Development of a Kinetic ELISA and Reactive B Cell Frequency Assay to Detect Respiratory Syncytial Virus Pre-Fusion F Protein-Specific Immune Responses in Infants

BACKGROUND

Respiratory syncytial virus (RSV) is a major cause of respiratory disease in infants, making vaccination an attractive preventive strategy. Due to earlier reports of vaccine-enhanced disease in RSV-naive children, assessing prior RSV infection is critical for determining eligibility for future infant vaccine trials. However, this is complicated by the presence of maternally transferred maternal antibodies. We sought to develop assays that measure immune responses to RSV pre-fusion (F) protein that discriminates between maternal and infant responses.

METHODS

We measured RSV-specific responses in two groups of children <3 years of age; those with laboratory-confirmed RSV (RSV-infected) and those enrolled prior to their first RSV season (RSV-uninfected). Serial blood samples were obtained and recent infections with RSV and other respiratory viruses were assessed during follow-up. An RSV pre-F-specific kinetic enzyme-linked immunosorbent assay (kELISA) and an F-specific reactive B cell frequency (RBF) assay were developed.

RESULTS

One hundred two young children were enrolled between July 2015 and April 2017; 74 were in the RSV-uninfected group and 28 were in the RSV-infected group. Participants were asked to provide sequential blood samples over time, but only 53 participants in the RSV-uninfected group and 22 participants in the RSV-infected groups provided multiple samples. In the RSV-infected group, most had positive kELISA and RBF during the study. In the RSV-uninfected group, two patterns emerged: declining kELISA values without reactive B cells, due to maternal transplacental antibody transfer, and persistently positive kELISA with reactive B cells, due to asymptomatic undiagnosed RSV infection.

CONCLUSIONS

A kELISA targeting RSV pre-F epitopes and an RBF assay targeting RSV F-specific B cells generally allow discrimination between maternally and infant-derived antibodies.

Using Administrative Billing Codes to Identify Acute Musculoskeletal Infections in Children

BACKGROUND AND OBJECTIVES

Acute hematogenous musculoskeletal infections (MSKI) are medical emergencies with the potential for life-altering complications in afflicted children. Leveraging administrative data to study pediatric MSKI is difficult as many infections are chronic, nonhematogenous, or occur in children with significant comorbidities. The objective of this study was to validate a case-finding algorithm to accurately identify children hospitalized with acute hematogenous MSKI using administrative billing codes.

METHODS

This was a multicenter validation study using the Pediatric Health Information System (PHIS) database. Hospital admissions for MSKI were identified from 6 PHIS hospitals using discharge diagnosis codes. A random subset of admissions underwent manual chart review at each site using predefined criteria to categorize each admission as either "acute hematogenous MSKI" (AH-MSKI) or "not acute hematogenous MSKI." Ten unique coding algorithms were developed using billing data. The sensitivity and specificity of each algorithm to identify AH-MSKI were calculated using chart review categorizations as the reference standard.

RESULTS

Of the 492 admissions randomly selected for manual review, 244 (49.6%) were classified as AH-MSKI and 248 (50.4%) as not acute hematogenous MSKI. Individual algorithm performance varied widely (sensitivity 31% to 91%; specificity 52% to 98%). Four algorithms demonstrated potential for future use with receiver operating characteristic area under the curve greater than 80%.

CONCLUSIONS

Identifying children with acute hematogenous MSKI based on discharge diagnosis alone is challenging as half have chronic or nonhematogenous infections. We validated several case-finding algorithms using administrative billing codes and detail them here for future use in pediatric MSKI outcomes.

597. Are We Dosing Correctly? Population Pharmacokinetic Modeling of Cefepime, Piperacillin-Tazobactam, and Meropenem in Individuals with Cystic Fibrosis

Background

Patients with cystic fibrosis (CF) experience recurrent bacterial pulmonary exacerbations. The management of these infections becomes increasingly complex due to decreased antimicrobial susceptibility and inadequate pharmacokinetic/pharmacodynamic (PK/PD) characterization of the most commonly used antimicrobial agents in this population.

Methods

One hundred fifty-five pediatric and adult participants receiving cefepime (n=82), meropenem (n=42), or piperacillin-tazobactam (n=31) were enrolled. Opportunistic blood samples were obtained during hospitalization. Population PK (PopPK) analysis was conducted using nonlinear mixed effects modeling in NONMEM, and clinical and demographic characteristics were evaluated as potential covariates. Monte Carlo simulations evaluated the probability of PK/PD target attainment (PTA) for different dosing regimens. Multiple targets, defined as percentage of a 24-h time period that the free drug concentration exceeds the MIC (fT &gt; MIC), were selected based on prior studies of beta-lactam antibiotics.

