Prognostic impact of ZAP-70 expression in chronic lymphocytic leukemia: mean fluorescence intensity T/B ratio versus percentage of positive cells

Current Landscape of Ancillary Diagnostic Testing in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia and is a heterogeneous disease with variable patient outcomes. A multidisciplinary technical evaluation, including flow cytometry, immunohistochemistry, molecular and cytogenetic analyses, can comprehensively characterize a patient's leukemia at diagnosis, identify important prognostic biomarkers, and track measurable residual disease; all of which can impact patient management. This review highlights the key concepts, clinical significance, and main biomarkers detectable with each of these technical approaches; the contents are a helpful resource for medical practitioners involved in the workup and management of patients with CLL.

Towards a Better Characterisation of Leukemic Cells in Chronic Lymphocytic Leukaemia: Cell-Size Heterogeneity Reflects Their Activation Status and Migratory Abilities

Simple Summary

Chronic lymphocytic leukaemia (CLL) is a heterogeneous chronic disease characterised by the clonal expansion of mature CD19⁺CD23⁺CD5⁺ B-cells in blood, bone marrow and lymphoid tissue. Despite the CLL tumour cell population showing considerable heterogeneity in cell size, the functional characteristics of leukemic cells that differ in size have not been explored. The results of our study demonstrate that differences in CLL cell size reflect their activation state, polarisation and migratory capacity, with large CLL cells being more activated, polarised and motile than the small CLL cells present in the CLL cell pool. Our data provide evidence of the importance of cell-size heterogeneity within the CLL cell pool and the dynamics of cell-size changes for disease pathogenesis.

Abstract

Chronic lymphocytic leukaemia (CLL) is a genetically, morphologically and phenotypically heterogeneous chronic disease with clinical variability between patients. Whether the significant heterogeneity of cell size within the CLL population contributes to the heterogeneous features of this disease has not been investigated. The present study aimed to characterise the phenotypic and functional properties of two subpopulations of typical CLL cells that differ in cell size: small (s-CLL) and large (l-CLL) CLL cells delineated by forward scatter cytometry. The s-CLL cells were characterised by the CD5^lowCXCR4^hi phenotype, while the l-CLL cells were characterised by the CD5^hiCXCR4^dim phenotype and indicated a higher expression of CXCR3, CD20, CD38 and HLA-DR. The l-CLL cells displayed higher migration activity towards CXCL12, a tendency towards a higher proliferation rate and an increased capacity to produce IgM in the presence of CpG compared with s-CLL cells. When stimulated with CpG and CXCL12, l-CLL cells were characterised by a higher polarisation phenotype and motility than s-CLL cells. Our study revealed that the differences in CLL cell size reflected their activation status, polarisation and migratory abilities. Our data provide evidence of the importance of cell-size heterogeneity within a CLL pool and the dynamics of cell-size changes for disease pathogenesis, thus deserving further investigation.

Prognostic models for newly-diagnosed chronic lymphocytic leukaemia in adults: a systematic review and meta-analysis

BACKGROUND

Chronic lymphocytic leukaemia (CLL) is the most common cancer of the lymphatic system in Western countries. Several clinical and biological factors for CLL have been identified. However, it remains unclear which of the available prognostic models combining those factors can be used in clinical practice to predict long-term outcome in people newly-diagnosed with CLL.

OBJECTIVES

To identify, describe and appraise all prognostic models developed to predict overall survival (OS), progression-free survival (PFS) or treatment-free survival (TFS) in newly-diagnosed (previously untreated) adults with CLL, and meta-analyse their predictive performances.

SEARCH METHODS

We searched MEDLINE (from January 1950 to June 2019 via Ovid), Embase (from 1974 to June 2019) and registries of ongoing trials (to 5 March 2020) for development and validation studies of prognostic models for untreated adults with CLL. In addition, we screened the reference lists and citation indices of included studies.

