Regeneron Pharmaceuticals' European patent EP 1360287 and its divisional EP 2264163 relate to methods of producing transgenic mice able to produce antibodies having human sequences, and the mice produced thereby. These patents covered the idea of producing mice having mixed human-murine gene sequences that could be subsequently modified to replace the murine portions with human sequences. This results in the mice producing antibodies having fully human sequences that can be used in human therapy without causing a common immunological reaction associated with part-human/part-mouse antibodies.

In challenging these patents in the UK Courts, Kymab contended that the disclosure of how to achieve this left too much for the skilled reader to determine by themself. In other words, Kymab argued that the patent was not sufficient. At first instance, much of the case rested on whether or not the method of Example 3 could have been put into effect by the skilled person without undue burden at the priority date of the patents.

In view of expert evidence, the Patents Court held that Example 3 could not be worked by the skilled person without undue burden. On appeal, Regeneron argued that it would be obvious to the skilled team as to how to modify Example 3 and get it to work as described.The Court of Appeal accepted this argument, and stated that the technique was a major scientific contribution that justified a broad claim. As such, the patents were held sufficient, bringing the UK position into line with that of the European Patent Office.

The case was heard by the UK's highest court in February of this year, and the Supreme Court issued its decision on 24 June 2020. By a majority of 4 to 1, the Supreme Court held that the patents lacked sufficiency, and allowed Kymab's appeal. In short, it decided that the claims covered more than was justified by the extent of the disclosure. Although the Supreme Court accepted that it was not necessary to provide a full teaching of everything that could possibly fall within the claim, it did appreciate that very valuable mice falling within the scope of the claims could not be obtained without undue burden at the priority date of the patents.In other words, the patent protected more than could be justified by the technical disclosure made.

This case goes to the heart of the bargain made between an inventor and the public. The monopoly awarded must be justified by the contribution to public knowledge attributable to the disclosure and the invention must be "in hand" at the priority date, not finally reduced to practice only years later as a result of later-developed technology.