Regeneron Seeks to Strike Amgen's Patent Counterclaims in Aflibercept Biosimilar Litigation
Key Insights
Regeneron filed a motion on November 12, 2025, to strike and dismiss multiple counterclaims from Amgen in their ongoing aflibercept patent litigation in West Virginia federal court.
The dispute centers on Amgen's aflibercept biosimilar PAVBLU®, which launched in October 2024 after a Federal Circuit ruling denied Regeneron's preliminary injunction request.
Regeneron challenges Amgen's inequitable conduct allegations, arguing they fail to meet heightened pleading requirements and mischaracterize patent law regarding inventorship and written description.
Regeneron Pharmaceuticals has escalated its legal battle with Amgen by filing a motion to strike and dismiss multiple counterclaims in their high-stakes aflibercept biosimilar patent litigation. On November 12, 2025, Regeneron filed the motion in the U.S. District Court for the Northern District of West Virginia, targeting what it characterizes as Amgen's "kitchen-sink approach" to patent defense.
The litigation centers on Amgen's aflibercept biosimilar, PAVBLU®, which successfully launched in October 2024 following a favorable Federal Circuit ruling. In March 2025, the U.S. Court of Appeals for the Federal Circuit affirmed the district court's denial of Regeneron's motion for a preliminary injunction concerning U.S. Patent No. 11,084,865, clearing the path for Amgen's market entry.
Patent Dispute Intensifies with New Claims
The legal conflict expanded in June 2025 when Regeneron filed a new lawsuit against Amgen, asserting the newly issued U.S. Patent No. 12,331,099 (the '099 patent). Amgen responded aggressively on September 12 with fourteen affirmative defenses and multiple counterclaims, including declaratory judgments of non-infringement, invalidity, and unenforceability due to prosecution laches, inequitable conduct, and patent misuse. The company also raised Sherman Act antitrust "Walker Process" fraud claims and unfair competition claims under California law.
Regeneron's recent motion specifically targets counterclaims for unclean hands, laches, inequitable conduct, and patent misuse, while also seeking dismissal of Amgen's antitrust and California Unfair Competition Law (UCL) counterclaims. According to Regeneron, Amgen's defenses demonstrate "Strangelovian nonchalance" toward Federal Circuit precedent.
Inequitable Conduct Allegations Under Fire
The most significant aspect of the dispute involves Amgen's inequitable conduct allegations, which Regeneron describes as the "atomic bomb" of patent litigation due to their potential to render entire patents unenforceable. Amgen asserted that the '099 patent is unenforceable because Regeneron's counsel allegedly misrepresented to the Patent and Trademark Office that the inventors of the '865 patent also invented the subject matter claimed in the '099 patent and falsely "asserting that the claims of the '099 [p]atent did not present new matter beyond the description in the originally filed application."
Regeneron argues that Amgen's Answer "inject[s] chaos into this already-complicated MDL" and "presents a bizarre picture of inequitable conduct law." The company contends that Amgen has failed to satisfy the heightened pleading requirements mandated by Federal Rule of Civil Procedure 9(b) for inequitable conduct claims and other fraud-based claims, which require parties to "state with particularity the circumstances constituting fraud or mistake."
Regarding inventorship, Regeneron insists that Amgen's theory "proceeds directly from its misreading of the claims." The company argues that Amgen's reduction to practice of a different, "buffer-free" species within the genus described and claimed in the '099 patent "does not make Amgen an inventor on the '099 patent—it makes Amgen an infringer."
Written Description Defense Challenged
On Amgen's "no new matter" theory, Regeneron characterizes it as "an impermissible repackaging of its written-description invalidity position." While Amgen argues that the '099 patent claims lack adequate written-description support, Regeneron maintains that "such disagreement does not establish or reasonably suggest Regeneron's counsel knew the claims lack support or offered its 'no new matter' argument with an intent to deceive."
Regeneron further contends that the "no new matter" theory could not have been material to the issuance of the '099 patent claims because the examiner possessed all relevant information to make a determination.
Antitrust Claims Face Dismissal Challenge
Amgen's antitrust counterclaims for monopolization, based on alleged fraud in the procurement and assertion of the '099 patent and twelve other patents, also face Regeneron's dismissal motion. Regeneron argues that no fraud occurred in the procurement of any of these patents and that none of Amgen's alleged losses constitute "antitrust injuries" attributable to Regeneron.
Regeneron invokes the purpose of the Biologics Price Competition and Innovation Act (BPCIA), noting that the patent dance framework affords biosimilar applicants like Amgen "substantial control over the scope of the first phase of litigation." Therefore, Amgen's claim for antitrust injuries in the form of litigation costs should fail, according to Regeneron.
The company argues that Amgen's California UCL claims arise from the same conduct underlying its federal antitrust claims and should be dismissed for identical reasons. Additionally, Regeneron contends that laches is inapplicable and that the patent misuse and equitable doctrines defenses are inadequately pleaded.
The outcome of this motion could significantly impact the scope and complexity of the ongoing litigation between these two pharmaceutical giants in the competitive aflibercept biosimilar market.