Illumina v MGI: Patents Court gives guidance on the skilled person, CGK, and insufficiency

General 9 min
March 26, 2021

In Illumina v Latvia MGI Tech (MGI) [2021] EWHC 57 (Pat), Birss J (as he then was) has handed down a 520 paragraph judgment providing some helpful practical guidance in respect of several issues that commonly arise in UK patent litigation, namely:

  • The definition of the skilled person for obviousness in cases where it is not same as the skilled person to whom the patent is addressed;

  • That common general knowledge can include things that do not work as well as things that do;

  • The application of Regeneron (claim breadth insufficiency) in practice.

The decision related to five of Illumina’s patents for DNA sequencing technology: three of the patents (all divisionals) related to azidomethyl groups as reversible chain terminators (“RCTs”) in sequencing by synthesis (“the modified nucleotide patents”); the fourth patent related to the use of ascorbic acid as a component in the fluorescent imaging buffer and the fifth patent related to a conjugate molecule. The fourth and fifth patents were used in such sequencing.  MGI wished to sell various DNA sequencing systems in the UK which were alleged to infringe one or more of Illumina’s five patents.  The validity attacks on the Illumina patents included obviousness, added matter, lack of technical contribution/insufficiency and insufficiency/obviousness squeeze based on the Supreme Court decision last summer in Regeneron v Kymab [2020] UKSC 27. The arguments on infringement included consideration of the application of the principles laid down in Actavis v Eli Lilly [2017] UKSC 48 for dealing with equivalents.

Birss J ultimately found that four of the five patents were valid as amended and infringed by MGI’s systems and the fifth was invalid for obviousness (although would have been infringed if valid).


The principal attack on the validity of the modified nucleotide patents was that they were obvious over a particular piece of prior art which disclosed an azidomethyl blocked nucleic acid molecule but made no mention of DNA sequencing.

The arguments on obviousness therefore centred on the related issues of (1) the attributes of the skilled team, i.e. whether they will be interested in sequencing by synthesis using RCTs or whether in fact they would only be interested in improvements to the known methods of sequencing including the most widely known (and used) method, so-called Sanger sequencing and (2) the common general knowledge of the skilled team.

The Skilled Person

In the course of dealing with these arguments, Birss J reviewed the cases which dealt with the situation where the skilled person for the purpose of determining obviousness was not the same as the person to whom the patent was addressed (being also therefore the skilled person for the determination of such matters as sufficiency).  Having considered both Schlumberger (Schlumberger v EMGS [2010] EWCA Civ 819) and Medimmune (Medimmune v Novartis [2012] EWCA Civ 1234), he proceeded to lay down the following approach to determining the attributes of the skilled person for the purpose of determining obviousness:

  1. Ask what problem the invention aims to solve;
  2. Then consider the established field in which the problem can be located;
  3. The notional person or team identified in that established field makes up the person skilled in the art for obviousness.

Following that approach, he concluded on the evidence that the skilled person for the purpose of determining obviousness was a team working on research into sequencing by synthesis.  Interestingly, having defined the team in this way, he came full circle and concluded that the same skilled team would be the one to whom the patent was addressed.

Common General Knowledge (‘CGK’)

Turning then to the issue of the CGK, Birss J pointed out that the reference in the case law to CGK being all that which is “generally regarded as a basis for further action” did not mean that only things which work are part of the CGK but that it includes those things that are known not to work.  Again, with that principle in mind, he concluded on the evidence that although the CGK would include knowledge of the concept of reversible chain termination, it also included the fact that the technique had not succeeded in practice.

The finding of an inventive step over a paper devoted to the synthesis of azidomethyl blocking groups but with no reference to their use in sequencing by synthesis by RCTs then followed inevitably from these two findings: the skilled team was one limited to working on research into sequencing by synthesis and their CGK included knowledge that reversible chain termination had not been made to work in practice.


In the event that the modified nucleotide patents were not held obvious, MGI contended that they were insufficient in two respects: read length and impractical linkers.

