Defining what the invention is not can be as important as defining what the invention is (T 0273/22, Chimeric antibodies/REGENERON)

A recent Board of Appeal decision T 0273/22 related to a patent in the same family as that of the landmark UK Supreme Court decision Regeneron v Kymab. The Supreme Court decision related to whole range sufficiency. The Board of Appeal decision relates to the basis requirement for disclaimers. In particular, in this divisional patent Regeneron had attempted to avoid a novelty attack by explicitly disclaiming embodiments of the invention from the claim. However, the EPO applies the same gold standard to disclaimers as it does to any other type of feature. Given the disclaimer lacked explicit basis in the original application the amendment exposed the granted patent to an added matter attack. 

Legal background: Undisclosed disclaimers

Patent claims generally define the essential features present in the claimed invention. However, it is also possible for patent claims to negatively define the invention by disclaiming certain features. The downside of disclaimer language is that it can be very easy to design around if including the absent feature does not prevent the invention from working. 


Disclaimers can however be useful for avoiding accidental anticipation of the invention (IPKat). According to the Enlarged Board of Appeal in G 1/03 and G 1/16, a disclaimer not mentioned in the application as filed may be added to the claim in order to restore novelty in view of an accidental anticipation by prior art. In order to qualify, as an allowable undisclosed disclaimer, the disclaimer must relate to prior art that is completely unrelated to the invention. If a disclaimer does not satisfy the criteria for allowability as an undisclosed disclaimer, then the normal test for added matter is applied. In other words, the disclaimer must have clear and unambiguous basis in the application as filed (EPO Boards of Appeal case law II-E, 1.7.2(c))

Disclaiming a non-enabled embodiment

The patent (EP2786657) related to Regeneron's genetically engineered mouse platform for generating new antibody therapeutics (the VelocImmune mouse). The claims were particularly addressed to methods for producing chimeric antibodies comprising both human and mouse components. The claims on appeal were directed to a method of producing chimeric antibodies in a rodent (main request) or a mouse (auxiliary request). Regeneron had introduced a claim amendment during prosecution in the form of a disclaimer specifying that the rodent did not produce fully human antibodies. The question on appeal was whether this disclaimer had basis in the application as filed (T 0273/22). 

Implicit and explicit undisclosed disclaimers

It was undisputed that the claimed disclaimer would not satisfy the criteria for an allowable undisclosed disclaimer, given that the relevant prior art was considered highly relevant to the invention (r. 5). The prior art was in fact mentioned in the application as filed. The Patentee argued, however, that the mention of the prior art in itself provided an implicit disclosure of the disclaimer. The argument put forward by the Patentee was that the mention of the prior art, and particularly the description of the prior art as comprising the disclaimed features, would be understood by the skilled person as implying that the invention did not have these features. 

The Board of Appeal was not convinced by this argument. Particularly, the Board of Appeal found that there existed a fundamental difference between 1) an implicit and vague disclosure derivable from an introductory description of the prior art, and 2) explicit and precise claim wording specifying the mandatory absence of certain features (r. 7). For the Board of Appeal, the nature of the implicit disclosure was too vague, and the questions that would arise too numerous, for this to be considered a disclosed disclaimer (r. 10). In view of the absence of an explicit disclosure of the negative feature, the Board of Appeal was therefore satisfied that the claimed disclaimer was an "undisclosed disclaimer" (G 1/03). 

Applying the test provided in G 1/03 for assessing the allowability of undisclosed disclaimers, the question then became whether clear and unambiguous basis could be found for the disclaimer in the application as filed. In the absence of any mention of the disclaimed subject matter (other than in reference to the prior art), the Board of Appeal concluded that the disclaimer lacked basis in the application as filed, and that the claims were therefore invalid for added matter. 

Applying the gold-standard and construing the claims

The question regarding added matter in the case also touched on the appropriate principles of claim interpretation. According to recent Boards of Appeal case law, the EPO construes claim language according to its normal meaning, ignoring any definitions in the description that may contradict or clarify this normal meaning (IPKat). The EPO's approach to claim construction contrasts with the purposive approach of the UK courts. In the UK claim language may be construed according to the functional definition of the invention provided in the description (IPKat).  

In the present case, the Opposition Division found at first instance that the meaning of the granted claim had not changed by the addition of the disclaimer language. All of the examples and descriptions of the invention provided in the application as filed related to rodents capable of producing chimeric antibodies. None of the examples related to rodents capable of producing fully human antibodies. The Opposition Division (OD) was therefore convinced that a skilled person, looking at the application as filed a whole with a mind willing to understand, would not construe the claim as encompassing methods of producing fully human antibodies. The OD concluded that disclaiming rodents capable of producing fully human antibodies did not change the meaning of the claim.

The Board of Appeal disagreed with this conclusion. The Board of Appeal, in line with recent case law, particularly looked at the normal meaning of the claim language absence recourse to the description. "Comprising" was construed in the normal way of meaning "including but not limited to". As such, for the Board of Appeal, the normal meaning of the claim did not exclude the possibility that the specified rodent or mouse produced fully human antibodies. The Board of Appeal thus concluded that the addition of the disclaimer did change the subject-matter of the claim (r. 15) and added matter in view of the original application (Article 76(1) EPC).  

Final thoughts

Following G 2/21, it may be possible for patentees to rely on a post-hoc technical effect for inventive step that is not explicitly mentioned in the application as filed (IPKat). As the present case clearly demonstrates, the same is not definitely not true for explicit features of the claim needed to distinguish the invention from the prior art. The only exception to this rule is in the case of an undisclosed disclaimer satisfying the special criteria outlined in G 1/03. In the present case, the Patentee attempted to rely on the argument that a skilled person would interpret the identification of the prior art in the description as an implicit disclosure that these features would be absent from the invention. If such an approach were allowable, it would create an absurd situation whereby the mere mention of the prior art could provide implicit disclosure of the distinguishing feature of the invention. Instead, T 0273/22 confirms that even an absence of features needs to meet the gold standard for basis. The description should therefore not only define what the invention is, but potentially also what it is not. 

Further reading

Undisclosed disclaimers

Regeneron sufficiency
Defining what the invention is not can be as important as defining what the invention is (T 0273/22, Chimeric antibodies/REGENERON) Defining what the invention is not can be as important as defining what the invention is (T 0273/22, Chimeric antibodies/REGENERON) Reviewed by Rose Hughes on Monday, November 13, 2023 Rating: 5

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