Exhibit 99.1

argenx reports half year 2019 financial results and

second quarter business update

August 1, 2019

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 its financial results for the first half of 2019 and provided its second quarter business update and the outlook for the remainder of the year.

"We continue to execute on accelerating and expanding our robust, late-stage innovative clinical development programs, as we invest in forward integration across our organization to maximize value.  Efgartigimod is the most advanced and also the broadest FcRn antagonist program with four indications and both intravenous and subcutaneous formulations. Enrollment for the Phase 3 ADAPT trial in generalized myasthenia gravis is progressing as planned and we are on track to initiate before the end of the year the first of two pivotal Phase 3 trials, ADVANCE, for our global primary immune thrombocytopenia program, as well as a Phase 2 trial in chronic inflammatory demyelinating polyneuropathy. Our Phase 2 trial of efgartigimod in pemphigus vulgaris remains a priority, and we expect to report topline data in the first half of 2020," commented Tim Van Hauwermeiren, CEO of argenx. "As we move towards becoming a fully-integrated biotechnology company, we continue to invest in commercial infrastructure with the build-out of our neuromuscular and hematology franchises and the expansion of our global supply chain through our longstanding collaboration with Lonza, which is expected to support the commercial launch of efgartigimod in generalized myasthenia gravis in 2021."

SECOND QUARTER 2019 AND RECENT HIGHLIGHTS

During its 2019 R&D Day in May, argenx announced its plan to become a fully integrated, global immunology company in accordance with its “argenx 2021” vision, which includes building two successful commercial franchises in neuromuscular and hematological disorders.

Efgartigimod (ARGX-113): Potential to be best-in-class with broad applicability

Efgartigimod is a human IgG1 Fc fragment engineered to increase affinity for FcRn versus endogenous IgG, whilst preserving characteristic pH-dependent binding, which may contribute to efgartigimod’s relatively long serum half-life and pharmacodynamic effect, and may promote tissue penetration. Treatment with efgartigimod results in a targeted reduction of IgG autoantibodies and is a rational approach to diseases where IgGs are directly pathogenic. argenx is evaluating efgartigimod as a potential treatment for four high-value indications, including:

argenx entered into a global collaboration with Halozyme in February 2019 to develop a SC formulation of efgartigimod using Halozyme’s proprietary ENHANZE® drug delivery technology, gaining exclusive rights to the technology for the FcRn target.

Cusatuzumab (ARGX-110): First-in-class opportunity in acute myeloid leukemia (AML)

Cusatuzumab is a first-in-class monoclonal antibody inhibiting CD70, a target that is uniquely present on both leukemic stem cells and AML blasts but not healthy cells. It is being developed under an exclusive global collaboration and license agreement with Janssen for the treatment of AML , high-risk myelodysplastic syndromes and other hematological malignancies.

Early Development Programs

argenx announced during its R&D Day the expansion of its product pipeline with the addition of two new proprietary therapeutic candidates, ARGX-117 and ARGX-118. Both emerged from argenx’s Innovative Access Program, in which it collaborates closely with disease biology experts, bringing the argenx cutting-edge antibody discovery and engineering technologies to the heart of novel target research.

Corporate Update

On June 30, 2019, cash, cash equivalents and current financial assets totaled €944.3 million, compared to €564.6 million on December 31, 2018. The increase in cash, cash equivalents and current financial assets resulted primarily from the closing of the exclusive global collaboration and license agreement for cusatuzumab with Janssen which resulted in a $300 million upfront payment and a $200 million equity investment in January 2019.

Total operating income increased by €30.8 million for the six months ended June 30, 2019 to reach €51.3 million, compared to €20.5 million for the six months ended June 30, 2018. The increase is primarily related to (i) a €16.0 million increase in the recognition of milestone payments following the initiation of a first-in-human clinical trial with ABBV-151 (formerly named ARGX-115) under the AbbVie collaboration, which triggered a $30 million milestone payment, (ii) an increase of €7.8 million related to the recognition of research and development service fees under the Janssen collaboration and (iii) an increase of €5.2 million, mainly driven by higher payroll tax rebates for employing certain research and development personnel.

