Bruton’s tyrosine kinase (BTK), a cytoplasmic tyrosine kinase, plays a pivotal role in B cell biology and function. As an essential component of the B cell receptor (BCR) signaling pathway, BTK is expressed not only in B cells but also in myeloid cells, including monocytes/macrophages, dendritic cells, neutrophils, and mast cells. BTK inhibitors (BTKis) have revolutionized the treatment of chronic lymphocytic leukemia (CLL) and other B cell malignancies. Besides their well-characterized role in inhibiting BCR signaling, BTKis also exert significant immunological influences outside the tumor cell that extend their therapeutic potential and impact on the immune system in different ways. This work elucidates the immunomodulatory mechanisms associated with BTK inhibition, focusing on CLL and other clinical contexts. We discuss how BTK inhibition affects various immune cells, including B cells, T cells, and macrophages. The effects of BTKis on the profiles of cytokines, also fundamental parts of the tumor microenvironment (TME), are summarized here as well. This review also appraises the implications of these immunomodulatory actions in the management of autoimmune diseases and infections. Summarizing the dual role of BTK inhibition in modulating malignant lymphocyte and immune cell functions, this paper highlights the broader potential clinical use of compounds targeting BTK.

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.

T-prolymphocytic leukemia (T-PLL) is a mature T-cell neoplasm associated with marked chemotherapy resistance and continued poor clinical outcomes. Current treatments, that is, the CD52-antibody alemtuzumab, offer transient responses, with relapses being almost inevitable without consolidating allogeneic transplantation. Recent more detailed concepts of T-PLL’s pathobiology fostered the identification of actionable vulnerabilities: (1) altered epigenetics, (2) defective DNA damage responses, (3) aberrant cell-cycle regulation, and (4) deregulated prosurvival pathways, including T-cell receptor and JAK/STAT signaling. To further develop related preclinical therapeutic concepts, we studied inhibitors of histone deacetylases ([H]DACs), B-cell lymphoma 2 (BCL2), cyclin-dependent kinase (CDK), mouse double minute 2 (MDM2), and classical cytostatics, using (1) single-agent and combinatorial compound testing in 20 well-characterized and molecularly profiled primary T-PLL (validated by additional 42 cases) and (2) 2 independent murine models (syngeneic transplants and patient-derived xenografts). Overall, the most efficient/selective single agents and combinations (in vitro and in mice) included cladribine, romidepsin ([H]DAC), venetoclax (BCL2), and/or idasanutlin (MDM2). Cladribine sensitivity correlated with expression of its target RRM2. T-PLL cells revealed low overall apoptotic priming with heterogeneous dependencies on BCL2 proteins. In additional 38 T-cell leukemia/lymphoma lines, TP53 mutations were associated with resistance toward MDM2 inhibitors. P53 of T-PLL cells, predominantly in wild-type configuration, was amenable to MDM2 inhibition, which increased its MDM2-unbound fraction. This facilitated P53 activation and downstream signals (including enhanced accessibility of target-gene chromatin regions), in particular synergy with insults by cladribine. Our data emphasize the therapeutic potential of pharmacologic strategies to reinstate P53-mediated apoptotic responses. The identified efficacies and their synergies provide an informative background on compound and patient selection for trial designs in T-PLL.

