argenx launches Phase II proof-of-concept clinical

• Interim data expected in H2 2018 

September 26, 2017

Breda, the Netherlands / Ghent, Belgium - argenx (Euronext & Nasdaq: ARGX), a clinical-stage biotechnology company developing a deep pipeline of differentiated antibody-based therapies for the treatment of severe autoimmune diseases and cancer, today announced the initiation of a Phase II proof-of-concept clinical trial of ARGX-113 in pemphigus vulgaris (PV) patients.

"PV is a chronic, severe and potentially life-threatening orphan auto-immune disease of the skin for which limited treatment options exist. Disease severity is directly correlated to pathogenic antibodies of the immunoglobulin G (IgG) type targeting desmoglein-1 and -3 in the skin, leading to painful blister formation and skin damage," commented Nicolas Leupin, Chief Medical Officer of argenx. "Current treatment options are limited to high-dose steroids and chronic immunosuppression. We are thrilled about the therapeutic potential of ARGX-113 in PV, based on its mode of action of clearing IgGs. PV represents a clean and rapid proof-of-concept indication and, we believe, is therefore our ideal beachhead into the field of severe auto-immune blistering diseases of the skin."

The open-label, non-controlled Phase II clinical trial will enroll up to 12 patients with mild to moderate PV who are either newly diagnosed or relapsing. The primary endpoints of the trial are safety and tolerability, and secondary endpoints include efficacy and an assessment of pharmacokinetics (PK) and pharmacodynamic (PD) markers. The study design will be presented in more detail during a PV Key Opinion Leader event which will take place in New York on November 10, 2017.

ARGX-113 is currently being tested in two additional Phase II clinical trials in myasthenia gravis (MG) and immune thrombocytopenia (ITP). Topline date for MG and ITP are expected in the first quarter and second half of 2018, respectively. In a Phase I clinical trial, ARGX-113 was well-tolerated across multiple doses and dosing regimens with promising pharmacodynamic effects relating to speed, depth and duration of IgG reduction.

About ARGX-113 ARGX-113 is an investigational 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 is a clinical-stage biotechnology company developing a deep pipeline of differentiated antibody-based therapies for the treatment of severe autoimmune diseases and cancer. We are focused on developing product candidates with the potential to be either first-in-class against novel targets or best-in-class against known, but complex, targets in order to treat diseases with a significant unmet medical need. Our ability to execute on this focus is enabled by our suite of differentiated technologies. Our SIMPLE Antibody(TM) Platform, based on the powerful llama immune system, allows us to exploit novel and complex targets, and our three antibody engineering technologies are designed to enable us to expand the therapeutic index of our product candidates.  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@argenx.com

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

Forward-looking Statements The contents of this announcement include statements that are, or may be deemed to be, "forward-looking statements." These forward-looking statements can be identified by the use of forward-looking terminology, including the terms "believes," "estimates," "anticipates," "expects," "intends," "may," "will," or "should," and include statements argenx makes concerning the intended results of its strategy and argenx's advancement of, and anticipated clinical development and regulatory milestones and plans related to ARGX-113. By their nature, forward-looking statements involve risks and uncertainties and readers are cautioned that any such forward-looking statements are not guarantees of future performance. argenx's actual results may differ materially from those predicted by the forward-looking statements as a result of various important factors, including argenx's expectations regarding its the inherent uncertainties associated with competitive developments, preclinical and clinical trial and product development activities and regulatory approval requirements; argenx's reliance on collaborations with third parties; estimating the commercial potential of argenx's product candidates; argenx's ability to obtain and maintain protection of intellectual property for its technologies and drugs; argenx's limited operating history; and argenx's ability to obtain additional funding for operations and to complete the development and commercialization of its product candidates. A further list and description of these risks, uncertainties and other risks can be found in argenx's U.S. Securities and Exchange Commission (SEC) filings and reports, including in the final prospectus related to argenx's initial U.S. public offering filed with the SEC pursuant to Rule 424(b) of the Securities Act of 1933, as amended, as well as subsequent filings and reports filed by argenx with the SEC. Given these uncertainties, the reader is advised not to place any undue reliance on such forward-looking statements. These forward-looking statements speak only as of the date of publication of this document. argenx undertakes no obligation to publicly update or revise the information in this press release, including any forward-looking statements, except as may be required by law.