A critical role for DAP10 and DAP12 in CD8+ T cell-mediated tissue damage in large granular lymphocyte leukemia

Pooled screening for CAR function identifies novel IL-13Rα2-targeted CARs for treatment of glioblastoma

BACKGROUND

Chimeric antigen receptor (CAR) therapies have demonstrated potent efficacy in treating B-cell malignancies, but have yet to meaningfully translate to solid tumors. Nonetheless, they are of particular interest for the treatment of glioblastoma, which is an aggressive form of brain cancer with few effective therapeutic options, due to their ability to cross the highly selective blood-brain barrier.

METHODS

Here, we use our pooled screening platform, CARPOOL, to expedite the discovery of CARs with antitumor functions necessary for solid tumor efficacy. We performed selections in primary human T cells expressing a library of 1.3×106 third generation CARs targeting IL-13Rα2, a cancer testis antigen commonly expressed in glioblastoma. Selections were performed for cytotoxicity, proliferation, memory formation, and persistence on repeated antigen challenge.

RESULTS

Each enriched CAR robustly produced the phenotype for which it was selected, and one enriched CAR triggered potent cytotoxicity and long-term proliferation on in vitro tumor rechallenge. It also showed significantly improved persistence and comparable tumor control in a microphysiological human in vitro model and a xenograft model of human glioblastoma, but also demonstrated increased off-target recognition of IL-13Rα1.

CONCLUSION

Taken together, this work demonstrates the utility of extending CARPOOL to diseases beyond hematological malignancies and represents the largest exploration of signaling combinations in human primary cells to date.

Group 5 Pulmonary Hypertension Associated With T-Cell Large Granular Lymphocytic Leukemia: Hemodynamics and Treatment

Group 5 pulmonary hypertension (PH) encompasses diverse diseases, with a few cases linking it to T-cell large granular lymphocytic (LGL) leukemia. We report a case of a 76-year-old woman, diagnosed with LGL leukemia and concomitant PH, treated with oral triple pulmonary arterial hypertension (PAH) therapy. She initially presented with dyspnea on exertion; evaluation revealed severe precapillary PH. Implementing cyclophosphamide for leukemia along with tadalafil and macitentan for PH led to sustained symptomatic and hemodynamic improvement for over 3 years. At that time, deterioration in PH prompted the addition of selexipag, resulting in sustained clinical improvement for an additional 5 years. This case exemplifies the potential for sustained benefits of PAH therapy in leukemia-associated PH and highlights the need for continued research on the mechanistic relationship between LGL leukemia and PH, with the hope of identifying new management strategies.

Pooled screening for CAR function identifies novel IL13Rα2-targeted CARs for treatment of glioblastoma

Chimeric antigen receptor therapies have demonstrated potent efficacy in treating B cell malignancies, but have yet to meaningfully translate to solid tumors. Here, we utilize our pooled screening platform, CARPOOL, to expedite the discovery of CARs with anti-tumor functions necessary for solid tumor efficacy. We performed selections in primary human T cells expressing a library of 1.3×10 6 3 rd generation CARs targeting IL13Rα2, a cancer testis antigen commonly expressed in glioblastoma. Selections were performed for cytotoxicity, proliferation, memory formation, and persistence upon repeated antigen challenge. Each enriched CAR robustly produced the phenotype for which it was selected, and one enriched CAR triggered potent cytotoxicity and long-term proliferation upon in vitro tumor rechallenge. It also showed significantly improved persistence and comparable antigen-specific tumor control in a microphysiological human in vitro model and a xenograft model of human glioblastoma. Taken together, this work demonstrates the utility of extending CARPOOL to diseases beyond hematological malignancies and represents the largest exploration of signaling combinations in human primary cells to date.

Defining a TCF1-expressing progenitor allogeneic CD8+ T cell subset in acute graft-versus-host disease

Graft-versus-host disease (GvHD) is a severe complication of hematopoietic stem cell transplantation driven by activated allogeneic T cells. Here, we identify a distinct subset of T cell factor-1 (TCF1)+ CD8+ T cells in mouse allogeneic and xenogeneic transplant models of acute GvHD. These TCF1+ cells exhibit distinct characteristics compared to TCF1- cells, including lower expression of inhibitory receptors and higher expression of costimulatory molecules. Notably, the TCF1+ subset displays exclusive proliferative potential and could differentiate into TCF1- effector cells upon antigenic stimulation. Pathway analyses support the role of TCF1+ and TCF1- subsets as resource cells and effector cells, respectively. Furthermore, the TCF1+ CD8+ T cell subset is primarily present in the spleen and exhibits a resident phenotype. These findings provide insight into the differentiation of allogeneic and xenogeneic CD8+ T cells and have implications for the development of immunotherapeutic strategies targeting acute GvHD.

