Allogeneic hematopoietic cell transplantation for high-risk CLL: 10-year follow-up of the GCLLSG CLL3X trial

Update on the management of relapsed/refractory chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) predominantly affects older adults, characterized by a relapsing and remitting pattern with sequential treatments available for many patients. Identification of progressive/relapsed CLL should prompt close monitoring and early discussion about the next therapies when treatment indications are present. The intervening period represents an opportunity to optimize patient health, including establishing adequate vaccination and surveillance for second primary malignancies, and treating non-CLL-related comorbidities which may impact well-being and CLL therapy. We now see patients with relapsed/refractory (RR) CLL in the clinic who have been previously treated with chemoimmunotherapy (CIT) and/or one or more novel therapies. Continuous covalent inhibitors of Bruton's tyrosine kinase (cBTKi) and fixed-duration venetoclax (Ven)-anti-CD20 monoclonal antibody (mAb) are preferred over CIT given the survival advantages associated with these therapies, although have never been evaluated head-to-head. While both classes are effective for RR CLL, potential side effects and the logistics of administration differ. Few randomized data demonstrate the sequential use of cBTKi and fixed-duration Ven-anti-CD20 mAb; however, they may be used in either sequence. Newer non-covalent BTKi, active against BTK C481 resistance mutations emerging with continuous cBTKi exposure, and novel approaches such as BTK degraders, bispecific antibodies, and chimeric antigen receptor T-cell therapies demonstrate impressive efficacy. In this review of RR CLL we explore relevant investigations, consideration of broader CLL- and non-CLL-related health needs, and evidence for efficacy and safety of B-cell receptor inhibitors and Ven, including available data to support drug sequencing or switching. We describe novel approaches to RR CLL, including rechallenging with fixed-duration therapies, allogeneic stem cell transplant indications in the novel therapy era, and highlight early data supporting the use of T-cell directing therapies and novel drug targets.

Chimeric Antigen Receptor T-cell Therapy for Chronic Lymphocytic Leukemia: What is the supporting evidence so far?

While acknowledging that newer therapies have improved survival rates in chronic lymphocytic leukemia (CLL), patients with high-risk disease features are at an increased risk of treatment failure. Allogeneic hematopoietic cell transplantation (allo-HCT) was traditionally offered as front-line consolidation in high-risk CLL; however, with the emergence of targeted therapies like Bruton tyrosine kinase (BTK) and B-cell lymphoma 2 (BCL-2) inhibitors, the role of allo-HCT has been relegated to later stages of the disease. Patients with relapsed/refractory (R/R) CLL who have failed both BTK and BCL-2 inhibitors represent a therapeutic challenge owing to a poor prognosis. Chimeric antigen receptor T-cell (CAR T) therapies targeting CD19 have improved response rates and overall survival in various types of R/R B-cell non-Hodgkin lymphomas. For CLL, no approved CAR T-cell therapies are yet available. Emerging data appear to show a therapeutic benefit of CAR T-cell therapy in patients with R/R CLL, even after failing an allo-HCT.

Cellular Therapy in Chronic Lymphocytic Leukemia: Have We Advanced in the Last Decade?

BACKGROUND

Chronic lymphocytic leukemia (CLL) is a heterogeneous B-cell malignancy, affecting mainly older adults. Despite the recent introduction of multiple targeted agents, CLL remains an incurable disease. Cellular therapy is a promptly evolving area that has developed over the last decades from such standard of care as hematopoietic cell transplantation (HCT) to the novel treatment modalities employing genetically engineered immune cells.

SUMMARY

Tailoring the proper treatment for each patient is warranted and should take into account the disease biology, patient characteristics, and the available treatment modalities. Nowadays, the most broadly applied cellular therapies for CLL management are HCT and chimeric antigen receptor-T (CAR-T) cells. However, CAR-T cell therapy is currently not yet approved in CLL, and the appropriate sequencing for the administration of these agents remains to be clarified.

KEY MESSAGES

The current review will discuss various available cellular treatment options, their advances and limitations, as well as the optimal timing for the employment of such therapies in CLL patients.

Current Treatment Options in Relapsed and Refractory Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma: a Review

OPINION STATEMENT

Treatment of relapsed and refractory (R/R) chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL) has changed dramatically over the past decade due to the development of oral targeted agents in several therapeutic classes, including BTK inhibitors (such as ibrutinib, acalabrutinib, zanubrutinib, and the non-covalent BTK inhibitor pirtobrutinib), the first in class BCL2 inhibitor venetoclax, PI3K inhibitors (idelalisib and duvelisib), and monoclonal antibodies in monotherapy and in combination. My approach to treatment of the R/R patient draws heavily on prior therapies, such that a patient with no exposure to prior novel therapies would be offered either a BTK or BCL2-based regimen, whereas patients with prior BTK inhibitor exposure would likely receive a BCL2 inhibitor and vice versa. For patients who are intolerant to a BTK inhibitor but are otherwise responding, an alternate BTK inhibitor may be considered. For those patients who have received a fixed-duration BCL2 inhibitor-based regimen and have maintained a response for greater than 12-24 months, re-treatment with a BCL2 inhibitor-based regimen at progression may be considered based on limited data, recognizing that robust prospective clinical trials are lacking in this space. For those patients who are "double refractory" and have progressed on both a BTK inhibitor and a BCL2 inhibitor-based regimen, clinical trials are strongly preferred. In absence of a clinical trial, these patients can be challenged with PI3K inhibitors, though responses are usually not durable, and toxicity is high. Combination cytotoxic chemotherapy with novel agents, allogeneic hematopoietic stem cell transplant, and cellular therapy may be considered for very high-risk populations, such as patients with Richter's transformation, though novel approaches are urgently needed and clinical trial enrollment is highly encouraged.

