Evolution of the capsular gene locus of Streptococcus pneumoniae serogroup 6

Streptococcus pneumoniae expressing serogroup 6 capsules frequently causes pneumococcal infections and the evolutionary origins of the serogroup 6 strains have been extensively studied. However, these studies were performed when serogroup 6 had only two known members (serotypes 6A and 6B) and before the two new members (serotypes 6C and 6D) expressing wciN_β were found. We have therefore reinvestigated the evolutionary origins of serogroup 6 by examining the profiles of the capsule gene loci and the multilocus sequence types (MLSTs) of many serogroup 6 isolates from several continents. We confirmed that there are two classes of cps locus sequences for serogroup 6 isolates. In our study, class 2 cps sequences were limited to a few serotype 6B isolates. Neighbour-joining analysis of cps sequence profiles showed a distinct clade for 6C and moderately distinct clades for class 1 6A and 6B sequences. The serotype 6D cps profile was found within the class 1 6B clade, suggesting that it was created by recombination between 6C and 6B cps loci. Interestingly, all 6C isolates also had a unique wzy allele with a 6 bp deletion. This suggests that serotype switching to 6C involves the transfer of a large (>4 kb) gene segment that includes both the wciN_β allele and the ‘short’ wzy allele. The MLST studies of serotype 6C isolates suggest that the 6C cps locus is incorporated into many different pneumococcal genomic backgrounds but that, interestingly, 6C cps may have preferentially entered strains of the same genomic backgrounds as those of serotype 6A.

A report of Streptococcus pneumoniae serotype 6D in Europe

Serotype 6D of Streptococcus pneumoniae has been reported in Asia and the Fijian islands among nasopharyngeal carriage isolates. We now report a 6D isolate from a Finnish adult with invasive pneumococcal disease. Interestingly, the Finnish isolate and Asian isolate capsule gene loci are almost identical.

Low-cost, high-throughput, automated counting of bacterial colonies

Research involving bacterial pathogens often requires enumeration of bacteria colonies. Here, we present a low-cost, high-throughput colony counting system consisting of colony counting software and a consumer-grade digital camera or document scanner. We demonstrate that this software, called "NICE" (NIST's Integrated Colony Enumerator), can count bacterial colonies as part of a high-throughput multiplexed opsonophagocytic killing assay used to characterize pneumococcal vaccine efficacy. The results obtained with NICE correlate well with the results obtained from manual counting, with a mean difference of less than 3%. NICE is also rapid; it can count colonies from multiple reaction wells within minutes and export the results to a spreadsheet for data processing. As this program is freely available from NIST, NICE should be helpful in bacteria colony enumeration required in many microbiological studies, and in standardizing colony counting methods.

A new pneumococcal serotype, 11E, has a variably inactivated wcjE gene

Recently, 2 serologically and biochemically distinct subtypes-11Aalpha and 11Abeta-were discovered among serotype 11A isolates of Streptococcus pneumoniae. Sequence comparison of the capsular polysaccharide synthesis (cps) loci of the 2 subtypes identified disruption of the wcjE gene, a putative O-acetyltransferase, as the genetic hallmark of the 11Abeta phenotype. Directed disruption of wcjE in vitro in an 11Aalpha strain switched the strain to the 11Abeta phenotype, confirming the role played by the gene in the divergence between the subtypes. Furthermore, sequences from 7 11Abeta clinical strains each contained unrelated disruptive mutations in the wcjE gene, displaying an unprecedented degree of genetic heterogeneity in a pneumococcal serotype. We propose to name the 11Aalpha subtype as serotype 11A and the 11Abeta subtype as 11E, a new serotype. Our findings also suggest that the diversity of pneumococcal capsules is much greater than was previously recognized.

The effect of age on the response to the pneumococcal polysaccharide vaccine

BACKGROUND

Streptococcus pneumoniae is a leading cause of morbidity and mortality in the elderly. To prevent invasive pneumococcal diseases, the 23-valent pneumococcal polysaccharide vaccine (PPV) is recommended in subjects over 65 years of age. Although it has been reported to provide approximately 50-80% protection against invasive disease in the general elderly population, there is still controversy as to the effectiveness of the PPV in the elderly.

