In this case comment, Caitlin Heard, Frances Denney and Robert Stephen, who all work within the intellectual property team at CMS, comment on the judgment handed down by the Supreme Court in June 2020 in the matter of Regeneron v Kymab [2020] UKSC 27, which concerns whether patents were invalid for insufficiency.

Who knew a mouse could cause so much trouble? The Supreme Court has handed down its judgment in the case of Regeneron v Kymab, ruling that the asserted claims of Regeneron’s European patent EP1360287 and its divisional EP2264163 (EP ‘287 and EP ‘163) are invalid for insufficiency.

This is the final stage in the saga between the two parties, after several years of litigation through the UK Courts.


This case concerns mice that have been genetically modified to produce human-mouse chimeric antibodies that can then be used for therapeutic uses in human patients.

EP ‘287 and EP ‘163 concern methods for producing mice having a reverse chimeric human-mouse locus, and mice made in that way.  Regeneron claimed that this reverse chimaeric feature has certain benefits, in particular mice are not “immunogenically sick”.

Kymab produces its own genetically modified mice (‘Kymouse’), which Regeneron claimed infringed EP’287 and EP’163. However, Kymab claimed that Regeneron’s product claims were not enabled and thus not valid.

Sufficiency – UK High Court and Court of Appeal findings

Sufficiency requires that a patent must disclose an invention in a manner sufficiently clear and complete for it to be carried out by a person skilled in the relevant art. It is part of the patent ‘bargain’ between an inventor and the state – proprietors are given a 20-year monopoly in return for full disclosure of the invention.

In this instance, the main question in dispute boiled down to whether disclosure is “sufficient” if the teaching in the patent enables only some but not all of the products within the claimed range to be made?

So, in this case, were EP ‘287 and EP ‘163 sufficient if they only enabled a skilled person to produce a mouse having a partially complete (but not a complete) reverse chimeric locus, the full replacement being covered by the claims?

In the High Court, Mr Justice Carr found in favour of Kymab and ruled that the Regeneron patents were insufficient.  However, the Court of Appeal disagreed. The Court of Appeal considered that all mice containing the reverse chimaeric locus would benefit from that invention, and that this was a principal of general application that justified a broad patent monopoly (even if some of those mice could not be made at the filing date of Regeneron’s patents).  In other words, the Court of Appeal focused more on the effect of the reverse chimaeric locus and less on the ability to make all mice within the scope of the claim.

The UK Supreme Court

With a majority of four to one Kymab’s appeal was allowed and the asserted claims of the patents found invalid. Lady Black provided the dissenting judgment. The majority judgment provides a detailed review of the principle of sufficiency in UK law and in jurisprudence of the European Patent Office.

The Supreme Court considered that the Court of Appeal had incorrectly tilted the balance of patent law in favour of patentees and away from the public, by providing the patentee with a monopoly which exceeded its contribution to the art.  The Supreme Court maintained that if a claim covers a range of products, sufficiency means that a patent must disclose enough information to enable a skilled person to make substantially the full range of products claimed.

Regeneron did not enable a skilled person to make mice containing more than a very small section of the human variable region.  Indeed, the most valuable end of the product range, which was a mouse having all of the human immunoglobulin DNA, was not enabled.  The majority therefore held the asserted claims to be invalid for insufficiency.  The judgment concludes that:

“What matters is that it is settled law, in relation to a product claim, that sufficiency requires substantially the whole of the range of products within the scope of the claim to be enabled to be made by means of the disclosure in the patent, and this both reflects and applies the principle that the contribution to the art is to be measured by the products which can thereby be made as at the priority date, not by the contribution which the invention may make to the value and utility of products, the ability to make which, if at all, lies in the future.”

Lady Black dissented, generally agreeing with the approach of the Court of Appeal. In her view, Regeneron’s invention was a principle of general application which solved the problem of immunological sickness, and this invention was deployed in all mice within the claimed range.