In re Xencor, Inc. v. USPTO — Federal Circuit Affirms Fc Variant Patent Unpatentable
Xencor, Inc. challenged the USPTO’s determination that its application US16/803690, covering Fc variants with altered binding to FcRn, was unpatentable. The Federal Circuit affirmed the agency’s ruling on 13 March 2025, ending a 289-day appellate proceeding and leaving Xencor’s Fc engineering claims without patent protection.
Federal Circuit closes door on Xencor’s FcRn-binding Fc variant claims
In re Xencor, Inc. (Case No. 24-1870) is an ex parte appeal filed on 28 May 2024 before the Court of Appeals for the Federal Circuit. Xencor, Inc., a clinical-stage biopharmaceutical company known for its Fc engineering platform, sought to reverse a USPTO ruling that application US16/803690 — directed to Fc variants with altered binding to the neonatal Fc receptor (FcRn) — was unpatentable. The application published as US20200262899A1.
On 13 March 2025, the Federal Circuit issued an order affirming the USPTO’s unpatentability determination. Affirmance at the appellate level means the court found no reversible legal or factual error in the agency’s analysis. The claims at issue therefore remain ungranted, and Xencor cannot enforce them against third parties working in the FcRn-binding Fc variant space — at least under this application number.
The 289-day timeline is notably shorter than average Federal Circuit briefing schedules, suggesting the panel may have resolved the appeal on a discrete, well-defined legal question rather than a broad factual record. The public order does not detail which specific patentability grounds — obviousness, written description, or enablement — proved fatal, leaving open questions about the narrowness or breadth of the ruling’s precedential reach.
Filing to Unpatentable in 289 days
289 days from filing to Federal Circuit decision — typical Federal Circuit appeals run 12–18 months
Federal Circuit affirms: what the USPTO unpatentability ruling means for both parties
Affirmance: the lower decision stands without reversible error
When the Federal Circuit ‘affirms’ a USPTO decision, it concludes that the agency applied the correct legal standard and that its factual findings were supported by substantial evidence. No new proceeding is ordered. For Xencor, this means the application US16/803690 is definitively unpatentable unless the company seeks en banc rehearing or certiorari — both rare and high-threshold remedies.
No reversible error foundXencor loses this Fc variant coverage pathway
Xencor’s application for Fc variants with altered FcRn binding is now closed at the Federal Circuit level. The company cannot enforce the claims in US16/803690 and loses any exclusivity that would have flowed from grant. Xencor may retain related protection through continuation applications, divisionals, or issued patents in the same family — but those are not resolved by this ruling.
Application claims unenforceableUSPTO’s patentability rejection is fully vindicated
The USPTO — represented by Acting Director Derrick Brent — successfully defended its unpatentability determination through Federal Circuit review. The affirmance reinforces the examiner-level and PTAB-level reasoning applied to these Fc variant claims. Competitors operating in the FcRn-binding antibody space gain certainty that these specific claims will not emerge as an enforcement risk from this application.
USPTO determination upheldFcRn-binding Fc engineering space: cleared of this claim set
Fc variants that modulate FcRn binding are central to extending antibody half-life, a commercially critical property in therapeutic biologics. The affirmance removes one potential patent barrier in this space. Companies developing long-acting antibodies or engineering Fc regions for enhanced pharmacokinetics should note that freedom-to-operate analyses should still account for related Xencor patents and pending family members not addressed by this ruling.
FcRn engineering space clarifiedFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | In re: XENCOR, INC. | Company | Biopharmaceutical Fc-engineering company — applicant for US16/803690Search in Eureka ↗ |
| Defendant | DERRICK BRENT, Acting Under Secretary of Commerce for Intellectual Property and Acting Director of the United States Patent and Trademark Office | Individual | Acting Director of the USPTO, defending the agency’s unpatentability determinationSearch in Eureka ↗ |
| Plaintiff counsel | Amanda Scott Williamson | Attorney | Counsel for In re: XENCOR, INC.Search in Eureka ↗ |
| Plaintiff counsel | Christopher John Betti Ph.D. | Attorney | Counsel for In re: XENCOR, INC.Search in Eureka ↗ |
| Plaintiff counsel | Julie S. Goldemberg | Attorney | Counsel for In re: XENCOR, INC.Search in Eureka ↗ |
| Plaintiff counsel | Maria Doukas | Attorney | Counsel for In re: XENCOR, INC.Search in Eureka ↗ |
| Plaintiff counsel | Michael J. Abernathy | Attorney | Counsel for In re: XENCOR, INC.Search in Eureka ↗ |
| Plaintiff counsel | William R. Peterson | Attorney | Counsel for In re: XENCOR, INC.Search in Eureka ↗ |
| Plaintiff law firm | Morgan, Lewis & Bockius, LLP | Law Firm | Representing In re: XENCOR, INC.Search in Eureka ↗ |
| Defendant counsel | Farheena Yasmeen Rasheed | Attorney | Counsel for DERRICK BRENT, Acting Under Secretary of Commerce for Intellectual Property and Acting Director of the United States Patent and Trademark OfficeSearch in Eureka ↗ |
| Presiding judge | Judge N/A | Judge | Court of Appeals for the Federal CircuitSearch in Eureka ↗ |
Official order — verbatim text
The Federal Circuit’s order — ‘THIS CAUSE having been considered, it is ORDERED AND ADJUDGED: AFFIRMED’ — is a summary affirmance on the merits of the USPTO’s unpatentability determination. At the appellate level, affirmance under substantial evidence review means the panel found the agency’s factual findings adequately supported and its legal conclusions free from reversible error. The brevity of the order suggests the appeal may not have raised a novel legal question warranting extended opinion, though it carries full precedential weight as a final disposition. Xencor’s application US16/803690 is now definitively closed.
