Humoral immune response of a pneumococcal conjugate vaccine: capsular polysaccharide serotype 14-Lysine modified PspA

Polysaccharide-protein conjugates are so far the current antigens used for pneumococcal vaccines for children under 2 years of age. In this study, pneumococcal surface protein A (PspA) was used as a carrier protein for pneumococcal capsular polysaccharide serotype 14 as an alternative to broaden the vaccine coverage. PspA was modified by reductive amination with formaldehyde in order to improve the specificity of the reaction between protein and polysaccharide, inhibiting polymerization and the gel formation reaction. In the synthesis process, the currently used activator, 1-[3-(dimethylamine)propyl]-3-ethylcarbodiimide hydrochloride (EDAC) was substituted for 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM). BALB/c mice were immunized with either the PS14-mPspA conjugate or the co-administered components in a three dose regimen and sera from the immunized animals were assayed for immunity induced against both antigens: PS14 and mPspA. Modification of more than 70% of lysine residues from PspA (mPspA) did not interfere in the immune response as evaluated by the anti-PspA titer and C3 complement deposition assay. Sera of mice immunized with conjugated PS14-mPspA showed similar IgG titers, avidity and isotype profile as compared to controls immunized with PspA or mPspA alone. The complement deposition was higher in the sera of mice immunized with the conjugate vaccine and the opsonophagocytic activity was similar for both sera. Conjugation improved the immune response against PS14. The anti PS14 IgG titer was higher in sera of mice immunized with the conjugate than with co-administered antigens and presented an increased avidity index, induction of a predominant IgG1 isotype and increased complement deposition on a bacteria with a surface serotype 14. These results strongly support the use of PspA as carrier in a conjugate vaccine where both components act as antigens.     

A bivalent vaccine to protect against Streptococcus pneumoniae and Salmonella typhi

Pneumococcal and Salmonella typhi infections are two major diseases for children in developing countries. For typhoid fever, licensed Vi polysaccharide vaccines are ineffective in children <2-year old. While investigational Vi conjugate vaccines have been shown effective in clinical trials, they are currently only available to restricted areas. Pneumococcal capsular polysaccharide conjugate vaccines are highly effective in children, but suffer from some limitations including cost and limited serotype coverage. We have previously shown that a fusion conjugate vaccine, consisting of pneumococcal fusion protein PsaA and pneumolysoid (PdT) conjugated to a polysaccharide, results in enhanced antibody and CD4+ Th17 cell responses as well as protection against pneumococcal colonization and disease in mice. Here we applied this approach to develop a bivalent vaccine against pneumococcus and S. typhi. Two species-conserved pneumococcal antigens (SP1572 or SP2070) were fused to the nonhemolytic pneumolysoid PdT. SP1572-PdT was then conjugated to Vi polysaccharide and SP2070-PdT was conjugated to the pneumococcal cell wall polysaccharide (CWPS; also conserved). Mice immunized with this bivalent conjugate were protected against pneumococcal colonization and sepsis challenges, and made anti-Vi antibody concentrations higher by 40-fold compared to mice that received equimolar mixtures of the antigens. An enhanced killing of Vi-bearing Salmonellae in vitro was demonstrated from plasma of mice that received the fusion conjugate but not the mixture of antigens. Our results support further evaluation of this bivalent immunogen for the prevention of pneumococcal colonization and disease, and of typhoid fever.     

Intranasal immunization with recombinant PspA fused with a flagellin enhances cross-protective immunity against Streptococcus pneumoniae infection in mice

