(Bloomberg) -- Biogen Inc. agreed to acquire Human Immunology Biosciences Inc. for as much as $1.8 billion in a deal aimed at bolstering the biotechnology giant’s pipeline of immune disease treatments. 

Biogen will pay $1.15 billion upfront for the privately held company and as much $650 million in potential payments for reaching business goals, according to a statement from the companies Wednesday. The deal will bring Biogen felzartamab, an experimental treatment that’s been tested clinically in some rare immune conditions.

Biogen Chief Executive Officer Chris Viehbacher has been searching for smaller deals as sales of its mainstay multiple sclerosis medications decline and it waits for revenues from Leqembi, its new Alzheimer’s drug developed with Eisai Co., to start rising. In an interview last week with Bloomberg News, Viehbacher said Biogen “could spend a couple of billion this year” on deals.

Human Immunology’s drug could work in a broad range of immune-mediated diseases. It’s being developed for a kidney condition called primary membranous nephropathy and for complications after kidney transplants. The company has completed mid-stage studies in those conditions and plans to advance into late-stage trials.

Use in those two conditions could drive annual sales of as much as $1 billion worldwide, RBC Capital Markets analyst Brian Abrahams said in a note. However, the deal will use most of Biogen’s cash and push back the timeline for large future transactions, he said in the note. 

Last year, Viehbacher led the company’s largest-ever acquisition, paying $7.3 billion for Reata Pharmaceuticals Inc. and its approved treatment for the rare neurological disease Friedreich’s ataxia.

Biogen shares fell less than 1% shortly after the start of trading on Wednesday. The stock lost 12% this year through Tuesday’s close.

(Updates with analyst’s comment in fifth paragraph and share trading in seventh paragraph.)

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