How Different Claim Construction Standards Can Ultimately Determine the Validity of a Patent

Recently, the Federal Circuit issued a decision in Immunex Corp. v. Sanofi-Aventis U.S. LLC addressing the different claim construction standards used by the Patent Trial and Appeal Board (“PTAB”) (broadest reasonable interpretation (“BRI”) standard) and the district courts (Phillips standard).1 The case stems from three inter partes reviews (“IPRs”)2 that were filed against Immunex Corp.’s (“Immunex”) patent prior to the PTAB’s adoption of the Phillips claim construction standard for interpreting claims in IPRs, post-grant review, and the covered business methods patent proceedings.3

On February 14, 2019, the PTAB held that Immunex’s U.S. Patent No. 8,679,487 (“the ’487 patent”), directed to an isolated “human” antibody that binds to interleukin-4, was invalid as being obvious over a combination of prior art references that did not disclose “human” antibodies.4

The invalidity case turned on whether the claims directed to a “human” antibody could be construed to include “partially-human” antibodies that were present in the prior art. The PTAB applied the BRI standard for claim construction and construed the term “human” antibody to include “partially human” antibodies.5 The PTAB’s construction conflicted with the district court’s construction, which used the Phillips standard, and construed the term “human” to mean “fully human.”6 The Phillips claim construction standard is similar to, but narrower than, the BRI standard, and may result in different outcomes.7,8

Immunex appealed the PTAB’s claim construction ruling to the Federal Circuit but before oral arguments, Immunex filed a terminal disclaimer dedicating the remainder of the ’487 patent’s life to the public.9 In doing so, Immunex argued that when a patent expires during the pendency of an administrative proceeding at the USPTO, or during an appeal, the Court should issue a new construction under the Phillips standard.10 Immunex was likely hoping that the Federal Circuit would use the district court’s construction under Phillips and reverse the PTAB’s finding of invalidity of the ’487 patent.

The Federal Circuit denied the request because Immunex had intentionally forced its patent to expire.11 The Court used the same BRI standard as the PTAB, affirmed the PTAB’s claim construction that a “human” antibody can include a “partially human” antibody, and affirmed the PTAB’s invalidity decision on Immunex’s ’487 patent.12

This case demonstrates why the PTAB’s recent change from BRI to Phillips may provide a greater degree of consistency and predictability to claim construction across different courts. However, it should be noted that the PTAB’s review of Ex Parte Reexaminations and Reissue Examinations still uses the BRI standard for claim construction.


On March 23, 2017, Sanofi-Aventis U.S. LLC, Genzyme Corp., and Regeneron Pharmaceuticals, Inc. (“Sanofi”) filed the first of three IPR petitions (“IPR-1”) against Immunex’s ’487 patent.13,14

Sanofi markets Dupixent, which the FDA approved in 2017 to treat certain adults with a moderate-to-severe eczema and as an add-on maintenance therapy for moderate-to-severe asthma.15 Dupixent contains a human monoclonal antibody of the IgG4 subclass called dupilumab that binds to the Interleukin (“IL”)-4Rα subunit and inhibits IL-4 and IL-13 signaling.16 The ’487 patent is directed to antibodies that bind to the human IL-4 receptor. Claim 1 of the ’487 patent is representative:

  • An isolated human antibody that competes with a reference antibody for binding to human IL-4 interleukin-4 (IL-4) receptor, wherein the light chain of said reference antibody comprises the amino acid sequence of SEQ ID NO:10 and the heavy chain of said reference antibody comprises the amino acid sequence of SEQ ID NO:12.

Two weeks later on April 5, 2017, Immunex filed suit against Sanofi in the Central District of California alleging infringement of the ’487 patent.17

Almost 3-months later, Sanofi filed two additional IPR petitions, IPR-2 and IPR-3, on the ’487 patent on different grounds.


