The role of Bruton's tyrosine kinase in the immune system and disease.

Bruton's tyrosine kinase (BTK) is a TEC kinase with a multifaceted role in B-cell biology and function, highlighted by its position as a critical component of the B-cell receptor signalling pathway. Due to its role as a therapeutic target in several haematological malignancies including chronic lymphocytic leukaemia, BTK has been gaining tremendous momentum in recent years. Within the immune system, BTK plays a part in numerous pathways and cells beyond B cells (i.e. T cells, macrophages). Not surprisingly, BTK has been elucidated to be a driving factor not only in lymphoproliferative disorders but also in autoimmune diseases and response to infection. To extort this role, BTK inhibitors such as ibrutinib have been developed to target BTK in other diseases. However, due to rising levels of resistance, the urgency to develop new inhibitors with alternative modes of targeting BTK is high. To meet this demand, an expanding list of BTK inhibitors is currently being trialled. In this review, we synopsize recent discoveries regarding BTK and its role within different immune cells and pathways. Additionally, we discuss the broad significance and relevance of BTK for various diseases ranging from haematology and rheumatology to the COVID-19 pandemic. Overall, BTK signalling and its targetable nature have emerged as immensely important for a wide range of clinical applications. The development of novel, more specific and less toxic BTK inhibitors could be revolutionary for a significant number of diseases with yet unmet treatment needs.

Transgenic mice overexpressing arginase 1 in monocytic cell lineage are affected by lympho-myeloproliferative disorders and disseminated intravascular coagulation.

Arginase (ARG) is a metabolic enzyme present in two isoforms that hydrolyze l-arginine to urea and ornithine. In humans, ARG isoform 1 is also expressed in cells of the myeloid lineage. ARG activity promotes tumour growth and inhibits T lymphocyte activation. However, the two ARG transgenic mouse lines produced so far failed to show such effects. We have generated, in two different genetic backgrounds, transgenic mice constitutively expressing ARG1 under the control of the CD68 promoter in macrophages and monocytes. Both heterozygous and homozygous transgenic mice showed a relevant increase in mortality at early age, compared with wild-type siblings (67/267 and 48/181 versus 8/149, respectively, both P < 0.005). This increase was due to high incidence of haematologic malignancies, in particular myeloid leukaemia, myeloid dysplasia, lymphomas and disseminated intravascular coagulation (DIC), diseases that were absent in wild-type mice. Atrophy of lymphoid organs due to reduction in T-cell compartment was also detected. Our results indicate that ARG activity may participate in the pathogenesis of lymphoproliferative and myeloproliferative disorders, suggest the involvement of alterations of L-arginine metabolism in the onset of DIC and confirm a role for the enzyme in regulating T-cell homeostasis.

A phospholipase C-γ1-independent, RasGRP1-ERK-dependent pathway drives lymphoproliferative disease in linker for activation of T cells-Y136F mutant mice.

Mice expressing a germline mutation in the phospholipase C-γ1-binding site of linker for activation of T cells (LAT) show progressive lymphoproliferation and ultimately die at 4-6 mo age. The hyperactivated T cells in these mice show defective TCR-induced calcium flux but enhanced Ras/ERK activation, which is critical for disease progression. Despite the loss of LAT-dependent phospholipase C-γ1 binding and activation, genetic analysis revealed RasGRP1, and not Sos1 or Sos2, to be the major Ras guanine exchange factor responsible for ERK activation and the lymphoproliferative phenotype in these mice. Analysis of isolated CD4(+) T cells from LAT-Y136F mice showed altered proximal TCR-dependent kinase signaling, which activated a Zap70- and LAT-independent pathway. Moreover, LAT-Y136F T cells showed ERK activation that was dependent on Lck and/or Fyn, protein kinase C-θ, and RasGRP1. These data demonstrate a novel route to Ras activation in vivo in a pathological setting.

Interleukin-2-inducible T-cell kinase (ITK) deficiency - clinical and molecular aspects.

In patients with underlying immunodeficiency, Epstein-Barr virus (EBV) may lead to severe immune dysregulation manifesting as fatal mononucleosis, lymphoma, lymphoproliferative disease (LPD), lymphomatoid granulomatosis, hemophagocytic lymphohistiocytosis (HLH) and dysgammaglobulinemia. Several newly discovered primary immunodeficiencies (STK4, CD27, MAGT1, CORO1A) have been described in recent years; our group and collaborators were able to reveal the pathogenicity of mutations in the Interleukin-2-inducible T-cell Kinase (ITK) in a cohort of nine patients with most patients presenting with massive EBV B-cell lymphoproliferation. This review summarizes the clinical and immunological findings in these patients. Moreover, we describe the functional consequences of the mutations and draw comparisons with the extensively investigated function of ITK in vitro and in the murine model.

