Emapalumab produces major responses in macrophage activation syndrome

MADRID – Initial results of an ongoing small pilot study of the anti-interferon gamma (IFN-gamma) monoclonal antibody emapalumab has demonstrated efficacy in the treatment of glucocorticoid-refractory macrophage activation syndrome (MAS) in patients with systemic juvenile idiopathic arthritis (SJIA).

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Dr. Fabrizio De Benedetti

“By week 4 there was a complete response in all six patients treated. All of them had failed conventional therapy,” Fabrizio De Benedetti, MD, PhD, head of the division of rheumatology at IRCCS Ospedale Pediatrico Bambino Gesù, Rome, reported at the European Congress of Rheumatology.

The results are the first of a multicenter, pilot study with twin protocols in Europe and North America. Emapalumab (Gamifant) is already approved by the Food and Drug Administration for the treatment of primary hemophagocytic lymphohistiocytosis (HLH) unresponsive to conventional therapy.

The study is enrolling children with MAS complicating SJIA that is unresponsive to high-dose intravenous glucocorticoids. Emapalumab, which has been shown to neutralize IFN-gamma in animal models, is being administered in an initial dose of 6 mg/kg followed by doses of 3 mg/kg every 3 days for 4 weeks.

MAS is a common complication of rheumatic diseases, particularly SJIA, according to Dr. De Benedetti. It has been characterized as a secondary form of HLH involving an excessive activation and expansion of macrophages as well as T cells. It can produce a wide variety of complications, including hepatosplenomegaly, liver dysfunction, and coagulation abnormalities. If uncontrolled, it can lead to organ failure and death.

Among the first six patients, four had confirmed SJIA and two had presumptive SJIA. The average age was 11 years with a range of 2 to 25 years. Four of the patients were female.

Many of the patients had failed therapies in addition to glucocorticoids, such as cyclosporine and anakinra. A diagnosis of HLH and prior treatment with a biologic therapy were exclusion criteria.

By 8 weeks, six had a complete response, which included the resolution of symptoms by normalization of ferritin, liver enzymes, and D-dimers. In three of the six patients, a complete response was achieved by week 4.

“Steroid tapering by investigator discretion was permitted, and four of the six patients had a meaningful tapering of steroids within 8 weeks,” Dr. De Benedetti reported.

Of the three serious adverse events recorded so far, only reactivation of cytomegalovirus (CMV) infection was attributed to emapalumab. This infection resolved with treatment. Several other infections observed over the course of the study were not thought to be related to treatment.

The initial results have encouraged an expansion of the study protocol in Europe where several treatment centers are expected to begin enrolling patients shortly. A second parallel study protocol will begin soon in North America, but no patient had been treated at the time that Dr. De Benedetti presented these initial findings.

Based on evidence that IFN-gamma drives hyperinflammation and hypercytokinemia in MAS, the initial results with emapalumab are encouraging, according to Dr. De Benedetti. He said the results not only provide evidence that emapalumab is active in MAS but support the pathogenic role of IFN-gamma in this disease.

Dr. De Benedetti reported financial relationships with multiple pharmaceutical companies, including SOBI, the sponsor of this study.

SOURCE: De Benedetti F et al. Ann Rheum Dis. Jun 2019;78(Suppl2):178. Abstract OPO204, doi: 10.1136/annrheumdis-2019-eular.3341.