Group B Streptococcus (GBS) disease is a major cause of infant morbidity and mortality. Capsular polysaccharide conjugate GBS vaccines have been evaluated for decades; however, none is licensed. This phase 1/2 trial evaluated an investigational maternal hexavalent polysaccharide-protein conjugate GBS vaccine (GBS6) in non-pregnant females and pregnant participants and their infants. In stage 1 (conducted in South Africa), healthy non-pregnant participants received GBS6, GBS6 + aluminum phosphate (AlPO4) or placebo; a subset received GBS6 + AlPO4 booster approximately 2 years later. Stage 2 (conducted in South Africa) maternal dose-finding data were reported previously and are not presented here. In stage 3, healthy pregnant participants from South Africa, the United States and the United Kingdom received GBS6 or placebo (24-36 weeks' gestation). In stage 1, 66 non-pregnant participants received GBS6, GBS6 + AlPO4 or placebo (n = 22 each); 26 also received GBS6 + AlPO4 booster. In stage 3, 216 pregnant participants were included (GBS6, n = 108; placebo, n = 108); 209 infants were born to maternal participants (GBS6, n = 104; placebo, n = 105). Primary objectives described GBS6 safety/tolerability profiles. Nearly all reactogenicity events were mild or moderate. Among non-pregnant participants, no serious adverse events (SAEs) or adverse event (AE)-associated withdrawals were reported after vaccination; medically attended adverse events (MAEs) were reported in similar percentages across primary vaccination groups (GBS6 groups = 41-45%; placebo = 41%). Rates of AEs (GBS6 = 75/108 (69%); placebo = 70/108 (65%)), SAEs (GBS6 = 21/108 (19%); placebo = 23/108 (21%)) and delivery outcome frequencies were similar in GBS6 and placebo maternal participants. Most infants were born full-term. Infant AE (GBS6 = 87/104 (84%); placebo = 86/105 (82%)), SAE (GBS6 = 45/104 (43%); placebo = 46/105 (44%)) and MAE (GBS6 = 65/104 (63%); placebo = 66/105 (63%)) frequencies were similar across groups. Two neonatal sepsis-associated deaths occurred (GBS6 = 1; placebo = 1); neither was considered vaccine related. Secondary objectives described immune responses. GBS6 elicited robust immune responses in non-pregnant and pregnant individuals; additionally, serotype-specific quantitative and functional antibody responses were observed in infants whose parent received GBS6. These data support continuing clinical investigation of maternal GBS6 vaccination. ClinicalTrials.gov identifier: NCT03765073 .

Urinary tract infections, caused primarily by uropathogenic E. coli, are a significant public health burden, affecting approximately 50% of women worldwide. The adhesin FimH is responsible for host receptor binding and is therefore a promising vaccine candidate, but prior studies showed that recombinant monomeric FimH is poorly immunogenic. Here we displayed FimH antigens on the two-component protein nanoparticle I53-50 to generate nanoparticle immunogens that elicit robust levels of receptor-blocking antibodies in mice and non-human primates. We produced nanoparticle immunogens displaying either the FimH lectin domain or a recently reported conformationally stabilized antigen, FimH-DSG, comprising both the lectin and pilin domains. When formulated on aluminum hydroxide, both nanoparticle immunogens elicited similar levels of receptor-blocking activity as a ten-fold higher dose of monomeric FimH-DSG formulated with a potent adjuvant. The improved manufacturability of the stabilized antigen, combined with the ability of nanoparticle display to obviate the need for complex adjuvants, provides important preclinical data for FimH-based vaccines intended to prevent urinary tract infections. More broadly, our data extend the applicability of the I53-50 nanoparticle platform, which to date has been mainly used for displaying viral and protozoan antigens, to bacterial indications.

