The US Patent and Trademark Office (PTO) issued a memorandum to patent examiners clarifying the written description requirement of 35 USC § 112(a) for claims drawn to antibodies. The memorandum was spurred by the US Court of Appeals for the Federal Circuit 2017 decision in Amgen v. Sanofi, which addressed adequate written description for claims drawn to antibodies. In Amgen, the Federal Circuit explained that when an antibody is claimed, § 112(a) requires adequate written description of the antibody itself. This is in contrast to MPEP 2163(II)(3)(a), which teaches “disclosure of an antigen fully characterized by its structure, formula, chemical name, physical properties, or deposit in a public depository provides an adequate written description of an antibody claimed by its binding affinity to that antigen, if generating the claimed antibody is so routine that possessing the [antigen] places the applicant in possession of an antibody” (the so-called newly characterized antigen test).

The Federal Circuit found that although the newly characterized antigen test was noted in dicta in several other Federal Circuit decisions, it could not stand because it contradicted the quid pro quo of the patent system whereby one must describe an invention in order to obtain a patent. Therefore, the memorandum instructs examiners that adequate written description of a newly characterized antigen alone should not be considered adequate written description of a claimed antibody to that newly characterized antigen, even when the preparation of such an antibody is routine and conventional. 

The memorandum further instructs examiners to continue to follow the guidance in the MPEP 2163 except for the portion teaching that disclosure of a fully characterized antigen may provide written descriptive support of an antibody to that antigen. The memorandum noted that the MPEP will be updated to reflect these changes.