Federal Circuit disposition — 24-1870

United States Court of Appeals
for the Federal Circuit
______________________
IN RE: XENCOR, INC.,
Appellant
______________________
2024-1870
______________________
Appeal from the United States Patent and Trademark
Office, Patent Trial and Appeal Board in No. 16/803,690.
______________________
Decided: March 13, 2025
______________________
J ULIE S. GOLDEMBERG, Morgan, Lewis & Bockius LLP,
Philadelphia, PA, argued for appellant. Also represented
by MICHAEL J. A BERNATHY, CHRISTOPHER J OHN B ETTI ,
MARIA DOUKAS, AMANDA SCOTT WILLIAMSON, Chicago, IL;
WILLIAM R. PETERSON, Houston, TX.
PETER J OHN SAWERT, Office of the Solicitor, United
States Patent and Trademark Office, Alexandria, VA, ar-
gued for appellee Coke Morgan Stewart. Also represented
by MARY L. KELLY, AMY J. NELSON, F ARHEENA YASMEEN
R ASHEED.
______________________
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IN RE: XENCOR, INC. 2
Before HUGHES and STARK, Circuit Judges, and
SCHROEDER , District Judge.1
SCHROEDER , District Judge.
Xencor, Inc. (“Xencor”) appeals a decision of the Ap-
peals Review Panel (“ARP”)2 of the Patent Trial and Appeal
Board (“Board”) rejecting the claims of its patent applica-
tion as unpatentable for lack of written description. Spe-
cifically, Xencor contends that the Board and the ARP
erred by construing part of one claim’s preamble as limit-
ing and requiring written description for the Jepson claim
preamble of another claim. The Director of the United
States Patent and Trademark Office (“Director”) responds
that the preamble should be read as a whole, with all parts
limiting and requiring written description, and neither the
specification nor Xencor’s extrinsic evidence established
that the relevant Jepson claim limitation had sufficient
written description.
We hold that the limiting preamble of a Jepson claim
must be supported with sufficient written description, and
what constitutes sufficiency varies depending on the
knowledge of the pertinent person of ordinary skill in the
art. A patentee has the burden of providing written de-
scription; in a Jepson claim, that burden extends to the lim-
iting preamble. We additionally hold that substantial
evidence supports the Board’s finding that Xencor failed to
1 The Honorable Robert W. Schroeder III, District
Judge, United States District Court for the Eastern Dis-
trict of Texas, sitting by designation.
2 The ARP—comprised of members of the Patent
Trial and Appeal Board including the Director of the
United States Patent and Trademark Office, the Commis-
sioner for Patents, and the Chief Judge of the Board—is
available to review Board decisions in ex parte appeals,
reexamination appeals, and reissue appeals.
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IN RE: XENCOR, INC. 3
provide adequate written description for its Jepson claim
and for its other claim, the preamble of which we agree
with the Board and the ARP is limiting. Accordingly, we
affirm.
B ACKGROUND
Anti-C5 antibodies are monoclonal antibodies that bind
to C5, a protein that performs complement activation. One
specific type of monoclonal antibody, 5G1.1, can bind hu-
man C5 protein to block the progression of the complement
cascade. A version of 5G1.1, called eculizumab, was used
in clinical trials and had a known sequence. At the time of
the patent application, eculizumab had been used to treat
paroxysmal nocturnal haemoglobinuria (“PNH”), “a
chronic blood disease caused by a defective enzyme that
leads to a lack of protective natural complement inhibi-
tors,” and was being studied in “the treatment of asthma
and transplantation.” J.A. 206. Xencor additionally con-
tends that anti-C5 antibodies have an anti-inflammatory
effect and may be useful in treating various autoimmune
disorders.
A. The Relevant Claims
The application at issue, U.S. Patent Application No.
