Comparative analysis of minimal residual disease detection using four-color flow cytometry, consensus IgH-PCR, and quantitative IgH PCR in CLL after allogeneic and autologous stem cell transplantation

Chronic Lymphocytic Leukemia: Time-Limited Therapy in the First-Line Setting and Role of Minimal Residual Disease

PURPOSE OF REVIEW

In this review, we provide an overview of different time-limited combination therapies of chronic lymphocytic leukemia (CLL) and summarize the data of pivotal clinical studies. Furthermore, we discuss the relevance of MRD in clinical trials and summarize the challenges that arise in routine clinical care. Finally, we provide an outlook on studies and datasets needed to optimize the use of time-limited treatment strategies and MRD assessments in modern CLL management.

RECENT FINDINGS

In recent years, first-line treatment of CLL has undergone a considerable transformation, with targeted substances having largely replaced chemoimmunotherapy (CIT) as a time-limited strategy in the frontline setting. BTK inhibitors were the first class of targeted agents introduced in CLL, which achieved longer progression-free survival (PFS) and in some cases also overall survival (OS) than CIT. However, this required an indefinite drug intake until disease progression, while CIT is generally administered over the course of few months. In contrast to BTK inhibitors, BCL2 inhibitors, another class of targeted agents, can achieve high rates of undetectable minimal residual disease (uMRD) levels and induce deep molecular remissions with the potential to stop treatment while maintaining remissions. Combinations of BCL2 inhibitors with CD20 antibodies or with BTK inhibitors have been explored to establish time-limited treatment strategies with targeted agents. In this context, one of the strongest predictors of long-term outcomes is MRD status at the end of treatment, which has been shown to correlate closely with PFS and OS in most cases.

Measurable residual disease in chronic lymphocytic leukemia: expert review and consensus recommendations

Assessment of measurable residual disease (often referred to as "minimal residual disease") has emerged as a highly sensitive indicator of disease burden during and at the end of treatment and has been correlated with time-to-event outcomes in chronic lymphocytic leukemia. Undetectable-measurable residual disease status at the end of treatment demonstrated independent prognostic significance in chronic lymphocytic leukemia, correlating with favorable progression-free and overall survival with chemoimmunotherapy. Given its utility in evaluating depth of response, determining measurable residual disease status is now a focus of outcomes in chronic lymphocytic leukemia clinical trials. Increased adoption of measurable residual disease assessment calls for standards for nomenclature and outcomes data reporting. In addition, many basic questions have not been systematically addressed. Here, we present the work of an international, multidisciplinary, 174-member panel convened to identify critical questions on key issues pertaining to measurable residual disease in chronic lymphocytic leukemia, review evaluable data, develop unified answers in conjunction with local expert input, and provide recommendations for future studies. Recommendations are presented regarding methodology for measurable residual disease determination, assay requirements and in which tissue to assess measurable residual disease, timing and frequency of assessment, use of measurable residual disease in clinical practice versus clinical trials, and the future usefulness of measurable residual disease assessment. Nomenclature is also proposed. Adoption of these recommendations will work toward standardizing data acquisition and interpretation in future studies with new treatments with the ultimate objective of improving outcomes and curing chronic lymphocytic leukemia.

Multiparametric Flow Cytometry for MRD Monitoring in Hematologic Malignancies: Clinical Applications and New Challenges

Simple Summary

In hematologic cancers, Minimal Residual Disease (MRD) monitoring, using either molecular (PCR) or immunophenotypic (MFC) diagnostics, allows the identification of rare cancer cells, readily detectable either in the bone marrow or in the peripheral blood at very low levels, far below the limit of classic microscopy. In this paper, we outlined the state-of-the-art of MFC-based MRD detection in different hematologic settings, highlighting main recommendations and new challenges for using such method in patients with acute leukemias or chronic hematologic neoplasms. The combination of new molecular technologies with advanced flow cytometry is progressively allowing clinicians to design a personalized therapeutic path, proportionate to the biological aggressiveness of the disease, in particular by using novel immunotherapies, in view of a modern decision-making process, based on precision medicine.

Abstract

Along with the evolution of immunophenotypic and molecular diagnostics, the assessment of Minimal Residual Disease (MRD) has progressively become a keystone in the clinical management of hematologic malignancies, enabling valuable post-therapy risk stratifications and guiding risk-adapted therapeutic approaches. However, specific prognostic values of MRD in different hematological settings, as well as its appropriate clinical uses (basically, when to measure it and how to deal with different MRD levels), still need further investigations, aiming to improve standardization and harmonization of MRD monitoring protocols and MRD-driven therapeutic strategies. Currently, MRD measurement in hematological neoplasms with bone marrow involvement is based on advanced highly sensitive methods, able to detect either specific genetic abnormalities (by PCR-based techniques and next-generation sequencing) or tumor-associated immunophenotypic profiles (by multiparametric flow cytometry, MFC). In this review, we focus on the growing clinical role for MFC-MRD diagnostics in hematological malignancies—from acute myeloid and lymphoblastic leukemias (AML, B-ALL and T-ALL) to chronic lymphocytic leukemia (CLL) and multiple myeloma (MM)—providing a comparative overview on technical aspects, clinical implications, advantages and pitfalls of MFC-MRD monitoring in different clinical settings.

Should Undetectable Minimal Residual Disease Be the Goal of Chronic Lymphocytic Leukemia Therapy?

With the advent of highly effective novel therapies for chronic lymphocytic leukemia, conventional response assessment is not able to sensitively capture depth of response. To achieve a more precise assessment of response, minimal residual disease has been introduced to more accurately classify and quantify treatment outcomes. It is now considered a strong predictor of outcome in chronic lymphocytic leukemia, although its interpretation depends on the therapeutic context. This review discusses available methods of minimal residual disease measurement. It summarizes minimal residual disease data from pivotal clinical trials and discusses potential implications for future studies and minimal residual disease-based clinical strategies.

Measurable residual disease in the treatment of chronic lymphocytic leukemia

Treatment outcomes of chronic lymphocytic leukemia (CLL) have improved since chemoimmunotherapy and novel drugs became available for CLL treatment; therefore, more sensitive methods to evaluate residual CLL cells in patients are required. Measurable residual disease (MRD) has been assessed in several clinical trials on CLL using flow cytometry, real-time quantitative PCR (RQ-PCR) with allele-specific oligonucleotide (ASO) primers, and high-throughput sequencing. MRD assessment is useful to predict the treatment outcomes in the context of chemotherapy and treatment with novel drugs such as venetoclax. In this review, we discuss major techniques for MRD assessment, data from relevant clinical trials, and the future of MRD assessment in CLL treatment.

