In late August of 2021, the Federal Circuit reversed a jury verdict of $1.2 billion in favor of Juno Therapeutics and Sloan Kettering Institute because the jury’s finding that four of the asserted patent claims did not lack adequate written description under 35 U.S.C. § 112 was not supported by substantial evidence.  The Federal Circuit reiterated that functional claiming of a genus can meet the written description requirement, but only if the specification either provides a representative number of species that are within the scope of the genus, or explains structural features that are common amongst the species within the scope so as to allow a person of ordinary skill in the art (“POSITA”) to recognize the genus members.

The patent concerns a nucleic acid molecule that encodes for a chimeric antigen receptor (“CAR”) which is found on a T cell. CAR enables the T cell to bind to a target cell, e.g. a cancer cell, and activate an immune response. Part of this claimed nucleic acid molecule concerns the “binding element,” which is the portion of CAR that recognizes specific antigens that it can bind to on the target cell in order to trigger the immune response. One type of “binding element” is the single-chain antibody variable fragment (scFv), which binds to a specific antigen.

The Federal Circuit held that the specification lacked adequate written description because the patent broadly claimed any scFv that binds to any target without a sufficient disclosure for a POSITA to recognize members of the genus. Here, the specification only disclosed two embodiments of scFV binding elements, but some of the dependent claims broadly claimed any scFv binding element that targets “any target of clinical interest.” Slip op., at 8-9. The Court found that the specification did not identify if the disclosed embodiments were representative of the genus, nor did the specification explain how the species within the scope of the genus were capable of binding to the limitless number of targets. In addition, and while not fatal, the inventor testified that at the time the application was filed, he only used and knew of the two disclosed embodiments, even though the patent attempts to claim any scFv that binds to any target. As the Federal Circuit pointed out, this would not render the patent invalid per se had the specification disclosed common characteristics or structural features of the species within the scope of the claimed genus.

The Federal Circuit also held that the narrower dependent claims that were limited to scFvs that bind to CD19, a specific target, lacked adequate written description. As Kite argued, while there were few scFvs known in the art at the priority date, limiting the claims to scFvs that bind to CD19 still allows for “millions of billions” of possible scFv sequences. The Federal Circuit agreed and found that the specification did not provide any details about CD19-specific scFvs, such as a common amino acid sequence or general common characteristics associated with enabling the specific scFv to bind with CD19. Instead, the specification disclosed two embodiments and did not provide further explanation about the specific scFvs that bind to CD19 when only few scFvs were known in the art and millions of possible scFvs exist.

Based on the Federal Circuit’s holding, patent applicants should note the following key takeaways:

1. The number of embodiments disclosed in the specification must be commensurate with the magnitude of the claimed genus, particularly if the genus is to cover species that are not known in the prior art. This is easier said than done, especially since the Federal Circuit has also counseled against over-inclusion of embodiments. For example, in Idenix v. Gilead, the Federal Circuit found that the lists of “tens or hundreds of thousands of possible” nucleosides in one position of the structure, which results in the disclosures of hundreds of thousands compounds, lacked adequate written description, because the specification did not explain how to distinguish effective compounds from ineffective compounds. Idenix Pharms. LLC v. Gilead Scis. Inc., 941 F.3d 1149, 1164-65 (Fed. Cir. 2019), cert. denied, 141 S. Ct. 1234 (2021). In short, if the disclosed embodiments are meant to be representative of members of the genus, then the disclosure should explicitly state that and explain why it is representative of the members of the genus.

2. The court is likely to find that written description is met when the specification discloses formulas and/or an explanation of common structural features within the species. As seen in Idenix and here, the Federal Circuit seems more likely to find that a patent meets the written description requirement when the specification provides “structural features common to the members of the genus” or explains the commonality between the members of the genus and why that commonality matters to the invention. As the Federal Circuit pointed out in Juno, even if the two embodiments were representative of the species that fell within the scope of genus, the specification did not provide further details about the commonality between the embodiments to allow a POSITA to recognize members of the genus.