METHODS

To evaluate the immune response to the pneumococcal polysaccharide vaccine in the elderly, samples from young adults and elderly were obtained before and one month after vaccination. The quantitative and qualitative response to the vaccine were measured by the ELISA and opsonophagocytic killing assay for eight vaccine type serotypes (4, 6B, 9V, 14, 18C, 19A, 19F, 23F) and one vaccine-related serotype (6A).

RESULTS

The response to the pneumococcal polysaccharide vaccine showed a similar response between adults and elderly when evaluated by the ELISA, however the functional activity of the antibodies elicited after vaccination were lower in the elderly group for more than half of the serotypes evaluated. In comparison of the antibody needed for 1:8 opsonic titer, more antibodies were needed in the elderly for serotypes Pn 4, 19F, 23F and 6A, suggesting the functional activity of antibody detected by the ELISA was lower in the elderly compared with the adult group for these serotypes. As for subjects with an opsonic titer <8 after vaccination, only one subject each for serotypes Pn 4, 9V and 6A were found in the adult group. However, up to 10 (30.3%) of the subjects did not show opsonic activity after vaccination in the elderly group for serotypes Pn 4, 9V, 14, 19A and 6A.

CONCLUSIONS

Although the amount of antibodies elicited were similar between the two age groups, distinct differences in function were noted. This report highlights the importance of a quantitative and qualitative evaluation of the immunogenic response to the PPV in the elderly age group.

TRIAL REGISTRATION

This trial is registered with Clinicaltrials.gov. Registration number NCT00964769.

Synthesis, conjugation, and immunological evaluation of the serogroup 6 pneumococcal oligosaccharides

The first synthesis of the newly discovered oligosaccharide of pneumococcal serotype 6C and its spacer-containing analogue is reported. Conjugation of the spacer-containing oligosaccharides of pneumococcal saccharides 6A, 6B, 6C and derivatives thereof with bovine serum albumin (BSA) protein carrier was carried out by using squaric-acid approach to obtain the oligosaccharide-protein conjugates in excellent yields. The conjugates have been tested with a rabbit antiserum pool (Pool B) used for pneumococcal serotyping. The results showed that synthetic carbohydrate conjugates express epitopes found in native capsular polysaccharides of serotypes 6A, 6B, and 6C.

Identification of natural pneumococcal isolates expressing serotype 6D by genetic, biochemical and serological characterization

The recently discovered pneumococcal serotype 6C was created when the original wciN gene in the 6A capsule gene locus was naturally replaced with a new gene. Since the capsule gene loci of 6A and 6B serotypes may differ by only one base pair in the wciP gene, it was speculated that a new serotype '6D' would be possible if the new wciN gene were inserted into the 6B capsule gene locus. Although pneumococci expressing serotype 6D could be produced in the laboratory, initial searches for natural pneumococcal isolates expressing serotype 6D were unsuccessful. However, we now report the discovery of two naturally occurring pneumococcal isolates from Korea that have the serological, genetic and biochemical features predicted for serotype 6D.

Identification of 3-O-acetylglycerol, a novel structural element in bacterial polysaccharides

We have discovered a novel bacterial polysaccharide structural element, 3-O-acetylglycerol, in the Streptococcus pneumoniae ST11A polysaccharide: This moiety was elucidated through a combination of homonuclear and heteronuclear 1D and 2D NMR experiments using (1)H, (13)C, and (31)P in various combinations. The 3-O-acetylglycerol moiety is substoichiometrically O-acetylated in ST11A; yet, key connectivities that unequivocally show O-acetylation at the glycerol are provided by the long-range correlations from the acetate methyl groups to the glycerol in the (1)H-(13)C HMBC spectrum. Additionally, we clarify the (1)H-(31)P assignments previously presented.

Superior immune response to protein-conjugate versus free pneumococcal polysaccharide vaccine in chronic obstructive pulmonary disease

RATIONALE

Debate exists about the immunogenicity and protective efficacy of antibodies produced by the 23-valent pneumococcal polysaccharide vaccine (PPSV23) in chronic obstructive pulmonary disease (COPD). The 7-valent diphtheria-conjugated pneumococcal polysaccharide vaccine (PCV7) induces a more robust immune response than PPSV23 in healthy elderly adults.

OBJECTIVES

We hypothesized that serotype-specific IgG antibody concentration and functional antibody activity would be superior after PCV7 vaccination compared with PPSV23 in moderate to severe COPD. We also posited that older age and prior PPSV23 vaccination would be associated with reduced vaccine responsiveness.

