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

Adult non-invasive pneumococcal pneumonia in Portugal is dominated by serotype 3 and non-PCV13 serotypes 3-years after near universal PCV13 use in children

Introduction

Non-invasive pneumococcal pneumonia (NIPP) is possibly the most frequent infection by Streptococcus pneumoniae in adults. However, the herd effect of vaccinating children in adult NIPP (aNIPP) remains poorly characterized.

Methods

We determined the serotype distribution and antimicrobial susceptibility of isolates causing aNIPP (>18 years) in 2016-2018 in Portugal; 3 years with near universal vaccination of children with the 13-valent conjugate vaccine (PCV13), following over a decade of significant PCV use in children in the private market.

Results and discussion

Among the 1,149 aNIPP isolates, the most frequent serotypes detected were: 3 (n = 168, 14.6%), 11A (n = 102, 8.9%), 19F (n = 70, 6.1%), 23A and 23B (n = 62, 5.4% each), 9N (n = 60, 5.2%), 8 and 29/35B (n = 43, 3.7% each); together accounting for 53% of all isolates. The serotype distribution causing aNIPP was stable in 2016-2018, with the serotypes included in PCV7 still being important causes of disease and serotype 3, a PCV13 serotype, remaining the leading cause of aNIPP. There was an increase in penicillin non-susceptibility from 17% in 2016 to 24% in 2018 (p = 0.018). Some PCV13 serotypes, such as 14, 19A and 19F were associated to resistance, which may have contributed to their persistence. The fact that close to 20% of aNIPP is caused by four non-vaccine serotypes (23A, 23B, 9N, and 29/35B) and that there were significant differences in serotype distribution relative to invasive disease, stress the importance of maintaining the surveillance of these infections. The lack of a continued herd effect from vaccinating children and the significant fraction of aNIPP potentially preventable by PCV13 (30%), PCV15 (34%), PCV20 (53%) and the 23-valent polysaccharide vaccine (61%) underscore the importance of considering the broader use of pneumococcal vaccines in adults.

Real-time in situ monitoring of CRM-197 and polysaccharide conjugation reaction by fluorescence spectroscopy

Aims: Process analytical technology (PAT) is increasingly being adopted within the pharmaceutical industry to build quality into a process. Development of PAT that provides real-time in situ analysis of critical quality attributes are highly desirable for rapid, improved process development. Conjugation of CRM-197 with pneumococcal polysaccharides to produce a desired pneumococcal conjugate vaccine is a significantly intricate process that can tremendously benefit from real-time process monitoring. Methods: In this work, a fluorescence-based PAT methodology is described to elucidate CRM-197-polysacharide conjugation kinetics in real time. Results & conclusion: In this work, a fluorescence-based PAT methodology is described to elucidate CRM-197-polysacharide conjugation kinetics in real time.

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

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

Antibody enhanced HPLC for serotype-specific quantitation of polysaccharides in pneumococcal conjugate vaccine

Bacterial infection remains as one of the major healthcare issues, despite significant scientific and medical progress in this field. Infection by Streptococcus Pneumoniae (S. Pneumoniae) can cause pneumonia and other serious infectious diseases, such as bacteremia, sinusitis and meningitis. The pneumococcal capsular polysaccharides (CPS) that constitute the outermost layer of the bacterial cell are the main immunogens and protect the pathogen from host defense mechanisms. Over 90 pneumococcal CPS serotypes have been identified, among which more than 30 can cause invasive pneumococcal diseases that could lead to morbidity and mortality. Multivalent pneumococcal vaccines have been developed to prevent diseases caused by S. Pneumoniae. These vaccines employ either purified pneumococcal CPSs or protein conjugates of these CPSs to generate antigen-specific immune responses for patient protection. Serotype-specific quantitation of these polysaccharides (Ps) antigen species are required for vaccine clinical dosage, product release and quality control. Herein, we have developed an antibody-enhanced high-performance liquid chromatography (HPLC) assay for serotype-specific quantitation of the polysaccharide contents in multivalent pneumococcal conjugate vaccines (PCVs). A fluorescence-labeled multiplex assay format has also been developed. This work laid the foundation for a serotype-specific antigen assay format that could play an important role for future vaccine research and development.

The remarkable history of pneumococcal vaccination: an ongoing challenge

Although it varies with age and geographical distribution, the global burden of infection with Streptococcus pneumoniae (pneumococcus) remains considerable. The elderly, and younger adults with comorbid conditions, are at particularly high risk of pneumococcal infection, and this risk will increase as the population ages. Vaccination should be the backbone of our current strategies to deal with this infection.

Main body: This manuscript reviews the history of the development of pneumococcal vaccines, and the impact of different vaccines and vaccination strategies over the past 111 years. It documents the early years of vaccine development in the gold mines of South Africa, when vaccination with killed pneumococci was shown to be effective, even before the recognition that different pneumococci were antigenically distinct. The development of type-specific vaccines, still with whole killed pneumococci, showed a high degree of efficacy. The identification of the importance of the pneumococcal capsule heralded the era of vaccination with capsular polysaccharides, although with the advent of penicillin, interest in pneumococcal vaccine development waned. The efforts of Austrian and his colleagues, who documented that despite penicillin therapy, patients still died from pneumococcal infection in the first 96 h, ultimately led to the licensing first of a 14-valent pneumococcal polysaccharide in 1977 followed by the 23-valent pneumococcal polysaccharide in 1983. The principal problem with these, as with other polysaccharide vaccines, was that that they failed to immunize infants and toddlers, who were at highest risk for pneumococcal disease. This was overcome by chemical linking or conjugation of the polysaccharide molecules to an immunogenic carrier protein. Thus began the era of pneumococcal conjugate vaccine (PCV), starting with PCV7, progressing to PCV10 and PCV13, and, most recently, PCV15 and PCV20. However, these vaccines remain serotype specific, posing the challenge of new serotypes replacing vaccine types. Current research addresses serotype-independent vaccines which, so far, has been a challenging and elusive endeavor.

