Unified Patents v. Merus BV

Unified Patents has initiated an Inter Partes Review (IPR) against Merus BV, challenging the validity of US Patent 11926859 before the Patent Trial and Appeal Board (PTAB). Unified Patents is a member-based organization focused on deterring frivolous patent litigation and reducing assertions by Non-Practicing Entities (NPEs) in various technology sectors, primarily by challenging the validity of patents through IPRs. Merus BV (now Merus N.V., recently acquired by Genmab in December 2025) is a clinical-stage oncology company based in the Netherlands, specializing in the development of innovative bispecific and trispecific antibody therapeutics for cancer treatment, utilizing proprietary Biclonics® and Triclonics® technology platforms.

The IPR focuses on US Patent 11926859, which claims a heterodimeric antibody. Specifically, the patent describes amino acid substitutions at positions 364 and 368 designed to create an oppositely charged pair of residues between two CH3 domains, thereby facilitating the creation of novel bispecific antibodies. While the case metadata identifies Unified Patents as the plaintiff, publicly available IPR documents for IPR2025-00605 consistently name Xencor, Inc. as the petitioner challenging Merus N.V. as the patent owner for this specific patent. The procedural posture places this matter before the PTAB under case number IPR2025-00605, where the petition for review has been instituted and is currently pending.

This IPR is notable due to several factors. The PTAB serves as an administrative tribunal within the USPTO, offering an avenue for challenging patentability that can be faster and more cost-effective than district court litigation. If Unified Patents is indeed the party bringing this challenge (as per the authoritative case metadata), it is noteworthy as Unified Patents typically targets NPEs, whereas Merus is an operating company in the biotechnology sector. However, if Xencor is the actual petitioner, as indicated in the IPR documents, the case then represents a patent validity dispute between two active players in the competitive oncology biopharmaceutical industry. The timing of the IPR also falls close to Merus's acquisition by Genmab, which could add a layer of complexity or strategic interest to the proceedings.

This analysis addresses the legal developments and outcome for US Patent 11,926,859, focusing on the provided IPR case number IPR2025-00605 and related litigation.

Important Note on Case Metadata Discrepancy: The prompt identifies the parties in IPR2025-00605 as "Unified Patents v. Merus BV." However, publicly available information for IPR2025-00605 consistently identifies the Petitioner as Xencor, Inc. and the Patent Owner as Merus N.V.. In accordance with the instruction to prefer the provided metadata for the caption, the official caption remains "Unified Patents v. Merus BV." However, for accuracy in describing the actual legal developments associated with IPR2025-00605 and related proceedings concerning US Patent 11,926,859, this summary will refer to Xencor, Inc. as the Petitioner and Merus N.V. as the Patent Owner/Plaintiff.

Patent at Issue: U.S. Patent No. 11,926,859, titled "Methods and means for the production of Ig-like molecules," issued on March 12, 2024.

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Key Legal Developments for US Patent 11,926,859

1. Parallel District Court Litigation: Merus N.V. v. Xencor, Inc.

• Filing & Initial Pleadings (Complaint, Answer, Counterclaims):
  • On August 5, 2024, Merus N.V. filed a patent infringement complaint against Xencor, Inc. in the U.S. District Court for the District of Delaware, Civil Action No. 1:24-cv-00913-CFC. The complaint alleged infringement of U.S. Patent Nos. 9,358,286, 9,944,695, and 11,926,859.
• Pre-trial Motions of Substance:
  • Xencor, Inc. filed a motion to dismiss the complaint under Rule 12(b)(6), arguing that its accused activities were protected by the Hatch-Waxman safe harbor provision (35 U.S.C. § 271(e)(1)). Merus's allegations included Xencor's making of "stable bispecific antibodies" using its XmAb® bispecific platform, and "generating 'early discovery,' 'preclinical,' and 'clinical . . . multispecific antibodies'."
• Judgment:
  • On September 30, 2025 (reported as October 16, 2025), the U.S. District Court for the District of Delaware granted Xencor's motion to dismiss the infringement suit. The court ruled that Xencor's alleged use of Merus's patented antibody technology was protected by the Hatch-Waxman safe harbor, as the activities were "solely for uses 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."

