Highlights
- Menin inhibition with revumenib triggers a differentiation-driven antileukemic effect in KMT2A-rearranged and NPM1-mutated AML.
- In a cohort of 48 patients, 52% of those treated with revumenib exhibited dynamic immunophenotypic changes, including lineage switches from stem-like to monocytic profiles.
- Measurable residual disease (MRD) negativity by flow cytometry is a critical prognostic indicator, with MRD-negative responders achieving a median overall survival of 23.6 months.
- The study highlights the necessity for adaptive flow cytometry protocols to track evolving leukemia-associated immunophenotypes (LAIPs) during targeted therapy.
Background: The Rise of Menin Inhibitors in AML
The treatment landscape for relapsed or refractory (R/R) acute myeloid leukemia (AML) has been historically challenging, particularly for patients harboring rearrangements in the lysine methyltransferase 2A (KMT2A) gene or mutations in nucleophosmin 1 (NPM1). These genetic alterations hijack the menin-KMT2A interaction, leading to the sustained expression of pro-leukemogenic genes such as HOXA9 and MEIS1, which arrest hematopoietic cells in a progenitor state.
Revumenib, a first-in-class small-molecule menin inhibitor, disrupts this interaction, prompting the leukemia cells to resume their differentiation program. While clinical trials have demonstrated the efficacy of revumenib in achieving remissions, the biological consequence of this “differentiation therapy” on the immunophenotype of leukemia cells has not been fully mapped. Understanding these changes is vital for clinicians and pathologists who rely on flow cytometry to assess treatment response and detect measurable residual disease (MRD).
Study Design: Tracking Phenotypic Evolution
Researchers led by Loghavi et al. conducted a longitudinal analysis of 48 patients with R/R AML treated with revumenib. The study focused on patients with KMT2A rearrangements or NPM1 mutations, populations known to be sensitive to menin inhibition. The primary objective was to characterize the immunophenotypic changes in leukemia cells using sequential bone marrow specimens and multi-parameter flow cytometry.
The team analyzed the expression of various surface markers, including myeloid, monocytic, and stem-cell-associated antigens. By comparing baseline (pre-treatment) profiles with those obtained during and after treatment, the researchers aimed to quantify the frequency and nature of phenotypic shifts and correlate these findings with clinical outcomes such as overall survival (OS).
Results: A Fluid Target Under Therapeutic Pressure
The study revealed a remarkably high degree of immunophenotypic plasticity. Out of 31 evaluable patients who had follow-up data, 16 (52%) demonstrated significant changes in their leukemia-associated immunophenotypes (LAIPs). These changes were not merely subtle variations in antigen density but often represented fundamental shifts in cell identity.
Lineage Switching and Differentiation
The most striking finding was the switch from a myeloid/stem-like immunophenotype to a monocytic or myelomonocytic immunophenotype, or vice versa. This transition is a direct reflection of the drug’s mechanism of action—inducing differentiation in blast cells. As the blasts lose their primitive markers (like CD34 or CD117) and gain mature markers (such as CD11b, CD14, or CD64), the traditional “blast gate” used in flow cytometry may no longer capture the surviving or evolving leukemic population accurately.
Intensity and Pattern Changes
Beyond lineage switches, the researchers observed substantial changes in the intensity of antigen expression. This “phenotypic drift” can make the identification of MRD difficult, as the original LAIP identified at diagnosis may disappear, only to be replaced by a new, treatment-emergent profile. This suggests that relying on a single, fixed set of markers for longitudinal monitoring could lead to false-negative results.
Survival Outcomes: The Enduring Value of MRD
Despite the complexity of these phenotypic shifts, the clinical significance of achieving a deep response remained clear. The study categorized patients into three groups based on their response and MRD status:
- Morphologic Response with MRD Negativity: Patients who achieved a morphologic remission and had no detectable MRD by flow cytometry had the best outcomes, with a median overall survival of 23.6 months.
- Morphologic Response with Persistent MRD: Patients who achieved remission but remained MRD-positive had a median survival of 20.8 months. While significantly better than non-responders, the persistent presence of leukemic clones suggests a higher risk of eventual relapse.
- Non-Responders: Patients who did not achieve a morphologic response had a dismal prognosis, with a median survival of only 3.2 months.
These data reinforce the role of flow cytometry-based MRD as a powerful surrogate for survival, provided the laboratory can account for the phenotypic changes induced by the therapy.
Expert Commentary: Navigating the ‘Phenotypic Drift’
The findings by Loghavi et al. present a dual challenge and opportunity for clinical pathology. From a mechanistic standpoint, the immunophenotypic shift validates the differentiation-inducing properties of menin inhibitors. It proves that we are successfully “forcing” leukemia cells to mature.
However, from a diagnostic standpoint, this study is a wake-up call. Traditional MRD monitoring often looks for the “different-from-normal” (DfN) pattern or the original LAIP. When a drug like revumenib fundamentally changes the cell’s surface architecture, the DfN pattern evolves. Pathologists must now adopt a more dynamic approach, perhaps utilizing broader antibody panels that cover the entire spectrum of myeloid and monocytic maturation to ensure that differentiating leukemic cells are not mistaken for normal regenerating marrow.
Furthermore, the narrow gap between the survival of MRD-negative (23.6 months) and MRD-positive (20.8 months) responders suggests that even a low level of persistent disease under menin inhibition behaves differently than in traditional chemotherapy contexts. Longer follow-up will be necessary to determine if these differentiated monocytic cells eventually lead to aggressive relapse or if they represent a stable, less malignant state.
Conclusion: Adapting to a New Era of AML Therapy
The study of revumenib-treated AML patients underscores the transformative impact of menin inhibition on leukemia biology. With over half of patients experiencing significant immunophenotypic evolution, the standard of care for monitoring treatment must evolve in tandem. Recognizing the transition from primitive blasts to more mature myelomonocytic forms is essential for accurate MRD assessment.
Ultimately, the correlation between MRD negativity and superior survival confirms that while the phenotype may change, the goal remains the same: the total eradication of the leukemic clone. As menin inhibitors move closer to standard clinical use, the integration of adaptive flow cytometry will be paramount in optimizing patient management and refining our understanding of therapeutic resistance.
References
- Loghavi S, Farhat A, Jamison TJ, et al. Immunophenotypic changes following menin inhibition in acute myeloid leukemia. Leukemia. 2026. PMID: 41814014.
- Issa GC, Aldoss I, DiNardo C, et al. The Menin Inhibitor Revumenib in KMT2ARearranged or NPM1-Mutant Leukaemia. Nature. 2023.
- Stein AS, et al. Menin Inhibitors: A New Class of Precision Medicine in AML. Blood Reviews. 2024.
