US 6146874

I'll search for authoritative information on this patent number, including any litigation or CAFC docket activity.

Let me search specifically for litigation or CAFC activity involving this patent.

Let me look for the actual claim text of this patent.

Summary of US Patent 6,146,874

Note on sourcing. This summary is grounded in (a) the full patent text you supplied (fetched from https://patents.google.com/patent/[US6146874](/patent/US6146874)/en) and (b) Google Patents / Unified Patents bibliographic records. I could not retrieve the verbatim issued claim set — the authoritative text I was given ends in the middle of the "Description" section and does not include the claims. My claim descriptions below are therefore reconstructed from the patent's own "Summary of the Invention" paragraph structure and should be treated as a plain-language approximation of the independent claim scope, not a verbatim quotation.

Bibliographic data

Related family members surfaced in the record: WO 1999061643 A1, EP 1080218 A1, US 6,660,514 B1 (a continuation, priority 2000-07-21), and US 2004/0121444 A1.

Abstract (as issued)

Disclosed are methods for the isolation and purification of high-titer recombinant adeno-associated virus (rAAV) compositions. Also disclosed are methods for reducing or eliminating the concentration of helper adenovirus in rAAV samples. Methods are disclosed that provide highly-purified rAAV stocks having titers up to about 10¹³ particles/ml at particle-to-infectivity ratios of less than 100 in processes that are accomplished about 24 hours or less.

Plain-language overview of the independent claims

Based on the "Summary of the Invention," the patent appears to claim the following independent subject matter (claim numbers unverified):

1. Iodixanol density-gradient purification of rAAV. A method of purifying recombinant AAV by centrifuging a sample containing (or suspected of containing) rAAV through at least a first iodixanol gradient, and collecting the purified virus / an rAAV-containing fraction from the gradient. The gradient is preferably discontinuous, with an exemplary set of steps at ~15%, ~25%, ~40%, and ~60% iodixanol; the virus is typically recovered from the ~40% step (banding density ~1.415 g/ml ≈ 52% iodixanol). Salt (e.g., ~1 M NaCl) is preferably added to the 15% step to reduce aggregation.

2. Heparin affinity purification of rAAV. A method of purifying rAAV by contacting a sample with at least a first matrix comprising heparin, under conditions effective to bind the virus; removing unbound protein/contaminants; and eluting the virus (e.g., with 1 M NaCl). Exemplary matrices are heparin-agarose Type I or Type II-S; the matrix may be an HPLC affinity column (e.g., POROS® HE/M).

3. Combined iodixanol + heparin process for preparing high-titer rAAV. A method comprising centrifuging through an iodixanol gradient, collecting the partially purified rAAV, contacting it with a heparin matrix, and collecting the virus — optionally followed by anion-exchange chromatography for high-titer stocks.

4. Reducing/eliminating adenovirus contamination in an rAAV composition. A method comprising centrifuging an Ad/rAAV sample through one or more iodixanol gradients and collecting rAAV from the gradient (with optional heparin-affinity, hydrophobic-interaction, heat, or anion-exchange steps to further deplete adenovirus).

5. Isolation methods with additional downstream matrices. Variants in which the iodixanol-derived fraction is further processed through a hydrophobic matrix (phenyl Sepharose) or through a cesium chloride equilibrium gradient, with the non-interacting virus or the purified band being collected.

6. Product-by-process composition. An rAAV composition prepared by applying an rAAV-containing sample to an iodixanol gradient and collecting the rAAV-containing fraction from the gradient.

7. Kit. A kit comprising, in a suitable container, iodixanol (optionally formulated as an iodixanol gradient) and a heparin-comprising matrix (e.g., heparin-agarose Type I or II-S), optionally with a hydrophobic (phenyl) matrix.

The patent reports the results these methods achieve: purification in ~1 day, ≥10-fold yield improvement over conventional ammonium-sulfate/CsCl protocols, >99% purity, and particle-to-infectivity ratios below 100 (versus ~200–1000 for CsCl-purified virus).

Litigation / CAFC 2026 docket check — no matching records found

I searched for CAFC 2026 docket activity and other litigation specifically tied to patent number 6,146,874 and found nothing on point. Results returned by those searches were unrelated to this patent, including:

• Australian Official Journal of Patents entries and Brazilian court documents containing the string "6146874" in unrelated contexts;
• University of Florida-related litigation (e.g., the Rashada NIL suit, faculty-arbitration cases, and medical-privilege appeals) that does not involve patent 6,146,874.

The Google Patents record shows only routine assignment/reassignment events (University of Florida → University of Florida Research Foundation; NIH confirmatory license under Executive Order 9424 in 2008), an "Expired – Lifetime" status, and no litigation or PTAB/CAFC flags.

Caveats / uncertainty:

• I cannot confirm verbatim claim language, exact claim count, or claim numbering, because the authoritative text provided did not include the claims section and I could not retrieve it via search.
• The CAFC/docket check reflects the public sources reachable in this session; a paid docket service (e.g., Lex Machina, Docket Navigator) or PACER/CAFC's own docket search would be needed for an exhaustive negative confirmation. If a 2026 CAFC appeal naming this patent exists, I did not find it.

I'll research litigation involving US Patent 6,146,874.

Let me check litigation-specific databases.

Let me query litigation-specific databases directly.

Litigation Search: US Patent 6,146,874

Result: No litigation found.

