TRAIL/Apo-2 ligand induces primary plasma cell apoptosis

Understanding the complexities of SARS-CoV2 infection and its immunology: A road to immune-based therapeutics

Emerging infectious diseases always pose a threat to humans along with plant and animal life. SARS-CoV2 is the recently emerged viral infection that originated from Wuhan city of the Republic of China in December 2019. Now, it has become a pandemic. Currently, SARS-CoV2 has infected more than 27.74 million people worldwide, and taken 901,928 human lives. It was named first 'WH 1 Human CoV' and later changed to 2019 novel CoV (2019-nCoV). Scientists have established it as a zoonotic viral disease emerged from Chinese horseshoe bats, which do not develop a severe infection. For example, Rhinolophus Chinese horseshoe bats harboring severe acute respiratory syndrome-related coronavirus (SARSr-CoV) or SARSr-Rh-BatCoV appear healthy and clear the virus within 2-4 months period. The article introduces first the concept of EIDs and some past EIDs, which have affected human life. Next section discusses mysteries regarding SARS-CoV2 origin, its evolution, and human transfer. Third section describes COVID-19 clinical symptoms and factors affecting susceptibility or resistance. The fourth section introduces the SARS-CoV2 entry in the host cell, its replication, and the establishment of productive infection. Section five describes the host's immune response associated with asymptomatic, symptomatic, mild to moderate, and severe COVID-19. The subsequent seventh and eighth sections mention the immune status in COVID-19 convalescent patients and re-emergence of COVID-19 in them. Thereafter, the eighth section describes viral strategies to hijack the host antiviral immune response and generate the "cytokine storm". The ninth section describes about transgenic humane ACE2 (hACE2) receptor expressing mice to study immunity, drugs, and vaccines. The article ends with the development of different immunomodulatory and immunotherapeutics strategies, including vaccines waiting for their approval in humans as prophylaxis or treatment measures.

Suppressed humoral immunity is associated with dengue nonstructural protein NS1-elicited anti-death receptor antibody fractions in mice

Dengue virus (DENV) infections may cause life-threatening dengue hemorrhagic fever (DHF). Suppressed protective immunity was shown in these patients. Although several hypotheses have been formulated, the mechanism of DENV-induced immunosuppression remains unclear. Previously, we found that cross-reactive antibodies against tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 1 (death receptor 4 [DR4]) were elicited in DHF patients, and that anti-DR4 autoantibody fractions were elicited by nonstructural protein 1 (NS1) immunizations in experimental mice. In this study, we found that anti-DR4 antibodies could suppress B lymphocyte function in vitro and in vivo. Treatment with the anti-DR4 immunoglobulin (Ig) induced caspase-dependent cell death in immortalized B lymphocyte Raji cells in vitro. Anti-DR4 Igs elicited by NS1 and DR4 immunizations markedly suppressed mouse spleen transitional T2 B (IgM+IgD+), bone marrow pre-pro-B (B220+CD43+), pre-B (B220+CD43-), and mature B cell (B220+IgD+) subsets in mice. Furthermore, functional analysis revealed that the pre-elicitation of anti-NS1 and anti-DR4 Ig titers suppressed subsequently neutralizing antibody production by immunization with DENV envelop protein. Our data suggest that the elicitation of anti-DR4 titers through DENV NS1 immunization plays a suppressive role in humoral immunity in mice.

The Role of TRAIL/DRs in the Modulation of Immune Cells and Responses

Expression of TRAIL (tumor necrosis factor–related apoptosis–inducing ligand) by immune cells can lead to the induction of apoptosis in tumor cells. However, it becomes increasingly clear that the interaction of TRAIL and its death receptors (DRs) can also directly impact immune cells and influence immune responses. Here, we review what is known about the role of TRAIL/DRs in immune cells and immune responses in general and in the tumor microenvironment in particular.

