Flow Cytometric Analysis of Different CD14 Epitopes Can Help Identify Immature Monocytic Populations

Flow Cytometric Assessment of Myelodysplastic Syndromes/Neoplasms

Myelodysplastic syndromes/neoplasms (MDS) are a heterogeneous class of hematopoietic stem cell neoplasms characterized by ineffective hematopoiesis leading to peripheral cytopenias. This group of diseases is typically diagnosed using a combination of clinical, morphologic, and genetic criteria. Many studies have described the value of multiparametric flow cytometry (MFC) in the diagnosis, classification, and prognostication of MDS. This review summarizes the approach to MDS diagnosis and immunophenotypic characterization using MFC and describes the current state while highlighting future opportunities and potential pitfalls.

Challenges facing minimal residual disease testing for acute myeloid leukemia and promising strategies to overcome them

INTRODUCTION

Minimal residual disease (MRD) has been an important biomarker for relapse prediction and treatment choice in patients with acute myeloid leukemia (AML). False-positive or false-negative MRD results due to the low specificity and sensitivity of techniques such as multiparameter flow cytometry (MFC), real-time quantitative polymerase chain reaction, and next-generation sequencing, as well as the biological characteristics of residual leukemia cells, including antigen shift, clone involution, heterogeneous genome of the blast cells, and lack of specific targets, all restrict the clinical use of MRD.

AREAS COVERED

We summarized the challenges of the techniques for MRD detection, and their application in the clinical setting. We also discussed strategies to overcome these challenges, such as the MFC MRD method based on leukemia stem cells, single-cell DNA sequencing or single-cell RNA sequencing for the investigation of biological characteristics of residual leukemia cells, and the potential of omics techniques for MRD detection. We further noted out that prospective clinical trials are needed to answer clinical questions related to MRD in patients with AML.

EXPERT OPINION

MRD is an important biomarker for individual therapy of patients with AML. In the future, it is important to increase the specificity and sensitivity of the detection techniques.

Challenges of detecting measurable/minimal disease in acute leukemia

Measurable/minimal residual disease (MRD) tracking has emerged as a powerful tool for assessing treatment response and predicting outcomes in acute leukemia. However, the clinical and technological challenges associated with MRD tracking must be addressed to improve its utility in routine patient care. This review article aims to provide a summary of the different MRD methodologies used in acute leukemia. It highlights the strengths, diagnostic pitfalls, and clinical utility associated with MRD tracking in this rapidly evolving field.

Classification of Monocytes, Promonocytes and Monoblasts Using Deep Neural Network Models: An Area of Unmet Need in Diagnostic Hematopathology

The accurate diagnosis of chronic myelomonocytic leukemia (CMML) and acute myeloid leukemia (AML) subtypes with monocytic differentiation relies on the proper identification and quantitation of blast cells and blast-equivalent cells, including promonocytes. This distinction can be quite challenging given the cytomorphologic and immunophenotypic similarities among the monocytic cell precursors. The aim of this study was to assess the performance of convolutional neural networks (CNN) in separating monocytes from their precursors (i.e., promonocytes and monoblasts). We collected digital images of 935 monocytic cells that were blindly reviewed by five experienced morphologists and assigned into three subtypes: monocyte, promonocyte, and blast. The consensus between reviewers was considered as a ground truth reference label for each cell. In order to assess the performance of CNN models, we divided our data into training (70%), validation (10%), and test (20%) datasets, as well as applied fivefold cross validation. The CNN models did not perform well for predicting three monocytic subtypes, but their performance was significantly improved for two subtypes (monocyte vs. promonocytes + blasts). Our findings (1) support the concept that morphologic distinction between monocytic cells of various differentiation level is difficult; (2) suggest that combining blasts and promonocytes into a single category is desirable for improved accuracy; and (3) show that CNN models can reach accuracy comparable to human reviewers (0.78 ± 0.10 vs. 0.86 ± 0.05). As far as we know, this is the first study to separate monocytes from their precursors using CNN.

Clinical and Molecular Approach to Adult-Onset, Neoplastic Monocytosis

PURPOSE OF REVIEW

In this review, we provide a comprehensive and contemporary understanding of malignant monocytosis and provide a framework by which the appropriate diagnosis with malignant monocytosis can be rendered.

