The Federal Circuit recently held an asserted patent was not entitled to its priority date because the priority application lacked written description support for the asserted claims. In so doing, the court explained that broad disclosures that do not provide reasonably specific support for narrower claims do not meet the written description requirement. The court also considered whether the inventor’s testimony showed they possessed the full scope of the claimed genus at the priority date or whether it was more likely the inventors first became aware of the claimed embodiments from public disclosures of the accused product.
The appeal in this case stemmed from a district court litigation in which a jury returned a verdict in favor of the patentee of infringement and no invalidity. The asserted patent relates to antibody-drug conjugate (ADC) technology. The claims are generally directed to an ADC that is comprised of an antibody, a multi-subunit linker that includes a tetrapeptide unit formed of only two amino acids (glycine and phenylalanine), and a drug moiety.
Defendants argued that the asserted patent was not entitled to claim benefit of its priority date because the priority application did not provide written description support for the asserted claims, and as a result, the asserted patent should be invalid for anticipation in view of the public disclosure of the accused product.
More specifically, Defendants argued that the priority application did not specifically describe the claimed subgenus of glycine/phenylalanine tetrapeptide units. Instead, the priority application disclosed a broad genus of linkers where the peptide unit was (1) optional and (2) when present, could vary in length and composition of amino acids. Because the peptide units disclosed in the priority application encompassed a huge number of possible options, including over 47 million species when limited to just four peptides (i.e., tetrapeptides), and did not specifically call out or suggest the claimed subgenus of glycine/phenylalanine tetrapeptides, it failed to provide written description support for the tetrapeptide limitation of the asserted claims.
Patentee responded that the priority document provides ample written description support by setting out the overall chemical formula for its ADC structure, disclosing tetrapeptides that can be used in the ADC linker, explaining that glycine and phenylalanine are suitable options for use in the peptide units, and providing a tetrapeptide example in which 3 of 4 amino acids are either glycine or phenylalanine.
The Federal Circuit agreed with Defendants. The court explained that the broad disclosures in the priority application, which covered peptide units that numbered between two to twelve amino acids, amounted to “effectively countless peptide units.” Despite that broad disclosure, the priority application never specifically mentioned the claimed subgenus of glycine/phenylalanine tetrapeptides. The court then reasoned that those facts, combined with testimony from the inventors indicating that they never contemplated the claimed tetrapeptides until after the priority date when they saw them in the accused product, supported the conclusion that the inventors did not possess the claimed invention as of the priority date.
The court also noted that testimony from Patentee’s expert indicating that the claimed tetrapeptide units would be a “straight forward leap” from the priority document’s disclosure of a similar tetrapeptide unit was “self-defeating” because “[t]hat which one must leap to is obviously not there.” That testimony, according to the court, “in effect admits that a skilled artisan would not understand the inventors of the [priority] application to have ‘possession’” of the claimed invention. And for these reasons, the court held that the priority document failed to provide written description support for the asserted patent, which in turn, was invalid as anticipated by the accused product.
Practice Tip: When proceeding through prosecution it is important to review priority dates for support for each new set of claims. Likewise, disclosure of a broad genus without reasonably specific supporting disclosure of a subgenus may leave later claims to such a subgenus open to written description challenges.
Seagen Inc. v. Daiichi Sankyo Co., Ltd., No. 23-2424 (Fed. Cir. Dec. 2, 2025)