Chronic lymphocytic leukaemia is driven by antigen-independent cell-autonomous signalling

Mechanistic Insights into CpG DNA and IL-15 Synergy in Promoting B Cell Chronic Lymphocytic Leukemia Clonal Expansion

Malignant cell growth within patients with B cell chronic lymphocytic leukemia (B-CLL) is largely restricted to lymphoid tissues, particularly lymph nodes. The recent in vitro finding that TLR-9 ligand (oligodeoxynucleotide [ODN]) and IL-15 exhibit strong synergy in promoting B-CLL growth may be particularly relevant to growth in these sites. This study shows IL-15-producing cells are prevalent within B-CLL-infiltrated lymph nodes and, using purified B-CLL cells from blood, investigates the mechanism for ODN and IL-15 synergy in driving B-CLL growth. ODN boosts baseline levels of phospho-RelA(S529) in B-CLL and promotes NF-κB-driven increases in IL15RA and IL2RB mRNA, followed by elevated IL-15Rα and IL-2/IL-15Rβ (CD122) protein. IL-15→CD122 signaling during a critical interval, 20 to 36-48 h following initial ODN exposure, is required for optimal induction of the cycling process. Furthermore, experiments with neutralizing anti-IL-15 and anti-CD122 mAbs indicate that clonal expansion requires continued IL-15/CD122 signaling during cycling. The latter is consistent with evidence of heightened IL2RB mRNA in the fraction of recently proliferated B-CLL cells within patient peripheral blood. Compromised ODN+IL-15 growth with limited cell density is consistent with a role for upregulated IL-15Rα in facilitating homotypic trans IL-15 signaling, although there may be other explanations. Together, the findings show that ODN and IL-15 elicit temporally distinct signals that function in a coordinated manner to drive B-CLL clonal expansion.

Association of blood IgG with tumor necrosis factor-alpha and clinical course of chronic lymphocytic leukemia

The intrinsic humoral immunodeficiency of chronic lymphocytic leukemia (CLL) is often managed with immunoglobulin replacement therapy (IgRT) to maintain IgG levels in the low-normal range (6–8 g/L) but optimal targets for IgG and timing to commence IgRT are unclear. IgG levels fell near 6 g/L at rates of −0.85±0.14 g/L/year in 51 patients who required treatment for CLL within 4.5±0.4 years from initial diagnosis and − 0.27±0.04 g/L/year in 40 patients with progressive disease who remained untreated after 8.5±0.5 years. In contrast, endogenous IgG levels remained above 8 g/L in patients with highly indolent disease (n = 25) and TNFα and beta-2-microglobulin (β2M) in blood decreased when IgRT was used to increase IgG levels over 9 g/L. At 15 g/L but not 5 g/L, the IgRT product Hizentra® inhibited B cell receptor (BCR)-activation, TNFα production, and survival in vitro, particularly of CLL cells that spontaneously made little TNFα. These findings suggest deterioration of the humoral immune system is associated with progressive CLL and altering the dosing of IgRT to achieve higher than conventional IgG target levels may have therapeutic activity.

•

Immunoglobulin levels decline at rates that reflect the clinical course of CLL.

•

IgG levels over 10 g/L achieved with replacement therapy are associated with evidence of disease control in vivo and inhibition of BCR-mediated activation of CLL cells in vitro.

•

Monitoring rates of decline of Ig levels in CLL patients gives biological information on disease severity.

•

Appropriate IgG target levels for immunoglobulin replacement therapy in CLL may be much higher than for patients with other immunodeficiencies.

Combined Influence of B-Cell Receptor Rearrangement and Somatic Hypermutation on B-Cell Class-Switch Fate in Health and in Chronic Lymphocytic Leukemia

A diverse B-cell receptor (BCR) repertoire is required to bind a wide range of antigens. BCRs are generated through genetic recombination and can be diversified through somatic hypermutation (SHM) or class-switch recombination (CSR). Patterns of repertoire diversity can vary substantially between different health conditions. We use isotype-resolved BCR sequencing to compare B-cell evolution and class-switch fate in healthy individuals and in patients with chronic lymphocytic leukemia (CLL). We show that the patterns of SHM and CSR in B-cells from healthy individuals are distinct from CLL. We identify distinct properties of clonal expansion that lead to the generation of antibodies of different classes in healthy, malignant, and non-malignant CLL BCR repertoires. We further demonstrate that BCR diversity is affected by relationships between antibody variable and constant regions leading to isotype-specific signatures of variable gene usage. This study provides powerful insights into the mechanisms underlying the evolution of the adaptive immune responses in health and their aberration during disease.

Calcium-RasGRP2-Rap1 signaling mediates CD38-induced migration of chronic lymphocytic leukemia cells

CD38 is a transmembrane exoenzyme that is associated with poor prognosis in chronic lymphocytic leukemia (CLL). High CD38 levels in CLL cells are linked to increased cell migration, but the molecular basis is unknown. CD38 produces nicotinic acid adenine dinucleotide phosphate and adenosine 5'-diphosphate-ribose, both of which can act to increase intracellular Ca2+ levels. Here we show that CD38 expression increases basal intracellular Ca2+ levels and stimulates CLL cell migration both with and without chemokine stimulation. We find that CD38 acts via intracellular Ca2+ to increase the activity of the Ras family GTPase Rap1, which is in turn regulated by the Ca2+-sensitive Rap1 guanine-nucleotide exchange factor RasGRP2. Both Rap1 and RasGRP2 are required for CLL cell migration, and RasGRP2 is polarized in primary CLL cells with high CD38 levels. These results indicate that CD38 promotes RasGRP2/Rap1-mediated CLL cell adhesion and migration by increasing intracellular Ca2+ levels.

NOTCH1 Aberrations in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is an incurable B-cell neoplasm characterized by highly variable clinical outcomes. In recent years, genomic and molecular studies revealed a remarkable heterogeneity in CLL, which mirrored the clinical diversity of this disease. These studies profoundly enhanced our understanding of leukemia cell biology and led to the identification of new biomarkers with potential prognostic and therapeutic significance. Accumulating evidence indicates a key role of deregulated NOTCH1 signaling and NOTCH1 mutations in CLL. This review highlights recent discoveries that improve our understanding of the pathophysiological NOTCH1 signaling in CLL and the clinical impact of NOTCH1 mutations in retrospective and prospective trials. In addition, we discuss the rationale for a therapeutic strategy aiming at inhibiting NOTCH1 signaling in CLL, along with an overview on the currently available NOTCH1-directed approaches.