16/803,690 (the “’690 application”), is a continuation appli-
cation and has an earliest claimed priority date of Febru-
ary 25, 2008.3 The ’690 application asserts that modifying
antibodies with certain amino acid substitutions provides
for longer staying power in the body and reduces the need
for more frequent treatment. For instance, the specifica-
tion states “[t]herapeutics against these targets are fre-
quently involved in the treatment of autoimmune diseases
and require multiple injections over long time periods.
3 The operative version of the patent application,
and the version we refer to throughout, is the version as
amended after an initial rejection in August 2020.
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IN RE: XENCOR, INC. 4
Therefore, longer serum half-lives and less frequent treat-
ments, brought about from the variants of the present in-
vention, are particularly preferred.” J.A. 157. It provides
one example of an anti-C5 antibody, 5G1.1.
There are two claims at issue on appeal, claim 8 (a Jep-
son claim) and claim 9 (a method claim).
8. In a method of treating a patient by administer-
ing an anti-C5 antibody with an Fc domain, the im-
provement comprising
said Fc domain comprising amino acid sub-
stitutions 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.
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 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 com-
pared to said antibody without said
substitutions.
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IN RE: XENCOR, INC. 5
J.A. 903 (emphasis added). As relevant here, the claims
were rejected by the examiner in March 2021 for lack of
written description.
B. Procedural History
Xencor appealed the examiner’s finding to the Board,
which issued its initial decision on January 10, 2023. Rel-
evant here,4 the Board concluded that the preambles to
claims 8 and 9 were limiting—but did not specifically grap-
ple with case law saying preambles are not always limit-
ing—and that Xencor had not shown that the application
had sufficient written description for either claim. The
Board also determined that Xencor had not demonstrated
that anti-C5 antibodies or methods of treating patients
with anti-C5 antibodies were well-known in the art.
Xencor petitioned for reconsideration and the Board is-
sued a second decision, finding against Xencor on the same
grounds. Of note, on rehearing, the Board further consid-
ered whether the preamble of claim 8 was limiting and held
that it was.
The decision on rehearing was appealed to us. See In
re Xencor, No. 23-2048. Before it could be heard, the Patent
Office asked us to remand the case for consideration by the
ARP. Id. at ECF No. 32. We agreed and remanded the case
for this purpose. Id. at ECF No. 35.
The ARP issued its decision on May 21, 2024. The ARP
first addressed whether written description was required
for Jepson claim preambles generally and found that it
was, because Jepson preambles define the scope of the
4 The Board’s decisions were superseded by the deci-
sion of the ARP, except to the extent that the ARP adopted
the findings of the Board. Because most of what we are
reviewing is the decision of the ARP, we discuss the Board’s
decisions only insofar as they were adopted by the ARP.
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IN RE: XENCOR, INC. 6
claim. It then, however, considered whether the preamble
language of “treating a patient,” even without the Jepson
claim format, was limiting. It found that “‘treating a pa-
tient’ is necessary to give life, meaning, and vitality to both
the ‘increased in vivo half-life’ limitation recited in the body
of the claim, and also to ‘administering,’ which is the sole
method step recited in the claim.” J.A. 13. The ARP then
applied its analysis to the same language in the non-Jepson
claim 9. The ARP found that the rest of the language in
claims 8 and 9, as well as the specification, indicated that
“treating a patient” should be considered limiting and that
this language was necessary to understanding the scope of
the claims.
The ARP then turned to whether the claims had suffi-
cient written description. It first found that claim 8 lacked
written description because the specification did not pro-
vide a representative number of species to sufficiently sup-
port the broad genus of anti-C5 antibodies being claimed.
The specification only disclosed one anti-C5 antibody,
5G1.1, which the ARP found was insufficient given the
“various specificities and epitopes” of the genus. J.A. 22.
The ARP also adopted the Board’s findings that Xencor’s
expert was not credible and that Xencor had not demon-
strated that anti-C5 antibodies were well-known and did
not require further support in the specification.
The ARP then turned to the claim language “treating a
patient” and found that it was not supported with adequate
written description. It found that “[t]he Specification does
not describe what patients with what diseases or condi-
tions can be successfully treated with an anti-C5 anti-
body . . . . Nor is there a single working example describing
treatment of patients with a disease or condition with an
anti-C5 antibody possessing the claimed Fc modifications.”