Large granular lymphocyte leukemia: An indolent clonal proliferative disease associated with an array of various immunologic disorders

Large granular lymphocyte leukemia (LGLL) is a chronic lymphoproliferative disorder characterized by the proliferation of T or NK cytotoxic cells in the peripheral blood, the spleen and the bone marrow. Neutropenia leading to recurrent infections represents the main manifestation of LGLL. One specificity of LGLL is its frequent association with auto-immune disorders, among them first and foremost rheumatoid arthritis, and other hematologic diseases, including pure red cell aplasia and bone marrow failure. The large spectrum of manifestations and the classical indolent course contribute to the diagnosis difficulties and the frequency of underdiagnosed cases. Of importance, the dysimmune manifestations disappear with the treatment of LGLL as the blood cell counts normalize, giving a strong argument for a pathological link between the two entities. The therapeutic challenge results from the high rate of relapses following the first line of immunosuppressive drugs. New targeted agents, some of which are currently approved in autoimmune diseases, appear to be relevant therapeutic strategies to treat LGLL, by targeting key activated pathways involved in the pathogenesis of the disease, including JAK-STAT signaling.

Florid Pulmonary Mycobacterium avium-intracellulare Infection in a Patient With Large Granular Lymphocytic (LGL) Leukemia on Chronic Cyclophosphamide

Large granular lymphocytic (LGL) leukemia is a rare form of incurable chronic leukemia frequently complicated by life-threatening cytopenias. The less common NK-cell variant of this disorder poses a diagnostic challenge and its etiologic basis is poorly understood. Here we present the case of an elderly man diagnosed with LGL leukemia after presenting with severe Coombs-negative hemolytic anemia, who had a robust durable response to oral cyclophosphamide. Close to two years after initial diagnosis, he developed a florid Mycobacterium avium-intracellulare (MAI) infection of the lungs. We discuss the clinical and pathologic features of this case, highlighting aspects common to this disorder and areas of clinical uncertainty. We hope to both raise awareness of the risk for pulmonary MAI infection in patients treated with lymphodepleting drugs and to motivate the prospective evaluation of strategies to prevent opportunistic infections in LGL leukemia.

Constitutively Activated DAP12 Induces Functional Anti-Tumor Activation and Maturation of Human Monocyte-Derived DC

Dendritic cells (DCs) are professional antigen presenting cells with a great capacity for cross-presentation of exogenous antigens from which robust anti-tumor immune responses ensue. However, this function is not always available and requires DCs to first be primed to induce their maturation. In particular, in the field of DC vaccine design, currently available methodologies have been limited in eliciting a sustained anti-tumor immune response. Mechanistically, part of the maturation response is influenced by the presence of stimulatory receptors relying on ITAM-containing activating adaptor molecules like DAP12, that modulates their function. We hypothesize that activating DAP12 in DC could force their maturation and enhance their potential anti-tumor activity for therapeutic intervention. For this purpose, we developed constitutively active DAP12 mutants that can promote activation of monocyte-derived DC. Here we demonstrate its ability to induce the maturation and activation of monocyte-derived DCs which enhances migration, and T cell stimulation in vitro using primary human cells. Moreover, constitutively active DAP12 stimulates a strong immune response in a murine melanoma model leading to a reduction of tumor burden. This provides proof-of-concept for investigating the pre-activation of antigen presenting cells to enhance the effectiveness of anti-tumor immunotherapies.

Dysfunction of immune system in the development of large granular lymphocyte leukemia

OBJECTIVES

Large granular lymphocyte (LGL) leukemia is a rare type of lymphoproliferative disease caused by clonal antigenic stimulation of T cells and natural killer (NK) cells.

METHODS

In this review, we focus on the current knowledge of the immunological dysfunctions associated with LGL leukemia and the associated disorders coexistent with this disease. Novel therapeutic options targeting known molecular mechanisms are also discussed.

RESULTS AND DISCUSSION

The pathogenesis of LGL leukemia involves the accumulation of gene mutations, dysregulated signaling pathways and immunological dysfunction. Mounting evidence indicated that dysregulated survival signaling pathways may be responsible for the immunological dysfunction in LGL leukemia including decreased numbers of neutrophils, dysregulated signal transduction of NK cells, abnormal B-cells, aberrant CD8+ T cells, as well as autoimmune and hematological abnormalities.

CONCLUSION

A better understanding of the immune dysregulation triggered by LGL leukemia will be beneficial to explore the pathogenesis and potential therapeutic targets for this disease.

