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Lagos, Rosanna MD*; DeVincenzo, John P. MD; Muñoz, Alma MD*; Hultquist, Micki MS; Suzich, JoAnn PhD; Connor, Edward M. MD; Losonsky, Genevieve A. MD

Author Information
The Pediatric Infectious Disease Journal: September 2009 - Volume 28 - Issue 9 - p 835-837
doi: 10.1097/INF.0b013e3181a165e4


Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and pneumonia in young children worldwide.1 Prophylaxis with palivizumab (Synagis; MedImmune LLC, Gaithersburg, MD), a monoclonal antibody specific for the F protein of RSV, can significantly reduce the rate of RSV hospitalizations in children with prematurity, chronic lung disease, and congenital heart disease.2,3 Motavizumab (MEDI-524; MedImmune LLC), developed by affinity maturation of palivizumab,4 is in clinical development. In the cotton rat model, motavizumab had 50- to 100-fold greater anti-RSV activity in the lower respiratory tract compared with palivizumab and similarly reduced RSV viral load in the upper respiratory tract whereas similar serum concentrations of palivizumab were associated with minimal effect.5

In children hospitalized with RSV disease, 1 15 mg/kg intravenous (IV) dose of palivizumab significantly reduced RSV load in the lower, but not the upper, respiratory tract.6 This study, not powered for clinical outcomes, did not suggest a correlation between reduction in viral load and clinical benefit. Although viral load may be an important predictor of RSV disease severity,7,8 some studies suggest that bronchiolitis may be associated with imbalances in host immune responses.9,10 Thus, there may be potential immunologic and antiviral strategies for treating severe RSV disease.

This phase I study assessed the safety, tolerability, serum and nasal concentrations, and immunogenicity of motavizumab in previously healthy children hospitalized with RSV infection. Because of enhanced activity of motavizumab in preclinical studies, the effect of motavizumab on RSV viral load in the upper respiratory tract was also assessed.


Study Population.

Previously healthy children aged <2 years (gestational age ≥36 weeks) were eligible. At randomization, patients were required to have been hospitalized <24 hours for RSV lower respiratory tract illness and RSV detected in respiratory secretions within the previous 72 hours by direct fluorescent antibody (Bartels, Trinity Biotech, Wicklow, Ireland; or SimulFluor Respiratory Screen, Chemicon International Inc., Temecula, CA) or rapid antigen detection (Directigen, Becton Dickinson, Sparks, MD) at the sites' clinical laboratories, or by Binax NOW bedside RSV test (Binax Inc., Scarborough, ME). Exclusion criteria included treatment with antiviral agents for the current RSV infection; medically significant underlying illness; previous supplemental oxygen use or mechanical ventilation; and use of palivizumab or other immunoglobulin products within the past 2 months. Complete exclusion criteria are described in the Table (Supplemental Digital Content 1,

The study was conducted in accordance with the principles of the Declaration of Helsinki, the International Conference on Harmonisation Guidance for Good Clinical Practice, and local regulations governing the use of investigational drugs in human subjects. The study protocol was approved by the Ethics Committee and/or Institutional Review Board at participating centers. Parents or legal guardians of all patients provided written informed consent.

Study Design.

This phase I, randomized, double-blind trial was conducted in the United States and Chile. Participants were randomized (1:1) to groups who received a single IV infusion of motavizumab in a dose-escalating manner (3, 15, 30 mg/kg) or identically appearing placebo (0.45% NaCl) by slow infusion on day 0 within 12 hours after randomization. Dose escalation occurred after ≥7 days of safety follow-up of the previous dose group.

Evaluation and Sample Collection.

Table, Supplemental Digital Content 2, details all evaluations and samples collected. Briefly, lower respiratory disease scores were assessed and blood and urine samples were collected. Nasal secretions were obtained for quantitative RSV cultures, quantitative reverse-transcriptase polymerase chain reaction (RT-PCR), analysis of motavizumab concentrations, and RSV antigen detection. The durations of hospitalization, supplemental oxygen use during hospitalization, intensive care unit stay, and mechanical ventilation were also recorded. Adverse events (AEs) and serious AEs were monitored through study day 30.

Pharmacokinetic and Immunogenicity Assessments.

Motavizumab concentrations in serum and nasal washes were determined using a validated enzyme-linked immunosorbent assay.11 Antimotavizumab antibody assays were similarly determined.11

Respiratory Syncytial Virus Quantitation by Viral Culture and Reverse-Transcriptase Polymerase Chain Reaction.

