What is the mechanism of action of efgartigimod and response rates in ITP?¶
Answer: Efgartigimod is a novel IgG1 Fc fragment that binds the neonatal Fc receptor (FcRn) with high affinity and thus reduces serum IgG concentrations, including autoantibodies.
- FcRn protects IgG and albumin from destruction and enables the long half-lives of these circulating proteins. Blocking or augmenting FcRn can decrease autoimmune antibodies and enhance drug delivery.
- It has been approved in Japan for the treatment of ITP based on the ADVANCE IV trial:
22% (17/78) of patients with chronic immune thrombocytopenia receiving efgartigimod reached the primary endpoint compared with 5% (2/40) of those receiving placebo (p=0·032; adjusted difference in response, 16% [95% CI 2·6–26·4])
— ADVANCE IV (Lancet 2023)
- It is approved in the US and Canada for the treatment of myasthenia gravis.
- Review on neonatal Fc receptor biology and therapeutics: Neonatal Fc Receptor — Biology and Therapeutics (NEJM 2025).