A Leukemia-Associated CD34/CD123/CD25/CD99+ Immunophenotype Identifies FLT3-Mutated Clones in Acute Myeloid Leukemia

Decoding human in vitro terminal erythropoiesis originating from umbilical cord blood mononuclear cells and pluripotent stem cells

Ex vivo red blood cell (RBC) production generates unsatisfactory erythroid cells. A deep exploration into terminally differentiated cells is required to understand the impairments for RBC generation and the underlying mechanisms. Here, we mapped an atlas of terminally differentiated cells from umbilical cord blood mononuclear cells (UCBMN) and pluripotent stem cells (PSC) and observed their dynamic regulation of erythropoiesis at single-cell resolution. Interestingly, we detected a few progenitor cells and non-erythroid cells from both origins. In PSC-derived erythropoiesis (PSCE), the expression of haemoglobin switch regulators (BCL11A and ZBTB7A) were significantly absent, which could be the restraint for its adult globin expression. We also found that PSCE were less active in stress erythropoiesis than in UCBMN-derived erythropoiesis (UCBE), and explored an agonist of stress erythropoiesis gene, TRIB3, could enhance the expression of adult globin in PSCE. Compared with UCBE, there was a lower expression of epigenetic-related proteins (e.g., CASPASE 3 and UBE2O) and transcription factors (e.g., FOXO3 and TAL1) in PSCE, which might restrict PSCE's enucleation. Moreover, we characterized a subpopulation with high proliferation capacity marked by CD99high in colony-forming unit-erythroid cells. Inhibition of CD99 reduced the proliferation of PSC-derived cells and facilitated erythroid maturation. Furthermore, CD99-CD99 mediated the interaction between macrophages and erythroid cells, illustrating a mechanism by which macrophages participate in erythropoiesis. This study provided a reference for improving ex vivo RBC generation.

FLT3-Mutated Leukemic Stem Cells: Mechanisms of Resistance and New Therapeutic Targets

Despite the availability of target drugs in the first and second line, only 30% of FLT3mut AMLs are cured. Among the multiple mechanisms of resistance, those of FLT3mut LSC are the most difficult to eradicate because of their metabolic and genomic characteristics. Reactivation of glycogen synthesis, inhibition of the RAS/MAPK pathway, and degradation of FLT3 may be potential aids to fight the resistance of LSC to FLT3i. LSC is also characterized by the expression of a CD34+/CD25+/CD123+/CD99+ immunophenotype. The receptor and ligand of FLT3, the natural killer group 2 member D ligand (NKGD2L), and CD123 are some of the targets of chimeric antigen receptor T cells (CAR-T), bispecific T-cell engager molecules (BiTEs), CAR-NK and nanoparticles recently designed and reported here. The combination of these new therapeutic options, hopefully in a minimal residual disease (MRD)-driven approach, could provide the future answer to the challenge of treating FLT3mut AML.

Identification of cells of leukemic stem cell origin with non-canonical regenerative properties

Despite most acute myeloid leukemia (AML) patients entering remission following chemotherapy, outcomes remain poor due to surviving leukemic cells that contribute to relapse. The nature of these enduring cells is poorly understood. Here, through temporal single-cell transcriptomic characterization of AML hierarchical regeneration in response to chemotherapy, we reveal a cell population: AML regeneration enriched cells (RECs). RECs are defined by CD74/CD68 expression, and although derived from leukemic stem cells (LSCs), are devoid of stem/progenitor capacity. Based on REC in situ proximity to CD34-expressing cells identified using spatial transcriptomics on AML patient bone marrow samples, RECs demonstrate the ability to augment or reduce leukemic regeneration in vivo based on transfusion or depletion, respectively. Furthermore, RECs are prognostic for patient survival as well as predictive of treatment failure in AML cohorts. Our study reveals RECs as a previously unknown functional catalyst of LSC-driven regeneration contributing to the non-canonical framework of AML regeneration.

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.

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.

Novel Tools for Diagnosis and Monitoring of AML

In recent years, major advances in the understanding of acute myeloid leukemia (AML) pathogenesis, together with technological progress, have led us into a new era in the diagnosis and follow-up of patients with AML. A combination of immunophenotyping, cytogenetic and molecular studies are required for AML diagnosis, including the use of next-generation sequencing (NGS) gene panels to screen all genetic alterations with diagnostic, prognostic and/or therapeutic value. Regarding AML monitoring, multiparametric flow cytometry and quantitative PCR/RT-PCR are currently the most implemented methodologies for measurable residual disease (MRD) evaluation. Given the limitations of these techniques, there is an urgent need to incorporate new tools for MRD monitoring, such as NGS and digital PCR. This review aims to provide an overview of the different technologies used for AML diagnosis and MRD monitoring and to highlight the limitations and challenges of current versus emerging tools.

CD123 a Therapeutic Target for Acute Myeloid Leukemia and Blastic Plasmocytoid Dendritic Neoplasm

In spite of consistent progress at the level of basic research and of clinical treatment, acute myeloid leukemia (AML) still represents an unmet clinical need for adult and pediatric patients. To improve the outcomes of these patients, it is necessary to identify new therapeutic targets. IL3RA (CD123, alpha subunit of the interleukin 3 receptor) is a cell membrane protein overexpressed in several hematologic malignancies, including AML blastic plasmocytoid dendritic cell neoplasms (BPDCN). Given the higher expression of CD123 on leukemic cells compared to normal hematopoietic cells and its low/absent expression on normal hematopoietic stem cells, it appears as a suitable and attractive target for therapy. Various drugs targeting CD123 have been developed and evaluated at clinical level: interleukin-3 conjugated with diphtheria toxin; naked neutralizing anti-CD123 antibodies; drug-antibody conjugates; bispecific antibodies targeting both CD123 and CD3; and chimeric antigen receptor (CAR) T cells engineered to target CD123. Some of these agents have shown promising results at the clinical level, including tagraxofusp (CD123 conjugated with diphtheria toxin) for the treatment of BPDCN and IMGN632 (anti-CD123 drug-conjugate), and flotetuzumab (bispecific anti-CD123 and anti-CD3 monoclonal antibody) for the treatment of AML. However, the therapeutic efficacy of CD123-targeting treatments is still unsatisfactory and must be improved through new therapeutic strategies and combined treatments with other antileukemic drugs.

CD25 targeting with the afucosylated human IgG1 antibody RG6292 eliminates regulatory T cells and CD25+ blasts in acute myeloid leukemia

Background

Acute Myeloid leukemia is a heterogeneous disease that requires novel targeted treatment options tailored to the patients' specific microenvironment and blast phenotype.

Methods

We characterized bone marrow and/or blood samples of 37 AML patients and healthy donors by high dimensional flow cytometry and RNA sequencing using computational analysis. In addition, we performed ex vivo ADCC assays using allogeneic NK cells isolated from healthy donors and AML patient material to test the cytotoxic potential of CD25 Mab (also referred to as RG6292 and RO7296682) or isotype control antibody on regulatory T cells and CD25+ AML cells.

Results

Bone marrow composition, in particular the abundance of regulatory T cells and CD25 expressing AML cells, correlated strongly with that of the blood in patients with time-matched samples. In addition, we observed a strong enrichment in the prevalence of CD25 expressing AML cells in patients bearing a FLT3-ITD mutation or treated with a hypomethylating agent in combination with venetoclax. We adopted a patient-centric approach to study AML clusters with CD25 expression and found it most highly expressed on immature phenotypes. Ex vivo treatment of primary AML patient samples with CD25 Mab, a human CD25 specific glycoengineered IgG1 antibody led to the specific killing of two different cell types, CD25+ AML cells and regulatory T cells, by allogeneic Natural Killer cells.

