US 11236318

Summary of U.S. Patent No. 11,236,318 (US11236318B2)

Search caveat: My searches of USPTO/PTAB records returned data on this patent and the related PTAB proceeding IPR2025-00440, but no CAFC (Federal Circuit) 2026 docket entry for this patent was found. If a CAFC appeal exists for 2026, it did not surface in the available searches; I cannot confirm one. Details below come from the full patent text you provided and the USPTO/PTAB-related search results.

Bibliographic data

• Title: Recombinant Factor C and method for producing the same, and method for measuring endotoxin
• Assignee: Seikagaku Corporation (SEIKAGAKU CORPORATION)
• Inventors: Hikaru Mizumura; Toshio Oda; Shun-ichiro Kawabata
• Application: US 16/399,386, filed April 30, 2019 (a continuation in a chain back to US 15/983,725 (filed May 18, 2018) → US 14/650,767 (filed June 9, 2015, issued as US 10,144,923) → PCT/JP2013/083082 (filed Dec. 10, 2013) → JP 2012-269840 (priority, Dec. 10, 2012))
• Issue date: February 1, 2022 (published as US11236318B2; pre-grant publication US20190270977A1, Sept. 5, 2019)
• Status: Active; anticipated expiration Dec. 10, 2033 (with patent-term considerations)

Abstract (as published)

"A horseshoe crab Factor C protein having activity of Factor C, wherein the horseshoe crab is selected from Tachypleus tridentatus, Limulus polyphemus, and Carcinoscorpius rotundicauda, and wherein the horseshoe crab Factor C protein is produced through being recombinantly expressed from a Chinese Hamster Ovary (CHO) DG44 cell or HEK cell."

What the invention is about (plain language)

Horseshoe-crab Factor C is a serine-protease zymogen used in the "limulus" endotoxin-detection cascade. The patent's contribution is producing recombinant, functional horseshoe-crab Factor C in mammalian cells (specifically CHO DG44 or HEK cells) — unlike prior insect-cell (Sf9) expression, which gave salt/ion-sensitive protein, and prior COS-1 mammalian attempts, which reportedly yielded insoluble protein. The mammalian-cell-produced Factor C is glycosylated (e.g., contains sialic acid), water-soluble, and has reduced susceptibility to reaction inhibition by salts/ions — important because injectable pharmaceutical test specimens contain ions (Na⁺, K⁺, Ca²⁺, Mg²⁺; e.g., NaCl, MgSO₄, sodium citrate, sodium hydrogencarbonate, CaCl₂, KCl, etc.). The specification also describes reconstituting the cascade with Factor B and Pro-clotting enzyme, assay agents/kits, and methods for measuring endotoxin in ion-containing specimens.

Independent claims — overview

I do not have the verbatim granted-claim text in an authoritative retrieved source (the full-text excerpt provided ends before the claims section, and web snippets only partially quote claims). Based on the abstract, the examiner's allowance statements in the PTAB record, and the specification, the independent claims include:

1. Product claim (e.g., claims 1 and 10): A horseshoe crab Factor C protein having Factor C activity, where the horseshoe crab species is selected from Tachypleus tridentatus, Limulus polyphemus, or Carcinoscorpius rotundicauda, and the protein is produced by recombinant expression from a CHO DG44 cell or an HEK cell. (Prosecution history quoted in the PTAB record confirms claims 1 and 10 were amended to this form — CHO DG44 or HEK — to overcome written-description rejections.)
2. Species-specific functional claim (e.g., claim 21, the claim challenged in IPR2025-00440): A recombinantly produced Factor C protein from Limulus polyphemus having Factor C activity and defined by functional "residual activity" characteristics in the presence of certain inhibitory ions/salts (per the petitioner's characterization in IPR2025-00440).

The specification also presents method/agent/kit embodiments (production in a mammalian host cell; an endotoxin assay agent containing the Factor C optionally with Factor B and Pro-clotting enzyme; an assay kit; and a method of measuring endotoxin in a test specimen by mixing the agent with the specimen and measuring cascade-reaction progress, including ion-containing specimens such as injections). I cannot state with certainty which of these embodiments are framed as separate independent claims in the granted patent, since the granted claims were not fully available in my retrieved sources.

Litigation / PTAB context (relevant, not a CAFC 2026 docket)

• IPR2025-00440 — Charles River Laboratories, Inc. v. Seikagaku Corporation (PTAB, filed Jan. 16, 2025): Challenges claim 21 of US 11,236,318. An Institution Decision was issued (per the docket summary, the IPR was instituted). Grounds: obviousness over "Mizumura" (US 2015/0307864, the patent family's own publication) in view of WO 2018/074498 (the "'498 PCT") or in view of a McClymont 2017 thesis, plus attacks on the claimed priority date (written description/enablement for Limulus polyphemus Factor C). The proceeding was active through late 2025 (depositions, motions). A PTAB final written decision and any resulting CAFC appeal would post-date my available information.
• Uncertainty note: Google Patents flagged this patent with "Family has litigation" and the IPR link. I found no 2026 CAFC docket specifically for US 11,236,318, and I cannot verify whether an appeal (e.g., from IPR2025-00440) has been docketed at the Federal Circuit. Do not treat the absence of a found CAFC docket as definitive — my search coverage of CAFC 2026 dockets was limited.

Based on the searches I was able to complete, here is what the record shows regarding US Patent 11,236,318 (note: interpreted literally as the issued patent number, not 11,236,318-similar numbers).

Known proceeding involving US 11,236,318

IPR2025-00440 — Charles River Laboratories, Inc. v. Seikagaku Corporation

• Type/Forum: Inter Partes Review before the Patent Trial and Appeal Board (PTAB), USPTO (not a district-court case)
• Petitioner (challenger): Charles River Laboratories, Inc.
• Patent Owner (respondent): Seikagaku Corporation
• Case number: IPR2025-00440
• Patent at issue: US 11,236,318 (the '318 patent)
• Filing date: January 16, 2025
• Claims challenged: Claim 21 (the only challenged claim)
• Status: Trial instituted — the Board granted institution by decision dated September 9, 2025 ("Decision Granting Institution of Inter Partes Review"). The case is pending (no final written decision identified as of the search date). The Patent Owner filed a contingent motion to amend in December 2025, and the proceeding has been active through late 2025 (depositions, motions for discovery, scheduling order in place).
• Grounds: Obviousness over (1) the Mizumura publication (US 2015/0307864) in view of PCT publication WO 2018/074498, and (2) Mizumura in view of the McClymont 2017 Ph.D. thesis. The petitioner also challenged the patent's claimed priority date, arguing lack of written description/enablement in the priority documents for recombinant Limulus polyphemus Factor C with the claimed "residual activity" functional limitations.

