Court Opinion

ID: 4911765
Source: CourtListenerOpinion
Date Created: 2021-09-17 15:02:24.369995+00
Date Added: 2024-06-11T08:13:34.977849
License: Public Domain

Case: 20-2220    Document: 55    Page: 1   Filed: 09/17/2021

        NOTE: This disposition is nonprecedential.

   United States Court of Appeals
       for the Federal Circuit
                  ______________________

      JENNEWEIN BIOTECHNOLOGIE GMBH,
                  Appellant

                            v.

      INTERNATIONAL TRADE COMMISSION,
                  Appellee

                    GLYCOSYN LLC,
                        Intervenor
                  ______________________

                        2020-2220
                  ______________________

    Appeal from the United States International Trade
 Commission in Investigation No. 337-TA-1120.
                 ______________________

                Decided: September 17, 2021
                  ______________________

    NICOLE A. SAHARSKY, Mayer Brown LLP, Washington,
 DC, argued for appellant. Also represented by GARY
 HNATH, BRYAN NESE, MINH NGUYEN-DANG; SCOTT
 MCMURRY, New York, NY.

    HOUDA MORAD, Office of the General Counsel, United
 States International Trade Commission, Washington, DC,
 argued for appellee. Also represented by WAYNE W.
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 2                    JENNEWEIN BIOTECHNOLOGIE GMBH      v. ITC

 HERRINGTON.

     MICHAEL NEWMAN, Mintz, Levin, Cohn, Ferris, Glovsky
 and Popeo, PC, Boston, MA, argued for intervenor. Also
 represented by COURTNEY PATRICE HERNDON, MATTHEW A.
 KARAMBELAS, MICHAEL RENAUD, THOMAS H. WINTNER,
 JAMES M. WODARSKI.
                 ______________________

     Before LOURIE, BRYSON, and CHEN, Circuit Judges.
 CHEN, Circuit Judge.
     Glycosyn LLC (Glycosyn) filed a complaint against
 Jennewein Biotechnologie GmbH (Jennewein) with the In-
 ternational Trade Commission (Commission) under 19
 U.S.C. § 1337, alleging that human milk oligosaccharides
 imported by Jennewein infringed Glycosyn’s U.S. Patent
 No. 9,970,018 (’018 patent). Jennewein used several Esch-
 erichia coli (E. coli) bacterial strains to produce the human
 milk oligosaccharides it imported into the United States.
 The Commission determined that of the three Jennewein
 strains at issue, two of the strains infringed the ’018 patent
 and one did not. In the Matter of Certain Hum. Milk Oli-
 gosaccharides & Methods of Producing the Same, Inv. No.
 337-TA-1120, 2020 WL 3073788 (U.S.I.T.C. June 8, 2020)
 (Comm’n Opinion) (Commission Opinion); see also In the
 Matter of Certain Hum. Milk Oligosaccharides & Methods
 of Producing the Same, Inv. No. 337-TA-1120, 2019 WL
 5677974 (U.S.I.T.C. Sept. 9, 2019) (Initial Determination)
 (Initial Determination); see also In the Matter of Certain
 Hum. Milk Oligosaccharides & Methods of Producing the
 Same, Inv. No. 337-TA-1120, 2018 WL 6837945 (U.S.I.T.C.
 Dec. 18, 2018) (Order No. 22: Construing the Terms of the
 Asserted Claims of the Patents at Issue) (Claim Construc-
 tion Order).
     Jennewein appeals aspects of the Commission’s claim
 construction and infringement determination. Because we
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 JENNEWEIN BIOTECHNOLOGIE GMBH         v. ITC                     3

 conclude that the Commission did not err in its claim con-
 struction or in its finding of infringement, we affirm its lim-
 ited exclusion order.
                          BACKGROUND
                                 A
      The ’018 patent relates to methods for producing fuco-
 sylated oligosaccharides found in human milk. ’018 patent
 col. 1 ll. 27–30. These oligosaccharides “serve critical roles
 in the establishment of a healthy gut microbiome, in the
 prevention of disease, and in immune function.” Id. at col.
 1 ll. 37–39. Through “use of an engineered bacterium E.
 coli (or other bacteria),” the claimed method enables syn-
 thesis of fucosylated human milk oligosaccharides (e.g., 2’-
 fucosyllactose (2’-FL)), id. at col. 15 l. 66–col. 16 l. 4, for use
 as dietary supplements, id. at col. 15 ll. 62–65, or for incor-
 poration into products (e.g., infant formula), id. at col. 11
 ll. 30–40. The engineered E. coli bacterium is genetically
 manipulated to comprise: (1) an increased intracellular
 guanosine diphosphate (GDP)-fucose pool; (2) an increased
 intracellular lactose pool; and (3) a fucosyltransferase. Id.
 at col. 5 ll. 1–5. The fucosyltransferase couples the lactose
 and GDP-fucose to form the desired human milk oligosac-
 charide, specifically 2’-FL. Id. at Figure 3.
     To increase the intracellular lactose pool, the engi-
 neered E. coli bacterium of the claimed method is modified
 to delete or functionally inactivate the endogenous β-galac-
 tosidase gene, lacZ. Id. at col. 5 ll. 13–14. As β-galacto-
 sidase is the enzyme responsible for the breakdown of
 lactose in E. coli, eliminating its activity in the engineered
 bacterium results in the accumulation of intracellular lac-
 tose when culturing the bacterium in the presence of exog-
 enous lactose. Id. at col. 16 ll. 47–49. This increased
 lactose pool ensures the availability of lactose for the pro-
 duction of 2’-FL. Id. at col. 5 ll. 16–19.
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 4                    JENNEWEIN BIOTECHNOLOGIE GMBH       v. ITC

