Monocyte — the graph's most-discussed undefined cell identity, and the confound sitting under its own DepMap haem signal
also called monocyte · monocytic · CD14+ monocyte · classical monocyte · mononuclear phagocyte
A monocyte is a large white blood cell that patrols the bloodstream for a few days and then settles into tissue as a macrophage, where one of its main jobs is to swallow worn-out red cells and recycle the iron locked inside them. That normal day job matters here because most of the KMT2A cell lines this project uses are monocytic, so an apparent iron-and-haem dependency of the fusion could simply be the physiology of the cell the fusion happens to be in.
The same thing, for a scientist
The monocyte (CL:0000576; classical CD14++CD16- subset CL:0000860) is the circulating mononuclear phagocyte that gives rise to tissue macrophages and to a substantial fraction of dendritic cells. Its defining physiology for this beat is metabolic rather than immunological: the monocyte-macrophage compartment is the body's principal site of erythrophagocytosis and haem-iron recycling, running high constitutive and inducible flux through HMOX1, FTH1/FTL, SLC11A1/SLC11A2 and SLC40A1 [E3]. Monocytic AML additionally carries a distinct metabolic and apoptotic programme: it loses BCL2, relies on MCL1 to sustain oxidative phosphorylation, and is consequently resistant to venetoclax-azacitidine, with monocytic subclones selected at relapse [E1]. Both properties bear directly on this project's own DepMap work, in which four haem-biosynthesis genes surfaced as selective requirements in KMT2A-rearranged lines while six of the seven rearranged AML lines in that panel are monocytic or monoblastic. Monocytic identity is therefore not background biology in this graph; it is the alternative explanation that the haem finding has not yet excluded.
What a monocyte is, and what it would be doing if it were healthy
A monocyte is one of the three kinds of white cell you see in a routine blood film, alongside neutrophils and lymphocytes. It is made in the bone marrow, spends roughly one to three days circulating, and then leaves the blood to become a macrophage or a dendritic cell in tissue. Its jobs are to eat things — bacteria, debris, dying cells — to present fragments of what it has eaten to the immune system, and to clean up after the destruction of red blood cells.
The international nomenclature recognised by the IUIS divides human blood monocytes into three subsets by CD14 and CD16: classical (CD14++CD16-), intermediate (CD14++CD16+) and non-classical (CD14+CD16++) 2. Classical monocytes are the large majority and are the phagocytic, inflammation-responsive workhorses.
The part of the job that matters most for this graph is the last one. When a red cell reaches the end of its life, a macrophage engulfs it, breaks the haemoglobin down, and must then do something with the haem, which is toxic when free. It opens the porphyrin ring with haem oxygenase 1 (HMOX1), releasing iron, which is either stored in ferritin or exported through ferroportin back to the plasma for reuse. Experimentally, macrophages in which both endosomal iron transporters (Nramp1/SLC11A1 and DMT1/SLC11A2) are disabled show a severely compromised ability to recycle haemoglobin-derived iron, a smaller labile iron pool, less iron released, and blunted upregulation of ferroportin and HMOX1 after erythrophagocytosis 3. In other words, the haem-and-iron handling machinery is not incidental to this lineage; it is what the lineage is for.
Why this is a confound for this project's own haem finding
This project's genome-wide DepMap scan found several haem-biosynthesis genes among the selective requirements of KMT2A-rearranged lines, and then flagged the obvious alternative: those lines are overwhelmingly monocytic. A monocytic cell is a cell whose normal programme already runs haem catabolism and iron handling hard. A gene-dependency difference between a monocytic panel and a non-monocytic comparison group is therefore ambiguous between 'the fusion creates this dependency' and 'monocytes have this dependency and the fusion merely happens to occur in monocytic disease'.
The follow-up analysis ana-depmap-haem-lineage-control could exclude the erythroid/megakaryocytic version of that alternative but explicitly could not settle the monocytic one: only four monocytic non-rearranged leukaemia lines exist in the panel, no haem gene reached significance (p 0.19-0.88), and the GAPDH control itself moved at p = 0.031, indicating a global offset between the groups. This entry exists so that the confound has a definition to point at rather than being restated each time.