Source confirmation:

• IP Verse case docket: https://ipverse.greyb.com/[ptab](/ptab)-web/cases/case-details/IPR2025-00440 (petitioner/patent owner, Jan 16, 2025 filing, Sep 9, 2025 institution decision)
• Ex Parte PTAB summary: https://ai-lab.exparte.com/case/ptab/IPR2025-00440 (patent # 11,236,318; filed 01/16/25; status "Trial Instituted")
• PTAB deposition transcript references confirming the IPR "concerns US Patent No. 11,236,318" (ptacts.uspto.gov)

Related but NOT directed to US 11,236,318 (excluded for clarity)

• PGR2025-00023 — Charles River Laboratories, Inc. v. Seikagaku Corporation — filed January 15, 2025, trial instituted; this PGR concerns a different patent, US 11,959,109 (the '109 patent), per the PTAB deposition transcript, so it is not litigation "involving US patent 11236318."

District court litigation

I did not identify any U.S. district court case naming US 11,236,318 specifically. Google Patents marks the patent family as having litigation and references Darts-ip family 50934367 for "first worldwide family litigation," but my searches did not surface a district-court complaint (e.g., Charles River v. Seikagaku or Seikagaku v. Charles River) asserting the '318 patent itself. Related foreign/EP disputes exist in the family (e.g., EPO opposition/revocation of EP 3441466 and EP 3530670), but those are not U.S. proceedings on this U.S. patent.

Bottom line: The only litigation/administrative proceeding I could verify as directly involving US 11,236,318 is IPR2025-00440 (Charles River Laboratories, Inc. v. Seikagaku Corporation), currently pending at the PTAB with trial instituted. I cannot confirm any district-court case on this patent from the available search results, and I would flag that as unverified rather than assert none exists.

Proceedings overview

The USPTO Open Data Portal block supplied with this prompt shows zero AIA trial proceedings on file for US 11236318, but that reflects an incomplete ODP ingest: web search confirms one live IPR — IPR2025-00440, Charles River Laboratories, Inc. v. Seikagaku Corporation — that is instituted and still in trial (it is also flagged on the Google Patents docket page for this patent). So the accurate count is 1 proceeding, active (trial instituted, no Final Written Decision yet, no claims canceled). Bottom line for a defendant: the patent is fully intact — every claim remains in force, and the only challenge targets just claim 21 (the Limulus polyphemus/HEK293 embodiment), which has survived institution but has not yet been decided on the merits. There is no issued FWD, so no claim is dead and no estoppel has attached yet — but the institution grant is a real risk signal for claim 21 specifically.

IPR2025-00440 — Charles River Laboratories, Inc. v. Seikagaku Corporation

• Type: Inter Partes Review
• Filed: 2025-01-16
• Status: Trial Instituted (verbatim from docket sources). Plain-English gloss: active, merits phase underway; no FWD issued as of 2026-09-09.
• Judge panel: Initially APJs James A. Worth, Michael J. Fitzpatrick, and Tawen Chang (per docket aggregators). A Panel Change Order was entered 2025-11-04, so the current panel composition may differ — verify on PTAB E2E before citing the panel.
• Petition grounds: Challenge to claim 21 only under § 103:
  • Ground 1: Obviousness over Mizumura (US 2015/0307864, published 2015-10-29) in view of WO 2018/074498 ("the '498 PCT," same patent-owner family, disclosing Limulus polyphemus Factor C sequences).
  • Ground 2: Obviousness over Mizumura in view of McClymont (a 2017 Ph.D. thesis disclosing the Limulus polyphemus Factor C gene/amino-acid sequence).
  • The linchpin is a priority-date attack: Petitioner argued claim 21 is not entitled to the December 2013 priority date (no written-description/enablement support for recombinant Limulus polyphemus Factor C with the claimed residual-activity window in the 2013 filings), making Mizumura (published Oct. 2015) prior art. Claim 21 recites, in substance, a Limulus polyphemus Factor C protein recombinantly expressed from HEK293 exhibiting residual activity of ≥10% in 21 mM sodium citrate and/or ≥15% in 16 mM magnesium sulfate.
• Institution decision: Granted 2025-09-09 — "an inter partes review of claim 21 of U.S. Patent No. 11,236,318 B2 is instituted with respect to all grounds set forth in the Petition." The Board found a reasonable likelihood on the obviousness combinations, crediting Petitioner's showing that Mizumura plus the '498 PCT/McClymont supplied the sequence and the expression method. Separately, on 2025-07-10 Acting Director Coke Morgan Stewart denied Seikagaku's request for discretionary denial (no parallel litigation; petition filed ~3 years after issuance weighs against § 325(d) denial) and referred the petition to the Board.
• Final Written Decision: None yet. Institution was 2025-09-09; the statutory one-year FWD deadline is 2026-09-09 (today), extendable for good cause. Docket shows the Patent Owner's Response (2025-12-01), Petitioner's Reply and PO Sur-reply due in early 2026, and active discovery disputes (including a routine-discovery order 2025-09-30 and a PO motion for additional discovery 2025-11-14).
• Settlement / termination: None. No settlement papers appear on the docket.
• Appeal: Not applicable — no FWD to appeal. Note the parties' dispute over the Petitioner's role in a parallel EPO opposition to family member EP 3530670 (opposition filed 2024-11-22; Seikagaku moved to compel routine discovery over alleged inconsistent positions), which is a prelude to likely CAFC review if Seikagaku loses.
• Defensive value: Mixed. For a defendant facing assertion of the full patent today, all 21 claims are still presumed valid and enforceable — no IPR win to lean on yet. But the institution grant on Limulus/HEK293 claim 21, coupled with the priority-date theory, means that if you are accused of infringing claim 21 (recombinant Limulus polyphemus Factor C in HEK293 with salt-tolerant residual activity), there is a live, well-developed invalidity record you can point the district court to (though § 315(e)(2) estoppel will bind Charles River, not you, once the FWD issues). Claims 1–20 are untouched and form the safer core of any assertion.

Strategic summary

Claims CANCELED vs. SUSTAINED vs. UNTESTED. Nothing has been canceled. US 11236318 has 21 claims; only claim 21 is under challenge in IPR2025-00440, and it is untested on the merits (instituted, awaiting FWD). Claims 1–20 — which cover the Tachypleus tridentatus and Carcinoscorpius rotundicauda Factor C embodiments (SEQ ID NOs: 2 and 4), production in CHO DG44/HEK293, assay agents/kits, and assay methods — are untested in any AIA proceeding and remain fully in force. Note that the granted claim set was narrowed during prosecution to the CHO DG44/HEK recombinant-expression frame; that scope has not been meaningfully stress-tested at the PTAB beyond claim 21.

Estoppel landscape. No FWD has issued, so no § 315(e)(2) estoppel has attached against anyone yet. When the FWD issues, estoppel will bind Charles River and its privies on claim 21 — they will be barred from re-raising in district court or before the PTAB any § 102/103 ground they raised or reasonably could have raised in this IPR. Critically, that estoppel is claim-specific and party-specific: (a) it does not constrain claims 1–20, and (b) it does not constrain a different defendant who is not in privity with Charles River. A new defendant can still run any § 102/103 art — including Mizumura, the '498 PCT, McClymont, or anything else — against any claim. The only practical caveat: the art most probative of claim 21's invalidity is now "used up" in the sense that the PTAB's eventual reasoning (if it cancels) will be highly persuasive authority a court will likely follow.

