argenx launches Phase II proof-of-concept study of

- Topline data from the study expected in second half of 2018 -

9 January 2017

Breda, the Netherlands / Ghent, Belgium - argenx (Euronext Brussels: ARGX), a clinical-stage biopharmaceutical company focused on creating and developing differentiated therapeutic antibodies for the treatment of cancer and severe autoimmune diseases, today announced the initiation of a Phase II proof-of-concept study of ARGX-113 in patients with myasthenia gravis (MG).

"MG is a rare and debilitating muscle disease with limited effective and sustainable treatments. ARGX-113 has the potential to eliminate patient symptoms while minimizing common side effects seen with current treatments by reducing the pathogenic IgG levels," commented Nicolas Leupin, CMO argenx. "The initiation of this Phase II study is an important milestone in understanding how ARGX-113 can be effective in a wide range of IgG-mediated autoimmune diseases including additional orphan indications, and larger indications like multiple sclerosis and lupus. We expect to start a Phase II trial in a second orphan IgG driven indication, immune thrombocytopenia (ITP), by the end of the first quarter of 2017."

The double-blind, placebo controlled Phase II study will enrol up to 24 MG patients with confirmed generalized muscle weakness. ARGX-113 will be dosed on top of current standard of care, corticosteroids and/or immunomodulatory agents. The primary endpoints of the trial are safety and tolerability and secondary endpoints include efficacy, impact on quality of life and an assessment of pharmacokinetics (PK) and pharmacodynamic (PD) markers.

In Phase I clinical trials, ARGX-113 demonstrated favorable safety and tolerability across multiple doses and dosing regimens with promising pharmacodynamics effects relating to speed, depth and duration of IgG reduction.

About ARGX-113 ARGX-113 is a potential breakthrough therapy for treatment of IgG-mediated autoimmune diseases. ARGX-113 is the Fc-portion of an antibody that has been modified by the argenx proprietary ABDEG(TM) technology to increase its affinity for FcRn beyond that of normal IgG antibodies. As a result, ARGX-113 blocks antibody recycling and leads to fast depletion of the autoimmune disease-causing IgG autoantibodies. The development work on ARGX-113 is done in close collaboration with Prof. E. Sally Ward (University of Texas Southwestern Medical and Texas A&M University Health Science Center, a part of Texas A&M University ("TAMHSC")).

About argenx argenx (ARGX) combines the diversity of the llama immune system with antibody engineering to advance a clinical pipeline to treat patients with cancer and autoimmune diseases. Our platforms allow us to unlock novel and complex targets and develop antibody-based drugs designed for greater efficacy and longer duration of effect. The strength of our team, our deep understanding of the biology, and our committed collaborations with industry leaders contribute to the success of our journey. www.argenx.com

For further information, please contact:

Joke Comijn, Corporate Communications Manager +32 (0)477 77 29 44 +32 (0)9 310 34 19 info@arGEN-X.com

Beth DelGiacco (US IR) Stern Investor Relations +1 212 362 1200 beth@sternir.com

Forward-looking Statements

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