Progression free survival of myeloma patients who become IFE-negative correlates with the detection of residual monoclonal free light chain (FLC) by mass spectrometry.

Deeper responses are associated with improved survival in patients being treated for myeloma. However, the sensitivity of the current blood-based assays is limited. Historical studies suggested that normalisation of the serum free light chain (FLC) ratio in patients who were negative by immunofixation electrophoresis (IFE) was associated with improved outcomes. However, recently this has been called into question. Mass spectrometry (MS)-based FLC assessments may offer a superior methodology for the detection of monoclonal FLC due to greater sensitivity. To test this hypothesis, all available samples from patients who were IFE negative after treatment with carfilzomib and lenalidomide-based induction and autologous stem cell transplantation (ASCT) in the Myeloma XI trial underwent FLC-MS testing. FLC-MS response assessments from post-induction, day+100 post-ASCT and six months post-maintenance randomisation were compared to serum FLC assay results. Almost 40% of patients had discordant results and 28.7% of patients with a normal FLC ratio had residual monoclonal FLC detectable by FLC-MS. FLC-MS positivity was associated with reduced progression-free survival (PFS) but an abnormal FLC ratio was not. This study demonstrates that FLC-MS provides a superior methodology for the detection of residual monoclonal FLC with FLC-MS positivity identifying IFE-negative patients who are at higher risk of early progression.

A complementary role of multiparameter flow cytometry and high-throughput sequencing for minimal residual disease detection in chronic lymphocytic leukemia: an European Research Initiative on CLL study.

In chronic lymphocytic leukemia (CLL) the level of minimal residual disease (MRD) after therapy is an independent predictor of outcome. Given the increasing number of new agents being explored for CLL therapy, using MRD as a surrogate could greatly reduce the time necessary to assess their efficacy. In this European Research Initiative on CLL (ERIC) project we have identified and validated a flow-cytometric approach to reliably quantitate CLL cells to the level of 0.0010% (10(-5)). The assay comprises a core panel of six markers (i.e. CD19, CD20, CD5, CD43, CD79b and CD81) with a component specification independent of instrument and reagents, which can be locally re-validated using normal peripheral blood. This method is directly comparable to previous ERIC-designed assays and also provides a backbone for investigation of new markers. A parallel analysis of high-throughput sequencing using the ClonoSEQ assay showed good concordance with flow cytometry results at the 0.010% (10(-4)) level, the MRD threshold defined in the 2008 International Workshop on CLL guidelines, but it also provides good linearity to a detection limit of 1 in a million (10(-6)). The combination of both technologies would permit a highly sensitive approach to MRD detection while providing a reproducible and broadly accessible method to quantify residual disease and optimize treatment in CLL.

Improving efficiency and sensitivity: European Research Initiative in CLL (ERIC) update on the international harmonised approach for flow cytometric residual disease monitoring in CLL.

Detection of minimal residual disease (MRD) in chronic lymphocytic leukaemia (CLL) is becoming increasingly important as treatments improve. An internationally harmonised four-colour (CLR) flow cytometry MRD assay is widely used but has limitations. The aim of this study was to improve MRD analysis by identifying situations where a less time-consuming CD19/CD5/κ/λ analysis would be sufficient for detecting residual CLL, and develop a six-CLR antibody panel that is more efficient for cases requiring full MRD analysis. In 784 samples from CLL patients after treatment, it was possible to determine CD19/CD5/κ/λ thresholds that identified cases with detectable MRD with 100% positive predictive value (PPV). However, CD19/CD5/κ/λ analysis was unsuitable for predicting iwCLL/NCI response status or identifying cases with no detectable MRD. For the latter cases requiring a full MRD assessment, a six-CLR assay was designed comprising CD19/CD5/CD20 with (1) CD3/CD38/CD79b and (2) CD81/CD22/CD43. There was good correlation between four-CLR and six-CLR panels in dilution studies and clinical samples, with 100% concordance for detection of residual disease at the 0.01% (10(-4)) level (n=59) and good linearity even at the 0.001-0.01% (10(-5)-10(-4)) level. A six-CLR panel therefore provides equivalent results to the four-CLR panel but it requires fewer reagents, fewer cells and a much simpler analysis approach.

