Research report

A research report is the sourced material a domain dossier is synthesized from — generated on a plan and a cadence, one topic per file. A report carries no confidence tags. Its bracketed markers say who might have an incentive to shade a line; none of them says anyone checked it. To reach a score, a line has to be drafted onto a candidate as unverified and pass the Verifier or the Corroborator, like everything else.

Section technology · Version 2026-09-25 · Cadence annual · Evidence class 2 published · Sources 19 · Supersedes none

Domain: ctdna-mrd-assay-validation · Scope: Settles idea-003 REQ-0033. Published methods for producing mononucleosome-sized variant-bearing DNA for spike-in (MNase digestion of cell-line chromatin, enzymatic or sonication shearing, synthetic dsDNA fragments, apoptotic or conditioned cell-culture media cfDNA (cell-free DNA), dilution into donor plasma), with vendors using them, whether a ~167 bp peak is reproduced, and IP (intellectual property) noted. PubMed via the literature connector at abstract depth (one PMC full text); vendor product pages and patent documents via WebFetch. Excludes a freedom-to-operate or landscape search (no capability exists here), vendor certificates of analysis and internal SOPs, full texts behind publisher paywalls, and jurisdictions other than US.

Sourcing: Rests on eleven PubMed abstracts (one read in full text) describing how reference-material fragments are made, three US patent documents read on Google Patents, and three vendor pages; the patent connector returned no record for any of the three patents, and no published process for spiking into native pooled donor plasma was found at abstract depth.

How variant-bearing cfDNA-like fragments are made and spiked for reference materials: established process, licensable method, or first-principles development

1. Summary

Micrococcal nuclease (MNase) digestion of chromatin from cancer cell lines has been published as a way to make ctDNA (circulating tumour DNA) reference material by at least two independent metrology groups, in Shanghai and at KRISS [1][2][3]. Patient-derived organoids release cfDNA into culture medium with a mononucleosome-associated size profile, as reported by two independent groups [9][10]. Across the reference-material abstracts and vendor pages read, fragment sizes are reported in several different ways, and none reports a peak at exactly ~167 bp [1][2][4][17]. The routes other than MNase, the vendor compositions and the patent claims each rest on one source and are set out in section 3.

2. What Changed

_Baseline (v1). No prior version; this establishes the starting point for future diffs._

3. Details

MNase digestion of cell-line chromatin

Shanghai Ocean University (Genes, 2025, n=2 TP53 variants): reference material made "by digesting nucleosomes from cultured cancer cell lines with micrococcal nuclease, followed by magnetic beads purification", with "single dominant peaks at 128 bp (R175H) and 143 bp (R248W)" [1] [single-source].
KRISS (Anal Bioanal Chem, 2026, 4 EGFR variants at 0%, 0.2%, 1% and 5% nominal VAF (variant allele frequency)): nucleosomal DNA was extracted "using the EZ Nucleosomal DNA Prep Kit (Zymo Research …), which incorporates MNase digestion". It "exhibited a fragment size distribution of approximately 150–170 bp", was supplied in Tris-EDTA buffer, not plasma, and was stable for three years at −70 °C (full text read) [2] [single-source].
The kit named is Zymo catalog no. D5220, which offers MNase or Atlantis dsDNase [18] [single-source · manufacturer].
KRISS (J Clin Lab Anal, 2020, 3 KRAS variants): the choice of Atlantis dsDNase or MNase "affects DNA quantification", and spiking nucleosomal DNA into fetal bovine serum changed dPCR (digital polymerase chain reaction) output significantly compared with no-serum conditions [3] [single-source].

Enzymatic or sonication shearing

China's National Institute of Metrology (2024, 9 hotspot variants, 0.33–23.9% VAF): cell-line DNA was enzymatically digested "into approximately 154-bp to 173-bp fragments using a laboratory-developed reaction system" [4] [single-source].
Horizon (Revvity) Mimix Multiplex I cfDNA, catalog nos. HD776–HD779: "derived from human cell lines, and are fragmented to an average size of 160 bp". The page does not name the fragmentation method. The format is Tris-EDTA buffer, at 5%, 1% and 0.1% AF [17] [single-source · manufacturer].
Seraseq ctDNA MRD (molecular residual disease) Panel Mix, catalog no. 0710-2146: made from a cancer cell line, its SNP-matched normal line and biosynthetic DNA. "Blended DNA is fragmented, sized to mimic ctDNA fragment sizes". It comes at 0.5%, 0.05% and 0.005% tumor fraction in Tris/EDTA buffer. The method is not named [16] [single-source · manufacturer].
NIST multilaboratory study (2019): a commercial material in which "Fragmented DNA was formulated to simulate the size distribution of circulating wild-type and tumor DNA in a synthetic plasma matrix", at 2%, 0.5%, 0.125% and 0% VAF [7] [single-source].
In a study of Seraseq NIPT materials (2026, 8 genotypes × 6 replicates), "Fragment size profiles exhibited slight but consistent deviations from natural plasma" [12] [single-source].