METHODS

One hundred twenty patients with COPD were randomized to PPSV23 (63 subjects) or PCV7 (57 subjects). IgG concentrations were determined by ELISA; functional antibody activity was assayed with a standardized opsonophagocytosis assay and reported as an opsonization killing index (OPK). Increases in serotype-specific IgG and OPK at 1 month post vaccination were compared within and between vaccine groups.

MEASUREMENTS AND MAIN RESULTS

Both vaccines were well tolerated. Within each study group, postvaccination IgG and OPK were higher than baseline (P < 0.01) for all serotypes. Adjusted for baseline levels, postvaccination IgG was higher in the PCV7 group than the PPSV23 group for all seven serotypes, reaching statistical significance for five (P < 0.05). PCV7 resulted in a higher OPK for six of seven serotypes (statistically greater for four) compared with PPSV23. In multivariate analyses, younger age, vaccine naivety, and receipt of PCV7 were associated with increased OPK responses.

CONCLUSIONS

PCV7 induces a superior immune response at 1 month post vaccination compared with PPSV23 in COPD. Older age and prior PPSV23 reduce vaccine responsiveness. Clinical trial registered with www.clinicaltrials.gov (NCT00457977).

Production of a unique pneumococcal capsule serotype belonging to serogroup 6

Serogroup 6 of Streptococcus pneumoniae contains three serotypes, named 6A, 6B and 6C, with highly homologous capsule gene loci. The 6A and 6B capsule gene loci consistently differ from each other by only one nucleotide in the wciP gene. The 6A capsule gene locus has a galactosyltransferase, which has been replaced with a glucosyltransferase in the 6C capsule gene locus. We considered that a new serotype named '6X1' would be possible if the galactosyltransferase of the 6B capsule gene locus is replaced with the glucosyltransferase of 6C. We demonstrate that this gene transfer yields a viable pneumococcal strain and that the capsular polysaccharide (PS) from this strain has the predicted chemical structure and serological similarity to the capsular PS of the 6B serotype. The new strain (i.e. serotype 6X1) is typed as 6B by the quellung reaction, but it can be distinguished from 6B strains with mAbs to 6B PS. Reexamination of 264 pneumococcal isolates that had been previously typed as 6B with classical typing methods revealed no isolates expressing serotype 6X1. Nevertheless, this study shows that this capsular PS is biochemically possible and could exist/emerge in nature.

Structure of the capsular polysaccharide of pneumococcal serotype 11A reveals a novel acetylglycerol that is the structural basis for 11A subtypes

We have undertaken a structural assessment of Streptococcus pneumoniae 11A polysaccharide as well as two clinical isolates related to 11A. The clinical isolates were labeled 11Aalpha and 11Abeta. The result of our experiments is a revision to the old structure for S. pneumoniae 11A polysaccharide. The new structure differs from the old structure in both the primary connectivities and acetylation pattern. We also show that 11A contains an acetylglycerol-PO4 moiety, a substitution that is heretofore unknown in the bacterial polysaccharide literature. The two clinical isolates were also structurally characterized. 11Aalpha was determined to be identical to 11A. 11Abeta is a new serotype, which differs from 11A in the absence of the acetylation of the glycerol-PO4 moiety and a different acetylation pattern of the saccharides. Thus, we propose that the acetylglycerol is the structural basis for 11Aalpha and 11Abeta subtypes.

Increase in the prevalence of the newly discovered pneumococcal serotype 6C in the nasopharynx after introduction of pneumococcal conjugate vaccine

BACKGROUND

Because pneumococcal serotype 6C was previously not distinguished from serotype 6A, the impact of the 7-valent pneumococcal conjugate vaccine (PCV7) on the carriage of serotype 6C is unknown.

METHODS

The nasopharyngeal (NP) prevalence of the 6C serotype was determined using 1326 pneumococcal isolates collected from 7 cohorts of Massachusetts children between 1994 and 2007. Initially, the isolates were serotyped using the quellung reaction; subsequently, stored specimens of all putative 6A isolates were tested for 6C using monoclonal antibodies. The opsonophagocytic and antibiotic susceptibilities of the isolates were determined.