The importance of the Erk pathway in the development of linker for activation of T cells-mediated autoimmunity.

The ability of the transmembrane adaptor protein linker for activation of T cells (LAT) to regulate T cell development, activation, survival, and homeostasis depends upon phosphorylation of its multiple tyrosine residues. The mutation of tyrosine 136 on LAT abrogates its interaction with phospholipase C-γ1, causing severe ramifications on TCR-mediated signaling. Mice harboring this mutation, LATY136F mice, have significantly impaired thymocyte development; however, they rapidly develop a fatal lymphoproliferative disease marked by the uncontrolled expansion of Th2-skewed CD4(+) T cells, high levels of IgE and IgG1, and autoantibody production. In this study, we assessed the contribution of multiple signaling pathways in LATY136F disease development. The deletion of the critical signaling proteins Gads and RasGRP1 caused a further block in thymocyte development, but, over time, could not prevent CD4(+) T cell hyperproliferation. Also, restoring signaling through the NF-κB and NFAT pathways was unable to halt the development of disease. However, expression of a constitutively active Raf transgene enhanced lymphoproliferation, indicating a role for the Ras-MAPK pathway in LAT-mediated disease.

Syk-induced phosphatidylinositol-3-kinase activation in Epstein-Barr virus posttransplant lymphoproliferative disorder.

Posttransplant lymphoproliferative disorder (PTLD)-associated Epstein-Barr virus (EBV)+ B cell lymphomas are serious complications of solid organ and bone marrow transplantation. The EBV protein LMP2a, a B cell receptor (BCR) mimic, provides survival signals to virally infected cells through Syk tyrosine kinase. Therefore, we explored whether Syk inhibition is a viable therapeutic strategy for EBV-associated PTLD. We have shown that R406, the active metabolite of the Syk inhibitor fostamatinib, induces apoptosis and cell cycle arrest while decreasing downstream phosphatidylinositol-3'-kinase (PI3K)/Akt signaling in EBV+ B cell lymphoma PTLD lines in vitro. However, Syk inhibition did not inhibit or delay the in vivo growth of solid tumors established from EBV-infected B cell lines. Instead, we observed tumor growth in adjacent inguinal lymph nodes exclusively in fostamatinib-treated animals. In contrast, direct inhibition of PI3K/Akt significantly reduced tumor burden in a xenogeneic mouse model of PTLD without evidence of tumor growth in adjacent inguinal lymph nodes. Taken together, our data indicate that Syk activates PI3K/Akt signaling which is required for survival of EBV+ B cell lymphomas. PI3K/Akt signaling may be a promising therapeutic target for PTLD, and other EBV-associated malignancies.

Role of xenobiotic metabolism enzyme gene polymorphism in the formation of chemotherapy resistance in patients with chronic lymphoproliferative diseases.

Enzymes of the cytochrome P450 and GSTP1 families play a pivotal role in the metabolism of a wide variety of antitumor drugs and polymorphisms of genes encoding for metabolizing enzymes can affect drug efficacy and toxicity. We studied the associations between functionally significant gene polymorphisms CYP2C8, CYP2C9, CYP2C19, CYP3A5, and GSTP1 and clinical response to chemotherapy in patients with chronic lymphoproliferative diseases. Significant correlations with chemotherapy resistance were observed for CYP2C8 3 (OR=7.05; CI 95%=1.76-29.55) and CYP2C9 2 polymorphisms (OR=4.1; CI 95%=1.03-16.81). No significant association between chemotherapy resistance and other examined polymorphisms were found.

IL-2-inducible T-cell kinase deficiency with pulmonary manifestations due to disseminated Epstein-Barr virus infection.

IL-2-inducible T-cell kinase (ITK) deficiency is a rare inherited immunodeficiency disease characterized by homozygous mutations in the ITK gene and the inability to control Epstein-Barr virus (EBV) infection leading to EBV-associated lymphoproliferative disorders of B cell origin. Many aspects of its clinical presentation and immunologic phenotype are still unclear to clinicians. We report on a 14-year-old female patient with complaints of an 8-month history of cough and fever. Imaging studies revealed diffuse pulmonary nodules and mediastinal lymphadenopathy. Transbronchial lung biopsy showed nonmalignant polyclonal B cell proliferation. High titers of EBV DNA were detected by PCR analysis in bronchoalveolar lavage fluid, bone marrow, and blood. Genomic analysis revealed a homozygous single base pair deletion in exon 5 of the ITK gene (c.468delT) in this patient. Treatment with rituximab (anti-CD20 mab) resulted in complete clinical remission with resolution of pulmonary lesions and a negative EBV titer in serum. All patients with EBV-associated lymphoproliferative disorders should be analyzed for mutations in ITK.

