The importance of a clear chain of entitlement
to patent priority
In the case of Edwards Lifesciences AG v Cook Biotech Incorporated the UK High
Court addressed the issues of loss of priority due to an incomplete assignment, as
well as the credibility of expert witnesses. This case highlights the importance of
ensuring a correct chain of title when filing a patent application.
Cook was the proprietor of a European patent which related to an artificial heart
valve, which Edwards had applied to have revoked in the UK. During the case the
Court considered whether Cook’s patent was entitled to its priority date. The
patent derived from a PCT patent application that was filed in the name of Cook as
applicant. However, it claimed priority from a US patent application that was in the
name of the three inventors. One of the inventors was an employee of Cook and
his rights in the invention were automatically assigned to Cook via his contract of
employment. However, the rights of the other two inventors were assigned to Cook
by an assignment document dated after the filing date of the PCT application. The
Court held that the priority claim was invalid because at the date of filing of the PCT
application the right to claim priority belonged jointly to Cook and the two nonemployee
inventors, and not to Cook alone.
Since Cook’s patent was not entitled to its priority date, a document published
between the priority and filing dates was citable as prior art. The Court held that
several claims of the patent were obvious in light of this document.
A question was also raised regarding the credibility of an expert witness and
specifically whether an expert changing his opinion undermined his value as an
expert. One expert witness appearing in the case had also appeared as an expert in an earlier decision of the UK High Court involving Edwards and another party. It was noted that the opinions of the expert differed in material respects between the
two cases. However, the Court decided that opinions may change during the course
of a case, particularly after cross examination and further consideration as to the
abilities of the ordinary skilled person. The expert’s opinions were found to be“cogent and reasonable” rather than partisan.
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