A further wrinkle, established here for the first time in this graph: the monocytic panel is smaller than it looks. MOLM-13 and MOLM-14 were established from the same peripheral blood draw of a single patient at relapse of FAB M5a acute monocytic leukaemia, and Cellosaurus records them as originating from the same individual 4. See ana-kmt2a-r-line-panel-monocytic-audit.
Monocytic identity changes how leukaemia responds to drugs
Monocytic identity is not only a classification; it predicts drug behaviour in at least two directions that matter to this graph.
Against venetoclax. Responses to venetoclax plus azacitidine track developmental stage: phenotypically primitive AML is sensitive, monocytic AML is more resistant. Resistant monocytic AML has a distinct transcriptome, loses expression of the venetoclax target BCL2, and relies on MCL1 to sustain oxidative phosphorylation and survival; this differential sensitivity selects for the outgrowth of monocytic subpopulations at relapse 1.
With menin inhibition, apparently in the opposite direction. A chromatin-focused CRISPR screen found that loss of PRC1.1 subunits (PCGF1, BCOR) confers menin-inhibitor resistance by epigenetic reactivation of non-canonical menin targets including MYC — and those resistant cells show reduced monocytic gene signatures and become susceptible to BCL2 inhibition 6. Read together with the observation that GMP-like AML shows the greatest ex vivo sensitivity to the menin-KMT2A inhibitor bleximenib (see cell-state-gmp-like), monocytic-leaning identity appears to co-segregate with menin dependence and against venetoclax dependence.
That is a clinically awkward pairing: the same cell identity that makes a KMT2A-rearranged AML a good candidate for a menin inhibitor may make it a poor candidate for the venetoclax backbone those inhibitors are increasingly combined with.
The word 'monocytic' is doing at least three different jobs
Before treating 'monocytic' as a variable, note that the literature uses it for three non-identical things:
- Morphology and cytochemistry — FAB M5a/M5b, monoblasts and promonocytes, non-specific esterase positivity 7.
- Immunophenotype — CD14, CD64, CD11b, CD4-dim, loss of CD34.
- A transcriptional signature scored on bulk or single-cell data, which is what most modern papers mean.
These diverge. In one cohort, cultured monocytic AML cells displayed upfront venetoclax resistance while monocytic differentiation was not clinically predictive of response; what predicted response was the combinatorial BCL2/BCL-xL/MCL1 protein ratio in leukaemic stem cells. Any analysis in this graph that conditions on 'monocytic' must state which of the three it means.
| ontology | CL:0000576 |
|---|---|
| location | Bone marrow (production) -> peripheral blood (1-3 days transit) -> tissue as macrophage or dendritic cell; spleen red pulp and liver Kupffer cells are the main erythrophagocytic sites |
ontology alternatives
[ "CL:0000860" ]
markers
[ "CD14", "CD16 (FCGR3A, subset-defining)", "CD11b", "CD64", "CD68", "CD4 (dim)", "non-specific esterase positive" ]
lineage potential
[ "macrophage", "monocyte-derived dendritic cell", "osteoclast (bone)" ]
subsets
[
{
"name": "classical",
"phenotype": "CD14++CD16-",
"ontology": "CL:0000860"
},
{
"name": "intermediate",
"phenotype": "CD14++CD16+"
},
{
"name": "non-classical",
"phenotype": "CD14+CD16++"
}
]haem iron genes characteristic of lineage
[ "HMOX1", "FTH1", "FTL", "SLC40A1 (ferroportin)", "SLC11A1 (NRAMP1)", "SLC11A2 (DMT1)" ]
kmt2a relevance
{
"confound": "6 of 7 KMT2A-rearranged AML lines in this project's DepMap panel are monocytic or monoblastic, which is an unexcluded alternative explanation for the selective haem-biosynthesis dependency reported by ana-depmap-kmt2a-selective-scan-full",
"panel_independence_caveat": "MOLM-13 and MOLM-14 are from the same patient (Cellosaurus OI CVCL_2119 <-> CVCL_7916), so the monocytic arm of the panel carries 5 independent patients, not 6",
"drug_response": "monocytic identity predicts venetoclax resistance (BCL2 loss, MCL1/OXPHOS dependence) while loss of the monocytic signature accompanies menin-inhibitor resistance"
}atlas refs
[
{
"label": "IUIS consensus nomenclature of blood monocytes and dendritic cells",
"pmid": "20628149",
"title": "Nomenclature of monocytes and dendritic cells in blood.",
"authors": "Ziegler-Heitbrock L, Ancuta P, Crowe S, et al.",
"venue": "Blood",
"year": 2010,
"title_provenance": "Title/authors/venue backfilled from PubMed esummary on 2026-09-20 because this citation stored a bare PMID with no title, which made it unscoreable by verify-citations.py. BACKFILLING IS NOT VERIFICATION: it confirms the PMID resolves to a real paper, not that this is the right paper for the claim. That still requires reading."
