A Long-term Study to Assess the Safety and Efficacy of Efgartigimod in Adult Patients With Primary Immune Thrombocytopenia (ITP).

Inclusion criteria:

1. Ability to understand the requirements of the trial, to provide written informedconsent (including consent for the use and disclosure of research-related healthinformation), and to comply with the trial protocol procedures (including requiredtrial visits).

2. Patients enrolled in the ARGX-113-1801 trial who completed the 24-weeks trialperiod.

3. Women of childbearing potential must have a negative urine pregnancy test atbaseline before trial medication (infusion) can be administered.

4. Women of childbearing potential should use a highly effective or acceptable methodof contraception during the trial and for 90 days after the last administration ofthe IMP. They must be on a stable regimen, for at least 1 month (as listed in theprotocol)

5. Ability to understand the requirements of the additional 52-week treatment period of the trial, to provide written informed consent (including consent for the use and disclosure of research-related health information), and to comply with the trial protocol procedures (including required trial visits).

6. Patient has completed a 52-week treatment period.

Exclusion criteria:

1. Introduction or continuation of non-permitted medications during the ARGX-113-1801trial (such as anti-CD20 therapy, romiplostim, monoclonal antibodies, Fc fusionproteins or live/live-attenuated vaccines).

2. Pregnant or lactating women, and those intending to become pregnant during the trialor within 90 days after the last dosing.

3. Patients with known medical history of hypersensitivity to any of the ingredients ofefgartigimod.

4. Use of any other investigational drug or participation in any other investigationaltrial.