Synthetic dsDNA fragments

China's National Institute of Metrology (2020): BRAF V600E material made "by gravimetrically mixing a 152 bp PCR amplicon and sonicated wild-type genomic DNA". It was characterised from 53.9% down to 0.1% [5] [single-source].
FDA (US Food and Drug Administration)-led SEQC2 (2021): "a synthetic internal standard spike-in was designed for each actionable mutation target" and mixed with contrived ctDNA samples [6] [single-source].
TÜBİTAK UME CRM 3022/3024 (2026): gravimetric synthetic dsDNA fragments of 80–240 bp. These are for isolation recovery, not variant detection [8] [single-source].

Culture-medium, apoptotic and conditioned-media cfDNA

Culture medium from gastric and lung organoids (9 lines): fragment sizes, "especially in apoptosis samples, was similar to that found in plasma, implying occupancy by mononucleosomes" [9] [single-source].
Supernatants from colorectal-cancer organoids (21 cultures, 13 patients): cf-nDNA showed a "mononucleosome-associated profile", at 0.009–209 ng/mL [10] [single-source].
Nuclease-treated conditioned media have been used "to simulate cfChromatin nucleosomal distributions" (iScience, 2025) [11] [single-source].
The release is not fixed. In A549, FLO-1 and OE19 cell lines, chemotherapy "induced a shift toward the release of larger DNA fragments" [19] [single-source].

Patents naming the method

US9499870B2 (Natera, priority 2013-09-27), claim 1: "a cell-free nucleic acid diagnostic proficiency testing standard composition comprising, a first nucleosomal nucleic acid preparation derived from a first cell source and a second nucleosomal nucleic acid preparation from a second cell source …". The description uses MNase on chromatin from primary cells or cell lines [13] [single-source].
US10577655B2 is a continuation claiming priority to the same application. Its claim text was not in the page retrieved [14] [single-source].
US11215622B2 (Covaris, priority 2017-01-27), claim 1 covers formaldehyde fixation, acoustic shearing to 1–5 kbp, enzymatic linker digestion to "nucleosome material having a size of 147 to 195 bp", and use "as synthetic cfDNA reference material" [15] [single-source].
None of the three vendor pages mentions a patent or a licence [16][17][18].

Dilution into donor plasma

The abstracts read describe materials supplied in buffer [2][16][17] or synthetic plasma [7]. No abstract read describes spiking into native pooled donor plasma as a characterised reference-material process.

