Two adjacent trimeric Fas ligands are required for Fas signaling and formation of a death-inducing signaling complex

CD95/Fas stoichiometry in future precision medicine

CD95, also known as Fas, belongs to the tumor necrosis factor (TNF) receptor superfamily. The main biological function of this receptor is to orchestrate and control the immune response since mutations in CD95 or deregulation of its downstream signaling pathways lead to auto-immunity and inflammation. Interestingly, more than twenty years ago, pioneer studies highlighted that like TNFR1, TRAILR1 or CD40, CD95 pre-associates at the plasma membrane in a ligand-independent fashion. This self-association occurs through a domain designated pre-ligand assembly domain or PLAD. Although the disruption of this pre-association prevents CD95 signaling, no drugs targeting this region have been generated because many questions remain on the stoichiometry and conformation of this receptor. Despite more than 40.000 publications, no crystal structure of CD95 alone or in combination with its ligand, CD95L, exists. Based on other TNFR members, we herein discuss the predicted conformation of CD95 at the plasma membrane and how these putative structures might account for the induction of the cell signaling pathways.

The inflammatory APRIL (a proliferation-inducing ligand) antagonizes chondroitin sulphate proteoglycans to promote axonal growth and myelination

Lesions in the CNS are frequently associated to a detrimental inflammatory reaction. In autoimmune neurodegenerative diseases, a proliferation-inducing ligand (APRIL) produced by CNS-infiltrating inflammatory cells binds to chondroitin sulphate proteoglycans (CSPGs). The latter are well-established obstacles to neural regeneration and remyelination in the CNS by interacting with receptor protein tyrosine phosphatase (RPTP) and Nogo receptor (NgR) families. Here, we are showing that APRIL blocks the interactions of RPTP and NgR with all types of chondroitin sulphate (CS). Functionally, APRIL neutralized the inhibitory effects of CS on mouse and human neuronal process growth. APRIL also blocked the inhibition of CS on mouse and human oligodendrocyte differentiation. Finally, APRIL increased myelination in an ex vivo organotypic model of demyelination in the presence of endogenous CSPG upregulation. Our data demonstrate the potential value for a recombinant form of soluble APRIL to achieve repair in the CNS.

Ribonuclease inhibitor and angiogenin system regulates cell type-specific global translation

Translation of mRNAs is a fundamental process that occurs in all cell types of multicellular organisms. Conventionally, it has been considered a default step in gene expression, lacking specific regulation. However, recent studies have documented that certain mRNAs exhibit cell type-specific translation. Despite this, it remains unclear whether global translation is controlled in a cell type-specific manner. By using human cell lines and mouse models, we found that deletion of the ribosome-associated protein ribonuclease inhibitor 1 (RNH1) decreases global translation selectively in hematopoietic-origin cells but not in the non-hematopoietic-origin cells. RNH1-mediated cell type-specific translation is mechanistically linked to angiogenin-induced ribosomal biogenesis. Collectively, this study unravels the existence of cell type-specific global translation regulators and highlights the complex translation regulation in vertebrates.

Adapting Ferritin, a Naturally Occurring Protein Cage, to Modulate Intrinsic Agonism of OX40

Ferritin is a multivalent, self-assembling protein scaffold found in most human cell types, in addition to being present in invertebrates, higher plants, fungi, and bacteria, that offers an attractive alternative to polymer-based drug delivery systems (DDS). In this study, the utility of the ferritin cage as a DDS was demonstrated within the context of T cell agonism for tumor killing. Members of the tumor necrosis factor receptor superfamily (TNFRSF) are attractive targets for the development of anticancer therapeutics. These receptors are endogenously activated by trimeric ligands that occur in transmembrane or soluble forms, and oligomerization and cell-surface anchoring have been shown to be essential aspects of the targeted agonism of this receptor class. Here, we demonstrated that the ferritin cage could be easily tailored for multivalent display of anti-OX40 antibody fragments on its surface and determined that these arrays are capable of pathway activation through cell-surface clustering. Together, these results confirm the utility, versatility, and developability of ferritin as a DDS.

Membrane-bound CD95 ligand modulates CD19-mediated B cell receptor signaling and EBV activation

Post-transplant lymphoproliferative disorders (PTLDs) are associated with Epstein-Barr virus (EBV) infection in transplant recipients. Most of lymphoblastoid cell lines (LCLs) derived from EBV-immortalized B cells or PTLDs are sensitive to CD95-mediated apoptosis and cytotoxic T cell (CTL) killing. CD95 ligand (CD95L) exists as a transmembrane ligand (mCD95L) or a soluble form (sCD95L). Using recombinant mCD95L and sCD95L, we observed that sCD95L does not affect LCLs. While high expression of mCD95L in CTLs promotes apoptosis of LCLs, low expression induces clathrin-dependent CD19 internalization, caspase-dependent CD19 cleavage, and proteasomal/lysosomal-dependent CD19 degradation. The CD95L/CD95-mediated CD19 degradation impairs B cell receptor (BCR) signaling and inhibits BCR-mediated EBV activation. Interestingly, although inhibition of the caspase activity restores CD19 expression and CD19-mediated BCR activation, it fails to rescue BCR-mediated EBV lytic gene expression. EBV-specific CTLs engineered to overexpress mCD95L exhibit a stronger killing activity against LCLs. This study highlights that engineering EBV-specific CTLs to express a higher level of mCD95L could represent an attractive therapeutic approach to improve T cell immunotherapy for PTLDs.

Non-apoptotic FAS signaling controls mTOR activation and extrafollicular maturation in human B cells

Defective FAS (CD95/Apo-1/TNFRSF6) signaling causes autoimmune lymphoproliferative syndrome (ALPS). Hypergammaglobulinemia is a common feature in ALPS with FAS mutations (ALPS-FAS), but paradoxically, fewer conventional memory cells differentiate from FAS-expressing germinal center (GC) B cells. Resistance to FAS-induced apoptosis does not explain this phenotype. We tested the hypothesis that defective non-apoptotic FAS signaling may contribute to impaired B cell differentiation in ALPS. We analyzed secondary lymphoid organs of patients with ALPS-FAS and found low numbers of memory B cells, fewer GC B cells, and an expanded extrafollicular (EF) B cell response. Enhanced mTOR activity has been shown to favor EF versus GC fate decision, and we found enhanced PI3K/mTOR and BCR signaling in ALPS-FAS splenic B cells. Modeling initial T-dependent B cell activation with CD40L in vitro, we showed that FAS competent cells with transient FAS ligation showed specifically decreased mTOR axis activation without apoptosis. Mechanistically, transient FAS engagement with involvement of caspase-8 induced nuclear exclusion of PTEN, leading to mTOR inhibition. In addition, FASL-dependent PTEN nuclear exclusion and mTOR modulation were defective in patients with ALPS-FAS. In the early phase of activation, FAS stimulation promoted expression of genes related to GC initiation at the expense of processes related to the EF response. Hence, our data suggest that non-apoptotic FAS signaling acts as molecular switch between EF versus GC fate decisions via regulation of the mTOR axis and transcription. The defect of this modulatory circuit may explain the observed hypergammaglobulinemia and low memory B cell numbers in ALPS.

Novel PI(3)K-p85α/p110δ-ITK-LAT-PLC-γ2 and Fyn-ADAP-Carma1-TAK1 Pathways Define Reverse Signaling via FasL

The role of FasL in initiating death signals through Fas is well characterized. However, the reverse signaling pathway downstream of FasL in effector lymphocytes is poorly understood. Here, we identify that FasL functions as an independent activation receptor in NK cells. Activation via FasL results in the production of LFN-γ, GM-CSF, RANTES, MIP-1α, and MIP1-β. Proximal signaling of FasL requires Lck and Fyn. Upon activation, FasL facilitates the phosphorylation of PI(3)K-p85α/p55α subunits. A catalytically inactive PI(3)K-p110δD910A mutation significantly impairs the cytokine and chemokine production by FasL. Activation of ITK and LAT downstream of FasL plays a central role in recruiting and phosphorylating PLC-γ2. Importantly, Fyn-mediated recruitment of ADAP links FasL to the Carmal/ Bcl10/Tak1 signalosome. Lack of Carma1, CARD domain of Carma1, or Tak1 significantly reduces FasL-mediated cytokine and chemokine production. These findings, for the first time, provide a detailed molecular blueprint that defines FasL-mediated reverse signaling.

