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SAT0189 Rapid Onset of Clinical Benefit in Patients with RA Treated with Mavrilimumab, A Fully Human Monoclonal Antibody Targeting GM–CSFR-ALPHA: Subanalysis of the Phase IIB Earth Explorer 1 Study
  1. I.B. McInnes1,
  2. G.R. Burmester2,
  3. J.M. Kremer3,
  4. P. Miranda4,
  5. M. Korkosz5,
  6. J. Vencovsky6,
  7. A. Rubbert-Roth7,
  8. E. Mysler8,
  9. D. Close9,
  10. M. Sleeman10,
  11. A. Godwood9,
  12. M. Albulescu9,
  13. M. Weinblatt11
  1. 1Institute of Infection Immunity and Inflammation, University of Glasgow, Glasgow, United Kingdom
  2. 2Department of Rheumatology and Clinical Immunology, Charité - University Medicine Berlin, Free University and Humboldt University Berlin, Berlin, Germany
  3. 3Department of Medicine, Albany Medical College, The Center for Rheumatology, Albany, United States
  4. 4Centro de estudios reumatologicos, Universidad de Chile and Hospital San Juan de Dios, Santiago, Chile
  5. 5Division of Rheumatology, Department of Internal Medicine and Gerontology, Jagiellonian University Hospital, Krakow, Poland
  6. 6Institute of Rheumatology, Charles University, Prague, Czech Republic
  7. 7Med Clinic I, University of Cologne, Cologne, Germany
  8. 8Department of Rheumatology, Organizacion Medica de Investigaciόn, Buenos Aires, Argentina
  9. 9MedImmune Ltd
  10. 10MedImmune, Cambridge, United Kingdom
  11. 11Department of Rheumatology, Brigham and Women's Hospital and Harvard Medical School, Boston, United States


Background Macrophages are pivotal to the pathogenesis of rheumatoid arthritis (RA), and their inflammatory products drive many of the signs and symptoms of disease. Mavrilimumab inhibits macrophage activation and survival via blockade of granulocyte-macrophage colony-stimulating factor receptor-α (GM–CSFR-α) and has demonstrated sustained clinical benefit in patients with RA.1

Objectives To examine time to onset of clinical response to mavrilimumab in the EARTH EXPLORER 1 study.

Methods In a 24-week, Phase IIb study (NCT01706926), patients with adult-onset RA (18–80 years; Disease Activity Score 28 C-reactive protein [DAS28–CRP] >3.2; ≥4 swollen joints; inadequate response to ≥1 disease-modifying antirheumatic drugs [DMARDs]) receiving concomitant methotrexate were enrolled. Patients received mavrilimumab (150, 100, or 30 mg every other week [eow]) or placebo, administered subcutaneously with methotrexate (7.5–25.0 mg/week). Efficacy assessments included DAS28–CRP, American College of Rheumatology (ACR)20/50/70 responses, CRP, erythrocyte sedimentation rate (ESR), swollen joint count (SJC), tender joint count (TJC), and pain assessments.

Results 326 patients with mean (SD) DAS28–CRP 5.8 (0.9) were randomized to mavrilimumab (150, 100, or 30 mg eow) or placebo (N=79, 85, 81, and 81, respectively). At Week 1 (first assessment), all mavrilimumab dosages demonstrated significant reductions from baseline in DAS28–CRP (p<0.001 vs. placebo), with treatment benefit increasing through Week 12. Significant improvements for mavrilimumab 150 mg eow vs. placebo were demonstrated at Week 1 for CRP, ESR, SJC, TJC, and pain (p=0.003 to p<0.001; Table). Effects of mavrilimumab 150 mg eow were near maximum compared with placebo for CRP, ESR, and pain at Week 1, and were sustained until Week 24. SJC and TJC for mavrilimumab 150 mg eow improved from baseline to Week 1, and continued to improve through Week 12. This improvement was sustained through Week 24.

Conclusions By targeting activated macrophages via inhibition of GM–CSFR-α, mavrilimumab substantially reduced patients' RA disease activity early in their treatment, from first dose (Week 1) to final assessment for many patients, as evaluated by several clinical outcomes.


  1. Burmester GR, et al. Ann Rheum Dis. 2013;72:1445–52.

Acknowledgements Funded: MedImmune Ltd. Editorial assistance: N Panagiotaki, QXV Communications, UK

Disclosure of Interest I. McInnes Grant/research support from: MedImmune (Research award to University of Glasgow), Consultant for: MedImmune, AstraZeneca, G. Burmester Grant/research support from: AbbVie, Pfizer, UCB, Roche, Consultant for: AbbVie, BMS, Novartis, MedImmune, MSD, Pfizer, UCB, Roche, Speakers bureau: AbbVie, BMS, Novartis, MSD, Pfizer, UCB, Roche, J. Kremer Shareholder of: Corrona, Grant/research support from: AbbVie, Amgen, Genentech, Lilly, Pfizer, Consultant for: AbbVie, Amgen, Genentech, Lilly, Pfizer, BMS, Employee of: Corrona, P. Miranda Grant/research support from: MedImmune (to support protocol), M. Korkosz: None declared, J. Vencovsky: None declared, A. Rubbert-Roth Grant/research support from: Pfizer, Chugai, Consultant for: MSD, UCB, Abbott, Pfizer, Roche, BMS, Chugai, Speakers bureau: Roche, Pfizer, UCB, E. Mysler Grant/research support from: MedImmune, Roche, BMS, Pfizer, D. Close Shareholder of: AstraZeneca, Employee of: MedImmune, M. Sleeman Shareholder of: AstraZeneca, Employee of: MedImmune, A. Godwood Shareholder of: AstraZeneca, Employee of: MedImmune, M. Albulescu Employee of: MedImmune, M. Weinblatt Grant/research support from: BMS, UCB, Crescendo Bioscience, Consultant for: MedImmune, AstraZeneca, Amgen, Abbvie, BMS, Crescendo bioscience, Lilly, Pfizer, UCB, Roche

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