Acute megakaryoblastic leukemia (AMKL) is a rare and heterogeneous subtype of acute myeloid leukemia (AML). We evaluated the immunophenotypic profile of 72 AMKL and 114 non-AMKL AML patients using the EuroFlow AML panel. Univariate and multivariate/multidimensional analyses were performed to identify most relevant markers contributing to the diagnosis of AMKL. AMKL patients were subdivided into transient abnormal myelopoiesis (TAM), myeloid leukemia associated with Down syndrome (ML-DS), AML—not otherwise specified with megakaryocytic differentiation (NOS-AMKL), and AMKL—other patients (AML patients with other WHO classification but with flowcytometric features of megakaryocytic differentiation). Flowcytometric analysis showed good discrimination between AMKL and non-AMKL patients based on differential expression of, in particular, CD42a.CD61, CD41, CD42b, HLADR, CD15 and CD13. Combining CD42a.CD61 (positive) and CD13 (negative) resulted in a sensitivity of 71% and a specificity of 99%. Within AMKL patients, TAM and ML-DS patients showed higher frequencies of immature CD34+/CD117+ leukemic cells as compared to NOS-AMKL and AMKL-Other patients. In addition, ML-DS patients showed a significantly higher expression of CD33, CD11b, CD38 and CD7 as compared to the other three subgroups, allowing for good distinction of these patients. Overall, our data show that the EuroFlow AML panel allows for straightforward diagnosis of AMKL and that ML-DS is associated with a unique immunophenotypic profile.

Acute lymphoblastic leukemia expressing the gamma delta T-cell receptor (γδ T-ALL) is a poorly understood disease. We studied 200 children with γδ T-ALL from 13 clinical study groups to understand the clinical and genetic features of this disease. We found age and genetic drivers were significantly associated with outcome. γδ T-ALL diagnosed in children under 3 years of age was extremely high-risk and enriched for genetic alterations that result in both LMO2 activation and STAG2 inactivation. Mechanistically, using patient samples and isogenic cell lines, we show that inactivation of STAG2 profoundly perturbs chromatin organization by altering enhancer–promoter looping, resulting in deregulation of gene expression associated with T-cell differentiation. High-throughput drug screening identified a vulnerability in DNA repair pathways arising from STAG2 inactivation, which can be targeted by poly(ADP-ribose) polymerase inhibition. These data provide a diagnostic framework for classification and risk stratification of pediatric γδ T-ALL. Significance: Patients with acute lymphoblastic leukemia expressing the gamma delta T-cell receptor under 3 years old or measurable residual disease ≥1% at end of induction showed dismal outcomes and should be classified as having high-risk disease. The STAG2/LMO2 subtype was enriched in this very young age group. STAG2 inactivation may perturb chromatin conformation and cell differentiation and confer vulnerability to poly(ADP-ribose) polymerase inhibition.

Objectives: Risk-based stratification approaches using measurable residual disease (MRD) successfully help to identify T-acute lymphoblastic leukemia (T-ALL) patients at risk of relapse, whose treatment outcomes are very poor. Because of T-ALL heterogeneity and rarity, a reliable and standardized approach for flow cytometry (FC)-based MRD measurement and analysis is often missing. Methods: Within the international AIEOP-BFM-ALL-FLOW study group we made a consensus on markers and a standard operating procedure for common 8- and 12-color T-ALL MRD panels. Custom manufactured tubes with dried backbone antibodies were tested in parallel to local FC standards. Results: Altogether, 66 diagnostic and 67 day 15 samples were analyzed. We designed two guided MRD gating strategies to identify blast cells in parallel to expert-based evaluation. We proved that the optimized tubes allowed the correct identification of blast cells in all diagnostic samples. Both, expert and guided analysis of day 15 samples correlated to local standard (Spearman R=0.98 and R=0.94, respectively). Only in 2 (3 %) and 4 (6 %) patients expert gating and guided analysis results were substantially discordant from local standard, respectively. The cases that require an individualized approach may be partially identified at diagnosis through a rare immunophenotype or mixed phenotype acute leukemia status. Conclusions: Our work shows that standardized operating procedures together with guided analysis are applicable in a great majority of T-ALL cases. Further improvement of MRD detection is needed, as in some cases an individualized analytical approach is still required due to the challenging nature of the T-ALL phenotype.

Lists of T-ALL related genes for filtering tumor-only and RNAseq samples.

Differential peaks of H3K27ac and expression difference in gene-edited MOLT-14 model.

Up-regulated pathways in PF382-STAG2KO (n = 4) compared to PF382-WT (n = 2) for LMO2 targets analyzed by gene-set enrichment analysis (GSEA).