The host immune dynamics of pneumococcal colonization: implications for novel vaccine development

Naturally-induced serum antibody levels in children to pneumococcal polysaccharide 15B that correlate with protection from nasopharyngeal colonization but anti-serotype 15B antibody has low functional cross-reactivity with serotype 15C

BACKGROUND

Serotypes 15B and 15C have been added to new different pneumococcal-conjugate vaccines (PCV20 and V116, respectively). We determined a serum anti-15B antibody level that would be a correlate of protection (COP) against nasopharyngeal colonization and assessed functional cross-reactivity against serotype 15B and 15C in children following natural immunization.

METHOD

IgG-antibody to serotype 15B polysaccharide was measured by ELISA in 341 sera from 6 to 36 month old children collected before, at the time of, and after pneumococcal colonization caused by serotypes 15B and 15C. 155 age-matched controls who had no detected colonization caused by serotype 15B or 15C strains were used as controls. A two-step method was used for construction of COP models: a generalized estimating equation followed by logistic-regression. Opsonophagocytic (OPA) assays assessed functional cross-reactivity between serotypes 15B and 15C.

RESULTS

The derived COP for prevention of colonization was 1.18 µg/ml for serotype 15B and 0.63 µg/ml for serotype 15C, with a predictive probability of 80 %. Antibody levels did not correlate with OPA titers. 30 % of child samples, with moderate to high amounts of ELISA-measured antibody, showed no OPA titer against either serotype 15B or 15C. For remaining samples, very low or no functional cross-reactivity between serotypes 15B and 15C was measured.

CONCLUSIONS

A COP for prevention of colonization in young children based on naturally-induced antibody levels was derived for serotypes 15B and 15C that differed. Antibody levels correlated poorly with OPA titers and low functional cross-reactivity between serotypes 15B and 15C in child sera was observed.

Design peptide and multi-epitope protein vaccine candidates against monkeypox virus using reverse vaccinology approach: an in-silico study

Monkeypox is a zoonotic virus that has recently affected different countries worldwide. On July 23, 2022, the WHO declared the outbreak of monkeypox as a public health emergency of international concern. Surveillance studies conducted in Central Africa in the 1980s and later during outbreaks in the same region showed smallpox vaccines to be clinically somewhat effective against Monkeypox virus. However, there is no specific vaccine against this virus. This research used bioinformatics techniques to establish a novel multi-epitope vaccine candidate against Monkeypox that can induce a strong immune response. Five well-known antigenic proteins (E8L, A30L, A35R, A29L, and B21R) of the virus were picked and assessed as possible immunogenic peptides. Two suitable peptide candidates were selected according to bio-informatics analysis. Based upon in silico evaluation, two multi-epitope vaccine candidates (ALALAR and ALAL) were built with rich-epitope domains consisting of high-ranking T and B-cell epitopes. After predicting and evaluating the 3D structure of the protein candidates, the most efficient 3D models were considered for docking studies with Toll-like receptor 4 (TLR4) and the HLA-A * 11:01, HLA-A*01:01, HLA-A*02:01, HLA-A*03:01, HLA-A*07:02, HLA-A*15:01, HLA-A*30:01 receptors. Subsequently, molecular dynamics (MD) simulation of up to 150 nanoseconds was employed to assess the durability of the interaction of the vaccine candidates with immune receptors. MD studies showed that M5-HLA-A*11:01, ALAL-TLR4, and ALALAR-TLR4 complexes were stable during simulation. Analysis of the in silico outcomes indicates that the M5 peptide and ALAL and ALALAR proteins may be suitable vaccine candidates against the Monkeypox virus.Communicated by Ramaswamy H. Sarma.

SARS-CoV-2 Spike Protein and Mouse Coronavirus Inhibit Biofilm Formation by Streptococcus pneumoniae and Staphylococcus aureus

The presence of co-infections or superinfections with bacterial pathogens in COVID-19 patients is associated with poor outcomes, including increased morbidity and mortality. We hypothesized that SARS-CoV-2 and its components interact with the biofilms generated by commensal bacteria, which may contribute to co-infections. This study employed crystal violet staining and particle-tracking microrheology to characterize the formation of biofilms by Streptococcus pneumoniae and Staphylococcus aureus that commonly cause secondary bacterial pneumonia. Microrheology analyses suggested that these biofilms were inhomogeneous soft solids, consistent with their dynamic characteristics. Biofilm formation by both bacteria was significantly inhibited by co-incubation with recombinant SARS-CoV-2 spike S1 subunit and both S1 + S2 subunits, but not with S2 extracellular domain nor nucleocapsid protein. Addition of spike S1 and S2 antibodies to spike protein could partially restore bacterial biofilm production. Furthermore, biofilm formation in vitro was also compromised by live murine hepatitis virus, a related beta-coronavirus. Supporting data from LC-MS-based proteomics of spike-biofilm interactions revealed differential expression of proteins involved in quorum sensing and biofilm maturation, such as the AI-2E family transporter and LuxS, a key enzyme for AI-2 biosynthesis. Our findings suggest that these opportunistic pathogens may egress from biofilms to resume a more virulent planktonic lifestyle during coronavirus infections. The dispersion of pathogens from biofilms may culminate in potentially severe secondary infections with poor prognosis. Further detailed investigations are warranted to establish bacterial biofilms as risk factors for secondary pneumonia in COVID-19 patients.

