Published September 2026
How Low Can You Go? T 0137/24, Percentage Sequence Identity Claims and Divergent EPO and USPTO Approaches
Key takeaways
- Increasing percentage sequence identity thresholds may be selected from a disclosed convergent list without adding matter, provided the amendment does not create a new technical combination;
- Broader percentage sequence identity definitions may be defensible before the EPO when combined with clear functional limitations, where the skilled person can generate and test variants without undue burden; and
- Enablement requirements for percentage sequence identity claims are generally stricter in the US than in Europe.
Decision T 0137/24
Background
The patent (EP 3615667, The Regents of the University of California) as granted claimed:
A genetically modified yeast cell for producing a cannabinoid or a cannabinoid derivative, the genetically modified yeast cell comprising one or more heterologous nucleic acids integrated into a chromosome of the genetically modified yeast cell and encoding a genranyl pyrophosphate:olivetolic acid geranyltransferase [GOT] polypeptide comprising an amino acid sequence having at least 85% sequence identity to SEQ ID NO:110 or SEQ ID NO:100.
The percentage sequence identity threshold in the claims was narrowed during prosecution from 65% to 85% and then to 90% sequence identity on appeal.
Added matter (Article 123(2) EPC)
On appeal, the Opponent argued that claim amendments directed to increasing the percentage sequence identity to at least 90%, in combination with other features that were not present in claims 1-3 as originally filed, constituted an unallowable selection from multiple independent lists, thereby adding matter.
The European Patent Office’s (EPO) Board of Appeal (BoA) rejected this argument. The application as filed disclosed a list of percentage sequence identity thresholds ranging from at least 65% up to 100%. The BoA held that lists of increasing percentage sequence identity thresholds are convergent lists of preferred options. Selecting a higher threshold merely narrows down the number of functionally defined polypeptides that fall within the claim’s scope of protection (in line with T 2134/10). Accordingly, the BoA concluded that the resulting combination was not distinct and that no added matter was introduced.
The decision reinforces the EPO’s “gold standard” for added matter: any amendment must be directly and unambiguously derivable from the application as filed. While combinations of features selected from separate independent lists may be objectionable as newly disclosed subject matter, amendments based on a convergent hierarchy of increasingly preferred embodiments are generally less problematic, because each narrower option is presented as a restriction of the broader option.
Practical considerations
First, percentage sequence identity thresholds should be drafted as a clearly convergent series of preferred fallback positions to provide amendment flexibility during prosecution while reducing the risk of added matter objections. In the description of EP 3615667, the thresholds were drafted (a) in a single sentence; (b) using ‘at least’ before each threshold; and (c) ending with ‘100%’ (i.e., “the GOT polypeptide … comprises an amino acid sequence having at least 65%, at least 70%, at least 75%, at least 80% … at least 99.9% or 100% amino acid sequence identity to SEQ ID NO …”). This structure made it clear that increasing the percentage sequence identity threshold simply narrowed the scope of the claimed variants rather than adding matter.
Second, applicants drafting biotechnology claims based on percentage sequence identity should consider pairing sequence identity thresholds with functional limitations. The BoA placed weight on the fact that the polypeptides were functionally defined by their enzymatic activity (genranyl pyrophosphate:olivetolic acid geranyltransferase (GOT)) in the claims as filed. Where sequence identity thresholds are coupled with functional limitations in a claim, an increase in the identity threshold may be more readily characterised as merely narrowing the class of molecules falling within the claim definition, rather than singling out previously undisclosed embodiments.
Sufficiency of disclosure (Article 83 EPC)
The Opponent further argued that the claims lacked sufficiency because they encompassed non‑functional variants. The application as filed disclosed polypeptides that satisfied the percentage sequence identity requirement but lacked enzymatic activity. The Opponent alleged that, as the application as filed did not provide guidance on which sequence variations would retain the required activity, identifying functional variants within the claim scope imposed an undue burden on the skilled person. The BoA did not agree.
The BoA emphasised that the claims did not cover all polypeptides meeting the sequence identity threshold. The claimed polypeptides also had to possess the relevant enzymatic activity. As a result, variants that met the percentage identity threshold but lacked the claimed activity were not within the scope of the claim.
Additionally, the application as filed disclosed generating and testing the polypeptide variants recited in the claims. Against this background, the BoA found that generating variants having an amino acid sequence with a given percentage sequence identity threshold (at least 90% in this case) to a preferred SEQ ID NO and testing their enzymatic activity involved only routine techniques for the skilled person working in the technical field of recombinant enzyme variants. The invention was therefore held to be sufficiently disclosed, and the patent was maintained in amended form.
Practical considerations
Whilst T 0137/24 suggests that broader percentage sequence identity definitions may be defensible in Europe where the claimed variants are limited by a specified functional property, this decision should not be taken to mean that functional language will save every broad percentage sequence identity claim.
Its outcome depended on the fact that the skilled person could generate and test variants falling within the claimed identity threshold using routine methods in the relevant technical field. For less predictable molecules, more complex functions, or cases where activity is difficult to assay, applicants should expect greater scrutiny of both sufficiency and claim scope.
Nevertheless, the decision may provide useful support when responding to clarity objections to percentage sequence identity definitions, particularly where issues of clarity and sufficiency overlap.
European vs US practice for sequence identities
The US approach differs from that in Europe regarding claims based on percentage sequence identity. While the EPO generally accepts that the routine generation and screening of functional variants can satisfy the sufficiency requirement, the US Patent Office (USPTO) applies a stricter enablement standard for claims defined by percentage sequence identity thresholds. Applicants must provide stronger support that the full scope of the claimed variants is enabled, and enablement rejections are common, particularly for antibodies.
In Amgen, the Supreme Court found that “aspects of antibody science remain unpredictable”, where “changing even one amino acid in the sequence can alter an antibody’s structure and function … [and] scientists cannot always accurately predict exactly how trading one amino acid for another will affect an antibody’s structure and function”. [1] The Court further held that disclosure of 26 different exemplary antibodies identified by their amino acid sequences “failed to enable all that it has claimed, even allowing for a reasonable degree of experimentation”. [2]
Practical considerations
US specifications should do more than recite a reference sequence and a percentage sequence identity threshold. Where broad sequence variant protection is desired, the applicant may wish to:
- Identify the permissible sequence variations, including which regions can tolerate substitution and, where possible, provide representative variants across the claimed percentage sequence identity range;
- Provide evidence that the variants retain the claimed function, supported by experimental data and appropriate functional assays; and
- Tailor the claim strategy to the technology, particularly for antibody inventions, where separate claims may be appropriate for exact sequences (e.g., for complementarity determining regions (CDRs) and light and heavy chain variable regions) and narrower variant groups.
Applicants may also consider first pursuing claims to the specific disclosed sequence and then seeking broader variant protection in a divisional or continuation application, supported by additional experimental data where available. This approach can help manage enablement risk while preserving the opportunity to obtain broader claim coverage.
[1] Amgen Inc. v. Sanofi, 598 U.S. 594 (2023), p. 3 of the Opinion of the Court.
[2] ibid p. 3 of the Syllabus.
This article was prepared by Trainee Patent Attorney, Esmae Badcock.