Assessing the Functional Relevance of Variants in the IKAROS Family Zinc Finger Protein 1 (IKZF1) in a Cohort of Patients With Primary Immunodeficiency

Common variable immunodeficiency (CVID) is the most frequent symptomatic primary immunodeficiency. Patients with CVID are prone to recurrent bacterial infection due to the failure of adequate immunoglobulin production. Monogenetic defects have been identified in ~25% of CVID patients. Recently, mutations in IKZF1, encoding the zinc-finger transcription factor IKAROS which is broadly expressed in hematopoietic cells, have been associated with a CVID-like phenotype. Herein we describe 11 patients with heterozygous IKZF1 variants from eight different families with autosomal dominant CVID and two siblings with an IKZF1 variant presenting with inflammatory bowel disease (IBD). This study shows that mutations affecting the DNA binding domain of IKAROS can impair the interaction with the target DNA sequence thereby preventing heterochromatin and pericentromeric localization (HC-PC) of the protein. Our results also indicate an impairment of pericentromeric localization of IKAROS by overexpression of a truncated variant, caused by an immature stop codon in IKZF1. We also describe an additional variant in TNFSF10, encoding Tumor Necrosis Factor Related Apoptosis Inducing Ligand (TRAIL), additionally presented in individuals of Family A. Our results indicate that this variant may impair the TRAIL-induced apoptosis in target cell lines and prohibit the NFκB activation by TRAIL and may act as a modifier in Family A.

Anti-interleukin-6 signalling therapy rebalances the disrupted cytokine production of B cells from patients with active rheumatoid arthritis

Rheumatoid arthritis (RA) is associated with abnormal B cell-functions implicating antibody-dependent and -independent mechanisms. B cells have emerged as important cytokine-producing cells, and cytokines are well-known drivers of RA pathogenesis. To identify novel cytokine-mediated B-cell functions in RA, we comprehensively analysed the capacity of B cells from RA patients with an inadequate response to disease modifying anti-rheumatic drugs to produce cytokines in comparison with healthy donors (HD). RA B cells displayed a constitutively higher production of the pathogenic factors interleukin (IL)-8 and Gro-α, while their production of several cytokines upon activation via the B cell receptor for antigen (BCR) was broadly suppressed, including a loss of the expression of the protective factor TRAIL, compared to HD B cells. These defects were partly erased after treatment with the IL-6-signalling inhibitor tocilizumab, indicating that abnormal IL-6 signalling contributed to these abnormalities. Noteworthy, the clinical response of individual patients to tocilizumab therapy could be predicted using the amounts of MIP-1β and β-NGF produced by these patients' B cells before treatment. Taken together, our study highlights hitherto unknown abnormal B-cell functions in RA patients, which are related to the unbalanced cytokine network, and are potentially relevant for RA pathogenesis and treatment.

Hetero-oligomerization between the TNF receptor superfamily members CD40, Fas and TRAILR2 modulate CD40 signalling

TNF receptor superfamily members (TNFRSF) such as CD40, Fas and TRAIL receptor 2 (TRAILR2) participate to the adaptive immune response by eliciting survival, proliferation, differentiation and/or cell death signals. The balance between these signals determines the fate of the immune response. It was previously reported that these receptors are able to self-assemble in the absence of ligand through their extracellular regions. However, the role of this oligomerization is not well understood, and none of the proposed hypotheses take into account potential hetero-association of receptors. Using CD40 as bait in a flow cytometry Förster resonance energy transfer assay, TNFRSF members with known functions in B cells were probed for interactions. Both Fas and TRAILR2 associated with CD40. Immunoprecipitation experiments confirmed the interaction of CD40 with Fas at the endogenous levels in a BJAB B-cell lymphoma cell line deficient for TRAILR2. TRAILR2-expressing BJAB cells displayed a robust CD40–TRAILR2 interaction at the expense of the CD40–Fas interaction. The same results were obtained by proximity ligation assay, using TRAILR2-positive and -negative BJAB cells and primary human B cells. Expression of the extracellular domains of Fas or TRAILR2 with a glycolipid membrane anchor specifically reduced the intrinsic signalling pathway of CD40 in 293T cells. Conversely, BJAB cells lacking endogenous Fas or TRAILR2 showed an increased NF-κB response to CD40L. Finally, upregulation of TRAILR2 in primary human B cells correlated with reduced NF-κB activation and reduced proliferation in response to CD40L. Altogether, these data reveal that selective interactions between different TNFRSF members may modulate ligand-induced responses upstream signalling events.