Altered Signal Transduction in the Immune Response to Influenza Virus and S. pneumoniae or S. aureus Co-Infections

Influenza virus is a well-known respiratory pathogen, which still leads to many severe pulmonary infections in the human population every year. Morbidity and mortality rates are further increased if virus infection coincides with co-infections or superinfections caused by bacteria such as Streptococcus pneumoniae (S. pneumoniae) and Staphylococcus aureus (S. aureus). This enhanced pathogenicity is due to complex interactions between the different pathogens and the host and its immune system and is mainly governed by altered intracellular signaling processes. In this review, we summarize the recent findings regarding the innate and adaptive immune responses during co-infection with influenza virus and S. pneumoniae or S. aureus, describing the signaling pathways involved and how these interactions influence disease outcomes.

Resistance Mechanisms to Antimicrobial Peptides in Gram-Positive Bacteria

With the alarming increase of infections caused by pathogenic multidrug-resistant bacteria over the last decades, antimicrobial peptides (AMPs) have been investigated as a potential treatment for those infections, directly through their lytic effect or indirectly, due to their ability to modulate the immune system. There are still concerns regarding the use of such molecules in the treatment of infections, such as cell toxicity and host factors that lead to peptide inhibition. To overcome these limitations, different approaches like peptide modification to reduce toxicity and peptide combinations to improve therapeutic efficacy are being tested. Human defense peptides consist of an important part of the innate immune system, against a myriad of potential aggressors, which have in turn developed different ways to overcome the AMPs microbicidal activities. Since the antimicrobial activity of AMPs vary between Gram-positive and Gram-negative species, so do the bacterial resistance arsenal. This review discusses the mechanisms exploited by Gram-positive bacteria to circumvent killing by antimicrobial peptides. Specifically, the most clinically relevant genera, Streptococcus spp., Staphylococcus spp., Enterococcus spp. and Gram-positive bacilli, have been explored.

Differential IL-17A response to S. pneumoniae in adenoid tissue of children with sleep disordered breathing and otitis media with effusion

Streptococcus pneumonia, one of the major colonizers in nasopharyngeal adenoids, has been the predominant pathogen causing acute otitis media (AOM) in children. Recent evidence suggests an association between IL-17A-mediated immune response and the clearance of pneumococcal colonization in nasopharyngeal adenoids. Here, we evaluated the expressions of IL-17A and associated genes in hypertrophic adenoid tissues of children with sleep-disordered breathing (SDB) and otitis media with effusion (OME) and their association with pneumococcal carriage. Sixty-six pediatric patients with adenoid hypertrophy were enrolled. During adenoidectomy, nasopharyngeal swab and adenoid tissues were used to determine pneumococcal carriage and IL-17A expression. Our results revealed significantly higher levels of IL-17A and IL-17A:IL-10 mRNA in the SDB patients positive for nasopharyngeal pneumococcal carriage than those negative. However, these differences were not significant in the OME group. These results suggested, in OME patients, prolonged or chronic pneumococcal carriage may occur because of insufficient IL-17A-mediated mucosal clearance, and could further lead to AOM and OME development.

Innate and adaptive nasal mucosal immune responses following experimental human pneumococcal colonization

Streptococcus pneumoniae (Spn) is a common cause of respiratory infection, but also frequently colonizes the nasopharynx in the absence of disease. We used mass cytometry to study immune cells from nasal biopsy samples collected following experimental human pneumococcal challenge in order to identify immunological mechanisms of control of Spn colonization. Using 37 markers, we characterized 293 nasal immune cell clusters, of which 7 were associated with Spn colonization. B cell and CD161⁺CD8⁺ T cell clusters were significantly lower in colonized than in noncolonized subjects. By following a second cohort before and after pneumococcal challenge we observed that B cells were depleted from the nasal mucosa upon Spn colonization. This associated with an expansion of Spn polysaccharide–specific and total plasmablasts in blood. Moreover, increased responses of blood mucosa-associated invariant T (MAIT) cells against in vitro stimulation with pneumococcus prior to challenge associated with protection against establishment of Spn colonization and with increased mucosal MAIT cell populations. These results implicate MAIT cells in the protection against pneumococcal colonization and demonstrate that colonization affects mucosal and circulating B cell populations.

Impact of different Streptococcus pneumoniae on the secretion of interleukin and adhesin from THP-1 monocytes

Background

To investigate the secretion of interleukin‐1β (IL‐1β), IL‐6, IL‐10, IL‐8, and soluble intercellular adhesin molecule 1 (sICAM‐1) from THP‐1 monocytes stimulated by different Streptococcus pneumoniae (S pneumoniae) strains.