Research and development expenses totaled €78.3 million and €34.4 million for the six months ended June 30, 2019 and 2018 respectively. The increase in the first six months of 2019 resulted primarily from higher external research and development expenses and personnel expenses, reflecting higher clinical trials costs and manufacturing expenses related to the development of argenx’s product candidate portfolio and the recruitment of additional employees to support research and development activities.

Selling, general and administrative expenses totaled €27.5 million and €11.5 million for the six months ended June 30, 2019 and 2018, respectively. The increase of €16.0 million in selling, general and administrative expenses for the six months ended June 30, 2019 primarily resulted from higher personnel expenses and consulting fees related to the preparation of a possible future commercialization of argenx’s lead product candidate efgartigimod.

For the six months ended June 30, 2019, financial income amounted to €7.2 million, compared to €1.3 million for the six months ended June 30, 2018. The increase of €5.9 million in the first six months of 2019 related primarily to an increase in the interest received on cash, cash equivalents and current financial assets.

Exchange gains totaled €2.5 million for the six months ended June 30, 2019, compared to the €4.0 million for the six months ended June 30, 2018 and were mainly attributable to unrealized exchange rate gains on argenx’s cash and current financial assets position in U.S. Dollars due to the favorable fluctuation of the EUR/USD exchange rate in the first six months of 2019.

The total comprehensive loss for the six months ended June 30, 2019 was €45.1 million, compared to €20.1 million for the six months ended June 30, 2018. 

The 90 day average number of shares outstanding per June 30, 2019 was 38,026,040.

Financial Outlook

Based on the current objectives of the Company’s business plan, argenx expects that its existing cash, cash equivalents and investments will fund planned operating and capital expense requirements into 2021. With the launch of a second global Phase 3 trial for efgartigimod, the execution of the development plan for cusatuzumab, the build-out of the commercial organization, and the expansion of the Company’s ambition level within its growing business plan, argenx expects operating and capital expense requirements to continue to increase year-over-year.

U.S. SEC and Statutory Financial Reporting

argenx’s primary accounting framework is International Financial Reporting Standards (IFRS) as issued by the International Accounting Standards Board (IASB). Unaudited condensed half yearly interim financial statements prepared in accordance with International Accounting Standards IAS 34 Interim Financial Reporting are available on www.argenx.com.

In addition to reporting financial figures in accordance with IFRS as issued by the IASB, argenx also reports financial figures in accordance with IFRS as adopted by the European Union (EU) for statutory purposes. The unaudited condensed consolidated statement of financial position, the unaudited condensed consolidated statements of profit and loss and other comprehensive income, the unaudited condensed consolidated statements of cashflow, and the unaudited condensed consolidated statement of changes in equity are not affected by any differences between IFRS as issued by the IASB and IFRS as adopted by the EU.

The condensed consolidated statement of profit and loss and other comprehensive income for the six months ended June 30, 2019 presented in this press release is unaudited.

2019 FINANCIAL CALENDAR

CONFERENCE CALL DETAILS

The half year results will be discussed during a conference call and webcast presentation today at 3:00 pm CEST/9:00 am ET. To participate in the conference call and Q&A session, please select your phone number provided below and use the confirmation code 7539308 . The live webcast may be accessed on the homepage of the argenx website at www.argenx.com or by clicking here.

About argenx

argenx is a clinical-stage biotechnology company developing a deep pipeline of differentiated antibody-based therapies for the treatment of severe auto-immune diseases and cancer. The company is 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. argenx’s ability to execute on this focus is enabled by its suite of differentiated technologies. The SIMPLE Antibody TM Platform, based on the powerful llama immune system, allows argenx to exploit novel and complex targets, and its three complementary Fc engineering technologies are designed to expand the therapeutic index of its product candidates.

www.argenx.com

For further information, please contact:

Beth DelGiacco, Vice President, Investor Relations

+1 518 424 4980

bdelgiacco@argenx.com

Marieke Vermeersch, Corporate Communications & Investor Relations Consultant

+32 (0)479 490 603

+32 (0)3 290 00 50

mvermeersch@argenx.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 its financial condition, results of operation and business outlook; the sufficiency of its cash, cash equivalents and current financial assets; its 2019 business and financial calendar and related plans; the clinical data of its product candidates; the intended results of its strategy; the momentum of its product candidate pipeline as well as argenx’s, and its collaboration partners’, advancement of, and anticipated clinical development, data readouts and regulatory milestones and plans, including the timing of planned clinical trials and expected data readouts; and interaction with regulators, including the potential approval of its current or future drug candidates. 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 argenx’s most recent annual report on Form 20-F filed with the SEC 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.