RECENT FINDINGS

Increasing data support the use of molecular data to refine the diagnostic approach to persistent monocytosis. The absence of a TET2, SRSF2, or ASXL1 mutation has ≥ 90% negative predictive value for a diagnosis of CMML. These data may also reliably differentiate chronic myelomonocytic leukemia, the malignancy that is most associated with mature monocytosis, from several other diseases that can be associated with typically a lesser degree of monocytosis. These include acute myelomonocytic leukemia, acute myeloid leukemia with monocytic differentiation, myelodysplastic syndromes, and myeloproliferative neoplasms driven by BCR-ABL1, PDGFRA, PDGFRB, or FGFR1 rearrangements or PCM1-JAK2 fusions among other rarer aberrations. The combination of monocyte partitioning with molecular data in patients with persistent monocytosis may increase the predictive power for the ultimate development of CMM but has not been prospectively validated. Many conditions, both benign and malignant, can be associated with an increase in mature circulating monocytes. After reasonably excluding a secondary or reactive monocytosis, there should be a concern for and investigation of malignant monocytosis, which includes hematopathologic review of blood and marrow tissues, flow cytometric analysis, and cytogenetic and molecular studies to arrive at an appropriate diagnosis.

How I investigate monocytosis

Monocytosis is a common finding that is caused by a wide variety of neoplastic and non-neoplastic conditions. The adequate evaluation of monocytosis involves the integration of laboratory data, morphology, clinical findings, and the judicious use of ancillary studies. We review the literature on monocytosis, including the 2017 revised 4th edition of the World Health Organization classification of hematopoietic neoplasms. We present a review of monocytosis with practical guidelines on how to approach both routine and challenging cases.

Immunophenotyping by Multiparameter Flow Cytometry

Multiparameter flow cytometry has become an indispensable tool for the diagnosis and classification of acute myeloid leukemia (AML). The basic method relies on the unique ability to detect immunophenotypic abnormalities on discrete subpopulations. The primary roles in the initial assessment of AML are to determine the immaturity of the leukemic population, define the lineage and the immunophenotypic aberrancies in blasts, and identify characteristic immunophenotypic features to predict important recurrent cytogenetic and genetic abnormalities and prognosis. The established immunophenotypic profile, a baseline "fingerprint," is used for follow-up assessment of residual disease. This chapter provides an overview of procedures for specimen processing, staining, and immunophenotyping of AML and describes our strategy for data analysis supplemented with illustrative case examples.

Blockade of the PD-1/PD-L1 axis augments lysis of AML cells by the CD33/CD3 BiTE antibody construct AMG 330: reversing a T-cell-induced immune escape mechanism

Bispecific T-cell engagers (BiTEs) are very effective in recruiting and activating T cells. We tested the cytotoxicity of the CD33/CD3 BiTE antibody construct AMG 330 on primary acute myeloid leukemia (AML) cells ex vivo and characterized parameters contributing to antileukemic cytolytic activity. The E:T ratio and the CD33 expression level significantly influenced lysis kinetics in long-term cultures of primary AML cells (n=38). AMG 330 induced T-cell-mediated proinflammatory conditions, favoring the upregulation of immune checkpoints on target and effector cells. Although not constitutively expressed at the time of primary diagnosis (n=123), PD-L1 was strongly upregulated on primary AML cells upon AMG 330 addition to ex vivo cultures (n=27, P<0.0001). This phenomenon was cytokine-driven as the sole addition of interferon (IFN)-γ and tumor necrosis factor-α also induced expression. Through blockade of the PD-1/PD-L1 interaction, AMG 330-mediated lysis (n=9, P=0.03), T-cell proliferation (n=9, P=0.01) and IFN-γ secretion (n=8, P=0.008) were significantly enhanced. The combinatorial approach was most beneficial in settings of protracted AML cell lysis. Taken together, we have characterized a critical resistance mechanism employed by primary AML cells under AMG 330-mediated proinflammatory conditions. Our results support the evaluation of checkpoint molecules in upcoming clinical trials with AMG 330 to enhance BiTE antibody construct-mediated cytotoxicity.

