The Board of Patent Appeals and Interferences affirmed the examiner's rejection of a patent application that claimed a method for recombining DNA in a eukaryotic cell. When DNA is recombined into a sequence that does not occur in nature, a protein is used to facilitate recombination. One particular naturally-occurring (or “wild-type”) protein is called “Int.” The claimed method used modified versions of wild-type Int to facilitate recombination at certain recognition sites. The Board held that the claimed method was obvious. There was no dispute that two prior art references, taken together, taught every limitation of the claimed method. But the Board also found that a skilled artisan would have had a reasonable expectation that she would succeed in combining the references.

The Federal Circuit affirmed. The two prior art references included a patent and an article. The patent disclosed that wild-type Int “can induce site-specific DNA recombination using the attB and attP recognition sites,” and “further disclose[d] that wild-type Int can induce recombination in both prokaryotic and eukaryotic host cells.” The article disclosed the use of the modified proteins, rather than wild-type proteins, in prokaryotic cells. The article also disclosed that the modified proteins have “an enhanced ability to execute recombination on wild-type att sites,” a disclosure which supplied the necessary motivation to combine the references.

The applicants contended that a skilled artisan would not have had a reasonable expectation that the modified proteins would facilitate recombination in a eukaryotic cell, as opposed to a prokaryotic cell. But the Federal Circuit affirmed the Board’s rejection of this argument. The applicants relied on two significant differences between prokaryotic and eukaryotic cells. First, prokaryotic cells contain a protein co-factor known as IHF that is absent from eukaryotic cells. Second, eukaryotic cells display a particular type of structure known as “supercoiling.” The prior art disclosed, however, that the modified proteins facilitate recombination with or without IHF, regardless of whether the DNA is supercoiled. Accordingly, there was sufficient reason to believe the references could be successfully combined, rendering the claimed method obvious.

A copy of the opinion can be found here