M B Vidriales

EuroFlow antibody panels for standardized n-dimensional flow cytometric immunophenotyping of normal, reactive and malignant leukocytes

Most consensus leukemia & lymphoma antibody panels consist of lists of markers based on expert opinions, but they have not been validated. Here we present the validated EuroFlow 8-color antibody panels for immunophenotyping of hematological malignancies. The single-tube screening panels and multi-tube classification panels fit into the EuroFlow diagnostic algorithm with entries defined by clinical and laboratory parameters. The panels were constructed in 2–7 sequential design–evaluation–redesign rounds, using novel Infinicyt software tools for multivariate data analysis. Two groups of markers are combined in each 8-color tube: (i) backbone markers to identify distinct cell populations in a sample, and (ii) markers for characterization of specific cell populations. In multi-tube panels, the backbone markers were optimally placed at the same fluorochrome position in every tube, to provide identical multidimensional localization of the target cell population(s). The characterization markers were positioned according to the diagnostic utility of the combined markers. Each proposed antibody combination was tested against reference databases of normal and malignant cells from healthy subjects and WHO-based disease entities, respectively. The EuroFlow studies resulted in validated and flexible 8-color antibody panels for multidimensional identification and characterization of normal and aberrant cells, optimally suited for immunophenotypic screening and classification of hematological malignancies.

EuroFlow standardization of flow cytometer instrument settings and immunophenotyping protocols

The EU-supported EuroFlow Consortium aimed at innovation and standardization of immunophenotyping for diagnosis and classification of hematological malignancies by introducing 8-color flow cytometry with fully standardized laboratory procedures and antibody panels in order to achieve maximally comparable results among different laboratories. This required the selection of optimal combinations of compatible fluorochromes and the design and evaluation of adequate standard operating procedures (SOPs) for instrument setup, fluorescence compensation and sample preparation. Additionally, we developed software tools for the evaluation of individual antibody reagents and antibody panels. Each section describes what has been evaluated experimentally versus adopted based on existing data and experience. Multicentric evaluation demonstrated high levels of reproducibility based on strict implementation of the EuroFlow SOPs and antibody panels. Overall, the 6 years of extensive collaborative experiments and the analysis of hundreds of cell samples of patients and healthy controls in the EuroFlow centers have provided for the first time laboratory protocols and software tools for fully standardized 8-color flow cytometric immunophenotyping of normal and malignant leukocytes in bone marrow and blood; this has yielded highly comparable data sets, which can be integrated in a single database.

Critical evaluation of ASO RQ-PCR for minimal residual disease evaluation in multiple myeloma. A comparative analysis with flow cytometry

We have analyzed the applicability, sensitivity and prognostic value of allele-specific oligonucleotide real-time quantitative PCR (ASO RQ-PCR) as a method for minimal residual disease (MRD) assessment in patients with multiple myeloma (MM), comparing the results with those of multiparameter flow cytometry (MFC). A total of 170 patients enrolled in three consecutive Spanish trials achieving at least partial response after treatment were included. Lack of clonality detection (n=31), unsuccessful sequencing (n=17) and suboptimal ASO performance (n=51) limited the applicability of PCR to 42% of cases. MRD was finally investigated in 103 patients (including 32 previously studied) with persistent disease identified by PCR and MFC in 54% and 46% of cases, respectively. A significant correlation in MRD quantitation by both the techniques was noted (r=0.881, P<0.001), being reflective of treatment intensity. Patients with <10−4 residual tumor cells showed longer progression-free survival (PFS) compared with the rest (not reached (NR) vs 31 months, P=0.002), with similar results observed with MFC. Among complete responders (n=62), PCR discriminated two risk groups with different PFS (49 vs 26 months, P=0.001) and overall survival (NR vs 60 months, P=0.008). Thus, although less applicable than MFC, ASO RQ-PCR is a powerful technique to assess treatment efficacy and risk stratification in MM.

Characterization of aberrant phenotypes in acute myeloblastic leukemia.

The existence of leukemic-associated phenotypes has been suggested to be a valuable tool for the detection of minimal residual disease (MRD) in AML patients, as they would allow to distinguish leukemic blast cells from normal hematopoietic progenitors. The present study was designed to analyze in which proportion of AML patients the immunological detection of MRD is feasible, based on the presence of aberrant phenotypes that allow the distinction of leukemic from normal cells. For this purpose we have prospectively investigated the blast cells from 40 AML patients at diagnosis with a large panel of MoAb in double and triple staining combinations analyzed at flow cytometry, in order to detect aberrant phenotypes on blast cells (lineage infidelity, antigenic overexpression, and asynchronous antigenic expression, as well as aberrant lightscatter pattern). In the analysis of the 40 AML cases more than one blast cell subset, distinguished by its different antigenic expression, was detected in 85% of the patients: five different phenotypic blast cell subsets were observed in six cases, four in 13 patients, three subsets in three cases, and two in 12 patients; only six cases showed a homogeneous phenotypical blast cell population. Twenty-nine of the 40 AML cases analyzed (73%) showed the existence of at least one aberrant phenotype: in 15 cases the myeloid blast cells co-expressed lymphoid-associated antigens (CD2, CD5, CD7, and/or CD19) - lineage infidelity -; asynchronous antigen expression was detected in 25 patients (CD34+CD56+, CD34+CD11b+, CD34+CD14+, CD117+CD15+, CD33-CD13+, CD13-CD15+, HLADR+CD15+++, HLADR-CD14+CD11b+ CD4+); seven cases displayed antigen overexpression (CD13, CD33, CD15, or CD14); and in 13 patients leukemic cells had an abnormal FSC/SSC distribution according to their phenotype. These results suggest that immunological methods for the detection of MRD based on the existence of aberrant phenotypes could be used in the majority of AML patients.