},
{
"label": "Single-cell taxonomy of human blood monocytes and dendritic cells",
"pmid": "28428369",
"title": "Single-cell RNA-seq reveals new types of human blood dendritic cells, monocytes, and progenitors.",
"authors": "Villani AC, Satija R, Reynolds G, et al.",
"venue": "Science",
"year": 2017,
"title_provenance": "Title/authors/venue backfilled from PubMed esummary on 2026-09-20 because this citation stored a bare PMID with no title, which made it unscoreable by verify-citations.py. BACKFILLING IS NOT VERIFICATION: it confirms the PMID resolves to a real paper, not that this is the right paper for the claim. That still requires reading."
}
]- If the haem-biosynthesis dependency is a property of monocytic physiology rather than of the fusion, a haem-pathway inhibitor would be expected to have the same effect on normal monocytes and tissue macrophages, predicting on-target loss of erythrophagocytosis, iron recycling and innate immune defence as a dose-limiting toxicity rather than a selective effect.
- Monocytic AML loses BCL2 and depends on MCL1, so a menin-plus-venetoclax combination may be least effective in the monocytic disease where menin inhibition is most indicated, and selection pressure from the venetoclax arm would favour exactly the monocytic subclones the menin arm was aimed at.
- Because monocytic subclones are selected at relapse under venetoclax-based therapy, any biomarker measured at diagnosis will describe a cell population that the first line of therapy then changes.
- Two of the six monocytic lines in the panel come from one patient, so any effect size estimated across that panel is less certain than its n suggests, and a per-patient rather than per-line analysis will have lower power than assumed.
- Does a KMT2A-rearranged monocytic blast actually run haem catabolism at the rate a normal monocyte-derived macrophage does, or does it merely carry the transcriptional signature? A labelled-haem flux measurement in MV4-11 versus a monocytic non-rearranged line would separate signature from flux and is the single measurement that would settle the DepMap confound.
- Is the haem dependency of KMT2A-rearranged lines abolished when the fusion is degraded but monocytic identity is retained? A degron time-course with haem-gene dependency read out at fixed lineage state is the clean design.
- If monocytic identity predicts menin sensitivity and venetoclax resistance simultaneously, what is the right sequence for a monocytic KMT2A-rearranged AML, and does the combination lose more than it gains in this subgroup specifically?
- Do infant KMT2A-rearranged ALL blasts that lineage-switch to monocytic disease acquire the monocytic metabolic programme (BCL2 loss, MCL1 dependence) at the same time as the monocytic immunophenotype, or is there a window in which they are phenotypically myeloid but still BCL2-dependent?
- E1strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
Responses to venetoclax plus azacitidine in AML correlate with developmental stage: phenotypically primitive AML is sensitive and monocytic AML is more resistant; resistant monocytic AML has a distinct transcriptomic profile, loses expression of the venetoclax target BCL2, and relies on MCL1 to mediate oxidative phosphorylation and survival, with selection for outgrowth of monocytic subpopulations at relapse.
