A novel anti-PcrV antibody providing enhanced protection against Pseudomonas aeruginosa in multiple animal infection models.

Pseudomonas aeruginosa is a major cause of hospital-acquired infections, particularly in mechanically ventilated patients, and it is the leading cause of death in cystic fibrosis patients. A key virulence factor associated with disease severity is the P. aeruginosa type III secretion system (T3SS), which injects bacterial toxins directly into the cytoplasm of host cells. The PcrV protein, located at the tip of the T3SS injectisome complex, is required for T3SS function and is a well-validated target in animal models of immunoprophylactic strategies targeting P. aeruginosa. In an effort to identify a highly potent and protective monoclonal antibody (MAb) that inhibits the T3SS, we generated and characterized a panel of novel anti-PcrV MAbs. Interestingly, some MAbs exhibiting potent inhibition of T3SS in vitro failed to provide protection in a mouse model of P. aeruginosa infection, suggesting that effective in vivo inhibition of T3SS with anti-PcrV MAbs is epitope dependent. V2L2MD, while not the most potent MAb as assessed by in vitro cytotoxicity inhibition assays, provided strong prophylactic protection in several murine infection models and a postinfection therapeutic model. V2L2MD mediated significantly (P < 0.0001) better in vivo protection than that provided by a comparator antibody, MAb166, a well-characterized anti-PcrV MAb and the progenitor of a clinical candidate, KB001-A. The results described here support further development of a V2L2MD-containing immunotherapeutic and may suggest even greater potential than was previously recognized for the prevention and treatment of P. aeruginosa infections in high-risk populations.

Early diagnostic BioMARKers in exacerbations of chronic obstructive pulmonary disease: protocol of the exploratory, prospective, longitudinal, single-centre, observational MARKED study.

INTRODUCTION: Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) play a pivotal role in the burden and progressive course of chronic obstructive pulmonary disease (COPD). As such, disease management is predominantly based on the prevention of these episodes of acute worsening of respiratory symptoms. However, to date, personalised prediction and early and accurate diagnosis of AECOPD remain unsuccessful. Therefore, the current study was designed to explore which frequently measured biomarkers can predict an AECOPD and/or respiratory infection in patients with COPD. Moreover, the study aims to increase our understanding of the heterogeneity of AECOPD as well as the role of microbial composition and hostmicrobiome interactions to elucidate new disease biology in COPD. METHODS AND ANALYSIS: The 'Early diagnostic BioMARKers in Exacerbations of COPD' study is an exploratory, prospective, longitudinal, single-centre, observational study with 8-week follow-up enrolling up to 150 patients with COPD admitted to inpatient pulmonary rehabilitation at Ciro (Horn, the Netherlands). Respiratory symptoms, vitals, spirometry and nasopharyngeal, venous blood, spontaneous sputum and stool samples will be frequently collected for exploratory biomarker analysis, longitudinal characterisation of AECOPD (ie, clinical, functional and microbial) and to identify host-microbiome interactions. Genomic sequencing will be performed to identify mutations associated with increased risk of AECOPD and microbial infections. Predictors of time-to-first AECOPD will be modelled using Cox proportional hazards' regression. Multiomic analyses will provide a novel integration tool to generate predictive models and testable hypotheses about disease causation and predictors of disease progression. ETHICS AND DISSEMINATION: This protocol was approved by the Medical Research Ethics Committees United (MEC-U), Nieuwegein, the Netherlands (NL71364.100.19). TRIAL REGISTRATION NUMBER: NCT05315674.

Associations of pathogen-specific and host-specific characteristics with disease outcome in patients with Staphylococcus aureus bacteremic pneumonia.