SELECTION CRITERIA

We included all prognostic models developed for CLL which predict OS, PFS, or TFS, provided they combined prognostic factors known before treatment initiation, and any studies that tested the performance of these models in individuals other than the ones included in model development (i.e. 'external model validation studies'). We included studies of adults with confirmed B-cell CLL who had not received treatment prior to the start of the study. We did not restrict the search based on study design.

DATA COLLECTION AND ANALYSIS

We developed a data extraction form to collect information based on the Checklist for Critical Appraisal and Data Extraction for Systematic Reviews of Prediction Modelling Studies (CHARMS). Independent pairs of review authors screened references, extracted data and assessed risk of bias according to the Prediction model Risk Of Bias ASsessment Tool (PROBAST). For models that were externally validated at least three times, we aimed to perform a quantitative meta-analysis of their predictive performance, notably their calibration (proportion of people predicted to experience the outcome who do so) and discrimination (ability to differentiate between people with and without the event) using a random-effects model. When a model categorised individuals into risk categories, we pooled outcome frequencies per risk group (low, intermediate, high and very high). We did not apply GRADE as guidance is not yet available for reviews of prognostic models.

MAIN RESULTS

From 52 eligible studies, we identified 12 externally validated models: six were developed for OS, one for PFS and five for TFS. In general, reporting of the studies was poor, especially predictive performance measures for calibration and discrimination; but also basic information, such as eligibility criteria and the recruitment period of participants was often missing. We rated almost all studies at high or unclear risk of bias according to PROBAST. Overall, the applicability of the models and their validation studies was low or unclear; the most common reasons were inappropriate handling of missing data and serious reporting deficiencies concerning eligibility criteria, recruitment period, observation time and prediction performance measures. We report the results for three models predicting OS, which had available data from more than three external validation studies: CLL International Prognostic Index (CLL-IPI) This score includes five prognostic factors: age, clinical stage, IgHV mutational status, B2-microglobulin and TP53 status. Calibration: for the low-, intermediate- and high-risk groups, the pooled five-year survival per risk group from validation studies corresponded to the frequencies observed in the model development study. In the very high-risk group, predicted survival from CLL-IPI was lower than observed from external validation studies. Discrimination: the pooled c-statistic of seven external validation studies (3307 participants, 917 events) was 0.72 (95% confidence interval (CI) 0.67 to 0.77). The 95% prediction interval (PI) of this model for the c-statistic, which describes the expected interval for the model's discriminative ability in a new external validation study, ranged from 0.59 to 0.83. Barcelona-Brno score Aimed at simplifying the CLL-IPI, this score includes three prognostic factors: IgHV mutational status, del(17p) and del(11q). Calibration: for the low- and intermediate-risk group, the pooled survival per risk group corresponded to the frequencies observed in the model development study, although the score seems to overestimate survival for the high-risk group. Discrimination: the pooled c-statistic of four external validation studies (1755 participants, 416 events) was 0.64 (95% CI 0.60 to 0.67); 95% PI 0.59 to 0.68. MDACC 2007 index score The authors presented two versions of this model including six prognostic factors to predict OS: age, B2-microglobulin, absolute lymphocyte count, gender, clinical stage and number of nodal groups. Only one validation study was available for the more comprehensive version of the model, a formula with a nomogram, while seven studies (5127 participants, 994 events) validated the simplified version of the model, the index score. Calibration: for the low- and intermediate-risk groups, the pooled survival per risk group corresponded to the frequencies observed in the model development study, although the score seems to overestimate survival for the high-risk group. Discrimination: the pooled c-statistic of the seven external validation studies for the index score was 0.65 (95% CI 0.60 to 0.70); 95% PI 0.51 to 0.77.