     Yet complete elimination of β-galactosidase activity
 creates purification issues at the end of the manufacturing
 process, as it is difficult to separate any remaining lactose
 from the desired 2’-FL product. See id. at col. 7 ll. 37–45;
 see also Appellant’s Br. 10 (“After production ends, there
 can be a significant amount of lactose remaining in the fer-
 mentation broth, and it can be difficult (and costly) to sep-
 arate lactose from 2’-FL.”). To overcome this challenge, the
 engineered E. coli bacterium of the claimed method in-
 cludes an exogenous functional β-galactosidase gene “to di-
 rect the expression of a low, but detectable level of β-
 galactosidase activity.” ’018 patent col. 6 ll. 7–11. The re-
 sult is an engineered bacterium comprising a low level of
 cytoplasmic β-galactosidase activity, between 0.05 and 200
 Miller units. 1 Id. at col. 7 ll. 22–37. This low level of β-
 galactosidase activity does not “significantly diminish the
 intracellular lactose pool” but can degrade any residual lac-
 tose remaining after the fermentation process, simplifying
 2’-FL purification. Id. at col. 7 ll. 37–45. In addition to
 being helpful for the removal of undesired residual lactose,

     1    To define a Miller unit, the ’018 patent points to the
 assay of β-galactosidase activity provided in Jeffrey H. Mil-
 ler, EXPERIMENTS IN MOLECULAR GENETICS 352–55 (1972)
 (Miller). See ’018 patent col. 7 ll. 34–37. In short, the Mil-
 ler protocol includes the following steps: (1) taking a sam-
 ple from a culture of growing bacterial cells; (2)
 permeabilizing the bacterial cells with chloroform or tolu-
 ene; (3) incubating the permeabilized bacterial cells with o-
 nitrophenyl-β-D-galactoside (ONPG), a colorless compound
 specifically recognized and cleaved by β-galactosidase to
 produce a yellow product; and (4) measuring with a spec-
 trophotometer the amount of yellow color that develops
 over a set period of time. See J.A. 60224–28. The values
 recorded by the spectrophotometer are then entered into a
 mathematical equation to provide the level of β-galacto-
 sidase activity in Miller units. See J.A. 60227.
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 JENNEWEIN BIOTECHNOLOGIE GMBH     v. ITC                    5

 the low level of β-galactosidase activity can also be useful
 for phenotypic marking or for detection of cell lysis due to
 bacteriophage contamination during fermentation. Id. at
 col. 7 ll. 40–43.
     The only independent claim of the ’018 patent, claim 1,
 covers Glycosyn’s method and engineered E. coli bacte-
 rium. The claim recites:
    1. A method for producing a fucosylated oligosac-
    charide in a bacterium, comprising providing an
    isolated E. coli bacterium comprising,
    (i) a deletion or functional inactivation of an endog-
    enous β-galactosidase gene;
    (ii) an exogenous functional β-galactosidase gene
    comprising a detectable level of β-galactosidase ac-
    tivity that is reduced compared to that of a wild-
    type E. coli bacterium, wherein the level of β-galac-
    tosidase activity comprises between 0.05 and 200
    units;
    (iii) an inactivating mutation in a colanic acid syn-
    thesis gene; and
    (iv) an exogenous lactose-accepting fucosyltrans-
    ferase gene;
    culturing said bacterium in the presence of lactose;
    and
    retrieving a fucosylated oligosaccharide from said
    bacterium or from a culture supernatant of said
    bacterium.
 Id. at claim 1 (emphases added). Claims 2, 3, 5, 8, 10, 12,
 18, and 24–28, also at issue in this appeal, all depend from
 claim 1.
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 6                   JENNEWEIN BIOTECHNOLOGIE GMBH      v. ITC

                              B
     In April 2018, Glycosyn filed a complaint against
 Jennewein with the Commission under § 1337. Glycosyn
 alleged that Jennewein violated § 1337(a)(1)(B) by import-
 ing 2’-FL produced by a process covered by the ’018 patent.2
 The Commission instituted an investigation based on Gly-
 cosyn’s complaint.
     At issue in the proceeding was whether three Jenne-
 wein E. coli strains engineered for making 2’-FL infringed
 certain claims of the ’018 patent. All three strains lack the
 lacZ gene. But two of the strains, #1540 and #2410, com-
 prise the gene fragments lacZα and lacZΩ, which when ex-
 pressed together produce β-galactosidase, resulting in β-
 galactosidase activity. See J.A. 45901–45902; J.A. 45912;
 Appellant’s Br. 17–19. Expression of the lacZΩ gene frag-
 ment in both strains is controlled by a temperature regula-
 tor. See id. Accordingly, the β-galactosidase activity of the
 strains may be modulated by changing the culture temper-
 ature from 30 °C to 42 °C, turning the activity on as de-
 sired. See J.A. 45901–45902. The third strain, TTFL12,
 lacks a functional β-galactosidase gene as it comprises the
 lacZα gene fragment but not the lacZΩ gene fragment. See
 Commission Opinion, 2020 WL 3073788, at *14; J.A.
 63549–63550. Further, unlike the other two strains at is-
 sue, TTFL12 does not use lactose to produce 2’-FL. See
 Commission Opinion, 2020 WL 3073788, at *10. Jenne-
 wein has Food and Drug Administration (FDA) approval to
 use the #1540 and #2410 3 strains to produce 2’-FL for

