The new EPO Guidelines, which entered into force on March 1, 2021, include a new section detailing EPO's practice of interpreting terms relating to amino acid or nucleic acid sequences (F-IV, 4.24), and a new chapter on the study of antibody claims (G-II, 5.6).

Terms relating to the sequence of amino acids or nucleic acids

First, if the sequence of an amino acid or nucleic acid is specified by percent identity, it is determined by the number of identical residues over a specified length in that alignment. Where an algorithm or calculation method to determine the percent identity is not specified in the application, the broadest interpretation using any reasonable algorithm or calculation method known at the date of filing shall be used.

In addition, the Guidelines acknowledge that amino acid sequences can also be determined by the degree of similarity, expressed as a percentage of similarity. Similarity is considered broader than identity because it allows the conservative replacement of amino acid residues with similar physicochemical properties over a given length of a given alignment. The percent similarity is only determinable when a similarity score matrix is defined. If such a matrix is not defined, a claim relating to a sequence showing a percent similarity to said sequence is deemed to encompass any sequence satisfying the similarity requirement as determined by any reasonable similarity scoring matrix known at the date of filing.

Finally, in the case of amino acid sequences, if the applicant uses percent homology as the only feature able to distinguish the subject matter of the claim from the prior art, such operation is considered to be contrary to Art. 84 EPC (not clear), unless the method for determining or calculating percent homology is clearly defined in the application. However, in the case of nucleic acid sequences, percent homology and percent identity are usually considered to have the same meaning.


A new section G-II, 5.6.1 summarizes EPO practice and jurisprudence on how to define antibodies. In short, it is acceptable to define the antibodies of conventional derivatives, recombinant antibodies (including antibody fragments, bispecific antibodies and fusions of antibodies) or novel formats for antibodies (such as antibodies, only heavy chain) in The reserved by reference to one or more of the following characteristics:
( (a) their own structure (amino acid sequences);
b) nucleic acid sequences encoding the antibody;
(c) references to the target antigen;
(d) target antigen and further functional characteristics;
(e) functional and structural features;
(f) the manufacturing process;
g) epitope; and
(h) an antibody producing hybridoma.

Each type of definition is discussed in the relevant paragraph, giving you a general idea of what should be generally acceptable and under what conditions.

In addition, a separate subsection G-II, 5.6.2 provides some insight into the specific requirements for new antigens to meet the inventive step criterion (Art. 56 EPC). Namely, the Guidelines state that a new, further antibody that binds to a known antigen does not have an inventive step, unless an application demonstrates a surprising technical effect such as increased affinity, increased therapeutic activity, decreased toxicity or immunogenicity, unexpected species cross-reactivity or a new type of antibody format with proven binding activity. If the inventive step is based on an improved property compared to the active antibodies of the prior art, the main features of the property determination method must also be indicated in the claim or by reference to the description.

In particular, with regard to binding affinity, the structural requirements for conventional antibodies which inherently reflect this affinity must include the six CDRs and the framework regions, since the latter can also affect the affinity.

The inventive step can be considered if the application overcomes the technical difficulties in producing or producing the claimed antibodies. AOMB Polska