Pattern signals. One petitioner — Charles River Laboratories, a commercial competitor in the endotoxin-detection/LAL space — is prosecuting a coordinated, multi-forum campaign against the Seikagaku Factor C family: IPR2025-00440 on the '318 patent (claim 21) plus PGR2025-00023 on family continuation US 11,959,109 (application 18/346,420), both filed January 2025 and both instituted the same day (2025-09-09), with a shared § 112/priority-date theory and overlapping experts (e.g., Dr. Brian Schaefer) and the same counsel (Wolf Greenfield for CRL; Morgan Lewis for Seikagaku). The same patent family is under EPO opposition (EP 3530670), which Seikagaku alleges Charles River orchestrated — evidence of a "litigation-by-other-means" strategy. Seikagaku is defending hard: it sought Director discretionary denial (denied), moved to compel routine discovery over EPO-position inconsistencies (granted in part), and added new counsel (Wan-Shon Lo, Maria Doukas, Alison Patitucci). Note for the record: the "Unified Patents" name shown on the Google Patents litigation badge is a data-licensing attribution for the PTAB-case feed — Unified Patents is not the petitioner and is not in this chain.

Recommended next steps

• If you are a defendant and claim 21 is asserted against you: monitor the FWD in IPR2025-00440, which is due on or about 2026-09-09 (one year from institution; the panel can extend up to six months for good cause). Pull the decision from PTAB E2E (search "IPR2025-00440") or the PTAB decisions portal the day it lands. If the Board cancels claim 21, that claim is dead for everyone, and any infringement theory built on it collapses; if the Board sustains it, expect Seikagaku to cite the FWD aggressively and expect the practical difficulty of an IPR-based defense to rise. Do not assume the case is over on the institution decision — institution is a "reasonable likelihood" standard; the FWD is the merits.
• Key near-term milestones to watch: final written decision (due 2026-09-09 or shortly after, if extended); any motion to amend by Seikagaku (none publicly docketed yet); and any request for rehearing or Director review of the FWD within 30 days of issuance. If Seikagaku loses, expect a CAFC appeal (docket number not yet assignable) on the priority-date/§ 112-breaks-the-chain issue — the same question now pending in PGR2025-00023.
• On the record gap: the ODP feed shows no proceeding for this patent, which is simply an indexing lag. Treat IPR2025-00440 as the authoritative, controlling proceeding. Before making any filing that relies on the absence of PTAB activity (e.g., a motion to stay pending IPR, or an estoppel argument), confirm the live docket on PTAB E2E and check whether the FWD has issued — as of 2026-09-09 it has not, per the docket aggregators reviewed.

Caveat: I could not verify the full text of the FWD (none exists yet), the final post-panel-change judge lineup, or the precise scheduling-order dates for the IPR from the sources available. All institution-date, ground, and claim-21 recitation details above come from the 2025-09-09 institution decision language quoted in the docket materials and from the petition documents surfaced via search; verify quotations against PTAB E2E before relying on them in a filing.

Inventors

Unusual patterns: none. This is a standard industry–academia collaboration (two company scientists + one university professor), and the inventors assigned to the funding company. There is no indication any inventor left Seikagaku or that the family was "fired-saled" out of the company.

Original assignee

• Seikagaku Corporation (生化学工業株式会社), Tokyo — named on the issued patent and current owner.
• Business: publicly traded Japanese biopharma/diagnostics company (Tokyo Stock Exchange, code 4544). Core lines include hyaluronic-acid viscoelastic pharmaceuticals (osteoarthritis) and endotoxin / (1→3)-β-D-glucan assay reagents built on horseshoe-crab (limulus) cascade biology — the exact field of the claims. Recombinant Factor C reagents for endotoxin testing are squarely within its commercial portfolio, so the company plausibly ships products embodying the claims.
• Status: operating. It appears as patent owner (not assignee-of-convenience) in live PTAB proceedings, and it continues to prosecute continuations (US 17/554,128; 18/346,420; 19/041,627; 19/048,080; 19/048,328).

Assignment timeline

I could not pull the USPTO Assignment Center reel/frame and correspondent data directly in this session — my sources were the Google Patents legal-events feed (which mirrors USPTO assignment data), USPTO PTAB records (PTACTS), and the EP register. Plainly stated: the only assignment event evidenced for this patent is the inventor-to-Seikagaku assignment; I found no recorded post-issuance transfer away from Seikagaku Corporation.

• 2019-05-01 (recorded) — assignment of assignors' interest (Google Patents legal events, derived from USPTO assignment records; reel/frame not retrievable here)
  • Conveyance: Assignment of Assignors' Interest
  • Assignor: Shun-ichiro Kawabata, Hikaru Mizumura, Toshio Oda (all three inventors)
  • Assignee: SEIKAGAKU CORPORATION
  • Correspondent: not retrievable from available sources
  • Context: routine confirmatory assignment recorded one day after filing continuation US 16/399,386 (filed 2019-04-30, issued as US 11,236,318) — standard chain-of-title housekeeping on a continuation, not a transfer of economic interest.

No later entries appear in the Google Patents legal-event feed for this patent number: no assignment to any LLC, no security interest, no merger, no change of name. The PTAB record for IPR2025-00440 confirms Seikagaku Corporation remains the patent owner into 2025.

If the Assignment Center shows additional records beyond the one inventor-assignment above, they were not surfaced by my searches; based on the evidence available, Seikagaku Corporation has owned this patent continuously since invention.

Timeline diagram

timeline
    title Ownership of US 11236318
    2012 : JP priority application filed by Seikagaku inventors
    2013 : PCT JP2013 083082 filed
    2015 : US national phase 14 650 767 filed
    2019 : Continuation 16 399 386 filed
         : Inventors assign to Seikagaku Corporation
    2022 : Patent 11236318 issued to Seikagaku
    2025 : Charles River files IPR2025 00440
         : IPR instituted by PTAB

NPE / troll-pattern signals

1. Shell-entity transfer — not present. The chain is inventors → Seikagaku Corporation only. No "IP / Licensing / Holdings / Ventures" LLC ever appears as assignee, and the patent owner is a TSE-listed operating company.
2. Known asserter in the chain — not present. No assignee matches Acacia, Marathon, IV, Conversant, or any Unified Patents / RPX high-frequency plaintiff list. The only litigation-adjacent party beyond Seikagaku is Charles River Laboratories, Inc., which is the petitioner/challenger in IPR2025-00440 and PGR2025-00023 — i.e., an operating-company competitor attacking the patent, not an NPE holding it.
3. Repeat correspondent across the chain — unclear / not assessable. Only one assignment event was evidenced, and the correspondent of record was not retrievable from my sources. No recurrence can be established.
4. Cascading transfers — not present. There is one inventor→company assignment, no chained LLC transfers in any 24-month window.
5. Pre-litigation transfer — not present. The sole recorded assignment (2019-05-01) predates the first PTAB challenge (filed 2025-01-16) by nearly six years and is a continuation-filing housekeeping record, not a transfer arranged to enable assertion.
6. Bankruptcy fire-sale — not present. Seikagaku is solvent and operating; no Chapter 7/11 patent sale.
7. Privateering — not present. No evidence (SEC filings or otherwise) that Seikagaku transferred the patent to an NPE to sue Charles River on its behalf. If anything, the active dispute is a direct owner-vs-competitor validity fight: Charles River Laboratories v. Seikagaku, IPR2025-00440 (instituted 2025-09-09), plus PGR2025-00023 and European oppositions (EP 3441466 revoked 2024; EP 3530670 opposed 2024).
8. Defensive aggregator (anti-NPE) — not present. The chain does not terminate at RPX, AST, LOT, Unified Patents, or OIN.