AUTHORS' CONCLUSIONS

Despite the large number of published studies of prognostic models for OS, PFS or TFS for newly-diagnosed, untreated adults with CLL, only a minority of these (N = 12) have been externally validated for their respective primary outcome. Three models have undergone sufficient external validation to enable meta-analysis of the model's ability to predict survival outcomes. Lack of reporting prevented us from summarising calibration as recommended. Of the three models, the CLL-IPI shows the best discrimination, despite overestimation. However, performance of the models may change for individuals with CLL who receive improved treatment options, as the models included in this review were tested mostly on retrospective cohorts receiving a traditional treatment regimen. In conclusion, this review shows a clear need to improve the conducting and reporting of both prognostic model development and external validation studies. For prognostic models to be used as tools in clinical practice, the development of the models (and their subsequent validation studies) should adapt to include the latest therapy options to accurately predict performance. Adaptations should be timely.

Impact of Enhancer of Zeste Homolog 2 on T Helper Cell-Mediated Allergic Rhinitis

Enhancer of zeste homolog 2 (Ezh2) has been shown to play a role in the differentiation of T helper (Th) 1 and 2 cells in mice studies using Ezh2-deficient T cells. However, the results have been inconsistent, and the function of Ezh2 in human Th1 and Th2 cell differentiation and its association with disease remains controversial. We measured the expression of Ezh2 in Th1 and Th2 cells in peripheral blood mononuclear cells after acute challenge with house dust mite using flow cytometry in patients with allergic rhinitis (AR) and controls. The role of Ezh2 was further explored by adding the p38 inhibitor to see if this affected allergen-induced Th1 and Th2 differentiation. The expression of Ezh2 in the Th1 and Th2 cells was significantly lower in the patients than in the controls and was negatively correlated with serum IL-17A levels in the patients. Ex vivo allergen challenge resulted in rapid Th2 cell differentiation, which was negatively associated with the Ezh2 expression in Th2 cells. Inhibiting p38 activity increased the expression of Ezh2 in Th2 cells and reduced the number of differentiated Th2 cells. Our findings suggest that Ezh2 expression is potentially associated with AR development.

Context-dependent intravital imaging of therapeutic response using intramolecular FRET biosensors

Intravital microscopy represents a more physiologically relevant method for assessing therapeutic response. However, the movement into an in vivo setting brings with it several additional considerations, the primary being the context in which drug activity is assessed. Microenvironmental factors, such as hypoxia, pH, fibrosis, immune infiltration and stromal interactions have all been shown to have pronounced effects on drug activity in a more complex setting, which is often lost in simpler two- or three-dimensional assays. Here we present a practical guide for the application of intravital microscopy, looking at the available fluorescent reporters and their respective expression systems and analysis considerations. Moving in vivo, we also discuss the microscopy set up and methods available for overlaying microenvironmental context to the experimental readouts. This enables a smooth transition into applying higher fidelity intravital imaging to improve the drug discovery process.

Using the geometric mean fluorescence intensity index method to measure ZAP-70 expression in patients with chronic lymphocytic leukemia

Expression of ζ-chain-associated protein kinase 70 kDa (ZAP-70) in chronic lymphocytic leukemia (CLL) is associated with more aggressive disease and can help differentiate CLL from cases expressing mutated or unmutated immunoglobulin heavy chain variable region (IgHV) genes. However, standardizing ZAP-70 expression by flow cytometric analysis has proved unsatisfactory. The key point is that ZAP-70 is weakly expressed with a continuous expression pattern rather than a clear discrimination between positive and negative CLL cells, which means that the resulting judgment is subjective. Thus, in this study, we aimed at assessing the reliability and repeatability of ZAP-70 expression using the geometric mean fluorescence intensity (geo MFI) index method based on flow cytometry with 256-channel resolution in a series of 402 CLL patients and to compare ZAP-70 with other biological and clinical prognosticators. According to IgHV mutational status, we were able to confirm that the optimal cut-off point for the geo MFI index was 3.5 in the test set. In multivariate analyses that included the major clinical and biological prognostic markers for CLL, the prognostic impact of ZAP-70 expression appeared to have stronger discriminatory power when the geo MFI index method was applied. In addition, we found that ZAP-70-positive patients according to the geo MFI index method had shorter time to first treatment or overall survival (P=0.0002, P=0.0491). This is the first report showing that ZAP-70 expression can be evaluated by a new approach, the geo MFI index, which could be a useful prognostic method as it is more reliable, less subjective, and therefore better associated with improvement of CLL prognostication and prediction of clinical course.

