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© The Author(s) 2020., Precise classification of acute leukemia (AL) is crucial for adequate treatment. EuroFlow has previously designed an AL orientation tube (ALOT) to guide toward the relevant classification panel and final diagnosis. In this study, we designed and validated an algorithm for automated (database-supported) gating and identification (AGI tool) of cell subsets within samples stained with ALOT. A reference database of normal peripheral blood (PB, n = 41) and bone marrow (BM; n = 45) samples analyzed with the ALOT was constructed, and served as a reference for the AGI tool to automatically identify normal cells. Populations not unequivocally identified as normal cells were labeled as checks and were classified by an expert. Additional normal BM (n = 25) and PB (n = 43) and leukemic samples (n = 109), analyzed in parallel by experts and the AGI tool, were used to evaluate the AGI tool. Analysis of normal PB and BM samples showed low percentages of checks ( 0.95 for all cell types in PB and r2 > 0.75 in BM) and resulted in highly concordant classification of leukemic cells by our previously published automated database-guided expert-supervised orientation tool for immunophenotypic diagnosis and classification of acute leukemia (Compass tool). Similar data were obtained using alternative, commercially available tubes, confirming the robustness of the developed tools. The AGI tool represents an innovative step in minimizing human intervention and requirements in expertise, toward a “sample-in and result-out” approach which may result in more objective and reproducible data analysis and diagnostics. The AGI tool may improve quality of immunophenotyping in individual laboratories, since high percentages of checks in normal samples are an alert on the quality of the internal procedures., The EuroFlow Consortium received support from the FP6- 2004-LIFESCIHEALTH-5 program of the European Commission (grant LSHB-CT-2006-018708) as Specific Targeted Research Project (STREP). The Prague team received support from the grant number NV18-03-00343. The Salamanca team received support from the Instituto de Salud Carlos III (ISCIII) (PI16/00787-FEDER) and from Agencia Estatal de Investigación (RTC-2016-4865-1-FEDER), Ministerio de Economía y Competitividad, Madrid, Spain. AHD is supported from the program DI-17-09591 from Agencia Estatal de Investigación, Ministerio de Ciencia, Innovación y Universidades, Madrid, Spain. SB is supported from the program PTQ16-08364 from Agencia Estatal de Investigación, Ministerio de Ciencia, Innovación y Universidades, Madrid, Spain. Medical University of Silesia in Katowice team was supported by the Strategmed III PersonALL grant [No. 304586/5/NCBR/2017] from the Polish National Center of Research and Development. The EuroFlow Consortium is part of the European Scientific Foundation for Hemato-Oncology (ESLHO), a Scientific Working Group (SWG) of the European Hematology Association (EHA).

This commentary discusses particularities of application of the EuroFlow standardization of flow cytometric analyses on three different flow cytometers. The EuroFlow consortium developed a fully standardized approach for flow cytometric immunophenotyping of hematological malignancies and primary immunodeficiencies. Standardized instrument setup is an essential part of EuroFlow standardization. Initially, the EuroFlow Consortium developed and optimized a step-by-step standard operating procedure (SOP) to setup 8-color BD FACSCanto II flow cytometer (Canto), with the later inclusion of Navios (Beckman Coulter) and BD FACSLyric (Lyric). Those SOPs were developed to enable standardized and fully comparable fluorescence measurements in the three flow cytometers. In Canto and Navios, mean fluorescence intensity (MFI) of a reference peak of Rainbow beads calibration particles is used to set up photomultiplier (PMT) voltages for each detector channel in individual instruments to reach the same MFI across distinct instruments. In turn, a new feature of Lyric instruments allows to share collection of attributes that are used to place the positive population at the same position among instruments in the form of assays, as one of its components integrated in the Cytometer Setup and Tracking (CS&T) module. The EuroFlow Lyric assays thus allow for standardized acquisition of 8-color EuroFlow panels on Lyric without the need to setup the PMT voltages on the individual instruments manually. In summary, the standardized instrument setup developed by EuroFlow enables cross-platform inter- and intra-laboratory standardization of flow cytometric measurements. This commentary provides a perspective on the modifications of the standardized EuroFlow instrument setup of Canto, Navios and Lyric instruments that are described in detail in individual instrument-specfic SOPs available at the EuroFlow website., TK and MN were supported by Ministry of Health of the Czech Republic, grant nr. NV18-03-00343, Ministry of Education, Youth and Sports of the Czech Republic, NPU I project nr.LO1604 and EU-Prague project CZ.2.16/3.1.00/24505. JFM and AO were supported by CB16/12/00400 grant (CIBER-ONC, Instituto de Salud Carlos III, Ministerio de Economía y Competitividad, Madrid, Spain and FONDOS FEDER).

