Few matters within patent law generate as much debate as the requirements for written description and enablement. These rules require that a patent adequately describe the invention in sufficient detail to allow others to make and use the invention. Inventors have to consider the rigorous demands for what counts as adequate disclosure, especially related to seemingly broad genus claims in biopharma patents. Recently, however, a federal appeals court clarified these rules in the context of antibody patents, particularly when it comes to distinguishing between patent claims directed to methods of treatment and claims directed to the therapeutic compounds themselves. The decision provides new and promising insights into patent drafting and protection strategies.
Teva accused Eli Lilly of infringing a group of patents informally referred to as the “headache patents.” These patents cover methods of treating headaches using humanized mouse antibodies that target a protein that has a key role in causing headaches. In response, Lilly challenged the validity of the headache patents, arguing that Teva’s patents failed to satisfy the written description and enablement requirements. Specifically, Lilly argued that Teva disclosed only a single working example in the patent specification and that this limited disclosure did not describe and enable claims covering a broader genus of antibodies. Initially, a jury ruled that Teva had met the written description and enablement requirement. The trial court, however, later ruled that Teva’s headache patents were invalid for lack of written description.
On appeal, the appeals court unanimously reversed the lower court’s decision by holding that Teva’s patents satisfied both written description and enablement requirements. Central to the court’s reasoning was the wording of the patent claims themselves, which are not directed to the humanized mouse antibodies themselves but rather to methods of using such antibodies to treat headaches. The court explained that a person of ordinary skill in the art would have understood from just reading the patent that all humanized antibodies are effective for treating headaches. As a result, the court held that the disclosure of a single representative antibody was sufficient to support the claimed methods of treatment.
This decision highlights the critical importance of claim type, particularly in pharmaceutical patents, in which method-of-treatment claims may be subject to a more flexible written description and enablement standard than product claims are. While the distinction between product claims and method-of-use claims may sound semantic to the layperson, this case demonstrated that the interpretation of such patent claims can have profound implications for both patent validity and enforcement.
This case is Teva Pharmaceuticals International GmbH v. Eli Lilly & Co., No. 2024-1094 (Fed. Cir. Apr. 16, 2026). If you would like additional information or have questions on this topic, please contact the authors or your lawyer at McCarter & English, LLP.