Cell death in the maintenance and abrogation of tolerance: the five Ws of dying cells

Extracellular Matrix Cues Regulate Mechanosensing and Mechanotransduction of Cancer Cells

Extracellular biophysical properties have particular implications for a wide spectrum of cellular behaviors and functions, including growth, motility, differentiation, apoptosis, gene expression, cell-matrix and cell-cell adhesion, and signal transduction including mechanotransduction. Cells not only react to unambiguously mechanical cues from the extracellular matrix (ECM), but can occasionally manipulate the mechanical features of the matrix in parallel with biological characteristics, thus interfering with downstream matrix-based cues in both physiological and pathological processes. Bidirectional interactions between cells and (bio)materials in vitro can alter cell phenotype and mechanotransduction, as well as ECM structure, intentionally or unintentionally. Interactions between cell and matrix mechanics in vivo are of particular importance in a variety of diseases, including primarily cancer. Stiffness values between normal and cancerous tissue can range between 500 Pa (soft) and 48 kPa (stiff), respectively. Even the shear flow can increase from 0.1-1 dyn/cm2 (normal tissue) to 1-10 dyn/cm2 (cancerous tissue). There are currently many new areas of activity in tumor research on various biological length scales, which are highlighted in this review. Moreover, the complexity of interactions between ECM and cancer cells is reduced to common features of different tumors and the characteristics are highlighted to identify the main pathways of interaction. This all contributes to the standardization of mechanotransduction models and approaches, which, ultimately, increases the understanding of the complex interaction. Finally, both the in vitro and in vivo effects of this mechanics-biology pairing have key insights and implications for clinical practice in tumor treatment and, consequently, clinical translation.

Disulfiram alleviates pristane-induced lupus via inhibiting GSDMD-mediated pyroptosis

Activation of multiple inflammasomes in monocytes/macrophages is associated with the pathogenesis of systemic lupus erythematosus (SLE). Gasdermin D (GSDMD)-mediated pyroptosis, a common consequence of multiple activated inflammasomes, is a programmed cell death with strong inflammatory responses. This suggested that targeting monocyte/macrophage pyroptosis might provide an opportunity to cure SLE. Here, we aimed to investigate the effect of disulfiram (DSF), a small molecule inhibitor of pyroptosis, and its potential therapeutic mechanism for SLE. The mRNA expression of GSDMD and IL-1β were significantly increased in peripheral blood mononuclear cells (PBMCs) from SLE patients. Importantly, we found serum from SLE patients rather than healthy controls induced GSDMD-mediated pyroptosis in THP-1 cells, as evidenced by enhanced LDH release, increased number of PI-positive cells, and high expression of full-length GSDMD and N-terminal GSDMD. Interestingly, treatment with DSF obviously inhibited pyroptosis of THP-1 cells induced by serum from SLE patients. Of note, DSF administration reduced proteinuria, serum anti-dsDNA level, and renal immune complex. It also attenuated renal damage in PIL mice. Further research found that the high level of serum IL-β and GSDMD-mediated pyroptosis of glomerular macrophages in PIL mice were rescued with DSF treatment. These data implied that GSDMD-mediated monocytes/macrophages pyroptosis played an important role in the pathogenesis of SLE and DSF might be a potential alternative therapeutic agent for SLE.

Serum pentraxin 3 concentration correlates with disease severity in patients with myasthenia gravis

OBJECTIVE

Myasthenia gravis (MG) is an antibody-mediated inflammatory disease affecting post-synaptic membranes of neuromuscular junctions, and objective biomarkers of MG disease activity are lacking. Pentraxin 3 (PTX3) is an acute-phase inflammatory glycoprotein in the same family as C-reactive protein that is associated with disease activity in several autoimmune disorders. Thus, we investigated whether circulating PTX3 is a useful biomarker of MG activity.

METHODS

Serum PTX3 was measured in 40 patients with MG who were positive for anti-acetylcholine receptor antibody, and in 30 healthy and disease controls, using a commercial enzyme-linked immunosorbent assay kit. In patients with MG, the correlation of serum PTX3 levels with disease severity scales at serum sampling, including MG Foundation of America (MGFA) classification, MG activity of daily living (MG-ADL) score, and quantitative MG (QMG) score, were investigated.

RESULTS

Although there was no significant difference in serum PTX3 between the MG and control groups (mean, 3346 pg/mL in MG group vs. 2870 pg/mL in control group, P = 0.56), serum PTX3 moderately correlated with all disease severity scores (MGFA classification: Spearman's ρ = 0.53, P = 0.0004; MG-ADL score: Spearman's ρ = 0.45, P = 0.004; QMG score: Spearman's ρ = 0.50, P = 0.004).

CONCLUSION

Our results suggest that circulating PTX3 may reflect the extent of neuromuscular junction damage and might be involved in the pathogenesis of MG.

Engineered RBCs Encapsulating Antigen Induce Multi-Modal Antigen-Specific Tolerance and Protect Against Type 1 Diabetes

Antigen-specific therapies that suppress autoreactive T cells without inducing systemic immunosuppression are a much-needed treatment for autoimmune diseases, yet effective strategies remain elusive. We describe a microfluidic Cell Squeeze® technology to engineer red blood cells (RBCs) encapsulating antigens to generate tolerizing antigen carriers (TACs). TACs exploit the natural route of RBC clearance enabling tolerogenic presentation of antigens. TAC treatment led to antigen-specific T cell tolerance towards exogenous and autoantigens in immunization and adoptive transfer mouse models of type 1 diabetes (T1D), respectively. Notably, in several accelerated models of T1D, TACs prevented hyperglycemia by blunting effector functions of pathogenic T cells, particularly in the pancreas. Mechanistically, TACs led to impaired trafficking of diabetogenic T cells to the pancreas, induced deletion of autoreactive CD8 T cells and expanded antigen specific Tregs that exerted bystander suppression. Our results highlight TACs as a novel approach for reinstating immune tolerance in CD4 and CD8 mediated autoimmune diseases.

PEBP balances apoptosis and autophagy in whitefly upon arbovirus infection

Apoptosis and autophagy are two common forms of programmed cell death (PCD) used by host organisms to fight against virus infection. PCD in arthropod vectors can be manipulated by arboviruses, leading to arbovirus-vector coexistence, although the underlying mechanism is largely unknown. In this study, we find that coat protein (CP) of an insect-borne plant virus TYLCV directly interacts with a phosphatidylethanolamine-binding protein (PEBP) in its vector whitefly to downregulate MAPK signaling cascade. As a result, apoptosis is activated in the whitefly increasing viral load. Simultaneously, the PEBP4-CP interaction releases ATG8, a hallmark of autophagy initiation, which reduces arbovirus levels. Furthermore, apoptosis-promoted virus amplification is prevented by agonist-induced autophagy, whereas the autophagy-suppressed virus load is unaffected by manipulating apoptosis, suggesting that the viral load is predominantly determined by autophagy rather than by apoptosis. Our results demonstrate that a mild intracellular immune response including balanced apoptosis and autophagy might facilitate arbovirus preservation within its whitefly insect vector.