Sanofi’s first two IPRs failed to invalidate the ’487 Patent. In IPR-1, Sanofi alleged all claims of the ’487 patent were invalid under pre-AIA 35 U.S.C. §§102(a) and 102(b) as being anticipated by Regeneron’s own prior art article to Stevens.18 The PTAB denied institution of IPR-1 because Sanofi failed to show that the ’487 patent claims were not entitled to the priority date of an earlier-filed application that predates Stevens.19 The PTAB did not construe the claims in order to render its decision based on priority.20

In Sanofi’s second IPR petition, the PTAB granted institution of the IPR but ultimately found that Sanofi failed to show that the prior art relied on (Immunex’s own patent publication) did not qualify under 35 U.S.C. § 102(e) as being by “another.”21 Likewise, the PTAB did not construe the claims to render its decision.22

Sanofi’s third IPR petition was instituted on the grounds of obviousness over the combination of prior art references to Hart (describing murine antibodies) and Schering-Plough (describing humanized antibodies).23 Sanofi argued that under the USPTO’s BRI standard24 the claim term “human” should mean “partially or fully human.”25 Although the ’487 patent did not expressly define “human” or “human antibody,” Sanofi argued that the specification provides multiple disclosures that human may include “partially human.”26 For example, the ’487 patent states that “[a]ntibodies of the invention include, but are not limited to partially human (preferably fully human) monoclonal antibodies that inhibit a biological activity of IL-4 and also inhibit a biological activity of IL-13.”27 The specification also states that, “Procedures have been developed for generating human antibodies in non-human animals. The antibodies may be partially human, or preferable completely human.”28 Sanofi also argued that one embodiment in the ’487 patent includes a chimeric antibody, which is known to be “partially human,” and that excluding embodiments from the construction of a claim is counseled against as a general principal.29

The PTAB did not find Immunex’s argument to be persuasive that “human” antibodies are distinct from “partially human” antibodies because during prosecution of the ’487 patent, Immunex amended claim 1 by adding in the term “human” to recite “an isolated human antibody” and cancelled dependent claim 11 that recited a “human, partially human, humanized, or chimeric antibody.”30 The PTAB recognized that the term “human” was added to claim 1 to overcome prior art directed to murine antibodies (e.g., mouse antibodies), but that nothing indicated that applicants added “human” to limit the scope of the claims to fully human antibodies.31 Further, the PTAB reasoned that claim 11 did not identify distinct classes of antibodies but rather described overlapping and even the same antibody.32 The PTAB explained that in cancelled claim 11, “chimeric antibodies are partially human antibodies” and “the specification of the ’487 patent equates chimeric and humanized antibodies.”33 The PTAB concluded that “in light of the ambiguity and overlap between the various claim terms [of claim 11], it is reasonable to interpret “human” and “partially human” as similarly overlapping, particularly given the interchangeable use of the terms.”34 The PTAB also reasoned that after Immunex amended claim 1 to a “human antibody” the Examiner continued to characterize the claims as a “humanized” antibody that included both fully and partially human antibodies, and Immunex never corrected the Examiner’s interpretation.35 Immunex further argued that in a parallel proceeding, the district court construed the term “human antibody” to mean a “fully human” antibody.36 The PTAB was not persuaded because of the PTAB’s used of the broader BRI standard for claim construction whereas the district court used the narrower Phillips standard (i.e., ordinary and customary meaning).37

Persuaded by Sanofi, the PTAB construed the claim limitation “human antibody” to encompass both “fully human and partially human antibodies.”38 Armed with this broader construction, the PTAB determined that Immunex’s ’487 patent was invalid over Hart (describing murine antibodies) and Schering-Plough (describing humanized antibodies).39


On April 5, 2017, and concurrent with IPR-1, Immunex sued Sanofi alleging patent infringement of the ’487 patent in the Central District of California.40 Over a year later, on August 24, 2018, the district court issued a claim construction ruling for the term “human.”41 Unlike the PTAB, the Court was persuaded by events that transpired during prosecution of the ’487 patent wherein claim 1 originally read “an isolated antibody” and dependent claim 11 limited claim 1 to “wherein said isolated antibody is a human, partially human, humanized, or chimeric antibody.”42 The Court noted that in response to a prior art rejection, Immunex cancelled claim 11 and amended claim 1 to read, “[a]n isolated human antibody.”43 The Court stated that broadening the term “human” to include “partially human” would be inconsistent with Immunex’s claim amendment and would be improperly importing embodiments from the specification into the claims.44