Streptococcus pneumoniae is a major respiratory pathogen that causes high levels of mortality and morbidity in infants and the elderly. Despite the use of antibiotics and vaccines, fatal pneumococcal disease remains prevalent. Pneumococcal surface protein A (PspA), a highly immunogenic surface protein produced by all strains of S. pneumoniae, can elicit protective immunity against fatal pneumococcal infection. We have previously demonstrated that the Vibrio vulnificus FlaB, a bacterial flagellin protein and agonist of TLR5, has strong mucosal adjuvant activity and induces protective immunity upon co-administration with tetanus toxoid. In this study, we have tested whether intranasal immunization with recombinant fusion proteins consisted of PspA and FlaB (PspA-FlaB and FlaB-PspA) is able to elicit more efficient protective mucosal immune responses against pneumococcal infection than immunization with PspA alone or with a stoichiometric mixture of PspA and FlaB. When mice were intranasally immunized with fusion proteins, significantly higher levels of anti-PspA IgG and IgA were induced in serum and mucosal secretions. The mice immunized intranasally with the FlaB-PspA fusion protein were the most protected from a lethal challenge with live S. pneumoniae, as compared to the mice immunized with PspA only, a mixture of PspA and FlaB, or the PspA-FlaB fusion protein. FlaB-PspA also induced a cross protection against heterologous capsular types. These results suggest that a FlaB-PspA fusion protein alone could be used as an anti-pneumococcal mucosal vaccine or as an effective partner protein for multivalent capsular polysaccharide conjugate vaccines.     

Immunogenicity in mice of pneumococcal glycoconjugate vaccines using pneumococcal protein carriers

Antibody response and protective immunity were evaluated in mice immunized with pneumococcal glycoconjugate vaccines using two pneumococcal protein carriers. Mice injected with type 9V polysaccharide (PS) conjugated to inactivated pneumolysin (Ply) or autolysin (Aly) produced high levels of IgG and IgM antibodies to both the PS and the protein carrier. Higher PS antibody titers to the pneumococcal PS conjugates were measured by ELISA using PS-Ply or PS-tetanus toxoid (TT) conjugate as a coating antigen compared with PS mixed with methylated human serum albumin. Type 9V PS (10 microg) inhibited most of the 9V IgM and IgG antibody binding to the 9V-TT coated plate. In contrast, absorption with 19F PS did not inhibit 9V antibody binding. The avidity index of IgG antibodies in the 9V PS-Ply serum was 55.5 +/- 0.9, compared with 47.8 +/- 1.4 for 9V PS-Aly serum. Thus, high avidity of serum antibodies in conjugate-immunized mice can provide more effective functional activity for protection against pneumococcal infection. Mice immunized with these glycoconjugates exhibited rapid bacterial clearance from blood and provided cross-protection against challenge with heterologous serotypes of virulent pneumococci. These results reveal that conjugates using pneumococcal protein carriers can induce opsonophagocytic activity to destroy homologous and heterologous pneumococci, indicating that such conjugates can confer broader protective immunity than conjugates using non-pneumococcal proteins.     

A bivalent conjugate vaccine containing PspA families 1 and 2 has the potential to protect against a wide range of Streptococcus pneumoniae strains and Salmonella Typhi

Previously we showed that conjugation of pneumococcal surface protein A (PspA) to Vi capsular polysaccharide from Salmonella Typhi enhanced the anti-PspA response without the need to add adjuvant. In the current study conjugates consisting of the α helical regions of PspA families 1 or 2 bound to Vi were used to vaccinate mice to test their ability to protect against a lethal intravenous challenge of a range of various strains of Streptococcus pneumoniae. Conjugate vaccine containing PspA family 1 provided good protection from PspA family 1 challenge strains but offered very little protection against PspA family 2 challenge strains. Similarly, PspA family 2 conjugates provided good protection from PspA family 2 challenge strains and poor protection against PspA family 1 challenge strains. This observation was supported by the low levels of cross-reactivity of PspA antibodies seen in ELISA plates coated with the heterologous PspA family. Cytokine profiles showed a mixed Th1/Th2 response to Vi and the Vi-PspA conjugates. IgG subclass analysis of the anti-Vi response showed a shift from predominantly IgG2a/3 to IgG1 after conjugation to PspA was consistent with other polysaccharide conjugate vaccines. The results demonstrate that conjugation of the α helical region of PspA to Vi enhances its capacity to induce a protective immune response and that a vaccine based on the α helical region of PspA should contain PspA from both families 1 and 2 to achieve broad cross-protection.     

