Eliminating minimal residual disease as a therapeutic end point: working toward cure for patients with CLL

Performance of a novel eight-color flow cytometry panel for measurable residual disease assessment of chronic lymphocytic leukemia

BACKGROUND

Measurable residual disease (MRD) is an important prognostic indicator of chronic lymphocytic leukemia (CLL). Different flow cytometric panels have been developed for the MRD assessment of CLL in Western countries; however, the application of these panels in China remains largely unexplored.

METHODS

Owing to the requirements for high accuracy, reproducibility, and comparability of MRD assessment in China, we investigated the performance of a flow cytometric approach (CD45-ROR1 panel) to assess MRD in patients with CLL. The European Research Initiative on CLL (ERIC) eight-color panel was used as the "gold standard."

RESULTS

The sensitivity, specificity, and concordance rate of the CD45-ROR1 panel in the MRD assessment of CLL were 100% (87/87), 88.5% (23/26), and 97.3% (110/113), respectively. Two of the three inconsistent samples were further verified using next-generation sequencing. In addition, the MRD results obtained from the CD45-ROR1 panel were positively associated with the ERIC eight-color panel results for MRD assessment (R = 0.98, p < 0.0001). MRD detection at low levels (≤1.0%) demonstrated a smaller difference between the two methods (bias, -0.11; 95% CI, -0.90 to 0.68) than that at high levels (>1%). In the reproducibility assessment, the bias was smaller at three data points (within 24, 48, and 72 h) in the CD45-ROR1 panel than in the ERIC eight-color panel. Moreover, MRD levels detected using the CD45-ROR1 panel for the same samples from different laboratories showed a strong statistical correlation (R = 0.99, p < 0.0001) with trivial interlaboratory variation (bias, 0.135; 95% CI, -0.439 to 0.709). In addition, the positivity rate of MRD in the bone marrow samples was higher than that in the peripheral blood samples.

CONCLUSIONS

Collectively, this study demonstrated that the CD45-ROR1 panel is a reliable method for MRD assessment of CLL with high sensitivity, reproducibility, and reliability.

Persistence of Chronic Lymphocytic Leukemia Stem-like Populations under Simultaneous In Vitro Treatment with Curcumin, Fludarabine, and Ibrutinib: Implications for Therapy Resistance

Leukemic stem cells (LSCs) possess similar characteristics to normal hematopoietic stem cells, including self-renewal capacity, quiescence, ability to initiate leukemia, and drug resistance. These cells play a significant role in leukemia relapse, persisting even after apparent remission. LSCs were first described in 1994 by Lapidot et al. Although they have been extensively studied in acute leukemia, more LSC research is still needed in chronic lymphocytic leukemia (CLL) to understand if reduced apoptosis in mature cells should still be considered as the major cause of this disease. Here, we provide new evidence suggesting the existence of stem-like cell populations in CLL, which may help to understand the disease as well as to develop effective treatments. In this study, we identified a potential leukemic stem cell subpopulation using the tetraploid CLL cell line I83. This subpopulation is characterized by diploid cells that were capable of generating the I83 tetraploid population. Furthermore, we adapted a novel flow cytometry analysis protocol to detect CLL subpopulations with stem cell properties in peripheral blood samples and primary cultures from CLL patients. These cells were identified by their co-expression of CD19 and CD5, characteristic markers of CLL cells. As previously described, increased alkaline phosphatase (ALP) activity is indicative of stemness and pluripotency. Moreover, we used this method to investigate the potential synergistic effect of curcumin in combination with fludarabine and ibrutinib to deplete this subpopulation. Our results confirmed the effectiveness of this ALP-based analysis protocol in detecting and monitoring leukemic stem-like cells in CLL. This analysis also identified limitations in eradicating these populations using in vitro testing. Furthermore, our findings demonstrated that curcumin significantly enhanced the effects of fludarabine and ibrutinib on the leukemic fraction, exhibiting synergistic effects (combination drug index, CDI 0.97 and 0.37, respectively). Our results lend support to the existence of potential stem-like populations in CLL cell lines, and to the idea that curcumin could serve as an effective adjuvant in therapies aimed at eliminating these populations and improving treatment efficacy.

Maintenance therapy for chronic lymphocytic leukaemia

BACKGROUND

Chronic lymphocytic leukaemia (CLL) is the most common lymphoproliferative disease in adults and currently remains incurable. As the progression-free period shortens after each successive treatment, strategies such as maintenance therapy are needed to improve the degree and duration of response to previous therapies. Monoclonal antibodies, immunomodulatory agents, and targeted therapies are among the available options for maintenance therapy. People with CLL who achieve remission after previous therapy may choose to undergo medical observation or maintenance therapy to deepen the response. Even though there is widespread use of therapeutic maintenance agents, the benefits and harms of these treatments are still uncertain.

OBJECTIVES

To assess the effects and safety of maintenance therapy, including anti-CD20 monoclonal antibody, immunomodulatory drug therapy, anti-CD52 monoclonal antibody, Bruton tyrosine kinase inhibitor, and B-cell lymphoma-2 tyrosine kinase inhibitor, for individuals with CLL.

SEARCH METHODS

We conducted a comprehensive literature search for randomised controlled trials (RCTs) with no language or publication status restrictions. We searched CENTRAL, MEDLINE, Embase, and three trials registers in January 2022 together with reference checking, citation searching, and contact with study authors to identify additional studies.

SELECTION CRITERIA

We included RCTs with prospective identification of participants. We excluded cluster-randomised trials, cross-over trial designs, and non-randomised studies. We included studies comparing maintenance therapies with placebo/observation or head-to-head comparisons.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodological procedures. We assessed risk of bias in the included studies using Cochrane's RoB 1 tool for RCTs. We rated the certainty of evidence for the following outcomes using the GRADE approach: overall survival (OS), health-related quality of life (HRQoL), grade 3 and 4 adverse events (AEs), progression-free survival (PFS), treatment-related mortality (TRM), treatment discontinuation (TD), and all adverse events (AEs).

MAIN RESULTS

We identified 11 RCTs (2393 participants) that met the inclusion criteria, including seven trials comparing anti-CD20 monoclonal antibodies (mAbs) (rituximab or ofatumumab) with observation in 1679 participants; three trials comparing immunomodulatory drug (lenalidomide) with placebo/observation in 693 participants; and one trial comparing anti-CD 52 mAbs (alemtuzumab) with observation in 21 participants. No comparisons of novel small molecular inhibitors were found. The median age of participants was 54.1 to 71.7 years; 59.5% were males. The type of previous induction treatment, severity of disease, and baseline stage varied among the studies. Five trials included early-stage symptomatic patients, and three trials included advanced-stage patients (Rai stage III/IV or Binet stage B/C). Six trials reported a frequent occurrence of cytogenic aberrations at baseline (69.7% to 80.1%). The median follow-up duration was 12.4 to 73 months. The risk of selection bias in the included studies was unclear. We assessed overall risk of performance bias and detection bias as low risk for objective outcomes and high risk for subjective outcomes. Overall risk of attrition bias, reporting bias, and other bias was low. Anti-CD20 monoclonal antibodies (mAbs): rituximab or ofatumumab maintenance versus observation Anti-CD20 mAbs maintenance likely results in little to no difference in OS (hazard ratio (HR) 0.94, 95% confidence interval (CI) 0.73 to 1.20; 1152 participants; 3 studies; moderate-certainty evidence) and likely increases PFS significantly (HR 0.61, 95% CI 0.50 to 0.73; 1255 participants; 5 studies; moderate-certainty evidence) compared to observation alone. Anti-CD20 mAbs may result in: an increase in grade 3/4 AEs (rate ratio 1.34, 95% CI 1.06 to 1.71; 1284 participants; 5 studies; low-certainty evidence); little to no difference in TRM (risk ratio 0.82, 95% CI 0.39 to 1.71; 1189 participants; 4 studies; low-certainty evidence); a slight reduction to no difference in TD (risk ratio 0.93, 95% CI 0.72 to 1.20; 1321 participants; 6 studies; low-certainty evidence); and an increase in all AEs (rate ratio 1.23, 95% CI 1.03 to 1.47; 1321 participants; 6 studies; low-certainty evidence) compared to the observation group. One RCT reported that there may be no difference in HRQoL between the anti-CD20 mAbs (ofatumumab) maintenance and the observation group (mean difference -1.70, 95% CI -8.59 to 5.19; 480 participants; 1 study; low-certainty evidence). Immunomodulatory drug (IMiD): lenalidomide maintenance versus placebo/observation IMiD maintenance therapy likely results in little to no difference in OS (HR 0.91, 95% CI 0.61 to 1.35; 461 participants; 3 studies; moderate-certainty evidence) and likely results in a large increase in PFS (HR 0.37, 95% CI 0.19 to 0.73; 461 participants; 3 studies; moderate-certainty evidence) compared to placebo/observation. Regarding harms, IMiD maintenance therapy may result in an increase in grade 3/4 AEs (rate ratio 1.82, 95% CI 1.38 to 2.38; 400 participants; 2 studies; low-certainty evidence) and may result in a slight increase in TRM (risk ratio 1.22, 95% CI 0.35 to 4.29; 458 participants; 3 studies; low-certainty evidence) compared to placebo/observation. The evidence for the effect on TD compared to placebo is very uncertain (risk ratio 0.71, 95% CI 0.47 to 1.05; 400 participants; 2 studies; very low-certainty evidence). IMiD maintenance therapy probably increases all AEs slightly (rate ratio 1.41, 95% CI 1.28 to 1.54; 458 participants; 3 studies; moderate-certainty evidence) compared to placebo/observation. No studies assessed HRQoL. Anti-CD52 monoclonal antibodies (mAbs): alemtuzumab maintenance versus observation Maintenance with alemtuzumab may have little to no effect on PFS, but the evidence is very uncertain (HR 0.55, 95% CI 0.32 to 0.95; 21 participants; 1 study; very low-certainty evidence). We did not identify any study reporting the outcomes OS, HRQoL, grade 3/4 AEs, TRM, TD, or all AEs.

