Stability Assessment of Fresh or Cryopreserved Whole Blood and Bone Marrow Samples from AML and B-ALL Patients to Monitor CD123 Receptor and Immune Cells Subsets

Introduction: Compounds targeting CD123 are currently under clinical development for the treatment of acute myeloid leukemia (AML) and high-risk myelodysplastic syndrome (MDS). As part of clinical trials, CD123 expression and immune cell subsets need be monitored by quantitative flow cytometry (qFC) in bone marrow (BM) aspirates and whole blood (WB) samples before and on-treatment.

One critical parameter for analysis is the poor stability of the fresh biological BM or WB samples.

No general rule can predict the stability of the expression of a given receptor on diseased or healthy cells thus the pre-analytical stability of each biomarker should be evaluated to design the sample logistics. The pre analytical stability of clinical samples is the main constraint for quantitative flow cytometry (qFC) in multicenter and worldwide clinical studies. The transportation of the samples is one of the limiting factor. The classical freezing method of peripherical whole blood (WB) or bone marrow (BM) isolated by Ficoll requires high skilled operators, is time consuming and may be difficult to set up at sampling site in hospitals. One option to make the clinical samples suitable for subsequent high dimensional analysis by qFC is to use a simple freezing method at -80°C. Our cryopreservation method could be a new option for easier preparation of clinical samples prior to centralized samples analysis.

This study aims to evaluate the pre-analytical fresh or cryopreserved stability of each pharmacodynamic monitoring endpoint over time: CD123 expression and receptor density, T-cell subsets and activation profile.

Methods: FreshBM and WB were collected in EDTA tubes from 5 AML/MDS patients at hospitals, in accordance with local regulations. The samples were stored at room temperature (RT) for 4, 24, 48 or 72 h before immunostaining with the standard operation procedures and analysis by qFC or mixed with the cryopreserved media (BioCytex) within 24 h post-collection before freezing at -80°C for months. After storage, the cryopreserved samples were thawed and immunostained before analysis by qFC.

Using a qFC assay (Multiplex FC panel assay developed by BioCytex, Marseille, France), CD123 receptor density/cell was collected. T-cell and blast cell immunophenotypes were also assessed on fresh samples for time point 4, 24, 48, or 72 h post-collection but also for cryopreserved WB sample within the 24hs post collection. The assay profiled blasts, monocytes, plasmacytoid dendritic cells, basophils and T-cells.

Results: CD123 density in blast and normal cells was stable at RT from 4 h up to 48 h after collection. The profiles of blast subsets were very similar in BM and WB samples from a particular patient, whether a single blast cell subset (CD45lowCD11b-CD34+CD38med) or several blast cell subsets (expressing CD34 and CD38 at different levels) were identified. Both T-cell distribution and activation markers were stable up to 48 h for BM and WB. A similar pattern of T-cell subsets was also observed in the BM and WB paired samples from the same donor. In addition, CD123 receptor density, immunophenotyping and percentage of blast subsets and T cells from fresh WB samples was comparable to paired cryopreserved samples with a new method and for at least 1 month.

Conclusions: Based on these observations, we conclude that CD123 density, blast cells and T-cell subsets in WB and BM samples from AML patients were stable for 48 h in our experimental conditions. As a consequence, fresh WB and BM samples can be processed and analyzed by qFC within 48 h of sample collection. Furthermore, the new cryopreservation method showed sample stabilization for blasts and T cells immunophenotyping. This data opens new perspectives in clinical studies for AML This new strategy would also help to standardize preparation of clinical samples and to centralize sample analysis.