MANAGEMENT REPORT  

FIRST QUARTER OF 2019

We refer to our Q1 2019 press release.

SECOND QUARTER OF 2019 AND RECENT HIGHLIGHTS

During its 2019 R&D Day in May, argenx SE (the Company or argenx) announced its plan to become a fully integrated, global immunology company in accordance with its “argenx 2021” vision, which includes building two successful commercial franchises in neuromuscular and hematological disorders.

Efgartigimod  (ARGX-113): Potential to be best-in-class with broad applicability

Efgartigimod is a human IgG1 Fc fragment engineered to increase affinity for FcRn versus endogenous IgG, whilst preserving characteristic pH-dependent binding, which may contribute to efgartigimod’s relatively long serum half-life and pharmacodynamic effect, and may promote tissue penetration. Treatment with efgartigimod results in a targeted reduction of IgG autoantibodies and is a rational approach to diseases where IgGs are directly pathogenic. argenx is evaluating efgartigimod as a potential treatment for four high-value indications, including:

argenx entered into a global collaboration with Halozyme in February 2019 to develop a SC formulation of efgartigimod using Halozyme’s proprietary ENHANZE® drug delivery technology, gaining exclusive rights to the technology for the FcRn target.

Cusatuzumab  (ARGX-110): First-in-class opportunity in acute myeloid leukemia (AML)

Cusatuzumab is a first-in-class monoclonal antibody inhibiting CD70, a target that is uniquely present on both leukemic stem cells and AML blasts but not healthy cells. It is being developed under an exclusive global collaboration and license agreement with Janssen for the treatment of AML, high-risk myelodysplastic syndromes and other hematological malignancies.

Early Development Programs

argenx announced during its R&D Day the expansion of its product pipeline with the addition of two new proprietary therapeutic candidates, ARGX-117 and ARGX-118. Both emerged from argenx’s Innovative Access Program, in which it collaborates closely with disease biology experts, bringing the argenx cutting-edge antibody discovery and engineering technologies to the heart of novel target research.

Corporate Update

2.       FINANCIAL HIGHLIGHTS

3.       RISK FACTORS AND 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 its financial condition, results of operation and business outlook; the

sufficiency of its cash, cash equivalents and current financial assets; its 2019 business and financial calendar and related plans; the clinical data of its product candidates; the intended results of its strategy; the momentum of its product candidate pipeline as well as argenx’s, and its collaboration partners’, advancement of, and anticipated clinical development, data readouts and regulatory milestones and plans, including the timing of planned clinical trials and expected data readouts; and interaction with regulators, including the potential approval of its current or future drug candidates. 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 argenx’s most recent annual report on Form 20-F filed with the SEC 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.

4.       FINANCIAL OUTLOOK

Based on the current objectives of the Company’s business plan, argenx expects that its existing cash, cash equivalents and investments will fund planned operating and capital expense requirements into 2021. With the launch of a second global Phase 3 trial for efgartigimod, the execution of the development plan for cusatuzumab, the build-out of the commercial organization, and the expansion of the Company’s ambition level within its growing business plan, argenx expects operating and capital expense requirements to continue to increase year-over-year.

The notes are an integral part of these unaudited condensed consolidated interim financial statements.

The notes are an integral part of these unaudited condensed consolidated interim financial statements.

The notes are an integral part of these unaudited condensed consolidated interim financial statements.

Please refer to note 9 for more information on the share capital and movement in number of shares and note 10 for more information on the share-based payments.

The notes are an integral part of these unaudited condensed consolidated interim financial statements.

ARGENX SE

The differences between our total operating lease commitments as reported in note 5.7 of our consolidated financial statements of December 31, 2018 and the total lease liabilities recognized in our statement of financial position as at January 1, 2019 are summarized below.

