Disclosure Of Antibody's Equivalents Not Necessary To Satisfy Written Description And Indefiniteness Requirements For A Means-Plus-Function Claim Term

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The United States Patent and Trademark Office's ("USPTO") Appeals Review Panel ("the Panel") recently clarified that means-plus-function claims do not require that the specification disclose equivalents.
United States Intellectual Property
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The United States Patent and Trademark Office's ("USPTO") Appeals Review Panel ("the Panel") recently clarified that means-plus-function claims do not require that the specification disclose equivalents. See Ex parte Chamberlain, No. 2022-001944 (P.T.A.B. May 21, 2024) ("Panel Decision"), 35–37. Although the Federal Circuit has not yet reviewed this decision, it provides some guidance for satisfying the written description and definiteness requirements for means-plus-function claims directed to antibodies.

Background and Procedural History

The claims of the application at issue (16/803,690 ("the '690 application")) relate to therapeutic methods of using an anti-C5 antibody variant that has increased in vivo half-life. Claim 9 of the '690 application recites:

A method of treating a patient by administering an anti-C5 antibody comprising:
a) means for binding human C5 protein; and
b) an Fc domain comprising amino acid substitutions M428L/N434S as compared to a human Fc polypeptide,
wherein numbering is according to the EU index of Kabat,
wherein said anti-C5 antibody with said amino acid substitutions has increased in vivo half-life as compared to said antibody without said substitutions.

The Examiner rejected claim 9 of the '690 application under the written description requirements of 35 U.S.C. § 112 ¶ 1. Panel Decision at 4. The application's assignee, Xencor Inc., appealed the rejection to the Patent Trial and Appeal Board ("the Board"). Id.

The Board entered new grounds of rejection. In its decision denying Xencor's Request for Rehearing, the Board explained that it found that claim 9 is a means-plus-function claim and determined that "there is only one example disclosed in the Specification of the claimed 'means for binding human C5 protein,' '5G1.1,' and no structure is disclosed for it." See Ex parte Chamberlain, No. 2022-001944 (P.T.A.B. June 1, 2023), 14. The Board also found that Xencor did "not establish that the structure of the 5G1.1 antibody was known at the time the application was filed." Id. The Board further reasoned that the "means for binding human C5 protein" is construed "as covering the binding structure disclosed in the Specification 'and equivalents thereof,'" but that equivalence "cannot be determined for claim 9 because there is no disclosed structure to make that determination." Id. at 13, 14. Subsequently, the Board entered a new ground of rejection holding claim 9 indefinite. Id. at 14–15. The Board also entered other new grounds of rejection and affirmed certain of the Examiner's rejections. Panel Decision at 4–5.

Following Xencor's appeal to the Federal Circuit, the USPTO requested, and was granted, remand for the purpose of "clarify[ing] the Office's position on the proper analysis of 'Jepson-format and means-plus[-]function claims in the field of biotechnology and in particular in the antibody art.'" Id. at 5 (citations omitted).

USPTO Appeals Review Panel's Decision

On remand, the Panel first confirmed that claim 9's recitation of "means for binding human C5 protein" falls under § 112 ¶ 6. See Panel Decision at 30–31. Because the specification's disclosure of anti-C5 antibodies is limited to 5G1.1, the Panel next considered whether this disclosure provides adequate structure for the "means for binding human C5 protein." Reviewing the prior art of record, the Panel determined that "a person of ordinary skill in the art would have understood '5G1.1' to refer to two related antibodies" whose structures were known based on deposited hybridoma and published sequences. Id. at 33, 34. Accordingly, the Panel found "means for binding human C5 protein" definite.

The Panel next considered whether "the Specification must disclose or describe the equivalents of the corresponding structure . . . for a means-plus-function claim limitation under 35 U.S.C. § 112 ¶ 6[] in order to meet the requirements of § 112 ¶ 1 (written description) and ¶ 2 (definiteness)." Id. at 35. The Panel noted that "[b]y the terms of § 112 ¶ 6, what must be 'described in the specification' is 'the corresponding structure, material, or acts' for the 'means . . . for performing a specified function," but the statute "does not state that the Specification must also describe equivalents of that structure." Id. at 36. Additionally, the Panel read the statute to require "a Specification [to] provide a corresponding structure for a recited means-plus-function claim limitation or else the claim is indefinite." Id. Finally, the Panel reasoned that Congress could have drafted the statute to require a description of equivalents if it had so intended and noted the Panel's statutory interpretation is consistent with the Supreme Court's and Federal Circuit's jurisprudence. See id. at 36, 37. The Panel concluded that "it is not necessary for the Specification here to describe equivalents of 5G1.1 to meet the definiteness or written description requirements." Id. at 37. The Panel thus overturned the Board's § 112 ¶ 1 (written description) and ¶ 2 (definiteness) rejections of this limitation. The Panel ultimately maintained the Board's rejection of the application on other grounds.

The per curiam opinion was issued by USPTO Director Kathi Vidal, Commissioner for Patents Vaishali Udupa, and Chief Administrative Patent Judge Scott Boalick. The Panel's decision provides guidance to patent applicants looking to patent antibodies using a means-plus-function format.

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