BACKGROUND:Invasive disease caused by typhoid and nontyphoidal Salmonella (NTS) is a threat confronting young children in sub-Saharan Africa. We are developing a trivalent Salmonella conjugate vaccine (TSCV) consisting of typhoid Vi conjugate and core-O-polysaccharide conjugates from 2 invasive NTS serovars (S. Typhimurium and S. Enteritidis). METHODS:We conducted a randomized-controlled Phase 1/2a trial assessing the safety and immunogenicity of a full-strength TSCV (FS; 25 µg of all 3 polysaccharides), half-strength TSCV (HS; 25 µg of Vi and 12.5 µg of both NTS polysaccharides), dilutional half-strength TSCV (dilHS; 12.5 µg of all 3 polysaccharides), or placebo. Local and systemic adverse events were recorded and blood was collected for serum antibody and antibody-secreting cells (ASCs). RESULTS:In total, 80 evaluable participants aged 20-47 years were enrolled. All vaccines were well tolerated; mild injection site pain and fatigue were the most common reactions reported. Serum antibody and ASC responses to the 3 primary polysaccharide antigens were robust, ranging between 85% and 100% response rates, with no statistically significant difference between the 3 formulations. No placebo recipients manifested significant antibody or ASC responses. CONCLUSIONS:These data encourage the further development of TSCV to address a pressing public health problem in young children of sub-Saharan Africa.

Background:Klebsiella pneumoniae (KPn) is a leading cause of invasive bacterial disease in African children, albeit with a scarcity of genotypic characterization. Methods:We sequenced invasive KPn isolates from infants ≤90 days, collected through observational hospital surveillance (n = 226) between March 4, 2019 and February 27, 2021, and between May 13, 2022 and October 31, 2023, and postmortem sampling (n = 111) between February 15, 2018 and April 18, 2023. Postmortem Kpn isolates were attributed in the causal pathway to death by the determination of the cause of death panel, which consists of local experts. Results:Three hundred and thirty-seven isolates (226 identified during hospital surveillance and 111 from postmortem sampling) were included in the final analysis. Genomic analysis identified 85 distinct clonotypes. Sequence type (ST) 17 (22.0%) predominated, followed by ST39 (12.7%). The dominant K-locus (KL) were KL25 (24.0%), KL2 (14.5%), and KL149 (13/4%), while the dominant O-antigens included O1αβ,2α(48.4%), and O5 (19.9%). Eighty-five percent (287/337) of the KPn isolates harbored multidrug resistant genes, including 32.9% to carbapenems. Notably, blaOXA-181, blaNDM-5, and blaNDM-1 were detected in 26.4%, 2.1% (7/337), and 0.3% (1/337) of isolates, respectively. Conclusions:Although a wide diversity of strains were associated with Kpn invasive disease, over 80% of the cases were attributed to 11 K loci. These data provide critical insights into KPn epidemiology and highlight potential antigen targets for vaccine development in young African children.

Lyme disease is a growing public health concern that is geographically focused in regions where ticks that carry the causative bacteria, Borrelia burgdorferi sensu lato (s.l.), are endemic. Outer surface protein A (OspA) is expressed by B. burgdorferi s.l. spirochetes during the tick phase and OspA antibodies introduced during tick feeding can block transmission and prevent B. burgdorferi infection. Candidate Lyme disease vaccine VLA15 is comprised of the C-terminal domains of the six B. burgdorferi s.l. OspA serotypes (ST) prevalent in North America and Europe. We report herein that non-human primates immunized with VLA15 were protected against challenge with Ixodes scapularis ticks bearing B. burgdorferi sensu stricto (s.s.) (OspA ST1). Levels of residual B. burgdorferi s.s. tick colonization were reduced in ticks that fed on VLA15-immunized primates compared to those immunized with full length-OspA ST1 (FL-OspA) at a point when OspA-binding IgG levels were similar. Furthermore, monoclonal antibodies targeting the C-terminal half of OspA, elicited by FL-OspA immunization in primates, were more effective at complement-mediated bactericidal killing in vitro and clearance of spirochetes in ticks versus those directed against other parts of the protein.