Next Generation Flow for highly sensitive and standardized detection of minimal residual disease in multiple myeloma

Flow cytometry has become a highly valuable method to monitor minimal residual disease (MRD) and evaluate the depth of complete response (CR) in bone marrow (BM) of multiple myeloma (MM) after therapy. However, current flow-MRD has lower sensitivity than molecular methods and lacks standardization. Here we report on a novel next generation flow (NGF) approach for highly sensitive and standardized MRD detection in MM. An optimized 2-tube 8-color antibody panel was constructed in five cycles of design-evaluation-redesign. In addition, a bulk-lysis procedure was established for acquisition of ⩾107 cells/sample, and novel software tools were constructed for automatic plasma cell gating. Multicenter evaluation of 110 follow-up BM from MM patients in very good partial response (VGPR) or CR showed a higher sensitivity for NGF-MRD vs conventional 8-color flow-MRD -MRD-positive rate of 47 vs 34% (P=0.003)-. Thus, 25% of patients classified as MRD-negative by conventional 8-color flow were MRD-positive by NGF, translating into a significantly longer progression-free survival for MRD-negative vs MRD-positive CR patients by NGF (75% progression-free survival not reached vs 7 months; P=0.02). This study establishes EuroFlow-based NGF as a highly sensitive, fully standardized approach for MRD detection in MM which overcomes the major limitations of conventional flow-MRD methods and is ready for implementation in routine diagnostics.

Clinical significance of CD81 expression by clonal plasma cells in high-risk smoldering and symptomatic multiple myeloma patients

The presence of CD19 in myelomatous plasma cells (MM-PCs) correlates with adverse prognosis in multiple myeloma (MM). Although CD19 expression is upregulated by CD81, this marker has been poorly investigated and its prognostic value in MM remains unknown. We have analyzed CD81 expression by multiparameter flow cytometry in MM-PCs from 230 MM patients at diagnosis included in the Grupo Español de Mieloma (GEM)05>65years trial as well as 56 high-risk smoldering MM (SMM). CD81 expression was detected in 45% (103/230) MM patients, and the detection of CD81+ MM-PC was an independent prognostic factor for progression-free (hazard ratio=1.9; P=0.003) and overall survival (hazard ratio=2.0; P=0.02); this adverse impact was validated in an additional series of 325 transplant-candidate MM patients included in the GEM05 <65 years trial. Moreover, CD81+ SMM (n=34/56, 57%) patients had a shorter time to progression to MM (P=0.02). Overall, our results show that CD81 may have a relevant role in MM pathogenesis and represent a novel adverse prognostic marker in myeloma.

Competition between clonal plasma cells and normal cells for potentially overlapping bone marrow niches is associated with a progressively altered cellular distribution in MGUS vs myeloma.

Disappearance of normal bone marrow (BM) plasma cells (PC) predicts malignant transformation of monoclonal gammopathy of undetermined significance (MGUS) and smoldering myeloma (SMM) into symptomatic multiple myeloma (MM). The homing, behavior and survival of normal PC, but also CD34+ hematopoietic stem cells (HSC), B-cell precursors, and clonal PC largely depends on their interaction with stromal cell-derived factor-1 (SDF-1) expressing, potentially overlapping BM stromal cell niches. Here, we investigate the distribution, phenotypic characteristics and competitive migration capacity of these cell populations in patients with MGUS, SMM and MM vs healthy adults (HA) aged >60 years. Our results show that BM and peripheral blood (PB) clonal PC progressively increase from MGUS to MM, the latter showing a slightly more immature immunophenotype. Of note, such increased number of clonal PC is associated with progressive depletion of normal PC, B-cell precursors and CD34+ HSC in the BM, also with a parallel increase in PB. In an ex vivo model, normal PC, B-cell precursors and CD34+ HSC from MGUS and SMM, but not MM patients, were able to abrogate the migration of clonal PC into serial concentrations of SDF-1. Overall, our results show that progressive competition and replacement of normal BM cells by clonal PC is associated with more advanced disease in patients with MGUS, SMM and MM.