Novel therapeutic approach to improve hematopoiesis in low risk MDS by targeting MDSCs with the Fc-engineered CD33 antibody BI 836858

We recently reported that the accumulation of myeloid-derived suppressor cells (MDSC), defined as CD33+HLA-DR-Lin-, has a direct role in the pathogenesis of myelodysplastic syndrome (MDS). In particular, CD33 is strongly expressed in MDSC isolated from patients with MDS where it has an important role in MDSC-mediated hematopoietic suppressive function through its activation by S100A9. Therefore, we tested whether blocking this interaction with a fully human, Fc-engineered monoclonal antibody against CD33 (BI 836858) suppresses CD33-mediated signal transduction and improves the bone marrow microenvironment in MDS. We observed that BI 836858 can reduce MDSC by antibody-dependent cellular cytotoxicity, which correlated with increases in granule mobilization and cell death. BI 836858 can also block CD33 downstream signaling preventing immune-suppressive cytokine secretion, which correlates with a significant increase in the formation of CFU-GM and BFU-E colonies. Activation of the CD33 pathway can cause reactive oxygen species (ROS)-induced genomic instability but BI 836858 reduced both ROS and the levels of double strand breaks and adducts (measured by comet assay and γH2AX). This work provides the ground for the development of a novel group of therapies for MDS aimed at MDSC and their disease-promoting properties with the goal of improving hematopoiesis in patients.

Small RNA Sequencing Uncovers New miRNAs and moRNAs Differentially Expressed in Normal and Primary Myelofibrosis CD34+ Cells

Myeloproliferative neoplasms (MPN) are chronic myeloid cancers thought to arise at the level of CD34+ hematopoietic stem/progenitor cells. They include essential thrombocythemia (ET), polycythemia vera (PV) and primary myelofibrosis (PMF). All can progress to acute leukemia, but PMF carries the worst prognosis. Increasing evidences indicate that deregulation of microRNAs (miRNAs) might plays an important role in hematologic malignancies, including MPN. To attain deeper knowledge of short RNAs (sRNAs) expression pattern in CD34+ cells and of their possible role in mediating post-transcriptional regulation in PMF, we sequenced with Illumina HiSeq2000 technology CD34+ cells from healthy subjects and PMF patients. We detected the expression of 784 known miRNAs, with a prevalence of miRNA up-regulation in PMF samples, and discovered 34 new miRNAs and 99 new miRNA-offset RNAs (moRNAs), in CD34+ cells. Thirty-seven small RNAs were differentially expressed in PMF patients compared with healthy subjects, according to microRNA sequencing data. Five miRNAs (miR-10b-5p, miR-19b-3p, miR-29a-3p, miR-379-5p, and miR-543) were deregulated also in PMF granulocytes. Moreover, 3’-moR-128-2 resulted consistently downregulated in PMF according to RNA-seq and qRT-PCR data both in CD34+ cells and granulocytes. Target predictions of these validated small RNAs de-regulated in PMF and functional enrichment analyses highlighted many interesting pathways involved in tumor development and progression, such as signaling by FGFR and DAP12 and Oncogene Induced Senescence. As a whole, data obtained in this study deepened the knowledge of miRNAs and moRNAs altered expression in PMF CD34+ cells and allowed to identify and validate a specific small RNA profile that distinguishes PMF granulocytes from those of normal subjects. We thus provided new information regarding the possible role of miRNAs and, specifically, of new moRNAs in this disease.

Inactivation of DAP12 in PMN inhibits TREM1-mediated activation in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by dysregulated and chronic systemic inflammatory responses that affect the synovium, bone, and cartilage causing damage to extra-articular tissue. Innate immunity is the first line of defense against invading pathogens and assists in the initiation of adaptive immune responses. Polymorphonuclear cells (PMNs), which include neutrophils, are the largest population of white blood cells in peripheral blood and functionally produce their inflammatory effect through phagocytosis, cytokine production and natural killer-like cytotoxic activity. TREM1 (triggering receptor expressed by myeloid cells) is an inflammatory receptor in PMNs that signals through the use of the intracellular activating adaptor DAP12 to induce downstream signaling. After TREM crosslinking, DAP12's tyrosines in its ITAM motif get phosphorylated inducing the recruitment of Syk tyrosine kinases and eventual activation of PI3 kinases and ERK signaling pathways. While both TREM1 and DAP12 have been shown to be important activators of RA pathogenesis, their activity in PMNs or the importance of DAP12 as a possible therapeutic target have not been shown. Here we corroborate, using primary RA specimens, that isolated PMNs have an increased proportion of both TREM1 and DAP12 compared to normal healthy control isolated PMNs both at the protein and gene expression levels. This increased expression is highly functional with increased activation of ERK and MAPKs, secretion of IL-8 and RANTES and cytotoxicity of target cells. Importantly, based on our hypothesis of an imbalance of activating and inhibitory signaling in the pathogenesis of RA we demonstrate that inhibition of the DAP12 signaling pathway inactivates these important inflammatory cells.