Based on my searches of the sources you specified and related patent-litigation databases, I was unable to identify any known litigation (district court, ITC, or Federal Circuit appeal) involving US Patent 6,146,874 ("Method of preparing recombinant adeno-associated virus compositions," Univ. of Florida / UF Research Foundation; filed 1999‑05‑27, granted 2000‑11‑14, expired 2019‑05‑27).

Sources checked and what they showed

Important caveats

• Do not treat this as a definitive negative. My search was constrained; I was not able to execute exhaustive, ID-filtered queries against PACER, Docket Alarm, MaxVal, or the full CourtListener API. A filing that is not indexed by the sources above (e.g., a pre‑2010 case, a sealed action, or a case where this patent was asserted alongside a related family member) could exist without appearing in these results.
• Be alert to family-member confusion. This patent belongs to a family that includes US 6,660,514 B1 (continuation, granted 2003‑12‑08) and published application US 2004/0121444 A1. Because 6,146,874 and 6,660,514 claim related subject matter, litigation may have been brought on the '514 patent or the family generally rather than on 6,146,874 itself. If you need a firm answer, the family (not just this one patent) should be searched.
• The patent is expired (anticipated expiration 2019‑05‑27), which limits (but does not eliminate) the likelihood of past assertion during its enforceability window.
• Per the operating rules, I have not auto-corrected any identifiers, and I am reporting only what the sources returned.

Recommendation: To obtain a defensible answer, run ID-specific queries on PACER (all districts), Docket Alarm, and RPX/Unified for the string 6,146,874 and 6,660,514, and check University of Florida Research Foundation as plaintiff in the relevant time window (1999–2019). If those return nothing, the conclusion that no litigation is known would be well supported.

If you can confirm whether you also want the sibling patent US 6,660,514 included in scope, I can frame the search accordingly.

I'll verify the structured data against the live web before drafting, since the task directs me to fill in claim-level outcomes from public sources if any proceeding exists.

The first pass returned only generic PTAB statistics and unrelated patents. Let me run more targeted queries on the patent's specific identity and family.

Two more targeted checks — the PTAB docket aggregators and the sibling patent — before I conclude the structured data is correct.

I hit the tool-step ceiling while running the last two confirmatory queries, so I'll flag that limitation explicitly. I did, however, complete enough searching to reach a defensible conclusion, and my live searches corroborated the structured "PTAB proceedings on file" block rather than contradicting it.

AIA Trial Proceedings — US Patent 6,146,874

Proceedings overview

Total AIA trial proceedings on file: 0. There are no Inter Partes Reviews (IPR), Post-Grant Reviews (PGR), or Covered Business Method (CBM) reviews of US 6,146,874 — zero active, zero claims invalidated, zero claims sustained, zero settled, zero institution denials. Because no petition was ever filed, the USPTO Open Data Portal structured data returns an empty set, and my web searches of PTAB-facing sources independently returned nothing to the contrary.

Bottom-line defensive posture: this is a "no PTAB record" case, not a "hardened by IPR" case. No claim of this patent has ever been tested at the Board — and, critically, the patent is expired (anticipated expiration 2019-05-27), so the entire PTAB question is now largely academic. A defendant today should read the absence of AIA activity as a signal that the patent was never economically significant enough to attract a validity challenge, and should focus its defense on the expiry/damages bar, not on an IPR-estoppel strategy. See "Strategic summary" below.

Per-proceeding detail

There are no proceedings to itemize. I will not manufacture proceeding numbers, panels, or dispositions — no petition number, institution decision, or Final Written Decision exists for this patent, so there is no FWD to quote and no claim numbers to report as canceled or sustained. Any per-proceeding template entries would be fabrication.

Adjacent matters that are not proceedings against this patent (important for avoiding a false positive)

Two categories of results can easily be mistaken for PTAB activity on the '874 patent. Neither is one:

1. The '874 patent as prior art inside other AIA petitions. The '874 specification (and its PCT counterpart WO 99/61643) surfaces in the exhibit record of at least one unrelated AIA petition hosted on the Board's petition viewer (e.g., the document set at https://ptacts.uspto.gov/ptacts/public-informations/petitions/1558104/download-documents). The Zolotukhin disclosure is being cited as a reference in someone else's trial; that is categorically different from a trial against 6,146,874. I could not, within my search budget, confirm the proceeding number or the patent-under-review for that petition, so treat this as a lead, not a finding.

2. "874" name collisions — a distinct and serious confusability risk. Multiple different patents share a "*874" suffix and appear prominently in case law search results:

• The furnace-tube inspection patent in Quest Integrity litigation (D. Del. Civ. No. 14-1482) — an "'874 patent" whose claims 1, 11–13, 24–25, 27–28, 30, 33, 37, 40 were the subject of § 102(b)/§ 103/§ 101 invalidity briefing. Not 6,146,874.
• U.S. Patent 7,245,874 (telephony/E1 time slots) in the E.D. Tex. claim-construction record. Not 6,146,874.
• The PerDiemCo "'874 patent" (administrative-privilege claims). Not 6,146,874.
  Any of these could be miscoded as "the '874 patent" in a secondary database. I have not auto-corrected or merged any of them, and none should be attributed to this patent.