The claim construction order issued two months before the oral hearing in IPR-2 and -3, and the parties discussed it in their briefing and at oral argument before the PTAB. The PTAB did not adopt the district court’s construction as it is not bound by a previous judicial construction of a claim term45, and concluded that it reached a different interpretation “based on the broader applicable case law” under the BRI standard.46


On appeal, Immunex argued only that the PTAB erred in the construction of “human” antibody in IPR-3.47 Sanofi cross-appealed, contending that the PTAB erred in IPR-2 regarding whether the cited prior art to was § 102(e) prior art “by another.”48 The Federal Circuit consolidated the appeals.49

At the time the IPRs were filed in 2017, two different standards for claim construction applied. The PTAB applied the BRI standard, whereas the Courts applied the narrower Phillips standard.50 Under the BRI standard, “words of the claim must be given their plain meaning, unless such meaning is inconsistent with the specification. The plain meaning of a term means the ordinary and customary meaning given to the term by those of ordinary skill in the art at the time of the invention.”51 The best source for determining the meaning of a claim term is the specification.52 Extrinsic evidence (i.e., dictionaries and expert testimony) may also be considered but only secondarily and in a limited manner to ensure that the interpretation is the broadest reasonable interpretation, not just the broadest interpretation.53

The Phillips standard differs by requiring that claims be given their ordinary and customary meaning to a person of ordinary skill in the art at the time of the invention, by considering the claims, specification, and prosecution history, as well as evidence extrinsic to the patent, when construing patent claims.54 Under Phillips, “the specification ‘is always highly relevant to the claim construction analysis. Usually, it is dispositive . . . .’”55 Although both standards have similarities, different outcomes have resulted.56

Interestingly, when a patent expires during the pendency of an administrative proceeding at the USPTO, the USPTO may switch the claim construction standard from BRI to Phillips.57 Likewise, when a patent expires during an appeal from the PTAB, the Federal Circuit applies the Phillips standard.58

Immunex attempted to capitalize on this switching during the Federal Circuit appeal by filing a terminal disclaimer with the USPTO on its ’487 patent surrendering the remaining term of the patent.59 Immunex then filed a Citation of Supplemental Authority under Federal Rule of Appellate Procedure 28(j) and informed the Federal Circuit of its terminal disclaimer and requested that the claim construction standard be changed from the BRI to Phillips.60 Immunex cited Wasica Fin. GmbH v. Cont’l Auto. Sys., Inc., 853 F.3d 1272, 1279 (Fed. Cir. 2017) for the proposition that the expiration status of a patent informs the applicable claim construction standard that the Federal Circuit uses in reviewing the PTAB’s patentability determination.61 The Federal Circuit noted, however, that Immunex did not request further briefing on the implications of a possible pivot to a Phillips construction, and beyond noting that a district court had already more narrowly construed the claim term at issue, Immunex did not advance any arguments that the Federal Circuit review should come out differently under Phillips.62

The Federal Circuit stated that although the PTAB and the Federal Circuit have applied the Phillips standard when a patent expires before a final judgment (citing Apple Inc. v. Andrea Elecs. Corp., 949 F.3d 697, 707 (Fed. Cir. 2020)), the Court does not read Andrea Elecs. to mean that Phillips should apply whenever a patent expires, “at any time and for any reason.”63 Here, after the parties fully briefed the claim construction under the BRI standard, then Immunex filed the terminal disclaimer.