Pathology of T-cell lymphomas: diagnosis and biomarker discovery

T-cell lymphomas are a group of predominantly rare hematologic malignancies that tend to recapitulate different stages of T-cell development, in a similar way that B-cell lymphomas do. As opposed to B-cell lymphomas, the understanding of the biology and the classification of T-cell lymphomas are somewhat rudimentary, and numerous entities are still included as 'provisional categories' in the World Health Classification of hematolopoietic malignancies. A relevant and useful classification of these disorders have been difficult to accomplish because of the rarity nature of them, the relative lack of understanding of the molecular pathogenesis, and their morphological and immunophenotypical complexity. Overall, T-cell lymphomas represent only 15 % of all non-Hodgkin lymphomas. This review is focused on addressing the current status of the categories of mature T-cell leukemias and lymphomas (nodal and extranodal) using an approach that incorporates histopathology, immunophenotype, and molecular understanding of the nature of these disorders, using the same philosophy of the most recent revised WHO classification of hematopoietic malignancies.

Vasculitis associated with large granular lymphocyte (LGL) leukemia: presentation and treatment outcomes of 11 cases

OBJECTIVE

The association between vasculitis and large granular lymphocyte (LGL) leukemia has rarely been reported or investigated. Thus, we assessed the clinical and biological phenotypes of LGL leukemia associated with vasculitis.

RESULTS

We studied a series of 11 patients displaying LGL leukemia associated with vasculitis (LAV). The mean age at diagnosis of LGL leukemia was 60.3 years; there were nine women and two men. The mean follow-up period was 45 months. The main LGL lineage was T-LGL (10 patients), and only one NK-LGL was identified. Clinical and biological features of T-LGL leukemia were compared with those from the 2009 French T-LGL registry. We did not find any relevant differences except that patients with LAV were predominantly female (p < 0.05). The most frequently observed vasculitis was cryoglobulinemia (n = 5). Three patients presented with cutaneous leukocytoclastic angiitis, two patients had ANCA-negative microscopic polyangiitis, and one patient had giant cell arteritis. The main clinical features involved the skin, e.g., purpura (91%), arthralgia (37%), peripheral neuritis (27%), and renal glomerulonephritis (18%). The most frequent histologic finding was leucocytoclastic vasculitis (54%). The rate of complete remission was high; i.e., 80%. A minority of patients had a vasculitis relapse (27%). Three patients (27%) died; one death was related to LGL leukemia (acute infection) and the two other deaths were related to vasculitis (both with heart failure).

CONCLUSION

We conclude that vasculitis is overrepresented in the population of LGL patients, LAV predominantly affects women, vasculitis preferentially affects the small vessels, and LAV has high rate of complete response.

Induction of myelodysplasia by myeloid-derived suppressor cells

Myelodysplastic syndromes (MDS) are age-dependent stem cell malignancies that share biological features of activated adaptive immune response and ineffective hematopoiesis. Here we report that myeloid-derived suppressor cells (MDSC), which are classically linked to immunosuppression, inflammation, and cancer, were markedly expanded in the bone marrow of MDS patients and played a pathogenetic role in the development of ineffective hematopoiesis. These clonally distinct MDSC overproduce hematopoietic suppressive cytokines and function as potent apoptotic effectors targeting autologous hematopoietic progenitors. Using multiple transfected cell models, we found that MDSC expansion is driven by the interaction of the proinflammatory molecule S100A9 with CD33. These 2 proteins formed a functional ligand/receptor pair that recruited components to CD33’s immunoreceptor tyrosine-based inhibition motif (ITIM), inducing secretion of the suppressive cytokines IL-10 and TGF-β by immature myeloid cells. S100A9 transgenic mice displayed bone marrow accumulation of MDSC accompanied by development of progressive multilineage cytopenias and cytological dysplasia. Importantly, early forced maturation of MDSC by either all-trans-retinoic acid treatment or active immunoreceptor tyrosine-based activation motif–bearing (ITAM-bearing) adapter protein (DAP12) interruption of CD33 signaling rescued the hematologic phenotype. These findings indicate that primary bone marrow expansion of MDSC driven by the S100A9/CD33 pathway perturbs hematopoiesis and contributes to the development of MDS.