Dendritic Cells Regulate Extrafollicular Autoreactive B Cells via T Cells Expressing Fas and Fas Ligand

The extrafollicular (EF) plasmablast response to self-antigens that contain Toll-like receptor (TLR) ligands is prominent in murine lupus models and some bacterial infections, but the inhibitors and activators involved have not been fully delineated. Here, we used two conventional dendritic cell (cDC) depletion systems to investigate the role of cDCs on a classical TLR-dependent autoreactive EF response elicited in rheumatoid-factor B cells by DNA-containing immune complexes. Contrary to our hypothesis, cDC depletion amplified rather than dampened the EF response in Fas-intact but not Fas-deficient mice. Further, we demonstrated that cDC-dependent regulation requires Fas and Fas ligand (FasL) expression by T cells, but not Fas expression by B cells. Thus, cDCs activate FasL-expressing T cells that regulate Fas-expressing extrafollicular helper T (Tefh) cells. These studies reveal a regulatory role for cDCs in B cell plasmablast responses and provide a mechanistic explanation for the excess autoantibody production observed in Fas deficiency.

Redox signaling and oxidative stress: Cross talk with TNF-related apoptosis inducing ligand activity

Redox regulation plays a key role in several physiopathological contexts and free radicals, from nitric oxide and superoxide anion up to other forms of reactive oxygen species (ROS), have been demonstrated to be involved in different biological and regulatory processes. The data reported in the current literature describe a link between ROS, inflammation and programmed cell death that is attracting interest as new pathways to be explored and targeted for therapeutic purposes. In this light, there is also growing attention to the involvement of this link in the activity of the TNF-related apoptosis inducing ligand (TRAIL). TRAIL is a member of the TNF ligands super family able to mediate multiple intracellular signals, with the potential to lead to a range of biological effects in different cell types. In particular, the hallmark of TRAIL is the ability to induce selective apoptosis in transformed cells leaving normal cells almost unaffected and this feature has already opened the door to several clinical studies for cancer treatment. Moreover, TRAIL plays a role in several physiological and pathological processes of both innate and adaptive immune systems and of the cardiovascular context, with a strong clinical potential. Nonetheless, several issues still need to be clarified about the signaling mediated by TRAIL to gain deeper insight into its therapeutic potential. In this light, the aim of this review is to summarize the main preclinical evidences about the interplay between TRAIL and redox signaling, with particular emphasis to the implications in vascular physiopathology and cancer.

A unique population of IgG-expressing plasma cells lacking CD19 is enriched in human bone marrow

Healthy human BM is enriched for PC lacking CD19 that express a prosurvival and distinctly mature phenotype. CD19− PC resist mobilization into blood during immune responses after vaccination as well as B-cell depletion with rituximab.

TRAIL modulates the immune system and protects against the development of diabetes

TRAIL or tumor necrosis factor (TNF) related apoptosis-inducing ligand is a member of the TNF superfamily of proteins, whose best characterized function is the induction of apoptosis in tumor, infected, or transformed cells through activation of specific receptors. In nontransformed cells, however, the actions of TRAIL are less well characterized. Recent studies suggest that TRAIL may be implicated in the development and progression of diabetes. Here we review TRAIL biological actions, its effects on the immune system, and how and to what extent it has been shown to protect against diabetes.