A standardized multiplex immunoassay (MIA) to quantify group B Streptococcus (GBS) anti-capsular polysaccharide (CPS) IgG serum concentrations was adopted by the Group B Streptococcal Assay Standardization (GASTON) consortium as a standardized serological assay with the most immediate applications for facilitating the licensure of GBS vaccines. However, dried blood spot (DBS) samples offer advantages for immunological studies, including cost-effectiveness, ease of transport, and storage. To determine suitability of DBS as an alternative sample matrix to serum in MIA, a contrived GBS seropositive panel, including matched DBS and serum samples, was prepared using established methods. The calculated geometric mean titers of GBS anti-CPS IgG values by individual serotype were compared using a paired t-test to establish serum equivalency. Geometric mean values for the matched panel were assessed via Deming regression for precision, accuracy, and concordance correlation coefficient (CCC). The initial acceptance criterion was set at 0.95 for CCC. Two additional criteria based on confidence intervals of CCC, slope, and intercept were used to determine the necessity of a serotype-specific conversion factor. The paired t-test p-values were >.05 for serum equivalency. For sample matrix concordance, CCC values were >0.95 and met correlation criteria for all serotypes. Conversion factors were applied to four serotypes (II, III, IV, and V) that did not meet the criteria for slope, intercept, or both. This demonstration of equivalency between DBS and serum supports the hypothesis that DBS is a suitable testing matrix from which to elucidate anti-CPS IgG concentrations in seroepidemiological and vaccine evaluation studies.

In sub-Saharan Africa, typhoidal and non-typhoidal Salmonella (NTS) are leading causes of invasive disease among young children. Trivalent Salmonella conjugate vaccine (TSCV) consists of Vi capsule polysaccharide conjugated to tetanus toxoid and core-plus-O-polysaccharides from the two most prevalent invasive NTS serovars conjugated to flagellin subunits. We conducted a first-in-human, randomized, placebo-controlled, phase 1 trial evaluating the safety and immunogenicity of TSCV. A total of 22 healthy adults aged 18-45 years were randomly allocated to 6.25-µg TSCV (n = 8), 12.5-µg TSCV (n = 10) or placebo (n = 4). The primary objective was the assessment of safety. The co-primary immunogenicity objective was the serum IgG response against the three vaccine polysaccharides and two flagellin carrier proteins. Here we show that TSCV was safe and well tolerated, meeting the prespecified safety endpoints, with the most common solicited symptom being short-lived injection site pain. For each of the three polysaccharides, immune responses, as demonstrated by ≥4-fold increases over baseline, were observed among all (100%) vaccinees, and no responses were elicited in the placebo group, meeting the prespecified immunogenicity endpoints. The two flagellin components elicited 88% (7/8) and 100% (8/8) responses among 6.25-µg and 12.5-µg TSCV recipients and no placebo recipients. These data warrant further evaluation of TSCV for protection against invasive Salmonella disease. ClinicalTrial.gov identifier: NCT03981952 .

In sub-Saharan Africa, non-typhoidal Salmonella (NTS) and Salmonella Typhi are leading causes of invasive disease among young children. Trivalent Salmonella Conjugate Vaccine (TSCV) consists of Vi capsule polysaccharide conjugated to tetanus toxoid and core-plus-O-polysaccharides from the two most prevalent invasive non-typhoidal serovars (Typhimurium, Enteritidis) conjugated to serovar-homologous flagellin subunits. We conducted a first-in-human, randomized, placebo-controlled, stepwise-dose-escalation phase 1 trial (NCT03981952) evaluating TSCV safety and immunogenicity; 22 healthy adults aged 18-45 years were randomly allocated 6.25 μg TSCV (n=8), 12.5 μg TSCV (n=10), or placebo (n=4). TSCV was safe and well-tolerated, with the most common solicited symptom being short-lived injection site pain. For each of the 3 polysaccharides, serum IgG and IgA ELISA antibody responses, as demonstrated by four-fold or greater increases over baseline, were observed among all vaccinees but among no placebo recipients. Binding and functional antibodies, gut-homing antibody secreting cells, and polysaccharide-specific memory B cells responses were also elicited. ClinicalTrials.gov Registry NCT03981952.