Conclusion

The in-depth characterization of patient samples by proteomic and genomic analyses supported the identification of a patient population that may benefit most by harnessing CD25 Mab's dual mode of action. In this pre-selected patient population, CD25 Mab could lead to the specific depletion of regulatory T cells, in addition to leukemic stem cells and progenitor-like AML cells that are responsible for disease progression or relapse.

Therapeutic Targeting of FLT3 in Acute Myeloid Leukemia: Current Status and Novel Approaches

FMS-like tyrosine kinase 3 (FLT3) is mutated in approximately 30% of acute myeloid leukemia (AML) patients. The presence of FLT3-ITD (internal tandem duplication, 20-25%) mutation and, to a lesser extent, FLT3-TKD (tyrosine kinase domain, 5-10%) mutation is associated with poorer diagnosis and therapy response since the leukemic cells become hyperproliferative and resistant to apoptosis after continuous activation of FLT3 signaling. Targeting FLT3 has been the focus of many pre-clinical and clinical studies. Hence, many small-molecule FLT3 inhibitors (FLT3is) have been developed, some of which are approved such as midostaurin and gilteritinib to be used in different clinical settings, either in combination with chemotherapy or alone. However, many questions regarding the best treatment strategy remain to be answered. On the other hand, various FLT3-dependent and -independent resistance mechanisms could be evolved during FLT3i therapy which limit their clinical impact. Therefore, identifying molecular mechanisms of resistance and developing novel strategies to overcome this obstacle is a current interest in the field. In this review, recent studies of approved FLT3i and knowledge about major resistance mechanisms of clinically approved FLT3i's will be discussed together with novel treatment approaches such as designing novel FLT3i and dual FLT3i and combination strategies including approved FLT3i plus small-molecule agents targeting altered molecules in the resistant cells to abrogate resistance. Moreover, how to choose an appropriate FLT3i for the patients will be summarized based on what is currently known from available clinical data. In addition, strategies beyond FLT3i's including immunotherapeutics, small-molecule FLT3 degraders, and flavonoids will be summarized to highlight potential alternatives in FLT3-mutated AML therapy.

Human acute myeloid leukemia stem cells: evolution of concept

The history of human acute myeloid leukemia stem cells (AMLSCs) began in a seminal study performed by Lapidot and Dick, proving that only CD34+CD38- human primary acute myeloid leukemia (AML) cells can repopulate in severe combined immunodeficient mice. The concept of leukemic stem cells (LSCs) has impeded a huge change in the treatment strategy against AML from killing proliferating leukemic cells to eradicating quiescent/dormant LSCs. As next-generation sequencing technologies have developed, multiple and recurrent genetic mutations have been discovered in large cohorts of patients with AML, and the updated understanding of leukemogenesis has improved the old concept of LSC to a revised version of a serial developmental model of LSC; that is, pre-LSCs are generated as seeds by the first hit on epigenetic regulators, and then, leukemia-initiating LSCs emerge from seeds by the second hits on genes involved in transcription and signaling. Dreams for universal and targetable AMLSC biomarker sparing healthy hematopoietic stem cells have weakened after the confrontation of significant heterogeneity of AMLSCs from genomic and immunophenotypic viewpoints. However, there is still hope for effective targets for AMLSCs since there is evidence that grouped gene signatures, such as 17-gene LSC score, and common epigenetic signatures, such as HOXA clusters, independent of various gene mutations, exist. Recently, the LSC niche in the bone marrow has been actively investigated and has expanded our knowledge of the physiology and vulnerability of AMLSCs. Presently, an applicable treatment that always works in AMLSCs is lacking. However, we will find a way, we always have.

Dissecting the Genetic and Non-Genetic Heterogeneity of Acute Myeloid Leukemia Using Next-Generation Sequencing and In Vivo Models

Simple Summary

Acute myeloid leukemia (AML) is an extremely aggressive form of blood cancer with high rates of treatment failure. AML arises from the stepwise acquisition of genetic aberrations and is a highly heterogeneous disorder. Recent research has shown that individual AML samples often contain several clones that are defined by a distinct combination of genetic lesions, epigenetic patterns and cell surface marker expression profiles. A better understanding of the clonal dynamics of AML is required to develop novel treatment strategies against this disease. In this review, we discuss the recent developments that have further deepened our understanding of clonal evolution and heterogeneity in AML.

Abstract

Acute myeloid leukemia (AML) is an extremely aggressive and heterogeneous disorder that results from the transformation of hematopoietic stem cells. Although our understanding of the molecular pathology of AML has greatly improved in the last few decades, the overall and relapse free survival rates among AML patients remain quite poor. This is largely due to evolution of the disease and selection of the fittest, treatment-resistant leukemic clones. There is increasing evidence that most AMLs possess a highly complex clonal architecture and individual leukemias are comprised of genetically, phenotypically and epigenetically distinct clones, which are continually evolving. Advances in sequencing technologies as well as studies using murine AML models have provided further insights into the heterogeneity of leukemias. We will review recent advances in the field of genetic and non-genetic heterogeneity in AML.

CD99 in malignant hematopoiesis

The CD99 gene encodes a transmembrane protein that is involved in cell differentiation, adhesion, migration, and protein trafficking. CD99 is differentially expressed on the surface of hematopoietic cells both in the myeloid and lymphoid lineages. CD99 has two isoforms, the long and short isoforms that play different roles depending on the cellular context. There has been extensive evidence supporting the role of CD99 in myeloid and lymphoblastic leukemias. Here we review research findings related to the CD99 in malignant hematopoiesis. We also summarize the significance of CD99 as a therapeutic target in hematological malignancies.

CD123 Expression Is Associated With High-Risk Disease Characteristics in Childhood Acute Myeloid Leukemia: A Report From the Children's Oncology Group

PURPOSE

Increased CD123 surface expression has been associated with high-risk disease characteristics in adult acute myeloid leukemia (AML), but has not been well-characterized in childhood AML. In this study, we defined CD123 expression and associated clinical characteristics in a uniformly treated cohort of pediatric patients with newly diagnosed AML enrolled on the Children's Oncology Group AAML1031 phase III trial (NCT01371981).

MATERIALS AND METHODS

AML blasts within diagnostic bone marrow specimens (n = 1,040) were prospectively analyzed for CD123 protein expression by multidimensional flow cytometry immunophenotyping at a central clinical laboratory. Patients were stratified as low-risk or high-risk on the basis of (1) leukemia-associated cytogenetic and molecular alterations and (2) end-of-induction measurable residual disease levels.

RESULTS

The study population was divided into CD123 expression-based quartiles (n = 260 each) for analysis. Those with highest CD123 expression (quartile 4 [Q4]) had higher prevalence of high-risk KMT2A rearrangements and FLT3-ITD mutations (P < .001 for both) and lower prevalence of low-risk t(8;21), inv(16), and CEBPA mutations (P < .001 for all). Patients in lower CD123 expression quartiles (Q1-3) had similar relapse risk, event-free survival, and overall survival. Conversely, Q4 patients had a significantly higher relapse risk (53% v 39%, P < .001), lower event-free survival (49% v 69%, P < .001), and lower overall survival (32% v 50%, P < .001) in comparison with Q1-3 patients. CD123 maintained independent significance for outcomes when all known contemporary high-risk cytogenetic and molecular markers were incorporated into multivariable Cox regression analysis.