J.A. 26. The limited disclosure of three potential uses, the
ARP held, was inadequate to demonstrate possession of
“treating a patient” with the claimed anti-C5 antibodies. It
then adopted the same reasoning it used in claim 8 for
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IN RE: XENCOR, INC. 7
claim 9. The ARP noted that while claim 9 was directed
only to 5G1.1, the specification of the ’690 application did
not provide any examples of treating patients with 5G1.1
or any other written description support even for the single
named anti-C5 antibody.
Xencor timely appealed the decision of the ARP.5
L EGAL STANDARDS
“[W]e review the Board’s legal determinations de novo
and its factual findings for substantial evidence.”6 See Al-
mirall, LLC v. Amneal Pharms. LLC, 28 F.4th 265, 271
(Fed. Cir. 2022). “A finding is supported by substantial ev-
idence if a reasonable mind might accept the evidence as
adequate to support the finding.” In re Couvaras, 70 F.4th
1374, 1378 (Fed. Cir. 2023). Sufficiency of written descrip-
tion is a question of fact. See Knowles Elecs. LLC v. Cirrus
Logic, Inc., 883 F.3d 1358, 1365 (Fed. Cir. 2018). Claim
construction, however, is a question of law. E.g., Teva
Pharms. USA, Inc. v. Sandoz, Inc., 574 U.S. 318, 332–33
(2015). Finally, we “defer to the Board’s findings concern-
ing the credibility of expert witnesses.” Incept LLC v. Pal-
ette Life Scis., Inc., 77 F.4th 1366, 1377 (Fed. Cir. 2023).
“What is required to meet the written description re-
quirement ‘varies with the nature and scope of the inven-
tion at issue, and with the scientific and technologic
knowledge already in existence.’” Juno Therapeutics, Inc.
v. Kite Pharma, Inc., 10 F.4th 1330, 1335 (Fed. Cir. 2021)
(quoting Capon v. Eshhar, 418 F.3d 1349, 1357 (Fed. Cir.
2005)). “Whether to treat a preamble as a limitation is a
determination ‘resolved only on review of the entire[] . . .
5 The Board had jurisdiction under 35 U.S.C.
§ 134(a) and we have jurisdiction under 35 U.S.C. § 141(a).
6 The Director states that the standard of review of
the ARP’s decisions is the same as for decisions from the
Board. Xencor does not disagree. Nor do we.
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IN RE: XENCOR, INC. 8
patent to gain an understanding of what the inventors ac-
tually invented and intended to encompass by the claim.’”
Catalina Mktg. Int’l, Inc. v. Coolsavings.com, Inc., 289 F.3d
801, 808 (Fed. Cir. 2002) (alteration in original) (quoting
Corning Glass Works v. Sumitomo Elec. U.S.A., Inc.,
868 F.2d 1251, 1257 (Fed. Cir. 1989)). “[T]he mere fact
that a structural term in the preamble is part of the claim
does not mean that the preamble’s statement of purpose or
other description is also part of the claim.” Marrin v. Grif-
fin, 599 F.3d 1290, 1295 (Fed. Cir. 2010). That is, “where
a patentee defines a structurally complete invention in the
claim body and uses the preamble only to state a purpose
or intended use for the invention, the preamble is not a
claim limitation.” Rowe v. Dror, 112 F.3d 473, 478
(Fed. Cir. 1997). However, we do read the preamble as lim-
iting “[i]f the claim preamble, when read in the context of
the entire claim, recites limitations of the claim, or, if the
claim preamble is ‘necessary to give life, meaning, and vi-
tality’ to the claim.” Pitney Bowes, Inc. v. Hewlett-Packard
Co., 182 F.3d 1298, 1305 (Fed. Cir. 1999) (citations omit-
ted).
