The Antibody Series #4 | pH points in antibody claims: when “same pH ” becomes an addition of matter

The Boards of Appeal of the EPO (BoA) are the appeal body that reviews EPO decisions; in this case, they reviewed a revocation in opposition of a patent relating to an antibody.

The real case: You optimize an antibody to improve antigen clearance via FcRn; you try to capture the idea in claim 1 by comparing binding to FcRn and binding to the antigen at specific pH points; the wording suggests that the two measurements are performed at the same pH values.

Claim 1:
“1. An antibody comprising an antigen-binding domain and a human Fc domain, which has a human FcRn-binding activity at pH 5.5 and at pH 7.0, wherein the antibody has reduced antigen-binding activity at pH 5.5 as compared to at pH 7.0, and wherein the antibody has improved human FcRn-binding activity at pH 5.5 and reduced human FcRn-binding activity at pH 7.0 as compared to a corresponding antibody not having the replacement of at least one amino acid in the antigen-binding domain or the insertion of at least one histidine.”

Beginning of the story: The opposition division revoked the patent for adding matter (Article 123(2) EPC) ; this was the central point of the appeal. The underlying problem was simple: claim 1 in practice links the comparison of binding to the antigen at the same pH points as those explicitly mentioned for binding to FcRn; however, the application as filed did not directly and unambiguously disclose that the two binding activities had to be tested at exactly the same pH values.

The BoA’s teaching: When drafting a claim that couples two measured functional criteria, the “logic” suggested by the wording matters. Here, even though it may seem intuitive, the Board sought clear disclosure in the application as filed that antigen binding and FcRn binding are evaluated at the same pH points, and found none. On the contrary, the examples in the application taught that the two activities could be tested under different pH conditions; therefore, importing a concept of “same pH points” into claim 1 added technical information.

Practical drafting tip: If your inventive concept is based on a comparison of properties measured under specific experimental conditions (e.g., pH points), make the exact link explicit from the outset. Clearly indicate whether multiple measurements (e.g., antigen binding and FcRn binding) are evaluated under the same conditions ; disclose the precise points/conditions that you may wish to claim later ; include at least one complete example where all these measurements are performed together under these conditions. Otherwise, a subsequent limitation may be challenged on the basis of adding matter, even if the wording seems “obvious” in hindsight.

Disclaimer : This is not legal advice; it is merely practical guidance to be incorporated early on in the filing strategy.

Source : ECLI:EP:BA:2022:T050920.20220728.