The U.S. Court of Appeals for the Federal Circuit delivered a decisive victory for Moderna in its ongoing patent battle with Alnylam Pharmaceuticals, affirming a district court's finding of noninfringement in a precedential decision issued June 4, 2025. The ruling centers on mRNA-based COVID-19 vaccine technology and establishes strict standards for overriding explicit patent definitions.
Patent Dispute Over Critical Vaccine Component
The case focused on whether Alnylam's patents, U.S. Patent Nos. 11,246,933 and 11,382,979, were infringed by Moderna's use of SM-102, a cationic lipid essential to Moderna's COVID-19 vaccine formulations. SM-102 enables intracellular delivery of mRNA in Moderna's SPIKEVAX vaccine, making it central to Alnylam's infringement theory.
Alnylam asserted that SM-102 fell within the scope of its patent claims, specifically limitations requiring a "branched alkyl" group in the hydrophobic tail of a cationic lipid. The company initiated two consolidated suits in the District of Delaware in 2022, shortly after each patent issued.
Lexicographic Definition Proves Decisive
The Federal Circuit's unanimous panel, led by Judge Taranto, upheld the district court's claim construction that Alnylam had acted as its own lexicographer in defining "branched alkyl." The specification contained a clear definition under a "Definitions" heading, stating that the term required "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" "unless otherwise specified."
Under this construction, the parties stipulated to noninfringement, as SM-102 did not meet the requirement for a tertiary or quaternary carbon. The district court entered final judgment in Moderna's favor based on this claim construction.
High Bar for Overriding Patent Definitions
Writing for the panel, Judge Taranto identified five key features supporting the finding of lexicography:
- Heading "Definitions" in the specification
- Quotation marks around the term "branched alkyl"
- Use of the definitional phrase "refer to"
- Contrast with other terms using non-limiting language like "e.g." or "include"
- The qualifying clause "Unless otherwise specified"
The court emphasized that "the phrase 'unless otherwise specified' does not invite ambiguity or speculation—it sets a high bar requiring an explicit, unambiguous exception elsewhere in the intrinsic record."
Alnylam's Arguments Rejected
Alnylam argued that its disclosed embodiments and prosecution history suggested broader claim scope, contending the definition should not apply universally to claims covering "branching" at the "alpha position" adjacent to biodegradable groups. The company pointed to dependent claim 14 of the '933 patent and prosecution history evidence as support for a broader interpretation.
The Federal Circuit rejected these arguments, finding that none of the embodiments cited by Alnylam were unambiguously covered by the asserted claims or clearly labeled as exceptions to the definition. Regarding dependent claim 14, which required "only one carbon atom" bound to three others, the panel found it was still narrower than the independent claim, which could cover lipids with multiple tertiary carbons.
On prosecution history, while acknowledging Alnylam's evidence as "some support," the panel found it insufficient to override the express definition in the specification, particularly given the lack of clarity or specificity in those arguments.
Implications for Patent Drafting
The decision reinforces the controlling force of explicit patent definitions and the demanding standard patentees face when seeking to establish exceptions. As the court noted, "once a patentee includes an express definition, it governs the claim term unless a clear exception is explicitly provided."
The ruling underscores both the power and potential peril of lexicography in patent drafting, demonstrating that patentees who choose to define claim terms must live with those definitions unless they clearly and specifically provide exceptions elsewhere in the patent.
