Can a Later-Filed Patent Ground an ODP Rejection? USPTO ARP Reviews PTAB’s Allergan Reading in Ex Parte Baurin

On April 9, 2026, the U.S. Patent and Trademark Office (USPTO) published amicus briefs filed in Ex Parte Baurin, a proceeding now under review by an Appeals Review Panel (ARP) that the USPTO sua sponte convened in March 2026. The case addresses a fundamental question in patent prosecution: may an examiner rely on a reference patent that was filed and issued later than the application under examination as the basis for an obviousness-type double patenting (ODP) rejection? The answer will shape how continuation and continuation-in-part applications are prosecuted across the biopharmaceutical and life sciences sectors.

The application at issue, U.S. Application No. 17/135,529, is directed to antibody-like binding proteins. The examiner issued ODP rejections based on U.S. Patent No. 10,882,922, which has a filing date of April 13, 2017—more than five years after the application’s own priority date of March 28, 2012, tracing back to U.S. Application No. 13/433,033. The ‘922 patent carries a 20-year statutory term expiring April 13, 2037 (with 70 days of Patent Term Adjustment), while the pending application has filed terminal disclaimers capping any issued patent’s term at March 28, 2032. In other words, the reference patent both was filed later and will expire later than the application it is being used to reject.

The Patent Trial and Appeal Board (PTAB) reversed the examiner’s ODP rejections in a November 8, 2024 decision, drawing on the Federal Circuit’s landmark ruling in Allergan USA, Inc. v. MSN Laboratories Private Ltd., 111 F.4th 1358 (Fed. Cir. 2024). In Allergan, the court held that “a first-filed, first-issued, later-expiring claim cannot be invalidated by a later-filed, later-issued, earlier-expiring reference claim having a common priority date,” emphasizing that the purpose of ODP is to prevent patentees from extending a first patent’s life—not to block an earlier patent from its full term.

The examiner requested rehearing, arguing the Board had misread Allergan. On December 18, 2025, PTAB denied rehearing. The Board acknowledged that the facts in Ex Parte Baurin differ from Allergan—the reference patent and the application share neither a priority date nor a common patent family—yet found Allergan’s reasoning “compelling” and maintained its reversal of the ODP rejections. USPTO Deputy Director Squires then convened the ARP sua sponte, directing amici to address three questions: (1) the applicability of Allergan to facts different from those in that case, and what constitutes “first-filed” for ODP purposes; (2) whether examiners should calculate projected expiration dates to support ODP rejections during prosecution; and (3) whether the risk of separate ownership and potential harassment from patentees holding rights to obvious variants should factor into the analysis.

The amicus brief drawing the most attention was filed by Professors Mark Lemley (Stanford) and Lisa Larrimore Oullette (Stanford), who argue against the Board’s position. Their brief states that the Federal Circuit has “repeatedly sustained ODP rejections where the reference patent has a later priority and patent-term filing date than the application under examination.” Lemley and Oullette contend that Allergan’s holding is limited to situations where claims share a common priority date and that the Board erred in extending it to unrelated patent families. The majority of other amici, by contrast, have sided with the Board’s analysis.

The practical stakes are high, particularly for the biopharmaceutical and chemical industries where continuation filing strategies are central to portfolio development. If the ARP adopts the Lemley-Oullette position, examiners would be empowered to issue ODP rejections using reference patents filed and issued after the application under examination, even without a shared priority date. This would require applicants to file terminal disclaimers or to distinguish claims—with significant consequences for portfolio duration and freedom to operate. Conversely, if the ARP affirms the Board’s reading of Allergan, applicants filing continuations from early-priority-date families would face reduced ODP risk even when later-issued reference patents exist within or outside their family.

The ARP review is ongoing and no timeline for a final decision has been announced. Given the sharp divergence of expert opinion on the scope of Allergan—even among leading academics—the outcome remains difficult to predict. Patent prosecutors in the life sciences and chemistry space should monitor this proceeding closely, as any clarification of ODP doctrine at the USPTO administrative level will carry immediate implications for pending prosecution strategy.