Platelets subvert T cell immunity against cancer via GARP-TGFβ axis

Role of platelets and platelet receptors in cancer metastasis

The interaction of tumor cells with platelets is a prerequisite for successful hematogenous metastatic dissemination. Upon tumor cell arrival in the blood, tumor cells immediately activate platelets to form a permissive microenvironment. Platelets protect tumor cells from shear forces and assault of NK cells, recruit myeloid cells by secretion of chemokines, and mediate an arrest of the tumor cell platelet embolus at the vascular wall. Subsequently, platelet-derived growth factors confer a mesenchymal-like phenotype to tumor cells and open the capillary endothelium to expedite extravasation in distant organs. Finally, platelet-secreted growth factors stimulate tumor cell proliferation to micrometastatic foci. This review provides a synopsis on the current literature on platelet-mediated effects in cancer metastasis and particularly focuses on platelet adhesion receptors and their role in metastasis. Immunoreceptor tyrosine-based activation motif (ITAM) and hemi ITAM (hemITAM) comprising receptors, especially, glycoprotein VI (GPVI), FcγRIIa, and C-type lectin-like-2 receptor (CLEC-2) are turned in the spotlight since several new mechanisms and contributions to metastasis have been attributed to this family of platelet receptors in the last years.

Importance of Feedback and Feedforward Loops to Adaptive Immune Response Modeling

The human adaptive immune system is a very complex network of different types of cells, cytokines, and signaling molecules. This complex network makes it difficult to understand the system level regulations. To properly explain the immune system, it is necessary to explicitly investigate the presence of different feedback and feedforward loops (FFLs) and their crosstalks. Considering that these loops increase the complexity of the system, the mathematical modeling has been proved to be an important tool to explain such complex biological systems. This review focuses on these regulatory loops and discusses their importance on systems modeling of the immune system.

Preoperative platelet-lymphocyte ratio is an independent prognostic factor in ampullary carcinoma following pancreaticoduodenectomy

The objective of the present study was to evaluate whether preoperative platelet-lymphocyte ratio (PLR) and neutrophil-lymphocyte ratio (NLR) could predict the prognosis for curative resected ampullary carcinoma. A total of 94 patients were retrospectively included over a 6-year period in which consecutive cases underwent pancreaticoduodenectomy for ampullary malignancy. Preoperative blood results were available in the 94 cases of resected ampullary carcinoma. Preoperative PLR and NLR cut-off values of 226.8 and 2.58 were determined to represent the optimal cut-off values in the cases for survival analysis. PLR remained a significant independent predictor of survival in multivariate analysis (Cox, P<0.001) in addition to tumor differentiation (P<0.001), nodal status (P<0.001) and stage (P<0.001). While NLR failed to serve as a prognostic factor in univariate (P=0.0637) and multivariate (P=0.164) survival analysis. Furthermore, the nodal involvement rate was higher in high PLR group (74.2 vs. 19.05%, P<0.001). Preoperative PLR and NLR merit further evaluation as a prognostic index in curative resected ampullary carcinoma. Additionally, it is a candidate predictor for the lymph node metastasis.

Deletion of GARP on mouse regulatory T cells is not sufficient to inhibit the growth of transplanted tumors

GARP is a transmembrane protein that presents latent TGF-β1 on the surface of regulatory T cells (Tregs). Neutralizing anti-GARP monoclonal antibodies that prevent the release of active TGF-β1, inhibit the immunosuppressive activity of human Tregs in vivo. In this study, we investigated the contribution of GARP on mouse Tregs to immunosuppression in experimental tumors. Unexpectedly, Foxp3 conditional garp knockout (KO) mice challenged orthotopically with GL261 tumor cells or subcutaneously with MC38 colon carcinoma cells did not show prolonged survival or delayed tumor growth. Also, the suppressive function of KO Tregs was similar to that of wild type Tregs in the T cell transfer model in allogeneic, immunodeficient mice. In conclusion, garp deletion in mouse Tregs is not sufficient to impair their immunosuppressive activity in vivo.

High Risk of Venous Thromboembolism After Surgery for Long Bone Metastases: A Retrospective Study of 682 Patients

BACKGROUND

Previous studies have shown that venous thromboembolism (VTE) is a complication associated with neoplastic disease and major orthopaedic surgery. However, many potential risk factors remain undefined.