Relevance of Minimal Residual Disease in the Era of Targeted Agents

The evaluation of minimal residual disease (MRD) in chronic lymphocytic leukemia (CLL) has evolved in parallel with the enormous progresses in the therapeutic armamentarium and the application of cutting-edge diagnostic techniques the CLL community witnessed in the past few years. Minimal residual disease is considered an objective measure of disease status defined by the number of residual leukemic cells detected in a sample of peripheral blood and/or bone marrow as proportion of the total white blood cells and defined undetectable if fewer than 1 CLL cell among 10,000 white blood cells (10 or 0.01%) is detected. In this review, we aim at shedding light on how to evaluate MRD, what we already know about MRD from the experience with chemoimmunotherapy, and why MRD evaluation remains still relevant in the era of targeted agents.

Minimal Residual Disease Assessment in CLL: Ready for Use in Clinical Routine?

The introduction of chemoimmunotherapy and more recently the implementation of novel agents into first-line and relapse treatment have substantially improved treatment outcomes in patients with chronic lymphocytic leukaemia (CLL). With longer progression-free survival and more frequently observed deep remissions there is an emerging need for sensitive methods quantitating residual disease after therapy. Over the last decade, assessment of minimal residual disease (MRD) has increasingly been implemented in CLL trials. The predictive value of MRD status on survival outcomes has repeatedly been proven in the context of chemoimmunotherapy and cellular therapies. Recent data suggests a similar correlation for Bcl-2 inhibitor-based therapy. While the relevance of MRD assessment as a surrogate endpoint in clinical trials is largely undisputed, its role in routine clinical practice has not yet been well defined. This review outlines current methods of MRD detection in CLL and summarizes MRD data from relevant trials. The significance of MRD testing in clinical studies and in routine patient care is assessed and new MRD-guided treatment strategies are discussed.

Minimal Residual Disease in Chronic Lymphocytic Leukemia: A New Goal?

In chronic lymphocytic leukemia (CLL), there is a growing interest for minimal residual disease (MRD) monitoring, due to the availability of drug combinations capable of unprecedented complete clinical responses. The standardized and most commonly applied methods to assess MRD in CLL are based on flow cytometry (FCM) and, to a lesser extent, real-time quantitative PCR (RQ-PCR) with allele-specific oligonucleotide (ASO) primers of immunoglobulin heavy chain genes (IgH). Promising results are being obtained using droplet digital PCR (ddPCR) and next generation sequencing (NGS)-based approaches, with some advantages and a potential higher sensitivity compared to the standardized methodologies. Plasma cell-free DNA can also be explored as a more precise measure of residual disease from all different compartments, including the lymph nodes. From a clinical point of view, CLL MRD quantification has proven an independent prognostic marker of progression-free survival (PFS) and overall survival (OS) after chemoimmunotherapy as well as after allogeneic transplantation. In the era of mechanism-driven drugs, the paradigms of CLL treatment are being revolutionized, challenging the use of chemoimmunotherapy even in first-line. The continuous administration of ibrutinib single agent has led to prolonged PFS and OS in relapsed/refractory and treatment naïve CLL, including those with TP53 deletion/mutation or unmutated IGHV genes, though the clinical responses are rarely complete. More recently, chemo-free combinations of venetoclax+rituximab, venetoclax+obinutuzumab or ibrutinib+venetoclax have been shown capable of inducing undetectable MRD in the bone marrow, opening the way to protocols exploring a MRD-based duration of treatment, aiming at disease eradication. Thus, beside a durable disease control desirable particularly for older patients and/or for those with comorbidities, a MRD-negative complete remission is becoming a realistic prospect for CLL patients in an attempt to obtain a long-lasting eradication and possibly cure of the disease. Here we discuss the standardized and innovative technical approaches for MRD detection in CLL, the clinical impact of MRD monitoring in chemoimmunotherapy and chemo-free trials and the future clinical implications of MRD monitoring in CLL patients outside of clinical trials.

Minimal Residual Disease Quantification in Chronic Lymphocytic Leukemia: Clinical Significance and Flow Cytometric Methods

The very sensitive quantification of leukemia cells that persist in chronic lymphocytic leukemia patients after successful therapy is steadily gaining interest with clinical scientists. Minimal residual disease (MRD) has demonstrated prognostic significance in the context of different treatment modalities leading to its approval as an intermediate endpoint for licensure in randomized trials by the European Medicine Agency. Data supporting the clinical impact of MRD as well as a highly standardized and broadly available method for MRD assessments by flow cytometry are described herein. Examples of gating strategies are provided with comprehensive explanations to allow the reader the application of the technology to blood and bone samples with high and very low level MRD, respectively. This chapter has a particular focus on samples acquired shortly after anti-CD20 treatment. The standardization developed by the EuroFlow consortium is additionally described as technical basis for reproducible and standardized flow cytometric MRD assessments.

Flow Cytometric MRD Detection in Selected Mature B-Cell Malignancies

The quantification of submicroscopic minimal residual disease (MRD) after therapy proved to have independent prognostic significance in many mature B-cell malignancies. With the advent of routine benchtop cytometers capable of simultaneously analyzing ≥4 colors and with improved standardization, flow cytometry has become the method of choice for MRD assessments in some lymphoma entities. Herein we describe general aspects of flow cytometric standardization. Chronic lymphocytic leukemia and multiple myeloma (MM) are used as examples to explain the technical standardization of flow cytometry for MRD detection according to EuroFlow strategies. MRD data acquisition and detailed analysis using a newly developed approach (so-called next generation flow, NGF) in MM is a particular focus of this chapter.

The potential combination of BCL-2 inhibitors and ibrutinib as frontline therapy in chronic lymphocytic leukemia

The recent development of small molecule inhibitors targeted at the B-cell receptor (BCR) pathway and the anti-apoptotic protein BCL-2 has revolutionized the care of patients with chronic lymphocytic leukemia (CLL). While durable responses to the BCR inhibitor ibrutinib have been observed in both previously untreated and relapsed/refractory CLL patients, residual disease is common in patients treated with single-agent ibrutinib. Interest remains high in therapeutic combinations that may lead to better quality remissions. A potential partner to ibrutinib with a distinct mechanism of action that is likely to lead to deeper responses is the BCL-2 inhibitor venetoclax. Preclinical studies have suggested synergism between inhibitors of BCR and BCL-2 and have paved the way to the development of ongoing clinical trials aimed at evaluating the combination of ibrutinib with venetoclax in CLL patients.