     2    Glycosyn initially alleged that Jennewein also in-
 fringed U.S. Patent No. 9,453,230 (’230 patent), related to
 the ’018 patent, but subsequently terminated the ’230 pa-
 tent from the investigation.
     3    Although the #2410 strain was not included in
 Jennewein’s Generally Recognized as Safe (GRAS) notice,
 see, e.g., J.A. 45902, Jennewein asserts that the #2410
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 JENNEWEIN BIOTECHNOLOGIE GMBH     v. ITC                  7

 human consumption. See Appellant’s Br. 20–21. The
 TTFL12 strain is not yet approved. See Appellant’s Letter,
 No. 20-2220 (July 7, 2021), ECF No. 54.
     The administrative law judge (ALJ) issued a claim con-
 struction order in December 2018. Relevant to this appeal,
 the ALJ construed the limitation “β-galactosidase activity
 comprises between 0.05 and 200 units” to mean “β-galacto-
 sidase activity is measurable at between exactly 0.05 and
 exactly [200] Miller Units, as defined in Miller.” Claim
 Construction Order, 2018 WL 6837945, at *18. The ALJ
 declined to include a temporal requirement in the construc-
 tion, asserting that the claimed activity need only be met
 “at some point in time.” Id. at *17–18. As for “functional
 β-galactosidase gene,” the ALJ construed this limitation to
 mean “a functional sequence of DNA that encodes β-galac-
 tosidase.” Id. at *22–23. The ALJ gave the term “exoge-
 nous” its plain and ordinary meaning of “originating
 outside an organism, tissue, or cell.” Id. at *9.
     Using these constructions, the ALJ’s September 2019
 Initial Determination found that Jennewein’s #1540 and
 #2410 strains infringe claims 1–3, 5, 8, 10, 12, 18, and 24–
 28 of the ’018 patent under the doctrine of equivalents. See
 Initial Determination, 2019 WL 5677974, at *26–32. Ac-
 cording to the ALJ, the combination of the lacZα and lacZΩ
 gene fragments in Jennewein’s #1540 and #2410 strains is
 equivalent to the “exogenous functional β-galactosidase
 gene” claim limitation because the combination is exoge-
 nous and the expression of the fragments results in produc-
 tion of β-galactosidase. See id. At the time of the Initial
 Determination, the ALJ left open the question of whether
 the TTFL12 strain infringed any of the ’018 patent claims

 strain is FDA approved to produce 2’-FL for human con-
 sumption, see Appellant’s Br. 20–21.
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 8                   JENNEWEIN BIOTECHNOLOGIE GMBH     v. ITC

 because the ALJ felt “the discovery on TTFL12 was not ad-
 equate” to adjudicate infringement. See id. at *25.
      The ALJ was unconvinced by Jennewein’s arguments
 that to assess infringement of the claim limitation
 “wherein the level of β-galactosidase activity comprises be-
 tween 0.05 and 200 units,” the β-galactosidase activity of a
 negative control strain measured in Miller units should be
 subtracted from the measured activity of Jennewein’s
 #1540 and #2410 strains. In other words, Jennewein
 wanted the activity of its accused strains measured against
 a bacterial strain lacking a functional β-galactosidase gene
 (i.e., a negative control strain) rather than in absolute
 terms. Instead, the ALJ concluded that subtraction of the
 Miller unit value of a negative control strain was inappro-
 priate for evaluating infringement because the Miller as-
 say—“the test to be used to determine if a bacterium falls
 within the scope of the claims,” id. at *32—does not include
 such a step and, moreover, Jennewein’s proposed negative
 controls were unreliable. See id. at *34–35 (noting that in
 many cases, Jennewein’s subtraction of a negative control
 strain resulted in negative Miller units for an accused
 strain).
     In January 2020, the Commission decided to review in
 part the ALJ’s Initial Determination, and in May 2020, is-
 sued its decision, adopting the ALJ’s findings “not incon-
 sistent” therewith. See Commission Opinion, 2020 WL
 3073788, at *1. The Commission affirmed the ALJ’s find-
 ing of infringement under the doctrine of equivalents,
 agreeing that the combination of the lacZα and lacZΩ gene
 fragments in Jennewein’s #1540 and #2410 strains is
 equivalent to an “exogenous functional β-galactosidase
 gene.” See id. at *7. In arriving at this conclusion, the
 Commission agreed with the ALJ that (1) the combination
 of lacZα and lacZΩ gene fragments does not exist in
 BL21(DE3), the engineered E. coli bacterium used by
 Jennewein to make the #1540 and #2410 strains; (2) the
 exogenous nature of lacZΩ—incorporated into the #1540
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 JENNEWEIN BIOTECHNOLOGIE GMBH     v. ITC                   9

