The Engagement Between MDSCs and Metastases: Partners in Crime

Tumor metastases represent the major cause of cancer-related mortality, confirming the urgent need to identify key molecular pathways and cell-associated networks during the early phases of the metastatic process to develop new strategies to either prevent or control distal cancer spread. Several data revealed the ability of cancer cells to establish a favorable microenvironment, before their arrival in distant organs, by manipulating the cell composition and function of the new host tissue where cancer cells can survive and outgrow. This predetermined environment is termed \u201cpre-metastatic niche\u201d (pMN). pMN development requires that tumor-derived soluble factors, like cytokines, growth-factors and extracellular vesicles, genetically and epigenetically re-program not only resident cells (i.e., fibroblasts) but also non-resident cells such as bone marrow-derived cells. Indeed, by promoting an \u201cemergency\u201d myelopoiesis, cancer cells switch the steady state production of blood cells toward the generation of pro-tumor circulating myeloid cells defined as myeloid-derived suppressor cells (MDSCs) able to sustain tumor growth and dissemination. MDSCs are a heterogeneous subset of myeloid cells with immunosuppressive properties that sustain metastatic process. In this review, we discuss current understandings of how MDSCs shape and promote metastatic dissemination acting in each fundamental steps of cancer progression from primary tumor to metastatic disease

Immunosuppression by monocytic myeloid-derived suppressor cells in patients with pancreatic ductal carcinoma is orchestrated by STAT3

Background: Pancreatic ductal adenocarcinoma (PDAC) is a highly devastating disease with an overall 5-year survival rate of less than 8%. New evidence indicates that PDAC cells release pro-inflammatory metabolites that induce a marked alteration of normal hematopoiesis, favoring the expansion and accumulation of myeloid-derived suppressor cells (MDSCs). We report here that PDAC patients show increased levels of both circulating and tumor-infiltrating MDSC-like cells. Methods: The frequency of MDSC subsets in the peripheral blood was determined by flow cytometry in three independent cohorts of PDAC patients (total analyzed patients, n = 117). Frequency of circulating MDSCs was correlated with overall survival of PDAC patients. We also analyzed the frequency of tumor-infiltrating MDSC and the immune landscape in fresh biopsies. Purified myeloid cell subsets were tested in vitro for their T-cell suppressive capacity. Results: Correlation with clinical data revealed that MDSC frequency was significantly associated with a shorter patients' overall survival and metastatic disease. However, the immunosuppressive activity of purified MDSCs was detectable only in some patients and mainly limited to the monocytic subset. A transcriptome analysis of the immunosuppressive M-MDSCs highlighted a distinct gene signature in which STAT3 was crucial for monocyte re-programming. Suppressive M-MDSCs can be characterized as circulating STAT3/arginase1-expressing CD14+ cells. Conclusion: MDSC analysis aids in defining the immune landscape of PDAC patients for a more appropriate diagnosis, stratification and treatment

Unraveling the role of lymph node metastasis in PDAC and dCCA progression

Tumor progression is characterized by the spread of cancer cells from the primary site to regional lymph nodes and distant organs. In order to colonize distant sites, cancer cells must acquire invasive capacity, while evading elimination by immune cells. Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer with the lowest survival rate of all solid tumors. PDAC shares many histological and molecular features with distal cholangiocarcinoma (dCCA), which is a biliary tract cancer usually located in the head of the pancreas albeit showing better prognosis than PDAC. Lymph node metastases (LNM) represent an immunological meeting place for tumor cells and components of the adaptive immunity. Moreover, the pathological N-status (presence and number of LNM) is superior to the T-status (size of the tumor) in predicting survival of PDAC and dCCA patients. However, the biological role of LNM in tumor progression remains undefined. Here, using patient-derived organoids (PDOs) established from matched primary tumor (TP-PDOs) and LNM (LN-PDOs) of 5 patients, we show that both TP- and LN-PDOs shared the histological features and immunophenotypes of parental tissues. Comparative whole-exome sequencing of paired TP- and LN-PDOs showed substantial genetic conservation when considering functional driver genes. Moreover, LN-PDOs did not exhibit increased tumorigenic and/or metastatic capacity in vivo compared to matched TP-PDOs. On the other hand, transcriptional profiles of the cultures showed an overrepresentation of immune-related programs in LN-PDOs and ex vivo experiments demonstrated an elevated immunosuppressive activity of LN-PDOs towards human T lymphocytes. Mechanistically, we found that the mitochondrial form of arginase (ARG2), which catalyzes the hydrolysis of L-arginine to L-ornithine and urea, is overexpressed in LN-PDOs compared to matched TP-PDOs and, accordingly, the addition of exogenous L-arginine partially rescued the suppressive effect of LN-PDOs on T lymphocytes. Taken together, our data show that LNM are able to inhibit T lymphocytes proliferation potentially through arginine depletion, and this may contribute to systemic immunosuppression in these diseases