ZAP70 in B-CLL cells related to the expression in NK cells is a surrogate marker for mutational status

The strongest prognostic factor in chronic B-cell lymphocytic leukemia (CLL) is the mutational status of the immunoglobulin heavy chain variable region (IGHV) genes. Determination of this mutational status is laborious and therefore not applied in routine diagnostics. A search for "surrogate markers" has been conducted over the past few years. One of the most promising surrogate markers is ZAP70, but standardization of the measurement of ZAP70 has proven to be difficult. Conventionally, ZAP70 expression in CLL cells is related to ZAP70 expression in T cells. We propose a new method in which ZAP70 expression in NK cells is used as reference (new NK-MFI method). We have measured ZAP70 expression in samples of 45 previously untreated CLL patients. ZAP70 in CLL cells related to ZAP70 in NK cells correlated better to cytogenetic risk profile and mutational status than the conventional methods. Negativity of both ZAP70 (new NK-MFI method) and CD38 resulted in a probability of 90% for mutated IGHV genes. In conclusion, ZAP70 expression in CLL cells related to ZAP70 expression in NK cells is a better surrogate marker for mutational status than the conventional T cell related methods.

T/B ratio does not reflect levels of ZAP70 expression in clonal CLL B-cells due to ZAP70 overexpression in patient T-cells

Flow cytometry is the reference technique for assessing ZAP70 expression, a marker of poor prognosis in CLL. One of the most common methods is to assess ZAP70 levels in CLL cells by calculating the ratio between ZAP70 mean fluorescence intensities (MFIs) in residual T-cells and CLL B-cells (ZAP70 T/B ratio). In this study, we developed a new method for ZAP70 labeling. Cells were labeled with a combination of anti ZAP70 phycoerythrin-conjugated SBZAP monoclonal antibody (mAb) and mAbs against CD45, CD19, and CD5. The latter three were used to specifically gate on different lymphocyte subsets. Staining was performed in absence (test) or in presence of excess unconjugated SBZAP mAb (isoclonic control). A so-called ZAP70 isoclonic ratio between SBZAP MFIs in the test and isoclonic control was calculated. A series of 32 patients with CLL and 10 normal controls were studied. Prediction of IGHV mutation status by ZAP70 isoclonic and T/B ratios was similar. By using the ZAP70 isoclonic ratio, we showed that ZAP70 expression was increased in T-cells from CLL patients. Nearly all cases with increased ZAP70 expression in CLL cells were associated with high ZAP70 expression in cognate T-cells. Therefore, the ZAP70 isoclonic ratio was more likely to closely reflect the biology of ZAP70 dysregulation rather than the T/B ratio. These results also explained why ZAP70 T/B ratios were artefactually close to normal in cells from CLL patients with high levels of ZAP70.

Pitfalls and limitations of ZAP-70 detection in chronic lymphocytic leukemia

Zeta-associated protein of 70 kDa (ZAP-70) is a tyrosine kinase that plays a role in signal transduction from the T-cell receptor. ZAP-70 is expressed in normal T-cells and NK-cells. Increased expression of ZAP-70 has been identified in chronic lymphocytic leukemia (CLL). CLL patients with increased ZAP-70 expression have significantly worse prognosis in terms of both progression-free survival and overall survival. There are several methods to quantify ZAP-70: polymerase chain reaction (PCR), immunoblotting, immunohistochemistry, and flow cytometry. Use of flow cytometry for ZAP-70 detection seems to be advantageous as this technique enables us to assess the presence of ZAP-70 separately on CLL clone, T-cells, and NK-cells. On the other hand, detection of ZAP-70 by flow cytometry is substantially influenced by many variables. The principal drawback of flow cytometry is the absence of consensus regarding selection of optimal anti-ZAP-70 antibody, fluorochrome conjugate, the most reliable staining technique, and optimal positivity threshold. This article summarizes pitfalls of flow cytometric analysis of ZAP-70 in CLL.

