UK court in Samsung Bioepis v Alexion adds to recent lessons on need to be pernickety when drafting patent specifications

In the recent UK High court case re Alexion’s EP (UK)3167888 Samsung Bioepis v Alexion [2025] EWHC 1240 (Pat), Alexion failed to overcome an error in the definition of their therapeutic antibody eculizumab – definition of the light chain of the antibody as consisting of a sequence designated as SEQ ID NO:4 but in fact specifying an extended light chain sequence with an additional 22 amino acid leader sequence. In antibody expression such a leader sequence is normally removed. However, the judge held there was no sound basis for reading this definition with purposive construction so as to implicitly ignore the leader sequence.

The judgment forms part of a larger battle between Alexion and others over biosimilars of its eculizumab SOLIRS® product, namely EPYSQLI® of Samsung Bioepis and BEKEMV® of Amgen. It is of particular interest as it followed (i) decision of the UPC Appeal Court (UPCAC) to refuse grant of a preliminary injunction against Samsung and Amgen in relation to sale of their eculizumab biosimilars [UPC_CoA_402/2024; UPC_CoA_405/2024] and (ii) EPO Board of Appeal Decision T1515/20 refusing claim amendment of the underlying European patent application to deal with the light chain issue on the basis of added subject matter. The UPCAC came to the same conclusion on the light chain definition although formally only considering dependent pharmaceutical composition claim 2.

In the judgment of the UK High Court, the judge preferred that “consisting of” is use of language that would generally be expected to be precise and that as matter of drafting convention “consisting of” means exactly this. Moreover, he shared the view of the alleged infringers that the skilled person would “lean away from a meaning that the patent covered something it said was old”. EP3167888 referred to a previous patent family which covered eculizumab generically and indeed had provided the foundation for an SPC covering the same antibody. The claims were originally focussed on antibody use but claim strategy changed. This was aided by the fact that a previous sequence submission to the Chemical Abstracts Service in relation to eculizumab was also incorrect! The judge additionally noted that a skilled reader would not automatically think binding ability was excluded by the stated light chain sequence and that an antibody as strictly claimed could be made. The judge was led to state:

Patents do sometimes claim things which are sub-optimal or whose purpose is not entirely evident. That is not a licence to rewrite the claims.

The above-noted case adds to a number of recent decisions from the EPO which highlight how simple oversights in specification drafting can come back to ‘bite’. By way of example, EPO Appeal Board Decision T1642/22 addressed the substitution of the term ‘about’ at both ends of property ranges in a claim 1 relating to injectable facial fillers. In its first communication, the Examining Division objected to such use of the term “about” for clarity reason under Article 84 EPC. Hence it was replaced for grant by ± calculations equating with ±10%. In opposition appeal proceedings, the board of appeal looked at boilerplate definition of the term “about” in the description and held that as filed it made clear that ±10% applied to numerical values but did not directly and unambiguously make clear that the lower endpoint of a range may be increased by 10% while the upper end point may be reduced by 10% resulting in added subject matter. The Patentee was able to solve the problem by removing modifiers entirely from the ranges but perhaps regrets that argument over range scope could even begin.

In EPO Appeal Board Decision T0345/24 concerning absorbent hygiene products, two issues arose over the definition in claim 1 of the acquisition distribution layer (ADL). In retrospect both could have been readily avoided at the specification drafting stage. Firstly, claim 1 defined the ADL as ‘in contact with’ another layer with omission of the qualifier ‘good’. The Appeal Board saw no direct and unambiguous basis in the application as filed for this and did not accept that ‘good’ in the context of the claimed subject matter was technically irrelevant such that omission could be permitted with reliance on Decision G1/93. Secondly, the Board of Appeal saw no basis in the specification as filed for changing the definition of the composition of the ADL from ‘comprises A and/or B layer type’ to ‘consisting of A or B layer type’ in the context of the breadth of claim 1 despite examples of sole A or B layers. Other formal issues with auxiliary requests led to revocation.

Final thoughts

It is frequently the case that patent attorneys are told, “I just want a quick filing at no great expense.” However, the cases above illustrate how easy it can be for oversights to occur in specification preparation and that there can be issues with overuse of boilerplate language. Good specification preparation demands good communication with inventors and for those patent attorneys needing to tackle drafting of a specification including one or more amino acid and/or nucleotide sequences, it is always good to ask: “Are you happy that I have the correct sequence(s)?”

More detailed report on Alexion’s sequence error saga as considered in the above-noted EWHC decision is due to be published in the CIPA Journal available via this link: The Chartered Institute of Patent Attorneys