On November 8, 2023, Regeneron Pharmaceuticals Inc. filed a BPCIA Complaint against Celltrion Inc. in the district court for the northern district of West Virginia, asking the Court to block CT-P42Celltrion’s proposed biosimilar of Regeneron’s drug Eylea® (aflibercept) – from entering the United States market. Regeneron Pharmaceuticals Inc. v. Celltrion Inc., N.D.W.Va., No. 1:23-cv-00089. In their Complaint, Regeneron alleges that Celltrion infringes 38 patents owned by Regeneron and directed at compositions and methods related to retinal-disease treatment.

42 U.S.C. § 262(l) outlines a framework for applicants and reference product sponsors (“RPS”) to resolve patent disputes and engage in the so-called “patent dance”.  Briefly, Celltrion publicly announced on June 30, 2023 that it had filed an abbreviated Biologics License Application (“aBLA”) for CT-P42 with the FDA, followed by serving Regeneron with a copy of the aBLA on September 13, 2023 and informing Regeneron that it intended to commercially market CT-P42 immediately upon receiving FDA approval, which could occur as early as May 18, 2024 when Regeneron’s regulatory exclusivity for Eylea expires.  On November 7, 2013 Regeneron provided Celltrion with a list of Regeneron’s patents that would be allegedly infringed by CT-P42 and on the next day filed a Complaint seeking declaratory judgment of patent infringement.  To our knowledge, this case presents the first BPCIA fact pattern where the RPS (i.e., Regeneron) brought suit after receiving the biosimilar applicant’s aBLA and responsively providing a list of patents without waiting for the “patent dance” to proceed beyond the patent list stage.

Judge Kleeh, who is assigned to the Celltrion action, held a 10-day bench trial in June 2023 in another BPCIA suit brought by Regeneron against Viatris Inc.’s Mylan Pharmaceutical unit, alleging that their proposed biosimilar for Eylea – “M710” or “Yesafili™” – infringes three of Regeneron’s patents. Regeneron Pharmaceuticals, Inc. v. Mylan Pharmaceuticals Inc., N.D.W.Va., No. 1-22-cv-00061 (filed August 2, 2022; pending). Two of the patents asserted in the Mylan action – U.S. Pat. Nos. 10,888,601 and 11,253,572, which cover dosing – are among the 38 patents asserted against Celltrion in the Celltrion action, and were subject to inequitable conduct counterclaims by Mylan. A week before trial, Judge Kleeh granted Regeneron’s request for judgment on the pleadings and cleared both patents from Mylan’s inequitable conduct counterclaims. Noteworthy, in August 2023, Celltrion brought a Motion to Intervene in the Mylan action seeking to unseal or redact certain sealed filings and noted that “At some point in the future, Regeneron may threaten to file a patent infringement suit against Celltrion asserting some or all of the patents against Mylan, to delay CT-P42 from coming to market and competing with Eylea.” Judge Kleeh ordered the unsealing of 30 docket entries and some related exhibits.

The Celltrion Complaint can be found here.  We continue to monitor both of these pending cases. For more information about these and other biosimilar patent disputes, visit Venable’s BiologicsHQ at


The authors would like to thank April Breyer Menon for her contributions to this article.


    Information contained in the Venable BiologicsHQ database relates to FDA-approved drug products listed in the CDER Purple Book or on the FDA website ( Information relating to FDA licensed products, FDA-approved indications, and aBLA and 505(b)(2) applications is obtained from public sources including the U.S. FDA website ( Information relating to litigations is given only for cases active from January 31, 2010 onward. Information relating to foreign biosimilar / biologics follow-on products approved in Australia, Canada, the E.U., Japan and South Korea is from public sources. Statistics graphics are compiled from information contained in the Venable BiologicsHQ database.


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