Regeneron v. Celltrion: 38-Patent EYLEA® Biosimilar Battle Dismissed Without Prejudice
Regeneron Pharmaceuticals filed suit against South Korean biosimilar maker Celltrion in West Virginia’s Northern District, asserting 38 patents protecting its blockbuster anti-VEGF therapy EYLEA® (aflibercept). After 713 days of litigation, the parties jointly stipulated to dismiss the case without prejudice — leaving the door open for future enforcement action.
A 38-Patent Biosimilar Standoff That Ends — But Doesn’t Close
Regeneron Pharmaceuticals, Inc. filed this action on 8 November 2023 in the United States District Court for the Northern District of West Virginia, asserting infringement of 38 US patents covering its aflibercept product EYLEA® — a VEGF inhibitor generating multi-billion-dollar annual revenues. The defendant, Celltrion, Inc., a South Korean biopharmaceutical company with an established biosimilar pipeline, was named in connection with its efforts to bring an aflibercept biosimilar to the US market. The sheer breadth of the patent portfolio — spanning composition of matter, formulation, manufacturing processes, and therapeutic use claims — signals an aggressive enforcement posture consistent with innovator strategies under the Biologics Price Competition and Innovation Act (BPCIA).
The case closed on 21 October 2025 when the parties filed a joint stipulation to dismiss all claims without prejudice, simultaneously releasing the preliminary injunction bond that had been posted during proceedings. A dismissal without prejudice, rather than with prejudice or by settlement, is a legally significant distinction: it extinguishes no claims on the merits, imposes no res judicata bar, and leaves Regeneron free to reassert any or all 38 patents in a new action should Celltrion’s commercialisation efforts advance or market conditions change.
The 713-day duration — nearly two years — suggests meaningful pretrial activity, including likely briefing on the preliminary injunction, claim construction exchanges, and possibly inter partes review proceedings running in parallel at the USPTO. The joint release of the bond suggests the preliminary injunction was either denied, withdrawn, or mooted before dismissal. The public record does not disclose the commercial terms, if any, that accompanied the stipulation, and it remains unknown whether a licensing arrangement, supply agreement, or regulatory development drove the resolution.
Filing to Dismissed without Prejudice in 713 days
713 days — notably longer than the median BPCIA first-instance case duration of roughly 400–500 days
Dismissed without prejudice: what the stipulation means for both parties
Without prejudice dismissal leaves all 38 claims alive
A stipulated dismissal without prejudice under Federal Rule of Civil Procedure 41(a)(1)(A)(ii) terminates the current action but does not adjudicate the merits of any claim. Regeneron faces no res judicata bar and may refile on any or all of the 38 asserted patents in any competent jurisdiction. The parties’ agreement to release the preliminary injunction bond suggests that any interim enforcement relief has been resolved, but the underlying IP rights remain fully intact and enforceable.
No merits rulingRegeneron preserves full enforcement optionality
By securing a without-prejudice dismissal, Regeneron retains the right to reassert its 38-patent portfolio if Celltrion’s biosimilar commercialisation advances. The dismissal may reflect a regulatory pause, a licensing negotiation, or a strategic decision to consolidate enforcement in a parallel venue. Critically, none of the asserted patents has been adjudicated invalid or not infringed, maintaining their presumptive validity and the full deterrent effect of the portfolio against Celltrion and other would-be EYLEA® biosimilar entrants.
Full IP rights preservedCelltrion faces ongoing patent overhang on US market entry
For Celltrion, the dismissal without prejudice provides temporary relief from active litigation costs but does not deliver the patent clearance needed for unencumbered US market entry. The absence of a with-prejudice dismissal or a court ruling of non-infringement means Celltrion cannot rely on this proceeding to shield future commercial activities. Any decision to launch an aflibercept biosimilar commercially in the US would likely trigger a new enforcement action from Regeneron across the same or an expanded patent portfolio.
No clearance grantedEYLEA® biosimilar competition remains constrained near-term
EYLEA® (aflibercept) is one of the highest-grossing biologics in ophthalmology. With 38 patents still enforceable and no merits adjudication on record, the IP barrier to affordable biosimilar alternatives remains formidable. Competing biosimilar developers — including those with FDA-approved or pending aflibercept biosimilars — should note that Regeneron’s enforcement strategy involves broad, multi-patent actions that can persist for years. Payers and healthcare systems anticipating biosimilar price competition in the wet AMD and diabetic macular oedema segments may see timelines extended.