4. Sources

[1] Establishment of Reference Measurement Procedure for TP53 R175H/R248W Detection and a Novel Preparation Method for ctDNA Reference Material — Genes (published 2025-05-14; accessed 2026-09-25). PMID (PubMed identifier) 40428398; DOI 10.3390/genes16050576 — https://pubmed.ncbi.nlm.nih.gov/40428398/ [peer-reviewed] [2] Development and characterization of nucleosomal DNA-based reference materials for the epidermal growth factor receptor gene liquid biopsy — Analytical and Bioanalytical Chemistry (published 2026-06, day not given in the PubMed record; accessed 2026-09-25). PMID 41936644; DOI 10.1007/s00216-026-06475-5 — https://pmc.ncbi.nlm.nih.gov/articles/PMC13221357/ [peer-reviewed] [3] Improvement of digital PCR conditions for direct detection of KRAS mutations — Journal of Clinical Laboratory Analysis (published 2020-08, day not given in the PubMed record; accessed 2026-09-25). PMID 32329932; DOI 10.1002/jcla.23344 — https://pubmed.ncbi.nlm.nih.gov/32329932/ [peer-reviewed] [4] Development of a nine-variant reference material panel to standardize cell-free DNA detection — Analytical and Bioanalytical Chemistry (published 2024-07, day not given in the PubMed record; accessed 2026-09-25). PMID 38782781; DOI 10.1007/s00216-024-05336-3 — https://pubmed.ncbi.nlm.nih.gov/38782781/ [peer-reviewed] [5] Interlaboratory assessment of droplet digital PCR for quantification of BRAF V600E mutation using a novel DNA reference material — Talanta (published 2020-01-15; accessed 2026-09-25). PMID 31594564; DOI 10.1016/j.talanta.2019.120293 — https://pubmed.ncbi.nlm.nih.gov/31594564/ [peer-reviewed] [6] Advancing NGS (next-generation sequencing) quality control to enable measurement of actionable mutations in circulating tumor DNA — Cell Reports Methods (published 2021-11-22; accessed 2026-09-25). PMID 35475002 — https://pubmed.ncbi.nlm.nih.gov/35475002/ [peer-reviewed] [7] Multilaboratory Assessment of a New Reference Material for Quality Assurance of Cell-Free Tumor DNA Measurements — The Journal of Molecular Diagnostics (published 2019-07, day not given in the PubMed record; accessed 2026-09-25). PMID 31055023; DOI 10.1016/j.jmoldx.2019.03.006 — https://pubmed.ncbi.nlm.nih.gov/31055023/ [peer-reviewed] [8] Certified Reference Materials for Standardization of Cell-Free DNA Isolation Recovery in Liquid Biopsy — The Journal of Molecular Diagnostics (published 2026-06, day not given in the PubMed record; accessed 2026-09-25). PMID 41936819 — https://pubmed.ncbi.nlm.nih.gov/41936819/ [peer-reviewed] [9] Multidimensional fragmentomic profiling of cell-free DNA released from patient-derived organoids — Human Genomics (published 2023-10-28; accessed 2026-09-25). PMID 37898819 — https://pubmed.ncbi.nlm.nih.gov/37898819/ [peer-reviewed] [10] Characterization of the cell-free DNA released by tumor organoids derived from colorectal cancer patients — European Journal of Cancer (published 2025-12-09; accessed 2026-09-25). PMID 41223563 — https://pubmed.ncbi.nlm.nih.gov/41223563/ [peer-reviewed] [11] Simulating cell-free chromatin using preclinical cancer models for liquid biopsy applications — iScience (published 2025-12-19; accessed 2026-09-25). PMID 41497400 — https://pubmed.ncbi.nlm.nih.gov/41497400/ [peer-reviewed] [12] SeraSeq reference materials support non-invasive cfDNA screening methods — Clinical Biochemistry (published 2026-01, day not given in the PubMed record; accessed 2026-09-25). PMID 41232587 — https://pubmed.ncbi.nlm.nih.gov/41232587/ [peer-reviewed] [13] Cell free DNA diagnostic testing standards — Natera Inc, patent document via Google Patents (published 2016-11-22; accessed 2026-09-25). US9499870B2 — https://patents.google.com/patent/US9499870B2/en [other] [14] Cell free DNA diagnostic testing standards (continuation) — Natera Inc, patent document via Google Patents (published 2020-03-03; accessed 2026-09-25). US10577655B2 — https://patents.google.com/patent/US10577655B2/en [other] [15] Generation of cfDNA reference material — Covaris LLC, patent document via Google Patents (published 2022-01-04; accessed 2026-09-25). US11215622B2 (published application US20180217161A1) — https://patents.google.com/patent/US11215622B2/en [other] [16] Seraseq ctDNA MRD Panel Mix — SeraCare / LGC Clinical Diagnostics product page (published date not stated; accessed 2026-09-25). catalog no. 0710-2146 — https://www.seracare.com/Seraseq-ctDNA-MRD-Panel-Mix-0710-2146/ [manufacturer] [17] Mimix Multiplex I, cfDNA Reference Standard Set — Horizon Discovery (Revvity) product page (published date not stated; accessed 2026-09-25). catalog no. HD776 (set also HD777, HD778, HD779) — https://horizondiscovery.com/en/reference-standards/products/multiplex-i-cfdna-reference-standard-set [manufacturer] [18] EZ Nucleosomal DNA Prep Kit — Zymo Research product page (published date not stated; accessed 2026-09-25). catalog no. D5220 — https://zymoresearch.com/products/ez-nucleosomal-dna-prep-kit [manufacturer] [19] Cell-Free DNA Release Kinetics and Fragmentation Reflect Treatment Response and Resistance In Vitro — Cells (published 2026-08-28; accessed 2026-09-25). PMID 42738856 — https://pubmed.ncbi.nlm.nih.gov/42738856/ [peer-reviewed]

5. Sourcing & Gaps

Well established: MNase digestion of cancer cell-line chromatin, as a published way to make ctDNA reference material. It rests on Shanghai Ocean University [1] and KRISS [2][3], which are separate institutions. Organoid culture medium carrying mononucleosome-sized cfDNA rests on two independent groups [9][10].

Thin: Every fragment-size figure is [single-source]. Vendor composition lines are [single-source · manufacturer] [16][17][18]. The three patent lines are [single-source]. They come from Google Patents renderings, because the patent connector returned no record ("No EPO (European Patent Office) OPS record found") for US9499870B2, US10577655B2 and US11215622B2. As a result, assignee, grant status, term and expiry were not established from any registry, and this report states no legal status or expiry date. Most papers were read at abstract depth. The exception is [2], read in PMC full text.