Monocytic Subclones Confer Resistance to Venetoclax-Based Therapy in Patients with Acute Myeloid Leukemia · Pei S, Pollyea DA, Gustafson A, Stevens BM, Minhajuddin M, Fu R, et al., Jordan CT · Cancer Discovery 2020What this evidence cannot show
Cohort is older, previously untreated AML receiving venetoclax plus azacitidine, not paediatric or KMT2A-rearranged disease; the mechanistic work rests on sorted subpopulations and cell lines. 'Monocytic' here is defined by immunophenotype and transcriptome together, and the boundary between primitive and monocytic is drawn by the authors. Read: abstract only.
Evidence that argues against this (1)
- Monocytic differentiation was NOT clinically predictive of azacitidine/venetoclax response in an independent integrated cohort, even though cultured monocytic AML cells did display upfront resistance in vitro. What predicted response was the combinatorial BCL2/BCL-xL/MCL1 protein ratio in leukaemic stem cells, formalised as a flow-based MAC-Score with a positive predictive value above 97%. This separates an in vitro property of monocytic cells from a clinical property of monocytic patients and cautions against using 'monocytic' as a treatment-assignment variable. Read: abstract only. Waclawiczek A et al. 2023
- E2established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.paper
The IUIS-approved nomenclature defines three types of human blood monocyte — classical, intermediate and non-classical — separated by CD14 and CD16 expression, alongside three dendritic cell types.
Nomenclature of monocytes and dendritic cells in blood · Ziegler-Heitbrock L, Ancuta P, Crowe S, Dalod M, Grau V, Hart DN, et al., Lutz MB · Blood 2010What this evidence cannot show
A consensus nomenclature document, not an experimental study; the three-subset scheme was fixed by committee on flow-cytometric grounds and predates single-cell transcriptomics.
Evidence that argues against this (1)
- Unbiased single-cell RNA-seq of roughly 2400 human blood cells resolved FOUR monocyte subtypes and six dendritic cell subtypes, redefining pDCs and subdividing the CD1C+ compartment. The three-subset CD14/CD16 scheme is therefore an operational gating convention rather than a complete taxonomy, and a 'monocytic signature' scored against it can merge biologically distinct cells. Read: abstract only. Villani AC et al. 2017
- E3strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
The macrophage arm of the monocyte lineage is the principal site of haem-iron recycling: macrophages in which both Nramp1/SLC11A1 and DMT1/SLC11A2 iron transport are disabled show severely compromised recycling of haemoglobin-derived iron, a blunted labile iron pool, reduced iron release and diminished upregulation of ferroportin and haem oxygenase 1 after erythrophagocytosis.
Both Nramp1 and DMT1 are necessary for efficient macrophage iron recycling · Soe-Lin S, Apte SS, Mikhael MR, Kayembe LK, Nie G, Ponka P · Experimental Hematology 2010What this evidence cannot show
Mouse RAW264.7 macrophage line with siRNA and pharmacological (ebselen) knockdown, not primary human monocytes and not leukaemia. It establishes that the recycling machinery is lineage-characteristic, not that a leukaemic monocytic blast runs it at the same rate. Read: abstract only.
Evidence that argues against this (1)
- Haem-pathway dependency is not monocyte-specific and can be induced in non-monocytic AML by oxidative stress alone. In TP53-mutant KMB3 AML cells, APR-246 drove HMOX1 up as one of the most induced genes via NFE2L2/Nrf2 nuclear translocation, independent of TP53 status. If HMOX1 and the oxidative-stress arm of haem handling are a general inducible AML response, then attributing a haem dependency in a monocytic panel to monocytic identity is itself under-determined — the lineage explanation and the fusion explanation may both be displaced by a stress-response explanation. Read: abstract only. Ali D et al. 2016
- E4established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.database
Cellosaurus records MV4-11 (CVCL_0064, KMT2A-AFF1), THP-1 (CVCL_0006, KMT2A-MLLT3), NOMO-1 (CVCL_1609, KMT2A-MLLT3), SHI-1 (CVCL_2191, KMT2A-AFDN) and MOLM-13 (CVCL_2119, KMT2A-MLLT3) under NCIt/ORDO terms for acute monocytic or acute monoblastic/monocytic leukaemia, and records MOLM-13 as originating from the same individual as MOLM-14 (CVCL_7916).
