Merus N.V. v. Xencor, Inc.

Case Overview and Background: Merus N.V. v. Xencor, Inc.

This patent infringement litigation involved two clinical-stage biopharmaceutical companies, Merus N.V. and Xencor, Inc., in the U.S. District Court for the District of Delaware. Merus N.V., headquartered in the Netherlands, is an oncology company focused on developing innovative multispecific antibody therapeutics using its proprietary Biclonics® and Triclonics® platforms. Xencor, Inc., based in Monrovia, California, is also a clinical-stage biopharmaceutical company dedicated to discovering and developing engineered antibody therapeutics for cancer and autoimmune diseases through its proprietary XmAb technology platform. Neither party is characterized as a Non-Practicing Entity (NPE) or Patent Assertion Entity (PAE); rather, both are operating companies actively engaged in drug development.

The lawsuit, filed on August 5, 2024, by Merus, alleged infringement of U.S. Patent No. 9,358,286, among others. The '286 patent is a method patent covering a method of producing a multispecific antibody by harvesting the antibody from a culture, an artificial laboratory condition that promotes cellular growth and the production of antigen-specific antibodies. Merus accused Xencor of infringing this patent through its "antibody generation and development work" on various drug candidates, including plamotamab, vudalimab, and XmAb819, which utilize Xencor's XmAb® technology and were undergoing clinical trials.

The case was heard in the U.S. District Court for the District of Delaware, case number 1:24-cv-00913. While initial docket information indicated Judge Colm F. Connolly, the opinion granting dismissal was issued by Judge John Campbell Barker. The District of Delaware is a prominent venue for patent litigation, particularly for pharmaceutical and technology companies, largely because a significant percentage of U.S. corporations are incorporated there, and the court possesses an experienced patent bench. The litigation is notable for its swift dismissal on September 30, 2025, based on the Hatch-Waxman safe harbor provision (35 U.S.C. § 271(e)(1)). This provision exempts activities "reasonably related to the development and submission of information under a Federal law which regulates the manufacture, use, or sale of drugs or veterinary biological products" from patent infringement. This outcome underscores the critical importance of the safe harbor for clinical-stage biopharmaceutical companies like Xencor, allowing them to conduct necessary research and development for FDA approval without facing immediate infringement liability. In a parallel development, Xencor, Inc. filed an inter partes review (IPR2025-00604) against Merus N.V.'s U.S. Patent No. 9,358,286 with the Patent Trial and Appeal Board (PTAB) on February 11, 2025, which was instituted on September 26, 2025, just days before the district court's dismissal.

The patent infringement litigation Merus N.V. v. Xencor, Inc. in the U.S. District Court for the District of Delaware, case number 1:24-cv-00913, was a relatively short-lived case that was dismissed based on the Hatch-Waxman safe harbor.

Here's a chronological breakdown of the key legal developments and outcome:

Filing & Initial Pleadings:

• 2024-08-05: Merus N.V. filed a patent infringement complaint against Xencor, Inc. in the District of Delaware. Merus asserted U.S. Patent No. 9,358,286, among others, alleging infringement by Xencor's antibody technology.

Pre-trial Motions of Substance:

• 2024-10-10: Xencor filed a motion to dismiss the action with prejudice pursuant to Federal Rule of Civil Procedure 12(b)(6). Xencor argued that Merus had not plausibly alleged that Xencor engaged in any activity outside the scope of the statutory "safe harbor" provision, 35 U.S.C. § 271(e)(1), which exempts activities "reasonably related to the development and submission of information under a Federal law which regulates the manufacture, use, or sale of drugs."
• 2025-09-30: The U.S. District Court for the District of Delaware granted Xencor's motion to dismiss the infringement suit. The court held that Xencor's accused use of Merus N.V.'s patented antibody technology was protected by the Hatch-Waxman safe harbor. The court's opinion clarified that the claims of the asserted patents, including the '286 patent, required the development of an antigen-specific antibody, and such activities fell within the safe harbor as being reasonably related to seeking FDA approval. The court did, however, permit Merus leave to amend the complaint.

Claim Construction (Markman) Outcomes, Discovery Milestones, Trial Events, and Post-Trial Motions:

• Given the early dismissal of the case on a motion to dismiss, the litigation did not reach the stages of claim construction (Markman), significant discovery milestones, trial events, or post-trial motions.

Settlement, Dismissal, Judgment, or Appeal:

• 2025-09-30: The case was terminated following the court's grant of Xencor's motion to dismiss. While the court allowed Merus leave to amend the complaint, the case record indicates termination on this date. No appeal to the Federal Circuit was found in the provided search results.

Parallel PTAB IPR/PGR Proceedings:

• 2025-02-11: Xencor, Inc. filed an Inter Partes Review (IPR) petition, IPR2025-00604, challenging the patentability of U.S. Patent No. 9,358,286. The petition challenged claims 1-2, 7-24, 26-28, and 30-32 of the '286 patent, arguing unpatentability based on prior art.
• 2025-07-17: The Director of the USPTO issued a decision referring the IPR petition (IPR2025-00604) to the Patent Trial and Appeal Board (PTAB), denying Merus N.V.'s request for discretionary denial of institution.
• 2025-09-26: The PTAB instituted IPR2025-00604 against the '286 patent.
• 2026-03-19: Xencor provided notice of deposition for Brian J. Sutton, Ph.D., for a cross-examination in both IPR2025-00604 and a related IPR2025-00605 (challenging U.S. Patent No. 11,926,859). The parallel IPR proceeding indicates that the validity of the '286 patent continues to be challenged at the PTAB, even after the district court case's dismissal on safe harbor grounds.

