Federal Circuit IP

Immunogen, Inc. v. Stewart

By Ziyu Ma Published March 19, 2025

CAFC No. 2023-1762, Decided March 6, 2025

(Lourie, Dyk, and Prost)

Background:

  1. USPTO: Immunogen filed the ’809 application in 2014; rejected (indefiniteness, obviousness, and obviousness-type double patenting).
  2. PTAB: ImmunoGen appeals to PTAB, which affirms the examiner’s rejection.
  3. D. Va.: 2020-2021, ImmunoGen files suit in E.D. Va. seeking a judgment declaring entitlement to a patent. Court granted SJ in favor of USPTO (indefiniteness, obviousness, and obviousness-type double patenting).
  4. Cir.: 2022, vacated the SJ ruling (improper resolution of factual disputes) and remanded.
  5. D. Va.: 2023, 3-day bench trial, reaffirming previous judgment (fatally indefinite and obvious)
  6. Cir.: 2025, affirmed, the claims are obvious.
  7. The ’809 application: a dosing regimen for administering IMGN853, a patented antibody drug conjugate (“ADC”) used for treating certain ovarian and peritoneal cancers.
    1. IMGN853: Antibody + Linker + DM4.

Issue: Obviousness—whether an unknown problem in the art necessarily makes the claimed solution non-obvious.

Holding: A claimed solution to a problem not previously recognized in the prior art is not necessarily non-obvious. The motivation analysis for obviousness is not limited to the specific problem identified by the inventors.

Federal Circuit Analysis:

  1. Rejected Plaintiff’s argument that “a claimed solution to an unknown problem is non-obvious.” Not necessarily.
    1. Unknown: IMGN853 causes ocular toxicity.
      1. Obvious: DM4, a component of IMGN853, was known to cause ocular toxicity.
    2. Unknown: using the AIBW dosing method to reduce ocular toxicity caused by ADC.
      1. Obvious: the AIBW method was known, AIBW has been used in anticancer drugs, and AIBW was known to reduce ocular toxicity. Within the range of knowledge of a POSITA when confronted with dosing-induced toxicities.
    3. The dose of “6 mg/kg of adjusted ideal body weight (AIBW)” would have been obvious – reasonable expectation of success. “5 mg/kg TBW” v. “6 mg/kg AIBW”: routine optimization, in some cases, the two dosing methods are identical.
      1. The claim does not recite treating ocular toxicity.
    4. Affirmed on obviousness ground, no need to address indefiniteness.

Takeaways:

  1. Pharmaceutical patents on dosing regimens face strong obviousness scrutiny; consider including data showing unexpected results in the spec., if possible.
  2. Obviousness motivation analysis isn’t confined to the inventor’s identified problem.