Roles of ligands from the TNF superfamily in B cell development, function, and regulation

Most ligands from the tumour necrosis factor (TNF) superfamily play very important roles in the immune system, and particularly so in B lymphocyte biology. TNF ligands are essential to many aspects of normal B cell biology from development in the bone marrow to maturation in the periphery as well as for activation and differentiation into germinal centre, memory or plasma cells. TNF ligands also influence other aspects of B cell biology such as their ability to present antigens or regulate immune responses. Importantly, inadequate regulation of many TNF ligands is associated with B cell disorders including autoimmunity and cancers. As a result, inhibitors of a number of TNF ligands have been tested in the clinic, with some becoming very successful approved treatments alleviating B cell-mediated pathologies.

Blockade of Death Ligand TRAIL Inhibits Renal Ischemia Reperfusion Injury

Renal ischemia-reperfusion injury (IRI) is a leading cause of acute kidney injury (AKI). Many investigators have reported that cell death via apoptosis significantly contributed to the pathophysiology of renal IRI. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor superfamily, and induces apoptosis and inflammation. However, the role of TRAIL in renal IRI is unclear. Here, we investigated whether TRAIL contributes to renal IRI and whether TRAIL blockade could attenuate renal IRI. AKI was induced by unilateral clamping of the renal pedicle for 60 min in male FVB/N mice. We found that the expression of TRAIL and its receptors were highly upregulated in renal tubular cells in renal IRI. Neutralizing anti-TRAIL antibody or its control IgG was given 24 hr before ischemia and a half-dose booster injection was administered into the peritoneal cavity immediately after reperfusion. We found that TRAIL blockade inhibited tubular apoptosis and reduced the accumulation of neutrophils and macrophages. Furthermore, TRAIL blockade attenuated renal fibrosis and atrophy after IRI. In conclusion, our study suggests that TRAIL is a critical pathogenic factor in renal IRI, and that TRAIL could be a new therapeutic target for the prevention of renal IRI.

CD27+ B cells from a subgroup of common variable immunodeficiency patients are less sensitive to apoptosis rescue regardless of interleukin-21 signalling

Common variable immunodeficiency (CVID) is a primary immunodeficiency characterized by hypogammaglobulinaemia and recurrent infections. Although the underlying cause is unknown, B cells from most CVID patients fail to differentiate to memory or plasma cells. We investigated if increased apoptosis could influence the fate of B cells. For this purpose we activated purified B lymphocytes of CVID patients with a surrogate T-dependent (anti-CD40) or T-independent [cytosine-phosphate-guanosine oligodeoxynucleotides (CpG-ODN) or anti-immunoglobulin (Ig)M)] stimulus with or without interleukin (IL)-21. We found that CD27(+) B cells were more sensitive than CD27(-) B cells to spontaneous apoptosis and less sensitive to rescue from apoptosis. The addition of IL-21 down-modulated the protective effect of all the stimuli on CD27(-) B cells and the protective effect of CpG-ODN and anti-IgM on CD27(+) B cells. In contrast, IL-21 rescued unstimulated CD27(-) B cells and improved the rescue of anti-CD40-stimulated CD27(+) B cells. When we compared patients and controls, mainly CD27(+) B cells from MB0 patients were less sensitive to rescue from apoptosis than those from MB1 patients and controls after activation, irrespective of the IL-21 effect. Increased apoptosis during an immune response could result in lower levels of immunoglobulin production in these patients.

Human TNF-related apoptosis-inducing ligand-expressing dendritic cells from transgenic pigs attenuate human xenogeneic T cell responses

BACKGROUND

Efficient and precise techniques for the genetic modification of pigs facilitate the generation of tailored donor animals for xenotransplantation. Numerous transgenic pig lines exist with the focus on inhibition of the complement system and of humoral immune responses. In addition, immune cell-based responses need to be controlled to prevent pig-to-primate xenograft rejection. Expression of human (hu) TNF-related apoptosis-inducing ligand (TRAIL) on porcine cells has the potential to ameliorate human T cell responses.

