Coronavirus disease 2019 (COVID-19) is characterized by distinct patterns of disease progression suggesting diverse host immune responses. We performed an integrated immune analysis on a cohort of 50 COVID-19 patients with various disease severity. A unique phenotype was observed in severe and critical patients, consisting of a highly impaired interferon (IFN) type I response (characterized by no IFN-β and low IFN-α production and activity), associated with a persistent blood viral load and an exacerbated inflammatory response. Inflammation was partially driven by the transcriptional factor NF-κB and characterized by increased tumor necrosis factor (TNF)-α and interleukin (IL)-6 production and signaling. These data suggest that type-I IFN deficiency in the blood could be a hallmark of severe COVID-19 and provide a rationale for combined therapeutic approaches.

Dying cells initiate adaptive immunity by providing both antigens and inflammatory stimuli for dendritic cells (DCs), which in turn activate CD8+ T cells through a process called antigen cross-priming. To define how different forms of programmed cell death influence immunity, we established models of necroptosis and apoptosis, where dying cells are generated by RIPK3 and CASP8 dimerization, respectively. We found that release of inflammatory mediators such as damage-associated molecular patterns (DAMPs) by dying cells was not sufficient for CD8+ T cell cross-priming. Instead, robust cross-priming required RIPK1 signaling and NF-κB-induced transcription within dying cells. Decoupling NF-κB signaling from necroptosis or inflammatory apoptosis reduced priming efficiency and tumor immunity. Our results reveal that coordinated inflammatory and cell death signaling pathways within dying cells orchestrate adaptive immunity.

Background: Coronavirus disease 2019 (Covid-19) is a major global threat that has already caused more than 100,000 deaths worldwide. It is characterized by distinct patterns of disease progression implying a diverse host immune response. However, the immunological features and molecular mechanisms involved in Covid-19 severity remain so far poorly known.

Background Coronavirus disease-2019 (COVID-19), a respiratory disease has been associated with ischemic complications, coagulation disorders, and an endotheliitis. Objectives To explore endothelial damage and activation-related biomarkers in COVID-19 patients with criteria of hospitalization for referral to intensive care unit (ICU) and/or respiratory worsening. Methods Analysis of endothelial and angiogenic soluble markers in plasma from patients at admission. Results Study enrolled 40 consecutive COVID-19 patients admitted to emergency department that fulfilled criteria for hospitalization. Half of them were admitted in conventional wards without any ICU transfer during hospitalization; whereas the 20 others were directly transferred to ICU. Patients transferred in ICU were more likely to have lymphopenia, decreased SpO2 and increased D-dimer, CRP and creatinine levels. In those patients, soluble E-selectin and angiopoietin-2 were significantly increased (p value at 0.009 and 0.003, respectively). Increase in SELE gene expression (gene coding for E-selectin protein) was confirmed in an independent cohort of 32 patients using a whole blood gene expression profile analysis. In plasma, we found a strong association between angiopoetin-2 and CRP, creatinine and D-dimers (with p value at 0.001, 0.001 and 0.003, respectively). ROC curve analysis identified an Angiopoietin-2 cut-off of 5000 pg/mL as the best predictor for ICU outcome (Se = 80.1%, Sp = 70%, PPV = 72.7%, NPV = 77%), further confirmed in multivariate analysis after adjustment for creatinine, CRP or D-dimers. Conclusion Angiopoietin-2 is a relevant predictive factor for ICU direct admission in COVID-19 patients. This result showing an endothelial activation reinforces the hypothesis of a COVID-19-associated microvascular dysfunction.