Cross-reference to previously generated sections

The earlier Litigation summary concluded "no litigation found" for this patent, with the caveat that sibling US 6,660,514 B1 (continuation, granted 2003-12-08) and published application US 2004/0121444 A1 should also be searched. That conclusion is consistent with what I found here: no PTAB record, no litigation record, no aggregator (Unified Patents) entry. There is no contradiction between sections. I would flag one uncertainty: the "PTAB proceedings on file" block is a point-in-time snapshot of the ODP ingest, and my attempts to reach Docket Alarm and a PTAB-docket-specific query were cut off by the step limit (see caveats).

Strategic summary

Claim status: 100% UNTESTED. No claim of 6,146,874 has been canceled, narrowed, or confirmed by the Board. The patent issued with a claim set including a kit claim (claim 24, with dependents 25–29 as reflected in the published claim listing) and method claims directed to iodixanol-gradient purification with heparin-matrix capture. Every one of those claims remains formally in force on the face of the record — but "in force" is the wrong frame now, because the patent expired 2019-05-27. There is no surviving-claims list to give you, because no claim was ever adjudicated; there is also no live claim to infringe.

Estoppel landscape: effectively zero. Because no IPR/PGR/CBM was ever instituted, 35 U.S.C. § 315(e)(2) estoppel never attached to anyone. No petitioner, real party in interest, or privy is barred from raising any ground — the statutory estoppel machinery simply was never triggered. Conversely, a defendant today has no FWD art combination to inherit and no Board-validated invalidity theory to point to. If you need an invalidity position, it must be built from scratch in district court (or in a declaratory-judgment posture), and the practical relevance is limited by expiry.

Pattern signals: none. No repeat petitioner (no petitioner at all). No patent-owner PTAB appeals — there being no adverse decisions to appeal, and no Federal Circuit docket tied to this patent via the PTAB route. No defensive aggregator in the chain: Unified Patents' patent page for US-6146874-A displays family data (WO-1999061643-A1, EP-1080218-A1, US-6660514-B1, US-20040121444-A1) but no IPR or litigation entry, which is the signature of a patent that was never targeted. The absence is itself informative: the Zolotukhin iodixanol/heparin method became a widely used laboratory standard and is cited extensively as background art in later AAV purification filings (e.g., later University of Florida Research Foundation applications citing the '874 disclosure), yet it never drew a validity challenge. Well-asserted, commercially significant patents attract IPRs; this one did not.

Recommended next steps

1. If you are a defendant, lead with expiry, not with an IPR story.
The patent's term ended 2019-05-27. Under 35 U.S.C. § 286, damages reach back only six years before the complaint is filed. For a complaint filed 2026-09-30, the earliest recoverable date is 2020-09-30 — after the patent expired. On that arithmetic, no pre-expiry infringement period is reachable, and no damages are recoverable even if a claim were somehow valid and infringed. Confirm the maintenance-fee history (the "Expired - Lifetime" status with a 2019-05-27 anticipated expiration is an assumption in the source, per Google Patents' own disclaimer) and confirm no term extension or adjustment moves the date; then move to dismiss or for summary judgment on remedy grounds.

2. There is nothing for you to inherit from the PTAB.
Do not represent to a court or an adversary that a claim has been "canceled by the PTAB" — it has not. Conversely, do not concede that any claim is "PTAB-validated" — it is not that either. If opposing counsel asserts an IPR outcome on this patent, demand the proceeding number; none exists for 6,146,874.

3. Disambiguate the family and the "874" collisions before you brief anything.
If a demand letter or complaint cites "the '874 patent," verify the number character-by-character. The Quest Integrity furnace patent, US 7,245,874, and the PerDiemCo "'874 patent" all circulate in the same search space. If the assertion is actually on sibling US 6,660,514 B1 (granted 2003-12-08; also expired, on approximately the same schedule), the analysis above transfers almost directly — same specification, same expiry window, likewise no PTAB record found — but it must be run separately against that patent number.

4. If you need a firm negative, close the two gaps I could not.
My searches of Unified Patents, Google Patents, the PTAB petition viewer, and general web/aggregator queries returned no proceeding, and I verified that adjacent hits are name collisions or prior-art citations rather than trials. Two checks were cut off by my step limit: an ID-filtered Docket Alarm / PTAB E2E query and a PTAB-docket-specific query on the sibling '514 patent. Run "6146874", "6,146,874", and "6660514" against PTAB E2E (https://ptacts.uspto.gov) and CourtListener (https://www.courtlistener.com) to make the negative airtight. Absent a hit there, "no PTAB activity on file" is well supported.

5. On active-proceeding milestones: not applicable — there are no pending trials, so there is no institution-deadline, oral-hearing, or statutory one-year FWD date to track.

Caveats and constraints observed

• Do not treat the zero count as infallible. The structured ODP block is the canonical source and it returns no AIA trials; my web corroboration was real but not exhaustive (two queries truncated by the step limit).
• No fabrication: no proceeding numbers, APJ panels, institution dates, FWD dispositions, settlements, or CAFC docket numbers are reported, because none exist for this patent.
• No claim-level outcome is asserted. Since no FWD issued, I make no statement that any specific claim was addressed, canceled, or sustained.
• Identifiers are reported literally — I have not auto-corrected "6,146,874," "6660514," or any collision patent.
• Primary sources reviewed: the structured PTAB block (ODP); https://portal.unifiedpatents.com/patents/patent/US-6146874-A; https://patents.google.com/patent/US6146874/en; https://ptacts.uspto.gov/ptacts/public-informations/petitions/1558104/download-documents (prior-art citation context only).

I'll research the assignment record for US 6,146,874 using the sources available to me.

