found to interact with a growing number of pathogenic bacteria, fungi, and viruses. Ficolin-2 also has proposed roles in host homeostasis, including the clearance of apoptotic cells. Consequently, there is an increased interest in studying ficolin-2, and access to purified ficolin-2 is necessary for these studies. Ficolin-2 purified from serum, plasma, or cell culture supernatants has been a useful tool in the characterization of ficolin-2 function; however, available protocols are laborious and inefficient, requiring additional processing of starting materials (e.g., polyethylene glycol precipitation or dialysis) and multiple steps of purification. Here, we investigated a simple solution to the problem: use of a simple, disposable bioreactor requiring only standard tissue culture equipment. Using this system, we generated cell culture supernatants containing high concentrations of recombinant ficolin-2, which permitted rapid purification of high-purity recombinant ficolin-2 without processing the supernatants. Purified recombinant ficolin-2 retained its binding capacity and supported complement activation in vitro. Bioreactor cultivation will likely be generally useful in the production of other recombinant proteins in the study of the complement system.

Low invasiveness of pneumococcal serotype 11A is linked to ficolin-2 recognition of O-acetylated capsule epitopes and lectin complement pathway activation

BACKGROUND

The divergent epidemiological behavior of Streptococcus pneumoniae serotypes suggests that serotype-specific features such as capsule O-acetylation influence the propensity of a strain to cause invasive pneumococcal disease (IPD). We hypothesize that innate host factors mediate the observed negative association between IPD and the serotype 11A (ST11A) capsule O-acetyltransferase gene, wcjE.

METHODS

We evaluated the ability of ficolin-2, an initiator of the lectin complement pathway that was previously shown to bind ST11A pneumococci, to recognize and mediate complement-dependent opsonophagocytosis of different pneumococcal serotypes. We supplemented findings with an epidemiological meta-analysis comparing invasiveness of the 30 most prevalent pneumococcal serotypes.

RESULTS

Ficolin-2 bound ST11A capsule polysaccharide and other wcjE-containing pneumococcal serotypes, except ST9V and ST20B. Ficolin-2 did not bind wcjE-null serotypes, including the wcjE-null variant of ST11A, ST11E. We observed C1q-independent complement deposition and phagocytic killing of pneumococci expressing ST11A but not those expressing ST11E. Inhibition of ficolin-2 binding abrogated ST11A-associated complement deposition and phagocytosis. In children, invasiveness of ST11A was the lowest among serotypes tested in our meta-analysis, while ST9V was among the highest.

CONCLUSIONS

Ficolin-2 mediates serum protection by recognizing specific O-acetylated epitopes of pneumococcal capsule polysaccharides, exemplifying a novel host-microbe interaction that innately offers serotype-specific immunity to IPD.

Commercially available complement component-depleted sera are unexpectedly codepleted of ficolin-2

The ficolins are a family of innate pattern recognition molecules that are known to bind acetylated compounds and activate complement through the association of mannose binding lectin (MBL)/ficolin-associated serine proteases (MASPs). Their importance has more recently become appreciated, as they have been shown to play a role in a variety of disease processes from infection to autoimmunity. While studying ficolin-2-mediated complement deposition on Streptococcus pneumoniae, we found that sera depleted of C1q or other complement components were also codepleted of ficolin-2 but not ficolin-1, ficolin-3, or MBL. MBL present in C1q-depleted sera was able to mediate complement deposition on Saccharomyces cerevisiae, suggesting the presence of MASPs. We found that complement was activated on pneumococci in C1q-depleted serum only after opsonization with exogenous recombinant ficolin-2 (rFicolin-2). Also, no complement deposition was observed in C1q-depleted serum when pneumococci were opsonized with rFicolin-2 mutated at its lysine-57 residue, where MASPs are known to associate. Thus, these depleted sera are a unique tool to study ficolin-2-mediated complement pathways; however, one should be aware that ficolin-2 is absent from complement component-depleted sera.

Nonencapsulated Streptococcus pneumoniae Cause Acute Otitis Media in the Chinchilla That Is Enhanced by Pneumococcal Surface Protein K

Nonencapsulated Streptococcus pneumoniae (NESp) is an emerging human pathogen, and NESp produced acute otitis media in the chinchilla. Increased epithelial cell adhesion correlated to pathogenesis. The expression of pneumococcal surface protein K (PspK) increased NESp virulence.