2. PTAB IPR Proceeding: IPR2025-00605 (Xencor, Inc. v. Merus N.V.)

• Filing & Initial Pleadings:
  • On February 10, 2025, Xencor, Inc. (as Petitioner) filed an Inter Partes Review (IPR) petition, IPR2025-00605, challenging U.S. Patent No. 11,926,859, owned by Merus N.V. (as Patent Owner).
• Pre-trial Motions of Substance:
  • Merus N.V. filed a reply on July 7, 2025, in support of its request for discretionary denial of institution. Merus argued that institution should be denied based on "settled expectations" because Xencor had known about the '859 patent family for over 10 years and the '859 patent itself since at least 2014, but waited until then to file its IPRs against the patent and its family member (U.S. Patent No. 9,358,286, challenged in IPR2025-00604).
• Institution Decision:
  • The Patent Trial and Appeal Board (PTAB) instituted Inter Partes Review on September 26, 2025, for claims 1-7 of U.S. Patent No. 11,926,859.
• Discovery Milestones with Strategic Significance:
  • On January 9, 2026, Merus N.V. filed a motion to submit supplemental information (EX2016 and EX2019) in the IPR proceeding.
• Trial Events:
  • An oral hearing for IPR2025-00605, along with the related IPR2025-00604, was scheduled for June 24, 2026.
• Present Posture:
  • The IPR is currently pending. Following the oral hearing, a final written decision from the PTAB is typically issued within 12 months of the institution date, which would be by September 26, 2026, though extensions are possible.

3. Parallel PTAB IPR Proceedings:

• In addition to IPR2025-00605 challenging U.S. Patent No. 11,926,859, Xencor, Inc. also filed IPR2025-00604 against Merus N.V., challenging U.S. Patent No. 9,358,286. Both patents were asserted in the District of Delaware litigation and both IPRs were instituted on September 26, 2025.

Based on the provided case metadata, Unified Patents is listed as the plaintiff in IPR2025-00605. However, publicly available docket information and search results for IPR2025-00605 consistently identify Xencor, Inc. as the Petitioner (the equivalent of a plaintiff in an Inter Partes Review) against Merus N.V..

Due to this discrepancy, specific counsel of record representing Unified Patents in IPR2025-00605 could not be identified through web searches of the docket or related filings, as all documents for this IPR name Xencor, Inc. as the petitioner.

While specific outside counsel for Unified Patents in this particular IPR are not identified through the available public records for IPR2025-00605, Unified Patents does employ an in-house legal team involved in their IPR activities. Key individuals associated with Unified Patents' legal department include:

• Jonathan Stroud

  • Role: Chief IP Counsel
  • Firm: Unified Patents (in-house)
  • Location: Washington, D.C. (Unified Patents has a presence in D.C.)
  • Experience: Frequently speaks on PTAB discretionary denials and patent quality, and is involved in managing patent office proceedings internally at Unified Patents.

• Michelle Aspen

  • Role: Senior Patent Counsel
  • Firm: Unified Patents (in-house)
  • Location: Not specified, but Unified Patents has a presence in Washington, D.C.
  • Experience: Has addressed topics such as Fintiv denials in PTAB proceedings.

• Roshan Mansinghani

  • Role: Legal Head-NPE
  • Firm: Unified Patents (in-house)
  • Location: Not specified, but Unified Patents has a presence in Washington, D.C.
  • Experience: Involved in discussions regarding patent litigation and non-practicing entities (NPEs).

Unified Patents regularly files IPR petitions, often utilizing both its internal legal team and various outside counsel firms. However, for IPR2025-00605, the public record clearly points to Xencor, Inc. as the petitioner, not Unified Patents.

Merus BV, the defendant in IPR2025-00605, is represented by attorneys from White & Case LLP.

The counsel of record for Merus BV includes:

• Elizabeth J. Holland

  • Role: Lead Counsel
  • Firm: White & Case LLP, New York, NY
  • Experience Note: Elizabeth J. Holland is a registered patent practitioner (Reg. No. 47,657) who regularly appears before the PTAB.

• Daniel P. Margolis

  • Role: Back-up Counsel
  • Firm: White & Case LLP, New York, NY
  • Experience Note: Daniel P. Margolis is a provisionally recognized PTAB attorney who has filed a pro hac vice application for this proceeding.

Earlier in the IPR proceeding, prior to the current White & Case representation, Merus N.V. (Patent Owner) was also associated with counsel from Cahill Gordon & Reindel LLP, including Peter J. Armenio and Colleen Tracy James, as indicated in a February 2026 notice of deposition for a combined deposition related to both IPR2025-00604 and IPR2025-00605. However, more recent filings, such as the Patent Owner's Updated Power of Attorney in March 2026 and Patent Owner's Request for Oral Argument in May 2026, list Elizabeth J. Holland and Daniel P. Margolis of White & Case LLP as the counsel for Merus B.V.