 and #2410 strains by Jennewein through genetic manipu-
 lation—is enough to make the resulting combination exog-
 enous; and (3) “any difference between the claim term ‘an
 exogenous functional β-galactosidase gene’ and the accused
 products is insubstantial.” See id. Additionally, the Com-
 mission found that the lacZα gene fragment, which exists
 in the BL21(DE3) strain because of genetic engineering, is
 exogenous to a wild-type E. coli bacterium, making both
 the lacZα and lacZΩ gene fragments exogenous to the
 #1540 and #2410 strains. See id. at *8–9. In so finding,
 the Commission determined that the bacterium of the
 claimed method should be compared to a wild-type bacte-
 rium, not a modified, engineered one, like the BL21(DE3)
 strain. See id. Regarding the TTFL12 strain, the Commis-
 sion found, contrary to the ALJ’s finding, that it could ad-
 judicate infringement because “Jennewein presented
 sufficient documentary evidence as well as fact and expert
 testimony to put Glycosyn on notice of the relevant features
 of the TTFL12 strain.” 4 See id. at *12. The Commission
 also found “that Glycosyn failed to satisfy its burden of es-
 tablishing infringement with respect to Jennewein’s
 TTFL12 strain,” as there was no evidence that the strain
 includes a lacZΩ gene fragment. See id. at *13–14. There-
 fore, the strain lacks an “exogenous functional β-galacto-
 sidase gene comprising a detectable level of β-galactosidase
 activity.” 5 See id. at *14.

     4   One Commissioner dissented as to this finding. In
 the Matter of Certain Hum. Milk Oligosaccharides & Meth-
 ods of Producing the Same, Inv. No. 337-TA-1120, 2020 WL
 3073787 (U.S.I.T.C. June 8, 2020) (Separate Views of
 Comm’r Schmidtlein Concurring in Part & Dissenting in
 Part).
     5   Jennewein’s strain #1242, not at issue in the pre-
 sent appeal, was found by the Intellectual Property Rights
 Branch of the U.S. Customs and Border Patrol not to
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 10                   JENNEWEIN BIOTECHNOLOGIE GMBH      v. ITC

     Accordingly, the Commission entered a limited exclu-
 sion order against the 2’-FL produced by Jennewein’s
 #1540 and #2410 strains. J.A. 5. The order did not apply
 to 2’-FL produced using the TTFL12 strain. J.A. 6. Jenne-
 wein timely appealed. We have jurisdiction under 28
 U.S.C. § 1295(a)(6).
                         DISCUSSION
                               A
     The Commission’s final determinations are reviewed
 under the Administrative Procedure Act. 5 U.S.C. § 706;
 Honeywell Int’l, Inc. v. Int’l Trade Comm’n, 341 F.3d 1332,
 1338 (Fed. Cir. 2003). We review the Commission’s legal
 determinations de novo and its factual findings for sub-
 stantial evidence. See Finnigan Corp. v. Int’l Trade
 Comm’n, 180 F.3d 1354, 1361–62 (Fed. Cir. 1999); Linear
 Tech. Corp. v. Int’l Trade Comm’n, 566 F.3d 1049, 1060
 (Fed. Cir. 2009).
                               B
      Jennewein presents three main arguments on appeal,
 namely that the Commission incorrectly determined that:
 (1) Jennewein’s #1540 and #2410 strains satisfy the claim
 limitation requiring that “the level of β-galactosidase activ-
 ity comprises between 0.05 and 200 units”; (2) Jennewein’s
 #1540 and #2410 strains satisfy the “exogenous functional
 β-galactosidase gene” claim limitation; and (3) “the level of
 β-galactosidase activity comprises between 0.05 and 200
 units” claim limitation does not require the β-galactosidase
 activity to occur “within the claimed range at substantially
 all times during 2’-FL production and retrieval,”

 infringe the asserted claims of the ’018 patent for reasons
 similar to those detailed for the TTFL12 strain. See J.A.
 63561–63569. Strain #1242 is FDA approved. See J.A.
 63553; Appellee’s Br. 9.
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 JENNEWEIN BIOTECHNOLOGIE GMBH     v. ITC                  11