CD95L concatemers highlight different stoichiometries of CD95-mediated apoptotic and nonapoptotic pathways

To better understand the stoichiometry of CD95L required to trigger apoptotic and nonapoptotic signals, we generated several CD95L concatemers from dimer to hexamer conjugated via a flexible link (GGGGS)2 . These ligands reveal that although the hexameric structure is the best stoichiometry to trigger cell death, a dimer is sufficient to induce the apoptotic response in CD95-sensitive Jurkat cells. Interestingly, only trimeric and hexameric forms can implement a potent Ca2+ response, suggesting that while CD95 aggregation controls the implementation of the apoptotic signal, both aggregation and conformation are required to implement the Ca2+ pathway.

CD95 (Fas) and CD95L (FasL)-mediated non-canonical signaling pathways

Although the interaction of CD95L (also known as FasL) with its so-called death receptor CD95 (Fas) induces an apoptotic signal responsible for the elimination of infected and cancer cells and maintenance of tissue homeostasis, this receptor can also implement non apoptotic signaling pathways. This latter signaling is involved in metastatic dissemination in certain cancers and the severity of auto-immune disorders. The signaling complexity of this pair is increased by the fact that CD95 expression itself seems to contribute to oncogenesis via a CD95L-independent manner and, that both ligand and receptor might interact with other partners modulating their pathophysiological functions. Finally, CD95L itself can trigger cell signaling in immune cells rendering complex the interpretation of mouse models in which CD95 or CD95L are knocked out. Herein, we discuss these non-canonical responses and their biological functions.

Fcγ receptor binding is required for maximal immunostimulation by CD70-Fc

Introduction

T cell expressed CD27 provides costimulation upon binding to inducible membrane expressed trimeric CD70 and is required for protective CD8 T cell responses. CD27 agonists could therefore be used to bolster cellular vaccines and anti-tumour immune responses. To date, clinical development of CD27 agonists has focussed on anti-CD27 antibodies with little attention given to alternative approaches.

Methods

Here, we describe the generation and activity of soluble variants of CD70 that form either trimeric (t) or dimer-of-trimer proteins and conduct side-by-side comparisons with an agonist anti-CD27 antibody. To generate a dimer-of-trimer protein (dt), we fused three extracellular domains of CD70 to the Fc domain of mouse IgG1 in a 'string of beads' configuration (dtCD70-Fc).

Results

Whereas tCD70 failed to costimulate CD8 T cells, both dtCD70-Fc and an agonist anti-CD27 antibody were capable of enhancing T cell proliferation in vitro. Initial studies demonstrated that dtCD70-Fc was less efficacious than anti-CD27 in boosting a CD8 T cell vaccine response in vivo, concomitant with rapid clearance of dtCD70-Fc from the circulation. The accelerated plasma clearance of dtCD70-Fc was not due to the lack of neonatal Fc receptor binding but was dependent on the large population of oligomannose type glycosylation. Enzymatic treatment to reduce the oligomannose-type glycans in dtCD70-Fc improved its half-life and significantly enhanced its T cell stimulatory activity in vivo surpassing that of anti-CD27 antibody. We also show that whereas the ability of the anti-CD27 to boost a vaccine response was abolished in Fc gamma receptor (FcγR)-deficient mice, dtCD70-Fc remained active. By comparing the activity of dtCD70-Fc with a variant (dtCD70-Fc(D265A)) that lacks binding to FcγRs, we unexpectedly found that FcγR binding to dtCD70-Fc was required for maximal boosting of a CD8 T cell response in vivo. Interestingly, both dtCD70-Fc and dtCD70-Fc(D265A) were effective in prolonging the survival of mice harbouring BCL1 B cell lymphoma, demonstrating that a substantial part of the stimulatory activity of dtCD70-Fc in this setting is retained in the absence of FcγR interaction.

Discussion

These data reveal that TNFRSF ligands can be generated with a tunable activity profile and suggest that this class of immune agonists could have broad applications in immunotherapy.

Rational multivalency construction enables bactericidal effect amplification and dynamic biomaterial design

The multivalency of bioligands in living systems brings inspiration for not only the discovery of biological mechanisms but also the design of extracellular matrix (ECM)-mimicking biomaterials. However, designing controllable multivalency construction strategies is still challenging. Herein, we synthesized a series of well-defined multivalent antimicrobial peptide polymers (mAMPs) by clicking ligand molecules onto polymers prepared by reversible addition-fragmentation chain transfer polymerization. The multiple cationic ligands in the mAMPs could enhance the local disturbance of the anionic phospholipid layer of the bacterial membrane through multivalent binding, leading to amplification of the bactericidal effect. In addition to multivalency-enhanced antibacterial activity, mAMPs also enable multivalency-assisted hydrogel fabrication with an ECM-like dynamic structure. The resultant hydrogel with self-healing and injectable properties could be successfully employed as an antibacterial biomaterial scaffold to treat infected skin wounds. The multivalency construction strategy presented in this work provides new ideas for the biomimetic design of highly active and dynamic biomaterials for tissue repair and regeneration.

Blocking soluble Fas Ligand ameliorates pemphigus: PC111 efficacy in ex-vivo human pemphigus models

Pemphigus is a life-threatening, chronic, autoimmune bullous disease affecting both the skin and the mucous membranes. Based on the mainstream concept that blister formation occurs upon binding of autoantibodies to their antigen proteins (desmoglein1, DSG1 and desmoglein3, DSG3), current therapies mostly aim to suppress the immune system. To avoid the severe side effects associated with the chronic use of immunosuppressive treatments, we have developed PC111, a fully human monoclonal antibody targeting human Fas ligand (FasL). We have provided a number of in vitro and in vivo evidences showing that soluble FasL induces keratinocyte apoptosis followed by acantholysis. An anti-murine FasL prevents blister formation in the pemphigus neonatal mouse model. To confirm the mechanism of action (MoA) and the efficacy of PC111 in a human pemphigus context, we used the keratinocyte dissociation assay and two independent Human Skin Organ Cultures (HSOC) pemphigus models. PC111 reduced acantholysis in vitro, as shown by the dose-dependent reduction of fragments in the monolayer cultures. In the first HSOC model, normal human skin was subcutaneously injected with a scFv antibody fragment directed against DSG1 and DSG3, resulting in a severe acantholysis (70-100%) after 24 hours. PC111 inhibited blister formation to around 50% of control. In the second model, normal human skin was injected with a mixture of pemphigus patients' autoantibodies resulting in a less severe acantholysis (20-30%). PC111 significantly suppressed blister formation to more than 75% up to 72 hours. These results confirm PC111 MoA and demonstrates the efficacy of the anti-FasL antibody also in a pemphigus setting.

ptARgenOM-A Flexible Vector For CRISPR/CAS9 Nonviral Delivery

Viral-mediated delivery of the CRISPR-Cas9 system is one the most commonly used techniques to modify the genome of a cell, with the aim of analyzing the function of the targeted gene product. While these approaches are rather straightforward for membrane-bound proteins, they can be laborious for intracellular proteins, given that selection of full knockout (KO) cells often requires the amplification of single-cell clones. Moreover, viral-mediated delivery systems, besides the Cas9 and gRNA, lead to the integration of unwanted genetic material, such as antibiotic resistance genes, introducing experimental biases. Here, an alternative non-viral delivery approach is presented for CRISPR/Cas9, allowing efficient and flexible selection of KO polyclonal cells. This all-in-one mammalian CRISPR-Cas9 expression vector, ptARgenOM, encodes the gRNA and the Cas9 linked to a ribosomal skipping peptide sequence followed by the enhanced green fluorescent protein and the puromycin N-acetyltransferase, allowing for transient, expression-dependent selection and enrichment of isogenic KO cells. After evaluation using more than 12 distinct targets in 6 cell lines, ptARgenOM is found to be efficient in producing KO cells, reducing the time required to obtain a polyclonal isogenic cell line by 4-6 folds. Altogether ptARgenOM provides a simple, fast, and cost-effective delivery tool for genome editing.

