No Takebacks: The High Bar for Departing From Patent Lexicography

Written by:Daniel Kiang and Dalton A. Couch

ALNYLAM PHARMACEUTICALS, INC. v. MODERNA, INC.

Before Taranto, Chen, and Hughes. Appeal from the United States District Court for the District of Delaware

Summary: Once the high threshold for lexicography is met, there must be a clear and unmistakable reason to depart from that controlling definition.

Alnylam sued Moderna, alleging that Moderna’s COVID-19 vaccine contained a lipid compound that infringed Alnylam’s patents. The asserted claims were directed toward a lipid compound with a hydrophobic tail which includes “a branched alkyl.” Moderna argued that Alnylam had acted as a lexicographer regarding “branched alkyl” based on the following sentence in the specification:

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.

In contrast, Alnylam proposed a different construction that it asserted to be the ordinary meaning.  The district court agreed with Moderna and construed “branched alkyl” according to the definition in the specification and further reasoned that any departure from that lexicography needed to be clear and unmistakable.  The parties stipulated to noninfringement under the court’s construction and Alnylam appealed.

On appeal, the Federal Circuit agreed that Alnylam had acted as a lexicographer in defining “branched alkyl.”  Further, the Federal Circuit agreed with the district court that once the high threshold for lexicography has been met, a high threshold must also be met before departing from that controlling definition. Alnylam’s definition of “branched alkyl” included the phrase “unless otherwise specified,” which Alnylam argued left room for a broader interpretation elsewhere in the patent. However, the Federal Circuit found no clear reason in the claims, specification, or prosecution history to depart from the definition. Thus, the Federal Circuit affirmed.

Editor: Sean Murray