Arbovirus has co-evolved with its insect vector, enabling efficient and persistent transmission by vectors. Here, the authors reveal an immune homeostatic mechanism shaped by apoptosis and autophagy that facilitates arbovirus preservation within its whitefly vector.

CD8+ T cells specific for cryptic apoptosis-associated epitopes exacerbate experimental autoimmune encephalomyelitis

The autoimmune immunopathology occurring in multiple sclerosis (MS) is sustained by myelin-specific and -nonspecific CD8⁺ T cells. We have previously shown that, in MS, activated T cells undergoing apoptosis induce a CD8⁺ T cell response directed against antigens that are unveiled during the apoptotic process, namely caspase-cleaved structural proteins such as non-muscle myosin and vimentin. Here, we have explored in vivo the development and the function of the immune responses to cryptic apoptosis-associated epitopes (AEs) in a well-established mouse model of MS, experimental autoimmune encephalomyelitis (EAE), through a combination of immunization approaches, multiparametric flow cytometry, and functional assays. First, we confirmed that this model recapitulated the main findings observed in MS patients, namely that apoptotic T cells and effector/memory AE-specific CD8⁺ T cells accumulate in the central nervous system of mice with EAE, positively correlating with disease severity. Interestingly, we found that AE-specific CD8⁺ T cells were present also in the lymphoid organs of unprimed mice, proliferated under peptide stimulation in vitro, but failed to respond to peptide immunization in vivo, suggesting a physiological control of this response. However, when mice were immunized with AEs along with EAE induction, AE-specific CD8⁺ T cells with an effector/memory phenotype accumulated in the central nervous system, and the disease severity was exacerbated. In conclusion, we demonstrate that AE-specific autoimmunity may contribute to immunopathology in neuroinflammation.

Research and application of hydrostatic high pressure in tumor vaccines (Review)

It is well known that hydrostatic pressure (HP) is a physical parameter that is now regarded as an important variable for life. High hydrostatic pressure (HHP) technology has influenced biological systems for more than 100 years. Food and bioscience researchers have shown great interest in HHP technology over the past few decades. The development of knowledge related to this area can better facilitate the application of HHP in the life sciences. Furthermore, new applications for HHP may come from these current studies, particularly in tumor vaccines. Currently, cancer recurrence and metastasis continue to pose a serious threat to human health. The limited efficacy of conventional treatments has led to the need for breakthroughs in immunotherapy and other related areas. Research into tumor vaccines is providing new insights for cancer treatment. The purpose of this review is to present the main findings reported thus far in the relevant scientific literature, focusing on knowledge related to HHP technology and tumor vaccines, and to demonstrate the potential of applying HHP technology to tumor vaccine development.

The immune system view of the coronavirus SARS-CoV-2

Knowing the "point of view" of the immune system is essential to understand the characteristic of a pandemic, such as that generated by the Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV)-2, responsible for the Coronavirus Disease (COVID)-19. In this review, we will discuss the general host/pathogen interactions dictating protective immune response or immunopathology, addressing the role of immunity or immunopathology in influencing the clinical infection outcome, and debate the potential immunoprophylactic and immunotherapy strategies required to fight the virus infection.

Genomic investigation of co-targeting tumor immune microenvironment and immune checkpoints in pan-cancer immunotherapy

Drugs that target immune checkpoints (ICPs) have become the most popular weapons in cancer immunotherapy; however, they are only beneficial for a small fraction of patients. Accumulating evidence suggests that the tumor immune microenvironment (TIME) plays a critical role in anti-cancer immunity. This study aimed to assess the potential merits and feasibility of combinational targeting ICPs and TIME in cancer immunotherapy. A total of 31 cancer type-specific datasets in TCGA were individually collected by the publicly available web servers for multiple bioinformatic analyses of ICPs and TIME factors. GEPIA was used to calculate the prognostic indexes, STRING was used to construct protein-protein interactions, cBioPortal was used for visualization and comparison of genetic alterations, and TISIDB was used to explore the correlation to tumor-infiltrating lymphocytes (TILs). Intriguingly, TIME factors were identified to have more global coverage and prognostic significance across multiple cancer types compared with ICPs, thus offering more general targetability in clinical therapy. Moreover, TIME factors showed interactive potential with ICPs, and genomic alteration of TIME factors coupled with that of ICPs, at least in pancreatic cancer. Furthermore, TIME factors were found to be significantly associated with TILs, including but not limited to pancreatic cancer. Finally, the clinical significance and translational potential of further combination therapies that incorporate both ICP inhibitors and TIME factor-targeted treatments were discussed. Together, TIME factors are promising immunotherapeutic targets, and a combination strategy of TIME factors-targeted therapies with ICP inhibitors may benefit more cancer patients in the future.

Pathogen-reduced PRP blocks T-cell activation, induces Treg cells, and promotes TGF-β expression by cDCs and monocytes in mice

Alloimmunization against platelet-rich plasma (PRP) transfusions can lead to complications such as platelet refractoriness or rejection of subsequent transfusions and transplants. In mice, pathogen reduction treatment of PRP with UVB light and riboflavin (UV+R) prevents alloimmunization and appears to induce partial antigen-specific tolerance to subsequent transfusions. Herein, the in vivo responses of antigen-presenting cells and T cells to transfusion with UV+R-treated allogeneic PRP were evaluated to understand the cellular immune responses leading to antigen-specific tolerance. Mice that received UV+R-treated PRP had significantly increased transforming growth factor β (TGF-β) expression by CD11b+ CD4+ CD11cHi conventional dendritic cells (cDCs) and CD11bHi monocytes (P < .05). While robust T-cell responses to transfusions with untreated allogeneic PRP were observed (P < .05), these were blocked by UV+R treatment. Mice given UV+R-treated PRP followed by untreated PRP showed an early significant (P < .01) enrichment in regulatory T (Treg) cells and associated TGF-β production as well as diminished effector T-cell responses. Adoptive transfer of T-cell-enriched splenocytes from mice given UV+R-treated PRP into naive recipients led to a small but significant reduction of CD8+ T-cell responses to subsequent allogeneic transfusion. These data demonstrate that pathogen reduction with UV+R induces a tolerogenic profile by way of CD11b+ CD4+ cDCs, monocytes, and induction of Treg cells, blocking T-cell activation and reducing secondary T-cell responses to untreated platelets in vivo.

Necroptosis in Immuno-Oncology and Cancer Immunotherapy

Immune-checkpoint blockers (ICBs) have revolutionized oncology and firmly established the subfield of immuno-oncology. Despite this renaissance, a subset of cancer patients remain unresponsive to ICBs due to widespread immuno-resistance. To "break" cancer cell-driven immuno-resistance, researchers have long floated the idea of therapeutically facilitating the immunogenicity of cancer cells by disrupting tumor-associated immuno-tolerance via conventional anticancer therapies. It is well appreciated that anticancer therapies causing immunogenic or inflammatory cell death are best positioned to productively activate anticancer immunity. A large proportion of studies have emphasized the importance of immunogenic apoptosis (i.e., immunogenic cell death or ICD); yet, it has also emerged that necroptosis, a programmed necrotic cell death pathway, can also be immunogenic. Emergence of a proficient immune profile for necroptosis has important implications for cancer because resistance to apoptosis is one of the major hallmarks of tumors. Putative immunogenic or inflammatory characteristics driven by necroptosis can be of great impact in immuno-oncology. However, as is typical for a highly complex and multi-factorial disease like cancer, a clear cause versus consensus relationship on the immunobiology of necroptosis in cancer cells has been tough to establish. In this review, we discuss the various aspects of necroptosis immunobiology with specific focus on immuno-oncology and cancer immunotherapy.