METHODS

We generated transgenic pigs expressing human tumor necrosis factor (TNF)-related apoptosis-inducing ligand (huTRAIL) under the control of either the mouse H2K(b) promoter or a CMV enhancer/chicken β-actin (CAG) promoter, the latter one (CAG-huTRAIL) on a GGTA1 knockout/huCD46 transgenic background. The biological activity of huTRAIL was demonstrated by its apoptosis-inducing effect on Jurkat lymphoma cells. To clarify whether huTRAIL affects also primary immune cells and whether its effects depend on the presence of co-stimulatory molecules, we exposed human peripheral blood mononuclear cells (PBMC) or isolated T cells to huTRAIL-expressing porcine fibroblasts or dendritic cells in vitro.

RESULTS

H2Kb-huTRAIL transgenic pigs express huTRAIL mainly in the spleen and secondary lymphoid tissues. The CAG-huTRAIL construct facilitated huTRAIL expression in multiple organs, the level being at least one order of magnitude higher than in H2Kb-huTRAIL transgenic pigs. Incubation with huTRAIL-expressing H2Kb-huTRAIL transgenic porcine dendritic cells decreased human T cell proliferation significantly without any signs of apoptosis. In spite of the high transgene expression level, CAG-huTRAIL transgenic fibroblasts did not affect proliferation of human PBMC, independent of their activation state.

CONCLUSIONS

These results suggest huTRAIL expression on porcine dendritic cells as a possible strategy to attenuate T cell responses against pig-to-primate xenografts.

Ultrastructural study of Rift Valley fever virus in the mouse model

Detailed ultrastructural studies of Rift Valley fever virus (RVFV) in the mouse model are needed to develop and characterize a small animal model of RVF for the evaluation of potential vaccines and therapeutics. In this study, the ultrastructural features of RVFV infection in the mouse model were analyzed. The main changes in the liver included the presence of viral particles in hepatocytes and hepatic stem cells accompanied by hepatocyte apoptosis. However, viral particles were observed rarely in the liver; in contrast, particles were extremely abundant in the CNS. Despite extensive lymphocytolysis, direct evidence of viral replication was not observed in the lymphoid tissue. These results correlate with the acute-onset hepatitis and delayed-onset encephalitis that are dominant features of severe human RVF, but suggest that host immune-mediated mechanisms contribute significantly to pathology. The results of this study expand our knowledge of RVFV-host interactions and further characterize the mouse model of RVF.

B lymphocytes are resistant to death receptor 5-induced apoptosis

Death Receptor 5 (DR5) induces apoptosis in various types of cells and is a potential therapeutic target. We have investigated whether targeting DR5 could be used to eliminate pathogenic B lymphocytes from systemic lupus erythematosus (SLE) patients. We examined DR5 expression and function on B lymphocytes from healthy controls subjects, SLE patients, and human tonsil. DR5 was expressed similarly on all B cell subpopulations, including resting and activated B cells. Expression of DR5 was equivalent on B cells from SLE patients and healthy subjects. Additionally, DR5 expression was unchanged after B lymphocyte stimulation. However, B cells were resistant to DR5-induced apoptosis, including after in vitro activation. No changes in subsets of B cells were observed in subjects of a trial of CS-1008, an agonist anti-DR5. While DR5 shows promise as a way to selectively eliminate tumor cells and activated synoviocytes, these data suggest DR5 alone cannot be used as a target to remove pathogenic SLE B cells.

A critical role of TRAIL expressed on cotransplanted hepatic stellate cells in prevention of islet allograft rejection

Hepatic stellate cells (HSCs) have demonstrated a strong T-cell inhibitory activity. In a mouse islet transplantation model, cotransplanted HSCs can protect islet allografts from rejection. The involved mechanism is not fully understood. We showed in this study that expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), an important apoptosis-inducing ligand, on HSCs was crucial in protection of islet allografts, since HSCs derived from TRAIL knockout mice demonstrated less inhibitory activity towards T-cell proliferative responses, and substantially lost their capacity in protecting cotransplanted islet allografts from rejection, suggesting that TRAIL-mediated T cell apoptotic death is important in HSC-delivered immune regulation activity.