AUTHORS' CONCLUSIONS

There is currently moderate- to very low-certainty evidence available regarding the benefits and harms of maintenance therapy in people with CLL. Anti-CD20 mAbs maintenance improved PFS, but also increased grade 3/4 AEs and all AEs. IMiD maintenance had a large effect on PFS, but also increased grade 3/4 AEs. However, none of the above-mentioned maintenance interventions show differences in OS between the maintenance and control groups. The effects of alemtuzumab maintenance are uncertain, coupled with a warning for drug-related infectious toxicity. We found no studies evaluating other novel maintenance interventions, such as B-cell receptor inhibitors, B-cell leukaemia-2/lymphoma-2 inhibitors, or obinutuzumab.

Measurable Residual Disease Testing in Multiple Myeloma Routine Clinical Practice: A Modified Delphi Study

We used a modified Delphi approach to establish areas of consensus and nonconsensus regarding the utility of determining measurable residual disease (MRD) to assess multiple myeloma (MM) treatment response, which may inform disease management and design of future clinical trials. This modified Delphi study incorporated 2 iterative rounds of surveys to evaluate the opinions of an expert panel of 61 practicing hematological oncologists from across 14 countries in Europe concerning the use of MRD testing in MM management. Survey 1 assessed experts' opinions on MRD testing in different clinical situations and associated challenges. Survey 2 focused on the lack of consensus areas identified in survey 1. Consensus to an individual question was defined a priori as 75% agreement or disagreement by the panel. From the 2 rounds of surveys, the experts reached consensus agreement that MRD testing should be performed in newly diagnosed or relapsed patients who achieved complete response (CR) or better after transplantation. In transplant-ineligible patients, experts recommended MRD testing in those who are ≤70 years old and in CR. If a patient was previously positive on positron-emission tomography and computed tomography (PET/CT), both MRD and PET/CT should be assessed at CR. MRD testing should be performed ≤6 months after transplantation and every 6-12 months in continuously treated patients in CR. There was no consensus on making treatment decisions based on MRD status. MRD testing is an important component of clinical management in MM. Additional data will further clarify the role of MRD in guiding treatment decisions.

Measurable residual disease in chronic lymphocytic leukemia

Measurable residual disease (MRD) is defined as the presence of residual cancer cells after treatment in patients with clinically undetectable disease, who would otherwise be considered in complete remission. It is a highly sensitive parameter which indicates the disease burden and predicts survival in this setting of patients. In recent years, MRD has gained a role in many hematological malignancies as a surrogate endpoint for clinical trials: undetectable MRD has been correlated to longer progression free survival (PFS) and overall survival (OS). New drugs and combinations have been developed with the aim to achieve MRD negativity, which would indicate favorable prognosis. Different methods to measure MRD have also been devised, which include flow cytometry, polymerase chain reaction (PCR) and next generation sequencing (NGS), with different sensitivity and accuracy in evaluating deep remission after treatment. In this review, we will analyze the current recommendations for the detection of MRD, with particular focus on its role in Chronic Lymphocytic Leukemia (CLL), as well as the different detection methods. Moreover, we will discuss the results of clinical trials and the role of MRD in new therapeutic schemes with inhibitors and monoclonal antibodies. MRD is not currently used in the clinical practice to evaluate response to treatment, due to technical and economical limitations, but it's gaining more and more interest in trials settings, especially since the introduction of venetoclax. The use of MRD in trials will likely be followed by a broader practical application in the future. The aim of this work is to provide a reader-friendly summary of the state of art in the field, as MRD will soon become an accessible tool to evaluate our patients, predict their survival and guide physician's therapeutic choices and preferences.

Patient specific real-time PCR in precision medicine - Validation of IG/TR based MRD assessment in lymphoid leukemia

Detection of patient- and tumor-specific clonally rearranged immune receptor genes using real-time quantitative (RQ)-PCR is an accepted method in the field of precision medicine for hematologic malignancies. As individual primers are needed for each patient and leukemic clone, establishing performance specifications for the method faces unique challenges. Results for series of diagnostic assays for CLL and ALL patients demonstrate that the analytic performance of the method is not dependent on patients' disease characteristics. The calibration range is linear between 10^-1 and 10^-5 for 90% of all assays. The detection limit of the current standardized approach is between 1.8 and 4.8 cells among 100,000 leukocytes. RQ-PCR has about 90% overall agreement to flow cytometry and next generation sequencing as orthogonal methods. Accuracy and precision across different labs, and above and below the clinically applied cutoffs for minimal/measurable residual disease (MRD) demonstrate the robustness of the technique. The here reported comprehensive, IVD-guided analytical validation provides evidence that the personalized diagnostic methodology generates robust, reproducible and specific MRD data when standardized protocols for data generation and evaluation are used. Our approach may also serve as a guiding example of how to accomplish analytical validation of personalized in-house diagnostics under the European IVD Regulation.

miRNA profile at diagnosis predicts treatment outcome in patients with B-chronic lymphocytic leukemia: A FILO study

During many years, chemo-immunotherapy fludarabine-cyclophosphamide-rituximab (FCR) was the gold standard for first line treatment of medically fit patients with symptomatic B-chronic lymphocytic leukemia (CLL). Over the last decade, targeted biotherapies have revolutionized the treatment of B-CLL patients and almost entirely supplanted FCR. However, no biomarker still exists to predict the complete remission (CR) with undetectable minimal residual disease (uMRD) in bone marrow (BM), which remains the best predictive factor for survival. MicroRNAs represent a class of molecular biomarkers which expression is altered in B-CLL. Our study aimed at identifying before treatment blood miRNAs that predict treatment outcome in previously untreated B-CLL patients (NCT 01370772, https://clinicaltrials.gov/ct2/show/NCT01370772). Using hierarchical clustering of miRNA expression profiles discriminating 8 patients who achieved CR with BM uMRD from 8 patients who did not achieve CR and displayed detectable BM MRD, we identified 25 miRNAs differentially expressed before treatment. The expression of 11 miRNAs was further validated on a larger cohort (n=123). Based on the dosage of 5 miRNAs at diagnosis, a decision tree was constructed to predict treatment outcome. We identified 6 groups of patients with a distinct probability of being CR with BM uMRD to FCR treatment, ranging from 72% (miR-125b, miR-15b and miR-181c high) to 4% (miR-125b and miR-193b low). None of the patients displaying high expression levels of miR-125b, miR-15b and miR-181c relapsed during study follow-up. In contrast, patients with low miR-15b and high miR-412, or with low miR-125b and miR-193b, demonstrated significant low PFS. RNA sequencing of blood at diagnosis identified that patients relapsing after treatment are characterized by significant enrichment of gene signatures related to cell cycle, MYC target genes, metabolism and translation regulation. Conversely, patients achieving CR with BM uMRD displayed significant enrichment in genes related to communication between CLL cells and the microenvironment, immune system activation and upregulation of polycomb PRC2 complex target genes. Our results suggest that blood miRNAs are potent predictive biomarkers for FCR treatment efficacy and might be implicated in the FCR efficacy in B-CLL patients, providing new insight into unmet need for the treatment of B-CLL patients and identifying pathways predictive of patients’ remission.

