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Chronic lymphocytic leukemia (CLL) is a heterogeneous B cell malignancy characterized by the accumulation of functionally incompetent B lymphocytes. Despite the availability of highly effective treatments, CLL remains incurable, and the factors contributing to disease progression are not fully understood. Autoimmune complications frequently arise in CLL patients and are associated with poor clinical prognosis. This study investigates the connection between plasma cell-mediated autoimmunity and CLL progression using a mouse model that expresses an active Receptor Activator of NF-κB (RANK) in B cells (RK mice), where autoimmune manifestations coexist with CLL. Transcriptional profiling of RANK-driven leukemic cells revealed a more indolent form of CLL compared to the classical TCL1 model. The discovery of near-identical CDR3 regions in both plasma and CLL cells of RK mice suggests a shared progenitor and antigen driving both conditions. Deletion of Blimp-1, which prevents plasma cell differentiation, initially enhanced B1/CLL formation in young mice but nearly halted CLL progression, highlighting the significant influence of autoimmune complications on disease outcomes. This research underscores the intertwined nature of autoimmunity and CLL, suggesting that targeting inflammatory pathways could offer therapeutic potential for managing both conditions. [ABSTRACT FROM AUTHOR]

The phosphoinositide 3‐kinase/protein kinase B (PI3K/AKT) signaling pathway is a central regulator of B cell biology, influencing survival, proliferation, metabolism, and immune responses. This Review explores how in both normal and malignant B cells, signaling operates within a finely tuned “comfort zone”, where appropriate levels support cell growth and survival. This comfort zone is dynamically modulated by the developmental stage, costimulatory signals, and the duration, magnitude, and subcellular localization of signaling events. In chronic lymphocytic leukemia, aberrant PI3K/AKT activation drives disease progression and resistance to therapy. Notably, deviations from the comfort zone—whether through excessive hyperactivation or insufficient signaling—can trigger cell death, presenting therapeutic opportunities. Signaling thresholds influence normal B cell development and chronic lymphocytic leukemia pathogenesis, including mechanisms of immune escape and Richter's transformation, an aggressive progression from chronic lymphocytic leukemia. Therapeutic strategies targeting PI3K/AKT are evaluated, with a focus on challenges such as toxicity. By understanding the nuanced modulation of the signaling comfort zone, we can refine therapies to selectively eliminate leukemic cells while preserving normal B cell function, offering new hope for improved treatment outcomes. [ABSTRACT FROM AUTHOR]

Phosphatase and tensin homolog (PTEN) is a negative regulator of the phosphatidylinositol 3-kinase (PI3K) and protein kinase B (AKT) signaling pathway and a potent tumor suppressor in many types of cancer. To test a tumor suppressive role for PTEN in pre-B acute lymphoblastic leukemia (ALL), we induced Cre-mediated deletion of Pten in mouse models of pre-B ALL. In contrast to its role as a tumor suppressor in other cancers, loss of one or both alleles of Pten caused rapid cell death of pre-B ALL cells and was sufficient to clear transplant recipient mice of leukemia. Small-molecule inhibition of PTEN in human pre-B ALL cells resulted in hyperactivation of AKT, activation of the p53 tumor suppressor cell cycle checkpoint and cell death. Loss of PTEN function in pre-B ALL cells was functionally equivalent to acute activation of autoreactive pre-B cell receptor signaling, which engaged a deletional checkpoint for the removal of autoreactive B cells. We propose that targeted inhibition of PTEN and hyperactivation of AKT triggers a checkpoint for the elimination of autoreactive B cells and represents a new strategy to overcome drug resistance in human ALL.

Studying mechanisms of malignant transformation of human pre-B cells, we found that acute activation of oncogenes induced immediate cell death in the vast majority of cells. Few surviving pre-B cell clones had acquired permissiveness to oncogenic signaling by strong activation of negative feedback regulation of Erk signaling. Studying negative feedback regulation of Erk in genetic experiments at three different levels, we found that Spry2, Dusp6, and Etv5 were essential for oncogenic transformation in mouse models for pre-B acute lymphoblastic leukemia (ALL). Interestingly, a small molecule inhibitor of DUSP6 selectively induced cell death in patient-derived pre-B ALL cells and overcame conventional mechanisms of drug-resistance.