I could not directly query the live USPTO Assignment Center interface in this session (the site returned no machine-readable records to my tools). The timeline below is reconstructed from the Google Patents legal-events record for US 6,146,874 (which mirrors the recorded-assignment data) plus the UFRF-recorded assignment documents that surfaced in search. Where a reel/frame is confirmed, I say so; where it is not, I say so rather than guess.

Inventors

Pattern note: No "inventor flight" pattern. All three are career University of Florida faculty, and the assignment record itself rebuts a departure theory: Sergei Zolotukhin reappears in a later UFRF assignment recorded 2018-06-12 (reel 046057/0102) as a conveying party assigning another invention to the University of Florida Research Foundation, i.e., he was still a UF affiliate ~19 years after this patent's 1999 filing. That is the opposite of the "all inventors departed within 12 months" precursor to a portfolio fire-sale. (This is a different patent, but it is evidence of the inventors' continuing UF affiliation.)

Original assignee

Entity named on the issued patent: University of Florida (original, per the 1999-08-24 record); the patent is listed on Google Patents with current assignee University of Florida Research Foundation, Inc. ("UFRF").

• Primary line of business: University of Florida is a public land-grant research university. UFRF is its nonstock, nonprofit Florida technology-transfer corporation — "The Research Foundation has no employees and is supported by employees of the University" (UFRF audited financial statements, FY2024). It exists to hold and license university IP; it is not a product company.
• Product embodying the claims? No. UFRF ships no goods. The patent claims laboratory purification methods (iodixanol gradients, heparin affinity, etc.). UFRF's business model is licensing, not manufacturing — but note that licensing university research tools is the ordinary function of a tech-transfer office, not an NPE-troll pattern.
• Current status: Operating (active, solvent, files audited financials). Its address of record is 223 Grinter Hall, Gainesville, Florida 32611. The patent itself expired 2019-05-27 ("Expired – Lifetime," anticipated expiration).

Assignment timeline

Sourcing caveat: reel/frame numbers are confirmed for the 2002 UFRF assignment only, and only indirectly — via the 2015 corrective assignment's own citation of "REEL: 012598 FRAME: 0440." For the other records I do not have a verified reel/frame and will not invent one. Correspondent/attorney-of-record data was not retrievable in this session.

1. 1999-05-27 (application filed; assignment executed in this window) / recorded 1999-08-24 — Reel/frame not surfaced

   • Conveyance: Assignment ("ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS)")
   • Assignor: Zolotukhin, Sergei; Byrne, Barry J.; Muzyczka, Nicholas (individual inventors)
   • Assignee: University of Florida ("FLORIDA, UNIVERSITY OF")
   • Correspondent: not retrievable
   • Context: Original inventor-to-university assignment — the standard academic employment/IP-policy assignment. Inventors assigned prospectively; filing and recordation within ~3 months.

2. 2002-02-19 / (recording date within the same window) — Reel 012598 / Frame 0440

   • Conveyance: Assignment
   • Assignor: University of Florida
   • Assignee: University of Florida Research Foundation
   • Correspondent: not retrievable
   • Context: Internal reorganization / housekeeping — UF routinely parks patent title in its affiliated research foundation; this is an intra-family transfer, not an arm's-length sale.

3. 2008-08-25 — Reel/frame not surfaced

   • Conveyance: License ("EXECUTIVE ORDER 9424, CONFIRMATORY LICENSE")
   • Assignor: University of Florida
   • Assignee: National Institutes of Health (NIH), U.S. Dept. of Health and Human Services (assignee of record per Google Patents)
   • Correspondent: not retrievable
   • Context: Government-interest confirmatory license — a conditional license tied to federal funding (grants P01 HL59412 and P01 NS36302, named in the patent), not a transfer of ownership. This is the routine EO 9424 recordation that appears on federally funded university patents. It is not a defensive aggregator and not a sale.

4. 2015-04-21 — Reel/frame not surfaced

   • Conveyance: Correction ("CORRECTIVE ASSIGNMENT TO CORRECT THE NAME OF ASSIGNEE PREVIOUSLY RECORDED AT REEL: 012598 FRAME: 0440")
   • Assignor: University of Florida
   • Assignee: University of Florida Research Foundation, Incorporated
   • Correspondent: not retrievable
   • Context: Change of name / scrivener's correction only — fixes the legal name of the same assignee that took title in 2002 (reel 012598/0440). No change in beneficial ownership.

No further assignment records. Title has rested at UFRF (and its NIH funding-interest license) since 2002/2015, and the patent expired in 2019. No transfer to any non-university, licensing-only, or aggregator entity appears anywhere in the chain.

Timeline diagram

timeline
    title Ownership of US 6146874
    1999 : Application filed 27 May
         : Inventors assign to Univ of Florida
    2000 : Patent issued 14 Nov
    2002 : University assigns to UFRF
         : Recorded reel 012598 frame 0440
    2008 : NIH confirmatory license only
    2015 : Corrective name fix to UFRF Inc
    2019 : Patent expires

NPE / troll-pattern signals

1. Shell-entity transfer — NOT PRESENT. No transfer to any "IP / Patents / Holdings / Ventures" entity. The only assignee change is University of Florida → UFRF (reel 012598/0440, 2002), an intra-family move to the university's existing nonprofit research foundation — not a single-purpose LLC, and UFRF is a long-established Florida corporation with audited financials and a public campus address (223 Grinter Hall).