Methods

Fifty‐eight strains of S pneumoniae were collected: ATCC49619, 23 from sputum (sd‐SP), 23 from blood (bd‐SP), and 11 from cerebrospinal fluid (CSF; cd‐SP). Such strains were cultured and suspended at 0.5 McFarland. THP‐1 monocytes were cultured and resuspended at 5.0 × 10⁸/L, which were stimulated by S pneumoniae for 4, 8, and 12 hours, respectively. The suspensions were analyzed for IL‐1β, IL‐6, IL‐10, IL‐8, and sICAM‐1 using an ELISA method. The data were assayed with SPSS 19.0.

Results

Contrary to IL‐10, the concentrations of IL‐1β, IL‐6, IL‐8, and sICAM‐1 all increased first and then decreased. IL‐1β and sICAM‐1 levels in the ATCC49619 group were both higher than all the clinical S pneumoniae groups (sd‐SP, bd‐SP, and cd‐SP), IL‐6 and IL‐8 versa, and IL‐10 equal. The difference among clinical S pneumoniae groups lay only in sICAM‐1. cd‐SP group showed lower sICAM‐1 concentrations than sd‐SP and bd‐SP groups at both 4 and 8 hours. However, they became equal at 12 hours.

Conclusions

The secretion summit is 8 hours for IL‐1β, IL‐6, IL‐8, and sICAM‐1, bottom for IL‐10. Different clinical S pneumoniae strains show similar ability to induce THP‐1 cells secreting interleukins. However, cd‐SP induces THP‐1 cells secreting lower sICAM‐1 than sd‐SP and bd‐SP, which may in turn facilitate its invasion into CSF.

Complementary Role of CD4+ T Cells in Response to Pneumococcal Polysaccharide Vaccines in Humans

Bacterial pathogens expressing capsular polysaccharides are common causes of mucosal infections (pneumonia, intestinal), as well as often fatal, invasive infections (meningitis, bloodstream infections) in children and adults worldwide. These chemically simple but structurally complex carbohydrate structures on the bacterial surface confer resistance to recognition and clearance by the immune system through a range of mechanisms. Such recognition of capsular polysaccharides may be reduced by their limited ability to directly stimulate B cells and the T cells that may facilitate these humoral responses. The capsules may promote the evasion of complement deposition and activation and may sterically shield the recognition of other subjacent protein antigens by innate factors. Antibodies to capsular polysaccharides, elicited by infection and vaccines, may overcome these obstacles and facilitate bacterial agglutination at mucosal surfaces, as well as the opsonization and clearance of these organisms in tissues and the systemic compartment. However, the immunogenicity of these antigens may be limited by their lack of direct recognition by T cells (“T-independent” antigens) and their restricted ability to generate effective memory responses. In this review, we consider the mechanisms by which polysaccharides may initiate B cell responses and specific antibody responses and the role of T cells, particularly CD4+ follicular helper (TFH) cells to support this process. In addition, we also consider more recent counterintuitive data that capsular polysaccharides themselves may bind major histocompatibility antigen HLA class II to provide a more physiologic mechanism of T cell enhancement of B cell responses to capsular polysaccharides. Defining the contributions of T cells in the generation of effective humoral responses to the capsular polysaccharides will have important implications for understanding and translating this immunobiology for the development of more effective vaccines, to prevent the morbidity and mortality associated with these common mucosal and invasive pathogens in populations at risk.

IL-17A expression in the adenoid tissue from children with sleep disordered breathing and its association with pneumococcal carriage

Tonsil and adenoid-tissue hypertrophy (AH) is the most common cause of pediatric sleep-disordered breathing (SDB), with AH possibly initiated by repeated exposure to infectious agents or allergens. Here, we evaluated IL-17A activity in adenoid tissue from children with SDB and its association with AH and pneumococcal carriage. Thirty-five children (aged 3-12 years) with SDB and receiving adenoidectomy and tonsillectomy were enrolled. During surgery, nasopharyngeal carriage was determined by bacterial culture and multiplex PCR via nasopharyngeal swab, and adenoid samples were collected. IL-17A and associated cytokine expression was evaluated by real-time PCR and western blotting. The mRNA analysis showed that IL-17A level, IL-17A:IL-10 ratio, and RAR-related orphan receptor-γt:forkhead box P3 ratio were significantly higher in adenoid tissues with AH, as were IL-17A level and IL-17A:IL-10 ratio in adenoid tissues with pneumococcal carriage. Additionally, pneumococcal carriage was more common in nasopharyngeal adenoids from patients without AH than those with AH. IL-17A was upregulated in adenoid tissues from patients with AH and with pneumococcal carriage. These results suggested that pneumococcal carriage initiates an IL-17A-mediated immune response in nasopharyngeal adenoids, which might be associated with AH in patients with SDB.