CONCLUSION

CD123 is strongly associated with disease-relevant cytogenetic and molecular alterations in childhood AML. CD123 is a critical biomarker and promising immunotherapeutic target for children with relapsed or refractory AML, given its prevalent expression and enrichment in patients with high-risk genetic alterations and inferior clinical outcomes with conventional therapy.

CD123-targeted therapy in acute myeloid leukemia

INTRODUCTION

Acute myeloid leukemia (AML) results from the neoplastic transformation of a hematopoietic stem cell. While therapeutic progress has stagnated for several decades, recent progress in the genomic classification of AML has paved the way for multiple new drug approvals. These long-awaited achievements represent a paradigm shift in the approach to a disease that has largely been managed with conventional chemotherapy since the 1970s. With the evolution of targeted AML therapies, novel agents continue to be developed with the goal to improve efficacy while minimizing toxicity. Monoclonal antibodies targeting AML-specific surface markers have emerged as promising candidates to improve outcomes. CD123, interleukin-3 receptor alpha chain [IL-3 Rα], is highly expressed in AML, particularly within the AML stem cell compartment. Several CD123-targeted strategies are currently being evaluated in clinical trials.

AREAS COVERED

The authors herein discuss recent clinical data in CD123-directed therapy in AML. A computerized PubMed search was conducted using key words relevant to the various sections of this article. Relevant abstracts presented at the American Society of Hematology, the European Hematology Association, and the American Society of Clinical Oncology were also reviewed.

EXPERT OPINION

CD123 represents a suitable therapeutic target that has the potential to improve AML patient outcomes.

Clinical value of CD25/CD123 co-expression in acute myeloid leukemia patients

BACKGROUND

This study aimed to assess the significance of combined expression of interleukin-2 receptor (CD25) and the interleukin-3 receptor (CD123) in acute myeloid leukemia (AML) patients.

METHODS

The expression of CD25 and CD123 on blast cells in bone marrow samples were identified by flowcytometry in 94 patients (⩽ 60 years old) with de novo acute myeloid leukemia (AML) treated at the Mansoura University Oncology Center (MUOC).

RESULTS

Of the 94 samples at diagnosis there were 17 (18.1%) CD25+/CD123+ (double positive) cases; 25 (26.6%) CD25+/CD123- (single positive); 32 (34.0%) CD25-/CD123+ (single positive) cases; 20 (21.3%). CD25-/CD123- (double negative). Most of the AML patients have double CD25+/CD123+ were significantly associated with poor and intermediate risk as compared to those associated with those in the good risk group (P= 0.005). The lowest induction of remission was recorded in AML patients have double CD25+/CD123+ expression as compared to the remaining AML patient group. Study the effect of these biomarkers on the overall survival reveal that AML patients exhibited double CD25+/CD123+ expression had significantly shorter overall survival as compared to negative ones.

CONCLUSION

Double CD25+/CD123+ co-expression in AML patients is a dismal prognostic marker and could be used as novel biomarker for risk stratification for AML patients.

Adaptive immunity-related gene expression profile is correlated with clinical phenotype in patients with acute myeloid leukemia

Background

Acute myeloid leukemia (AML) is a common and lethal hematopoietic malignancy that is highly dependent on the immune microenvironment. However, light has yet to be shed on the landscape of adaptive immunity-related genes. This work aimed to uncover the novel molecular events in AML and potential therapeutic strategies for AML treatment.

Methods

For the current research, the transcriptional information of 732 genes that participate in adaptive immunity was collected from 173 patients with AML, and the patients were grouped into different cohorts based on the different expression patterns. The correlations between gene expression and clinical characteristics, including prognosis, were studied.

Results

According to the notably different expressions of adaptive immunity-related genes, the 173 patients were divided into 2 clusters and 3 subclusters. No significant differences in overall survival (OS) or progression-free survival (PFS) were detected between the clusters or subclusters. There were obvious discrepancies found in age, peripheral blood (PB) blast percentage, and French-American-British (FAB) classification between each cluster or subcluster. The patients in cluster 1 were older and more of them had M5 type; the patients in cluster 2 were younger and more of them had M2 type. Further, 81 genes were significantly correlated with age and 101 genes were significantly correlated with PB blast percentage. Comparison of the prognosis between each FAB type revealed that patients with M3 type displayed the most favorable OS and PFS. Among the differentially expressed genes (DEGs), CLEC2B expression was much lower in M2 patients than in patients with other types (P<0.001), and its high expression indicated a worse outcome (12.4 vs. 46.5 months of OS).

Conclusions

This study has uncovered the expression profile of adaptive immunity-related genes in AML. The different gene expression patterns are not associated with survival, but are significantly correlated the FAB types. CLEC2B expression is low in patients with M2 type and is negatively correlated with prognosis, thus revealing a potential therapeutic target for AML.

Quantitative analyses of CD7, CD33, CD34, CD56, and CD123 within the FLT3-ITD/NPM1-MUT myeloblastic/monocytic bulk AML blastic populations

The most frequent mutations in acute myeloid leukemia (AML) - FLT3-ITD and NPM1 - are associated with a specific immunophenotype. We evaluated the levels of surface antigens in an uninvestigated AML patient population according to the combination of FLT3-ITD/NPM1 mutations. Antigen levels were calculated as the geometric mean fluorescence index (MFI) ratio between myeloblasts or monoblasts/monocytes and a negative population for the specific antigen. In myeloblastic populations, FLT3-ITD cases presented CD7^high MFI values (p < .001), while NPM1-MUT cases presented CD33^high (p < .001), and CD34^low (p < .001) MFI values. Within the monoblastic/monocytic populations, CD56^high expression was observed only in the FLT3-WT/NPM1-MUT population (p=.003). The single common antigen expression between myeloblasts and monoblasts/monocytes was CD123^high expression only within the FLT3-ITD/NPM1-MUT subgroup. Our results present a subtle influence of FLT3-ITD/NPM1 mutations upon antigen expression profiles in myeloblasts vs monoblasts/monocytes, and we described a novel correlation between the presence of NPM1 and CD56^high values within bulk leukemic monoblasts/monocytes.

Emerging Immunotherapy for Acute Myeloid Leukemia

Several immune checkpoint molecules and immune targets in leukemic cells have been investigated. Recent studies have suggested the potential clinical benefits of immuno-oncology (IO) therapy against acute myeloid leukemia (AML), especially targeting CD33, CD123, and CLL-1, as well as immune checkpoint inhibitors (e.g., anti-PD (programmed cell death)-1 and anti-CTLA4 (cytotoxic T-lymphocyte-associated protein 4) antibodies) with or without conventional chemotherapy. Early-phase clinical trials of chimeric antigen receptor (CAR)-T or natural killer (NK) cells for relapsed/refractory AML showed complete remission (CR) or marked reduction of marrow blasts in a few enrolled patients. Bi-/tri-specific antibodies (e.g., bispecific T-cell engager (BiTE) and dual-affinity retargeting (DART)) exhibited 11-67% CR rates with 13-78% risk of cytokine-releasing syndrome (CRS). Conventional chemotherapy in combination with anti-PD-1/anti-CTLA4 antibody for relapsed/refractory AML showed 10-36% CR rates with 7-24 month-long median survival. The current advantages of IO therapy in the field of AML are summarized herein. However, although cancer vaccination should be included in the concept of IO therapy, it is not mentioned in this review because of the paucity of relevant evidence.