Measurable Residual Disease in Chronic Lymphocytic Leukemia: Current Understanding and Evolving Role in Clinical Practice

OPINION STATEMENT

Treatment of chronic lymphocytic leukemia (CLL) has evolved dramatically during the last decade, from chemoimmunotherapy (CIT)-based therapies to newer B-cell receptor (BCR) signaling targeting agents, which are sometimes given as continuous schemes. Response to treatment was traditionally defined according to clinical variables designed to assign a response category. Interest in assessing for deeper responses in CLL by the means of measurable residual disease (MRD) testing has been the subject of research during the last several years. Analyses and sub-analyses of clinical trials have shown that achieving undetectable MRD (uMRD) in CLL is an important prognostic factor. In this review, we summarize the available evidence about MRD in CLL, from the various assays available for measurement, the compartment to test, the impact of reaching uMRD according to the treatment regimen, and the results of fixed duration treatment guided by MRD trials. Finally, we summarize how MRD can be incorporated in clinical practice and how it may guide fixed duration treatment in the future should evidence continue to accumulate in that direction.

The European landscape on allogeneic haematopoeietic cell transplantation in Chronic Lymphocytic Leukaemia between 2009 and 2019: a perspective from the Chronic Malignancies Working Party of the EBMT

Allogeneic transplantation (allo-HCT) is a curative treatment in CLL whose efficacy including the most severe forms had led to the 2006 EBMT recommendations. The advent after 2014 of targeted therapies has revolutionized CLL management, allowing prolonged control to patients who have failed immunochemotherapy and/or have TP53 alterations. We analysed the pre COVID pandemic 2009-2019 EBMT registry. The yearly number of allo-HCT raised to 458 in 2011 yet dropped from 2013 onwards to an apparent plateau above 100. Within the 10 countries who were under the EMA for drug approval and performed 83.5% of those procedures, large initial differences were found but the annual number converged to 2-3 per 10 million inhabitants during the 3 most recent years suggesting that allo-HCT remains applied in selected patients. Long-term follow-up on targeted therapies shows that most patients relapse, some early, with risk factors and resistance mechanisms being described. The treatment of patients exposed to both BCL2 and BTK inhibitors and especially those with double refractory disease will become a challenge in which allo-HCT remains a solid option in competition with emerging therapies that have yet to demonstrate their long-term effectiveness.

The end of the beginning: application of single-cell sequencing to chronic lymphocytic leukemia

Single-cell analysis has emerged over the past decade as a transformative technology informative for the systematic analysis of complex cell populations such as in cancers and the tumor immune microenvironment. The methodologic and analytical advancements in this realm have evolved rapidly, scaling from but a few cells at its outset to the current capabilities of processing and analyzing hundreds of thousands of individual cells at a time. The types of profiling attainable at individual cell resolution now range from genetic and transcriptomic characterization and extend to epigenomic and spatial analysis. Additionally, the increasing ability to achieve multiomic integration of these data layers now yields ever richer insights into diverse molecular disease subtypes and the patterns of cellular circuitry on a per-cancer basis. Over the years, chronic lymphocytic leukemia (CLL) consistently has been at the forefront of genomic investigation, given the ready accessibility of pure leukemia cells and immune cells from circulating blood of patients with this disease. Herein, we review the recent forays into the application of single-cell analysis to CLL, which are already revealing a new understanding of the natural progression of CLL, the impact of novel therapies, and the interactions with coevolving nonmalignant immune cell populations. As we emerge from the end of the beginning of this technologic revolution, CLL stands poised to reap the benefits of single-cell analysis from the standpoints of uncovering fresh fundamental biological knowledge and of providing a path to devising regimens of personalized diagnosis, treatment, and monitoring.

The role of allogeneic hematopoietic cell transplantation for chronic lymphocytic leukemia: A review

Although the use of allogeneic hematopoietic cell transplantation (HCT) for chronic lymphocytic leukemia (CLL) has declined with the development of novel targeted agents, it continues to play an important role for eligible patients with high-risk or heavily pretreated CLL who lack other treatment options. CLL is susceptible to a potent graft-versus-leukemia (GVL) effect which produces long-lasting remissions in 30-50% of transplanted patients. While allogeneic HCT is associated with significant risks of graft-versus-host disease (GVHD), infection, and non-relapse mortality (NRM), improvements in patient and donor selection, reduced intensity conditioning (RIC), GVHD prophylaxis, and supportive care have rendered this an increasingly safe and effective procedure in the current era. In this review, we discuss recent advances in allogeneic HCT for CLL, with a focus on the optimal evidence-based strategies to maximize benefit and minimize toxicity of this potentially curative cellular therapy.

Management of relapsed/refractory Chronic Lymphocytic Leukemia

The therapeutic landscape for chronic lymphocytic leukemia (CLL) has changed dramatically over the past decade as our understanding of the biology of CLL has advanced, allowing the development of oral therapies targeting key drivers of CLL. Currently, inhibitors of Bruton's Tyrosine Kinase and the BH3 mimetic venetoclax are standards of care for both frontline and relapsed/refractory CLL. Sequencing of available therapies, therefore, has become a major challenge of therapy. In this review, we will focus on the current landscape for the treatment of relapsed/refractory CLL. We will also discuss important considerations when sequencing these available treatments. The recent advances in this disease are significant steps forward, and raise new questions of how these available drugs should be given as well as how we can continue to improve the treatment of CLL.