Preparation of pneumococcal capsular polysaccharide-protein conjugate vaccines utilizing new fragmentation and conjugation technologies

There is a global urgent need for a new efficient and inexpensive vaccine to combat pneumococcal disease, which should also be affordable in developing countries. In view of this need a simple low-cost technique to prepare such a vaccine was developed. The preparation of serotype 14 and 23F pneumococcal capsular polysaccharide (PnPS)-protein conjugates to be included in a forthcoming multivalent PnPS conjugate vaccine is described. Commercial lots of PnPSs produced according to Good Manufacturing Practice from Streptococcus pneumoniae serotype 14 (PS14) and 23F (PS23F) were partially depolymerized by sonication or irradiation in an electron beam accelerator. The PnPS fragments were conjugated to tetanus toxoid (TT) using a recently developed conjugation chemistry. The application of these new simple, efficient and inexpensive fragmentation and conjugation technologies allowed the synthesis of several PnPS-protein conjugates containing PnPS fragments of preselected sizes and differing in the degree of substitution. The PS14TT and PS23FTT conjugate vaccine candidates were characterized chemically and their immunogenicity was evaluated in rabbits and mice. All PnPS conjugate vaccines, unlike the corresponding plain polysaccharides, produced high IgG titres in both animal species. The PS14TT conjugates tended to be more immunogenic than the PS23FTT conjugates. The immune response to the PS14TT conjugates, but not to the PS23FTT conjugates, was related to the size of the conjugated polysaccharide hapten. Both types of conjugates elicited strong booster effects upon secondary immunizations, resulting in high IgG1, IgG2a and IgG2b titres.     

Immunization of healthy adults with a single recombinant pneumococcal surface protein A (PspA) variant stimulates broadly cross-reactive antibodies to heterologous PspA molecules

Pneumococcal surface protein A (PspA) is a highly variable protein found on all strains of pneumococci. To be successful, a PspA-based vaccine for S. pneumoniae must induce antibodies that are broadly cross-reactive. To address whether cross-reactive antibodies could be induced in man, we evaluated serum from adults immunized with recombinant clade 2 PspA from strain Rx1. Immunization with 5-125 microg rPspA lead to a significant increase in circulating anti-PspA antibodies, as well as antibodies reactive to heterologous rPspA molecules. Increased binding of post-immune sera to 37 pneumococcal strains expressing a variety of PspA and capsule types was observed, versus pre-immune sera. The extent of cross-clade reactivity of human anti-rPspA followed roughly the amount of sequence homology to the non-clade 2 antigens. It is hypothesized that priming of humans by natural exposure to S. pneumoniae contributes to the breadth of the cross-reactivity of antibody to PspA.     

Differences in the avidity of antibodies evoked by four different pneumococcal conjugate vaccines in early childhood

Avidity of antibodies to Streptococcus pneumoniae type 6B, 14, 19F and 23F polysaccharides (PS) evoked by four different pneumococcal conjugate vaccines was compared. Infants were primed with pneumococcal PS conjugated to the variant diphtheria toxin CRM197 (PncCRM), diphtheria toxoid (PncD), tetanus toxoid (PncT) or meningococcal protein complex (PncOMPC) and boosted with the homologous conjugate or PS vaccine. No booster was given to children in the PncOMPC group. Relative antibody avidity was measured by thiocyanate EIA. No vaccine specific differences were found in avidity of anti-14 or -19F antibodies. By contrast, antibody avidity to 6B and 23F differed significantly between the vaccine groups, PncCRM and PncT inducing antibodies of highest avidity.     

Preparation and testing of a Vi conjugate vaccine using pneumococcal surface protein A (PspA) from Streptococcus pneumoniae as the carrier protein

In the current study pneumococcal surface protein A (PspA) was conjugated to Vi capsular polysaccharide from Salmonella Typhi to make available a vaccine against typhoid fever that has the potential to also provide broad protection from Streptococcus pneumoniae. High yielding production processes were developed for the purification of PspAs from families 1 and 2. The purified PspAs were conjugated to Vi with high recovery of both Vi and PspA. The processes developed especially for PspA family 2 could readily be adapted for large scale production under cGMP conditions. Previously we have shown that conjugation of diphtheria toxoid (DT) to Vi polysaccharide improves the immune response to Vi but can also enhance the response to DT. In this study it was shown that conjugation of PspA to Vi enhanced the anti-PspA response and that PspA was a suitable carrier protein as demonstrated by the characteristics of a T-cell dependent response to the Vi. We propose that a bivalent vaccine consisting of PspA from families 1 and 2 bound to Vi polysaccharide would protect against typhoid fever and has the potential to also protect against pneumococcal disease and should be considered for use in developing countries.     