Caspase-8 deficiency in T cells leads to a lethal lymphoinfiltrative immune disorder.

Caspase-8 is best known for its cell death function via death receptors. Recent evidence indicates that caspase-8 also has nonapoptotic functions. Caspase-8 deficiency is associated with pathologies that are unexpected for a proapoptotic molecule, such as abrogation of activation-induced lymphocyte proliferation, perturbed immune homeostasis, and immunodeficiency. In this study, we report the long-term physiological consequences of T cell-specific deletion of caspase-8 (tcasp8-/-). We show that tcasp8-/- mice develop an age-dependent lethal lymphoproliferative and lymphoinfiltrative immune disorder characterized by lymphoadenopathy, splenomegaly, and accumulation of T cell infiltrates in the lungs, liver, and kidneys. Peripheral casp8-/- T cells manifest activation marker up-regulation and are proliferating in the absence of any infection or stimulation. We also provide evidence suggesting that this immune disorder is different from the autoimmune lymphoproliferative syndrome. Interestingly, the condition described in tcasp8-/- mice manifests features consistent with the disorder described in humans with Caspase-8 deficiency. These findings suggest that tcasp8-/- mice may serve as an animal model to evaluate Caspase-8-deficient patient prognosis and therapy. Overall, our study uncovers novel in vivo functions for caspase-8 in immune regulation.

Constitutive JAK3 activation induces lymphoproliferative syndromes in murine bone marrow transplantation models.

The tyrosine kinase JAK3 plays a well-established role during normal lymphocyte development and is constitutively phosphorylated in several lymphoid malignancies. However, its contribution to lymphomagenesis remains elusive. In this study, we used the newly identified activating JAK3A572V mutation to elucidate the effect of constitutive JAK3 signaling on murine lymphopoiesis. In a bone marrow transplantation model, JAK3A572V induces an aggressive, fatal, and transplantable lymphoproliferative disorder characterized by the expansion of CD8(+)TCRalphabeta(+)CD44(+)CD122(+)Ly-6C(+) T cells that closely resemble an effector/memory T-cell subtype. Compared with wild-type counterparts, these cells show increased proliferative capacities in response to polyclonal stimulation, enhanced survival rates with elevated expression of Bcl-2, and increased production of interferon-gamma (IFNgamma) and tumor necrosis factor-alpha (TNFalpha), correlating with enhanced cytotoxic abilities against allogeneic target cells. Of interest, the JAK3A572V disease is epidermotropic and produces intraepidermal microabscesses. Taken together, these clinical features are reminiscent of those observed in an uncommon but aggressive subset of CD8(+) human cutaneous T-cell lymphomas (CTCLs). However, we also observed a CD4(+) CTCL-like phenotype when cells are transplanted in an MHC-I-deficient background. These data demonstrate that constitutive JAK3 activation disrupts T-cell homeostasis and induces lymphoproliferative diseases in mice.

Angiomyomatous hamartoma of lymph nodes, revisited: clinicopathologic study of 21 cases, emphasizing its distinction from lymphangioleiomyomatosis of lymph nodes.

Angiomyomatous hamartoma of lymph nodes (AMH-LN) is an uncommon benign proliferation of smooth muscle, blood vessels, collagenous stroma, and adipocytes, most commonly affecting inguinal LN. A similar constellation of cell types constitutes various members of the perivascular epithelioid cell tumor (PEComa) family, including lymphangioleiomyomatosis (LAM), which can involve LN in women. Because some LN-LAM patients have tuberous sclerosis complex and/or other PEComa family lesions, it is clinically relevant to distinguish LN-LAM from AMH-LN. Given their similar features, however, the possibility that AMH-LN is a morphologic variant of LN-LAM merits inquiry. The dual melanocytic and myoid immunophenotype distinguishes the PEComa family from its mimics. Cathepsin K has recently emerged as a more sensitive marker for the PEComa family than HMB-45, which can be weak and focal, but cathepsin K has not been studied in AMH-LN. This study evaluated 21 AMH-LNs for clinical, morphologic, and immunophenotypic features of LN-LAM. None (0/21) had tuberous sclerosis complex or PEComas. Thirteen (62%) were male, unlike LN-LAM, which is restricted to women. All cases exhibited intraparenchymal proliferation of variable-sized, thick-walled blood vessels within collagenous stroma containing a sparse to focally cellular population of haphazardly distributed smooth muscle cells. Admixed adipocytes were commonly present. None exhibited classical features of LN-LAM such as subcapsular localization, extranodal extension, intralymphatic growth, compact nests, branching lymphatic channels, plump cell shape, or foamy/clear cytoplasm. None exhibited any staining for cathepsin K, HMB-45, or microphthalmia transcription factor. There is no clinical, morphologic, or immunohistochemical evidence to suggest that AMH-LN is a variant of LN-LAM.