In a Jepson claim, a patentee uses the preamble to re-
cite “elements or steps of the claimed invention which are
conventional or known.” 37 C.F.R. § 1.75(e) (1996). “[T]his
court has held that Jepson claiming generally indicates in-
tent to use the preamble to define the claimed invention,
thereby limiting claim scope.” Catalina Mktg. Int’l,
289 F.3d at 808 (collecting cases).
DISCUSSION
Before us, Xencor argues that the method claim’s pre-
amble of “treating a patient” is not limiting, that the pre-
amble of the Jepson claim does not require written
description, and that in the alternative, written description
was satisfied for the preambles of both claims. We first ad-
dress the method claim and then the Jepson claim.
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IN RE: XENCOR, INC. 9
Claim 9
The preamble of claim 9 recites “[a] method of treating
a patient by administering an anti-C5 antibody compris-
ing,” and the first question we must address is whether the
phrase “treating a patient” is limiting here. Xencor agrees
that the “administering” portion of the term is limiting but
contends that we should deconstruct the preamble and find
all other parts of it are non-limiting. Specifically, Xencor
argues that the “treating a patient” portion is not limiting
because “administering” inherently includes “administer-
ing to a patient” and nothing else in the claim relies upon
treatment or a patient. Accordingly, it contends that the
Board erred in holding that “treating a patient” is neces-
sary to give life, meaning, and vitality to the claim. Xencor
further argues that the only portion of the preamble that
requires adequate written description is the portion that is
limiting; that is, the requirement that an anti-C5 antibody
is administered. Xencor also argues in the alternative that
if we find “treating a patient” to be limiting, there is ade-
quate written description for the limitation. The Director
responds that “treating a patient” is not merely a state-
ment of purpose but is necessary to give meaning to the
claim, particularly because the claim associates a thera-
peutic use with the “increased in vivo half-life” of the anti-
bodies.
1
We first address whether “treating a patient” is limit-
ing in the preamble of claim 9.7
As Xencor argues, the different sections of a preamble
may be considered independently. See Marrin, 599 F.3d
at 1295. A preamble or a portion of it is limiting when
7 Most of the ARP’s analysis regarding claim 9’s lim-
itations relies on its discussion of claim 8. We therefore
cite to the claim 8 section for this discussion as needed.
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IN RE: XENCOR, INC. 10
other parts of the patent’s claims rely on predicates in the
preamble, or when the preamble is otherwise necessary to
give “life, meaning, and vitality” to the claim language.
E.g., Eli Lilly & Co. v. Teva Pharms. Int’l GmbH, 8 F.4th
1331, 1342 (Fed. Cir. 2021). It should not be read as limit-
ing, on the other hand, when it merely gives a statement of
purpose or intended result. E.g., Bristol-Myers Squibb Co.
v. Ben Venue Lab’ys, Inc., 246 F.3d 1368, 1375–76
(Fed. Cir. 2001).
In Rapoport v. Dement, 254 F.3d 1053, 1056, 1059
(Fed. Cir. 2001), we found that the preamble language “[a]
method for treatment of sleep apneas comprising admin-
istration of a [therapeutically effective regimen]” was nec-
essary to give meaning to the limitation “to a patient in
need of such treatment.” And in Jansen v. Rexall Sun-
down, Inc., 342 F.3d 1329, 1330, 1332–33 (Fed. Cir. 2003),
we held that the preamble language of “[a] method of treat-
ing or preventing macrocytic-megaloblastic anemia in hu-
mans which anemia is caused by either folic acid deficiency
or by vitamin B 12 deficiency which comprises” was limiting
because the claim then recited a “human in need thereof,”
and the “need” linked back to the previously recited ane-
mia. “In both cases,” we found, “the claims’ recitation of a
patient or a human ‘in need’ gives life and meaning to the
preambles’ statement of purpose.” Id. at 1333.
Similarly, “preamble language will [also] limit the
claim if it recites not merely a context in which the inven-
tion may be used, but the essence of the invention without
which performance of the recited steps is nothing but an
academic exercise.” Boehringer Ingelheim Vetmedica, Inc.
v. Schering-Plough Corp., 320 F.3d 1339, 1345 (Fed. Cir.
