The question of the proper scope of protection for inventions in the field of biotechnology is one that is attracting attention worldwide. In an opposition filed by eleven parties against the grant of a European patent to Mycogen Plant Science, Inc. on a method for genetically modifying a plant cell, the EPO Technical Board of Appeal set aside an interlocutory decision of the opposition division maintaining the patent with broad claims and remanded the case to the opposition division with an order to maintain the patent on the basis of claims of markedly narrower scope. The broad claims under consideration by the Board recited a method for genetically modifying "a plant cell" (including both monocotyledonous and dicotyledonous plant cells) by transferring into the plant cell T-DNA comprising a plant promoter and a plant structural gene operably linked "such that expression of the protein encoded by the said plant structural gene is detectable in said plant cell."

T-DNA describes DNA whose introduction into the plant cell is mediated by a Ti (tumor inducing) plasmid of the bacterium Agrobacterium tumefaciens. Upon insertion of a foreign DNA segment into the T-region (transfer region) of the Ti-plasmid, the natural genetic transfer functions of these bacteria introduce the foreign segment into the plant cell genome. Using its own cell machinery, the plant cell then strives to transcribe the T-DNA segment and translate the peptide it encodes. However, numerous factors affect successful expression of the encoded peptide, and previous attempts to transfer a variety of genes into plant cells did not lead to expression of the foreign genes because the endogenous control sequences of these genes were not recognized by the plant machinery. The patent in suit exemplifies the successful expression of detectable levels of phaseolin in sunflower plant cells into which the DNA coding sequence was transferred with its own promoter (i.e., the phaseolin promoter). The patent provides no other examples of successful expression using, for example, a different promoter, structural gene or plant cell.

In its decision, the Board considered whether the disclosure of the patent specification was sufficient to support the broadly formulated claims. In so doing, the Board analyzed the technical contribution to the state of the art by the patent and concluded that the contribution consisted of providing experimental support for a technical effect that was anticipated at a theoretical level in the prior art. The Board reasoned that, for this contribution to have patentable merit, the achievement of the technical effect had to involve overcoming certain technical difficulties, such as stability of alien DNA into T-DNA and into the plant genome, presence of introns, stability of the proteins, effects of regulatory controls, etc. The Board emphasized that the patent disclosure contained only a single example of a plant structural gene/plant promoter combination and decided that the skilled person would face similar technical difficulties when trying to obtain the same technical effect with the whole range of different combinations of plant structural gene/plant promoter claimed. Under these circumstances, the Board concluded that the patent specification did not provide adequate guidance to enable the skilled person routinely to practice the invention as broadly claimed with different plant gene/promoter combinations. The Board did, however, consider the specification to be enabling for narrower claims wherein the method was limited to the modification of a dicotyledonous plant cell by transfer of a phaseolin promoter with a phaseolin gene.