Pentraxin 3: A promising therapeutic target for autoimmune diseases

Pentraxin 3 (PTX3) is a prototypic humoral soluble pattern recognition molecule that exerts a pivotal role in innate immune response and inflammation, as well as in tissue damage and remodeling. Recently, emerging evidence has revealed that PTX3 is involved in the occurrence and development of various autoimmune diseases, such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), ankylosing spondylitis (AS), systemic sclerosis (SSc), inflammatory bowel disease (IBD), multiple sclerosis (MS) and psoriasis, etc. In this review, we have succinctly summarized the complex immunological functions of PTX3 and mostly focused on recent findings of the pleiotropic activities played by PTX3 in the pathogenesis of autoimmune diseases, aiming at hopefully offering possible future therapeutic alternatives.

Combination of chemotherapy and PD-1 blockade induces T cell responses to tumor non-mutated neoantigens

Here, we developed an unbiased, functional target-discovery platform to identify immunogenic proteins from primary non-small cell lung cancer (NSCLC) cells that had been induced to apoptosis by cisplatin (CDDP) treatment in vitro, as compared with their live counterparts. Among the multitude of proteins identified, some of them were represented as fragmented proteins in apoptotic tumor cells, and acted as non-mutated neoantigens (NM-neoAgs). Indeed, only the fragmented proteins elicited effective multi-specific CD4+ and CD8+ T cell responses, upon a chemotherapy protocol including CDDP. Importantly, these responses further increased upon anti-PD-1 therapy, and correlated with patients' survival and decreased PD-1 expression. Cross-presentation assays showed that NM-neoAgs were unveiled in apoptotic tumor cells as the result of caspase-dependent proteolytic activity of cellular proteins. Our study demonstrates that apoptotic tumor cells generate a repertoire of immunogenic NM-neoAgs that could be potentially used for developing effective T cell-based immunotherapy across multiple cancer patients.

Trial watch: chemotherapy-induced immunogenic cell death in immuno-oncology

The term ‘immunogenic cell death’ (ICD) denotes an immunologically unique type of regulated cell death that enables, rather than suppresses, T cell-driven immune responses that are specific for antigens derived from the dying cells. The ability of ICD to elicit adaptive immunity heavily relies on the immunogenicity of dying cells, implying that such cells must encode and present antigens not covered by central tolerance (antigenicity), and deliver immunostimulatory molecules such as damage-associated molecular patterns and cytokines (adjuvanticity). Moreover, the host immune system must be equipped to detect the antigenicity and adjuvanticity of dying cells. As cancer (but not normal) cells express several antigens not covered by central tolerance, they can be driven into ICD by some therapeutic agents, including (but not limited to) chemotherapeutics of the anthracycline family, oxaliplatin and bortezomib, as well as radiation therapy. In this Trial Watch, we describe current trends in the preclinical and clinical development of ICD-eliciting chemotherapy as partner for immunotherapy, with a focus on trials assessing efficacy in the context of immunomonitoring.

Pas de Deux: Control of Anti-tumor Immunity by Cancer-Associated Inflammation

In many settings, tumor-associated inflammation, supported mainly by innate immune cells, contributes to tumor growth. Initial innate activation triggers secretion of inflammatory, regenerative, and anti-inflammatory cytokines, which in turn shape the adaptive immune response to the tumor. Here, we review the current understanding of the intricate dialog between cancer-associated inflammation and anti-tumor immunity. We discuss the changing nature of these interactions during tumor progression and the impact of the tissue environment on the anti-tumor immune response. In this context, we outline important gaps in current understanding by considering basic research and findings in the clinic. The future of cancer immunotherapy and its utility depend on improved understanding of these interactions and the ability to manipulate them in a predictable and beneficial manner.

Paraneoplastic Pemphigus: Paraneoplastic Autoimmune Disease of the Skin and Mucosa

Paraneoplastic pemphigus (PNP) is a rare but life-threatening mucocutaneous disease mediated by paraneoplastic autoimmunity. Various neoplasms are associated with PNP. Intractable stomatitis and polymorphous cutaneous eruptions, including blisters and lichenoid dermatitis, are characteristic clinical features caused by humoral and cell-mediated autoimmune reactions. Autoreactive T cells and IgG autoantibodies against heterogeneous antigens, including plakin family proteins and desmosomal cadherins, contribute to the pathogenesis of PNP. Several mechanisms of autoimmunity may be at play in this disease on the type of neoplasm present. Diagnosis can be made based on clinical and histopathological features, the presence of anti-plakin autoantibodies, and underlying neoplasms. Immunosuppressive agents and biologics including rituximab have been used for the treatment of PNP; however, the prognosis is poor due to underlying malignancies, severe infections during immunosuppressive treatment, and bronchiolitis obliterans mediated by autoimmunity. In this review, we overview the characteristics of PNP and focus on the immunopathology and the potential pathomechanisms of this disease.

Counter-regulation of regulatory T cells by autoreactive CD8+ T cells in rheumatoid arthritis

The mechanisms whereby autoreactive T cells escape peripheral tolerance establishing thus autoimmune diseases in humans remain an unresolved question. Here, we demonstrate that autoreactive polyfunctional CD8⁺ T cells recognizing self-antigens (i.e., vimentin, actin cytoplasmic 1, or non-muscle myosin heavy chain 9 epitopes) with high avidity, counter-regulate Tregs by killing them, in a consistent percentage of rheumatoid arthritis (RA) patients. Indeed, these CD8⁺ T cells express a phenotype and gene profile of effector (eff) cells and, upon antigen-specific activation, kill Tregs indirectly in an NKG2D-dependent bystander fashion in vitro. This data provides a mechanistic basis for the finding showing that AE-specific (CD107a⁺) CD8⁺ T killer cells correlate, directly with the disease activity score, and inversely with the percentage of activated Tregs, in both steady state and follow-up studies in vivo. In addition, multiplex immunofluorescence imaging analyses of inflamed synovial tissues in vivo show that a remarkable number of CD8⁺ T cells express granzyme-B and selectively contact FOXP3⁺ Tregs, some of which are in an apoptotic state, validating hence the possibility that CD8⁺ Teff cells can counteract neighboring Tregs within inflamed tissues, by killing them. Alternatively, the disease activity score of a different subset of patients is correlated with the expansion of a peculiar subpopulation of autoreactive low avidity, partially-activated (pa)CD8⁺ T cells that, despite they conserve the conventional naïve (N) phenotype, produce high levels of tumor necrosis factor (TNF)-α and exhibit a gene expression signature of a progressive activation state. Tregs directly correlate with the expansion of this autoreactive (low avidity) paCD8⁺ TN cell subset in vivo, and efficiently control their differentiation rather their proliferation in vitro. Interestingly, autoreactive high avidity CD8⁺ Teff cells or low avidity paCD8⁺ TN cells are significantly expanded in RA patients who would become non-responders or patients who would become responders to TNF-α inhibitor therapy, respectively. These data provide evidence of a previously undescribed role of such mechanisms in the progression and therapy of RA.