The cumulative effect of adopting IFRS 16 to the unaudited condensed consolidated interim statement of financial position as of January 1, 2019 is as follows:

The adoption of IFRS 16 does not have a significant impact on the metrics used to measure financial performance.

In applying IFRS 16 for the first time, the Company has used the following practical expedients permitted by the standard:

The Company has also elected not to reassess whether a contract is, or contains, a lease at the date of initial application. Instead, for contracts entered into before the transition date, the Company relied on its assessment made applying IAS 17 and IFRIC 4 Determining whether an Arrangement contains a Lease .

Other new standards and interpretations applicable for the first time for the financial year beginning January 1, 2019 did not have any impact on our unaudited condensed consolidated interim financial statements. The Company has not early adopted any other standard, interpretation or amendment that has been issued but is not yet effective.

Change in accounting policies with effect as from January 1, 2019 as a result of the adoption of IFRS 16.

Until December 31, 2018, leases of property, plant and equipment were classified as either finance or operating leases. Payments made under operating leases were charged to profit and loss on a straight-line basis over the period of the lease.

As from January 1, 2019, leases are recognized as a right-of-use asset and a corresponding liability at the date at which the leased asset is available for use by the Company. Each lease payment is allocated between the liability and finance cost. The finance cost is charged to profit and loss over the lease period so as to produce a constant periodic rate of interest on the remaining balance of the liability for each period. The right-of-use asset is depreciated over the shorter of the asset’s useful life and the lease term on a straight-line basis. Assets and liabilities arising from a lease are initially measured on a present value basis. The lease payments are discounted using the interest rate implicit in the lease. If that rate cannot be determined, the lessee’s incremental borrowing rate is used.

The right-of-use assets are presented in the statement of financial position under the caption “Property, plant and equipment” and the lease liabilities are presented as current and non-current lease liabilities.

3. Critical accounting judgements and key sources of estimation uncertainty

In the application of the Company’s accounting policies, the Company is required to make judgments, estimates and assumptions about the carrying amounts of assets and liabilities that are not readily apparent from other sources. The estimates and associated assumptions are based on historical experience and other factors that are considered to be relevant. Actual results may differ from these estimates.

The estimates and underlying assumptions are reviewed on an ongoing basis. Revisions to accounting estimates are recognized in the period in which the estimate is revised if the revision affects only that period or in the period of the revision and future periods if the revision affects both current and future periods.

The following areas are areas where key assumptions concerning the future, and other key sources of estimation uncertainty at the end of the reporting period, have a significant risk of causing a material adjustment to the carrying amounts of assets and liabilities within the next financial year.

Critical judgements in applying accounting policies

Revenue recognition

Revenue from certain arrangements is recognized as the Company satisfies a single performance obligation. The Company recognizes upfront payments and milestone payments, allocated to a combined performance obligation over the estimated service period based on a pattern that reflects the transfer of the services. The revenue recognized would reflect the level of service during each period. In this case, the Company would use an input model that considers estimates of the percentage of total research and development service costs that are completed each period compared to the total estimated services costs (percentage of completion method). Research and development service fees are recognized as revenue when costs are incurred and agreed by the parties as the Company is acting as a principal in the scope of its stake in the research and development activities of its ongoing license and collaboration agreements.

Research and development cost accruals

Research and development costs are charged to expense as incurred and are typically made up of payroll costs, clinical and preclinical activities, drug development and manufacturing costs, including costs for clinical research organizations and investigative sites. Costs for certain development activities, such as clinical trials, are recognized based on an evaluation of the progress to completion of specific tasks using data such as information provided by vendors on their actual costs incurred. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the financial statements as prepaid expenses.

Critical accounting estimates

Going concern

The Company has incurred net losses since its inception and for the six months ended June 30, 2019, its unaudited condensed consolidated interim statement of profit and loss and other comprehensive income reflects a net loss, and its unaudited condensed consolidated interim statement of financial position includes a loss carried forward. On July 31, 2019, the Board reviewed and approved the unaudited condensed consolidated interim financial statements and accounting standards. Taking into account the cash and cash equivalents and current financial asset position of €944.3 million on June 30, 2019, the Board is of the opinion that the Company can submit its unaudited condensed consolidated financial statements on a going concern basis.