Potential impact of conjugate pneumococcal vaccines on pediatric pneumococcal diseases

Children younger than age 2 years have the highest rates of invasive pneumococcal disease and play an important role in its transmission. In the United States, seven pneumococcal serotypes cause approximately 80% of invasive disease and represent approximately 60% of middle-ear isolates in children younger than age 2 years; the majority of penicillin-resistant strains are confined to these same few serogroups. Although unconjugated polysaccharide pneumococcal vaccines have demonstrated effectiveness in preventing invasive disease in adults, these vaccines fail to protect against otitis media or nasopharyngeal carriage and are poorly immunogenic in children younger than age 2 years. A new generation of pneumococcal vaccines has been developed, linking the capsular polysaccharide of seven to 11 serotypes to a protein carrier. The only pneumococcal vaccine approved to date for children younger than age 2 years is a seven-valent conjugate vaccine (PnCRM-7) (Prevnar; Wyeth Vaccines, Pearl River, New York), which contains serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F. PnCRM-7 is more immunogenic than the polysaccharide pneumococcal vaccines and is 80-100% effective against vaccine-type invasive disease and 50-60% effective against vaccine-type pneumococcal otitis media. Routine immunization with pneumococcal conjugate vaccines should substantially reduce the morbidity, mortality, and costs associated with pneumococcal disease in children.     

Immunogenicity of a combination vaccine containing pneumococcal conjugates and meningococcal PorA OMVs

The pre-clinical immunogenicity of a combination vaccine containing 13-valent pneumococcal conjugate (13vPnC) vaccine (serotypes 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F and 23F conjugated to CRM197) and nine-valent meningococcal B PorA vaccine (NonaMen; serosubtypes P1.7,16; P1.5-1,2-2; P1.19,15-1; P1.5-2,10; P1.12-1,13; P1.7-2,4; P1.22,14; P1.7-1,1 and P1.18-1,3,6), and any potential immunological interference between pneumococcal and MenB components of the vaccine were evaluated. NIH mice were immunized twice subcutaneously with the vaccines combined in one syringe, or given individually. Combining 13vPnC vaccine with NonaMen vaccine in one syringe had no negative effect on the induced antibody response against any MenB serosubtypes compared to separate injection of the vaccines, and the anti-pneumococcal antibody responses were enhanced. Furthermore, co-administration of the combination vaccine with a combined diphtheria/tetanus/acellular pertussis/inactivated poliomyelitis vaccine/Haemophilus influenzae type b-TT conjugate (DTaP/IPV-Hib) vaccine to New Zealand white rabbits at a different injection site did not affect the anti-pneumococcal polysaccharide and anti-PorA antibody titres. We conclude that no immunological interference was observed by combined administration of pneumococcal conjugate and meningococcal B vaccines in one syringe.     

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

BackgroundPCV13 (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.MethodsTen 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.ResultsVaccine-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.ConclusionsThese findings demonstrate age related differences in immune response and the potential importance of Tfh in modulating functional antibody responses following pneumococcal vaccination.     

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

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

Immune responses and protection against Streptococcus pneumoniae elicited by recombinant Bordetella pertussis adenylate cyclase (CyaA) carrying fragments of pneumococcal surface protein A,PspA

Streptococcus pneumoniae is a common agent of important human diseases such as otitis media, pneumonia, meningitis and sepsis. Current available vaccines that target capsular polysaccharides induce protection against invasive disease and nasopharyngeal colonization in children, yet their efficacy is limited to the serotypes included in the formulations. The virulence factor Pneumococcal Surface Protein A (PspA) interacts with host immune system and helps the bacteria to evade phagocytosis. Due to its essential role in virulence, PspA is an important vaccine candidate. Here we have tested a delivery system based on the adenylate cyclase toxin of Bordetella pertussis (CyaA) to induce immune responses against PspA in mice. CyaA was engineered to express fragments of the N-terminal region of PspAs from clades 2 and 4 (A2 and A4) and the resulting proteins were used in immunization experiments in mice. The recombinant CyaA-A2 and CyaA-A4 proteins were able to induce high levels of anti-PspA antibodies that reacted with pneumococcal strains expressing either PspA2 or PspA4. Moreover, reactivity of the antibodies against pneumococcal strains that express PspAs from clades 3 and 5 (PspA3 and PspA5) was also observed. A formulation containing CyaA-A2 and CyaA-A4 was able to protect mice against invasive pneumococcal challenges with isolates that express PspA2, PspA4 or PspA5. Moreover, a CyaA-A2-A4 fusion protein induced antibodies at similar levels and with similar reactivity as the formulation containing both proteins, and protected mice against the invasive challenge. Our results indicate that CyaA-PspA proteins are good candidates to induce broad protection against pneumococcal isolates.     