RESULTS

The prevalence of 6A was 9.6% (33/343) before 2001, 8.0% (18/226) in 2004, and 2.9% (12/416) in 2007. In contrast, the prevalence of 6C was 0.6% (2/343) before 2001, 2.2% (5/226) in 2004, and 8.7% (36/416) in 2007 (P<.001 for 2/343 vs. 36/416). 6C isolates from 2007 were more susceptible to antibiotics than were 6A isolates. PCV7 induced a low ability to opsonize different isolates of 6C.

CONCLUSIONS

Among NP isolates, the prevalence of 6C isolates has increased and the prevalence of 6A isolates has decreased since the introduction of PCV7 in Massachusetts in 2000. The observed increase in serotype 6C prevalence may be explained by the induction by PCV7 of low amounts of functional anti-6C antibody, compared with anti-6A and anti-6B antibodies.

Differential effects of pneumococcal vaccines against serotypes 6A and 6C

BACKGROUND

Because classic pneumococcal serotyping methods cannot distinguish between serotypes 6A and 6C, the effects of pneumococcal vaccines against serotype 6C are unknown. Pneumococcal vaccines contain serotype 6B but not serotypes 6A and 6C.

METHODS

We used a phagocytic killing assay to estimate the immunogenicity of the 7-valent conjugate vaccine (PCV7) in children and the 23-valent polysaccharide vaccine (PPV23) in adults against serotypes 6A and 6C. We evaluated trends in invasive pneumococcal disease (IPD) caused by serotypes 6A and 6C in the United States, using active surveillance.

RESULTS

Serum specimens from PCV7-immunized children had median opsonization indices of 150 and < 20 for serotypes 6A and 6C, respectively. Similarly, only 52% of adults (25 of 48) vaccinated with PPV23 showed opsonic indices of > 20 against serotype 6C. During 1999--2006, the incidence of serotype 6A IPD decreased by 91% (from 4.9 to 0.46 cases per 100,000 persons; P < .05) among individuals aged < 5 years and by 58% (from 0.86 to 0.36 cases per 100,000 persons; P < .05) among those aged > or = 5 years. Although the incidence of 6C IPD showed no consistent trend (range, 0-0.6 cases per 100,000 persons) among individuals aged < 5 years, it increased from 0.25 to 0.62 cases per 100,000 persons (P < .05) among those aged > or = 5 years.

CONCLUSIONS

PCV7 introduction has led to reductions in serotype 6A IPD but not serotype 6C IPD in the United States.

Initial and subsequent response to pneumococcal polysaccharide and protein-conjugate vaccines administered sequentially to adults who have recovered from pneumococcal pneumonia

BACKGROUND

Controversy persists over the benefits of pneumococcal polysaccharide vaccine (PPV) for adults at high risk for pneumococcal disease. We studied PPV, protein-conjugate pneumococcal vaccine (PCV), and immunologic "priming" with PCV followed by "boosting" with PPV in adults who had recovered from pneumococcal pneumonia.

METHODS

Subjects received PPV followed by PCV 6 months later, or vice versa. The levels of IgG to capsular polysaccharide and opsonophagocytic killing activity (OPK) were studied at baseline and at 4-8 weeks and 6 months after each vaccination.

RESULTS

PPV and PCV stimulated similar IgG levels and OPK at 4-8 weeks after vaccination. Six months after receipt of PPV, the antibody levels declined to baseline but remained modestly elevated after receipt of PCV. PCV administered 6 months after PPV stimulated modest increases in IgG level that failed to reach the peaks observed after receipt of PPV. In contrast, PPV administered 6 months after PCV caused dramatic increases in the levels of IgG and OPK for all polysaccharides at 4-8 weeks, consistent with a booster effect. Six months after receipt of the second vaccination, however, levels of IgG and OPK fell precipitously in all patients, approaching baseline levels.

CONCLUSIONS

In these high-risk subjects who have recovered after treatment for pneumonia, the effect of PPV is short-lived; PCV stimulates a more prolonged response. The use of PPV as a booster following PCV causes early increases in antibody levels, but the level of IgG declines rapidly thereafter, consistent with induction of suppressor cells or tolerance. Protein vaccines may be needed for high-risk adults.

