A Real-world Perspective of CD123 Expression in Acute Leukemia as Promising Biomarker to Predict Treatment Outcome in B-ALL and AML

Intricate relationship between cancer stemness, metastasis, and drug resistance

Cancer stem cells (CSCs) are widely acknowledged as the drivers of tumor initiation, epithelial-mesenchymal transition (EMT) progression, and metastasis. Originating from both hematologic and solid malignancies, CSCs exhibit quiescence, pluripotency, and self-renewal akin to normal stem cells, thus orchestrating tumor heterogeneity and growth. Through a dynamic interplay with the tumor microenvironment (TME) and intricate signaling cascades, CSCs undergo transitions from differentiated cancer cells, culminating in therapy resistance and disease recurrence. This review undertakes an in-depth analysis of the multifaceted mechanisms underlying cancer stemness and CSC-mediated resistance to therapy. Intrinsic factors encompassing the TME, hypoxic conditions, and oxidative stress, alongside extrinsic processes such as drug efflux mechanisms, collectively contribute to therapeutic resistance. An exploration into key signaling pathways, including JAK/STAT, WNT, NOTCH, and HEDGEHOG, sheds light on their pivotal roles in sustaining CSCs phenotypes. Insights gleaned from preclinical and clinical studies hold promise in refining drug discovery efforts and optimizing therapeutic interventions, especially chimeric antigen receptor (CAR)-T cell therapy, cytokine-induced killer (CIK) cell therapy, natural killer (NK) cell-mediated CSC-targeting and others. Ultimately use of cell sorting and single cell sequencing approaches for elucidating the fundamental characteristics and resistance mechanisms inherent in CSCs will enhance our comprehension of CSC and intratumor heterogeneity, which ultimately would inform about tailored and personalized interventions.

Site-discordant expression of myeloid cell nuclear differentiation antigen in blastic plasmacytoid dendritic cell neoplasm

OBJECTIVES

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematologic neoplasm that can show clinical, morphologic, and immunophenotypic overlap with acute myeloid leukemia. Myeloid cell nuclear differentiation antigen (MNDA) is a nuclear protein expressed by myelomonocytic cells previously reported to be reliably absent in BPDCN and proposed as a useful adjunct for the distinction of BPDCN and acute myeloid leukemia. We encountered a case of BPDCN that showed strong nuclear expression of MNDA in bone marrow and breast samples and weak to absent expression in skin samples, prompting us to reevaluate the expression of MNDA in BPDCN.

METHODS

We collected all available BPDCN cases from the Stanford University archives collected in the past 10 years and subjected them to MNDA immunohistochemistry. In select cases, molecular profiling by next-generation sequencing was performed.

RESULTS

We found 4 cases (of 8 total examined [50%]) with convincing site-discordant MNDA expression. This expression was seen in 3 of 6 (50%) bone marrow samples, 1 of 2 (50%) breast soft tissue samples, and 3 of 14 (up to 21%) skin samples and was not obviously predicted by age, sex, history of myeloid neoplasm, or treatment history. In 2 cases, MNDA was strongly expressed in 2 distinct sites (breast/bone marrow, skin/bone marrow) and negative in subsequent samples.

CONCLUSIONS

Our findings suggest that MNDA expression in BPDCN is anatomic site dependent and transient, with noncutaneous infiltrates showing more frequent expression than cutaneous infiltrates. These results caution against the use of MNDA to exclude BPDCN when considering the differential diagnosis of a blastic extramedullary infiltrate.

Advances in the pathogenesis of FLT3-mutated acute myeloid leukemia and targeted treatments

PURPOSE OF REVIEW

FLT3 mutations are among the most common myeloid drivers identified in adult acute myeloid leukemia (AML). Their identification is crucial for the precise risk assessment because of the strong prognostic significance of the most recurrent type of FLT3 alterations, namely internal tandem duplications (ITDs). Recent advances in the pathogenesis and biology of FLT3-mutated AML have opened an opportunity for development and application of selective inhibition of FLT3 pathway.

