Development and Qualification of an Opsonophagocytic Killing Assay To Assess Immunogenicity of a Bioconjugated Escherichia coli Vaccine

The Development of Immunological Assays to Evaluate the Level and Function of Antibodies Induced by Klebsiella pneumoniae O-Antigen Vaccines

Klebsiella pneumoniae, a Gram-negative bacterium, has been listed as a critical pathogen for urgent intervention by the World Health Organization. With no licensed vaccine and increasing resistance to antibiotics, Klebsiella pneumoniae causes a high incidence of hospital- and community-acquired infections. Recently, there has been progress in anti-Klebsiella pneumoniae vaccine development, which has highlighted the lack of standardized assays to measure vaccine immunogenicity. We have developed and optimized methods to measure antibody level and function after vaccination with an in-development Klebsiella pneumoniae O-antigen vaccine. We describe the qualification of a Luminex-based multiplex antibody binding assay and both an opsonophagocytic killing assay and serum bactericidal assay to measure antibody function. Serum from immunized animals were immunogenic and capable of binding to and killing specific Klebsiella serotypes. Cross-reactivity was observed but limited among serotypes sharing antigenic epitopes. In summary, these results demonstrate the standardization of assays that can be used to test new anti-Klebsiella pneumoniae vaccine candidates, which is important for moving them into clinical trials. IMPORTANCE There is no licensed vaccine for the prevention of Klebsiella pneumoniae infections, and increasing levels of antibiotic resistance make this pathogen a high priority for vaccine and therapeutic development. Standardized assays for testing vaccine immunogenicity are paramount for the development of vaccines, and so in this study, we optimized and standardized both antibody-level and function assays for evaluating in-development K. pneumoniae bioconjugate vaccine response in rabbits.

Optimization and qualification of an assay that demonstrates that a FimH vaccine induces functional antibody responses in women with histories of urinary tract infections

Recurrent urinary tract infections (rUTI) are a serious disease associated with morbidities and mortality. Resistance to the standard of care antibiotics is now widespread because of the continued use of antibiotics among people who suffer from rUTI. We are therefore developing a vaccine to prevent recurrences among patients with rUTI. The antigen of the vaccine is FimH, a bacterial adhesin protein, and the vaccine is adjuvanted with a TLR-4 agonist. In a Phase 1 clinical study evaluating the vaccine, immunized individuals produced FimH-binding antibodies. Here we describe the optimization, qualification, and use of an assay to assess the functionality of these anti-FimH antibodies. The suitability of the assay for its intended purpose was demonstrated by selectivity, specificity, sensitivity, and intra-assay and inter-assay precision. The acceptance criteria were achieved for all parameters including intra-assay precision with ≤10% relative standard deviations and inter-assay precision with ≤25% relative standard deviations. The results presented herein suggest this functional assay will be important for supporting the vaccine’s efficacy in future human studies. Furthermore and of great significance, these results prove that vaccine-induced functional antibodies can be elicited in rUTI patients against an essential virulence factor, FimH.

Effect of flagellin on inhibition of infectious mechanisms by activating opsonization and salmonella flagellum disruption

Some serovars of salmonella cause huge global diseases such as enteric fever and invasive non typhoidal Salmonella disease. Flagellin as a key antigenic component of salmonella, can induce humoral and cellular immunity responses. In this research, we performed an opsonophagocytic killing assay (OPKA) as an important mechanism of the host-defense system, for salmonella to study the activity of anti-sera of native FliC, truncated modified recombinant FliC (tmFliC) and full length recombinant FliC proteins (flFliC). Also, the potency of antibodies for inhibiting bacterial movement was evaluated by traditional and newly-designed motility inhibition assay methods. Results showed both recombinant FliC anti-sera and native FliC (nFliC) anti-serum had the ability to opsonize Salmonella typhimurim, which led to bacterial clearance by mice macrophages. Also, inhibition of bacterial motility was observed for all anti-sera. Anti-nFliC and anti-flFliC sera showed higher effects on Salmonella typhimurim motility than that of tmFliC. In traditional method, about 88%, 86% and 80% inhibition were observed by using 5% nFliC, anti-flFliC and anti-tmFliC sera, respectively. In the newly-designed method using SIM (Sulfide indole motility) medium, results confirmed the traditional method for motility inhibition. Our findings suggest that salmonella fliC as a protective antigen may disrupt the flagellum apparatus activity.

Nasal Pneumococcal Density Is Associated with Microaspiration and Heightened Human Alveolar Macrophage Responsiveness to Bacterial Pathogens