Results

Preliminary PopPK modeling results show that lean body weight, creatinine clearance, daily dose, mode of administration (standard vs. extended infusion), and age affect PK parameters, with varying effects by drug. As anticipated, extended or continuous infusions resulted in higher PTA (Table 1). In the cefepime group, the 3-h infusion regimen achieved higher PTAs than the 0.5-h regimen across all age groups (Figure 1, Figure 2). Estimated breakpoints (in which ≥ 90% of patients are expected to achieve a PK/PD target) were 2-4 fold higher in pediatric participants receiving a 3-h infusion vs. 0.5-h infusion, based on age and target fT &gt; MIC (Table 1). In the meropenem group, increased creatinine clearance led to reduced PTA, and in the piperacillin-tazobactam group, total daily dose and interval were the principal drivers of PTA. Table 1:Breakpoints (mg/L, highest minimum inhibitory concentration (MIC) with ≥ 90% PK target attainment) for different infusion durations, based on Monte Carlo simulations.Figure 1:Comparison of PTA between the two durations of infusion for 50 mg/kg (3 to 11 years) or 2 g (12 years and above) cefepime q8h at the target of 65% fT&gt; MIC.Figure 2:Comparison of PTA between two durations of infusion for 50 mg/kg (3 to 11 years) or 2 g (12 years and above) cefepime q8h at the target of 100% fT&gt; MIC.

Conclusion

To our knowledge, this is the largest PopPK study to date of these antimicrobials in individuals with CF. Clinicians should incorporate local antibiograms with these PopPK models to determine optimal dosing in patients with CF, since standard dosing regimens may fail to achieve specific PK/PD targets. This population may also benefit from beta-lactam therapeutic drug monitoring.

Disclosures

C. Buddy Creech, MD, MPH, Altimmune: Advisor/Consultant|Astellas: Advisor/Consultant|Merck: Grant/Research Support|Premier: Advisor/Consultant.

127. Development of a Kinetic ELISA (kELISA) and Reactive B-cell Frequency (RBF) Assay to Detect Respiratory Syncytial Virus (RSV) Pre-Fusion F Protein-Specific Immune Responses in Infants

Background

RSV is a major cause of pediatric respiratory disease. Antibodies to the prefusion conformation of the RSV fusion (pre-F) protein are needed for virus neutralization.

Methods

We measured RSV-specific responses in two groups of children &lt; 3 years of age; subjects with laboratory-confirmed RSV (RSV-infected) or infants born in the period May to September and enrolled prior to their first RSV season (RSV-uninfected). RSV-infected infants had blood samples obtained at 1, 6, 9, and 12 months after infection. RSV-uninfected infants had blood samples obtained at enrollment, at the end of their first RSV season, and 6 months later. A kELISA to measure RSV pre-F-specific antibodies and an RBF assay to identify RSV F-specific B cells were developed.

Results

102 subjects were enrolled; 11 were excluded due to missed visits or withdrawal. Of the 65 subjects in the RSV-uninfected group, all were kELISA positive at enrollment, consistent with maternal antibody transfer. 53 subjects had sufficient samples for analysis at multiple time points; 29 became seronegative and 24 remained seropositive. In the seronegative group, the kELISA value decreased rapidly to &lt; 0.25 by 6 months after the RSV season in 27/29 (93%), (Figure 1a). In the persistently seropositive group, all 24 subjects maintained a positive kELISA value, with some developing higher values over time, consistent with asymptomatic infection (Figure 1b). An RBF assay was used to determine whether antibodies were due to persistent maternal antibodies or endogenous production (Figure 2). In the seronegative group, 24/29 (80%) had a negative RBF; in the seropositive group, 23/24 (96%) had a positive RBF during follow-up.

There were 26 subjects in the RSV-infected group; 22 had sufficient samples for analysis at multiple time points. All were seropositive by kELISA at one month post-infection with variable kELISA values during follow-up (Figure 3). 17/22 (77%) had a positive RBF, although 4 of the subjects without a positive RBF had indeterminate results at ≥ 1 visit.

Conclusion

Assays measuring F-specific immune responses in infants will be critical for RSV vaccine development. A kELISA targeting RSV pre-F epitopes, with an RBF assay targeting RSV F-specific B cells, may allow discrimination for maternal and infant-derived antibodies.