In chronic lymphocytic leukemia (CLL), epigenetic alterations are considered to centrally shape the transcriptional signatures that drive disease evolution and that underlie its biological and clinical subsets. Characterizations of epigenetic regulators, particularly histone-modifying enzymes, are very rudimentary in CLL. In efforts to establish effectors of the CLL-associated oncogene T-cell leukemia 1A (TCL1A), we identified here the lysine-specific histone demethylase KDM1A to interact with the TCL1A protein in B-cells in conjunction with an increased catalytic activity of KDM1A. We demonstrate that KDM1A is upregulated in malignant B-cells. Elevated KDM1A and associated gene expression signatures correlated with aggressive disease features and adverse clinical outcomes in a large prospective CLL trial cohort. Genetic Kdm1a knockdown (Kdm1a-KD) in Eμ-TCL1A mice reduced leukemic burden and prolonged animal survival, accompanied by upregulated p53 and pro-apoptotic pathways. Genetic KDM1A depletion also affected milieu components (T-, stromal, monocytic cells), resulting in significant reductions of their capacity to support CLL cell survival and proliferation. Integrated analyses of differential global transcriptomes (RNA-seq) and H3K4me3 marks (ChIP-seq) in Eµ-TCL1A vs. iKdm1aKD;Eµ-TCL1A mice (confirmed in human CLL) implicate KDM1A as an oncogenic transcriptional repressor in CLL by altering histone methylation patterns with pronounced effects on defined cell death and motility pathways. Finally, pharmacologic KDM1A inhibition altered H3K4/9 target methylation and revealed marked anti-B-cell-leukemic synergisms. Overall, we established the pathogenic role and effector networks of KDM1A in CLL, namely via tumor-cell intrinsic mechanisms and impacts in cells of the microenvironment. Our data also provide rationales to further investigate therapeutic KDM1A targeting in CLL.

T-prolymphocytic leukemia (T-PLL) is a rare and mature T-cell malignancy with characteristic chemotherapy-refractory behavior and a poor prognosis. Molecular concepts of disease development have been restricted to protein-coding genes. Recent global microRNA (miR) expression profiles revealed miR-141-3p and miR-200c-3p (miR-141/200c) as two of the highest differentially expressed miRs in T-PLL cells versus healthy donor-derived T cells. Furthermore, miR-141/200c expression separates T-PLL cases into two subgroups with high and low expression, respectively. Evaluating the potential pro-oncogenic function of miR-141/200c deregulation, we discovered accelerated proliferation and reduced stress-induced cell death induction upon stable miR-141/200c overexpression in mature T-cell leukemia/lymphoma lines. We further characterized a miR-141/200c-specific transcriptome involving the altered expression of genes associated with enhanced cell cycle transition, impaired DNA damage responses, and augmented survival signaling pathways. Among those genes, we identified STAT4 as a potential miR-141/200c target. Low STAT4 expression (in the absence of miR-141/200c upregulation) was associated with an immature phenotype of primary T-PLL cells as well as with a shortened overall survival of T-PLL patients. Overall, we demonstrate an aberrant miR-141/200c-STAT4 axis, showing for the first time the potential pathogenetic implications of a miR cluster, as well as of STAT4, in the leukemogenesis of this orphan disease.

T-prolymphocytic leukemia (T-PLL) is a rare, aggressive T-cell malignancy with poor outcomes and an urgent need for new therapeutic approaches. Integrating genomic data and new transcriptomic profiling, we identified recurrent JAK/STAT mutations (predominantly in JAK3 and STAT5B) as hallmarks in a cohort of 335 T-PLL cases. In line, transcriptomic and protein analyses revealed constitutive JAK/STAT activation in virtually all samples. Consequently, we explored the anti-leukemic potential of dual STAT3/STAT5 non-PROTAC degraders in T-PLL, with JPX-1244 as our lead substance. JPX-1244 efficiently and selectively induced cell death in primary T-PLL samples, including those resistant to conventional therapies, by blocking STAT3 and STAT5 phosphorylation and by inducing their degradation. The extent of STAT3/STAT5 degradation directly correlated with cytotoxicity. RNA-sequencing confirmed the treatment-related downregulation of STAT5 target genes. While JAK/STAT mutations did not predict responses to pharmacologic STAT3/STAT5 degradation, elevated expression of TOX, PAK6, and SPINT1 were associated with drug sensitivity. In subsequent combination screenings, cladribine, venetoclax, and azacytidine emerged as most effective combination partners of STAT3/STAT5 degraders, even in low-responding T-PLL samples, all synergistically reducing STAT5 phosphorylation. These findings highlight dual STAT3/STAT5 inhibition, particularly in combination with hypomethylating and BCL2-targeting agents, as a promising interventional approach in T-PLL, warranting further investigation.