INTRODUCTION:Lyme disease is caused by the tick-borne spirochete pathogen Borrelia burgdorferi sensu lato (s.l.). Outer surface protein A (OspA) is expressed by B. burgdorferi s.l. while in the tick and antibodies against OspA introduced into the tick with the bloodmeal can prevent transmission. OspA-based vaccines have been validated in people, however, there are currently no available human Lyme disease vaccines. Hexavalent OspA vaccine VLA15 is designed to cover the dominant B. burgdorferi s.l. genospecies causing disease in North America and Europe and is currently the most advanced candidate human Lyme disease vaccine in clinical development. AREAS COVERED:A historical retrospective of the discovery and evolving burden of Lyme disease is covered, as well as relevant aspects of the vector biology, preclinical research underpinning development of VLA15, and its clinical development to date. EXPERT OPINION:Lyme disease has expanded over the past two decades in both incidence and geographic footprint and is anticipated to continue to increase in the future due to changing climate and human encroachment into wildlife areas. VLA15 is currently in the last stage of clinical development, and if found to be safe and efficacious, may offer an important prophylactic modality for prevention of Lyme disease.

A standardized multiplex immunoassay (MIA) to quantify group B Streptococcus (GBS) anti-capsular polysaccharide (CPS) IgG serum concentrations was adopted by the Group B Streptococcal Assay Standardization (GASTON) consortium as a standardized serological assay with the most immediate applications for facilitating the licensure of GBS vaccines. However, dried blood spot (DBS) samples offer advantages for immunological studies, including cost-effectiveness, ease of transport, and storage. To determine suitability of DBS as an alternative sample matrix to serum in MIA, a contrived GBS seropositive panel, including matched DBS and serum samples, was prepared using established methods. The calculated geometric mean titers of GBS anti-CPS IgG values by individual serotype were compared using a paired t-test to establish serum equivalency. Geometric mean values for the matched panel were assessed via Deming regression for precision, accuracy, and concordance correlation coefficient (CCC). The initial acceptance criterion was set at 0.95 for CCC. Two additional criteria based on confidence intervals of CCC, slope, and intercept were used to determine the necessity of a serotype-specific conversion factor. The paired t-test p-values were >.05 for serum equivalency. For sample matrix concordance, CCC values were >0.95 and met correlation criteria for all serotypes. Conversion factors were applied to four serotypes (II, III, IV, and V) that did not meet the criteria for slope, intercept, or both. This demonstration of equivalency between DBS and serum supports the hypothesis that DBS is a suitable testing matrix from which to elucidate anti-CPS IgG concentrations in seroepidemiological and vaccine evaluation studies.

Abstract Background Lyme borreliosis (LB) is the most common tick-borne disease in the US, with approximately 476,000 cases diagnosed and treated annually and nearly 90 million individuals living in high incidence jurisdictions. Vector-focused prevention measures have varying levels of effectiveness due to low utilization, poor adherence, or high cost. A safe and efficacious vaccine to prevent LB is warranted. We provide an update on the Pfizer-Valneva VLA15 vaccine clinical development program, specifically the safety and immunogenicity booster data of the phase 2 trial (NCT04801420). Methods A randomized, observer-blinded, multi-centre Phase 2 study investigated the safety and immunogenicity of VLA15 in adult and pediatric study populations. A total of 625 participants aged 5-65 years were enrolled in three age groups (5-11 years, 12-17 years, and 18-65 years) and randomized 1:1:1 to receive VLA15 180 mcg with alum in a three-dose (Month 0-2-6) or a two-dose schedule (Month 0-6), or three injections of placebo (Month 0-2-6) followed by booster doses at Month 18 and Month 30. Safety and immunogenicity data up to one month after completion of the primary vaccination series and yearly booster doses are presented. Results Up to Month 19, VLA15 was safe and well tolerated in all age groups after all doses. Most adverse reactions were mild or moderate in severity. No related SAEs or other safety concerns were reported. The VLA15 booster dose induced a robust, anamnestic immune response against all six OspA vaccine serotypes in all age groups. Immune responses in children were higher than in adults across both schedules. Conclusion The Month 18 VLA15-221 booster dose was safe and immunogenic in both adults and children. The Month 30 booster data is under analysis. The ongoing blinded Phase 3 trials in Europe and North America will provide additional data which may support use of this vaccine as the primary preventative measure to protect against LB. Disclosures Marc D. Messier, PhD, SOBI: Advisor/Consultant|Valneva: employee|Valneva: Ownership Interest Laura Wagner, M.Sc., Valneva: employee Romana Hochreiter, PhD, Valneva Austria GmbH: WO2021/207615 A1|Valneva Austria GmbH: Employee, owner of stock options Erik Lamberth, MD, Pfizer: Employee|Pfizer: Stocks/Bonds (Public Company) Julian Larcher-Senn, PhD, Valneva: Advisor/Consultant Raphael Simon, PhD, Pfizer: Stocks/Bonds (Private Company) James groark, MD, Pfizer: Stocks/Bonds (Public Company) James H. Stark, PhD, Pfizer: Employee|Pfizer: Stocks/Bonds (Public Company)