CD33 target validation and sustained depletion of AML blasts in long-term cultures by the bispecific T-cell-engaging antibody AMG 330

Antibody-based immunotherapy represents a promising strategy to target and eliminate chemoresistant leukemic cells. Here, we evaluated the CD33/CD3-bispecific T cell engaging (BiTE) antibody (AMG 330) for its suitability as a therapeutic agent in acute myeloid leukemia (AML). We first assessed CD33 expression levels by flow cytometry and found expression in >99% of patient samples (n = 621). CD33 was highest expressed in AMLs with NPM1 mutations (P < .001) and lower in AMLs with complex karyotypes and t(8;21) translocations (P < .001). Furthermore, leukemic stem cells within the CD34(+)/CD38(-) compartment displayed CD33 at higher levels than healthy donor stem cells (P = .047). In MS-5 feeder cell-based long-term cultures that supported the growth of primary AML blasts for up to 36 days, AMG 330 efficiently recruited and expanded residual CD3(+)/CD45RA(-)/CCR7(+) memory T cells within the patient sample. Even at low effector to target ratios, the recruited T cells lysed autologous blasts completely in the majority of samples and substantially in the remaining samples in a time-dependent manner. This study provides the first correlation of CD33 expression levels with AML genotype in a comprehensive analysis of adult patients. Targeting CD33 ex vivo using AMG 330 in primary AML samples led to T cell recruitment and expansion and remarkable antibody-mediated cytotoxicity, suggesting efficient therapeutic potential in vivo.

The value of immunohistochemistry for CD14, CD123, CD33, myeloperoxidase and CD68R in the diagnosis of acute and chronic myelomonocytic leukaemias

AIMS

In the absence of adequate aspirate films and touch imprints, distinction of chronic myelomonocytic leukaemia (CMML) from acute myeloid leukaemia with monocytic differentiation (Mo-AML) may be difficult solely on the basis of bone marrow biopsy morphological features. The aim of this study was to evaluate the diagnostic utility of a novel immunohistochemical panel for the diagnosis of acute and chronic myelomonocytic leukaemias in bone marrow biopsies.

METHODS AND RESULTS

Immunohistochemical labelling for CD14, CD123, CD33, myeloperoxidase (MPO) and CD68R was assessed in 49 myeloid neoplasms with monocytic differentiation (24 CMMLs and 25 Mo-AMLs) and compared with that of 15 non-monocytic acute myeloid leukaemias (NM-AMLs) and 17 non-neoplastic controls. More than 20% CD14 immunohistochemistry (IHC)+ cells were seen only in Mo-AMLs and CMMLs, although Mo-AMLs showed wide variability and overlapped with other categories. More than 20% CD68R IHC+ cells had the highest sensitivity and specificity for Mo-AML. Discrepant MPO-/CD33+ expression was specific for Mo-AML but insensitive. A subset of blasts in Mo-AMLs and NM-AMLs were weakly CD123+.

CONCLUSIONS

A significantly increased number of CD14+ cells raises the possibility of a myelomonocytic neoplasm but does not distinguish between CMML and Mo-AML. Significantly increased numbers of CD68R IHC+ cells and a discrepant MPO-/CD33+ staining pattern are specific for Mo-AML but are best utilized in a comprehensive panel.

Immunohistochemical analysis of monocytic leukemias: usefulness of CD14 and Kruppel-like factor 4, a novel monocyte marker

Detection of monocytic differentiation in myeloid neoplasms by immunohistochemical analysis is challenging owing to a lack of sensitive and/or specific antibodies. We tested the usefulness of immunohistochemical analysis for CD14, an antigen commonly detected by flow cytometry, and Krüppel-like factor 4 (KLF4), a potentially novel marker of monocytic differentiation, in a series of myeloid leukemias, including 53 acute myeloid leukemias with monocytic differentiation. These findings were compared with immunohistochemical findings for CD68 (KP-1), CD34, and CD163 and were also correlated with flow cytometric and enzyme cytochemical results. CD163 and CD14 are the most specific markers of monocytic differentiation, followed by KLF4. CD68, in contrast, is the most sensitive monocytic marker, and KLF4 is also significantly more sensitive than CD14 and CD163. These studies show that KLF4 is another marker of monocytic differentiation and that the combination of CD14 and CD163 can increase the diagnostic sensitivity for monocytic neoplasms.