Role of Inflammatory Risk Factors in the Pathogenesis of Streptococcus pneumoniae

Streptococcus pneumoniae (Spn) is a colonizer of the human nasopharynx (NP), causing a variety of infections in humans including otitis media, pneumonia, sepsis, and meningitis. The NP is an immune permissive site which allows for the persistence of commensal bacteria. Acute or chronic respiratory airway inflammation constitutes a significant risk factor for the manifestation of Spn infections. The inflammatory conditions caused by an upper respiratory viral infection or respiratory conditions such as allergic asthma and chronic obstructive pulmonary disorders (COPDs) are implicated in the dysregulation of airway inflammation and tissue damage, which compromise the respiratory barrier integrity. These immune events promote bacterial outgrowth leading to Spn dissemination and invasion into the bloodstream. Therefore, suppression of inflammation and restoration of respiratory barrier integrity could contain Spn infections manifesting in the backdrop of an inflammatory disease condition. The gained knowledge could be harnessed in the design of novel therapeutic interventions to circumvent Spn bacterial infections.

Pneumococcal Vaccines: Host Interactions, Population Dynamics, and Design Principles

Streptococcus pneumoniae (the pneumococcus) is a nasopharyngeal commensal and respiratory pathogen. Most isolates express a capsule, the species-wide diversity of which has been immunologically classified into ∼100 serotypes. Capsule polysaccharides have been combined into multivalent vaccines widely used in adults, but the T cell independence of the antibody response means they are not protective in infants. Polysaccharide conjugate vaccines (PCVs) trigger a T cell–dependent response through attaching a carrier protein to capsular polysaccharides. The immune response stimulated by PCVs in infants inhibits carriage of vaccine serotypes (VTs), resulting in population-wide herd immunity. These were replaced in carriage by non-VTs. Nevertheless, PCVs drove reductions in infant pneumococcal disease, due to the lower mean invasiveness of the postvaccination bacterial population; age-varying serotype invasiveness resulted in a smaller reduction in adult disease. Alternative vaccines being tested in trials are designed to provide species-wide protection through stimulating innate and cellular immune responses, alongside antibodies to conserved antigens.

Immunogenicity and protective efficacy of monovalent PCVs containing 22F and 33F polysaccharides in mouse models of colonization and co-infection

BACKGROUND

In the current transmission, we studied the immunogenicity and protective efficacy of serotypes 22F and 33F in the prevention of colonization and of invasive Streptococcus pneumoniae (Spn) pathogenesis during an influenza co-infection. Serotypes 22F and 33F are emerging Spn serotypes, which are not part of currently administered pneumococcal conjugate vaccine formulations (PCVs). Spn serotype 6A is an ingredient in the currently administered PCV13 vaccine and was therefore included in the study as a control.

METHODS

Adult (six weeks) and infant (two weeks) C57BL/6 mice were intranasally infected in the nasopharynx (NP) with Spn serotypes 22F, 33F, or 6A. Influenza A H1N1 A/Puerto Rico/8/193 virus (PR8) was introduced one day after the NP Spn colonization. In an immunization challenge study, mice were vaccinated with monovalent 22F, 33F, or 6A polysaccharide conjugated to the CRM₁₉₇ antigen. The immunized mice were colonized or co-infected to study the vaccines efficacy.

RESULTS

All three Spn serotypes established colonization in adult and infant mice. The co-infected mice showed an increase in Spn NP density. Invasive Spn infection (bacteremia) was observed following the co-infection with serotypes 22F and 6A but not 33F in adult mice, whereas infant mice developed bacteremia following co-infection with all three Spn serotypes. The vaccinations led to robust serum antibody responses to capsular polysaccharides 22F, 6A, and less for 33F. The vaccinations resulted in reductions of Spn NP colonization density for all three serotypes, prevention of bacteremia, and increased survival with Spn serotypes 22F and 6A. Passive transfer of antisera was associated with a reduction of Spn colonization densities in infant mice.

CONCLUSION

Vaccinations with monovalent 22F, 33F, or 6A formulations protect against Spn colonization, and the efficacy of the 22F vaccination was comparable to the 6A vaccination in preventing an invasive Spn bacterial infection during an influenza co-infection.

Toll-Interleukin 1 Receptor Domain-Containing Adaptor Protein 180L Single-Nucleotide Polymorphism Is Associated With Susceptibility to Recurrent Pneumococcal Lower Respiratory Tract Infections in Children

Lower respiratory tract infections (LRTI) are often caused by Streptococcus pneumoniae (Spn) and can be recurrent in 8% of children older than 2 years of age. Spn is recognized by pattern-recognition receptors (PRRs) of the innate immune system, in particular toll-like receptors (TLRs) 2 and 4. To assess whether a defect somewhere along this TLR signaling pathway increases susceptibility to recurrent pneumococcal LRTI, we conducted a prospective case-control study with 88 healthy individuals and 45 children with recurrent LRTI aged 2-5 years old. We examined cell surface expression of TLR2 and TLR4, as well as eight genetic variants of these receptors or associated co-receptors TLR1 and TLR6. Interleukin-6 production was measured after whole blood stimulation assays with specific agonists and heat-killed Spn. Our findings reveal that single-nucleotide polymorphisms within toll-interleukin 1 receptor domain-containing adaptor protein (TIRAP) alone or in combination with TLR1 N248S, TLR1 I602S, or TLR6 S249P polymorphisms contributes to various degree of susceptibility to recurrent pneumococcal LRTI in children by modulating the inflammatory response. In that respect, carriage of the TIRAP S180L heterozygous trait increases the likelihood to protect against pneumococcal LRTI, whereas children carrying the mutant homozygous TIRAP 180L polymorphism might be more likely susceptible to recurrent pneumococcal LRTI.