Fluorochrome selection is a key step in designing multi-color antibody panels. The list of available fluorochromes is continuously growing, fitting current needs in clinical flow cytometry to simultaneously use more markers to better define multiple leukocyte subpopulations in a single tube. Several criteria guide fluorochrome selection: i) the fluorescence profiles (excitation and emission), ii) relative brightness, iii) fluorescence overlap, iv) fluorochrome stability, and v) reproducible conjugation to antibodies. Here we used 75 samples (45 bone marrow and 30 blood) to illustrate EuroFlow strategies for evaluation of compatible fluorochromes, and how the results obtained guide fluorochrome selection as a critical step in the antibody-panel building process. Our results allowed identification of optimal fluorescence profiles (e.g. higher fluorescence intensity and/or resolution with limited fluorescence overlap into neighbor channels) for brilliant violet (BV)421 and BV510 in the violet laser and allophycocyanin (APC) hilite 7 (H7) or APC C750 in the red laser vs. other candidate fluorochromes generally applied for the same detectors and here evaluated. Moreover, evaluation of the same characteristics for another group of fluorochromes (e.g. BV605, BV650, PE CF594, AF700 or APC AF700) guided selection of the most appropriate fluorochrome conjugates to be combined in a multi-color antibody panel. Albeit this is a demanding approach, it could be successfully applied for selection of fluorochrome combinations for the EuroFlow antibody panels for diagnosis, classification and monitoring of hematological malignancies and primary immunodeficiencies. Consequently, sets of 8-, 10- and 12-color fluorochrome combinations are proposed as frame of reference for initial antibody panel design., This work was supported by CB16/12/00400 grant (CIBER-ONC, Instituto de Salud Carlos III, Ministerio de Economía y Competitividad, Madrid, Spain and FONDOS FEDER) and grant PI16/00787 from Instituto de Salud Carlos III, Ministerio de Economía y Competitividad, Madrid, Spain. TK and KR were supported by project NPU LO1604 and EU-Prague project CZ.2.16/3.1.00/24505.

© 2019 The Authors., In recent years the volume and complexity of flow cytometry data has increased substantially. This has led to a greater number of identifiable cell populations in a single measurement. Consequently, new gating strategies and new approaches for cell population definition are required. Here we describe how the EuroFlow Lymphoid Screening Tube (LST) reference data base for peripheral blood (PB) samples was designed, constructed and validated for automated gating of the distinct lymphoid (and myeloid) subsets in PB of patients with chronic lymphoproliferative disorders (CLPD). A total of 46 healthy/reactive PB samples which fulfilled pre-defined technical requirements, were used to construct the LST-PB reference data base. In addition, another set of 92 PB samples (corresponding to 10 healthy subjects, 51 B-cell CLPD and 31 T/NK-cell CLPD patients), were used to validate the automated gating and cell-population labeling tools with the Infinicyt software. An overall high performance of the LST-PB data base was observed with a median percentage of alarmed cellular events of 0.8% in 10 healthy donor samples and of 44.4% in CLPD data files containing 49.8% (range: 1.3–96%) tumor cells. The higher percent of alarmed cellular events in every CLPD sample was due to aberrant phenotypes (75.6% cases) and/or to abnormally increased cell counts (86.6% samples). All 18 (22%) data files that only displayed numerical alterations, corresponded to T/NK-cell CLPD cases which showed a lower incidence of aberrant phenotypes (41%) vs B-cell CLPD cases (100%). Comparison between automated vs expert-bases manual classification of normal (r2 = 0.96) and tumor cell populations (rho = 0.99) showed a high degree of correlation. In summary, our results show that automated gating of cell populations based on the EuroFlow LST-PB data base provides an innovative, reliable and reproducible tool for fast and simplified identification of normal vs pathological B and T/NK lymphocytes in PB of CLPD patients., This work was supported by the CB16/12/00400 and CB16/12/00369 grants, CIBER-ONC, Instituto de Salud Carlos III, Ministerio de Economía y Competitividad, Madrid, Spain and FONDOS FEDER; DTS 15/00119 grant, Instituto de Salud Carlos III, Ministerio de Economía y Competitividad, Madrid, Spain and FONDOS FEDER; and, RETOS (RTC–2016–4865–1) grant, Sociedad de la Acción Estratégica de Economía y Sociedad Digital-Impulso Tecnológico; Ministerio de Economía y Competitividad, Madrid, Spain.

