A Fully Automated Method for Isolating Highly Enriched Population of Multiple Myeloma Plasma Cell From Whole Bone Marrow for Enhanced Sensitivity in Downstream Assays

Abstract 5064

Introduction, Multiple myeloma (MM) is characterized by a huge clinical heterogeneity despite the homogenous morphologic appearance of malignant plasma cells (PCs). The advent of interphase fluorescence in situ hybridization (FISH) or MicroArrays (MA) allows an increased rate of aberration detection and identification of some recurrent cryptic changes, which have been increasingly implemented as additional diagnostic and prognostic factors. To heighten sensitivity of Single Nucleotide Polymorphism (SNP) arrays, or FISH it is necessary to have a purified population of cells as starting material. Screening must be performed systematically on the purified CD138+ PCs.

After testing different systems for cell purification, we encountered some challenges. We didn't obtain enough PCs for FISH and SNP array studies. This was due to excess M-protein accumulating in the blood stream, increasing hyper viscosity and also due to the morphology and size variations of PCs at various stages of differentiation. Additionally, downstream DNA extraction can be a challenge since EDTA found in most buffers is an inhibitor for chemical PCR reaction for some MA chips.

Given the challenges, CERBA laboratory and Miltenyi Biotec GmbH have developed a fully automated process (FAP) for purification for CD138+ PCs. In a study of 100 BM patient samples, we compared the specificity, efficiency, performance, purity, ease of use, technologists' time and the quality of DNA after CD138⁺ PCs purification. Two methods were compared. In the first method, cells were directly purified from bone marrow samples by FAP using Automated Magnetic Cell Sorter (AMCS). In the second method, mononuclear cells from fresh whole bone marrow (WBM) were enriched by Ficoll, followed by cell selection procedure with anti-CD138+ MicroBeads using the AutoMACS®. Before separation and following the separation, the percentage of PCs was determined by Flow cytometry (FC) on WBM by multiparameter FC (MFC) for CD138/CD38 expression. Additionally, DNA quality on separated cells was assessed by Nanodrop. A fraction of the CD138+ PCs were used after hypotonic shock and Carnoy fixation, applied to glass slides for FISH application and another fraction for DNA extraction for MA (SNP.6 Affymetrix®) FISH was performed with the recommended unbalanced alterations & reciprocal rearrangements: del(13) (q14)(D13S25), del(17)(p13)(TP53),+3(D3Z), +9(D9Z1), +15(D15Z14), t(4;14)(p16;q32)/IGH-FGFR3.

Results, the specificity and purity were the same for both process but the efficiency and performance were considerably better for FAP than mononuclear cells enriched by Ficoll (MCEFicoll) process. With FAP, in 95% of the MM cases we obtained enough PCs for performance of the recommended panel of FISH and for 50% of them we could extract DNA for SNP array. For the MCEFicoll, we observed inferior performance, with very few plasma cells after isolation. Having enough PSc for only 65% of the cases and we could only extract DNA for 28% of them. The quality of DNA was the same for both process and the technologists' time was longer by 30' /patient for MCEFicoll process than for FAP.

Currently in CERBA lab, we realize more than 20 plasma cells isolation per week for patients with MM and from October 2007 to July 2011 we have separated more than 5.000 specimens using CD138 Whole Blood MicroBeads (CD 138 WBMB) from Miltenyi Biotec, in combination with the AMCS. This has allowed isolation directly from WBM without any sample preparation required, such as density gradient centrifugation (ficoll) or erythrocyte lysis.

The detection rate of chromosomal abnormalities and the number of abnormalities per case in MM and PCs dyscrasia significantly improves when there are enough CD138+PCs for analysis.

Conclusion, in this report we describe the benefits of fully automated isolations of CD138+ cells from WBM. We have developed an SOP for an automated reliable and standardized method which allows the processing of multiple samples in a single day, while maintaining sample integrity and increasing sensitivity of FISH analysis and WG arrays for a diagnosis lab.