CXCR4 hyperactivation cooperates with TCL1 in CLL development and aggressiveness

Role of the tumor microenvironment in CLL pathogenesis

Chronic lymphocytic leukemia (CLL) cells extensively interact with and depend on their surrounding tumor microenvironment (TME). The TME encompasses a heterogeneous array of cell types, soluble signals, and extracellular vesicles, which contribute significantly to CLL pathogenesis. CLL cells and the TME cooperatively generate a chronic inflammatory milieu, which reciprocally reprograms the TME and activates a signaling network within CLL cells, promoting their survival and proliferation. Additionally, the inflammatory milieu exerts chemotactic effects, attracting CLL cells and other immune cells to the lymphoid tissues. The intricate CLL-TME interactions also facilitate immune evasion and compromise leukemic cell surveillance. We also review recent advances that have shed light on additional aspects that are substantially influenced by the CLL-TME interplay.

CXCR4 overexpression in chronic lymphocytic leukemia associates with poorer prognosis: A prospective, single-center, observational study

Controversial data have been reported on the prognostic value of C-X-C motif chemokine receptor 4 (CXCR4) in chronic lymphocytic leukemia (CLL). This prospective, single-center, observational study aimed to evaluate the role of CXCR4 in the pathophysiology of CLL and its prognostic role. A total of 158 patients of CLL were enrolled, and CXCR4 expression on CLL cells was detected by flow cytometry (FCM) at initial diagnosis. The patients were divided into 2 groups according to the CXCR4 mean fluorescence intensity (MFI) median. Also, four patient specimens from the CXCR4low and CXCR4high groups were selected for RNASeq analysis. The progression-free survival (PFS) of CLL patients in the CXCR4high group was significantly shorter than the CXCR4low group, with a median follow-up time of 27 months (log-rank P < 0.001). Moreover, CXCR4 overexpression (MFI > 3376) was an independent marker of poor PFS in CLL patients (P < 0.001). Analysis of RNASeq results revealed that CXCR4 plays an important role in the migration of CLL. Collectively, CXCR4 expression levels on leukemia cells can be detected rapidly by FCM. CXCR4 overexpression was significantly associated with poorer prognosis in CLL patients within a shorter follow-up time.

B cell receptor signaling and associated pathways in the pathogenesis of chronic lymphocytic leukemia

B cell antigen receptor (BCR) signaling is a key driver of growth and survival in both normal and malignant B cells. Several lines of evidence support an important pathogenic role of the BCR in chronic lymphocytic leukemia (CLL). The significant improvement of CLL patients' survival with the use of various BCR pathway targeting inhibitors, supports a crucial involvement of BCR signaling in the pathogenesis of CLL. Although the treatment landscape of CLL has significantly evolved in recent years, no agent has clearly demonstrated efficacy in patients with treatment-refractory CLL in the long run. To identify new drug targets and mechanisms of drug action in neoplastic B cells, a detailed understanding of the molecular mechanisms of leukemic transformation as well as CLL cell survival is required. In the last decades, studies of genetically modified CLL mouse models in line with CLL patient studies provided a variety of exciting data about BCR and BCR-associated kinases in their role in CLL pathogenesis as well as disease progression. BCR surface expression was identified as a particularly important factor regulating CLL cell survival. Also, BCR-associated kinases were shown to provide a crosstalk of the CLL cells with their tumor microenvironment, which highlights the significance of the cells' milieu in the assessment of disease progression and treatment. In this review, we summarize the major findings of recent CLL mouse as well as patient studies in regard to the BCR signalosome and discuss its relevance in the clinics.

Human and mouse early B cell development: So similar but so different

Early B cell development in the bone marrow ensures the replenishment of the peripheral B cell pool. Immature B cells continuously develop from hematopoietic stem cells, in a process guided by an intricate network of transcription factors as well as chemokine and cytokine signals. Humans and mice possess somewhat similar regulatory mechanisms of B lymphopoiesis. The continuous discovery of monogenetic defects that impact early B cell development in humans substantiates the similarities and differences with B cell development in mice. These differences become relevant when targeted therapeutic approaches are used in patients; therefore, predicting potential immunological adverse events is crucial. In this review, we have provided a phenotypical classification of human and murine early progenitors and B cell stages, based on surface and intracellular protein expression. Further, we have critically compared the role of key transcription factors (Ikaros, E2A, EBF1, PAX5, and Aiolos) and chemo- or cytokine signals (FLT3, c-kit, IL-7R, and CXCR4) during homeostatic and aberrant B lymphopoiesis in both humans and mice.

