As the saying goes, ‘the best laid plans of mice and men often go awry’. And unfortunately for Regeneron, so too, it seems, have the carefully constructed patent claims that aimed to protect Regeneron’s invention in successfully producing human antibodies in transgenic mice. However, in a notable majority ruling by the UK Supreme Court, it was found that the patents owned by Regeneron were invalid for insufficiency.


Already by the priority date, 16 February 2001, the use of artificially produced antibodies (ie those produced outside of a patient’s own immune system) as a way of treating disease was common knowledge and, given the ethical impossibility of testing in humans, mice were considered a suitable alternative platform for the development of antibodies that could then be injected into humans.

As is summarised in the legal judgment, the twofold difficulty with this method, however, was that humans tended to reject murine antibodies while mice tended to suffer a reduced immune response, or become ‘immunologically sick’ after the genetic implantation of human antibodies. This in turn made the mice ineffective in producing the desired antibodies for injection into humans.

The inventive solution to this dilemma, and key to the dispute in this case, was the development of a hybrid antibody gene structure – part human and part murine – known as a ‘reverse chimeric locus’.

The test of sufficiency

The principle of sufficiency or sufficient disclosure of a claimed invention in a patent is one of the fundamental tenets of patent law. The disclosures made in the patent claims should enable a ‘person skilled in the art’ to, in the case of a product claim, make the claimed product using knowledge already readily available (prior art) and without need for additional invention of their own. It is part of the ‘bargain’ made between patentee and the state; in exchange for a time-limited monopoly granted to a patentee over the commercialisation of the claimed inventive product or process, the patentee fully discloses the invention so as to encourage innovation and wider dissemination of the invention’s benefits once the monopoly expires. The importance of this case lies in the comprehensive examination of the sufficiency principle by the UK’s highest court.

Insufficiency of Regeneron’s patents

Regeneron owned two patents, which both related to the reverse chimeric locus. Regeneron claimed at first instance that Kymab infringed three claims in these patents by offering its own ‘Kymouse’ with a reverse chimeric locus to the pharmaceutical industry. While the judge did find infringement, the claims of the Regeneron patent were also found to be invalid for insufficiency by the Supreme Court.

At each stage of this litigation (going through first the High Court, then the Court of Appeal before ending in the Supreme Court), the courts’ differing approaches as to whether Regeneron’s claims were insufficient or not revolved around the relevance of there being a range of products claimed by the key claim in dispute.

The following extract neatly summarises the position of the Supreme Court:

‘[…] in relation to a product claim, […] 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 […] 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.’

Key points

The skill in drafting patent claims has always been a delicate balancing act. On the one hand there is a desire to include claims that offer the broadest possible protection to the invention so that a company, which has invested a great deal of time and resources in developing the invention, can ensure it is economically rewarded without a competitor taking unfair advantage. On the other, there is the risk of straying into the claims of another patent or of the claims being held invalid for insufficiency where not all products claimed could actually be made by a person skilled in the art on the basis of the relevant disclosures. The finding against Regeneron in this case will only serve to make that tightrope all the narrower, particularly where, as here, there is a core inventive principle common to a range of products that a patentee seeks to protect, but where not all relevant embodiments or variations of that product are yet developed or capable of being made.

The ruling may come as a blow to research and development companies, and may result in some being more reluctant to claim patent infringement and subject their own claims to scrutiny as these may be invalidated if found to be insufficient. Nevertheless, the decision firmly redresses any unfair bias towards the patentee in the patentee-state bargain and ensures a patentee cannot take advantage of and monopolise unduly wide patent claims where the state has not received its due in return, ie sufficient disclosure. As suggested by the judgment’s concluding principles, narrower claims that more accurately reflect the current potential of the invention and contribution of the patentee should allow innovation and competition to flourish – a public-spirited approach to IP protection that, particularly in light of the Covid-19 pandemic, is needed now more than ever.