Immunopeptidome Diversity in Chronic Lymphocytic Leukemia Identifies Patients with Favorable Disease Outcome

Simple Summary

Immunosurveillance of cancer is mediated by T cell-based recognition of tumor-associated antigens, i.e., short peptides that are presented on the surface of cells on human leukocyte antigen (HLA) molecules. This encourages the analysis of the entirety of HLA-presented peptides, the so-called immunopeptidome, of malignant and benign cells, in order to identify novel therapeutic targets presented exclusively on malignant cells. In the present study, we aim to investigate the role of previously described immunopeptidome-defined antigen presentation in chronic lymphocytic leukemia (CLL) patients for clinical characteristics and disease outcome. We observed that higher yields of presented total and CLL-exclusive peptides were associated with a more favorable disease course, suggesting efficient immunosurveillance in a subgroup of patients and the possibility of further investigating T cell-based therapeutic approaches for CLL.

Abstract

Chronic lymphocytic leukemia (CLL) is characterized by recurrent relapses and resistance to treatment, even with novel therapeutic approaches. Despite being considered as a disease with low mutational burden and thus poor immunogenic, CLL seems to retain the ability of eliciting specific T cell activation. Accordingly, we recently found non-mutated tumor-associated antigens to play a central role in CLL immunosurveillance. Here, we investigated the association of total and CLL-exclusive HLA class I and HLA class II peptide presentation in the mass spectrometry-defined immunopeptidome of leukemic cells with clinical features and disease outcome of 57 CLL patients. Patients whose CLL cells present a more diverse immunopeptidome experienced fewer relapses. During the follow-up phase of up to 10 years, patients with an HLA class I-restricted presentation of high numbers of total and CLL-exclusive peptides on their malignant cells showed a more favorable disease course with a prolonged progression-free survival (PFS). Overall, our results suggest the existence of an efficient T cell-based immunosurveillance mediated by CLL-associated tumor antigens, supporting ongoing efforts in developing T cell-based immunotherapeutic strategies for CLL.

Enduring undetectable MRD and updated outcomes in relapsed/refractory CLL after fixed-duration venetoclax-rituximab

The MURANO trial (A Study to Evaluate the Benefit of Venetoclax Plus Rituximab Compared With Bendamustine Plus Rituximab in Participants With Relapsed or Refractory Chronic Lymphocytic Leukemia [CLL]; ClinicalTrials.gov identifier #NCT02005471) reported superior progression-free survival (PFS) and overall survival (OS) with venetoclax-rituximab (VenR) vs bendamustine-rituximab (BR) in relapsed/refractory (R/R) CLL. Patients were randomized to 2 years of VenR (n = 194; rituximab for the first 6 months) or 6 months of BR (n = 195). Although undetectable minimal residual disease (uMRD) was achieved more often with VenR, the long-term implications of uMRD with this fixed-duration, chemotherapy-free regimen have not been explored. We report MRD kinetics and updated outcomes with 5 years' follow-up. Survival benefits with VenR vs BR were sustained (median PFS [95% confidence interval]: 53.6 [48.4, 57.0] vs 17.0 [15.5, 21.7] months, respectively, P < .0001; 5-year OS [95% confidence interval]: 82.1% [76.4, 87.8] vs 62.2% [54.8, 69.6], P < .0001). VenR was superior to BR, regardless of cytogenetic category. VenR-treated patients with uMRD at end of treatment (EOT; n = 83) had superior OS vs those with high-MRD+ (n = 12): 3-year post-EOT survival rates were 95.3% vs 72.9% (P = .039). In those with uMRD at EOT, median time to MRD conversion was 19.4 months. Of 47 patients with documented MRD conversion, 19 developed progressive disease (PD); median time from conversion to PD was 25.2 months. A population-based logistic growth model indicated slower MRD median doubling time post-EOT with VenR (93 days) vs BR (53 days; P = 1.2 × 10-7). No new safety signals were identified. Sustained survival, uMRD benefits, and durable responses support 2-year fixed-duration VenR treatment in R/R CLL.

Artificial Intelligence Enhances Diagnostic Flow Cytometry Workflow in the Detection of Minimal Residual Disease of Chronic Lymphocytic Leukemia

Flow cytometric (FC) immunophenotyping is critical but time-consuming in diagnosing minimal residual disease (MRD). We evaluated whether human-in-the-loop artificial intelligence (AI) could improve the efficiency of clinical laboratories in detecting MRD in chronic lymphocytic leukemia (CLL). We developed deep neural networks (DNN) that were trained on a 10-color CLL MRD panel from treated CLL patients, including DNN trained on the full cohort of 202 patients (F-DNN) and DNN trained on 138 patients with low-event cases (MRD < 1000 events) (L-DNN). A hybrid DNN approach was utilized, with F-DNN and L-DNN applied sequentially to cases. “Ground truth” classification of CLL MRD was confirmed by expert analysis. The hybrid DNN approach demonstrated an overall accuracy of 97.1% (95% CI: 84.7−99.9%) in an independent cohort of 34 unknown samples. When CLL cells were reported as a percentage of total white blood cells, there was excellent correlation between the DNN and expert analysis [r > 0.999; Passing−Bablok slope = 0.997 (95% CI: 0.988−0.999) and intercept = 0.001 (95% CI: 0.000−0.001)]. Gating time was dramatically reduced to 12 s/case by DNN from 15 min/case by the manual process. The proposed DNN demonstrated high accuracy in CLL MRD detection and significantly improved workflow efficiency. Additional clinical validation is needed before it can be fully integrated into the existing clinical laboratory practice.

Long term follow-up of a phase II study of cladribine with concurrent rituximab with hairy cell leukemia variant

CDAR achieved 95% CR and 80% negative MRD, durable up to 10 years.

Carrying TP53 mutation and not achieving negative MRD after CDAR were associated with shorter survival outcomes.

Hairy cell leukemia variant (HCLv) responds poorly to purine analogue monotherapy. Rituximab concurrent with cladribine (CDAR) improves response rates, but long-term outcomes are unknown. We report final results of a phase 2 study of CDAR for patients with HCLv. Twenty patients with 0 to 1 prior courses of cladribine and/or rituximab, including 8 who were previously untreated, received cladribine 0.15 mg/kg on days 1 to 5 with 8 weekly rituximab doses of 375 mg/m² beginning day 1. Patients received a second rituximab course ≥6 months after cladribine, if and when minimal residual disease (MRD) was detected in blood. The complete remission (CR) rate from CDAR was 95% (95% confidence interval, 75-100). Sixteen (80%) of 20 patients (95% confidence interval, 56-94) became MRD negative according to bone marrow at 6 months. The median duration of MRD-negative CR was 70.1 months, and 7 of 16 are still MRD negative up to 120 months. With a median follow-up of 69.7 months, 11 patients received delayed rituximab, and the 5-year progression-free survival (PFS) and overall survival (OS) were 63.3% and 73.9%, respectively. Five patients with TP53 mutations had shorter PFS (median, 36.4 months vs unreached; P = .0024) and OS (median, 52.4 months vs unreached; P = .032). MRD-negative CR at 6 months was significantly associated with longer PFS (unreached vs 17.4 months; P < .0001) and OS (unreached vs 38.2 months; P < .0001). Lack of MRD in blood at 6 months was also predictive of longer PFS and OS (P < .0001). After progression following CDAR, median OS was 29.7 months. CDAR is effective in HCLv, with better outcomes in patients who achieve MRD-negative CR. This trial is registered at www.clinicaltrials.gov as #NCT00923013.

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.