BACKGROUND:A hexavalent group B streptococcus (GBS) polysaccharide conjugate vaccine (GBS6) is being developed to prevent invasive group B streptococcal disease in infants through active maternal immunisation. We previously reported results for GBS6 administered to non-pregnant adults (NCT03170609). Here, we aim to extend these results to determine safety and immunogenicity of a second dose of GBS6 in non-pregnant adults who received a primary dose of GBS6. METHODS:This phase 2, open-label extension of a phase 1/2 randomised controlled trial was done at four sites in the USA to assess the safety, tolerability, and immunogenicity of a booster dose (20 μg capsular polysaccharide per serotype per dose) of GBS6 formulated with and without aluminium phosphate (AlPO4). Healthy adults who were aged 18-49 years during participation in the phase 1/2 study approximately 2 years before and received one of the six GBS6 formulations were enrolled. Participants received a single dose of GBS6 20 μg capsular polysaccharide (CPS) per serotype on study day 1, with or without AlPO4 based on the formulation received in the phase 1/2 study. Primary endpoints evaluated GBS6 safety (in participants receiving one or more doses) based on solicited local reactions and systemic events within 14 days, adverse events within 1 month, and unsolicited serious adverse events and medically attended adverse events up to 6 months after vaccination. Secondary immunogenicity endpoints (in the evaluable population of participants in compliance with key protocol criteria) included assessments of GBS serotype-specific IgG geometric mean concentrations (GMCs) and geometric mean fold-rises (GMFRs) in serum samples collected at 1 month after versus before booster vaccination. This study is registered with ClinicalTrials.gov (NCT04258995). FINDINGS:Of 297 participants who completed the base study, 151 received the GBS6 booster dose (76 participants with and 75 without AlPO4) and were included in the safety analysis. The median time to booster from primary vaccination was 2·4 years (IQR 2·3-2·5). Most participants were women (114 [75%] of 151) and White (125 [83%] of 151). The mean age was 36·7 years (SD 8·67). Pain at the injection site was the most frequently reported solicited local reaction (52 [68%] of 76 participants who received GBS6 with AlPO4 and 32 [43%] of 75 without AlPO4) and was severe in two (3%) of 76 participants who received GBS6 with AlPO4 and no participant who received the vaccine without adjuvant. Systemic events occurred at similar frequencies in both groups (45 [59%] of 76 with AlPO4 and 46 [61%] of 75 without AlPO4), and were mostly mild or moderate in severity. The number of participants reporting any type of unsolicited adverse event was low and similar for GBS6 with AlPO4 versus GBS6 without AlPO4 (11 [14%] of 76 vs 12 [16%] of 75). No adverse event was deemed to be related to GBS6. One serious adverse event, assessed as not related to the product being investigated, of thermal burn was reported in a participant who received GBS6 with AlPO4. Low rates of medically attended adverse events were reported in both groups of participants receiving a booster dose of GBS6 (nine [12%] of 76 with AlPO4 and seven [9%] of 75 without AlPO4). For all serotypes, serotype-specific anti-CPS IgG GMCs mostly waned over the 2-year period after the primary vaccination but remained elevated before the booster dose compared with before the primary dose of GBS6. A booster dose of GBS6 elicited robust GBS serotype-specific anti-CPS IgG responses that were two-fold to 18-fold higher 1 month after the booster dose (GMC range 6·025-60·304 μg/mL) than 1 month after the primary dose (0·365-35·173 μg/mL). Anti-CPS IgG GMFRs ranged from approximately ten-fold to 59-fold across the serotypes and formulations from before the booster dose (GMC range 0·130-5·274 μg/mL) to 1 month after the booster dose. INTERPRETATION:The results of this study showed that a single 20 μg booster dose of GBS6 given approximately 2 years after a primary dose to healthy, non-pregnant adults was safe and elicited robust immune responses that were consistently higher than those after the primary dose. As there is precedent for repeat doses of vaccines to augment or sustain circulating antibodies available for placental transfer with each pregnancy, results from this study might inform decisions around future dosing strategies for GBS6 for maternal immunisation with subsequent pregnancies should GBS6 be approved for use in pregnancy. FUNDING:Pfizer.