B cell receptor triggering sensitizes human B cells to TRAIL-induced apoptosis

TRAIL is known to cause death in tumor cells, but physiological regulation of its activity remains poorly characterized. We demonstrate that BCR triggering sensitizes transformed centroblast-like BL cells and peripheral blood memory B cells to TRAIL-mediated apoptosis. The sensitization correlated with surface down-regulation and intracellular retention of TRAIL-R4, along with changes in the expression of several Bcl-2 protein family members. Although enhancing FAS-mediated cell death, CD40 activation protected B cells from TRAIL-induced apoptosis. Combination of Ig cross-linking with CD40 ligation did not prevent TRAIL-R4 down-regulation but induced changes in the mitochondria-regulated pathway of apoptosis that are known to be associated with resistance to TRAIL. Human CD5(+) B cells, presumably stimulated by reactivity to self without immunological help, exhibited very high ex vivo sensitivity to TRAIL. Our results define the first B-lymphocyte-specific physiological signal that increases cellular sensitivity to TRAIL. This may be important for our understanding of TRAIL involvement in the control of B cell responses and aid in designing TRAIL-based therapies for B cell lymphomas.

Human monomeric antibody fragments to TRAIL-R1 and TRAIL-R2 that display potent in vitro agonism

Apoptosis through the TRAIL receptor pathway can be induced via agonistic IgG to either TRAIL-R1 or TRAIL-R2. Here we describe the use of phage display to isolate a substantive panel of fully human anti-TRAIL receptor single chain Fv fragments (scFvs); 234 and 269 different scFvs specific for TRAIL-R1 and TRAIL-R2 respectively. In addition, 134 different scFvs that were cross-reactive for both receptors were isolated. To facilitate screening of all 637 scFvs for potential agonistic activity in vitro, a novel high-throughput surrogate apoptosis assay was developed. Ten TRAIL-R1 specific scFv and 6 TRAIL-R2 specific scFv were shown to inhibit growth of tumor cells in vitro in the absence of any cross-linking agents. These scFv were all highly specific for either TRAIL-R1 or TRAIL-R2, potently inhibited tumor cell proliferation, and were antagonists of TRAIL binding. Moreover, further characterization of TRAIL-R1 agonistic scFv demonstrated significant anti-tumor activity when expressed and purified as a monomeric Fab fragment. Thus, scFv and Fab fragments, in addition to whole IgG, can be agonistic and induce tumor cell death through specific binding to either TRAIL-R1 or TRAIL-R2. These potent agonistic scFv were all isolated directly from the starting phage antibody library and demonstrated significant tumor cell killing properties without any requirement for affinity maturation. Some of these selected scFv have been converted to IgG format and are being studied extensively in clinical trials to investigate their potential utility as human monoclonal antibody therapeutics for the treatment of human cancer.

TRAIL, DR4 and DR5 are upregulated in kidneys from patients with lupus nephritis and exert proliferative and proinflammatory effects

We have previously reported that TRAIL is upregulated on T cells from patients with lupus and that T cell associated TRAIL enhances autoimmune parameters in a murine model of lupus. Whether TRAIL/TRAIL-R interaction plays a role in organ involvement such as lupus nephritis has not yet been assessed. We demonstrate here that TRAIL, DR4 and DR5 are upregulated in proximal and distal tubules of patients with proliferative lupus nephritis. In vitro, expression of TRAIL, DR4 and DR5 on primary proximal tubular epithelial cells (PTEC) was induced by TNFalpha and IFNgamma. Functionally, TRAIL did not induce apoptosis but rather enhanced the proliferation of PTEC through activation of PI3 kinase/AKT and ERK1/2, increased IL-8 production and upregulated ICAM-1 expression. These data demonstrate that cytokine induced upregulation of TRAIL, DR4 and DR5 in tubules from patients with proliferative lupus nephritis may play a protective role by enhancing PTEC survival while also exerting a proinflammatory effect that may contribute to local inflammation and injury.