The Light Chain IgLV3-21 Defines a New Poor Prognostic Subgroup in Chronic Lymphocytic Leukemia: Results of a Multicenter Study

Purpose: Unmutated (UM) immunoglobulin heavy chain variable region (IgHV) status or IgHV3-21 gene usage is associated with poor prognosis in chronic lymphocytic leukemia (CLL) patients. Interestingly, IgHV3-21 is often co-expressed with light chain IgLV3-21, which is potentially able to trigger cell-autonomous BCR-mediated signaling. However, this light chain has never been characterized independently of the heavy chain IgHV3-21.Experimental Design: We performed total RNA sequencing in 32 patients and investigated IgLV3-21 prognostic impact in terms of treatment-free survival (TFS) and overall survival (OS) in 3 other independent cohorts for a total of 813 patients. IgLV3-21 presence was tested by real-time PCR and confirmed by Sanger sequencing.Results: Using total RNA sequencing to characterize 32 patients with high-risk CLL, we found a high frequency (28%) of IgLV3-21 rearrangements. Gene set enrichment analysis revealed that these patients express higher levels of genes responsible for ribosome biogenesis and translation initiation (P < 0.0001) as well as MYC target genes (P = 0.0003). Patients with IgLV3-21 rearrangements displayed a significantly shorter TFS and OS (P < 0.05), particularly those with IgHV mutation. In each of the three independent validation cohorts, we showed that IgLV3-21 rearrangements-similar to UM IgHV status-conferred poor prognosis compared with mutated IgHV (P < 0.0001). Importantly, we confirmed by multivariate analysis that this was independent of IgHV mutational status or subset #2 stereotyped receptor (P < 0.0001).Conclusions: We have demonstrated for the first time that a light chain can affect CLL prognosis and that IgLV3-21 light chain usage defines a new subgroup of CLL patients with poor prognosis. Clin Cancer Res; 24(20); 5048-57. ©2018 AACR.

Constitutive IP3 signaling underlies the sensitivity of B-cell cancers to the Bcl-2/IP3 receptor disruptor BIRD-2

Anti-apoptotic Bcl-2 proteins are upregulated in different cancers, including diffuse large B-cell lymphoma (DLBCL) and chronic lymphocytic leukemia (CLL), enabling survival by inhibiting pro-apoptotic Bcl-2-family members and inositol 1,4,5-trisphosphate (IP₃) receptor (IP₃R)-mediated Ca²⁺-signaling. A peptide tool (Bcl-2/IP₃R Disruptor-2; BIRD-2) was developed to abrogate the interaction of Bcl-2 with IP₃Rs by targeting Bcl-2′s BH4 domain. BIRD-2 triggers cell death in primary CLL cells and in DLBCL cell lines. Particularly, DLBCL cells with high levels of IP₃R2 were sensitive to BIRD-2. Here, we report that BIRD-2-induced cell death in DLBCL cells does not only depend on high IP₃R2-expression levels, but also on constitutive IP₃ signaling, downstream of the tonically active B-cell receptor. The basal Ca²⁺ level in SU-DHL-4 DLBCL cells was significantly elevated due to the constitutive IP₃ production. This constitutive IP₃ signaling fulfilled a pro-survival role, since inhibition of phospholipase C (PLC) using U73122 (2.5 µM) caused cell death in SU-DHL-4 cells. Milder inhibition of IP₃ signaling using a lower U73122 concentration (1 µM) or expression of an IP₃ sponge suppressed both BIRD-2-induced Ca²⁺ elevation and apoptosis in SU-DHL-4 cells. Basal PLC/IP₃ signaling also fulfilled a pro-survival role in other DLBCL cell lines, including Karpas 422, RI-1 and SU-DHL-6 cells, whereas PLC inhibition protected these cells against BIRD-2-evoked apoptosis. Finally, U73122 treatment also suppressed BIRD-2-induced cell death in primary CLL, both in unsupported systems and in co-cultures with CD40L-expressing fibroblasts. Thus, constitutive IP₃ signaling in lymphoma and leukemia cells is not only important for cancer cell survival, but also represents a vulnerability, rendering cancer cells dependent on Bcl-2 to limit IP₃R activity. BIRD-2 seems to switch constitutive IP₃ signaling from pro-survival into pro-death, presenting a plausible therapeutic strategy.

Continuous signaling of CD79b and CD19 is required for the fitness of Burkitt lymphoma B cells

Expression of the B-cell antigen receptor (BCR) is essential not only for the development but also for the maintenance of mature B cells. Similarly, many B-cell lymphomas, including Burkitt lymphoma (BL), require continuous BCR signaling for their tumor growth. This growth is driven by immunoreceptor tyrosine-based activation motif (ITAM) and PI3 kinase (PI3K) signaling. Here, we employ CRISPR/Cas9 to delete BCR and B-cell co-receptor genes in the human BL cell line Ramos. We find that Ramos B cells require the expression of the BCR signaling component Igβ (CD79b), and the co-receptor CD19, for their fitness and competitive growth in culture. Furthermore, we show that in the absence of any other BCR component, Igβ can be expressed on the B-cell surface, where it is found in close proximity to CD19 and signals in an ITAM-dependent manner. These data suggest that Igβ and CD19 are part of an alternative B-cell signaling module that use continuous ITAM/PI3K signaling to promote the survival of B lymphoma and normal B cells.

Targeting the B cell receptor pathway in non-Hodgkin lymphoma

INTRODUCTION

Dysregulated B cell receptor (BCR) signaling has been identified as a potent contributor to tumor survival in B cell non-Hodgkin lymphomas (NHLs). This pathway's emergence as a rational therapeutic target in NHL led to development of BCR-directed agents, including inhibitors of Bruton's tyrosine kinase (BTK), spleen tyrosine kinase (SYK), and phosphatidylinositol 3 kinase (PI3K). Several drugs have become valuable assets in the anti-lymphoma armamentarium.

AREAS COVERED

We provide an overview of the BCR pathway, its dysregulation in B cell NHL, and the drugs developed to target BCR signaling in lymphoma. Mechanisms, pharmacokinetics, pharmacodynamics, efficacy, and toxicity of currently available BTK, SYK, and PI3K inhibitors are described.

EXPERT OPINION

While the excellent response rates and favorable toxicity profile of the BTK inhibitor ibrutinib in certain NHL subtypes have propelled it to consideration as frontline therapy in selected populations, additional data and clinical studies are needed before other agents targeting BCR signaling influence clinical practice similarly. PI3K inhibitors remain an option for some relapsed indolent lymphomas and chronic lymphocytic leukemia, but their widespread use may be limited by adverse effects. Future research should include efforts to overcome resistance to BTK inhibitors, combination therapy using BCR-targeted agents, and exploration of novel agents.

Chronic lymphocytic leukemia and mantle cell lymphoma: crossroads of genetic and microenvironment interactions

Chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) are 2 well-defined entities that diverge in their basic pathogenic mechanisms and clinical evolution but they share epidemiological characteristics, cells of origin, molecular alterations, and clinical features that differ from other lymphoid neoplasms. CLL and MCL are classically considered indolent and aggressive neoplasms, respectively. However, the clinical evolution of both tumors is very heterogeneous, with subsets of patients having stable disease for a long time whereas others require immediate intervention. Both CLL and MCL include 2 major molecular subtypes that seem to derive from antigen-experienced CD5⁺ B cells that retain a naive or memory-like epigenetic signature and carry a variable load of immunoglobulin heavy-chain variable region somatic mutations from truly unmutated to highly mutated, respectively. These 2 subtypes of tumors differ in their molecular pathways, genomic alterations, and clinical behavior, being more aggressive in naive-like than memory-like-derived tumors in both CLL and MCL. The pathogenesis of the 2 entities integrates the relevant influence of B-cell receptor signaling, tumor cell microenvironment interactions, genomic alterations, and epigenome modifications that configure the evolution of the tumors and offer new possibilities for therapeutic intervention. This review will focus on the similarities and differences of these 2 tumors based on recent studies that are enhancing the understanding of their pathogenesis and creating solid bases for new management strategies.