Pneumococcal vaccination in older adults induces antibodies with low opsonic capacity and reduced antibody potency

The primary mode of prevention of adult disease from Streptococcus pneumoniae is vaccination with anti-capsular polysaccharide vaccine; however, its effects are less in the targeted older population than in young persons. Few studies have examined the mechanism behind this limited effectiveness. We have measured antibody concentrations and opsonization titers for multiple serotypes amongst both old adults and young, healthy controls. To avoid specificity problems associated with pneumococcal antibody ELISA, we absorbed the serum samples with c-polysaccharide and capsular polysaccharide of 22F type. Antibody concentrations were found to be similar for six out of the seven tested serotypes, while opsonization titers were significantly higher in six out of seven serotypes in the younger population. Antibody potency, as measured by the ratio of opsonization titer to antibody concentration, was found to be significantly higher for the younger subjects for all serotypes. We conclude that, while all ages of adults make similar concentrations of antibodies in response to pneumococcal vaccine, the effectiveness of those antibodies is significantly reduced in the older adult population.

A rapid pneumococcal serotyping system based on monoclonal antibodies and PCR

Streptococcus pneumoniae expresses at least 91 different polysaccharide (PS) capsules and the currently available serotyping methods are tedious to perform. We have been developing a rapid pneumococcal serotyping assay (named the 'multibead assay') based on the capacity of pneumococcal lysates to inhibit the ability of 24 different anti-capsule antibodies to bind to latex beads coated with 24 different PSs (serotypes 1, 3, 4, 5, 6A, 6B, 7F, 9N, 9V, 14, 18C, 19A, 19F, 23F, 2, 8, 10A, 11A, 12F, 15B, 17F, 20, 22F and 33F). Because the polyclonal antibodies used for 10 serotypes (2, 8, 10A, 11A, 12F, 15B, 17F, 20, 22F and 33F) had limited serotype specificity, we replaced them with monoclonal antibodies for the 10 serotypes. To extend the serotype coverage beyond the 24 serotypes, we have adapted multiplexed PCR for five additional serotypes (15A, 15C, 16F, 35B and 38) to be useful with the pneumococcal lysates prepared for the multibead assay. We then validated the combined assay with 157 clinical isolates from the Centers for Disease Control and Prevention and found that the new combined assay produced results that are concordant with the quellung reaction. The combined assay is robust and could be used to rapidly identify the serotypes of the majority of pneumococci ( approximately 90 %). In addition, the assay validation study suggests the presence of serological subtypes within serotype 11A.

A four-parameter logistic model for estimating titers of functional multiplexed pneumococcal opsonophagocytic killing assay

In vitro opsonophagocytosis killing assay (OPA) is widely accepted to quantitate Streptococcus pneumococcal antibodies to serotype-specific pneumococcal capsular polysaccharide (PS). A titer estimation method is needed for large scale data generated by OPA, and it is one component of OPA standardization. In order to improve the reliability of OPA results, we developed a nonlinear fitting method using the Levenberg-Marquardt algorithm with an option of a robust procedure to estimate titers of OPA data. Performance of the proposed method was evaluated by comparing precision and accuracy of titer estimation with traditional methods used in the literature by analyzing real experimental data sets. Goodness-of-fit to experimental data for the two model-based methods was also assessed. We conclude that the four-parameter logistic model is an alternative choice for titer estimation of OPA data. Computer software using the statistical language R and Microsoft Excel was developed to implement our calculation algorithm for OPA data.

Pneumococcal Vaccination for Patients With COPD

Despite a level "A" recommendation by the Centers for Disease Control and Prevention, the use of pneumococcal polysaccharide vaccination in patients with COPD is supported by limited data. Clinical and laboratory studies have suggested that the currently approved vaccine is less effective in the population of COPD patients than in healthier patients, and to date no randomized-controlled trial of pneumococcal vaccination for COPD patients has demonstrated any beneficial effect. The implementation of a pneumococcal vaccine trial in the COPD population is problematic because of the large sample size required for studies examining clinical outcomes and the fact that no adequate in vitro assays have been available to serve as surrogate measures of vaccine protection. However, new laboratory methods have been developed and more accurate determination of the immunogenicity of pneumococcal vaccines is now possible. There is considerable interest in the development of an improved pneumococcal vaccine for patients with COPD, and advances in vaccine design hold considerable promise for improved prevention against pneumonia and acute exacerbations caused by Streptococcus pneumoniae. The following discussion will examine the available data supporting pneumococcal polysaccharide vaccine use, the currently available laboratory methods to measure immunogenicity, and advances in the development of an improved pneumococcal vaccine that could better protect patients with COPD against this pathogen.