Marked Variability in Reported Minimal Residual Disease Lower Level of Detection of 4 Hematolymphoid Neoplasms: A Survey of Participants in the College of American Pathologists Flow Cytometry Proficiency Testing Program

Context

Flow cytometry is often applied to minimal residual disease (MRD) testing in hematolymphoid neoplasia. Because flow-based MRD tests are developed in the laboratory, testing methodologies and lower levels of detection (LODs) are laboratory dependent.

Objectives

To broadly survey flow cytometry laboratories about MRD testing in laboratories, if performed, including indications and reported LODs.

Design

Voluntary supplemental questions were sent to the 549 laboratories participating in the College of American Pathologists (CAP) FL3-A Survey (Flow Cytometry—Immunophenotypic Characterization of Leukemia/Lymphoma) in the spring of 2014.

Results

A total of 500 laboratories (91%) responded to the supplemental questions as part of the FL3-A Survey by April 2014; of those 500 laboratories, 167 (33%) currently perform MRD for lymphoblastic leukemia, 118 (24%) for myeloid leukemia, 99 (20%) for chronic lymphocytic leukemia, and 91 (18%) for plasma cell myeloma. Other indications include non-Hodgkin lymphoma, hairy cell leukemia, neuroblastoma, and myelodysplastic syndrome. Most responding laboratories that perform MRD for lymphoblastic leukemia reported an LOD of 0.01%. For myeloid leukemia, chronic lymphocytic leukemia, and plasma cell myeloma, most laboratories indicated an LOD of 0.1%. Less than 3% (15 of 500) of laboratories reported LODs of 0.001% for one or more MRD assays performed.

Conclusions

There is major heterogeneity in the reported LODs of MRD testing performed by laboratories subscribing to the CAP FL3-A Survey. To address that heterogeneity, changes to the Flow Cytometry Checklist for the CAP Laboratory Accreditation Program are suggested that will include new requirements that each laboratory (1) document how an MRD assay's LOD is measured, and (2) include the LOD or lower limit of enumeration for flow-based MRD assays in the final diagnostic report.

Minimal residual disease surveillance in chronic lymphocytic leukemia by fluorescence-activated cell sorting

Achievement of complete response (CR) to therapy in chronic lymphocytic leukemia (CLL) has become a feasible goal, directly correlating with prolonged survival. It has been established that the classic definition of CR actually encompasses a variety of disease loads, and more sensitive multiparameter flow cytometry and polymerase chain reaction methods can detect the disease burden with a much higher sensitivity. Detection of malignant cells with a sensitivity of 1 tumor cell in 10,000 cells (10(-4)), using the abovementioned sophisticated techniques, is the current cutoff for minimal residual disease (MRD). Tumor burdens lower than 10(-4) are defined as MRD-negative. Several studies in CLL have determined the achievement of MRD negativity as an independent favorable prognostic factor, leading to prolonged disease-free and overall survival, regardless of the treatment protocol or the presence of other pre-existing prognostic indicators. Minimal residual disease evaluation using flow cytometry is a sensitive and applicable approach which is expected to become an integral part of future prospective trials in CLL designed to assess the role of MRD surveillance in treatment tailoring.

Frontline low-dose alemtuzumab with fludarabine and cyclophosphamide prolongs progression-free survival in high-risk CLL

Frontline FCA increases progression-free survival in CLL and, in a post hoc analysis, also survival in younger patients. With the low-dose approach, no increase in treatment related mortality is seen.

Minimal residual disease monitoring in chronic lymphocytic leukaemia patients. A comparative analysis of flow cytometry and ASO IgH RQ-PCR

Minimal residual disease (MRD) is becoming increasingly important in chronic lymphocytic leukaemia (CLL) as treatment strategies are progressively improving. The primary objective of this study was to compare the applicability of three different flow cytometric approaches: basic 4-colour analysis, European Research Initiative in CLL (ERIC) consensus method and 8-colour analysis. Secondly, we investigated the sensitivity and specificity of flow cytometry (FC) compared to molecular analyses for MRD detection. A total of 462 CLL samples were evaluated by basic FC; in 143, ERIC consensus method was also performed and all three FC methodologies were applied in a subgroup of 10 cases. No discordance in defining MRD-positive/negative samples was observed between the FC methods; within positive samples, the ERIC consensus method and 8-colour analysis showed the most accurate results. MRD was analysed by FC and polymerase chain reaction (PCR) in 243 cases: concordant results were obtained in 199/243 samples (81·9%); 42/243 were FC-/PCR+. Overall, the sensitivity and specificity of FC compared to PCR was 96·5% and 77·2%, respectively. Both FC and PCR proved suitable for the detection of MRD and prediction of progression-free survival, which was significantly reduced in MRD-positive patients, regardless of the methodology. These results offer the rationale for a strategy to monitor MRD in CLL patients.

Peripheral blood 8 colour flow cytometry monitoring of hairy cell leukaemia allows detection of high-risk patients

Although purine analogues have significantly improved the outcome of hairy cell leukaemia (HCL) patients, 30-40% relapse, illustrating the need for minimal residual disease (MRD) markers that can aid personalized therapeutic management. Diagnostic samples from 34 HCL patients were used to design an 8-colour flow cytometry (8-FC) tube for blood MRD (B/RD) analysis (188 samples) which was compared to quantitative IGH polymerase chain reaction (Q-PCR) on 83 samples and to qualitative consensus IGH PCR clonality analysis on 165 samples. Despite heterogeneous HCL phenotypes at diagnosis, discrimination from normal B lymphocytes was possible in all cases using a single 8-FC tube, with a robust sensitivity of detection of 10(-4) , comparable to Q-PCR at this level, but preferable in terms of informativeness, simplicity and cost. B/RD assessment of 15 patients achieving haematological complete remission after purine analogues was predictive of a clinically significant relapse risk: with a median follow-up of 95 months; only one of the nine patients with reproducible 8-FC B/RD levels below 10(-4) (B/RD(neg) ) relapsed, compared to 5/6 in the B/RD(pos) group (P = 0.003). These data demonstrate the clinical interest of a robust 8-FC HCL B/RD strategy that could become a surrogate biomarker for therapeutic stratification and new drug assessment, which should be evaluated prospectively.

