Federal Circuit Affirms Claim Construction Where Patentee Acted as Lexicographer

In Alnylam Pharmaceuticals, Inc. v. Moderna Inc., No. 23-2357 (Fed. Cir. June 4, 2025), the Federal Circuit affirmed the district court’s judgment that Moderna’s SPIKEVAX^®vaccine did not infringe two of Alnylam’s patents. The dispute focused on the construction of the term “branched alkyl,” which the parties agreed was dispositive of infringement. The district court determined that Alnylam acted as a lexicographer by stating in the specification that a “branched alkyl,” “[u]nless otherwise specified, [is] an alkyl . . . group in which one carbon atom in the group (1) is bound to at least three other carbon atoms.” The district court also found that Alnylam did not otherwise specify a meaning of “branched alkyl” for purposes of the asserted claims. After issuing its claim construction order, the district court entered a final judgment of noninfringement. Alnylam appealed.

On appeal, the Federal Circuit rejected Alnylam’s argument that it did not act as a lexicographer. The Federal Circuit concluded that the “branched alkyl” language was definitional because it appeared in the “Definitions” section of the specification; was placed in quotation marks; used the term “refer to”; and used the phrase “unless otherwise specified,” which suggested that the rest of the sentence set out a generally applicable definition. The Federal Circuit further found insufficient evidence in the claims, specification, or prosecution history to support a departure from the definition of “branched alkyl.”