The utility of endotracheal aspirate bacteriology in identifying mechanically ventilated patients at risk for ventilator associated pneumonia: a single-center prospective observational study.

BACKGROUND: Ventilator-associated pneumonia (VAP) is a well-known, life-threatening disease that persists despite preventative measures and approved antibiotic therapies. This prospective observational study investigated bacterial airway colonization, and whether its detection and quantification in the endotracheal aspirate (ETA) is useful for identifying mechanically ventilated ICU patients who are at risk of developing VAP. METHODS: 240 patients admitted to 3 ICUs at the Lahey Hospital and Medical Center (Burlington, MA) between June 2014 and June 2015 and mechanically ventilated for > 2 days were included. ETA samples and clinical data were collected. Airway colonization was assessed, and subsequently categorized into "heavy" and "light" by semi-quantitative microbiological analysis of ETAs. VAP was diagnosed retrospectively by the study sponsor according to a pre-specified pneumonia definition. RESULTS: Pathogenic bacteria were isolated from ETAs of 125 patients. The most common species isolated was S. aureus (56.8%), followed by K. pneumoniae, P. aeruginosa, and E. coli (35.2% combined). VAP was diagnosed in 85 patients, 44 (51.7%) with no bacterial pathogen, 18 associated with S. aureus and 18 Gram-negative-only cases, and 5 associated with other Gram-positive or mixed species. A higher proportion of patients who were heavily colonized with S. aureus developed VAP (32.4%) associated with S. aureus compared to those lightly colonized (17.6%). The same tendency was seen for patients heavily and lightly colonized with Gram-negative pathogens (30.0 and 0.0%, respectively). Detection of S. aureus in the ETA preceded S. aureus VAP by approximately 4 days, while Gram-negative organisms were first detected 2.5 days prior to Gram-negative VAP. VAP was associated with significantly longer duration of mechanical ventilation and hospitalization regardless of microbiologic cause when compared to patients who did not develop VAP. CONCLUSIONS: The overall VAP rate was 35%. Heavy tracheal colonization supported identification of patients at higher risk of developing a corresponding S. aureus or Gram-negative VAP. Detection of bacterial ETA-positivity tended to precede VAP.

Randomized, Double-Blind, Placebo-Controlled, Single-Ascending-Dose Study of the Penetration of a Monoclonal Antibody Combination (ASN100) Targeting Staphylococcus aureus Cytotoxins in the Lung Epithelial Lining Fluid of Healthy Volunteers.

ASN100 is a novel antibody combination of two fully human IgG1(κ) monoclonal antibodies (MAbs), ASN-1 and ASN-2, which neutralize six Staphylococcus aureus cytotoxins, alpha-hemolysin (Hla) and five bicomponent leukocidins. We assessed the safety, tolerability, and serum and lung pharmacokinetics of ASN100 in a randomized, double-blind, placebo-controlled single-dose-escalation first-in-human study. Fifty-two healthy volunteers were enrolled and randomized to receive either ASN-1, ASN-2, a combination of both MAbs (ASN100), or a corresponding placebo. Thirty-two subjects in the double-blind dose escalation portion of the study received ASN-1 or ASN-2 at a 200-, 600-, 1,800-, or 4,000-mg dose, or placebo. Eight subjects received both MAbs simultaneously in a 1:1 ratio (ASN100) at 3,600 or 8,000 mg, or they received placebos. Twelve additional subjects received open-label ASN100 at 3,600 or 8,000 mg to assess the pharmacokinetics of ASN-1 and ASN-2 in epithelial lining fluid (ELF) by bronchoalveolar lavage fluid sampling. Subjects were monitored for 98 days (double-blind cohorts) or 30 days (open-label cohorts) for safety assessment. No dose-limiting toxicities were observed, and all adverse events were mild and transient, with only two adverse events considered possibly related to the investigational product. ASN100 exhibited linear serum pharmacokinetics with a half-life of approximately 3 weeks and showed detectable penetration into the ELF. No treatment-emergent anti-drug antibody responses were detected. The toxin neutralizing potency of ASN100 in human serum was confirmed up to 58 days postdosing. The favorable safety profile, ELF penetration, and maintained functional activity in serum supported the further clinical development of ASN100.