New approaches to manipulate minimal residual disease after allogeneic stem cell transplantation

Minimal residual disease (MRD) is a complex topic that has been studied extensively in hematologic malignancies given its clinical implications related to prognosis. However, methods to monitor and treat MRD, especially after stem cell transplantation, are not well defined and vary in different disease processes. Alternative transplant strategies, such as reduced-intensity conditioning, have altered the way we assess and address MRD after transplantation. Development of new diagnostic tools have allowed for higher sensitivity and specificity of testing. Both targeted chemotherapeutic agents and immunotherapies have been developed to treat MRD in hopes of improving patient outcomes. This article aims to address ways to define and manipulate MRD specifically after stem cell transplantation.

Postallogeneic monitoring with molecular markers detected by pretransplant next-generation or Sanger sequencing predicts clinical relapse in patients with myelodysplastic/myeloproliferative neoplasms

Relapse is the major cause of treatment failure after allogeneic stem-cell transplantation (AHSCT) for patients with myelodysplastic syndrome/myeloproliferative syndrome neoplasms (MDS/MPN). We evaluated the impact of molecular mutations on outcome and the value of molecular monitoring post-transplantation. We screened 45 patients with chronic myelomonocytic leukemia (n = 39 patients, including seven with transformed-acute myeloid leukemia), MDS/MPN unclassifiable (n = 5), and atypical BCR-ABL1-negative CML (n = 1) for mutations in ASXL1, CBL, NRAS, and TET2 genes by molecular genetics including a sensitive next-generation sequencing (NGS) technique. In 36 patients, sufficient DNA was available for molecular analyses. In particular, TET2 and CBL mutations were screened applying amplicon deep sequencing. In 89% of cases, at least one mutation could be detected: ASXL1: n = 18 (50%); CBL: n = 7 (19%); TET2: n = 15 (42%); and NRAS: n = 11 (32%). Survival after AHSCT at 5 yr was 46% (95% CI 28-64%) and was not influenced by any mutation. After a median of 6 months after AHSCT in 33% of the patients, one of the molecular markers was still detectable, resulting in a higher incidence of relapse than in patients with undetectable mutations (50% vs. 15%, P = 0.04). In conclusion, pretransplant molecular mutation analysis can help to detect biomarkers in patients with MPN/MDS, which may be subsequently used as minimal residual disease markers after AHSCT.

Retrospective monitoring of minimal residual disease using hairpin-shaped clone specific primers in B-cell lymphoma affected dogs

Lymphoma is one of the most common forms of cancer in dogs as it is in humans but, unlike humans, the cure rates in canines are still very low. Despite the fact that high grade B-cell lymphomas are considered to be chemotherapy responsive, almost all treated dogs ultimately relapse and die due to the residual malignant lymphocytes, namely minimal residual disease (MRD). It would be extremely valuable for clinicians to detect, monitor and quantify MRD for risk group stratification, effective treatment intervention and outcome prediction. The PCRs targeting the Ig gene rearrangements constitute one of the most reliable tools to this end. We have recently validated a method which exploits hairpin-shaped primers for quantifying MRD. In the present study, that method is conveniently used for retrospectively monitoring MRD in the peripheral blood of 8 dogs diagnosed with B-cell lymphoma who underwent chemotherapy. All dogs attained complete remission. The median disease-free interval was 254.5 days (range 63-774) while the median survival time was 313.5 days (range 143-817 days). At admission, all dogs, except one which had already been treated with prednisone, had circulating neoplastic cells. All dogs attained complete remission (CR) which was almost always matched with a complete MRD response. The persistence of MRD despite apparent CR indicated a worse prognosis and a short duration of CR. Finally, the relapse is consistently anticipated by the reappearance of MRD in the peripheral blood. The study confirmed the suitability of an MRD monitoring assay as a clinical decision-making tool.

An automated high-throughput counting method for screening circulating tumor cells in peripheral blood

Enumeration of circulating tumor cells (CTCs) has proved valuable for early detection and prognosis in cancer treatment. This paper describes an automated high-throughput counting method for CTCs based on microfluidics and line-confocal microscopy. Peripheral blood was directly labeled with multiple antibodies, each conjugated with a different fluorophore, pneumatically pumped through a microfluidic channel, and interrogated by a line-confocal microscope. On the basis of the fluorescence signals and labeling schemes, the count of CTCs was automatically reported. Due to the high flow rate, 1 mL of whole blood can be analyzed in less than 30 min. We applied this method in analyzing CTCs from 90 stage IV breast cancer patient samples and performed a side-by-side comparison with the results of the CellSearch assay, which is the only method approved by the U.S. Food and Drug Administration at present for enumeration of CTCs. This method has a recovery rate for cultured breast cancer cells of 94% (n = 9), with an average of 1.2 counts/mL of background level of detected CTCs from healthy donors. It detected CTCs from breast cancer patients ranging from 15 to 3375 counts/7.5 mL. Using this method, we also demonstrate the ability to enumerate CTCs from breast cancer patients that were positive for Her2 or CD44(+)/CD24(-), which is a putative cancer stem cell marker. This automated method can enumerate CTCs from peripheral blood with high throughput and sensitivity. It could potentially benefit the clinical diagnosis and prognosis of cancer.

Minimal residual disease quantification using consensus primers and high-throughput IGH sequencing predicts post-transplant relapse in chronic lymphocytic leukemia

Quantification of minimal residual disease (MRD) following allogeneic hematopoietic cell transplantation (allo-HCT) predicts post-transplant relapse in patients with chronic lymphocytic leukemia (CLL). We utilized an MRD-quantification method that amplifies immunoglobulin heavy chain (IGH) loci using consensus V and J segment primers followed by high-throughput sequencing (HTS), enabling quantification with a detection limit of one CLL cell per million mononuclear cells. Using this IGH–HTS approach, we analyzed MRD patterns in over 400 samples from 40 CLL patients who underwent reduced-intensity allo-HCT. Nine patients relapsed within 12 months post-HCT. Of the 31 patients in remission at 12 months post-HCT, disease-free survival was 86% in patients with MRD <10⁻⁴ and 20% in those with MRD ⩾10⁻⁴ (relapse hazard ratio (HR) 9.0; 95% confidence interval (CI) 2.5–32; P<0.0001), with median follow-up of 36 months. Additionally, MRD predicted relapse at other time points, including 9, 18 and 24 months post-HCT. MRD doubling time <12 months with disease burden ⩾10⁻⁵ was associated with relapse within 12 months of MRD assessment in 50% of patients, and within 24 months in 90% of patients. This IGH–HTS method may facilitate routine MRD quantification in clinical trials.