Evolving strategies and application of proteins and peptide therapeutics in cancer treatment

Several proteins and peptides have therapeutic potential and can be used for cancer therapy. By binding to cell surface receptors and other indicators uniquely linked with or overexpressed on tumors compared to healthy tissue, protein biologics enhance the active targeting of cancer cells, as opposed to the passive targeting of cells by conventional small-molecule chemotherapeutics. This study focuses on peptide medications that exist to slow or stop tumor growth and the spread of cancer, demonstrating the therapeutic potential of peptides in cancer treatment. As an alternative to standard chemotherapy, peptides that selectively kill cancer cells while sparing healthy tissue are developing. A mountain of clinical evidence supports the efficacy of peptide-based cancer vaccines. Since a single treatment technique may not be sufficient to produce favourable results in the fight against cancer, combination therapy is emerging as an effective option to generate synergistic benefits. One example of this new area is the use of anticancer peptides in combination with nonpeptidic cytotoxic drugs or the combination of immunotherapy with conventional therapies like radiation and chemotherapy. This review focuses on the different natural and synthetic peptides obtained and researched. Discoveries, manufacture, and modifications of peptide drugs, as well as their contemporary applications, are summarized in this review. We also discuss the benefits and difficulties of potential advances in therapeutic peptides.

Revisiting autoimmune lymphoproliferative syndrome caused by Fas ligand mutations

BACKGROUND

Fas ligand (FasL) is expressed by activated T cells and induces death in target cells upon binding to Fas. Loss-of-function FAS or FASLG mutations cause autoimmune-lymphoproliferative syndrome (ALPS) characterized by expanded double-negative T cells (DNT) and elevated serum biomarkers. While most ALPS patients carry heterozygous FAS mutations, FASLG mutations are rare and usually biallelic. Only 2 heterozygous variants were reported, associated with an atypical clinical phenotype.

OBJECTIVE

We revisited the significance of heterozygous FASLG mutations as a cause of ALPS.

METHODS

Clinical features and biomarkers were analyzed in 24 individuals with homozygous or heterozygous FASLG variants predicted to be deleterious. Cytotoxicity assays were performed with patient T cells and biochemical assays with recombinant FasL.

RESULTS

Homozygous FASLG variants abrogated cytotoxicity and resulted in early-onset severe ALPS with elevated DNT, raised vitamin B₁₂, and usually no soluble FasL. In contrast, heterozygous variants affected FasL function by reducing expression, impairing trimerization, or preventing Fas binding. However, they were not associated with elevated DNT and vitamin B₁₂, and they did not affect FasL-mediated cytotoxicity. The dominant-negative effects of previously published variants could not be confirmed. Even Y166C, causing loss of Fas binding with a dominant-negative effect in biochemical assays, did not impair cellular cytotoxicity or cause vitamin B₁₂ and DNT elevation.

CONCLUSION

Heterozygous loss-of-function mutations are better tolerated for FASLG than for FAS, which may explain the low frequency of ALPS-FASLG.

Role of metalloproteases in the CD95 signaling pathways

CD95L (also known as FasL or CD178) is a member of the tumor necrosis family (TNF) superfamily. Although this transmembrane ligand has been mainly considered as a potent apoptotic inducer in CD95 (Fas)-expressing cells, more recent studies pointed out its role in the implementation of non-apoptotic signals. Accordingly, this ligand has been associated with the aggravation of inflammation in different auto-immune disorders and in the metastatic occurrence in different cancers. Although it remains to decipher all key factors involved in the ambivalent role of this ligand, accumulating clues suggest that while the membrane bound CD95L triggers apoptosis, its soluble counterpart generated by metalloprotease-driven cleavage is responsible for its non-apoptotic functions. Nonetheless, the metalloproteases (MMPs and ADAMs) involved in the CD95L shedding, the cleavage sites and the different stoichiometries and functions of the soluble CD95L remain to be elucidated. To better understand how soluble CD95L triggers signaling pathways from apoptosis to inflammation or cell migration, we propose herein to summarize the different metalloproteases that have been described to be able to shed CD95L, their cleavage sites and the biological functions associated with the released ligands. Based on these new findings, the development of CD95/CD95L-targeting therapeutics is also discussed.

FcγRs and Their Relevance for the Activity of Anti-CD40 Antibodies

Inhibitory targeting of the CD40L-CD40 system is a promising therapeutic option in the field of organ transplantation and is also attractive in the treatment of autoimmune diseases. After early complex results with neutralizing CD40L antibodies, it turned out that lack of Fcγ receptor (FcγR)-binding is the crucial factor for the development of safe inhibitory antibodies targeting CD40L or CD40. Indeed, in recent years, blocking CD40 antibodies not interacting with FcγRs, has proven to be well tolerated in clinical studies and has shown initial clinical efficacy. Stimulation of CD40 is also of considerable therapeutic interest, especially in cancer immunotherapy. CD40 can be robustly activated by genetically engineered variants of soluble CD40L but also by anti-CD40 antibodies. However, the development of CD40L-based agonists is biotechnologically and pharmacokinetically challenging, and anti-CD40 antibodies typically display only strong agonism in complex with FcγRs or upon secondary crosslinking. The latter, however, typically results in poorly developable mixtures of molecule species of varying stoichiometry and FcγR-binding by anti-CD40 antibodies can elicit unwanted side effects such as antibody-dependent cellular cytotoxicity (ADCC) or antibody-dependent cellular phagocytosis (ADCP) of CD40 expressing immune cells. Here, we summarize and compare strategies to overcome the unwanted target cell-destroying activity of anti-CD40-FcγR complexes, especially the use of FcγR type-specific mutants and the FcγR-independent cell surface anchoring of bispecific anti-CD40 fusion proteins. Especially, we discuss the therapeutic potential of these strategies in view of the emerging evidence for the dose-limiting activities of systemic CD40 engagement.

MMP7 cleavage of amino-terminal CD95 death receptor switches signaling toward non-apoptotic pathways

CD95 is a death receptor that can promote oncogenesis through molecular mechanisms that are not fully elucidated. Although the mature CD95 membrane receptor is considered to start with the arginine at position 17 after elimination of the signal peptide, this receptor can also be cleaved by MMP7 upstream of its leucine at position 37. This post-translational modification occurs in cancer cells but also in normal cells such as peripheral blood leukocytes. The non-cleaved CD95 amino-terminal region consists in a disordered domain and its in silico reconstitution suggests that it might contribute to receptor aggregation and thereby, regulate the downstream death signaling pathways. In agreement with this molecular modeling analysis, the comparison of CD95-deficient cells reconstituted with full-length or N-terminally truncated CD95 reveals that the loss of the amino-terminal region of CD95 impairs the initial steps of the apoptotic signal while favoring the induction of pro-survival signals, including the PI3K and MAPK pathways.

TAK1 Limits Death Receptor Fas-Induced Proinflammatory Cell Death in Macrophages

Fas, a member of the death receptor family, plays a central role in initiating cell death, a biological process crucial for immune homeostasis. However, the immunological and pathophysiological impacts to which enhanced Fas signaling gives rise remain to be fully understood. Here we demonstrate that TGF-β–activated kinase 1 (TAK1) works as a negative regulator of Fas signaling in macrophages. Upon Fas engagement with high concentrations of FasL, mouse primary macrophages underwent cell death, and, surprisingly, Fas stimulation led to proteolytic cleavage of gasdermin (GSDM) family members GSDMD and GSDME, a hallmark of pyroptosis, in a manner dependent on caspase enzymatic activity. Remarkably, TAK1-deficient macrophages were highly sensitive to even low concentrations of FasL. Mechanistically, TAK1 negatively modulated RIPK1 kinase activity to protect macrophages from excessive cell death. Intriguingly, mice deficient for TAK1 in macrophages (TAK1mKO mice) spontaneously developed tissue inflammation, and, more important, the emergence of inflammatory disease symptoms was markedly diminished in TAK1mKO mice harboring a catalytically inactive RIPK1. Taken together, these findings not only revealed an unappreciated role of TAK1 in Fas-induced macrophage death but provided insight into the possibility of perturbation of immune homeostasis driven by aberrant cell death.