Deregulation of c-Myc Confers distinct survival requirements for memory B cells, plasma cells, and their progenitors

Deregulation of the c-Myc oncogene is tightly associated with human and murine plasma cell (PC) neoplasms. Through the analysis of Ag-specific B cell responses in mice where Myc is targeted to the Igh Calpha locus, we show here that c-Myc dramatically impairs the primary and secondary Ab response. This impairment is differentiation stage specific, since germinal center B cell formation, affinity maturation, and class switch recombination were intact. Examination of PC viability revealed that c-Myc triggered apoptosis only upon final maturation when Ab is secreted and is resistant to the survival factor BAFF (B cell-activating factor belonging to the TNF family). In contrast, PC precursors (PC(pre)) that ultimately give rise to mature PCs survived normally and vigorously expanded with BAFF signaling. We further show that c-Myc also facilitates the apoptosis of memory B cells. Thus, Calpha-Myc controls both cellular arms of long-lived B cell immunity than previously anticipated. Only when deregulation of c-Myc was combined with enforced Bcl-x(L) expression were mature PCs able to survive in response to BAFF. These data indicate that the survival requirements for tumor-susceptible PC(pre) and PCs are distinct and that tumor progression likely develops as PC(pre) transition to functional PCs when apoptotic pathways such as members of the Bcl-2 family are disabled.

Catalytically active Yersinia outer protein P induces cleavage of RIP and caspase-8 at the level of the DISC independently of death receptors in dendritic cells

Yersinia outer protein P (YopP) is injected by Y. enterocolitica into host cells thereby inducing apoptotic and necrosis-like cell death in dendritic cells (DC). Here we show the pathways involved in DC death caused by the catalytic activity of YopP. Infection with Yersinia enterocolitica, translocating catalytically active YopP into DC, triggered procaspase-8 cleavage and c-FLIPL degradation. YopP-dependent caspase-8 activation was, however, not mediated by tumor necrosis factor (TNF) receptor family members since the expression of both CD95/Fas/APO-1 and TRAIL-R2 on DC was low, and DC were resistant to apoptosis induced by agonistic anti-CD95 antibodies or TNF-related apoptosis-inducing ligand (TRAIL). Moreover, DC from TNF-Rp55-/- mice were not protected against YopP-induced cell death demonstrating that TNF-R1 is also not involved in this process. Activation of caspase-8 was further investigated by coimmunoprecitation of FADD from Yersinia-infected DC. We found that both cleaved caspase-8 and receptor interacting protein 1 (RIP1) were associated with the Fas-associated death domain (FADD) indicating the formation of an atypical death-inducing signaling complex (DISC). Furthermore, degradation of RIP mediated by the Hsp90 inhibitor geldanamycin significantly impaired YopP-induced cell death. Altogether our findings indicate that Yersinia-induced DC death is independent of death domain containing receptors, but mediated by RIP and caspase-8 at the level of DISC.

Normal human primary CD4+ T lymphocytes synthesize and release functional osteoprotegerin in vitro

Osteoprotegerin (OPG) acts as a decoy receptor for receptor activator of nuclear factor-kappaB ligand (RANKL) and TNF-related apoptosis-inducing ligand (TRAIL). OPG regulates bone remodeling and the immune response. The primary objective was to decipher, among human peripheral blood mononuclear leukocytes (PBML) that produce OPG, the subset(s) responsible for this synthesis and its regulation. To this end, normal human PBML and CD4-, 8-, 19-, 14-enriched subpopulations were studied in vitro for OPG synthesis. PBML were subjected to adherence and immunomagnetic separation, and OPG expression was analyzed by PCR, northern and western blotting, and ELISA. The antiapoptotic effects of OPG were studied on TRAIL-stimulated RPMI 8226 myeloma cells. OPG was time-dependently produced by primary CD4+ T lymphocytes exclusively. OPG secretion was upregulated by anti-CD3 antibody stimulation or incubation with interleukin (IL)-4, IL-1beta, TNF-alpha, GM-CSF, and vitamin D(3). In contrast, IL-10 inhibited the basal and IL-4-induced production of OPG by T cells. Conditioned media from activated T lymphocytes decreased TRAIL-induced apoptosis of RPMI 8226 cells. This effect was reversed by addition of RANKL to the T-cell conditioned media. As human immunodeficiency virus-1 (HIV-1) targets CD4+ T cells, we evaluated the effects of recombinant HIV-1 gp120 proteins on OPG synthesis. The gp120 from three different HIV-1 strains significantly reduced the basal output of OPG from T cells. Furthermore, all four protease inhibitors (PIs) used in highly active antiretroviral therapy decreased OPG synthesis by human blood T cells, nelfinavir being the most efficient PI. The simultaneous presence of an HIV-1 gp120 and a PI abrogated the basal output of OPG. In conclusion, these results highlight a new role for T lymphocytes involved in pathologies. Activated CD4+ T cells could, through OPG release, have a paracrine effect on adjacent cells and contribute to reduce the local process of bone remodeling and cellular apoptosis.