Chronic Lymphocytic Leukemia B-Cell Normal Cellular Counterpart: Clues From a Functional Perspective

Chronic lymphocytic leukemia (CLL) is characterized by the clonal expansion of small mature-looking CD19+ CD23+ CD5+ B-cells that accumulate in the blood, bone marrow, and lymphoid organs. To date, no consensus has been reached concerning the normal cellular counterpart of CLL B-cells and several B-cell types have been proposed. CLL B-cells have remarkable phenotypic and gene expression profile homogeneity. In recent years, the molecular and cellular biology of CLL has been enriched by seminal insights that are leading to a better understanding of the natural history of the disease. Immunophenotypic and molecular approaches (including immunoglobulin heavy-chain variable gene mutational status, transcriptional and epigenetic profiling) comparing the normal B-cell subset and CLL B-cells provide some new insights into the normal cellular counterpart. Functional characteristics (including activation requirements and propensity for plasma cell differentiation) of CLL B-cells have now been investigated for 50 years. B-cell subsets differ substantially in terms of their functional features. Analysis of shared functional characteristics may reveal similarities between normal B-cell subsets and CLL B-cells, allowing speculative assignment of a normal cellular counterpart for CLL B-cells. In this review, we summarize current data regarding peripheral B-cell differentiation and human B-cell subsets and suggest possibilities for a normal cellular counterpart based on the functional characteristics of CLL B-cells. However, a definitive normal cellular counterpart cannot be attributed on the basis of the available data. We discuss the functional characteristics required for a cell to be logically considered to be the normal counterpart of CLL B-cells.

NF-κB Activation in Lymphoid Malignancies: Genetics, Signaling, and Targeted Therapy

The NF-κB transcription factor family plays a crucial role in lymphocyte proliferation and survival. Consequently, aberrant NF-κB activation has been described in a variety of lymphoid malignancies, including diffuse large B-cell lymphoma, Hodgkin lymphoma, and adult T-cell leukemia. Several factors, such as persistent infections (e.g., with Helicobacter pylori), the pro-inflammatory microenvironment of the cancer, self-reactive immune receptors as well as genetic lesions altering the function of key signaling effectors, contribute to constitutive NF-κB activity in these malignancies. In this review, we will discuss the molecular consequences of recurrent genetic lesions affecting key regulators of NF-κB signaling. We will particularly focus on the oncogenic mechanisms by which these alterations drive deregulated NF-κB activity and thus promote the growth and survival of the malignant cells. As the concept of a targeted therapy based on the mutational status of the malignancy has been supported by several recent preclinical and clinical studies, further insight in the function of NF-κB modulators and in the molecular mechanisms governing aberrant NF-κB activation observed in lymphoid malignancies might lead to the development of additional treatment strategies and thus improve lymphoma therapy.

Molecular control of B-cell homeostasis in health and malignancy

Altered B-cell homeostasis underlies a wide range of pathologies, from cancers to autoimmunity and immunodeficiency. The molecular safeguards against those disorders, which also allow effective immune responses, are therefore particularly critical. Here, we review recent findings detailing the fine control of B-cell homeostasis, during B-cell development, maturation in the periphery and during activation and differentiation into antibody-producing cells.

Critical molecular pathways in CLL therapy

Chronic lymphocytic leukemia (CLL), the most frequent type of leukemia in western countries, is characterized by the progressive accumulation in blood, bone marrow and lymphoid tissues of monoclonal B lymphocytes with a characteristic immunophenotype. Despite advances in therapy and improved outcome, in most instances CLL is an incurable disorder. Signaling via the B-cell receptor (BCR), the upregulation of anti-apoptotic proteins, and the cross-talk between CLL cells and microenvironment constitute key factors in the pathogenesis of CLL. Currently, inhibitors of kinases like BTK or PI3K blocking BCR signaling, and molecules that mimic the BH3 domain to compete with BCL-2 are established tools in the treatment of CLL. As the complex biology of CLL is rapidly unfolding, the number of small molecules targeting CLL molecular pathways is increasing and it is likely that they will further improve the outcome of patients with this form of leukemia.

Targeting B cell receptor signalling in cancer: preclinical and clinical advances

B cell receptor (BCR) signalling is crucial for normal B cell development and adaptive immunity. BCR signalling also supports the survival and growth of malignant B cells in patients with B cell leukaemias or lymphomas. The mechanism of BCR pathway activation in these diseases includes continuous BCR stimulation by microbial antigens or autoantigens present in the tissue microenvironment, activating mutations within the BCR complex or downstream signalling components and ligand-independent tonic BCR signalling. The most established agents targeting BCR signalling are Bruton tyrosine kinase (BTK) inhibitors and PI3K isoform-specific inhibitors, and their introduction into the clinic is rapidly changing how B cell malignancies are treated. B cells and BCR-related kinases, such as BTK, also play a role in the microenvironment of solid tumours, such as squamous cell carcinoma and pancreatic cancer, and therefore targeting B cells or BCR-related kinases may have anticancer activity beyond B cell malignancies.

Depth and durability of response to ibrutinib in CLL: 5-year follow-up of a phase 2 study

The safety and efficacy of ibrutinib (420 mg) in chronic lymphocytic leukemia (CLL) were evaluated in a phase 2 study; 51 patients had TP53 aberration (TP53 cohort) and 35 were enrolled because of age 65 years or older (elderly cohort). Both cohorts included patients with treatment-naive (TN) and relapsed/refractory (RR) CLL. With the median follow-up of 4.8 years, 49 (57.0%) of 86 patients remain on study. Treatment was discontinued for progressive disease in 20 (23.3%) patients and for adverse events in 5 (5.8%). Atrial fibrillation occurred in 18 (20.9%) patients for a rate of 6.4 per 100 patient-years. No serious bleeding occurred. The overall response rate at 6 months, the primary study endpoint, was 95.8% for the TP53 cohort (95% confidence interval, 85.7%-99.5%) and 93.9% for the elderly cohort (95% confidence interval, 79.8%-99.3%). Depth of response improved with time: at best response, 14 (29.2%) of 48 patients in the TP53 cohort and 9 (27.3%) of 33 in the elderly cohort achieved a complete response. Median minimal residual disease (MRD) in peripheral blood was 3.8 × 10^-2 at 4 years, with MRD-negative (<10^-4) remissions in 5 (10.2%) patients. In the TP53 cohort, the estimated 5-year progression-free survival (PFS) was 74.4% in TN-CLL compared with 19.4% in RR-CLL (P = .0002), and overall survival (OS) was 85.3% vs 53.7%, respectively (P = .023). In the elderly cohort, the estimated 5-year PFS and OS in RR-CLL were 64.8% and 71.6%, respectively, and no event occurred in TN-CLL. Long-term administration of ibrutinib was well tolerated and provided durable disease control for most patients. This trial was registered at www.clinicaltrials.gov as #NCT01500733.