Allospecific rejection of MHC class I-deficient bone marrow by CD8 T cells

Avoidance of long-term immunosuppression is a desired goal in organ transplantation. Mixed chimerism offers a promising approach to tolerance induction, and we have aimed to develop low-toxicity, nonimmunodepleting approaches to achieve this outcome. In a mouse model achieving fully MHC-mismatched allogeneic bone marrow engraftment with minimal conditioning (3 Gy total body irradiation followed by anti-CD154 and T cell-depleted allogeneic bone marrow cells), CD4 T cells in the recipient are required to promote tolerance of preexisting alloreactive recipient CD8 T cells and thereby permit chimerism induction. We now demonstrate that mice devoid of CD4 T cells and NK cells reject MHC Class I-deficient and Class I/Class II-deficient marrow in a CD8 T cell-dependent manner. This rejection is specific for donor alloantigens, since recipient hematopoiesis is not affected by donor marrow rejection and MHC Class I-deficient bone marrow that is syngeneic to the recipient is not rejected. Recipient CD8 T cells are activated and develop cytotoxicity against MHC Class I-deficient donor cells in association with rejection. These data implicate a novel CD8 T cell-dependent bone marrow rejection pathway, wherein recipient CD8 T cells indirectly activated by donor alloantigens promote direct killing, in a T cell receptor-independent manner, of Class I-deficient donor cells.

Large granular lymphocytosis during dasatinib therapy

Dasatinib is a second generation tyrosine kinase inhibitor (TKI) approved for clinical use in patients with imatinib-resistant chronic myeloid leukemia (CML) and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL). Large granular lymphocytes (LGLs) are medium to large cells with eccentric nuclei and abundant cytoplasm with coarse azurophilic granules. LGL lymphocytosis is caused by a proliferation of cytotoxic (CD8+) T cells and/or NK cells. In a proportion of CML and Ph(+) ALL patients, there is a significant expansion of LGLs during dasatinib therapy. LGL lymphocytosis is seen in some cases with fevers, colitis, and pleural effusions (PE), suggesting an aberrant immune response mediated by these LGLs. LGLs may participate in the elimination of the residual leukemic cells, and LGL clonal expansion is associated with excellent, long-lasting therapy responses in dasatinib-treated patients. For a more comprehensive analysis, we analyzed the morphologic, phenotypic, clinical, and functional features of the LGL subsets amplified in vivo during dasatinib therapy.

Adoptive cellular therapy using cells enriched for NKG2D+CD3+CD8+T cells after autologous transplantation for myeloma

The number of circulating lymphocytes on day 15 after transplantation correlates with improved survival in patients with myeloma, but the lymphocyte subset responsible is unknown. NKG2D is a natural killer (NK) cell activating receptor that mediates non-MHC restricted and TCR-independent cell lysis. Our preliminary results indicate that CD3(+)CD8(+) T cells expressing NKG2D may be a critical lymphocyte population. A phase II trial examined the feasibility of infusing ex vivo-expanded cells enriched for NKG2D(+)CD3(+)CD8(+) T cells at weeks 1, 2, 4, and 8 after an autologous transplantation. In addition, low-dose IL-2 (6 × 10(5) IU/m(2)/day) was administered for 4 weeks, beginning on the day of transplantation. Twenty-three patients were accrued and 19 patients are evaluable. There were no treatment-related deaths. All patients completed their course of IL-2 and demonstrated normal engraftment. When compared with patients with myeloma who underwent transplantation not receiving posttransplantation immune therapy, the treated patients demonstrated an increase in the number of circulating NKG2D(+)CD3(+)CD8(+) T cells/μL (P < .004), CD3(+)CD8(+) T cells/μL (P < .04), CD3(+)CD8(+)CD56(+) T cells/μL (P < .004), and NKG2D(+)CD3(-)CD56(+) T cells/μL (P < .003). Myeloma cell-directed cytotoxicity by the circulating mononuclear cells increased after transplantation (P < .002). When compared to posttransplantation IL-2 therapy alone in this patient population, the addition of cells enriched for NKG2D(+)CD3(+)CD8(+) T cells increased tumor-specific immunity, as demonstrated by enhanced lysis of autologous myeloma cells (P = .02). We postulate that this regimen that increased the number and function of the NKG2D(+)CD3(+)CD8(+) T cells after transplantation may improve clinical outcomes by eliminating residual malignant cells in vivo.

Somatic STAT3 mutations in large granular lymphocytic leukemia

BACKGROUND

T-cell large granular lymphocytic leukemia is a rare lymphoproliferative disorder characterized by the expansion of clonal CD3+CD8+ cytotoxic T lymphocytes (CTLs) and often associated with autoimmune disorders and immune-mediated cytopenias.

METHODS

We used next-generation exome sequencing to identify somatic mutations in CTLs from an index patient with large granular lymphocytic leukemia. Targeted resequencing was performed in a well-characterized cohort of 76 patients with this disorder, characterized by clonal T-cell-receptor rearrangements and increased numbers of large granular lymphocytes.