Background

 Use of the pneumococcal conjugate vaccine has led to serotype replacement of carriage and acute otitis media (AOM) pneumococcal isolates. Increases in nonencapsulated Streptococcus pneumoniae (NESp) isolates have also occurred, and there are increasing reports of NESp-associated disease. Disease prevalence and virulence factors of NESp isolates have not been studied.

Methods

 A chinchilla model of pneumococcal AOM was utilized, and disease was assessed through bacterial enumeration along with scoring visible signs of pathology. An adhesion-invasion assay using a human epithelial cell line was performed.

Results

 Nonencapsulated Streptococcus pneumoniae strains containing pneumococcal surface protein K (PspK) were more likely to cause AOM and pathology upon infection. Deletion of PspK from an isolate significantly reduced bacterial loads. Increased epithelial cell adhesion correlated with increased virulence of NESp isolates naturally lacking PspK. Furthermore, expression of PspK by an avirulent NESp resulted in virulence.

Conclusions

 The presence of PspK increased the disease potential of NESp. Pneumococcal surface protein K is not the only virulence factor of NESp in AOM. Expression of PspK in an avirulent NESp mediated the progression to pneumococcal disease. Genetic exchange between pneumococci may allow dissemination of PspK, increasing the potential of NESp disease. The current study is the first report of a NESp-specific virulence factor.

Identification of Streptococcus pneumoniae serotype 11E, serovariant 11Av and mixed populations by high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) spectroscopy and flow cytometric serotyping assay (FCSA)

Background

Recent studies have identified Streptococcus pneumoniae serotype 11E and serovariant 11Av among isolates previously typed as 11A by classical serotyping methods. Serotype 11E and serovariant 11Av differ from serotype 11A by having totally or partially inactive wcjE, a gene in cps locus coding for an O-acetyl transferase. Serotype 11E is rare among carriage isolates but common among invasive isolates suggesting that it survives better during invasion. Aim of this work was to investigate the epidemiology of serotype 11A in a pneumococcal collection using a new serotyping approach based on High-Resolution Magic Angle Spinning Nuclear Magnetic Resonance (HR-MAS NMR) spectroscopy to distinguish serotypes 11A and 11E.

Methods

A collection of 48 (34 invasive and 14 carriage) S. pneumoniae isolates from Italy, previously identified as serotype 11A by the Quellung reaction, were investigated by wcjE sequencing, HR-MAS NMR spectroscopy and the reference flow cytometric serotyping assay (FCSA) based on monoclonal antibodies.

Results

HR-MAS NMR spectra from serotypes 11A and 11E showed different NMR peaks indicating that HR-MAS NMR could be used to distinguish these serotypes, although HR-MAS NMR could not distinguish serotype 11Av from serotype 11E unambiguously. Thirty-eight isolates were confirmed to be serotype 11A, 8 isolates with a mutated wcjE were serotype 11E, 1 isolate belonged to serovariant 11Av, and 1 isolate was a mixed population 11A/11Av. All 11E isolates were identified among invasive isolates.

Conclusions

We proved that HR-MAS NMR can be of potential use for pneumococcal serotyping. The detection of serotype 11E among invasive isolates in our collection, supports previous epidemiological studies suggesting that mutations in wcjE can represent a mechanism promoting pneumococcal survival during invasion. The discovery of a spectrum of immunochemical diversity within established serotypes should stimulate efforts to develop new serotyping approaches.

Impact of preceding flu-like illness on the serotype distribution of pneumococcal pneumonia

BACKGROUND

Even though the pathogenicity and invasiveness of pneumococcus largely depend on capsular types, the impact of serotypes on post-viral pneumococcal pneumonia is unknown.