2003). In Boehringer, the language of the preamble did not
provide an antecedent basis for other parts of a claim. Id.
Rather, it provided the “raison d’être of the claimed method
itself” because without the preamble language, the claim
did not make sense—“[d]ivorced from the process of grow-
ing and isolating virus, the claimed method reduces to
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IN RE: XENCOR, INC. 11
nothing more than a process for producing cytopathic ef-
fects in sheets of cultured MA–104 cells[—]a process whose
absence of fathomable utility rather suggests the academic
exercise.” Id.
Here, we agree with the Director that the preamble
term “treating a patient by” is limiting. First, it is im-
portant that Xencor does not dispute that the second part
of the preamble, “administering an anti-C5 antibody,” is
limiting. The claim language refers back to this section of
the preamble—“wherein said anti-C5 antibody with said
amino acid substitutions has increased in vivo half-life as
compared to said antibody without said substitutions.” At
least one portion of the preamble is therefore limiting. Alt-
hough we may split a preamble into limiting and non-lim-
iting parts, and have done so in cases such as TomTom, Inc.
v. Adolph, 790 F.3d 1315, 1323–24 (Fed. Cir. 2015), the
preamble here “cannot be neatly packaged into two sepa-
rate portions.” Bio-Rad Lab’ys, Inc. v. 10X Genomics Inc.,
967 F.3d 1353, 1371 (Fed. Cir. 2020). Here, the phrase
“treating a patient” is directly connected with the word “by”
to the phrase “administering an anti-C5 antibody.” And
given our “disinclination” to “splic[e]” a preamble into lim-
iting and non-limiting parts, id. at 1371, this lends cre-
dence to the argument that the entire preamble should be
considered limiting.
Second, we do not find convincing Xencor’s contention
that “administering an anti-C5 antibody” inherently in-
cludes a patient. Rather, when the claim is read as a
whole, the more reasonable reading is that both sections of
the preamble, the “administering” part and the “treating a
patient” part, give color and meaning to the other. See
Storage Tech. Corp. v. Cisco Sys., Inc., 329 F.3d 823, 831
(Fed. Cir. 2003). The treating of the patient is done by ad-
ministering the anti-C5 antibody. This is not a mere state-
ment of purpose or a statement of intended result that does
not affect the performance of the claimed method. See, e.g.,
Bristol-Myers Squibb, 246 F.3d at 1375–76. As the ARP
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IN RE: XENCOR, INC. 12
noted, the claim “lacks a specifically recited dosage and
rate,” which means “a person of ordinary skill in the art
reading the claims would have to read ‘increased in vivo
half-life’” in light of “treating a patient” to make sense of
the scope of the claim. J.A. 14. The specification discloses
that “[t]he exact dose will depend on the purpose of the
treatment” and on characteristics of the patient. J.A.
175–76 (¶ 187). “[T]reating a patient” therefore gives life
to “administering,” the sole method step otherwise recited
in the claim. J.A. 13.
Third, as the ARP and the Board found, the language
in the preamble provides a raison d’être for the claim. An
increased in vivo half-life (a) only makes sense with respect
to a living being, because it could not otherwise be “in vivo,”
and (b) has a specific utility with respect to treatment.
When a patient is treated with a modified anti-C5 anti-
body, the treatment lasts longer, allowing the treatment to
be administered less frequently. The preamble therefore
informs the meaning of the claim language. See generally
Deere & Co. v. Bush Hog, LLC, 703 F.3d 1349, 1358
(Fed. Cir. 2012) (concluding “rotary cutter deck” in the pre-
amble informed the meaning of the “torsional stiffness”
limitation). Otherwise, performing the claim would be, as
we said in Boehringer, a mere “academic exercise.”