Descriptive and Functional Genomics in Acute Myeloid Leukemia (AML): Paving the Road for a Cure

Over the past decades, genetic advances have allowed a more precise molecular characterization of AML with the identification of novel oncogenes and tumor suppressors as part of a comprehensive AML molecular landscape. Recent advances in genetic sequencing tools also enabled a better understanding of AML leukemogenesis from the preleukemic state to posttherapy relapse. These advances resulted in direct clinical implications with the definition of molecular prognosis classifications, the development of treatment recommendations based on minimal residual disease (MRD) measurement and the discovery of novel targeted therapies, ultimately improving AML patients' overall survival. The more recent development of functional genomic studies, pushed by novel molecular biology technologies (short hairpin RNA (shRNA) and CRISPR-Cas9) and bioinformatics tools design on one hand, along with the engineering of humanized physiologically relevant animal models on the other hand, have opened a new genomics era resulting in a greater knowledge of AML physiopathology. Combining descriptive and functional genomics will undoubtedly open the road for an AML cure within the next decades.

Influence of different lipid emulsions on specific immune cell functions in head and neck cancer patients receiving supplemental parenteral nutrition: An exploratory analysis

OBJECTIVES

The effect of diet on immune responses is an area of intense investigation. Dietary lipids have been shown to differently influence and fine-tune the reactivity of immune cell subsets, thus potentially affecting clinical outcomes. Patients with head and neck squamous cell carcinoma face malnutrition, due to swallowing impairment related to the tumor site or to treatment sequalae, and may need supplemental parenteral nutrition (SPN) in addition to oral feeding when enteral nutrition is not feasible. Additionally, immune depression is a well-known complication in these patients. Parenteral nutrition (PN) bags contain amino acids, minerals, electrolytes and mostly lipids that provide calories in a concentrated form and are enriched with essential fatty acids. The aim of this study was to investigate multiple parameters of the immune responses in a cohort of patients with head and neck squamous cell carcinoma undergoing supplemental PN with bags enriched in ω-3 or ω-9 and ω-6 fatty acids.

METHODS

To our knowledge, this was the first exploratory study to investigate the effects of two different PN lipid emulsions on specific immune cells function of patients with advanced head and neck squamous carcinoma. ω-3-enriched fish-oil-based- and ω-6- and ω-9-enriched olive-oil-basedSPN was administered to two groups of patients for 1 wk in the context of an observational multicentric study. Polychromatic flow cytometry was used to investigate multiple subsets of leukocytes, with a special focus on cellular populations endowed with antitumor activity.

RESULTS

Patients treated with olive-oil-based PN showed an increase in the function of the innate (natural killer cells and monocytes) and adaptive (both CD4 and CD8 cells) arms of the immune response.

CONCLUSION

An increase in the function of the innate and adaptive arms of the immune response may favor antitumoral responses.

CD123 Is Consistently Expressed on NPM1-Mutated AML Cells

Simple Summary

One-third of adult acute myeloid leukemia (AML) harbors NPM1 mutations. A deep knowledge of the distribution of selected antigens on the surface of NPM1-mutated AML cells may help optimizing new therapies for this frequent AML subtype. CD123 is known to be expressed on leukemic cells but also on healthy hematopoietic and endothelial cells, although at lower levels. Differences in antigen densities between AML and healthy cells may enlighten therapeutic windows, where targeting CD123 could be effective without triggering “on-target off-tumor” toxicities. Here, we perform a thorough analysis of CD123 expression demonstrating high expression of this antigen on both NPM1-mutated bulk leukemic cells and CD34⁺CD38⁻ cells.

Abstract

NPM1-mutated (NPM1mut) acute myeloid leukemia (AML) comprises about 30% of newly diagnosed AML in adults. Despite notable advances in the treatment of this frequent AML subtype, about 50% of NPM1mut AML patients treated with conventional treatment die due to disease progression. CD123 has been identified as potential target for immunotherapy in AML, and several anti-CD123 therapeutic approaches have been developed for AML resistant to conventional therapies. As this antigen has been previously reported to be expressed by NPM1mut cells, we performed a deep flow cytometry analysis of CD123 expression in a large cohort of NPM1mut and wild-type samples, examining the whole blastic population, as well as CD34⁺CD38⁻ leukemic cells. We demonstrate that CD123 is highly expressed on NPM1mut cells, with particularly high expression levels showed by CD34⁺CD38⁻ leukemic cells. Additionally, CD123 expression was further enhanced by FLT3 mutations, which frequently co-occur with NPM1 mutations. Our results identify NPM1-mutated and particularly NPM1/FLT3 double-mutated AML as disease subsets that may benefit from anti-CD123 targeted therapies.

The impact of FLT3 mutation clearance and treatment response after gilteritinib therapy on overall survival in patients with FLT3 mutation-positive relapsed/refractory acute myeloid leukemia

The FLT3 inhibitor gilteritinib has clinical activity in patients with FLT3‐mutated (FLT3^mut+) relapsed/refractory (R/R) acute myeloid leukemia (AML). The impact of FLT3 mutation clearance and the achievement of composite complete remission (CRc) and complete remission/complete remission with partial hematologic recovery (CR/CRh) on overall survival (OS) in patients with FLT3^mut+ R/R AML treated with single‐agent gilteritinib in a phase 1/2 trial were evaluated. Using next‐generation sequencing, a FLT3‐ITD variant allele frequency of ≤10⁻⁴ was used to define FLT3‐ITD clearance in patients with no morphologic leukemia (ie, CRc). A total of 108 patients with FLT3‐ITD‐positive (FLT3‐ITD+) R/R AML were analyzed; 95 of these patients had received ≥80‐mg/day gilteritinib. Ten of the 95 patients had FLT3‐ITD clearance; eight of these 10 patients achieved CRc and were considered negative for measurable residual disease. There was a trend toward longer OS in patients who attained CRc with FLT3‐ITD clearance (131.4 weeks) versus those who achieved CRc and did not have FLT3‐ITD clearance (n = 41; 43.3 weeks; HR = 0.416; p = 0.066). Among patients treated with ≥80‐mg/day gilteritinib who achieved CR/CRh (n = 24), seven had FLT3‐ITD clearance. Among patients who received 120‐mg/day gilteritinib, those who achieved CR/CRh had a longer median OS (70.6 weeks) and higher 52‐week survival probability (66.7%) than patients who did not achieve CR/CRh (n = 71; median OS, 41.7 weeks; 52‐week survival probability, 20.2%). Overall, these data suggest that gilteritinib can induce deep molecular responses in patients with FLT3‐ITD+ R/R AML, and in the setting of CRc or CR/CRh, these responses may be associated with prolonged survival.