Context matters: The importance of dimerization-induced conformation of the LukGH leukocidin of Staphylococcus aureus for the generation of neutralizing antibodies.

LukGH (LukAB) is a potent leukocidin of Staphylococcus aureus that lyses human phagocytic cells and is thought to contribute to immune evasion. Unlike the other bi-component leukocidins of S. aureus, LukGH forms a heterodimer before binding to its receptor, CD11b expressed on professional phagocytic cells, and displays significant sequence variation. We employed a high diversity human IgG1 library presented on yeast cells to discover monoclonal antibodies (mAbs) neutralizing the cytolytic activity of LukGH. Recombinant LukG and LukH monomers or a LukGH dimer were used as capture antigens in the library selections. We found that mAbs identified with LukG or LukH as bait had no or very low toxin neutralization potency. In contrast, LukGH dimer-selected antibodies proved to be highly potent, and several mAbs were able to neutralize even the most divergent LukGH variants. Based on biolayer interferometry and mesoscale discovery, the high affinity antibody binding site on the LukGH complex was absent on the individual monomers, suggesting that it was generated upon formation of the LukG-LukH dimer. X-ray crystallography analysis of the complex between the LukGH dimer and the antigen-binding fragment of a very potent mAb (PDB code 5K59) indicated that the epitope is located in the predicted cell binding region (rim domain) of LukGH. The corresponding IgG inhibited the binding of LukGH dimer to target cells. Our data suggest that knowledge of the native conformation of target molecules is essential to generate high affinity and functional mAbs.

Bactericidal monoclonal antibodies specific to the lipopolysaccharide O antigen from multidrug-resistant Escherichia coli clone ST131-O25b:H4 elicit protection in mice.

The Escherichia coli sequence type 131 (ST131)-O25b:H4 clone has spread worldwide and become responsible for a significant proportion of multidrug-resistant extraintestinal infections. We generated humanized monoclonal antibodies (MAbs) that target the lipopolysaccharide O25b antigen conserved within this lineage. These MAbs bound to the surface of live bacterial cells irrespective of the capsular type expressed. In a serum bactericidal assay in vitro, MAbs induced >95% bacterial killing in the presence of human serum as the complement source. Protective efficacy at low antibody doses was observed in a murine model of bacteremia. The mode of action in vivo was investigated by using aglycosylated derivatives of the protective MAbs. The significant binding to live E. coli cells and the in vitro and in vivo efficacy were corroborated in assays using bacteria grown in human serum to mimic relevant clinical conditions. Given the dry pipeline of novel antibiotics against multidrug-resistant Gram-negative pathogens, passive immunization with bactericidal antibodies offers a therapeutic alternative to control infections caused by E. coli ST131-O25b:H4.

Five birds, one stone: neutralization of α-hemolysin and 4 bi-component leukocidins of Staphylococcus aureus with a single human monoclonal antibody.

Staphylococcus aureus is a major human pathogen associated with high mortality. The emergence of antibiotic resistance and the inability of antibiotics to counteract bacterial cytotoxins involved in the pathogenesis of S. aureus call for novel therapeutic approaches, such as passive immunization with monoclonal antibodies (mAbs). The complexity of staphylococcal pathogenesis and past failures with single mAb products represent considerable barriers for antibody-based therapeutics. Over the past few years, efforts have focused on neutralizing α-hemolysin. Recent findings suggest that the concerted actions of several cytotoxins, including the bi-component leukocidins play important roles in staphylococcal pathogenesis. Therefore, we aimed to isolate mAbs that bind to multiple cytolysins by employing high diversity human IgG1 libraries presented on the surface of yeast cells. Here we describe cross-reactive antibodies with picomolar affinity for α-hemolysin and 4 different bi-component leukocidins that share only ∼26% overall amino acid sequence identity. The molecular basis of cross-reactivity is the recognition of a conformational epitope shared by α-hemolysin and F-components of gamma-hemolysin (HlgAB and HlgCB), LukED and LukSF (Panton-Valentine Leukocidin). The amino acids predicted to form the epitope are conserved and known to be important for cytotoxic activity. We found that a single cross-reactive antibody prevented lysis of human phagocytes, epithelial and red blood cells induced by α-hemolysin and leukocidins in vitro, and therefore had superior effectiveness compared to α-hemolysin specific antibodies to protect from the combined cytolytic effect of secreted S. aureus toxins. Such mAb afforded high levels of protection in murine models of pneumonia and sepsis.