RECENT FINDINGS

In the last decade, at least three targeted treatments have been approved by regulatory agencies and several others are currently under investigations. Here, we review the latest advance in the role of FLT3 mutations in AML, providing an outline of the available therapeutic strategies, their mechanisms of actions and of resistance, as well as routes for potential improvement.

SUMMARY

The availability of FLT3 inhibitors has improved outcomes in AML harboring such mutations, currently also reflected in disease stratification and recommendations. Newer inhibitors are under investigations, and combinations with chemotherapy or other targeted treatments are being explored to further improve disease outcomes.

Immunophenotypic characterization of leukemic stem cells in acute myeloid leukemia using single tube 10-colour panel by multiparametric flow cytometry: Deciphering the spectrum, complexity and immunophenotypic heterogeneity

INTRODUCTION

Despite extensive research, comprehensive characterization of leukaemic stem cells (LSC) and information on their immunophenotypic differences from normal haematopoietic stem cells (HSC) is lacking. Herein, we attempted to unravel the immunophenotypic (IPT) characteristics and heterogeneity of LSC using multiparametric flow cytometry (MFC) and single-cell sequencing.

MATERIALS AND METHODS

Bone marrow aspirate samples from patients with acute myeloid leukaemia (AML) were evaluated using MFC at diagnostic and post induction time points using a single tube-10-colour-panel containing LSC-associated antibodies CD123, CD45RA, CD44, CD33 and COMPOSITE (CLL-1, TIM-3, CD25, CD11b, CD22, CD7, CD56) with backbone markers that is, CD45, CD34, CD38, CD117, sCD3. Single-cell sequencing of the whole transcriptome was also done in a bone marrow sample.

RESULTS

LSCs and HSCs were identified in 225/255 (88.2%) and 183/255 (71.6%) samples, respectively. Significantly higher expression was noted for COMPOSITE, CD45RA, CD123, CD33, and CD44 in LSCs than HSCs (p < 0.0001). On comparing the LSC specific antigen expressions between CD34+ (n = 184) and CD34- LSCs (n = 41), no difference was observed between the groups. More than one sub-population of LSC was demonstrated in 4.4% of cases, which further revealed high concordance between MFC and single cell transcriptomic analysis in one of the cases displaying three LSC subpopulations by both methods.

CONCLUSION

A single tube-10-colour MFC panel is proposed as an easy and reproducible tool to identify and discriminate LSCs from HSCs. LSCs display both inter- and intra-sample heterogeneity in terms of antigen expressions, which opens the facets for single cell molecular analysis to elucidate the role of subpopulations of LSCs in AML progression.

[Clinical characteristics and prognosis of childhood acute lymphoblastic leukemia with CD123 expression]

OBJECTIVES

To investigate the expression of CD123 in children with acute lymphoblastic leukemia (ALL) and its effect on the clinical characteristics and prognosis of children with B-lineage acute lymphoblastic leukemia (B-ALL).

METHODS

A retrospective analysis was conducted on the clinical data of 251 children with ALL who were admitted to the Department of Hematology and Oncology, Children's Hospital of Kunming Medical University, from December 2019 to June 2022. According to the expression of CD123 at initial diagnosis, the children were divided into CD123+ group and CD123- group, and the two groups were compared in terms of clinical characteristics and treatment outcome. The factors influencing the prognosis were analyzed.

RESULTS

Among the 251 children with ALL, there were 146 children (58.2%) in the CD123+ group. The B-ALL group had a significantly higher positive expression rate of CD123 than the acute T lymphocyte leukemia group (P<0.05). Compared with the CD123- group, the CD123+ group had significantly lower peripheral blood leukocyte count and percentage of juvenile cells and a significantly higher proportion of children with high hyperdiploid karyotype or an age of 1-10 years, with a relatively low proportion of children with E2A-PBX1 fusion gene (P<0.05). The multivariate Cox proportional-hazards regression model analysis showed that compared with the >10 years group, the 1-10 years group had a significantly higher overall survival rate (P<0.05), and compared with the high risk group, the moderate risk group had a significantly higher event-free survival rate in children with B-ALL (P<0.05).

