Background
Immunex Corporation (an Amgen subsidiary) held U.S. Patent No. 8,679,487, directed to isolated human antibodies that compete with a reference antibody for binding to human interleukin-4 receptor (IL-4R). IL-4R is a protein involved in allergic and inflammatory signaling; antibodies that block it are therapeutically important for treating conditions like atopic dermatitis and asthma. Sanofi and Regeneron developed dupilumab (Dupixent), a bispecific antibody that blocks both IL-4 and IL-13 signaling by binding to the IL-4 receptor — the same receptor covered by Immunex’s patent.
Immunex sued Sanofi, alleging Dupixent — which became one of the best-selling drugs in the world — infringed the ‘487 patent. Sanofi simultaneously filed inter partes review (IPR) petitions challenging the patent’s validity. The PTAB found the claims unpatentable as obvious and Immunex appealed to the Federal Circuit.
The Court’s Holding
The Federal Circuit affirmed invalidity. The central dispute was claim construction: specifically, whether the term “human antibodies” in Immunex’s patent covered only “fully human” antibodies or also “humanized” antibodies (antibodies derived from non-human (e.g., murine) sources but engineered to replace most mouse sequences with human ones). Immunex argued the claims covered only fully human antibodies; Sanofi argued humanized antibodies fell within the claim’s scope because the specification and prosecution history used the terms broadly.
The court agreed with Sanofi’s broader construction, finding the intrinsic evidence — the claim language, specification, and prosecution history — supported including humanized antibodies within “human antibodies.” Under this broader construction, the prior art — which disclosed murine antibodies targeting IL-4R and techniques for humanizing such antibodies — rendered the claims obvious. The Federal Circuit found no error in the PTAB’s analysis.
Key Takeaways
- Claim construction disputes in antibody patent cases often turn on the breadth of terms like “human” vs. “humanized,” and the intrinsic record (specification and prosecution history) is the primary guide.
- When patent specifications describe antibodies using broad language that encompasses both fully human and humanized antibodies, courts may construe claims broadly — bringing more prior art within striking distance for obviousness challenges.
- IPR proceedings are an effective tool for generic and biosimilar manufacturers to challenge broad biologic drug patents, even for blockbuster products with significant commercial success.
- The case illustrates the ongoing tension between innovator pharmaceutical companies, which invest in antibody discovery, and the biosimilar/generic industry’s use of IPR to challenge that IP.
Why It Matters
Dupixent (dupilumab) became one of the most commercially successful biologic drugs in history, generating billions in annual sales for Sanofi and Regeneron. The validity of Immunex’s IL-4R antibody patent was therefore high-stakes: had the patent been upheld, it could have supported claims for enormous royalties or blocked Dupixent’s commercialization. The Federal Circuit’s affirmance of invalidity removed that threat.
More broadly, the case is important for antibody patent practice. As the antibody drug industry grows, the boundaries between “human” and “humanized” antibodies, and how prior art disclosures of related antibody families affect validity, are critical questions. The decision underscores the importance of precise drafting and prosecution in antibody patent applications to ensure claims are both broad enough to cover important products and narrow enough to distinguish the prior art.