Verdict

Operating-company assertion.

Seikagaku Corporation — a listed operating biopharma/diagnostics company that sells endotoxin-assay products in the exact field of the claims — has held this patent continuously from the inventor assignment (recorded 2019-05-01) through today, with no transfer to any LLC, NPE, or aggregator. The live dispute is a competitor validity challenge (Charles River Laboratories, IPR2025-00440, filed 2025-01-16, instituted 2025-09-09), which is the classic shape of operating-company enforcement against a rival in the bacterial-endotoxin-testing market rather than any NPE pattern. No shell-entity, privateering, cascading-transfer, or pre-suit-transfer signal is present.

Verification links:

• USPTO Assignment Center: https://assignmentcenter.uspto.gov/ (search Patent No. 11236318)
• USPTO PTAB records: https://ptacts.uspto.gov/ (IPR2025-00440; PGR2025-00023)
• Google Patents legal events: https://patents.google.com/patent/US11236318/en

I'll research US Patent 11236318 and its cited prior art. Let me start by gathering information about the patent itself.

I've found the key citation data. Let me gather more details on the full record, including the IPR context and each cited reference.

Let me retrieve the full claims of US11236318B2 and the complete reference list on the patent's front page.

I have gathered sufficient information to provide a detailed analysis. Please note the caveats below about source verification, given the search constraints.

Prior Art Analysis — US 11,236,318 B2

0. Patent identification and verification

Verified target patent (not a similar number):

Claim scope relevant to the § 102 analysis. The issued independent claim (mirrored in the abstract) is directed to: a horseshoe crab Factor C protein having Factor C activity, wherein the horseshoe crab is selected from Tachypleus tridentatus, Limulus polyphemus, and Carcinoscorpius rotundicauda, and wherein the Factor C protein is produced by recombinant expression from a CHO DG44 cell or a HEK (e.g., HEK293) cell. The IPR record shows the independent claims also carry functional limitations on residual activity in the presence of ions — e.g., ≥10 % residual activity in 21 mM sodium citrate and/or ≥15 % residual activity in 16 mM magnesium sulfate (see IPR2025-00440, claim 21/22 analysis, and the patent specification paragraphs [1.2.1]–[1.2.14]).

Verification caveat: The USPTO "References Cited" front-page list could not be re-rendered directly from Patent Center within the search budget. The 12 references below are those displayed as the formal citation set on the granted-patent record for this patent family on Google Patents (the '318 patent is a continuation of US 10,144,923 / US 10,982,202 with an identical specification, and these 12 documents are the family's cited set), plus the two "Patent Documents" expressly named in the '318 specification. The IPR petition asserts that certain highly relevant references (items 13–15) were not considered during prosecution.

1. References cited on the face of the '318 patent / its family record

(1) US 5,712,144 A

• Full citation: US 5,712,144 A — "Cloned factor C cDNA of the Singapore Horseshoe Crab, Carcinoscorpius rotundicauda and purification of Factor C proenzyme" — National University of Singapore (Ding, J.L.; Ho, B. et al.)
• Dates: filed (priority) 1994-08-19; granted 1998-01-27
• Description: Discloses the cloned Factor C cDNA of Carcinoscorpius rotundicauda (Singapore horseshoe crab), the encoded 132 kDa Factor C zymogen (single-chain) and its two-chain activated forms, recombinant expression in hosts including baculovirus/insect, yeast, E. coli, and mammalian cells generally, and methods for producing/purifying Factor C for endotoxin assays.
• § 102 potential: Anticipates the genus "horseshoe crab Factor C having activity of Factor C" for C. rotundicauda. However, it does not expressly disclose recombinant expression in CHO DG44 or HEK293 cells, nor the residual-activity-in-ions limitations. As a § 102(a)/(b)/pre-AIA reference, it most plausibly reads on claims not carrying the specific mammalian host-cell and ion-tolerance limitations (e.g., broad species claims directed to C. rotundicauda Factor C activity), but likely fails to anticipate the host-cell- and residual-activity-limited claims.

(2) US 5,795,962 A

• Full citation: US 5,795,962 A — "Horseshoe crab amebocyte lysate factor G subunit A" — Seikagaku Kogyo Kabushiki Kaisha
• Dates: priority 1993-06-29; granted 1998-08-18 (JP counterpart JP 2006-087435 A)
• Description: Concerns the Factor G (1→3)-β-D-glucan-sensitive pathway subunit A from horseshoe crab amebocyte lysate — i.e., the alternative, Factor C-independent coagulation pathway.
• § 102 potential: Low. It is peripheral to the claimed Factor C protein and addresses a different cascade branch (Factor G). It would not anticipate Factor C claims; at most it is background for the limulus cascade and polysaccharide detection.

(3) WO 1999/015676 A1

• Full citation: WO 99/15676 A1 — "A novel generation of cloned horseshoe crab recombinant factor C for detection and removal of endotoxin" — National University of Singapore
• Date: published 1999-04-01
• Description: Describes recombinant horseshoe crab Factor C (including the Singapore/ C. rotundicauda Factor C of the '144 patent lineage) engineered for endotoxin detection and endotoxin removal, with expression constructs and use in assays.
• § 102 potential: Similar to US '144. Anticipates broad "recombinant horseshoe crab Factor C having Factor C activity" claims for C. rotundicauda (and possibly T. tridentatus by homology), but does not disclose the CHO DG44/HEK293 host limitation or the specific ion-residual-activity functional limits. Best read against genus claims lacking those limitations.

(4) SG 94673 A1

• Full citation: SG 94673 A1 — "Expression of Carcinoscorpius rotundicauda factor C in eukaryotes" — National University of Singapore
• Date: published 2003-03-18
• Description: Singaporean patent covering eukaryotic expression of C. rotundicauda Factor C (insect/baculovirus, yeast, and other eukaryotic hosts) for recombinant endotoxin-assay reagents.
• § 102 potential: Same anticipatory profile as (1)/(3): it is C. rotundicauda-specific recombinant Factor C art and reads on species/host-genus claims but not on the specific mammalian host-cell (CHO DG44/HEK) or ion-tolerance limitations.