Flow cytometric detection of minimal residual disease (MRD) in children with B-cell precursor acute lymphoblastic leukaemia (BCP-ALL) requires immunophenotypic discrimination between residual leukaemic cells and B-cell precursors (BCPs) which regenerate during therapy intervals. In this study, EuroFlow-based 8-colour flow cytometry and innovative analysis tools were used to first characterize the immunophenotypic maturation of normal BCPs in bone marrow (BM) from healthy children, resulting in a continuous multiparametric pathway including transition stages. This pathway was subsequently used as a reference to characterize the immunophenotypic maturation of regenerating BCPs in BM from children treated for BCP-ALL. We identified pre-B-I cells that expressed low or dim CD34 levels, in contrast to the classical CD34 pre-B-I cell immunophenotype. These CD34 pre-B-I cells were relatively abundant in regenerating BM (11–85% within pre-B-I subset), while hardly present in healthy control BM (9–13% within pre-B-I subset; P = 0·0037). Furthermore, we showed that some of the BCP-ALL diagnosis immunophenotypes (23%) overlapped with CD34 pre-B-I cells. Our results indicate that newly identified CD34 pre-B-I cells can be mistaken for residual BCP-ALL cells, potentially resulting in false-positive MRD outcomes. Therefore, regenerating BM, in which CD34 pre-B-I cells are relatively abundant, should be used as reference frame in flow cytometric MRD measurements., The research for this manuscript was (in part) performed within the framework of the Erasmus Postgraduate School Molecular Medicine and was financially supported by PrioMedChild, project 40-41800-98-027. This study was performed within the EuroFlow Consortium, the EU-supported LSHB-CT2006-018708 FP6 Specific Targeted Research Project, which obtained sustainability based on income from the development of intellectual property and related patents, which have been licensed to industry. The work was supported through AZV (15-28525A) to EM and to MN.

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., This work has been supported by the International Myeloma Foundation-Black Swan Research Initiative, the Red Temática de Investigación Cooperativa en Cáncer (RTICC); grant SA079U14 from the Consejería de Educación, Junta de Castilla y León, Valladolid, Spain and; grant DTS15/00119 from Instituto de Salud Carlos III, Ministerio de Economía y Competitividad, Madrid, Spain.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivative Works 3.0 Unported License.-- EuroFlow Consortium (EU-FP6, LSHB-CT-2006-018708): et al., 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., The research activities of the EuroFlow Consortium were supported by the European Commission (grant STREP EU-FP6, LSHB-CT-2006-018708, entitled ‘Flow cytometry for fast and sensitive diagnosis and follow-up of hematological malignancies’) and the following national grants: Spanish Network of Cancer Research Centers (ISCIII RTICC-RD06/0020/0035-FEDER), FIS 08/90881 from the ‘Fondo de Investigación Sanitaria’, Ministerio de Ciencia e Innovación (Madrid, Spain), SA016-A-09 from the Consejería de Educación, Junta de Castilla y León, Valladolid, Spain, and PIB2010BZ-00565 from the Dirección General de Cooperación Internacional y Relaciones Institucionales, Secretaría de Estado de Investigación, Ministerio de Ciencia e Innovación (Madrid, Spain). T Kalina, E Mejstrikova and O Hrusak were supported by the Czech Ministry of Education Grant No. MSM0021620813, Czech Ministry of Health grant NT/12425-4 and TK is supported as an ISAC Scholar by The International Society for Advancement of Cytometry.

