Federal Circuit: Body Weight Limitations Are Obvious

The Federal Circuit has affirmed a district court’s summary judgment ruling in favor of the US Patent and Trademark Office (USPTO) following a civil action by ImmunoGen seeking to obtain a patent after an unsuccessful ex parte appeal of a patent application at the Patent Trial and Appeal Board (PTAB or Board).

The case is Immunogen, Inc. v. Stewart.

ImmunoGen sought a patent for the invention claimed in US Patent Application 14/509,809 (“the ’809 application”). Determining that the claims of the application were “fatally indefinite and obvious,” and that the claims were unpatentable under the doctrine of obviousness-type double patenting, the district court entered judgment in favor of the US government, denying ImmunoGen’s claim for entitlement to a patent.

The application is for a dosing regimen for administering IMGN853 (i.e., mirvetuximab soravtansine), a patented antibody drug conjugate (“ADC”) used for treating certain ovarian and peritoneal cancers.

The ’809 application explains that, although IMGN853 exhibits promise as a cancer therapy, it can cause ocular toxicity in humans, resulting in keratitis and blurred vision. The inventors, therefore, set out to develop “a therapeutically effective dosing regimen [of IMGN853] that results in minimal adverse effects.”

Claim 1 of the application includes the following language:

wherein the immunoconjugate is administered at a dose of 6 milligrams (mg) per kilogram (kg) of adjusted ideal body weight (AIBW) of the patient.

The parties didn’t dispute that “[a] method of using IMGN853 to treat FOLR1-expressing ovarian cancer or peritoneum cancer was known in the art” at the time of the invention. Thus, the patentability of the claims of the ’809 application turned only on the dosing limitation.

After a patent examiner rejected the claims of the ’809 application and the PTAB affirmed, ImmunoGen sued in federal district court seeking a judgment pursuant to 35 U.S.C. § 145 that would declare ImmunoGen’s entitlement to a patent for the claimed invention.

At summary judgment, the government argued that the claims are unpatentable because:

1. the claimed “AIBW” renders the claims indefinite;
2. the dosing limitation renders the claims obvious over the asserted prior art; and
3. the claims are unpatentable under the doctrine of obviousness-type double patenting.

The Federal Circuit vacated and remanded that decision, and the case proceeded to a bench trial at which the district court again determined that the patent claims were “fatally indefinite.”

The district court explained that the ’809 application “fails to define AIBW... anywhere in its claims.” This failure was particularly important because the district court found that the intrinsic and extrinsic evidence established that there are various formulas for AIBW from which a person of ordinary skill in the art could have chosen.

Thus, the court determined that the claims fail to inform a person of ordinary skill in the art with reasonable certainty of the scope of the invention.

The district court also found the claims are unpatentable as obvious over ImmunoGen’s own prior art that discloses treatment of ovarian and peritoneal cancers with IMGN853 using “total body weight,” or “TBW,” dosing, and other prior art disclosing AIBW dosing for other compounds.

Specifically, the district court found that a person of ordinary skill in the art would have been motivated to arrive at the claimed dosing limitation because

1. the problem of ocular toxicity was known,
2. skilled artisans understood that changing the dose was a possible solution for adverse side effects such as ocular toxicity, and
3. the prior art disclosed AIBW dosing as a potential means to eliminate or ameliorate ocular toxicity.

In the view of the district court, even the unpredictability of immunoconjugates was insufficient to overcome that obviousness determination.

On appeal, the Federal Circuit noted that

Obviousness is a question of law, which we review de novo, with underlying factual questions, which we review for clear error following a bench trial.

According to the Federal Circuit,

To determine whether a particular claimed invention would have been obvious over cited prior art, a factfinder must consider, among other things, whether “a skilled artisan would have been motivated to combine the teachings of the prior art references to achieve the claimed invention, and [whether] the skilled artisan would have had a reasonable expectation of success in doing so.”

ImmunoGen argued that the district court erred in its motivation-to-combine analysis because it was undisputed that at the time of the invention, a person of ordinary skill in the art would not have known that IMGN853 caused ocular toxicity in humans. According to ImmunoGen, because “[t]here was no motivation to solve the problem of ocular toxicity,” the claimed dosing limitation could not have been obvious.

The Federal Circuit agreed that “[w]here a problem was not known in the art, the solution to that problem may not be obvious.”

However, said the court, “it does not follow that a claimed solution to an unknown problem is necessarily non-obvious.”

The district court had acknowledged that the prior art does not “specifically disclose that IMGN853 caused ocular toxicity in humans.” However, the district court proceeded to explain that because ocular toxicity was “a well-known adverse event in the administration of immunoconjugates that contain as a toxic payload the maytansinoid known as DM4 and because IMGN853 includes that DM4 payload, a person of ordinary skill in the art “would [have] underst[oo]d the potential risk of ocular toxicity and would [have] monitor[ed] for ocular toxicity when testing IMGN853 in humans.”

ImmunoGen also argued that the district court 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.

However, said the Federal Circuit,

[t]he district court’s findings, which are not clearly erroneous, reasonably support the conclusion that AIBW dosing, though never used for ADCs, would have been within the range of knowledge of a person of ordinary skill in the art when confronted with dosing-induced toxicities, and particularly when confronted with dosing-induced ocular toxicity.

Thus, the Federal Circuit affirmed the district court’s judgment denying ImmunoGen’s claim for entitlement to a patent.