OBJECTIVE: To understand the relationships of Staphylococcus aureus (SA) bacteremic pneumonia (SABP) outcome with patient-specific and SA-specific variables. METHODS: We analysed SA bloodstream isolates and matching sera in SABP patients by sequencing SA isolates (n = 50) and measuring in vitro AT production, haemolytic activity and expression of ClfA and ClfB. Controls were sera from gram-negative bacteremia patients with or without pneumonia and uninfected subjects. Levels of IgGs, IgMs and neutralizing antibodies (NAbs) against SA antigens were quantified and analysed by one-way ANOVA. Associations of patient outcomes with patient variables, antibody levels and isolate characteristics were evaluated by univariate and multivariate logistic regression analyses. RESULTS: SABP patients had higher levels of IgGs against eight virulence factors and anti-alpha toxin (AT) NAbs than uninfected controls. Levels of IgG against AT and IgMs against ClfA, FnbpA and SdrC were higher in clinically cured SABP patients than in clinical failures. Anti-LukAB NAb levels were elevated in all cohorts. Increased odds of cure correlated with higher haemolytic activity of SA strains, longer time between surgery and bacteremia (> 30 days), longer duration of antibiotic therapy, lower acute physiology and total APACHE II scores, lack of persistent fever for > 72 h and higher levels of antibodies against AT (IgG), ClfA (IgM), FnbpA (IgM) and SdrC (IgM). DISCUSSION: Limitations included the cross-sectional observational nature of the study, small sample size and inability to measure antibody levels against all SA virulence factors. CONCLUSION: Our results suggest that SABP patients may benefit from immunotherapy targeting multiple SA antigens.

Staphylococcus aureus drives expansion of low-density neutrophils in diabetic mice.

Diabetic individuals are at considerable risk for invasive infection by Staphylococcus aureus, however, the mechanisms underlying this enhanced susceptibility to infection are unclear. We observed increased mortality following i.v. S. aureus infection in diabetic mice compared with nondiabetic controls, correlating with increased numbers of low-density neutrophils (LDNs) and neutrophil extracellular traps (NETs). LDNs have been implicated in the inflammatory pathology of diseases such as lupus, given their release of large amounts of NETs. Our goal was to describe what drives LDN increases during S. aureus infection in the diabetic host and mechanisms that promote increased NET production by LDNs. LDN development is dependent on TGF-ß, which we found to be more activated in the diabetic host. Neutralization of TGF-ß, or the TGF-ß-activating integrin αvß8, reduced LDN numbers and improved survival during S. aureus infection. Targeting S. aureus directly with MEDI4893*, an α toxin-neutralizing monoclonal antibody, blocked TGF-ß activation, reduced LDNs and NETs, and significantly improved survival. A comparison of gene and protein expression in high-density neutrophils and LDNs identified increased GPCRs and elevated phosphatase and tensin homolog (PTEN) in the LDN subset. Inhibition of PTEN improved the survival of infected diabetic mice. Our data identify a population of neutrophils in infected diabetic mice that correlated with decreased survival and increased NET production and describe 3 therapeutic targets, a bacterial target and 2 host proteins, that prevented NET production and improved survival.

Structure and characterization of a high affinity C5a monoclonal antibody that blocks binding to C5aR1 and C5aR2 receptors.

C5a is a potent anaphylatoxin that modulates inflammation through the C5aR1 and C5aR2 receptors. The molecular interactions between C5a-C5aR1 receptor are well defined, whereas C5a-C5aR2 receptor interactions are poorly understood. Here, we describe the generation of a human antibody, MEDI7814, that neutralizes C5a and C5adesArg binding to the C5aR1 and C5aR2 receptors, without affecting complement-mediated bacterial cell killing. Unlike other anti-C5a mAbs described, this antibody has been shown to inhibit the effects of C5a by blocking C5a binding to both C5aR1 and C5aR2 receptors. The crystal structure of the antibody in complex with human C5a reveals a discontinuous epitope of 22 amino acids. This is the first time the epitope for an antibody that blocks C5aR1 and C5aR2 receptors has been described, and this work provides a basis for molecular studies aimed at further understanding the C5a-C5aR2 receptor interaction. MEDI7814 has therapeutic potential for the treatment of acute inflammatory conditions in which both C5a receptors may mediate inflammation, such as sepsis or renal ischemia-reperfusion injury.