Preclinical characterization and clinical translation of pharmacodynamic markers for MK-5890: a human CD27 activating antibody for cancer immunotherapy

Background

Immune checkpoint inhibitors (ICI) have radically changed cancer therapy, but most patients with cancer are unresponsive or relapse after treatment. MK-5890 is a CD27 agonist antibody intended to complement ICI therapy. CD27 is a member of the tumor necrosis factor receptor superfamily that plays a critical role in promoting responses of T cells, B cells and NK cells.

Methods

Anti-CD27 antibodies were generated and selected for agonist activity using NF-кB luciferase reporter assays. Antibodies were humanized and characterized for agonism using in vitro T-cell proliferation assays. The epitope recognized on CD27 by MK-5890 was established by X-ray crystallography. Anti-tumor activity was evaluated in a human CD27 knock-in mouse. Preclinical safety was tested in rhesus monkeys. Pharmacodynamic properties were examined in mouse, rhesus monkeys and a phase 1 dose escalation clinical study in patients with cancer.

Results

Humanized anti-CD27 antibody MK-5890 (hIgG1) was shown to bind human CD27 on the cell surface with sub-nanomolar potency and to partially block binding to its ligand, CD70. Crystallization studies revealed that MK-5890 binds to a unique epitope in the cysteine-rich domain 1 (CRD1). MK-5890 activated CD27 expressed on 293T NF-κB luciferase reporter cells and, conditional on CD3 stimulation, in purified CD8+ T cells without the requirement of crosslinking. Functional Fc-receptor interaction was required to activate CD8+ T cells in an ex vivo tumor explant system and to induce antitumor efficacy in syngeneic murine subcutaneous tumor models. MK-5890 had monotherapy efficacy in these models and enhanced efficacy of PD-1 blockade. MK-5890 reduced in an isotype-dependent and dose-dependent manner circulating, but not tumor-infiltrating T-cell numbers in these mouse models. In rhesus monkey and human patients, reduction in circulating T cells was transient and less pronounced than in mouse. MK-5890 induced transient elevation of chemokines MCP-1, MIP-1α, and MIP-1β in the serum of mice, rhesus monkeys and patients with cancer. MK-5890 was well tolerated in rhesus monkeys and systemic exposure to MK-5890 was associated with CD27 occupancy at all doses.

Conclusions

MK-5890 is a novel CD27 agonistic antibody with the potential to complement the activity of PD-1 checkpoint inhibition in cancer immunotherapy and is currently undergoing clinical evaluation.

Super-Resolution Imaging of Fas/CD95 Reorganization Induced by Membrane-Bound Fas Ligand Reveals Nanoscale Clustering Upstream of FADD Recruitment

Signaling through the TNF-family receptor Fas/CD95 can trigger apoptosis or non-apoptotic cellular responses and is essential for protection from autoimmunity. Receptor clustering has been observed following interaction with Fas ligand (FasL), but the stoichiometry of Fas, particularly when triggered by membrane-bound FasL, the only form of FasL competent at inducing programmed cell death, is not known. Here we used super-resolution microscopy to study the behavior of single molecules of Fas/CD95 on the plasma membrane after interaction of Fas with FasL on planar lipid bilayers. We observed rapid formation of Fas protein superclusters containing more than 20 receptors after interactions with membrane-bound FasL. Fluorescence correlation imaging demonstrated recruitment of FADD dependent on an intact Fas death domain, with lipid raft association playing a secondary role. Flow-cytometric FRET analysis confirmed these results, and also showed that some Fas clustering can occur in the absence of FADD and caspase-8. Point mutations in the Fas death domain associated with autoimmune lymphoproliferative syndrome (ALPS) completely disrupted Fas reorganization and FADD recruitment, confirming structure-based predictions of the critical role that these residues play in Fas–Fas and Fas–FADD interactions. Finally, we showed that induction of apoptosis correlated with the ability to form superclusters and recruit FADD.

Vesicle Induced Receptor Sequestration: Mechanisms behind Extracellular Vesicle-Based Protein Signaling

Extracellular vesicles (EVs) are fundamental for proper physiological functioning of multicellular organisms. By shuttling nucleic acids and proteins between cells, EVs regulate a plethora of cellular processes, especially those involved in immune signalling. However, the mechanistic understanding concerning the biophysical principles underlying EV-based communication is still incomplete. Towards holistic understanding, particular mechanisms explaining why and when cells apply EV-based communication and how protein-based signalling is promoted by EV surfaces are sought. Here, the authors study vesicle-induced receptor sequestration (VIRS) as a universal mechanism augmenting the signalling potency of proteins presented on EV-membranes. By bottom-up reconstitution of synthetic EVs, the authors show that immobilization of the receptor ligands FasL and RANK on EV-like vesicles, increases their signalling potential by more than 100-fold compared to their soluble forms. Moreover, the authors perform diffusion simulations within immunological synapses to compare receptor activation between soluble and EV-presented proteins. By this the authors propose vesicle-triggered local clustering of membrane receptors as the principle structural mechanism underlying EV-based protein presentation. The authors conclude that EVs act as extracellular templates promoting the local aggregation of membrane receptors at the EV contact site, thereby fostering inter-protein interactions. The results uncover a potentially universal mechanism explaining the unique structural profit of EV-based intercellular signalling.

MMP-7 marks severe pancreatic cancer and alters tumor cell signaling by proteolytic release of ectodomains

Pancreatic cancer incurs the worst survival rate of the major cancers. High levels of the protease matrix metalloproteinase-7 (MMP-7) in circulation correlate with poor prognosis and limited survival of patients. MMP-7 is required for a key path of pancreatic tumorigenesis in mice and is present throughout tumor progression. Enhancements to chemotherapies are needed for increasing the number of pancreatic tumors that can be removed and for preventing relapses after surgery. With these ends in mind, selective inhibition of MMP-7 may be worth investigation. An anti-MMP-7 monoclonal antibody was recently shown to increase the susceptibility of several pancreatic cancer cell lines to chemotherapeutics, increase their apoptosis, and decrease their migration. MMP-7 activities are most apparent at the surfaces of innate immune, epithelial, and tumor cells. Proteolytic shedding of multiple protein ectodomains by MMP-7 from such cell surfaces influence apoptosis, proliferation, migration, and invasion. These activities warrant targeting of MMP-7 selectively in pancreatic cancer and other tumors of mucosal epithelia. Competitive and non-competitive modes of MMP-7 inhibition are discussed.

Therapeutic approaches targeting CD95L/CD95 signaling in cancer and autoimmune diseases

Cell death plays a pivotal role in the maintenance of tissue homeostasis. Key players in the controlled induction of cell death are the Death Receptors (DR). CD95 is a prototypic DR activated by its cognate ligand CD95L triggering programmed cell death. As a consequence, alterations in the CD95/CD95L pathway have been involved in several disease conditions ranging from autoimmune diseases to inflammation and cancer. CD95L-induced cell death has multiple roles in the immune response since it constitutes one of the mechanisms by which cytotoxic lymphocytes kill their targets, but it is also involved in the process of turning off the immune response. Furthermore, beyond the canonical pro-death signals, CD95L, which can be membrane-bound or soluble, also induces non-apoptotic signaling that contributes to its tumor-promoting and pro-inflammatory roles. The intent of this review is to describe the role of CD95/CD95L in the pathophysiology of cancers, autoimmune diseases and chronic inflammation and to discuss recently patented and emerging therapeutic strategies that exploit/block the CD95/CD95L system in these diseases.

DNA nanotechnology-facilitated ligand manipulation for targeted therapeutics and diagnostics

Ligands, mostly binding to proteins to form complexes and catalyze chemical reactions, can serve as drug and probe molecules, as well as sensing elements. DNA nanotechnology can integrate the high editability of DNA nanostructures and the biological activity of ligands into functionalized DNA nanostructures in a manner of controlled ligand stoichiometry, type, and arrangement, which provides significant advantages for targeted therapeutics and diagnostics. As therapeutic agents, multiple- and multivalent-ligands functionalized DNA nanostructures increase ligand-receptor affinity and activate multivalent ligand-receptor interactions, enabling improved regulation of cell signaling and enhanced control of cell behavior. As diagnostic agents, multiple ligands interaction via DNA nanostructures endows DNA nanosensors with high sensitivity and excellent signal transduction capability. Herein, we review the principles and advantages of using DNA nanostructures to manipulate ligands for targeted therapeutics and diagnostics and provide future perspectives.

