FcRn Antagonist Boosts Platelet Counts, Reduces Bleeding Risk in Patients with Immune Thrombocytopenic Purpura

Efgartigimod, an investigational human IgG1 Fc fragment, induced a rapid reduction in total IgG levels and clinically relevant increases in platelet counts in patients with primary immune thrombocytopenia (ITP), according to findings from a Phase II, placebo-controlled multinational study.

In this randomized, double-blinded, placebo-controlled study, 38 ITP patients at 19 European study centers were randomized 1:1:1 to receive four weekly intravenous infusions of either placebo or efgartigimod at a dose of 5 mg/kg or 10 mg/kg body weight. Patients were followed for up to 21 weeks. Most patients enrolled in this study were refractory to previous lines of therapy.

Forty-six percent of patients on efgartigimod experienced platelet counts of greater than or equal to 50 x 109/L on at least two occasions, compared with 25 percent of those who received placebo; 38 percent of efgartigimod-treated patients achieved greater than or equal to 50 x 109/L on at least 10 cumulative days.

The proportion of patients with bleeding decreased in both the efgartigimod 5 and 10 mg/kg groups, from 46.2 percent at baseline to a minimum of 7.7 percent at day 64, and from 38.5 percent at baseline to a minimum of 7.7 percent at day 29. In the placebo group, the proportion with bleeding decreased from 33.3 percent at baseline to a minimum of 25.0 percent at day 50. Taken together, these data “suggest that targeted IgG reduction with efgartigimod is a potential new treatment modality in primary ITP and warrants further evaluation of longer-term treatment in a larger Phase III study,” the investigators concluded.