Monoclonal B-cell lymphocytosis in a hospital-based UK population and a rural Ugandan population: a cross-sectional study

Background

Reported incidence of B-cell malignancies shows substantial geographical variation, being more common in the Americas and Europe than in Africa. This variation might reflect differences in diagnostic capability, inherited susceptibility, and infectious exposures. Monoclonal B-cell lymphocytosis (MBL) is a precursor lesion that can be screened for in apparently healthy people, allowing comparison of prevalence across different populations independently of health-care provision. We aimed to compare the prevalence and phenotypic characteristics of MBL in age-and-sex-matched populations from rural Uganda and the UK.

Methods

In this cross-sectional study, we recruited volunteers aged at least 45 years who were seronegative for HIV-1 from the established Ugandan General Population Cohort and obtained their whole-blood samples. We also obtained blood samples from anonymised waste material of age-and-sex-matched individuals (aged >45 years, with a normal blood count and no history of cancer) in the UK. We used flow cytometry to determine the presence of MBL, defined according to standard diagnostic criteria, in the samples and compared differences in the proportion of cases with chronic lymphocytic leukaemia (CLL)-phenotype MBL and CD5-negative MBL, as well as differences in absolute monoclonal B-cell count between the two cohorts.

Findings

Between Jan 15 and Dec 18, 2012, we obtained samples from 302 Ugandan volunteers and 302 UK individuals who were matched by age and sex to the Ugandan population. Overall MBL prevalence was higher in the Ugandan participants (42 [14%] individuals) than in the UK cohort (25 [8%]; p=0·038). CLL-phenotype MBL was detected in three (1%) Ugandan participants and 21 (7%) UK participants (p=0·00021); all three Ugandan participants had absolute monoclonal B-cell count below one cell per μL, whereas the 21 UK participants had a median absolute number of circulating neoplastic cells of 4·6 (IQR 2–12) cells per μL. The prevalence of CD5-negative MBL was higher in the Ugandan cohort (41 [14%], of whom two [5%] also had CLL-phenotype MBL) than in the UK cohort (six [2%], of whom two [33%] also had CLL-phenotype MBL; p<0·0001), but the median absolute B-cell count was similar (227 [IQR 152–345] cells per μL in the Ugandan cohort vs 135 [105–177] cells per μL in the UK cohort; p=0·13).

Interpretation

MBL is common in both Uganda and the UK, but the substantial phenotypic differences might reflect fundamental differences in the pathogenesis of B-cell lymphoproliferative disorders.

Funding

UK Medical Research Council and UK Department for International Development.

Low catalase expression confers redox hypersensitivity and identifies an indolent clinical behavior in CLL

B-cell receptor (BCR) signaling is a key determinant of variable clinical behavior and a target for therapeutic interventions in chronic lymphocytic leukemia (CLL). Endogenously produced H₂O₂ is thought to fine-tune the BCR signaling by reversibly inhibiting phosphatases. However, little is known about how CLL cells sense and respond to such redox cues and what effect they have on CLL. We characterized the response of BCR signaling proteins to exogenous H₂O₂ in cells from patients with CLL, using phosphospecific flow cytometry. Exogenous H₂O₂ in the absence of BCR engagement induced a signaling response of BCR proteins that was higher in CLL with favorable prognostic parameters and an indolent clinical course. We identified low catalase expression as a possible mechanism accounting for redox signaling hypersensitivity. Decreased catalase could cause an escalated accumulation of exogenous H₂O₂ in leukemic cells with a consequent greater inhibition of phosphatases and an increase of redox signaling sensitivity. Moreover, lower levels of catalase were significantly associated with a slower progression of the disease. In leukemic cells characterized by redox hypersensitivity, we also documented an elevated accumulation of ROS and an increased mitochondrial amount. Taken together, our data identified redox sensitivity and metabolic profiles that are linked to differential clinical behavior in CLL. This study advances our understanding of the redox and signaling heterogeneity of CLL and provides the rationale for the development of therapies targeting redox pathways in CLL.

Role of Bruton's tyrosine kinase in B cells and malignancies

Bruton’s tyrosine kinase (BTK) is a non-receptor kinase that plays a crucial role in oncogenic signaling that is critical for proliferation and survival of leukemic cells in many B cell malignancies. BTK was initially shown to be defective in the primary immunodeficiency X-linked agammaglobulinemia (XLA) and is essential both for B cell development and function of mature B cells. Shortly after its discovery, BTK was placed in the signal transduction pathway downstream of the B cell antigen receptor (BCR). More recently, small-molecule inhibitors of this kinase have shown excellent anti-tumor activity, first in animal models and subsequently in clinical studies. In particular, the orally administered irreversible BTK inhibitor ibrutinib is associated with high response rates in patients with relapsed/refractory chronic lymphocytic leukemia (CLL) and mantle-cell lymphoma (MCL), including patients with high-risk genetic lesions. Because ibrutinib is generally well tolerated and shows durable single-agent efficacy, it was rapidly approved for first-line treatment of patients with CLL in 2016. To date, evidence is accumulating for efficacy of ibrutinib in various other B cell malignancies. BTK inhibition has molecular effects beyond its classic role in BCR signaling. These involve B cell-intrinsic signaling pathways central to cellular survival, proliferation or retention in supportive lymphoid niches. Moreover, BTK functions in several myeloid cell populations representing important components of the tumor microenvironment. As a result, there is currently a considerable interest in BTK inhibition as an anti-cancer therapy, not only in B cell malignancies but also in solid tumors. Efficacy of BTK inhibition as a single agent therapy is strong, but resistance may develop, fueling the development of combination therapies that improve clinical responses. In this review, we discuss the role of BTK in B cell differentiation and B cell malignancies and highlight the importance of BTK inhibition in cancer therapy.

Autoimmunity checkpoints as therapeutic targets in B cell malignancies

Targeted therapy of cancer typically focuses on inhibitors (for example, tyrosine kinase inhibitors) that suppress oncogenic signalling below a minimum threshold required for survival and proliferation of cancer cells. B cell acute lymphoblastic leukaemia and B cell lymphomas originate from various stages of development of B cells, which, unlike other cell types, are under intense selective pressure. The vast majority of newly generated B cells are autoreactive and die by negative selection at autoimmunity checkpoints (AICs). Owing to ubiquitous encounters with self-antigen, autoreactive B cells are eliminated by the overwhelming signalling strength of their autoreactive B cell receptor (BCR). A series of recent findings suggests that, despite malignant transformation, AICs are fully functional in B cell malignancies. This Opinion article proposes targeted engagement of AICs as a previously unrecognized therapeutic opportunity to overcome drug resistance in B cell malignancies.

Functional and clinical relevance of VLA-4 (CD49d/CD29) in ibrutinib-treated chronic lymphocytic leukemia

Tissino et al. demonstrate that in chronic lymphocytic leukemia, the VLA-4 (CD49d/CD29) integrin remains activable by B cell receptor stimulation also upon in vitro and in vivo ibrutinib exposure. Clinically, ibrutinib-treated CD49d-positive CLL patients experience reduced recirculation lymphocytosis and nodal response and inferior outcomes.

The Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib, which antagonizes B cell receptor (BCR) signals, demonstrates remarkable clinical activity in chronic lymphocytic leukemia (CLL). The lymphocytosis experienced by most patients under ibrutinib has previously been attributed to inhibition of BTK-dependent integrin and chemokine cues operating to retain the tumor cells in nodal compartments. Here, we show that the VLA-4 integrin, as expressed by CD49d-positive CLL, can be inside-out activated upon BCR triggering, thus reinforcing the adhesive capacities of CLL cells. In vitro and in vivo ibrutinib treatment, although reducing the constitutive VLA-4 activation and cell adhesion, can be overcome by exogenous BCR triggering in a BTK-independent manner involving PI3K. Clinically, in three independent ibrutinib-treated CLL cohorts, CD49d expression identifies cases with reduced lymphocytosis and inferior nodal response and behaves as independent predictor of shorter progression-free survival, suggesting the retention of CD49d-expressing CLL cells in tissue sites via activated VLA-4. Evaluation of CD49d expression should be incorporated in the characterization of CLL undergoing therapy with BCR inhibitors.

Ibrutinib

Abnormal B-cell receptor (BCR) signalling is a key mechanism of disease progression in B-cell malignancy. Bruton's tyrosine kinase (BTK) has a pivotal role in BCR signalling. Ibrutinib (PCI-32765) is a small molecule which serves as a covalent irreversible inhibitor of BTK. It is characterized by high selectivity for BTK and high potency. Ibrutinib is currently approved by the FDA and EMA for use in chronic lymphocytic leukaemia in any line of treatment, for treatment of Waldenstrom macroglobulinemia in patients who have received previous treatments or are not suitable to receive immunochemotherapy as well as for second line treatment of mantle cell lymphoma and for patients with marginal zone lymphoma who have received at least one prior anti-CD20-based therapy. In addition, there is emerging clinical data on its efficacy in ABC subtype diffuse large B-cell lymphoma, multiple myeloma and primary central nervous system lymphoma. Ibrutinib has opened new options for treatment of those patients that have relapsed or have been refractory to more classical modes of treatment. Moreover, Ibrutinib has been shown to be effective in patients that have been known to have little sensitivity to classical immunochemotherapy. Having a favourable risk profile, the substance is, unlike conventional immunochemotherapy, also suitable for the less physical fit patients. Cases of primary and secondary resistance to Ibrutinib have emerged and there is an ongoing effort to identify their mechanism and develop strategies to overcome them. Beyond its direct effects on survival and apoptosis of malignant B-cells, there is increasing evidence that Ibrutinib is able to modulate the tumour microenvironment to overcome mechanisms of immune evasion. This has sparked interest in use of the substance beyond lymphoid malignancy. This chapter discusses structure, mechanism of action and toxicities of Ibrutinib and also presents important preclinical and clinical data as well as mechanisms of Ibrutinib resistance. Combination strategies with immunotherapeutic strategies such as immune checkpoint blockade and CAR T-cell therapy may be synergistic and are currently under investigation.

Idelalisib

Idelalisib (GS-1101, CAL-101, Zydelig^®) is an orally bioavailable, small-molecule inhibitor of the delta isoform (p110δ) of the enzyme phosphoinositide 3-kinase (PI3K). In contrast to the other PI3K isoforms, PI3Kδ is expressed selectively in hematopoietic cells. PI3Kδ signaling is active in many B-cell leukemias and lymphomas. By inhibiting the PI3Kδ protein, idelalisib blocks several cellular signaling pathways that maintain B-cell viability. Idelalisib is the first PI3K inhibitor approved by the US Food and Drug Administration (FDA). Treatment with idelalisib is indicated in relapsed/refractory chronic lymphocytic leukemia (CLL), follicular lymphoma (FL), and small lymphocytic lymphoma (SLL). This review presents the preclinical and clinical activity of idelalisib with a focus on clinical studies in CLL.

Mature lymphoid malignancies: origin, stem cells, and chronicity

The chronic behavior of mature lymphoid malignancies, with relapses occurring years apart in many patients, has until recently been unexplained. Patterns of relapse also differ vastly between disease entities, with some being highly curable by chemotherapy whereas others are destined to reemerge after treatment. Lately, the use of next-generation sequencing techniques has revealed essential information on the clonal evolution of lymphoid malignancies. Also, experimental xenograft transplantation point to the possible existence of an ancestral (stem) cell. Such a malignant lymphoid stem cell population could potentially evade current therapies and be the cause of chronicity and death in lymphoma patients; however, the evidence is divergent across disease entities and between studies. In this review we present an overview of genetic studies, case reports, and experimental evidence of the source of mature lymphoid malignancy and discuss the perspectives.

Biology Informs Treatment Choices in Diffuse Large B Cell Lymphoma

The effective deployment of rationally developed therapies for diffuse large B cell lymphoma (DLBCL) requires rapid assimilation of new biological data. Within this framework, here we address topical issues at the intersection of DLBCL biology and the clinic. We discuss targeting of B cell receptor (BCR) signaling, with emphasis on identifying patients who may benefit from this maneuver and how to best achieve it. We address strategies to modulate the DLBCL microenvironment, including the use of immune checkpoint inhibitors in selected DLBCL subsets, and the potential activity of alternative antiangiogenic therapies. Lastly, we highlight the emerging recognition of MYC and BCL2 coexpression as the most robust predictor of DLBCL outcome, and discuss rationally conceived experimental approaches to treat these high-risk patients.

Role of LFA-1 and ICAM-1 in Cancer

The lymphocyte function-associated antigen-1 (LFA-1) (also known as CD11a/CD18 and α_Lβ₂), is just one of many integrins in the human body, but its significance is derived from its exclusive presence in leukocytes. In this review, we summarize the studies relating LFA-1 and its major ligand ICAM-1 (or CD54) with cancer, through the function of lymphocytes and myeloid cells on tumor cells. We consider how LFA-1 mediates the interaction of leukocytes with tumors and the role of ICAM-1 in tumor dynamics, which can be independent of its interaction with LFA-1. We also offer a more detailed examination of the role of LFA-1 within B-cell chronic lymphocytic leukemia. Finally, we discuss the role that exosomes harboring LFA-1 play in tumor growth and metastasis.

A model integrating tonic and antigen-triggered BCR signals to predict the survival of primary B cells

The BCR constitutively transmits a “tonic” survival signal in the absence of exogenous antigen-binding. However, the strength of tonic BCR signal and its relationship with antigen-triggered survival signal are poorly understood. We found that primary B cells expressing high levels of BCR had elevated BCR tonic signal and increased survival compared with those expressing low levels of BCR. In addition, we found that crosslinking BCR with low doses of F(ab′)₂ α-IgM antibodies did not enhance, but rather decreased, B cell survival and that only when most of the BCR were occupied by F(ab′)₂ α-IgM antibodies was B cell survival enhanced. Based on these experimental results, we present a mathematical model integrating tonic and antigen-triggered BCR signals. Our model indicates that the signal generated from crosslinked BCR is 4.3 times as strong as the tonic signal generated from free BCR and that the threshold of B cell activation corresponds to the signal generated by crosslinking 61% of the surface BCR. This model also allows the prediction of the survival probability of a B cell based on its initial BCR level and the strength and duration of antigen stimulation, and fits with the mechanism of B cell tolerance.