TLR ligands upregulate RIG-I expression in human plasmacytoid dendritic cells in a type I IFN-independent manner.

Plasmacytoid dendritic cells (pDCs) are professional type I interferon (IFN)-producing cells that play an essential role in antiviral immunity. In many cell types, detection of intracellular pathogens is mostly dependent on endosomal Toll-like receptors (TLRs) and cytosolic sensors, such as retinoic acid-inducible gene I (RIG-I). However, the possible interplay between these two systems has not yet been elucidated. Here we aimed to study the collaboration of endosomal TLRs and RIG-I in primary human pDCs. We found that under steady-state conditions, pDCs express RIG-I at very low level, but the expression of this receptor is rapidly and dramatically upregulated upon stimulation by the TLR7 ligand imiquimod or the TLR9 ligand type A CpG. We also demonstrated that pDCs are able to sense and respond to 5'-triphosphate double-stranded RNA (5'-ppp-dsRNA) only following activation by endosomal TLRs. Experiments on primary pDCs with functionally blocked IFN-α/ß receptor 1 (IFNAR1) and those on human pDC leukemia (pDC-L) cells defective in type I IFN secretion indicated that the upregulation of RIG-I expression in pDCs upon stimulation by endosomal TLR occurs in a type I IFN-independent manner. Selective phosphorylation of signal transducer and activator of transcription 1 (STAT1) on tyrosine 701 could be identified as an early signaling event in this process. Our results show that in contrast to many other cell types, where RIG-I expression is induced by type I IFN, in pDCs a disparate mechanism is responsible for the upregulation of RIG-I. Our findings also indicate that along with autophagy, an additional mechanism is operating in pDCs to promote the detection of replicating viruses.

Diagnostic potential of monoclonal antibodies specific to the unique O-antigen of multidrug-resistant epidemic Escherichia coli clone ST131-O25b:H4.

The Escherichia coli lineage sequence type 131 (ST131)-O25b:H4 is a globally spread multidrug-resistant clone responsible for a great proportion of extraintestinal infections. Driven by the significant medical needs associated with this successful pathogenic lineage, we generated murine monoclonal antibodies (MAbs) against its lipopolysaccharide (LPS) O25b antigen in order to develop quick diagnostic tests. Murine monoclonal antibodies were generated by immunizing mice with whole killed nonencapsulated ST131-O25b E. coli cells and screening hybridoma supernatants for binding to purified LPS molecules obtained from an E. coli ST131-O25b clinical isolate. The MAbs selected for further study bound to the surface of live E. coli O25b strains irrespective of the capsular type expressed, while they did not bind to bacteria or purified LPS from other serotypes, including the related classical O25 antigen (O25a). Using these specific MAbs, we developed a latex bead-based agglutination assay that has greater specificity and is quicker and simpler than the currently available typing methods. The high specificities of these MAbs can be explained by the novel structure of the O25b repeating unit elucidated in this article. Based on comparative analysis by nuclear magnetic resonance (NMR) and mass spectrometry, the N-acetyl-fucose in the O25a O-antigen had been replaced by O-acetyl-rhamnose in the O25b repeating unit. The genetic determinants responsible for this structural variation were identified by aligning the corresponding genetic loci and were confirmed by trans-complementation of a rough mutant by the subserotype-specific fragments of the rfb operons.

Modulatory effects of low-dose hydrogen peroxide on the function of human plasmacytoid dendritic cells.

