EPO Board of Appeal in T 0655/24: Improvements must be credible from the application as filed
T 0655/24 concerns Genmab’s patent EP2943507 disclosing an antibody with an engineered triple Fc region mutation (L234F/L235E/D265A) – the “FEA” variant – designed to effectively reduce immune effector function whilst having good plasma clearance.
By mediating effector function and plasma clearance, unwanted adverse effects such as toxicity and platelet aggregation are minimised whilst effective treatment efficacy and drug stability is achieved.
In this recent decision at the European Patent Office (EPO), the Board of Appeal (BoA) 3.3.04 had to apply the principles of G 2/21 to assess the utility of post-filed data in the analysis of inventive step.
Post-filed evidence of an improvement for inventive step
For inventive step, the closest prior art was considered to disclose an antibody having a double Fc region mutation: L234F/L235E (the “FE” variant). Though the effector function of this variant had not been tested in the prior art, combining mutations L234F/L235E with a third mutation P331S (“the FES” variant) had been shown to elicit reduced effector function. Only separately had the D265A mutation shown reduced effector function.
The distinguishing feature of the claimed antibody over the prior art is therefore the D265A mutation combined with the FE variant.
To argue the FEA variant has an inventive step, Genmab submitted post-filed data showing a greater reduction in effector function compared with the FE variant and referred to case law noting that if a patent discloses a technical effect (in the present case reduced effector function), then an improvement in that technical effect (in the present case greater reduction) is also implicitly derivable from the teaching of the application as filed, and thus post-filed data can be used to evidence the improvement.
However, when deciding whether Genmab could rely on the post-filed evidence the BoA disagreed with Genmab’s reasoning, stating (Reason 58):
“Applying the principles of G 2/21, the board does not consider that an improvement of an effect…is encompassed by the technical teaching and embodied by the same originally disclosed invention merely because the effect itself (but not the improvement), was shown to be achieved in the application as filed (see G 2/21, Headnote, Reasons 67 and 72).”
In other words, an improvement cannot be treated as implicitly disclosed just because the underlying technical effect is disclosed; the improvement must also be credible from the application as filed.
Having set out this strict standard, the BoA found that the original application already contained data showing that the FEA variant produced less CD69 expression and thus achieved reduced effector function i.e. is improved over the FE variant. The extensive discussion on admissibility of post-filed evidence was therefore somewhat moot to the eventual decision.
It is interesting that the BoA opined so heavily on this topic, since the case could have been resolved in a simpler manner i.e., by holding that the improvement was already identifiable in the application as filed. We could speculate this is an attempt to influence other Boards as they continue to grapple with the interpretation of G 2/21.
An alternative may still have an inventive step
The BoA then formulated the technical problem as providing an improved Fc mutant that abolished T cell activation (CD69 expression) and retained a plasma clearance comparable to the wild type i.e. reduced effector function and good plasma clearance relative to the standard, naturally occurring form of the antibody.
The skilled person, according to the BoA, would have had no reasonable expectation of success in arriving at the FEA variant having the improved properties because “it is common general knowledge that minimal modifications in an Fc region can affect its structure and function in an unpredictable manner”, so it was unclear whether effector function would be reduced when the FE variant was combined with the D265A mutation.
The BoA concluded that even when the technical problem was reduced to merely providing an alternative Fc variant, the combination was still not obvious because its functional properties remained unpredictable (Reason 86).
Key takeaways
Overall, T 0655/24 emphasises that an alleged improvement over the prior art must be credible in the application as filed to support an inventive step.
This raises the bar for proprietors, as it emphasises the importance of pre-filing awareness of the prior art as well as comparative data in the as-filed application showing improvements over known antibodies. Both are easier said than done in the fast-moving and competitive field of antibody development.
When drafting patent applications, it may be wise to include language that addresses the specific improvement in any particular technical effects that (at the time of drafting) are deemed credible but are not yet necessarily proven with data that can be included in the application. In light of T 0655/24, simply mentioning the technical effect could be held by some Boards not to be enough.
Proprietors who nonetheless are in a position of needing to utilise post-filed evidence may find it helpful, like Genmab, to point to the decisions of other Boards of Appeal (T 1989/19, T 2716/19 and T 840/22; Reasons 59-62) who conversely decided that as long as an effect is credible from the application as filed then an improvement may be substantiated by post-filed evidence.
The decision also emphasises that an alternative may still be inventive. Though the prior art may already disclose individual mutations, if it can be argued that the skilled person would have had no reasonable expectation that combining the mutations will retain or even improve the desired properties then an inventive step could be acknowledged.
Barker Brettell has a dedicated life sciences team who can assist and advise you on how to achieve the best protection for your innovation. To continue the conversation, please contact the authors of this article, Laura Riggall and Jonathan Myers, or your usual Barker Brettell attorney.
Published: September 2026