Streptococcus pneumoniae's Virulence and Host Immunity: Aging, Diagnostics, and Prevention

Streptococcus pneumoniae is an infectious pathogen responsible for millions of deaths worldwide. Diseases caused by this bacterium are classified as pneumococcal diseases. This pathogen colonizes the nasopharynx of its host asymptomatically, but overtime can migrate to sterile tissues and organs and cause infections. Pneumonia is currently the most common pneumococcal disease. Pneumococcal pneumonia is a global health concern and vastly affects children under the age of five as well as the elderly and individuals with pre-existing health conditions. S. pneumoniae has a large selection of virulence factors that promote adherence, invasion of host tissues, and allows it to escape host immune defenses. A clear understanding of S. pneumoniae's virulence factors, host immune responses, and examining the current techniques available for diagnosis, treatment, and disease prevention will allow for better regulation of the pathogen and its diseases. In terms of disease prevention, other considerations must include the effects of age on responses to vaccines and vaccine efficacy. Ongoing work aims to improve on current vaccination paradigms by including the use of serotype-independent vaccines, such as protein and whole cell vaccines. Extending our knowledge of the biology of, and associated host immune response to S. pneumoniae is paramount for our improvement of pneumococcal disease diagnosis, treatment, and improvement of patient outlook.

Pneumococcal Phenotype and Interaction with Nontypeable Haemophilus influenzae as Determinants of Otitis Media Progression

All-cause otitis media (OM) incidence has declined in numerous settings following introduction of pneumococcal conjugate vaccines (PCVs) despite increases in carriage of nonvaccine pneumococcal serotypes escaping immune pressure. To understand the basis for the declining incidence, we assessed the intrinsic capacity of pneumococcal serotypes to cause OM independently and in polymicrobial infections involving nontypeable Haemophilus influenzae (NTHi) using samples obtained from middle ear fluid and nasopharyngeal cultures before PCV7/13 rollout. Data included samples from OM episodes (11,811) submitted for cultures during a 10-year prospective study in southern Israel and nasopharyngeal samples (1,588) from unvaccinated asymptomatic children in the same population. We compared data representing pneumococcal serotype diversity across carriage and disease isolates with and without NTHi coisolation. We also measured associations between the pneumococcal phenotype and the rate of progression from colonization to OM in the presence and absence of NTHi. Whereas pneumococcal serotype diversity was lower in single-species OM than in single-species colonization, levels of serotype diversity did not differ significantly between colonization and OM in mixed-species episodes. Serotypes differed roughly 100-fold in progression rates, and those differences were attenuated in polymicrobial episodes. Vaccine serotype pneumococci had higher rates of progression than nonvaccine serotypes. While serotype invasiveness was a weak predictor of the OM progression rate, efficient capsular metabolic properties-traditionally thought to serve as an advantage in colonization-predicted an enhanced rate of progression to complex OM. The lower capacity of nonvaccine serotypes to cause OM may partially account for reductions in all-cause OM incidence despite serotype replacement in carriage following rollout of PCVs.

Identification of SP1683 as a pneumococcal protein that is protective against nasopharyngeal colonization

Serotype-independent protein-based pneumococcal vaccines represent attractive alternatives to capsular polysaccharide-based vaccines. The aim of this study was to identify novel immunogenic proteins from Streptococcus pneumoniae that may be used in protein-based pneumococcal vaccine. An immunoproteomics approach and a humanized severe combined immunodeficient mouse model were used to identify S. pneumoniae proteins that are immunogenic for the human immune system. Among the several proteins identified, SP1683 was selected, recombinantly produced, and infection and colonization murine models were used to evaluate the capacity of SP1683 to elicit protective responses, in comparison to known pneumococcal immunogenic proteins (PhtD and detoxified pneumolysin, dPly). Immunisation with SP1683 elicited a weaker antibody response than immunisation with PhtD and did not provide protection in the model of invasive disease. However, similar to PhtD, it was able to significantly reduce colonization in the mouse model of nasopharyngeal carriage. Treatment with anti-IL17A and anti-IL17F antibodies abolished the protection against colonization elicited by SP1683 or PhtD + dPly, which indicated that the protection afforded in this model was Th17-dependent. In conclusion, intranasal immunization with the pneumococcal protein SP1683 conferred IL17-dependent protection against nasopharyngeal carriage in mice, but systemic immunization did not protect against invasive disease. These results do not support the use of SP1683 as an isolated pneumococcal vaccine antigen. Nevertheless, SP1683 could be used as a first line of defence in formulations combining several proteins.

