What is a “clear and unmistakable” prosecution history disclaimer?

The Federal Circuit’s March 21, 2025 decision in Maquet Cardiovascular LLC v. Abiomed Inc. et al. (No. 2023-2045) and the recent Patent Trial and Appeal Board (PTAB) Delegated Rehearing Panel decision in SynAffix B.V. v. Hangzhou DAC Biotech Co., Ltd. (IPR 2022-01531, Paper 23) have provided new insights into how courts determine the applicability and scope of prosecution history disclaimers.

In this alert, we provide a summary of the decisions and provide key takeaways for avoiding clear and unmistakable disavowal of claim scope.

SynAffix v. Hangzhou: Mapping of prior art and use of ambiguous examples supporting amendment

The claims at issue in the PTAB decision in SynAffix v. Hangzhou were drawn to a hydrophilic linker containing, inter alia, a functional group containing Q or T compounds (sulfone, sulfonide, or phosphinate) that enables a reaction of the linker with a cell binding agent or a cytotoxic drug. During prosecution, the applicant distinguished its claims from a prior art compound disclosed in Lees, which was said to anticipate the claimed heterobifunctional linker of compound 55 of the patent and contain a vinyl group enabling its linkage to a cytotoxic drug.

To traverse the § 102(b) rejection, the applicant made two amendments to claim 1. First, the applicant added the conditional limitation that where groups “Q or T is —S(O2)—, m and n are not 0”, ie, that if Q or T is a sulfide group, then both a Q-R2 and a T-R3 group must exist. The applicant’s remarks mirrored this amendment. Second, the applicant added that the “R” groups R1-R6 throughout the claimed compound are not required – they may be the same, different, or “absent.”

The prior Board Decision found two distinct prosecution disclaimers: one disclaimed an example in the specification and a second disclaimed compounds “in which the sole terminal group is vinyl sulfone without one or more adjacent Q and T groups.” This second disclaimer meant that if there were two sulfone groups (and no other groups drawn from the group of sulfone, sulfoxide, and phosphinate), these must be in addition to the vinylsulfone group, and thus the applicant relinquished embodiments 55, 75, 99, 119, and 138.

The director ordered review to a Delegated Rehearing Panel, which upheld only the first disclaimer, finding that the applicant disclaimed compound 55 in order to traverse the Lees rejection.

The Panel disagreed with the second disclaimer. The predicate for the disclaimer was the applicant’s mapping of Z (as vinyl, which the Examiner had not specifically mapped) and Q (or T) (as sulfone) from compound 55 vis-à-vis Lees. Considering the record as a whole, the Panel explained that the applicant had provided a detailed mapping of Lees that surpassed the Examiner’s statement of the prior art. The applicant did not map Z as vinylsulfone, because it would not satisfy the condition for amendment (m and n to be non-zero). Importantly, the applicant relied on compounds 75 and 138 in the specification as support for the entirety of its amendments, including that R1-R6 may be absent. Because the applicant did not distinguish different parts of the amendment in its statements, the Panel was unconvinced that there was a clear and unmistakable disavowal of disclosed embodiment compounds 75 and 138.

Maquet Cardiovascular LLC v. Abiomed Inc. et al.: Disclaimer across related applications

The disclaimer arguments in the Federal Circuit focused on three terms in Maquet Cardiovascular’s patents, claiming an intravascular blood pump system: the “guide mechanism comprising a lumen” of claim 1 and “guide wire” of claims 1 and 24.

The district court construed “guidewire mechanism comprising a lumen” to include a negative limitation (“distal to the cannula”) based on a disclaimer in the prosecution history in the patent’s parent application. The Federal Circuit reversed on this ground, given the limitation in the parent application (“entire elongate lumen distal to the intravascular blood pump,” which was later amended to a lumen “distal to the rotor”) included positional limitations missing from the application at issue. In so holding, the Federal Circuit rejected the proposition that the law of prosecution history disclaimer broadly applies when patents claim “common subject matter,” rather, “parity between the limitations” at issue is required.

The district court also applied prosecution history disclaimer to the “guide wire” terms, limiting them to a specific configuration (the “guide wire does not extend through the free space in between the rotor blades”), based on the prosecution history of the great-great-grandparent application. Here, the “guide wire” limitation in the asserted patent and great-great-grandparent were identical. The balance of the claims provided some fodder for arguing differently (“comprising a lumen” versus “configured as a second lumen” and “a circulatory system” versus “the circulatory system”), but the Federal Circuit found the claims “sufficiently similar” such that the earlier prosecution history was relevant.

Despite the similarity, the Federal Circuit held that there was no disclaimer. The applicant had failed to reply to the Examiner’s second Notice of Allowance discussing a prior art reference (Vӧlker), and “silence in response” to the Examiner is insufficient. Further, the applicant did not disavow claim scope by later arguing in inter partes review that the Examiner “found the claims patentable over. . . Vӧlker” despite its “similar teachings.” These “broad and vague statements” did not “refer to any particular claim” or the “guide wire” feature, and “do not rise to a clear and unmistakable disclaimer.”

Key takeaways: What makes a clear and unmistakable disavowal?

While these cases demonstrate the high bar for a clear and unmistakable disavowal of claim scope, practitioners are encouraged to exercise care with respect to statements made during prosecution, and consider the following:

• Refrain from correcting examiner statements. Given there is no duty to respond to or correct the examiner’s statements with respect to the prior art, refraining from comment may prevent disclaimer arguments later on, if the situation allows.


• Keep comments general. As demonstrated in Maquet, broad and vague statements that do not refer to a specific amendment, claim, or feature of the invention are more difficult to characterize as a disclaimer of scope. The same holds true whether in litigation or inter partes review.


• Consider changes to claim language in related applications. Because parity between the limitations is required, consider whether alterations may be made to the claim language that both preserve scope and provide more than “minor” differences to those in related applications where specific prior art was traversed. This may provide the necessary degree of separation to avoid a disavowal of scope affecting other applications.

For more information, please contact the authors.