CONCLUSIONS

CD123 is widely expressed in children with B-ALL, and positive expression of CD123 might be an indicator for good prognosis in children with B-ALL, which is of great significance for evaluating the efficacy of remission induction therapy and survival prognosis of children with B-ALL.

Overcoming the challenges of primary resistance and relapse after CAR-T cell therapy

INTRODUCTION

While CAR T-cell therapy has led to remarkable responses in relapsed B-cell hematologic malignancies, only 50% of patients ultimately have a complete, sustained response. Understanding the mechanisms of resistance and relapse after CAR T-cell therapy is crucial to future development and improving outcomes.

AREAS COVERED

We review reasons for both primary resistance and relapse after CAR T-cell therapies. Reasons for primary failure include CAR T-cell manufacturing problems, suboptimal fitness of autologous T-cells themselves, and intrinsic features of the underlying cancer and tumor microenvironment. Relapse after initial response to CAR T-cell therapy may be antigen-positive, due to CAR T-cell exhaustion or limited persistence, or antigen-negative, due to antigen-modulation on the target cells. Finally, we discuss ongoing efforts to overcome resistance to CAR T-cell therapy with enhanced CAR constructs, manufacturing methods, alternate cell types, combinatorial strategies, and optimization of both pre-infusion conditioning regimens and post-infusion consolidative strategies.

EXPERT OPINION

There is a continued need for novel approaches to CAR T-cell therapy for both hematologic and solid malignancies to obtain sustained remissions. Opportunities for improvement include development of new targets, optimally combining existing CAR T-cell therapies, and defining the role for adjunctive immune modulators and stem cell transplant in enhancing long-term survival.

The Evolving Landscape of Flowcytometric Minimal Residual Disease Monitoring in B-Cell Precursor Acute Lymphoblastic Leukemia

Detection of minimal residual disease (MRD) is a major independent prognostic marker in the clinical management of pediatric and adult B-cell precursor Acute Lymphoblastic Leukemia (BCP-ALL), and risk stratification nowadays heavily relies on MRD diagnostics. MRD can be detected using flow cytometry based on aberrant expression of markers (antigens) during malignant B-cell maturation. Recent advances highlight the significance of novel markers (e.g., CD58, CD81, CD304, CD73, CD66c, and CD123), improving MRD identification. Second and next-generation flow cytometry, such as the EuroFlow consortium's eight-color protocol, can achieve sensitivities down to 10-5 (comparable with the PCR-based method) if sufficient cells are acquired. The introduction of targeted therapies (especially those targeting CD19, such as blinatumomab or CAR-T19) introduces several challenges for flow cytometric MRD analysis, such as the occurrence of CD19-negative relapses. Therefore, innovative flow cytometry panels, including alternative B-cell markers (e.g., CD22 and CD24), have been designed. (Semi-)automated MRD assessment, employing machine learning algorithms and clustering tools, shows promise but does not yet allow robust and sensitive automated analysis of MRD. Future directions involve integrating artificial intelligence, further automation, and exploring multicolor spectral flow cytometry to standardize MRD assessment and enhance diagnostic and prognostic robustness of MRD diagnostics in BCP-ALL.

EP300-ZNF384 transactivates IL3RA to promote the progression of B-cell acute lymphoblastic leukemia