Treatment strategies for a rapidly evolving landscape in chronic lymphocytic leukemia management

With the advent of targeted therapies for chronic lymphocytic leukemia (CLL), treatment choice has expanded and patients are living longer. Careful consideration is needed regarding treatment duration and sequence, how best to meet patients' needs, balancing toxicities while improving long-term survival and maximizing depth of response. This review addresses these considerations and discusses current targeted treatment dilemmas. Targeted therapies have dramatically transformed the CLL treatment landscape. Two treatment paradigms have emerged using B-cell lymphoma 2 inhibitors (BCL2i) and Bruton's tyrosine kinase (BTK): (i) fixed duration and (ii) continuous treatment. The BCL2i venetoclax can attain deep remissions with a fixed-duration approach, resulting in high rates of undetectable minimal residual disease (uMRD) in treatment-naïve and relapsed/refractory (R/R) patients with CLL. BTKis such as ibrutinib and acalabrutinib achieve high objective response rates and long-term disease control, although they rarely attain complete response or uMRD status as monotherapy. Numerous studies are evaluating the clinical utility of BTKi and BCL2i as combination therapies, where deep remissions have been found to occur. MRD status may also be a useful marker for deciding when to stop continuous therapy, and randomized trials on MRD-guided treatment strategies are currently ongoing. The current treatment choice between continuous or fixed-duration therapy should be based on comorbidities, risks, preferences, and treatment goals, whilst areas of emerging clinical interest include the potential utility of BTKi-BCL2i combination therapies, as well as an MRD-guided treatment strategies in the future.

BTK Inhibitors Combined With Chemoimmunotherapy in CLL - The Best of Both Worlds?

Chemoimmunotherapy (CIT) remains a standard-of-care in many regions for first line (1L) therapy of CLL. In fit patients, fludarabine, cyclophosphamide, and rituximab (FCR) has the advantage of achieving undetectable measurable residual disease (MRD) with time-limited treatment and prolonged treatment-free remissions with a plateau on the PFS curve, but have several limitations, most notably the inferior PFS and survival outcomes for patients with unmutated IGHV compared to ibrutinib + rituximab seen in the E1912 study and a risk for long-term toxicities such as therapy-related myeloid neoplasms. Given the nonoverlapping toxicity profile with CIT and its efficacy in patients with high risk genomics, ibrutinib is a potentially useful agent to combine with CIT, with the aim of achieving deep and durable remissions, with time-limited treatment. Three recent phase 2 studies have combined ibrutinib with chemoimmunotherapy, utilizing different approaches in terms of patient selection, sequencing and duration of therapy and choice of monoclonal antibody. These studies all demonstrated favorable toxicity profiles and higher rates of undetectable MRD than with any other previously utilized 1L regimen. This review will focus on this novel treatment approach in CLL.

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.

Undetectable minimal residual disease is an independent prognostic factor in splenic marginal zone lymphoma

The role of minimal residual disease (MRD) in splenic marginal zone lymphoma (SMZL) has not been well studied. We prospectively designed a study to evaluate undetectable MRD (uMRD) by multiparameter flow cytometry as a prognostic factor. Residual disease level of <0·01% was defined as uMRD. A total of 71 newly diagnosed patients with bone marrow involvement were enrolled and all received rituximab-based therapy. The overall response rate (ORR) was 98·5% (70/71), with a complete remission (CR) rate of 54·9% (39/71). There were a total of 295 MRD detections in bone marrow and 77·4% patients (55/71) had uMRD. The 5-year progression-free survival (PFS) [(74·8 ± 6·5)% vs. (31·4 ± 12·6)%, P < 0·001] and 5-year overall survival (OS) [(87·2 ± 5·6)% vs. (68·9 ± 13·4)%, P = 0·035] were significantly higher in uMRD patients than in MRD-positive patients. The 5-year PFS in partial remission (PR) patients with positive MRD was significantly poorer than that of PR patients with uMRD [(21·1 ± 12·9)% vs. (83·3 ± 8·8)%, P = 0·005]. Multivariate prognostic analysis revealed that uMRD was an independent good prognostic factor for PFS (hazard ratio 0·162, 95% confidence interval 0·041-0·635; P = 0·009). All these results highlight uMRD as an independent prognostic factor in patients with SMZL, especially for patients who only achieve PR.

Phase III Clinical Trials in First-Line Follicular Lymphoma: A Review of Their Design and Interpretation

Follicular lymphoma (FL) is one of the most common subtypes of non-Hodgkin lymphoma worldwide. Improved survival outcomes with rituximab-based therapy in clinical trials led to the establishment of rituximab-based immunochemotherapy as standard of care for first-line (1L) treatment of FL. In the GALLIUM trial, obinutuzumab-based immunochemotherapy demonstrated improved progression-free survival (PFS), prolonged time-to-next antilymphoma treatment (TTNT) and comparable overall survival (OS) compared with rituximab-based immunochemotherapy as 1L treatment for FL. Using GALLIUM as an example, this article aims to explain how improved outcomes in 1L treatment of FL have changed the landscape for the design and interpretation of future trials. As approved therapies for 1L FL already achieve good responses, it is becoming more difficult to design trials that demonstrate further treatment benefits with the currently accepted primary endpoints. New endpoints are needed to reflect the long remission times, low relapse rates, and impact of subsequent therapies in FL. PFS is used as a primary efficacy endpoint in registrational clinical trials for indolent malignancies like FL, where improvement in OS is not always observed due to the large number of patients and long study duration required to demonstrate a clear survival benefit. However, there are limitations to using PFS as the primary endpoint. Other potential endpoints, including TTNT, progression of disease within 2 years, response rate, and minimal residual disease status are explored.

Phase III Clinical Trials in First-Line Follicular Lymphoma: A Review of Their Design and Interpretation

Follicular lymphoma (FL) is one of the most common subtypes of non-Hodgkin lymphoma worldwide. Improved survival outcomes with rituximab-based therapy in clinical trials led to the establishment of rituximab-based immunochemotherapy as standard of care for first-line (1L) treatment of FL. In the GALLIUM trial, obinutuzumab-based immunochemotherapy demonstrated improved progression-free survival (PFS), prolonged time-to-next antilymphoma treatment (TTNT) and comparable overall survival (OS) compared with rituximab-based immunochemotherapy as 1L treatment for FL. Using GALLIUM as an example, this article aims to explain how improved outcomes in 1L treatment of FL have changed the landscape for the design and interpretation of future trials. As approved therapies for 1L FL already achieve good responses, it is becoming more difficult to design trials that demonstrate further treatment benefits with the currently accepted primary endpoints. New endpoints are needed to reflect the long remission times, low relapse rates, and impact of subsequent therapies in FL. PFS is used as a primary efficacy endpoint in registrational clinical trials for indolent malignancies like FL, where improvement in OS is not always observed due to the large number of patients and long study duration required to demonstrate a clear survival benefit. However, there are limitations to using PFS as the primary endpoint. Other potential endpoints, including TTNT, progression of disease within 2 years, response rate, and minimal residual disease status are explored.

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.

Integrated Mechanistic Model of Minimal Residual Disease Kinetics With Venetoclax Therapy in Chronic Lymphocytic Leukemia

Minimal residual disease (MRD) is an important emerging clinical end point in chronic lymphocytic leukemia (CLL). The objective of this research was to develop an integrated mechanistic model to evaluate the impact of venetoclax-rituximab combination therapy on MRD kinetics. Using data from 435 patients with relapsed or refractory CLL, an integrated model was developed and validated that accounted for venetoclax dosing and pharmacokinetics, rituximab treatment, absolute lymphocyte count, and blood and bone marrow (BM) MRD data. Simulations of venetoclax-rituximab (six cycles) combination predicted the proportion (90% confidence interval) of patients with BM MRD below 10-4 to be 57% (54-61%) and 63% (59-67%) at 12 and 24 months of treatment, respectively. Continued venetoclax treatment to 48 months only increased the predicted rate of negative BM MRD to 66% (63-70%). These results indicate that treatment with venetoclax-rituximab combination for a finite 2-year period would nearly maximize the rate of negative BM MRD (< 10-4 ). Preliminary clinical data agree with these predictions and more long-term follow-up data are awaited to confirm the same.

