Immunology company argenx announced on November 9, 2026, a definitive agreement to acquire Unnatural Products (UNP), a Santa Cruz, California-based macrocyclic peptide discovery company, in a transaction valuing UNP at up to approximately $1.15 billion.¹ argenx already holds a minority stake in UNP and will acquire all remaining shares. The company said UNP's peptide discovery engine could support oral or long-acting medicines for people with serious immune-mediated diseases.¹
Key facts
- Target: Unnatural Products, Santa Cruz, California
- Deal value: Up to approximately $1.15 billion
- Upfront: $550 million in cash on hand
- Milestones: Up to $595 million (development and regulatory)
- Technology: Macrocyclic peptide discovery (parallel experimentation plus machine learning)
- Therapeutic focus: Oral or long-acting medicines for immune-mediated diseases
- Prior relationship: Multi-target collaboration announced July 2025; argenx holds a minority stake
- Expected close: End of 2026, subject to customary conditions
- Site: UNP team stays in Santa Cruz as argenx's peptide discovery hub
“UNP adds macrocyclic peptide capabilities that are highly complementary to our antibody engineering and creates new possibilities for oral and long-acting medicines,” said Karen Massey, CEO of argenx, in a company press release.¹
What are the terms of the deal?
argenx will pay $550 million upfront from cash on hand and up to $595 million in payments contingent on specified development and regulatory milestones, for total potential consideration of up to approximately $1.15 billion.¹ The boards of directors of both companies have approved the transaction, which is expected to close by the end of 2026, subject to customary closing conditions.¹
How does the acquisition build on the existing partnership?
argenx said the deal builds on more than 2 years of collaboration and investment.¹ In July 2025, UNP announced a multi-target collaboration that gave argenx an exclusive option to develop and commercialize oral macrocyclic peptides against targets argenx identified, across multiple indications.² Under that agreement, UNP was eligible for up to approximately $1.5 billion in research, development, regulatory, and commercial milestones and option payments, plus tiered royalties. argenx also agreed to make an equity investment in UNP.²
After closing, UNP's team and leadership will continue to work from Santa Cruz, which will serve as argenx's home for peptide discovery.¹ UNP will continue to lead discovery work within a strategic framework agreed on with argenx, and argenx will contribute its clinical development and commercialization capabilities.¹
Why do oral macrocyclic peptides matter in immunology?
argenx's portfolio has been built on antibody engineering, including the first approved antibody fragment targeting the neonatal Fc receptor (FcRn).¹ The company said adding macrocyclic peptides could extend its immunology work to more patients through potential oral and long-acting medicines.¹ UNP's platform combines parallel experimentation with machine learning to address the medicinal chemistry challenges of macrocyclic peptides. The company is pursuing high-value targets that have traditionally been difficult to drug.¹ Cyclic peptides are an established drug class that can bind a broad range of protein targets while remaining capable of oral availability, although a 2024 review noted that identifying membrane-permeable, orally available cyclic peptides will still require technological improvements.³