Anti-LPS antibodies protect against Klebsiella pneumoniae by empowering neutrophil-mediated clearance without neutralizing TLR4.

Initial promising results with immune sera guided early human mAb approaches against Gram-negative sepsis to an LPS neutralization mechanism, but these efforts failed in human clinical trials. Emergence of multidrug resistance has renewed interest in pathogen-specific mAbs. We utilized a pair of antibodies targeting Klebsiella pneumoniae LPS, one that both neutralizes LPS/TLR4 signaling and mediates opsonophagocytic killing (OPK) (54H7) and one that only promotes OPK (KPE33), to better understand the contribution of each mechanism to mAb protection in an acutely lethal pneumonia model. Passive immunization 24 hours prior to infection with KPE33 protected against lethal infection significantly better than 54H7, while delivery of either mAb 1 hour after infection resulted in similar levels of protection. These data suggest that early neutralization of LPS-induced signaling limits protection afforded by these mAbs. LPS neutralization prevented increases in the numbers of γδT cells, a major producer of the antimicrobial cytokine IL-17A, the contribution of which was confirmed using il17a-knockout mice. We conclude that targeting LPS for OPK without LPS signaling neutralization has potential to combat Gram-negative infection by engaging host immune defenses, rather than inhibiting beneficial innate immune pathways.

Enhancement of antibody functions through Fc multiplications.

Antibodies carry out a plethora of functions through their crystallizable fragment (Fc) regions, which can be naturally tuned by the adoption of several isotypes and post-translational modifications. Protein engineering enables further Fc function modulations through modifications of the interactions between the Fc and its functional partners, including FcγR, FcRn, complement complex, and additions of auxiliary functional units. Due to the many functions embedded within the confinement of an Fc, a suitable balance must be maintained for a therapeutic antibody to be effective and safe. The outcome of any Fc engineering depends on the interplay among all the effector molecules involved. In this report, we assessed the effects of Fc multiplication (or tandem Fc) on antibody functions. Using IgG1 as a test case, we found that, depending on the specifically designed linker, Fc multiplication led to differentially folded, stable molecules with unique pharmacokinetic profiles. Interestingly, the variants with 3 copies of Fc improved in vitro opsonophagocytic killing activity and displayed significantly improved protective efficacies in a Klebsiella pneumoniae mouse therapeutic model despite faster clearance compared with its IgG1 counterpart. There was no adverse effect observed or pro-inflammatory cytokine release when the Fc variants were administered to animals. We further elucidated that enhanced binding to various effector molecules by IgG-3Fc created a "sink" leading to the rapid clearance of the 3Fc variants, and identified the increased FcRn binding as one strategy to facilitate "sink" escape. These findings reveal new opportunities for novel Fc engineering to further expand our abilities to manipulate and improve antibody therapeutics.

Anti-MrkA Monoclonal Antibodies Reveal Distinct Structural and Antigenic Features of MrkA.

Antibody therapy against antibiotics resistant Klebsiella pneumoniae infections represents a promising strategy, the success of which depends critically on the ability to identify appropriate antibody targets. Using a target-agnostic strategy, we recently discovered MrkA as a potential antibody target and vaccine antigen. Interestingly, the anti-MrkA monoclonal antibodies isolated through phage display and hybridoma platforms all recognize an overlapping epitope, which opens up important questions including whether monoclonal antibodies targeting different MrkA epitopes can be generated and if they possess different protective profiles. In this study we generated four anti-MrkA antibodies targeting different epitopes through phage library panning against recombinant MrkA protein. These anti-MrkA antibodies elicited strong in vitro and in vivo protections against a multi-drug resistant Klebsiella pneumoniae strain. Furthermore, mutational and epitope analysis suggest that the two cysteine residues may play essential roles in maintaining a MrkA structure that is highly compacted and exposes limited antibody binding/neutralizing epitopes. These results suggest the need for further in-depth understandings of the structure of MrkA, the role of MrkA in the pathogenesis of Klebsiella pneumoniae and the protective mechanism adopted by anti-MrkA antibodies to fully explore the potential of MrkA as an efficient therapeutic target and vaccine antigen.