Conclusion: While there has been enormous progress in the development of pneumococcal vaccines during the past century, attempts to develop a vaccine that will retain its efficacy for most pneumococcal serotypes are ongoing.

Modeling of pneumococcal serogroup 10 capsular polysaccharide molecular conformations provides insight into epitopes and observed cross-reactivity

Streptococcus pneumoniae is an encapsulated gram-negative bacterium and a significant human pathogen. The capsular polysaccharide (CPS) is essential for virulence and a target antigen for vaccines. Although widespread introduction of pneumococcal conjugate vaccines (PCVs) has significantly reduced disease, the prevalence of non-vaccine serotypes has increased. On the basis of the CPS, S. pneumoniae serogroup 10 comprises four main serotypes 10A, 10B, 10C, and 10F; as well as the recently identified 10D. As it is the most prevalent, serotype 10A CPS has been included as a vaccine antigen in the next generation PCVs. Here we use molecular modeling to provide conformational rationales for the complex cross-reactivity reported between serotypes 10A, 10B, 10C, and 10F anti-sera. Although the highly mobile phosphodiester linkages produce very flexible CPS, shorter segments are conformationally defined, with exposed β-D-galactofuranose (β DGalf) side chains that are potential antibody binding sites. We identify four distinct conformational epitopes for the immunodominant β DGalf that assist in rationalizing the complex asymmetric cross-reactivity relationships. In particular, we find that strongly cross-reactive serotypes share common epitopes. Further, we show that human intelectin-1 has the potential to bind the exposed exocyclic 1,2-diol of the terminal β DGalf in each serotype; the relative accessibility of three- or six-linked β DGalf may play a role in the strength of the innate immune response and hence serotype disease prevalence. In conclusion, our modeling study and relevant serological studies support the inclusion of serotype 10A in a vaccine to best protect against serogroup 10 disease.

The First-in-Human Synthetic Glycan-Based Conjugate Vaccine Candidate against Shigella

Shigella, the causative agent of shigellosis, is among the main causes of diarrheal diseases with still a high morbidity in low-income countries. Relying on chemical synthesis, we implemented a multidisciplinary strategy to design SF2a-TT15, an original glycoconjugate vaccine candidate targeting Shigella flexneri 2a (SF2a). Whereas the SF2a O-antigen features nonstoichiometric O-acetylation, SF2a-TT15 is made of a synthetic 15mer oligosaccharide, corresponding to three non-O-acetylated repeats, linked at its reducing end to tetanus toxoid by means of a thiol-maleimide spacer. We report on the scale-up feasibility under GMP conditions of a high yielding bioconjugation process established to ensure a reproducible and controllable glycan/protein ratio. Preclinical and clinical batches complying with specifications from ICH guidelines, WHO recommendations for polysaccharide conjugate vaccines, and (non)compendial tests were produced. The obtained SF2a-TT15 vaccine candidate passed all toxicity-related criteria, was immunogenic in rabbits, and elicited bactericidal antibodies in mice. Remarkably, the induced IgG antibodies recognized a large panel of SF2a circulating strains. These preclinical data have paved the way forward to the first-in-human study for SF2a-TT15, demonstrating safety and immunogenicity. This contribution discloses the yet unreported feasibility of the GMP synthesis of conjugate vaccines featuring a unique homogeneous synthetic glycan hapten fine-tuned to protect against an infectious disease.

Glycan Array Evaluation of Synthetic Epitopes between the Capsular Polysaccharides from Streptococcus pneumoniae 19F and 19A

Vaccination represents the most effective way to prevent invasive pneumococcal diseases. The glycoconjugate vaccines licensed so far are obtained from capsular polysaccharides (CPSs) of the most virulent serotypes. Protection is largely limited to the specific vaccine serotypes, and the continuous need for broader coverage to control the outbreak of emerging serotypes is pushing the development of new vaccine candidates. Indeed, the development of efficacious vaccine formulation is complicated by the high number of bacterial serotypes with different CPSs. In this context, to simplify vaccine composition, we propose the design of new saccharide fragments containing chemical structures shared by different serotypes as cross-reactive and potentially cross-protective common antigens. In particular, we focused on Streptococcus pneumoniae (Sp) 19A and 19F. The CPS repeating units of Sp 19F and 19A are very similar and share a common structure, the disaccharide ManNAc-β-(1→4)-Glc (A-B). Herein, we describe the synthesis of a small library of compounds containing different combinations of the common 19F/19A disaccharide. The six new compounds were tested with a glycan array to evaluate their recognition by antibodies in reference group 19 antisera and factor reference antisera (reacting against 19F or 19A). The disaccharide A-B, phosphorylated at the upstream end, emerged as a hit from the glycan array screening because it is strongly recognized by the group 19 antisera and by the 19F and 19A factor antisera, with similar intensity compared with the CPSs used as controls. Our data give a strong indication that the phosphorylated disaccharide A-B can be considered a common epitope among different Sp 19 serotypes.