The Federal Circuit reviewed the PTAB’s claim construction, de novo, under the BRI standard and agreed with the PTAB that the intrinsic evidence supports the correctness of the PTAB’s construction.64 First, the Court examined the claim language itself and determined that nothing in the claim’s language restricts “human antibodies” to those that are fully human.65 Second, the Court found no express definition of a “human antibody” in the specification, but the usage of “human” throughout the specification confirms its broadest reasonable interpretation, that “human antibodies” is a broad category encompassing both partially and completely human antibodies.66 Third, the prosecution history supports the Board’s construction because nothing indicates that Immunex added “human” to limit the scope to fully human.67 Fourth, in a post-amendment office action, the Examiner expressly wrote that the amended “human” antibodies encompassed “humanized” antibodies and Immunex made no effort to disabuse the Examiner of this understanding.68 While hardly dispositive, the Federal Circuit stated that this uncontested characterization is consistent with the Board’s construction.69 Fifth, Immunex’s extrinsic evidence (testimony of its two experts) was considered by the Board but nothing credible was found to call its interpretation into question.70 Furthermore, the Court stated that extrinsic evidence may be of assistance if the intrinsic record is equivocal, in which the Court would be looking for further guidance.71

Using the BRI standard, the Federal Circuit affirmed that the PTAB’s construction for “human” antibodies included “partially human” antibodies and affirmed that Immunex’s ’487 patent was invalid.72

As a result of different tribunals using different claim construction standards, and the resulting inconsistencies therefrom, on May 9, 2018 the USPTO issued a notice of proposed rulemaking to adopt the Phillips standard of interpreting disputed terms in claims in IPRs, post-grant review, and covered business method review proceedings before the PTAB73. The rule was adopted on November 13, 2018.74


The PTABs adoption of the Phillips standard will likely result in increased harmonization with district court decisions. There are at least eight prior cases whereby switching the claim construction standard from BRI to Phillips resulted in a different outcome.75 The Immunex case adds to this list. However, since the PTAB adopted the Phillips standard of claim construction on November 13, 2018, this practice of switching legal standards will soon come to an end. Patent owners and challengers should enjoy one legal standard for claim construction providing certainty that a different legal standard will not be used when a patent expires during the PTAB proceeding, in a district court case, or on appeal. Nonetheless, a party wishing to take advantage of the BRI standard may still pursue an Ex Parte Reexamination or Reissue Examination.

