Merck & Co. is acquiring Prometheus Biosciences in a $10.8 billion deal.

All the shares of Prometheus Biosciences will be acquired by a subsidiary of Merck for $200 per share..

The deal gives Merck promising immune disease treatments.

The acquisition is subject to Prometheus Biosciences shareholder approval.

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"The agreement with Prometheus will accelerate our growing presence in immunology where there remains substantial unmet patient need," said Robert M. Davis, Merck's chairman and chief executive officer. "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 had a market cap of $5.4 billion as of Friday’s market close. Its shares are up about 4% year-to-date.

Merck is looking to add new products to its pipeline as its top-selling drug cancer therapy Keytruda, is expected to lose patent protection this decade.

Merck’s sales last year came to $59.3 billion, with Keytruda sales making up roughly $21 billion of it.

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The San Diego-based Prometheus develops immune treatments and doesn’t have any approved products.

The company's pipeline drug in development treats immune diseases including ulcerative colitis and Crohn’s disease and recently reported separate positive study results in mid-stage testing.

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Company sales totaled $6.8 million last year.

Merck recently made another deal, agreeing to acquire blood-cancer biotech Imago BioSciences for $1.35 billion.

The Wall Street Journal first reported that talks were underway.