Argenx to buy macrocyclic peptide biotech Unnatural Products

Argenx, the Amsterdam-based immunology company best known for the antibody fragment Vyvgart, has agreed to buy Unnatural Products (UNP), a privately held California biotech that designs macrocyclic peptides. The deal, announced on November 9, 2026, is the second large bet on ring-shaped oral peptides by a major drugmaker in less than three weeks.

According to argenx’s announcement, filed with the SEC, argenx will pay $550 million upfront from cash on hand. It will also pay up to $595 million more if specified development and regulatory milestones are reached, putting the total potential value at up to approximately $1.15 billion. Argenx already owned a minority stake in UNP and is buying the remaining shares. Both boards have approved the transaction, and argenx expects it to close by the end of the year, subject to customary conditions.

What argenx is buying

UNP does not have a disclosed drug in clinical testing. What argenx is acquiring is a discovery engine. In its own release, UNP says it spent 10 years building a platform that combines AI-guided design with massively parallel synthesis and direct-to-biology screening. The goal is to make drug-like macrocycles against targets that ordinary small molecules and antibodies struggle to reach, including targets inside cells.

Macrocyclic peptides are amino acid chains closed into a ring. Most peptide drugs today are injected because the gut breaks them down. A ring structure can make a peptide sturdier and, in some cases, able to work as a pill. Fierce Biotech pointed to Johnson & Johnson’s Icotyde and Merck’s Lipfendra as examples of oral delivery with this class.

UNP was founded in 2016 by Cameron Pye, now its CEO, and Joshua Schwochert, its chief scientific officer, while they were finishing doctoral work at the University of California, Santa Cruz. After the deal closes, the team will keep working from Santa Cruz, which argenx says will be its “home for peptide discovery.” UNP will keep leading discovery “within a strategic framework agreed upon with argenx,” while argenx handles clinical development and commercialization.

Argenx CEO Karen Massey said UNP “adds macrocyclic peptide capabilities that are highly complementary to our antibody engineering and creates new possibilities for oral and long-acting medicines.”

A crowded partner list

UNP says it also has partnerships with Novartis, Merck, and BridgeBio. BioSpace reported that the original argenx collaboration, announced in July 2025, carried $1.5 billion in potential milestones, and that UNP raised $45 million in a Series B round in March with argenx and Merck’s venture arm taking part. Neither company said what happens to the other partnerships after the acquisition.

Why it matters

Argenx’s main business is antibodies given by infusion or injection. Buying a peptide platform signals that it wants oral or longer-acting options for immune-mediated diseases. The deal follows Gilead’s agreement in October to buy an oral macrocyclic IL-23 receptor program from PepStar Therapeutics, and comes as J&J’s Icotyde, an oral IL-23 receptor peptide, reaches more markets. Taken together, large companies are paying for the ability to make peptides into pills, not only for individual drugs.

What is not known

• Which diseases or targets argenx will pursue first. Neither release names a program.
• What the milestones are. Argenx described them only as specified development and regulatory milestones.
• How long it will take. No drug from the platform has been shown to work or be tolerable in people, and peptide discovery programs typically take years to reach patients.
• The fate of UNP’s other partnerships with Novartis, Merck, and BridgeBio.

We will update this story when the deal closes or argenx names its first peptide candidate.