The EP300-ZNF384 fusion gene is an oncogenic driver in B-cell acute lymphoblastic leukemia (B-ALL). In the present study, we demonstrated that EP300-ZNF384 substantially induces the transcription of IL3RA and the expression of IL3Rα (CD123) on B-ALL cell membranes. Interleukin 3 (IL-3) supplementation promotes the proliferation of EP300-ZNF348-positive B-ALL cells by activating STAT5. Conditional knockdown of IL3RA in EP300-ZF384-positive cells inhibited the proliferation in vitro, and induced a significant increase in overall survival of mice, which is attributed to impaired propagation ability of leukemia cells. Mechanistically, the EP300-ZNF384 fusion protein transactivates the promoter activity of IL3RA by binding to an A-rich sequence localized at -222/-234 of IL3RA. Furthermore, forced EP300-ZNF384 expression induces the expression of IL3Rα on cell membranes and the secretion of IL-3 in CD19-positive B precursor cells derived from healthy individuals. Doxorubicin displayed a selective killing of EP300-ZNF384-positive B-ALL cells in vitro and in vivo. Collectively, we identify IL3RA as a direct downstream target of EP300-ZNF384, suggesting CD123 is a potent biomarker for EP300-ZNF384-driven B-ALL. Targeting CD123 may be a novel therapeutic approach to EP300-ZNF384-positive patients, alternative or, more likely, complementary to standard chemotherapy regimen in clinical setting.

Minimal Residual Disease in the Management of B-Cell Acute Lymphoblastic Leukemia: A Systematic Review of Studies from Indian Settings

Minimal residual disease (MRD) has become an essential tool in the management of B-cell acute lymphoblastic leukemia (B-ALL) and aids in tailoring treatment strategies to suit specific patient needs. Although much progress has been made in this area, there is limited data on the use of MRD in the Indian context. Our objective was to identify relevant literature that discusses the utility of MRD in the management of B-cell ALL in adolescents and young adults (AYA) and adults in Indian settings. A systematic search and screening of articles were performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The primary data source was PubMed followed by Google Scholar for articles and conference proceedings. Of the 254 records screened, 24 records were retained for analysis. MRD monitoring had a significant role in the management of AYA/adult B-cell ALL patients. Variability of results was observed across these studies with respect to methods, techniques, and use. However, these studies evidenced and validated the importance of MRD assessment in risk-adapted management of B-cell ALL and highlighted the need for optimization. The advances in MRD diagnostics and applications are yet to be tested and adopted in Indian settings. Hence, there is a need for in-depth research to develop and optimize approaches for calibrating country-specific management strategies. The potential role of MRD assessments in anticipating relapse or treatment failures warrants more attention for the preemptive positioning of novel strategies involving immunotherapies.

Immunophenotypic portrait of leukemia-associated-phenotype markers in B acute lymphoblastic leukemia

BACKGROUND

Multiparametric flow cytometry (MFC) is an essential diagnostic tool in B acute lymphoblastic leukemia (B ALL) to determine the B-lineage affiliation of the blast population and to define their complete immunophenotypic profile. Most MFC strategies used in routine laboratories include leukemia-associated phenotype (LAP) markers, whose expression profiles can be difficult to interpret. The aim of our study was to reach a better understanding of 7 LAP markers' landscape in B ALL: CD9, CD21, CD66c, CD58, CD81, CD123, and NG2.

METHODS

Using a 10-color MFC approach, we evaluated the level of expression of 7 LAP markers including CD9, CD21, CD66c, CD58, CD81, CD123, and NG2, at the surface of normal peripheral blood leukocytes (n = 10 healthy donors), of normal precursor B regenerative cells (n = 40 uninvolved bone marrow samples) and of lymphoblasts (n = 100 peripheral blood samples or bone marrow samples from B ALL patients at diagnosis). The expression profile of B lymphoblasts was analyzed according the presence or absence of recurrent cytogenetic aberrations. The prognostic value of the 7 LAP markers was examined using Maxstat R algorithm.

