Blocking Nucleic Acid Amendment Tangential to Accused Peptic Equivalent

In University of California v. Dakocytomation (February 28, 2008) an appeal of preliminary relief offered the parties an opportunity to obtain an interlocutory judgment on claim construction. Although the applicant amended the claim to a method of staining chromosomal DNA to recite providing a "blocking nucleic acid," the Federal Circuit held that this amendment was only tangential to the accused peptic nucleic acid equivalent which was not surrendered during prosecution:

According to the opinion by Circuit Judge Lourie,

Here, the patentees identified two main reasons for the narrowing amendment. First, the patentees narrowed the claims in order to "facilitate prosecution." In deciding to limit the claims of the ’841 patent to the blocking method and to pursue other means of disabling in a separate application, the patentees argued that "[b]y separating the different inventions into separate applications, it is believed that prosecution will be facilitated." Such a reason for amending the claim is clearly nonsubstantive and does not help us in our analysis.

Second, and more significantly, however, the patentees did amend the claim in order to distinguish the invention over the prior art. The examiner issued prior art jejections in view of, inter alia, Weissman et al., Sealey et al., and Yunis et al. To overcome those references, the patentees argued that the invention was new and nonobvious because it used the blocking method in connection with in situ hybridization for the detection of unique sequences. In contrast, the Weissman reference involved the use of pure unique sequence probes—or probes from which repetitive sequences have been removed—as opposed to blocking. Both the Sealey and Yunis references, however, disclosed the use of the blocking method, but that method was limited to testing the hybridization of repetitive sequences and did not concern targeting unique sequences, as does the claimed use of blocking nucleic acids.
argued that the invention would not have been obvious in view of the prior art because a person of ordinary skill would not have considered the use of blocking for the detection of unique sequences.

The prosecution history therefore reveals that in narrowing the claim to overcome the prior art rejections, the focus of the patentees’ arguments centered on the method of blocking—not on the particular type of nucleic acid that could be used for blocking. Indeed, the "nucleic acid" limitation was never narrowed during prosecution and was not at issue in the office action rejecting the claims, the Examiner Interview Summary Record, or the patentees’ remarks accompanying the amendment. Moreover, Dako does not dispute that none of the cited references concerned the type of nucleic acid that could perform the blocking, or mentioned the accused equivalent. We thus conclude that appellants have met their burden of showing that the amendment did not surrender the equivalent in question because the narrowing amendment was only tangential to the accused PNA equivalent, i.e., the peptide nucleic acid. Accordingly, the court erred in concluding that appellants are precluded by estoppel from asserting that Dako’s products infringe under the doctrine of equivalents. Whether they do infringe is a question of fact for the trial court to consider on remand.