Pathogen-specific B-cell receptors drive chronic lymphocytic leukemia by light-chain-dependent cross-reaction with autoantigens

Several lines of evidence indirectly suggest that antigenic stimulation through the B-cell receptor (BCR) supports chronic lymphocytic leukemia (CLL) development. In addition to self-antigens, a number of microbial antigens have been proposed to contribute to the selection of the immunoglobulins expressed in CLL. How pathogen-specific BCRs drive CLL development remains, however, largely unexplored. Here, we utilized mouse models of CLL pathogenesis to equip B cells with virus-specific BCRs and study the effect of antigen recognition on leukemia growth. Our results show that BCR engagement is absolutely required for CLL development. Unexpectedly, however, neither acute nor chronic exposure to virus-derived antigens influenced leukemia progression. Rather, CLL clones preferentially selected light chains that, when paired with virus-specific heavy chains, conferred B cells the ability to recognize a broad range of autoantigens. Taken together, our results suggest that pathogens may drive CLL pathogenesis by selecting and expanding pathogen-specific B cells that cross-react with one or more self-antigens.

Early stages in the ontogeny of small B-cell lymphomas: genetics and microenvironment

In this review, we focus on the mechanisms underlying lymphomagenesis in chronic lymphocytic leukaemia, follicular lymphoma, mantle cell lymphoma and splenic marginal zone lymphoma. The cells of origin of these small B-cell lymphomas are distinct, as are the characteristic chromosomal lesions and clinical courses. One shared feature is retention of expression of surface immunoglobulin. Analysis of this critical receptor reveals the point of differentiation reached by the cell of origin. Additionally, the sequence patterns of the immunoglobulin-variable domains can indicate a role for stimulants of the B-cell receptor before, during and after malignant transformation. The pathways driven via the B-cell receptor are now being targeted by specific kinase inhibitors with exciting clinical effects. To consider routes to pathogenesis, potentially offering earlier intervention, or to identify causative factors, genetic tools are being used to track pretransformation events and the early phases in lymphomagenesis. These methods are revealing that chromosomal changes are only one of the many steps involved, and that the influence of surrounding cells, probably multiple and variable according to tissue location, is required, both to establish tumours and to maintain growth and survival. Similarly, the influence of the tumour microenvironment may protect malignant cells from eradication by treatment, and the resulting minimal residual disease will eventually give rise to relapse. The common and different features of the four lymphomas will be summarized to show how normal B lymphocytes can be subverted to generate tumours, how these tumours evolve and how their weaknesses can be attacked by targeted therapies.

The role of B cell antigen receptors in mantle cell lymphoma

Mantle cell lymphoma (MCL) is characterized by an aggressive clinical course and secondary resistance to currently available therapies in most cases. Therefore, despite recent advances in the treatment of this disease, it is still considered to be incurable in the majority of cases. MCL B cells retain their B cell antigen receptor (BCR) expression during and after neoplastic transformation. BCRs in MCL show distinct patterns of antigen selection and ongoing BCR signaling. However, little is known about the involved antigens and the mechanisms leading to lymphomagenesis and lymphoma progression in MCL. Recent preclinical and clinical studies have established a crucial role of the BCR and the potential of inhibiting its signaling in this disease. This has established the B cell antigen receptor signaling cascade as a very promising therapeutic target to improve outcome in MCL alone or in combination with chemo-immunotherapy in recent years.

Novel synthetic drugs currently in clinical development for chronic lymphocytic leukemia

INTRODUCTION

Over the last few years, several new synthetic drugs, particularly Bruton's tyrosine kinase (BTK), phosphatidylinositol 3-kinase (PI3K) and BCL-2 inhibitors have been developed and investigated in chronic lymphocytic leukemia (CLL). Areas covered: This review highlights key aspects of BTK, PI3K and BCL-2 inhibitors that are currently at various stages of preclinical and clinical development in CLL. A literature review of the MEDLINE database for articles in English concerning CLL, B-cell receptor, BCL-2 antagonists, BTK inhibitors and PI3K inhibitors, was conducted via PubMed. Publications from 2000 through July 2017 were scrutinized. The search terms used were acalabrutinib, ACP-196, BGB-3111, ONO-4059, GS-4059, duvelisib, IPI-145, TGR-1202, copanlisib, Bay 80-6946, buparlisib, BKM-120, BCL-2 inhibitors, venetoclax, ABT-263, navitoclax, CDK inhibitors, alvocidib, flavopiridol, dinaciclib, SCH 727,965, palbociclib, PD-0332991, in conjunction with CLL. Conference proceedings from the previous five years of the ASH and EHA Annual Scientific Meetings were searched manually. Additional relevant publications were obtained by reviewing the references from the chosen articles. Expert opinion: The use of new synthetic drugs is a promising strategy for the treatment of CLL. Data from ongoing and future clinical trials will aid in better defining the status of new drugs in the treatment of CLL.

Cardiac side effects of bruton tyrosine kinase (BTK) inhibitors

The development of bruton tyrosine kinase inhibitors (BTKi) has been a significant advancement in the treatment of chronic lymphocytic leukemia and related B-cell malignancies. As experience in using ibrutinib increased, the first drug to be licensed in its class, atrial fibrillation (AF) emerged as an important side effect. The intersection between BTKi therapy for B-cell malignancies and AF represents a complex area of management with scant evidence for guidance. Consideration needs to be taken regarding the interplay of increased bleeding risk versus thromboembolic complications of AF, drug interactions between ibrutinib and anticoagulants and antiarrhythmic agents, and the potential for other, as yet seldom reported cardiac side effects. This review describes the current knowledge regarding BTKi and potential pathophysiologic mechanisms of AF and discusses the management of BTKi-associated AF. Finally, a review of the second generation BTKi is provided and gaps in knowledge in this evolving field are highlighted.

Regulation of MAPK signaling and implications in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a heterogeneous B cell malignancy that still remains incurable. Recent studies have highlighted cellular and non-cellular components of the tissue microenvironment in CLL that help nurture the growth of leukemic cells by providing the necessary stimuli for their proliferation and survival. The diverse stimuli in the specialized tissue microenvironment of CLL lead to constitutive activation of several signaling pathways that includes B cell receptor signaling and the associated mitogen-activated protein kinase (MAPK) signaling. Recent findings have described aberrant activation of MAPK signaling and its interactions with other cellular signaling pathways in the pathogenesis of CLL. These studies have shed light on the deregulated molecular mechanisms contributing to hyperactivation of MAPK signaling and provided avenues for therapeutic options for aggressive CLL. In this review, we describe and discuss the current status of our understanding into the role of MAPK signaling in the pathogenesis of CLL.