Platelets promote thromboinflammation in SARS-CoV-2 pneumonia

OBJECTIVE: Pulmonary thrombosis is observed in severe acute respiratory syndrome coronavirus 2 pneumonia. Aim was to investigate whether subpopulations of platelets were programmed to procoagulant and inflammatory activities in coronavirus disease 2019 (COVID-19) patients with pneumonia, without comorbidities predisposing to thromboembolism. Approach and Results: Overall, 37 patients and 28 healthy subjects were studied. Platelet-leukocyte aggregates, platelet-derived microvesicles, the expression of P-selectin, and active fibrinogen receptor on platelets were quantified by flow cytometry. The profile of 45 cytokines, chemokines, and growth factors released by platelets was defined by immunoassay. The contribution of platelets to coagulation factor activity was selectively measured. Numerous platelet-monocyte (mean\ub1SE, 67.9\ub14.9%, n=17 versus 19.4\ub13.0%, n=22; P<0.0001) and platelet-granulocyte conjugates (34.2\ub14.04% versus 8.6\ub10.7%; P<0.0001) were detected in patients. Resting patient platelets had similar levels of P-selectin (10.9\ub12.6%, n=12) to collagen-activated control platelets (8.7\ub11.5%), which was not further increased by collagen activation on patient platelets (12.4\ub12.5%, P=nonsignificant). The agonist-stimulated expression of the active fibrinogen receptor was reduced by 60% in patients (P<0.0001 versus controls). Cytokines (IL [interleukin]-1alpha, IL-1beta, IL-1RA, IL-4, IL-10, IL-13, IL, 17, IL-27, IFN [interferon]-alpha, and IFN-gamma), chemokines (MCP-1/CCL2), and growth factors (VEGF [vascular endothelial growth factor]-A/D) were released in significantly larger amounts upon stimulation of COVID-19 platelets. Platelets contributed to increased fibrinogen, VWF (von Willebrand factor), and factor XII in COVID-19 patients. Patients (28.5\ub10.7 s, n=32), unlike controls (31.6\ub10.5 s, n=28; P<0.001), showed accelerated factor XII-dependent coagulation.CONCLUSIONS: Platelets in COVID-19 pneumonia are primed to spread proinflammatory and procoagulant activities in systemic circulation

The immune modulatory effects of umbilical cord-derived mesenchymal stromal cells in severe COVID-19 pneumonia

Coronavirus disease 2019 (COVID-19) may result in a life-threatening condition due to a hyperactive immune reaction to severe acute respiratory syndrome-coronavirus-2 infection, for which no effective treatment is available. Based on the potent immunomodulatory properties of mesenchymal stromal cells (MSCs), a growing number of trials are ongoing. This prompted us to carry out a thorough immunological study in a patient treated with umbilical cord-derived MSCs and admitted to the Intensive Care Unit for COVID-19-related pneumonia. The exploratory analyses were assessed on both peripheral blood and bronchoalveolar fluid lavage samples at baseline and after cellular infusion by means of single-cell RNA sequencing, flow cytometry, ELISA, and functional assays. Remarkably, a normalization of circulating T lymphocytes count paralleled by a reduction of inflammatory myeloid cells, and a decrease in serum levels of pro-inflammatory cytokines, mostly of interleukin-6 and tumor necrosis factor-\u3b1, were observed. In addition, a drop of plasma levels of those chemokines essential for neutrophil recruitment became evident that paralleled the decrease of lung-infiltrating inflammatory neutrophils. Finally, circulating monocytes and low-density gradient neutrophils acquired immunosuppressive function. This scenario was accompanied by an amelioration of respiratory, renal, inflammatory, and pro-thrombotic indexes. Our results provide the first immunological data possibly related to the use of umbilical cord-derived MSCs in severe COVID-19 context

Baricitinib restrains the immune dysregulation in severe COVID-19 patients

COVID-19 patients develop pneumonia generally associated to lymphopenia and severe inflammatory response due to uncontrolled cytokine release. These mediators are transcriptionally regulated by the JAK-STAT signaling pathways, which can be disabled by small molecules

Fatal cytokine release syndrome by an aberrant FLIP/STAT3 axis

Inflammatory responses rapidly detect pathogen invasion and mount a regulated reaction. However, dysregulated anti-pathogen immune responses can provoke life-threatening inflammatory pathologies collectively known as cytokine release syndrome (CRS), exemplified by key clinical phenotypes unearthed during the SARS-CoV-2 pandemic. The underlying pathophysiology of CRS remains elusive. We found that FLIP, a protein that controls caspase-8 death pathways, was highly expressed in myeloid cells of COVID-19 lungs. FLIP controlled CRS by fueling a STAT3-dependent inflammatory program. Indeed, constitutive expression of a viral FLIP homolog in myeloid cells triggered a STAT3-linked, progressive, and fatal inflammatory syndrome in mice, characterized by elevated cytokine output, lymphopenia, lung injury, and multiple organ dysfunctions that mimicked human CRS. As STAT3-targeting approaches relieved inflammation, immune disorders, and organ failures in these mice, targeted intervention towards this pathway could suppress the lethal CRS inflammatory state