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Regeneron v Kymab – Part II: Interpretation and Infringement

25th Apr 2018

Given the complex nature of the technology, claim interpretation and infringement were dealt with in a deceptively straightforward fashion by the Court of Appeal. The matter effectively hinged on the meaning of a single phrase (“in situ replacement”), for which the Court of Appeal employed the general principles of purposive construction, rejecting Kymab’s arguments that the phrase has, and would be understood by a skilled person as having, a technical meaning distinct from its common usage.


The Kymab mouse differs from the VelcoImmune mouse in that the mouse gene segments are not deleted but instead moved to a different part of the genome and inactivated. The parties disagreed over whether the phrase “in situ replacement” used in the claims should be interpreted as covering both of these scenarios, or such that it only covers deletion of the mouse gene segments. Kymab’s case was that an in situ replacement requires a deletion of the mouse variable gene segments coupled with the insertion of the human variable segments in the same place. Regeneron’s case was that “in situ replacement” merely requires replacement in the position of the mouse gene segment (“positional replacement”), and does not require deletion .

Construction by the High Court

The expert witness for Kymab argued that 3 possible constructions of “in situ replacement” had been discussed in the High Court (a) deletion from the genome (Kymab’s construction), (b) displacement within the genome (Regeneron’s primary construction), and (c) displacement and inactivation within the genome (Regeneron’s alternative construction). The expert then argued that the High Court judge had rejected (a), Regeneron’s primary construction, in favour of construction (c), at which the expert then directed his criticism.

The Court of Appeal disagreed with this interpretation of the High Court’s reasoning.  Particularly, the Court of Appeal judge pointed out that what a term “means” (i.e. requires as a minimum) is different to what a term “covers” (i.e. over its entire scope). The Court of Appeal went on to argue that the expert witness for Kymab had confused these two concepts. Mr Justice Carr, the Court of Appeal reasoned, had interpreted “in situ replacement” as meaning “replacing in the position of” and as covering both “deletion” and “moving to a different location and inactivation”. 

Kymab’s arguments

Kymab’s expert submitted that in the art, the word “replacement” had a specific and well-understood meaning, and particularly that it is possible to distinguish replacement (with insertion and deletion) from mere insertion (without deletion) and mere deletion (without insertion). Further, it was argued that the specification uses the term replacement as a skilled person would have normally understood it, namely as requiring both insertion and deletion, in contrast to mere insertion or mere deletion, supported by the fact that the Examples only demonstrate deletion of the mouse sequence, not insertion and inactivation. 

Regeneron: Matter of language

Regeneron argued in response that the phrase “in situ replacement” includes, as a matter of language, insertion of a human gene segment into the place formerly occupied by the mouse segment, where the mouse segment may be deleted or moved elsewhere. To demonstrate the linguistic meaning of the term, the expert witness drew an analogy with “replacement” of a person at the front of the queue, where the person is merely moved to the second position. Replacement in this context does not require the person to be removed entirely from the queue. The Court of Appeal indicated that they thought this analogy helpful in demonstrating the meaning of the term. 

Regeneron: Purposive construction

Adopting a purposive construction, Regeneron further argued that a person skilled in the art would understand the primary purpose of the invention as the insertion of human sequence into the position occupied by the corresponding mouse sequence, with the fate of the mouse sequence being of subsidiary importance, provided that it is removed from the relevant position.

The Court of Appeal Judge agreed, particularly given that he could see no teaching in the specification that the mouse segments must necessarily be deleted or inactivated, and that he believed a skilled person would understand that the advantages of the invention could be reaped without deletion of the displaced mouse sequences. 

Contrast with the prior art and effect of the examples

The Court of Appeal also agreed with the High Court’s contention that the person skilled in the art would understand the Patentee to be using the phrase “in situ replacement” so as to distinguish targeted positional replacement of the invention from the random integration techniques in the prior art, and not to distinguish between deleting a sequence and moving the sequence elsewhere. 

Examples and “Means” v “Covers”

The Court of Appeal further rejected Kymab’s arguments that, because all the examples provided in the specification include deletion, the claim should be interpreted as limited to this embodiment. The Court of Appeal reasoned that, just because the examples show only one type of replacement, this is not a sufficient indication that replacement is similarly restricted in the claims. 

Finally, coming back to his earlier point that what a claim means at the minimum is not equivalent to what it covers over it’s entire scope, the Judge reasoned that just because a particular paragraph in the specification indicated that the mouse sequences are preferably deleted in their entirety, it does not follow that inactivation is a requirement of the claim (given that this preferable effect can be achieved by deletion). 

Sufficiency versus construction?

Kymab’s expert further argued that the process steps of the claim do not correspond to Regeneron’s construction. The Court of Appeal summarized this argument as being that, because a method of displacement and inactivation is not sufficiently disclosed in the specification, a construction that covers such a method is not supported. The Judge did not agree with this argument. He reasoned that “[o]nce it is appreciated that Regeneron’s construction does not require inactivation, inactivation is simply an optional further step that the claim does not need to specify any more than it needs to specify deletion. If the argument is that the claim is broader than the subject matter which it enables, then that is an argument directed to sufficiency, not construction.” See Rose Hugh’s article here for a discussion of the sufficiency issues.

The Court of Appeal concluded by accepting Regeneron’s construction that the term “in situ replacement” requires positional replacement only.


Infringement was dealt with comparatively briefly. Given the court’s construction of the claims, it was decided that the Kymab mice, in which mouse variable locus sequence is displaced and inactivated, and replaced by equivalent human gene regions, infringed the product claims of the patent (EP1360287) and its divisional (EP2264163), in agreement with the High Court decision. Kymab’s process was found not to infringe the process claims of either patent because it does not use the particular vector or assay specified by the claim. 

Doctrine of Equivalents?

The Court of Appeal heard arguments regarding whether, if they had accepted Kymab’s construction of “in situ replacement”, they could nevertheless have found infringement on the basis of Actavis v Eli Lilly. However, the Court decided that because they had found that the Kymab mice infringe as a matter of normal interpretation, it was not necessary to them to consider the case of equivalent variants, and that “had it been necessary, [they] would have been troubled by the suggestion that we could have approached this issue for the first time on this appeal.”


The issue of infringement for this case was decided based on a relatively straightforward claim construction. Key to the claimants arguments were an appeal to the literal meaning and purpose of the claims, in contrast to the more esoteric interpretation argued for by the defendant. The Court of Appeal employed the strategy of claim interpretation with which they are comfortable and have thorough grounding in case law, namely analyzing the literal meaning and purpose of the claim language, and declined to comment on the issue of equivalents.

This article appeared on IPKat on 6 April 2018.

This article is for general information only. Its content is not a statement of the law on any subject and does not constitute advice. Please contact Reddie & Grose LLP for advice before taking any action in reliance on it.

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