A multiparameter flow cytometry immunophenotypic algorithm for the identification of newly diagnosed symptomatic myeloma with an MGUS-like signature and long-term disease control

Achieving complete remission (CR) in multiple myeloma (MM) translates into extended survival, but two subgroups of patients fall outside this paradigm: cases with unsustained CR, and patients that do not achieve CR but return into a monoclonal gammopathy of undetermined significance (MGUS)-like status with long-term survival. Here, we describe a novel automated flow cytometric classification focused on the analysis of the plasma-cell compartment to identify among newly diagnosed symptomatic MM patients (N=698) cases with a baseline MGUS-like profile, by comparing them to MGUS (N=497) patients and validating the classification model in 114 smoldering MM patients. Overall, 59 symptomatic MM patients (8%) showed an MGUS-like profile. Despite achieving similar CR rates after high-dose therapy/autologous stem cell transplantation vs other MM patients, MGUS-like cases had unprecedented longer time-to-progression (TTP) and overall survival (OS; ∼60% at 10 years; P<0.001). Importantly, MGUS-like MM patients failing to achieve CR showed similar TTP (P=0.81) and OS (P=0.24) vs cases attaining CR. This automated classification also identified MGUS patients with shorter TTP (P=0.001, hazard ratio: 5.53) and ultra-high-risk smoldering MM (median TTP, 15 months). In summary, we have developed a biomarker that identifies a subset of symptomatic MM patients with an occult MGUS-like signature and an excellent outcome, independently of the depth of response.

Multiparameter flow cytometry for the identification of the Waldenstrom's clone in IgM-MGUS and Waldenstrom's Macroglobulinemia: new criteria for differential diagnosis and risk stratification

Although multiparameter flow cytometry (MFC) has demonstrated clinical relevance in monoclonal gammopathy of undetermined significance (MGUS)/myeloma, immunophenotypic studies on the full spectrum of Waldenström’s Macroglobulinemia (WM) remain scanty. Herein, a comprehensive MFC analysis on bone marrow samples from 244 newly diagnosed patients with an immunoglobulin M (IgM) monoclonal protein was performed, including 67 IgM-MGUS, 77 smoldering and 100 symptomatic WM. Our results show a progressive increase on the number and light-chain-isotype-positive B-cells from IgM-MGUS to smoldering and symptomatic WM (P<.001), with only 1% of IgM-MGUS patients showing >10% B cells or 100% light-chain-isotype-positive B-cells (P<.001). Complete light-chain restriction of the B-cell compartment was an independent prognostic factor for time-to progression in smoldering WM (median 26 months; HR: 19.8, P=0.001) and overall survival in symptomatic WM (median 44 months; HR: 2.6, P=0.004). The progressive accumulation of light-chain-isotype-positive B-cells accompanied the emergence of a characteristic Waldenstrom’s phenotype (CD22+dim/CD25+/CD27+/IgM+) that differed from other B-NHL by negative expression of CD5, CD10, CD11c or CD103. In contrast to myeloma, light-chain-isotype-positive plasma cells in IgM monoclonal gammopathies show otherwise normal antigenic expression. Our results highlight the potential value of MFC immunophenotyping for the characterization of the Waldenström’s clone, as well as for the differential diagnosis, risk of progression and survival in WM.

Phenotypic identification of subclones in multiple myeloma with different chemoresistant, cytogenetic and clonogenic potential

Knowledge about clonal diversity and selection is critical to understand multiple myeloma (MM) pathogenesis, chemoresistance and progression. If targeted therapy becomes reality, identification and monitoring of intraclonal plasma cell (PC) heterogeneity would become increasingly demanded. Here we investigated the kinetics of intraclonal heterogeneity among 116 MM patients using 23-marker multidimensional flow cytometry (MFC) and principal component analysis, at diagnosis and during minimal residual disease (MRD) monitoring. Distinct phenotypic subclones were observed in 35/116 (30%) newly diagnosed MM patients. In 10/35 patients, persistent MRD was detected after 9 induction cycles, and longitudinal comparison of patient-paired diagnostic vs MRD samples unraveled phenotypic clonal tiding after therapy in half (5/10) of the patients. After demonstrating selection of distinct phenotypic subsets by therapeutic pressure, we investigated whether distinct fluorescence-activated cell-sorted PC subclones had different clonogenic and cytogenetic profiles. In half (5/10) of the patients analyzed, distinct phenotypic subclones showed different clonogenic potential when co-cultured with stromal cells, and in 6/11 cases distinct phenotypic subclones displayed unique cytogenetic profiles by interphase fluorescence in situ hybridization, including selective del(17p13). Collectively, we unravel potential therapeutic selection of preexisting diagnostic phenotypic subclones during MRD monitoring; because phenotypically distinct PCs may show different clonogenic and cytogenetic profiles, identification and follow-up of unique phenotypic-genetic myeloma PC subclones may become relevant for tailored therapy.