Combined normal donor and CLL: Single tube ZAP-70 analysis

INTRODUCTION

Zeta-chain-associated protein kinase 70 (ZAP-70) has been identified as an independent prognostic marker in chronic lymphocytic leukemia (CLL). Based on our previous studies, we have developed a combined one-tube technology with multiple internal controls to optimize ZAP-70 assessment.

METHODS

Forty-eight untreated CLL cases were examined for ZAP-70 expression using a modified 7-color one-tube assay. Normal donor (ND) whole blood is stained with CD3 APC-Cy7 and CD19 APC. In a second tube, patient whole blood is stained with CD5 PE-Cy7, CD19 PerCP-Cy5.5, and CD20 eFluor450. After surface staining and fixation, these two tubes are combined. After saponin permeabilization, the cells were stained with two anti-ZAP-70 clones (1E7.2/AF488 and SBZAP/PE). The results obtained from this modified tube were compared with those obtained concurrently using the non-mixed single sample tubes. Five different methods of ZAP-70 expression analysis were evaluated: percentage positive cells using ND T-cells as a reference; the internal patient T-cell/clone ratio; ND T-cell/clone ratio; clone/ND B-cell ratio; and modified Z-index.

RESULT

Overall, the combined patient and ND mix tube performed better than the non-mixed single sample tube. The strongest correlations between ZAP-70 expression and immunoglobulin heavy chain variable (IGHV) mutational status were seen with percentage positive ND T-cell, ND T-cell/clone ratio, and clone/ND B-cell ratio for both 1E7.2 and SBZAP clone (P < 0.0001).

CONCLUSION

The modified one tube method combining the ND and patient sample provides highly reliable results that correlate with the IGHV mutational status. This method should be considered as part of the next step in standardization of the ZAP-70 assay in CLL.

IGHV gene mutational status and 17p deletion are independent molecular predictors in a comprehensive clinical-biological prognostic model for overall survival prediction in chronic lymphocytic leukemia

Background

Prognostic index for survival estimation by clinical-demographic variables were previously proposed in chronic lymphocytic leukemia (CLL) patients. Our objective was to test in a large retrospective cohort of CLL patients the prognostic power of biological and clinical-demographic variable in a comprehensive multivariate model. A new prognostic index was proposed.

Methods

Overall survival and time to treatment in 620 untreated CLL patients were analyzed retrospectively to evaluate the multivariate independence and predictive power of mutational status of immunoglobulin heavy chain variable gene segments (IGHV), high-risk chromosomal aberration such as 17p or 11q deletions, CD38 and ZAP-70 expression, age, gender, Binet stage, β2-microglobulin levels, absolute lymphocyte count and number of lymph node regions.

Results

IGHV mutational status and 17p deletion were the sole biological variables with independent prognostic relevance in a multivariate model for overall survival, which included easily measurable clinical parameters (Binet staging, β2-microglobulin levels) and demographics (age and gender). Analysis of time to treatment in Binet A patients below 70 years of age showed that IGHV was the most important predictor. A novel 6-variable clinical-biological prognostic index was developed and internally validated, which assigned 3 points for Binet C stage, 2 points/each for Binet B stage and for age > 65 years, 1 point/each for male gender, high β2-microglobulin levels, presence of an unmutated IGHV gene status or 17p deletion. Patients were classified at low-risk (score = 0-1; 21%), intermediate-risk (score 2-5; 63% of cases), high-risk (score 6-9; 16% of cases). Projected 5-year overall survival was 98%, 90% and 58% in low-, intermediate- and high-risk groups, respectively. A nomogram for individual patient survival estimation was also proposed.

Conclusions

Data indicate that IGHV mutational status and 17p deletion may be integrated with clinical-demographic variables in new prognostic tools to estimate overall survival.