A Chromatin-Mimetic Nanomedicine for Therapeutic Tolerance Induction

The undesirable immune response poses a life-threatening challenge to human health. It not only deteriorates the therapeutic performance of biologic drugs but also contributes to various diseases such as allergies and autoimmune diseases. Inspired by the role of chromatin in the maintenance of natural immune tolerance, here we report a DNA-protein polymeric nanocomplex that can mimic the tolerogenic function of chromatin and induce an immune tolerance to its protein cargos. We first proved that the chromatin-mimetic nanomedicine loaded with keyhole limpet hemocyanin (KLH), a highly immunogenic model protein, could elicit a durable antigen-specific immune tolerance to KLH lasting for at least five weeks in mice. Following the proof-of-concept study, we demonstrated that this nanomedicine could be applied to improve the safety and efficacy of a biologic drug, PEGylated uricase, by attenuating the relevant antibody (Ab) responses. Moreover, we also demonstrated that prophylactic treatments with this nanomedicine could tolerize the immune system with the allergen of ovalbumin (OVA) and thus inhibit the occurrence of airway inflammation in an OVA-induced allergic asthma murine model. Collectively, our work illustrates a nature-inspired concept of immune tolerance induction and establishes a useful tool to specifically suppress unwanted immune responses for therapeutic purposes.

CD169+ Macrophages Capture and Dendritic Cells Instruct: The Interplay of the Gatekeeper and the General of the Immune System

Since the seminal discovery of dendritic cells (DCs) by Steinman and Cohn in 1973, there has been an ongoing debate to what extent macrophages and DCs are related and perform different functions. The current view is that macrophages and DCs originate from different lineages and that only DCs have the capacity to initiate adaptive immunity. Nevertheless, as we will discuss in this review, lymphoid tissue resident CD169⁺ macrophages have been shown to act in concert with DCs to promote or suppress adaptive immune responses for pathogens and self-antigens, respectively. Accordingly, we propose a functional alliance between CD169⁺ macrophages and DCs in which a division of tasks is established. CD169⁺ macrophages are responsible for the capture of pathogens and are frequently the first cell type infected and thereby provide a confined source of antigen. Subsequently, cross-presenting DCs interact with these antigen-containing CD169⁺ macrophages, pick up antigens and activate T cells. The cross-priming of T cells by DCs is enhanced by the localized production of type I interferons (IFN-I) derived from CD169⁺ macrophages and plasmacytoid DCs (pDCs) that induces DC maturation. The interaction between CD169⁺ macrophages and DCs appears not only to be essential for immune responses against pathogens, but also plays a role in the induction of self-tolerance and immune responses against cancer. In this review we will discuss the studies that demonstrate the collaboration between CD169⁺ macrophages and DCs in adaptive immunity.

Cell death and immunity in cancer: From danger signals to mimicry of pathogen defense responses

The immunogenicity of cancer cells is an emerging determinant of anti-cancer immunotherapy. Beyond developing immunostimulatory regimens like dendritic cell-based vaccines, immune-checkpoint blockers, and adoptive T-cell transfer, investigators are beginning to focus on the immunobiology of dying cancer cells and its relevance for the success of anticancer immunotherapies. It is currently accepted that cancer cells may die in response to anti-cancer therapies through regulated cell death programs, which may either repress or increase their immunogenic potential. In particular, the induction of immunogenic cancer cell death (ICD), which is hallmarked by the emission of damage-associated molecular patterns (DAMPs); molecules analogous to pathogen-associated molecular patterns (PAMPs) acting as danger signals/alarmins, is of great relevance in cancer therapy. These ICD-associated danger signals favor immunomodulatory responses that lead to tumor-associated antigens (TAAs)-directed T-cell immunity, which paves way for the removal of residual, treatment-resistant cancer cells. It is also emerging that cancer cells succumbing to ICD can orchestrate "altered-self mimicry" i.e. mimicry of pathogen defense responses, on the levels of nucleic acids and/or chemokines (resulting in type I interferon/IFN responses or pathogen response-like neutrophil activity). In this review, we exhaustively describe the main molecular, immunological, preclinical, and clinical aspects of immunosuppressive cell death or ICD (with respect to apoptosis, necrosis and necroptosis). We also provide an extensive historical background of these fields, with special attention to the self/non-self and danger models, which have shaped the field of cell death immunology.

The synergy between ionizing radiation and immunotherapy in the treatment of prostate cancer

There has been a surge in the use of immunotherapy for genitourinary malignancies. Immunotherapy is an established treatment for metastatic renal cell carcinoma and nonmuscle invasive bladder cancer, but its potential for treating prostate cancer (PCa) remains under investigation. Despite reported survival benefits, no published Phase III PCa trials using immunotherapy only as a treatment has demonstrated direct antitumor effects by reducing prostate-specific antigen levels. Subsequently, the thought of combining immunotherapy with other treatment modalities has gained traction as a way to achieving optimal results. Based on data from other malignancies, it is hypothesized that radiotherapy and immunotherapy can act synergistically to improve outcomes. We will discuss the clinical potential of combining immune-based treatments with radiotherapy as a treatment for advanced PCa.

The oscillation of intracellular Ca2+ influx associated with the circadian expression of Piezo1 and TRPV4 in the bladder urothelium

We previously showed that bladder functions are controlled by clock genes with circadian rhythm. The sensation of bladder fullness (SBF) is sensed by mechano-sensor such as Piezo1 and TRPV4 in the mouse bladder urothelium. However, functional circadian rhythms of such mechano-sensors remain unknown. To investigate functional circadian changes of these mechano-sensors, we measured circadian changes in stretch-evoked intracellular Ca²⁺ influx ([Ca²⁺] _i ) using mouse primary cultured urothelial cells (MPCUCs). Using Ca²⁺ imaging, stretch-evoked [Ca²⁺] _i was quantified every 4 h in MPCUCs derived from wild-type (WT) and Clock ^Δ19/Δ19 mice, which showed a nocturia phenotype. Furthermore, a Piezo1 inhibitor GsMTx4 and a TRPV4 inhibitor Ruthenium Red were applied and stretch-evoked [Ca²⁺] _i in MPCUCs was measured to investigate their contribution to SBF. Stretch-evoked [Ca²⁺] _i showed a circadian rhythm in the WT mice. In contrast, Clock ^Δ19/Δ19 mice showed disrupted circadian rhythm. The administration of both GsMTx4 and Ruthenium Red eliminated the circadian rhythm of stretch-evoked [Ca²⁺] _i in WT mice. We conclude that SBF may have a circadian rhythm, which is created by functional circadian changes of Piezo1 and TRPV4 being controlled by clock genes to be active during wakefulness and inactive during sleep. Abnormalities of clock genes disrupt SBF, and induce nocturia.