B cells are selected for an intermediate level of B-cell antigen receptor (BCR) signalling strength: attenuation below minimum (for example, non-functional BCR) or hyperactivation above maximum (for example, self-reactive BCR) thresholds of signalling strength causes negative selection. In ∼25% of cases, acute lymphoblastic leukaemia (ALL) cells carry the oncogenic BCR-ABL1 tyrosine kinase (Philadelphia chromosome positive), which mimics constitutively active pre-BCR signalling. Current therapeutic approaches are largely focused on the development of more potent tyrosine kinase inhibitors to suppress oncogenic signalling below a minimum threshold for survival. We tested the hypothesis that targeted hyperactivation--above a maximum threshold--will engage a deletional checkpoint for removal of self-reactive B cells and selectively kill ALL cells. Here we find, by testing various components of proximal pre-BCR signalling in mouse BCR-ABL1 cells, that an incremental increase of Syk tyrosine kinase activity was required and sufficient to induce cell death. Hyperactive Syk was functionally equivalent to acute activation of a self-reactive BCR on ALL cells. Despite oncogenic transformation, this basic mechanism of negative selection was still functional in ALL cells. Unlike normal pre-B cells, patient-derived ALL cells express the inhibitory receptors PECAM1, CD300A and LAIR1 at high levels. Genetic studies revealed that Pecam1, Cd300a and Lair1 are critical to calibrate oncogenic signalling strength through recruitment of the inhibitory phosphatases Ptpn6 (ref. 7) and Inpp5d (ref. 8). Using a novel small-molecule inhibitor of INPP5D (also known as SHIP1), we demonstrated that pharmacological hyperactivation of SYK and engagement of negative B-cell selection represents a promising new strategy to overcome drug resistance in human ALL.

Richter's transformation (RT) is a progression of chronic lymphocytic leukemia (CLL) to aggressive lymphoma. MGA (Max gene associated), a functional MYC suppressor, is mutated at 3% in CLL and 36% in RT. However, genetic models and molecular mechanisms of MGA deletion that drive CLL to RT remain elusive. We established an RT mouse model by knockout of Mga in the Sf3b1/Mdr CLL model using CRISPR-Cas9 to determine the role of Mga in RT. Murine RT cells exhibited mitochondrial aberrations with elevated oxidative phosphorylation (OXPHOS). Through RNA sequencing and functional characterization, we identified Nme1 (nucleoside diphosphate kinase) as an Mga target, which drives RT by modulating OXPHOS. Given that NME1 is also a known MYC target without targetable compounds, we found that concurrent inhibition of MYC and electron transport chain complex II substantially prolongs the survival of RT mice in vivo. Our results suggest that the Mga-Nme1 axis drives murine CLL-to-RT transition via modulating OXPHOS, highlighting a potential therapeutic avenue for RT. Editor's summary: Richter's transformation (RT) involves the progression of chronic lymphocytic leukemia (CLL) to a more aggressive lymphoma with poor outcomes. Understanding the transition into RT is key to more targeted therapeutic strategies. Iyer et al. examined the role of the MYC suppressor MGA, which is differentially expressed in RT, in an in vivo CLL model with MGA dysfunction. MGA loss resulted in increased mitochondrial function and reactive oxygen species and led to aberrant cell morphology and up-regulated MYC as commonly observed in patients. Combined inhibition of MYC and mitochondrial respiration prolonged in vivo survival in this model, highlighting potential therapeutic strategies for RT with this genetic profile. —Catherine Charneski [ABSTRACT FROM AUTHOR]

B-cell antigen receptor (BCR) expression is an important feature of chronic lymphocytic leukaemia (CLL), one of the most prevalent B-cell neoplasias in Western countries (1). The presence of stereotyped and [...]

Author(s): Zhengshan Chen; Seyedmehdi Shojaee; Maike Buchner; Huimin Geng; Jae Woong Lee; Lars Klemm; Bjrn Titz; Thomas G. Graeber; Eugene Park; Ying Xim Tan; Anne Satterthwaite; Elisabeth Paietta; Stephen P. [...]

Abstract Background The non-signalling chemokine receptors, including receptors DARC, D6 and CCX-CKR, have recently been shown to be involved in chemokine clearance and activity regulation. The human chemokine receptor CRAM (also known as HCR or CCRL2) is the most recently identified member of this atypical group. CRAM is expressed on B cells in a maturation-stage dependent manner and absent on T cells. We have recently shown that it competitively binds CCL19. CCL19 and its signalling receptor CCR7 are critical components involved in cell recruitment to secondary lymphoid organs and in maturation. B cell Chronic Lymphocytic Leukemia (B-CLL) is a low-grade lymphoma characterized by proliferative centres (or pseudofollicles). Proliferative centres develop due to abnormal cellular localisation and they are involved in the development of malignant cells. CCR7 is highly expressed on B cells from CLL patients and mediates migration towards its ligands CCL19 and CCL21, while CRAM expression and potential interferences with CCR7 are yet to be characterized. Results In this study, we show that B cells from patients with B-CLL present highly variable degrees of CRAM expression in contrast to more consistently high levels of CCR7. We investigated the hypothesis that, similar to the atypical receptor DARC, CRAM can modulate chemokine availability and/or efficacy, resulting in the regulation of cellular activation. We found that a high level of CRAM expression was detrimental to efficient chemotaxis with CCL19. MAP-kinase phosphorylation and intracellular calcium release induced by CCL19 were also altered by CRAM expression. In addition, we demonstrate that CRAM-induced regulation of CCL19 signalling is maintained over time. Conclusions We postulate that CRAM is a factor involved in the fine tuning/control of CCR7/CCL19 mediated responses. This regulation could be critical to the pivotal role of CCL19 induced formation of proliferation centres supporting the T/B cells encounter as well as disease progression in B-CLL.