METHODS AND FINDINGS

This study was performed to evaluate the impact of capsular serotypes on the development of pneumococcal pneumonia after preceding respiratory viral infections. Patients with a diagnosis of pneumococcal pneumonia were identified. Pneumonia patients were divided into two groups (post-viral pneumococcal pneumonia versus primary pneumococcal pneumonia), and then their pneumococcal serotypes were compared. Nine hundred and nineteen patients with pneumococcal pneumonia were identified during the study period, including 327 (35.6%) cases with post-viral pneumococcal pneumonia and 592 (64.4%) cases with primary pneumococcal pneumonia. Overall, serotypes 3 and 19A were the most prevalent, followed by serotypes 19F, 6A, and 11A/11E. Although relatively uncommon (33 cases, 3.6%), infrequently colonizing invasive serotypes (4, 5, 7F/7A, 8, 9V/9A, 12F, and 18C) were significantly associated with preceding respiratory viral infections (69.7%, P<0.01). Multivariate analysis revealed several statistically significant risk factors for post-viral pneumococcal pneumonia: immunodeficiency (OR 1.66; 95% CI, 1.10-2.53), chronic lung diseases (OR 1.43; 95% CI, 1.09-1.93) and ICI serotypes (OR 4.66; 95% CI, 2.07-10.47).

CONCLUSIONS

Infrequently colonizing invasive serotypes would be more likely to cause pneumococcal pneumonia after preceding respiratory viral illness, particularly in patients with immunodeficiency or chronic lung diseases.

Impaired serotype-specific immune function following pneumococcal vaccination in infants with prior carriage

The impact of prior nasopharyngeal carriage on serotype-specific IgG responses following immunization with pneumococcal conjugate vaccines (PCV) has recently been described. This report extends these findings to describe the attenuation of functional immune responses following 23-valent pneumococcal polysaccharide vaccination (PPS). We report the attenuation of immune responses following booster with the 23-valent pneumococcal polysaccharide vaccination (PPS) in infants with prior nasopharyngeal carriage of Streptococcus pneumoniae. Fijian infants who were part of a phase II randomized, controlled trial of reduced dose PCV7 schedules were the basis of this study. Pneumococcal carriage was determined at 6, 9 and 12 months of age, prior to PPS immunization. Serum samples collected at 18 weeks (post-PCV7), 12 months (pre-PPS), 12.5 months and 17 months (post-PPS) of age were assessed for serotype-specific IgG and opsonophagocytic responses. The most frequently carried serotypes were 6B (N=11), 19F (N=14) and 23F (N=23). Significantly lower serotype-specific IgG for 19F, 23F but not 6B post-PPS were detected in infants with homologous serotype carriage prior to PPS compared with non-carriers (N=230). However, OPA levels for 6B and 23F were lower in infants that carried these serotypes. Pneumococcal carriage with 19F or 23F at any time prior to PPS immunization in infants at 12 months of age who were previously primed with PCV resulted in serotype-specific hyporesponsiveness that persisted until 17 months of age. These results may have implications for the timing of infant vaccine schedules, particularly in high disease burden settings.

Towards New Broader Spectrum Pneumococcal Vaccines: The Future of Pneumococcal Disease Prevention

Seven-valent pneumococcal conjugate vaccine (PCV7) introduction and routine pediatric use has substantially reduced the burden of Streptococcus pneumoniae disease worldwide. However, a significant amount of disease burden, due to serotypes not contained in PCV7, still exists globally. A newly recognized serotype, 6C, was until recently, identified and reported as serotype 6A. This review summarizes the serotype epidemiology of pneumococcal disease pre- and post-introduction of PCV7, available post-marketing surveillance data following the introduction of higher valency pneumococcal vaccines (PCV10, PCV13) and future prospects for the development of new pneumococcal vaccines.

Blood collection tubes influence serum ficolin-1 and ficolin-2 levels

The ficolins are members of a recently discovered family of host innate opsonins that can activate the lectin pathway of complement. The ficolins bind many ligands, although they are typically described as binding acetylated sugars. Ficolin-1 (M-ficolin) and ficolin-2 (L-ficolin) are known to bind Streptococcus pneumoniae serotypes 19C and 11A, respectively. While studying the binding of ficolins to pneumococci, we found variations in ficolin-2 binding among serum samples collected in different types of blood collection tubes. Plastic tubes, which contain a silica clot activator, yielded sera with reduced ficolin-2 binding and apparent ficolin-2 levels. We found that the silica clot activator eluted from plastic red-top tubes inhibited ficolin-2 ligand binding, while other related proteins, like mannose-binding lectin (MBL) and ficolin-1, were not affected. These tube types did not affect the concentrations of other related opsonins (C1q, MBL, or ficolin-3 [H-ficolin]). Interestingly, we also found that ficolin-1 levels were increased 2- to 3-fold in plastic serum separator tubes compared to the increases in other tube types. These findings have implications for future ficolin-1 and ficolin-2 studies, as proper sample collection and handling are essential.