QUESTIONS/PURPOSES

(1) What proportion of patients develop symptomatic VTE after surgery for long bone metastases? (2) What factors are associated with the development of symptomatic VTE among patients receiving surgery for long bone metastases? (3) Is there an association between the development of symptomatic VTE and 1-year survival among patients undergoing surgery for long bone metastases? (4) Does chemoprophylaxis increase the risk of wound complications among patients undergoing surgery for long bone metastases?

METHODS

A retrospective study identified 682 patients undergoing surgical treatment of long bone metastases between 2002 and 2013 at the Massachusetts General Hospital and Brigham and Women's Hospital. We included patients 18 years of age or older who had a surgical procedure for impending or pathologic metastatic long bone fracture. We considered the humerus, radius, ulna, femur, tibia, and fibula as long bones; metastatic disease was defined as metastases from solid organs, multiple myeloma, or lymphoma. In general, we used 40 mg enoxaparin daily for lower extremity surgery and 325 mg aspirin daily for lower or upper extremity surgery. The primary outcome was a VTE defined as any symptomatic pulmonary embolism (PE) or symptomatic deep vein thrombosis (DVT; proximal and distal) within 90 days of surgery as determined by chart review. The tertiary outcome was defined as any documented wound complication that might be attributable to chemoprophylaxis within 90 days of surgery. At followup after 90 days and 1 year, respectively, 4% (25 of 682) and 8% (53 of 682) were lost to followup. Statistical analysis was performed using multivariable logistic and Cox regression and Kaplan-Meier.

RESULTS

Overall, 6% (44 of 682) of patients had symptomatic VTE; 22 patients sustained a DVT, and 22 developed a PE. After controlling for relevant confounding variables, higher preoperative hemoglobin level was independently associated (odds ratio [OR], 0.75; 95% confidence interval [CI], 0.60-0.93; p = 0.011) with decreased symptomatic VTE risk, the presence of symptomatic VTE was associated with a worse 1-year survival rate (VTE: 27% [95% CI, 14%-40%] and non-VTE: 39% [95% CI, 35%-43%]; p = 0.041), and no association was found between wound complications and the use of chemoprophylaxis (OR, 3.29; 95% CI, 0.43-25.17; p = 0.252).

CONCLUSIONS

The risk of symptomatic 90-day VTE is high in patients undergoing surgery for long bone metastases. Further study would be needed to determine the VTE prevention strategy that best balances risks and benefits to address this complication.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Two-stage oxygen delivery for enhanced radiotherapy by perfluorocarbon nanoparticles

Tumors are usually hypoxic, which limits the efficacy of current tumor therapies, especially radiotherapy in which oxygen is essential to promote radiation-induced cell damage. Herein, by taking advantage of the ability of perfluorocarbon (PFC) to promote red blood cell penetration, we developed a simple but effective two-stage oxygen delivery strategy to modulate the hypoxic tumor microenvironment using PFC nanoparticles. Methods: We first examined the two-stage oxygen delivery ability of PFC nanoparticles on relieving tumor hypoxia through platelet inhibition. To evaluate the effect of PFC nanoparticles on radiation sensitization, CT26 tumor and SUM49PT tumor model were used. Results: In this study, PFC was encapsulated into albumin and intravenously injected into tumor-bearing mice without hyperoxic breathing. After accumulation in the tumor, PFC nanoparticles rapidly released the oxygen that was physically dissolved in PFC as the first-stage of oxygen delivery. Then, PFC subsequently promoted red blood cell infiltration, which further released O2 as the second-stage of oxygen delivery. Conclusion: The hypoxic tumor microenvironment was rapidly relieved via two-stage oxygen delivery, effectively increasing radiotherapy efficacy. The safety of all substances used in this study has been clinically demonstrated, ensuring that this simple strategy could be rapidly and easily translated into clinical applications to solve the clinical problems associated with tumor hypoxia.

Mean platelet volume and lymphocyte-to-monocyte ratio are associated with shorter progression-free survival in EGFR-mutant lung adenocarcinoma treated by EGFR tyrosine kinase inhibitor

Background

A growing body of evidence supports the role of platelets in cancer metastasis, escape from immune surveillance, and angiogenesis. Mean platelet volume (MPV), which reflects platelet turnover, is reported routinely as part of automated complete blood count. Accumulating evidence suggests that MPV is a useful biomarker in several diseases including cancer. However, its role in cancer patients receiving molecular targeted therapy has not been described in the literature.