Under normal conditions, plasmacytoid dendritic cells (pDCs) are located in peripheral lymphoid organs or circulate in the blood, from where they can migrate to sites of infection or inflammation. In inflamed tissues, pDCs can be exposed to elevated levels of reactive oxygen species produced by inflammatory cells and we presume that oxidative stress could affect the cellular responses of pDCs to microenvironmental stimuli. To explore this possibility, human pDCs isolated from peripheral blood of healthy donors were treated with H(2)O(2) and R837 (a Toll-like receptor 7 ligand), separately and in combination. Our results demonstrate that treatment with a low concentration (0.01 µM) of H(2)O(2) resulted in only slight changes in the expression of CD40, CD80, CD86, and CD83; however, low-dose H(2)O(2) markedly decreased the expression of HLA-DQ on pDCs. Exposure to H(2)O(2) did not trigger the release of IL-6, TNF-α, IL-8, or IFN-α from pDCs. Although addition of H(2)O(2) did not modify the capacity of pDCs to activate allogeneic IL-17- or IFN-γ-producing T cells, it significantly increased the ability of pDCs to stimulate IL-4-secreting T cells. Exposure of pDCs to H(2)O(2) before cocultivation with naïve autologous T cells significantly lowered IL-10 production by T cells, but did not affect IL-17 release. It was also observed that H(2)O(2)-exposed pDCs provided stronger stimuli for Th2 than for Th1 differentiation upon autologous activation, compared to untreated pDCs, possibly because of elevated surface expression of OX40-L. Most importantly, when pDCs were stimulated with R837 in the presence of H(2)O(2), decreased phenotypic activation, decreased chemokine and cytokine release, and impaired allo- and autostimulatory functions of pDCs were detected, indicating that pDCs exposed to oxidative stress in vivo may have an anti-inflammatory or tolerogenic role in regulating adaptive immune responses.

Th17/Th1 biased immunity to the pneumococcal proteins PcsB, StkP and PsaA in adults of different age.

Streptococcus pneumoniae is a major human pathogen, causing high morbidity and mortality in children, and also in the elderly, who are particularly susceptible to S. pneumoniae infections due to the dysregulated function of the aged immune system. As the current generation of polysaccharide vaccines do not provide sufficient protection for elderly, new vaccination strategies are urgently needed. To learn whether pneumococcal proteins are able to induce adaptive immune responses in adults in different age groups, we determined serum IgG antibody titers and T cell immunity (IFN-γ, IL-17A and IL-5 production) to three pneumococcal antigens, PcsB, StkP and PsaA, that are components of an investigational protein-based pneumococcal vaccine, IC47. Therefore, sera and PBMCs of 108 healthy adults in three different age groups (young, middle-aged and elderly) were analyzed by ELISA and ELISpot, respectively. We found naturally acquired antibodies to all three proteins in all age groups against all three antigens. However, elderly individuals had significantly lower IgG levels to PcsB and PsaA compared to those of younger donors. There was no significant age-related difference in the overall rate of T cell immunity for the three pneumococcal proteins. We found that the Th17 response was dominant in all age groups and was frequently combined with a Th1 or Th2 response in young and middle-aged subjects. However, in elderly persons there was a lower percentage of PBMC samples producing more than one cytokine upon antigenic stimulation. The narrow cytokine secretion pattern was the most striking difference between elderly and younger adult age groups. Our results demonstrate that in the majority of adults there is a naturally acquired humoral and cellular immune response to the three pneumococcal proteins tested. The dominance of the Th17 response is especially interesting in the light of new insights regarding the role of Th17 cells in mucosal protection against this pathogen.

Pollen-induced oxidative stress influences both innate and adaptive immune responses via altering dendritic cell functions.

It has been demonstrated that pollen grains contain NAD(P)H oxidases that induce oxidative stress in the airways, and this oxidative insult is critical for the development of allergic inflammation in sensitized mice. On the basis of this observation, we have examined whether pollen grain exposure triggers oxidative stress in dendritic cells (DCs), altering their functions. To test this hypothesis, human monocyte-derived DCs were treated with ragweed pollen grains. Our findings show that exposure to pollen grains induces an increase in the intracellular levels of reactive oxygen species in DCs. Our data also indicate that besides the NAD(P)H oxidases, other component(s) of pollen grains contributes to this phenomenon. Elevated levels of intracellular reactive oxygen species triggered the production of IL-8 as well as proinflammatory cytokines, such as TNF-alpha and IL-6. Treatment with pollen grains initiated the maturation of DCs, strongly upregulated the membrane expression of CD80, CD86, CD83, and HLA-DR, and caused only a slight increase in the expression of CD40. The pollen-treated DCs induced the development of naive T lymphocytes toward effector T cells with a mixed profile of cytokine production. Antioxidant inhibited both the phenotypic and functional changes of DCs, underlining the importance of oxidative stress in these processes. Collectively, these data show that pollen exposure-induced oxidative stress may contribute to local innate immunity and participate in the initiation of adaptive immune responses to pollen Ags.