US16/803690 — Fc Variants with Altered Binding to FcRn
US16/803690 (published as US20200262899A1) is directed to engineered variants of antibody Fc regions that exhibit altered binding to FcRn — the neonatal Fc receptor responsible for recycling IgG antibodies and extending their serum half-life. Filed in late February 2020, the application sits at the intersection of antibody engineering and pharmacokinetic optimisation, a technically dense area with significant commercial value in long-acting therapeutic biologics. The USPTO determined the claims were unpatentable, and the Federal Circuit has now affirmed that determination.
Control of FcRn binding is a foundational competitive battleground in the therapeutic antibody industry. Companies including Xencor, AstraZeneca (with YTE technology), and others have sought broad protection over Fc mutations that modulate half-life. A granted patent here would have provided Xencor leverage over competitors engineering extended-half-life antibodies. The affirmance of unpatentability removes this specific application from the enforcement landscape but does not resolve the status of Xencor’s broader Fc engineering portfolio, which includes issued patents that may cover related subject matter.
Should your team run an FTO against US16/803690 and the Xencor Fc variant family?
Any R&D team developing antibody therapeutics with engineered Fc regions — particularly those targeting extended serum half-life via FcRn modulation — should assess their exposure to the Xencor Fc variant patent family. While US16/803690 is now unpatentable, the underlying technology family may include issued patents and pending continuations that could still present infringement risk. A narrow FTO relying solely on this case outcome is insufficient.
PatSnap Eureka’s FTO Search Agent can map the full Xencor Fc engineering portfolio, identify related family members across jurisdictions, flag claim language that survived examination, and surface third-party prior art that shaped the prosecution history. For biologics teams preparing IND filings or partnership discussions involving FcRn-modulating antibodies, this analysis is a critical risk-management step before committing to a lead candidate structure.
Run a freedom-to-operate analysis on US20200262899A1 to assess your product’s exposure
Run FTO in Eureka →Similar Federal Circuit antibody patent unpatentability appeals
Federal Circuit appeals affirming USPTO unpatentability findings in the antibody Fc engineering and biologics patent space, relevant to this case.
What this case signals for the antibody engineering IP landscape
A Federal Circuit affirmance of USPTO unpatentability in Fc variant technology carries real commercial weight for biologics developers and Xencor competitors.
FcRn-binding claims face high patentability scrutiny at the Federal Circuit
The affirmance signals that the Federal Circuit found the USPTO’s rejection on Fc variant claims legally sound. Biologics companies pursuing similar Fc engineering patents should expect rigorous written description and/or enablement scrutiny, particularly for broadly-drawn variant claims. Prosecution strategy should anticipate these challenges early.
Xencor’s broader Fc platform may still present enforcement risk
This ruling applies only to US16/803690. Xencor holds an extensive Fc engineering portfolio, and related family members, continuations, or issued patents covering overlapping technology remain active risks. Freedom-to-operate clearance in the FcRn or Fc variant space cannot rely on this affirmance alone — a full family-level search is essential.
In v DERRICK — key questions answered
The Federal Circuit affirmed the USPTO’s determination that Xencor’s patent application US16/803690, covering Fc variants with altered binding to FcRn, was unpatentable. The order issued on 13 March 2025, closing the appeal after 289 days. The affirmance means the agency’s rejection stands and no patent will issue from this application.
US16/803690 claims engineered variants of antibody Fc regions with altered binding to the neonatal Fc receptor (FcRn). FcRn controls IgG recycling and serum half-life — a critical parameter for therapeutic antibodies. Patents in this space confer commercial leverage over long-acting biologics development. The unpatentability ruling removes this specific application as an enforcement tool but does not affect Xencor’s broader issued Fc patent portfolio.
The public record identifies the basis of termination as ‘unpatentable’ but does not specify whether the rejection rested on obviousness, written description deficiency, or enablement. Post-Amgen v. Sanofi, broad antibody genus claims face heightened enablement scrutiny at the Federal Circuit, and this outcome is consistent with that trend — though the specific ground cannot be confirmed from the available case data.
No — the affirmance is specific to application US16/803690. Xencor’s issued patents covering related Fc variants or FcRn-binding technology are not directly affected by this ruling. Companies seeking freedom to operate in the Fc engineering space must conduct a full family-level analysis of Xencor’s portfolio rather than relying on this decision alone.
Following a Federal Circuit panel affirmance, an applicant may petition for rehearing en banc before the full Federal Circuit, or seek a writ of certiorari from the US Supreme Court. Both are high-threshold remedies granted rarely. Xencor may alternatively pursue continuation applications or file new claims directed to subject matter distinguishable from the rejected claims, subject to prior art and written description constraints.
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