Materials and methods

We retrospectively analysed the prognostic impact of MPV in advanced or recurrent EGFR mutant lung adenocarcinoma treated with EGFR tyrosine kinase inhibitors (EGFR-TKIs). Lymphocyte-to-monocyte ratio (LMR) has been previously reported to be a poor prognostic factor in EGFR mutant non-small cell lung cancer and was also included as a covariate.

Results

Using the previously described Cutoff Finder algorithm, the cut-off points for MPV and LMR that best predicted progression free survival (PFS) of EGFR-TKI were determined as 10.3 and 2.8, respectively. The median PFS was 14.7 and 8.2 months in MPV low and high groups (p = 0.013, log-rank test). The median PFS was 13.5 and 6.2 months in LMR high and low groups (p < 0.001, log-rank test). MPV and LMR were independently distributed (chi square test) and the multivariate analysis using Cox’s proportional hazards regression model revealed that high MPV, low LMR, and pleural effusion were significant predictors for shorter PFS.

Conclusion

MPV and LMR, measured as part of routine complete blood count, can be utilized to predict the outcome of EGFR-TKI therapy with no additional costs. Our results suggest a mechanism of EGFR-TKI resistance which is associated with the functional status of the platelets.

Antithrombotic Agents and Cancer

Platelet activation is the first response to tissue damage and, if unrestrained, may promote chronic inflammation-related cancer, mainly through the release of soluble factors and vesicles that are rich in genetic materials and proteins. Platelets also sustain cancer cell invasion and metastasis formation by fostering the development of the epithelial-mesenchymal transition phenotype, cancer cell survival in the bloodstream and arrest/extravasation at the endothelium. Furthermore, platelets contribute to tumor escape from immune elimination. These findings provide the rationale for the use of antithrombotic agents in the prevention of cancer development and the reduction of metastatic spread and mortality. Among them, low-dose aspirin has been extensively evaluated in both preclinical and clinical studies. The lines of evidence have been considered appropriate to recommend the use of low-dose aspirin for primary prevention of cardiovascular disease and colorectal cancer by the USA. Preventive Services Task Force. However, two questions are still open: (i) the efficacy of aspirin as an anticancer agent shared by other antiplatelet agents, such as clopidogrel; (ii) the beneficial effect of aspirin improved at higher doses or by the co-administration of clopidogrel. This review discusses the latest updates regarding the mechanisms by which platelets promote cancer and the efficacy of antiplatelet agents.

Intracellular and extracellular TGF-β signaling in cancer: some recent topics

Transforming growth factor (TGF)-β regulates a wide variety of cellular responses, including cell growth arrest, apoptosis, cell differentiation, motility, invasion, extracellular matrix production, tissue fibrosis, angiogenesis, and immune function. Although tumor-suppressive roles of TGF-β have been extensively studied and well-characterized in many cancers, especially at early stages, accumulating evidence has revealed the critical roles of TGF-β as a pro-tumorigenic factor in various types of cancer. This review will focus on recent findings regarding epithelial-mesenchymal transition (EMT) induced by TGF-β, in relation to crosstalk with some other signaling pathways, and the roles of TGF-β in lung and pancreatic cancers, in which TGF-β has been shown to be involved in cancer progression. Recent findings also strongly suggested that targeting TGF-β signaling using specific inhibitors may be useful for the treatment of some cancers. TGF-β plays a pivotal role in the differentiation and function of regulatory T cells (Tregs). TGF-β is produced as latent high molecular weight complexes, and the latent TGF-β complex expressed on the surface of Tregs contains glycoprotein A repetitions predominant (GARP, also known as leucine-rich repeat containing 32 or LRRC32). Inhibition of the TGF-β activities through regulation of the latent TGF-β complex activation will be discussed.

Aspirin, platelet inhibition and cancer prevention

Several lines of evidence are consistent with the hypothesis that activated platelets contribute to colorectal tumorigenesis and metastatization through direct cell-cell interactions and the release of different lipid and protein mediators, and microvesicles. This review examines the clinical pharmacology of low-dose aspirin as a basis for discussing the mechanisms underlying the contribution of platelets to neoplastic transformation and progression of cancer via the development of metastases.

