Menin primacy was established on the der(11) product alone and has never been tested against the der(4) product
also called menin primacy is half the translocation · the untested other oncoprotein
The argument that menin is the fusion's one indispensable handle was built by studying the famous half of the swap. The other half is present in roughly half of these children, keeps the entire enzyme machinery, and has no menin handle at all - so the drug cannot reach it, and nobody has checked whether that matters.
The same thing, for a scientist
Every experiment underpinning menin primacy uses a 5'-KMT2A direct fusion: Yokoyama 2004's MLL-p300 and MLL-ENL; Thiel 2010's MLL-AF9; the menin-inhibitor pharmacology; this graph's own DepMap scans. None uses a reciprocal der product. Yet AFF1::KMT2A retains the WIN motif and SET domain and has LOST the menin-binding motif, is expressed in about 45% of t(4;11) infant B-ALL, and is sufficient to induce acute leukaemia in transplanted murine progenitors where MLL-AF4 alone is not [E1][E2][E3]. The hypothesis is that **menin primacy is a property of the der(11) product and not of the disease**, and that in reciprocal-positive patients a menin inhibitor is by construction a partial intervention. The one natural experiment that speaks to this is NUP98::KMT2A, which has the same menin-blind, WRAD-competent architecture and is menin-inhibitor resistant [E4]. The obvious prediction - that reciprocal-positive patients respond worse to menin inhibitors - is contradicted by the prognostic data, which show reciprocal-positive patients doing markedly better on conventional therapy [E2]. That tension is the most interesting thing in this hypothesis and the reason its prior is low rather than zero.
Why the prognostic data cut against the hypothesis, and why that is not fatal
Reciprocal-positive t(4;11) infants had 4-year event-free survival of 62.4% versus 11.7% for reciprocal-negative, adjusted for risk stratification 2. If AF4-MLL were a second driver, the expectation is the opposite sign. Three readings survive:
- AF4-MLL is an initiator, not a maintainer. Marschalek's own model is a hit-and-run mechanism: 48 hours of AF4-MLL expression produces chromatin and transcriptional changes still present at day 28 5. An initiator need not be a therapeutic target.
- Reciprocal loss is a marker of clonal evolution. Losing the der(4) allele may select for a more aggressive clone, in which case reciprocal status reports on clonal history rather than on the protein's current contribution.
- Breakpoint position is the real variable. This graph's
hyp-reciprocal-product-as-enforceable-remainderproposes exactly this: reciprocal expression is a deterministic consequence of partner-side breakpoint position, which could carry its own prognostic weight.
All three are compatible with the reciprocal protein being untouched by a menin inhibitor and none of them makes that fact therapeutically relevant. The hypothesis is worth stating because the response data that would decide it have never been stratified.
What would settle it, cheaply
Reciprocal transcript status is a single RT-PCR and has been assayed in at least one Interfant cohort. Menin-inhibitor trials in KMT2A-rearranged leukaemia enrol t(4;11) patients and do not record it. Adding reciprocal status as a stratification variable to an existing menin-inhibitor cohort is a retrospective analysis on banked material, not a new trial. If reciprocal-positive patients respond identically, the hypothesis is dead and the menin argument is strengthened in a way it currently is not.
| statement | Menin primacy in KMT2A-rearranged leukaemia was established entirely on 5'-KMT2A direct fusion products and has never been tested against the reciprocal der product, which is present in about half of t(4;11) patients and is menin-blind by construction. |
|---|---|
| origin | literature-gap |
| prior probability | 0.2 |
predictions
[ "Reciprocal-positive t(4;11) patients show shallower or shorter menin-inhibitor responses than reciprocal-negative patients", "A reciprocal-positive t(4;11) cell line is less sensitive to a menin inhibitor than an otherwise comparable reciprocal-negative line", "Residual chromatin occupancy of the KMT2A C-terminus after saturating menin inhibition is higher in reciprocal-positive cells", "WRAD subunits remain on fusion target loci after saturating menin inhibition in reciprocal-positive cells and fall in reciprocal-negative cells" ]
experiments
[ "exp-reciprocal-status-stratified-menin-inhibitor-reanalysis" ]
analyses
[ "ana-wrad-fusion-evidence-enumeration" ]
falsifiers
[ "Reciprocal-positive and reciprocal-negative patients show indistinguishable menin-inhibitor response rates and durations in any adequately powered cohort", "The reciprocal product is undetectable at the protein level in patient blasts, making the entire argument about an mRNA", "Acute degradation of the reciprocal product in a reciprocal-positive line has no effect on growth, HOXA output or menin-inhibitor sensitivity", "Reciprocal expression is shown to be a pure marker of breakpoint position with no independent biological effect" ]
- If reciprocal-positive patients respond worse to menin inhibitors, current eligibility criteria are enrolling a mixed population and the class effect is being averaged across two different diseases.