L-rhamnose is often an important part of immunodominant epitope for pneumococcal serotype 23F polysaccharide antibodies in human sera immunized with PPV23

Streptococcus pneumoniae is a major human pathogen which expresses more than 90 serologically distinct capsular polysaccharides (PS) on the surface. Since pneumococcal PSs elicit protective antibodies against pneumococcal diseases, it is important to identify the immunological epitope eliciting anti-pneumococcal PS antibodies. L-rhamnose is a part of the 23F PS repeating unit and is known to be a critical part of immunodominant epitope which elicits antibodies against pneumococcal serotype 23F PS. In order to determine if L-rhamnose is a part of epitope recognized by functional antibodies specific for serotype 23F PS in human serum samples, we evaluated the opsonophagocytic killing of serotype 23F pneumococci by serum antibodies specific for L-rhamnose. Using 10 mM L-rhamnose, opsonic capacities (opsonic indices) of serum antibodies were inhibited by 60% in 19 sera (36%) and 30–60% in 16 sera (30%) out of 53 sera from young and old adults immunized with 23-valent pneumococcal polysaccharide vaccine (PPV23). Interestingly, when IgM antibodies were depleted from immune sera in order to preferentially study IgG antibodies, the proportion of young adult sera showing more than 60% inhibition in opsonic capacity by 10 mM of L-rhamnose increased from 33% (11/31) to 68% (21/31). On the other hand, IgM depletion did not alter the proportion for old adult sera. Therefore, young and old adults may produce different antigen binding profiles of IgG antibodies against serotype 23F PS.

Diagnosis of pneumococcal pneumonia: current pitfalls and the way forward

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia. However, it can also asymptomatically colonize the upper respiratory tract. Because of the need to distinguish between S. pneumoniae that is simply colonizing the upper respiratory tract and S. pneumoniae that is causing pneumonia, accurate diagnosis of pneumococcal pneumonia is a challenging issue that still needs to be solved. Sputum Gram stains and culture are the first diagnostic step for identifying pneumococcal pneumonia and provide information on antibiotic susceptibility. However, these conventional methods are relatively slow and insensitive and show limited specificity. In the past decade, new diagnostic tools have been developed, particularly antigen (teichoic acid and capsular polysaccharides) and nucleic acid (ply, lytA, and Spn9802) detection assays. Use of the pneumococcal antigen detection methods along with biomarkers (C-reactive protein and procalcitonin) may enhance the specificity of diagnosis for pneumococcal pneumonia. This article provides an overview of current methods of diagnosing pneumococcal pneumonia and discusses new and future test methods that may provide the way forward for improving its diagnosis.

The 7-valent pneumococcal conjugate vaccine elicits cross-functional opsonophagocytic killing responses to Streptococcus pneumoniae serotype 6D in children

Background

We investigated the immune response to serogroup 6 with the opsonophagocytic killing assay (OPKA) in children aged 12–23 months of age after immunization with the 7-valent pneumococcal conjugate vaccine (PCV7) containing serotype 6B.

Methods

Blood samples were obtained from 59 children who had blood sampling for medical examination. Immunization status against PCV7 was confirmed by immunization records and samples were categorized according to immunization status into a booster, primary, or control group. The OPKA was performed for serotypes 6A, 6B, 6C, and 6D.

Results

Subjects with no previous PCV7 immunization history showed opsonic activity for serogroup 6 in 5-30% (according to serotype). In subjects vaccinated with a 3-dose primary series, 81% showed opsonic activity for serotypes 6B and 6D, and 29% showed opsonic activity for serotypes 6A and 6C. Among subjects vaccinated with a booster dose, all subjects had opsonic activity against serotype 6B. Subjects in the booster group with opsonic activity against serotypes 6A, 6C, and 6D were 100%, 78%, and 89%, respectively.

Conclusions

In subjects aged 12–23 months, an immune response is elicited after a primary series of immunizations with PCV7 for serotypes 6B and 6D, and a booster dose enhances a cross reactive immune response against serotypes 6A, 6C and 6D.