A Study to Evaluate the Safety, Efficacy, and Pharmacokinetics of ARGX-113 in Patients With ITP

This is a randomized, double-blind, placebo-controlled Phase II study in which approximately 36 patients will be randomized in a 1:1:1 ratio to receive either ARGX-113 Dose A, or ARGX-113 Dose B body weight or placebo in 4 infusions administered 1-week apart in addition to Standard-of-Care (SoC) treatment. Patients aged 18 to 85 years (inclusive) with confirmed primary immune thrombocytopenia (ITP) who have a platelet count ˂ 30 × 109/L and who are receiving oral corticosteroids and/or permitted oral immunosuppressants and/or Thrombopoietin receptor (TPO-R) agonist as SoC which must be maintained on a stable dose and frequency for at least 4 weeks prior to Screening.

The study will include a 2-week Screening, a 3-week Treatment period, and an 21-week follow-up (FU) period. The study is followed by an open label period where patients will be given the option to be treated with ARGX-113 Dose A in cycles of 4 weekly infusions with a minimum of 4 weeks apart. Patients may receive rescue therapy during the study at the discretion the investigator when deemed medically necessary.

Inclusion criteria

• Male or female patients aged ≥ 18 to ≤ 85 years.
• Must receive SoC treatment for ITP that has been stable in dose and frequency for at least 4 weeks prior to Screening. SoC may include oral corticosteroids and/or permitted oral immunosuppressants and/or TPO-R agonist.
• Confirmed diagnosis of ITP with blood platelet counts < 30 × 109/L and who have not experienced major bleeding in the last 4 weeks prior to Screening.

Exclusion criteria

• Use of anticoagulants, or any drug with antiplatelet effect within 3 weeks prior to Screening.
• Patients who have received any blood support or transfusion within 4 weeks prior to Screening.
• Use of Intravenous immunoglobulin G (IVIg) or anti-D immunoglobulin treatment within 4 weeks prior to screening.
• Use of recombinant thrombopoietin at any time.
• Use of rituximab within 6 months prior to Screening. Use of any anti-CD20 other than rituximab at any time is not permitted.
• Use of immunosuppressants is not permitted within 4 weeks prior to Screening, with the exception of the following oral immunosuppressants: azathioprine, danazol, mycophenolate mofetil, mycophenolate sodium which must have been stable for at least 4 weeks prior to Screening.
• Use of any other biological therapy or investigational drug than those previously indicated within 3 months or 5 half-lives of the drug (whichever is longer) prior to Screening.
• Received vaccinations within 4 weeks prior to Screening or planned during the study.
• At Screening, have clinically significant laboratory abnormalities
• History of any thrombotic or embolic event within 12 months prior to Screening.
• Known auto-immune disease other than ITP.