One of the challenges in prosecuting patent applications is dealing with patent examiners who reject claims based on clearly erroneous misreading of a prior art reference. And sometimes appeal to the Board of Patent Appeals and Interferences does not rectify the situation, forcing the applicant to make a “federal case” out of it. An example of this can be seen in the recently decided case of In re Chapman, where the patent applicants needed to appeal all the way to the Federal Circuit in order to correct an examiner’s misreading of a prior art patent.
Chapman's patent application claims divalent antibody fragments comprising two antibody heavy chains covalently linked by means of a polymer molecule (e.g., polyethylene glycol, or "PEG") through linkage to the sulfur atom in cysteine residues located outside the variable region domain of each chain. The use of the polymer to link the chains increases the antibody fragments’ half-life in the body, which can be beneficial in therapeutic and diagnostic uses of antibody fragments. PEG is often used to extend the half-life of protein biologics, and more generally to modify the pharmacological characteristics of these molecules - Roche's PEGylated version of erythropoietin MIRCERA, the subject of the recently resolved Amgen v. Roche litigation, is a good for example.
The patent examiner rejected Chapman’s claims as obvious in view of a prior art patent (the “Gonzalez" patent) that disclosed, inter alia, linking antibody fragments to a polymer through a cysteine residue in order to increase antibodiy's circulating half-life and thus improve the antibody's therapeutic characteristics. The Federal Circuit vacated this rejection based on its determination that the examiner and the Board of Patent Appeals and Interferences had clearly misread the Gonzalez patent, and this misinterpretation of the reference could have resulted in an erroneous finding of obviousness.
For example, the patent examiner and the B oardboth concluded that Gonzalez described a divalent antibody formed by linking light and heavy antibody chains by means of a polymer linker. In fact, as noted by the Federal Circuit, Gonzalez actually describes attachment of a polymer to either the light or the heavy chain - critically, the polymer is not serving as a link between the chains. Even the government attorney representing the patent office conceded during oral argument that the Board and examiner had misread the reference.
The Board also held that Gonzalez only disclosed three types of antibody fragments, when in fact, as conceded by the government attorney during oral arguments, the reference discloses six different possible antibody fragments. The Federal Circuit held that either of these errors could have led the patent office to erroneously reached its determination of obviousness. Because Gonzalez does not disclose linking the fragments, there is less suggestion of making the linked antibody fragments claimed by Chapman. Particularly since KSR, the number of possible alternate choices presented by the prior art can be critical in assessing the obviousness of invention, so the availability of six types of fragments (rather than the three erroneously cited by the examiner and board) frm which to choose could affect the determination of obviousness.