Biogen agreed to acquire Apellis Pharmaceuticals for about $5.6 billion, expanding the Massachusetts-based biotech’s immunology and rare-disease portfolio with two marketed assets. The deal gives Biogen access to Empaveli (C3G and primary IC-MPGN) and Syfovre (geographic atrophy secondary to age-related macular degeneration). Under the terms described, Biogen will pay $41 per Apellis share upfront, with additional contingent value right payments tied to Syfovre global net sales milestones. The acquisition is expected to add near-term revenue and commercial infrastructure as Biogen prepares launches including felzartamab. The transaction further signals that large-cap immunology strategy is increasingly being built through buying approved late-stage franchises rather than relying only on internal pipeline execution.