Acute Myeloid Leukemia Stem Cells: The Challenges of Phenotypic Heterogeneity

Patients suffering from acute myeloid leukemia (AML) show highly heterogeneous clinical outcomes. Next to variabilities in patient-specific parameters influencing treatment decisions and outcome, this is due to differences in AML biology. In fact, different genetic drivers may transform variable cells of origin and co-exist with additional genetic lesions (e.g., as observed in clonal hematopoiesis) in a variety of leukemic (sub)clones. Moreover, AML cells are hierarchically organized and contain subpopulations of more immature cells called leukemic stem cells (LSC), which on the cellular level constitute the driver of the disease and may evolve during therapy. This genetic and hierarchical complexity results in a pronounced phenotypic variability, which is observed among AML cells of different patients as well as among the leukemic blasts of individual patients, at diagnosis and during the course of the disease. Here, we review the current knowledge on the heterogeneous landscape of AML surface markers with particular focus on those identifying LSC, and discuss why identification and targeting of this important cellular subpopulation in AML remains challenging.

Radar plots facilitate differential diagnosis of acute promyelocytic leukemia and NPM1+ acute myeloid leukemia by flow cytometry

BACKGROUND

Acute promyelocytic leukemia (APL) is one of the most life-threatening hematological emergencies and requires a prompt correct diagnosis by cytomorphology and flow cytometry (FCM) with later confirmation by cytogenetics/molecular genetics. However, nucleophosmin 1 muted acute myeloid leukemia (NPM1+ AML) can mimic APL, especially the hypogranular variant of APL. Our study aimed to develop a novel, Radar plot-based FCM strategy to distinguish APLs and NPM1+ AMLs quickly and accurately.

METHOD

Diagnostic samples from 52 APL and 32 NPM1+ AMLs patients were analyzed by a 3-tube panel of 10-color FCM. Radar plots combining all markers were constructed for each tube. Percentages of positive leukemic cells and mean fluorescence intensity were calculated for all the markers.

RESULTS

APL showed significantly higher expression of CD64, CD2, and CD13, whereas more leukemic cells were positive for CD11b, CD11c, CD15, CD36, and HLA-DR in NPM1+ AMLs. Radar plots featured CD2 expression, a lack of a monocytic component, lack of expression of HLA-DR and CD15, and a lack of a prominent CD11c+ population as recurring characteristics of APL. The presence of blasts with low SSC, presence of at least some monocytes, some expression of HLA-DR and/or CD15, and a prominent CD11c population were recurrent characteristics of NPM1+ AMLs. Radar plot analysis could confidently separate all hypergranular APL cases from any NPM1+ AML and in 90% of cases between variant APL and blastic NPM1+ AML.

CONCLUSION

Radar plots can potentially add to differential diagnostics as they exhibit characteristic patterns distinguishing APL and different types of NPM1+ AMLs.

Antigen Expression Varies Significantly between Molecular Subgroups of Acute Myeloid Leukemia Patients: Clinical Applicability Is Hampered by Establishment of Relevant Cutoffs

INTRODUCTION

In this single-center study of 268 acute myeloid leukemia (AML) patients, we have tested if a subset of 4 routinely employed immunophenotypic stem cell-associated markers correlated with the presence of recurrently mutated genes and if the markers were predictive for mutational status.

METHODS

Immunophenotypic data from 268 diagnostic AML samples obtained in 2009-2018 were analyzed retrospectively for the antigens CD34, CD117, CD123, and CLEC12A. Correlation between immunophenotypes and mutations was analyzed by Fischer's exact test. Clinical applicability of the markers for predicting mutational status was evaluated by receiver operating characteristics analyses, where an area under the curve (AUC) of at least 0.85 was accepted as clinically relevant.

RESULTS

For a number of genes, the antigen expression differed significantly between mutated and wild-type gene expression. Despite low AUCs, CD123 and CLEC12A correlated with FLT3+NPM1- and FLT3+NPM1+. Three subsets met the AUC requirements (CD34+, CD34+CD117+, and CD34-CD117+) for predicting FLT3-NPM1+ or FLT3+NPM1+.

CONCLUSION

The value of immunophenotypes as surrogate markers for mutational status in AML seems limited when employing CD123 and CLEC12A in combination with CD34 and CD117. Defining relevant cutoffs for given markers is challenging and hampered by variation between laboratories and patient groups.

Terminal deoxynucleotidyl transferase (TdT) expression is associated with FLT3-ITD mutations in Acute Myeloid Leukemia

The terminal deoxynucleotidyl transferase (TdT) is a DNA polymerase expressed in acute myeloid leukemias (AMLs), where it may be involved in the generation of NPM1 and FLT3-ITD mutations. We studied the correlations between TdT expression and FLT3-ITD or NPM1 mutations in primary AML samples, and the impact on patients' survival. TdT expression was analyzed in 143 adult AML patients by flow cytometry as percentage of positivity and mean fluorescence intensity (MFI) on blasts. TdT was positive in 49 samples (34.2%), with a median of 48% TdT-positivity (range 7-98) and a median MFI of 2.70 (range 1.23-30.54). FLT3-ITD and NPM1 mutations were present in 24 (16.7%) and 34 (23.7%) cases, respectively. Median TdT expression on blasts was significantly higher in FLT3-ITD+, as compared with FLT3-ITD- AMLs (median 8% vs 0% respectively, p = 0.035). NPM1 mutational status, FLT3-ITD allelic ratio, karyotype, and ELN risk groups, did not correlate with TdT expression or MFI on blasts. TdT + patients had poorer survival as compared to TdT-, but this result was not confirmed by the multivariable analysis, where ELN risk stratification as well as age and type of treatment remained independent prognostic factors for OS. In summary, our results support the possible implication of TdT enzyme in the generation of FLT3-ITD mutations in AML.

Characterization of FLT3-ITDmut acute myeloid leukemia: molecular profiling of leukemic precursor cells

Acute myeloid leukemia (AML) with FLT3-ITD mutations (FLT3-ITDmut) remains a therapeutic challenge, with a still high relapse rate, despite targeted treatment with tyrosine kinase inhibitors. In this disease, the CD34/CD123/CD25/CD99+ leukemic precursor cells (LPCs) phenotype predicts for FLT3-ITD-positivity. The aim of this study was to characterize the distribution of FLT3-ITD mutation in different progenitor cell subsets to shed light on the subclonal architecture of FLT3-ITDmut AML. Using high-speed cell sorting, we sequentially purified LPCs and CD34+ progenitors in samples from patients with FLT3-ITDmut AML (n = 12). A higher FLT3-ITDmut load was observed within CD34/CD123/CD25/CD99+ LPCs, as compared to CD34+ progenitors (CD123+/-,CD25-,CD99low/-) (p = 0.0005) and mononuclear cells (MNCs) (p < 0.0001). This was associated with significantly increased CD99 mean fluorescence intensity in LPCs. Significantly higher FLT3-ITDmut burden was also observed in LPCs of AML patients with a small FLT3-ITDmut clones at diagnosis. On the contrary, the mutation burden of other myeloid genes was similar in MNCs, highly purified LPCs and/or CD34+ progenitors. Treatment with an anti-CD99 mAb was cytotoxic on LPCs in two patients, whereas there was no effect on CD34+ cells from healthy donors. Our study shows that FLT3-ITD mutations occur early in LPCs, which represent the leukemic reservoir. CD99 may represent a new therapeutic target in FLT3-ITDmut AML.

41BB-based and CD28-based CD123-redirected T-cells ablate human normal hematopoiesis in vivo

BACKGROUND

Acute myeloid leukemia (AML) is a hematopoietic malignancy which is biologically, phenotypically and genetically very heterogeneous. Outcome of patients with AML remains dismal, highlighting the need for improved, less toxic therapies. Chimeric antigen receptor T-cell (CART) immunotherapies for patients with refractory or relapse (R/R) AML are challenging because of the absence of a universal pan-AML target antigen and the shared expression of target antigens with normal hematopoietic stem/progenitor cells (HSPCs), which may lead to life-threating on-target/off-tumor cytotoxicity. CD33-redirected and CD123-redirected CARTs for AML are in advanced preclinical and clinical development, and they exhibit robust antileukemic activity. However, preclinical and clinical controversy exists on whether such CARTs are myeloablative.