Rationale: Pneumococcal pneumonia remains a global health problem. Colonization of the nasopharynx with Streptococcus pneumoniae (Spn), although a prerequisite of infection, is the main source of exposure and immunological boosting in children and adults. However, our knowledge of how nasal colonization impacts on the lung cells, especially on the predominant alveolar macrophage (AM) population, is limited.Objectives: Using a controlled human infection model to achieve nasal colonization with 6B serotype, we investigated the effect of Spn colonization on lung cells.Methods: We collected BAL from healthy pneumococcal-challenged participants aged 18-49 years. Confocal microscopy and molecular and classical microbiology were used to investigate microaspiration and pneumococcal presence in the lower airways. AM opsonophagocytic capacity was assessed by functional assays in vitro, whereas flow cytometry and transcriptomic analysis were used to assess further changes on the lung cellular populations.Measurements and Main Results: AMs from Spn-colonized individuals exhibited increased opsonophagocytosis to pneumococcus (11.4% median increase) for approximately 3 months after experimental pneumococcal colonization. AMs also had increased responses against other bacterial pathogens. Pneumococcal DNA detected in the BAL samples of Spn-colonized individuals were positively correlated with nasal pneumococcal density (r = 0.71; P = 0.029). Similarly, AM-heightened opsonophagocytic capacity was correlated with nasopharyngeal pneumococcal density (r = 0.61, P = 0.025).Conclusions: Our findings demonstrate that nasal colonization with pneumococcus and microaspiration prime AMs, leading to brisker responsiveness to both pneumococcus and unrelated bacterial pathogens. The relative abundance of AMs in the alveolar spaces, alongside their potential for nonspecific protection, render them an attractive target for novel vaccines.

Safety and immunogenicity of a vaccine for extra-intestinal pathogenic Escherichia coli (ESTELLA): a phase 2 randomised controlled trial

BACKGROUND

ExPEC4V (JNJ-63871860) is a bioconjugate vaccine, containing O-antigens from Escherichia coli serotypes O1A, O2, O6A, and O25B, developed for the prevention of invasive extra-intestinal pathogenic E coli (ExPEC) disease. We aimed to assess safety, reactogenicity, and immunogenicity of ExPEC4V in healthy adults.

METHODS

In this phase 2 randomised, double-blind placebo-controlled study, we recruited healthy adults (≥18 years with a body-mass index of 35 kg/m² or less) between Nov 16, 2015, and Aug 8, 2017, and randomly assigned them to receive a single dose of ExPEC4V (antigen O1A:O2:O6A:O25B content 4:4:4:4 μg [group 1]; 4:4:4:8 μg [group 2], 8:8:8:8 μg [group 3], 8:8:8:16 μg [group 4], or 16:16:16:16 μg [group 5]) or placebo. The primary objectives were evaluation of the safety, tolerability, and immunogenicity of ExPEC4V and determination of its dose-dependent immunogenicity 15 days after vaccination by ELISA in individuals who had received at least one vaccination dose. Antibody titres and safety evaluation were used to select two ExPEC4V doses for assessment up to day 360. This trial is registered at ClinicalTrials.gov, number NCT02546960.

FINDINGS

Of 848 enrolled participants, 843 (99%) received the ExPEC4V vaccine (757) or placebo (86) and were included in the safety analysis. Of 757 participants vaccinated with ExPEC4V, 222 (29%) had a solicited local adverse event and 325 (43%) had any solicited systemic adverse event, compared with 11 (13%) and 30 (35%) of 86 participants in the control group. Symptoms were mild-to-moderate. The most frequently reported solicited local adverse event was pain or tenderness (205 [27·1%] of 757 in combined ExPEC4V groups) and the most frequently reported solicited systemic adverse event was fatigue (208 [27·6%] of 757). Only 13 (2%) of 843 had a grade 3 event. At day 15, 80% or more of all participants achieved a two times or greater increase in serotype-specific IgG antibodies (except O25B at the lowest dose, 103 [72%] of 144). At day 360, 66% (95% CI 56·47-74·33) of participants in group 2 and 71% (62·13-78·95) of participants in group 4 selected for long-term follow-up maintained a two times or greater increase in serotype-specific antibody compared with baseline.

INTERPRETATION

EXPEC4V seemed well tolerated and elicited robust and functional antibody responses across all serotypes, doses, and age groups. For the two dosages evaluated (4:4:4:8 μg and 8:8:8:16 μg), the immune response persisted for 1 year.

FUNDING

Janssen Pharmaceuticals.

Development of an opsonophagocytic killing assay for group a streptococcus

Group A Streptococcus (GAS) or Streptococcus pyogenes is responsible for an estimated 500,000 deaths worldwide each year. Protection against GAS infection is thought to be mediated by phagocytosis, enhanced by bacteria-specific antibody. There are no licenced GAS vaccines, despite many promising candidates in preclinical and early stage clinical development, the most advanced of which are based on the GAS M-protein. Vaccine progress has been hindered, in part, by the lack of a standardised functional assay suitable for vaccine evaluation. Current assays, developed over 50 years ago, rely on non-immune human whole blood as a source of neutrophils and complement. Variations in complement and neutrophil activity between donors result in variable data that is difficult to interpret. We have developed an opsonophagocytic killing assay (OPKA) for GAS that utilises dimethylformamide (DMF)-differentiated human promyelocytic leukemia cells (HL-60) as a source of neutrophils and baby rabbit complement, thus removing the major sources of variation in current assays. We have standardised the OPKA for several clinically relevant GAS strain types (emm1, emm6 and emm12) and have shown antibody-specific killing for each emm-type using M-protein specific rabbit antisera. Specificity was demonstrated by pre-incubation of the antisera with homologous M-protein antigens that blocked antibody-specific killing. Additional qualifications of the GAS OPKA, including the assessment of the accuracy, precision, linearity and the lower limit of quantification, were also performed. This GAS OPKA assay has the potential to provide a robust and reproducible platform to accelerate GAS vaccine development.