Federal Circuit Upholds PTAB Enablement Finding Against Dual Herbicide-Degrading Enzyme Patent

The U.S. Court of Appeals for the Federal Circuit (CAFC) issued a decision Friday in Pioneer Hi-Bred International, Inc. v. Inari Agriculture, Inc. affirming a Patent Trial and Appeal Board (PTAB) final written decision that found claims 1 through 33 of a patent on herbicide-degrading enzymes unpatentable for lack of enablement. The CAFC rejected arguments that the PTAB improperly relied on experimental data generated after the patent’s priority date and abused its discretion in crediting an expert witness.

Inari Agriculture, Inc. filed a petition for post-grant review (PGR) challenging U.S. Patent No. 11,371,055, owned by Pioneer Hi-Bred International, Inc. The ‘055 patent describes enzymes that make crops resistant to two classes of herbicides, pyridyloxyacetate auxins such as triclopyr and fluroxypyr and phenoxy auxins such as 2,4-D and MCPA.

Representative claim 1 defines a genus of enzymes by function and structure. The preamble requires an activity that degrades a phenoxy auxin herbicide and a pyridyloxy auxin herbicide, which Pioneer and Inari referred to as a “dual herbicide-degrading function.” The body requires a sequence at least 85% identical to SEQ ID NO. 2 and an AAD-12 motif.

Inari argued in its petition that the claimed genus was “unfathomably large,” while the specification disclosed only two example species, SEQ ID NO. 2 and SEQ ID NO. 4, the latter having 99.3% sequence identity to the former. Pioneer argued that the 85% sequence identity limitation was a shared feature across the genus that ensured more than 90% of the claimed species would exhibit the dual function. Pioneer also pointed to Figure 2 of the ‘055 patent for guidance on which residues could be varied without altering function.

With its patent owner response, Pioneer submitted experimental data generated more than a decade after the ‘055 patent’s priority date. The data covered eight enzymes that met the claimed structural limitations. Inari argued that the results showed the guidance in the ‘055 patent did not reliably correlate with the claimed function. The PTAB agreed, and Pioneer appealed.

On appeal, Pioneer argued that the PTAB committed legal error by relying on Pioneer’s own post-priority data, since enablement must be determined as of a patent’s priority date. Judge Prost wrote for the CAFC that the argument appeared forfeited because Pioneer did not raise it before the PTAB, but that it was unpersuasive regardless.

The CAFC pointed to Amgen Inc. v. Sanofi, in which it held that excluding post-priority enablement evidence was an error, and stated that “the use of post-priority-date evidence to show that a patent does not disclose a representative number of species of a claimed genus is proper.” In re Hogan and In re Entresto were distinguished since each involved technology that did not exist at the priority date. In In re Hogan, an amorphous polymer developed after the priority date could not be used to show non-enablement because doing so would “impose an impossible burden on inventors.” The CAFC reached the same conclusion in In re Entresto regarding valsartan-sacubitril complexes that did not exist at the priority date. Each enzyme Pioneer tested fell within the claimed genus and could have been made as of the priority date, though Pioneer tested the enzymes later. The CAFC held that the PTAB did not err in relying on the data.

Pioneer also argued that the PTAB should not have credited Dr. Silverstone, Inari’s expert, who Pioneer said lacked enzymology experience. Under the abuse of discretion standard that governs review of such a decision, the CAFC noted that Pioneer did not tell the PTAB how additional enzymology experience would have changed the analysis. Dr. Silverstone has enzymology experience in any event, including leading enzyme development for transgenic corn and rice, and the CAFC found no abuse of discretion.

Moreover, Judge Prost explained that the PTAB’s enablement decision was rooted in the Supreme Court’s reasoning in Amgen Inc. v. Sanofi, in which the Court said that “[t]he more one claims, the more one must enable.” The ‘055 patent claims 2.14 × 10¹?? species, a number that Figure 2’s guidance reduces to 1.23 × 10??, which the CAFC still described as “staggering.” Pioneer did not dispute the number at oral argument, and the specification provides two examples. According to Judge Prost, the gap between the number of species claimed and the number disclosed supports the PTAB’s finding of lack of enablement.

The CAFC added that, even setting the numbers aside, Pioneer’s own test results contradicted the predictions of Dr. Bollinger, Pioneer’s expert, that the disclosed structures correlated with the dual function. Only two of the eight enzymes that had at least 85% sequence identity and the claimed motif exhibited the function. Variants 17 and 19 differed by only six amino acids, none located at positions that Figure 2 identified as presumptively important to structure or function, but one variant exhibited the function, and the other did not. Judge Prost wrote that “the ‘055 [patent’s] [s]pecification and working examples fail to provide guideposts that would have illuminated a path toward embodiments at the 85% sequence identity level.”

The CAFC considered Pioneer’s remaining arguments unpersuasive and affirmed the PTAB’s final written decision holding claims 1 through 33 of the ‘055 patent unpatentable for lack of enablement.