RESULTS

In order to help the interpretation of the MFC data in routine laboratories, we first determined internal positive and negative populations among normal leukocytes for each of the seven evaluated LAP markers. Second, their profile of expression was evaluated in normal B cell differentiation in comparison with B lymphoblasts to establish a synopsis of their expression in normal hematogones. We then evaluated the frequency of expression of these LAP markers at the surface of B lymphoblasts at diagnosis of B ALL. CD9 was expressed in 60% of the cases, CD21 in only 3% of the cases, CD58 in 96% of the cases, CD66c in 45% of the cases, CD81 in 97% of the cases, CD123 in 72% of the cases, and NG2 in only 2% of the cases. We confirmed the interest of the CD81/CD58 MFI expression ratio as a way to discriminate hematogones from lymphoblasts. We observed a significant lower expression of CD9 and of CD81 at the surface of B lymphoblasts with a t(9;22)(BCR-ABL) in comparison with B lymphoblasts without any recurrent cytogenetic alteration (p = 0.0317 and p = 0.0011, respectively) and with B lymphoblasts harboring other cytogenetic recurrent abnormalities (p = 0.0032 and p < 0.0001, respectively). B lymphoblasts with t(1;19) at diagnosis significantly overexpressed CD81 when compared with B lymphoblasts with other recurrent cytogenetic abnormalities or without any recurrent alteration (p = 0.0001). An overexpression of CD58 was also observed in the cases harboring this abnormal cytogenetic event, when compared with B lymphoblasts with other recurrent cytogenetic abnormalities (p = 0.030), or without any recurrent alteration (p = 0.0002). In addition, a high expression of CD123, of CD58 and of CD81 was associated with a favorable prognosis in our cohort of pediatric and young adult B ALL patients. We finally built a risk score based on the expression of these 3 LAP markers, this scoring approach being able to split these patients into a high-risk group (17%) and a better outcome group (83%, p < 0.0001).

CONCLUSION

The complexity of the phenotypic signature of lymphoblasts at diagnosis of B ALL is illustrated by the variability in the expression of LAP antigens. Knowledge of the expression levels of these markers in normal leukocytes and during normal B differentiation is crucial for an optimal interpretation of diagnostic cytometry results and serves as a basis for the biological follow-up of B ALL.

Clinico-Hematological Profile of Acute Myeloid Leukemia: Experience From a Tertiary Care Cancer Center in North India

INTRODUCTION

Complete diagnosis of acute myeloid leukemia (AML) requires knowledge of clinical information combined with morphologic evaluation, immunophenotyping, karyotyping, and molecular genetic testing. The study intends to evaluate the demographic profile, clinical workup, and investigation, including flow cytometric immunophenotyping, in adult and pediatric age groups of AML.

MATERIALS AND METHODS

This is a retrospective study of AML patients treated between January 2017 and December 2021. Clinical and demographic characteristics and investigation findings were recorded from case files and the hematology database.

RESULT

A total of 896 cases of AML were registered during the given period, of which 819 cases were de-novo AML. Among those 819 cases, more than two-thirds of cases, i.e., 78.9% (N = 646), received induction chemotherapy. A significantly higher male-to-female ratio was observed (1.5:1). The median age was 22 years. The median time for diagnosis was three days and the median time for treatment intervention was four days. There were significant differences in the Eastern Cooperative Oncology Group (ECOG) performance status scores between pediatric and adult AML patients. Pediatric AML patients presented with better ECOG performance scores (ECOG performance scores 0 and 1) than adult patients (74.76% vs. 43.14%, p < 0.001). Further comparing adult vs. pediatric AML patients, normal karyotype (60.56% vs. 31.93%, p < 0.001) and NPM1 (22.25% vs. 6.72%, p < 0.001) and FLT3-ITD mutations (20.28% vs. 7.98%, p<0.001) were more common in the adult group, whereas AML-ETO (40.76% vs. 16.34%, p < 0.001) was more common in the pediatric group.

CONCLUSION

The study highlights the presenting age is lower than global figures. The median time for initial diagnosis and the start of treatment is within the acceptable norms. Normal karyotype and NPM1 and FLT3 mutations were common in adult AML patients, whereas AML-ETO was more common in the pediatric cohort. These findings will help plan prospective studies and see the correlation with treatment outcomes. The laboratory workup practice currently complies with the standard guidelines at our center.