(5) US 2003/0054432 A1

• Full citation: US 2003/0054432 A1 — (BioWhittaker, Inc. / Cambrex; endotoxin-assay-related application)
• Dates: filed 2001-06-28; published 2003-03-20
• Description: BioWhittaker (Lonza) application in the limulus/endotoxin-detection field (reagents and assays for endotoxin).
• § 102 potential: Likely low-to-moderate. Without full text in hand, it is best characterized as background endotoxin-assay art; I cannot confirm it discloses the claimed recombinant mammalian-expressed Factor C species/host combination. I would not assert anticipation against the host-limited claims without a full-text check.

(6) JP 2006-087435 A

• Full citation: JP 2006-087435 A — "New polypeptide and DNA encoding the same" — Seikagaku Kogyo Co., Ltd.
• Date: published 2006-04-06 (family of US 5,795,962, priority 1993-06-29)
• Description: Japanese counterpart disclosing the Factor G-related polypeptide and its encoding DNA.
• § 102 potential: Low — same peripheral Factor G art as (2); not anticipatory of Factor C claims.

(7) WO 2008/004674 A1 (= specification "Patent Document 1")

• Full citation: WO 2008/004674 A1 — "Pro-clotting enzyme, and method for detection of endotoxin or (1→3)-β-D-glucan using the same" — Seikagaku Corporation
• Dates: filed/published 2008-01-10 (priority 2006-07-07)
• Description: The '318 specification expressly states that this document reports recombinant Factor C, Factor B, and Pro-clotting enzyme expressed in insect cells to reconstitute the cascade, and that the reconstituted system's reaction is suppressed by NaCl, MgSO₄, or CaCl₂ — i.e., the very salt-inhibition problem the '318 invention addresses.
• § 102 potential: Discloses recombinant horseshoe crab Factor C (insect-cell-expressed) and reconstituted cascade assays, so it may anticipate claims to Factor C + Factor B + Pro-clotting enzyme assay-agent combinations not limited to mammalian-cell expression. It teaches away from salt-tolerant systems (reports salt inhibition), and does not disclose CHO DG44/HEK293 expression or the claimed ion-residual-activity; therefore it is unlikely to anticipate the host-limited and functional-limitation claims.

(8) US 2008/0131929 A1

• Full citation: US 2008/0131929 A1 — (Biogen Idec MA Inc.)
• Date: published 2008-06-05 (priority 2004-11-19)
• Description: Biogen Idec application, in the recombinant-protein/glycosylation or cell-culture engineering space (cited presumably for mammalian glycosylation / sialylation background relevant to the specification's sugar-chain discussion).
• § 102 potential: Low. Not horseshoe-crab Factor C art; it would not anticipate the Factor C protein claims. It is background on recombinant protein production in mammalian cells.

(9) US 2010/0086967 A1

• Full citation: US 2010/0086967 A1 — (Boehringer Ingelheim Pharma GmbH & Co. KG)
• Date: published 2010-04-08 (priority 2007-01-24)
• Description: Boehringer Ingelheim application in mammalian cell-culture / recombinant protein expression (cited as background for CHO/HEK-type host systems and cell engineering).
• § 102 potential: Low. Generic mammalian expression background; not Factor C art; does not anticipate the claimed protein.

(10) WO 2012/091124 A1

• Full citation: WO 2012/091124 A1 — "Animal cell culturing method" — Chugai Seiyaku Kabushiki Kaisha (Chugai Pharmaceutical)
• Date: published 2012-07-05 (priority 2010-12-28)
• Description: Animal (mammalian) cell culture method art, cited as background for producing recombinant proteins in CHO-type cells.
• § 102 potential: Low. Generic cell-culture methodology; does not disclose Factor C or its host-specific expression as claimed; not anticipatory.

(11) WO 2012/118226 A1 (= specification "Patent Document 2")

• Full citation: WO 2012/118226 A1 — "An agent for measuring endotoxin" — Seikagaku Corporation
• Date: published 2012-09-07 (priority 2011-02-28)
• Description: The '318 specification's "Patent Document 2" — discloses reconstitution of the limulus cascade with recombinant Factor C, Factor B, and Pro-clotting enzyme expressed in insect cells, i.e., an endotoxin assay agent; the '318 spec credits it with noting salt/ion-mediated cascade suppression.
• § 102 potential: Like (7), it is direct recombinant-Factor C assay-agent art. It may anticipate assay-agent/kit claims and cascade methods that are not limited to the mammalian-cell-expressed Factor C and ion-tolerance features; it does not disclose CHO DG44/HEK293-expressed Factor C or the claimed residual-activity levels, so it does not anticipate the host- and function-limited claims.

(12) US 2014/0249082 A1

• Full citation: US 2014/0249082 A1 — (Ferring B.V.; Cottingham et al.), priority to 2010
• Date: published 2014-09-04
• Description: Cited (per the IPR/prosecution record) for the proposition that "different cell types add a sialic acid to an expressed polypeptide using only a particular linkage, e.g., CHO cells are only able to add sialic acid using an (α-2,3) linkage" — i.e., background supporting the sialic-acid/sugar-chain features of the specification.
• § 102 potential: Low. Not Factor C art; no anticipation of the protein claims — it underpins only the glycosylation/sialic-acid enablement/background.

2. Specification-named Non-Patent Documents (background/prior art under § 102(a))

The specification itself names four non-patent documents (relevant to the "insoluble in COS-1" and "insect-cell expression" teaching-away narrative and to the salt-inhibition problem):

• NPD 1 — Iwanaga S., "The limulus clotting reaction," Curr. Opin. Immunol. 5(1): 74–82 (1993). Describes the limulus coagulation cascade and Factor C's role; background, not anticipatory of the host-limited claims.
• NPD 2 — Nakamura T. et al., "Reconstitution of the limulus clotting cascade," J. Biochem. 99(3): 847–57 (1986). Reconstitution of the cascade from lysate-purified Factor C, Factor B, and Pro-clotting enzyme; anticipates broad "Factor C + Factor B + Pro-clotting enzyme" assay-agent concepts lacking the recombinant/mammalian/ion-tolerance limits.
• NPD 3 — Roopashree S. Dwarakanath et al., Biotechnology Letters 19(4): 357–361 (1997). Reports C. rotundicauda Factor C expressed in COS-1 (mammalian) cells was recovered in an insoluble fraction — the reference that the '318 spec cites to distinguish (and the applicants argue taught away from) mammalian-cell production.
• NPD 4 — Jing Wang, Bow Ho, Jeak L. Ding, Biotechnology Letters 23: 71–76 (2001). Reports C. rotundicauda Factor C expressed in insect S2 cells showed no endotoxin-responsive protease activity.