As regards read length, MGI argued the claim covered unspecified read lengths and yet the specification only taught how to perform the claimed sequencing method on short read lengths.  As regards linkers MGI argued that the claim included nucleotides that it was not possible to use in the claimed sequencing method.

The application of Regeneron in practice

Birss J examined the principles set out by Lord Briggs in Regeneron relating to a claim’s sufficiency.

The first point made by the Judge was that those principles were clearly not limited to product claims (the subject of the Supreme Court’s decision).

The second point made by the Judge was that nevertheless care should be taken in transposing the principles summarised by Lord Briggs in one context in order to apply them in different circumstances.  He pointed out that in Regeneron the issue was whether the product itself could be made whereas in other cases even about product claims, the issue would be not whether the products could be made but rather whether the property said to be what makes the products inventive was shared by all of the products within the claimed range.  He pointed out that in that latter case the claim may exceed its technical contribution and thereby be vulnerable to an Agrevo obviousness/insufficiency attack (i.e. in accordance with the principles first recognised by the EPO in T939/92 (AGREVO)).

The Judge then went on to consider cases concerning two other related issues relating to insufficiency, namely undue burden and functional limitations, before returning to Regeneron and summarising the position as regards relevant and irrelevant ranges in a claim for the purpose of Regeneron insufficiency.  He set out the principles he derived from his review of the authorities as follows:

  1. When examining any aspect of claim scope for the purpose of enablement it is necessary to distinguish between ranges relevant in the Regeneron sense and other ranges.
  2. For ranges relevant in the Regeneron sense, to be sufficient, there must be enablement across the whole scope of the claim within that relevant range at the relevant date. …
  • Not all claims will necessarily contain a range relevant in the Regeneron sense but if they do then this principle applies to that range.
  1. An example of a range not relevant in the Regeneron sense, will be a descriptive feature in a claim (whether structural or functional) which can cover a variety of things, but for which that variety does not significantly affect the value or utility of the claimed product or process in achieving its relevant purpose …
  2. For a claim feature which amounts to a range in this other sense, the skilled person must still be able to make a suitable selection, without undue burden, in order for the claim to be sufficiently disclosed. …
  3. When examining enablement of any kind, the test is always about what the skilled person is able to do within undue burden. …


In Regeneron, Lord Briggs had referred to the length of the mouse’s tail as being an example of an irrelevant range.  In Illumina, Birss J illustrated the same point by reference to a claim to a teapot with a spout shaped so as to avoid dripping.  He used the example however to explain a number of points that he had previously drawn from his review of the cases.

“The claim [to a teapot with a spout shaped in a new way so as not to drip] will not say anything about the material from which to make the teapot.  … Now the patentee needs to enable the skilled person to make the product.  I will assume the skilled could choose, identify and test suitable materials at the priority date without undue burden.  China would work and chocolate would not.  However, the claim would be infringed later on even if a teapot was made using a new inventive form of Pyrex glass which had not been invented at the teapot patent’s priority date.  Furthermore, in my judgment this fact, that the claim covers types of teapot, which it does not enable, does not reveal some insufficiency.  The fact that the skilled person could not make such a teapot at the priority date of the teapot patent does not matter.  What does matter is that the descriptive feature of the claim, which is at least implicit in the claim, that the teapot has to be made of a suitable material, is not a relevant range in the Regeneron sense.  However, note the potential for error here.  The material from which the teapot is made is plainly crucial to its function as a teapot.  There are materials which are not suitable to use for teapots.  That is not the kind of relevance which Regeneron is referring to.  Relevance in the Regeneron sense is a much more particular concept which depends on examining all the circumstances and depends not simply on the invention (that is to say the claim as drafted) but also on what I can only think of calling the essence or core of that invention (closely related to the technical contribution and/or the inventive concept).”


Birss J then returned to the facts of the case and concluded that neither of the two matters that were said to render the claims insufficient (impracticable linkers and read length) related to the “essence of the invention” and were not therefore relevant ranges in the Regeneron sense.





Written by
Neil Jenkins
Neil Jenkins
My practice is focussed on litigating patents especially patents protecting pharmaceutical products in the UK as well as advising on and co-ordinating European patent litigation strategies more broadly.

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