T 0528/18 (Method for producing a stabilised antibody/CHUGAI) 12-07-2019

1. The appeal complies with Articles 106 to 108 and Rule 99 EPC and is therefore admissible.

Main request and first to fifth auxiliary request

Sufficiency of disclosure (Article 83 EPC)- claim 1

2. One embodiment falling within the scope of claim 1 of all claim requests is a method for producing a stabilised antibody which comprises the step of substituting a glycine (Gly) that is located adjacent to the C-terminal side of an asparagine (Asn) with another amino acid, wherein the asparagine exists in the complementary determining region (CDR) of the antibody, and wherein the antigen-binding activity of

the stabilised antibody is 70% or higher than the antigen-binding activity of the antibody before the amino acid substitution (see sections IV to IX).

3. Under Article 83 EPC, a European patent application must disclose the invention in a manner sufficiently clear and complete for it to be carried out by a person skilled in the art. In interpreting Article 83 EPC it has been established in the jurisprudence of the Boards of Appeal that the claimed invention must be sufficiently disclosed on the filing date (Case Law of the Boards of Appeal of the EPO, 8th edition 2016, II.C.1.) based on the application as a whole (ibid., II.C.2.), in consideration of the common general knowledge of the skilled person (ibid., II.C.3.). At least one way of carrying out the claimed invention must be disclosed, but this disclosure is sufficient only if it allows the invention to be performed in the whole range claimed (ibid., II.C.4.2., II.C.4.4 and II.C.6.1.2). Furthermore, the disclosure must be reproducible without undue burden. Where the person skilled in the art has to find out by trial and error which compound, if any, meets the parameter set out in the claim, this constitutes an undue burden, even if it involves routine experimentation (ibid., II.C.5.7.).

4. Thus, the criterion that needs to be assessed in determining whether the disclosure of the invention is sufficient is whether the application as filed provides the skilled person, in the light of their common general knowledge, with all the information necessary for carrying out the claimed invention (here: a method for stabilising any antibody comprising an Asn-Gly sequence in one of its CDRs, wherein the antigen-binding activity of the stabilised antibody is 70% or

higher than the antigen-binding activity of the antibody before the amino acid substitution) without undue burden.

5. In developing a method to suppress deamidation of Asn without affecting the antibody's activity, the application focuses on an anti-human tissue factor (TF) antibody with an Asn-Gly sequence in the CDR2 region (see page 2, line 29 to page 3, line 5). The application provides one relevant example (Example 2), in which one specific amino acid in the heavy chain CDR2, namely Gly at position 55 (Gly55), of the anti-TF antibody has been substituted with 19 different amino acids and the binding activity of the resultant mutants measured. The results are shown in Figure 11 of the application.

6. The board notes that not all replacements resulted in a binding activity which was "70% or higher than the antigen-binding activity of the antibody before the

amino acid substitution". Consequently, the nature of the amino acid replacing the Gly seems to be critical.

7. The application does not provide any further examples or technical guidance for substitutions of glycines in Asn-Gly sequences occurring in CDR regions of any antibody that would help the skilled person find substitutions that result in an antibody as claimed, i.e. a stabilised antibody with antigen-binding activity which is 70% or higher than the antigen-binding activity of the antibody before the amino acid substitution.

8. As regards the available common general knowledge (see point 3 above), the appellant acknowledges (see document D11, point 6) that at the priority date of the application "it was known to persons skilled in the art that Gly residues readily form a flexible structure and play an important role in maintaining the canonical structure of antibody. It was believed that replacing a Gly residue in the variable regions (responsible for antigen-binding activity) with another amino acid would prevent the antibody from maintaining the structure that could retain the binding activity because it was thought that glycine residues in the CDR sequences may play a critical role in maintaining the canonical structure of an antibody (see, for example, Chothia et al., 1992, J. Mol. Biol., 227:799-817 [note by the board: document D12 in the appeal proceedings], in particular page 803, left hand column, lines 3 to 4; page 809, right hand column, lines 3 to 5; and page 825, left hand column, section headed "(d) Canonical structures in human expressed Vh segments)."