The plaintiff, Merus N.V., was represented by the following counsel:

• Jack B. Blumenfeld

  • Role: Lead Local Counsel
  • Firm: Morris, Nichols, Arsht & Tunnell LLP, Wilmington, DE
  • Experience Note: Blumenfeld is a highly experienced patent litigator frequently appearing in the District of Delaware, handling complex intellectual property disputes.

• Jeremy A. Tigan

  • Role: Local Counsel
  • Firm: Morris, Nichols, Arsht & Tunnell LLP, Wilmington, DE
  • Experience Note: Tigan's practice focuses on intellectual property litigation, particularly in the District of Delaware.

• Colleen Tracy James

  • Role: Counsel (admitted Pro Hac Vice)
  • Firm: Cahill Gordon & Reindel LLP, New York, NY (Presumed, based on typical firm structures for pro hac vice admissions)
  • Experience Note: James is known for her work in patent litigation, particularly in the life sciences sector.

• Peter J. Armenio

  • Role: Counsel (admitted Pro Hac Vice)
  • Firm: Cahill Gordon & Reindel LLP, New York, NY (Presumed)
  • Experience Note: Armenio has experience in patent litigation, often representing pharmaceutical and biotechnology companies.

• Camille H. Mangiaratti

  • Role: Counsel (admitted Pro Hac Vice)
  • Firm: Cahill Gordon & Reindel LLP, New York, NY (Presumed)
  • Experience Note: Mangiaratti focuses on intellectual property litigation, including patent disputes in the biopharmaceutical industry.

• Jessica M. Stookey

  • Role: Counsel (admitted Pro Hac Vice)
  • Firm: Cahill Gordon & Reindel LLP, New York, NY (Presumed)
  • Experience Note: Stookey's practice includes complex patent litigation, particularly within the life sciences.

No specific in-house counsel for Merus N.V. was listed on the publicly available docket information for this case.

Defendant's Counsel in Merus N.V. v. Xencor, Inc.

The defendant, Xencor, Inc., is represented by a team of attorneys from Paul Hastings LLP and Young, Conaway, Stargatt & Taylor LLP, along with in-house counsel.

Lead Counsel (Paul Hastings LLP):

• Naveen Modi (Lead Counsel)

  • Firm: Paul Hastings LLP (Washington, D.C. office implied by email context in IPR filings)
  • Experience: Co-chairs Paul Hastings's global intellectual property practice and is known for representing pharmaceutical and biotechnology companies in complex patent litigation, particularly Hatch-Waxman and biosimilar cases, and Post-Grant proceedings before the PTAB.

• Eric W. Dittmann (Pro Hac Vice, Lead Counsel)

  • Firm: Paul Hastings LLP (New York, NY)
  • Experience: Focuses on patent litigation in the pharmaceutical and biotechnology sectors, including Hatch-Waxman and BPCIA disputes, with significant experience in federal district courts and at the Federal Circuit.

• Daniel Zeilberger (Pro Hac Vice, Lead Counsel)

  • Firm: Paul Hastings LLP (Washington, D.C.)
  • Experience: A partner in the intellectual property practice, with experience in patent litigation across various technologies, particularly in the life sciences and pharmaceutical industries, and IPR proceedings.

• Isaac S. Ashkenazi (Pro Hac Vice)

  • Firm: Paul Hastings LLP (New York, NY)
  • Experience: Specializes in patent litigation, particularly in the biotechnology and pharmaceutical fields, and has experience with PTAB proceedings.

• Ashley N. Mays-Williams (Pro Hac Vice)

  • Firm: Paul Hastings LLP (Washington, D.C.)
  • Experience: An associate focusing on intellectual property litigation, including patent infringement defense, particularly in the life sciences sector.

Local Counsel (Young, Conaway, Stargatt & Taylor LLP):

• Adam Wyatt Poff (Lead Local Counsel)

  • Firm: Young, Conaway, Stargatt & Taylor LLP (Wilmington, DE)
  • Experience: Extensive experience in patent litigation in the District of Delaware, frequently serving as local counsel for both plaintiffs and defendants in complex intellectual property disputes.

• Robert M. Vrana (Lead Local Counsel)

  • Firm: Young, Conaway, Stargatt & Taylor LLP (Wilmington, DE)
  • Experience: Focuses on intellectual property litigation in Delaware, representing clients in patent, trademark, and copyright matters.

• Daniel G. Mackrides (Local Counsel)

  • Firm: Young Conaway Stargatt & Taylor LLP (Wilmington, DE)
  • Experience: Practices in intellectual property litigation, including patent infringement cases in the District of Delaware.

In-House Counsel:

• Celia Eckert (Senior Vice President, General Counsel and Corporate Secretary)
  • Firm: Xencor, Inc. (Monrovia, CA)
  • Experience: Oversees all legal and compliance matters for Xencor, including intellectual property, transactions, and corporate governance. Previously managed substantial patent litigation at Prometheus Laboratories, Inc.