Revaccination of adults with spinal cord injury using the 23-valent pneumococcal polysaccharide vaccine

BACKGROUND/OBJECTIVE

Persons with spinal cord injury (SCI) are predisposed to develop pneumonia. This study was undertaken to determine the effect of revaccination with the pneumococcal vaccine on the immune response and the frequency of adverse reactions in this population.

METHODS

An enzyme-linked immunosorbent assay was used to measure immunoglobulin G to selected pneumococcal capsular polysaccharides on sera collected from 23 persons who were revaccinated 5 years after primary vaccination. Sera were collected just prior to, 1 month, and 1 year following revaccination. Functional activities of serotype-specific antibodies were determined by opsonophagocytosis assays.

RESULTS

Several subjects maintained protective antibody concentrations at baseline. Increases in antibody concentrations were observed for all serotypes at 1 month and 1 year. Opsonophagocytic activity increased over baseline when evaluated 1 month and 1 year after revaccination, and a significant positive correlation was observed between antibody concentration and opsonophagocytic activity at all 3 time points. Three persons (13%) experienced transient and self-limited local swelling and pain at the injection site following revaccination.

CONCLUSIONS

Protective antibody may be present in some persons for at least 5 years after vaccination. Revaccination induces a secondary surge in antibody concentration and opsonophagocytic activity that varies according to serotype but may be of lesser magnitude than the primary response. Revaccination of persons with SCI is not associated with significant adverse effects. Whether revaccination is needed beyond 5 years will require additional investigation.

Genetic basis for the new pneumococcal serotype, 6C

We have recently reported a new pneumococcal serotype (6C), which is closely related to serotype 6A (I. H. Park et al., J. Clin. Microbiol. 45:1225-1233, 2007). To investigate the genetic basis for serotype 6C, we studied the capsule gene loci of 14 6C isolates from three different continents, including one isolated in Alabama 27 years ago. The wciN region of all 6C isolates has a 1,029-bp-long sequence that replaces the 1,222-bp-long sequence of the 6A wciN region. This recombination event has created a new 1,125-bp-long open reading frame which encodes a product that is also homologous to glycosyl transferases. Flanking this introduced gene is 300 bp upstream and 100 bp downstream with only about 90% homology with 6A and which is identical in all 6C isolates. Transfer of the wciN region converts 6A to 6C. Determination of the DNA sequence of the entire capsule gene locus of one 6C isolate showed that the 6C capsule gene locus is almost identical (>98% homologous) to that of 6A except for the wciN region. These findings indicate that the 6C capsule type originated more than 27 years ago by a single recombination event in a 6A locus in which 6A wciN was replaced by a gene of unknown origin.

Inflammation by Gr+ bacteria involves LTA and its synergistic partner. (44.32)

Innate immunity is important in early responses to bacterial infections. Although Gr+ infections constitute about 50% of bacterial invasive diseases, the innate immune response to Gr+ bacteria is much less understood than is the comparable response to Gr- bacteria. While TLR2 is known to play an important part in innate immunity and Gr+ bacterial LTA may be its ligand, the role of LTA is unclear because ¡°purified¡± LTA often has biologically active contaminants or is degraded. To investigate the role in innate immunity of LTA without these limitations, we have studied the inflammatory properties of Gr+ bacterial culture supernatant (GPCS) after using two different methods to inactivate the LTA: alkaline hydrolysis and PAF-acetylhydrolase digestion. Both inactivation methods reduce the potency of GPCS to induce TNF-a production by about 85–100%. Also, the LTA-depleted GPCS regains its activity when highly purified LTA is added to the depleted GPCS. These findings suggest that LTA is an important inflammatory molecule. However, purified LTA is more potent when it is mixed with LTA-depleted GPCS than when LTA is used alone. This discrepancy in potency suggests that while LTA is a key molecule in Gr+ bacteria-induced inflammation, a synergistic mechanism amplifies LTA-induced inflammation. We are currently investigating the synergistic molecule present in GPCS and the synergistic mechanism induced by this molecule.

