In the wake of the 2023 Supreme Court’s decision in Amgen, Inc. v Sanofi, the remaining means by which patent practitioners can claim antibodies while satisfying the requirements of 35 U.S.C. § 112 remained unclear. The case, In re Xencor, represented a potential remaining avenue for obtaining meaningful protection, as Xencor had drafted at least one of the claims at issue in the Jepson claim format in hopes that this claiming strategy would avoid a finding of lack of written description. In its March 13, 2025 decision, the Federal Circuit disagreed.

There were two claims at issue before the Federal Circuit: Claim 8, which was written as a Jepson claim, and Claim 9, which was written as a regular method of treatment claim (note the Federal Circuit did not address the means plus function limitation). Those claims can be seen below:

8. In a method of treating a patient by administering an anti-C5 antibody with an Fc domain, the improvement comprising:

          said Fc domain comprising amino acid substitutions M428L/N434S as compared to a human Fc polypeptide,

          wherein numbering is according to the EU index of Kabat,

          wherein said anti-C5 antibody with said amino acid substitutions has increased in vivo half-life as compared to said antibody without said substitutions.

9. A method of treating a patient by administering an anti-C5 antibody comprising:

   a) means for binding human C5 protein; and

   b) an Fc domain comprising amino acid substitutions M428L/N434S as compared to a human Fc polypeptide,

          wherein numbering is according to the EU index of Kabat,

          wherein said anti-C5 antibody with said amino acid substitutions has                                                                        increased vivo half-life as compared to said antibody without said                                                                                       substitutions.

As to Claim 8, Xencor had contended that anti-C5 antibodies were well known in the art, and therefore required no further written description support. The invention itself, Xencor argued, related to the specific use of their anti-C5 antibody to treat a patient.

Affirming both the Patent Trial and Appeals Board and Appeals Review Panel’s decisions, the Federal Circuit explained that Jepson claim preambles require written description, and not just written description of the improvement claimed. This, they said, is because the claimed invention consists of not only the claimed improvement, but also includes the claimed improvement as applied to the prior art. Therefore, the inventor must provide written description sufficient to establish that what is claimed to be well-known in the prior art is actually well-known in the prior art. The amount and content of that disclosure, the court explained, will vary depending on factors such as “the level of knowledge of the person of ordinary skill in the art, the unpredictability of the art, and the newness of the technology.”

As to Claim 9, the Court explained, citing Boehringer Ingelheim Vetmedica, Inc.v. Schering-Plough Corp., 320 F.3d 1339, 1345 (Fed. Cir. 2003), that preamble language will limit a claim where it recites “not merely a context in which the invention may be used, but the essence of the invention without which performance of the recited steps is nothing but an academic exercise. The preamble phrase “treating a patient,” the Court found, limited Claim 9 for four reasons. First, “treating a patient” is directly connected to the phrase “administering an anti-C5 antibody,” because the treatment of the patient cannot occur without the administration of the antibody. Second, “treating a patient” gives life to “administering,” because the claim itself lacks a specifically recited dosage and rate, which would cause an ordinary skilled person in the art to read “increased in vivo half-life” in light of “treating a patient” in order to make sense of the claim’s scope. Third, the Court said, the preamble provided a raison d’être for the claim, with the preamble informing the meaning of the claim language. Finally, the specification discloses that administering the antibodies and proteins as therapeutics requires injections whose frequency is dependent on the half-life characteristics of the protein, which gives additional color to the remaining language of the claims and furthers the Court’s finding that the preamble language is limiting.

The Court additionally found that Claim 9 lacked written description because the application did not define the word “treating” and did not “describe or provide any data associated with treating any patient with any disease or condition with any anti-C5 antibody, including an anti-C5 antibody with the claimed Fc modifications.”

For now, it seems the best and most practical strategies for obtaining the broadest antibody protection in the U.S. are:

1. Describe in the specification, with particularity, as many embodiments of the antibody as reasonably possible, preferably in both functional terms and structural (at least the CDR sequences) terms;
2. Describe experiments that set out how one skilled in the art can reliably produce antibodies that perform the intended function;
3. Ensure description of relevant experimental data and treatment steps within the specification as it pertains to the invention;
4. Ensure description ofthe prior art at large such that it is clear that the applicant understands the scope of the relevant prior art; and
5. Describe a common quality amongst all of the functional embodiments that enable a person skilled in the art to make all or most of what is claimed, rather than only the isolated antibodies.