Klebsiella pneumoniae (KPn) colonizes multiple anatomical sites and is a leading cause of invasive disease and death in African children; however, there is no comparative genomic analysis between colonizing and invasive strains. This study investigated the genomic relatedness of KPn colonizing and invasive isolates in South African infants; and evaluated the relative invasiveness of KPn isolates based on sequence types (ST), capsular (KL), and lipopolysaccharide (O) loci by calculating case-carrier ratios (CCRs). There was less genomic diversity amongst invasive (22 ST, 17 K-loci) than colonizing isolates (31 ST, 29 K-loci), with invasive isolates being 8.59-fold and 3.49-fold more likely to harbour genes encoding for multi-drug resistance and yersiniabactin production compared with colonizing isolates. The CCRs for KL102 and O1/O2v2 were > 1, and < 1 for KL8, ST1414, and O1O2v1. Identifying high-risk strains, including KL102 and O1O2v2, that may have a higher potential to cause invasive disease, could enhance risk assessment and management strategies in vulnerable populations.

Klebsiella pneumoniae (KP) and Pseudomonas aeruginosa (PA) are leading causes of healthcare-associated and community-acquired infections. Despite decades of efforts, there are no licensed vaccines for either pathogen. The surface O polysaccharides (OPS) of Klebsiella pneumoniae and Pseudomonas aeruginosa are essential virulence factors for these bacteria and are targets of protective antibacterial antibodies. The multiple antigen presenting system (MAPS) vaccine platform was used to create a multivalent Klebsiella/Pseudomonas vaccine in which the surface OPS of four Klebsiella and eight Pseudomonas strains were linked to a high MW biotinylated Klebsiella oxytoca (KO) K19 capsular polysaccharide backbone and subsequently linked to pathogen-specific fusion proteins, consisting of Klebsiella MrkA, the Pseudomonas flagellin B D2 subunit, and PcrV. We show here that these MAPS complexes incorporating KP and PA OPS, as well as pathogen-specific proteins, were highly immunogenic in rabbits and mice and induced functionally active antibodies in vitro and in murine animal models.IMPORTANCEInfections caused by Klebsiella pneumoniae (KP) and Pseudomonas aeruginosa (PA) are widely recognized to be of "urgent" and "serious" concern, in part because of their widespread antimicrobial resistance. To date, there is no licensed vaccine for either pathogen. We developed a novel multiple antigen presenting system (MAPS) vaccine platform that contains eight O polysaccharides (OPS) of PA and four OPS of KP, which will cover over 80% of clinical infections with these pathogens. In addition, this vaccine includes three pathogen-relevant proteins acting both as carrier proteins to provide T cell help for these polysaccharides as well as to elicit functionally active antibodies that may also protect against KP and PA infection. The use of pathogen-relevant proteins that may contribute to vaccine efficacy in place of the more traditional carrier proteins is a novel concept. The MAPS vaccine platform also generates Th17 and Th1 responses. This KP/PA MAPS vaccine may prevent infection with these pathogens and reduce their transmissibility.