Cancer immune therapy for myeloid malignancies: present and future

The myelodysplastic syndromes, the chronic myeloproliferative neoplasms, and the acute myeloid leukemia are malignancies of the myeloid hematopoietic stem cells of the bone marrow. The diseases are characterized by a dysregulation of the immune system as both the cytokine milieu, immune phenotype, immune regulation, and expression of genes related to immune cell functions are deregulated. Several treatment strategies try to circumvent this deregulation, and several clinical and preclinical trials have shown promising results, albeit not in the same scale as chimeric antigen receptor T cells have had in the treatment of refractory lymphoid malignancies. The use of immune checkpoint blocking antibodies especially in combination with hypomethylating agents has had some success-a success that will likely be enhanced by therapeutic cancer vaccination with tumor-specific antigens. In the chronic myeloproliferative neoplasms, the recent identification of immune responses against the Januskinase-2 and calreticulin exon 9 driver mutations could also be used in the vaccination setting to enhance the anti-tumor immune response. This immune response could probably be enhanced by the concurrent use of immune checkpoint inhibitors or by vaccination with epitopes from immune regulatory proteins such as arginase-1 and programmed death ligand-1. Herein, we provide an overview of current cancer immune therapeutic treatment strategies as well as potential future cancer immune therapeutic treatment options for the myeloid malignancies.

Tumor-Educated Platelets as a Noninvasive Biomarker Source for Cancer Detection and Progression Monitoring

Liquid biopsies represent a potential revolution in cancer diagnostics as a noninvasive method for detecting and monitoring diseases, complementary to or even replacing current tissue biopsy approaches. Several blood-based biosources and biomolecules, such as cell-free DNA and RNA, proteins, circulating tumor cells, and extracellular vesicles, have been explored for molecular test development. We recently discovered the potential of tumor-educated blood platelets (TEP) as a noninvasive biomarker trove for RNA biomarker panels. TEPs are involved in the progression and spread of several solid tumors, and spliced TEP RNA surrogate signatures can provide specific information on the presence, location, and molecular characteristics of cancers. So far, TEP samples from patients with different tumor types, including lung, brain, and breast cancers, have been tested, and it has been shown that TEPs from patients with cancer are distinct from those with inflammatory and other noncancerous diseases. It remains to be investigated how platelets are "educated," which mechanisms cause intraplatelet RNA splicing, and whether the relative contribution of specific platelet subpopulations changes in patients with cancer. Ultimately, TEP RNA may complement currently used biosources and biomolecules employed for liquid biopsy diagnosis, potentially enhancing the detection of cancer in an early stage and facilitating noninvasive disease monitoring. Cancer Res; 78(13); 3407-12. ©2018 AACR.

Cancer prevention by aspirin in children with Constitutional Mismatch Repair Deficiency (CMMRD)

Constitutional MisMatch Repair Deficiency (CMMRD) is caused by homozygous or compound heterozygous germline variants in one of the mismatch repair (MMR) genes (MSH2, MSH6, PMS2, MLH1). This syndrome results in early onset colorectal cancer, leukemia and lymphoma, brain tumors and other malignancies. Children with CMMRD are at high risk of developing multiple cancers and cancer surveillance does not guarantee detection of cancer at a curable stage. The development of a preventive treatment strategy would be a major step forward. Long-term daily use of acetylsalicylic acid (ASA) has been shown to reduce cancer risk in individuals with Lynch syndrome (LS). LS is caused by heterozygous germline variants of MSH2, MSH6, PMS2 and MLH1 and characterized by an increased risk of developing colorectal and endometrial cancer at adult age. Here we discuss the potential use of ASA for cancer prevention in patients with CMMRD.

The Platelet Lifeline to Cancer: Challenges and Opportunities

Besides their function in limiting blood loss and promoting wound healing, experimental evidence has highlighted platelets as active players in all steps of tumorigenesis including tumor growth, tumor cell extravasation, and metastasis. Additionally, thrombocytosis in cancer patients is associated with adverse patient survival. Due to the secretion of large amounts of microparticles and exosomes, platelets are well positioned to coordinate both local and distant tumor-host crosstalk. Here, we present a review of recent discoveries in the field of platelet biology and the role of platelets in cancer progression as well as challenges in targeting platelets for cancer treatment.