2. Known asserter in the chain — NOT PRESENT. No assignee matches Acacia, Marathon, Intellectual Ventures, IPNav, Wi-LAN, Conversant/Mosaid, Vringo, Pendrell, Innovatio, MPHJ, Lumen View, Round Rock, Document Generation Corp, Spangenberg, or any Unified Patents / RPX high-frequency-plaintiff list. The chain contains only (i) individual inventors, (ii) a state university, (iii) its nonprofit research foundation, and (iv) the U.S. NIH as a funding-interest licensee. Prior litigation searches for this patent (and its family; see below) returned nothing.

3. Repeat correspondent across the chain — UNCLEAR / NO DATA. The Assignment Center correspondent-of-record field was not retrievable in this session, so I cannot test for a recurring attorney or recording firm. I am flagging this explicitly as a data gap rather than calling it "not present." (Note: for other UFRF filings the correspondent of record has been outside counsel such as Amy J. McMahon, Wolf Greenfield, Boston — see reel 046057/0102 on an unrelated 2018 UFRF assignment — but I have no evidence such a firm appears on this patent's records, and UFRF uses multiple outside firms.)

4. Cascading transfers — NOT PRESENT. No <24-month chained-LLC sequence. The 1999 and 2002 transfers are 3 years apart; the 2008 NIH record is a license, not a sale; the 2015 entry is a name correction. There is no chain of assignees sharing a correspondent address or common principals.

5. Pre-litigation transfer — NOT PRESENT. No infringement suit naming this patent was identified (see the prior litigation section of this analysis). There is therefore no transfer dated within 6 months before any suit.

6. Bankruptcy fire-sale — NOT PRESENT. Neither the University of Florida nor UFRF filed for bankruptcy; no Chapter 7/11 sale of this patent appears.

7. Privateering — NOT PRESENT. No operating company transferred this patent to an NPE for assertion on its behalf. The transferor (the university) never left the chain and retained the patent's enforcement rights through its own foundation.

8. Defensive aggregator (anti-NPE) — NOT PRESENT, though the practical effect is similar. The chain does not terminate at RPX, AST, LOT Network, Unified Patents, or OIN. It terminates at the original university-affiliated foundation. The 2008 NIH entry is a funding-interest confirmatory license, which is categorically different from a defensive-aggregator acquisition.

Verdict

Defensive / non-asserting.

Justification: the entire recorded chain is academic and internal — inventors → University of Florida (1999-08-24), then University of Florida → University of Florida Research Foundation (reel 012598/0440, corrected 2015-04-21), with only a NIH Executive Order 9424 confirmatory license (2008-08-25) interposed, which is a federal funding-interest recordation rather than a transfer of title. Zero of the eight NPE signals is present, there is no asserter entity in the chain, and the patent expired 2019-05-27 — so no NPE-troll hypothesis is supported on any evidence. Two definitional caveats I want to be precise about rather than paper over: (i) UFRF is an academic tech-transfer office, not a classic defensive aggregator like RPX/AST/LOT, so this verdict is the non-asserting half of that category rather than the aggregator half; and (ii) I could not retrieve correspondent-of-record data, so signal #3 is a genuine data gap, not a cleared negative. If you want a fully airtight record, verify the reel/frame for the 1999 and 2015 entries and pull the correspondent names at the USPTO Assignment Center (or the legacy search) by searching patent number 6146874; and if you want the sibling covered too, search US 6,660,514 B1 (continuation, granted 2003-12-08) and US 2004/0121444 A1, which share this family and this same UFRF ownership chain.

I'll research US Patent 6,146,874 on the USPTO/Google Patents record, focusing on its cited prior art (both references cited in the patent and patents/applications citing it).

Let me get the specific "References Cited" (patent citations) section from the USPTO/Google Patents full record.

Let me retrieve the actual front-page "References Cited" section of US 6,146,874 itself and its family/related references.

Prior-Art Analysis — US Patent 6,146,874

Sourcing note and verification status (read first)

Two things had to be reconciled before producing this analysis, and both should be flagged explicitly rather than smoothed over:

1. The authoritative patent text supplied to me does not contain (a) the "References Cited" (front-page citation) list, or (b) the issued claims. The provided full text ends mid-"Description." So I cannot quote the patent's own citation list verbatim, nor map references to verbatim claim language.
2. I reached the session's search-step limit before I could pull the US 6,146,874 front page (e.g., the patentimages PDF) directly. The citation list below is therefore reconstructed from the closest available corroborating records, in descending order of reliability:
   • the front page of the sibling patent US 6,660,514 B1, which the record states is a continuation of application 09/321,897 (i.e., of US 6,146,874) and shares its specification — this is the strongest proxy;
   • the Unified Patents "Patent Art" listing for US-6146874-A (7 documents);
   • the Google Patents record for US6146874A itself, and its forward-citation ("Cited By") entries.

This is a proxy reconstruction, not a verbatim quotation of US 6,146,874's front page. Where the two sources conflict on titles/assignees, I say so. Under the operating rules I have not auto-corrected any patent number, date, or identifier.

Because the claims were unavailable, the § 102 mapping below uses the claim taxonomy reconstructed in the earlier "Patent summary" section (iodixanol-gradient method; heparin-affinity method; combined iodixanol+heparin method; adenovirus-reduction method; hydrophobic/CsCl variants; product-by-process; kit). It should be treated as provisional.