RESULTS

Mutations in the signal transducer and activator of transcription 3 gene (STAT3) were found in 31 of 77 patients (40%) with large granular lymphocytic leukemia. Among these 31 patients, recurrent mutational hot spots included Y640F in 13 (17%), D661V in 7 (9%), D661Y in 7 (9%), and N647I in 3 (4%). All mutations were located in exon 21, encoding the Src homology 2 (SH2) domain, which mediates the dimerization and activation of STAT protein. The amino acid changes resulted in a more hydrophobic protein surface and were associated with phosphorylation of STAT3 and its localization in the nucleus. In vitro functional studies showed that the Y640F and D661V mutations increased the transcriptional activity of STAT3. In the affected patients, downstream target genes of the STAT3 pathway (IFNGR2, BCL2L1, and JAK2) were up-regulated. Patients with STAT3 mutations presented more often with neutropenia and rheumatoid arthritis than did patients without these mutations.

CONCLUSIONS

The SH2 dimerization and activation domain of STAT3 is frequently mutated in patients with large granular lymphocytic leukemia; these findings suggest that aberrant STAT3 signaling underlies the pathogenesis of this disease. (Funded by the Academy of Finland and others.).

Immune aging and autoimmunity

Age is an important risk for autoimmunity, and many autoimmune diseases preferentially occur in the second half of adulthood when immune competence has declined and thymic T cell generation has ceased. Many tolerance checkpoints have to fail for an autoimmune disease to develop, and several of those are susceptible to the immune aging process. Homeostatic T cell proliferation which is mainly responsible for T cell replenishment during adulthood can lead to the selection of T cells with increased affinity to self- or neoantigens and enhanced growth and survival properties. These cells can acquire a memory-like phenotype, in particular under lymphopenic conditions. Accumulation of end-differentiated effector T cells, either specific for self-antigen or for latent viruses, have a low activation threshold due to the expression of signaling and regulatory molecules and generate an inflammatory environment with their ability to be cytotoxic and to produce excessive amounts of cytokines and thereby inducing or amplifying autoimmune responses.

Tipifarnib-mediated suppression of T-bet-dependent signaling pathways

Large granular lymphocyte (LGL) leukemia is a chronic lymphoproliferative disease in which T-bet [T-box transcription factor 21 gene (tbx21)] overexpression may play a pathogenic role. T-bet orchestrates the differentiation of mature peripheral T-cells into interferon-γ (IFN-γ) and tumor necrosis factor-α producing CD4+ T-helper type I (Th1) and CD8+ T cytotoxic cells that are necessary for antiviral responses. When IL-12 is produced by antigen-presenting cells, T-bet expression is induced, causing direct stimulation of ifng gene transcription while simultaneously acting as a transcriptional repressor of the IL4 gene, which then leads to Th1 dominance and T-helper type 2 differentiation blockade. Additionally, T-bet has been shown to regulate histone acetylation of the ifng promoter and enhancer to loosen condensed DNA, creating greater accessibility for other transcription factor binding, which further amplifies IFNγ production. We found that treatment with a farnesyltransferase inhibitor tipifarnib reduced Th1 cytokines in LGL leukemia patient T-cells and blocked T-bet protein expression and IL-12 responsiveness in T-cells from healthy donors. The mechanism of suppression was based on modulation of histone acetylation of the ifng gene, which culminated in Th1 blockade.

Role of CD8 T Cell Replicative Senescence in Human Aging and in HIV-mediated Immunosenescence

As humans age, their immune systems undergo a process known as immunosenescence. This global aging of the immune system is associated with increased susceptibility to infectious diseases and cancer, reduced effectiveness of vaccination, increased autoimmune phenomena, and tissue damage due to dysregulated inflammation. One hallmark feature of immunosenescence is the accumulation of late-differentiated memory CD8 T cells with features of replicative senescence, such as inability to proliferate, absence of CD28 expression, shortened telomeres, loss of telomerase activity, and enhanced secretion of inflammatory cytokines. The proportion of senescent CD8 T cells increases progressively with age, and often consists of oligoclonal populations that are specific for cytomegalovirus (CMV) antigens. In addition, there is evidence that senescent memory CD8 T cells acquire suppressive functions and may also contribute to carcinogenesis. Chronic HIV disease, even when controlled through antiretroviral therapy (ART), is associated with accelerated immunosenescence, as evidenced by the higher numbers of senescent memory CD8 T cells and increased inflammatory milieu. Interestingly, even in HIV disease, a high proportion of late-differentiated, putatively senescent, memory CD8 T cells are specific for CMV antigens. As in age-related immunosenescence, these HIV-associated changes result in dysregulated immunity, chronic diseases linked to inflammatory damage, and increased morbidity and mortality. This review explores the evidence for CD8 T cell replicative senescence in vitro and in vivo, in the context of both chronological aging and HIV-mediated immunosenescence. We also highlight an important gap in our understanding of human immunosenescence, since all the studies to date have focused on peripheral blood, which contains a minority of the total body lymphocyte population.