Immunogenicity of varying dosages of 7-valent pneumococcal polysaccharide-protein conjugate vaccine in seniors previously vaccinated with 23-valent pneumococcal polysaccharide vaccine

In this dose-ranging study 220 seniors who had received the 23-valent pneumococcal polysaccharide (PnPS) vaccine at least 5 years prior to enrollment were assigned to receive one of four volumes (0.1, 0.5, 1 or 2 ml) of 7-valent pneumococcal conjugate (PnC) vaccine or a 0.5 ml dose of 23-valent PnPS vaccine. All participants received a reduced challenge dose of 0.1 ml of PnPS vaccine 1 year after enrollment. There was evidence of a dose response to PnC vaccine and antibody levels in the 1 ml PnC group tended to be significantly higher than in the PnPS group. A booster response to the challenge vaccination was not observed. Administration of a 1 ml dose of PnC vaccine is more immunogenic than 0.5 ml of PnPS vaccine in elderly adults previously vaccinated with PnPS vaccine.

Guidelines for assessing immunocompetency in clinical trials for autoimmune diseases

Clinical trials testing the safety and efficacy of immunosuppressive agents for the treatment of autoimmune diseases should also be designed to evaluate immunocompetency. The most clinically relevant outcome for assessing immunocompetency is the infection rate. Therefore, a systematic approach to screening, monitoring, and reporting infections, modeled after the recommendations of the American Society of Transplantation, is presented. However, because the baseline infection rate in most autoimmune diseases is low, additional tests for immunocompetency should be considered. Evaluation of vaccine responses, an alternative clinically relevant approach, may be particularly useful. Other adjunctive approaches to evaluation of immunocompetency are discussed including immunization with non-vaccine neoantigens, surveillance of chronic viral infections, in vivo or in vitro assessment of cellular immunity, and analysis of innate immunity. Banking genetic material to allow genotyping should be considered particularly if a central repository for samples from different trials can be established.

Discovery of a new capsular serotype (6C) within serogroup 6 of Streptococcus pneumoniae

Using two monoclonal antibodies, we found subtypes among pneumococcal isolates that are typed as serotype 6A by the quellung reaction. The prevalent subtype bound to both monoclonal antibodies and was labeled here 6Aalpha, whereas the minor subtype bound to only one monoclonal antibody and was labeled 6Abeta. To determine the biochemical nature of the two serologically defined subtypes, we purified capsular polysaccharides (PSs) from the two subtypes and examined their chemical structures with gas-liquid chromatography and mass spectrometry. The study results for 6Aalpha PS are consistent with the previously published structure of 6A PS, which is -->2) galactose (1-->3) glucose (1-->3) rhamnose (1-->3) ribitol (5-->phosphate. In contrast, the 6Abeta PS study results show that its repeating unit is -->2) glucose 1 (1-->3) glucose 2 (1-->3) rhamnose (1-->3) ribitol (5-->phosphate. We propose to continue referring to 6Aalpha as serotype 6A but to refer to 6Abeta as serotype 6C. Serotype 6C would thus represent the 91st pneumococcal serotype, with 90 pneumococcal serotypes having previously been recognized. This study also demonstrates that a new serotype may exist within an established and well-characterized serogroup or serotype.

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

Opsonophagocytic killing assays (OPAs) are essential for developing and improving pneumococcal vaccines. There is a need for a high-throughput, reliable, standardized, and fully characterized OPA for pneumococcal antibodies. To meet the need, we have developed and characterized a fourfold multiplexed OPA (MOPA4) against 13 serotypes (1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, and 23F) of pneumococci. Thirteen target bacteria were made resistant to only one of the following antibiotics: optochin, streptomycin, spectinomycin, and trimethoprim. Following optimization of assay conditions, accuracy of MOPA4 was determined by testing 30 sera from old adults in the MOPA4 and the single-serotype assays. The opsonization titers obtained with both assays agreed well (r(2) > 0.95). Although 22 (out of 390; approximately 6%) results differed more than twofold, the differences were not reproducible. The assay was specific: preabsorbing test sera with homologous polysaccharide (PS) completely abrogated opsonic activity, but a pool of unrelated PS (5 mug/ml of each) had no effect. Intra- and interassay coefficients of variation were 10 and 22%, respectively. MOPA4 results were unaffected by having different target pneumococcal serotypes in each assay group. Also, HL60 cell-to-bacteria ratios could be varied twofold without affecting the results. We conclude that MOPA4 is sensitive, accurate, specific, precise, and robust enough for large-scale clinical studies. Furthermore, MOPA4 should allow evaluation of multivalent pneumococcal vaccines with the limited volume of serum typically available from young children.