A. Bibliographic anchors for the § 102 analysis

B. References cited in / against the 6146874 family (the "prior art" set)

B.1 U.S. patent documents

B.2 Foreign patent documents

B.3 Non-patent literature (listed from the US 6,660,514 front page)

B.4 Documents surfaced by Unified Patents but not in the front-page list

The Unified "Patent Art (7)" listing includes two documents absent from the US 6,660,514 front page, so their status as cited references (vs. algorithmic "similar documents") is unconfirmed:

• WO 1998000524 A1 — "Method for Producing Recombinant Adenovirus," Aventis Pharma SA, priority 1996-06-30.
• WO 1996039495 A1 — "AAV Directed Targeted Integration," University of Pittsburgh, priority 1995-06-05.

Caveat: because these do not appear on the family front page, I would not treat them as official 6146874 citations without confirming on the PDF/PTO record.

C. § 102 anticipation analysis

Legal framework. Anticipation under pre-AIA § 102 requires that a single reference disclose every element of a claim, arranged as in the claim (Net MoneyIN / Verdegaal Bros.). It is not enough that a reference is in the field. Most of the references here are § 102(a) or § 102(e) art by virtue of their grant dates/filing dates relative to the 1998 priority date; only WO 93/24641 (and arguably WO 97/08298) are clean § 102(b) art.

The decisive fact. Every independent claim in the reconstructed claim set (see prior summary, items 1–7) contains, as an express element, either:

• (i) centrifugation through an iodixanol gradient (claims 1, 3, 4, 5, 6, 7), or
• (ii) contact with a heparin-comprising matrix (claims 2, 3, 7).

None of references 1–6 discloses iodixanol (OptiPrep) density-gradient centrifugation, and none discloses heparin-affinity purification of rAAV. The cited patents operate in the classic paradigm the specfication itself disparages — ammonium-sulfate precipitation and CsCl (or sucrose) equilibrium gradients, or chromatographic media other than heparin.

Bottom line on anticipation: On the record available, no cited reference anticipates any claim of US 6,146,874 on an element-by-element basis. The novelty of the 6146874 claims resides precisely in the iodixanol step-gradient (the ~15/25/40/60% stack, virus recovered from the ~40% step, banding density ≈1.415 g/ml ≈52% iodixanol, 1 M NaCl in the 15% step) and in the heparin-affinity step — features absent from every cited patent. If anything, the cited art is § 103 obviousness material, and the strongest § 103 combination would run through US 5,658,776 (rAAV production/high titer) + WO 97/08298 (unknown) + the Dracopoli/Hermans methods references.

D. Forward citations (for completeness — these are not prior art to 6146874)

Because the record shows several later documents citing 6146874, I note them only to prevent conflation with prior art. All post-date 2000-11-14 and therefore cannot be § 102 art against it:

• US 6,143,548 A (O'Riordan et al., Genzyme; "Chromatographic purification of adeno-associated virus") — appears in the cited-by/similar-art arrays alongside 6146874.
• US 7,419,817 B2 (Chiorini) — lists US 6,146,874 A in its "References Cited."
• US 11,000,561 B2 (AAV purification methods) — lists US6146874A among cited documents.
• DE 19738292 C1 (1997-09-02, Deutsches Krebsforschungszentrum; "Chromatographic purification of AAV-2") — contemporaneous DKR art that cross-cites the family.
• Numerous later CN/EP/US applications (e.g., CN112770812A, CN113631225A, CN119242711A) incorporate US6146874 by reference as a known AAV-isolation method.

E. Explicit uncertainty flags

1. Claim text not available → the § 102 mapping is against a reconstructed claim taxonomy, not verbatim claims. Re-verify against the issued claims before relying on any anticipation conclusion.
2. Front page not directly retrieved → the citation list is corroborated via US 6,660,514 (a verified continuation of 09/321,897) plus Unified Patents, not read off 6146874's own front page.
3. WO 97/08298 subject matter unknown — a material gap, since the US 6,660,514 front page asterisks it. This is the single reference I would pull first on a follow-up.
4. US 5,646,034 attribution conflict (Leavitt et al. per the front page vs. University of California per Unified).
5. Hermans et al. — potential closest art to the iodixanol limitation, but status unverified.
6. Search-step limit reached; a full USPTO PatentCenter / Global Dossier pull of US 6,146,874 and of PCT/US99/11945's ISR would close items 2–5 and should be the next step.

Most relevant prior art, ranked (provisional): US 5,658,776 (Flotte) > US 5,681,731 (Lebkowski) > WO 97/08298 (unverified) > Us 5,646,034 (Leavitt) > US 5,139,941 (Muzyczka) — with Hermans et al. the wildcard for the iodixanol element.

I'll research the key prior-art references cited in this patent to ground the § 103 analysis.

Let me verify additional key references and try to obtain the issued claims.

Obviousness Analysis of US 6,146,874 under 35 U.S.C. § 103

Scope note and caveat. The authoritative text furnished for this analysis ends mid-Description and does not contain the issued claim set of the '874 patent. I therefore reconstruct the claim scope from (a) the patent's own "Summary of the Invention" paragraphs and (b) verbatim claim language recovered from the sibling patent US 6,660,514 B1 and a Justia transcription of the '874 claims. The Justia excerpt shows '874 claim 23 recites an iodixanol-gradient → heparin-matrix method (steps b–e) and claims 24–29 recite kits (iodixanol + heparin matrix, optionally phenyl-Sepharose). This is consistent with the Summary but I flag that the full verbatim '874 claim set remains unverified. Statements below about "claim scope" should be read with that limitation.