Mertk on tumor macrophages is a therapeutic target to prevent tumor recurrence following radiation therapy

Radiation therapy provides a means to kill large numbers of cancer cells in a controlled location resulting in the release of tumor-specific antigens and endogenous adjuvants. However, by activating pathways involved in apoptotic cell recognition and phagocytosis, irradiated cancer cells engender suppressive phenotypes in macrophages. We demonstrate that the macrophage-specific phagocytic receptor, Mertk is upregulated in macrophages in the tumor following radiation therapy. Ligation of Mertk on macrophages results in anti-inflammatory cytokine responses via NF-kB p50 upregulation, which in turn limits tumor control following radiation therapy. We demonstrate that in immunogenic tumors, loss of Mertk is sufficient to permit tumor cure following radiation therapy. However, in poorly immunogenic tumors, TGFβ inhibition is also required to result in tumor cure following radiation therapy. These data demonstrate that Mertk is a highly specific target whose absence permits tumor control in combination with radiation therapy.

DNA induction of MDM2 promotes proliferation of human renal mesangial cells and alters peripheral B cells subsets in pediatric systemic lupus erythematosus

The study is aimed to investigate the role of MDM2 in the pathogenesis of lupus nephritis (LN) in pediatric SLE (pSLE). We confirmed that MDM2 expression was increased in peripheral blood mononuclear cells (PBMCs) as well as renal specimen of SLE compared with that of controls by western blot and immunofluorescence staining. Percentage of apoptotic and necrotic CD4⁺T, CD8⁺T and B cells were detected by flow cytometry respectively and levels of plasma cell free DNA (cfDNA) were quantified in SLE and healthy controls (HC). We also proved that elevated apoptotic and necrotic CD4⁺T cells were the main cause for increased plasma levels of cfDNA in pSLE. Additionally, upon DNA transfection MDM2 increased while P53 and P21 decreased in human renal mesangial cells (HRMC), with concomitant increase in proliferation rate and proportion of cells in S phase, as demonstrated by cell proliferation assay and cell cycle analysis. However, MDM2 inhibition reversed the trend. Furthermore, percentage of switched memory B cells decreased and proportion of double negative B cells increased upon blockage of MDM2 in PBMC. In summary, our study provided the first evidence that DNA induction of MDM2 promotes proliferation of HRMC and alters peripheral B cells subsets in pSLE. Thus our study has not only elucidated the pathogenesis of MDM2 in pediatric LN but also provided a novel target for drug development. In conclusion, our data suggested that apoptosis, cfDNA and MDM2 could form a pathological axis in SLE, especially in pSLE.

The TAM family as a therapeutic target in combination with radiation therapy

Radiation therapy is primarily a modality to kill cancer cells in the treatment field. It is becoming increasingly clear that radiation therapy can also be used to direct immune responses that have the potential to clear residual local or distant disease outside the treatment field. We believe that cancer cell death is the critical link between these processes. Understanding the handling of dying cancer cells by immune cells in the tumor environment is crucial to facilitate immune responses following radiation therapy. We review the role of the TAM (Tyro3 Axl Mertk) group of receptor tyrosine kinases and their role following radiation-induced cancer cell death in the tumor environment.

Trial watch: Immunogenic cell death induction by anticancer chemotherapeutics

The expression "immunogenic cell death" (ICD) refers to a functionally unique form of cell death that facilitates (instead of suppressing) a T cell-dependent immune response specific for dead cell-derived antigens. ICD critically relies on the activation of adaptive responses in dying cells, culminating with the exposure or secretion of immunostimulatory molecules commonly referred to as "damage-associated molecular patterns". Only a few agents can elicit bona fide ICD, including some clinically established chemotherapeutics such as doxorubicin, epirubicin, idarubicin, mitoxantrone, bleomycin, bortezomib, cyclophosphamide and oxaliplatin. In this Trial Watch, we discuss recent progress on the development of ICD-inducing chemotherapeutic regimens, focusing on studies that evaluate clinical efficacy in conjunction with immunological biomarkers.

Bioengineering strategies for inducing tolerance in autoimmune diabetes

Type 1 diabetes is an autoimmune disease marked by the destruction of insulin-producing beta cells in the pancreatic islets. Strategies to delay onset or prevent the autoimmune recognition of beta cell antigens or T cell-mediated killing of beta cells have mainly focused on systemic immunomodulation and antigen-specific immunotherapy. To bridge the fields of type 1 diabetes immunology and biomaterials engineering, this article will review recent trends in the etiology of type 1 diabetes immunopathology and will focus on the contributions of emerging bioengineered strategies in the fight against beta cell autoimmunity in type 1 diabetes.

Engineered erythrocytes covalently linked to antigenic peptides can protect against autoimmune disease

Current therapies for autoimmune diseases rely on traditional immunosuppressive medications that expose patients to an increased risk of opportunistic infections and other complications. Immunoregulatory interventions that act prophylactically or therapeutically to induce antigen-specific tolerance might overcome these obstacles. Here we use the transpeptidase sortase to covalently attach disease-associated autoantigens to genetically engineered and to unmodified red blood cells as a means of inducing antigen-specific tolerance. This approach blunts the contribution to immunity of major subsets of immune effector cells (B cells, CD4⁺ and CD8⁺ T cells) in an antigen-specific manner. Transfusion of red blood cells expressing self-antigen epitopes can alleviate and even prevent signs of disease in experimental autoimmune encephalomyelitis, as well as maintain normoglycemia in a mouse model of type 1 diabetes.

Listeria monocytogenes-Induced Cell Death Inhibits the Generation of Cell-Mediated Immunity

The influence of cell death on adaptive immunity has been studied for decades. Despite these efforts, the intricacies of how various cell death pathways shape immune responses in the context of infection remain unclear, particularly with regard to more recently discovered pathways such as pyroptosis. The emergence of Listeria monocytogenes as a promising immunotherapeutic platform demands a thorough understanding of how cell death induced in the context of infection influences the generation of CD8⁺ T-cell-mediated immune responses. To begin to address this question, we designed strains of L. monocytogenes that robustly activate necrosis, apoptosis, or pyroptosis. We hypothesized that proinflammatory cell death such as necrosis would be proimmunogenic while apoptosis would be detrimental, as has previously been reported in the context of sterile cell death. Surprisingly, we found that the activation of any host cell death in the context of L. monocytogenes infection inhibited the generation of protective immunity and specifically the activation of antigen-specific CD8⁺ T cells. Importantly, the mechanism of attenuation was unique for each type of cell death, ranging from deficits in costimulation in the context of necrosis to a suboptimal inflammatory milieu in the case of pyroptosis. Our results suggest that cell death in the context of infection is different from sterile-environment-induced cell death and that inhibition of cell death or its downstream consequences is necessary for developing effective cell-mediated immune responses using L. monocytogenes-based immunotherapeutic platforms.