A distinct CD38+CD45RA+ population of CD4+, CD8+, and double-negative T cells is controlled by FAS

The identification and characterization of rare immune cell populations in humans can be facilitated by their growth advantage in the context of specific genetic diseases. Here, we use autoimmune lymphoproliferative syndrome to identify a population of FAS-controlled TCRαβ⁺ T cells. They include CD4⁺, CD8⁺, and double-negative T cells and can be defined by a CD38⁺CD45RA⁺T-BET⁻ expression pattern. These unconventional T cells are present in healthy individuals, are generated before birth, are enriched in lymphoid tissue, and do not expand during acute viral infection. They are characterized by a unique molecular signature that is unambiguously different from other known T cell differentiation subsets and independent of CD4 or CD8 expression. Functionally, FAS-controlled T cells represent highly proliferative, noncytotoxic T cells with an IL-10 cytokine bias. Mechanistically, regulation of this physiological population is mediated by FAS and CTLA4 signaling, and its survival is enhanced by mTOR and STAT3 signals. Genetic alterations in these pathways result in expansion of FAS-controlled T cells, which can cause significant lymphoproliferative disease.

Soluble CD95L in cancers and chronic inflammatory disorders, a new therapeutic target?

Although CD95L (also known as FasL) is still predominantly considered as a death ligand that induces apoptosis in infected and transformed cells, substantial evidence indicate that it can also trigger non-apoptotic signaling pathways whose pathophysiological roles remain to be fully elucidated. The transmembrane ligand CD95L belongs to the tumor necrosis factor (TNF) superfamily. After cleavage by metalloprotease, its soluble form (s-CD95L) fails to trigger the apoptotic program but instead induces signaling pathways promoting the aggressiveness of certain inflammatory disorders such as autoimmune diseases and cancers. We propose to evaluate the various pathologies in which the metalloprotease-cleaved CD95L is accumulated and analyze whether this soluble ligand may play a significant role in the pathology progression. Based on the TNFα-targeting therapeutics, we envision that targeting the soluble form of CD95L may represent a very attractive therapeutic option in the pathologies depicted herein.

Nanoscale FasL Organization on DNA Origami to Decipher Apoptosis Signal Activation in Cells

Cell signaling is initiated by characteristic protein patterns in the plasma membrane, but tools to decipher their molecular organization and activation are hitherto lacking. Among the well-known signaling pattern is the death inducing signaling complex with a predicted hexagonal receptor architecture. To probe this architecture, DNA origami-based nanoagents with nanometer precise arrangements of the death receptor ligand FasL are introduced and presented to cells. Mimicking different receptor geometries, these nanoagents act as signaling platforms inducing fastest time-to-death kinetics for hexagonal FasL arrangements with 10 nm inter-molecular spacing. Compared to naturally occurring soluble FasL, this trigger is faster and 100× more efficient. Nanoagents with different spacing, lower FasL number or higher coupling flexibility impede signaling. The results present DNA origami as versatile signaling scaffolds exhibiting unprecedented control over molecular number and geometry. They define molecular benchmarks in apoptosis signal initiation and constitute a new strategy to drive particular cell responses.

Reconstruction of the Fas-Based Death-Inducing Signaling Complex (DISC) Using a Protein-Protein Docking Meta-Approach

The death-inducing signaling complex (DISC) is a fundamental multiprotein complex, which triggers the extrinsic apoptosis pathway through stimulation by death ligands. DISC consists of different death domain (DD) and death effector domain (DED) containing proteins such as the death receptor Fas (CD95) in complex with FADD, procaspase-8, and cFLIP. Despite many experimental and theoretical studies in this area, there is no global agreement neither on the DISC architecture nor on the mechanism of action of the involved species. In the current work, we have tried to reconstruct the DISC structure by identifying key protein interactions using a new protein-protein docking meta-approach. We combined the benefits of five of the most employed protein-protein docking engines, HADDOCK, ClusPro, HDOCK, GRAMM-X, and ZDOCK, in order to improve the accuracy of the predicted docking complexes. Free energy of binding and hot spot interacting residues were calculated and determined for each protein-protein interaction using molecular mechanics generalized Born surface area and alanine scanning techniques, respectively. In addition, a series of in-cellulo protein-fragment complementation assays were conducted to validate the protein-protein docking procedure. The results show that the DISC formation initiates by dimerization of adjacent Fas_DD trimers followed by recruitment of FADD through homotypic DD interactions with the oligomerized death receptor. Furthermore, the in-silico outcomes indicate that cFLIP cannot bind directly to FADD; instead, cFLIP recruitment to the DISC is a hierarchical and cooperative process where FADD initially recruits procaspase-8, which in turn recruits and heterodimerizes with cFLIP. Finally, a possible structure of the entire DISC is proposed based on the docking results.

The bioactivity of soluble Fas ligand is modulated by key amino acids of its stalk region

We have previously reported that the 26-amino acid N-terminus stalk region of soluble Fas ligand (sFasL), which is separate from its binding site, is required for its biological function. Here we investigate the mechanisms that link the structure of the sFasL stalk region with its function. Using site-directed mutagenesis we cloned a mutant form of sFasL in which all the charged amino acids of the stalk region were changed to neutral alanines (mut-sFasL). We used the Fas-sensitive Jurkat T-cell line and mouse and human alveolar epithelial cells to test the bioactivity of sFasL complexes, using caspase-3 activity and Annexin-V externalization as readouts. Finally, we tested the effects of mut-sFasL on lipopolysaccharide-induced lung injury in mice. We found that mutation of all the 8 charged amino acids of the stalk region into the non-charged amino acid alanine (mut-sFasL) resulted in reduced apoptotic activity compared to wild type sFasL (WT-sFasL). The mut-sFasL attenuated WT-sFasL function on the Fas-sensitive human T-cell line Jurkat and on primary human small airway epithelial cells. The inhibitory mechanism was associated with the formation of complexes of mut-sFasL with the WT protein. Intratracheal administration of the mut-sFasL to mice 24 hours after intratracheal Escherichia coli lipopolysaccharide resulted in attenuation of the inflammatory response 24 hours later. Therefore, the stalk region of sFasL has a critical role on bioactivity, and changes in the structure of the stalk region can result in mutant variants that interfere with the wild type protein function in vitro and in vivo.

TRAIL-Armed ER Nanosomes Induce Drastically Enhanced Apoptosis in Resistant Tumor in Combination with the Antagonist of IAPs (AZD5582)

Although mesenchymal stem cells (MSCs) can be engineered to deliver the TNF-related apoptosis-inducing ligand (TRAIL) as an effective anticancer therapy, the clinical application is hampered by the costly manufacturing of therapeutic MSCs. Therefore, it is needed to find an alternative cell-free therapy. In this study, TRAIL-armed endoplasmic reticulum (ER)-derived nanosomes (ERN-T) are successfully prepared with an average size of 70.6 nm in diameter from TRAIL transduced MSCs. It is demonstrated that the ERN-T is significantly more efficient for cancer cell killing than the soluble recombinant TRAIL (rTRAIL). AZD5582 is an antagonist of the inhibitors of apoptosis proteins (IAPs), and its combination with ERN-T induces strikingly enhanced apoptosis in cancerous but not normal cells. AZD5582 sensitizes resistant cancer cells to TRAIL through concomitant downregulation of IAP members like XIAP and the Bcl2 family member Mcl-1. Intravenously infused ERN-Ts accumulate in tumors for over 48 h indicating good tumor tropism and retention. The combination of ERN-T and AZD5582 drastically promotes therapeutic efficacy comparing with the cotreatment by rTRAIL and AZD5582 in a subcutaneous MDA-MB-231 xenograft tumor model. The data thus demonstrate that ERN-T can be a novel cell-free alternative to TRAIL-expressing MSC-based anticancer therapy and its efficacy can be drastically enhanced through combination with AZD5582.

