Combined blockade of granulocyte-macrophage colony stimulating factor and interleukin 17 pathways potently suppresses chronic destructive arthritis in a tumour necrosis factor α-independent mouse model

Objective:A pathogenic role for granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin (IL)17 in rheumatoid arthritis (RA) has been suggested. In previously published work, the therapeutic potentials of GM-CSF and IL17 blockade in arthritis have been described. In the present study, the simultaneous blockade of both pathways in a mouse model for chronic arthritis was investigated to identify whether this double blockade provides a superior therapeutic efficacy.Methods:A chronic relapsing arthritis was induced in C57Bl/6 wild type (WT) and C57Bl/6 genetically deficient for IL17 receptor (IL17R knockout (KO)) mice by intra-articular injection of Streptococcal cell wall (SCW) fragments into knees on days 0, 7, 14 and 21. Treatments (intraperitoneal) were given weekly starting on day 14. Animals were analysed for inflammation, joint damage and a range of inflammatory mediators.Results:Joint swelling and cartilage damage were significantly reduced in the IL17R KO mice and in WT mice receiving anti-GM-CSF neutralising mAb 22E9 compared to isotype control antibodies. The therapeutic effect was significantly more pronounced in mice where IL17 and GM-CSF pathways were inhibited (eg, IL17R KO mice treated with 22E9 mAb). Tumour necrosis factor (TNF)α blockade had essentially no effect.Conclusion:Our data further support the therapeutic potentials of GM-CSF and IL17 blockade in a RA model that is no longer responsive to an established TNFα antagonist, moreover, our results suggest that concomitant inhibition of both pathways may provide the basis for a highly effective treatment of chronic RA in patients that are resistant to treatment by TNFα inhibitors.