Complex roles of the old drug aspirin in cancer chemoprevention and therapy

The nonsteroidal anti-inflammatory agent aspirin is widely used for preventing and treating cardiovascular and cerebrovascular diseases. In addition, epidemiologic evidences reveal that aspirin may prevent a variety of human cancers, while data on the association between aspirin and some kinds of cancer are conflicting. Preclinical studies and clinical trials also reveal the therapeutic effect of aspirin on cancer. Although cyclooxygenase is a well-known target of aspirin, recent studies uncover other targets of aspirin and its metabolites, such as AMP-activated protein kinase, cyclin-dependent kinase, heparanase, and histone. Accumulating evidence demonstrate that aspirin may act in different cell types, such as epithelial cell, tumor cell, endothelial cell, platelet, and immune cell. Therefore, aspirin acts on diverse hallmarks of cancer, such as sustained tumor growth, metastasis, angiogenesis, inflammation, and immune evasion. In this review, we focus on recent progress in the use of aspirin for cancer chemoprevention and therapy, and integratively analyze the mechanisms underlying the anticancer effects of aspirin and its metabolites. We also discuss mechanisms of aspirin resistance and describe some derivatives of aspirin, which aim to overcome the adverse effects of aspirin.

Role of GARP in the activation of latent TGF-β1

TGF-β1, 2 and 3 cytokines are involved in many cellular processes including cell proliferation, differentiation, migration and survival. Whereas TGF-β2 and 3 play important roles in embryonic development, TGF-β1 is mostly implicated in controlling immune responses after birth. The production of TGF-β1 is a tightly regulated process, occurring mostly at a post-translational level. Virtually all cells produce the latent, inactive form of TGF-β1. In latent TGF-β1, the mature TGF-β1 dimer is non-covalently associated to the Latency Associated Peptide, or LAP, which prevents binding to the TGF-β1 receptor. Activation of the cytokine implies release of mature TGF-β1 from LAP. Only a few cell types activate latent TGF-β1, via mechanisms that are cell type specific. Proteins such as integrins, proteases and thrombospondin-1 activate TGF-β1 in epithelial cells, fibroblasts and dendritic cells. More recently, the protein GARP was shown to be involved in TGF-β1 activation by regulatory T cells (Treg), a subset of CD4⁺ T lymphocytes specialized in suppression of immune responses. GARP is a transmembrane protein that binds latent-TGF-β1 and tethers it on the Treg surface. The role of GARP was studied mostly in Tregs, and this was recently reviewed in L. Sun, H. Jin and H. Li, Oncotarget, 2016, 7, 42826-42836. However, GARP is also expressed in non-immune cells. This review focuses on the roles of GARP in latent TGF-β1 activation by immune and non-immune cells.

Human Cancer and Platelet Interaction, a Potential Therapeutic Target

Cancer patients experience a four-fold increase in thrombosis risk, indicating that cancer development and progression are associated with platelet activation. Xenograft experiments and transgenic mouse models further demonstrate that platelet activation and platelet-cancer cell interaction are crucial for cancer metastasis. Direct or indirect interaction of platelets induces cancer cell plasticity and enhances survival and extravasation of circulating cancer cells during dissemination. In vivo and in vitro experiments also demonstrate that cancer cells induce platelet aggregation, suggesting that platelet-cancer interaction is bidirectional. Therefore, understanding how platelets crosstalk with cancer cells may identify potential strategies to inhibit cancer metastasis and to reduce cancer-related thrombosis. Here, we discuss the potential function of platelets in regulating cancer progression and summarize the factors and signaling pathways that mediate the cancer cell-platelet interaction.

Platelet Metabolism and Other Targeted Drugs; Potential Impact on Immunotherapy

The role of platelets in cancer progression has been well recognized in the field of cancer biology. Emerging studies are elaborating further the additional roles and added extent that platelets play in promoting tumorigenesis. Platelets release factors that support tumor growth and also form heterotypic aggregates with tumor cells, which can provide an immune-evasive advantage. Their most critical role may be the inhibition of immune cell function that can negatively impact the body’s ability in preventing tumor establishment and growth. This review summarizes the importance of platelets in tumor progression, therapeutic response, survival, and finally the notion of immunotherapy modulation being likely to benefit from the inclusion of platelet inhibitors.