SOHO State of the Art Updates and Next Questions | Management of Most Difficult Cases of Chronic Lymphocytic Leukemia: Relapse After Both BTK and BCL2 Inhibition and Richter Transformation

The introduction of targeted therapies in chronic lymphocytic leukemia (CLL) has ushered in a new era in which patients achieve better control of their disease, survive longer, and experience fewer toxicities than before. Despite this progress, a subgroup of patients with CLL will develop resistance to both Bruton tyrosine kinase (BTK) and B-cell lymphoma 2 inhibitors. In addition, a subgroup of CLL cases will transform into aggressive lymphoma - called Richter transformation - either before or during targeted therapy. These two subgroups of patients have a poor prognosis, and available therapies lead to long-term remission in only a minority of patients. In this paper, two cases are presented that are reflective of these difficult scenarios. In the first case, a patient with CLL, complex karyotype, del 17p, and a mutation in TP53 experiences progression after ibrutinib, venetoclax, bendamustine, rituximab, and idelalisib. In the second case, a patient with CLL and del 17p develops a Richter transformation to diffuse large B-cell lymphoma after treatment with obinutuzumab, chlorambucil, ibrutinib, venetoclax, and idelalisib. The aggressive lymphoma is refractory to chemoimmunotherapy, and she expires. The literature pertaining to these two scenarios is reviewed, including the role of available targeted therapies, chemoimmunotherapy, and hematopoietic cell transplantation. Emerging novel therapies, including reversible BTK inhibitors and CAR T cell therapy, are discussed.

Cellular Therapy in High-Risk Relapsed/Refractory Chronic Lymphocytic Leukemia and Richter Syndrome

Despite the development of highly effective, targeted inhibitors of B-cell proliferation and anti-apoptotic pathways in chronic lymphocytic leukemia (CLL), these treatments are not curative, and many patients will develop either intolerance or resistance to these treatments. Transformation of CLL to high-grade lymphoma—the so-called Richter syndrome (RS)—remains a highly chemoimmunotherapy-resistant disease, with the transformation occurring following targeted inhibitors for CLL treatment being particularly adverse. In light of this, cellular therapy in the form of allogenic stem cell transplantation and chimeric antigen receptor T-cell therapy continues to be explored in these entities. We reviewed the current literature assessing these treatment modalities in both high-risk CLL and RS. We also discussed their current limitations and place in treatment algorithms.

Clinical outcome of allogeneic stem cell transplantation in patients with B-cell lymphoid malignancies following treatment with targeted small molecule inhibitors

We aimed to study the risks of graft-versus-host disease (GVHD), non-relapse mortality (NRM) and survival outcomes of allogeneic stem cell transplantation (alloSCT) in patients with chronic lymphocytic leukemia (n = 17), Richter's syndrome (n = 14), or lymphoma (n = 18) after small molecule inhibitors (SMIs). Patients had a median of 4 prior therapies, including ibrutinib (n = 46; 94%), venetoclax (n = 19; 39%), and idelalisib (n = 6; 12%). Twenty-one (43%) had >1 SMI. P53 mutation was detected in 58% of patients. The 3-year overall and progression-free survival rates were 68% and 59%, respectively. The rates of grade II-IV and III-IV acute GVHD were 33% and 7%. The 1-year rates of chronic GVHD, NRM and relapse were 19%, 10% and 21%, respectively. Results were comparable to a historical control of patients who received alloSCT without a prior exposure to SMI. We conclude that a prior use of SMI does not impair the outcomes after alloSCT.

Autophagy in acute myeloid leukemia: a paradoxical role in chemoresistance

Autophagy is a lysosomal degradation pathway that is constitutively active in almost every cell of our body at basal level. This self-eating process primarily serves to remove superfluous constituents of the cells and recycle the degraded products. Autophagy plays an essential role in cell homeostasis and can be enhanced in response to stressful conditions. Impairment in the regulation of the autophagic pathway is implicated in pathological conditions such as neurodegeneration, cardiac disorders, and cancer. However, the role of autophagy in cancer initiation and development is controversial and context-dependent. Evidence from various studies has shown that autophagy serves dual purpose and may assist in cancer progression or suppression. In the early stages of cancer initiation, autophagy acts as a quality control mechanism and prevents cancer development. When cancer is established and progresses to a later stage, autophagy helps in the survival of these cells through adaptation to stresses, including exposure to anti-cancer drugs. In this review, we highlight various studies on autophagic pathways and describe the role of autophagy in cancer, specifically acute myeloid leukemia (AML). We also discuss the prognostic significance of autophagy genes involved in AML leukemogenesis and implications in conferring resistance to chemotherapy.

The Difficult-to-Treat del 17 p Patient—A Case Report in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) treatment strategies have evolved to include mechanism-driven drugs but now raise new questions regarding their optimum timing and sequencing. In high-risk patients, switching from pathway inhibitors to allogeneic stem cell transplantation (allo-HCT) is still a matter of intense debate. We report the case of a CLL patient with 17 p deletion treated with ibrutinib as a bridge to allo-HCT. Early relapse after allo-HCT urged the initiation of salvage therapy, including donor lymphocytes infusions, ibrutinib, and venetoclax. We aim to outline and discuss the potential benefits of novel therapies, the current role of allo-HCT in CLL, drug timing and sequencing, and the unmet need to improve the long-term outcome of high-risk CLL patients.