Cellosaurus cell line records CVCL_0064 (MV4-11), CVCL_0006 (THP-1), CVCL_1609 (NOMO-1), CVCL_2191 (SHI-1), CVCL_2119 (MOLM-13) and CVCL_7916 (MOLM-14), retrieved via the Cellosaurus API · Bairoch A; SIB Swiss Institute of Bioinformatics · Cellosaurus 2026What this evidence cannot show
Cellosaurus disease terms are curated from the establishing publication and depositor catalogues; this Queen read the API text records on 2026-09-19 rather than the original DSMZ certificates. Disease-term granularity is inconsistent across records, which is exactly the discrepancy noted in the counter-evidence.
Evidence that argues against this (1)
- The database annotation is internally inconsistent and understates the monocytic fraction. MOLM-14 carries only NCIt C9154 'Adult acute myeloid leukemia' and ORDO Orphanet_519, with no monocytic term, whereas the founding publication establishes both MOLM-13 and MOLM-14 from the same patient at relapse of FAB M5a acute monocytic leukaemia, with both lines expressing monocyte-specific esterase. Taking Cellosaurus disease terms at face value would misclassify MOLM-14; taking the founding paper at face value would treat two lines from one patient as two independent observations. Read: abstract only. Matsuo Y et al. 1997
- E6strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
Loss of PRC1.1 subunits (PCGF1, BCOR) confers menin-inhibitor resistance in KMT2A-rearranged AML by epigenetic reactivation of non-canonical menin targets including MYC, and those resistant cells exhibit reduced monocytic gene signatures and become susceptible to BCL2 inhibition, so that venetoclax overcomes the resistance.
Epigenetic regulation of noncanonical menin targets modulates menin inhibitor response in acute myeloid leukemia · Zhou X, Zhang L, Aryal S, Veasey V, Tajik A, Restelli C, et al., Lu R · Blood 2024What this evidence cannot show
Human and mouse KMT2A-rearranged AML models with CRISPR-engineered PRC1.1 loss; the monocytic-signature reduction is a correlate of the resistant state rather than a demonstrated cause of it, and no patient series has yet shown that PRC1.1-deficient KMT2A-r AML is less monocytic at diagnosis. Read: abstract only.
Evidence that argues against this (1)
- The directionality is not safe to generalise, because the same label points in opposite directions across drug classes and cohorts. In the same disease, monocytic AML is venetoclax-RESISTANT with loss of BCL2 and MCL1 dependence, yet here loss of the monocytic signature is what confers menin-inhibitor resistance and restores BCL2 sensitivity. Whether 'monocytic' predicts response therefore depends on the drug and on whether the label is scored morphologically, immunophenotypically or transcriptionally; a cohort in which monocytic differentiation was not clinically predictive of venetoclax response makes that point directly. Read: abstract only. Waclawiczek A et al. 2023
- E7established confidence 5 of 5: Multiple independent lines of evidence; treated as settled in the field.paper
The French-American-British cooperative group's revised criteria formalised the monocytic subtypes of acute myeloid leukaemia (M4 myelomonocytic, M5a monoblastic, M5b monocytic) on morphological and cytochemical grounds.
Proposed revised criteria for the classification of acute myeloid leukemia. A report of the French-American-British Cooperative Group · Bennett JM, Catovsky D, Daniel MT, Flandrin G, Galton DA, Gralnick HR, Sultan C · Annals of Internal Medicine 1985What this evidence cannot show
A 1985 consensus criteria document with no abstract in PubMed; superseded for diagnostic purposes by genetically defined classifications. Cited here only for the origin and meaning of the M5a/M5b terminology that the cell-line literature still uses. Read: PubMed record only, no abstract exists.