Immunophenotypic changes of human articular chondrocytes during monolayer culture reflect bona fide dedifferentiation rather than amplification of progenitor cells

In this study, a time-course comparison of human articular chondrocytes (HAC) and bone marrow-derived mesenchymal stem cells (MSC) immunophenotype was performed in order to determine similarities/differences between both cell types during monolayer culture, and to identify HAC surface markers indicative of dedifferentiation. Our results show that dedifferentiated HAC can be distinguished from MSC by combining CD14, CD90, and CD105 expression, with dedifferentiated HAC being CD14+/CD90bright/CD105dim and MSC being CD14-/CD90dim/CD105bright. Surface markers on MSC showed little variation during the culture, whereas HAC showed upregulation of CD90, CD166, CD49c, CD44, CD10, CD26, CD49e, CD151, CD51/61, and CD81, and downregulation of CD49a, CD54, and CD14. Thus, dedifferentiated HAC appear as a bona fide cell population rather than a small population of MSC amplified during monolayer culture. While most of the HAC surface markers showed major changes at the beginning of the culture period (Passage 1-2), CD26 was upregulated and CD49a downregulated at later stages of the culture (Passage 3-4). To correlate changes in HAC surface markers with changes in extracellular matrix gene expression during monolayer culture, CD14 and CD90 mRNA levels were combined into a new differentiation index and compared with the established differentiation indices based on the ratios of mRNA levels of collagen type II to I (COL2/COL1) and of aggrecan to versican (AGG/VER). A correlation of CD14/CD90 ratio at the mRNA and protein level with the AGG/VER ratio during HAC dedifferentiation in monolayer culture validated CD14/CD90 as a new membrane and mRNA based HAC differentiation index.

Myeloid Malignancies: Myelodysplastic Syndromes, Myeloproliferative Disorders, and Acute Myeloid Leukemia

As hematopoietic cells proceed in differentiation from stem cells to committed progenitors to later stage mature forms, they undergo a sequence of morphologic, immunophenotypic, and functional changes that are a consequence of interaction between the underlying cellular genetic program and environmental cues, are linear for each cell lineage, and result in a pattern of antigenic expression related to lineage and stage of maturation. The antigenic patterns characteristic of normal maturation have been elucidated systematically and found invariant between individuals. Deviation from this pattern is a hallmark of hematopoietic neoplasia. Application of these principles to myelodysplastic syndromes, myeloproliferative disorders, and acute myeloid leukemia is presented and illustrated.

The Value of CD64 Expression in Distinguishing Acute Myeloid Leukemia With Monocytic Differentiation From Other Subtypes of Acute Myeloid Leukemia: A Flow Cytometric Analysis of 64 Cases

Context.—Flow cytometric immunophenotyping is a useful ancillary tool in the diagnosis and subclassification of acute myeloid leukemias (AMLs). A recent study concluded that CD64 is sensitive and specific for distinguishing AMLs with a monocytic component (ie, AML M4 and AML M5) from other AML subtypes. However, in that study, the intensity of CD64 was not well defined and the number of non-M4/non-M5 AMLs was small.

Objective.—To evaluate the usefulness of CD64 by flow cytometric immunophenotyping in distinguishing AMLs with monocytic differentiation from other AML subtypes.

Design.—Sixty-four AMLs subclassified based on the French-American-British and World Health Organization classifications on pretreatment bone marrows were retrieved from our files (7 M0s, 11 M1s, 17 M2s, 7 M3s, 9 M4s, 7 M5s, 4 M6s, and 2 M7s). A standard panel of markers, including CD2, CD3, CD5, CD7, CD10, CD11b, CD13, CD14, CD15, CD19, CD20, CD33, CD34, CD45, CD56, CD64, CD117, and HLA-DR, were analyzed by flow cytometric immunophenotyping in all AMLs (52 bone marrow samples; 12 peripheral blood samples).

Results.—CD64 was expressed in AML subtypes M0 to M5 in varying intensities: heterogeneously expressed in 1 of 7 M0s; dimly expressed in 3 of 11 M1s; dimly and moderately expressed in 6 and 2 of 17 M2s, respectively; dimly and moderately expressed in 5 and 1 of 7 M3s, respectively; dimly expressed in 4 of 9 M4s; and heterogeneously, moderately, and strongly expressed in 1, 3, and 3 of 7 M5s, respectively.

Conclusions.—Strong CD64 expression distinguishes AML M5; however, heterogeneous, dim, or moderate expression in itself does not distinguish M0 through M4 subtypes from M5 with dim to moderate CD64 expression. However, any CD64 expression associated with strong CD15 expression distinguishes AML M4 or M5, from other AML subtypes.