Proper Claim Drafting: An Essential Skill for Patent Practitioners

The claims of a patent define its scope.  Drafting the claims can be a tricky business.  Drafting the claims too narrowly makes it easy for competitors to design around the patent.  Drafting the claims too broadly makes the claims subject to attack. 

Usually, the attack is based on the assertion that the prior art teaches the invention.  An attack may also be based on the assertion that the patent specification fails to enable one of ordinary skill to practice the full scope of the invention covered by the patent’s claims.  Sanofi successfully attacked several Amgen patents for lack of enablement in a case decided by the U.S. Court of Appeals for the Federal Circuit (“Federal Circuit”) on February 11, 2021.

The Invention

Elevated levels of low-density lipoprotein (“LDL”) cholesterol in the blood stream causes heart disease.  LDL receptors remove LDL cholesterol from the blood stream thus regulating the amount of circulating LDL cholesterol. 

PCSK9, a protein, binds to LDL receptors preventing LDL receptors from doing their job of removing LDL cholesterol from the blood stream.  Thus, the PCSK9 protein causing LDL levels to rise.

Amgen owns patents describing antibodies that bind to the PCSK9 protein.  These antibodies block PCSK9 from binding to LDL receptors enabling the LDL receptors to more effectively lower LDL levels.  An exemplary claim from one of these patents reads:

1. An isolated monoclonal antibody, wherein, when bound to PCSK9, the monoclonal antibody binds to at least one of the following residues: S153, I154, P155, R194, D238, A239, I369, S372, D374, C375, T377, C378, F379, V380, or S381 of SEQ ID NO:3, and wherein the monoclonal antibody blocks binding of PCSK9 to LDLR.

The Lawsuit

Amgen sued Sanofi for patent infringement.  Sanofi stipulated to infringement, raising only patent invalidity as a defense.  Sanofi argued Amgen’s patent claims are invalid for lack of enablement. 

Two separate juries found Sanofi failed to establish its non-enablement defense.  The first jury’s decision was overturned because the Federal Circuit found that the district court judge’s evidentiary rulings and jury instructions were erroneous.  A new trial was ordered on the issue of enablement.  After the second jury also found that Sanofi failed to establish its non-enablement defense, the district court judge granted Sanofi’s motion for a judgement of a matter of law overturning the second jury’s verdict.  Amgen then appealed the district court judge’s ruling.

Legal Principles Applied

According to the Federal Circuit,

The statutory basis for the enablement requirement is found in Section 112 of the patent statute, which provides in relevant part that a patent’s specification must “enable any person skilled in the art . . .to make and use” the patented invention.  35 U.S.C. § 112(a).  The purpose of the enablement requirement is to ensure that the public is told how to carry out the invention, i.e., to make and use it. We have held that such disclosure must be “at least commensurate with the scope of the claims.”

To prove that a claim is invalid for lack of enablement, a challenger must show by clear and convincing evidence that a person of ordinary skill in the art would not be able to practice the claimed invention, after studying the patent’s written description and drawings, without “undue experimentation.” Alcon Research, 745 F.3d at 1188 (quoting In re Wands, 858 F.2d 731, 736–37 (Fed. Cir. 1988)).

Determining whether undue experimentation is needed involves consideration of a variety of factors.  These include:

(1) the quantity of experimentation necessary,

(2) the amount of direction or guidance presented,

(3) the presence or absence of working examples,

(4) the nature of the invention,

(5) the state of the prior art,

(6) the relative skill of those in the art,

(7) the predictability or unpredictability of the art, and

(8) the breadth of the claims.

Wands, 858 F.2d at 737.  “After the challenger has put forward evidence that some experimentation is needed to practice the patented claim, the factors set forth in Wands then provide the factual considerations that a court may consider when determining whether the amount of that experimentation is either ‘undue’ or sufficiently routine such that an ordinarily skilled artisan would reasonably be expected to carry it out.” Alcon Research, 745 F.3d at 1188 (quoting Wands, 858 F.2d at 737).

But what if the specification clearly describes how to make and use some of the variants of the invention, but not all?  According to the Federal Circuit, “Although a specification does not need to ‘describe how to make and use every possible variant of the claimed invention, when a range is claimed, there must be reasonable enablement of the scope of the range.’” citing McRO, Inc. v. Bandai Namco Games Am. Inc., 959 F.3d 1091, 1100.

Federal Circuit Application of the Principles

The Federal Circuit noted that the limitations of Amgen’s claim are all functional.  The claim in question does not identify any specific isolated monoclonal antibody or any specific set of such antibodies.  Instead, the claim purports to cover all such antibodies that perform two functions: the monoclonal antibody when bound to PCSK9 (1) binds to at least one of the following residues: S153, I154, P155, R194, D238, A239, I369, S372, D374, C375, T377, C378, F379, V380, or S381 of SEQ ID NO:3; and (2) blocks binding of PCSK9 to LDLR. 

The Federal Circuit noted, “[w]hile functional claim limitations are not necessarily precluded in claims that meet the enablement requirement, such limitations pose high hurdles in fulfilling the enablement requirement for claims with broad functional language.”  The Federal Circuit then concluded that the specification of Amgen’s patents “did not enable preparation of the full scope of these double-function claims without undue experimentation.”

At least four sets of facts led the Federal Circuit to this conclusion:

1. The claims are indisputably broad, so broad that the parties could not even agree as to the number of antibodies that would satisfy the claims.
2. This invention is in an unpredictable field of science with respect to satisfying the full scope of the functional limitations, so unpredictable that Amgen’s experts had to acknowledge that translating an antibody’s amino acid “sequence into a known three-dimensional structure is still not possible,” and “substitutions in the amino acid sequence of an antibody can affect the antibody’s function, and testing would be required to ensure that a substitution does not alter the binding and blocking functions.”
3. The only ways for a person of ordinary skill to discover undisclosed claimed embodiments would be through either “trial and error, by making changes to the disclosed antibodies and then screening those antibodies for the desired binding and blocking properties,” or else “by discovering the antibodies de novo” according to a randomization-and-screening “roadmap.”
4. The functional limitations here are broad, the disclosed examples and guidance are narrow, and no reasonable jury could conclude under these facts that anything, but “substantial time and effort” would be required to reach the full scope of claimed embodiments.

The U.S. Patent Office and two different juries reached a different conclusion than the trial judge and the Federal Circuit on the issue of enablement.  And there is no bright line test for resolving the issue.  Many factors need to be considered.

Dewitt’s Patent Practice Group is a team of experienced lawyers with diverse technical backgrounds.  These lawyers are well equipped to address these issues and do so daily as patents are secured on behalf of Dewitt clients and as Dewitt lawyers defend our clients against claims of infringement.