Argenx to Pay $550M Upfront in Up to $1.15B Peptide Biotech Buyout

Argenx, the Netherlands-based immunology company, has agreed to buy Unnatural Products, a biotech in Santa Cruz, California. The deal is worth up to about $1.15 billion. Argenx announced it on Nov. 9 and said it already holds a minority stake in the company.

What happened

Argenx will pay $550 million in cash upfront, using cash it has on hand. Up to $595 million more depends on development and regulatory milestones. The boards of both companies have approved the agreement, according to argenx.

• Timing: argenx expects the deal to close by the end of the year, subject to customary conditions.
• Technology: Unnatural Products designs macrocyclic peptides using parallel experiments and machine learning.
• Site: the team and its leaders stay in Santa Cruz, which becomes the home of peptide discovery at argenx.

The two companies have worked together for more than two years, argenx said. Pharmaphorum reports that in July 2025 they signed a research and option to license deal valued at up to $1.5 billion. That deal aimed mainly at once-daily pills, including one that blocks FcRn.

Why it matters

Argenx built its business on antibody drugs. Its flagship product, Vyvgart, earned $4.5 billion in net product sales from January through September, BioPharma Dive reports. Argenx said the deal opens new possibilities for oral or long-acting medicines, which could add a different kind of drug alongside its antibodies.

BioPharma Dive explains that these molecules are larger and more complex than typical small molecule drugs, yet still small enough to take by mouth. A few are already approved, including Rhythm's Imcivree in 2020 and UCB's Zilbrysq in 2023.

Chief executive Karen Massey said the peptide work fits well with the antibody engineering argenx already does. A Leerink Partners analyst, Thomas Smith, wrote that the deal points to more focus on growing and broadening the pipeline. Argenx shares rose nearly 3% to about $953 by late Monday morning, according to BioPharma Dive.

What it means for people in the industry

Argenx plans to keep the Unnatural Products team in place, so the California discovery group should continue under new ownership. Neither company gave staff numbers or hiring plans. Under the plan, Unnatural Products leads discovery while argenx handles clinical development and sales.

Things to watch include the closing before year end, which peptide programs move into the clinic first, and whether argenx adds discovery roles in Santa Cruz.

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Sources

• argenx to Acquire Unnatural Products, Inc., Adding Peptide Discovery Engine to Broaden Immunology Capabilities, argenx (via SEC EDGAR)
• Argenx to buy peptide platform in potentially billion-dollar deal, BioPharma Dive
• argenx agrees Unnatural takeover deal worth up to $1.15bn, pharmaphorum