Efficacy and safety of emapalumab in macrophage activation syndrome.

Macrophage activation syndrome (MAS) is a severe, life-threatening complication of systemic juvenile idiopathic arthritis (sJIA) and adult-onset Still's disease (AOSD). The objective of this study was to confirm the adequacy of an emapalumab dosing regimen in relation to interferon-γ (IFNγ) activity by assessing efficacy and safety. The efficacy outcome was MAS remission by week 8, based on clinical and laboratory criteria. We studied emapalumab, a human anti-IFNγ antibody, administered with background glucocorticoids, in a prospective single-arm trial involving patients who had MAS secondary to sJIA or AOSD and had previously failed high-dose glucocorticoids, with or without anakinra and/or ciclosporin. The study foresaw 4-week treatment that could be shortened or prolonged based on investigator's assessment of response. Patients entered a long-term (12 months) follow-up study. Fourteen patients received emapalumab. All patients completed the trial, entered the long-term follow-up and were alive at the end of follow-up. The investigated dosing regimen, based on an initial loading dose followed by maintenance doses, was appropriate, as shown by rapid neutralisation of IFNγ activity, demonstrated by a prompt decrease in serum C-X-C motif chemokine ligand 9 (CXCL9) levels. By week 8, MAS remission was achieved in 13 of the 14 patients at a median time of 25 days. Viral infections and positive viral tests were observed. Neutralisation of IFNγ with emapalumab was efficacious in inducing remission of MAS secondary to sJIA or AOSD in patients who had failed high-dose glucocorticoids. Screening for viral infections should be performed, particularly for cytomegalovirus. NCT02069899 and NCT03311854.

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Competing interests: FDB: consultant and research grants from AbbVie, Sobi, Pfizer, Roche, Sanofi, Novartis, Novimmune; AAG: consultant for Novartis, AB2 Bio, Novimmune, Sobi; PAB: consultant for Sobi, Novartis, Roche, UCB; CB, MP, GM: none declared; DE: speaker bureau for Sobi; CP: speaker bureau for Sobi; GS: consultant for Novartis, Sobi, Novimmune, AB2 Bio; PQ: consultant for AbbVie, Chugai-Roche, Lilly, Novartis, Pfizer, Sobi and speaker bureau for AbbVie, Chugai-Roche, Lilly, Novartis, Pfizer, Sobi; JA: consultant for Sobi, Novartis, Roche, Pfizer, AbbVie, GSK; CL: consultant for Sobi; RF: previously employed by Sobi; VA: previously employed by Sobi; MB: previously employed by Sobi; PJ: consultant for Sobi; CdM: consultant for Sobi, previously employed by Sobi.