320 F.3d at 1345; see also Eli Lilly, 8 F.4th at 1341.
Finally, the specification discloses that “[t]he admin-
istration of antibodies and Fc fusion proteins as therapeu-
tics requires injections with a prescribed frequency
relating to the clearance and half-life characteristics of the
protein. Longer in vivo half-lives allow more seldom injec-
tions or lower dosing, which is clearly advantageous.” J.A.
131 (¶ 5). The ARP credited the Board’s reference to this
section of the specification and “not[ed] repeated reference
to beneficial use of the invention as applied to antibodies in
clinical trials or otherwise intended for therapeutic
use/treatment.” J.A. 13. In this way, the specification
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IN RE: XENCOR, INC. 13
gives further color to the language of the claims and the
understanding we have of the language as limiting.
The ARP therefore correctly determined that “treating
a patient” is limiting in the context of the claim 9 preamble.
2
We next address whether the ’690 application satisfies
the written description requirement for “treating a pa-
tient.” Substantial evidence supports the ARP’s determi-
nation that it does not.
To assess whether the written description support for
“treating a patient” is sufficient, it is necessary to under-
stand the scope of this limitation. The ARP acknowledged
Xencor’s argument that “treating” does not require a par-
ticular effectiveness or result, and we agree. But while no
specific amount of efficacy is claimed, and therefore no spe-
cific amount of efficacy requires written description sup-
port, the ARP also correctly observed that the application
“does not define the term ‘treating,’ and it does not describe
or provide any data associated with treating any patient
with any disease or condition with any anti-C5 antibody,
including an anti-C5 antibody with the claimed Fc modifi-
cations.” J.A. 16. Because the specification did not limit
the treatment to any specific disease, “‘treating a patient’
means ‘treating all patients and all diseases.’” J.A. 18. We
agree with this analysis as well.
The ARP then comprehensively addressed whether
there was written description for treating a patient:
The Specification does not describe what patients
with what diseases or conditions can be success-
fully treated with an anti-C5 antibody possessing
the claimed Fc modifications. Nor is there a single
working example describing treatment of patients
with a disease or condition with an anti-C5 anti-
body possessing the claimed Fc modifications. At
best, the Specification lists three classes of
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IN RE: XENCOR, INC. 14
diseases/conditions that might benefit from admin-
istration of various antibodies with an Fc modifica-
tion, and lists various unmodified antibodies,
including an anti-C5 antibody (5G1.1), that could
be modified and used to that end.
J.A. 26. This disclosure, it found, was “inadequate to
demonstrate possession of a method of treating any partic-
ular disease/condition with the claimed anti-C5 antibodies,
let alone all diseases/conditions within the three enumer-
ated classes.” J.A. 26–27. Specific to claim 9, which is lim-
ited to the anti-C5 antibody 5G1.1 and equivalents thereof,
the ARP found that the specification likewise did not
demonstrate possession of even the use of 5G1.1 in treating
a patient—“the Specification does not describe treating any
disease or condition with an anti-C5 antibody, and merely
mentions three general classes of diseases/conditions as
possible avenues to pursue.” J.A. 38.
Substantial evidence supports this finding. For in-
stance, as the ARP stated, the specification does not in-
clude any example of treating a disease or condition with
an anti-C5 antibody. This is in comparison to other exam-
ples in the specification, such as a description of how to ad-
minister IgG antibodies in cancer treatment. Moreover,
Xencor only presented evidence of trials—that had already
been discontinued when they were submitted—studying
the use of eculizumab, which was not sufficient to show
eculizumab was used to treat those diseases, let alone all
diseases.
Xencor does not point to any error of fact the Board or
the ARP made.8 Instead, it reiterates its argument that
8 Neither party suggests that the originally filed
claims provide written description support for the limita-
tions at issue. Allergan USA, Inc. v. MSN Lab’ys Priv. Ltd.,
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IN RE: XENCOR, INC. 15
the “claim does not require the treatment to be effective,”
that the claim merely requires the intent of treatment. Ap-
pellant’s Opening Br. at 30–31. Contrary to Xencor’s argu-
ment, the ARP did not import any requirements, including
efficacy. The ARP merely required that the application
demonstrate that the applicant had possession of a method
of treating a patient with 5G1.1 and its equivalents and
found it did not.