 Appellant’s Br. 25. We disagree with Jennewein and ad-
 dress each issue in turn.
                              1
      We first consider Jennewein’s argument that its #1540
 and #2410 strains do not produce any β-galactosidase ac-
 tivity, let alone at the level recited in the claims. Patent
 infringement, whether literal or under the doctrine of
 equivalents, is a question of fact, which we review for sub-
 stantial evidence. See Linear Tech., 566 F.3d at 1060. The
 patent owner bears the burden to prove infringement by a
 preponderance of the evidence. See Spansion, Inc. v. Int’l
 Trade Comm’n, 629 F.3d 1331, 1349 (Fed. Cir. 2010). Here,
 substantial evidence supports the Commission’s finding
 that Jennewein’s #1540 and #2410 strains literally meet
 the limitation requiring that “the level of β-galactosidase
 activity comprises between 0.05 and 200 units.”
     To assess infringement of the claimed activity range,
 all parties acknowledge that the Miller protocol is the ap-
 propriate test. See, e.g., Reply Br. 5. Yet the parties disa-
 gree on how to conduct the assay. Jennewein argues that
 the plain meaning of the claim language requires that the
 Miller unit readings reflect the activity of the inserted β-
 galactosidase gene and not activity from a different source.
 Therefore, to assess infringement, Jennewein asserts that
 a negative control strain lacking a functional β-galacto-
 sidase gene must be used to ensure that the measured β-
 galactosidase activity of an accused strain is from the in-
 serted β-galactosidase gene, not from another source or
 from background noise. Per Jennewein, the Commission
 erred by not requiring a negative control strain in the Mil-
 ler assay.
     The Commission acknowledged Jennewein’s conten-
 tion that, to assess infringement of the activity claim limi-
 tation, one must “properly identify exactly [the] amount of
 Miller Unit activity . . . attributable to what would be the
 ‘functional β-galactosidase gene’ (i.e., the combination of
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 12                   JENNEWEIN BIOTECHNOLOGIE GMBH       v. ITC

 the lacZα and lacZΩ gene fragments) in the strain.” Initial
 Determination, 2019 WL 5677974, at *32. 6 Yet the Com-
 mission, agreeing with Glycosyn, concluded that the inclu-
 sion of a negative control strain was unnecessary to
 measure this activity. See id. at *34–35. Ample evidence
 supports the Commission’s conclusion.
     As an initial matter, the record evidence links the Mil-
 ler unit activity detected in both parties’ assays to the in-
 serted functional β-galactosidase gene, not to background
 noise or other enzyme activity. As discussed by the Com-
 mission, the “record [did] not identify any . . . ‘other enzyme
 besides β-galactosidase’” in Jennewein’s strains that would
 result in Miller assay activity. See id. at *34; J.A. 29596;
 Appellee’s Br. 36 (discussing Jennewein’s expert’s testi-
 mony “that he does not know of ‘any enzymes other than
 beta-galactosidase that will cleave ONPG’” (quoting J.A.
 29822)). Because of “Jennewein’s expert’s immense meta-
 bolic engineering experience . . . and the well-studied prop-
 erties of E. coli,” the Commission did not understand how
 another agent with β-galactosidase activity was not identi-
 fied if it existed. Initial Determination, 2019 WL 5677974,
 at *34. And the “parties’ experts testified they were una-
 ware of such substances.” See id.; J.A. 29596; Appellee’s
 Br. 36.
     Jennewein further argues that the #1540 and #2410
 strains cannot produce β-galactosidase activity at the low
 temperature (i.e., 30 °C) it uses for 2’-FL production, so any
 observed activity must be background noise. See Reply Br.
 20. But possible “leakage” rebuts Jennewein’s argument.
 The temperature regulator controlling expression of the
 lacZΩ gene fragment in Jennewein’s #1540 and #2410
 strains can “leak,” resulting in a low-level of temperature-

      6  Because the Commission adopted the ALJ’s find-
 ings, we refer to these findings herein as the Commission’s
 findings.
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 JENNEWEIN BIOTECHNOLOGIE GMBH     v. ITC                  13

 independent β-galactosidase production and activity. See
 Initial Determination, 2019 WL 5677974, at *30; J.A.
 29682 (Glycosyn’s expert stating, “I don’t think I’ve ever
 met a repressor that didn’t leak, and it’s very common to
 measure leakiness of promoters when you’re dealing with
 repressible systems.”); Appellee’s Br. 33–34 (Glycosyn’s ex-
 pert stating, “‘I have no reason to suspect it was anything
 other than beta-galactosidase activity, because I have a
 strain that I know possesses beta-galactosidase activity.’”
 (quoting J.A. 29685)). Regardless, the Miller assay speci-
 fies several controls to account for any background noise
 and does not use a negative control strain to do so. See
 Initial Determination, 2019 WL 5677974, at *34 n.3; J.A.
 47486–47487. Glycosyn included these controls in its test-
 ing for β-galactosidase activity. See Initial Determination,
 2019 WL 5677974, at *37; J.A. 62173–62174.
     Turning to Jennewein’s proposed negative control
 strains, Jennewein asserts that it tested two such strains
 using the same procedure Glycosyn used to assess Jenne-
 wein’s #1540 and #2410 strains. As the Miller unit values
 for the two control strains were greater than Glycosyn’s
 Miller unit values for the #1540 and #2410 strains, Jenne-
 wein contends that Glycosyn’s results for the #1540 and
 #2410 strains must represent only background noise. Ap-
 pellant’s Br. 41–42. Jennewein argues that if Glycosyn had
 used the negative control strains, Glycosyn’s results for the
 #1540 and #2410 strains would have fallen below the
 claimed range. Id.
     Yet in almost every sample tested, the two negative
 control strains selected by Jennewein had higher Miller
 unit values than the #1540 and #2410 strains. See Initial
 Determination, 2019 WL 5677974, at *34–35; see also Ap-
 pellant’s Br. 41 (citing J.A. 44238–44246 (data from Miller
 assays of the #1540 and #2410 strains), J.A. 60031–60033
 (data from Miller assays of the two control strains)).
 Jennewein argues this is due to background noise. But be-
 cause the negative control strains should be almost
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 14                   JENNEWEIN BIOTECHNOLOGIE GMBH      v. ITC