All virologic assays were performed blind with respect to treatment assignment. Nasal secretions obtained quantitatively and control standards were thawed and RSV concentrations were determined in triplicate by plaque assay on low-passage HEp-2 cells. After fixing and staining, individual plaques were counted using prespecified counting rules.7,12 RSV was also quantified by real-time RT-PCR, amplifying a portion of the N-gene, using procedures that have been previously described and validated in infants using separate primers, probes, and standards for RSV-A and RSV-B.13 Viral quantities by PCR were expressed as plaque-forming unit equivalents/mL.

Statistical Methods.

Categorical data were summarized by the number and percentage of patients in each category. Continuous variables were summarized by descriptive statistics (mean, SD, and range). Because of the small sample size, data for the placebo cohorts at each dose level were combined. Fisher exact test was used to compare treatment groups for categorical data and a Wilcoxon rank sum test was used to compare continuous data. Statistical comparisons of prespecified exploratory antiviral endpoints were conducted.


Patient Population.

Thirty-one children (Chile, n = 27; United States, n = 4) were randomized to receive placebo (n = 15) or motavizumab at 3 mg/kg (n = 5), 15 mg/kg (n = 5), or 30 mg/kg (n = 6). Twenty-nine patients (93.5%) completed the study. Baseline characteristics of the study population are shown in the Table (Supplemental Digital Content 3,

Safety Evaluation.

AEs were representative of those expected in infants hospitalized for RSV infection. The frequency of AEs was similar between the combined motavizumab groups and the placebo group. Six of 15 (40%) placebo recipients reported 25 AEs and 11 of 16 (73%) motavizumab recipients experienced 39 AEs (not statistically significant). None of the AEs were considered related to study drug. Respiratory failure occurring after hospitalization and dosing was reported in 2 patients as a serious AE; 1 each among 30-mg/kg motavizumab and placebo recipients. Two days after dosing, 1 additional placebo recipient experienced respiratory failure considered moderate in severity by the site investigator (reported as an AE). All 3 children received mechanical ventilation and fully recovered.

The mean duration of hospitalization was 4.9 days (range: 2–23 days) for the combined motavizumab groups, and 6.8 days (range: 2–31 days) for the combined placebo groups (not statistically significant; Table 1). A total of 11 (73%) motavizumab and 10 (67%) placebo patients required supplemental oxygen. No significant differences were seen between treatment groups in patients requiring intensive care or mechanical ventilation (Table 1). Improvement in lower respiratory disease scores did not differ between motavizumab and placebo recipients.

Severity of Hospitalization
Effect of Motavizumab Treatment on Cultivatable Respiratory Syncytial Virus and Viral RNA in Nasal Wash Aspirates.

All (30/30) children who received study drug were positive for RSV at baseline by RT-PCR and 90% (27/30) were positive by culture. Quantitative cultures and RT-PCR measures of viral load were not significantly different between motavizumab groups at baseline (Table, Supplemental Digital Content 4,, which shows quantitative virology). Mean viral loads among all motavizumab and placebo recipients at baseline (study day 0) were 3.87 and 3.90 log10 plaque-forming unit (PFU)/mL, respectively. One day after administration of motavizumab, 11 of 15 (73%) children in the combined motavizumab dose groups (9/10 patients receiving the higher motavizumab dose levels of 15 or 30 mg/kg compared with 2/5 patients receiving 3 mg/kg) and 4 (27%) placebo recipients tested negative for RSV in nasal secretion cultures (P < 0.05). The RSV load (by culture) for all motavizumab groups combined and the 15- and 30-mg/kg groups combined at study day 1 was significantly different from placebo (1.3 vs. 3.0 log10 PFU/mL, P = 0.01; and 0.9 vs. 3.0 log10 PFU/mL, P < 0.01; respectively). A mean reduction of ≥2 log10 PFU/mL from study day 0 to study day 1 was seen in the 15- and 30-mg/kg groups combined, compared with a mean reduction of 0.9 log10 PFU/mL in the placebo group over this same time interval (P < 0.05 for the motavizumab groups combined vs. placebo). By study day 7, no RSV growth in culture was seen in nasal secretions from any patient.

After study day 1, detection of RSV RNA by RT-PCR analysis persisted in all patients (Table, Supplemental Digital Content 4, However, by study day 7, the percentage of patients with detectable viral RNA from nasal secretions was significantly lower in motavizumab recipients compared with placebo recipients (57% vs. 93%, P < 0.05).

Respiratory Syncytial Virus Antigen in Nasal Secretions.

Nonquantitative detection of RSV antigen from frozen nasal secretions collected on day 0 was negative for 7 (47%) motavizumab recipients and 2 (13%) placebo recipients (not significant). On study day 1, frozen nasal secretions were negative for RSV antigen in 13 (87%) motavizumab recipients and 5 (33%) placebo recipients (P < 0.01). Similar results were observed for fresh nasal secretions. Nasal secretions from all patients were negative for RSV antigen by study day 7.

Motavizumab Concentrations and Immunogenicity.

Mean trough serum concentrations of motavizumab on study day 2 were 62, 171, and 333 μg/mL for the 3-, 15-, and 30-mg/kg groups, respectively and 17, 59, and 80 μg/mL for the 3-, 15-, and 30-mg/kg groups, respectively, on day 30. Motavizumab was detected in nasal secretions from all motavizumab recipients; higher nasal concentrations were generally associated with increased doses. Mean concentrations of motavizumab in nasal secretions at study day 1 were 0.2, 0.9, and 1.3 μg/mL for the 3-, 15-, and 30-mg/kg groups, respectively. Motavizumab continued to be detected in nasal secretions at study day 30 in 3 patients (15 mg/kg, n = 1; 30 mg/kg, n = 2). No antimotavizumab antibodies were detected in serum from any patient at any time during the study.


In this study evaluating the safety and immunogenicity of 1 dose of motavizumab administered to RSV-infected children, no AEs related to motavizumab were reported and antimotavizumab antibodies were not detected. RSV infection did not seem to change the pharmacokinetics of motavizumab: the mean 30-day trough serum motavizumab concentrations after IV administration in these children were comparable with those seen in uninfected high-risk children after intramuscular administration.11

Cultivatable RSV in the upper respiratory tract 1 day post-treatment with motavizumab was significantly reduced compared with placebo. The effect of motavizumab on RSV loads appeared to be dose-related; greater numbers of patients had negative RSV culture results at the combined higher dose levels of 15- and 30-mg/kg motavizumab compared with patients given 3 mg/kg, although these findings were not statistically significant. It is uncertain whether the presence of motavizumab in nasal secretions 2 to 30 days post-treatment affected the cultivation or antigen-based detection of RSV in vitro during sample testing. The reduction in viral nucleic acid detectable by real time RT-PCR, which would not be affected by the presence of motavizumab, makes this unlikely. The apparent antiviral activity of motavizumab in the upper respiratory tract differentiates it from palivizumab. In a similarly designed and sized placebo-controlled study in children hospitalized for RSV and given palivizumab 15 mg/kg IV, no significant differences in cultivatable RSV in nasal secretions from baseline to later time points between treatment groups were found,6 although a significant reduction of viral load measured from lower respiratory aspirates was observed. This observation is consistent with preclinical comparison of these 2 molecules5 and with the known presence of higher concentrations of IgG in the lower, versus upper, respiratory tract.

RSV RNA persistence after clinical RSV infection and in RSV challenge models has been reported.8 Despite the unclear clinical significance, RSV persistence is thought to contribute to prolonged inflammation or hyperreactivity in the respiratory tract.8 The persistence of viral RNA in upper respiratory secretions suggests that viral clearance may not be as rapid as indicated by the lack of cultivatable RSV.14 If viral persistence or load plays a role in clinical outcomes in advanced RSV disease, a potent antiviral agent may have clinical benefit.15 Alternatively, because of the potent inflammatory response induced by RSV infection, antiviral treatment in conjunction with an anti-inflammatory agent may be more appropriate.

A monoclonal antibody with antiviral activity against RSV in the upper and lower respiratory tracts may be clinically useful for treatment of early or late RSV infection. Clear delineation of the antiviral effect of motavizumab as a therapy for early or late RSV infection in infected children will require larger clinical trials.


The authors thank Lisa Harrison for her technical expertise in performing the many quantitative viral assays employed in this study The authors also thank Pam Mattes, PhD; Rhonda Croxton, PhD; Jeannie M. Fiber, PhD; John E. Fincke, PhD; and Gerard P. Johnson, PhD; for editorial assistance in preparing this manuscript.


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antibodies; bronchiolitis; monoclonal; antiviral agents clinical trial; motavizumab; pediatric; respiratory syncytial virus; viral load

Supplemental Digital Content

© 2009 Lippincott Williams & Wilkins, Inc.