Flow cytometric assessment for minimal/measurable residual disease in B lymphoblastic leukemia/lymphoma in the era of immunotherapy

Flow Cytometric Assessment of Malignant Hematologic Disorders

Multiparameter flow cytometry (MPF) is an essential component of the diagnostic workup of hematologic malignancies. Recently developed tools have expanded the utility of MPF in detecting T-cell clonality and myelomonocytic dysplasia. Minimal/measurable residual disease analysis has long been established as critical in the management of B-lymphoblastic leukemia and is emerging as a useful tool in myeloid malignancies. With the continued increased complexity of MPF assays, emerging tools for data collection and analysis will allow users to take full advantage of MPF in the diagnosis of hematologic disease.

Deciphering stage 0 hematogones by flow cytometry in follow-up bone marrow samples of pediatric B-Acute lymphoblastic leukemia cases: A potential mimicker of residual disease after anti CD19 therapy

CD19 is frequently targeted for immunotherapy in B cell malignancies, which may result in loss of CD19 expression in leukemic cells as an escape mechanism. Stage 0 hematogones (Hgs) are normal CD19-negative very early B cell precursors that can be potentially mistaken for CD19 negative residual leukemic cells by flow cytometry (FCM) in B cell acute lymphoblastic leukemia (BCP-ALL) cases treated with anti CD19 therapy. Our main objective was to characterize and study the incidence of stage 0 hematogones in follow-up bone marrow samples of pediatric BCP-ALL cases. We analyzed the flow cytometry standard files of 61 pediatric BCP-ALL cases treated with conventional chemotherapy and targeted anti-CD19 therapy, for identifying the residual disease and normal B cell precursors including stage 0 Hgs. A non-CD19 alternate gating strategy was used to isolate the B cells for detecting the residual disease and stage 0 Hgs. The stage 0 Hgs were seen in 95% of marrow samples containing CD19+ Hgs. When compared with controls and posttransplant marrow samples, the fraction of stage 0 Hgs was higher in patients receiving anti CD19 therapy (p = 0.0048), but it was not significant when compared with patients receiving chemotherapy (p = 0.1788). Isolated stage 0 Hgs are found in samples treated with anti-CD19 therapy simulating CD19 negative residual illness. Our findings aid in understanding the stage 0 Hgs and its association with CD19+ Hgs in anti CD19 therapy and conventional chemotherapy. This is crucial as it can be potentially mistaken for residual disease in patients treated with anti CD19 therapy.

15-color highly sensitive flow cytometry assay for post anti-CD19 targeted therapy (anti-CD19-CAR-T and blinatumomab) measurable residual disease assessment in B-lymphoblastic leukemia/lymphoma: Real-world applicability and challenges

OBJECTIVES

Measurable residual disease (MRD) is the most relevant predictor of disease-free survival in B-cell acute lymphoblastic leukemia (B-ALL). We aimed to establish a highly sensitive flow cytometry (MFC)-based B-ALL-MRD (BMRD) assay for patients receiving anti-CD19 immunotherapy with an alternate gating approach and to document the prevalence and immunophenotype of recurrently occurring low-level mimics and confounding populations.

METHODS

We standardized a 15-color highly-sensitive BMRD assay with an alternate CD19-free gating approach. The study included 137 MRD samples from 43 relapsed/refractory B-ALL patients considered for anti-CD19 immunotherapy.

RESULTS

The 15-color BMRD assay with CD22/CD24/CD81/CD33-based gating approach was routinely applicable in 137 BM samples and could achieve a sensitivity of 0.0005%. MRD was detected in 29.9% (41/137) samples with 31.7% (13/41) of them showing <.01% MRD. Recurrently occurring low-level cells that showed immunophenotypic overlap with leukemic B-blasts included: (a) CD19+CD10+CD34+CD22+CD24+CD81+CD123+CD304+ plasmacytoid dendritic cells, (b) CD73bright/CD304bright/CD81bright mesenchymal stromal/stem cells (CD10+) and endothelial cells (CD34+CD24+), (c) CD22dim/CD34+/CD38dim/CD81dim/CD19-/CD10-/CD24- early lymphoid progenitor/precursor type-1 cells (ELP-1) and (d) CD22+/CD34+/CD10heterogeneous/CD38moderate/CD81moderate/CD19-/CD24- stage-0 B-cell precursors or ELP-2 cells.

CONCLUSIONS

We standardized a highly sensitive 15-color BMRD assay with a non-CD19-based gating strategy for patients receiving anti-CD19 immunotherapy. We also described the immunophenotypes of recurrently occurring low-level populations that can be misinterpreted as MRD in real-world practice.

Resolving 31 colors on a standard 3-laser full spectrum flow cytometer for immune monitoring of human blood samples

Immune monitoring of patients on a single-cell level is becoming increasingly important in various diseases. Due to the often very limited availability of human specimens and our increased understanding of the immune systems there is an increasing demand to analyze as many markers as possible simultaneously in one panel. Full spectrum flow cytometry is emerging as a powerful tool for immune monitoring since 5-laser instruments enable characterization of 40 parameters or more in a single sample. Nevertheless, even if only machines with fewer lasers are available, development of novel fluorophore families enables increasing panel sizes. Here, we demonstrate that careful panel design enables the use of 31-color panels on a 3-laser Cytek® Aurora cytometer for analyzing human peripheral blood leukocytes, without the need for custom configuration and using only commercially available fluorochromes. The panel presented here should serve as an example of a 31-fluorochrome combination that can be resolved on a 3-laser full spectrum cytometer and that can be adapted to comprise other (and possibly more) markers of interest depending on the research focus.