 identical to the accused strains, differing only in the
 amount of β-galactosidase activity observed as a result of
 the inserted β-galactosidase gene, the expected Miller unit
 values for the negative control strains should be equal to or
 less than the values measured for the accused strains.
 Therefore, one rational inference to be drawn from Jenne-
 wein’s data is that its two proposed negative controls are
 not valid. Additionally, Jennewein’s proposed negative
 controls inexplicably have Miller unit values quite differ-
 ent from each other, with the values for one strain about
 twice as high as the values for the other. In view of these
 data, we believe substantial evidence supports the Com-
 mission’s finding that the resulting negative Miller unit
 values produced by Jennewein’s assays for its accused
 strains “should have put Jennewein on notice that its neg-
 ative control technique was unreliable on its face, or imple-
 mented unreliably, or some other assumption was
 incorrect.” Initial Determination, 2019 WL 5677974, at
 *35.
     Moreover, communications between Jennewein and a
 third-party company it hired to conduct infringement test-
 ing suggest that the two negative control strains preferred
 by Jennewein are not suitable. See Appellee’s Br. 38–39
 (“‘unfortunately, the Miller activity at your 1540 (30 °C)
 batch is still above 0.05 after subtracting [a third possible
 negative control strain],’ and ‘if we subtract [one of the two
 previously discussed negative control strains] instead of
 the [third possible negative control strain] as reference, the
 value would fall below 0.05’” (quoting J.A. 51523–51524)
 (cleaned up)). Because of these communications, the Com-
 mission found that “Jennewein sought a control strain that
 would minimize the measured Miller Units.” Initial Deter-
 mination, 2019 WL 5677974, at *35. Substantial evidence
 supports this finding.
     The Commission reasonably found that use of a nega-
 tive control strain was unnecessary for assessing infringe-
 ment in light of the unreliability in Jennewein’s testing
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 JENNEWEIN BIOTECHNOLOGIE GMBH     v. ITC                  15

 with negative control strains and after accounting for pos-
 sible sources of background noise or enzyme activity in the
 Miller protocol, detailed supra. 7 See Spansion, Inc., 629
 F.3d at 1344 (noting that under the substantial evidence
 test, we “must affirm a Commission determination if it is
 reasonable and supported by the record as a whole, even if
 some evidence detracts from the Commission’s conclusion”
 (internal quotation marks omitted)); see also Nutrinova
 Nutrition Specialties & Food Ingredients GmbH v. Int’l
 Trade Comm’n, 224 F.3d 1356, 1359 (Fed. Cir. 2000) (dis-
 cussing that as an appellate court, we are not “to reweigh
 the evidence and reexamine the credibility of the wit-
 nesses”). Once the Commission concluded a negative con-
 trol was not needed, it credited Glycosyn’s testing of
 Jennewein’s #1540 and #2410 strains, finding “Glycosyn’s
 testing simply hewed more closely to the Miller protocol,
 i.e., the terms in which the invention is defined.” 8 Initial
 Determination, 2019 WL 5677974, at *37. The Commission
 then determined that “a large majority of [the] samples ex-
 hibit[ed] Miller Unit activities within the claimed range.”
 Id.
    In view of the above, substantial evidence supports the
 Commission’s finding that Jennewein’s #1540 and #2410

     7    Jennewein argues that peer-reviewed studies in
 the scientific literature report that E. coli strains without
 a functional β-galactosidase gene can register Miller units.
 See, e.g., Appellant’s Br. 35. But we do not know the exact
 testing conditions in these studies, making comparison to
 the testing in the present litigation difficult.
      8   Because Jennewein does not challenge the Com-
 mission’s determinations that Jennewein’s incubation time
 for the Miller assay and ONPG control were improper, Ini-
 tial Determination, 2019 WL 5677974, at *32–37, we do not
 review those findings here. See SmithKline Beecham Corp.
 v. Apotex Corp., 439 F.3d 1312, 1319 (Fed. Cir. 2006).
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 16                  JENNEWEIN BIOTECHNOLOGIE GMBH      v. ITC