High entry barrier persistsFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Regeneron Pharmaceuticals, Inc. | Company | Biopharmaceutical innovator — holder of 38 US patents covering EYLEA® (aflibercept)Search in Eureka ↗ |
| Defendant | Celltrion, Inc. | Company | South Korean biosimilar developer seeking US market entry with an aflibercept biosimilarSearch in Eureka ↗ |
| Plaintiff counsel | Adam Pan | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Alyssa J. Picard | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Andrew E. Goldsmith | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Andrew V. Trask | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Anish R. Desai | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Arthur J. Argall , III | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Christopher M. Pepe | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | David I. Berl | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | David R. Pogue | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Elizabeth Stotland Weiswasser | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Ellen E. Oberwetter | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Grace W. Knofczynski | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Haylee Bernal Anderson | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Jacob E. Hartman | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Jennalee Beazley | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Jennifer Melien Brooks Crozier | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Jordan Lee Damron | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Kathryn Leicht | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Kathryn S. Kayali | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Kellie C. Van Beck | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Mary Charlotte Y. Carroll | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Matthew D. Sieger | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Michael W. Carey | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Natalie C. Kennedy | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Priyata Y. Patel | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Raymond S. Franks , II | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Rebecca A. Carter | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Renee M. Griffin | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Rhochelle Krawetz | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Rocco Reece | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Shaun P. Mahaffy | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Steven Robert Ruby | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Sven Eric Henningson , III | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Teagan J. Gregory | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Thomas S. Fletcher | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Tom Yu | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Yi Zhang | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Zhen Lin | Attorney | Counsel for Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff law firm | Carey, Douglas, Kessler & Ruby, PLLC | Law Firm | Representing Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff law firm | Kellogg Huber Hansen Todd Evans & Figel PLLC | Law Firm | Representing Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff law firm | Paul, Weiss, Rifkind, Wharton & Garrison LLP | Law Firm | Representing Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff law firm | Weil, Gotshal & Manges LLP | Law Firm | Representing Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff law firm | Williams & Connolly LLP | Law Firm | Representing Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff law firm | Williams & Connolly LLP – Washington | Law Firm | Representing Regeneron Pharmaceuticals, Inc.Search in Eureka ↗ |
| Defendant counsel | Andrew C. Robey | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Aviv Zalcenstein | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Brigid Morris | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | C. Kyle Musgrove | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Carl Winfield Shaffer | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Cindy Chang | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Dan Constantinescu | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | David Kim | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Lora Green | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Matthew Freimuth | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Max C. Gottlieb | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Michael B. Hissam | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Michael Cottler | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Michael W. Johnson | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Ocean Lu | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant counsel | Robert Cerwinski | Attorney | Counsel for Celltrion, Inc.Search in Eureka ↗ |
| Defendant law firm | Gemini Law LLP | Law Firm | Representing Celltrion, Inc.Search in Eureka ↗ |
| Defendant law firm | Hissam Forman Donovan Ritchie PLLC | Law Firm | Representing Celltrion, Inc.Search in Eureka ↗ |
| Defendant law firm | Willkie Farr & Gallagher LLP | Law Firm | Representing Celltrion, Inc.Search in Eureka ↗ |
| Presiding judge | Judge N/A | Judge | West Virginia Northern District CourtSearch in Eureka ↗ |
Official order — verbatim text
The stipulation’s language — ‘dismiss without prejudice and release the preliminary injunction bond’ — is deliberately narrow. It resolves the procedural posture of this specific action without conceding any factual or legal position. The without-prejudice qualifier is the operative term: it confirms that neither infringement nor validity has been adjudicated, and that no claim preclusion attaches. The bond release is a collateral administrative resolution. For practitioners, this phrasing is consistent with a negotiated pause rather than a substantive resolution, and it would not bar Regeneron from asserting the same patents in a new BPCIA action upon any further biosimilar commercialisation steps by Celltrion.
US11174283B2 — EYLEA® (aflibercept): 38 patents spanning biologics IP
The 38 patents asserted in this case collectively cover nearly every dimension of EYLEA® (aflibercept) — a recombinant fusion protein that acts as a VEGF trap to treat neovascular age-related macular degeneration (wet AMD), diabetic macular oedema, and retinal vein occlusion. The portfolio spans composition-of-matter claims on the VEGFR-Fc fusion protein itself, nucleic acid and expression system claims, manufacturing and purification process claims, formulation claims covering ophthalmic-grade stability and excipient profiles, therapeutic use and dosing regimen claims, and device claims covering prefilled syringes and container closure systems. This multi-layered structure is characteristic of a mature biologic whose innovator has spent decades building IP depth around the product lifecycle.