Clonal Evolution of High-Risk Chronic Lymphocytic Leukemia: A Contemporary Perspective

Clonal evolution represents the natural process through which cancer cells continuously search for phenotypic advantages that enable them to develop and expand within microenvironmental constraints. In chronic lymphocytic leukemia (CLL), clonal evolution underpins leukemic progression and therapeutic resistance, with differences in clonal evolutionary dynamics accounting for its characteristically diverse clinical course. The past few years have witnessed profound changes in our understanding of CLL clonal evolution, facilitated by a maturing definition of high-risk CLL and an increasing sophistication of next-generation sequencing technology. In this review, we offer a modern perspective on clonal evolution of high-risk CLL, highlighting recent discoveries, paradigm shifts and unresolved questions. We appraise recent advances in our understanding of the molecular basis of CLL clonal evolution, focusing on the genetic and non-genetic sources of intratumoral heterogeneity, as well as tumor-immune dynamics. We review the technological innovations, particularly in single-cell technology, which have fostered these advances and represent essential tools for future discoveries. In addition, we discuss clonal evolution within several contexts of particular relevance to contemporary clinical practice, including the settings of therapeutic resistance to CLL targeted therapy and immunotherapy, as well as Richter transformation of CLL to high-grade lymphoma.

Driving Out Chronic Lymphocytic Leukemia With CAR T Cells

Chronic lymphocytic leukemia (CLL) is the most prevalent leukemia in the Western hemisphere. The recent availability of novel targeted therapies, namely Bruton's tyrosine kinase, phosphoinositide-3 kinase, and BCL-2 inhibitors, have revolutionized the treatment algorithm for CLL but have not yet resulted in cure. Advances in the field of immuno-oncology and T cell engineering brought chimeric antigen receptor (CAR) T cell therapy from the laboratory to the clinic for treatment of B cell lymphoid malignancies and has improved the disease response and survival outcomes of various types of relapsed and/or refractory B cell lymphomas. While acknowledging that there are no approved CAR T cell therapies for CLL at this time, in this comprehensive review we explore novel targets for CAR T cell therapy in CLL and highlight the promising results of CAR T cell trials reported to date. Furthermore, we shed light on future areas of development, including multitarget CAR T cell products for this disease.

Autologous and allogeneic hematopoietic cell transplantation for diffuse large B-cell lymphoma-type Richter syndrome

Richter syndrome (RS) represents a transformation from chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) to aggressive lymphoma, most commonly diffuse large B-cell lymphoma (DLBCL), which is associated with a dismal prognosis. Patients with DLBCL-RS have poor outcomes with DLBCL-directed therapy; thus, consolidation with hematopoietic cell transplantation (HCT) has been used, with durable remissions observed. Studies reporting HCT outcomes in patients with DLBCL-RS have been small, have not evaluated the prognostic impact of cytogenetic risk factors, and were conducted prior to the era of novel targeted therapy of CLL/SLL. We performed a Center for International Blood and Transplant Research registry study evaluating outcomes after autologous HCT (auto-HCT; n = 53) and allogeneic HCT (allo-HCT; n = 118) in patients with DLBCL-RS treated in the modern era. More auto-HCT recipients were in complete response (CR) at HCT relative to allo-HCT recipients (66% vs 34%), whereas a higher proportion of allo-HCT recipients had 17p deletion (33% vs 7%) and had previously received novel agents (39% vs 10%). In the auto-HCT cohort, the 3-year relapse incidence, progression-free survival (PFS), and overall survival (OS) were 37%, 48%, and 57%, respectively. Among allo-HCT recipients, the 3-year relapse incidence, PFS, and OS were 30%, 43%, and 52%, respectively. In the allo-HCT cohort, deeper response at HCT was associated with outcomes (3-year PFS/OS, 66%/77% CR vs 43%/57% partial response vs 5%/15% resistant; P < .0001 for both), whereas cytogenetic abnormalities and prior novel therapy did not impact outcomes. In our study, HCT resulted in durable remissions in therapy-sensitive patients with DLBCL-RS treated in the era of targeted CLL/SLL therapy, including patients with high-risk features.

Cell therapy of chronic lymphocytic leukaemia: Transplants and chimeric antigen receptor (CAR)-T cells

There is substantial progress in the therapy of chronic lymphocytic leukaemia (CLL), much of it the result of new drug development. As such the definition of high-risk CLL is changing. Nevertheless, few persons with CLL are cured with current therapy. Two types of cell therapies of CLL are currently being evaluated or re-evaluated in the context of these advances: haematopoietic cell transplants and chimeric antigen receptor (CAR)-T-cells. We discuss the potential role of these cell therapies in the context of the evolving therapy topography of CLL including how these therapies work and who, if anyone, is an appropriate candidate for cell therapy.

Is There a Role for Cellular Therapy in Chronic Lymphocytic Leukemia?

ABSTRACT

Despite multiple advances in the treatment landscape of chronic lymphocytic leukemia (CLL) during recent years, cellular therapies, such as allogeneic hematopoietic cell transplantation and chimeric antigen-engineered T cells, represent valuable therapeutic options for patients with multiply relapsed or poor-risk disease. This brief overview will summarize current results of cellular therapies in CLL including Richter transformation, suggest an indication algorithm and strategies for performing cellular therapies in these conditions, and discuss the impact of COVID-19 (coronavirus disease 2019) on allogeneic hematopoietic cell transplantation and chimeric antigen-engineered T cells in CLL.

