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Dependent claim can be construed to be broader than independent claim based on prosecution history
March 03, 2008
In a decision last week, the Federal Circuit held a district court construed 1 of 2 claim terms correctly, and incorrectly concluded that prosecution history estoppel barred application of the doctrine of equivalents to a third claim term because the narrowing amendment was only tangentially related to the equivalent at issue. As a result, the court affirmed in part, reversed in part, and remanded.One of the claim construction issues was interesting in that the court held that the prosecution history of the patent overcame the "presumption" of claim differentiation, namely that "dependent claims are presumed to be of narrower scope than the independent claims from which they depend." This led to the strange result that the scope of some dependent claims was outside the scope of the independent claim from which they depended. This seems to be contrary to § 112 ¶ 4, which requires a dependent claim "shall be construed to incorporate by reference all the limitations of the claim to which it refers."Judge Prost dissented from the portion of the ruling regarding prosecution history estoppel, and would have held that the amendment was not tangential to the equivalent in question and therefore that prosecution history estoppel applied.More detail of Regents of the U. of Cal. v. Dakocytomation Cal., Inc. after the jump.The University of California owns two patents relating to methods of chromosome staining and classification that may be used when a cell is in interphase and the chromosomes are spread throughout the nucleus. Previous methods required the cells to be in metaphase, when the chromosomes are aligned along the middle of the cell just before division. The claimed methods work by disabling hybridization capacity of repetitive DNA sequences, and disclose three methods to achieve this: (1) blocking, (2) selective removal, and (3) screening of repetitive sequences. The claims of the '841 patent are directed toward the blocking method, and during prosecution the patentee indicated that the other methods would be pursued in another application. That application led to the '479 patent, which addresses the removing or screening methods.The University and its exclusive licensee, Abbott Laboratories, sued Dako for infringement by its manufacture and sale of its HER2 FISH pharmDX kit. The district court denied the plaintiffs' motion for a preliminary injunction, and the plaintiffs appealed. While the appeal was pending, the district court amended its basis for the denial of the preliminary injunction, and the plaintiffs appealed from that order as well. While both the previous appeals were pending, the district court construed the claims and granted partial summary judgment of noninfringement. The parties sought leave to appeal this interlocutory order, which the district court and Federal Circuit granted as the issues raised were also implicated in the preliminary injunction appeals. All three appeals were heard together.The construction of two claim terms were at issue on appeal, namely "heterogeneous mixture of labeled unique sequence nucleic acid fragments" and "morphologically identifiable." The first term is required in every claim of the '479 patent, and the second term appears in both patents. The court addressed the two in turn.Heterogeneous mixture of labeled unique sequence nucleic acid fragmentsThe district court construed this term to mean a "heterogeneous mixture of labeled nucleic acid fragments that includes only unique sequence fragments." This construction was dispositive of the question of infringement of the '479 patent, as it was undisputed that Dako's kits contain repetitive sequences. The district court's basis for this conclusion, however, was incorrect. The court construed the claims in this was as to preserve the claims' validity, because the district court considered the '841 patent to be prior art to the '479 patent, when in fact the application that led to the '479 patent was a divisional of the application that led to the '841 patent, and therefore claimed priority to the '841 patent's filing date. There were also no obviousness-type double patenting issues, as a terminal disclaimer had already been filed.Nevertheless, the court affirmed the district court's construction, largely on the basis of the prosecution history. As stated by the court, the "prosecution history in the present case sheds decisive light on the scope of the disputed claim term." The originally-filed application did not include the phrase "unique sequence" in its single claim. That limitation was added in response to an enablement rejection, and overcame the rejection "by restricting the heterogeneous mixture to labeled probes of unique sequences," as that avoids the problem of probes binding to repetitive sequences. As a result, the prosecution history showed "a clear intent to limit the claims of the '479 patent to those embodiments in which the repetitive sequences have been excluded from the heterogeneous mixture in order to disable the hybridization capacity of repetitive sequences." The appellants attempted to avoid this result by arguing that the doctrine of claim differentiation precluded this result, given that there were dependent claims requiring the inclusion of repetitive sequences. The court was unpersuaded, however, characterizing the presumption that dependent claims are of "narrower scope than the independent claims from which they depend" as a presumption which was rebutted in this case based on the prosecution history. The court did not address the fact that under § 112 ¶ 4, "A claim in dependent form shall be construed to incorporate by reference all the limitations of the claim to which it refers," which is written in mandatory language rather than in "presumptive" language.Because the district court's claim construction was affirmed, the concomitant grant of summary judgment of noninfringement of the '479 patent was also affirmed.Morphologically identifiableThe district court construed this term to mean "a single cell nucleus that contains the full complement of chromosomal DNA." According to the appellants, this term does not require the full complement of DNA, just that the nucleus be "capable of being identified by its form or function."Here, the court sided with the appellants. First, the court noted that the appellant's construction was in line with the plain language of the claim, which has no requirement that the full set of chromosomal DNA be present. The prosecution history also supported this conclusion, as there was no "indication that the 'morphologically identifiable' language was added to impose a requirement that the cell nucleus must retain its full complement of chromosomal DNA." As a result, the court held the proper definition was "capable of being identified by its form or structure."

Prosecution history estoppel
There was an additional issue regarding the district court's grant of partial summary judgment as to the '841 patent. The district court held that prosecution history estoppel barred application of the doctrine of equivalents to the term "blocking nucleic acid" in that patent. The term was added during prosecution, and the district court found that the Festo presumption of surrender of all equivalents had not been rebutted.The Federal Circuit disagreed. The court acknowledged that the term was added for a substantial reason relating to patentability, and therefore the Festo presumption of surrender of equivalents applied. However, the court held that the amendment was only tangentially related to the equivalent in question, and therefore the presumption had been rebutted. Focusing on the "objectively apparent reason for the narrowing amendment," the court noted that the amendment was to distinguish the claim over the prior art. The focus of the relevant arguments was on the method of blocking, not the particular type of nucleic acid that could be used for blocking. Accordingly, because the equivalent in question related to the type of nucleic acid, the court held that the amendment was only tangentially related to the equivalent, and therefore prosecution history estoppel did not apply.Judge Prost dissented from this portion of the decision. In her view, the reason for the amendment was not tangential to the equivalent in question, but rather directly related to the amendment. As stated in her dissent:
In making the amendment, the appellants presumptively surrendered any other means of disabling repetitive sequences. The equivalent, PNA, however, functions to do exactly that, i.e., to disable repetitive sequences. Hence, the purpose for the amendment is not unrelated to the equivalent.
As a result, Judge Prost would hold that prosecution history estoppel applied.To read the full decision in Regents of the U. of Cal. v. Dakocytomation Cal., Inc., click here.
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