Evaluation of Protective Efficacy of Selected Immunodominant B-Cell Epitopes within Virulent Surface Proteins of Streptococcus pneumoniae

Four previously identified immunodominant B-cell epitopes, located within known virulent pneumococcal proteins CbpD, PhtD, PhtE, and ZmpB, had shown promising in vivo immunological characteristics, indicating their potential to be used as vaccine antigens. In this study, we further evaluated the opsonophagocytic activity of antibodies against these epitopes and their capacity to protect mice from pneumococcal sepsis. An opsonophagocytic killing assay (OPKA) revealed that OPKA titers of human anti-peptide antibodies against pneumococcal serotypes 1, 3, and 19A were significantly higher (P < 0.001) than those of the control sera, suggesting their functional potential against virulent clinical isolates. Data obtained from mice actively immunized with any of the selected epitope analogues or with a mixture of these (G_Mix group) showed, compared to controls, enhanced survival against the highly virulent pneumococcal serotype 3 (P < 0.001). Moreover, passive transfer of hyperimmune serum from G_Mix to naive mice also conferred protection to a lethal challenge with serotype 3, which demonstrates that the observed protection was antibody mediated. All immunized murine groups elicited gradually higher antibody titers and avidity, suggesting a maturation of immune response over time. Among the tested peptides, PhD_pep19 and PhtE_pep40 peptides, which reside within the zinc-binding domains of PhtD and PhtE proteins, exhibited superior immunological characteristics. Recently it has been shown that zinc uptake is of high importance for the virulence of Streptococcus pneumoniae; thus, our findings suggest that these epitopes deserve further evaluation as novel immunoreactive components for the development of a polysaccharide-independent pneumococcal vaccine.

Kinetics of antibodies against pneumococcal proteins and their relationship to nasopharyngeal carriage in the first two months of life

Introduction

The currently used Streptococcus pneumoniae vaccines have had a significant impact on the pneumococcal diseases caused by the serotypes they cover. Their limitations have stimulated a search for alternate vaccines that will cover all serotypes, be affordable and effective in young children. Pneumococcal protein antigens are potential vaccine candidates that may meet some of the shortfalls of the current vaccines. Thus, this study aimed to determine the relationship between antibodies against pneumococcal protein antigens and nasopharyngeal carriage in infants.

Methods

One hundred and twenty mother-infant pairs were enrolled into the study. They had nasopharyngeal swabs(NPS) taken at birth and every two weeks for the first eight weeks after delivery, and blood samples were obtained at birth and every four weeks for the first eight weeks after delivery. Nasopharyngeal carriage of S. pneumoniae was determined from the NPS and antibodies against the pneumococcal proteins CbpA, PspA and rPly were measured in the blood samples.

Results

The S. pneumoniae carriage rate in infants increased to that of mothers by eight weeks of age. The odds of carriage in infants was 6.2 times (95% CI: 2.0–18.9) higher when their mothers were also carriers. Bacterial density in infants was lower at birth compared to their mothers (p = 0.004), but increased with age and became higher than that of their mothers at weeks 4 (p = 0.009), 6 (p = 0.002) and 8 (p<0.0001). At birth, the infants’ antibodies against CbpA, and rPly pneumococcal protein antigens were similar, but that of PspA was lower (p<0.0001), compared to their mothers. Higher antibody concentrations to CbpA [OR (95% CI): 0.49 (0.26–0.92, p = 0.03)], but not PspA and rPly, were associated with protection against carriage in the infants.

Conclusion

Naturally induced antibodies against the three pneumococcal protein antigens were transferred from mother to child. The proportion of infants with nasopharyngeal carriage and the bacterial density of S. pneumoniae increased with age within the first eight weeks of life. Higher concentrations of antibodies against CbpA, but not PspA and rPly, were associated with reduced risk of nasopharyngeal carriage of S. pneumoniae in infants.

Efficacy of a novel, protein-based pneumococcal vaccine against nasopharyngeal carriage of Streptococcus pneumoniae in infants: A phase 2, randomized, controlled, observer-blind study

BACKGROUND

Conserved pneumococcal proteins are potential candidates for inclusion in vaccines against pneumococcal diseases. In the first part of a two-part study, an investigational vaccine (PHiD-CV/dPly/PhtD-30) containing 10 pneumococcal serotype-specific polysaccharide conjugates (10VT) combined with pneumolysin toxoid and pneumococcal histidine triad protein D (30μg each) was well tolerated by Gambian children. Part two, presented here, assessed the efficacy of two PHiD-CV/dPly/PhtD formulations against pneumococcal nasopharyngeal carriage (NPC) prevalence in infants.

METHODS

In this phase 2, randomized, controlled, observer-blind trial, healthy infants aged 8-10weeks, recruited from a peri-urban health center, were randomized (1:1:1:1:1:1) into six groups. Four groups received PHiD-CV/dPly/PhtD (10 or 30μg of each protein), PHiD-CV, or 13-valent pneumococcal conjugate vaccine at ages 2-3-4months (3+0 infant schedule) and two groups PHiD-CV/dPly/PhtD-30 or PHiD-CV at 2-4-9months (2+1 infant schedule). The primary objective was impact on non-10VT NPC at ages 5-9-12months. Secondary objectives included confirmatory analysis of protein dose superiority and safety/reactogenicity. Impact on pneumococcal NPC acquisition, bacterial load, and ply and phtD gene sequencing were explored.