CD43 in the malignant flow cytometry laboratory in 2020

Objectives: CD43 can be useful in routine flow cytometry. We conducted a systematic review aiming to describe when CD43 is used by flow cytometry in malignant hematology and to determine its value in these settings. Methods: Systematic review of MEDLINE (search 'CD43' AND 'flow cytometry,' starting in 2010). Results: Twenty-one of 103 entries retrieved were included in this systematic review. CD43 is used in three settings: 1) in the classification of mature B cell lymphoproliferative disorders, 2) as part of a strategy to quantify residual disease in chronic lymphocytic leukemia (CLL) and 3) to help classify CD10-positive B cell populations. In this section, the published data is summarized, the clinical usefulness in each of these settings is evaluated and illustrative cases are shown. Conclusion: CD43 has a growing role in the diagnosis and management of B cell malignancies; it has become essential for the classification of B cell lymphoproliferative disorders and may be of help in the differential diagnosis of CD10-positive lymphomas by FC. It is also required for optimal quantification of CLL residual disease, which will soon be used to guide therapeutic decisions.

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.

CD49d promotes disease progression in chronic lymphocytic leukemia: new insights from CD49d bimodal expression

CD49d is a remarkable prognostic biomarker of chronic lymphocytic leukemia (CLL). The cutoff value for the extensively validated 30% of positive CLL cells is able to separate CLL patients into 2 subgroups with different prognoses, but it does not consider the pattern of CD49d expression. In the present study, we analyzed a cohort of 1630 CLL samples and identified the presence of ∼20% of CLL cases (n = 313) characterized by a bimodal expression of CD49d, that is, concomitant presence of a CD49d+ subpopulation and a CD49d- subpopulation. At variance with the highly stable CD49d expression observed in CLL patients with a homogeneous pattern of CD49d expression, CD49d bimodal CLL showed a higher level of variability in sequential samples, and an increase in the CD49d+ subpopulation over time after therapy. The CD49d+ subpopulation from CD49d bimodal CLL displayed higher levels of proliferation compared with the CD49d- cells; and was more highly represented in the bone marrow compared with peripheral blood (PB), and in PB CLL subsets expressing the CXCR4dim/CD5bright phenotype, known to be enriched in proliferative cells. From a clinical standpoint, CLL patients with CD49d bimodal expression, regardless of whether the CD49d+ subpopulation exceeded the 30% cutoff or not, experienced clinical behavior similar to CD49d+ CLL, both in chemoimmunotherapy (n = 1522) and in ibrutinib (n = 158) settings. Altogether, these results suggest that CD49d can drive disease progression in CLL, and that the pattern of CD49d expression should also be considered to improve the prognostic impact of this biomarker in CLL.

Prognostic value of high-sensitivity measurable residual disease assessment after front-line chemoimmunotherapy in chronic lymphocytic leukemia

Measurable residual disease (MRD) status is widely adopted in clinical trials in patients with chronic lymphocytic leukemia (CLL). Findings from FILO group trials (CLL2007FMP, CLL2007SA, CLL2010FMP) enabled investigation of the prognostic value of high-sensitivity (0.7 × 10^-5) MRD assessment using flow cytometry, in blood (N = 401) and bone marrow (N = 339), after fludarabine, cyclophosphamide, and rituximab (FCR)-based chemoimmunotherapy in a homogeneous population with long follow-up (median 49.5 months). Addition of low-level positive MRD < 0.01% to MRD ≥ 0.01% increased the proportion of cases with positive MRD in blood by 39% and in bone marrow by 27%. Compared to low-level positive MRD < 0.01%, undetectable MRD was associated with significantly longer progression-free survival (PFS) when using blood (72.2 versus 42.7 months; hazard ratio 0.40, p = 0.0003), but not when using bone marrow. Upon further stratification, positive blood MRD at any level, compared to undetectable blood MRD, was associated with shorter PFS irrespective of clinical complete or partial remission, and a lower 5-year PFS rate irrespective of IGHV-mutated or -unmutated status (all p < 0.05). In conclusion, high-sensitivity (0.0007%) MRD assessment in blood yielded additional prognostic information beyond the current standard sensitivity (0.01%). Our approach provides a model for future determination of the optimal MRD investigative strategy for any regimen.

Dual-action CXCR4-targeting liposomes in leukemia: function blocking and drug delivery

CXC chemokine receptor 4 (CXCR4) is overexpressed by a broad range of hematological disorders, and its interaction with CXC chemokine ligand 12 (CXCL12) is of central importance in the retention and chemoprotection of neoplastic cells in the bone marrow and lymphoid organs. In this article, we describe the biological evaluation of a new CXCR4-targeting and -antagonizing molecule (BAT1) that we designed and show that, when incorporated into a liposomal drug delivery system, it can be used to deliver cancer therapeutics at high levels to chronic lymphocytic leukemia (CLL) cells. CXCR4 targeting and antagonism by BAT1 were demonstrated alone and following its incorporation into liposomes (BAT1-liposomes). Antagonism of BAT1 against the CXCR4/CXCL12 interaction was demonstrated through signaling inhibition and function blocking: BAT1 reduced ERK phosphorylation and cell migration to levels equivalent to those seen in the absence of CXCL12 stimulation (P < .001). Specific uptake of BAT1-liposomes and delivery of a therapeutic cargo to the cell nucleus was seen within 3 hours of incubation and induced significantly more CLL cell death after 24 hours than control liposomes (P = .004). The BAT1 drug-delivery system is modular, versatile, and highly clinically relevant, incorporating elements of proven clinical efficacy. The combined capabilities to block CXCL12-induced migration and intracellular signaling while simultaneously delivering therapeutic cargo mean that the BAT1-liposome drug-delivery system could be a timely and relevant treatment of a range of hematological disorders, particularly because the therapeutic cargo can be tailored to the disease being treated.

Statistics and measurable residual disease (MRD) testing: uses and abuses in hematopoietic cell transplantation

SERIES EDITORS' NOTE

The decision whether to recommend a transplant to someone with acute leukemia in first remission is complex and challenging. Diverse, often confounded co-variates interact to influence one's recommendation. Briefly, the decision metric can be viewed in three spheres: (1) subject-; (2) transplant-; and (3) disease-related co-variates. Subject-related co-variates include items such as age and comorbidities. Transplant-related co-variates include items such as donor-types, graft source, proposed conditioning and pre- and post-transplant immune suppression.But what of disease-related variables? Previously haematologists relied on co-variates such as WBC at diagnosis, chemotherapy cycles to achieve first remission, cytogenetics and most recently, mutation topography. However, these co-variates have largely been replaced by results of measurable residual disease (MRD)-testing. Many chemotherapy-only and transplant studies report strong correlations between results of MRD-testing on therapy outcomes such as cumulative incidence of relapse (CIR), leukemia-free survival (LFS) or survival. (CIR makes biological sense in a transplant context whereas LFS and survival do not give competing causes of death such as transplant-related mortality (TRM), graft-versus-host disease and interstitial pneumonia unrelated to relapse probability).This raises the question of how useful results are of MRD-testing in predicting CIR after transplants. Elsewhere we discussed accuracy and precision of MRD-testing in predicting outcomes of therapy of acute myeloid leukemia (Estey E, Gale RP. Leukemia 31:1255-1258, 2017; Hourigan CS, Gale RP, Gormley NJ, Ossenkoppele GJ, Walter RB. Leukemia 31:1482-1490, 2017). Briefly put, not terribly good. Although results of MRD-testing are often the most powerful predictor of CIR in multivariable analyses, the C-statistic (a measure of prediction accuracy) is often only about 0.75. This is much better than flipping a fair coin but far from ideal.In the typescript which follows, Othus and colleagues discuss statistical issues underlying MRD-testing in the context of haematopoietic cell transplants. We hope readers, especially haematologists who often need to make transplant recommendations to people with acute leukemia in first remission, will read it carefully and critically. The bottom line is MRD-test data are useful but considerable uncertainty is unavoidable with substantial false-positive and -negative rates. We need to acknowledge this uncertainty to ourselves and to the people we counsel. The authors quote Voltaire who said: Doubt is not a pleasant condition, but certainty is an absurd one. Sadly so, but we do the best we can. Robert Peter Gale, Imperial College London, and Mei-Jie Zhang, Medical College of Wisconsin and CIBMTR.

Gene expression workflow to analyze residual leukemic cells in Chronic Lymphocytic Leukemia

BACKGROUND

In chronic lymphocytic leukemia, a better understanding of leukemic cell characteristics after treatment would help to design specific therapeutic approaches aimed at preventing clinical relapse. Gene arrays have become a powerful approach to perform gene expression profiling; nevertheless, to work with residual cells entails an intensive labor. The aim of this study was to set forth an effective gene expression approach to analyze residual leukemic cells.

