A recent court decision in AbbVie Deutschland v. Janssen Biotech and Centocor Biologics will likely make functional claims for antibodies more challenging in the future. On July 1, the US Court of Appeals for the Federal Circuit upheld a jury verdict that Janssen's Stelara (ustekinumab), a fully-humanized anti-IL-12 antibody product, did not infringe AbbVie's patent claims for fully human interleukin (IL)-12–neutralizing antibodies. The court asserted that AbbVie's functional claims—based on the antibodies' ability to neutralize IL-12 and their affinity—were invalid for lack of an adequate description. One ground for invalidity was the so-called “written description requirement” of US patent law. Going forward, instead of functional claims (e.g., binding, neutralizing, competing with, affinity), antibodies may have to be claimed by their structures (e.g., variable regions) in most instances.