Inter-laboratory validation of a harmonized PNH flow cytometry assay

The flow cytometry myeloid progenitor count: A reproducible parameter for diagnosis and prognosis of myelodysplastic syndromes

BACKGROUND

The bone marrow blast count is central to the diagnosis and monitoring of myelodysplastic syndromes (MDS). It is an independent risk factor for worse prognosis whether based on the morphology blast count or the flow cytometry (FC) myeloid progenitor (MyP) count. It is a principal population in FC MDS analysis also because once defined; it provides significant contributions to the overall FC MDS score.

METHODS

We elected to investigate inter-analyst agreement for the most fundamental parameter of the FC MDS diagnostic score: the MyP count. A common gating strategy was agreed and used by seven cytometrists for blind analysis of 34 routine bone marrows sent for MDS work-up. Additionally, we compared the results with a computational approach.

RESULTS

Concordance was excellent: Intraclass correlation was 0.993 whether measuring %MyP of total cells or CD45+ cells, and no significant difference was observed between files from different centers or for samples with abnormal MyP phenotypes. Computational and manual results were similar. Applying the common strategy to individual laboratories' control cohorts produced similar MyP reference ranges across centers.

CONCLUSION

The FC MyP count offers a reliable diagnostic and prognostic measurement in MDS. The use of manual and computational approaches side by side may allow for optimizing both strategies. Considering its known prognostic power, the MyP count could be considered a useful and reliable addition to existing prognostic scoring systems.

Methodological and conceptual challenges to the flow cytometric classification of leukemic lymphoproliferative disorders

The diagnosis of leukemic B-cell lymphoproliferative disorders (B-LPDs) is made by integrating clinical, cytological, cytometric, cytogenetic, and molecular data. This leaves room for differences and inconsistencies between experts. In this study, we examine methodological and conceptual aspects of the flow cytometric classification of leukemic B-LPDs that could explain them. Among methodological aspects, we discuss (1) the different statistical tests used to select and evaluate markers, (2) how these markers are analyzed, (3) how scores are interpreted, (4) different degrees to which diagnostic information is used, and (5) and the impact of differences in study populations. Among conceptual aspects, we discuss (1) challenges to integrating different biological data points, (2) the under examination of the costs of misclassification (false positives and false negatives), and finally, (3) we delve into the impact of the lack of a true diagnostic gold standard and the indirect evidence suggesting poor reproducibility in the diagnosis of leukemic B-LPDs. We then outline current harmonization efforts and our personal approach. We conclude that numerous flow cytometry scores and diagnostic systems are now available; however, as long as the considerations discussed remain unaddressed, external reproducibility and interobserver agreement will not be achieved, and the field will not be able to move forward if a true gold standard is not found.

Detection of CAR-T19 cells in peripheral blood and cerebrospinal fluid: An assay applicable to routine diagnostic laboratories

BACKGROUND

Chimeric antigen receptor-modified T-cells targeting CD19 (CAR-T19) are licensed for treating relapsed/refractory diffuse large B-cell lymphoma and B-acute lymphoblastic leukemia. Predicting treatment responses and toxicity (e.g., cytokine release syndrome and neurotoxicity) remains a big challenge. CAR-T19 monitoring could increase our understanding of treatment responses and be of relevance to patient management. A robust method for accurate CAR-T19 detection is therefore extremely desirable.

METHODS

An assay that uses fluorochrome-conjugated human recombinant soluble CD19 was tested against two commercially available CAR-T19 therapies and a CAR-T19 cell line developed in-house. Precision, concordance, and analyte stability were tested using peripheral blood obtained from CAR-T19-treated patients and controls.

RESULTS

The assay showed good accuracy, and had a limit of blank for whole blood samples of 0.13%. Reproducibility and inter-operator concordance were satisfactory (CVs <15%). The assay distinguished CAR-T19 from reactive T-cells in cerebrospinal fluid (CSF) from patients with suspected immune effector cell-associated neurotoxicity syndrome (ICANS), and was adapted to study memory T-cell compartments in treated patients.

CONCLUSION

The assay enabled routine monitoring of CAR-T19 in blood and CSF samples. Despite profound cytopenia in many lymphoma patients, results were obtained regularly from only 4 ml of blood. The assay can be adapted easily to characterize the memory and exhaustion status of CAR-T19 and native T-cells. Importantly, it does not rely on CAR construct specificity; thus, it can be used to detect any CD19-targeted CAR cell. Finally, our validation process can serve as a blueprint for other fluorochrome proteins used to detect CAR cells.