On April 16, 2026, the U.S. Court of Appeals for the Federal Circuit (the court) issued a precedential decision in Teva Pharmaceuticals International GmbH v. Eli Lily and Company, determining that the claims of Teva’s U.S. Patent Nos. 8,586,045 (the ’045 patent), 9,884,907 (the ’907 patent), and 9,884,908 (the ’908 patent) (collectively, the Headache Patents) relating to methods of reducing headache by administration of humanized anti-CGRP antagonist antibodies are not invalid for lack of written description or enablement. The decision reversed a district court’s judgment as a matter of law (JMOL) decision concluding otherwise, and reinstated the jury’s findings that Eli Lilly’s Emgality® product willfully infringed the Headache Patents.
Background: Written Description and Enablement Analysis
Under U.S. patent law, a patent must satisfy the written description and enablement requirements. To satisfy the written description requirement, a patent must reasonably convey to those skilled in the art that the inventor had possession of the claimed invention as of the filing date of the patent. To satisfy the enablement requirement, a patent must enable those skilled in the art to make and use the full scope of the claimed invention, without undue experimentation.
For claims to a class or “genus” of claim elements, such as a class of antibodies, there are two recognized ways to satisfy the written description requirement. The first option is to set forth in the patent “a representative number of species falling within the scope of the genus.” The second option is to set forth “structural features common to the members of the genus so that one of skill in the art can ‘visualize and recognize’ the members of the genus.”1
The Headache Patents: Method of Treatment Claims
The claims of the Headache Patents, while reciting a genus of humanized anti-CGRP antagonist antibodies, are not directed to the antibodies themselves. Rather, the claims are directed to methods of using the humanized anti-CGRP antagonist antibodies to treat headaches. Specifically, representative claims 17 and 30 of the ’405 patent recite “administering to the human an effective amount of an anti-CGRP antagonist antibody, wherein said anti-CGRP antagonist antibody is a … humanized monoclonal antibody.”
The Federal Circuit’s Decision: Written Description
The Court determined that because the claims of the Headache Patents are directed to methods of using a well-known genus of antibodies, and a person of skill in the art would understand from the patents that every species in the well-known genus could be used in the claimed methods, the Headache Patents satisfy the written description requirement.
In support of its decision, the court referenced previous precedential cases that distinguish between an invention to a genus itself, and the use of a known genus as part of a different invention. In Ajinomoto2, the court determined that a claim to a method of producing particular amino acids from a bacterium having a “more potent promoter” for its yddG gene was adequately described by a patent disclosing four examples of “more potent promoters” because “enhancing promoter activity was well-known” and the invention was identifying the yddG gene’s role in amino acid production, rather than the already-known methods of enhancing promoter activity. Similarly, in In re Herschler3, the court determined that a claim to a method of enhancing skin penetration of a “physiologically active steroidal agent” by applying it with dimethyl sulfoxide (DMSO) was adequately described because, even though only one example steroidal agent was disclosed, a skilled artisan reading the patent would understand that any member of the known genus of “physiologically active steroidal agent[s]” would work in the claimed method.
In analogizing the present case to its precedent, the court noted that although the Headache Patents disclose just one humanized anti-CGRP antagonist antibody and several murine anti-CGRP antagonist antibodies, because: a) anti-CGRP antibodies and methods of making them was well known; b) humanization of such antibodies is routine; and c) a skilled artisan would have understood from the patents that all humanized anti-CGRP antagonist antibodies treat headaches, a jury could have reasonably found that the Headache Patents disclose a representative number of species of humanized anti-CGRP antagonist antibodies for treating headache, reversing the JMOL of no written description.
The Court’s Decision: Enablement
The court’s enablement analysis distinguished the present case from the Supreme Court’s most recent decision regarding enablement in Amgen Inc. v. Sanofi.4 In Amgen, a patent claiming a genus of antibodies that bind to certain amino acids of the PCSK9 protein was held invalid for lack of enablement because the patent offered the skilled person “little more than advice to engage in ‘trial and error’” to identify species within the genus of claimed antibodies, and thus would require undue experimentation to perform the full scope of the invention.5 In contrasting the Headache Patents to the claims of Amgen, the court noted that the Headache Patents are directed to the use of humanized anti-CGRP antagonist antibodies for the limited purpose of treating headaches, rather than to the antibodies themselves. Further, while in Amgen the patent failed to teach the skilled artisan how to find species of the claimed antibodies without undue experimentation, the Headache Patents disclose that all humanized anti-CGRP antagonist antibodies would work for the purpose of treating headaches. Therefore, since anti-CGRP antagonist antibodies, and methods of making them, were well-known, no undue experimentation is needed to perform the full scope of the invention, and the JMOL of lack of enablement was reversed.
Conclusion
This decision provides some clarity regarding the requirements for written description and enablement as they relate to methods of using a well-known class of molecules, such as antibodies. Although recent decisions regarding patents directed to a broad genus of molecules have held such patents invalid,6 the court distinguishes those decisions from the present case where the claims relate to methods of using a well-known genus of molecules, and every species of the well-known genus can be used in the methods. This case underscores the importance of careful patent drafting for method of treatment inventions in manner that conveys that the genus is well-known, and that the methods are applicable to each species in the genus.
For additional information or questions regarding patent strategies, please contact any member of Wilson Sonsini’s Patents and Innovations and Patent Litigation practice groups.
[1] Ariad Pharmaceuticals, Inc. v. Eli Lilly and Co., 598 F.3d 1336, 1350 (Fed. Cir. 2010).
[2] Ajinomoto Co. v. ITC, 932 F.3d 1342, 1346-47 (Fed. Cir. 2019).
[3] In re Herschler, 591 F.2d 693, 695 (CCPA 1979).
[4] Amgen Inc. v. Sanofi, 598 U.S. 594 (2023).
[5] For further information, see the Wilson Sonsini article summarizing the Amgen case at https://www.wsgr.com/en/insights/broad-genus-patents-must-be-enabled-over-the-full-scope-of-the-claims.html.
[6] Id. See also the Wilson Sonsini article regarding Seagen Inc. v. Daiichi Sankyo Co., Ltd., 2023-2424 (Fed. Cir. Dec. 2, 2025) at https://www.wsgr.com/en/insights/continued-scrutiny-of-genus-claims-the-written-description-and-enablement-requirements-for-broad-and-previously-undisclosed-subgenera.html.