1. The person of ordinary skill in the art (POSITA)

A molecular biologist/virologist holding a Ph.D. (or M.S. + several years) with 2–5 years of practical experience in (i) recombinant AAV vector production and (ii) preparative purification of biological macromolecules and viruses — i.e., competent in density-gradient ultracentrifugation (CsCl, sucrose) and in affinity/ion-exchange/hydrophobic-interaction chromatography, and familiar with the FPLC/HPLC literature of the mid-1990s.

2. The prior-art landscape (all references cited within the patent itself)

Key point: the two load-bearing references for obviousness — Summerford & Samulski 1998 and Tamayose 1996 — are both cited on the face of the patent and both pre-date the May 27, 1998 priority date. The patent's own background affirmatively characterizes iodixanol and its advantageous properties.

3. Claim-by-claim § 103 analysis

3.1 The iodixanol-gradient claims (the "bulk purification" genus)

Representative scope: centrifuging an rAAV sample through at least a first iodixanol gradient (preferably discontinuous 15/25/40/60%), optionally with NaCl (e.g., ~1 M) in the 15% step, and collecting the rAAV-containing fraction (the ~40% step / ~1.415 g/ml band).

Combination 1 → Snyder 1996 + Tamayose 1996 + the known iodixanol/OptiPrep virus-purification art + routine optimization.

• Motivation. Snyder's CsCl protocol was the acknowledged standard and was known to be slow, hyperosmotic, toxic, and to destroy infectivity; iodixanol was known to be iso-osmotic, non-toxic, low-viscosity and dialysis-free. A POSITA seeking the long-felt need of faster, higher-yield, higher-infectivity rAAV had a clear reason to substitute an iodixanol gradient for the CsCl gradient — a substitution of one known density-gradient medium for another in the same unit operation.
• Reasonable expectation of success. Iodixanol gradients were already in routine virological use and, as the OptiPrep application literature confirms, "CsCl in particular leads to major reductions in infectivity … OptiPrep gradients show infectivity:particle ratios at least 100× those from CsCl." The improvement in yield/infectivity is therefore predictable, not surprising.
• The specific numbers. A discontinuous 15/25/40/60% step gradient bracketing the rAAV buoyant density is routine design. Selecting ~40% as the collection step is simply reading the band off the gradient; the patent itself concedes "the design of both continuous and discontinuous gradients is well-known." Adding ~1 M NaCl to the least-dense step to suppress aggregation is an obvious application of the known salting-in/salting-out principle (and mirrors the 1 M NaCl already used by Tamayose for elution). Under KSR v. Teleflex (2007) these are "a matter of design choice" / "obvious to try."

Assessment: the independent iodixanol-gradient claim is strongly obvious over Snyder 1996 in view of the known iodixanol virus-purification art (with Tamayose 1996 as a secondary reference for rAAV-specific affinity/salt handling).

3.2 The heparin-affinity claims

Representative scope: contacting an rAAV sample with a matrix comprising heparin (e.g., heparin-agarose Type I or II-S; conventionally or in an HPLC column), removing unbound species, and eluting (e.g., with 1 M NaCl).

Combination 2 → Summerford & Samulski 1998 + Neyts et al. 1992 (+ Tamayose 1996).

• Motivation (explicit). Summerford & Samulski establish that AAV-2 binds heparan sulfate, that heparin is a functional analog/competitor, and expressly state the finding "should facilitate development of new reagents for virus purification." That is a teaching, suggestion, and motivation to build a heparin-based AAV purification reagent.
• Enablement/expectation. Neyts 1992 had already reduced the general concept to practice for a virus: CMV binds heparin-Sepharose and is eluted from it. Tamayose 1996 had already shown rAAV binds an anionic sulfonated resin and elutes with 1 M NaCl. Combining these gives a POSITA a heparin-agarose rAAV purification with a reasonable expectation of success — including the specific Type-I/Type-II-S resins and the 1 M NaCl elution, which are catalogue choices and the known elution condition.
• HPLC format. Running a known affinity resin in an HPLC column (e.g., POROS HE/M) is a straightforward engineering choice for speed/back-pressure, and the patent itself notes no more than that the HPLC format "is easier to use" and "allows higher flow rates."

Assessment: the heparin-affinity claim is obvious over Summerford & Samulski 1998 in view of Neyts 1992 and Tamayose 1996. This is the single most vulnerable independent claim because the patent's own background contains the express suggestion to use the receptor discovery for purification.

3.3 The combined iodixanol + heparin process (this appears to be '874 claim 23; cf. '514 claim 1)

Representative scope: (a) iodixanol-gradient centrifugation → (b) collect rAAV fraction → (c) contact with heparin matrix → (d) remove non-bound species → (e) elute.

Combination 3 → Combination 1 + Combination 2 (i.e., Snyder 1996 + known iodixanol art + Summerford & Samulski 1998 + Neyts 1992 + Tamayose 1996).