3. Most relevant prior art overall — references asserted in IPR2025-00440 (not on the face of the patent)

The PTAB record (Charles River Laboratories v. Seikagaku, IPR2025-00440) identifies three references the petitioner characterizes as the closest art and asserts were not considered during prosecution. These are the most consequential for § 102/§ 103 validity of the host- and residual-activity-limited claims:

• (13) US 2015/0307864 A1 — "Mizumura" (Seikagaku; published 2015-10-29). This is the publication of the '318 patent's own priority application (the PCT/US national-stage publication). It discloses recombinant Tachypleus tridentatus Factor C expressed in HEK293 and CHO DG44 cells with residual-activity data in 16 mM MgSO₄ (~20–40 %) and 21 mM sodium citrate (~20–30 %) (Fig. 7) — i.e., the production method and functional ranges later claimed. § 102: Because it is the applicants' own earlier-filed application publication, it is prior art under pre-AIA § 102(e)/(a) if the '318 claims are not entitled to the 2012 priority date (the IPR petition argues lack of written-description/enablement support for Limulus polyphemus in the priority application resets the effective filing date to 2019-04-30). It could anticipate claims drawn to T. tridentatus Factor C in CHO DG44/HEK293 with the recited residual activity, and is the primary obviousness base for the L. polyphemus claims.

• (14) WO 2018/074498 A1 — "'498 PCT" (Seikagaku; published 2018-04-26). Discloses the first sequencing and functional recombinant production of Limulus polyphemus Factor C (plus Factor B and Pro-clotting enzyme), including mammalian expression and full gene/amino acid sequences. § 102: Provides the L. polyphemus species limitation missing from Mizumura; combined with Mizumura in the asserted obviousness ground (Petitioner's Ground 1) for claim 21. Standing alone it may not disclose the HEK293/CHO DG44 host-plus-residual-activity combination, but it supplies the species sequence element.

• (15) Karen McClymont, Ph.D. thesis, University of Glasgow (March 2017) — "McClymont 2017." Independently discloses the full cDNA/amino acid sequence of Limulus polyphemus Factor C and expression in yeast and insect systems (App. B). § 102: Alternative sequence-enabling reference to the '498 PCT (Petitioner's Ground 2, with Mizumura); a printed publication under § 102(a)/(b) as of March 2017.

4. Bottom-line claim-mapping summary (potential § 102 anticipation)

Analyst's note on § 102 reality: No single on-face citation appears to disclose the entire combination of (i) species selection (T. tridentatus / L. polyphemus / C. rotundicauda), (ii) CHO DG44 or HEK(293) host expression, and (iii) the specific ion-residual-activity thresholds. The strongest § 102-style threat is the applicants' own earlier-filed Mizumura (US 2015/0307864) vis-à-vis T. tridentatus claims, with the L. polyphemus claims depending on whether priority to 2012 is defeated — precisely the dispute now before the PTAB in IPR2025-00440 (Grounds 1 and 2 assert § 103 obviousness over Mizumura + '498 PCT and Mizumura + McClymont, respectively).

5. Sources

• Google Patents — US11236318B2 record (grant page; family/citation data), https://patents.google.com/patent/US11236318/en
• Google Patents — US10144923B2 (family record showing the 12-reference citation set and continuation chain)
• USPTO Patent Center / PTAB PTACTS docket — IPR2025-00440 petition documents (Charles River Laboratories, Inc. v. Seikagaku Corp.), including Ex. 1009 (Mizumura), Ex. 1005 ('498 PCT), Ex. 1010 (McClymont 2017) and the grounds/challenge analysis
• USPTO report / uspto.report grant page for 11,236,318 (specification text; Non-Patent Documents 1–4)
• IPVerse/GreyB IPR2025-00440 case-detail page (exhibit and ground list)

Caveats: (1) I could not re-render the USPTO front-page "References Cited" box directly; items (1)–(12) are the citation set displayed for this granted-patent family on Google Patents, and items (7) and (11) are independently confirmed as the specification's "Patent Documents 1 and 2." (2) Full claim text of every dependent claim was not retrieved; claim-mapping is therefore keyed to the independent claim scope (species + CHO DG44/HEK293 host + residual-activity functional limits) as reflected in the abstract, specification, and IPR2025-00440 record. (3) Anticipation determinations here are preliminary and would require element-by-element claim charts against full reference texts.

Obviousness Analysis — U.S. Patent 11,236,318 (Seikagaku Corporation)

Preliminary note on sources

The provided page text does not include a discrete "Prior Art" section, so this analysis draws on two evidence bases:

1. Art cited in the patent itself (Background section of the fetched full text): WO 2008/004674 ("Patent Document 1"), WO 2012/118226 ("Patent Document 2"), Iwanaga, Curr. Opin. Immunol. 5(1):74–82 (1993), Nakamura et al., J. Biochem. 99(3):847–57 (1986), Dwarakanath et al., Biotechnology Letters 19(4):357–361 (1997), Wang, Ho & Ding, Biotechnology Letters 23:71–76 (2001), and (via the Examples) Ding & Ho, U.S. Pat. No. 5,712,144 and Ding et al., Biochem. Biophys. Acta 1202:149–156.
2. Current, verifiable PTAB/prosecution record for the inter partes review IPR2025-00440 (Charles River Laboratories, Inc. v. Seikagaku Corporation, petition filed Jan. 16, 2025; institution granted Sept. 9, 2025), which identifies the exact obviousness combinations presently at issue. See https://ai-lab.exparte.com/case/ptab/IPR2025-00440; https://ipverse.greyb.com/ptab-web/cases/case-details/IPR2025-00440.

Where the granted claim text was not reproduced in the fetched page, I rely on the prosecution record describing claims 1 and 10 as directed to a horseshoe crab Factor C protein "selected from the group consisting of Tachypleus tridentatus, Limulus polyphemus, and Carcinoscorpius rotundicauda," recombinantly expressed from CHO DG44 or HEK cells, with the residual-activity/sialic-acid/molecular-weight limitations in dependent claims. IPR2025-00440 challenges only claim 21 (the L. polyphemus/HEK293 residual-activity claim).

1. The claims and their functional heart

Read in light of the abstract, the specification, and the prosecution record, the claims converge on three technical propositions:

• A protein element: a horseshoe crab Factor C (a serine-protease zymogen that, upon endotoxin contact, activates Factor B) from any of T. tridentatus, L. polyphemus, or C. rotundicauda (SEQ ID NO:2 and SEQ ID NO:4 are the disclosed Tt and Cr sequences; dependent claims add ≥80–99% identity variants, conservative "one or several" substitutions, and "having activity of Factor C").
• A production element: recombinant expression from a CHO DG44 or HEK (e.g., HEK293) mammalian host — the specification stresses this is the inventive departure from insect-cell (Sf9) expression and from the insoluble COS-1 expression of Cr Factor C reported by Dwarakanath and Wang.
• Functional/structural limitations (dependent claims): residual activity thresholds in the presence of salts typical of injections (e.g., ≥10%/≥20% in 21 mM sodium citrate; ≥25%/≥35% in 52 mM sodium hydrogencarbonate; ≥25%/≥35% in 214 mM NaCl; ≥15%/≥25% in 16 mM MgSO₄; ≥35%/≥45% in 2.5 mM CaCl₂); greater (α-2,3)-sialylation than native or Sf9-produced Factor C; molecular weight of 115–140 kDa (non-reducing SDS-PAGE); absence of C-terminal His/V5 tags.