Updates on lymphoblastic leukemia/lymphoma classification and minimal/measurable residual disease analysis

Lymphoblastic leukemia/lymphoma (ALL/LBL), especially certain subtypes, continues to confer morbidity and mortality despite significant therapeutic advances. The pathologic classification of ALL/LBL, especially that of B-ALL, has recently substantially expanded with the identification of several distinct and prognostically important genetic drivers. These discoveries are reflected in both current classification systems, the World Health Organization (WHO) 5th edition and the new International Consensus Classification (ICC). In this article, novel subtypes of B-ALL are reviewed, including DUX4, MEF2D and ZNF384-rearranged B-ALL; the rare pediatric entity B-ALL with TLF3::HLF, now added to the classifications, is discussed; updates to the category of B-ALL with BCR::ABL1-like features (Ph-like B-ALL) are summarized; and emerging genetic subtypes of T-ALL are presented. The second half of the article details current approaches to minimal/measurable residual disease (MRD) detection in B-ALL and T-ALL and presents anticipated challenges to current approaches in the burgeoning era of antigen-directed immunotherapy.

Comparison and Development of Immunohistochemical Diagnostic Criteria for Blastic Plasmacytoid Dendritic Cell Neoplasm

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematological malignancy derived from the precursors of plasmacytoid dendritic cells. Diagnostic criteria for BPDCN have not been fully established. BPDCN is often diagnosed without other BPDCN markers than the 3 conventional markers (CD4, CD56, and CD123) in practice and case reports, although acute myeloid leukemia/myeloid sarcoma (AML/MS), which is always considered in the differential diagnosis of BPDCN, can express them. We reviewed published case reports on BPDCN and found that the diagnosis was made without any other BPDCN markers than the conventional markers in two-thirds of the cases. Next, 4 representative existing diagnostic criteria were applied to 284 cases of our cohort of BPDCN and mimics. The results differed in 20% (56/284) of the cases. The criterion based on the 3 conventional markers alone had a low concordance rate (80%-82%) with the other 3 criteria, which were almost concordant with each other. However, newly found minor limitations in these criteria prompted us to devise new diagnostic criterion for BPDCN composed of TCF4, CD123, TCL1, and lysozyme. We also revealed that CD123-positive AML/MS patients had a significantly poorer outcome than those with BPDCN and that 12% (24/205) of the cases were non-BPDCN even if all 3 conventional markers were positive, thus clarifying the risk of diagnosing BPDCN without more specific markers. In addition, histopathological features, such as the reticular pattern, which is not seen in BPDCN and suggests AML/MS, were also identified.

CAR-T Cells Immunotherapies for the Treatment of Acute Myeloid Leukemia-Recent Advances

In order to increase the effectiveness of cancer therapies and extend the long-term survival of patients, more and more often, in addition to standard treatment, oncological patients receive also targeted therapy, i.e., CAR-T cells. These cells express a chimeric receptor (CAR) that specifically binds an antigen present on tumor cells, resulting in tumor cell lysis. The use of CAR-T cells in the therapy of relapsed and refractory B-type acute lymphoblastic leukemia (ALL) resulted in complete remission in many patients, which prompted researchers to conduct tests on the use of CAR-T cells in the treatment of other hematological malignancies, including acute myeloid leukemia (AML). AML is associated with a poorer prognosis compared to ALL due to a higher risk of relapse caused by the development of resistance to standard treatment. The 5-year relative survival rate in AML patients was estimated at 31.7%. The objective of the following review is to present the mechanism of action of CAR-T cells, and discuss the latest findings on the results of anti-CD33, -CD123, -FLT3 and -CLL-1 CAR-T cell therapy, the emerging challenges as well as the prospects for the future.