RESULTS

1200 infants were enrolled between June 2011 and May 2012. Prevalences of pneumococcal (60-67%) and non-10VT (55-61%) NPC were high at baseline. Across all post-vaccination time points, efficacy of PHiD-CV/dPly/PhtD-10 and PHiD-CV/dPly/PhtD-30 against non-10VT NPC (3+0 schedule) was 1.1% (95% CI -21.5, 19.5) and 2.1% (-20.3, 20.3), respectively; efficacy of PHiD-CV/dPly/PhtD-30 (2+1 schedule) was 0.5% (-22.1, 18.9) versus PHiD-CV. No differences were observed in pneumococcal NPC acquisition, clearance, or bacterial load. Both protein-based vaccines elicited immune responses to pneumococcal proteins.

CONCLUSIONS

In this high carriage prevalence setting, inclusion of pneumococcal proteins in the PHiD-CV/dPly/PhtD investigational vaccine had no impact on pneumococcal NPC in infants, regardless of protein dose or schedule. Future evaluations will assess its impact against pneumococcal disease endpoints.

FUNDING

PATH, GlaxoSmithKline Biologicals SA. ClinicalTrials.gov identifier NCT01262872.

Protection against Streptococcus pneumoniae Invasive Pathogenesis by a Protein-Based Vaccine Is Achieved by Suppression of Nasopharyngeal Bacterial Density during Influenza A Virus Coinfection

An increase in Streptococcus pneumoniae nasopharynx (NP) colonization density during a viral coinfection initiates pathogenesis. To mimic natural S. pneumoniae pathogenesis, we commensally colonized the NPs of adult C57BL/6 mice with S. pneumoniae serotype (ST) 6A or 8 and then coinfected them with mouse-adapted H1N1 influenza A virus (PR/8/34). S. pneumoniae established effective commensal colonization, and influenza virus coinfection caused S. pneumoniae NP density to increase, resulting in bacteremia and mortality. We then studied histidine triad protein D (PhtD), an S. pneumoniae adhesin vaccine candidate, for its ability to prevent invasive S. pneumoniae disease in adult and infant mice. In adult mice, the efficacy of PhtD vaccination was compared with that of PCV13. Vaccination with PCV13 led to a greater reduction of S. pneumoniae NP density (>2.5 log units) than PhtD vaccination (∼1-log-unit reduction). However, no significant difference was observed with regard to the prevention of S. pneumoniae bacteremia, and there was no difference in mortality. Depletion of CD4⁺ T cells in PhtD-vaccinated adult mice, but not PCV13-vaccinated mice, caused a loss of vaccine-induced protection. In infant mice, passive transfer of antisera or CD4⁺ T cells from PhtD-vaccinated adult mice led to a nonsignificant reduction in NP colonization density, whereas passive transfer of antisera and CD4⁺ T cells was needed to cause a significant reduction in NP colonization density. For the first time, these data show an outcome with regard to prevention of invasive S. pneumoniae pathogenesis with a protein vaccine similar to that which occurs with a glycoconjugate vaccine despite a less robust reduction in NP bacterial density.

Rationale and prospects for novel pneumococcal vaccines

Streptococcus pneumoniae remains one of the most frequent bacterial causes of morbidity and mortality worldwide. National immunization programs implementing pneumococcal polysaccharide conjugate vaccines (PCVs) have successfully reduced rates of vaccine-type invasive disease and colonization both via direct effects in immunized children and, in some settings, indirect effects in unimmunized individuals. Limitations of the current PCV approach include the emergence of non-vaccine serotypes contributing to carriage and invasive disease in high-PCV coverage settings and the high cost of goods of PCVs which limits their accessibility in developing countries where the burden of disease remains highest. Furthermore, the distribution of serotypes causing disease varies geographically and includes more serotypes than are currently covered in a single PCV formulation. Researchers have long been exploring the potential of genetically conserved non-capsular pneumococcal antigens as vaccine candidates that might overcome such limitations. To better evaluate the rationale of such approaches, an understanding of the mechanisms of immunity to the various phases of pneumococcal infection is of paramount importance. Herein we will review the evolving understanding of both vaccine-induced and naturally acquired immunity to pneumococcal colonization and infection and discuss how this informs current approaches using serotype-independent pneumococcal vaccine candidates. We will then review the alternative vaccine candidates that have been or are currently under evaluation in clinical trials.