Salivary anti-capsular antibodies in infants and children immunised with Streptococcus pneumoniae capsular polysaccharides conjugated to diphtheria or tetanus toxoid

Saliva samples of infants and children immunised with pneumococcal vaccines were analysed for anti-polysaccharide (PS) antibodies against the Streptococcus pneumoniae (Pnc) vaccine serotypes 6B, 14, 19F, and 23F. The children received Pnc conjugate vaccine (1, 3, or 10 micrograms of PSs conjugated to diphtheria or tetanus toxoid) or placebo at 2, 4, and 6 months. At 7 months of age salivary PS antibodies were detected rarely. All children received Pnc conjugate or PS vaccine at 14 months of age. At 15 months, both IgA and IgG anti-Pnc PS were found, anti-19F and anti-14 antibodies occurring most frequently and in the highest concentrations. IgA was in the secretory form and predominantly IgA1. A negative dose dependency was observed in IgA anti-19F response. In general, no clear differences in salivary antibody responses were found between the children primed with conjugate vaccine in infancy and those who received their first Pnc vaccine at 14 months of age, suggesting that priming with Pnc conjugate vaccines does not lead to remarkable mucosal memory responses.     

Serotype of Streptococcus pneumoniae capsular polysaccharide can modify the Th1/Th2 cytokine profile and IgG subclass response to pneumococal-CRM(197) conjugate vaccines in a murine model

The cellular and antibody responses to type 14 and type 19F Streptococcus pneumoniae capsular polysaccharides (PS) conjugated to CRM(197) were investigated in a mouse model developed for pre-clinical evaluation and quality control of pneumococcal conjugate vaccines. Total IgG antibody and IgG subclasses against PS and the carrier protein for both conjugates were measured in addition to the T cell proliferation and cytokine profiles induced by these conjugates. While unconjugated PS 14 and 19F were at best only weakly immunogenic, both types of conjugate induced strong primary and secondary IgG responses to PS. The responses induced by the two conjugates to the carrier protein were very different; a high level of anti-CRM(197) IgG was induced only by the PS19F conjugate whereas a very weak response was induced by the PS14 conjugate. Interestingly, the IgG subclass distribution was different for the two conjugates; for PS19F conjugate, the IgG response was almost completely of IgG1 subclass with low levels of IgG3 and IgG2a while the response to PS14 conjugate was mainly of the IgG1 and IgG2a subclasses with a low level of IgG3. The anti-CRM(197) IgG subclass distribution was identical with that to the corresponding conjugated PS. Both types of conjugate induced strong T cell proliferation to recall antigens but induced different patterns of cytokine response in immune spleen cells which were indicative of a Th0 response or a mixture of Th1 and Th2 responses with a bias towards Th2 response in PS19F-CRM(197) immunised mice. In conclusion, PS14- and PS19F-CRM(197) conjugates induced different IgG subclass patterns as a result of inducing different patterns of cytokine response to the carrier protein. This indicates that the serotype of PS can modify the Th1/Th2 response to the carrier protein, which has a direct effect and can predict the IgG subclass of the PS response. Finally, we conclude that this model appears suitable for studying the immunogenicity and immune interaction of different components of multivalent pneumococcal conjugate vaccines and may be applicable to their pre-clinical evaluation and quality control.     