Nowadays, the presence of specific genetic aberrations is progressively used for classification and treatment stratification, because acute leukemias with the same oncogenetic aberration generally form a clinically and diagnostically homogenous disease entity with comparable prognosis. Many oncogenetic aberrations in acute leukemias result in a fusion gene, which is transcribed into fusion transcripts and translated into fusion proteins, which are assumed to play a critical role in the oncogenetic process. Fusion gene aberrations are detected by karyotyping, FISH, or RT-PCR analysis. However, these molecular genetic techniques are laborious and time consuming, which is in contrast to flow cytometric techniques. Therefore we developed a flow cytometric immunobead assay for detection of fusion proteins in lysates of leukemia cell samples by use of a bead-bound catching antibody against one side of the fusion protein and fluorochrome-conjugated detection antibody. So far, we have been able to design such fusion protein immunobead assays for BCR-ABL, PML-RARA, TEL-AML1, E2A-PBX1, MLL-AF4, AML1-ETO and CBFB-MYH11. The immunobead assay for detection of fusion proteins can be performed within 3 to 4 hours in a routine diagnostic setting, without the need of special equipment other than a flow cytometer. The novel immunobead assay will enable fast and easy classification of acute leukemia patients that express fusion proteins. Such patients can be included at an early stage in the right treatment protocols, much faster than by use of current molecular techniques. The immunobead assay can be run in parallel to routine immunophenotyping and is particularly attractive for clinical settings without direct access to molecular diagnostics. © 2010 Elsevier Ltd. All rights reserved., The research and development of the flow cytometric immunobead assay and the EuroFlow Consortium were supported by the European Commission (grant STREP EU-FP6, LSHB-CT-2006- 018708).

An increasing number of evidences suggest a genetic predisposition in acute lymphoblastic leukemia (ALL) that might favor the occurrence of the driver genetic alterations. Such genetic background might also translate into phenotypic alterations of residual hematopoietic cells. Whether such phenotypic alterations are present in bone marrow (BM) cells from childhood B-cell precursor (BCP)-ALL remains to be investigated. Here we analyzed the immunophenotypic profile of BM and peripheral blood (PB) maturing/matured neutrophils from 118 children with BCP-ALL and their relationship with the features of the disease. Our results showed altered neutrophil phenotypes in most (77%) BCP-ALL cases. The most frequently altered marker was CD10 (53%), followed by CD33 (34%), CD13 (15%), CD15/CD65 (10%) and CD123 (7%). Of note, patients with altered neutrophil phenotypes had younger age (p = 0.03) and lower percentages of BM maturing neutrophils (p = 0.004) together with greater BM lymphocyte (p = 0.04), and mature B-cell (p = 0.03) counts. No significant association was found between an altered neutrophil phenotype and other disease features. These findings point out the potential existence of an altered residual hematopoiesis in most childhood BCP-ALL cases., This work was supported by the following grants: Bilateral Cooperation Program between Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES (Brasília/Brazil) and Dirección General de Políticas Universitárias – Ministério de Educación, Cultura y Deportes - DPGU (Madrid/Spain) (311/15) and RD12/0036/0048 from RETICS, (Instituto de Salud Carlos III, Ministerio de Economia y Competitividad, Madrid, Spain and Fondos FEDER); Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro of Brazil (E26/110.105/2014; E26/102.191/2013); Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPQ of Brazil (400194/2014–7). EO and DNRG were both supported by grants from CAPES (Brazil). NLD was partly supported by a grant from CNPQ (Brazil). TS and LS were supported by the internal grants from the Medical University of Silesia (Katowice, Poland).

A better description of the leukemia cell surface proteome (surfaceome) is a prerequisite for the development of diagnostic and therapeutic tools. Insights into the complexity of the surfaceome have been limited by the lack of suitable methodologies. We combined a leukemia xenograft model with the discovery-driven chemoproteomic Cell Surface Capture technology to explore the B-cell precursor acute lymphoblastic leukemia (BCP-ALL) surfaceome; 713 cell surface proteins, including 181 CD proteins, were detected through combined analysis of 19 BCP-ALL cases. Diagnostic immunophenotypes were recapitulated in each case, and subtype specific markers were detected. To identify new leukemia-associated markers, we filtered the surfaceome data set against gene expression information from sorted, normal hematopoietic cells. Nine candidate markers (CD18, CD63, CD31, CD97, CD102, CD157, CD217, CD305, and CD317) were validated by flow cytometry in patient samples at diagnosis and during chemotherapy. CD97, CD157, CD63, and CD305 accounted for the most informative differences between normal and malignant cells. The ALL surfaceome constitutes a valuable resource to assist the functional exploration of surface markers in normal and malignant lymphopoiesis. This unbiased approach will also contribute to the development of strategies that rely on complex information for multidimensional flow cytometry data analysis to improve its diagnostic applications.