Disclosures

Isaac Thomsen, MD, MSCI, Horizon Therapeutics (Individual(s) Involved: Self): Consultant James E. Crowe, Jr., MD, Astra Zeneca (Grant/Research Support)IDBiologics (Board Member, Grant/Research Support, Shareholder)Luna Biologics (Consultant)Meissa Vaccines (Advisor or Review Panel member)Takeda Vaccines (Grant/Research Support) Kathryn M. Edwards, MD, Bionet (Individual(s) Involved: Self): Consultant; CDC (Individual(s) Involved: Self): Research Grant or Support; IBM (Individual(s) Involved: Self): Consultant; Merck (Individual(s) Involved: Self): member DSMC, Other Financial or Material Support; Moderna (Individual(s) Involved: Self): member DSMC, Other Financial or Material Support; NIH (Individual(s) Involved: Self): Research Grant or Support; Pfizer (Individual(s) Involved: Self): member DSMC, Other Financial or Material Support; Roche (Individual(s) Involved: Self): member of DSMB, Other Financial or Material Support; Sanofi Pasteur (Individual(s) Involved: Self): member DSMB, Other Financial or Material Support; Sequiras (Individual(s) Involved: Self): Member DSMB, Other Financial or Material Support; X4 Pharmaceuticals (Individual(s) Involved: Self): Consultant Buddy Creech, MD, MPH, Altimmune (Consultant)Astellas (Other Financial or Material Support, Data and Safety Monitoring Committee)Diotheris (Consultant)GSK (Consultant)Horizon (Consultant)Merck (Scientific Research Study Investigator)Premier Healthcare (Advisor or Review Panel member)Vir (Consultant)

Assessing the epidemiology and seasonality of influenza among children under two hospitalized in Amman, Jordan, 2010-2013

Background

The disease burden of influenza‐associated hospitalizations among children in Jordan is not well established. We aimed to characterize hospitalizations attributed to influenza in a pediatric population.

Methods

We conducted a cross‐sectional study from our viral surveillance cohort in children under 2 years hospitalized with acute respiratory symptoms and/or fever from March 2010 to March 2013. We collected demographic and clinical characteristics, and calculated the frequency of children who met the severe acute respiratory illness (SARI) criteria. Nasal specimens were tested using real‐time reverse transcriptase polymerase chain reaction to detect influenza A, B, or C. Further subtyping for influenza A‐positive isolates was conducted.

Results

Of the 3168 children enrolled in our study, 119 (4%) were influenza‐positive. Influenza types and subtypes varied by season but were predominantly detected between December and February. Codetection of multiple respiratory pathogens was identified in 58% of children with the majority occurring among those <6 months. Bronchopneumonia and rule‐out sepsis were the most common admission diagnoses, with influenza A accounting for over 2/3 of children with a rule‐out sepsis admission status. One‐third of children under 6 months compared to 3/4 of children 6‐23 months met the SARI criteria.

Conclusions

Influenza was an important cause of acute respiratory illness in children under 2 years. Children <6 months had the highest burden of influenza‐associated hospitalizations and were less likely to meet the SARI global surveillance case definition. Additional surveillance is needed in the Middle East to determine the true influenza burden on a global scale.

In vitro assays to monitor the activity of Pseudomonas aeruginosa Type III secreted proteins

Pseudomonas aeruginosa secretes numerous toxins and destructive enzymes that play distinct roles in pathogenesis. The Type III secretion system (T3SS) of Pseudomonas is a system that delivers a subset of toxins directly into the cytoplasm of eukaryotic cells. The secreted effectors include ExoS, ExoT, ExoU, and ExoY. In this chapter, we describe methods to induce T3S expression and measure the enzymatic activities of each effector in in vitro assays. ExoU is a phospholipase and its activity can be measured in a fluorescence-based assay monitoring the cleavage of the fluorogenic substrate, PED6. ExoS and ExoT both possess ADP-ribosyltransferase (ADPRT) and GTPase-activating protein (GAP) activity. ADPRT activity can be assessed by using radiolabeled nicotinamide adenine dinucleotide (NAD(+)) and measuring the covalent incorporation of ADP-ribose into a target protein. GAP activity is measured by the release of radiolabeled phosphate from [γ-(32)P]GTP-bound target proteins. In accordance with recent trends towards reducing the use of radioactivity in the laboratory, alternative assays using fluorescent or biotin-labeled reagents are described. ExoY is a nucleotidyl cyclase; cAMP production stimulated by ExoY can be monitored using reverse-phase HPLC or with commercially available immunological assays.