METHODS

We set out to comparatively characterize in vitro and in vivo the efficacy and safety of 41BB-based and CD28-based CARCD123. We analyzed 97 diagnostic and relapse AML primary samples to investigate whether CD123 is a suitable immunotherapeutic target, and we used several xenograft models and in vitro assays to assess the myeloablative potential of our second-generation CD123 CARTs.

RESULTS

Here, we show that CD123 represents a bona fide target for AML and show that both 41BB-based and CD28-based CD123 CARTs are very efficient in eliminating both AML cell lines and primary cells in vitro and in vivo. However, both 41BB-based and CD28-based CD123 CARTs ablate normal human hematopoiesis and prevent the establishment of de novo hematopoietic reconstitution by targeting both immature and myeloid HSPCs.

CONCLUSIONS

This study calls for caution when clinically implementing CD123 CARTs, encouraging its preferential use as a bridge to allo-HSCT in patients with R/R AML.

Prognostic value of CD25/CD123 pattern of expression in acute myeloid leukemia patients with normal cytogenetic

This study was designed to assess the significance of interleukin-2 receptor (CD25) and inteleukin-3 receptor (CD123) expression in cytogenetically normal acute myeloid leukemia (CN-AML) patients. The current study includes 80 CN-AML (≤ 60 years) before the start of therapy. Blast cells expression for CD25 and CD123 were identified by flowcytometry in fresh bone marrow samples. CD25+/CD123-; CD25-/CD123+. CD25+/CD123+, CD25-/CD123- expression were as follow: 10/80 (12.5%); 18/80 (22.5%); 17/80; (21.25%), 35/80 (43.5%) respectively. The total CD25 expression was detected in 27/80 (33.75%), and CD123 expression was detected in 35/80 (43.75%%). CN-AML patients showed CD25+/CD123+ co-expression had the lowest induction remission rate and the shortest overall survival as compared to those lack co-expressions (P <0.01; P = 0.023 respectively). Also, there is strong positive association between CD25+/CD123+ co-expression and FLT3 mutations (P<0.001) and negative one with NPM1 mutation (P<0.001). In conclusion: CD25+/CD123+ co-expression in CN-AML patients define a subgroup of patients with adverse outcome. Identification of CD25/CD123 expression in CN-AML patents at diagnosis could be included in risk stratification. There is strong association between CD25+/CD123+ positive expression and FLT3 mutations.

Follistatin is a novel therapeutic target and biomarker in FLT3/ITD acute myeloid leukemia

Internal tandem duplication of Fms-like tyrosine kinase 3 (FLT3/ITD) occurs in about 30% of acute myeloid leukemia (AML) and is associated with poor response to conventional treatment and adverse outcome. Here, we reported that human FLT3/ITD expression led to axis duplication and dorsalization in about 50% of zebrafish embryos. The morphologic phenotype was accompanied by ectopic expression of a morphogen follistatin (fst) during early embryonic development. Increase in fst expression also occurred in adult FLT3/ITD-transgenic zebrafish, Flt3/ITD knock-in mice, and human FLT3/ITD AML cells. Overexpression of human FST317 and FST344 isoforms enhanced clonogenicity and leukemia engraftment in xenotransplantation model via RET, IL2RA, and CCL5 upregulation. Specific targeting of FST by shRNA, CRISPR/Cas9, or antisense oligo inhibited leukemic growth in vitro and in vivo. Importantly, serum FST positively correlated with leukemia engraftment in FLT3/ITD AML patient-derived xenograft mice and leukemia blast percentage in primary AML patients. In FLT3/ITD AML patients treated with FLT3 inhibitor quizartinib, serum FST levels correlated with clinical response. These observations supported FST as a novel therapeutic target and biomarker in FLT3/ITD AML.

CD45dimCD34+CD38-CD133+ cells have the potential as leukemic stem cells in acute myeloid leukemia

Background

Leukemia stem cells (LSCs) in play an important role in the initiation, relapse, and progression of acute myeloid leukemia (AML), and in the development of chemotherapeutic drug resistance in AML. Studies regarding the detection of LSCs and the development of novel therapies for targeting them are extensive. The identification of LSCs and targeting therapies for them has been continuously under investigation.

Methods

We examined the levels of CD45^dimCD34⁺CD38⁻CD133⁺ cells in bone marrow samples from patients with hematological malignancies and healthy controls, using four-color flow cytometry.

Results

Interestingly, the CD45^dimCD34⁺CD38⁻CD133⁺ cells were highly expressed in the bone marrow of patients with AML compared to that in healthy controls (HC). Moreover, the proportions of CD45^dimCD34⁺CD38⁻CD133⁺ cells were also examined in diverse hematological malignancies, including AML, CML, DLBCL, MM, MDS, HL, ALL, and CLL. LSCs were prominently detected in the BMCs isolated from patients with AML and CML, but rarely in BMCs isolated from patients with DLBCL, MM, MDS, ALL, CLL, and HL. Additionally, the high CD45^dimCD34⁺CD38⁻CD133⁺ cell counts in AML patients served as a significantly poor risk factor for overall and event free survival.

Conclusions

Therefore, our results suggest that CD45^dimCD34⁺CD38⁻CD133⁺ cells in AML might potentially serve as LSCs. In addition, this cell population might represent a novel therapeutic target in AML.

Early intravenous administration of nutritional support (IVANS) in metastatic gastric cancer patients at nutritional risk, undergoing first-line chemotherapy: study protocol of a pragmatic, randomized, multicenter, clinical trial

Background

Malnutrition is common in cancer patients, particularly in those affected by gastrointestinal malignancies, and negatively affects treatment tolerance, survival, functional status, and quality of life (QoL). Nutritional support, including supplemental parenteral nutrition (SPN), has been recommended at the earliest opportunity in malnourished cancer patients. The limited available evidence on the efficacy of SPN in gastrointestinal cancer patients is positive, particularly with regards to QoL, body composition, and energy intake, but the evidence on survival is still scanty. Furthermore, studies regarding the early administration of SPN in combination with nutritional counseling from the beginning of first-line chemotherapy (CT) are lacking. We hypothesize that early systematic SPN in combination with nutritional counseling (NC), compared with NC alone, can benefit patients with previously untreated metastatic gastric cancer at nutritional risk undergoing first-line CT.

Methods

The aim of this pragmatic, multicenter, randomized (1:1), parallel-group, open-label, controlled clinical trial is to evaluate the efficacy in terms of survival, weight maintenance, body composition, QoL and feasibility of cancer therapy of early systematic SNP. This is in combination with NC, compared with NC alone, in treatment-naïve metastatic gastric cancer patients at nutritional risk undergoing first-line CT.

Discussion

Malnutrition in oncology remains an overlooked problem. Although the importance of SPN in gastrointestinal cancer patients has been acknowledged, no studies have yet evaluated the efficacy of early SPN in metastatic gastric patients undergoing CT. The present study, which guarantees the early provision of nutritional assessment and support to all the enrolled patients in accordance with the recent guidelines and recommendations, could represent one of the first proofs of the clinical effectiveness of early intensive nutritional support in cancer patients undergoing CT. This study could stimulate further large randomized trials in different cancer types, potentially resulting in the improvement of supportive care quality.