Whilst the current cash position is sufficient for the Company’s immediate and mid‑term needs, the Board pointed out that if the research and development activities continue to deliver added value, the Company may seek additional funding to support the continuing development of its portfolio of products or to be able to execute other business opportunities.

Measurement of share‑based payments

In accordance with IFRS 2— Share‑based Payment , the fair value of the options at grant date is recognized as an expense in the statement of profit and loss and other comprehensive income over the vesting period. Subsequently, the fair value recognized in equity is not re‑measured.

The fair value of each stock option granted during the year is calculated using the Black‑Scholes pricing model. This pricing model requires the input of subjective assumptions, which are detailed in note 10.

Recognition of deferred tax assets

Deferred tax assets are recognized only if management assesses that these tax assets can be offset against positive taxable income within a foreseeable future.

This judgment is made by management on an ongoing basis and is based on budgets and business plans for the coming years, including planned commercial initiatives. These budgets and business plans are reviewed and approved by the Board.

Since inception, the Company has reported losses, and consequently, the Company has unused tax losses. The deferred tax assets are currently not deemed to meet the criteria for recognition as management is not able to provide any convincing positive evidence that deferred tax assets should be recognized. Therefore, management has concluded that deferred tax assets should not be recognized as of June 30, 2019.

4. Cash and cash equivalents

On June 30, 2019, cash and cash equivalents amounted to €167.8 million, compared to €281.0 million on December 31, 2018 and included cash equivalents and cash and bank balances held in different financial institutions. Cash positions are invested with selected financial institutions, which are considered to be high-quality financial institutions with sound credit ratings, or in highly-rated money market funds. Policies are in place that limit the amount of credit exposure to any specific financial institution.

5. Current financial assets

On June 30, 2019, the current financial assets amounted to €776.5 million, compared to €283.5 million on December 31, 2018. These current financial assets relate to:

Please also refer to note 16 for more information on the financial instruments.

6. Prepaid expenses

Prepaid expenses on June 30, 2019 amounted to €8.3 million, compared to €3.0 million on December 31, 2018. The increase in prepaid expenses is mainly driven by upfront fees paid in the first six months of 2019 to a third-party drug product manufacturer as the Company is further advancing its clinical development and manufacturing activities of efgartigimod.

7. Trade and other receivables

Trade and other receivables are composed of receivables which are detailed below:

The nominal amounts of all trade and other receivables approximate their respective fair values. The VAT receivable relates to VAT amounts to be recovered in the second half of 2019.

Trade receivables correspond to amounts invoiced to the collaborators or strategic allies of the Company. No bad debt allowance was recorded, nor were any trade receivables impaired on June 30, 2019 and December 31, 2018. The Flanders Innovation and Entrepreneurship Agency (VLAIO) grant receivable consists of earned income from government grants for which no payments have been received but for which the relating expenditures have been incurred.

For more information on the Flanders Innovation and Entrepreneurship Agency grants, see note 12.

8         Intangible assets

The intangibles assets held by the Company increased substantially as a result of the in-licensing of the ENHANZE® drug delivery technology from Halozyme. Under the terms of the agreement, the Company paid an upfront payment of $30 million and exercised the option to nominate an additional target, triggering a $10 million development milestone payment. In line with its accounting policies, the Company has capitalized this upfront payment upon commencement of the in-license agreement. The development milestone payment has been capitalized when the development milestone was triggered.

These intangible assets relating to products in development that are not yet available for use are not amortized. These intangible assets are assessed for impairment on an annual basis, or more frequently if indicators of a potential impairment exist. An impairment is recorded if the carrying value exceeds the recoverable amount of the

intangible assets. Intangible assets relating to products which fail during development, or for which development ceases for any reason are written down to their recoverable amount, which is typically nil. If and when the Company obtains approval for the commercial application of a product in development, the related in-process research and development assets will be reclassified to intangible assets associated with products and amortized over its estimated useful life from marketing approval.

9        Shareholders’ capital

Roll forward of number of shares outstanding: