Comparative effects of two neutralizing anti-respiratory syncytial virus (RSV) monoclonal antibodies in the RSV murine model: time versus potency

Abstract

Respiratory syncytial virus (RSV) is the leading viral pathogen responsible for bronchiolitis and pneumonia in infants and young children worldwide. We have previously shown in the mouse model that treatment with an anti-RSV neutralizing monoclonal antibody (MAb) against the F glycoprotein of RSV, palivizumab, decreased lung inflammation, airway obstruction, and postmethacholine airway hyperresponsiveness. MEDI-524, or Numax, is a new MAb derived from palivizumab with enhanced neutralizing activity against RSV. We compared the effects of these two MAbs on different markers of disease severity using the murine model of RSV infection. BALB/c mice were intranasally inoculated with RSV A2. Palivizumab or MEDI-524 was administered once at either 24 h before or 48 h after RSV inoculation. Regardless of the time of administration, all treated mice showed significantly decreased RSV loads in bronchoalveolar lavage samples measured by plaque assay. Only MEDI-524 given at -24 h significantly decreased lung RSV RNA loads on days 5 and 28 after RSV inoculation. Pulmonary histopathologic scores, airway obstruction, and postmethacholine airway hyperresponsiveness were significantly reduced in mice treated with MEDI-524 at 24 h before inoculation, compared with untreated controls and the other regimens evaluated. MEDI-524 was superior to palivizumab on several outcome variables of RSV disease assessed in the mouse model: viral replication, inflammatory and clinical markers of acute disease severity, and long-term pulmonary abnormalities.

FIG. 1.

Comparative effects of anti-RSV antibodies on RSV replication determined by quantitative culture of BAL samples and lung supernatant homogenates. Mice were intranasally inoculated with RSV (10^7.5 PFU/ml) or 10% EMEM (uninfected controls) and treated with a single dose of either palivizumab or MEDI-524 at one of several different time points. On days 1 and 5 after RSV inoculation, mice were sacrificed, and BAL and lung samples from the same mice were harvested (n = 8 to 16). The RSV loads in BAL samples (A) and both BAL samples and lung specimens (B) were determined by plaque assays. (A) The treatment groups consisted of uninfected controls, RSV-infected untreated mice, and RSV-infected mice receiving either palivizumab or MEDI-524 at either −24 h (before) or +48 h (after) with respect to RSV infection. (B) Viral load was significantly higher (P < 0.05) on day 5 in lung specimens than in BAL samples for RSV-infected untreated mice and mice that received palivizumab at −24 h or +48 h of RSV infection. The values are represented as median RSV log₁₀ PFU/ml (with error bars indicating 25th to 75th percentiles) in BAL fluid (*, P < 0.001) or lung supernatant (‡, P < 0.001) by way of Kruskal-Wallis analysis of variance on ranks for comparison with RSV-infected untreated controls. VL, viral load; dashed line, lower limit of detection of the plaque assay.

FIG. 2.

Impact of treatment with anti-RSV neutralizing MAbs on lung HPS of mice infected with RSV. Mice were inoculated with RSV and treated as described in Materials and Methods. On days 5 and 70, lung specimens were obtained and subsequently fixed and stained for further evaluation by a pathologist unaware of the status of the animals. Bars represent the results of three independent experiments with 8 to 10 mice per time point in each treatment group. Treatment groups consisted of uninfected controls, RSV-infected untreated mice, and RSV-infected mice treated with either palivizumab or MEDI-524 at −24 h (before) or at +48 h (after) with respect to RSV infection. Values are shown as medians, with error bars indicating 25th to 75th percentiles. *, P of <0.001 (day 5) and P of 0.002 (day 70) by Kruskal-Wallis analysis of variance on ranks for comparison with RSV-infected untreated controls.

FIG. 3.

Effect of MEDI-524 on lung histopathology of RSV-infected mice. Lung histopathology results for days 5 and 70 postinfection of sham-inoculated controls, RSV-infected untreated controls, and RSV-infected mice treated with MEDI-524 at −24 h are shown. Hematoxylin and eosin stain. Magnification, ×40.

FIG. 4.

Effects of anti-RSV neutralizing antibodies on AHR. To assess AHR, mice were challenged weekly with aerosolized methacholine, and delta Penh was recorded for up to 10 weeks postinfection. Bars represent means ± standard errors of the means for 12 to 16 mice per group. *, P of 0.03 and 0.04 by one-way analysis of variance for comparison with RSV-infected untreated controls at 4 and 8 weeks after infection, respectively.