METHODS

Leukocytes from CLL patient's samples were sorted by flow cytometry using a 6-color panel. The quality and quantity of RNA isolated from different inputs of cells were compared by two silica column protocols: RNeasy Micro and RNeasy Mini. RNA amplifications were carried out according to two manufacturer's protocols: Ovation Pico SL and Ovation Pico WTA. A total of 3.5 μg of cDNA was labeled and hybridized to Human Gene 2.0 ST arrays.

RESULTS

RNA extracted from low number of input cells by RNeasy Micro showed similar RNA integrity number to that obtained from RNeasy Mini; however, the RNA quantity was higher using the RNeasy Micro Kit. In addition, those RNA samples obtained with RNeasy Micro and amplified with Ovation Pico WTA showed good quality to proceed for a gene array study, independently of the number of input cells (range: 1 × 10⁴ -5 × 10⁵ cells).

CONCLUSIONS

We observed that this workflow is a feasible approach to obtain genomic material extracted from leukemic cells as little as 1 × 10⁴ cells and it can be useful to carry out gene expression profile experiments to characterize residual leukemic cells in chronic lymphocytic leukemia.

Breast Implant-associated Anaplastic Large Cell Lymphoma: Review and Multiparametric Imaging Paradigms

Breast implant-associated anaplastic large cell lymphoma (BIA-ALCL) is a new provisional category in the 2016 World Health Organization (WHO) classification of lymphoid neoplasms, and its incidence is rising owing to increasing recognition of this complication of breast implant insertion. At a median of 10 years after implant insertion, the typical presenting features are sudden-onset breast swelling secondary to peri-implant effusion and less frequently mass-forming disease. Histologic features comprise pleomorphic cells expressing CD30 and negative anaplastic lymphoma kinase (ALK) receptor, similar to systemic and cutaneous ALK-negative anaplastic large cell lymphoma (ALCL). The effusion-only subtype is generally indolent and curable with surgery, unlike the more aggressive mass-forming disease, for which systemic therapy is advocated. High clinical suspicion and pertinent use of radiologic and pathology modalities are essential for timely and accurate diagnosis of BIA-ALCL. Contemporary imaging techniques including US, mammography, breast MRI, CT, and PET/CT are routinely used in breast disease and lymphomas; however, the unique behavior of BIA-ALCL presents significant diagnostic and radiologic interpretative challenges, with numerous nuanced imaging features being pertinent, and current lymphoma staging and response guidelines are not easily applicable to BIA-ALCL. The authors evaluate available evidence in this evolving field; detail key indications, strengths, and limitations of the panoply of radiologic techniques for BIA-ALCL; and propose multiparametric imaging paradigms for management of the peri-implant effusion and mass-forming or advanced disease subtypes, with the goal of accurate optimal patient care. The authors also predict a future model of multimodal assessment using novel imaging and molecular techniques and define key research directions. ^©RSNA, 2020.

Evolution in the management of chronic lymphocytic leukemia in Japan: should MRD negativity be the goal?

Advances in the molecular biology of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) and development of molecularly targeted therapies have resulted in treatment innovations. Therapeutic approaches for previously untreated CLL/SLL patients are changing from chemoimmunotherapy (CIT) to molecularly targeted drugs. The aim of therapy for CLL patients has been to control the disease; however, FCR (fludarabine, cyclophosphamide, rituximab) has improved outcomes and reduced the high incidence of undetectable minimum/measurable residual disease (MRD) in previously untreated CLL patients with no 17p deletion/TP53 disruption and mutated immunoglobulin heavy chain gene (IGHV). Patients achieving undetectable MRD in the bone marrow are expected to be cured. BTK inhibitors and BCL-2 inhibitors are effective for CLL/SLL patients. However, atrial fibrillation and bleeding are associated with the BTK inhibitor, ibrutinib, while tumor lysis syndrome is an adverse event (AE) of the BCL-2 inhibitor, venetoclax. Although these novel targeted drugs are very useful, they are also expensive. Emergence of resistant clones of CLL cells must also be addressed. Therefore, treatments of indefinite duration until progression have been replaced by fixed-duration treatments. This review introduces advances in the treatment of previously untreated CLL/SLL patients in Europe and the United States.

Minimal residual disease undetectable by next-generation sequencing predicts improved outcome in CLL after chemoimmunotherapy

Patients with chronic lymphocytic leukemia (CLL) who achieve blood or bone marrow (BM) undetectable minimal residual disease (U-MRD) status after first-line fludarabine, cyclophosphamide, and rituximab (FCR) have prolonged progression-free survival (PFS), when assessed by an assay with sensitivity 10-4 (MRD4). Despite reaching U-MRD4, many patients, especially those with unmutated IGHV, subsequently relapse, suggesting residual disease <10-4 threshold and the need for more sensitive MRD evaluation. MRD evaluation by next-generation sequencing (NGS) has a sensitivity of 10-6 (MRD6). To better assess the depth of remission following first-line FCR treatment, we used NGS (Adaptive Biotechnologies Corporation) to assess MRD in 62 patients, all of whom had BM U-MRD by multicolor flow cytometry (sensitivity 10-4) at end-of-FCR treatment. Samples from these patients included 57 BM samples, 29 peripheral blood mononuclear cell (PBMC) samples, and 32 plasma samples. Only 27.4% of the 62 patients had U-MRD by NGS. Rate of U-MRD by NGS was lowest in BM (25%), compared with PBMC (55%) or plasma (75%). No patient with U-MRD by NGS in BM or PBMC was MRD+ in plasma. Patients with mutated IGHV were more likely to have U-MRD by NGS at the end of treatment (EOT; 41% vs 13%, P = .02) than those with unmutated IGHV. Median follow-up was 81.6 months. Patients with U-MRD at EOT had superior PFS vs MRD+ patients, regardless of sample type assessed (BM, P = .02, median not reached [NR] vs 67 months; PBMC, P = .02, median NR vs 74 months). More sensitive MRD6 testing increases prognostic discrimination over MRD4 testing.

Targeting Mitochondrial Apoptosis to Overcome Treatment Resistance in Cancer

Deregulated cellular apoptosis is a hallmark of cancer and chemotherapy resistance. The B-cell lymphoma 2 (BCL-2) protein family members are sentinel molecules that regulate the mitochondrial apoptosis machinery and arbitrate cell fate through a delicate balance between pro- and anti-apoptotic factors. The recognition of the anti-apoptotic BCL2 gene as an oncogenic driver in hematological malignancies has directed attention toward unraveling the biological significance of each of the BCL-2 superfamily members in cancer progression and garnered interest in the targeting of apoptosis in cancer therapy. Accordingly, the approval of venetoclax (ABT-199), a small molecule BCL-2 inhibitor, in patients with chronic lymphocytic leukemia and acute myeloid leukemia has become the proverbial torchbearer for novel candidate drug approaches selectively targeting the BCL-2 superfamily. Despite the inspiring advances in this field, much remains to be learned regarding the optimal therapeutic context for BCL-2 targeting. Functional assays, such as through BH3 profiling, may facilitate prediction of treatment response, development of drug resistance and shed light on rational combinations of BCL-2 inhibitors with other branches of cancer therapy. This review summarizes the pathological roles of the BCL-2 family members in cancer, discusses the current landscape of their targeting in clinical practice, and highlights the potential for future therapeutic inroads in this important area.

A network meta-analysis of maintenance therapy in chronic lymphocytic leukemia

Background

Chronic lymphocytic leukemia (CLL) is incurable through conventional chemoimmunotherapy regimens. Despite durable responses to front-line therapy and sustained remission rates in patients with CLL, a majority of patients eventually relapse in 5 years of initial treatment. The depth of the response may affect the length of response. Maintenance therapies were aimed to deep remissions and extend the period of disease quiescence. Lenalidomide, rituximab and ofatumumab had demonstrated some efficacy as a maintenance therapy compared to no intervention for CLL patients. The relative effect on disease control and safety between different maintenance therapies were unclear.