Reduced-intensity conditioning hematopoietic stem cell transplantation for chronic lymphocytic leukemia and Richter's transformation

Allogeneic hematopoietic stem cell transplantation (HSCT) may potentially cure patients with chronic lymphocytic leukemia (CLL) and Richter's transformation (CLL-RT) or CLL without RT, but the impact of novel agents on HSCT is unclear. CLL-RT patients have a grave prognosis, and their outcomes after HSCT are uncertain. We conducted a retrospective analysis of all 58 CLL patients, including 23 CLL-RT patients, who underwent reduced intensity conditioning (RIC) HSCT at Memorial Sloan Kettering Cancer Center (New York, NY) between September 2006 and April 2017. With a median follow-up of 68 months (range, 24-147 months), 5-year progression-free survival (PFS) was 40% (95% confidence interval [CI], 28%-56%), and overall survival (OS) was 58% (95% CI, 48%-74%). The 1-year graft-versus-host disease/relapse-free survival (GRFS) was 38% (95% CI, 25%-50%). Patients with CLL-RT and CLL patients without RT had comparable outcomes. In both cohorts, treatment-sensitive response and ≤3 previous lines of therapy produced superior PFS and OS. Outcomes were agnostic to adverse cytogenetic and molecular features. Novel agents did not have a negative impact on HSCT outcomes. Total body irradiation (TBI)-containing RIC yielded inferior PFS, OS, and GRFS. CLL-RT patients older than age 55 years who had an HSCT Comorbidity Index score of ≥2 demonstrated inferior OS. This study, which is the largest series of RIC-HSCT for patients with CLL-RT, provides evidence supporting RIC-HSCT in early remission courses for patients with CLL-RT and poor-risk CLL patients. TBI-containing RIC should be considered with caution.

Efficacy of minimal residual disease driven immune-intervention after allogeneic hematopoietic stem cell transplantation for high-risk chronic lymphocytic leukemia: results of a prospective multicenter trial

Allogeneic hematopoietic stem cell transplantation (HSCT) remains a potentially curative and useful strategy in high-risk relapsing chronic lymphocytic leukemia (CLL). Minimal residual disease (MRD) assessment at 12 months (M12) post-HSCT is predictive of relapse. This phase II study aimed to achieve M12 MRD negativity (MRDneg) using an MRD-driven immune-intervention (Md-PII) algorithm based on serial flow-cytometry blood MRD, involving cyclosporine tapering followed in case of failure by donor lymphocytes infusions. Patients had high-risk CLL according to the 2006 European Society for Blood and Marrow Transplantation consensus, in complete or partial response with lymphadenopathy <5 cm and comorbidity score ≤2. Donors were HLA-matched sibling or matched unrelated (10/10). Fortytwo enrolled patients with either 17p deletion (front-line, n=11; relapse n=16) or other high-risk relapse (n=15) received reduced intensity-conditioning regimen before HSCT and were submitted to Md-PII. M12- MRDneg status was achieved in 27 of 42 patients (64%) versus 6 of 42 (14.2%) before HSCT. With a median follow-up of 36 months (range, 19-53), 3-year overall survival, non-relapse mortality and cumulative incidence of relapse are 86.9% (95% Confidence Interval [CI]: 70.8-94.4), 9.5% (95% CI: 3.7-23.4) and 29.6% (95% CI: 17.3-47.7). Incidence of 2-year limited and extensive chronic graft versus host disease (cGVHD) is 38% (95% CI: 23-53) and 23% (95% CI: 10-36) including two cases post Md-PII. Fifteen patients converted to MRDneg either after cyclosporine A withdrawal (n=12) or after cGvHD (n=3). As a time-dependent variable, MRDneg achievement at any time-point correlates with reduced relapse (Hazard ratio [HR] 0.14 [range, 0.04-0.53], P=0.004) and improvement of both progression free (HR 0.18 [range, 0.06-0.6], P<0.005) and overall (HR 0.18 [range, 0.03-0.98], P=0.047) survival. These data highlight the value of MRD-driven immune-intervention to induce prompt MRD clearance in the therapy of CLL (clinicaltrials gov. Identifier: NCT01849939).

Will New Drugs Replace Transplants for Chronic Lymphocytic Leukaemia?

Transplants have been used to treat chronic lymphocytic leukemia (CLL) for more than 35 years. Use has been restricted to <1 percent of highly selected persons typically failing concurrent conventional therapies. As therapies of CLL have evolved, so have indications for transplantation and transplant techniques. The data that we review indicate that transplants can result in long-term leukemia-free survival in some persons but are associated with substantial transplant-related morbidity and mortality. We discuss the mechanisms underlying the anti-leukemia effects of transplants including drugs, ionizing radiations, immune-mediated mechanisms and/or a combination. We discuss prognostic and predicative covariates for transplant outcomes. Importantly, we consider whether there is presently a role of transplants in CLL and who, if anyone, is an appropriate candidate in the context of new drugs.

Immune Therapy for Chronic Lymphocytic Leukemia: Allogeneic Transplant, Chimeric Antigen Receptor T-cell Therapy, and Beyond

Despite significant improvement in clinical outcomes of chronic lymphocytic leukemia (CLL), patients who experience failure of Bruton tyrosine kinase inhibitors or venetoclax benefit from immune therapy approaches. Allogeneic transplant is a potentially curative treatment of CLL but is associated with risk of morbidity and mortality. Although still experimental, chimeric antigen receptor T-cell therapy provides durable remissions in patients with deep molecular responses. This review summarizes the relevant literature and discusses an approach to treatment sequencing and timing of referral for immune therapy. Novel immunotherapy approaches are being investigated and potentially can be utilized in sequence or combination with targeted agents.

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.

Novel Agents in Chronic Lymphocytic Leukemia: New Combination Therapies and Strategies to Overcome Resistance

Simple Summary

Nowadays, many patients with chronic lymphocytic leukemia (CLL) are treated with so-called novel agents, including BTK inhibitors, Bcl-2 inhibitors and PI3K inhibitors. As CLL is a chronic disease, most patients will relapse on or after treatment with these drugs and various mechanisms behind this resistance to novel agents have been described. In this review, we present the current evidence on resistance to novel agents, discuss approaches to prevent its development and provide guidance on the treatment of patients who have already acquired resistance.

