Authored by: Jeremy J. Gustrowsky
In a recent decision, the Federal Circuit affirmed the rejection of Xencor, Inc.’s patent application (U.S. Patent Application No. 16/803,690) for failing to provide an adequate written description, particularly focusing on the requirements for Jepson claims and method claims involving medical treatments. Xencor’s application sought to patent methods of treating patients with anti-C5 antibodies that have specific amino acid substitutions to increase their half-life in the body, which could mean less frequent treatments for patients.
The heart of the dispute was whether the preamble language in Xencor’s claims—specifically, “treating a patient”—was limiting, and if so, whether the patent application provided enough detail to support that limitation. The court held that in both Jepson claims (a type of claim that identifies an improvement over existing technology) and regular method claims, the preamble can be limiting if it gives “life and meaning” to the rest of the claim. In this case, “treating a patient” was found to be essential for understanding the scope of the invention, especially since the claims also referred to the increased in vivo half-life of the antibodies.
Importantly, the court clarified that for Jepson claims, the inventor must provide a written description not just for the improvement, but also for the elements described in the preamble—even if those elements are supposedly “well-known” in the field. The written description must show that the inventor actually possessed the full scope of what is claimed, including any prior art elements. Xencor’s application only described one specific anti-C5 antibody and did not provide enough detail or examples to show that treating patients with the broader genus of anti-C5 antibodies was within their possession at the time of filing.
This decision serves as a reminder that when drafting patent applications that includes Jepson claims, applicants must ensure their specifications thoroughly describe both the new and the old elements of the relevant technology. Simply asserting that something is “well-known” is not enough; the written description must make clear to a person skilled in the art that the inventor truly possessed the claimed invention.