Regeneron v. Celltrion: 25-Patent EYLEA® Biosimilar Dispute Dismissed Without Prejudice
Regeneron Pharmaceuticals filed suit against Celltrion in the Northern District of West Virginia, asserting 25 patents covering EYLEA® (aflibercept) formulations and biologics manufacturing against Celltrion’s biosimilar candidate CT-P42. After 522 days of litigation, the parties jointly stipulated to dismiss the case without prejudice, releasing the preliminary injunction bond — leaving the door open to future proceedings.
A 25-patent EYLEA® biosimilar battle ends without a verdict — but not without consequence
Regeneron Pharmaceuticals, Inc. filed Case No. 1:24-cv-00053 on 17 May 2024 in the U.S. District Court for the Northern District of West Virginia before Judge Thomas S. Kleeh. The complaint asserted 25 U.S. patents covering aflibercept protein formulations, biologics manufacturing processes, container systems, and related EYLEA® technology against Celltrion, Inc.’s biosimilar candidate CT-P42, which was seeking regulatory approval to compete with EYLEA® in the U.S. market.
On 21 October 2025, after 522 days of litigation, Regeneron and Celltrion entered into a joint stipulation — subject to court approval — to dismiss all claims without prejudice and to release the preliminary injunction bond that had been posted during the proceedings. The dismissal without prejudice means no court has ruled on the merits of infringement or validity for any of the 25 asserted patents, and Regeneron retains the right to reassert these claims in future proceedings.
The release of the preliminary injunction bond alongside the dismissal suggests the dispute had reached a stage where injunctive relief was actively sought — consistent with BPCIA litigation patterns where patent holders seek to block commercial launch. The absence of a public settlement agreement leaves the commercial terms, if any, undisclosed. The voluntary, mutual nature of the stipulation, combined with the scope of the original complaint, suggests the parties may have reached a business arrangement outside the public record — though this cannot be confirmed from available filings.
Filing to Dismissed without Prejudice in 522 days
522 days — longer than the median BPCIA district court biosimilar dispute before resolution
Dismissed without prejudice: what the stipulated exit means for both parties
Dismissal without prejudice preserves Regeneron’s right to refile
A stipulated dismissal without prejudice under Federal Rules of Civil Procedure means the court has made no ruling on the merits of infringement or patent validity. Unlike a dismissal with prejudice, this outcome does not bar Regeneron from reasserting any or all of the 25 patents against Celltrion’s CT-P42 in future litigation. The release of the preliminary injunction bond indicates the parties resolved the immediate injunctive threat as part of the exit.
No merits ruling; refile rights preservedRegeneron exits with patents intact and no adverse validity finding
For Regeneron, dismissal without prejudice is a strategically neutral-to-positive exit: none of its 25 EYLEA® patents have been invalidated or found non-infringed by the court. The patents remain fully enforceable and can be asserted again — against Celltrion or other biosimilar entrants — should commercial or regulatory circumstances change. Whether this exit reflects a licensing arrangement, a market-entry agreement, or purely a tactical pause is not ascertainable from the public record.
25 patents remain enforceableCelltrion avoids adverse judgment but faces ongoing patent uncertainty for CT-P42
Celltrion secures dismissal of the immediate case without any court finding of infringement — a meaningful procedural win. However, the without-prejudice nature means the threat of relitigation persists for CT-P42’s commercial path. Celltrion’s position is consistent with a party that has either reached a private accommodation with Regeneron or is willing to accept continued uncertainty in exchange for near-term commercial flexibility. The injunction bond release suggests the acute threat of launch delay has passed, at least for now.
No infringement finding; uncertainty persistsEYLEA® biosimilar market entry remains commercially unsettled
With 25 patents spanning formulation, manufacturing, and device aspects of aflibercept, Regeneron’s IP estate around EYLEA® is among the most layered in the biologics space. This dismissal does not clear CT-P42 of patent risk — it simply removes the immediate litigation pressure. Competitors and payers monitoring the EYLEA® biosimilar market should note that the patent landscape for aflibercept remains heavily defended, and the resolution of this case provides no precedential guidance on infringement or validity of any asserted claim.
Patent thicket around EYLEA® unresolvedFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Regeneron Pharmaceuticals, Inc. | Company | Biopharmaceutical innovator — holder of 25 EYLEA® (aflibercept) patentsSearch in Eureka ↗ |
| Defendant | Celltrion, Inc. | Company | South Korean biopharmaceutical company seeking U.S. approval for CT-P42 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 | Evan T. Leo | 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 | 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 | 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 | 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 Recce | 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 Thomas S Kleeh | Judge | West Virginia Northern District CourtSearch in Eureka ↗ |
Official order — verbatim text
The stipulation records a joint agreement to dismiss ‘without prejudice’ and to ‘release the preliminary injunction bond’ — two legally distinct actions combined in one filing. The without-prejudice language confirms no merits adjudication occurred on any of the 25 asserted patents. The bond release clause is significant: it resolves any financial undertaking Celltrion may have provided as a condition of avoiding or lifting an injunction, formally closing the injunctive phase of the dispute. Neither party is bound by any court finding on infringement or validity.
