Annaliesa S. Anderson

A Novel Staphylococcus aureus Vaccine: Iron Surface Determinant B Induces Rapid Antibody Responses in Rhesus Macaques and Specific Increased Survival in a Murine S. aureus Sepsis Model

ABSTRACT Staphylococcus aureus is a major cause of nosocomial infections worldwide, and the rate of resistance to clinically relevant antibiotics, such as methicillin, is increasing; furthermore, there has been an increase in the number of methicillin-resistant S. aureus community-acquired infections. Effective treatment and prevention strategies are urgently needed. We investigated the potential of the S. aureus surface protein iron surface determinant B (IsdB) as a prophylactic vaccine against S. aureus infection. IsdB is an iron-sequestering protein that is conserved in diverse S. aureus clinical isolates, both methicillin resistant and methicillin sensitive, and it is expressed on the surface of all isolates tested. The vaccine was highly immunogenic in mice when it was formulated with amorphous aluminum hydroxyphosphate sulfate adjuvant, and the resulting antibody responses were associated with reproducible and significant protection in animal models of infection. The specificity of the protective immune responses in mice was demonstrated by using an S. aureus strain deficient for IsdB and HarA, a protein with a high level of identity to IsdB. We also demonstrated that IsdB is highly immunogenic in rhesus macaques, inducing a more-than-fivefold increase in antibody titers after a single immunization. Based on the data presented here, IsdB has excellent prospects for use as a vaccine against S. aureus disease in humans.

Sequence Diversity of the Factor H Binding Protein Vaccine Candidate in Epidemiologically Relevant Strains of Serogroup B Neisseria meningitidis

BACKGROUND Recombinant forms of Neisseria meningitidis human factor H binding protein (fHBP) are undergoing clinical trials in candidate vaccines against invasive meningococcal serogroup B disease. We report an extensive survey and phylogenetic analysis of the diversity of fhbp genes and predicted protein sequences in invasive clinical isolates obtained in the period 2000-2006. METHODS Nucleotide sequences of fhbp genes were obtained from 1837 invasive N. meningitidis serogroup B (MnB) strains from the United States, Europe, New Zealand, and South Africa. Multilocus sequence typing (MLST) analysis was performed on a subset of the strains. RESULTS Every strain contained the fhbp gene. All sequences fell into 1 of 2 subfamilies (A or B), with 60%-75% amino acid identity between subfamilies and at least 83% identity within each subfamily. One fHBP sequence may have arisen via inter-subfamily recombination. Subfamily B sequences were found in 70% of the isolates, and subfamily A sequences were found in 30%. Multiple fHBP variants were detected in each of the common MLST clonal complexes. All major MLST complexes include strains in both subfamily A and subfamily B. CONCLUSIONS The diversity of strains observed underscores the importance of studying the distribution of the vaccine antigen itself rather than relying on common epidemiological surrogates such as MLST.

Broad vaccine coverage predicted for a bivalent recombinant factor H binding protein based vaccine to prevent serogroup B meningococcal disease

Factor H binding proteins (fHBP), are bacterial surface proteins currently undergoing human clinical trials as candidate serogroup B Neisseria meningitidis (MnB) vaccines. fHBP protein sequences segregate into two distinct subfamilies, designated A and B. Here, we report the specificity and vaccine potential of mono- or bivalent fHBP-containing vaccines. A bivalent fHBP vaccine composed of a member of each subfamily elicited substantially broader bactericidal activity against MnB strains expressing heterologous fHBP than did either of the monovalent vaccines. Bivalent rabbit immune sera tested in serum bactericidal antibody assays (SBAs) against a diverse panel of MnB clinical isolates killed 87 of the 100 isolates. Bivalent human immune sera killed 36 of 45 MnB isolates tested in SBAs. Factors such as fHBP protein variant, PorA subtype, or MLST were not predictive of whether the MnB strain could be killed by rabbit or human immune sera. Instead, the best predictor for killing in the SBA was the level of in vitro surface expression of fHBP. The bivalent fHBP vaccine candidate induced immune sera that killed MnB isolates representing the major MLST complexes, prevalent PorA subtypes, and fHBP variants that span the breadth of the fHBP phylogenetic tree. Importantly, epidemiologically prevalent fHBP variants from both subfamilies were killed.