BACKGROUND:Lyme borreliosis (LB), the most common vector-borne disease in the Northern Hemisphere, is caused by a multitude of pathogenic Borrelia burgdorferi sensu lato (sl) species endemic to northern, western, and central regions of Europe. We utilized whole genome sequencing (WGS) to characterize the genetic diversity of 130 clinical B. burgdorferi sl isolates collected from LB cases in the Netherlands between 1988 and 2023, the majority of which were B. afzelii. RESULTS:WGS analysis revealed significant diversity, including 29 different multi-locus sequence types (MLSTs) across four genospecies. Plasmids from B. garinii and B. bavariensis were found to exhibit greater sequence diversity than those from B. burgdorferi sensu stricto and B. afzelii. We further characterized the Borrelia membrane protein antigens OspA, OspC and DbpA for sequence diversity and correlation with LB disease state. CONCLUSIONS:This large-scale genomic analysis of clinical Dutch B. burgdorferi sl isolates furthers our understanding of LB and may indicate potential coverage for LB vaccine candidates in clinical development.

A US collection of invasive Escherichia coli serotype O1 bloodstream infection (BSI) isolates were assessed for genotypic and phenotypic diversity as the basis for designing a broadly protective O-antigen vaccine. Eighty percent of the BSI isolate serotype O1 strains were genotypically ST95 O1:K1:H7. The carbohydrate repeat unit structure of the O1a subtype was conserved in the three strains tested representing core genome multi-locus sequence types (MLST) sequence types ST95, ST38, and ST59. A long-chain O1a CRM197 lattice glycoconjugate antigen was generated using oxidized polysaccharide and reductive amination chemistry. Two ST95 strains were investigated for use in opsonophagocytic assays (OPA) with immune sera from vaccinated animals and in murine lethal challenge models. Both strains were susceptible to OPA killing with O1a glycoconjugate post-immune sera. One of these, a neonatal sepsis strain, was found to be highly lethal in the murine challenge model for which virulence was shown to be dependent on the presence of the K1 capsule. Mice immunized with the O1a glycoconjugate were protected from challenges with this strain or a second, genotypically related, and similarly virulent neonatal isolate. This long-chain O1a CRM197 lattice glycoconjugate shows promise as a component of a multi-valent vaccine to prevent invasive E. coli infections. IMPORTANCE The Escherichia coli serotype O1 O-antigen serogroup is a common cause of invasive bloodstream infections (BSI) in populations at risk such as newborns and the elderly. Sequencing of US BSI isolates and structural analysis of O polysaccharide antigens purified from strains that are representative of genotypic sub-groups confirmedthe relevance of the O1a subtype as a vaccine antigen. O polysaccharide was purifiedfrom a strain engineered to produce long-chain O1a O-antigen and was chemically conjugated to CRM197 carrier protein. The resulting glycoconjugate elicited functional antibodies and was protective in mice against lethal challenges with virulent K1-encapsulated O1a isolates

Flagellum-mediated motility is essential to Pseudomonas aeruginosa (P. aeruginosa) virulence. Antibody against flagellin reduces motility and inhibits the spread of the bacteria from the infection site. The standard soft-agar assay to demonstrate anti-flagella motility inhibition requires long incubation times, is difficult to interpret, and requires large amounts of antibody. We have developed a time-lapse video microscopy method to analyze anti-flagellin P. aeruginosa motility inhibition that has several advantages over the soft agar assay. Antisera from mice immunized with flagellin type A or B were incubated with Green Fluorescent Protein (GFP)-expressing P. aeruginosa strain PAO1 (FlaB+) and GFP-expressing P. aeruginosa strain PAK (FlaA+). We analyzed the motion of the bacteria in video taken in ten second time intervals. An easily measurable decrease in bacterial locomotion was observed microscopically within minutes after the addition of small volumes of flagellin antiserum. From data analysis, we were able to quantify the efficacy of anti-flagellin antibodies in the test serum that decreased P. aeruginosa motility. This new video microscopy method to assess functional activity of anti-flagellin antibodies required less serum, less time, and had more robust and reproducible endpoints than the standard soft agar motility inhibition assay.