Interobserver Agreement Rates on C-X-C Motif Chemokine Receptor 4-Directed Molecular Imaging and Therapy

BACKGROUND

We aimed to evaluate the interobserver agreement rates in patients scanned with C-X-C motif chemokine receptor 4 (CXCR4)-directed PET/CT, including the rate of patients eligible for CXCR4-targeted radioligand therapy (RLT) based on scan results.

METHODS

Four independent observers reviewed 50 CXCR4-targeted [ 68 Ga]pentixafor PET/CT of patients with various solid cancers. On a visual level, the following items were assessed by each reader: overall scan impression, number of organ and lymph node (LN) metastases and number of affected organs and LN regions. For a quantitative investigation, readers had to choose a maximum of 3 target lesions, defined as largest in size and/or most intense uptake per organ compartment. Reference tissues were also quantified, including unaffected hepatic parenchyma and blood pool. Last, all observers had to decide whether patients were eligible for CXCR4-targeted RLT. Concordance rates were tested using intraclass correlation coefficients (ICCs). For interpretation, we applied the definition of Cicchetti (with 0.4-0.59 indicating fair; 0.6-0.74, good; 0.75-1, excellent agreement).

RESULTS

On a visual level, fair agreement was achieved for an overall scan impression (ICC, 0.58; 95% confidence interval, 0.45-0.71). Organ and LN involvement (ICC, ≥0.4) demonstrated fair, whereas CXCR4 density and number of LN and organ metastases showed good agreement rates (ICC, ≥0.65). Number of affected organs and affected LN areas, however, showed excellent concordance (ICC, ≥0.76). Quantification in LN and organ lesions also provided excellent agreement rates (ICC, ≥0.92), whereas quantified uptake in reference organs provided fair concordance (ICC, ≥0.54). Again, excellent agreement rates were observed when deciding on patients eligible for CXCR4-RLT (ICC, 0.91; 95% confidence interval, 0.85-0.95).

CONCLUSIONS

In patients scanned with CXCR4-targeted PET/CT, we observed fair to excellent agreement rates for both molecular imaging and therapy parameters, thereby favoring a more widespread adoption of [ 68 Ga]pentixafor in the clinic.

Biology and Treatment of Richter Transformation

Richter transformation (RT), defined as the development of an aggressive lymphoma on a background of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), represents a clinical unmet need because of its dismal prognosis. An increasing body of knowledge in the field of RT is arising from the recent development of preclinical models depicting the biology underlying this aggressive disease. Consistently, new therapeutic strategies based on a genetic rationale are exploring actionable pathogenic pathways to improve the outcome of patients in this setting. In this review, we summarize the current understandings on RT biology and the available treatment options.

The Modes of Dysregulation of the Proto-Oncogene T-Cell Leukemia/Lymphoma 1A

Simple Summary

T-cell leukemia/lymphoma 1A (TCL1A) is a proto-oncogene that is mainly expressed in embryonic and fetal tissues, as well as in some lymphatic cells. It is frequently overexpressed in a variety of T- and B-cell lymphomas and in some solid tumors. In chronic lymphocytic leukemia and in T-prolymphocytic leukemia, TCL1A has been implicated in the pathogenesis of these conditions, and high-level TCL1A expression correlates with more aggressive disease characteristics and poorer patient survival. Despite the modes of TCL1A (dys)regulation still being incompletely understood, there are recent advances in understanding its (post)transcriptional regulation. This review summarizes the current concepts of TCL1A’s multi-faceted modes of regulation. Understanding how TCL1A is deregulated and how this can lead to tumor initiation and sustenance can help in future approaches to interfere in its oncogenic actions.

Abstract

Incomplete biological concepts in lymphoid neoplasms still dictate to a large extent the limited availability of efficient targeted treatments, which entertains the mostly unsatisfactory clinical outcomes. Aberrant expression of the embryonal and lymphatic TCL1 family of oncogenes, i.e., the paradigmatic TCL1A, but also TML1 or MTCP1, is causally implicated in T- and B-lymphocyte transformation. TCL1A also carries prognostic information in these particular T-cell and B-cell tumors. More recently, the TCL1A oncogene has been observed also in epithelial tumors as part of oncofetal stemness signatures. Although the concepts on the modes of TCL1A dysregulation in lymphatic neoplasms and solid tumors are still incomplete, there are recent advances in defining the mechanisms of its (de)regulation. This review presents a comprehensive overview of TCL1A expression in tumors and the current understanding of its (dys)regulation via genomic aberrations, epigenetic modifications, or deregulation of TCL1A-targeting micro RNAs. We also summarize triggers that act through such transcriptional and translational regulation, i.e., altered signals by the tumor microenvironment. A refined mechanistic understanding of these modes of dysregulations together with improved concepts of TCL1A-associated malignant transformation can benefit future approaches to specifically interfere in TCL1A-initiated or -driven tumorigenesis.