Dying cells have an important role in the initiation of CD8 T cell-mediated immunity. The cross-presentation of antigens derived from dying cells enables dendritic cells to present exogenous tissue-restricted or tumour-restricted proteins on MHC class I molecules. Importantly, this pathway has been implicated in multiple autoimmune diseases and accounts for the priming of tumour antigen-specific T cells. Recent data have revealed that in addition to antigen, dying cells provide inflammatory and immunogenic signals that determine the efficiency of CD8 T cell cross-priming. The complexity of these signals has been evidenced by the multiple molecular pathways that result in cell death and that have now been shown to differentially influence antigen transfer and immunity. In this Review, we provide a detailed summary of both the passive and active signals that are generated by dying cells during their initiation of CD8 T cell-mediated immunity. We propose that molecules generated alongside cell death pathways - inducible damage-associated molecular patterns (iDAMPs) - are upstream immunological cues that actively regulate adaptive immunity.

Necroptosis is a form of programmed cell death that depends on the activation of receptor interacting protein kinase-1 (RIPK1) and RIPK3 by receptors such as tumor necrosis factor (TNF) receptor-1. Structural studies indicate that activation of RIPK3 by RIPK1 involves the formation of oligomers via interactions of the RIP homotypic interaction motif (RHIM) domains shared by both proteins; however, the molecular mechanisms by which this occurs are not fully understood. To gain insight into this process, we constructed versions of RIPK3 that could be induced to dimerize or oligomerize in response to a synthetic drug. Using this system, we find that although the formation of RIPK3 dimers is itself insufficient to trigger cell death, this dimerization seeds a RHIM-dependent complex, the propagation and stability of which is controlled by caspase-8 and RIPK1. Consistent with this idea, we find that chemically enforced oligomerization of RIPK3 is sufficient to induce necroptosis, independent of the presence of the RHIM domain, TNF stimulation or RIPK1 activity. Further, although RIPK1 contributes to TNF-mediated RIPK3 activation, we find that RIPK1 intrinsically suppresses spontaneous RIPK3 activation in the cytosol by controlling RIPK3 oligomerization. Cells lacking RIPK1 undergo increased spontaneous RIPK3-dependent death on accumulation of the RIPK3 protein, while cells containing a chemically inhibited or catalytically inactive form of RIPK1 are protected from this form of death. Together, these data indicate that RIPK1 can activate RIPK3 in response to receptor signaling, but also acts as a negative regulator of spontaneous RIPK3 activation in the cytosol.

Summary Programmed necrosis (or necroptosis) is a form of cell death triggered by the activation of receptor interacting protein kinase-3 (RIPK3). Several reports have implicated mitochondria and mitochondrial reactive oxygen species (ROS) generation as effectors of RIPK3-dependent cell death. Here, we directly test this idea by employing a method for the specific removal of mitochondria via mitophagy. Mitochondria-deficient cells were resistant to the mitochondrial pathway of apoptosis, but efficiently died via TNF-induced, RIPK3-dependent programmed necrosis or as a result of direct oligomerization of RIPK3. Although the ROS scavenger butylated hydroxyanisol (BHA) delayed TNF-induced necroptosis, it had no effect on necroptosis induced by RIPK3 oligomerization. Further, while TNF-induced ROS production was dependent on mitochondria, the inhibition of TNF-induced necroptosis by BHA was observed in mitochondria-depleted cells. Our data indicate that mitochondrial ROS production accompanies, but does not cause, RIPK3-dependent necroptotic cell death.

The success of antitumor immune responses depends on the infiltration of solid tumors by effector T cells, a process guided by chemokines. Here we show that in vivo post-translational processing of chemokines by dipeptidylpeptidase 4 (DPP4, also known as CD26) limits lymphocyte migration to sites of inflammation and tumors. Inhibition of DPP4 enzymatic activity enhanced tumor rejection by preserving biologically active CXCL10 and increasing trafficking into the tumor by lymphocytes expressing the counter-receptor CXCR3. Furthermore, DPP4 inhibition improved adjuvant-based immunotherapy, adoptive T cell transfer and checkpoint blockade. These findings provide direct in vivo evidence for control of lymphocyte trafficking via CXCL10 cleavage and support the use of DPP4 inhibitors for stabilizing biologically active forms of chemokines as a strategy to enhance tumor immunotherapy.