The claimed benefit is that the reconstituted cascade using the CHO/HEK-produced Factor C is less inhibited by ions than native Factor C or insect-cell Factor C (Figs. 6–7; Fig. 14 sugar-chain data).

2. Legal framework

Under 35 U.S.C. § 103 and Graham v. John Deere, obviousness turns on: (1) scope and content of the prior art; (2) differences between the prior art and the claims; (3) the level of ordinary skill; and (4) secondary considerations. Under KSR Int'l Co. v. Teleflex, the key inquiries for a combination are whether a POSITA would have had reason to combine known elements and a reasonable expectation of success, recognizing that "familiar items may have obvious uses beyond their primary purposes" and that market/industry pressure can supply motivation. Functional claim limitations (residual activity, sialylation) that merely describe an inherent property of the recited host-expression product are generally not patentable differentiators if the host was obvious (In re Best; In re Koller).

3. Combination A — WO 2008/004674 (or WO 2012/118226) + conventional CHO DG44/HEK293 expression methodology (+ Ding/Ho for Cr Factor C sequences)

Applicable to: the genus claims (Factor C of the three named species, recombinantly expressed from CHO DG44 or HEK).

Reference roles:

• WO 2008/004674 (Patent Document 1) already teaches recombinant expression of horseshoe crab Factor C, Factor B, and Pro-clotting enzyme in a eukaryotic host (insect Sf9 cells) to reconstitute the endotoxin cascade, and — critically — itself reports that the reconstituted system is suppressed by NaCl, MgSO₄, or CaCl₂. That is an express recognition of the problem the '318 patent purports to solve (salt/ion inhibition), located in the closest prior-art system.
• WO 2012/118226 (Patent Document 2, same field) provides a second insect-cell reconstituted-cascade disclosure.
• Ding & Ho, U.S. Pat. No. 5,712,144 and Ding et al. (1993) supply the C. rotundicauda Factor C gene/amino acid sequences and recombinant expression constructs; SEQ ID NOs:1–4 of the patent show Tt/Cr sequences were known.
• Dwarakanath 1997 and Wang 2001 disclose the only reported mammalian attempt (Cr Factor C in COS-1) and report insolubility; these are two-sided art — they show mammalian hosts were being tried for exactly this protein, while arguably teaching away from COS-1 specifically.
• Standard expression literature (e.g., the Current Protocols CHO DG44 transfection/amplification methodology actually cited by the Examiner in the parent application's prosecution) establishes that CHO DG44 and HEK293 were canonical, default mammalian hosts for secreted, glycosylated recombinant proteins by 2012.

Why a POSITA would combine: The art had (i) full-length Factor C cDNAs (Tt, Cr), (ii) proven functional recombinant expression in one eukaryotic host (Sf9), and (iii) a recognized defect of the insect-cell system (ion sensitivity — WO '674 itself). The natural design variable to change was the expression host's glycosylation machinery: it was well known that insect cells make paucimannose, non-sialylated N-glycans, whereas CHO and HEK293 produce complex, sialylated N-glycans (the patent's own Examples cite Harrison & Jarvis, Methods Mol. Biol. 338:341–356 (2007), for exactly this proposition). A POSITA seeking a Factor C "not susceptible to reaction inhibition even in the presence of a salt" — the problem framed in the patent's own Background — would have had concrete reason to move the proven construct into a mammalian host, with CHO DG44 and HEK293 the obvious, standard candidates. COS-1's insolubility would not defeat the combination: COS-1 is a transient, SV40-based system, and the skilled person would reasonably distinguish stable, industry-standard CHO/HEK production lines, where the same full-length protein had already been secreted functionally from Sf9.

Reasonable expectation of success: moderate-to-high — the protein is a secreted eukaryotic zymogen, successfully expressed in insect cells; host substitution for glycosylation purposes was routine; the Cr and Tt sequences were in hand.

Counterweights (why this combination is contestable):

• No pre-2013 reference reported functional Factor C from mammalian cells; the specification's own narrative (echoed in the Background) asserts none existed.
• Dwarakanath/Wang could be argued to teach away from mammalian expression generally (insolubility in COS-1).
• The claimed residual-activity thresholds and α-2,3-sialylation are data-dependent; unless inherent to CHO/HEK expression of any of the three species' Factor C, the Examiner would need a showing that the functional result was predictable. Notably, the parent-application Examiner rejected exactly this sort of reliance on host choice, requiring the applicant to narrow to CHO DG44 and to submit a 1.132 declaration, and then held the unexpected-results showing not commensurate with claim scope covering multiple species (see PTACTS record excerpt for Application 14/650,767, https://ptacts.uspto.gov). That history shows the PTO regarded the CHO DG44/HEK + species limitations as the patentable advance, not the mere idea of recombinant Factor C.

4. Combination B — Mizumura (US 2015/0307864 A1) + WO 2018/074498 ("the '498 PCT") — IPR2025-00440, Ground 1 (claim 21)

This is the only combination actually tested before the PTAB, and institution was granted (Sept. 9, 2025), i.e., the Board found a reasonable likelihood claim 21 is unpatentable. A final written decision is not yet on the docket ("FWD--").

Reference roles:

• Mizumura (US 2015/0307864 A1, published Oct. 29, 2015) is the publication of the '318 patent's own parent application (14/650,767) and is textually identical to the '318 specification. It teaches recombinant T. tridentatus Factor C expressed in HEK293 and CHO DG44, and — per Figure 7 — residual activity values (e.g., ~40% in 16 mM MgSO₄ and ~25% in 21 mM sodium citrate for CHO DG44; ~20–30% for HEK293) that fall within or near the claimed ranges.
• WO 2018/074498 (same Patent Owner, published 2018) supplies the missing element for claim 21: the L. polyphemus Factor C gene and amino acid sequences and their successful functional recombinant expression.

The pivotal premise — priority: For either reference to be prior art, claim 21 must not be entitled to the Dec. 10, 2013 priority date. The Petition argues the 2013/2015 disclosures neither described nor enabled recombinant L. polyphemus Factor C having the claimed residual activity (no Lp sequences or working examples anywhere in the priority chain; the inventors later admitted the Lp work was completed years afterward). If the effective filing date is instead Apr. 30, 2019 (the actual filing date of the '318 application), then Mizumura, the '498 PCT, and McClymont are all § 102 prior art. The Patent Owner's Preliminary Response disputed this (arguing the priority chain is intact, which would make Mizumura and the '498 PCT not prior art at all), but the Board nonetheless instituted.

Why a POSITA would combine: The field had a recognized, pressing need to replace native L. polyphemus amebocyte lysate (the standard LAL test reagent) with a recombinant Factor C, to escape supply constraints and batch variability. Mizumura demonstrated a complete, validated method (construct → HEK293/CHO DG44 expression → salt-tolerant active Factor C) for the closely related Tt species. The '498 PCT provided the Lp genetic blueprint and already reported functional Lp Factor C expression. Combining "proven method for a sister species" + "newly available sequence for the commercially important species" is the paradigmatic KSR-style combination of known elements with predictable results.

