Context: Alnylam first sued Moderna in the District of Delaware in 2022 for allegedly infringing two patents related to lipid nanoparticle (LNP) technology in its COVID-19 vaccine Spikevax. Last October, the parties jointly agreed to dismiss the case without prejudice after Judge Colm Connolly of the United States District Court for the District of Delaware issued an opinion in favour of Moderna. More specifically, Judge Connolly wrote that Alnylam had acted as lexicographer when defining in the patent specification the term “branched alkyl” and that, based on this definition, Moderna did not infringe the asserted patent claims. Alnylam filed an appeal based on the issue of claim construction.
What’s new: In a precedential decision issued on Wednesday, the United States Court of Appeals for the Federal Circuit has upheld the district court’s judgment, finding Moderna did not infringe Alnylam’s patents (June 5, 2025 CAFC opinion). The court concluded that Alnylam had acted as its own lexicographer in defining the term “branched alkyl” in its patent specifications and this definition foreclosed Alnylam’s infringement allegations against Moderna.
Direct impact: An Alnylam spokesperson said the company is reviewing the Wednesday ruling and considering its options, while a Moderna spokesperson said it was “pleased” with the decision and that its vaccine was “a product of many years of pioneering mRNA platform research and development.”
Wider ramifications: The case is significant as it is uncommon to see a patentee go back on a definition it wrote itself in a patent specification. This tactic is often employed by defendants in an effort to invalidate a patent. But, in this case, Alnylam attempted to undercut its own definition. Despite its attempts, the Federal Circuit decided its arguments were not sufficient enough to override its own definition.
The patents-in-suit, both entitled “Biodegradable lipids for the delivery of active agents”, include:
In Alnylam’s original allegations, the plaintiff alleged that Moderna’s Spikevax contains a cationic lipid (for drug and gene delivery), SM-102, that is claimed by the asserted patents. But, in its decision last year, the district court concluded that its definition of “branched alkyl” is so specific that Moderna’s vaccine could not possibly meet the requirement listed under that definition, which is:
“Unless otherwise specified, the term “branched alkyl”… refer[s] to an alkyl… group in which one carbon atom in the group (1) is bound to at least three other carbon atoms and (2) is not a ring atom of a cyclic group.”
Alnylam argued in its appeal that the definition did not apply to claims covering “branching” at the “alpha position” adjacent to biodegradable groups, where the chemical structure would permit only two carbon-carbon bonds rather than three.
But the Federal Circuit rejected this argument, concluding:
“Though the prosecution history comes closest to suggesting that Alnylam understood a branched alkyl to include a secondary carbon, we conclude that it is not sufficiently decisive to override the definition set forth in column 412.”
In this paragraph, the Federal Circuit is suggesting that Alnylam had attempted to claim something broader but limited itself. This was for the following five reasons (pages 9 and 10):
- Heading “Definitions” in the specification;
- Quotation marks around the term “branched alkyl”;
- Use of the phrase “refer to”, which courts often treat as definitional;
- Contrast with other terms in the section that used non-limiting language like “e.g.” or “include”; and
- The clause “Unless otherwise specified,” imposes a strict standard: any departure must be clearly and unambiguously specified elsewhere in the intrinsic record.
The Federal Circuit also upheld the district court’s findings that Alnylam acted as lexicographer in its requirement of a carbon bound to at least three other carbons “[u]nless otherwise specified”, ruling that Alnylam did not otherwise specify for purposes of the asserted claims.
Counsel
Alnylam was represented by McDermott Will & Emery LLP’s Paul Whitfield Hughes, III, Ian Barnett Brooks, Sarah Chapin Columbia, Sarah J. Fischer, William G. Gaede, III, and Bhanu Sadasivan.
Moderna was represented by MoloLamken LLP’s Jeffrey A. Lamken, Sara Margolis, and Sara Tofighbakhsh, as well as Cooley LLP’s Geoffrey Donovan Biegler, W. Chad Shear, and Elizabeth M. Flanagan.