- If reciprocal-positive patients respond better, the reciprocal product becomes a favourable biomarker and removing it therapeutically would be harmful - so the hypothesis has a live failure mode in which acting on it hurts patients.
- Any agent designed to hit the reciprocal product would necessarily hit the wild-type KMT2A allele, which shares its entire retained sequence, in infants who need that allele.
- Do any banked menin-inhibitor trial samples have reciprocal transcript status available? The assay is a single RT-PCR and the material exists.
- Is MV4-11 reciprocal-positive? **Answered 2026-09-19.** RS4;11 and SEMK2-M1 (a SEM subline) **both express MLL-AF4 and AF4-MLL** - stated directly in the abstract of PMID 20869771, whose own experiment was to knock AF4-MLL down in them. So both standard lines are **reciprocal-positive**, and there is no reciprocal-negative t(4;11) line: no cell-based experiment in this disease has ever had a comparator arm. **MV4-11 remains open** - it is t(4;11) AML, and this beat did not find its status stated anywhere. For this hypothesis that is the worse of the two possible answers: the preclinical menin-inhibitor package is unstratified in a **known** direction - every line carries the product the drug cannot engage.
- Does the reciprocal product exist as protein in patient blasts? Every clinical number in this hypothesis is RT-PCR, and taspase1-dependent destabilisation is a documented reason it might not.
- E1strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
The reciprocal t(4;11) product AF4-MLL comprises AF4 exons 1-3 fused to MLL exons 12-37, retaining the KMT2A WIN motif and SET domain while losing the N-terminal menin-binding motif; the AF4-MLL allele is eliminated in about 40% of patients.
The role of reciprocal fusions in MLL-r acute leukemia: studying the chromosomal translocation t(4;11). · Wilhelm A, Marschalek R · Oncogene 2021What this evidence cannot show
Construct description from an engineered HEK293T model rather than a patient survey; the 40% figure is stated with a citation rather than measured in that paper.
Evidence that argues against this (1)
- About half of KMT2A::MLLT1 cases break upstream of the partner's first exon and express no reciprocal transcript, so reciprocal expression is partner- and breakpoint-dependent and any generalisation beyond t(4;11) is unsupported. Meyer C et al. 2023
- E2strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
The reciprocal AFF1::KMT2A transcript was expressed in 45% of t(4;11) cases among 124 Interfant-treated infants and predicted 4-year event-free survival of 62.4% versus 11.7%, retaining significance in a Cox model adjusted for risk stratification.
Unraveling the cellular origin and clinical prognostic markers of infant B-cell acute lymphoblastic leukemia using genome-wide analysis. · Agraz-Doblas A, Bueno C, Bashford-Rogers R, et al. · Haematologica 2019What this evidence cannot show
Retrospective cohort; transcript detection, not protein; and the effect direction is opposite to a second-driver model. None of these patients received a menin inhibitor.
Evidence that argues against this (1)
- A CRISPR-engineered t(4;11) in human HSPCs with both products present shows lineage plasticity rather than a fixed aggressive phenotype, which offers a different explanation for the prognostic difference than either a driver or a marker model. Benz T et al. 2026
- E3strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
AF4.MLL expressed in murine Lin-/Sca1+ progenitors induced pro-B ALL, B/T biphenotypic acute leukaemia or mixed-lineage leukaemia, whereas MLL.AF4 alone caused no disease over 13 months.
The AF4.MLL fusion protein is capable of inducing ALL in mice without requirement of MLL.AF4. · Bursen A, Schwabe K, Rüster B, et al. · Blood 2010What this evidence cannot show
Retroviral overexpression in mouse; a small cohort; and the human-cell experiment by a different group did not reproduce leukaemia initiation.
Evidence that argues against this (1)
- AF4-MLL in human cord-blood CD34+ HSPCs augmented engraftment transiently but initiated no leukaemia within 36 weeks, so the sufficiency result does not transfer to human cells. Prieto C et al. 2017
- E4moderate confidence 3 of 5: One strong study, or several smaller consistent ones.paper
NUP98::KMT2A, which like the reciprocal product lacks the menin-binding region while retaining the WIN motif and SET domain, is transforming in an inducible transgenic mouse and is reported resistant to menin inhibition with reduced rather than elevated HOXA output.