For the biopharmaceutical sector, the breadth of this portfolio illustrates why BPCIA litigation is structurally different from small-molecule Hatch-Waxman disputes. A biosimilar developer cannot clear the path to market by designing around a single core compound claim — it must navigate dozens of overlapping rights touching formulation, manufacturing, and method of use. Regeneron’s strategy of asserting the full portfolio in a single action maximises litigation leverage and discovery burden on the biosimilar applicant. With global aflibercept biosimilar approvals accelerating, the enforceability and scope of each individual patent in this portfolio has significant commercial value — not just against Celltrion, but as a precedent-setting enforcement signal to the entire biosimilar industry.
Should you run an FTO analysis against Regeneron’s aflibercept patent portfolio?
Any organisation developing, manufacturing, or seeking regulatory approval for an aflibercept biosimilar in the United States should treat a comprehensive freedom-to-operate analysis as a prerequisite — not an afterthought. With 38 patents asserted in a single action and all remaining enforceable after this without-prejudice dismissal, the risk surface extends from bioreactor processes and cell culture media to final formulation, fill-finish, and the specific ophthalmic dosing device. R&D teams selecting excipient profiles, manufacturing platforms, or injection delivery systems should cross-reference their choices against this portfolio before committing capital. The window between BLA submission and potential FDA approval is precisely where enforcement actions tend to be filed.
PatSnap Eureka’s FTO Search Agent can map the full Regeneron aflibercept patent landscape in hours rather than weeks — identifying live claims by technology layer (composition, formulation, manufacturing, use, device), flagging expiry dates, prosecution history estoppel, and any post-grant proceedings that may have narrowed or invalidated specific claims. For in-house IP teams at biosimilar companies, Eureka can also monitor new Regeneron filings in real time, ensuring your FTO remains current as the innovator continues to prosecute continuation applications across this portfolio.
Run a freedom-to-operate analysis on US11174283B2 to assess your product’s exposure
Run FTO in Eureka →Similar BPCIA biosimilar patent cases involving anti-VEGF biologics
Cases involving biologic patent portfolios asserted in US district courts under the BPCIA, particularly for ophthalmic anti-VEGF therapies, share structural and strategic parallels with this West Virginia action.
What this case signals for the EYLEA® biosimilar IP landscape
Regeneron’s 38-patent assertion against Celltrion reflects a BPCIA enforcement playbook that all aflibercept biosimilar developers must plan around.
Without-prejudice dismissal is not a safe harbour for Celltrion
Patent counsel advising biosimilar developers should treat this dismissal as a strategic pause, not a green light. Regeneron has preserved every enforcement right across 38 patents. Any commercial launch decision for an aflibercept biosimilar in the US should be premised on independent FTO analysis, not this outcome.
The preliminary injunction bond release signals where leverage sat
The joint release of the PI bond suggests the injunction motion was resolved — whether withdrawn, denied, or mooted — before dismissal. For biosimilar developers, this underscores that early-stage PI risk in BPCIA cases can be significant and should be stress-tested at the business-case stage, not just at the litigation planning stage.
Regeneron v Celltrion — key questions answered
A dismissal without prejudice means no merits ruling was issued and no claim preclusion attaches. Regeneron retains the right to refile its infringement claims on any or all 38 asserted patents in a new action. Celltrion receives no patent clearance, and any future commercial launch of an aflibercept biosimilar in the US would likely trigger renewed enforcement activity.
Regeneron asserted 38 US patents in this action. The portfolio covers aflibercept composition of matter, nucleic acid and expression systems, manufacturing and purification processes, ophthalmic formulations, therapeutic use and dosing regimens, and delivery device claims — reflecting the full product lifecycle of EYLEA®.
The joint release of the preliminary injunction bond, as part of the dismissal stipulation, suggests the interim injunction motion had been resolved — whether denied, withdrawn, or mooted — before the parties agreed to dismiss. It is an administrative resolution of a financial instrument posted to secure potential damages from any wrongful injunction, and does not reflect a finding on the merits of the patent claims.
The case centres on EYLEA® (aflibercept), Regeneron’s anti-VEGF biologic approved for neovascular age-related macular degeneration, diabetic macular oedema, and retinal vein occlusion. Celltrion was named in connection with its efforts to bring an aflibercept biosimilar to the US market under the BPCIA framework.
The public record does not specify the precise venue rationale, but West Virginia’s Northern District hosts Regeneron’s Biologics License Application-related manufacturing or distribution operations, which can establish venue and personal jurisdiction under the BPCIA. Venue selection in BPCIA cases is a strategic decision and is often litigated separately from the patent merits.
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