Extracellular Soluble Membranes from Retinal Pigment Epithelial Cells Mediate Apoptosis in Macrophages

A central characterization of retinal immunobiology is the prevention of proinflammatory activity by macrophages. The retinal pigment epithelial cells (RPEs) are a major source of soluble anti-inflammatory factors. This includes a soluble factor that induces macrophage apoptosis when the activity of the immunomodulating neuropeptide alpha-melanocyte-stimulating hormone (α-MSH) is neutralized. In this manuscript, isolated extracellular soluble membranes (ESMs) from primary RPE were assayed to see if they could be the soluble mediator of apoptosis. Our results demonstrated that RPE ESMs mediated the induction of macrophage apoptosis that was suppressed by α-MSH. In contrast, the RPE line ARPE-19, cultured under conditions that induce similar anti-inflammatory activity to primary RPEs, did not activate apoptosis in the macrophages. Moreover, only the ESMs from primary RPE cultures, and not those from the ARPE-19 cell cultures, expressed mFasL. The results demonstrate that RPE ESMs are a soluble mediator of apoptosis and that this may be a mechanism by which the RPEs select for the survival of α-MSH-induced suppressor cells.

Receptor Oligomerization and Its Relevance for Signaling by Receptors of the Tumor Necrosis Factor Receptor Superfamily

With the exception of a few signaling incompetent decoy receptors, the receptors of the tumor necrosis factor receptor superfamily (TNFRSF) are signaling competent and engage in signaling pathways resulting in inflammation, proliferation, differentiation, and cell migration and also in cell death induction. TNFRSF receptors (TNFRs) become activated by ligands of the TNF superfamily (TNFSF). TNFSF ligands (TNFLs) occur as trimeric type II transmembrane proteins but often also as soluble ligand trimers released from the membrane-bound form by proteolysis. The signaling competent TNFRs are efficiently activated by the membrane-bound TNFLs. The latter recruit three TNFR molecules, but there is growing evidence that this is not sufficient to trigger all aspects of TNFR signaling; rather, the formed trimeric TNFL–TNFR complexes have to cluster secondarily in the cell-to-cell contact zone for full TNFR activation. With respect to their response to soluble ligand trimers, the signaling competent TNFRs can be subdivided into two groups. TNFRs of one group, designated as category I TNFRs, are robustly activated by soluble ligand trimers. The receptors of a second group (category II TNFRs), however, failed to become properly activated by soluble ligand trimers despite high affinity binding. The limited responsiveness of category II TNFRs to soluble TNFLs can be overcome by physical linkage of two or more soluble ligand trimers or, alternatively, by anchoring the soluble ligand molecules to the cell surface or extracellular matrix. This suggests that category II TNFRs have a limited ability to promote clustering of trimeric TNFL–TNFR complexes outside the context of cell–cell contacts. In this review, we will focus on three aspects on the relevance of receptor oligomerization for TNFR signaling: (i) the structural factors which promote clustering of free and liganded TNFRs, (ii) the signaling pathway specificity of the receptor oligomerization requirement, and (iii) the consequences for the design and development of TNFR agonists.

MiR-7e-5p downregulation promotes transformation of low-grade follicular lymphoma to aggressive lymphoma by modulating an immunosuppressive stroma through the upregulation of FasL in M1 macrophages

BACKGROUND

In follicular lymphoma (FL), histologic transformation to high-grade FL and diffuse large B-cell lymphoma (DLBCL) is a critical adverse step in disease progression. Activation of the oncogene c-MYC and tumor microenvironment remodeling account for FL progression. A panel of microRNA (miRNA) was downregulated in transformed FL (tFL).

METHODS

Differentially expressed miRNAs were systematically compared in 11 lymph nodes from patients at different stages of disease. Expression of miR-7e-5p was analyzed in 46 B-cell lymphomas, including 30 FL tissues and 16 DLBCL tissues. In FL cells, transcriptional regulation of the oncogene c-MYC on its target miR-7e-5p was revealed by Chromatin Immunoprecipitation (ChIP) assay. Exosome, carrying differentially expressed miR-7e-5p was isolated and visualized by transmission electron microscope and fluorescence tracing. The effect of miR-7e-5p on recipient macrophage was determined by target gene quantification, flow cytometry, and TUNEL method in a cocultured system with miR-7e-5p-mimics or inhibitors treatment. Expression of miR-7e-5p targets, macrophage proportions, and clinical parameters were included for correlation analysis.

RESULTS

We determined that downregulation of miR-7e-5p, driven by c-MYC overexpression, was associated with poorer prognosis in FL patients. The decreased expression of miR-7e-5p in lymphoma cells led to a reduced exosomal transfer to surrounding macrophages. As a result, the target gene of miR-7e-5p, Fas ligand (FasL), was upregulated and activated the caspase signaling, which led to the apoptosis of M1 macrophages in tumor stroma. Finally, in transformed FL tissues, overexpression of FasL and activation of caspase proteins was detected in tumor stromal macrophages. Downregulation of miR-7e-5p was associated with poorer clinical outcomes.

CONCLUSION

Downregulation of exosomal miR-7e-5p induces stromal M1 macrophage apoptosis, which leads to immunosurveillance and transformation of FL.

Molecular mechanisms of FasL-mediated 'reverse-signaling'

Effector lymphocytes, including NK and T cells, express FasL. Expression of Fas, the receptor for FasL in tumor cells, renders them susceptible to NK and T cell-mediated killing. The functional relevance of FasL in initiating death signals in tumor cells is well-characterized. However, the cytoplasmic interacting partners and the potential signaling pathways downstream of FasL are far from fully defined. FasL possesses an 81 amino acid long cytoplasmic tail with multiple unique recruitment motifs. We predict multiple interdependent signaling complexes form the core of the 'reverse signaling' downstream of FasL. A direct interaction between the proline-rich domain of FasL and the SH3 domain of PI(3)K-p85α initiates the first pathway. This cascade helps FasL to link to PLC-γ2 via PIP₃ or the Akt-dependent activation of mTOR complexes. Independently, a GRB2/GADs-binding PXXP cytoplasmic motif of FasL can initiate a Ras-GTP-dependent PAK1→C-Raf→MEK1/2→ERK1/2 activation. FasL can recruit Fyn via the proline-rich domain leading to the recruitment of ADAP. Through its ability to directly interact with Carma1 and TAK1, ADAP initiates the formation of the Carma1/Bcl10/Malt1-based CBM signalosome that is primarily responsible for inflammatory cytokine production. Here, we explore the conserved cytoplasmic domains of FasL, the potential signaling molecules that interact, and the functional downstream consequences within the effector lymphocytes to define the FasL-mediated 'reverse signaling'.

Death Receptors and Their Ligands in Inflammatory Disease and Cancer

On binding to their cognate ligands, death receptors can initiate a cascade of events that can result in two distinct outcomes: gene expression and cell death. The study of three different death receptor-ligand systems, the tumor necrosis factor (TNF)-TNF receptor 1 (TNFR1), the CD95L-CD95, and the TNF-related apoptosis-inducing ligand (TRAIL)-TRAIL-R1/2 system, has drawn the attention of generations of scientists over the past 50 years. This scientific journey, as often happens in science, has been anything but a straight line to success and discoveries in this field were often made by serendipity, catching the scientists by surprise. However, as Louis Pasteur pointed out, luck prefers the prepared mind. It is therefore not surprising that the most impactful discovery of the field to date, the fact that TNF inhibition serves as an effective treatment for several inflammatory and autoimmune diseases, has been like this. Luckily, the scientists who made this discovery were prepared and, most importantly, determined to harness their discovery for therapeutic benefit. Today's research on these death receptor-ligand systems has led to the discovery of a causal link between cell death induced by a variety of these systems and inflammation. In this review, we explain why we predict that therapeutic exploitation of this discovery may profoundly impact the future treatment of inflammatory disease and cancer.

