Merck Serono SA v. TWI Pharmaceuticals Inc.

The patent infringement litigation involves Merck Serono SA, a biopharmaceutical division of German science and technology company Merck KGaA, which specializes in innovative therapies for neurology, fertility, and oncology. Merck Serono is known for its multiple sclerosis treatment, Mavenclad (cladribine tablets). The opposing party is TWI Pharmaceuticals Inc., a Taiwan-based specialty pharmaceutical company focused on developing, manufacturing, and commercializing high-barrier generic prescription products.

The core of the dispute centers on US Patent No. 8,377,903 ("the '903 patent"), which claims a specific cladribine oral dosing regimen for the treatment of relapsing forms of multiple sclerosis. Merck Serono's branded product, Mavenclad, utilizes this cladribine tablet therapy. TWI Pharmaceuticals Inc. sought to market a generic version of cladribine, leading them to challenge the validity of Merck Serono's patents. The case before the Federal Circuit, number 25-1464, was an appeal from a Patent Trial and Appeal Board (PTAB) decision that found claims of the '903 patent unpatentable as obvious over prior art, specifically the Bodor and Stelmasiak references. The Federal Circuit (with Judge Linn on the panel) affirmed the PTAB's finding of unpatentability on October 30, 2025, a decision that clarifies the "by another" prior art standard under pre-AIA law.

This case is notable as it represents a significant challenge to the exclusivity of Merck Serono's Mavenclad, a drug that generated worldwide sales of €1.1 billion (approximately $1.3 billion) in 2024. The Federal Circuit's affirmance of the PTAB's unpatentability ruling effectively extinguishes a key exclusivity claim for Merck Serono in the multiple sclerosis therapeutics space, strengthening TWI Pharmaceuticals' position in bringing a generic cladribine product to market. The appellate decision, delivered in a swift 253 days from filing, also provided important clarification on the interpretation of "by another" for prior art determinations under pre-America Invents Act (AIA) patent law, emphasizing that for a reference to be excluded as prior art, the inventive entity must be exactly the same.

Key Legal Developments and Outcome:

This case, Merck Serono SA v. TWI Pharmaceuticals Inc. (CAFC Case No. 25-1464), represents an appeal of a Patent Trial and Appeal Board (PTAB) decision. As such, the procedural history primarily revolves around the PTAB proceedings and the subsequent Federal Circuit appeal, rather than a traditional district court infringement litigation with initial pleadings, discovery, and trial events.

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

1. Parallel PTAB IPR Proceedings:

• 2022-10-14: TWI Pharmaceuticals Inc. filed an inter partes review (IPR) petition, IPR2023-00050, challenging the patentability of claims 17, 19, 20, and 22-29 of U.S. Patent No. 8,377,903.
• 2023-12-20: The PTAB instituted review of all challenged claims in IPR2023-00050.
• 2024-09-18: The PTAB issued its Final Written Decision in IPR2023-00481 (related to the '903 patent) and IPR2023-00480 (related to U.S. Patent No. 7,713,947), finding several claims of both patents unpatentable as obvious over prior art, specifically the Bodor and Stelmasiak references. This decision was appealed, leading to the Federal Circuit case 25-1464 (and its companion case 25-1463).

2. Federal Circuit Appeal (25-1464):

• 2025-02-19: Merck Serono SA filed its appeal with the U.S. Court of Appeals for the Federal Circuit under Case No. 25-1464, challenging the PTAB's unpatentability ruling for US8377903B2.
• 2025-03-12: The Federal Circuit consolidated appeal Nos. 25-1463 and 25-1464, and established a briefing schedule. These cases were also considered companion cases to Merck Serono S.A. v. Hopewell Pharma Ventures, Inc. (Appeal Nos. 25-1210, 25-1211) and assigned to the same merits panel.
• 2025-07-11: Oral arguments were heard.
• 2025-10-30: The Federal Circuit issued its decision, affirming the PTAB's finding of unpatentability for claims of US8377903B2. The court found no reversible error in the Board's analysis and clarified the "by another" standard under pre-AIA Section 102(e), emphasizing that any difference in named inventors rendered a prior art reference "by another." Judge Linn was on the panel.
• 2025-10-30: The case was terminated with a judgment of "Unpatentable."
• 2026-01-29: Merck sought a rehearing of the October 2025 opinion, but the Federal Circuit declined to reconsider its decisions that invalidated Merck's patents.