Methods

We performed a systematic literature review and network meta-analysis to evaluate relative effect on disease control and safety of current available maintenance therapies. We searched PubMed, Embase and Cochrane database up to March 6, 2019. Relevant reference of review article and conference abstract including European Hematology Association Annual Meeting (EHA 2018), American Society of Hematology Annual Meeting (ASH 2018) and American Society of Clinical Oncology Annual Meeting (ASCO 2018) were searched. Randomized controlled trials (RCT) involving current available maintenance therapy including “Lenalidomide”, “Rituximab”, “Ofatumumab”, “Ibrutinib”, “Idelalisib”, “Venetoclax”and “Obinutuzumab”were eligible. Outcomes of interest included progression-free survival (PFS), overall survival (OS) and serious adverse events (SAE) in CLL patients received subsequent maintenance therapy. Two authors CHL and CL) independently assessed eligibility for all identified citations and extracted data from the original trial reports. The selected studies’ risk of bias was assessed following the guidelines of Cochrane Collaboration Handbook.

Results

In total, six phase III RCTs with total 1,615 CLL patients were identified. Maintenance therapy using lenalidomide, rituximab, and ofatumumab demonstrated a statistically significant effect in prolongation of progression-free survival (HR:0.37, 95% CI: 0.27–0.50 of lenalidomide; HR:0.50, 95% CI: 0.38–0.66 of rituximab; HR:0.52, 95% CI:0.41–0.66 of ofatumumab, separately) compared with no intervention; however, for overall survival, the effect of maintenance therapy showed no significant difference versus no intervention (HR: 0.89, 95% CI: 0.70–1.14). Lenalidomide showed the best efficacy for PFS (HR: 0.37, 95% CI: 0.27–0.50, Probability of being best treatment: 96%).

Conclusions

Our network meta-analysis provided an integrated overview of relative efficacy and safety of different maintenance therapies in CLL. All maintenance therapies were effective in reducing the risk of disease progression versus no intervention. Based on current best evidence, maintenance therapy with lenalidomide is the most efficacious option.

Venetoclax: evidence to date and clinical potential

The emergence of targeted therapy for patients with hematological diseases has permanently altered the therapeutic landscape. Immunochemotherapy regimes are now more and more being replaced by targeted therapies due to superior efficacy and better safety profiles. However, evolution and selection of subclones with continuous treatment leads to disease relapse and resistance toward these novel drugs. Venetoclax, the highly selective BCL-2 inhibitor (ABT-199), has an acceptable safety profile. To date, it has been approved for the treatment of first-line and relapsed/refractory chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML). However, extension of indications can be expected in monotherapy and in combination regimens with promising outcomes in other hematological diseases. In this article, we describe the mechanism of action that stands behind the efficacy of venetoclax and provide a summary of available results from clinical trials.

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.

Frontline therapies for untreated chronic lymphoid leukemia

Therapy for chronic myeloid leukemia (CLL) is going through a major paradigm shift. Combination chemoimmunotherapy regimens have been the frontline therapies for CLL, whereas chlorambucil remained the standard frontline therapy for older patients (65 years or older) with CLL until recently. Monoclonal antibodies including rituximab, ofatumumab and obinutuzumab have been used for CLL therapy. Novel immunotherapeutics with chimeric antigen receptor (CAR) engineered T cells is rapidly migrating to clinical applications. Targeted therapies with small molecule inhibitors against Bruton tyrosine kinase (BTK) such as ibrutinib and acalabrutinib are playing a major role for treatment of patients with either treatment-naïve or refractory/relapsed CLL. Several major clinical trials including RESONATE-2, iLLUMINATE, ALLIANCE, ECOG 1912, CLL10, CLL14 as well as ibrutinib plus venetoclax have been ongoing in patients with untreated CLL. Frontline therapy of patients with untreated CLL appears to be shifting from chemotherapy to chemotherapy-free regimens. This review summarized latest development for frontline therapies of untreated CLL.

Ibrutinib plus fludarabine, cyclophosphamide, and rituximab as initial treatment for younger patients with chronic lymphocytic leukaemia: a single-arm, multicentre, phase 2 trial

BACKGROUND

Fludarabine, cyclophosphamide, and rituximab (FCR) can improve disease-free survival for younger (age ≤65 years) fit patients with chronic lymphocytic leukaemia with mutated IGHV. However, patients with unmutated IGHV rarely have durable responses. Ibrutinib is active for patients with chronic lymphocytic leukaemia irrespective of IGHV mutation status but requires continuous treatment. We postulated that time-limited ibrutinib plus FCR would induce durable responses in younger fit patients with chronic lymphocytic leukaemia.

METHODS

We did a multicentre, open-label, non-randomised, single-arm phase 2 trial at seven sites in the USA. We enrolled patients aged 65 years or younger with previously untreated chronic lymphocytic leukaemia. Our initial cohort (original cohort) was not restricted by prognostic marker status and included patients who had del(17p) or TP53 aberrations. After a protocol amendment (on March 21, 2017), we enrolled an additional cohort (expansion cohort) that included patients without del(17p). Ibrutinib was given orally (420 mg/day) for 7 days, then up to six 28-day cycles were administered intravenously of fludarabine (25 mg/m2, days 1-3), cyclophosphamide (250 mg/m2, days 1-3), and rituximab (375 mg/m2 day 1 of cycle 1; 500 mg/m2 day 1 of cycles 2-6) with continuous oral ibrutinib (420 mg/day). Responders continued on ibrutinib maintenance for up to 2 years, and patients with undetectable minimal residual disease in bone marrow after 2 years were able to discontinue treatment. The primary endpoint was the proportion of patients who achieved a complete response with undetectable minimal residual disease in bone marrow 2 months after the last cycle of ibrutinib plus FCR. Analyses were done per-protocol in all patients who received at least one dose of study treatment. This trial is registered with ClinicalTrials.gov (NCT02251548) and is ongoing.

FINDINGS

Between Oct 23, 2014, and April 23, 2018, 85 patients with chronic lymphocytic leukaemia were enrolled. del(17p) was detected in four (5%) of 83 patients and TP53 mutations were noted in three (4%) of 81 patients; two patients had both del(17p) and TP53 mutations. Median patients' age was 55 years (IQR 50-58). At data cutoff, median follow-up was 16·5 months (IQR 10·6-34·1). A complete response and undetectable minimal residual disease in bone marrow 2 months after the last cycle of ibrutinib plus FCR was achieved by 28 (33%, 95% CI 0·23-0·44) of 85 patients (p=0·0035 compared with a 20% historical value with FCR alone). A best response of undetectable minimal residual disease in bone marrow was achieved by 71 (84%) of 85 patients during the study. One patient had disease progression and one patient died (sudden cardiac death after 17 months of ibrutinib maintenance, assessed as possibly related to ibrutinib). The most common all-grade toxic effects were haematological, including thrombocytopenia in 63 (74%) patients, neutropenia in 53 (62%), and anaemia in 41 (49%). Grade 3 or 4 non-haematological serious adverse events included grade 3 atrial fibrillation in three (4%) patients and grade 3 Pneumocystis jirovecii pneumonia in two (2%).

INTERPRETATION

The proportion of patients who achieved undetectable minimal residual disease in bone marrow with ibrutinib plus FCR is, to our knowledge, the highest ever published in patients with chronic lymphocytic leukaemia unrestricted by prognostic marker status. Ibrutinib plus FCR is promising as a time-limited combination regimen for frontline chronic lymphocytic leukaemia treatment in younger fit patients.

FUNDING

Pharmacyclics and the Leukemia & Lymphoma Society.

Oxidative stress as candidate therapeutic target to overcome microenvironmental protection of CLL

Chronic lymphocytic leukemia (CLL) cells depend on microenvironmental non-malignant cells for survival. We compared the transcriptomes of primary CLL cells cocultured or not with protective bone marrow stromal cells (BMSCs) and found that oxidative phosphorylation, mitochondrial function, and hypoxic signaling undergo most significant dysregulation in non-protected CLL cells, with the changes peaking at 6-8 h, directly before induction of apoptosis. A subset of CLL patients displayed a gene expression signature resembling that of cocultured CLL cells and had significantly worse progression-free and overall survival. To identify drugs blocking BMSC-mediated support, we compared the relevant transcriptomic changes to the Connectivity Map database. Correlation was found with the transcriptomic signatures of the cardiac glycoside ouabain and of the ipecac alkaloids emetine and cephaeline. These compounds were highly active against protected primary CLL cells (relative IC₅₀'s 287, 190, and 35 nM, respectively) and acted by repressing HIF-1α and disturbing intracellular redox homeostasis. We tested emetine in a murine model of CLL and observed decreased CLL cells in peripheral blood, spleen, and bone marrow, recovery of hematological parameters and doubling of median survival (31.5 vs. 15 days, P = 0.0001). Pathways regulating redox homeostasis are thus therapeutically targetable mediators of microenvironmental support in CLL cells.