Rescoped from class 3: None in this report. REQ-0033 asks what exists, not what anyone would do.

Out of scope: Freedom-to-operate or landscape search (no capability exists; claims 18 and C1 on idea-003 already record this). Whether Natera or Covaris license these patents, and on what terms: no licensing statement was found or searched for beyond the patent texts and the three vendor pages. Vendor certificates of analysis and manufacturing SOPs. Twist Bioscience's cfDNA product pages. The full text of the Zymo kit protocol.

Not searched vs. not found:

Not found: a PubMed abstract describing a characterised process for spiking variant-bearing fragments into native pooled human donor plasma as a reference material. Searches tried: "healthy donor plasma spiked limit of detection circulating tumor DNA" and "contrived samples ctDNA limit of detection". MRD validation abstracts (Haystack PMID 42624249, PhasED-Seq PMID 40353795) mention reference materials or contrived samples but do not describe the matrix.
Not found: a published peak at exactly ~167 bp in any reference-material abstract read. The figures found were 128/143 bp [1], 150–170 bp [2], 154–173 bp [4], an average of 160 bp [17], and a claimed range of 147–195 bp [15].
Not found: a publication using "gBlocks" by name. The synthetic-fragment route is covered by [5][6][8] only.
Not searched: sonication specifics beyond [5], because the Horizon and Seraseq pages do not name their method.
Not retrieved: the Justia page for US20180217161 (HTTP 403). The granted patent was read instead [15].

[inference] Fragment production appears to be an established published process with several routes and an off-the-shelf MNase kit [1][2][4][5][18]. The same MNase-nucleosomal route is the subject of issued US patent claims held by Natera and Covaris [13][15], so it may be licensable or encumbered rather than free. Whether it is either is not determined here. The step specific to the candidate — spiking into native pooled donor plasma with a dPCR uncertainty budget at 0.001–0.01% VAF — was not found as a published process. On this evidence it reads as development work. The KRISS serum matrix effect [3] and the Seraseq fragment-periodicity deviation [12] suggest that matrix and fragment source are where that development risk sits.

6. Claim Candidates

Proposition	Evidence class	Resolvable identifier	Dossier section
A ctDNA reference material prepared by MNase digestion of cancer cell-line nucleosomes showed dominant peaks at 128 bp (TP53 R175H) and 143 bp (R248W)	2 published	PMID 40428398	technology
KRISS nucleosomal-DNA EGFR reference materials (0–5% nominal VAF) had a fragment size distribution of about 150–170 bp and were stable three years at −70 °C	2 published	PMID 41936644	technology
Enzymatic digestion of cell-line DNA produced reference-material fragments of about 154–173 bp for a nine-variant cfDNA panel at 0.33–23.9% VAF	2 published	PMID 38782781	technology
Spiking nucleosomal or genomic DNA into fetal bovine serum significantly changed dPCR output compared with non-serum conditions	2 published	PMID 32329932	technology
US9499870B2 claim 1 claims a cfDNA proficiency-testing standard made of nucleosomal nucleic acid preparations from two cell sources, in unequal quantities	2 published	US9499870B2	technology
US11215622B2 claim 1 claims generating cfDNA reference material by formaldehyde fixation, acoustic shearing, and enzymatic linker digestion to 147–195 bp nucleosome material	2 published	US11215622B2	technology
Seraseq ctDNA MRD Panel Mix is supplied as purified DNA in Tris/EDTA at 0.5%, 0.05% and 0.005% tumor fraction	2 published	catalog no. 0710-2146	reference-products
Seraseq NIPT reference materials showed slight but consistent fragment-size-profile deviations from natural maternal plasma	2 published	PMID 41232587	technology

Words on this page10 abbreviation(s) and code(s), with what each stands for — copied from _shared/plain-language.md

cfDNA: cell-free DNA — DNA fragments floating in the blood, most of them from normal cells
ctDNA: circulating tumour DNA — fragments of a tumour's DNA found in the blood
dPCR: digital polymerase chain reaction — a laboratory method that counts individual DNA molecules
EPO: European Patent Office — the European patent office
FDA: US Food and Drug Administration — the US regulator that clears or approves a device before it can be sold
IP: intellectual property — patents and the other rights that let a company stop others copying it
MRD: molecular residual disease — cancer left behind after treatment, too little to see on a scan, detected through DNA in the blood
NGS: next-generation sequencing — the laboratory method that reads many DNA fragments at once
PMID: PubMed identifier — the public id of one published medical paper
VAF: variant allele frequency — what share of the DNA fragments at one position carry the tumour's mutation; the lower it is, the harder the test

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