The United States Court of Appeals for the Federal Circuit (CAFC) recently decided that Moderna’s mRNA-based COVID-19 vaccine, SPIKEVAX®, did not infringe Alnylam’s patents because the cationic lipid used in the vaccine, SM-102, was not a cationic lipid with a ‘branched alkyl’ group.[1] The case turned on the proper construction of ‘branched alkyl’.
Alnylam argued that ‘branched alkyl’ should be given its ordinary meaning, whereas Moderna argued that the claims were limited by a definitional sentence in the specification. The CAFC held Moderna had not infringed because Alnylam had effectively been its own lexicographer.
This decision underscores the delicate balance between the ordinary meanings of terms used in a patent claim and the meaning given to those terms in the drafting of the specification.
Background: Lipid nanoparticles and the ‘branched alkyl’ debate
Lipid nanoparticles are used to deliver nucleic acids, such as mRNA, into cells. Cationic lipids, which form part of those lipid nanoparticles, typically have hydrophobic tails (i.e. a part that is water-repelling). Alnylam’s patents claimed a cationic lipid that has a ‘branched alkyl’ group at a particular position in that tail.
Alnylam alleged that Moderna’s vaccine infringed because the SM-102 lipid contained a ‘branched alkyl’ group. Alnylam argued that the term should be given a broad, ordinary meaning whereas Moderna’s preferred construction was that the term should be given the meaning defined by the specification:[2]
‘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.’
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In more detail (for those who have an interest in chemistry), the issue was:[3]
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District Court decision
The District Court agreed with Moderna, holding that the definitional sentence in the specification (extracted above) was ‘clear and unequivocal lexicography’.[4] The Court found that there was no ‘clear and unmistakable’ departure from that lexicography in the asserted claims or specification that would broaden the meaning of ‘branched alkyl’.[5] On this construction, the parties agreed that Moderna’s vaccine did not infringe.
CAFC: Affirming lexicography and the limits of ‘unless otherwise specified’
On appeal, Alnylam challenged the District Court’s construction, contending that a narrow definition of ‘branched alkyl’ was not intended and, alternatively, even if the extracted paragraph was definitional, the ‘unless otherwise specified’ clause permitted a broader construction.
The CAFC rejected these arguments, emphasising several key points:
- Lexicography in the specification: The CAFC confirmed the general principle that a patentee ‘may choose to be his own lexicographer and use terms in a manner other than their ordinary meaning, as long as the special definition of the term is clearly stated in the patent specification’.[6] Like in Australia, in the US there is a high threshold for lexicography — the CAFC found that the definitional sentence of ‘branched alkyl’ was clear, explicit, and intended to be controlling. The presence of that sentence under the title ‘Definitions’, the use of quotation marks and the use of the phrases ‘refer to’ and ‘unless otherwise specified’ in contrast to non-limiting phrases used elsewhere such as ‘include’ all pointed to lexicography.
- High threshold for exceptions: The ‘unless otherwise specified’ language supported a conclusion that to avoid the definition, there would need to be a clear, explicit exception. No such exception was found.
- No support in claims or specification: The CAFC found that the claims were coherent when read in light of the definition and dismissed Alnylam’s argument that the dependent claims could not be read as properly narrowing the claimed invention when the definitional approach was adopted.
Implications
The CAFC’s decision highlights the importance of consistency and clarity of use of defined terms. Consistent with the approach taken by IP Australia, patent claims in Australia will be construed in light of (and may be limited by) the specification, including where terms are defined more narrowly than an ordinary meaning in the art. In Synthetic Turf Development v Sports Technology International (2005) FCA 69 (affirmed in (2005) FCAFC 270) it was said that:
‘[in this case,] the specification described a process where artificial turf was laid and packed with sand, with subsequent rolling to ‘crimp’ the ends of the fibres. An alleged infringing product crimped the fibre before the turf was laid. The claim merely referred to ‘crimp’ and the specification did not contain a ‘dictionary definition’ of ‘crimp’. Nevertheless, the court construed ‘crimp’ in the context of the specification as being crimped after laying.’
For innovators in the life sciences and pharmaceutical sectors, the CAFC’s decision is a reminder that careful drafting and internal consistency in patents is critical.
[1] Alnylam Pharmaceuticals, Inc. v Moderna, Inc, Appeal No. 2023-2357 (Fed. Cir. 4 June 2025) (Alnylam v Moderna).
[2] See Alnyam v Modena at p 2.
[3] Alnyam v Modena at p 5.
[4] See Alnyam v Modena at p 7.
[5] See Alnyam v Modena at p 8.
[6] Alnyam v Modena at p 9.
