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Board’s Misunderstanding of Prior Art Calls into Question Conclusions on Obviousness and Constitutes Harmful Error

February 24, 2010
Watson, Jeff T.

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Last Month at the Federal Circuit - March 2010

Judges: Gajarsa, Clevenger, Dyk (author)

[Appealed from: Board]

In In re Chapman, No. 09-1270 (Fed. Cir. Feb. 24, 2010), the Federal Circuit vacated the Board’s decision sustaining the examiner’s rejection of claims 1-10 and 12-15 of U.S. Patent Application No. 09/719,045 (“the ’045 application”) as obvious and remanded for further proceedings.

The ’045 application claims, among other things, “[a] divalent antibody fragment comprising . . . two antibody heavy chains and . . . at least one polymer molecule . . . , each heavy chain being covalently linked to the other by at least one non-disulphide interchain bridge linking the sulphur atom of a cysteine residue in one chain to the sulphur atom of a cysteine residue in the other chain . . . .”  By using a polymeric interchain bridge to link cysteines on two opposing heavy chains, the claimed invention avoids the use of a disulphide bond and achieves a circulating half-life that is intermediate between that of an individual fragment and a whole antibody. 

U.S. Patent No. 6,025,158 (“the ’158 patent”) is prior art to the ’045 application.  The ’158 patent describes linking antibody fragments to a polymer to increase an antibody’s circulating half-life for therapeutic purposes.  The ’158 patent teaches how to attach the polymer to a particular amino acid residue or a particular region; in some embodiments, it teaches doing so without using a disulphide bond.  Furthermore, the ’158 patent teaches a preference for the cysteine residue in the hinge region of the antibody fragment as an attachment point.

The examiner rejected various claims of the ’045 application as anticipated by, or in the alternative, as obvious over, the ’158 patent.  The examiner also rejected claims as obvious over the ’158 patent and U.S. Patent No. 5,436,154.  Although the Board reversed the examiner’s anticipation rejection over the ’158 patent, the Board affirmed the examiner’s findings of obviousness.  The applicants appealed to the Federal Circuit.

The Court began its analysis by taking note of Chapman’s argument that the subject matter of the ’045 application is nonobvious as a matter of law because the ’158 patent “does not specify how and where the antibody molecules are linked by the polymer molecules, or what fragments are to be used.”  Slip op. at 11 (citation omitted).  The Court declined, however, to address this argument, stating that the issue of whether there exists any motivation to modify the ’158 patent to arrive at Chapman’s claimed invention is best left to the Board for consideration on remand.

The Court next analyzed whether the ’158 patent “teaches away” from the invention claimed in the ’045 application.  Chapman argued that the ’158 patent teaches the existence of multiple locations on an antibody fragment to which a polymer molecule, or multiple polymer molecules, can be attached and therefore “teaches away” from using the hinge cysteine, particularly as an attachment point for the polymer.  The Court rejected this argument, noting that the ’158 patent specifically discloses a preference for the hinge cysteine as an attachment point for a polymer and, furthermore, offers this teaching to solve the very problem that Chapman was trying to solve.  Chapman then proffered another “teaching away” argument, contending that while the ’158 patent teaches attaching a polymer to an F(ab’)2 fragment, it does not teach using the polymer as a bridge.  The Court rejected this argument as well.  Although the Court acknowledged that the ’158 patent does not explicitly teach using the polymer as a bridge, the Court nevertheless concluded that it does not teach away from such a use.

Lastly, the Court considered the impact of three erroneous factual findings the Board made concerning the scope and content of the ’158 patent.  Because the government agreed with the inventor that the findings in question were indeed erroneous, the Court’s analysis of these findings primarily focused not on their accuracy, but rather on whether they constituted harmful error.

The first erroneous finding considered by the Court was the Board’s statement that “the Examiner finds [the ’158 patent] teaches a dumbbell-shaped antibody structure comprised of two monovalent Fab’ fragments . . . and describes linking them via a polymer molecule.”  Id. at 13 (citation omitted).  The government argued that the error was harmless because the Board did not base its obviousness rejection on this particular statement, and the Court agreed, noting that the Board’s decision on rehearing makes clear that the Board is not relying on any such explicit disclosures in the ’158 patent.

The Court next considered erroneous statements made by both the examiner and the Board regarding the function of the polymer molecule.  The Board stated that the ’158 patent “describes a divalent antibody in which the polymer is linked between light and heavy chains and only one cysteine residue is present.”  Id. at 14 (citation omitted).  Similarly, the examiner’s Factual Finding (“FF”) 7 stated that the ’158 patent describes conjugates containing an “F(ab’)2 antibody fragment in which the polymer is attached between the disulphide bridge that would ordinarily link the light and heavy chains.”  Id. (citation omitted).  Chapman argued that the examiner and the Board misinterpreted the ’158 patent and that, in the disclosed embodiment, the polymer is not serving as a link between the light and heavy chain—it is attached to either the light or the heavy chain.  The government conceded at oral argument that Chapman’s reading was correct, and the Court agreed.

Finally, the Court assessed FF 3, wherein the Board stated that “[t]he antibody [described in the ’158 patent] can be a monovalent Fab fragment, a monovalent Fab’ fragment which includes one or more cysteine residues in the constant region, or an F(ab’)2 antibody fragment which has a hinge cysteine between the Fab’ fragments.”  Id. at 15 (citation omitted).  Because the ’158 patent teaches six different possible antibody fragments (F(ab), F(ab’), F(ab’)-SH, F(ab’)2, scFv, and Fv) rather than only the three listed in FF 3, the Court found that FF 3 was incorrect.

The Court concluded that the second and third erroneous findings were harmful because they increase the likelihood that Chapman was erroneously denied a patent on the ground of obviousness.  According to the Court, “[i]f the Board based its decision on a misunderstanding of [the ’158 patent], its conclusions regarding obviousness are called into question.”   Id. at 16.  With respect to the second error, the Court found that the Board was mistaken as to the use of the polymer molecule in the ’158 patent, so the use of the polymer claimed in the ’045 application may be less likely to be obvious.  As to the third error, the Court found that if the Board did not appreciate the full scope of antibody fragments disclosed in the ’158 patent, then the Court could not be confident in the Board’s ultimate conclusion that the selection of one of them to form the molecule claimed in the ’045 application is obvious.  Because the Court could not say with confidence that the Board would have reached the same conclusion in the absence of these two errors, it concluded they were indeed harmful.


Summary authored by Jeff T. Watson, Esq.