Claim 8
1
The question arising with respect to claim 8 is whether
the preamble of a Jepson claim requires written descrip-
tion, and if so, whether Xencor’s application contained suf-
ficient written description for said preamble.9 Xencor
argues that because the “invention” in a Jepson claim is the
improvement, it needed only to have written description for
that improvement—here, everything other than the pre-
amble. It argues that because the sufficiency of the written
description supporting its improvement has never been
doubted, the Board erred as a matter of law. The Director
responds that Jepson claim preambles are part of the in-
vention and, therefore, require written description. The
Director further contends that Xencor’s application does
not have this written description because it does not con-
tain an adequate description in the specification and
111 F.4th 1358, 1374 (Fed. Cir. 2024) (“Originally filed
claims have long been held to be part of the specification to
be considered in any § 112 analysis.”) (citing In re Gardner,
480 F.2d 879, 879 (CCPA 1973)). Therefore, we do not con-
sider this argument for any of the limitations at issue in
claims 9 and 8.
9 Xencor does not dispute that the preamble of its
Jepson claim is limiting.
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IN RE: XENCOR, INC. 16
because the genus of anti-C5 antibodies was not well-
known in the art.
Pursuant to 35 U.S.C. § 112, a specification must “con-
tain a written description of the invention . . . , in such full,
clear, concise, and exact terms as to enable any person
skilled in the art to which it pertains, or with which it is
most nearly connected, to make and use the same.” As we
have previously noted, while
claimed subject matter need not be described in
haec verba in the specification to satisfy the writ-
ten description requirement, it is also true that the
requirement must still be met in some way so as to
describe the claimed invention so that one skilled
in the art can recognize what is claimed.
Univ. of Rochester v. G.D. Searle & Co., Inc., 358 F.3d 916,
922–23 (Fed. Cir. 2004) (internal quotation marks and ci-
tation omitted). Such a description is context-specific:
“[T]he level of detail required to satisfy the written descrip-
tion requirement varies depending on the nature and scope
of the claims and on the complexity and predictability of
the relevant technology.” Ariad Pharms., Inc. v. Eli Lilly
& Co., 598 F.3d 1336, 1351 (Fed. Cir. 2010); see also Univ.
of Rochester, 358 F.3d at 923 (explaining that merely stat-
ing “automobile” in a claim would not have been sufficient
written description at the time of invention of the automo-
bile).
We agree with the ARP that a Jepson claim preamble
requires written description. This is because when the Jep-
son form is employed, the claim preamble is used “to define
the claimed invention, thereby limiting claim scope.” Cat-
alina Mktg. Int’l, 289 F.3d at 808; see Rowe, 112 F.3d
at 479 (“When [the Jepson] form is employed, the claim
preamble defines not only the context of the claimed inven-
tion, but also its scope.”); Pentec, Inc. v. Graphic Controls
Corp., 776 F.2d 309, 315 (Fed. Cir. 1985) (“Although a pre-
amble is impliedly admitted to be prior art when a Jepson
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IN RE: XENCOR, INC. 17
claim is used, . . . the claimed invention consists of the pre-
amble in combination with the improvement.”) (internal ci-
tations omitted). In other words, the Jepson claim
invention is the totality of what is set out in the claim, just
as it is for a non-Jepson claim. The invention is not only
the claimed improvement, but the claimed improvement as
applied to the prior art, so the inventor must provide writ-
ten description sufficient to show possession of the claimed
improvement to what was known in the prior art.
While a Jepson claim is directed to the improvement it
makes to the prior art, the claim is a singular thing and
cannot be separated; its totality is what must have written
description support, which necessarily includes support
sufficient to lead an ordinary artisan to understand that
the inventor did, indeed, possess what the patent contends
was in the prior art.