Clinical and Laboratory Prognostic Indicators in Chronic Lymphocytic Leukemia

Background

The clinical course of patients with chronic lymphocytic leukemia (CLL) is heterogeneous, with some patients experiencing rapid disease progression and others living for decades without requiring treatment. The Rai and Binet clinical staging systems are used to define disease extent and predict survival. The pathology laboratory also provides important prognostic information.

Methods

A review of the literature was performed on the subject of staging in CLL from clinical and pathologic standpoints. This article also reviews currently available diagnostic approaches related to disease prognosis and to timing of treatment and follow-up in patients with CLL.

Results

Novel biological and cytogenetic features such as immunoglobulin heavy-chain variable gene segment [IgVH], genomic aberrations including del(17p13), del(11q23), del(13q14), and trisomy 12, serum markers (thymidine kinase and beta-2 microglobulin), and cellular markers (CD38 and ZAP70) have become increasingly important in predicting prognosis at the time of diagnosis.

Conclusions

Current prognostic factors directly or indirectly influence the management of patients with CLL and help to predict treatment-free and overall survival.

Methodological comparison of two anti-ZAP-70 antibodies

BACKGROUND

ZAP-70 expression is a stage independent prognostic marker in CLL. However, interlaboratory variation is large, and there is neither a consensus nor a regulatory approved methodology.

METHODS

Two anti-ZAP70 clones (1E7.2 and SBZAP) were compared in 45 untreated CLL patients. Nine different methods for ZAP-70 expression analysis were evaluated: M1, isotype control to determine negative; M2, internal residual T-cell to determine positive; M3, normal donor (ND) T-cell to determine positive; M4, internal T-cell/clone ratio; M5, ND residual T-cell/clone ratio; M6, clone/normal remaining B-cell ratio; M7, clone/ND B- cell ratio; M8, CLL-Z score; M9, modified CLL-Z score. A scoring system was designed integrating both 1E7.2 and SBZAP clones to assign ZAP-70 expression.

RESULTS

The correlation coefficients for the four selected highest statistically significant methods were as follows (M1 = 0.71, M3 = 0.72, M7 = 0.67, and M9 = 0.64). These four methods were used to generate a combined score. The two reagents showed agreement using the designed scoring system for 37/45 samples (82%), and 8/45 (18%) showed equivocal result with one of the two clones. Seven of the eight equivocal samples were resolved using the scoring system.

CONCLUSIONS

Four of the nine methods of analysis were compared for each reagent. The use of two independent ZAP-70 reagents increases analytical certitude and the scoring method aids in the resolution of equivocal results. The combined use of two reagents, four methods of analysis, and a scoring method allowed for assignment of ZAP-70 expression in 44/45 samples (98%) tested and improved performance of this important prognostic assay.

Detection methods of ZAP-70 in chronic lymphocytic leukemia

The clinical course of patients with chronic lymphocytic leukemia (CLL) is highly heterogeneous, with some patients experiencing rapid disease progression and others living for decades without requiring treatment. Immunoglobulin heavy chain variable region (IGHV) mutation status is a powerful prognostic factor in patients with CLL. The presence or absence of IGHV mutation status is currently the gold-standard prognostic factor, but this technique is labor-intensive and costly. The expression of ζ-chain-associated protein kinase 70 kDa (ZAP-70), detected by flow cytometry, has been served as a potential surrogate for the absence of IGHV mutation status since 2003. Given the current problems with the standardization of ZAP-70 assessment by flow cytometry, this chapter reviews the analysis of ZAP-70 expression by flow cytometry and the relative experimental conditions using the associated publications for "ZAP-70" and "detection method" on Medline since 2003. Thus, mean fluorescence intensity (MFI) ratio method yielded a more reproducible and easily adaptable method to routine use in the clinical diagnostic laboratory. In conclusion, though ZAP-70 is a valuable prognostic factor in CLL, detection methods of ZAP-70 remain to be fully standardized.