In a precedential opinion issued on March 6, the Federal Circuit affirmed the US District Court for the Eastern District of Virginia that the claims in ImmunoGen’s US patent application 14/509,809 (“the ’809 application,” published on May 14, 2015, as US 2015/0132323) were obvious.

ImmunoGen, Inc. v COKE MORGAN STEWART, ACTING UNDER SECRETARY OF COMMERCE FOR INTELLECTUAL PROPERTY AND ACTING DIRECTOR OF THE UNITED STATES PATENT AND TRADEMARK OFFICE, (2023-1762, Decided: March 6, 2025).

This case highlights the distinctions between the US law where the obviousness inquiry is generally agnostic to the particular motivation of the inventor, versus that in Europe and many other countries that evaluate inventive step/inventiveness based on a “problem–solution” approach not required in the US. The case also serves as a reminder of the risks attendant with the use of so-called boilerplate language, particularly when used in the context of ascribing a level of skill in the art regarding optimization of parameters. And it further underscores the challenges faced by patent applicants, particularly in the pharmaceutical and life sciences sectors, in balancing the scope of its own seminal patents covering new chemical entities, per se, against a reasonable foreseeability of filing of later, second-, and later-generation patent applications on various improvements, such as treatment regimens, dosage formulations, etc. This challenge has been exacerbated by a growing hostility towards building “patent thickets” around new drugs, based on the notion that they are responsible for high drug prices. This decision further adds to the growing arsenal of jurisprudence on which generic drug companies may rely on attacking later-generation Orange Book-listed patents covering drug compositions and uses thereof. 

The claims at issue are directed to a dosing regimen for administering IMGN853 (mirvetuximab soravtansine), which is ImmunoGen’s patented and US Food and Drug Administration- (FDA) approved antibody drug conjugate (ADC) used for treating certain ovarian and peritoneal cancers. IMGN853 is a conjugate of an antibody known as “huMov19” linked via a charged sulfopSPDB linker to a toxic maytansinoid payload known as “DM4.” The key limitation in the claims was the recitation that immunoconjugate is administered at a dose of 6 milligrams (mg) per kilogram (kg) of adjusted ideal body weight (AIBW) of the patient.” The Patent Trial and Appeal Board (PTAB) affirmed the Examiner’s obviousness rejection, which was based primarily on ImmunoGen’s own prior patent publication [2012/0282282] directed to IMGN853, per se. Immunogen filed a civil action under 35 U.S.C. § 145. The Eastern District Court of the Eastern District of Virginia affirmed PTAB’s decision.

On appeal, ImmunoGen stressed that at the time the invention was made, the art did not appreciate that IMGN853 caused ocular toxicity in humans. Thus, in its view, the solution to an unknown problem could not have been obvious — such as found in some prior Federal Circuit and the US Court of Customs and Patent Appeals (CCPA) cases. See, e.g., In re Sponnoble, 405 F.2d 578, 585 (C.C.P.A. 1969) (“a patentable invention may lie in the discovery of the source of a problem even though the remedy may be obvious once the source of the problem is identified.”); In re Omeprazole Patent Litigation, 536 F.3d 1361, 1380-81 (Fed. Cir. 2008) (upholding patent where coatings for omeprazole were discovered by the inventors to negatively interact with each other, and solution of providing a barrier therebetween was non-obvious even if providing a barrier would have been obvious if the interaction problem were known); Leo Pharmaceutical Products v. Rea, 726 F.3d 1346, 1353-54 (Fed. Cir. 2013) (“The inventors of the ‘013 patent recognized and solved a problem with the storage stability of certain formulations—a problem that the prior art did not recognize and a problem that was not solved for over a decade.”)

This position is also consistent with jurisdictions, such as Europe, that apply a “problem-solution” approach to the determination of inventive step. Indeed, the European Patent Office granted to ImmunoGen at least one patent with claims similar to those at issue in the United States.

However, the District Court determined that because ocular toxicity was “a well-known adverse event in the administration of immunoconjugates that contain DM4,” and because IMGN853 includes a DM4 payload, a person of ordinary skill in the art would have been motivated to monitor for those side effects when administering the drug to humans, despite not knowing of IMGN853’s ocular toxicity.

The Federal Circuit agreed. It pointed to its prior decisions in reasoning that “[a]s an initial matter, although ImmunoGen is correct that “[w]here a problem was not known in the art, the solution to that problem may not be obvious,” Forest Lab’ys, LLC v. Sigmapharm Lab’ys, LLC, 918 F.3d 928, 935 (Fed. Cir. 2019), it does not follow that a claimed solution to an unknown problem is necessarily non-obvious.” (Emphasis in original). Relying on KSR for the proposition that “[i]n determining whether the subject matter of a patent claim [was] obvious, neither the particular motivation nor the avowed purpose of the patentee controls,” the Federal Circuit found no clear error in the District Court’s reasoning.

ImmunoGen also argued that the district court clearly erred in finding that a person of ordinary skill in the art would have been motivated to try AIBW dosing as a dosing methodology for IMGN853 to eliminate ocular toxicity or arrive at a dose of 6 mg/kg AIBW with a reasonable expectation of success. Regarding the former, AIBW was a known technique but had never been used as a methodology for an ADC. So, in ImmunoGen’s view, the district court “simply plucked AIBW dosing out of [a] multitude of possibilities.” In finding no clear error in the District Court’s reasoning, the Federal Circuit relied on ImmunoGen’s ‘282 publication and, in particular, for its teaching that “[t]he dosing regimen and dosages [of the disclosed ADCs] will depend on the particular cancer being treated, the extent of the disease and other factors familiar to the physician of skill in the art and can be determined by the physician.” (Emphasis in original). This reference to the level of skill in the art, especially at the time of drafting, most certainly came back to haunt ImmunoGen.

Regarding the latter, ImmunoGen was again thwarted by its own prior publication. Indeed, in view of its findings that Immunogen’s ’282 publication discloses dosing IMGN853 at around 6 mg/kg of TBW (total body weight) of the patient, an abstract from the American Society of Clinical Oncology disclosing that IMGN853 had been tested on humans at a dose of 5 mg/kg TBW, AIBW dosing was well known, and that “for patients who weigh exactly their ideal body weight, a dose of 6 mg/kg AIBW is identical to a dose of 6 mg/kg TBW,” the district court viewed ImmunoGen’s ‘809 application as an attempt “to cover a dose that was already disclosed in the prior art.” The Federal Circuit agreed, concluding: “[a] doctor dosing a patient at his or her IBW with IMGN853 at a dose of 6 mg/kg TBW would necessarily be dosing that patient at 6 mg/kg AIBW, as claimed. This would be true regardless of whether a doctor knew of AIBW dosing.” (Emphasis in original).

In sum, this case shows that, even if a problem was unknown at the time an invention was made, it may still be obvious. Moreover, this case demonstrates the difficulties of obtaining a patent to a specific method of treatment and dosage formulations in view of one’s own prior art.