If we were to accept Xencor’s argument, we would be
doing away with the requirement that the written descrip-
tion “clearly allow persons of ordinary skill in the art to
recognize that [the inventor] invented what is claimed.”
Ariad, 598 F.3d at 1351 (alteration in original). “[W]ritten
description requires that the specification reasonably con-
vey to those skilled in the art that the inventor had posses-
sion of the claimed invention as of the filing date.” United
Therapeutics Corp. v. Liquidia Techs., Inc., 74 F.4th 1360,
1370 (Fed. Cir. 2023). If an inventor were permitted to
simply assert, without showing, that she possessed what is
claimed to be in the prior art, she might be able, improp-
erly, to obtain a patent on something she does not actually
possess.
A patentee cannot be permitted to use a Jepson claim
to avoid the requirement that she be in possession of the
claimed invention simply by asserting something is well-
known in the art. For example, a patentee cannot obtain a
Jepson claim with a preamble that says that a time ma-
chine is well-known in the art without describing a time
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IN RE: XENCOR, INC. 18
machine, in sufficient detail to make clear to a person of
ordinary skill in the art that the inventor is in possession
of such a time machine. Adoption of Xencor’s position
would leave the patent system vulnerable to such abuse.
2
To provide adequate written description for a Jepson
claim, the applicant must establish that what is claimed to
be well-known in the prior art is, in fact, well-known in the
prior art. What matters, as with all written description in-
quiries, is the disclosure in the patent (or patent applica-
tion) itself, but the finder of fact conducting the written
description inquiry may consider evidence outside the pa-
tent to understand what a person of ordinary skill in the
art would have known as of the pertinent date. The
amount and content of the disclosure that is necessary to
supply an adequate written description will vary depend-
ing on factors including the level of knowledge of the person
of ordinary skill in the art, the unpredictability of the art,
and the newness of the technology. For example, while us-
ing the claim term “automobile” in the nineteenth century
would have been insufficient without extensive explana-
tion in the specification, the same term today in a patent
directed to mechanical engineering is likely to be well-
known and need no further elaboration. See Univ. of Roch-
ester, 358 F.3d at 923.
Here, the ARP and the Board, serving as fact-finders,
determined that Xencor had not established that the limi-
tation in the Jepson preamble, the anti-C5 antibodies, was
well-known in the art. The Board found that Xencor’s ex-
pert was not credible and that none of the other evidence
indicated that anti-C5 antibodies were well-known in the
art, and the ARP agreed. The ARP summarized the
Board’s findings as follows: “the Board found that the ex-
amples of anti-C5 antibodies in the prior art were insuffi-
cient to establish that anti-C5 antibodies were well-known
and thus did not require further written description
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IN RE: XENCOR, INC. 19
support in the Specification.” J.A. 23–24. With respect to
Xencor’s expert, the Board held that “Dr. Dahiyat does not
explain how the publications, coupled with the [disclosure]
of the 5G 1.1 antibody in the Specification, convey posses-
sion of the full scope of the claimed genus.” J.A. 83. The
ARP agreed, pointing to the large number of possible anti-
bodies in the genus and finding no evidence that they were
well-known in art. The Board and the ARP also deter-
mined that Xencor had not otherwise shown adequate writ-
ten description support.
Xencor does not argue that there was any error in the
Board’s determination or in that of the ARP. Instead, as
we have explained, Xencor contends that the invention was
the “specific improvement to treating patients”—and that
it did not need to provide written description for what was
already in the prior art. Appellant’s Opening Br. at 16–17;
see also id. at 39 (“If the inventor provides a written de-
scription of the improvement, then nothing more should be
required.”). As discussed above, this position is unavailing.
Because the Board’s findings are supported by substan-
tial evidence, and even Xencor does not contend otherwise,
our legal conclusion regarding the necessity of written de-
scription for Jepson claims compels us to affirm.
C ONCLUSION
We have considered Xencor’s other arguments and find
them unpersuasive. For the reasons stated above, we af-
firm the ARP’s decision.
AFFIRMED
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