Biogen Inc. has announced a definitive agreement to acquire Apellis Pharmaceuticals in a deal valued at approximately $5.6 billion, marking a significant step in Biogen’s strategy to expand its portfolio in immunology and rare diseases.
Under the terms of the agreement, Biogen will purchase all outstanding Apellis shares for $41.00 per share in cash. In addition, shareholders will receive a nontransferable contingent value right (CVR), which could provide up to an additional $4 per share based on future sales performance of SYFOVRE. The payments are tied to specific annual global net sales milestones between 2027 and 2031.
The acquisition is expected to strengthen Biogen’s growth trajectory by adding two commercially available therapies—EMPAVELI and SYFOVRE—to its portfolio. Together, these treatments generated $689 million in net sales in 2025 and are projected to grow at a mid-to-high teens rate through at least 2028.
EMPAVELI is approved for multiple rare immune-mediated conditions, including paroxysmal nocturnal hemoglobinuria and certain kidney diseases such as C3 glomerulopathy and primary immune-complex membranoproliferative glomerulonephritis. Meanwhile, SYFOVRE is approved for geographic atrophy secondary to age-related macular degeneration, a leading cause of vision loss. Both therapies target complement component 3 (C3), a key part of the immune system involved in inflammation and disease progression.
Biogen expects the addition of Apellis to enhance both its near-term revenue and long-term earnings potential. The company also anticipates leveraging Apellis’ established U.S. commercial infrastructure, particularly in nephrology, to support the future launch of felzartamab, an investigational therapy currently in Phase 3 trials for kidney diseases.
Leadership from both companies emphasized the strategic alignment of the deal. Biogen noted that the acquisition complements its existing capabilities and accelerates its transformation into a diversified biotech leader. Apellis executives highlighted the opportunity to scale their innovation and reach more patients globally through Biogen’s resources and expertise.
The transaction, which has been approved by the boards of both companies, is expected to close in the second quarter of 2026, pending regulatory approvals and customary conditions. Biogen plans to finance the acquisition through a combination of cash and debt, with expectations to reduce leverage by the end of 2027.
Overall, the deal represents a major consolidation in the biotech sector and underscores the growing importance of complement-based therapies in treating complex and rare diseases.