A single tube 10-color flow cytometry assay optimizes detection of minimal residual disease in chronic lymphocytic leukemia

Levels of residual disease (RD) are an independent predictor of progression-free survival (PFS) and overall survival (OS) in patients treated for chronic lymphocytic leukemia (CLL). We modified the international standardized approach (ISA) to RD detection using flow cytometry by developing a single tube 10 color antibody assay.

METHOD

A single tube incorporated the following monoclonal antibodies: CD81FITC, CD22PE, CD3ECD, CD5PercP5.5, CD20PECY7, CD79bAPC, CD38A700, CD43APC Alexa750, CD19eFluor 450, and CD45KO. A modified ISA gating strategy was developed that removed contaminating events. Sensitivity assays were performed using dilution with normal peripheral blood and bone marrow. Clinical samples were compared using the ISA and the single tube assay.

RESULTS

Dilution studies showed that sensitivity of 0.001% was achievable when a minimum of 1.8 × 10(6) total events were acquired. One hundred twenty-nine samples were analyzed and showed RD levels from 0.003 to 22%. In 80 samples analyzed with both assays, there was an excellent correlation between the two methods (slope = 1.0, intercept = 0.07 and R2 = 0.992) and results from Bland-Altman analysis showed a bias of 0.04 ± 0.38 with 95% confidence interval of -0.71 to 0.79. Removal of contaminating events in the single tube assay led to a significant reduction in RD values (P = 0.0014).

CONCLUSION

The single tube 10-color assay for the detection of RD in CLL provides equivalent results to the ISA but requires fewer cells, uses fewer reagents, and allows for simpler analysis. By directly removing contaminating events, it improves the accuracy of CLL RD detection and may reclassify the status of some patients following chemotherapy.

Flow cytometric MRD detection in selected mature B-cell malignancies

The quantification of submicroscopic minimal residual disease (MRD) after therapy proved to have independent prognostic significance in many mature B-cell malignancies. With the advent of routine bench-top cytometers capable of simultaneously analyzing ≥ 4 colors and with improved standardization, flow cytometry has become the method of choice for MRD assessments in some lymphoma entities. Herein we describe general aspects of flow cytometric standardization. Using chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) as examples we explain in detail the application of flow cytometry for MRD detection.

A look into the future: can minimal residual disease guide therapy and predict prognosis in chronic lymphocytic leukemia?

Over the past 2 decades, dramatic improvements in the efficacy of treatments for chronic lymphocytic leukemia have led to progressively higher percentages of clinical complete remissions. A molecular eradication of the leukemia has become not only a desirable, but also an achievable, end point that needs to be evaluated within clinical trials. The assessment of complete remission only at the clinical and morphological level is insufficient, at least for physically fit patients. The detection of minimal residual disease (MRD) in chronic lymphocytic leukemia has become feasible using PCR-based or flow cytometric techniques that reproducibly allow reaching the detection level of less than 1 leukemic cell per 10 000 leukocytes (10−4), the level currently defined as MRD− status. Emerging data indicate that the MRD status during and at the end of treatment is one of the most powerful predictors of progression-free and overall survival. This predictor appears to be independent of clinical response, type or line of therapy, and known biological markers. For these reasons, the time is ripe to test the use of MRD as a surrogate marker of clinical end points and as a real-time marker of efficacy and/or resistance to the administered therapies. In the near future, clinical trials will determine whether MRD assessment can be used for guiding therapy, either to improve quality of responses through consolidation or to prevent relapses through preemptive therapies based on the reappearance of MRD.

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.

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.

Minimal residual disease detection in mantle cell lymphoma: technical aspects and clinical relevance

The prognostic impact of minimal residual disease (MRD) has been demonstrated for several hematologic malignancies. While in acute lymphoblastic leukemias MRD assessment by polymerase chain reaction (PCR)-based methods has been established as an important tool for clinical risk assessment and is part of clinical management, data demonstrating a prognostic value of MRD in mantle cell lymphoma (MCL) were sparse and results from randomized trials have been published only recently. In the present review technical aspects of different MRD detection methods are discussed, as well as the prognostic relevance of MRD in the context of clinical trials in patients with MCL. Furthermore, recommendations are given for workflow and useful implication of MRD in future clinical trials design.

High-throughput VDJ sequencing for quantification of minimal residual disease in chronic lymphocytic leukemia and immune reconstitution assessment

The primary cause of poor outcome following allogeneic hematopoietic cell transplantation (HCT) for chronic lymphocytic leukemia (CLL) is disease recurrence. Detection of increasing minimal residual disease (MRD) following HCT may permit early intervention to prevent clinical relapse; however, MRD quantification remains an uncommon diagnostic test because of logistical and financial barriers to widespread use. Here we describe a method for quantifying CLL MRD using widely available consensus primers for amplification of all Ig heavy chain (IGH) genes in a mixture of peripheral blood mononuclear cells, followed by high-throughput sequencing (HTS) for disease-specific IGH sequence quantification. To achieve accurate MRD quantification, we developed a systematic bioinformatic methodology to aggregate cancer clone sequence variants arising from systematic and random artifacts occurring during IGH-HTS. We then compared the sensitivity of IGH-HTS, flow cytometry, and allele-specific oligonucleotide PCR for MRD quantification in 28 samples collected from 6 CLL patients following allogeneic HCT. Using amplimer libraries generated with consensus primers from patient blood samples, we demonstrate the sensitivity of IGH-HTS with 454 pyrosequencing to be 10(-5), with a high correlation between quantification by allele-specific oligonucleotide PCR and IGH-HTS (r = 0.85). From the same dataset used to quantify MRD, IGH-HTS also allowed us to profile IGH repertoire reconstitution after HCT-information not provided by the other MRD methods. IGH-HTS using consensus primers will broaden the availability of MRD quantification in CLL and other B cell malignancies, and this approach has potential for quantitative evaluation of immune diversification following transplant and nontransplant therapies.

Long-term outcomes among older patients following nonmyeloablative conditioning and allogeneic hematopoietic cell transplantation for advanced hematologic malignancies

CONTEXT

A minimally toxic nonmyeloablative regimen was developed for allogeneic hematopoietic cell transplantation (HCT) to treat patients with advanced hematologic malignancies who are older or have comorbid conditions.

OBJECTIVE

To describe outcomes of patients 60 years or older after receiving minimally toxic nonmyeloablative allogeneic HCT.