Leukemia Stem Cell Frequency at Diagnosis Correlates With Measurable/Minimal Residual Disease and Impacts Survival in Adult Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a heterogenous disease in which the initiation and maintenance of the malignant clone is blamed on a rare population of leukemia stem cells (LSCs). The persistence of such a malignant population is referred to as measurable/minimal residual disease (MRD). Evaluation of MRD is the gold standard for follow-up of therapy and constitutes an independent prognostic parameter. As LSCs are the main contributor to the persistence of MRD, then MRD should correlate with the bulk of LSCs at the individual case level. MRD is measured at defined time points during therapy. However, LSCs can be evaluated at diagnosis, which ensures the advantage of early prediction of high-risk patients and allows for early therapeutic decisions. Using two simple four-color monoclonal antibody combinations (CD38/CD123/CD34/CD45 and CD90/CD133/CD45/CD33) and the prism function of the Coulter Navios flow cytometer, the frequency of LSC subsets was evaluated in 84 newly diagnosed adult AML patients. For each panel, 16 possible combinations were detected. Our results showed that there was extreme variability in the percentage of the LSC fraction between different cases, as well as at the individual case level. For each LSC subset, the median value was used to divide cases into low and high expressors. LSC subsets that showed an impact on overall survival (OS) and disease-free survival (DFS) included CD123+, CD 123+/CD34-, CD34-/CD38+/CD123+, CD34+/CD38-/CD123+, CD133+, and CD133+/CD33-. On multivariate analysis, only CD123 (p ≤ 0.001, SE = 0.266, HR = 2.8, 95% CI = 1.74.7) and CD133+/CD33- (p = 0.017, SE = 0.263, HR = 1.9, 95% CI = 1.1–3.1) retained their significance for OS. Likewise, only CD34+/CD38-/CD123+ (p ≤ 0.001, HR 2.3, SE: 0.499, 95% CI: 2.4–17.4) and CD133 (p = 0.015, HR 2.3, SE 0.34, 95% CI: 1.2–4.4) retained their statistical significance for DFS. The LSC frequency at diagnosis showed a moderate to strong correlation with MRD status at day 14 and day 28. In conclusion, the level of LSCs at diagnosis correlated with MRD status at day 14 and day 28 in AML patients and had a deleterious impact on OS and DFS. It may be used as an early marker for high-risk patients allowing for early therapeutic decisions.

Evaluation of switch-mediated costimulation in trans on universal CAR-T cells (UniCAR) targeting CD123-positive AML

Chimeric antigen receptor T cells (CAR-T) targeting CD19 have achieved significant success in patients with B cell malignancies. To date, implementation of CAR-T in other indications remains challenging due to the lack of truly tumor-specific antigens as well as control of CAR-T activity in patients. CD123 is highly expressed in acute myeloid leukemia (AML) blasts including leukemia-initiating cells making it an attractive immunotherapeutic target. However, CD123 expression in normal hematopoietic progenitor cells and endothelia bears the risk of severe toxicities and may limit CAR-T applications lacking fine-tuned control mechanisms. Therefore, we recently developed a rapidly switchable universal CAR-T platform (UniCAR), in which CAR-T activity depends on the presence of a soluble adapter called targeting module (TM), and confirmed clinical proof-of-concept for targeting CD123 in AML with improved safety. As costimulation via 4–1BB ligand (4–1BBL) can enhance CAR-T expansion, persistence, and effector functions, a novel CD123-specific TM variant (TM123-4-1BBL) comprising trimeric single-chain 4–1BBL was developed for transient costimulation of UniCAR-T cells (UniCAR-T) at the leukemic site in trans. TM123-4-1BBL-directed UniCAR-T efficiently eradicated CD123-positive AML cells in vitro and in a CDX in vivo model. Moreover, additional costimulation via TM123-4-1BBL enabled enhanced expansion and persistence with a modulated UniCAR-T phenotype. In addition, the increased hydrodynamic volume of TM123-4-1BBL prolonged terminal plasma half-life and ensured a high total drug exposure in vivo. In conclusion, expanding the soluble adapter optionality for CD123-directed UniCAR-T maintains the platforms high anti-leukemic efficacy and immediate control mechanism for a flexible, safe, and individualized CAR-T therapy of AML patients.

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.