 strains satisfy the limitation “the level of β-galactosidase
 activity comprises between 0.05 and 200 units.”
                              2
     The Commission’s finding that Jennewein’s #1540 and
 #2410 strains satisfy the “exogenous functional β-galacto-
 sidase gene” claim limitation, at least under the doctrine of
 equivalents, is supported by substantial evidence. As for
 the “exogenous” claim term, Jennewein argues that the
 Commission’s construction reads the term “exogenous” out
 of the patent and that the combination of the lacZα and
 lacZΩ gene fragments in its #1540 and #2410 strains is not
 equivalent to an exogenous functional β-galactosidase gene.
 Jennewein appears to contest only the Commission’s find-
 ings as to the term “exogenous,” not the Commission’s con-
 clusion that the combination of the lacZα and lacZΩ gene
 fragments in Jennewein’s #1540 and #2410 strains is
 equivalent to a “functional β-galactosidase gene.”
     Jennewein does not dispute that the lacZΩ gene frag-
 ment is exogenous to the #1540 and #2410 strains. See Ap-
 pellant’s Br. 47. Jennewein instead contends that the
 lacZα gene fragment is not exogenous but endogenous,
 making the combination of lacZα and lacZΩ gene frag-
 ments endogenous because the combination does not “orig-
 inate outside” of the host strain. We disagree.
     As found by the Commission, “the combination [of
 lacZα and lacZΩ gene fragments] does not exist in the orig-
 inal strain [used to make the #1540 and #2410 strains], and
 therefore the combination itself does not originate from
 within the organism,” making it exogenous. Commission
 Opinion, 2020 WL 3073788, at *7. That finding is sup-
 ported by substantial evidence. Thus, the exogenous na-
 ture of the lacZΩ gene fragment is enough to make the
 accused strains meet the exogenous claim limitation, re-
 gardless of whether the lacZα gene fragment is endogenous
 or exogenous. As to Jennewein’s contentions that the lacZα
 gene fragment is endogenous, substantial evidence
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 JENNEWEIN BIOTECHNOLOGIE GMBH      v. ITC                  17

 supports the Commission’s finding that the fragment is ex-
 ogenous. The lacZα gene fragment originates outside of a
 wild-type E. coli bacterium—it was derived from a pro-
 phage—and exists in the BL21(DE3) genome only because
 of human intervention. See id. at *8–9. Substantial evi-
 dence therefore supports the Commission’s finding that
 Jennewein’s #1540 and #2410 strains satisfy the “exoge-
 nous” claim term of the “exogenous functional β-galacto-
 sidase gene” limitation.
                               3
      Finally, Jennewein challenges the Commission’s con-
 struction of the limitation “the level of β-galactosidase ac-
 tivity comprises between 0.05 and 200 units,” arguing that
 its proper interpretation requires that the modified bacte-
 rium’s level of β-galactosidase activity be “within the
 claimed range substantially throughout 2’-FL production
 and retrieval.” Appellant’s Br. 56. But the claim language
 and intrinsic evidence support the Commission’s construc-
 tion, which does not adopt Jennewein’s proposed temporal
 requirement: The level of “β-galactosidase activity is meas-
 urable at between exactly 0.05 and exactly [200] Miller
 units, as defined in Miller.”
     Claim construction is a question of law. Teva Pharms.
 USA, Inc. v. Sandoz, Inc., 135 S. Ct. 831, 841–42 (2015).
 When the Commission relies only on intrinsic evidence,
 such as the patent claims, specification, and prosecution
 history, we review that construction de novo. Id. at 841.
 Subsidiary factual findings are reviewed under the sub-
 stantial evidence standard. See Finnigan, 180 F.3d at
 1361–62. Although we begin any claim construction anal-
 ysis with the language of the claim itself, see Phillips v.
 AWH Corp., 415 F.3d 1303, 1312 (Fed. Cir. 2005) (en banc),
 the claims “do not stand alone. Rather, they are part of ‘a
 fully integrated written instrument,’ . . . consisting princi-
 pally of a specification that concludes with the claims,” id.
 at 1315 (quoting Markman v. Westview Instruments, Inc.,
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 18                   JENNEWEIN BIOTECHNOLOGIE GMBH      v. ITC

 52 F.3d 967, 978 (Fed. Cir. 1995) (en banc)). Thus, “claims
 ‘must be read in view of the specification, of which they are
 a part.’” Id. (quoting Markman, 52 F.3d at 979). Addition-
 ally, “the prosecution history can often inform the meaning
 of the claim language by demonstrating how the inventor
 understood the invention.” Id. at 1317.
      Looking initially to the claim language, we see nothing
 suggesting that the recited β-galactosidase activity must be
 present substantially throughout 2’-FL production and re-
 trieval. Three aspects of the claim language guide us to
 this conclusion. First, the claimed method comprises three
 steps: (1) providing an isolated E. coli bacterium compris-
 ing four characteristics, one of which is “an exogenous func-
 tional β-galactosidase gene comprising a detectable level of
 β-galactosidase activity that is reduced compared to that of
 a wild-type E. coli bacterium, wherein the level of β-galac-
 tosidase activity comprises between 0.05 and 200 units”; (2)
 culturing said bacterium in the presence of lactose; and (3)
 retrieving a fucosylated oligosaccharide from said bacte-
 rium or from a culture supernatant of said bacterium. The
 Miller unit limitation is one of the four characteristics the
 engineered bacterium must possess to meet the claim’s
 first step. In other words, the recited level of β-galacto-
 sidase activity, measured and detected in the context of the
 Miller assay, is an inherent property of the provided bacte-
 rium, not the level of activity required throughout perfor-
 mance of the claimed method. 9 Second, the claim language