DESIGN, SETTING, AND PARTICIPANTS

From 1998 to 2008, 372 patients aged 60 to 75 years were enrolled in prospective clinical HCT trials at 18 collaborating institutions using conditioning with low-dose total body irradiation alone or combined with fludarabine, 90 mg/m(2), before related (n = 184) or unrelated (n = 188) donor transplants. Postgrafting immunosuppression included mycophenolate mofetil and a calcineurin inhibitor.

MAIN OUTCOME MEASURES

Overall and progression-free survival were estimated by Kaplan-Meier method. Cumulative incidence estimates were calculated for acute and chronic graft-vs-host disease, toxicities, achievement of full donor chimerism, complete remission, relapse, and nonrelapse mortality. Hazard ratios (HRs) were estimated from Cox regression models.

RESULTS

Overall, 5-year cumulative incidences of nonrelapse mortality and relapse were 27% (95% CI, 22%-32%) and 41% (95% CI, 36%-46%), respectively, leading to 5-year overall and progression-free survival of 35% (95% CI, 30%-40%) and 32% (95% CI, 27%-37%), respectively. These outcomes were not statistically significantly different when stratified by age groups. Furthermore, increasing age was not associated with increases in acute or chronic graft-vs-host disease or organ toxicities. In multivariate models, HCT-specific comorbidity index scores of 1 to 2 (HR, 1.58 [95% CI, 1.08-2.31]) and 3 or greater (HR, 1.97 [95% CI, 1.38-2.80]) were associated with worse survival compared with an HCT-specific comorbidity index score of 0 (P = .003 overall). Similarly, standard relapse risk (HR, 1.67 [95% CI, 1.10-2.54]) and high relapse risk (HR, 2.22 [95% CI, 1.43-3.43]) were associated with worse survival compared with low relapse risk (P < .001 overall).

CONCLUSION

Among patients aged 60 to 75 years treated with nonmyeloablative allogeneic HCT, 5-year overall and progression-free survivals were 35% and 32%, respectively.

Use of the receptor tyrosine kinase-like orphan receptor 1 (ROR1) as a diagnostic tool in chronic lymphocytic leukemia (CLL)

Flow cytometry is commonly used to establish the diagnosis of chronic lymphocytic leukemia (CLL). A defined combination of antibodies discriminates between normal B cells and CLL cells (coexpression of CD5, CD19, and CD23). The receptor tyrosine-like orphan receptor one (ROR1) is an embryonic glycoprotein involved in several developmental processes. It was shown to be highly and specifically expressed on circulating B lymphoma cells, but not on normal B cells. Here, we examined the potential of ROR1 as a diagnostic marker in initial and follow-up diagnostics of patients with CLL. 105 untreated and 72 treated patients, as well as healthy volunteers were examined using flow cytometry assays. Furthermore, we examined 10 patients with various B cell non-Hodgkin lymphomas (B-NHL). ROR1 was detected using a directly labeled antibody. We detected uniformly high ROR1 expression levels in all CLL samples. In marked contrast, only low or absent ROR1 expression levels were found on B cells from healthy donors. ROR1 expression in CLL patients was not influenced by various treatments. Taken together, ROR1 may be used as a diagnostic marker for CLL. As it is the only antigen which can exclusively be detected on neoplastic B cells it may greatly increase both, specificity as well as sensitivity, in lymphoma diagnostics.

Allogeneic stem cell transplantation for chronic lymphocytic leukemia: lessons to be learned from minimal residual disease studies

Allogeneic stem cell transplantation (alloSCT) is a potentially curative treatment strategy for poor-risk chronic lymphocytic leukemia (CLL). The crucial anti-leukemic principle of alloSCT in CLL appears to be the graft-versus-leukemia effect (GVL). Evidence for GVL in CLL is particularly provided by studies analysing the kinetics of minimal residual disease (MRD). The purpose of this review is to summarize the methodologies of MRD assessment, its proven benefits and its further perspectives for optimizing the outcome of transplantation. Proven value of quantitative MRD monitoring by RQ-PCR or MRD-flow consists in using it as an indicator of long-term disease control and potential cure. As MRD kinetics correlates with GVL activity, its suitability for guiding GVL-inducing immunomodulation is currently under investigation. In conclusion, quantitative MRD monitoring seems to be mandatory to assure safe and effective immunotherapy in the context of alloSCT for CLL, which should, however, be best performed within clinical studies.

Is MRD eradication a desirable goal in CLL?

Among chronic lymphocytic leukaemia (CLL) patients who require therapy, their response to therapy is the most important prognostic factor, with a better response predicting longer progression-free and overall survival. In this context, patients who achieve minimal residual disease (MRD)-negative status have better prognosis than those with inferior response to therapy, including those with MRD-positive complete response (CR). MRD can be assessed by either allele-specific polymerase chain reaction (PCR) or four-colour cytofluorometry. Importantly, methods to determine MRD in CLL have been standardised. Nevertheless, MRD status should not be used as a goal of therapy outside clinical studies. This is because the issue of the benefits of achieving MRD-negative status in patients with CLL requires further investigation in large controlled trials, in which patients should be stratified according to not only clinical variables but also biological parameters such as cytogenetics, IGHV mutations or ZAP-70 expression.

Flow cytometry and polymerase chain reaction-based analyses of minimal residual disease in chronic lymphocytic leukemia

New therapeutic strategies developed recently for chronic lymphocytic leukemia (CLL) have led to remarkable treatment response rates and complete hematological remissions. This means highly sensitive and specific techniques are increasingly needed to evaluate minimal residual disease (MRD) in CLL patients. Quantitative MRD levels can be used as prognostic markers, where total MRD eradication is associated with prolonged survival. Nowadays, PCR and flow cytometry techniques used to detect MRD in CLL patients can generate reliable and quantitative results with the highest sensitivity. MRD Flow is based on four-color flow cytometry using specific antibody combinations. For allele specific oligonucleotide real-time quantification (ASO RQ) PCR individual primers are designed to detect a specific immunoglobulin heavy chain (IgH) rearrangement in each patient clone. Five comprehensive studies investigated and compared the sensitivity and specificity of both methods. Groups of patients receiving different therapies were analyzed at different time points to generate quantitative MRD levels and MRD kinetics. All studies confirmed that both methods generate equivalent results with regard to sensitivity and MRD quantification, although each method has advantages and disadvantages in the daily routine of a standard hematological laboratory. Here, we review these investigations and compare their results in the light of modern therapies.