Vaccine review: "Staphyloccocus aureus vaccines: Problems and prospects"

Staphylococcus aureus is a leading cause of both healthcare- and community-associated infections globally. S. aureus exhibits diverse clinical presentations, ranging from benign carriage and superficial skin and soft tissue infections to deep wound and organ/space infections, biofilm-related prosthesis infections, life-threatening bacteremia and sepsis. This broad clinical spectrum, together with the high incidence of these disease manifestations and magnitude of the diverse populations at risk, presents a high unmet medical need and a substantial burden to the healthcare system. With the increasing propensity of S. aureus to develop resistance to essentially all classes of antibiotics, alternative strategies, such as prophylactic vaccination to prevent S. aureus infections, are actively being pursued in healthcare settings. Within the last decade, the S. aureus vaccine field has witnessed two major vaccine failures in phase 3 clinical trials designed to prevent S. aureus infections in either patients undergoing cardiothoracic surgery or patients with end-stage renal disease undergoing hemodialysis. This review summarizes the potential underlying reasons why these two approaches may have failed, and proposes avenues that may provide successful vaccine approaches to prevent S. aureus disease in the future.

Prevalence and genetic diversity of candidate vaccine antigens among invasive Neisseria meningitidis isolates in the United States

Neisseria meningitidis (Nm) serogroups B, C and Y are the major causes of meningococcal diseases in the United States. NmB accounts for ∼1/3 of the disease but no licensed vaccine is yet available. Two candidate vaccines are being developed specifically to target NmB, but may also provide protection against other serogroups. To assess the potential impact of these vaccines on NmB and other serogroups causing disease in the US, we determined the prevalence, genetic diversity and epidemiological characteristics of three candidate antigen genes in Nm isolates collected through Active Bacterial Core surveillance (ABCs), a population-based active surveillance program. fHbp was detected in all NmB, NmY and NmW135 isolates. Eleven NmC isolates contain fHbp with a single base-pair deletion creating a frame shift in the C-terminal region. Among NmB, 59% were FHbp subfamily/variant B/v1 and 41% A/v2-3. Among NmC and NmY, 39% and 3% were B/v1, respectively. nadA was detected in 39% of NmB, 61% of NmC and 4% of NmY. Among isolates tested, nhbA was present in all NmB and 96% of non-B. For the subset of strains sequenced for NadA and NhbA, pairwise identity was greater than 93% and 78%, respectively. The proportion of FHbp subfamily/variant was different between ABCs site and year, but no linear temporal trend was observed. Although assessment of the vaccine coverage also requires understanding of the antigen expression and the ability to induce bactericidal activity, our finding that all isolates contain one or more antigen genes suggests these candidate vaccines may protect against multiple Nm serogroups.

Detection of LP2086 on the cell surface of Neisseria meningitidis and its accessibility in the presence of serogroup B capsular polysaccharide

The outer membrane protein LP2086, a human factor H binding protein, is undergoing clinical trials as a vaccine against invasive serogroup B meningococcal (MnB) disease. As LP2086 is a surface protein, expression of capsular polysaccharide could potentially limit accessibility of anti-LP2086 antibodies to LP2086 expressed on the surface of bacteria. To determine whether variability in expression levels of the serogroup B capsule (Cap B) might interfere with accessibility of anti-LP2086 antibody binding to LP2086, we evaluated the ability of anti-Cap B and anti-LP2086 antibodies to bind to the surface of 1263 invasive clinical MnB strains by flow cytometry. One of the anti-LP2086 monoclonal antibodies used recognizes virtually all LP2086 sequence variants. Our results show no correlation between the amount of Cap B expressed and the binding of anti-LP2086 antibodies. Furthermore, the susceptibility of MnB bacteria to lysis by anti-LP2086 immune sera was independent of the level of Cap B expressed. The data presented in this paper demonstrates that Cap B does not interfere with the binding of antibodies to LP2086 expressed on the outer membrane of MnB clinical isolates.

Staphylococcus aureus Manganese Transport Protein C Is a Highly Conserved Cell Surface Protein That Elicits Protective Immunity Against S. aureus and Staphylococcus epidermidis

Staphylococcus aureus and other staphylococci cause severe human disease, and there are currently no vaccines available. We evaluated whether manganese transport protein C (MntC), which is conserved across the staphylococcal species group, could confer protection against S. aureus and Staphylococcus epidermidis. In vivo analysis of S. aureus MntC expression revealed that expression occurs very early during the infectious cycle. Active immunization with MntC was effective at reducing the bacterial load associated with S. aureus and S. epidermidis infection in an acute murine bacteremia model. Anti-MntC monoclonal antibodies have been identified that can bind S. aureus and S. epidermidis cells and are protective in an infant rat passive protection model and induce neutrophil respiratory burst activity. This is the first description of a protein that has the potential to provide protection across the staphylococcal species group.