Cancer and platelet crosstalk: opportunities and challenges for aspirin and other antiplatelet agents

Platelets have long been recognized as key players in hemostasis and thrombosis; however, growing evidence suggests that they are also significantly involved in cancer, the second leading cause of mortality worldwide. Preclinical and clinical studies showed that tumorigenesis and metastasis can be promoted by platelets through a wide variety of crosstalk between platelets and cancer cells. For example, cancer changes platelet behavior by directly inducing tumor-platelet aggregates, triggering platelet granule and extracellular vesicle release, altering platelet phenotype and platelet RNA profiles, and enhancing thrombopoiesis. Reciprocally, platelets reinforce tumor growth with proliferation signals, antiapoptotic effect, and angiogenic factors. Platelets also activate tumor invasion and sustain metastasis via inducing an invasive epithelial-mesenchymal transition phenotype of tumor cells, promoting tumor survival in circulation, tumor arrest at the endothelium, and extravasation. Furthermore, platelets assist tumors in evading immune destruction. Hence, cancer cells and platelets maintain a complex, bidirectional communication. Recently, aspirin (acetylsalicylic acid) has been recognized as a promising cancer-preventive agent. It is recommended at daily low dose by the US Preventive Services Task Force for primary prevention of colorectal cancer. The exact mechanisms of action of aspirin in chemoprevention are not very clear, but evidence has emerged that suggests a platelet-mediated effect. In this article, we will introduce how cancer changes platelets to be more cancer-friendly and highlight advances in the modes of action for aspirin in cancer prevention. We also discuss the opportunities, challenges, and opposing viewpoints on applying aspirin and other antiplatelet agents for cancer prevention and treatment.

B lymphocytes confer immune tolerance via cell surface GARP-TGF-β complex

GARP, a cell surface docking receptor for binding and activating latent TGF-β, is highly expressed by platelets and activated Tregs. While GARP is implicated in immune invasion in cancer, the roles of the GARP-TGF-β axis in systemic autoimmune diseases are unknown. Although B cells do not express GARP at baseline, we found that the GARP-TGF-β complex is induced on activated human and mouse B cells by ligands for multiple TLRs, including TLR4, TLR7, and TLR9. GARP overexpression on B cells inhibited their proliferation, induced IgA class-switching, and dampened T cell-independent antibody production. In contrast, B cell-specific deletion of GARP-encoding gene Lrrc32 in mice led to development of systemic autoimmune diseases spontaneously as well as worsening of pristane-induced lupus-like disease. Canonical TGF-β signaling more readily upregulates GARP in Peyer patch B cells than in splenic B cells. Furthermore, we demonstrated that B cells are required for the induction of oral tolerance of T cell-dependent antigens via GARP. Our studies reveal for the first time to our knowledge that cell surface GARP-TGF-β is an important checkpoint for regulating B cell peripheral tolerance, highlighting a mechanism of autoimmune disease pathogenesis.

Immune checkpoint blockade therapy

Immune checkpoints are accessory molecules that either promote or inhibit T-cell activation. Two inhibitory molecules, cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed cell death protein 1 (PD-1), got high attention, as inhibition of CTLA-4 or PD-1 signaling provides the first immune therapy that significantly improves the survival of patients with metastatic solid cancers. Inhibition of CTLA-4 or PD-1 was first studied in and approved for patients with metastatic melanoma. Blocking immune checkpoints is also efficient in non-small-cell lung cancer, renal cell cancers, hypermutated gastrointestinal cancers, and others. Immune responses, whether directed against infections or against tumors, are divided into 2 phases: an initiation phase and an activation phase, where the immune system recognizes a danger signal and becomes activated by innate signals to fight the danger. This reaction is fundamental for the control of infections and cancer, but needs to be turned off once the danger is controlled, because persistence of this activation ultimately causes severe tissue damage. Therefore, each activation of the immune system is followed by a termination phase, where endogenous immune suppressor molecules arrest immune responses to prevent harmful damage. In the case of cancer immune therapies, therapeutic approaches classically enhanced the initiation and activation of immune responses to increase the emergence and the efficacy of cytotoxic T lymphocytes (CTL) against cancers. In sharp contrast, immune checkpoint blockade focuses on the termination of immune responses by inhibiting immune suppressor molecules. It thus prevents the termination of immune responses or even awakes those CTLs that became exhausted during an immune response. Therefore, blocking negatively regulating immune checkpoints restores the capacity of exhausted CTL to kill the cancer they infiltrate. In addition, they drive surviving cancer cells into a still poorly defined state of dormancy. As the therapy also awakes self-reactive CTL, one downside of the therapy is the induction of organ-specific autoimmune diseases. The second downside is the exorbitant drug price that withdraws patients in need from a therapy that was developed by academic research, which impairs further academic treatment development and financially charges the public health system.