Trial registration

This study is registered on ClinicalTrials.gov: NCT03949907.

Applications and efficiency of flow cytometry for leukemia diagnostics

Introduction: Multiparametric flow cytometry immunophenotype (MFCI) plays a crucial role in the diagnosis of acute leukemia (AL). Through the comprehensive assessment of surface and intracellular antigens expressed by blasts, MFCI permits to distinguish myeloid or B/T lymphoid AL, or AL of ambiguous lineages. By means of MFCI, the blasts can be characterized in bone marrow, peripheral blood, and body fluids, such as cerebrospinal fluid.Area covered: This review discusses how MFCI is currently applied in the diagnostic evaluation of AL; it also focuses on 'peculiar' issues such as the role of MFCI for the diagnosis of central nervous system leukemic involvement.Expert commentary: Despite the improved knowledge about the biology of AL, MFCI remains a fundamental tool to make a prompt and accurate diagnosis. MFCI also provides prognostic information for some antigens are associated with specific cytogenetic/genetic abnormalities and, recently, it became a powerful tool to evaluate the quality and depth of response (the so called 'measurable residual disease'). Its role as an efficient detector of residual disease paved the way to the investigation of tissues other than bone marrow and peripheral blood, demonstrating that even small amounts of AL appear to have a prognostic impact and may require personalized intervention.

CD123 as a Therapeutic Target in the Treatment of Hematological Malignancies

The interleukin-3 receptor alpha chain (IL-3Rα), more commonly referred to as CD123, is widely overexpressed in various hematological malignancies, including acute myeloid leukemia (AML), B-cell acute lymphoblastic leukemia, hairy cell leukemia, Hodgkin lymphoma and particularly, blastic plasmacytoid dendritic neoplasm (BPDCN). Importantly, CD123 is expressed at both the level of leukemic stem cells (LSCs) and more differentiated leukemic blasts, which makes CD123 an attractive therapeutic target. Various agents have been developed as drugs able to target CD123 on malignant leukemic cells and on the normal counterpart. Tagraxofusp (SL401, Stemline Therapeutics), a recombinant protein composed of a truncated diphtheria toxin payload fused to IL-3, was approved for use in patients with BPDCN in December of 2018 and showed some clinical activity in AML. Different monoclonal antibodies directed against CD123 are under evaluation as antileukemic drugs, showing promising results either for the treatment of AML minimal residual disease or of relapsing/refractory AML or BPDCN. Finally, recent studies are exploring T cell expressing CD123 chimeric antigen receptor-modified T-cells (CAR T) as a new immunotherapy for the treatment of refractory/relapsing AML and BPDCN. In December of 2018, MB-102 CD123 CAR T developed by Mustang Bio Inc. received the Orphan Drug Designation for the treatment of BPDCN. In conclusion, these recent studies strongly support CD123 as an important therapeutic target for the treatment of BPDCN, while a possible in the treatment of AML and other hematological malignancies will have to be evaluated by in the ongoing clinical studies.

Clinical and preclinical characterization of CD99 isoforms in acute myeloid leukemia

In an effort to identify target genes in acute myeloid leukemia (AML), we compared gene expression profiles between normal and AML cells from various publicly available datasets. We identified CD99, a gene that is up-regulated in AML patients. In 186 patients from The Cancer Genome Atlas AML dataset, CD99 was over-expressed in patients with FLT3-ITD and was down-regulated in patients with TP53 mutations. CD99 is a trans-membrane protein expressed on leukocytes and plays a role in cell adhesion, trans-endothelial migration, and T-cell differentiation. The CD99 gene encodes two isoforms with distinct expression and functional profiles in both normal and malignant tissues. Here we report that, although the CD99 long isoform initially induces an increase in cell proliferation, it also induces higher levels of reactive oxygen species, DNA damage, apoptosis and a subsequent decrease in cell viability. In several leukemia murine models, the CD99 long isoform delayed disease progression and resulted in lower leukemia engraftment in the bone marrow. Furthermore, the CD99 monoclonal antibody reduced cell viability, colony formation, and cell migration, and induced cell differentiation and apoptosis in leukemia cell lines and primary blasts. Mechanistically, CD99 long isoform resulted in transient induction followed by a dramatic decrease in both ERK and SRC phosphorylation. Altogether, our study provides new insights into the role of CD99 isoforms in AML that could potentially be relevant for the preclinical development of CD99 targeted therapy.

MRD in AML: The Role of New Techniques

In the context of precision medicine, assessment of minimal residual disease (MRD) has been used in acute myeloid leukemia (AML) to direct individual treatment programs, including allogeneic stem cell transplantation in patients at high-risk of relapse. One of the limits of this approach has been in the past the paucity of AML markers suitable for MRD assessment. Recently, the number of biomarkers has increased, due to the identification of highly specific leukemia-associated immunophenotypes by multicolor flow-cytometry, and of rare mutated gene sequences by digital droplet PCR, or next-generation sequencing (NGS). In addition, NGS allowed unraveling of clonal heterogeneity, present in AML at initial diagnosis or developing during treatment, which influences reliability of specific biomarkers, that may be unstable during the disease course. The technological advances have increased the application of MRD-based strategies to a significantly higher number of AML patients, and the information deriving from MRD assessment has been used to design individual post-remission protocols and pre-emptive treatments in patients with sub-clinical relapse. This led to the definition of MRD-negative complete remission as outcome definition in the recently published European Leukemianet MRD guidelines. In this review, we summarized the principles of modern technologies and their clinical applications for MRD detection in AML patients, according to the specific leukemic markers.

High Constitutive Cytokine Release by Primary Human Acute Myeloid Leukemia Cells Is Associated with a Specific Intercellular Communication Phenotype

Acute myeloid leukemia (AML) is a heterogeneous disease, and this heterogeneity includes the capacity of constitutive release of extracellular soluble mediators by AML cells. We investigated whether this capacity is associated with molecular genetic abnormalities, and we compared the proteomic profiles of AML cells with high and low release. AML cells were derived from 71 consecutive patients that showed an expected frequency of cytogenetic and molecular genetic abnormalities. The constitutive extracellular release of 34 soluble mediators (CCL and CXCL chemokines, interleukins, proteases, and protease regulators) was investigated for an unselected subset of 62 patients, and they could be classified into high/intermediate/low release subsets based on their general capacity of constitutive secretion. FLT3-ITD was more frequent among patients with high constitutive mediator release, but our present study showed no additional associations between the capacity of constitutive release and 53 other molecular genetic abnormalities. We compared the proteomic profiles of two contrasting patient subsets showing either generally high or low constitutive release. A network analysis among cells with high release levels demonstrated high expression of intracellular proteins interacting with integrins, RAC1, and SYK signaling. In contrast, cells with low release showed high expression of several transcriptional regulators. We conclude that AML cell capacity of constitutive mediator release is characterized by different expression of potential intracellular therapeutic targets.