Oral immunization with a Streptococcal pneumoniae polysaccharide conjugate vaccine in enterocoated microparticles induces serum antibodies against type specific polysaccharides

The authors examined the antibody responses of mice orally immunized with pneumococcal polysaccharide (type 23F) or a pneumococcal polysaccharide conjugated to the outer membrane protein complex of Neisseria meningitides (23F-OMPC). These antigens were administered either in solution or entrapped within microcapsules. Only the mice receiving the encapsulated conjugate vaccine produced significant levels of anti-polysaccharide serum antibodies. These responses, observed after a second oral immunization with the conjugate, were predominantly IgG. Thus, the conversion from a T-cell-independent to a T-cell dependent response, achieved through conjugation was maintained following oral delivery. However, no local secretory IgA anti-polysaccharide response was detected in these mice indicating that while the OMPC carrier augments orally induced IgG responses, it was insufficient for the induction of secretory IgA.     

Tolerability and immunogenicity of an 11-valent pneumococcal conjugate vaccine in adults

We studied the safety and immunogenicity in healthy adults of an 11-valent pneumococcal conjugate vaccine. Capsular polysaccharides (PS) of serotypes 1, 4, 5, 7F, 9V, 19F and 23F were conjugated to tetanus toxoid, and of serotypes 3, 6B, 14 and 18C to diphtheria toxoid. Ten subjects received the conjugate vaccine with and the other ten subjects without aluminium hydroxide adjuvant. The reference vaccine was a marketed 23-valent PS vaccine. Safety data were recorded over 5 days after the immunisation. IgG antibody concentrations, avidity and subclass distribution were measured by EIA. The conjugate without aluminium induced more local adverse effects than the conjugate with aluminium or PS vaccine. All vaccines evoked significant antibody increases to all vaccine specific antigens. Both conjugate vaccines induced antibodies mainly of IgG(2) subclass, and adjuvanted conjugate vaccine induced IgG antibodies with increased avidity. This first administration, to man, of a mixed protein carrier 11-valent pneumococcal conjugate vaccine demonstrated its ability to induce an immune response without significant adverse effects, enabling further study on its use in paediatric populations.     

A modified surface killing assay (MSKA) as a functional in vitro assay for identifying protective antibodies against pneumococcal surface protein A (PspA)

Streptococcus pneumoniae causes otitis media, meningitis and pneumonia in patients worldwide; predominantly affecting young children, the elderly, and the immune compromised. Current vaccines against invasive pneumococcal disease are based on the polysaccharide capsules of the most clinically relevant serotypes. Due to serotype replacement, non-vaccine serotypes of S. pneumoniae have become more clinically relevant and as a result pneumococcal vaccines are becoming increasingly complex. These events emphasize the need to evaluate the potential for pneumococcal cross-reactive proteins to contribute to future vaccines. Antibody elicited by the immunization of humans with pneumococcal surface protein A (PspA) can passively protect mice from infection. However, robust in vitro functional assays for antibody to PspA are not available to predict the protective capacity of immune serum. For polysaccharide based vaccines, a standardized opsonophagocytosis killing assay (OPKA) is used. Antibody to PspA, however, does not work well in the standard OPKA. The present studies take advantage of past observations that phagocytosis is more efficient on tissue surfaces than in solution. In a modified surface killing assay (MSKA), monoclonal antibody to PspA, in the presence of complement, opsonized pneumococci for killing by phagocytes on an agar surface. Five monoclonal antibodies to PspA were tested; three demonstrated increased amounts of killing compared to the diluent control and protected mice by passive protection against type 3 pneumococci. The two antibodies that were not functional in the MSKA also failed to protect mice. Thus, an MSKA might be useful as a functional assay for immunity to PspA.     

New vaccines for the prevention of pneumococcal infections.

Streptococcus pneumoniae is a major cause of acute otitis media, pneumonia, bacteremia, and meningitis. Because in recent years antibiotic-resistant pneumococcal strains have been emerging throughout the world, vaccination against pneumococcal infections has become more urgent. The capsular polysaccharide vaccine that has been available is neither immunogenic nor protective in young children and other immunocompromised patients. Several pneumococcal proteins have been proposed as candidate vaccines, but no human studies associated with them have been reported. Clinical trials of first-generation pneumococcal conjugate vaccines have shown that covalent coupling of pneumococcal capsular polysaccharides to protein carriers improves the immunogenicity of the polysaccharides. The protective efficacy of the conjugate vaccines against carriage, acute otitis media, and invasive infections is being studied.