NCI first international workshop on the biology, prevention, and treatment of relapse after allogeneic hematopoietic stem cell transplantation: report from the committee on disease-specific methods and strategies for monitoring relapse following allogeneic stem cell transplantation. part II: chronic leukemias, myeloproliferative neoplasms, and lymphoid malignancies

Relapse has become the major cause of treatment failure after allogeneic hematopoietic stem cell transplantation. Outcome of patients with clinical relapse after transplantation generally remains poor, but intervention prior to florid relapse improves outcome for certain hematologic malignancies. To detect early relapse or minimal residual disease, sensitive methods such as molecular genetics, tumor-specific molecular primers, fluorescence in situ hybridization (FISH), and multiparameter flow cytometry (MFC) are commonly used after allogeneic stem cell transplantation to monitor patients, but not all of them are included in the commonly employed disease-specific response criteria. The highest sensitivity and specificity can be achieved by molecular monitoring of tumor- or patient-specific markers measured by polymerase chain reaction-based techniques, but not all diseases have such targets for monitoring. Similar high sensitivity can be achieved by determination of recipient-donor chimerism, but its specificity regarding detection of relapse is low and differs substantially among diseases. Here, we summarize the current knowledge about the utilization of such sensitive monitoring techniques in chronic leukemias, myeloproliferative neoplasms, and lymphoid malignancies based on tumor-specific markers and cell chimerism and how these methods might augment the standard definitions of posttransplant remission, persistence, progression, relapse, and the prediction of relapse. Critically important is the need for standardization of the different residual disease techniques and to assess the clinical relevance of minimal residual disease and chimerism surveillance in individual diseases, which in turn must be followed by studies to assess the potential impact of specific interventional strategies.

First-line treatment of chronic lymphocytic leukemia: role of alemtuzumab

The CD52-targeting antibody alemtuzumab is established in clinical practice with convincing activity in relapsed and refractory chronic lymphocytic leukemia (CLL), particularly in patients with high-risk features and adverse prognosis. In the CAM307 study alemtuzumab was tested and finally approved as a first-line single agent, even though the hurdle with chlorambucil as the contender was not set very high. Within clinical trials, the drug demonstrated an excellent ability to eliminate minimal residual disease in blood and bone marrow, which has been correlated with a corresponding survival advantage in patients. However, in the maintenance setting, infectious complications due to severe T cell suppression have been highlighted and do not allow clinicans to use alemtuzumab outside of clinical trials. This review discusses potential therapeutic niches and future applications of alemtuzumab with a focus on CLL front-line treatment.

Real-time quantitative PCR using hairpin-shaped clone-specific primers for minimal residual disease assessment in an animal model of human non-Hodgkin lymphoma

A multitude of molecular techniques for monitoring minimal residual disease in lymphoproliferative disorders have been described to date. Real-Time Quantitative PCR targeting Immunoglobulin Heavy chain patient-specific sequences is increasingly being used for molecular detection of residual neoplastic B-cells using allele-specific oligos. The establishment of individually tailored PCR assays with the extensive use of patient-specific fluorescent-labeled oligos may be cumbersome and expensive. The present study was aimed at evaluating the usefulness of recently described hairpin-shaped allele-specific primers, originally intended for typing single-nucleotide polymorphisms, for the assessment of minimal residual disease using SYBR Green intercalating dye. Three cloned and 2 sequenced clonogenic Ig heavy chain rearranged gene loci, obtained from 5 cases of canine spontaneous B-cell lymphoma, were used as an experimental model. Both standard linear and hairpin-shaped forward and reverse clone-specific primers were evaluated in terms of specificity, sensitivity and PCR efficiency. Hairpin-shaped primers were demonstrated to have achieved accurate results more consistently than the respective linear primers allowing the specific and sensitive quantification of minimal residual disease of lymphoproliferative disorders with fewer validation procedures and more flexibility on the assay design.

Standardized MRD flow and ASO IGH RQ-PCR for MRD quantification in CLL patients after rituximab-containing immunochemotherapy: a comparative analysis

Rituximab-containing regimens are becoming a therapeutic standard in chronic lymphocytic leukemia (CLL), so that a validation of flow cytometric minimal residual disease (MRD) quantification (MRD flow) in the presence of this antibody is necessary. We therefore compared results obtained by real-time quantitative (RQ)-PCR to MRD flow in 530 samples from 69 patients randomized to receive chemotherapy or chemotherapy plus rituximab. Quantitative MRD levels assessed by both techniques were closely correlated irrespective of therapy (r=0.95). The sensitivity and specificity of MRD flow was not influenced by the presence of rituximab. With 58.9% positive and 26.4% negative samples by both techniques, 85.3% of assessments (452/530) were qualitatively concordant between MRD flow and RQ-PCR. Discordant samples were typically negative by MRD flow and simultaneously positive close to the detection limit of the PCR assays, indicating a higher sensitivity of PCR for very low MRD levels. However, 93.8% of all samples were concordantly classified by both methods using a threshold of 10(-4) to determine MRD positivity. MRD flow and PCR are equally effective for MRD quantification in rituximab-treated CLL patients within a sensitivity range of up to 10(-4), whereas PCR is more sensitive for detecting MRD below that level.

Ki-67 as a prognostic marker in mantle cell lymphoma-consensus guidelines of the pathology panel of the European MCL Network

Mantle cell lymphoma (MCL) has a heterogeneous clinical course and is mainly an aggressive B cell non-Hodgkin lymphoma; however, there are some indolent cases The Ki-67 index, defined by the percentage of Ki-67-positive lymphoma cells on histopathological slides, has been shown to be a very powerful prognostic biomarker. The pathology panel of the European MCL Network evaluated methods to assess the Ki-67 index including stringent counting, digital image analysis, and estimation by eyeballing. Counting of 2 × 500 lymphoma cells is the gold standard to assess the Ki-67 index since this value has been shown to predict survival in prospective randomized trials of the European MCL Network. Estimation by eyeballing and digital image analysis showed a poor concordance with the gold standard (concordance correlation coefficients [CCC] between 0.29 and 0.61 for eyeballing and CCC of 0.24 and 0.37 for two methods of digital image analysis, respectively). Counting a reduced number of lymphoma cells (2 × 100 cells) showed high interobserver agreement (CCC = 0.74). Pitfalls of the Ki-67 index are discussed and guidelines and recommendations for assessing the Ki-67 index in MCL are given.

Five-year follow-up of patients with advanced chronic lymphocytic leukemia treated with allogeneic hematopoietic cell transplantation after nonmyeloablative conditioning

PURPOSE

We reported encouraging early results of allogeneic hematopoietic cell transplantation (HCT) after nonmyeloablative conditioning in 64 patients who had advanced chronic lymphocytic leukemia (CLL). Here, we have extended the follow-up to a median of 5 years and have included data on an additional 18 patients.