Characterization of resistance to a recombinant hexameric Fas-ligand (APO010) in human cancer cell lines

Multiple myeloma remains a hard-to-treat cancer as all patients eventually progress because of drug resistance. Thus, there is a need for novel and non-cross-resistant treatment options, and we aimed to address this issue by introducing a new immuno-oncology drug (APO010) in multiple myeloma treatment. APO010 is a hexameric Fas-ligand that mimics cytotoxic T-lymphocyte signaling through the Fas-receptor to induce apoptosis. APO010 is currently in clinical trials with multiple myeloma patients. Thus, an understanding of the mechanisms contributing to resistance to APO010 will be essential for future clinical studies with APO010, and it might be possible to develop strategies to circumvent this resistance. We developed APO010-resistant variants of human multiple myeloma cell lines (LP1, MOLP-8, and KMS-12-BM) and a human Burkitt's lymphoma cell line (Raji) by exposing the cells to gradually increasing concentrations of APO010 over a period of 6-12 months. The resistant cell lines were characterized on the basis of immunocytochemistry, Fas-receptor protein expression, mRNA expression analysis, and pathway analysis. APO010-resistant cell lines exhibited a 4- to 520-fold increase in resistance to APO010 and still remained sensitive to other chemotherapeutics. Downregulation of the Fas-receptor protein expression was observed in all resistant cell lines. mRNA expression analysis of the resistant versus parental cell lines confirmed a significant alteration in FAS expression between sensitive and resistant cell lines (p = 0.03), while pathway analysis revealed alterations in mRNA signaling pathways of Fas. On the basis of the pre-clinical data obtained, it can be concluded that downregulation of Fas-receptor can mediate resistance to APO010.

Tissue-Engineered Models for Glaucoma Research

Glaucoma is a group of optic neuropathies characterized by the progressive degeneration of retinal ganglion cells (RGCs). Patients with glaucoma generally experience elevations in intraocular pressure (IOP), followed by RGC death, peripheral vision loss and eventually blindness. However, despite the substantial economic and health-related impact of glaucoma-related morbidity worldwide, the surgical and pharmacological management of glaucoma is still limited to maintaining IOP within a normal range. This is in large part because the underlying molecular and biophysical mechanisms by which glaucomatous changes occur are still unclear. In the present review article, we describe current tissue-engineered models of the intraocular space that aim to advance the state of glaucoma research. Specifically, we critically evaluate and compare both 2D and 3D-culture models of the trabecular meshwork and nerve fiber layer, both of which are key players in glaucoma pathophysiology. Finally, we point out the need for novel organ-on-a-chip models of glaucoma that functionally integrate currently available 3D models of the retina and the trabecular outflow pathway.

Activation of OX40 and CD27 Costimulatory Signalling in Sheep through Recombinant Ovine Ligands

Members of the tumour necrosis factor (TNF) superfamily OX40L and CD70 and their receptors are costimulating signalling axes critical for adequate T cell activation in humans and mice but characterisation of these molecules in other species including ruminants is lacking. Here we cloned and expressed the predicted ovine orthologues of the receptors OX40 and CD27, as well as soluble recombinant forms of their potential ovine ligands, OaOX40L and OaCD70. Using biochemical and immunofluorescence analyses, we show that both signalling axes are functional in sheep. We show that oligomeric recombinant ligand constructs are able to induce signalling through their receptors on transfected cells. Recombinant defective human adenoviruses were constructed to express the soluble forms of OaOX40L and OaCD70. Both proteins were detected in the supernatant of adenovirus-infected cells and shown to activate NF-κB signalling pathway through their cognate receptor. These adenovirus-secreted OaOX40L and OaCD70 forms could also activate ovine T cell proliferation and enhance IFN-γ production in CD4⁺ and CD8⁺ T cells. Altogether, this study provides the first characterisation of the ovine costimulatory OX40L-OX40 and CD70-CD27 signalling axes, and indicates that their activation in vivo may be useful to enhance vaccination-induced immune responses in sheep and other ruminants.

CD95 Structure, Aggregation and Cell Signaling

CD95 is a pre-ligand-associated transmembrane (TM) receptor. The interaction with its ligand CD95L brings to a next level its aggregation and triggers different signaling pathways, leading to cell motility, differentiation or cell death. This diversity of biological responses associated with a unique receptor devoid of enzymatic property raises the question of whether different ligands exist, or whether the fine-tuned control of CD95 aggregation and conformation, its distribution within certain plasma membrane sub-domains or the pattern of post-translational modifications account for this such broad-range of cell signaling. Herein, we review how the different domains of CD95 and their post-translational modifications or the different forms of CD95L can participate in the receptor aggregation and induction of cell signaling. Understanding how CD95 response goes from cell death to cell proliferation, differentiation and motility is a prerequisite to reveal novel therapeutic options to treat chronic inflammatory disorders and cancers.

Extracellular Vesicle Delivery of TRAIL Eradicates Resistant Tumor Growth in Combination with CDK Inhibition by Dinaciclib

Tumour necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) is a promising anti-cancer agent that rapidly induces apoptosis in cancer cells. Unfortunately, the clinical application of recombinant TRAIL (rTRAIL) has been hampered by its common cancer resistance. Naturally TRAIL is delivered as a membrane-bound form by extracellular vesicles (EV-T) and is highly efficient for apoptosis induction. SCH727965 (dinaciclib), a potent cyclin-dependent kinase (CDK) inhibitor, was shown to synergize with other drugs to get better efficacy. However, it has never been investigated if dinaciclib coordinates with EV-T to enhance therapeutic results. This study explores the potential of combination therapy with EV-T and dinaciclib for cancer treatment. EV-T was successfully derived from human TRAIL transduced cells and shown to partially overcome resistance of A549 cells. Dinaciclib was shown to drastically enhance EV-T killing effects on cancer lines that express good levels of death receptor (DR) 5, which are associated with suppression of CDK1, CDK9 and anti-apoptotic proteins. Combination therapy with low doses of EV-T and dinaciclib induced strikingly enhanced apoptosis and led to complete regression in A549 tumors without any adverse side effects observed in a subcutaneous xenograft model. Tumor infiltration of mass NK cells and macrophages was also observed. These observations thus indicate that the combination of EV-T with dinaciclib is a potential novel therapy for highly effective and safe cancer treatment.

Stress Management: Death Receptor Signalling and Cross-Talks with the Unfolded Protein Response in Cancer

Throughout tumour progression, tumour cells are exposed to various intense cellular stress conditions owing to intrinsic and extrinsic cues, to which some cells are remarkably able to adapt. Death Receptor (DR) signalling and the Unfolded Protein Response (UPR) are two stress responses that both regulate a plethora of outcomes, ranging from proliferation, differentiation, migration, cytokine production to the induction of cell death. Both signallings are major modulators of physiological tissue homeostasis and their dysregulation is involved in tumorigenesis and the metastastic process. The molecular determinants of the control between the different cellular outcomes induced by DR signalling and the UPR in tumour cells and their stroma and their consequences on tumorigenesis are starting to be unravelled. Herein, I summarize the main steps of DR signalling in relation to its cellular and pathophysiological roles in cancer. I then highlight how the UPR and DR signalling control common cellular outcomes and also cross-talk, providing potential opportunities to further understand the development of malignancies.

A Two-Cell Model for IL-1β Release Mediated by Death-Receptor Signaling

Interleukin-1β (IL-1β) is a key orchestrator of anti-microbial immunity whose secretion is typically dependent on activation of inflammasomes. However, many pathogens have evolved strategies to evade inflammasome activation. Here we describe an alternative, two-cell model for IL-1β release where invariant natural killer T (iNKT) cells use the death receptor pathway to instruct antigen-presenting cells to secrete IL-1β. Following cognate interactions with TLR-primed bone marrow-derived dendritic cells (BMDCs), iNKT cells rapidly translocate intracellular Fas ligand to the surface to engage Fas on BMDCs. Fas ligation activates a caspase-8-dependent signaling cascade in BMDCs that drives IL-1β release largely independent of inflammasomes. The apoptotic program initiated by Fas ligation rapidly transitions into a pyroptosis-like form of cell death mediated by gasdermin D. Together, our findings support a two-cell model for IL-1β secretion that may supersede inflammasome activation when cytosolic triggers fail.

