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Last week, the U.S. Court of Appeals for the Federal Circuit issued a decision in <a href="https://www.cafc.uscourts.gov/opinions-orders/23-2357.OPINION.6-4-2025_2525006.pdf">Alnylam Pharmaceuticals, Inc. v. Moderna, Inc. et al., No. 2023-2357 (June 4, 2025)</a>, affirming a district court's claim construction and its resulting final judgment of noninfringement.

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In 2023, Alnylam sued Moderna alleging that Moderna's COVID-19 vaccine SPIKEVAX® infringed two patents addressed to “biodegradable lipids” used for nucleic acid delivery. In its claim construction ruling, the district court noted that Alnylam had specifically defined a contested term, “branched alkyl,” as follows: "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." The district court’s construction, therefore, limited a “branched alkyl” to molecules with a certain carbon atom bound to three or four other carbons, excluding those where the carbon is bound to one other carbon. The parties stipulated to judgment of non-infringement under the district court’s construction. Alnylam appealed.

The Federal Circuit affirmed. First, the Court concluded that Alnylam had clearly "acted as lexicographer" and provided a specific definition for “branched alkyl.” The definition was included in a dedicated "Definitions" section of the written description and the term "branched alkyl" was set off in quotation marks. Additionally, the definition used the limiting phrase "refer to" rather than looser language like "include" or "for example," which was used elsewhere in the Definitions section. Finally, the phrase "unless otherwise specified" suggested Alnylam intended the definition to apply with limited exceptions.

The Court explained that once the high threshold for lexicography is met, an equally high threshold must be satisfied to depart from that definition and rejected Alnylam’s alternative argument that the claims fall under the “unless otherwise specified” exception to the definition. The Court determined there was no clear reason to conclude that the term encompassed a different definition as used in the asserted claims because the claims were not nonsensical when read in light of the definition, such that an alternative definition would be required. Moreover, although certain examples in the written description could support an alternative definition, the disclosures were limited, included in a lengthy specification, and were not directed to the asserted claims. The Court further held the prosecution history failed to clearly show that a different definition applied to the asserted claims.

CAFC Affirms Claim Construction in Patent Suit over COVID-19 Vaccine

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