Immune stealth-driven O2 serotype prevalence and potential for therapeutic antibodies against multidrug resistant Klebsiella pneumoniae.

Emerging multidrug-resistant bacteria are a challenge for modern medicine, but how these pathogens are so successful is not fully understood. Robust antibacterial vaccines have prevented and reduced resistance suggesting a pivotal role for immunity in deterring antibiotic resistance. Here, we show the increased prevalence of Klebsiella pneumoniae lipopolysaccharide O2 serotype strains in all major drug resistance groups correlating with a paucity of anti-O2 antibodies in human B cell repertoires. We identify human monoclonal antibodies to O-antigens that are highly protective in mouse models of infection, even against heavily encapsulated strains. These antibodies, including a rare anti-O2 specific antibody, synergistically protect against drug-resistant strains in adjunctive therapy with meropenem, a standard-of-care antibiotic, confirming the importance of immune assistance in antibiotic therapy. These findings support an antibody-based immunotherapeutic strategy even for highly resistant K. pneumoniae infections, and underscore the effect humoral immunity has on evolving drug resistance.

Effects of low-level inhalation exposure to cyclosarin on learned behaviors in Sprague-Dawley rats.

Behavioral and biochemical effects of low-level whole-body inhalation exposure to the chemical warfare nerve agent cyclosarin (GF) were evaluated. Sprague-Dawley rats were first trained on a variable-interval, 56-s (VI56) schedule of food reinforcement. The VI56 schedule specifies that a single lever press, following an average interval of 56 s, produces food reinforcement (i.e., a single food pellet). Subjects were then exposed to GF vapor at concentrations of 1.6-5.2 mg/m3, or air control, for 60 min. Following exposures, performance on the VI56 and acquisition and maintenance of a radial-arm maze (RAM) spatial memory task were evaluated during 55 test sessions over approximately 11 wk. GF exposures produced miosis in all subjects and other mild clinical signs of toxicity at the highest concentration. Convulsions were not observed in any subjects. GF exposures produced concentration-dependent decreases in acetylcholinesterase and butyrylcholinesterase activity. Additionally, blood assays revealed concentration-dependent levels of regenerated GF, thus verifying systemic exposure. The largest concentration of GF disrupted performance on the VI56 task. The deficit, however, resolved by the third postexposure test session. All subjects acquired, and maintained, performance on the RAM task, and no significant differences were seen as a result of GF exposure. No delayed effects from exposures were observed. These results demonstrate that, in rats, inhalation exposure to GF at levels below those producing convulsions and other severe clinical signs of toxicity may produce performance deficits on learned behaviors, but the deficits appear to not be persistent.

Complement C5a induces PD-L1 expression and acts in synergy with LPS through Erk1/2 and JNK signaling pathways.

Severe bacterial infection results in both uncontrolled inflammation and immune suppression in septic patients. Although there is ample evidence that complement activation provokes overwhelming pro-inflammatory responses, whether or not it plays a role in immune suppression in this case is unclear. Here, we identify that complement C5a directly participates in negative regulation of immune responses to bacteria-induced inflammation in an ex vivo model of human whole blood. Challenge of whole blood with heat-killed Pseudomonas aeruginosa induces PD-L1 expression on monocytes and the production of IL-10 and TGF-ß, which we show to be inhibited by C5a blockade. The induction of PD-L1 expression by C5a is via C5aR1but not C5aR2. Furthermore, C5a synergises with P. aeruginosa LPS in both PD-L1 expression and the production of IL-10 and TGF-ß. Mechanistically, C5a contributes to the synergy in PD-L1 expression by specifically activating Erk1/2 and JNK signaling pathways. Our study reveals a new role for C5a in directly promoting immunosuppressive responses. Therefore, aberrant production of complement C5a during bacterial infection could have broader effect on compromising host defense including the induction of immune suppression.