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.

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.

Heterogeneity of histological transformation events in Waldenström's macroglobulinemia (WM) and related disorders.

Histological transformation, typically to diffuse large B-cell lymphoma (DLBCL) is reported to occur in 5%-10% of patients with WM and recent studies have highlighted a possible aetiological role for the nucleoside analogues. It is however becoming increasingly clear that histological transformation is a complex phenomenon and may include clonally unrelated disorders. In order to highlight this pathological heterogeneity we describe 5 patients with diverse histological progression events. These included EBV-associated events namely DLBCL, peripheral T-cell lymphoma and spontaneously resolving mucocutaneous ulcer. A further 2 patients demonstrated a localised plasma cell rich lesion simulating plasmacytoma and a de novo DLBCL arising in an unrelated B-cell clone. It is clear therefore that detailed pathological assessments are required in all suspected cases of transformation and that the pathological heterogeneity demonstrated by this study needs to be taken into account when potential aetiological factors are being assessed.

Anti-CD22-MCC-DM1: an antibody-drug conjugate with a stable linker for the treatment of non-Hodgkin's lymphoma.

Antibody-drug conjugates (ADCs) are potent cytotoxic drugs linked to antibodies through chemical linkers, and allow specific targeting of drugs to neoplastic cells. The expression of CD22 is limited to B-cells, and we show that CD22 is expressed on the vast majority of non-Hodgkin's lymphomas (NHLs). An ideal target for an ADC for the treatment of NHL would have limited expression outside the B-cell compartment and be highly effective against NHL. We generated an ADC consisting of a humanized anti-CD22 antibody conjugated to the anti-mitotic agent maytansine with a stable linker (anti-CD22-MCC-DM1). Anti-CD22-MCC-DM1 was broadly effective in in vitro killing assays on NHL B-cell lines. We did not find a strong correlation between in vitro potency and CD22 surface expression, internalization of ADC or sensitivity to free drug. We show that anti-CD22-MCC-DM1 was capable of inducing complete tumor regression in NHL xenograft mouse models. Further, anti-CD22-MCC-DM1 was well tolerated in cynomolgus monkeys and substantially decreased circulating B-cells as well as follicle size and germinal center formation in lymphoid organs. These results suggest that anti-CD22-MCC-DM1 has an efficacy, safety and pharmacodynamic profile that support its use as a treatment for NHL.

Flow cytometric protein expression profiling as a systematic approach for developing disease-specific assays: identification of a chronic lymphocytic leukaemia-specific assay for use in rituximab-containing regimens.

Depletion of disease below the levels detected by sensitive minimal residual disease (MRD) assays is associated with prolonged survival in chronic lymphocytic leukaemia (CLL). Flow cytometric MRD assays are now sufficiently sensitive and rapid to guide the duration of therapy in CLL, but generally rely on assessment of CD20 expression, which cannot be accurately measured during and after therapeutic approaches containing rituximab. The aim of this study was to use analytical software developed for microarray analysis to provide a systematic approach for MRD flow assay development. Samples from CLL patients (n=49), normal controls (n=21) and other B-lymphoproliferative disorders (n=12) were assessed with a panel of 66 antibodies. The DNA-Chip analysis program was used to identify discriminating antibodies, with hierarchical cluster analysis to identify complementary combinations. An iterative process was used: increasing numbers of patients were assessed with smaller, more targeted antibody panels until a highly specific combination (CD81/CD22/CD19/CD5) was identified. This combination was as sensitive and specific as previously reported assays and potentially applicable to blood and marrow samples from patients treated with current therapeutic approaches including rituximab. This approach to the identification of disease-specific antibody combinations for MRD analysis is readily applicable to a variety of haematological disorders.