Background Juvenile myelomonocytic leukemia (JMML) is a lethal myeloproliferative disease (MPD) of young childhood characterized by an overproduction of myelomonocytic cells and an increased in vitro sensitivity of hematopoietic progenitors to granulocyte-macrophage colony-stimulating factor [GM-CSF] (Emanuel PD et al, Blood 1991). Diagnostic criteria for JMML are currently well-established and based on clinical features and laboratory findings. However, in some patients diagnosis of JMML vs other overlapping disease entities, still remains a challenge, immunophenotyping being not part of the diagnostic work-up of JMML. Here, we aimed at detailed characterization of the CD34+ cell compartment in JMML bone marrow (BM) using the standardized EuroFlow myeloid panel in combination with innovative EuroFlow software maturation tools. Our major goal was to determine the potential utility of immunophenotyping of CD34 cells in the diagnostic work-up of JMML. Methods Overall, we analyzed BM cells from 10 JMML patients at diagnosis (age range: 0-7 years), 17 control subjects (age range: 0-15 years) and 5 patients (age range: 0-5 years) with a suspected diagnosis of JMML that was subsequently not confirmed following standardized EuroFlow antibody combinations: 1) cyCD3/ CD45/ cyMPO/ cyCD79a/ CD34/ CD19 / CD7/smCD3 (for early lineage assignement); 2) HLADR/CD45/CD16/CD13/CD34/CD117/CD11b/CD10 (neutrophilic maturation); 3) HLADR/CD45/CD35/CD64/CD34/CD117/CD300e (IREM2)/CD14 (monocytic maturation); 4) HLADR/CD45/CD36/CD105/CD34/CD117/CD33/CD71 (erythroid vs plasmacytoid dendritic cell maturation). Samples were processed and analyzed according to the Euroflow standard operating protocols (van Dongen JJM et al, Leukemia 2012, Kalina T et al, Leukemia 2012). Data analysis was specifically focused on the immunophenotypic profile of CD34+ gated cells. Results Within the CD34+ BM cell compartment the proportion (mean % ± 1SD) of granulocytic and monocytic precursors were not significantly different in JMML as compared to controls: 33% ± 15% vs 25% ± 12% (p = 0.16) and 14% ± 6.3% vs 12% ± 7.1% (p = 0.68) respectively. Otherwise we observed a slightly decreased in erythroid CD34+ progenitors in JMML vs controls (1.0% ± 1.2% vs 2.8% ± 1.7%, p Conclusions CD34+ precursor cells from JMML patients display a unique immunophenotypic profile characterized by an inverted ratio of CD19+ B/CD7+ lymphoid precursors, associated with unusual marker coexpressions, which might contribute to fast and more precise diagnostic work-up of JMML. Further studies in larger patient series are required to confirm our observations. Disclosures Biondi: Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board; BMS: Membership on an entity's Board of Directors or advisory committees; Cellgene: Other: Advisory Board.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivative Works 3.0 Unported License.-- EuroFlow Consortium: et al., The PML-RARA fusion protein is found in approximately 97% of patients with acute promyelocytic leukemia (APL). APL can be associated with life-threatening bleeding complications when undiagnosed and not treated expeditiously. The PML-RARA fusion protein arrests maturation of myeloid cells at the promyelocytic stage, leading to the accumulation of neoplastic promyelocytes. Complete remission can be obtained by treatment with all-trans-retinoic acid (ATRA) in combination with chemotherapy. Diagnosis of APL is based on the detection of t(15;17) by karyotyping, fluorescence in situ hybridization or PCR. These techniques are laborious and demand specialized laboratories. We developed a fast (performed within 4-5 h) and sensitive (detection of at least 10% malignant cells in normal background) flow cytometric immunobead assay for the detection of PML-RARA fusion proteins in cell lysates using a bead-bound anti-RARA capture antibody and a phycoerythrin-conjugated anti-PML detection antibody. Testing of 163 newly diagnosed patients (including 46 APL cases) with the PML-RARA immunobead assay showed full concordance with the PML-RARA PCR results. As the applied antibodies recognize outer domains of the fusion protein, the assay appeared to work independently of the PML gene break point region. Importantly, the assay can be used in parallel with routine immunophenotyping for fast and easy diagnosis of APL., The research and development of the flow cytometric immunobead assay and the EuroFlow Consortium were supported by the European Commission (grant STREP EU-FP6, LSHB-CT-2006-018708; Flow cytometry for fast and sensitive diagnosis and follow-up of hematological malignancies).