Identification and Characterization of Two Human Monocyte-Derived Dendritic Cell Subpopulations with Different Functions in Dying Cell Clearance and Different Patterns of Cell Death

Human monocyte-derived dendritic cells (mdDCs) are versatile cells that are used widely for research and experimental therapies. Although different culture conditions can affect their characteristics, there are no known subpopulations. Since monocytes differentiate into dendritic cells (DCs) in a variety of tissues and contexts, we asked whether they can give rise to different subpopulations. In this work we set out to characterize two human mdDC subpopulations that we identified and termed small (DC-S) and large (DC-L). Morphologically, DC-L are larger, more granular and have a more complex cell membrane. Phenotypically, DC-L show higher expression of a wide panel of surface molecules and stronger responses to maturation stimuli. Transcriptomic analysis confirmed their separate identities and findings were consistent with the phenotypes observed. Although they show similar apoptotic cell uptake, DC-L have different capabilities for phagocytosis, demonstrate better antigen processing, and have significantly better necrotic cell uptake. These subpopulations also have different patterns of cell death, with DC-L presenting an inflammatory, "dangerous" phenotype while DC-S mostly downregulate their surface markers upon cell death. Apoptotic cells induce an immune-suppressed phenotype, which becomes more pronounced among DC-L, especially after the addition of lipopolysaccharide. We propose that these two subpopulations correspond to inflammatory (DC-L) and steady-state (DC-S) DC classes that have been previously described in mice and humans.

A hypofractionated radiation regimen avoids the lymphopenia associated with neoadjuvant chemoradiation therapy of borderline resectable and locally advanced pancreatic adenocarcinoma

Background

Preclinical studies have shown synergy between radiation therapy and immunotherapy. However, in almost all preclinical models, radiation is delivered in single doses or short courses of high doses (hypofractionated radiation). By contrast in most clinical settings, radiation is delivered as standard small daily fractions of 1.8-2 Gy to achieve total doses of 50–54 Gy (fractionated radiation). We do not yet know the optimal dose and scheduling of radiation for combination with chemotherapy and immunotherapy.

Methods

To address this, we analyzed the effect of neoadjuvant standard fractionated and hypofractionated chemoradiation on immune cells in patients with locally advanced and borderline resectable pancreatic adenocarcinoma.

Results

We found that standard fractionated chemoradiation resulted in a significant and extended loss of lymphocytes that was not explained by a lack of homeostatic cytokines or response to cytokines. By contrast, treatment with hypofractionated radiation therapy avoided the loss of lymphocytes associated with conventional fractionation.

Conclusion

Hypofractionated neoadjuvant chemoradiation is associated with reduced systemic loss of T cells.

Trial registration

ClinicalTrials.gov NCT01342224, April 21, 2011; NCT01903083, July 2, 2013.

Electronic supplementary material

The online version of this article (doi:10.1186/s40425-016-0149-6) contains supplementary material, which is available to authorized users.

Immune responses against protozoan parasites: a focus on the emerging role of Nod-like receptors

Nod-like receptors (NLRs) have gained attention in recent years because of the ability of some family members to assemble into a multimeric protein complex known as the inflammasome. The role of NLRs and the inflammasome in regulating innate immunity against bacterial pathogens has been well studied. However, recent studies show that NLRs and inflammasomes also play a role during infections caused by protozoan parasites, which pose a significant global health burden. Herein, we review the diseases caused by the most common protozoan parasites in the world and discuss the roles of NLRs and inflammasomes in host immunity against these parasites.

Death in the intestinal epithelium-basic biology and implications for inflammatory bowel disease

Every 4-5 days, intestinal epithelial cells (IEC) are terminated as they reach the end of their life. This process ensures that the epithelium is comprised of the fittest cells that maintain an impermeable barrier to luminal contents and the gut microbiota, as well as the most metabolically able cells that conduct functions in nutrient absorption, digestion, and secretion of antimicrobial peptides. IEC are terminated by apical extrusion-or shedding-from the intestinal epithelial monolayer into the gut lumen. Whether death by apoptosis signals extrusion or death follows expulsion by younger IEC has been a matter of debate. Seemingly a minor detail, IEC death before or after apical extrusion bears weight on the potential contribution of apoptotic IEC to intestinal homeostasis as a consequence of their recognition by intestinal lamina propria phagocytes. In inflammatory bowel disease (IBD), excessive death is observed in the ileal and colonic epithelium. The precise mode of IEC death in IBD is not defined. A highly inflammatory milieu within the intestinal lamina propria, rich in the proinflammatory cytokine, TNF-α, increases IEC shedding and compromises barrier integrity fueling more inflammation. A milestone in the treatment of IBD, anti-TNF-α therapy, may promote mucosal healing by reversing increased and inflammation-associated IEC death. Understanding the biology and consequences of cell death in the intestinal epithelium is critical to the design of new avenues for IBD therapy.

Exploiting natural anti-tumor immunity for metastatic renal cell carcinoma

Clinical observations of spontaneous disease regression in some renal cell carcinoma (RCC) patients implicate a role for tumor immunity in controlling this disease. Puzzling, however, are findings that high levels of tumor infiltrating lymphocytes (TIL) are common to RCC. Despite expression of activation markers by TILs, functional impairment of innate and adaptive immune cells has been consistently demonstrated contributing to the failure of the immune system to control RCC. Immunotherapy can overcome the immunosuppressive effects of the tumor and provide an opportunity for long-term disease free survival. Unfortunately, complete response rates remain sub-optimal indicating the effectiveness of immunotherapy remains limited by tumor-specific factors and/or cell types that inhibit antitumor immune responses. Here we discuss immunotherapies and the function of multiple immune system components to achieve an effective response. Understanding these complex interactions is essential to rationally develop novel therapies capable of renewing the immune system's ability to respond to these tumors.

Concise Review: Mechanisms Behind Apoptotic Cell-Based Therapies Against Transplant Rejection and Graft versus Host Disease

The main limitations to the success of transplantation are the antigraft response developed by the recipient immune system, and the adverse side effects of chronic immunosuppression. Graft-versus-host disease (GVHD) triggered by donor-derived T lymphocytes against the recipient tissues is another serious obstacle in the field of hematopoietic stem cell transplantation. Several laboratories have tested the possibility of promoting antigen (Ag)-specific tolerance for therapy of graft rejection, GVHD, and autoimmune disorders, by developing methodologies that mimic the mechanisms by which the immune system maintains peripheral tolerance in the steady state. It has been long recognized that the silent clearance of cells undergoing apoptosis exerts potent immune-regulatory effects and provides apoptotic cell-derived Ags to those Ag-presenting cells (APCs) that internalize them, in particular macrophages and dendritic cells. Therefore, in situ-targeting of recipient APCs by systemic administration of leukocytes in early apoptosis and bearing donor Ags represents a relatively simple approach to control the antidonor response against allografts. Here, we review the mechanisms by which apoptotic cells are silently cleared by phagocytes, and how such phenomenon leads to down-regulation of the innate and adaptive immunity. We discuss the evolution of apoptotic cell-based therapies from murine models of organ/tissue transplantation and GVHD, to clinical trials. We make emphasis on potential limitations and areas of concern of apoptotic cell-based therapies, and on how other immune-suppressive therapies used in the clinics or tested experimentally likely also function through the silent clearance of apoptotic cells by the immune system. Stem Cells 2016;34:1142-1150.