Transforming activities of the NUP98-KMT2A fusion gene associated with myelodysplasia and acute myeloid leukemia. · Fisher JN, Thanasopoulou A, Juge S, et al. · Haematologica 2020What this evidence cannot show
Two human patients and one mouse model with 80-week median latency. The menin-inhibitor resistance and low-HOXA phenotype are recorded in this graph's fusion-nup98-kmt2a entry from this source; only the abstract was read here.
Evidence that argues against this (1)
- NUP98::KMT2A produces a low-HOXA, weakly transforming leukaemia unlike t(4;11) disease, so it is a poor model for what a menin-blind KMT2A oncoprotein would do inside a t(4;11) blast that also contains the direct fusion. Kaltenbach S et al. 2010
- E5moderate confidence 3 of 5: One strong study, or several smaller consistent ones.paper
Expression of the reciprocal AF4-MLL fusion for only 48 hours was sufficient to change the transcriptional and chromatin-accessibility landscape in a way still detectable at day 28, supporting a hit-and-run mechanism in which the reciprocal product sets up pre-leukaemic conditions but is dispensable for later progression.
The role of reciprocal fusions in MLL-r acute leukemia: studying the chromosomal translocation t(4;11). · Wilhelm A, Marschalek R · Oncogene 2021What this evidence cannot show
HEK293T cells with Sleeping Beauty transposon constructs, not haematopoietic cells; the day-28 persistence is equally consistent with clonal selection, which the authors acknowledge.
Evidence that argues against this (1)
- Wilkinson et al. propose instead that the reciprocal product acts continuously as part of a RUNX1:MLL-C:AF4-MLL activating complex in established t(4;11) lines, which is a maintenance role rather than a hit-and-run one, and the two models have never been tested against each other. Wilkinson AC et al. 2013
- E-linesstrong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.journal-article
The two standard t(4;11) cell lines used for essentially all mechanistic work in this disease, RS4;11 and SEMK2-M1 (a SEM subline), both express the reciprocal AF4-MLL transcript as well as MLL-AF4. There is therefore no reciprocal-negative t(4;11) line in routine use.
t(4;11) leukemias display addiction to MLL-AF4 but not to AF4-MLL · Leukemia Research 2011What this evidence cannot show
Abstract read verbatim 2026-09-19: *"In the human leukemia cell lines - RS4;11 and SEMK2-M1, both of which express MLL-AF4 and AF4-MLL, we knocked down the expression of AF4-MLL using siRNA."* This is an RT-PCR-level statement about transcript, not protein, and it is made in passing as a premise rather than tested. SEMK2-M1 is a subline, so it does not strictly settle SEM itself, and **MV4-11 is not addressed**.
Evidence that argues against this (1)
- The same paper reports the reciprocal product is **dispensable** in both lines - siRNA knockdown of AF4-MLL had no effect on growth, cell cycle or apoptosis, while MLL-AF4 knockdown arrested and killed them. So 'every line is reciprocal-positive' is a weaker complaint than it sounds: the one experiment that removed the reciprocal product from those lines found nothing changed. The unstratified preclinical package matters for initiation and for drug response, not obviously for maintenance. Leukemia Research 2011
The simplest form of that hypothesis predicts worse outcomes for reciprocal-positive patients; the observed direction is the opposite and strongly so.
Adds a pharmacodynamic consequence to that hypothesis: the HOXA readout tracks the menin-blind subgroup.
Answers that entry's second open question on the reciprocal status of the standard t(4;11) lines: both lymphoid lines are positive.
Confirms that hypothesis's central claim as a counted absence with stated queries.
- depends on →Forty-five percent of t(4;11) patients express a KMT2A fusion transcript that keeps the whole WRAD interface
The hypothesis exists because the der(4) product is menin-blind and present in about half of t(4;11) patients.
The MBM1 interface is absent from the reciprocal product, so a menin-interface agent cannot engage it - and menin primacy was argued entirely on direct 5'-KMT2A fusions.
A second, independent challenge to menin primacy: not that the geometry is accidental, but that the argument was made on one of two fusion products.
Reciprocal status is not recorded in any menin-inhibitor eligibility criterion, and reciprocal-positive patients carry an oncoprotein the drug cannot reach.
The only existing observation on menin-blind, SET-retaining KMT2A architecture: menin-inhibitor resistant with reduced HOXA output.
The retrospective stratification that would decide this hypothesis on banked material.