EuroFlow Consortium (EU-FP6, LSHB-CT-2006-018708): et al., This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivative Works 3.0 Unported License., 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., We are grateful to Dr Jean-Luc Sanne of the European Commission for his support and monitoring of the EuroFlow project. The research activities of the EuroFlow Consortium were supported by the European Commission (grant STREP EU-FP6, LSHB-CT-2006-018708, entitled ‘Flow cytometry for fast and sensitive diagnosis and follow-up of hematological malignancies’) and the following national grants: Spanish Network of Cancer Research Centers (ISCIII RTICC-RD06/0020/0035-FEDER), FIS 08/90881 and FIS PS09/02430 from the ‘Fondo de Investigación Sanitaria’, Ministerio de Ciencia e Innovación (Madrid, Spain); GR37 EDU/894/2009 and SA016-A-09 from the Consejería de Educación, Junta de Castilla y León (Valladolid, Spain); PIB2010BZ-00565 from the Dirección General de Cooperación Internacional y Relaciones Institucionales, Secretaría de Estado de Investigación, Ministerio de Ciencia e Innovación (Madrid, Spain); Ministry of Health Czech Republic (NT/12425-4 and NS/10480-3); and Charles University grant No. 23010 and UNCE No. 204012; Tomas Kalina is supported as an ‘ISAC Scholar’ by the International Society for Advancement of Cytometry (ISAC); Andy Rawstron was supported by Leukemia and Lymphoma Research (LLR).

Abstract 2700 Objective: Infant acute lymphoblastic leukemia (ALL) is characterized by distinct biological and clinical features. In this study, we aimed at detailed evaluation of infant ALL immunophenotype based on the large cohort of patients treated homogeneously on INTERFANT'99 protocol. Patients and Methods: We were able to obtain sufficient flow cytometry based immunophenotypic data from 286 (130 boys and 156 girls) of 483 infant ALL cases treated on INTERFANT'99 protocols. The distribution of patient and leukemia characteristics as well as clinical outcome were very similar to the entire study cohort (Pieters et al, Lancet 2007; 370: 240–250). The positivity for a certain antigen was defined at the cut-off value of >20% of cells expressing this antigen. In B-cell precursor ALL (BCP-ALL), evaluated antigens included CD10, CD20, CD34, myeloid markers (CD13, CD33, CD15 and/or CD65) and NG2 antigen assessed with 7.1 antibody. The strength of association between characteristics (patient's age and gender, initial white blood count [WBC], CNS involvement, presence of MLL gene rearrangements, prednisone response [PR]) and antigen expression was analyzed with Fisher exact test adjusted for multiple comparisons. Univariate analysis of outcome by immunophenotype was based on event free survival (EFS) and compared by log-rank test. Multivariate analysis was performed using Cox model in MLL-rearranged cases. P values < 0.05 were considered to be significant. Results: Altogether, 272 cases of infant BCP-ALL and 14 of infant T-ALL were analyzed. Most BCP-ALL cases were CD10 negative (66%), CD20 negative (88%), CD34 positive (60%), and NG2 positive (58%). Co-expression of myeloid antigens was less frequent and concerned CD13 in 8%, CD33 in 17%, CD15 in 31%, and CD65 in 28%. CD10 negativity and NG2 expression were significantly more frequent in younger infants, patients with initial high leukocytosis and with MLL rearrangements. CD34 expression was observed more frequently in younger infants, while CD20 positivity was significantly associated with lower initial leukocytosis and absence of MLL rearrangement. For myeloid antigen expression, the only significant association was more frequent CNS involvement in infants with CD13+ and/or CD33+ BCP-ALL. Analysis of outcome showed significantly better prognosis for CD10 positivity (4-year EFS of 56.3 as compared to 37.2 for CD10 negative BCP-ALL), absence of NG2 expression (4-year EFS of 63.9 as compared to 34.9 for NG2 positive BCP-ALL) and CD33 negativity (4-year EFS of 47.6 as compared to 27.7 for CD33 positive BCP-ALL). There was also a trend towards better outcome in CD20 positive infant BCP-ALL. While CD10 negativity and NG2 positivity were associated with well-known high-risk features, prognostic significance of CD33 expression is somewhat more difficult to explain. Of note, CD10 negativity was not associated to a worst outcome in MLL-rearranged patients. Moreover, in this subset, multivariate analysis showed that none of the markers analyzed had independent prognostic significance, after adjustment for sex, age at diagnosis, WBC and PR. In rare infant T-ALL cases, we observed equal distribution to different immunophenotypic subgroups as defined by EGIL classification. Conclusion: Infant BCP-ALL has distinct immunophenotypic features. However, immunophenotype has no independent prognostic relevance when MLL, age, WBC, PR and other factors are included. Disclosures: No relevant conflicts of interest to declare.