8.1 Moreover, document D14, cited in the application on page 1, lines 32 to 33, discloses that simultaneously changing Asp in CDR-L2 and Asn in CDR-H2 to Ala in antibody D3 reduces the binding-activity of the antibody 4-fold (see page 386, right hand column, fourth paragraph).

8.2 Document D15 discloses that changing Asp in an Asp-Gly sequence located in a CDR decreases the relative binding affinity significantly (see page 1901, paragraph bridging columns, Table 4). The authors conclude that their studies "demonstrate sensitivity of antigen recognition to subtle sequence changes in the CDRs and the tradeoffs incurred in engineering out a labile sequence" (see page 1903, left hand column, end of first paragraph).

9. The board concludes that it can be inferred from the evidence on file (see points 8 to 8.2) that on the priority date of the application it was part of the common general knowledge of the skilled person that the substitution of an amino acid within a CDR of an antibody was likely to negatively affect the antigen-binding activity of the antibody.

10. Indeed, the application also states that "[g]enerally, an antibody is inactivated by amino acid substitution in the CDR" (see page 12, lines 32 to 33).

11. In the board's view, in these circumstances, providing a single example (see points 5 to 7) which shows that the antigen-binding activity of a specific antibody is retained after some particular substitutions, even when taken together with the general information in the application and the common general knowledge, cannot be considered to provide the information necessary to allow the skilled person to perform the claimed method for any antibody without undue burden, for the following reason:

12. The skilled person does not have at their disposal, either from the application as filed (see points to 5 to 7) or from common general knowledge (see points 8

to 9), any information that would reliably lead them to the amino acid substitutions which result in an antibody fulfilling the functional requirements of the claim. Accordingly, for each and every antibody comprising an Asn-Gly sequence in one of its CDRs, the skilled person has to identify each time, by trial and error, which amino acid replacement will result in antigen-binding activity of the stabilised antibody which is 70% or higher than the antigen-binding activity of the antibody before the amino acid substitution - without any guarantee that a substitution that fulfils the functional requirements of the claim will be found at all. On the contrary, given the common general knowledge (see points 8 to 9), the skilled person's expectation must be that most substitutions will not be successful (see also point 10 above).

13. The fact that the specific amino acid to be substituted - Gly in an Asn-Gly sequence - is disclosed, and that the number of amino acids that can be incorporated into polypeptides is finite, does not make the skilled person's task any easier because testing is still necessary for each of the possible substitute amino acids. The board is also not persuaded by the appellant's argument that once the skilled person had the information as to which amino acid to substitute, namely the Gly in an Asn-Gly sequence occurring in the antibody's CDR, selecting of the substituting amino acid and implementing the chosen substitution were a matter of routine. Even if the testing required in the present circumstances (see point 12 above) can be done by routine methods, it is considered to place an undue burden on the skilled person seeking to carry out the claimed invention because there is absolutely no guarantee that a substitution that works will be found for any antibody.

14. Given the wording of the claim, the appellant's submission that substitutions which result in binding activity below 70% of the antigen-binding activity before the substitution are outside the scope of the claims is correct, but misses the point when considering whether the requirements of Article 83 EPC are fulfilled. As explained above, the point is that the skilled person does not know beforehand whether any of the possible amino acid substitutions will result in an antibody with binding activity above 70% of the antibody before the substitution.

15. Finally, in the circumstances of the present case the appellant cannot rely on post-filed evidence, i.e. documents D8 and D10, because the invention must be sufficiently disclosed at the effective date (see

point 3 above).

16. From the above the board concludes that the application as filed does not provide the skilled person, in light of their common general knowledge, with all the information necessary for carrying out the claimed invention over the entire breadth of claim 1 of all claim requests without undue burden.

17. Therefore, none of the claim requests is allowable.

Reimbursement of the appeal fee

18. Pursuant to Rule 103(1)(a) EPC the appeal fee will be reimbursed in full where the board deems an appeal to be allowable, if such reimbursement is equitable by reason of a substantial procedural violation.

19. Since the appeal is not allowable (see point 17 above), the appellant's request for reimbursement of the appeal fee has to be refused.