• Motivation to combine the two steps. Two independent, converging reasons: (i) Tamayose 1996 itself warns that affinity chromatography on crude lysate gives poor binding — "affinity chromatography using Cellufine Sulphate alone was itself unlikely to purify rAAV to high levels" — which supplies a reason to interpose a bulk/pre-purification step before chromatography; and (ii) the known property of iodixanol (low viscosity, dialyzable-free, salt-tolerant, non-aggregating) makes its eluate a convenient feedstock "that could be loaded on virtually any kind of chromatographic matrix" (the patent's own characterization). Coupling a bulk density-gradient step to an affinity polishing step is the paradigmatic two-step purification scheme in protein/virus purification.
• Predictable result. Each step's contribution is known; the combined recovery/purity gain is the expected additive effect.

Assessment: the combined-process claim is obvious. The only candidate for non-obviousness is the degree of the improvement (see § 4).

3.4 Adenovirus-contamination-reduction claims

Representative scope: centrifuging an rAAV/adenovirus sample through iodixanol gradient(s) and collecting rAAV; optionally further depleting Ad via heparin, hydrophobic-interaction, heat, or anion-exchange steps.

• The Ad/rAAV separation is an inherent consequence of a density-gradient step: rAAV and adenovirus have different buoyant densities, so banding rAAV in a density gradient necessarily removes Ad. A claim to the result of a known separating step does not import patentability where the result is a natural property of the separation. The patent's own data (Ad titer 4.5×10¹⁰ → 4.2×10⁸ pfu after iodixanol) merely quantifies the known density difference.
• The auxiliary Ad-removal options (heparin affinity; HIC; heat; anion exchange) are all conventional virus-clarification techniques individually disclosed or suggested in the art (Neyts 1992 for heparin; standard practice for heat inactivation of Ad; routine for anion exchange).

Assessment: obvious, either as an inherent property of Combination 1/3 or as an aggregation of known decontamination steps.

3.5 Downstream CsCl / hydrophobic-interaction / anion-exchange dependent claims

• CsCl after iodixanol/heparin: CsCl equilibrium gradients were the conventional rAAV polishing step (Snyder 1996). Appending the old final step to the new front-end steps is straightforward.
• Hydrophobic-interaction chromatography (phenyl-Sepharose): HIC is a long-established protein-purification technique; using it to bind hydrophobic contaminant proteins while a hydrophilic virus flows through is an obvious choice, and both "low sub" and "high sub" phenyl-Sepharose were catalogue products.
• Anion exchange: standard, and the patent itself treats it as an optional polishing step.

Assessment: each is obvious as a routine optimization / known-technique addition (KSR).

3.6 Product-by-process and kit claims

• Product-by-process composition ("rAAV prepared by applying a sample to an iodixanol gradient and collecting the fraction") — obvious where the process is obvious; the composition is not distinguished by structure.
• Kits (claims 24–29) — a kit packaging iodixanol + a heparin matrix (± phenyl-Sepharose) with instructions is the mere commercial aggregation of two reagents the primary references already teach for the same purpose; no new synergy is claimed.

Assessment: obvious.

4. Articulated motivation to combine (TSM + KSR rationales)

1. Explicit teaching/suggestion: Summerford & Samulski 1998 expressly direct the skilled artisan to convert the HSPG/heparin receptor finding into "new reagents for virus purification" — a direct TSM for the heparin claims.
2. Known problem + known solution: the admitted CsCl protocol (Snyder 1996) suffered slow turnaround, poor recovery and lost infectivity; iodixanol was the known remedy (non-toxic, iso-osmotic, low-viscosity, dialysis-free) → motivation to substitute.
3. Secondary reference teaching the result: Tamayose 1996 shows rAAV affinity chromatography with 1 M NaCl elution, and simultaneously teaches away from chromatography-only (poor binding from crude lysate), motivating the iodixanol pre-step in the combination claim.
4. Predictable results / design choice (KSR): the step percentages, the 40% collection layer, the 1 M NaCl addition, and the choice of Type-I vs Type-II-S resin are optimization of known parameters with predictable outcomes.
5. Two-step purification is conventional wisdom: bulk-capture → polish is the standard downstream paradigm; combining pressure/gravity affinity with a density step is routine engineering.

5. Counterarguments a patentee would raise (and their strength)

Bottom line: most claims (the iodixanol method; the heparin method; the combined method; the Ad-reduction, CsCl/HIC/anion-exchange dependent claims; and the kits) are, on the face of the patent's own cited art, invalid as obvious under § 103. The combined iodixanol+heparin process (claim 23 / '514 claim 1) would survive only if the patentee could show the recovery and P:I improvements are unexpected in kind, which the pre-existing OptiPrep virus-purification literature renders difficult.

6. Procedural flags and caveats

• Unverified claim text. The full verbatim '874 claims were not in the supplied text; the above maps to reconstructed/paralle'514 claim language. A definitive opinion requires the issued claim set.
• Possible post-grant challenge. My searches surfaced a USPTO PTACTS petition record (petition 1558103) whose exhibits reproduce this specification — suggesting a possible post-grant proceeding (e.g., reexamination or an inter partes review) touching this family. I could not confirm its nature, filing date, or outcome, and I do not assert that any prior-art ground recited above mirrors that proceeding. Treat as an unverified flag only.
• Sibling patent. US 6,660,514 B1 (continuation, priority 2000-07-21) contains claim 1 in the reversed order (heparin → iodixanol) and may have been the actual target of any challenge; the same prior art applies to it.
• Per operating rules I have not auto-corrected any patent or reference identifiers; all citations are reported as they appear in the patent text and in the search results. All reference dates should be independently confirmed against original publications before being relied upon in a legal filing.