Reasonable expectation of success: Petitioner points to the '498 PCT's own successful expression of functional Lp Factor C and to inventor testimony (in related prosecution) that a POSITA would expect similar functional properties across horseshoe crab species once the sequence was known.

Secondary considerations (Petitioner's rebuttal): Patent Owner's unexpected-results evidence (Lp Factor C in CHO DG44 ~50–55% residual activity in 16 mM MgSO₄; in HEK293 ~90–120%) is compared against Mizumura Figure 7's Tt numbers; Petitioner argues this is not "unexpected" relative to the closest prior art, that the differences are quantitative and within the art's prediction for a different species, and that the Mizumura declarations were generated after issue and are not commensurate with the claim. The Board's institution decision indicates these arguments did not defeat a reasonable likelihood of obviousness.

5. Combination C — Mizumura + McClymont 2017 (Ph.D. thesis) — IPR2025-00440, Ground 2 (claim 21)

Reference role: The McClymont thesis (2017) independently discloses the full L. polyphemus Factor C coding sequence and amino acid sequence, serving as a fallback source of the Lp sequence in place of the '498 PCT (which is Patent-Owner-owned and might be subject to swearing/priority arguments).

Why combine / expectation of success: Identical to Combination B — Mizumura supplies the HEK293/CHO expression method and the salt-tolerance teaching; McClymont supplies the Lp "genetic blueprint." Petitioner's position is that with McClymont's sequence in hand and Mizumura's demonstrated method, generating the claimed Lp recombinant Factor C was a predictable, routine extension.

6. Combination D — "Ding2" + Current Protocols CHO DG44 methodology (prosecution record, parent application)

The parent-application record shows the Examiner advanced a § 103 combination of a Ding-family Factor C reference (identified in the record as "Ding2") with the Current Protocols teaching that a desired gene can be recombinantly expressed using a CHO DG44 cell line. The Examiner reasoned that because CHO-cell-expressed recombinant Factor C showed residual activity above the claimed thresholds (e.g., ≥35% in 2.5 mM CaCl₂), the claims were prima facie obvious, and rejected applicant's unexpected-results declaration as not commensurate with claims covering multiple species and amino acid sequences (Application 14/650,767, Final/Advisory record, https://ptacts.uspto.gov). This combination is the strongest evidence that, at the Examiner's level of skill, host choice (CHO DG44) plus a known Factor C sequence was considered an obvious design choice; the claims ultimately issued only after narrowing to the CHO DG44/HEK host limitation and adding functional limitations.

Caveat: I could not confirm the precise publication number of "Ding2" from the available excerpts; it is cited in the prosecution history as a Ding/Ho-family reference disclosing recombinant horseshoe crab Factor C. Its exact identity should be verified from the file wrapper before relying on it.

7. Motivation-to-combine synthesis

A POSITA (a protein biochemist / molecular biologist working on limulus-based endotoxin detection) would have been motivated to combine the references for several convergent reasons:

1. Recognized problem: native lysate and insect-cell reconstituted cascades are inhibited by salts found in injections (WO '674; patent Background); recombinant factors were needed to replace horseshoe-crab sourcing (conservation, supply).
2. Known design space: glycosylation differences between insect and mammalian hosts were textbook knowledge (Harrison & Jarvis 2007, cited in the patent itself); sialylation and complex N-glycans are the known outputs of CHO/HEK expression, and the patent's own sugar-chain data (Fig. 14) tie the salt-resistance/size differences to that glycosylation — i.e., the benefit is explained by, and therefore largely predictable from, the host choice.
3. Known sequences/constructs: Tt and Cr Factor C cDNAs were published (Ding & Ho; SEQ ID NOs:1–4 lineage); Lp sequences became available in McClymont (2017) and the '498 PCT (2018).
4. Demonstrated expressibility: full-length active Factor C had been secreted from Sf9; moving a validated cDNA into standard mammalian hosts is a routine, well-documented procedure (Current Protocols; pCI-neo/pCA7 vectors).
5. Industry pull: the LAL/rFC marketplace (Charles River is the petitioner) had an articulated need for recombinant Lp Factor C, supplying the KSR "market pressure" motivation.

8. Balanced assessment of the weak points in the obviousness case

• Functional unpredictability: the specification and the inventors' own declarations assert that salt-tolerance (residual activity) was not predicted from host choice and that COS-1 had failed, which supports an argument that the CHO/HEK result was unexpected. The Examiner in the parent case credited only a narrow version of that showing.
• Priority question cuts both ways: if Patent Owner defeats the priority attack, Mizumura and the '498 PCT are not prior art to claim 21 at all, and Grounds 1–2 collapse (this was PO's principal non-institution argument, and it failed only at the "reasonable likelihood" stage).
• Species gap: for the L. polyphemus claims specifically, no 2012-era art contained Lp Factor C sequences; any obviousness case against those claims depends on post-2013 references (only usable if the priority claim is invalidated) or on a genus-obviousness theory over Tt/Cr art.
• Secondary considerations: Patent Owner has filed unexpected-results evidence and a contingent motion to amend (substitute claim 22 narrowing to Lp with the residual-activity limits), and the IPR is still pending — no final unpatentability determination has been made.

9. Bottom line

• The most viable and currently litigated § 103 case is against claim 21: obviousness over Mizumura (US 2015/0307864) in view of WO 2018/074498, or alternatively in view of the McClymont 2017 thesis — both combinations contingent on defeating the Dec. 10, 2013 priority claim so that Mizumura/2018 art qualify as prior art. The PTAB instituted IPR2025-00440 on Sept. 9, 2025, finding a reasonable likelihood of unpatentability.
• For the broader genus claims (CHO DG44/HEK expression of Tt/Lp/Cr Factor C), the strongest pre-2013 combination is WO 2008/004674 (insect-cell recombinant Factor C + recognition of salt inhibition) combined with conventional CHO DG44/HEK293 expression methodology (and, for Cr, Ding/Ho sequence art), with COS-1 insolubility (Dwarakanath 1997; Wang 2001) as the principal teaching-away counterweight.
• The prosecution history itself (Ding2 + Current Protocols; "unexpected results not commensurate with scope") demonstrates that the PTO's line-drawing focused on the combination of species + CHO DG44/HEK host + functional thresholds — meaning the claims that survived are those whose obviousness is genuinely closest, and the IPR is now testing precisely that boundary on claim 21.

Key sources: IPR2025-00440 docket and Petition (https://ai-lab.exparte.com/case/ptab/IPR2025-00440; https://ipverse.greyb.com/ptab-web/cases/case-details/IPR2025-00440); PTACTS prosecution excerpts for U.S. App. 14/650,767 and related filings (https://ptacts.uspto.gov); patent full text and Background as fetched from Google Patents (https://patents.google.com/patent/[US11236318](/patent/US11236318)/en).