A multifunctional bispecific antibody protects against Pseudomonas aeruginosa.

Widespread drug resistance due to empiric use of broad-spectrum antibiotics has stimulated development of bacteria-specific strategies for prophylaxis and therapy based on modern monoclonal antibody (mAb) technologies. However, single-mechanism mAb approaches have not provided adequate protective activity in the clinic. We constructed multifunctional bispecific antibodies, each conferring three mechanisms of action against the bacterial pathogen Pseudomonas aeruginosa by targeting the serotype-independent type III secretion system (injectisome) virulence factor PcrV and persistence factor Psl exopolysaccharide. A new bispecific antibody platform, BiS4, exhibited superior synergistic protection against P. aeruginosa-induced murine pneumonia compared to parent mAb combinations or other available bispecific antibody structures. BiS4αPa was protective in several mouse infection models against disparate P. aeruginosa strains and unexpectedly further synergized with multiple antibiotic classes even against drug-resistant clinical isolates. In addition to resulting in a multimechanistic clinical candidate (MEDI3902) for the prevention or treatment of P. aeruginosa infections, these antibody studies suggest that multifunctional antibody approaches may be a promising platform for targeting other antibiotic-resistant bacterial pathogens.

Identification of broadly protective human antibodies to Pseudomonas aeruginosa exopolysaccharide Psl by phenotypic screening.

Pseudomonas aeruginosa is a leading cause of hospital-associated infections in the seriously ill, and the primary agent of chronic lung infections in cystic fibrosis patients. A major obstacle to effective control of P. aeruginosa infections is its intrinsic resistance to most antibiotic classes, which results from chromosomally encoded drug-efflux systems and multiple acquired resistance mechanisms selected by years of aggressive antibiotic therapy. These factors demand new strategies and drugs to prevent and treat P. aeruginosa infections. Herein, we describe a monoclonal antibody (mAb) selection strategy on whole P. aeruginosa cells using single-chain variable fragment phage libraries derived from healthy individuals and patients convalescing from P. aeruginosa infections. This approach enabled identification of mAbs that bind three distinct epitopes on the product of the Psl. This exopolysaccharide is important for P. aeruginosa attachment to mammalian cells, and for the formation and maintenance of biofilms produced by nonmucoid and mucoid P. aeruginosa isolates. Functional screens revealed that mAbs to one epitope exhibit superior activity in opsonophagocytic killing and cell attachment assays, and confer significant protection in multiple animal models. Our results indicate that Psl is an accessible serotype-independent surface feature and promising novel protective antigen for preventing P. aeruginosa infections. Furthermore, our mAb discovery strategy holds promise for application to other bacterial pathogens.

Potent immune responses and in vitro pro-inflammatory cytokine suppression by a novel adenovirus vaccine vector based on rare human serotype 28.

Adenovirus vaccine vectors derived from rare human serotypes have been shown to be less potent than serotype 5 (Ad5) at inducing immune responses to encoded antigens. To identify highly immunogenic adenovirus vectors, we assessed pro-inflammatory cytokine expression, binding to the CD46 receptor, and immunogenicity. Species D adenoviruses uniquely suppressed pro-inflammatory cytokines and induced high levels of type I interferon. Thus, it was unexpected that a vector derived from a representative serotype, Ad28, induced significantly higher transgene-specific T cell responses than an Ad35 vector. Prime-boost regimens with Ad28, Ad35, Ad14, or Ad5 significantly boosted T cell and antibody responses. The seroprevalence of Ad28 was confirmed to be <10% in the United States. Together, this shows that a rare human serotype-based vector can elicit strong immune responses, which was not predicted by in vitro results.