US Patent Office ARP Affirms the Use of Means-Plus-Function Limitations to Claim Antibodies

In the recent decision Ex parte Chamberlain, Appeal 22-1944 (Xencor), the United States Patent and Trademark Office’s new Appeals Review Panel provided clarity regarding its stance on means-plus-function claims. Its decision underscores the strategic advantage of employing means-plus-function limitations in cases where genus claims are not practicable or otherwise subject to attack under the Supreme Court’s reasoning in Amgen Inc. v. Sanofi.

The United States Patent and Trademark Office (USPTO) Appeals Review Panel (ARP) noted in its decision that “the Director convened this Appeals Review Panel to clarify the Office’s position and issue a revised decision on the proper analysis of Jepson and means-plus-function claims in this case.”[1] The opinion (the first ARP decision since its inception in 2023) was issued by USPTO Director Kathi Vidal, Commissioner for Patents Vaishali Udupa, and Chief Administrative Patent Judge Scott Boalick.

In the decision, the ARP noted that it “disagree[d] with the Board that 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).”[2]

Despite this finding, the ARP nonetheless maintained the rejection of the means-plus-function claim (claim 9) as lacking written description support because it held the preamble reciting a “method of treating a patient” to be limiting and lacking sufficient support in the Specification.[3]

Background

The Xencor case revolves around a patent application (U.S. Application No. 16/803,690) titled “Fc Variants With Altered Binding to FcRn” that was filed by biopharmaceutical company Xencor Inc. Central to the dispute are claim 8—drafted in Jepson format—and claim 9—utilizing means-plus-function language. Claims 8 and 9 are reproduced below (emphasis added).

8. In a method of treating a patient by administering an anti-C5 antibody with an Fc domain, the improvement comprising said Fc domain comprising amino acid substitutions M428L/N434S (…), wherein said anti-C5 antibody with said amino acid substitutions has increased in vivo half-life as compared to said antibody without said substitutions.

9. 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 (…), wherein said anti-C5 antibody with said amino acid substitutions has increased in vivo half-life as compared to said antibody without said substitutions.

During prosecution, the Examiner rejected claims 8-9 for lack of written description support under 35 USC § 112(a) and under the doctrine of obviousness-type double-patenting. Xencor appealed the Examiner’s obviousness-type double-patenting rejection, and the Patent Trial and Appeal Board (PTAB) not only upheld that rejection but also set forth new grounds of rejection under 35 USC § 112(a) and § 112(b).

Xencor subsequently filed a Request for Rehearing. In its request, Xencor contended, among other things, that the preamble of claims 8-9 was not limiting and thus did not require written description support. It also disagreed with the PTAB that claim 9’s means-plus-function limitation rendered the claim indefinite for lack of corresponding structure or that it lacked written description support.

The PTAB reaffirmed these rejections in its decision. Specifically, as to claim 8, the PTAB held that the preamble requiring a “method of treating a patient” was limiting and, thus, claim 8 lacked written description support. As for claim 9, in its decision, the PTAB affirmed the rejection of claim 9, noting that it considered “the recited ‘means for binding human C5 protein’ to be a chemical genus because § 112(f) construes the recited ‘means’ as covering the binding structure disclosed in the Specification ‘and equivalents thereof,’” and “[t]he ‘equivalents thereof’ broadens any structure disclosed in a specification to a group or genus of structures.”[4] Given this, the PTAB found claim 9 was not only indefinite, but also lacked written description support.

Following the PTAB’s final written decision rejecting pending claims 8-9, Xencor appealed the decision to the Federal Circuit. After Xencor filed its Opening Brief, the director of the USPTO moved to remand the case back to the ARP “to ‘clarify the USPTO’s position on the proper analysis of Jepson-format and means-plus-function claims in the field of biotechnology, and particularly in the antibody art,’ and issue ‘a revised decision.’”[5] The Federal Circuit granted the motion to remand.[6]

ARP Decision

In its decision, the ARP largely sided with Xencor by reversing the PTAB’s rejection of claim 9 for indefiniteness and reversing the Examiner's obviousness-type double patenting rejections of claims 8 and 9 over (1) claims 1-5 of the '818 patent and Schwaeble and (2) claim 1 of the ’543 patent and Schwaeble.[7] Ultimately, however, the ARP maintained the PTAB’s rejection of claims 8-9 for lack of written description support solely because it considered the preamble in each claim to be limiting.

As for Jepson claim 8, the ARP expressly held that “[t]he preamble of a Jepson claim is limiting, by necessity, because it defines the scope of the claim.”[8] As such, the ARP held that the preamble language “treating a patient” “is limiting and accordingly requires written description support.”[9] It construed the phrase “treating a patient’ to mean “‘treating all patients and all diseases.’”[10] The ARP relied, among other things, on this preamble language to uphold the PTAB’s written description rejection, noting that the “Specification does not provide adequate written description support for ‘treating a patient,’ as broadly recited in claim 8.”[11]

As for claim 9, the ARP likewise determined that the preamble language “treating a patient” is limiting and that “the Specification does not provide adequate written description support for the full breadth of ‘treating a patient.’”[12]

Despite ultimately upholding the PTAB’s rejection of claim 9 for lack of written description support based on the “treating a patient” preamble language, notably, the ARP held that the means-plus-function limitation in claim 9 (i.e., “means for binding human C5 protein”) not only was definite under 35 USC § 112 ¶2, but that it “is adequately described under 35 U.S.C. § 112 ¶ 1 (written description).”[13] Specifically, the ARP determined that the disclosure of monoclonal antibody 5G1.1 in the Specification provides adequate structure corresponding to the “means for binding human C5 protein,” thereby satisfying the written description requirement and that a person of ordinary skill in the art would understand the meaning of 5G1.1 and thus the limitation “means for binding human C5 protein” is definite.[14]

Moreover, for claim 9, the ARP expressly held, contrary to the PTAB, that the disclosure of equivalents is not necessary to satisfy the written description and indefiniteness requirements for a means-plus-function claim term.[15] Hence, the ARP agreed with Xencor that an antibody claimed using a means-plus-function format could satisfy the written description requirement.

Takeaways

The ARP’s decision in Xencor has significant legal implications for patent practitioners and applicants in the biotechnology and pharmaceutical industry. It provides an avenue to secure patent protection that not only covers an innovator’s biologic but also “equivalents” of that biologic without running afoul of the Supreme Court’s holding in Amgen[16]. Indeed, such a claim occupies a unique space between a “picture” claim and a genus claim thereby providing an applicant an opportunity to cover biosimilars that contain minor modifications as compared to an innovator biologic. Further, since “equivalents” may include molecules that come into existence up to issuance of a patent, there may be an incentive for patent practitioners to keep patent families with means-plus-function claims alive as long as possible to frustrate biosimilar competition.