Shares of Apellis Pharmaceuticals Inc. exploded more than 135% Tuesday after the biotech company announced it would be acquired by larger rival Biogen Inc., in a deal that promises to supercharge growth in immunology, rare diseases and nephrology.

Apellis Pharmaceuticals
Apellis Pharmaceuticals

Apellis stock (NASDAQ: APLS) surged to around $40.30 in morning trading, up $23.20 or 135.78% from Monday's close near $17.10, with heavy volume exceeding 33 million shares. The dramatic move pushed the stock to a new 52-week high and erased months of pressure that had seen shares trade as low as the mid-teens in recent weeks.

The acquisition, announced early Tuesday, marks a significant exit for Apellis, a company known for its pioneering work in complement system inhibitors. Biogen will gain access to Apellis' portfolio led by SYFOVRE (pegcetacoplan injection), the first approved therapy for geographic atrophy (GA) secondary to age-related macular degeneration, and EMPAVELI (pegcetacoplan), approved for paroxysmal nocturnal hemoglobinuria (PNH) and as the first treatment for C3 glomerulopathy (C3G) and primary immune complex membranoproliferative glomerulonephritis (IC-MPGN) in patients 12 and older.

"Biogen to Acquire Apellis, Enhancing the Company's Growth Portfolio in Immunology and Rare Disease, Bolstering Growth Outlook and Accelerating Expansion into Nephrology," the companies said in a joint statement. The deal is expected to strengthen Biogen's pipeline in high-unmet-need areas while providing Apellis shareholders with a premium and immediate liquidity after a volatile period.

Analysts and investors had been watching Apellis closely in recent months. The stock had faced headwinds, declining about 17% since its last earnings report and trading down more than 30% year-to-date as of late March amid broader biotech sector pressures and mixed commercial performance signals. SYFOVRE, while holding roughly 60% market share in GA injections according to some analyst notes, saw fourth-quarter U.S. net product revenue dip slightly to $155 million from $168 million a year earlier. Full-year 2025 SYFOVRE sales reached $587 million.

EMPAVELI showed stronger momentum, with U.S. net product revenue climbing to $35 million in the fourth quarter and $102 million for the full year 2025. The drug's expansion into rare kidney diseases following its July 2025 FDA approval generated excitement, with data showing a 68% reduction in proteinuria and stabilization of kidney function in the Phase 3 VALIANT study.

Apellis reported total revenue of nearly $200 million for the fourth quarter of 2025 and $1 billion for the full year, boosted in part by a one-time $275 million upfront payment related to a royalty repurchase agreement with Sobi. The company swung to a full-year net income of $22.4 million in 2025 from a loss the prior year, though it posted a fourth-quarter net loss of $58.9 million. Cash and equivalents stood at about $466 million at year-end.

Wall Street had remained broadly bullish despite the recent slump. Analysts maintained a consensus "Buy" rating with average price targets around $31–$33 before Tuesday's news, implying substantial upside even from the pre-surge levels. Recent initiations, such as Roth MKM's "Buy" at $31 in mid-March, cited strong underlying demand for SYFOVRE and EMPAVELI's potential in nephrology. JPMorgan had also expressed an overweight stance.

The Biogen deal comes as Apellis continues to invest in its pipeline. The company highlighted plans for an investigational new drug submission in the second half of 2026 and presented long-term data, including five-year GALE study results for SYFOVRE showing it could delay GA progression by approximately 1.5 years. It also added high-profile talent, appointing Mikael Dolsten, M.D., Ph.D., former chief scientific officer at Pfizer, to its board in early March.

For patients, the transaction could accelerate access and development. Complement inhibition represents a relatively new but powerful approach to treating diseases driven by overactive immune responses. SYFOVRE addressed a previously untreatable leading cause of blindness in older adults, while EMPAVELI offers hope for rare conditions like PNH and C3G/IC-MPGN that affect thousands in the U.S. and have limited options.

Biogen, known for its multiple sclerosis franchise and Alzheimer's efforts, gains a complementary immunology platform that could diversify revenue and bolster its rare disease ambitions. The deal is expected to close subject to customary conditions, including regulatory approvals.

Market reaction was swift and overwhelmingly positive for Apellis shareholders. The more than doubling of the stock price in a single session reflects both relief after recent weakness and enthusiasm for the strategic fit with Biogen. Trading volume was among the highest in the company's history for a single day.

Apellis, founded in 2009 and headquartered in Waltham, Massachusetts, has focused on developing targeted C3 therapies. Its success with pegcetacoplan — marketed as both SYFOVRE for the eye and EMPAVELI for systemic use — positioned it as a leader in complement medicine, a field that has seen renewed interest in recent years.

Industry observers noted that while the acquisition premium appears rich, it aligns with Biogen's strategy to build scale in growing therapeutic areas. Nephrology expansion, in particular, could open new markets given the chronic nature of kidney diseases and the high value of therapies that slow progression.

Looking ahead, the combined entity will likely prioritize commercialization efforts for existing approvals while advancing earlier-stage programs. Apellis had guided for modestly higher operating expenses in 2026 to support new pivotal trials and milestone payments.

Tuesday's surge also highlights the biotech sector's sensitivity to M&A news. After a period of subdued dealmaking and pressure from high interest rates and clinical setbacks, positive corporate actions can trigger rapid repricing.

Investors should note that while the deal provides certainty, integration risks and execution on commercial targets remain. Gross-to-net adjustments for SYFOVRE trended in the mid-20% range in late 2025 and were expected to rise slightly in 2026.

Apellis did not immediately respond to requests for additional comment beyond the official release. Biogen officials similarly pointed to the joint announcement.

The transaction underscores ongoing consolidation in biotech, where larger players with deeper pockets acquire innovative but smaller companies to fuel pipelines amid patent cliffs and R&D challenges.

As of mid-morning Tuesday, Apellis shares were trading at $40.33, up sharply on the news, while broader markets showed modest gains.

This deal could reshape competitive dynamics in complement therapeutics and eye disease treatments. For Apellis employees and patients relying on its therapies, the backing of a larger pharmaceutical company may bring greater resources for manufacturing, global expansion and further research.

Analysts will now turn their attention to the final deal terms, expected synergies and any potential divestitures. Until the acquisition closes, Apellis will continue operating independently, advancing its commercial execution and pipeline milestones.

The dramatic stock reaction — one of the largest single-day percentage gains in recent biotech memory — is likely to fuel discussion about undervaluation in the sector and the appetite for strategic combinations.

Apellis Pharmaceuticals had faced a challenging 2025-early 2026 period with shares pressured by quarterly sales fluctuations and broader market sentiment. The Biogen agreement appears to validate the long-term potential of its science and commercial assets.