PATIENTS AND METHODS

Eighty-two patients, age 42 to 72 years, who had fludarabine-refractory CLL were conditioned with 2 Gy total-body irradiation alone or combined with fludarabine followed by HCT from related (n = 52) or unrelated (n = 30) donors.

RESULTS

Complete remission (CR) and partial remission were achieved in 55% and 15% of patients, respectively. Higher CR rates were noted after unrelated HCT (67% v 48%). The 5-year incidences of nonrelapse mortality (NRM), progression/relapse, overall survival, and progression-free survival were 23%, 38%, 50%, and 39%, respectively. Among 25 patients initially reported in CR, 8% relapsed and 8% died as a result of NRM, whereas 84% have remained alive and in CR. Among 14 responding patients who were tested and who had molecular eradication of their disease, two died as a result of NRM, two relapsed, and 10 have remained negative. At 5 years, 76% of living patients were entirely well, whereas 24% continued to receive immunosuppression for chronic graft-versus-host disease; the median performance status in each group was 100% and 90%, respectively. Lymphadenopathy > or = 5 cm, but not cytogenetic abnormalities at HCT, predicted relapse. In a risk-stratification model, patients who had lymphadenopathy less than 5 cm and no comorbidities had a 5-year OS of 71%.

CONCLUSION

Nonmyeloablative HCT resulted in a median survival of 5 years for patients who had fludarabine-refractory CLL with sustained remissions and in the continued resolution of chronic graft-versus-host disease in surviving patients.

Quantitative MRD monitoring identifies distinct GVL response patterns after allogeneic stem cell transplantation for chronic lymphocytic leukemia: results from the GCLLSG CLL3X trial

The purpose of this study was to prospectively analyze minimal residual disease(MRD) kinetics after reduced-intensity allogeneic stem cell transplantation (allo-SCT) in high-risk chronic lymphocytic leukemia (CLL). Subjects were the first 30 consecutive patients from a prospective clinical trial, and seven pilot patients treated identically. Using real-time quantitative-PCR (RQ-PCR) and/or flow-based MRD monitoring (sensitivity >or=10(-4)), five distinct patterns of MRD kinetics could be identified: patients who promptly achieved durable MRD negativity without direct evidence of graft-versus-leukemia (GVL) effects (Group 1) (n=4; no clinical relapse); patients with complete and sustained MRD response after GVL induced by immunosuppression tapering (Group 2) or donor lymphocyte infusions (Group 3) (n=18; one relapse); patients without MRD response due to lack of GVL (Group 4) (n=2; two relapses); patients with incomplete and transient MRD response to GVL (Group 5) (n=4; three relapses). In summary, this study provides a comprehensive map of possible MRD courses and their prognostic implications after T-replete allo-SCT in high-risk CLL, indicating that effective GVL activity is induced virtually in all patients who develop chronic GVHD. However, in a significant proportion of cases, this does not translate into sustained disease control due to development of secondary GVL resistance.

Stem cell transplantation in poor-risk chronic lymphocytic leukemia: assessment of post-transplant minimal residual disease using four- and six-color flow cytometry and allele-specific RQ-PCR

A total of 178 bone marrow samples were taken for minimal residual disease (MRD) analysis after 34 stem cell transplantations for poor-risk chronic lymphocytic leukemia, and 86 of them were analyzed in parallel by flow cytometry and allele-specific oligonucleotide-PCR (ASO-PCR). ASO primer was successfully designed for all patients whose frozen diagnosis samples were available. Flow cytometry and ASO-PCR were concordant, i.e. both either positive or both negative, in 78% of the analyses. Flow cytometry did not detect MRD in any of the samples that were PCR-negative cases. In contrast, ASO-PCR detected MRD in samples that were negative for MRD by flow cytometry in 22% of the analyses. In one patient, the immunophenotype but not the IgV(H) gene sequence had changed during a course of the disease, and MRD could not be followed by flow cytometry. In the remaining cases, the discrepancy was due to a higher sensitivity of ASO-PCR. Autologous stem cell transplantation resulted in clinical complete response in 87% (20/23) of the patients. By flow cytometry, 35% (8/23) of autotransplanted patients became MRD-negative, but only 12.5% (2/16) PCR-negative (sensitivity of ASO-PCR <0.001 and <0.01, respectively). All allotransplanted patients achieved or maintained hematological CR, and five out of nine patients (56%) became PCR-negative (sensitivity of PCR between <0.001 and <0.003), two of them having non-myeloablative conditioning. None of the patients who became PCR-negative after allogeneic transplantation have relapsed.

Chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia is the commonest form of leukaemia in Europe and North America, and mainly, though not exclusively, affects older individuals. It has a very variable course, with survival ranging from months to decades. Major progress has been made in identification of molecular and cellular markers that could predict disease progression in patients with chronic lymphocytic leukaemia. In particular, the mutational profile of immunoglobulin genes and some cytogenetic abnormalities are important predictors of prognosis. However, these advances have raised new questions about the biology, prognosis, and management of chronic lymphocytic leukaemia, some of which are addressed here. In particular, we discuss how better understanding of the function of the B-cell receptor, the nature of genetic lesions, and the balance between proliferation and apoptosis have affected our ability to assess prognosis and to manage chronic lymphocytic leukaemia. Available treatments generally induce remission, although nearly all patients relapse, and chronic lymphocytic leukaemia remains an incurable disease. Advances in molecular biology have enhanced our understanding of the pathophysiology of the disease and, together with development of new therapeutic agents, have made management of chronic lymphocytic leukaemia more rational and more effective than previously. Unfortunately, we know of no way that chronic lymphocytic leukaemia can be prevented. Early detection is practised widely, but seemingly makes no difference to the patient's eventual outcome.

Minimal residual disease assessment in chronic lymphocytic leukaemia

The concept of minimal residual disease (MRD) eradication in chronic lymphocytic leukaemia (CLL) is a relatively new one, as conventional therapy with alkylating agents is relatively ineffective and responding patients almost always have a significant tumour burden remaining at the end of treatment. However, a variety of novel therapies is now yielding higher response rates, and responses of better quality are now routinely achieved. This progress in therapy has been paralleled by an improvement in laboratory assays, allowing detection of CLL cells to levels as low as ten CLL cells in a million leukocytes. In this chapter we briefly review the existing methods for MRD assessment, the clinical relevance of MRD eradication in CLL, and the therapies available to attain this endpoint.