BACKGROUND:Group B streptococcus is a major cause of neonatal disease. Natural history studies have linked maternally transferred anti-group B streptococcus capsular polysaccharide antibodies with protection against infant group B streptococcus disease. Previous studies of capsular polysaccharide antibody concentration in European populations have used maternal (not infant) sera and a non-standardised assay. This study aimed to evaluate anti-capsular polysaccharide IgG concentrations associated with protection against invasive group B streptococcus disease in Finnish infants. METHODS:In this retrospective case-control study, we used cord sera from the Finnish DIPP study repository, which was obtained between Jan 1, 1995, and Dec 31, 2017. We included infants aged 6 months or younger with group B streptococcus infection (cases) and healthy infants (controls). We enrolled infants with invasive neonatal group B streptococcus (55 cases) and matched controls (229 controls) aged 6 months or younger after identification from Finnish health registers. We measured anti-capsular polysaccharide IgG (serotypes Ia-V) concentration using a standardised immunoassay and we estimated its relationship to disease risk using a Bayesian model. We used the derived risk-concentration curve to predict potential efficacy of six-valent group B streptococcus capsular polysaccharide vaccine (GBS6) based on previously reported immunogenicity data. FINDINGS:Most (32 [58%] of 55 cases) group B streptococcus cases were due to serotype III and anti-serotype III streptococcus capsular IgG concentrations were higher in serotype III-matched controls than in cases (p<0·001). 0·120-0·266 μg/mL serotype III-specific IgG was estimated to confer 75-90% risk reduction against serotype III disease. A universal risk-concentration curve, aggregating results across all six serotypes, yielded similar results. Application of this curve to GBS6 immunogenicity data predicted maternal immunisation to be more than 80% efficacious for prevention of infant group B streptococcus disease. INTERPRETATION:Higher neonatal anti-capsular polysaccharide serum IgG concentration at birth correlated with reduced risk of infant group B streptococcus disease in Finland. Based on these results, a maternal group B streptococcus capsular conjugate vaccine currently in development is predicted to be efficacious. FUNDING:Pfizer.

Background:Vaccine candidate VLA15 is designed to protect against the dominant Borrelia genospecies-causing Lyme disease in North America and Europe. Active immunization with VLA15 has protected in the mouse model of tick challenge. VLA15 is currently under evaluation in clinical studies for the prevention of Lyme borreliosis. Methods:Mice were passively administered sera from clinical trial participants vaccinated with VLA15, or normal human serum from unvaccinated individuals as control. Posttransfer serum anti-outer surface protein A (OspA) immunoglobulin G titers were assessed by enzyme-linked immunosorbent assay. Following passive transfer, mice were challenged with Ixodes ticks colonized with Borrelia burgdorferi (OspA serotype 1) or Borrelia afzelii (OspA serotype 2) and infection was determined by serology for VlsE C6 or by polymerase chain reaction and culture to assess the presence of Borrelia bacteria. Results:Passive transfer of immune sera prevented transmission of Borrelia from the tick vector and protected mice against challenge. Posttransfer protective threshold immunoglobulin G antibody titers were observed in this animal model of 131 U/mL for B burgdorferi (OspA serotype 1) and 352 U/mL for B afzelii (serotype 2). Conclusions:Passive transfer of sera from trial participants immunized with VLA15 protected mice from borreliosis in a tick challenge model. This indicates that VLA15 induces functional immune responses in people that can be linked to efficacy in a stringent preclinical model.

Measurement of IgG antibodies against group B streptococcus (GBS) capsular polysaccharide (CPS) by use of a standardized and internationally accepted multiplex immunoassay is important for the evaluation of candidate maternal GBS vaccines in order to compare results across studies. A standardized assay is also required if serocorrelates of protection against invasive GBS disease are to be established in infant sera for the six predominant GBS serotypes since it would permit the comparison of results across the six serotypes. We undertook an interlaboratory study across five laboratories that used standardized assay reagents and protocols with a panel of 44 human sera to measure IgG antibodies against GBS CPS serotypes Ia, Ib, II, III, IV, and V. The within-laboratory intermediate precision, which included factors like the lot of coated beads, laboratory analyst, and day, was generally below 20% relative standard deviation (RSD) for all six serotypes, across all five laboratories. The cross-laboratory reproducibility was < 25% RSD for all six serotypes, which demonstrated the consistency of results across the different laboratories. Additionally, anti-CPS IgG concentrations for the 44-member human serum panel were established. The results of this study showed assay robustness and that the resultant anti-CPS IgG concentrations were reproducible across laboratories for the six GBS CPS serotypes when the standardized assay was used.