Activation of the B-cell receptor successively activates NF-κB and STAT3 in chronic lymphocytic leukemia cells

In chronic lymphocytic leukemia (CLL) cells, both interleukin-6 (IL-6) and the B-cell receptor (BCR) activate Janus kinase 2 (JAK2) and induce the phosphorylation of signal transduction and activator of transcription 3 (STAT3) on tyrosine 705 residues. However, whereas IL-6 phosphorylates STAT3 within 15 min, stimulation of the BCR with anti-immunoglobulin M (IgM) antibodies phosphorylates STAT3 in 2-4 hr. Here, we show that this process takes longer because it requires transcriptional activity of NF-κB. Using an electromobility shift assay, we found that incubation with IgM antibodies for 4 or 18 hr, but not 15 min, increased NF-κB DNA-binding of CLL cells and increased binding was translated to increased transcriptional activity. Hence, 42% of the 83 NF-κB target genes were constitutively expressed in all CLL cells prior to any inducible stimuli. However, activation of the BCR increased the number of NF-κB target genes with detectable expression by 23%. Remarkably, prolonged incubation with anti-IgM antibodies induced a time-dependent transcription, production and secretion of IL-6 protein. The IgM-induced production of IL-6 prompted the phosphorylation of STAT3 on tyrosine residues. This effect was inhibited by the JAK1/2 inhibitor of the JAK/STAT3 pathway ruxolitinib. Taken together, these results suggest that in CLL cells, constitutive tonic activation of NF-κB can be further enhanced by the BCR and that the BCR-induced activation of the JAK/STAT3 pathway depends on the NF-κB induced production of IL-6.

Distinct homotypic B-cell receptor interactions shape the outcome of chronic lymphocytic leukaemia

Cell-autonomous B-cell receptor (BcR)-mediated signalling is a hallmark feature of the neoplastic B lymphocytes in chronic lymphocytic leukaemia (CLL). Here we elucidate the structural basis of autonomous activation of CLL B cells, showing that BcR immunoglobulins initiate intracellular signalling through homotypic interactions between epitopes that are specific for each subgroup of patients with homogeneous clinicobiological profiles. The molecular details of the BcR–BcR interactions apparently dictate the clinical course of disease, with stronger affinities and longer half-lives in indolent cases, and weaker, short-lived contacts mediating the aggressive ones. The diversity of homotypic BcR contacts leading to cell-autonomous signalling reconciles the existence of a shared pathogenic mechanism with the biological and clinical heterogeneity of CLL and offers opportunities for innovative treatment strategies.

Chronic lymphocytic leukaemia (CLL) is characterized by cell-autonomous B-cell receptor (BcR)-mediated signalling of neoplastic B lymphocytes. Here the authors unveil the structural basis and diversity of activatory homotypic BcR contacts and link them with CLL heterogeneity and the clinical outcome.

Whole-genome sequencing of chronic lymphocytic leukaemia reveals distinct differences in the mutational landscape between IgHVmut and IgHVunmut subgroups

Chronic lymphocytic leukaemia (CLL) consists of two biologically and clinically distinct subtypes defined by the abundance of somatic hypermutation (SHM) affecting the Ig variable heavy-chain locus (IgHV). The molecular mechanisms underlying these subtypes are incompletely understood. Here, we present a comprehensive whole-genome sequencing analysis of somatically acquired genetic events from 46 CLL patients, including a systematic comparison of coding and non-coding single-nucleotide variants, copy number variants and structural variants, regions of kataegis and mutation signatures between IgHV^mut and IgHV^unmut subtypes. We demonstrate that one-quarter of non-coding mutations in regions of kataegis outside the Ig loci are located in genes relevant to CLL. We show that non-coding mutations in ATM may negatively impact on ATM expression and find non-coding and regulatory region mutations in TCL1A, and in IgHV^unmut CLL in IKZF3, SAMHD1,PAX5 and BIRC3. Finally, we show that IgHV^unmut CLL is dominated by coding mutations in driver genes and an aging signature, whereas IgHV^mut CLL has a high incidence of promoter and enhancer mutations caused by aberrant activation-induced cytidine deaminase activity. Taken together, our data support the hypothesis that differences in clinical outcome and biological characteristics between the two subgroups might reflect differences in mutation distribution, incidence and distinct underlying mutagenic mechanisms.

Pharmacotherapy of relapsed/refractory chronic lymphocytic leukemia

INTRODUCTION

The treatment of relapsed/refractory (RR) CLL has been revolutionized by the advent of the new oral inhibitors of B-cell receptor (BCR) signaling and the pro-survival protein, B-cell lymphoma 2 (BCL2). Additionally, new and more potent monoclonal antibodies against CD20 have replaced/may replace rituximab in many settings. Areas covered: Herein, we review the entire therapeutic landscape of RR CLL, with particular attention to the new small-molecule kinase inhibitors and BH3-mimetics. We discuss preclinical data with these agents in CLL, cover available efficacy and safety information, and examine potential resistance mechanisms and possible rational combinations to circumvent them. Expert opinion: The availability of potent and selective inhibitors of BCR signaling and of the anti-apoptotic functions of BCL2 has enormously enhanced our therapeutic armamentarium, with unprecedented efficacy now observed in patients who historically had poor outcomes with chemoimmunotherapy (CIT), e.g., those with deletion 17p/11q and/or IGHV-unmutated disease. The next challenge is to optimally sequence these agents and develop rational combinations that will hopefully lead to deeper and more durable remissions than ever seen before. Indeed, long term relapse free survival, already achievable with CIT in patients with genetically favorable-risk disease, now appears to be a realistic possibility for most patients with CLL.

Cell lines generated from a chronic lymphocytic leukemia mouse model exhibit constitutive Btk and Akt signaling

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of mature CD5⁺ B cells in blood. Spontaneous apoptosis of CLL cells in vitro has hampered in-depth investigation of CLL pathogenesis. Here we describe the generation of three monoclonal mouse cell lines, EMC2, EMC4 and EMC6, from the IgH.TEμ CLL mouse model based on sporadic expression of SV40 large T antigen. The cell lines exhibit a stable CD5⁺CD43⁺IgM⁺CD19⁺ CLL phenotype in culture and can be adoptively transferred into Rag1^−/− mice. RNA-seq analysis revealed only minor differences between the cell lines and their primary tumors and suggested that NF-κB and mTOR signaling pathways were involved in cell line outgrowth. In vitro survival and proliferation was dependent on constitutive phosphorylation of Bruton's tyrosine kinase (Btk) at Y551/Y223, and Akt(S473). Treatment of the cell lines with small molecule inhibitors specific for Btk (ibrutinib) or PI3K (idelalisib), which is upstream of Akt, resulted in reduced viability, proliferation and fibronectin-dependent cell adhesion. Treatment of cell line-engrafted Rag1^−/− mice with ibrutinib was associated with transient lymphocytosis, reduced splenomegaly and increased overall survival. Thus, by generating stable cell lines we established a novel platform for in vitro and in vivo investigation of CLL signal transduction and treatment modalities.