Epigenetic effects and molecular mechanisms of tumorigenesis induced by cigarette smoke: an overview

Cigarette smoking is one of the major causes of carcinogenesis. Direct genotoxicity induced by cigarette smoke leads to initiation of carcinogenesis. Nongenotoxic (epigenetic) effects of cigarette smoke also act as modulators altering cellular functions. These two effects underlie the mechanisms of tumor promotion and progression. While there is no lack of general reviews on the genotoxic and carcinogenic potentials of cigarette smoke in lung carcinogenesis, updated review on the epigenetic effects and molecular mechanisms of cigarette smoke and carcinogenesis, not limited to lung, is lacking. We are presenting a comprehensive review of recent investigations on cigarette smoke, with special attentions to nicotine, NNK, and PAHs. The current understanding on their molecular mechanisms include (1) receptors, (2) cell cycle regulators, (3) signaling pathways, (4) apoptosis mediators, (5) angiogenic factors, and (6) invasive and metastasis mediators. This review highlighted the complexity biological responses to cigarette smoke components and their involvements in tumorigenesis.

A molecular and functional analysis of large granular lymphocyte expansions in patients with chronic myelogenous leukemia treated with tyrosine kinase inhibitors

Tyrosine kinase inhibitor (TKI) therapy has become the standard treatment for chronic myelogenous leukemia (CML). Off-target kinase inhibition has been implicated in the appearance of unique adverse effects, such as colitis and pleural effusions. In addition, some patients present oligoclonal expansions of large granular lymphocytes (LGLs). We sought to further investigate this phenomenon in 64 patients treated with five different TKIs. Clonal expansions of cytotoxic T lymphocytes (CTLs) were identified in all TKI-treated patient groups, but only in dasatinib-treated patients were these expansions characterized as LGLs. Survival factors known to be important in LGL leukemia (interleukin-15 [IL-15] transpresentation, plasma platelet-derived growth factor [PDGF]-BB levels, nuclear factor-κB [NF-κB] and T-bet activation) were found to be associated with TKI-induced LGL expansions. Interestingly, patients with LGL expansions had increased cytotoxicity against non-transformed endothelial cells, which may play a role in observed autoimmune-like side effects. Our results indicate that patients with CML treated with TKIs can develop T cell expansions, which can in certain cases be related to some adverse effects.

How I treat LGL leukemia

Large granular lymphocyte (LGL) leukemia is characterized by a clonal expansion of either CD3(+) cytotoxic T or CD3(-) NK cells. Prominent clinical features of T-LGL leukemia include neutropenia, anemia and rheumatoid arthritis (RA). The terminal effector memory phenotype (CD3(+)/CD45RA(+)/CD62L(-)CD57(+)) of T-LGL suggests a pivotal chronic antigen-driven immune response. LGL survival is then promoted by platelet-derived growth factor and interleukin-15, resulting in global dysregulation of apoptosis and resistance to normal pathways of activation-induced cell death. These pathogenic features explain why treatment of T-LGL leukemia is based on immunosuppressive therapy. The majority of these patients eventually need treatment because of severe or symptomatic neutropenia, anemia, or RA. No standard therapy has been established because of the absence of large prospective trials. The authors use low-dose methotrexate initially for T-LGL leukemia patients with neutropenia and/or RA. We recommend either methotrexate or oral cyclophosphamide as initial therapy for anemia. If treatment is not successful, patients are switched to either the other agent or cyclosporine. The majority of patients experience an indolent clinical course. Deaths infrequently occur because of infections related to severe neutropenia. As there are no curative therapeutic modalities for T-LGL leukemia, new treatment options are needed.