Immune Tolerance for Autoimmune Disease and Cell Transplantation

The undesired destruction of healthy cells, either endogenous or transplanted, by the immune system results in the loss of tissue function or limits strategies to restore tissue function. Current therapies typically involve nonspecific immunosuppression that may prevent the appropriate response to an antigen, thereby decreasing humoral immunity and increasing the risks of patient susceptibility to opportunistic infections, viral reactivation, and neoplasia. The induction of antigen-specific immunological tolerance to block undesired immune responses to self- or allogeneic antigens, while maintaining the integrity of the remaining immune system, has the potential to transform the current treatment of autoimmune disease and serve as a key enabling technology for therapies based on cell transplantation.

Immunogenic versus tolerogenic phagocytosis during anticancer therapy: mechanisms and clinical translation

Phagocytosis of dying cells is a major homeostatic process that represents the final stage of cell death in a tissue context. Under basal conditions, in a diseased tissue (such as cancer) or after treatment with cytotoxic therapies (such as anticancer therapies), phagocytosis has a major role in avoiding toxic accumulation of cellular corpses. Recognition and phagocytosis of dying cancer cells dictate the eventual immunological consequences (i.e., tolerogenic, inflammatory or immunogenic) depending on a series of factors, including the type of 'eat me' signals. Homeostatic clearance of dying cancer cells (i.e., tolerogenic phagocytosis) tends to facilitate pro-tumorigenic processes and actively suppress antitumour immunity. Conversely, cancer cells killed by immunogenic anticancer therapies may stimulate non-homeostatic clearance by antigen-presenting cells and drive cancer antigen-directed immunity. On the other hand, (a general) inflammatory clearance of dying cancer cells could have pro-tumorigenic or antitumorigenic consequences depending on the context. Interestingly, the immunosuppressive consequences that accompany tolerogenic phagocytosis can be reversed through immune-checkpoint therapies. In the present review, we discuss the pivotal role of phagocytosis in regulating responses to anticancer therapy. We give particular attention to the role of phagocytosis following treatment with immunogenic or immune-checkpoint therapies, the clinical prognostic and predictive significance of phagocytic signals for cancer patients and the therapeutic strategies that can be employed for direct targeting of phagocytic determinants.

Neutrophil extracellular traps: a walk on the wild side of exercise immunology

Intense exercise evokes a rapid and transient increase in circulating cell-free DNA (cf-DNA), a phenomenon that is commonly observed in a variety of acute and chronic inflammatory conditions. While the potential value of cf-DNA for the prediction of disease outcome and therapeutic response is well documented, the release mechanisms and biological relevance of cf-DNA have long remained enigmatic. The discovery of neutrophil extracellular traps (NETs) provided a novel mechanistic explanation for increased cf-DNA levels. Now there is increasing evidence that NETs may contribute to cf-DNA in diverse infectious, non-infectious and autoinflammatory conditions, as well as in response to acute exercise. NETs have now been firmly established as a fundamental immune mechanism used by neutrophils to respond to infection and tissue injury. On the other side, aberrant formation of NETs appears to be a driving force in the pathogenesis of autoimmunity and cardiovascular disease. Thus, the emergence of NETs in the 'exercising vasculature' raises important questions considering beneficial effects, as well as occasional adverse effects, of exercise on immune homeostasis. This review gives an overview of the current state of research into the mechanisms of how NETs are released, contribute to host defence and participate in inflammatory disorders. We discuss the impact of exercise-induced NETs, considering a potentially beneficial role in the prevention of lifestyle-related diseases, as well as putative detrimental effects that may arise in elite sports. Finally, we propose that exercise-induced cf-DNA responses could be exploited for diagnostic/prognostic purposes to identify individuals who are at increased risk of cardiovascular events or autoimmunity.

Transmembrane TNF-α Reverse Signaling Inhibits Lipopolysaccharide-Induced Proinflammatory Cytokine Formation in Macrophages by Inducing TGF-β: Therapeutic Implications

TNF-α, a potent proinflammatory cytokine, is generated in a precursor form called transmembrane (m)TNF-α that is expressed as a type II polypeptide on the surface of certain cells. mTNF-α was shown to act both as a ligand by binding to TNF-α receptors, as well as a receptor that transmits outside-to-inside (reverse) signals back into the mTNF-α-bearing cells. In this study, we show that nonactivated macrophages express basal levels of mTNF-α and respond to anti-TNF-α Abs by triggering the MAPK kinase 4 signaling pathway. The pathway induces TGF-β. Based on inhibitory experiments, the production of TGF-β1 is regulated via Jun kinases, whereas that of other TGF-βs is regulated via p38 MAPKs. Exposure to LPS further induced the expression of mTNF-α, and triggering of mTNF-α strongly suppressed the LPS-induced proinflammatory response. Neutralizing TGF-β by Abs prevented the mTNF-α-mediated suppression of LPS-induced proinflammatory cytokine formation, indicating that the immune-suppressive effect of mTNF-α is mediated via TGF-β. Although apoptotic cells are also known to suppress LPS-induced proinflammatory cytokine formation in macrophages by upregulating TGF-β, we show that they do not use the mTNF-α signaling pathway. Because TGF-β possesses a wide range of immune-suppressive effects, our data indicate that upregulation of TGF-β synthesis by those TNF-α-targeting molecules, which are able to trigger mTNF-α, might contribute to their therapeutic effect in the treatment of certain inflammatory diseases such as Crohn's disease, Wegener's granulomatosis, or sarcoidosis. Additionally, none of the TNF-α-targeting molecules is expected to interfere with the immune-silencing effects of apoptotic cells.

Therapeutic Opportunities in Damage-Associated Molecular Pattern-Driven Metabolic Diseases

SIGNIFICANCE

Sterile inflammation is a common finding present in various metabolic disorders. This type of inflammation is mediated by damage-associated molecular patterns (DAMPs) that are released upon cellular injury to activate pattern recognition receptors on innate immune cells and amplify organ damage.

RECENT ADVANCES

In the last decade, DAMPs, such as high-mobility group protein B1, nucleic acids (DNA, RNA), adenosine triphosphate, and other metabolites, were found to contribute to the inflammatory response in diabetes, gout, obesity, steatohepatitis, and atherosclerosis. Varied receptors, including Toll-like receptors (TLRs), the purinergic P2X(7) receptors, and nucleotide-binding domain, and leucine-rich repeat protein 3 (NLRP3)-inflammasome sense DAMPs and DAMP-like molecules and release the proinflammatory cytokines, interleukin (IL)-1β and IL-18.

CRITICAL ISSUES

Available therapeutic approaches that interfered with the signaling of TLRs, P2X(7), NLRP3-inflammasome, and IL-1β showed encouraging results in metabolic diseases, which will be also highlighted in this review.