Background CXCR4 (CD184) is a receptor specific to the Stromal Derived Factor 1 (SDF-1), a ligand also known as CXCL12. The ligand-receptor interaction has a pleiotropic effect on hematopoietic cell proliferation, migration and activation through several signaling pathways. CXCR4 expression on neoplastic cells might be responsible for their dissemination to particular organs with cells expressing CXCL12 (e.g. lymph nodes, bones, and within bone marrow). In B-cell precursor acute lymphoblastic leukemia (BCP-ALL), expression of CXCR4 was associated with higher capacity of leukemic blasts to seed into bone marrow niches. Aim of the study The study aimed at thorough analysis of CXCR4 expression on BCP-ALL blasts and correlation of CXCR4 expression with the expression of other antigens such as CD66c, CD34, CD10, CD38, CD20 and CD45 as well as with the levels of minimal residual disease on day 15. Patients and Methods The study group consisted of 198 consecutive children aged 0-18 years (median 4.4 years) treated for BCP-ALL in the centers of the Polish Pediatric Leukemia/Lymphoma Study Group. Bone marrow samples obtained at initial diagnosis were stained with monoclonal antibodies (CD58, CD66c, CD34, CD19, CD10, CD38, CD20, CD45, CXCR4) in two 8-color tubes and analyzed with multiparameter flow cytometry (BD FACSCanto II, Becton Dickinson, San Jose, CA, USA) according to the EuroFlow standard protocols. The expression of particular antigens on BCP-ALL blasts was defined by median fluorescence. In 177 patients the samples from day 15 were available and analyzed for the presence of minimal residual disease (MRD) with multicolor flow cytometry. Infinicyt software (Cytognos, Salamanca, Spain) was used for more detailed analyses of the flow cytometric data. Results The expression of CXCR4 in BCP-ALL was highly variable with median fluorescence ranging from 252 to 24 388 (median 4011). There was no obvious correlation of CXCR4 expression with immunophenotype and with the expression of other analyzed markers (CD66, CD34, CD10, CD38 i CD45). The only borderline significant correlation found was between CXCR4 and CD20 expression. On day 15, 70 children (39%) demonstrated MRD levels below 0.1%, which is consistent with MRD-based low-risk group. Among these patients, 41 children had undetectable MRD already at this time point. In contrary, MRD levels > 10% were recorded in 21 patients (12%), who were stratified to high-risk group, accordingly. Maximal MRD levels recorded at day 15 were 85.6%. In remaining 86 children (49%), MRD levels at day 15 were in-between 0.1% and 10%, which reflects intermediate response to the treatment. There was no correlation between CXCR4 expression and MRD levels at day 15. Conclusion CXCR4 expression on BCP-ALL blasts is highly heterogeneous and is not associated with particular leukemia immunophenotype. Further analyses should characterize clinical features of leukemia and treatment response with regard to CXCR4 expression. The study was supported by Polish National Center of Science grant N N407 687040. Disclosures: No relevant conflicts of interest to declare.

