Affirming an invalidity finding by the Patent and Trial Appeal Board (PTAB), the US Court of Appeals for the Federal Circuit found that the claims of the now-expired patent should be construed under the broadest reasonable interpretation (BRI) standard, and not under the Phillips standard, because the patent owner intentionally gave up the remainder of the patent term only after the appeal was fully briefed. Immunex Corp. v. Sanofi-Aventis U.S. LLC, Case Nos. 19-1749, -1777 (Fed. Cir. Oct. 13, 2020) (Prost, C.J.).

Immunex owns a patent directed to human antibodies that inhabit certain receptors to treat inflammatory diseases such as arthritis. After being sued for infringement, Sanofi and Regeneron (collectively, Sanofi) requested inter partes review (IPR) of the patent, which the PTAB instituted. Based on the IPR filing date and because the patent was unexpired during the pendency of the IPR proceeding, the PTAB used the BRI standard to construe various claim terms. Had the patent been expired, the PTAB would have used the more stringent Phillips standard to construe the claims. Ultimately, the PTAB found all of the challenged claims unpatentable. Immunex appealed.

After appellate briefing was complete, Immunex filed a terminal disclaimer of its patent. The US Patent and Trademark Office accepted the terminal disclaimer, and as a result the patent term expired approximately two months before oral argument. Immunex then filed a citation of supplemental authority informing the Federal Circuit of the terminal disclaimer and asking the Court to change the applicable claim construction standard from BRI to Phillips.

The Federal Circuit found that the application of the BRI standard to Immunex’s patent was appropriate. Although the PTAB currently applies the Phillips claim construction standard in all newly filed IPRs, at the time that Sanofi filed its IPRs, the PTAB applied the Phillips standard only to expired patents. For unexpired patents, it applied the BRI standard. The Court noted that the use of the Phillips standard in cases where the patent expired during the appellate process should not be an absolute, particularly when the patent term expired at an unexpected early date, such as through the filing of a terminal disclaimer.

The Federal Circuit further affirmed the PTAB’s claim construction under the BRI standard and the invalidity finding predicated on that claim construction. The issue on appeal was whether a “human antibody” must be entirely human (as asserted by Immunex) or whether it may also be “partially human,” including “humanized” (as asserted by Sanofi and construed by the PTAB). The Court agreed with the PTAB and found that the patent’s specification supported the conclusion that the BRI of “human antibody” “includes both fully human and partially human antibodies.” The Court also found that “human antibodies” in the context of the patent-in-suit is a broad category that encompasses both partially and completely human antibodies. The Court therefore affirmed the PTAB’s finding.

The Federal Circuit also commented on the PTAB’s departure from an earlier claim construction ruling by a district court in which “human” was construed to mean “fully human” based on the Phillips standard. Immunex argued that the PTAB must explain in detail why it reached a broader construction than the district court. The Federal Circuit disagreed, finding that the PTAB “is not generally bound by a previous judicial construction of a claim term,” and that the PTAB’s decision was sufficiently detailed to permit meaningful appellate review.