FUTURE DIRECTIONS

It is important to understand the origination of DAMPs and how they contribute to the inflammatory response in metabolic disorders to develop selective and efficient therapeutics for intervention.

Therapeutic applications of TRAIL receptor agonists in cancer and beyond

TRAIL/Apo-2L is a member of the TNF superfamily first described as an apoptosis-inducing cytokine in 1995. Similar to TNF and Fas ligand, TRAIL induces apoptosis in caspase-dependent manner following TRAIL death receptor trimerization. Because tumor cells were shown to be particularly sensitive to this cytokine while normal cells/tissues proved to be resistant along with being able to synthesize and release TRAIL, it was rapidly appreciated that TRAIL likely served as one of our major physiologic weapons against cancer. In line with this, a number of research laboratories and pharmaceutical companies have attempted to exploit the ability of TRAIL to kill cancer cells by developing recombinant forms of TRAIL or TRAIL receptor agonists (e.g., receptor-specific mAb) for therapeutic purposes. In this review article we will describe the biochemical pathways used by TRAIL to induce different cell death programs. We will also summarize the clinical trials related to this pathway and discuss possible novel uses of TRAIL-related therapies. In recent years, the physiological importance of TRAIL has expanded beyond being a tumoricidal molecule to one critical for a number of clinical settings - ranging from infectious disease and autoimmunity to cardiovascular anomalies. We will also highlight some of these conditions where modulation of the TRAIL/TRAIL receptor system may be targeted in the future.

Engineered binding to erythrocytes induces immunological tolerance to E. coli asparaginase

Antigen-specific immune responses to protein drugs can hinder efficacy and compromise safety because of drug neutralization and secondary clinical complications. We report a tolerance induction strategy to prevent antigen-specific humoral immune responses to therapeutic proteins. Our modular, biomolecular approach involves engineering tolerizing variants of proteins such that they bind erythrocytes in vivo upon injection, on the basis of the premise that aged erythrocytes and the payloads they carry are cleared tolerogenically, driving the deletion of antigen-specific T cells. We demonstrate that binding the clinical therapeutic enzyme Escherichia coli l-asparaginase to erythrocytes in situ antigen-specifically abrogates development of antibody titers by >1000-fold and extends the pharmacodynamic effect of the drug 10-fold in mice. Additionally, a single pretreatment dose of erythrocyte-binding asparaginase tolerized mice to multiple subsequent doses of the wild-type enzyme. This strategy for reducing antigen-specific humoral responses may enable more effective and safer treatment with therapeutic proteins and drug candidates that are hampered by immunogenicity.

Targeting of prosurvival pathways as therapeutic approaches against primary effusion lymphomas: past, present, and Future

Constitutively activated prosurvival pathways render cancer cells addicted to their effects. Consequently they turn out to be the Achilles' heels whose inhibition can be exploited in anticancer therapy. Primary effusion lymphomas (PELs) are very aggressive non-Hodgkin's B cell lymphomas, whose pathogenesis is strictly linked to Kaposi's sarcoma herpesvirus (KSHV) infection. Here we summarized previous studies from our and other laboratories exploring the cytotoxic effect of drugs inhibiting the main prosurvival pathways activated in PEL cells. Moreover, the immunogenicity of cell death, in terms of dendritic cell (DC) activation and their potential side effect on DCs, is discussed.

Engulfment of activated apoptotic cells abolishes TGF-β-mediated immunoregulation via the induction of IL-6

Phagocytosis of apoptotic cells (ACs) is usually a potent immunoregulatory signal but can also promote inflammation. In this article, we show that administration of apoptotic dendritic cells (DCs) inhibited inflammation in vivo through increasing production of TGF-β from intrinsic DCs and B cells. However, ACs derived from LPS-activated DCs failed to restrain inflammation because of a short-lived but marked IL-6 response, which abolished the increase in TGF-β. Inhibition of IL-6 restored the protective anti-inflammatory properties of aACs and the TGF-β response. DCs isolated from mice that had received resting but not activated ACs could transfer the suppression of inflammation to recipient mice. These transferred DCs stimulated B cell TGF-β production and relied on an intact B cell compartment to limit inflammation. These results highlight how the activation state of AC governs their ability to control inflammation through reciprocal regulation of IL-6 and TGF-β.

Activation of dendritic cells by tumor cell death

A growing number of studies indicate that cell death can be either immunogenic or not, depending on its modalities, the type and the activation state of the cells, and finally, the environment where it happens. Increased understanding of the immunogenicity of cancer cell death will significantly improve the outcome of chemotherapeutic treatments.

Analysis of the anti-apoptotic activity of four vaccinia virus proteins demonstrates that B13 is the most potent inhibitor in isolation and during viral infection

Vaccinia virus (VACV) is a large dsDNA virus encoding ~200 proteins, several of which inhibit apoptosis. Here, a comparative study of anti-apoptotic proteins N1, F1, B13 and Golgi anti-apoptotic protein (GAAP) in isolation and during viral infection is presented. VACVs strains engineered to lack each gene separately still blocked apoptosis to some degree because of functional redundancy provided by the other anti-apoptotic proteins. To overcome this redundancy, we inserted each gene separately into a VACV strain (vv811) that lacked all these anti-apoptotic proteins and that induced apoptosis efficiently during infection. Each protein was also expressed in cells using lentivirus vectors. In isolation, each VACV protein showed anti-apoptotic activity in response to specific stimuli, as measured by immunoblotting for cleaved poly(ADP ribose) polymerase-1 and caspase-3 activation. Of the proteins tested, B13 was the most potent inhibitor, blocking both intrinsic and extrinsic stimuli, whilst the activity of the other proteins was largely restricted to inhibition of intrinsic stimuli. In addition, B13 and F1 were effective blockers of apoptosis induced by vv811 infection. Finally, whilst differences in induction of apoptosis were barely detectable during infection with VACV strain Western Reserve compared with derivative viruses lacking individual anti-apoptotic genes, several of these proteins reduced activation of caspase-3 during infection by vv811 strains expressing these proteins. These results illustrated that vv811 was a useful tool to determine the role of VACV proteins during infection and that whilst all of these proteins have some anti-apoptotic activity, B13 was the most potent.

Prospects of apoptotic cell-based therapies for transplantation and inflammatory diseases

Apoptotic cell removal or interactions of early-stage apoptotic cells with immune cells are associated with an immunomodulatory microenvironment that can be harnessed to exert therapeutic effects. While the involved immune mechanisms are still being deciphered, apoptotic cell infusion has been tested in different experimental models where inflammation is deregulated. This includes chronic and acute inflammatory disorders such as arthritis, contact hypersensitivity and acute myocardial infarction. Apoptotic cell infusion has also been used in transplantation settings to prevent or treat acute and chronic rejection, as well as to limit acute graft-versus-host disease associated with allogeneic hematopoietic cell transplantation. Here, we review the mechanisms involved in apoptotic cell-induced immunomodulation and data obtained in preclinical models of transplantation and inflammatory diseases.