SOHO State of the Art Updates and Next Questions: The Conundrum in Assessing the Therapy Response of Patients With Chronic Lymphocytic Leukemia

In 2018, the International Workshop on Chronic Lymphocytic Leukemia (iwCLL) updated the guidelines for diagnosis, indications for treatment, response assessment, and supportive management of patients with chronic lymphocytic leukemia. Included were definitions for response, which incorporated consideration of the significance of minimal residual disease. Here we discuss the clinical significance of complete response or partial response, as defined in the 2018 iwCLL guidelines, and the relative value of assessing for minimal residual disease.

Evolution of CLL treatment - from chemoimmunotherapy to targeted and individualized therapy

During the past 5 years, a number of highly active novel agents, including kinase inhibitors targeting BTK or PI3Kδ, an antagonist of the antiapoptotic protein BCL-2, and new anti-CD20 monoclonal antibodies, have been added to the therapeutic armamentarium for patients with chronic lymphocytic leukaemia (CLL). In these exciting times, care is needed to optimally integrate these novel agents into the traditional treatment algorithm without overlooking or compromising the benefits of established treatments, especially chemoimmunotherapy. A more personalized approach to CLL therapy that takes into account individual risk factors, patient characteristics, and their treatment preferences is now possible. Herein, we discuss the biological basis for the novel therapeutic agents and outline not only the major advantages of these agents over traditional therapies but also their adverse effects and the rationale for continued use of older versus newer types of therapy for selected patients with CLL. We conclude by providing recommendations for an individualized therapy approach for different populations of patients with CLL.

Updated results from the phase 3 HELIOS study of ibrutinib, bendamustine, and rituximab in relapsed chronic lymphocytic leukemia/small lymphocytic lymphoma

We report follow-up results from the randomized, placebo-controlled, phase 3 HELIOS trial of ibrutinib+bendamustine and rituximab (BR) for previously treated chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) without deletion 17p. Overall, 578 patients were randomized 1:1 to either ibrutinib (420 mg daily) or placebo, in combination with 6 cycles of BR, followed by ibrutinib or placebo alone. Median follow-up was 34.8 months (range: 0.1-45.8). Investigator-assessed median progression-free survival (PFS) was not reached for ibrutinib+BR, versus 14.3 months for placebo+BR (hazard ratio [HR] [95% CI], 0.206 [0.159-0.265]; P < 0.0001); 36-month PFS rates were 68.0% versus 13.9%, respectively. The results are consistent with the primary analysis findings (HR = 0.203, as assessed by independent review committee, with 17-month median follow-up). Median overall survival was not reached in either arm; HR (95% CI) for ibrutinib+BR versus placebo: 0.652 (0.454-0.935; P = 0.019). Minimal residual disease (MRD)-negative response rates were 26.3% for ibrutinib+BR and 6.2% for placebo+BR (P < 0.0001). Incidence of treatment-emergent adverse events (including grades 3-4) were generally consistent with the initial HELIOS report. These long-term data support improved survival outcomes and deepening responses with ibrutinib+BR compared with BR in relapsed CLL/SLL.

High prognostic value of measurable residual disease detection by flow cytometry in chronic lymphocytic leukemia patients treated with front-line fludarabine, cyclophosphamide, and rituximab, followed by three years of rituximab maintenance

It has been postulated that monitoring measurable residual disease (MRD) could be used as a surrogate marker of progression-free survival (PFS) in chronic lymphocytic leukemia (CLL) patients after treatment with immunochemotherapy regimens. In this study, we analyzed the outcome of 84 patients at 3 years of follow-up after first-line treatment with fludarabine, cyclophosphamide and rituximab (FCR) induction followed by 36 months of rituximab maintenance thearpy. MRD was assessed by a quantitative four-color flow cytometry panel with a sensitivity level of 10⁻⁴. Eighty out of 84 evaluable patients (95.2%) achieved at least a partial response or better at the end of induction. After clinical evaluation, 74 patients went into rituximab maintenance and the primary endpoint was assessed in the final analysis at 3 years of follow-up. Bone marrow (BM) MRD analysis was performed after the last planned induction course and every 6 months in cases with detectable residual disease during the 36 months of maintenance therapy. Thirty-seven patients (44%) did not have detectable residual disease in the BM prior to maintenance therapy. Interestingly, 29 patients with detectable residual disease in the BM after induction no longer had detectable disease in the BM following maintenance therapy. After a median followup of 6.30 years, the median overall survival (OS) and PFS had not been reached in patients with either undetectable or detectable residual disease in the BM, who had achieved a complete response at the time of starting maintenance therapy. Interestingly, univariate analysis showed that after rituximab maintenance OS was not affected by IGHV status (mutated vs. unmutated OS: 85.7% alive at 7.2 years vs. 79.6% alive at 7.3 years, respectively). As per protocol, 15 patients (17.8%), who achieved a complete response and undetectable peripheral blood and BM residual disease after four courses of induction, were allowed to stop fludarabine and cyclophosphamide and complete two additional courses of rituximab and continue with maintenance therapy for 18 cycles. Surprisingly, the outcome in this population was similar to that observed in patients who received the full six cycles of the induction regimen. These data show that, compared to historic controls, patients treated with FCR followed by rituximab maintenance have high-quality responses with fewer relapses and improved OS. The tolerability of this regime is favorable. Furthermore, attaining an early undetectable residual disease status could shorten the duration of chemoimmunotherapy, reducing toxicities and preventing long-term side effects. The analysis of BM MRD after fludarabine-based induction could be a powerful predictor of post-maintenance outcomes in patients with CLL undergoing rituximab maintenance and could be a valuable tool to identify patients at high risk of relapse, influencing further treatment strategies. This trial is registered with EudraCT n. 2007-002733-36 and ClinicalTrials.gov Identifier: NCT00545714.

The expanding role of venetoclax in chronic lymphocytic leukemia and small lymphocytic lymphoma

The BCL-2 protein family members inhibit cellular apoptosis, and their overexpression represents a common survival adaption in cancer. Recently, a selective BCL-2 inhibitor ABT-199, venetoclax, has demonstrated remarkable activity in relapsed/refractory chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), both as a single agent and in combination with anti-CD20 immunotherapies, such as rituximab. In this article, we review the development and latest clinical data that have led to the expanded approval of venetoclax with rituximab in relapsed/refractory CLL/SLL. We also discuss ongoing and future clinical trials designed to evaluate the efficacy of venetoclax in previously untreated patients and to investigate venetoclax combinations with inhibitors of B-cell receptor signaling pathway. These studies hope to offer an expanded list of chemotherapy-free regimens for patients with CLL/SLL.

SERS-based dynamic monitoring of minimal residual disease markers with high sensitivity for clinical applications

Minimal residual disease (MRD) measurement is important for the diagnosis and prognosis of B cell hematological malignancies in the clinic. Thus, a sensitive and accurate method for monitoring the corresponding surface markers is in high demand for early diagnosis and treatment instruction. Herein, we developed a surface enhanced Raman scattering (SERS)-based sandwich-type immunoassay for the simultaneous detection of two surface markers (i.e., CD19 and CD20) in Raji cell lines as well as in clinical blood samples. First, to compare with the results obtained by flow cytometry, we evaluated the sensitivity and reproducibility of the SERS immunoassay for real-time detection of CD19 and CD20 expressions in Raji cells and blood samples. Then, we conducted follow-up tests on 13 B cell hematological malignancy patients for one month and dynamically monitored their CD19 and CD20 expressions by the SERS immunoassay. In addition to the improved sensitivity of the SERS method, good linear correlations between the SERS intensities and flow cytometry results were also observed for both CD19 and CD20, which indicated the accuracy of this SERS-based strategy. Therefore, this SERS-based simultaneous detection approach shows great potential for accurate and early diagnosis of MRD in B cell hematological malignancies.