Abstract

The approval of Bruton’s tyrosine kinase (BTK) inhibitors such as ibrutinib and acalabrutinib and the Bcl-2 inhibitor venetoclax have revolutionized the treatment of chronic lymphocytic leukemia (CLL). While these novel agents alone or in combination induce long lasting and deep remissions in most patients with CLL, their use may be associated with the development of clinical resistance. In this review, we elucidate the genetic basis of acquired resistance to BTK and Bcl-2 inhibition and present evidence on resistance mechanisms that are not linked to single genomic alterations affecting these target proteins. Strategies to prevent resistance to novel agents are discussed in this review with a special focus on new combination therapies.

Relapsed Chronic Lymphocytic Leukaemia with Concomitant Extensive Chronic Graft versus Host Disease after Allogeneic Haematopoietic Stem Cell Transplantation Successfully Treated with Oral Venetoclax

A middle-aged gentleman who was diagnosed with high-risk chronic lymphocytic leukaemia (CLL), Rai stage IV, Binet C with del(17p) and del(13q) underwent allogeneic haematopoeitic stem cell transplantation (allo-HSCT) from a human leukocyte antigen (HLA) identical sister. The patient developed extensive skin, oral, and liver chronic graft versus host disease (GVHD) required tacrolimus, mycophenolate mofetil (MMF), and prednisolone. At seventh month after allo-HSCT, the patient presented with systemic symptoms, right cervical lymphadenopathy, splenomegaly, marked pancytopaenia, and elevated lactate dehydrogenase (LDH). Bone marrow study, immunophenotyping (IP), chromosome analysis, and PET-CT scan confirmed relapsed CLL with no evidence of Richter's transformation or posttransplant lymphoproliferative disease (PTLD). Withdrawal of immunosuppressant (IS) worsened cutaneous and liver GVHD. Chemotherapy was not a suitable treatment option in view of immunodeficiency. The patient underwent extracorporeal photopheresis (ECP) therapy eventually for extensive chronic GVHD, and the IS were gradually tapered to the minimal effective dose. The relapsed CLL was treated successfully with oral venetoclax accessible via a compassionate drug program. This case highlights challenges in managing relapsed CLL and loss of graft-versus-leukaemia (GVL) effect despite extensive chronic GVHD. Venetoclax is an effective and well-tolerated oral novel agent for relapsed CLL after allo-HSCT.

Immune dysfunction complexity in chronic lymphocytic leukemia ‒ an issue to consider when designing novel therapeutic strategies

A complex interplay between chronic lymphocytic leukemia (CLL) cells and different constituents of the immune system generally results in immune tolerance. As targeted therapies are gaining a critical role in the therapeutic landscape of this disease, their impact on the already perturbed immune milieu needs to be considered. This review addresses the issues of basic immune dysfunction in CLL which is further complicated by the effects of a number of novel targeted therapies used for this malignancy. These new approaches may simultaneously facilitate both anti- and pro-cancer activity, potentially compromising the depth of response to therapy. Current evidence suggests that exploiting combination therapy could potentially overcome at least part of these deleterious effects, thereby prolonging response to treatment and helping to restore immune activity.

PTCy-based haploidentical vs matched related or unrelated donor reduced-intensity conditioning transplant for DLBCL

This study retrospectively compared long-term outcomes of nonmyeloablative/reduced intensity conditioning (NMC/RIC) allogeneic hematopoietic cell transplantation (allo-HCT) from a haploidentical family donor (haplo-HCT) using posttransplant cyclophosphamide (PTCy) with those of matched sibling donor (MSD) and matched unrelated donor (MUD) with or without T-cell depletion (TCD+/TCD-) in patients with relapsed diffuse large B-cell lymphoma (DLBCL). Adult patients with DLBCL who had undergone their first NMC/RIC allo-HCT between 2008 and 2015 were included. Recipients of haplo-HCT were limited to those receiving graft-versus-host disease (GVHD) prophylaxis with PTCy. GVHD prophylaxis in MSD was limited to calcineurin inhibitor (CNI)-based approaches without in vivo TCD, while MUD recipients received CNI-based prophylaxis with or without TCD. Outcome analyses for overall survival (OS) and progression-free survival (PFS), nonrelapse mortality (NRM), and disease relapse/progression were calculated. A total of 1438 patients (haplo, 132; MSD, 525; MUD TCD+, 403; and MUD TCD-, 378) were included. Patients with haplo donors were significantly older, had a better performance status and had more frequently received total body irradiation-based conditioning regimens and bone marrow grafts than MSD and MUD TCD+ or TCD-. 3-year OS, PFS, NRM and relapse/progression incidence after haplo-HCT was 46%, 38%, 22%, and 41%, respectively, and not significantly different from outcomes of matched donor transplants on multivariate analyses. Haplo-HCT was associated with a lower cumulative incidence of chronic GVHD compared with MSD, MUD TCD+/TCD-. NMC/RIC haplo-HCT with PTCy seems to be a valuable alternative for patients with DLBCL considered for allo-HCT but lacking a matched donor.

