Court Confirms Moderna’s Victory Over Alnylam's 'Branched Alkyl'

In a landmark decision that could have profound implications for future patent disputes, the Court of Appeals for the Federal Circuit (CAFC) has made a significant clarification on the strict interpretation of the term ‘unless otherwise specified’ in patent claims. This precedential decision, issued on June 4, 2025, affirmed a district court’s finding of noninfringement in favor of Moderna, Inc. in its ongoing patent battle with Alnylam Pharmaceuticals over mRNA-based COVID-19 vaccine technology.

The crux of the case was whether Alnylam’s patents, specifically U.S. Patent Nos. 11,246,933 and 11,382,979, were infringed by Moderna’s use of SM-102, a cationic lipid utilized in Moderna’s COVID-19 vaccine formulations. Alnylam had posited that SM-102 fell within the scope of its patent claims, particularly those requiring a “branched alkyl” group in the hydrophobic tail of a cationic lipid. The relevance of SM-102 in enabling intracellular delivery of mRNA in Moderna’s vaccine made it a vital piece in Alnylam’s infringement theory.

However, the court held that Alnylam had acted as its own lexicographer by defining the term “branched alkyl” in its patent specifications. This definition effectively blocked Alnylam’s infringement allegations against Moderna’s SPIKEVAX® vaccine. The district court ruled that Alnylam’s specification contained a clear definition of “branched alkyl”: a carbon atom in the group must be bound to at least three other carbon atoms. Under that construction, both parties agreed that SM-102 did not infringe the asserted claims.

Alnylam appealed, arguing that the definition should not apply universally or that the claims at issue constituted an exception. The Federal Circuit disagreed, stating that Alnylam had unambiguously defined the term in its specification under a heading labeled “Definitions.” The panel noted the use of quotation marks, definitional language, and a qualifying phrase, which all signaled a lexicographic intent. Finding no “otherwise specified” language in the asserted claims to override the stated definition, the CAFC affirmed the judgment of noninfringement.

The court underscored the importance of explicit exceptions in the intrinsic record to deviate from an express definition provided by the patentee. Despite Alnylam’s arguments for a broader claim scope based on disclosed embodiments and prosecution history, the panel rejected them, stressing the need for unambiguous coverage or clear labeling of exceptions in the claims.

This ruling resonates far beyond this specific case, setting a precedent for patent claim interpretation and the value given to explicit definitions. Patentees are now urged to provide clear and precise definitions within their claims to avoid ambiguity and speculation. This decision underscores the relevance of the intrinsic record in determining claim scope and could influence future patent disputes involving similar linguistic or interpretative challenges. For biotech firms navigating the intricate landscape of intellectual property, adherence to strict claim construction principles becomes critical to safeguarding their innovations and retaining a competitive edge in the market.