25 EYLEA® (aflibercept) Patents — Formulation, Process & Device Portfolio
The 25 patents asserted by Regeneron span a comprehensive EYLEA® (aflibercept) patent estate covering multiple technology layers: protein formulation chemistry, biologics manufacturing and purification processes, cell culture methods, and container/device systems for intravitreal drug delivery. The portfolio includes patents issued across a decade-long filing window, reflecting iterative innovation and lifecycle management of the aflibercept franchise. This layered architecture — combining composition-of-matter, process, and device claims — is characteristic of a mature biologic’s patent thicket strategy designed to extend market exclusivity beyond the core molecule.
For biosimilar developers, the breadth of this 25-patent portfolio represents one of the most significant IP barriers in the ophthalmic biologics market. Competing aflibercept biosimilar sponsors — not just Celltrion — face potential infringement exposure across formulation choice, manufacturing process design, and device selection. Because no court has invalidated or construed any claim in this dispute, the full scope of each patent remains untested. This creates material commercial uncertainty for any company seeking to launch an EYLEA® biosimilar in the U.S. without either a license from Regeneron or successful IPR proceedings against the asserted patents.
Should you run an FTO against Regeneron’s 25-patent EYLEA® portfolio?
Any company developing, manufacturing, or commercialising an aflibercept biosimilar — including CT-P42 and competing programs — should treat this case as a clear signal to conduct a comprehensive freedom-to-operate analysis against Regeneron’s 25-patent EYLEA® estate. The portfolio spans formulation, upstream and downstream biologics manufacturing, cell culture, and drug-device combination claims. A standard single-patent FTO is insufficient; the analysis must be segmented by technology layer to identify which specific manufacturing choices or formulation decisions create infringement exposure.
PatSnap Eureka’s FTO Search Agent can map the full claim landscape across all 25 asserted patents, cross-reference your product’s technical specifications against independent and dependent claims, and flag high-risk claims for attorney review. Eureka’s biologics patent analytics also surface related continuation and divisional applications in Regeneron’s prosecution pipeline — giving your team early warning on patents not yet issued that may cover next-generation EYLEA® formulations or manufacturing improvements. Start your FTO review before your IND or BLA filing window, not after.
Run a freedom-to-operate analysis on US9222106B2 to assess your product’s exposure
Run FTO in Eureka →Similar BPCIA Biosimilar Patent Disputes Involving Ophthalmic Biologics
Cases involving BPCIA patent litigation over aflibercept and ophthalmic biologics in U.S. district courts, including multi-patent infringement actions against biosimilar candidates.
What this case signals for the EYLEA® biosimilar and BPCIA IP landscape
A 25-patent BPCIA filing dismissed without prejudice is a rare and commercially significant signal for the entire aflibercept biosimilar market.
Regeneron’s 25-patent assertion strategy raises the cost of biosimilar entry
Filing 25 patents in a single BPCIA infringement action signals a maximalist enforcement posture. Even without a merits ruling, the litigation cost and injunction risk imposed on Celltrion demonstrates the deterrent value of a broad patent estate. Companies planning CT-P42 or competing aflibercept biosimilars should anticipate multi-front patent challenges covering formulation, process, and device claims.
Bond release as a dismissal term warrants close monitoring in BPCIA disputes
The explicit release of the preliminary injunction bond as part of the stipulated dismissal is structurally notable. It suggests Regeneron had secured bond-backed injunctive relief or a bond undertaking during the 522-day dispute. IP teams tracking BPCIA cases should treat injunction bond terms as a key indicator of litigation leverage and potential settlement timing in biosimilar patent disputes.
Regeneron v Celltrion — key questions answered
Regeneron Pharmaceuticals filed suit against Celltrion in the Northern District of West Virginia on 17 May 2024, asserting 25 patents covering EYLEA® (aflibercept) formulations and biologics technology against Celltrion’s biosimilar CT-P42. After 522 days of litigation, the parties stipulated to dismiss all claims without prejudice and release the preliminary injunction bond, with the case closing on 21 October 2025. No court ruled on the merits of infringement or patent validity.
A dismissal without prejudice means no court has adjudicated infringement or validity for any of the 25 asserted patents. All patents remain in force and fully enforceable. Regeneron retains the right to assert any or all of these patents against Celltrion’s CT-P42 or other biosimilar products in future litigation. The patents are not weakened or narrowed by this outcome.
CT-P42 is Celltrion’s aflibercept biosimilar candidate referencing Regeneron’s EYLEA®, an anti-VEGF therapy used to treat wet age-related macular degeneration and other retinal conditions. Under the Biologics Price Competition and Innovation Act (BPCIA), biosimilar sponsors must notify the reference product sponsor of their regulatory filing, triggering a patent dispute resolution process. Regeneron responded by asserting 25 patents covering multiple aspects of aflibercept technology.
The joint stipulation explicitly included release of the preliminary injunction bond, indicating that during the 522-day litigation, Regeneron had sought or obtained a preliminary injunction — or a bond undertaking was required as a condition of injunctive proceedings. Releasing the bond as part of the dismissal formally resolves any financial security posted in connection with that injunctive relief, confirming that the injunctive phase of the dispute is closed alongside the substantive claims.
Regeneron asserted 25 U.S. patents in Case No. 1:24-cv-00053. The patents cover a broad range of EYLEA® (aflibercept) technology including protein formulations, biologics manufacturing and purification processes, cell culture methods, and container and device systems. The multi-patent assertion is consistent with BPCIA litigation strategy, where reference product sponsors assert comprehensive patent estates to maximise barriers to biosimilar market entry.
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