Soluble Fas affects erythropoiesis in vitro and acts as a potential predictor of erythropoiesis-stimulating agent therapy in patients with chronic kidney disease

Serum soluble Fas (sFas) levels are associated with erythropoietin (Epo) hyporesponsiveness in patients with chronic kidney disease (CKD). Whether sFas could predict the need for erythropoiesis-stimulating agent (ESA) usage and its influence in erythropoiesis remain unclear. We evaluated the relation between sFas and ESA therapy in patients with CKD with anemia and its effect on erythropoiesis in vitro. First, we performed a retrospective cohort study with 77 anemic patients with nondialysis CKD. We performed in vitro experiments to investigate whether sFas could interfere with the behavior of hematopoietic stem cells (HSCs). HSCs were isolated from umbilical cord blood and incubated with recombinant sFas protein in a dose-dependent manner. Serum sFas positively correlated with Epo levels (r = 0.30, P = 0.001) but negatively with hemoglobin (r = -0.55, P < 0.001) and glomerular filtration rate (r = -0.58, P < 0.001) in patients with CKD at baseline. Elevated sFas serum levels (4,316 ± 897 vs. 2,776 ± 749, P < 0.001) with lower estimated glomerular filtration rate (26.2 ± 10.1 vs. 33.5 ± 14.3, P = 0.01) and reduced hemoglobin concentration (11.1 ± 0.9 vs. 12.5 ± 1.2, P < 0.001) were identified in patients who required ESA therapy compared with patients with non-ESA. Afterward, we detected that the sFas level was slight correlated with a necessity of ESA therapy in patients with nondialysis CKD and anemia. In vitro assays demonstrated that the erythroid progenitor cell frequency negatively correlated with sFas concentration (r = -0.72, P < 0.001). There was decreased erythroid colony formation in vitro when CD34+ HSCs were incubated with a higher concentration of sFas protein (1.56 ± 0.29, 4.33 ± 0.53, P < 0.001). Our findings suggest that sFas is a potential predictor for ESA therapy in patients with nondialysis CKD and that elevated sFas could affect erythropoiesis in vitro.

Nongenetic engineering strategies for regulating receptor oligomerization in living cells

Nongenetic strategies for regulating receptor oligomerization in living cells based on DNA, protein, small molecules and physical stimuli.

Toxicology and Pharmacokinetic Studies in Mice and Nonhuman Primates of the Nontoxic, Efficient, Targeted Hexameric FasL: CTLA4-FasL

Cytotoxic T-lymphocyte antigen 4 (CTLA4)-FasL, a homo-hexameric signal converter protein, is capable of inducing robust apoptosis in malignant cells of the B-cell lineage expressing its cognate B7 and Fas targets, while sparing nonmalignant ones. This fusion protein's striking proapoptotic efficacy stems from its complementary abilities to coordinately activate apoptotic signals and abrogate antiapoptotic ones. A limiting factor in translating FasL or Fas receptor agonists into the clinic has been lethal hepatotoxicity. Here, we establish CTLA4-FasL's in vivo efficacy in multiple murine and xenograft models, for both systemic and subcutaneous tumors. Significantly, good laboratory practice (GLP) toxicology studies in mice indicate that CTLA4-FasL given repeatedly at doses up to five times the effective dose was well-tolerated and resulted in no significant adverse events. An equivalent single dose of CTLA4-FasL administered to nonhuman primates was also well-tolerated, albeit with a moderate dose-dependent leukopenia that was completely reversible. Interestingly, monkey peripheral blood mononuclear cells were more sensitive to CTLA4-FasL-induced apoptosis when tested in vitro. In both species, there was short-term elevation in serum levels of IL6, IL2, and IFNγ, although this was not associated with clinical signs of proinflammatory cytokine release, and further, this cytokine elevation could be completely prevented by dexamethasone premedication. Liver toxicity was not observed in either species, as confirmed by serum liver enzyme levels and histopathologic assessment. In conclusion, CTLA4-FasL emerges from animal model studies as an effective and safe agent for targeted FasL-mediated treatment of B7-expressing aggressive B-cell lymphomas.

Membrane-bound TNF mediates microtubule-targeting chemotherapeutics-induced cancer cytolysis via juxtacrine inter-cancer-cell death signaling

Microtubule-targeting agents (MTAs) are a class of most widely used chemotherapeutics and their mechanism of action has long been assumed to be mitotic arrest of rapidly dividing tumor cells. In contrast to such notion, here we show—in many cancer cell types—MTAs function by triggering membrane TNF (memTNF)-mediated cancer-cell-to-cancer-cell killing, which differs greatly from other non-MTA cell-cycle-arresting agents. The killing is through programmed cell death (PCD), either in way of necroptosis when RIP3 kinase is expressed, or of apoptosis in its absence. Mechanistically, MTAs induce memTNF transcription via the JNK-cJun signaling pathway. With respect to chemotherapy regimens, our results establish that memTNF-mediated killing is significantly augmented by IAP antagonists (Smac mimetics) in a broad spectrum of cancer types, and with their effects most prominently manifested in patient-derived xenograft (PDX) models in which cell–cell contacts are highly reminiscent of human tumors. Therefore, our finding indicates that memTNF can serve as a marker for patient responsiveness, and Smac mimetics will be effective adjuvants for MTA chemotherapeutics. The present study reframes our fundamental biochemical understanding of how MTAs take advantage of the natural tight contact of tumor cells and utilize memTNF-mediated death signaling to induce the entire tumor regression.

Molecular Mode of Action of TRAIL Receptor Agonists-Common Principles and Their Translational Exploitation

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its death receptors TRAILR1/death receptor 4 (DR4) and TRAILR2/DR5 trigger cell death in many cancer cells but rarely exert cytotoxic activity on non-transformed cells. Against this background, a variety of recombinant TRAIL variants and anti-TRAIL death receptor antibodies have been developed and tested in preclinical and clinical studies. Despite promising results from mice tumor models, TRAIL death receptor targeting has failed so far in clinical studies to show satisfying anti-tumor efficacy. These disappointing results can largely be explained by two issues: First, tumor cells can acquire TRAIL resistance by several mechanisms defining a need for combination therapies with appropriate sensitizing drugs. Second, there is now growing preclinical evidence that soluble TRAIL variants but also bivalent anti-TRAIL death receptor antibodies typically require oligomerization or plasma membrane anchoring to achieve maximum activity. This review discusses the need for oligomerization and plasma membrane attachment for the activity of TRAIL death receptor agonists in view of what is known about the molecular mechanisms of how TRAIL death receptors trigger intracellular cell death signaling. In particular, it will be highlighted which consequences this has for the development of next generation TRAIL death receptor agonists and their potential clinical application.

TRAIL-R1 and TRAIL-R2 Mediate TRAIL-Dependent Apoptosis in Activated Primary Human B Lymphocytes

The maintenance of B cell homeostasis requires a tight control of B cell generation, survival, activation, and maturation. In lymphocytes upon activation, increased sensitivity to apoptotic signals helps controlling differentiation and proliferation. The death receptor Fas is important in this context because genetic Fas mutations in humans lead to an autoimmune lymphoproliferative syndrome that is similar to lymphoproliferation observed in Fas-deficient mice. In contrast, the physiological role of TNF-related apoptosis-inducing ligand receptors (TRAIL-Rs) in humans has been poorly studied so far. Indeed, most studies have focused on tumor cell lines and on mouse models whose results are difficult to transpose to primary human B cells. In the present work, the expression of apoptosis-inducing TRAIL-R1 and TRAIL-R2 and of the decoy receptors TRAIL-R3 and TRAIL-R4 was systematically studied in all developmental stages of peripheral B cells isolated from the blood and secondary lymphoid organs. Expression of TRAIL-Rs is modulated along development, with highest levels observed in germinal center B cells. In addition, T-dependent and T-independent signals elicited induction of TRAIL-Rs with distinct kinetics, which differed among B cell subpopulations: switched memory cells rapidly upregulated TRAIL-R1 and -2 upon activation while naïve B cells only reached similar expression levels at later time points in culture. Increased expression of TRAIL-R1 and -2 coincided with a caspase-3-dependent sensitivity to TRAIL-induced apoptosis in activated B cells but not in freshly isolated resting B cells. Finally, both TRAIL-R1 and TRAIL-R2 could signal actively and both contributed to TRAIL-induced apoptosis. In conclusion, this study provides a systematic analysis of the expression of TRAIL-Rs in human primary B cells and of their capacity to signal and induce apoptosis. This dataset forms a basis to further study and understand the dysregulation of TRAIL-Rs and TRAIL expression observed in autoimmune diseases. Additionally, it will be important to foresee potential bystander immunomodulation when TRAIL-R agonists are used in cancer treatment.