Rituximab-based allogeneic transplant for chronic lymphocytic leukemia with comparison to historical experience

Relapse of chronic lymphocytic leukemia (CLL) after allogeneic hematopoietic cell transplantation (HCT) remains a clinical challenge. We studied in a phase II trial whether the addition of peri-transplant rituximab would reduce the relapse risk compared with historical controls (n = 157). Patients (n = 55) received fludarabine and low-dose total body irradiation combined with rituximab on days -3, + 10, + 24, + 36. Relapse rate at 3 years was significantly lower among rituximab-treated patients versus controls (17% versus 31%; P = 0.04). Overall survival (OS), progression-free survival (PFS) and nonrelapse mortality (NRM) were statistically similar: (53% versus 50%; P = 0.8), (44% versus 42%; P = 0.63), and (38% versus 28%; P = 0.2), respectively. In multivariate analysis, rituximab treatment was associated with lower relapse rates both in the overall cohort [hazard ratio (HR): 0.34, P = 0.006] and in patients with high-risk cytogenetics (HR: 0.21, P = 0.0003). Patients with no comorbidities who received rituximab conditioning had an OS rate of 100% and 75% at 1 and 3 years, respectively, with no NRM. Peri-transplant rituximab reduced relapse rates regardless of high-risk cytogenetics. HCT is associated with minimal NRM in patients without comorbidities and is a viable option for patients with high-risk CLL. Clinical trial information: NCT00867529.

Relapsed disease and aspects of undetectable MRD and treatment discontinuation

Continuous treatment vs fixed duration of monotherapies and combinations of targeted agents are treatment options in relapsed chronic lymphocytic leukemia. The optimal choice of relapse treatment is dependent on the prior frontline therapy, duration of remission after frontline, genetic markers, and patients' condition, including age and comorbidities. Combination therapies may result in deep responses with undetectable minimal residual disease (uMRD). Although uMRD is an excellent predictive marker for disease progression, it is rarely used in clinical practice and needs additional evaluation in clinical trials before discontinuation of therapy should be guided according to uMRD.

Allogeneic Haploidentical Blood or Marrow Transplantation with Post-Transplantation Cyclophosphamide in Chronic Lymphocytic Leukemia

Allogeneic blood or marrow transplantation (allo-BMT) remains the only treatment for chronic lymphocytic leukemia (CLL) with curative potential. Although post-transplantation cyclophosphamide (PTCy) reduces allo-BMT toxicity by decreasing the risk of graft-versus-host disease (GVHD), its effect on CLL allo-BMT outcomes is unknown. We studied 64 consecutive patients with CLL who underwent nonmyeloablative (NMA) haploidentical allo-BMT at Johns Hopkins Sidney Kimmel Comprehensive Cancer Center. In this cohort, the 4-year overall survival was 52% (95% confidence interval [CI], 40% to 68%), and progression-free survival was 37% (95% CI, 26% to 54%). Six patients experienced engraftment failure. PTCy prophylaxis was associated with a modest cumulative incidence of 1-year grade II-IV acute GVHD (27%; %95% CI, 15% to 38%) and %%%2-year chronic GVHD (17%; 95% CI, 7% to 26%). We demonstrate that NMA haploidentical allo-BMT with PTCy is a safe and effective treatment option.

Ibrutinib as a salvage therapy after allogeneic HCT for chronic lymphocytic leukemia

The purpose of our study is to provide information on safety and efficacy of ibrutinib as salvage treatment after allo-HSCT for CLL. A total of 56 patients were included, 36 (64%) males; median age at transplantation was 48 years (range: 35-64) and the median number of treatment lines prior to transplantation was 3 (1-10). The median time between allo-HSCT and Ibrutinib was 30 months (range: 1-140). Overall, 40 (71%) patients responded to Ibrutinib; 23 (41%) PR, and 17 (30%) CR. At time of ibrutinib initiation, ten patients had active chronic GVHD that resolved under Ibrutinib, whilst a single patient developed limited de novo chronic GVHD on Ibrutinib. Fourteen patients discontinued ibrutinib, four because of toxicity and ten because of disease progression. Overall, 14 patients progressed (median PFS = 24 months) among them 10 died. Two-year OS and PFS probabilities were 72% (95% CI: 52-84) and 50% (95% CI: 32-66), respectively. Patients with late relapse after allo-HSCT (≥24 months) had a better PFS after ibrutinib. Our study shows that ibrutinib can be safely administered for CLL relapse after allo-HSCT, with comparable efficacy to non-transplanted patients with high-risk disease.

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.

Predicting the outcome of patients with chronic lymphocytic leukemia: Progress and uncertainty

Because chronic lymphocytic leukemia is a heterogeneous disease, there are considerable efforts underway to develop increasingly accurate and precise analytics with which to estimate the probability of future events such as the need for and probability of response to therapy, progression-free survival, and survival. These analytics typically are constructed from clinical and laboratory variables. These variables often are combined into scores or staging systems, some of which are prognostic (therapy-independent), whereas others are predictive (therapy-dependent). Predictive variables differ with different therapies. Because response to therapy is a necessary condition for the improvement of survival, predictive biomarkers are extremely important. However, despite some progress to identify new predictive biomarkers, del(17p)/TP53 mutation remains the only widely accepted variable used to guide therapy. New laboratory techniques and analytical tools may contribute to improvements in the precision and accuracy of outcome indicators. However, there are inherent limitations when applying cohort-based estimates to individuals within the cohort. The accuracy and precision of prediction also are limited by measurement error and chance. Ultimately, estimating outcomes requires a careful balance between clinical experience, imperfect prediction, and uncertainty.

Chronic lymphocytic leukemia patients with HLA-B27 referred for allogeneic hematopoietic stem cell transplantation do not have worse outcomes: Results of a population-based case series analysis in British Columbia, Canada

Human leukocyte antigen B27 (HLA-B27), associated with spondyloarthritis, was suggested to be protective against chronic lymphocytic leukemia (CLL). It is hypothesized that HLA-B27 patients may have worse outcome in part related to their other comorbidities.