Poly(A) polymerase activity in murine serum. Elevation in animals with proliferative changes.

Sera of normal rats contain polynucleotide adenylyltransferase [poly(A) polymerase] activity. The enzymatic activity has been optimized with regard to primer concentration, ion requirements, kinetics, and protein. Results based on inclusion of inhibitors in the assay system show that the enzyme is poly(A) polymerase. High levels of the enzymatic activity were prevalent in sera of (a) BUF/SimfBR rats bearing sc transplanted hepatomas; (b) Sprague-Dawley rats with hepatoma cells grown in ascites; (c) partially hepatectomized Sprague-Dawley rats; and (d) MRL/lpr mice, which are in a massive lymphoproliferative autoimmune state.

Thymidine kinase isoenzymes in human malignant lymphoma.

The activities of thymidine kinase (TK) isoenzyme 1 and 2 were examined in extracts of human benign or malignant lymphoid tissue and correlated with degrees of morphological differentiation. TK2 activity occurred in peripheral blood lymphocytes of normal individuals, patients with chronic lymphocytic leukemia, or solid lymphoid tissue, exhibiting either nonneoplastic histological findings or those of diffuse well-differentiated lymphocytic lymphoma. TK1 activity occurred in solid, non-Hodgkin's lymphoma tissue, exhibiting lesser degrees of cellular differentiation, or in peripheral blood lymphocytes of patients with clinical aggressive chronic lymphocytic leukemia or lymphosarcoma leukemia. In non-Hodgkin's lymphoma tissue, the range of TK1 activities correlated broadly with the Rappaport classification, with higher values occurring in tissue exhibiting changes of diffuse poorly differentiated lymphocytic lymphoma or diffuse histiocytic lymphoma.

Down-regulation of regulatory subunit type 1A of protein kinase A leads to endocrine and other tumors.

Mutations of the human type Ialpha regulatory subunit (RIalpha) of cyclic AMP-dependent protein kinase (PKA; PRKAR1A) lead to altered kinase activity, primary pigmented nodular adrenocortical disease, and tumors of the thyroid and other tissues. To bypass the early embryonic lethality of Prkar1a(-/-) mice, we established transgenic mice carrying an antisense transgene for Prkar1a exon 2 (X2AS) under the control of a tetracycline-responsive promoter. Down-regulation of Prkar1a by up to 70% was achieved in transgenic mouse tissues and embryonic fibroblasts, with concomitant changes in kinase activity and increased cell proliferation, respectively. Mice developed thyroid follicular hyperplasia and adenomas, adrenocortical hyperplasia, and other features reminiscent of primary pigmented nodular adrenocortical disease, histiocytic and epithelial hyperplasias, lymphomas, and other mesenchymal tumors. These were associated with allelic losses of the mouse chromosome 11 Prkar1a locus, an increase in total type II PKA activity, and higher RIIbeta protein levels. This mouse provides a novel, useful tool for the investigation of cyclic AMP, RIalpha, and PKA functions and confirms the critical role of Prkar1a in tumorigenesis in endocrine and other tissues.

Coexistence of lymphoproliferative and myeloproliferative neoplasms with simultaneous CALR and JAK2 V617F mutations.

BACKGROUND: Hematopoietic malignancies are a group of blood cell disorders characterized by abnormal hematopoietic proliferation. OBJECTIVE: The identification of specific clinicopathologic characteristics and tumor-related gene status provides critical information on potential therapeutic targets. METHODS: The specimens were tested with immunohistochemistry, flow cytometry, RT-PCR and fragment analysis. RESULTS: In this study, a patient with a long history of tobacco use was reported with a diagnosis of simultaneous low-grade B-cell lymphoproliferative disorder (LPD) and myeloproliferative neoplasm (MPN). Mutational analysis revealed that JAK2 V617F mutation and CALR mutation with 52bp deletion were present in this patient. CONCLUSION: These results suggest that lymphoproliferative and myeloproliferative neoplasms may coexist, although the pathogenetic mechanism of coexisting hematologic requires further investigation. Additionally, the data indicate that JAK2 V617F and CALR mutations are not mutually exclusive and the actual frequency of simultaneous JAK2 V617F and CALR mutations is unknown. Whether the coexistence of these mutations imposes any biological or clinical significance awaits further investigation.