3. Outcome:
The Federal Circuit's affirmance of the PTAB's decision rendered the challenged claims of U.S. Patent No. 8,377,903 invalid and unenforceable. This outcome effectively extinguished a key exclusivity claim for Merck Serono's Mavenclad in the multiple sclerosis therapeutics space, strengthening TWI Pharmaceuticals' position to market a generic cladribine product. The decision also provided important clarification on the interpretation of "by another" for prior art determinations under pre-America Invents Act (AIA) patent law, requiring an exact identity of inventive entities to exclude a reference as prior art. Merck Serono's remaining options are limited to petitioning the Federal Circuit for en banc rehearing or seeking certiorari before the U.S. Supreme Court, both considered low-probability paths.

Merck Serono SA was represented by attorneys from WilmerHale, as well as by in-house counsel.

Here is a list of the counsel of record for Merck Serono SA:

• David B. Bassett (Lead Counsel)

  • Firm: Wilmer Cutler Pickering Hale and Dorr LLP (WilmerHale), New York, NY, and Washington D.C.
  • Experience: Bassett is a partner at WilmerHale and frequently handles appellate arguments before the Federal Circuit, particularly in pharmaceutical patent litigation. He was involved in Merck's appeals concerning cladribine patents.

• Emily R. Whelan (Counsel)

  • Firm: Wilmer Cutler Pickering Hale and Dorr LLP (WilmerHale), Washington D.C.
  • Experience: Whelan is an attorney at WilmerHale, focusing on intellectual property litigation. She appeared on behalf of Merck Serono S.A. in this case.

• Mark C. Fleming (Counsel)

  • Firm: Wilmer Cutler Pickering Hale and Dorr LLP (WilmerHale), Boston, MA
  • Experience: Fleming is a partner at WilmerHale, with significant experience in appellate litigation, particularly before the Federal Circuit.

• Helena Rachael Million-Perez (Counsel)

  • Firm: Wilmer Cutler Pickering Hale and Dorr LLP (WilmerHale)
  • Experience: Million-Perez is an attorney at WilmerHale and was listed as counsel for Merck Serono S.A.

• Nora N. Xu (Counsel)

  • Firm: Wilmer Cutler Pickering Hale and Dorr LLP (WilmerHale)
  • Experience: Xu is an attorney at WilmerHale and was listed as counsel for Merck Serono S.A.

• Richard Parr (In-house Counsel / Of Counsel)

  • Firm: Formerly with Merck, currently Senior Counsel at Kim IP
  • Experience: Richard Parr spent over 30 years with Merck, focusing on pharmaceutical patent law matters, including prosecuting numerous US patents and managing patent portfolios. While not explicitly listed as appearing counsel in the CAFC docket for this specific case, individuals like Richard Parr often play a key in-house role in shaping litigation strategy and overseeing external counsel for pharmaceutical companies like Merck Serono.

It is important to note that WilmerHale represented Merck Serono SA in the Federal Circuit appeal. The Justia Dockets for case 25-1464 also list the entry of appearance for David B. Bassett, Emily R. Whelan, Helena Rachael Million-Perez, Nora N. Xu, and Mark C. Fleming as counsel for Appellant Merck Serono S.A.

In the Federal Circuit case Merck Serono SA v. TWI Pharmaceuticals Inc., the counsel of record representing defendant TWI Pharmaceuticals Inc. is:

• Philip D. Segrest Jr. (Lead Counsel)
  • Firm: Sterne, Kessler, Goldstein & Fox P.L.L.C. (Washington, D.C. office)
  • Experience Note: Sterne Kessler is known for its extensive experience in pharmaceutical IP litigation, including Hatch-Waxman cases, and is one of the top firms at the Federal Circuit.

While a Justia Dockets entry from March 7, 2025, shows Philip Segrest filed a reply on behalf of TWI Pharmaceuticals, Inc., the specific role (e.g., lead, local, of counsel) is inferred from his filing activity and the firm's reputation in this area. It's important to note that the provided Justia docket information was last retrieved on April 1, 2025, and a more recent listing may be available from PACER.