Influenza A Virus Infection Predisposes Hosts to Secondary Infection with Different Streptococcus pneumoniae Serotypes with Similar Outcome but Serotype-Specific Manifestation

Influenza A virus (IAV) and Streptococcus pneumoniae are major causes of respiratory tract infections, particularly during coinfection. The synergism between these two pathogens is characterized by a complex network of dysregulated immune responses, some of which last until recovery following IAV infection. Despite the high serotype diversity of S. pneumoniae and the serotype replacement observed since the introduction of conjugate vaccines, little is known about pneumococcal strain dependency in the enhanced susceptibility to severe secondary S. pneumoniae infection following IAV infection. Thus, we studied how preinfection with IAV alters host susceptibility to different S. pneumoniae strains with various degrees of invasiveness using a highly invasive serotype 4 strain, an invasive serotype 7F strain, and a carrier serotype 19F strain. A murine model of pneumococcal coinfection during the acute phase of IAV infection showed a significantly increased degree of pneumonia and mortality for all tested pneumococcal strains at otherwise sublethal doses. The incidence and kinetics of systemic dissemination, however, remained bacterial strain dependent. Furthermore, we observed strain-specific alterations in the pulmonary levels of alveolar macrophages, neutrophils, and inflammatory mediators ultimately affecting immunopathology. During the recovery phase following IAV infection, bacterial growth in the lungs and systemic dissemination were enhanced in a strain-dependent manner. Altogether, this study shows that acute IAV infection predisposes the host to lethal S. pneumoniae infection irrespective of the pneumococcal serotype, while the long-lasting synergism between IAV and S. pneumoniae is bacterial strain dependent. These results hold implications for developing tailored therapeutic treatment regimens for dual infections during future IAV outbreaks.

A dynamic relationship between mucosal T helper type 17 and regulatory T-cell populations in nasopharynx evolves with age and associates with the clearance of pneumococcal carriage in humans

Pneumococcal carriage is common in young children, which may account for the high incidence of disease in this age group. Host factors determining the clearance of carriage in humans remain unclear. We aimed to study the relationships between T helper type 17 (Th17) and Foxp3(+) regulatory T (Treg) cells in nasopharynx-associated lymphoid tissue (NALT) and carriage in children and adults. Frequencies of Th17 and Treg cells in NALT were analysed by flow cytometry in association with age and pneumococcal carriage status. Cytokine responses following pneumococcal stimulation were analysed by cytometric beads array. The frequencies of Th17 and Treg cells in NALT were inversely correlated (R -0.60). Whereas Treg cell frequency decreased with age (R -0.63), both Th17 and the Th17: Treg ratio increased with age (R 0.62 and R 0.64, respectively). Also, the Th17: Treg ratio was higher in carriage-negative than in carriage-positive children (p <0.01). Pneumococcal stimulation of tonsillar cells increased both Th17 and Treg cell numbers, but the Th17: Treg ratio and pattern of cytokine responses differed between carriage-negative and carriage-positive children. The former showed markedly higher Th17: Treg and interleukin-17A: interleukin-10 ratios than in the latter (p <0.01). Pneumococcal stimulation also induces Th17, although the capacity of this Th17 differentiation from naive T cells of young children was low, but increased with age. We demonstrated a dynamic relationship between Th17 and Treg cells in human nasopharynx that evolves with age. The balance between Th17 and Treg cells in NALT appears to be a major host factor closely associated with the clearance of Streptococcus pneumoniae from the nasopharynx.

Next generation protein based Streptococcus pneumoniae vaccines

All currently available Streptococcus pneumoniae (Spn) vaccines have limitations due to their capsular serotype composition. Both the 23-valent Spn polysaccharide vaccine (PPV) and 7, 10, or 13-valent Spn conjugate vaccines (PCV-7, 10, -13) are serotype-based vaccines and therefore they elicit only serotype-specific immunity. Emergence of replacement Spn strains expressing other serotypes has consistently occurred following introduction of capsular serotype based Spn vaccines. Furthermore, capsular polysaccharide vaccines are less effective in protection against non-bacteremic pneumonia and acute otitis media (AOM) than against invasive pneumococcal disease (IPD). These shortcomings of capsular polysaccharide-based Spn vaccines have created high interest in development of non-serotype specific protein-based vaccines that could be effective in preventing both IPD and non-IPD infections. This review discusses the progress to date on development of Spn protein vaccine candidates that are highly conserved by all Spn strains, are highly conserved, exhibit maximal antigenicity and minimal reactogenicity to replace or complement the current capsule-based vaccines. Key to development of a protein based Spn vaccine is an understanding of Spn pathogenesis. Based on pathogenesis, a protein-based Spn vaccine should include one or more ingredients that reduce NP colonization below a pathogenic inoculum. Elimination of all Spn colonization may not be achievable or even advisable. The level of expression of a target protein antigen during pathogenesis is another key to the success of protein based vaccines.. As with virtually all currently licensed vaccines, production of a serum antibody response in response to protein based vaccines is anticipated to provide protection from Spn infections. A significant advantage that protein vaccine formulations can offer over capsule based vaccination is their potential benefits associated with natural priming and boosting to all strains of Spn. One of the most universal and comprehensive approaches of identifying novel vaccine candidates is the investigation of human sera from different disease stages of natural infections. Antigens that are robustly reactive in preliminary human serum screening constitute a pathogen-specific antigenome. This strategy has identified a number of Spn protein vaccine candidates that are moving forward in human clinical trials.