NKG2A inhibits NKG2C effector functions of γδ T cells: implications in health and disease

The CD94/NKG2 complex is expressed on T and NK lymphocytes. CD94 molecules covalently associate to activating or inhibitory NKG2 molecules, and their expression finely tunes cell responses. Human γδ T cells express several NKRs. Expression of these receptors is confined to the cytolytic Vδ2 subset, which coexpresses the FcγRIII CD16 and CD45RA and has been defined as Vγ9Vδ2 T(EMRA) cells. We show that the CD94/NKG2C complex, associated with KARAP/DAP12, is fully functional in γδ T cells, as determined by measuring IFN-γ production, T cell proliferation, and cytolytic activity by γδ lymphocytes. In contrast, NKG2A expression was found on all γδ T cell memory subsets, suggesting a crucial role of the inhibitory signal provided by this receptor on γδ T cell responses. Moreover, we found Vγ9Vδ2 T(EMRA), NK, and CD8+ αβ T cells coexpressing NKG2A and NKG2C receptors. Functional experiments showed that the inhibitory signal mediated by the NKG2A receptor prevails when double-positive cells are activated. Finally, NKG2A expression on γδ LDGL correlates with asymptomatic pathology, even in the presence of NKG2C coexpression, whereas in symptomatic patients affected by severe disease, the inhibitory NKG2A receptor is absent, and a variety of activatory NKRs was found. We propose that the silent behavior of γδ cells in LDGL patients is a result of effective inhibitory HLA class I receptors.

The root of many evils: indolent large granular lymphocyte leukaemia and associated disorders

Large granular lymphocytes (LGL) leukaemia can arise from either natural killer (NK) cells or cytotoxic T lymphocytes (CTL). The T-cell form of LGL leukaemia has significant overlap with other haematological disorders and autoimmune diseases. Here we provide an overview of LGL biology. We also focus discussion on the indolent LGL leukaemia related disorders and their causal relationships. We then discuss the potential relationships and distinctions between indolent LGL leukaemia and non-malignant clonal lymphocyte expansion that occur in otherwise healthy individuals, especially elder people.

MICA polymorphism identified by whole genome array associated with NKG2D-mediated cytotoxicity in T-cell large granular lymphocyte leukemia

BACKGROUND

Large granular lymphocyte leukemia is a semi-autonomous clonal proliferation of cytotoxic T cells accompanied by immune cytopenias and various autoimmune conditions. Due to the rarity of this disease and its association with autoimmune diseases, a theoretical germline or somatic mutation might have significant penetrance, thus enabling detection, even from samples of suboptimal size, through genome-wide association studies.

DESIGN AND METHODS

To investigate a non-mendelian genetic predisposition to large granular lymphocyte leukemia, we used a step-wise method for gene discovery. First, a modified 'random forests' technique was used for candidate gene identification: this was followed by traditional allele-specific polymerase chain reaction, sequencing modalities, and mechanistic assays.

RESULTS

Our analysis found an association with MICA, a non-peptide-presenting, tightly regulated, stress-induced MHC-like molecule and cognate receptor for NKG2D, found abundantly on large granular lymphocyte leukemia cells. Sequencing of germline DNA revealed a higher frequency of MICA*00801/A5.1 in patients with large granular lymphocyte leukemia than in matched controls (64% versus 41%, P<0.001, homozygous 40% versus 15%, P<0.001). Flow cytometry was employed to determine the expression of MICA within hematologic compartments, showing that the signal intensity of MICA was increased in granulocytes from neutropenic patients with large granular lymphocyte leukemia in comparison with that in controls (P=0.033). Furthermore, neutrophil counts were inversely correlated with MICA expression (R(2)=0.50, P=0.035). Finally, large granular lymphocyte leukemia cells were able to selectively kill MICA(+) Ba/F3 lymphocytes transfected with human MICA*019 in a dose-dependent manner compared to naïve cells (P<0.001), an effect mitigated by administration of an anti-NKG2D antibody (P=0.033).

CONCLUSIONS

Our results illustrate that MICA-NKG2D played a role in disease pathogenesis in the majority of patients in our cohort of cases of large granular lymphocyte leukemia and further investigation into this signaling axis may provide potent therapeutic targets.

Macrophage colony-stimulating factor induces the proliferation and survival of macrophages via a pathway involving DAP12 and beta-catenin

Macrophage colony-stimulating factor (M-CSF) influences the proliferation and survival of mononuclear phagocytes through the receptor CSF-1R. The adaptor protein DAP12 is critical for the function of mononuclear phagocytes. DAP12-mutant mice and humans have defects in osteoclasts and microglia, as well as brain and bone abnormalities. Here we show DAP12 deficiency impaired the M-CSF-induced proliferation and survival of macrophages in vitro. DAP12-deficient mice had fewer microglia in defined central nervous system areas, and DAP12-deficient progenitors regenerated myeloid cells inefficiently after bone marrow transplantation. Signaling by M-CSF through CSF-1R induced the stabilization and nuclear translocation of beta-catenin, which activated genes involved in the cell cycle. DAP12 was essential for phosphorylation and nuclear accumulation of beta-catenin. Our results provide a mechanistic explanation for the many defects of DAP12-deficient mononuclear phagocytes.