High-Affinity Binding of the Staphylococcal HarA Protein to Haptoglobin and Hemoglobin Involves a Domain with an Antiparallel Eight-Stranded β-Barrel Fold

Iron scavenging from the host is essential for the growth of pathogenic bacteria. In this study, we further characterized two staphylococcal cell wall proteins previously shown to bind hemoproteins. HarA and IsdB harbor homologous ligand binding domains, the so called NEAT domain (for “near transporter”) present in several surface proteins of gram-positive pathogens. Surface plasmon resonance measurements using glutathione S-transferase (GST)-tagged HarAD1, one of the ligand binding domains of HarA, and GST-tagged full-length IsdB proteins confirmed high-affinity binding to hemoglobin and haptoglobin-hemoglobin complexes with equilibrium dissociation constants (KD) of 5 to 50 nM. Haptoglobin binding could be detected only with HarA and was in the low micromolar range. In order to determine the fold of this evolutionarily conserved ligand binding domain, the untagged HarAD1 protein was subjected to nuclear magnetic resonance spectroscopy, which revealed an eight-stranded, purely antiparallel β-barrel with the strand order (-β1↓-β2↑-β3↓-β6↑-β5↓-β4↑-β7↓-β8↑), forming two Greek key motifs. Based on structural-homology searches, the topology of the HarAD1 domain resembles that of the immunoglobulin (Ig) fold family, whose members are involved in protein-protein interactions, but with distinct structural features. Therefore, we consider that the HarAD1/NEAT domain fold is a novel variant of the Ig fold that has not yet been observed in other proteins.

Role of Factor H Binding Protein in Neisseria meningitidis Virulence and Its Potential as a Vaccine Candidate To Broadly Protect against Meningococcal Disease

SUMMARY Neisseria meningitidis is a Gram-negative microorganism that exists exclusively in humans and can cause devastating invasive disease. Although capsular polysaccharide-based vaccines against serogroups A, C, Y, and W135 are widely available, the pathway to a broadly protective vaccine against serogroup B has been more complex. The last 11 years has seen the discovery and development of the N. meningitidis serogroup B (MnB) outer membrane protein factor H binding protein (fHBP) as a vaccine component. Since the initial discovery of fHBP, a tremendous amount of work has accumulated on the diversity, structure, and regulation of this important protein. fHBP has proved to be a virulence factor for N. meningitidis and a target for functional bactericidal antibodies. fHBP is critical for survival of meningococci in the human host, as it is responsible for the primary interaction with human factor H (fH). Binding of hfH by the meningococcus serves to downregulate the host alternative complement pathway and helps the organism evade host innate immunity. Preclinical studies have shown that an fHBP-based vaccine can elicit serum bactericidal antibodies capable of killing MnB, and the vaccine has shown very encouraging results in human clinical trials. This report reviews our current knowledge of fHBP. In particular, we discuss the recent advances in our understanding of fHBP, its importance to N. meningitidis, and its potential role as a vaccine for preventing MnB disease.

Safety and immunogenicity of a meningococcal B bivalent rLP2086 vaccine in healthy toddlers aged 18-36 Months: a phase 1 randomized-controlled clinical trial

Background: A bivalent, recombinant, factor H–binding protein (rLP2086) vaccine was developed to protect against invasive Neisseria meningitidis serogroup B (MnB) in children and adolescents. Methods: Healthy toddlers (N = 99) were enrolled to 3 ascending dose-level cohorts (20, 60 or 200 &mgr;g). Within each cohort (n = 33), subjects were randomized to receive an initial formulation of the bivalent rLP2086 vaccine at 0, 1 and 6 months or hepatitis A vaccine/placebo control (2:1 ratio). Reactogenicity was assessed by parental reporting of local and systemic reactions using electronic diaries and reports of unsolicited adverse events. Immunogenicity was assessed by serum bactericidal activity assay using human complement and rLP2086-specific IgG binding. Results: The vaccine was considered to be well tolerated. Tenderness was the most frequently reported local reaction. Upper respiratory tract infection was the most commonly reported adverse event and occurred more frequently in the control group. Three cases (200 &mgr;g dose) of severe erythema that did not interfere with limb movement were reported. Four toddlers developed fever >40.0°C, 3 in the 200 &mgr;g group and 1 in the 60 &mgr;g group. Postdose 3, seroconversion (serum bactericidal activity assay using human complement ≥4-fold rise from baseline) was observed in 61.1–88.9% of participants against MnB strains expressing LP2086 variants homologous or nearly homologous to vaccine antigens and 11.1–44.4% against MnB strains expressing heterologous LP2086 variants. Seroconversion was observed in 77.8–100% of participants against additional, exploratory MnB strains expressing vaccine-homologous or heterologous LP2086 variants. Conclusions: This study shows that the bivalent rLP2086 vaccine is well tolerated and immunogenic in toddlers.