Fresh Evidence for Platelets as Neuronal and Innate Immune Cells: Their Role in the Activation, Differentiation, and Deactivation of Th1, Th17, and Tregs during Tissue Inflammation

Recent studies suggest that in addition to their common function in the regulation of thrombosis and hemostasis, platelets also contribute to tissue inflammation affecting adaptive immunity. Platelets have a number of pro-inflammatory and regulatory mediators stored in their α-granules and dense granules, which are promptly released at sites of inflammation or tissue injury. Platelet-derived mediators include cytokines (IL-1α, IL-1β, and TGFβ1), chemokines (CXCL4 and CCL3), immunomodulatory neurotransmitters (serotonin, dopamine, epinephrine, histamine, and GABA), and other low-molecular-weight mediators. In addition, activated platelets synthesize a number of lipid pro-inflammatory mediators such as platelet-activating factor and prostaglandins/thromboxanes. Notably, platelets express multiple toll-like receptors and MHC class I on their surface and store IgG in their α-granules. Platelet-derived factors are highly effective in directly or indirectly modulating the priming and effector function of various subsets of T cells. Besides secreting soluble factors, activated platelets upregulate a number of integrins, adhesion molecules, and lectins, leading to the formation of platelet–T cells aggregates. Activated platelets are able to instantly release neurotransmitters acting similar to neuronal presynaptic terminals, affecting CD4 T cells and other cells in close contact with them. The formation of platelet–T cell aggregates modulates the functions of T cells via direct cell–cell contact interactions and the local release of soluble factors including neurotransmitters. New data suggest an important role for platelets as neuronal and innate-like cells that directly recognize damage- or pathogen- associated molecular patterns and instantly communicate with T cells.

Immunoregulatory functions and the therapeutic implications of GARP-TGF-β in inflammation and cancer

GARP (glycoprotein-A repetitions predominant) is a type I transmembrane cell surface docking receptor for latent transforming growth factor-β (TGF-β) that is abundantly expressed on regulatory T lymphocytes and platelets. GARP regulates the availability of membrane-bound latent TGF-β and modulates its activation. For this reason, GARP expression on immune and non-immune cells is involved in maintaining peripheral tolerance. It plays an important role in preventing inflammatory diseases such as allergy and graft versus host disease (GvHD). GARP is also frequently hijacked by cancer cells to promote oncogenesis. This review summarizes the most important features of GARP biology described to date including gene regulation, protein expression and mechanism in activating latent TGF-β, and the function of GARP in regulatory T cell biology and peripheral tolerance, as well as GARP’s increasingly recognized roles in platelet-mediated cancer immune evasion. The promise for GARP-targeted strategy as a novel immunotherapy of cancer is also highlighted.

P2Y12 Receptors in Tumorigenesis and Metastasis

Platelets, beyond their role in hemostasis and thrombosis, may sustain tumorigenesis and metastasis. These effects may occur via direct interaction of platelets with cancer and stromal cells and by the release of several platelet products. Platelets and tumor cells release several bioactive molecules among which a great amount of adenosine triphosphate (ATP) and adenosine diphosphate (ADP). ADP is also formed extracellularly from ATP breakdown by the ecto-nucleoside-triphosphate-diphosphohydrolases. Under ATP and ADP stimulation the purinergic P2Y₁ receptor (R) initiates platelet activation followed by the ADP-P2Y₁₂R-mediated amplification. P2Y₁₂R stimulation amplifies also platelet response to several platelet agonists and to flow conditions, acting as a key positive feed-forward signal in intensifying platelet responses. P2Y₁₂R represents a potential target for an anticancer therapy due to its involvement in platelet-cancer cell crosstalk. Thus, P2Y₁₂R antagonists, including clopidogrel, ticagrelor, and prasugrel, might represent potential anti-cancer agents, in addition to their role as effective antithrombotic drugs. However, further studies, in experimental animals and patients, are required before the recommendation of the use of P2Y₁₂R antagonists in cancer prevention and progression can be made.