Dendritic cell subtypes as primary targets of vaccines: the emerging role and cross-talk of pattern recognition receptors.

Preventive vaccination is the most successful approach against infectious diseases and has a great impact on world health. Vaccines operate through the activation of innate immunity that helps to stimulate antigen-specific T- and B-lymphocytes. These events are orchestrated by dendritic cells (DCs) that are able to sample foreign structures and concomitantly sense 'danger signals'. Thus, DCs provide a functional link between innate and acquired immunity, and due to their regulatory potential are referred to as natural adjuvants. Human conventional and plasmacytoid DCs express different sets of well-characterized Toll-like membrane receptors (TLRs) that recognize a broad range of conserved molecular patterns of pathogens. The recently discovered cytosolic Nod-like receptors (NLRs) and RIG-like helicases (RLHs) also turned out to participate in pathogen recognition and modulation of immune responses through interacting signaling pathways. As a result of their collaboration, the TLR, NLR and RLH recognition systems induce the secretion of different combinations of cytokines that play a fundamental role in T-cell activation and instruction. Ligands of the innate recognition systems emerge as new adjuvants for vaccine design, whereas manipulation of the signaling pathways mediated by these receptors offers new avenues for fine tuning immune responses and optimizing immunotherapies.

Novel and recurrent STAT3 mutations in hyper-IgE syndrome patients from different ethnic groups.

We performed clinical, immunological and genetic studies of 12 hyper-IgE syndrome (HIES) patients from 4 Hungarian, 2 Lebanese, one Russian, one Polish, and one Swedish families with autosomal dominant (AD) or sporadic forms of the disease to reveal cross-ethnicity of recurrent and novel mutations in the signal transducer and activator of transcription-3 gene (STAT3). Four patients from 3 Hungarian families, and one Russian, and one Swedish patient carried the heterozygous R382W germline mutation at the DNA-binding site of STAT3. The recurrent V637M mutation affecting the SRC homology 2 (SH2) domain was detected in one Lebanese and one Polish family, and the V463del deletion located in the DNA-binding domain was unveiled in another Lebanese family. A novel H332Y mutation affecting the DNA-binding site of STAT3 in three Hungarian patients from a Gypsy family was also found. The segregation of this mutation with HIES, restriction fragment length polymorphism analysis of STAT3 from patients and controls and the negligible production upon IL-6 stimulation of monocyte chemotactic protein-1 by the patient's blood mononuclear cells suggested that the H332Y mutation was disease-causing. These data suggest, that dominant negative mutations of the DNA-binding and SH2 domains of STAT3 cause AD and sporadic cases of HIES in different ethnic groups with R382W as the predominant mutation found in 5 of the 9 families. Functional and genetic data support that the novel H332Y mutation may result in the loss of function of STAT3 and leads to the HIES phenotype.

Identification of plasmacytoid pre-dendritic cells by one-color flow cytometry for phenotype screening.

Plasmacytoid pre-dendritic cells (pDCs) are able to prime and polarize naive T-cells, while also having an important effector function in antiviral immunity through the rapid and robust production of interferon-alpha. The main setback of pDCs investigation is the rarity and ex vivo fragility of these cells. Relative simple, reliable, and accurate methods for phenotypic analysis and functional studies of pDCs without isolation would be a great deal of interest. Fresh whole blood samples were analyzed by two-color and one-color flow cytometric pDC-identification assays. The changes in the surface expression of CD62L and HLA-DQ on pDCs in whole blood samples after 24-h treatment with imiquimod, a toll-like receptor 7 agonist, were analyzed. Our data demonstrate that the identification of pDCs in peripheral blood samples can be achieved by using only one fluorescent channel for blood dendritic cell antigen (BDCA)-4 staining combined with the light scatter parameters, thus leaving the other channels open for further phenotypic and/or functional analysis. Recently, several lines of evidence supported the involvement of pDCs in the development of several human diseases, so our new one-color identification approach may provide a useful tool for investigation of the pathomechanism of the relevant diseases by using common, 2-laser benchtop cytometers.