Merck, known as MSD outside the US, and Canada, has agreed to acquire US-based biotechnology company Prometheus Biosciences, for a total consideration of about $10.8bn.

Under the terms of the agreement, Merck, through its subsidiary, will acquire all the outstanding shares of Prometheus at a price of $200 per share.

Prometheus is a clinical-stage biotechnology company engaged in the discovery, development, and marketing of novel therapeutic and companion diagnostics for immune-mediated diseases.

Its lead candidate, PRA023, is a humanised monoclonal antibody directed to tumour necrosis factor (TNF)-like ligand 1A (TL1A), which targets both intestinal inflammation and fibrosis.

The transaction is expected to be completed in the third quarter of 2023, subject to certain conditions, including the Hart-Scott-Rodino Antitrust Improvements Act and other conditions.

Prometheus Biosciences chairman and chief executive officer Mark McKenna said: “This agreement with Merck, a leader in biopharmaceutical research and development, allows Prometheus to maximise the potential for PRA023, while continuing to apply our technology and expertise to fuel further discoveries to address the needs of patients with immune disorders.”

Merck chairman and chief executive officer Robert M Davis said: “The agreement with Prometheus will accelerate our growing presence in immunology where there remains a substantial unmet patient need.

“This transaction adds diversity to our overall portfolio and is an important building block as we strengthen the sustainable innovation engine that will drive our growth well into the next decade.”

Prometheus is developing PRA023 to treat immune-mediated diseases, including ulcerative colitis (UC), Crohn’s disease (CD), and other autoimmune conditions.

In December last year, the company announced positive results from ARTEMIS-UC, a Phase 2, placebo-controlled, study evaluating the safety and efficacy of PRA023, in active UC patients.

The company also announced positive results for PRA023 from Phase 2A APOLLO-CD study evaluating safety and efficacy in patients with moderate to severe CD.

Morgan Stanley & Co. served as a financial advisor, while Paul, Weiss, Rifkind, Wharton & Garrison as legal advisors to Merck, on this transaction.

Centerview Partners and Goldman Sachs & Co. served as financial advisors and Latham & Watkins as legal advisor to Prometheus.

In a separate development, Merck, and its partner Moderna, announced the first presentation of detailed results from the Phase 2b KEYNOTE-942/mRNA-4157-P201 trial.

The trial evaluated Moderna’s investigational individualised neoantigen therapy (INT) mRNA-4157 (V940), in combination with Merck’s anti-PD-1 therapy KEYTRUDA, in patients with resected high-risk melanoma.

In the study, treatment using mRNA-4157 (V940) plus KEYTRUDA showed a statistically significant and clinically meaningful improvement in recurrence-free survival (RFS), reducing the risk of recurrence or death by 44%, compared with KEYTRUDA alone.

Moderna senior vice president and development, therapeutics and oncology head Kyle Holen said: “Today’s results provide further encouragement for the potential of mRNA as an individualised neoantigen therapy to positively impact patients with high-risk resected melanoma.

“The profound observed reduction in the risk of recurrence-free survival suggests this combination may be a novel means of potentially extending the lives of patients with high-risk melanoma.”