Significance of CD34/CD123 expression in detection of minimal residual disease in B-ACUTE lymphoblastic leukemia in children

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.

Evaluation of fixed-panel, multicolour ClearLLab 10C at an academic flow cytometry laboratory in Johannesburg, South Africa

Background

Flow cytometric immunophenotyping is well established for the diagnosis of haematological neoplasms. New commercially available systems offer fixed, pre-aliquoted multi-parameter analysis to simplify sample preparation and standardise data analysis.

Objective

The Beckman Coulter (BC) ClearLLab™ 10C (4-tube) system was evaluated against an existing laboratory developed test (LDT).

Methods

Peripheral blood and bone marrow aspirates (n = 101), tested between August 2019 and November 2019 at an academic pathology laboratory in Johannesburg, South Africa, were analysed. Following daily instrument quality control, samples were prepared for LDT (using > 20 2–4-colour in-house panels and an extensive liquid monoclonal reagent repertoire) or ClearLLab 10C, and respectively analysed using in-house protocols on a Becton Dickinson FACSCalibur, or manufacturer-directed protocols on a BC Navios. Becton Dickinson Paint-a-Gate or BC Kaluza C software facilitated data interpretation. Diagnostic accuracy (concordance) was established by calculating sensitivity and specificity outcomes.

Results

Excellent agreement (clinical diagnostic concordance) with 100% specificity and sensitivity was established between LDT and ClearLLab 10C in 67 patients with a haematological neoplasm and 34 participants with no haematological disease. Similar acceptable diagnostic concordance (97%) was noted when comparing ClearLLab 10C to clinicopathological outcomes. Additionally, the ClearLLab 10C panels, analysed with Kaluza C software, enabled simultaneous discrimination of disease and concurrent background myeloid and lymphoid haematological populations, including assessing stages of maturation or sub-populations.

Conclusion

ClearLLab 10C panels provide excellent agreement to existing LDTs and may reliably be used for immunophenotyping of haematological neoplasms, simplifying and standardising sample preparation and data acquisition.

CD123: A Novel Biomarker for Diagnosis and Treatment of Leukemia

Leukemia is a group of progressive hematologic malignancies derived from stem cells in bone marrow which causes a large number of cancer deaths. Even with treatment such as traditional chemotherapy, targeted therapy, and allogeneic stem cell transplantation (allo-HSCT), many patients suffer from relapse/refractory disease, and the overall survival is dismal. Leukemic stem cells (LSCs) are induced by gene mutations and undergo an aberrant and poorly regulated proliferation process which is involved in the evolution, relapse, and drug-resistance of leukemia. Emerging studies demonstrate that CD123, the interleukin 3 receptor alpha (IL-3Rα), is highly expressed in LSCs, while not normal hematopoietic stem cells (HSCs), and associates with treatment response, minimal residual disease (MRD) detection and prognosis. Furthermore, CD123 is an important marker for the identification and targeting of LSCs for refractory or relapsed leukemia. Anti-CD123 target-therapies in pre-clinical studies and clinical trials confirm the utility of anti-CD123 neutralizing antibody-drugs, CD3×CD123 bispecific antibodies, dual-affinity retargeting (DART), and anti-CD123 chimeric antigen receptor-modified T-cell (CAR-T) therapies in progress. This review summarizes the most recent progress on the study of CD123 biology and the development of novel CD123-targeted therapies.

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

INTRODUCTION

CD123 is overexpressed in many hematologic malignancies and found to be useful in characterizing leukemic blasts of both acute myeloid leukemia (AML) and B-acute lymphoblastic leukemia (B-ALL). CD123 has been recently found to be a marker of leukemic stem cells, and its utility to measure residual disease and potential role in disease relapse is under evaluation.

MATERIALS AND METHODS

Herein, we have evaluated the expression of CD123 in 757 samples of acute leukemia including 479 treatment-naive and 278 follow-up samples and compared with post-induction morphologic complete remission and measurable residual disease (MRD) status. Multiparametric flow cytometry was used for assessment of CD123 expression and immunophenotypic characterization of leukemic blasts at diagnostic and MRD assessment time points.

RESULTS

Using variable cutoffs of 5%, 10%, and 20% to define a case as CD123-positive, expression of CD123 was observed in 75.6%, 66.2%, and 50% of AML and 88.6%, 81.8%, and 75% of B-ALL, respectively. Of 11 patients, 7 (63.63%) had mixed phenotype acute leukemia, but none of the 12 patients with T-acute lymphoblastic leukemia showed positivity for CD123. CD123 expression at diagnosis was associated with post-induction MRD-positive status in both B-ALL (P < .001) and AML (P = .001). We also evaluated the utility of CD123 as a leukemia-associated aberrant immunophenotype and found it to be useful in both patients with AML (baseline, 50.6%; follow-up, 53%) and B-ALL (baseline, 75%; follow-up, 73.07%).

CONCLUSIONS

In conclusion, CD123 may be considered as a cardinal marker for residual disease assessment and response evaluation in AML and B-ALL.

Isolation and characterization of a CD34+ sub-clone in B-cell lymphoma

Non-Hodgkin's lymphoma (NHL) is the most common hematological malignancy in the US. Many types remain incurable despite response to initial therapy and achievement of complete remission (CR). Advanced laboratory techniques like multicolor flow cytometry (FCM) and polymerase chain reaction (PCR) have demonstrated persistence of rare malignant cell population post therapy. However, the functional and biological characteristics of this population have not been elucidated. Established B-lymphoma cell lines (B-NHL) and patient-derived samples (PDS) were analyzed using 8-color FCM. CD34+ sub-population was enriched using in vitro exposure to 2-chlorodeoxyadenosine (2-CdA) and by CD34 magnetic beads. Genetic analysis of cell fractions was done by karyotyping and array comparative genomic hybridization (aCGH). Sensitivity to chemotherapy was assayed by short-term in vitro exposure to chemotherapy. Clonogenicity was determined by soft agar colony formation assay, and proliferation was determined using DNA staining with propidium iodide and FCM. FCM demonstrated the presence of a minute sub-clone of monotypic B-cells that express CD34 in B-NHL cell lines (3 of 3) and in PDS (8 of 8). This sub-population enriched up to 50 fold in vitro by exposure to 2-CdA and up to 80% purity by CD34 magnetic bead column isolation. Except for CD34 expression, this population expressed identical phenotype and genotype to parent cells, but was more proliferative, Hoechst 33342-positive, clonogenic, and resistant to chemotherapy compared with the CD34- population. The isolated CD34+ monotypic B-cells may contribute to resistance of certain NHL to treatment and should be targeted by potential new drugs for NHL.

Flow Cytometric Minimal Residual Disease Analysis in Acute Leukemia: Current Status

Minimal residual disease (MRD) analysis for patients of acute leukemia has evolved as a significant prognostic factor. Based on the MRD results, the cases are risk-stratified after induction chemotherapy, and an alteration in further management is made to yield maximal therapeutic benefits. The two primary methodologies for MRD detection are multi-parameter flow cytometry (MFC) and polymerase chain reaction. MFC identifies the MRD based on characteristic 'leukemia-associated immunophenotypes' on the residual leukemia cells. MRD analysis by MFC is most frequently done at the post-induction stage of treatment and often can achieve a sensitivity of detecting one leukemic cell in 10,000 normal cells, or even higher at times. This review outlines the technical aspects and provides inputs on standard antibody panels used for MRD detection in B-, T-lineage acute lymphoblastic leukemias, and acute myeloid leukemia.