Preclinical efficacy and safety of mepolizumab (SB-240563), a humanized monoclonal antibody to IL-5, in cynomolgus monkeys

J Allergy Clin Immunol. 2001 Aug;108(2):250-7. doi: 10.1067/mai.2001.116576.


Background: Allergic respiratory diseases are characterized by large numbers of eosinophils and their reactive products in airways and blood; these are believed to be involved in progressive airway damage and remodeling. IL-5 is the principal cytokine for eosinophil maturation, differentiation, and survival. Mepolizumab (SB-240563), a humanized monoclonal antibody (mAb) specific for human IL-5, is currently in clinical trials for treatment of asthma.

Objective: The purpose of this study was to characterize the pharmacologic activity and long-term safety profile of an anti--human IL-5 mAb to support clinical trials in asthmatic patients.

Methods: Naive and Ascaris suum -sensitive cynomolgus monkeys received various dose levels of mepolizumab and were monitored for acute and chronic pharmacologic and toxic responses.

Results: To support preclinical safety assessment, cynomolgus monkey IL-5 was cloned, expressed, and characterized. Although monkey IL-5 differs from human IL-5 by 2 amino acids (Ala27Gly and Asn40His), mepolizumab has comparable inhibitory activity against both monkey IL-5 and human IL-5. In A suum--sensitive monkeys, single doses of mepolizumab significantly reduced blood eosinophilia, eosinophil migration into lung airways, and levels of RANTES and IL-6 in lungs for 6 weeks. However, mepolizumab did not affect acute bronchoconstrictive responses to inhaled A suum. In an IL-2--induced eosinophilia model (up to 50% blood eosinophilia), 0.5 mg/kg mepolizumab blocked eosinophilia by >80%. Single-dose and chronic (6 monthly doses) intravenous and subcutaneous toxicity studies in naive monkeys found no target organ toxicity or immunotoxicity up to 300 mg/kg. Monkeys did not generate anti-human IgG antibodies. Monthly mepolizumab doses greater than 5 mg/kg caused an 80% to 100% decrease in blood and bronchoalveolar lavage eosinophils lasting 2 months after dosing, and there was no effect on eosinophil precursors in bone marrow after 6 months of treatment. Eosinophil decreases correlated with mepolizumab plasma concentrations (half-life = 13 days).

Conclusion: These studies demonstrate that chronic antagonism of IL-5 by mepolizumab in monkeys is safe and has the potential, through long-term reductions in circulating and tissue-resident eosinophils, to be beneficial therapy for chronic inflammatory respiratory diseases.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Asthmatic Agents / pharmacology
  • Anti-Asthmatic Agents / therapeutic use*
  • Anti-Asthmatic Agents / toxicity
  • Antibodies, Monoclonal / pharmacology
  • Antibodies, Monoclonal / therapeutic use*
  • Antibodies, Monoclonal / toxicity
  • Antibodies, Monoclonal, Humanized
  • Asthma / therapy*
  • Cell Count
  • Cloning, Molecular
  • Drug Evaluation, Preclinical
  • Eosinophils / cytology
  • Eosinophils / drug effects*
  • Immunotherapy
  • Interleukin-5 / antagonists & inhibitors
  • Interleukin-5 / genetics
  • Interleukin-5 / immunology*
  • Macaca fascicularis
  • Male
  • Safety
  • Species Specificity


  • Anti-Asthmatic Agents
  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • Interleukin-5
  • mepolizumab