Evidence that argues against this (1)
- The FAB morphological categories have been deliberately demoted: the WHO 5th edition organises acute myeloid leukaemia primarily by defining genetic abnormality, with 'AML with KMT2A rearrangement' as its own entity and differentiation-based categories reserved for cases without a defining genetic lesion. Reporting a KMT2A-rearranged case as 'M5a' therefore describes the cell, not the disease entity, and morphological monocytic classification carries known interobserver variability. Read: abstract only. Khoury JD et al. 2022
monocytic/monoblastic morphology dominates KMT2A-rearranged AML
the lineage alternative that analysis could not exclude
- confers resistance to →Venetoclax in KMT2A-rearranged leukemia — the apoptotic partner every other drug needs
monocytic AML loses BCL2, depends on MCL1/OXPHOS
- related to →BCL2 — the one co-dependency in this beat that already has an approved drug pointed at it
monocytic identity is defined in part by loss of BCL2 expression
- related to →Lineage switch in KMT2A-rearranged leukemia — the same clone changes what kind of blood cell it is
monocytic is the usual destination of a B-to-myeloid lineage switch
line-by-line Cellosaurus basis for the monocytic confound
tests whether haem dependency is monocytic physiology
the GMP is the immediate progenitor of the monocyte
predicted trajectory toward the monocytic metabolic configuration and venetoclax resistance
the monoblast is the immature form of the monocyte
shared CD123/CD4/CD56 phenotype makes monocytic leukaemia the main differential and the main misdiagnosis
the lineage physiology the hypothesis invokes
MV4-11 is annotated as childhood acute MONOCYTIC leukaemia and is the myeloid arm of the same-fusion contrast
- ← expressed inCDK9 - the kinase the whole SEC story runs through, which this graph held only as half of a two-protein summary entry
42k and 55k CDK9 isoforms differentially expressed across primary monocytes, macrophages and lymphocytes from separately regulated promoters; expression, not dependency
the only cell type in which HDAC3's localisation has been resolved is the macrophage, where SMRT controls its nuclear localisation and the two scaffolds split inflammatory from metabolic control
Mef2c increases monopoiesis at the expense of granulopoiesis and Mef2c(Delta/-) marrow shows reduced monocytic differentiation (murine; PMID 18326819)
myeloid leukocyte expression; FUT4 contributes, as the lesser partner to FUT7, to the selectin ligands leukocytes use to roll on endothelium (human HL-60 and murine neutrophils; PMID 23192350)
- ← expressed inTCF7L2 - the protein IntAct's 'DOT1L-TCF4' row is actually about, and the Wnt effector that DOT1L and AF10 coactivate
HPA Blood Atlas group-enriched; non-classical monocyte 61.8 nTPM, intermediate monocyte 24.2 nTPM (RNA)
HPA Blood Atlas immune-cell-enhanced, intermediate monocyte 13.3 nTPM; LXR-alpha's canonical sterol-efflux function is a monocyte/macrophage one
UniProt P20138 tissue specificity: monocytic/myeloid lineage cells; the CD33M/CD33m isoform split was measured in primary human blood monocytes and neutrophils (PMID 28747436) (Q89 2026-09-21)
- ← expressed inFUT9 - the dedicated Lewis-x synthase, structurally solved, and untouched by the KMT2A literature
A NEGATIVE residency, measured: FUT9 is HIGHLY EXPRESSED IN GRANULOCYTES AND NOT EXPRESSED IN MONOCYTES by competitive RT-PCR, and CD15 in monocytes and promyelocytes is built by FUT4 instead, while in mature granulocytes it is built by FUT9 (PMID 11278338). The enzyme behind the epitope switches with maturation stage (Q93 2026-09-21)
SOURCE versus TARGET, which must not be merged for a secreted ligand: TNF comes from myeloid and lymphoid immune cells (processing documented in ACTIVATED DENDRITIC CELLS, PMID 16829952), while the cell whose state matters here is the KMT2A::AFF1 blast, which RESISTS TNF killing via S100A6 (PMID 22829076). A localisation field on this entry would have been the wrong instrument (Q95 2026-09-22)