Deregulated expression of HDAC9 in B cells promotes development of lymphoproliferative disease and lymphoma in mice.

Histone deacetylase 9 (HDAC9) is expressed in B cells, and its overexpression has been observed in B-lymphoproliferative disorders, including B-cell non-Hodgkin lymphoma (B-NHL). We examined HDAC9 protein expression and copy number alterations in primary B-NHL samples, identifying high HDAC9 expression among various lymphoma entities and HDAC9 copy number gains in 50% of diffuse large B-cell lymphoma (DLBCL). To study the role of HDAC9 in lymphomagenesis, we generated a genetically engineered mouse (GEM) model that constitutively expressed an HDAC9 transgene throughout B-cell development under the control of the immunoglobulin heavy chain (IgH) enhancer (Eµ). Here, we report that the Eµ-HDAC9 GEM model develops splenic marginal zone lymphoma and lymphoproliferative disease (LPD) with progression towards aggressive DLBCL, with gene expression profiling supporting a germinal center cell origin, as is also seen in human B-NHL tumors. Analysis of Eµ-HDAC9 tumors suggested that HDAC9 might contribute to lymphomagenesis by altering pathways involved in growth and survival, as well as modulating BCL6 activity and p53 tumor suppressor function. Epigenetic modifications play an important role in the germinal center response, and deregulation of the B-cell epigenome as a consequence of mutations and other genomic aberrations are being increasingly recognized as important steps in the pathogenesis of a variety of B-cell lymphomas. A thorough mechanistic understanding of these alterations will inform the use of targeted therapies for these malignancies. These findings strongly suggest a role for HDAC9 in B-NHL and establish a novel GEM model for the study of lymphomagenesis and, potentially, preclinical testing of therapeutic approaches based on histone deacetylase inhibitors.

Telomeres and telomerase in hematologic neoplasia.

Normal hematopoietic cells express telomerase activity, however the presence of telomerase does not necessarily imply stable and thus unchanging telomere length. Gradual telomere loss with aging and rapid cycling of hematopoietic stem cells might contribute to immunosenescence, exhausted hematopoiesis, and increased likelihood of malignant transformation. In leukemias and lymphomas, telomere length may reflect the cellular proliferative history, prior to immortalization. The level of telomerase activity is generally influenced by the fraction of cells in the proliferative pool. Shortened telomeres and high telomerase activity almost always correlates with disease severity in hematologic neoplasias such as relapsed leukemia and high-grade lymphomas, indicating that measurement of telomere length and telomerase activity might be useful to monitor disease condition. Since the mode of action of telomerase inhibitors may require telomeric shortening before induction of apoptosis, anti-telomerase therapy might be helpful for adjuvant therapy following conventional chemotherapy, in vitro purging of neoplastic cells in stem cell transplantation, and treating minimal residual disease. Some promising areas of tissue engineering include rejuvenation of hematopoietic stem cells for improving stem cell transplants or enhancing general immunity for older patients.

Monocyte esterase? A factor involved in the pathogenesis of lymphoproliferative neoplasia.

Monocyte esterase activity was studied in 1,000 doctor-attending patients with normal hematological indices and in 56 patients with non-Hodgkin's lymphoma (NHL) or B chronic lymphocytic leukemia (CLL). The incidence of esterase deficiency was significantly greater in the NHL-CLL patients (7.1%) than in the population group (1.7%; p less than 0.05). In the NHL-CLL group, study of the families showed the esterase deficiency to be a familial characteristic. We postulate that the presence of the anomaly may be either a factor predisposing to the development of the NHL or CLL or a factor indicating a predisposition to these disorders.

Evidence of abnormality of lymphocyte uroporphyrinogen synthase in family members of patients with lymphoproliferative diseases.

Patients with active lymphoproliferative diseases (LPD) were shown to have high activity of lymphocyte uroporphyrinogen synthase (L-UROS), the enzyme which converts porphobilinogen to uroporphyrinogen. The mean L-UROS activity of 64 first-degree relatives of patients with LPD was significantly higher than that of a control group and 45% of these relatives had pathological values of L-UROS. L-UROS activity was also determined in the spouses of 2 patients and was pathologically elevated in both. The pattern of pathological values among family members may indicate the presence of a communicable agent.