Hematopoietic niche drives FLT3-ITD acute myeloid leukemia resistance to quizartinib via STAT5-and hypoxia-dependent upregulation of AXL

Internal tandem duplication in Fms-like tyrosine kinase 3 (FLT3-ITD) is the most frequent mutation observed in acute myeloid leukemia (AML) and correlates with poor prognosis. FLT3 tyrosine kinase inhibitors are promising for targeted therapy. Here, we investigated mechanisms dampening the response to the FLT3 inhibitor quizartinib, which is specific to the hematopoietic niche. Using AML primary samples and cell lines, we demonstrate that convergent signals from the hematopoietic microenvironment drive FLT3-ITD cell resistance to quizartinib through the expression and activation of the tyrosine kinase receptor AXL. Indeed, cytokines sustained phosphorylation of the transcription factor STAT5 in quizartinib-treated cells, which enhanced AXL expression by direct binding of a conserved motif in its genomic sequence. Likewise, hypoxia, another well-known hematopoietic niche hallmark, also enhanced AXL expression. Finally, in a xenograft mouse model, inhibition of AXL significantly increased the response of FLT3-ITD cells to quizartinib exclusively within a bone marrow environment. These data highlight a new bypass mechanism specific to the hematopoietic niche that hampers the response to quizartinib through combined upregulation of AXL activity. Targeting this signaling offers the prospect of a new therapy to eradicate resistant FLT3-ITD leukemic cells hidden within their specific microenvironment, thereby preventing relapses from FLT3-ITD clones.

A CD123-targeting antibody-drug conjugate, IMGN632, designed to eradicate AML while sparing normal bone marrow cells

The outlook for patients with refractory/relapsed acute myeloid leukemia (AML) remains poor, with conventional chemotherapeutic treatments often associated with unacceptable toxicities, including severe infections due to profound myelosuppression. Thus there exists an urgent need for more effective agents to treat AML that confer high therapeutic indices and favorable tolerability profiles. Because of its high expression on leukemic blast and stem cells compared with normal hematopoietic stem cells and progenitors, CD123 has emerged as a rational candidate for molecularly targeted therapeutic approaches in this disease. Here we describe the development and preclinical characterization of a CD123-targeting antibody-drug conjugate (ADC), IMGN632, that comprises a novel humanized anti-CD123 antibody G4723A linked to a recently reported DNA mono-alkylating payload of the indolinobenzodiazepine pseudodimer (IGN) class of cytotoxic compounds. The activity of IMGN632 was compared with X-ADC, the ADC utilizing the G4723A antibody linked to a DNA crosslinking IGN payload. With low picomolar potency, both ADCs reduced viability in AML cell lines and patient-derived samples in culture, irrespective of their multidrug resistance or disease status. However, X-ADC exposure was >40-fold more cytotoxic to the normal myeloid progenitors than IMGN632. Of particular note, IMGN632 demonstrated potent activity in all AML samples at concentrations well below levels that impacted normal bone marrow progenitors, suggesting the potential for efficacy in AML patients in the absence of or with limited myelosuppression. Furthermore, IMGN632 demonstrated robust antitumor efficacy in multiple AML xenograft models. Overall, these findings identify IMGN632 as a promising candidate for evaluation as a novel therapy in AML.

Immunophenotyping of Acute Myeloid Leukemia

Immunophenotyping by multiparameter flow cytometry is a rapid and efficient technique to simultaneously assess and correlate multiple individual cell properties like size and internal complexity along with antigen expression in a population of cells. This method is utilized for rapid characterization of the blasts and classification of acute myeloid leukemia (AML), in both the peripheral blood (PB) and bone marrow (BM). This technique is not only useful in the initial diagnosis but also in monitoring and determining prognosis of the disease through minimal residual disease (MRD) testing. This chapter provides an overview of procedures for specimen processing, staining, and immunophenotyping of AML and describes the principles of data analysis for AML classification and MRD testing.

Flow-Cytometric Monitoring of Minimal Residual Disease in Pediatric Patients With Acute Myeloid Leukemia: Recent Advances and Future Strategies

Minimal residual disease (MRD) by multiparametric flow cytometry (MFC) has been recently shown as a strong and independent prognostic marker of relapse in pediatric AML (pedAML) when measured at specific time points during Induction and/or Consolidation therapy. Hence, MFC-MRD has the potential to refine the current strategies of pedAML risk stratification, traditionally based on the cytogenetic and molecular genetic aberrations at diagnosis. Consequently, it may guide the modulation of therapy intensity and clinical decision making. However, the use of non-standardized protocols, including different staining panels, analysis, and gating strategies, may hamper a broad implementation of MFC-MRD monitoring in clinical routine. Besides, the thresholds of MRD positivity still need to be validated in large, prospective and multi-center clinical studies, as well as optimal time points of MRD assessment during therapy, to better discriminate patients with different prognosis. In the present review, we summarize the most relevant findings on MFC-MRD testing in pedAML. We examine the clinical significance of MFC-MRD and the recent advances in its standardization, including innovative approaches with an automated analysis of MFC-MRD data. We also touch upon other technologies for MRD assessment in AML, such as quantitative genomic breakpoint PCR, current challenges and future strategies to enable full incorporation of MFC-MRD into clinical practice.

Targeting Oncogenic Signaling in Mutant FLT3 Acute Myeloid Leukemia: The Path to Least Resistance

The identification of recurrent driver mutations in genes encoding tyrosine kinases has resulted in the development of molecularly-targeted treatment strategies designed to improve outcomes for patients diagnosed with acute myeloid leukemia (AML). The receptor tyrosine kinase FLT3 is the most commonly mutated gene in AML, with internal tandem duplications within the juxtamembrane domain (FLT3-ITD) or missense mutations in the tyrosine kinase domain (FLT3-TKD) present in 30–35% of AML patients at diagnosis. An established driver mutation and marker of poor prognosis, the FLT3 tyrosine kinase has emerged as an attractive therapeutic target, and thus, encouraged the development of FLT3 tyrosine kinase inhibitors (TKIs). However, the therapeutic benefit of FLT3 inhibition, particularly as a monotherapy, frequently results in the development of treatment resistance and disease relapse. Commonly, FLT3 inhibitor resistance occurs by the emergence of secondary lesions in the FLT3 gene, particularly in the second tyrosine kinase domain (TKD) at residue Asp835 (D835) to form a ‘dual mutation’ (ITD-D835). Individual FLT3-ITD and FLT3-TKD mutations influence independent signaling cascades; however, little is known about which divergent signaling pathways are controlled by each of the FLT3 specific mutations, particularly in the context of patients harboring dual ITD-D835 mutations. This review provides a comprehensive analysis of the known discrete and cooperative signaling pathways deregulated by each of the FLT3 specific mutations, as well as the therapeutic approaches that hold the most promise of more durable and personalized therapeutic approaches to improve treatments of FLT3 mutant AML.

Prospective Isolation and Characterization of Genetically and Functionally Distinct AML Subclones

Intra-tumor heterogeneity caused by clonal evolution is a major problem in cancer treatment. To address this problem, we performed label-free quantitative proteomics on primary acute myeloid leukemia (AML) samples. We identified 50 leukemia-enriched plasma membrane proteins enabling the prospective isolation of genetically distinct subclones from individual AML patients. Subclones differed in their regulatory phenotype, drug sensitivity, growth, and engraftment behavior, as determined by RNA sequencing, DNase I hypersensitive site mapping, transcription factor occupancy analysis, in vitro culture, and xenograft transplantation. Finally, we show that these markers can be used to identify and longitudinally track distinct leukemic clones in patients in routine diagnostics. Our study describes a strategy for a major improvement in stratifying cancer diagnosis and treatment.