Tissue factor as a mediator of coagulation and signaling in cancer and chronic inflammation

Thrombosis is frequently diagnosed as a first symptom in tumor patients and the clinical management of hypercoagulability in cancer patients remains challenging due to concomitant changes in risk factors for severe bleeding. It therefore remains a priority to better understand interactions of the hemostatic system with cancer biology. Specifically, further research is needed to elucidate the details and effects of new anticoagulants on extravascular coagulation and the interplay between cancer progression and chronic inflammation. In addition, it will be important to identify subgroups of cancer patients benefiting from specific modulations of the coagulation system without increasing the bleeding risk. Here, we review recent findings on tissue factor (TF) regulation, its procoagulant activity and TF signaling in the various cell types of the tumor microenvironment.

Carpe low-dose aspirin: the new anti-cancer face of an old anti-platelet drug

Cancer metastasis is a dynamic process during which cancer cells separate from a primary tumor, migrate through the vessel wall into the bloodstream, and extravasate at distant sites to form secondary colonies. During this process, circulating tumor cells are subjected to shear stress forces from blood flow, and in contact with plasma proteins and blood cells of the immune and hemostatic system, including platelets. Many studies have shown an association between high platelet count and cancer metastasis, suggesting that platelets may play an occult role in tumorigenesis. This mini-review summarizes recent and emerging discoveries of mechanisms by which cancer cells activate platelets and the role of activated platelets in promoting tumor growth and metastasis. Moreover, the review discusses how aspirin has the potential for being clinically used as an adjuvant in cancer therapy.

Cancer and Thrombotic Risk: The Platelet Paradigm

Hematologic malignancies and solid tumors increase the risk of venous and arterial thrombosis and contribute greatly to patient morbidity and mortality. Thrombosis occurs when the intricate balance of circulating antithrombotic and prothrombotic blood elements are disrupted. In recent years, the interplay between paraneoplastic cells and platelets has become apparent, with a change in platelet phenotype causing dysregulated platelet activity. This review discusses mechanism of thrombosis in cancer, evidence for using drug therapy, and exciting research efforts to understand and hopefully control aberrant thrombotic events in patients with cancer.

Targeting myeloid cells in the tumor sustaining microenvironment

Myeloid cells are the most abundant cells in the tumor microenvironment (TME). The tumor recruits and modulates endogenous myeloid cells to tumor-associated macrophages (TAM), dendritic cells (DC), myeloid-derived suppressor cells (MDSC) and neutrophils (TAN), to sustain an immunosuppressive environment. Pathologically overexpressed mediators produced by cancer cells like granulocyte-macrophage colony-stimulating- and vascular endothelial growth factor induce myelopoiesis in the bone marrow. Excess of myeloid cells in the blood, periphery and tumor has been associated with tumor burden. In cancer, myeloid cells are kept at an immature state of differentiation to be diverted to an immunosuppressive phenotype. Here, we review human myeloid cells in the TME and the mechanisms for sustaining the hallmarks of cancer. Simultaneously, we provide an introduction into current and novel therapeutic approaches to redirect myeloid cells from a cancer promoting to a rather inflammatory, cancer inhibiting phenotype. In addition, the role of platelets for tumor promotion is discussed.

Glycoprotein A repetitions predominant (GARP) positively regulates transforming growth factor (TGF) β3 and is essential for mouse palatogenesis

Glycoprotein A repetitions predominant (GARP) (encoded by the Lrrc32 gene) plays important roles in cell-surface docking and activation of TGFβ. However, GARP's role in organ development in mammalian systems is unclear. To determine the function of GARP in vivo, we generated a GARP KO mouse model. Unexpectedly, the GARP KO mice died within 24 h after birth and exhibited defective palatogenesis without apparent abnormalities in other major organs. Furthermore, we observed decreased apoptosis and SMAD2 phosphorylation in the medial edge epithelial cells of the palatal shelf of GARP KO embryos at embryonic day 14.5 (E14.5), indicating a defect in the TGFβ signaling pathway in the GARP-null developing palates. Of note, the failure to develop the secondary palate and concurrent reduction of SMAD phosphorylation without other defects in GARP KO mice phenocopied TGFβ3 KO mice, although GARP has not been suggested previously to interact with TGFβ3. We found that GARP and TGFβ3 co-localize in medial edge epithelial cells at E14.5. In vitro studies confirmed that GARP and TGFβ3 directly interact and that GARP is indispensable for the surface expression of membrane-associated latent TGFβ3. Our findings indicate that GARP is essential for normal morphogenesis of the palate and demonstrate that GARP plays a crucial role in regulating TGFβ3 signaling during embryogenesis. In conclusion, we have uncovered a novel function of GARP in positively regulating TGFβ3 activation and function.