OBJECTIVES

We sought to compare the clinical characteristics and outcomes of CLL and small lymphocytic lymphoma (SLL) patients referred for allogeneic hematopoietic stem cell transplantation (allo-HSCT) based on their HLA-B27 status.

METHODS

This retrospective population-based case series analyzed CLL/SLL patients who were HLA-typed for potential allo-HSCT in British Columbia, Canada.

RESULTS

of 279 CLL/SLL patients referred for potential allo-HSCT, 34 patients were HLA-B27 positive. For HLA-B27 patients, median age at CLL diagnosis was 53.5 years (range, 27-67) and 71% were male. Seven patients had 11q deletion and nine patients had 17p deletion detected prior to first CLL therapy or at relapse. Eleven HLA-B27 patients received allo-HSCT. Two patients developed acute myeloid leukemia. One patient with ankylosing spondylitis had Richter's transformation prior to any CLL therapy. Spondyloarthritis-related disorders were diagnosed in 12 HLA-B27 patients but there was no temporal correlation with development of CLL. Overall survival (OS) and treatment-free survival (TFS) were not significantly different between HLA-B27 patients with or without spondyloarthritis-related disorders. There were no significant differences in clinical characteristics at CLL diagnosis or OS/TFS between HLA-B27 positive and negative patients referred for allo-HSCT.

CONCLUSIONS

HLA-B27 positivity does not appear to influence outcome for CLL/SLL patients referred for allo-HSCT. Further studies are needed to evaluate the clinical significance of HLA-B27 in a general CLL population.

Prognostic Score and Cytogenetic Risk Classification for Chronic Lymphocytic Leukemia Patients: Center for International Blood and Marrow Transplant Research Report

PURPOSE

To develop a prognostic model and cytogenetic risk classification for previously treated patients with chronic lymphocytic leukemia (CLL) undergoing reduced intensity conditioning (RIC) allogeneic hematopoietic cell transplantation (HCT).

EXPERIMENTAL DESIGN

We performed a retrospective analysis of outcomes of 606 patients with CLL who underwent RIC allogeneic HCT between 2008 and 2014 reported to the Center for International Blood and Marrow Transplant Research.

RESULTS

On the basis of multivariable models, disease status, comorbidity index, lymphocyte count, and white blood cell count at HCT were selected for the development of prognostic model. Using the prognostic score, we stratified patients into low-, intermediate-, high-, and very-high-risk [4-year progression-free survival (PFS) 58%, 42%, 33%, and 25%, respectively, P < 0.0001; 4-year overall survival (OS) 70%, 57%, 54%, and 38%, respectively, P < 0.0001]. We also evaluated karyotypic abnormalities together with del(17p) and found that del(17p) or ≥5 abnormalities showed inferior PFS. Using a multivariable model, we classified cytogenetic risk into low, intermediate, and high (P < 0.0001). When the prognostic score and cytogenetic risk were combined, patients with low prognostic score and low cytogenetic risk had prolonged PFS (61% at 4 years) and OS (75% at 4 years).

CONCLUSIONS

In this large cohort of patients with previously treated CLL who underwent RIC HCT, we developed a robust prognostic scoring system of HCT outcomes and a novel cytogenetic-based risk stratification system. These prognostic models can be used for counseling patients, comparing data across studies, and providing a benchmark for future interventions. For future study, we will further validate these models for patients receiving targeted therapies prior to HCT.

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.

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.

Hematopoietic Stem Cell Transplantation in the Era of Engineered Cell Therapy

PURPOSE OF REVIEW

Cellular therapy using T cells modified to express chimeric antigen receptors (CAR-T cells) has had striking success in patients that have failed previous treatment for CD19+ B cell non-Hodgkin lymphoma (NHL), chronic lymphocytic leukemia (CLL), or acute lymphoblastic leukemia (ALL). Curative therapy for this group of diseases has previously been limited to allogeneic hematopoietic cell transplantation HCT (alloHCT). The recent results of CAR-T cell therapy raise the question of how best to integrate CAR-T cell therapy and alloHCT in the care of these patients.

RECENT FINDINGS

Within the past 2 years, results from larger trials and increased follow-up of patients treated with CD19 CAR-T cell therapy suggest that some may achieve durable remission without transplant. The balance of efficacy and toxicity for CAR-T cell therapy and alloHCT vary by disease type, disease status at the time of treatment, patient characteristics, and the specific therapy employed. There are early signals that subsequent transplantation of patients who have achieved remission with CAR-T may be a potentially viable (though expensive) strategy.

[Minimal residual disease in chronic lymphocytic leukemia: A still current issue in 2018]

Minimal residual disease (MRD) is widely used in oncohematology. In chronic lymphocytic leukemia (CLL), it can be measured by flow cytometry or polymerase chain reaction and is getting a greater place, owing to the dramatic therapeutic advances in the management this disease. As MRD decrease after chemoimmunotherapy is associated with improved progression free and overall survivals, its measure is now recommended as a surrogate marker for cytotoxic drugs licensures. This association is independent from treatment received and raises a few questions, such as sequential MRD measures to stop treatment in case of an early deep response and on the opposite, treatment continuation until reaching undetectable MRD (with the possible use of maintenance therapy). Furthermore, following MRD after a cytotoxic treatment could lead clinical trials investigators to propose pre-emptive treatments in case of MRD re-growth, to avoid overt relaspe. MRD re-growth kinetics and CD4 count after treatment completion can improve MRD-based survival predictions. On the other hand, BCR inhibitors do not lead to undetectable MRD, but their association with chemoimmunotherapy increases the proportion of patients reaching that goal. Moreover, BCL2 inhibitors do lead to deep response including in the relapse/refractory setting, giving to MRD a central place in currently investigated treatments evaluation.