Abstract 2506 Comprehensive identification of leukemia-associated cell surface molecules is required to improve the specificity and sensitivity of flow cytometric analysis of minimal residual disease. A more comprehensive map of leukemia-associated cell surface features could facilitate the selection and subsequent evaluation of new minimal residual disease (MRD) markers as a resource and provide direct cues for new therapeutic targets. Here, we used the chemoproteomic Cell Surface Capturing technology (CSC) to establish a surfaceome map consisting of 807 cell surface detectable proteins detected in an xenograft model derived from diagnostic samples from 19 pediatric patients with acute lymphoblastic leukemia (ALL). Because CSC is based on direct chemical tagging of protein and glycoprotein residues on the surface of living cells, highly viable samples are required to avoid intracellular contaminants. Direct processing of xenograft samples provided optimal conditions for CSC. We included 8 cases with resistant disease based on persistence of minimal residual disease (MRD) during chemotherapy, which represents a group of patients at need for innovative approaches. Comparative analysis of this proteomic dataset showed that CSC recapitulated and expanded the diagnostic immunophenotype of each patient. To select and test for new proteins with potential value for MRD detection within the large set of identified leukemia proteins, the dataset was filtered against gene expression data from sorted populations of the normal human hematopoietic tree according to their relative RNA expression levels in normal hematopoiesis (DMAP, Novershtern et al, 2011, Cell, 144, 296–309). Based on expected low levels of mRNA expression in normal early and late B-cell precursors in the bone marrow, a subset of markers was identified. These included cell surface features that were previously implicated in leukemogenesis, such as IL7R or FLT3, or shown to serve as diagnostic markers for flow cytometry such as CD58, CD99 and CD300A. For a first clinical validation phase, we selected 38 markers based on their frequency in the CSC dataset to evaluate whether they could contribute to a better distinction of leukemic blasts from their normal counterparts. We tested monoclonal antibodies that were available for 15 candidate markers on diagnostic and remission samples from ALL patients for relevant expression on leukemia cells. Data is currently available for 9 markers that were evaluated prospectively on 51 patients enrolled in current clinical treatment protocols. All markers detected leukemia-associated features in at least a subset of the patients. As anticipated, differences in antigen abundance and antigenic shifts under treatment varied from case to case, underscoring the advantage of increasing the number of available markers for MRD detection. Taken together, our surfaceome data provides an unprecedented view at the cell surface landscape of ALL cells including new prequalified candidate MRD markers, which will accelerate the introduction and subsequent evaluation of multiple parameters for leukemia diagnostics. This also constitutes a valuable resource for functional studies and evaluation of new options for therapeutic targeting. Disclosures: No relevant conflicts of interest to declare.

The BCR-ABL fusion gene results from the translocation t(9;22). It is the hallmark of chronic myeloid leukemia (CML) and is present in a poor-risk subgroup of precursor B cell acute lymphoblastic leukemia (ALL), which represents 25–30% of adult ALL and 3–5% of childhood ALL. Consequently the detection of the BCR-ABL aberration is of utmost importance for diagnosis and classification of leukemia patients and can also be used as marker for monitoring of BCR-ABL+ leukemias to evaluate treatment effectiveness. So far, the BCR-ABL aberration has been detected by cytogenetics, FISH or PCR, all techniques that are time consuming and require special facilities. We developed a simple flow cytometric bead assay for detection of the BCR-ABL fusion protein in cell lysates, using a bead-bound catching antibody against one side of the fusion protein and a fluorochrome-conjugated detection antibody against the other side of the fusion protein. The anti-BCR antibody was developed against a non-homologous region of ~80 amino acids, encoded by exon 1 in order to detect all know BCR-ABL variants, including p190, p210, and p230. The assay appeared to be specific and sufficiently sensitive to detect BCR-ABL proteins in leukemic cell lysates. However, protein stability problems were encountered when cell samples contained high frequencies of mature myeloid cells with high levels of protease activity, such as CML cells and granulocyte fractions. This problem could be significantly reduced by adding protease inhibitors to several steps of the immunobead assay. The immunobead assay was further developed and standardized by BD Biosciences into the Cytometric Bead Array (CBA) assay (BCR-ABL Protein Kit; BD Biosciences, San Jose, CA) for Research Use Only. Large scale testing of this kit in 9 diagnostic laboratories of the EuroFlow Consortium showed that the results of the flow cytometric BCR-ABL immunobead assay were fully concordant with the PCR results in a series of 83 freshly collected samples from newly diagnosed (n=75) or relapsed (n=8) leukemia patients: 13 CML patients, 53 ALL patients, and 17 acute myeloid leukemia (AML) patients (see table). All blood samples tested from 61 healthy controls were negative in the immunobead assay. BCR-ABL PCR assay BCR-ABL immunobead assay negative p190 p210 negative* weak* medium* high* * negative: MFI value We conclude that the flow cytometric immunobead assay is a fast and easy technique for specific detection of BCR-ABL proteins in leukemic cells. The assay is independent of the breakpoint position in the BCR gene, does not need special laboratory facilities other than a routine flow cytometer, provides results within several hours, and can be run in parallel to routine immunophenotyping. Since differentially labeled beads allow multiplexing, it will be possible to develop single tube assays for combined evaluation of multiple different fusion proteins, e.g. per disease category. Consequently, the flow cytometric immunobead assay can contribute to fast and easy diagnosis and classification of leukemias. If sufficient sensitivity can be reached, also monitoring of minimal residual disease becomes possible.