1Immunex Corp. v. Sanofi-Aventis U.S. LLC, 977 F.3d 1212 (Fed. Cir. 2020) (“Immunex Fed. Cir.”).
2Sanofi-Aventis U.S. LLC, et al. v. Immunex Corp., IPR2017-01129 (“IPR-1”), Paper 1, Petition, p.1 (P.T.A.B. Mar. 23, 2017); Sanofi-Aventis U.S. LLC, et al. v. Immunex Corp., IPR2017-01179 (“IPR-2”), Paper 1, Petition, p.1 (P.T.A.B. Jul. 28, 2017); Sanofi-Aventis U.S. LLC, et al. v. Immunex Corp., IPR2017-01884 (“IPR-3”), Paper 1, Petition, p.1 (P.T.A.B. Jul. 31, 2017).
3See 83 Fed. Reg. 21,221, Changes to the Claim Construction Standard for Interpreting Claims in Trial Proceedings Before the Patent Trial and Appeal Board (May 9, 2018). The new rule went into effect on Nov. 13, 2018 but did not apply to petitions filed before that date. See 83 Fed. Reg. 51,340 (Nov. 13, 2018).
4IPR-3, Paper 96, Final Written Decision, p.1 (P.T.A.B. Feb.14, 2019).
5Id. at 6-7.
6Immunex Corp. v. Sanofi, No. CV 17-02613 (“Immunex C.D. Cal.”) SJO (PLAx), 2018 U.S. Dist. LEXIS 146563, at *42 (C.D. Cal. Aug. 24, 2018).
7See Facebook, Inc. v. Pragmatus AV, LLC, 2014 WL 4454956, 4 (Fed. Cir. 2014) (nonprecedential).
8The trial date in the district court case was rescheduled for February 23, 2021, but Immunex submitted a notice on October 23, 2020 that they are considering whether to seek further appellate review of the Federal Circuit’s decision (due by November 27, 2020) and that the trial date could be vacated. Immunex C.D. Cal., ECF No. 397 (Oct. 23, 2020).
9Immunex Fed. Cir. at 1212.
13IPR-1, Paper 1, Petition, p.1 (P.T.A.B. Mar. 23, 2017).
14Immunex was acquired by Amgen in 2002. See The New York Times, July 17, 2002, available at
15See Dupixent® Product Label and Full Prescribing Information, p.1, Revised March 2017, available at
16Id. at 9.
17Immunex C.D. Cal., ECF No. 1, Complaint at 2 (Apr. 5, 2017).
18IPR-1, Paper 1, Petition, p.3 (P.T.A.B. Mar. 23, 2017).
19Id., Paper 19, Decision, p.7 (P.T.A.B. Oct. 4, 2017).
20Id. at 6.
21IPR-2, Paper 88, Final Written Decision, p.24 (P.T.A.B. Feb. 15, 2018).
22Id. at 6.
23 IPR-3, Paper 14, Decision, pp.1,13,14 (P.T.A.B. Feb. 15, 2018).
24See 37 C.F.R. § 100(b); Cuozzo Speed Techs., LLC v. Lee, 136 S. Ct. 2131, 2142 (2016) (affirming applicability of broadest reasonable construction standard to inter partes review proceedings).
25IPR-3, Paper 1, Petition, p.20 (P.T.A.B. Jul. 31, 2017).
26Id. at 24-25.
27Id.; ’487 patent, 20:57-60.
28’487 patent, 21:1-2.
29IPR-3, Paper 1, Petition, p.21 (P.T.A.B. Jul. 31, 2017) (citing Nissan N. Am., Inc. v. Norman IP Holdings, LLC, IPR2014-00564, Paper 36 at 7 (P.T.A.B. Aug. 26, 2015)); Oatey Co. v. IPS Corp., 514 F.3d 1271, 1276-77 (Fed. Cir. 2008).
30Id. at 9.
31Id. at 11.
32Id. at 10.
35Id. at 11-12.
36Id. at 13-14.
37Id. at 14.
38Id., Paper 96, Final Written Decision, p.14 (P.T.A.B. Feb. 14, 2019).
39Id. at 14.
40Immunex C.D. Cal., ECF No. 1, p.2 (C.D. Cal. Apr. 5, 2017).
41Id., ECF No. 334, pp.20-21 (C.D. Cal. Aug. 24, 2018).
42Id. at 11-12.
44Id. at 20.
45See Immunex Fed. Cir. at *21.
46IPR-3, Paper 96, Final Written Decision, p.14 (P.T.A.B. Feb. 14, 2019).
47Immunex Fed. Cir. at *6.
48Id. at *6-7.
49Id. at *7.
50K. Greenleaf et al., “How Different Are the Broadest Reasonable Interpretation and Phillips Claim Construction Standards?” Intellectual Property Owners Association, 2018, p.1, available at (“Greenleaf”).
51MPEP § 2111.01 (9th ed. Rev. 10, Jun. 2020).
53See PPC Broadband, Inc. v. Corning Optical Communications RF, LLC, 815 F. 3d 747, 755 (Fed. Cir. 2016).
54Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005) (en banc).
55Id. (quoting Vitronics Corp. v. Conceptronic, Inc., 90 F.3d 1576, 1582 (Fed. Cir. 1996)).
56Greenleaf at 9.
57See MPEP § 2258.G (ex parte reexamination) and 37 C.F.R. § 42.100, 200, and 300 (AIA trials).
59See Immunex Fed. Cir. at *7.
61Id. at *8.
62Id. at *9, n.3.
63Id. at *9.
65Id. at *10.
66Id. at *11-12.
67Id. at *13-14.
68Id. at *17.
70Id. at *18.
71Id. at *19 (“A court may look to extrinsic evidence so long as the extrinsic evidence does not contradict the meaning otherwise apparent from the intrinsic record. Accordingly, the intrinsic record trumps.”).
72Id. at *21.
7383 Fed. Reg. 21,221 (May 9, 2018).
7483 Fed. Reg. 51,340 (Nov. 13, 2018).
75Greenleaf at 4-6.