High SYK Expression Drives Constitutive Activation of CD21low B Cells

Human CD21^low B cells present with an activated phenotype and accumulate in distinct disorders connected with chronic immune stimulation. Signaling studies had revealed an increased basal phosphorylation of spleen tyrosine kinase (SYK) and phospholipase Cγ2. Additional BCR stimulation of these constitutively active cells, however, led to reduced activation of these signaling molecules and subsequently NF-κB and Ca²⁺ activation. In this article, we demonstrate that high SYK expression is a common feature of CD21^low B cells independent of the underlying disorder, and that this high expression is sufficient to drive constitutive phosphorylation of SYK and its immediate targets Bruton's tyrosine kinase and phospholipase Cγ2. Inhibition of SYK activity eliminated features of the constitutive activation in these cells and partly restored BCR signaling. High SYK expression is especially induced by CpG or CD40L in combination with IL-21, but not BCR stimulation, suggesting the importance of the immune-stimulatory context for the induction of this B cell phenotype. In summary, high SYK expression is a common feature of human CD21^low B cells and presumably results from chronic activation in inflammatory environments present in a subgroup of patients with heterogeneous disorders like chronic infection, autoimmunity, and immunodeficiency. High SYK expression by itself drives the constitutive activation observed in these B cells, which in turn may contribute to the hyporesponsiveness upon BCR stimulation. Given the high prevalence of autoreactive clones among CD21^low B cells in autoimmune disorders, the dominant role of SYK in CD21^low B cells may provide a new option for therapeutic interventions in patients with expanded CD21^low B cells and humoral autoimmunity.

Targeting antigen-independent proliferation in chronic lymphocytic leukemia through differential kinase inhibition

The clinical success of B-cell receptor (BCR) signaling pathway inhibitors in chronic lymphocytic leukemia (CLL) is attributed to inhibition of adhesion in and migration towards the lymph node. Proliferation of CLL cells is restricted to this protective niche, but the underlying mechanism(s) is/are not known. Treatment with BCR pathway inhibitors results in rapid reductions of total clone size, while CLL cell survival is not affected, which points towards inhibition of proliferation. In vitro, BCR stimulation does not induce proliferation of CLL, but triggering via Toll-like receptor, tumor necrosis factor or cytokine receptors does. Here, we investigated the effects of clinically applied inhibitors that target BCR signaling, in the context of proliferation triggered either via CD40L/IL-21 or after CpG stimulation. CD40L/IL-21-induced proliferation could be inhibited by idelalisib and ibrutinib. We demonstrate this was due to blockade of CD40L-induced ERK-signaling. Targeting JAKs, but not SYK, blocked CD40L/IL-21-induced proliferation. In contrast, PI3K, BTK as well as SYK inhibition prevented CpG-induced proliferation. Knockdown experiments showed that CD40L/IL-21 did not co-opt upstream BCR components such as CD79A, in contrast to CpG-induced proliferation. Our data indicate that currently applied BTK/PI3K inhibitors target antigen-independent proliferation in CLL, and suggest that targeting of JAK and/or SYK might be clinically useful.

Coevolution of Leukemia and Host Immune Cells in Chronic Lymphocytic Leukemia

Cumulative studies on the dissection of changes in driver genetic lesions in cancer across the course of the disease have provided powerful insights into the adaptive mechanisms of tumors in response to the selective pressures of therapy and environmental changes. In particular, the advent of next-generation-sequencing (NGS)-based technologies and its implementation for the large-scale comprehensive analyses of cancers have greatly advanced our understanding of cancer as a complex dynamic system wherein genetically distinct subclones interact and compete during tumor evolution. Aside from genetic evolution arising from interactions intrinsic to the cell subpopulations within tumors, it is increasingly appreciated that reciprocal interactions between the tumor cell and cellular constituents of the microenvironment further exert selective pressures on specific clones that can impact the balance between tumor immunity and immunologic evasion and escape. Herein, we review the evidence supporting these concepts, with a particular focus on chronic lymphocytic leukemia (CLL), a disease that has been highly amenable to genomic interrogation and studies of clonal heterogeneity and evolution. Better knowledge of the basis for immune escape has an important clinical impact on prognostic stratification and on the pursuit of new therapeutic opportunities.

Activity of the novel BCR kinase inhibitor IQS019 in preclinical models of B-cell non-Hodgkin lymphoma

Background

Pharmacological inhibition of B cell receptor (BCR) signaling has recently emerged as an effective approach in a wide range of B lymphoid neoplasms. However, despite promising clinical activity of the first Bruton’s kinase (Btk) and spleen tyrosine kinase (Syk) inhibitors, a small fraction of patients tend to develop progressive disease after initial response to these agents.

Methods

We evaluated the antitumor activity of IQS019, a new BCR kinase inhibitor with increased affinity for Btk, Syk, and Lck/Yes novel tyrosine kinase (Lyn), in a set of 34 B lymphoid cell lines and primary cultures, including samples with acquired resistance to the first-in-class Btk inhibitor ibrutinib. Safety and efficacy of the compound were then evaluated in two xenograft mouse models of B cell lymphoma.

Results

IQS019 simultaneously engaged a rapid and dose-dependent de-phosphorylation of both constitutive and IgM-activated Syk, Lyn, and Btk, leading to impaired cell proliferation, reduced CXCL12-dependent cell migration, and induction of caspase-dependent apoptosis. Accordingly, B cell lymphoma-bearing mice receiving IQS019 presented a reduced tumor outgrowth characterized by a decreased mitotic index and a lower infiltration of malignant cells in the spleen, in tight correlation with downregulation of phospho-Syk, phospho-Lyn, and phospho-Btk. More interestingly, IQS019 showed improved efficacy in vitro and in vivo when compared to the first-in-class Btk inhibitor ibrutinib, and was active in cells with acquired resistance to this latest.

Conclusions

These results define IQS019 as a potential drug candidate for a variety of B lymphoid neoplasms, including cases with acquired resistance to current BCR-targeting therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-017-0447-6) contains supplementary material, which is available to authorized users.

High-throughput sequencing of the B-cell receptor in African Burkitt lymphoma reveals clues to pathogenesis

Burkitt lymphoma (BL), the most common pediatric cancer in sub-Saharan Africa, is a malignancy of antigen-experienced B lymphocytes. High-throughput sequencing (HTS) of the immunoglobulin heavy (IGH) and light chain (IGK/IGL) loci was performed on genomic DNA from 51 primary BL tumors: 19 from Uganda and 32 from Ghana. Reverse transcription polymerase chain reaction analysis and tumor RNA sequencing (RNAseq) was performed on the Ugandan tumors to confirm and extend the findings from the HTS of tumor DNA. Clonal IGH and IGK/IGL rearrangements were identified in 41 and 46 tumors, respectively. Evidence for rearrangement of the second IGH allele was observed in only 6 of 41 tumor samples with a clonal IGH rearrangement, suggesting that the normal process of biallelic IGHD to IGHJ diversity-joining (DJ) rearrangement is often disrupted in BL progenitor cells. Most tumors, including those with a sole dominant, nonexpressed DJ rearrangement, contained many IGH and IGK/IGL sequences that differed from the dominant rearrangement by < 10 nucleotides, suggesting that the target of ongoing mutagenesis of these loci in BL tumor cells is not limited to expressed alleles. IGHV usage in both BL tumor cohorts revealed enrichment for IGHV genes that are infrequently used in memory B cells from healthy subjects. Analysis of publicly available DNA sequencing and RNAseq data revealed that these same IGHV genes were overrepresented in dominant tumor-associated IGH rearrangements in several independent BL tumor cohorts. These data suggest that BL derives from an abnormal B-cell progenitor and that aberrant mutational processes are active on the immunoglobulin loci in BL cells.