Comprehensive immunophenotypic study of acute myeloid leukemia with KMT2A (MLL) rearrangement in adults: A single-institution experience

Identification of single-cell blasts in pediatric acute myeloid leukemia using an autoencoder

Pediatric acute myeloid leukemia (AML) is an aggressive blood cancer with a poor prognosis and high relapse rate. Current challenges in the identification of immunotherapy targets arise from patient-specific blast immunophenotypes and their change during disease progression. To overcome this, we present a new computational research tool to rapidly identify malignant cells. We generated single-cell flow cytometry profiles of 21 pediatric AML patients with matched samples at diagnosis, remission, and relapse. We coupled a classifier to an autoencoder for anomaly detection and classified malignant blasts with 90% accuracy. Moreover, our method assigns a developmental stage to blasts at the single-cell level, improving current classification approaches based on differentiation of the dominant phenotype. We observed major immunophenotype and developmental stage alterations between diagnosis and relapse. Patients with KMT2A rearrangement had more profound changes in their blast immunophenotypes at relapse compared to patients with other molecular features. Our method provides new insights into the immunophenotypic composition of AML blasts in an unbiased fashion and can help to define immunotherapy targets that might improve personalized AML treatment.

Advances in Acute Myeloid Leukemia Classification, Prognostication and Monitoring by Flow Cytometry

Although final classification of acute myeloid leukemia (AML) integrates morphologic, cytogenetic, and molecular data, flow cytometry remains an essential component of modern AML diagnostics. Here, we review the current role of flow cytometry in the classification, prognostication, and monitoring of AML. We cover immunophenotypic features of key genetically defined AML subtypes and their effects on biological and clinical behaviors, review clinically tractable strategies to differentiate leukemias with ambiguous immunophenotypes more accurately and discuss key principles of standardization for measurable residual disease monitoring. These advances underscore flow cytometry's continued growth as a powerful diagnostic, management, and discovery tool.

Acute promyelocytic leukemia: Immunophenotype and differential diagnosis by flow cytometry

BACKGROUND

Prompt diagnosis of acute promyelocytic leukemia (APL) is critical for patient care. In this study, we aimed to characterize the immunophenotype of APL and explore immunophenotypic difference between APL and its mimics using flow cytometric analysis.

METHODS

Eighty-five cases were collected, including 47 APL, 26 NPM1-mutated acute myeloid leukemia (AML) and 12 KMT2A-rearranged AML with an APL-like immunophenotype. Immunophenotypes were analyzed using flow cytometric analysis.

RESULTS

APL showed four distinct patterns (designated a-d) based on CD45/SSC plots. Blasts in patterns a-c showed high side scatter, whereas blasts in pattern d had low side scatter and were located in the traditional blast gate. Compared with patterns a-c, pattern d of APL (APL-D) was more often positive for CD2 (p = 0.0005) and CD34 (p = 0.0002) in blasts. All NPM1-mutated AML and KMT2A-rearranged AML cases with an APL-like immunophenotype had blasts in the traditional blast gate on CD45/SSC, mimicking APL-D. In comparison, uniform CD13 and positive CD64 were seen in 100% (n = 13) APL-D cases and in only 2 of 26 (8%) NPM1-mutated AML cases (p < 0.0001). In addition, APL-D cases were more likely to be positive for CD2 and/or CD34 than NPM1-mutated AML (p < 0.0001 and p = 0.0007, respectively). In comparison with APL-D, KMT2A-rearranged AML cases were less often positive for myeloperoxidase (MPO) (p = 0.001), with none being strongly positive. Similar to NPM1-mutated AML and different from APL-D, KMT2A-rearranged AML cases were rarely positive for CD34 and all negative for CD2.

CONCLUSIONS

APL and its immunophenotypic mimics share some immunophenotypic similarities but can be distinguished by CD2, CD13, CD34, CD64, and MPO.

Progress in understanding the mechanisms of resistance to BCL-2 inhibitors

Venetoclax is a new type of BH3 mimetic compound that can target the binding site in the BCL-2 protein and induce apoptosis in cancer cells by stimulating the mitochondrial apoptotic pathway. Venetoclax is especially used to treat haematological malignancies. However, with the recent expansion in the applications of venetoclax, some cases of venetoclax resistance have appeared, posing a major problem in clinical treatment. In this article, we explored several common mechanisms of venetoclax resistance. Increased expression of the antiapoptotic proteins MCL-1 and BCL-XL plays a key role in conferring cellular resistance to venetoclax. These proteins can bind to the released BIM in the context of venetoclax binding to BCL-2 and thus continue to inhibit mitochondrial apoptosis. Structural mutations in BCL-2 family proteins caused by genetic instability lead to decreased affinity for venetoclax and inhibit the intrinsic apoptosis pathway. Mutation or deletion of the BAX gene renders the BAX protein unable to anchor to the outer mitochondrial membrane to form pores. In addition to changes in BCL-2 family genes, mutations in other oncogenes can also confer resistance to apoptosis induced by venetoclax. TP53 mutations and the expansion of FLT3-ITD promote the expression of antiapoptotic proteins MCL-1 and BCL-XL through multiple signalling pathways, and interfere with venetoclax-mediated apoptosis processes depending on their affinity for BH3-only proteins. Finally, the level of mitochondrial oxidative phosphorylation in venetoclax-resistant leukaemia stem cells is highly abnormal. Not only the metabolic pathways but also the levels of important metabolic components are changed, and all of these alterations antagonize the venetoclax-mediated inhibition of energy metabolism and promote the survival and proliferation of leukaemia stem cells. In addition, venetoclax can change mitochondrial morphology independent of the BCL-2 protein family, leading to mitochondrial dysfunction. However, mitochondria resistant to venetoclax antagonize this effect, forming tighter mitochondrial cristae, which provide more energy for cell survival.