      9  The ALJ discusses this issue at several points in
 the Initial Determination. See, e.g., Initial Determination,
 2019 WL 5677974, at *33 (“Jennewein’s manufacturing
 process could involve . . . [a] number of variations, but that
 would not bear on whether the E. coli which Jennewein
 ‘provides’ to its process exhibits Miller Unit activity within
 the claimed range when put through Miller’s protocol.”); Id.
 at *36 (discussing the “flexibility in the temporal scope of
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 JENNEWEIN BIOTECHNOLOGIE GMBH        v. ITC                   19

 specifies that the fucosylated oligosaccharide product is re-
 trieved from the bacterium or from the culture superna-
 tant. As retrieval from the bacterium involves killing the
 bacterium (e.g., lysis of the bacterium), adopting Jenne-
 wein’s proposed construction requiring the bacterium to
 have the recited β-galactosidase activity during retrieval
 would improperly exclude a key embodiment identified in
 the claim. See Primos, Inc. v. Hunter’s Specialties, Inc., 451
 F.3d 841, 848 (Fed. Cir. 2006) (“[W]e . . . should not nor-
 mally interpret a claim term to exclude a preferred embod-
 iment.”); see also MobileMedia Ideas LLC v. Apple Inc., 780
 F.3d 1159, 1181 (Fed. Cir. 2015). Last, the claims do not
 mandate monitoring of the β-galactosidase activity via the
 Miller assay throughout 2’-FL production and retrieval nor
 is there a limit on which stage or stages of the process the
 claimed β-galactosidase activity must be observed. Accord-
 ingly, the claim language supports the Commission’s con-
 struction.
     The written description also confirms the Commis-
 sion’s decision not to include a temporal limitation in its
 construction. As with the claim language, the written de-
 scription indicates that the recited Miller unit activity is an
 inherent characteristic of the provided bacterium, see ’018
 patent col. 6 ll. 7–11, col. 7 ll. 22–37, and discusses retrieval
 of the fucosylated oligosaccharide product from the bacte-
 rium as one of two favored embodiments, see id. at col. 2 ll.
 58–62, col. 19 ll. 42–46. Further, to successfully carry out
 the invention, the written description does not require that
 β-galactosidase activity (1) remain low during both 2’-FL
 production and retrieval or (2) be monitored while perform-
 ing the claimed method. In fact, the written description
 makes clear that a low level of β-galactosidase activity is

 the claim” in the context of when to stop the Miller assay
 and noting that the claimed β-galactosidase activity range
 “need only be met at some point in time”).
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 20                    JENNEWEIN BIOTECHNOLOGIE GMBH         v. ITC

 not necessary during the entirety of the method but may be
 useful at particular, distinct stages. See id. at col. 5 l. 65–
 col. 6 l. 11; see also id. at col. 7 ll. 37–45 (“This low level of
 cytoplasmic β-galactosidase activity, while not high enough
 to significantly diminish the intracellular lactose pool, is
 nevertheless very useful for tasks such as phenotypic
 marking of desirable genetic loci during construction of
 host cell backgrounds, for detection of cell lysis due to un-
 desired bacteriophage contamination in fermentation pro-
 cesses, or for the facile removal of undesired residual
 lactose at the end of fermentations.”); see also id. at col. 9
 ll. 34–50. Thus, despite Jennewein’s assertions to the con-
 trary, a low level of β-galactosidase activity substantially
 throughout the claimed process is not the only way for
 there to be a beneficial effect. The written description
 therefore supports the Commission’s construction. See
 Hill-Rom Servs., Inc. v. Stryker Corp., 755 F.3d 1367, 1373
 (Fed. Cir. 2014) (declining to narrowly construe a claim
 term “absent some language in the specification or prose-
 cution history suggesting that the [feature] is important,
 essential, necessary, or the ‘present invention’”).
      Finally, we note that the prosecution history does not
 support Jennewein’s preferred construction of “the level of
 β-galactosidase activity comprises between 0.05 and 200
 units.” Per Jennewein, “[d]uring the prosecution of the [re-
 lated] ’230 patent, Glycosyn explained that the claimed ac-
 tivity range ‘maximizes 2’-FL end product production while
 preserving the advantage of depleting . . . residual lactose
 at the end of production runs.’” Appellant’s Br. 59 (quoting
 J.A. 32294) (cleaned up). Jennewein contends that this
 statement demonstrates “that the inventors understood
 that the β-galactosidase gene would register Miller unit
 readings throughout production and retrieval.” Id. We dis-
 agree. At most the statement implies that β-galactosidase
 activity may be useful at the end of production to eliminate
 remaining lactose. It is not an unequivocal disavowal of
 claim scope supporting Jennewein’s proposed construction.
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 JENNEWEIN BIOTECHNOLOGIE GMBH     v. ITC                21

 See Schindler Elevator Corp. v. Otis Elevator Co., 593 F.3d
 1275, 1285 (Fed. Cir. 2010) (“The doctrine of prosecution
 disclaimer attaches where an applicant, whether by
 amendment or by argument, unequivocally disavowed a
 certain meaning to obtain his patent.” (internal quotation
 marks omitted)); see also id. (“An argument made to an ex-
 aminer constitutes a disclaimer only if it is clear and un-
 mistakable.” (internal quotation marks omitted)).
                          *   *   *
     For the foregoing reasons, we affirm the Commission’s
 claim construction and its finding of infringement under
 the doctrine of equivalents.
                        CONCLUSION
     We have considered Jennewein’s remaining arguments
 and find them unpersuasive. For the reasons stated above,
 we affirm the Commission’s claim construction and judg-
 ment as to infringement, and hence its issuance of the lim-
 ited exclusion order.
                       AFFIRMED