Biogen Inc (NASDAQ:BIIB, XETRA:IDP) will acquire Apellis Pharmaceuticals Inc (NASDAQ:APLS) for $41 per share in cash, in a deal valued at approximately $5.6 billion, it was announced on Tuesday.

Apellis shareholders will also receive a nontransferable contingent value right (CVR) worth up to $4 per share if certain global sales milestones for SYFOVRE are achieved.

Shares of Apellis surged more than 135% to about $40 on the news, while Biogen stock fell 5% to $178.

The acquisition brings two approved complement C3 therapies—EMPAVELI for rare kidney diseases and SYFOVRE for geographic atrophy secondary to age-related macular degeneration—into Biogen’s portfolio. In 2025, combined sales of the two products totaled $689 million, with mid-to-high teen growth expected at least through 2028.

Biogen said the deal will expand its presence in immunology and rare disease and strengthen its nephrology franchise, particularly supporting the development of felzartamab, currently in Phase III trials for multiple kidney diseases.

Jefferies views Biogen’s $5.6 billion acquisition of Apellis as a strategic move that strengthens the company’s portfolio in immunology, rare disease, and nephrology.

The firm highlighted that the deal provides immediate revenue from two commercialized complement C3 therapies, EMPAVELI and SYFOVRE, while also positioning Biogen for long-term growth through pipeline opportunities such as felzartamab, currently in Phase III trials for multiple kidney diseases.

From a financial perspective, Jefferies expects the transaction to be non-GAAP EPS accretive starting in 2027 and notes that Biogen is likely to de-lever by year-end 2027. The acquisition also diversifies Biogen’s revenue base, potentially adding $700 million to $1 billion annually through 2028, and improves the company’s commercial readiness in nephrology, the analysts wrote.

Jefferies also noted that while SYFOVRE’s current sales are below CVR milestone targets, the planned prefilled syringe and ongoing market expansion could support future growth. EMPAVELI is expected to reinforce Biogen’s position in nephrology and prepare the market for upcoming launches like felzartamab.

Overall, Jefferies considers the deal “multimodal,” offering both immediate revenue and strategic positioning for Biogen in high-value rare disease markets.

The transaction is expected to close in the second quarter of 2026.