Building and operating an antibody factory: redox control during B to plasma cell terminal differentiation

When small B lymphocytes bind their cognate antigens in the context of suitable signals, a dramatic differentiation program is activated that leads to the formation of plasma cells. These are short-lived specialized elements, each capable of secreting several thousands antibodies per second. The massive increase in Ig synthesis and transport entails a dramatic architectural and functional metamorphosis that involves the development of the endoplasmic reticulum (ER) and secretory organelles. Massive Ig secretion poses novel metabolic requirements, particularly for what concerns aminoacid import, ATP synthesis and redox homeostasis. Ig H and L chains enter the ER in the reduced state, to be rapidly oxidised mainly via protein driven relays based on the resident enzymes PDI and Ero1. How do plasma cells cope with the ensuing metabolic and redox stresses? In this essay, we discuss the physiological implications that increased Ig production could have in the control of plasma cell generation, function and lifespan, with emphasis on the potential role of ROS generation in mitochondria and ER.

Definition of germinal-center B cell migration in vivo reveals predominant intrazonal circulation patterns

Proliferation, mutation, and selection in the germinal center (GC) are thought to occur in distinct microanatomical compartments-the dark zone (DZ) and the light zone (LZ). Thus, affinity maturation has been posited to require frequent trafficking between zones. Here we report the use of multiphoton in vivo microscopy to determine migration patterns of GC B cells. Analysis of time-resolved images revealed unexpected patterns of movement as well as GC B cell morphology. Though frequent movement between the DZ and LZ was anticipated, few cells were observed to cross the interface between the two compartments. Moreover, cell-track trajectories indicated that cell movement in this region is predominantly parallel to the interface, suggesting that B cells circulate within individual LZ and DZ compartments. The results suggest a revision to our views of B cell circulation within GCs and the functional relationship of its two major compartments.

Doxorubicin enhances TRAIL-induced cell death via ceramide-enriched membrane platforms

Previous studies indicated that signalling via CD95 and DR5 is greatly enhanced by the formation of ceramide-enriched membrane platforms. Here, we employed this concept to convert doses of subtherapeutic TRAIL that were unable to release ceramide and kill leukemic B-cells or ex vivo T lymphocytes, into a very effective apoptotic stimulus. Ceramide production was induced by application of sub-toxic doses of doxorubicin that resulted in an activation of the acid sphingomyelinase (ASM), release of ceramide and formation of ceramide-enriched membrane platforms. The latter served DR5 to cluster after application of very low doses of TRAIL in combination with doxorubicin. Genetic deficiency of the ASM abrogated doxorubicin-induced ceramide release, as well as clustering of DR5 and apoptosis induced by the combined treatment of doxorubicin and TRAIL. These data show that local release of ceramide potentiates very low, otherwise inactive doses of TRAIL that may represent a novel therapeutic concept to treat tumors.

T Cell TRAIL Promotes Murine Lupus by Sustaining Effector CD4 Th Cell Numbers and by Inhibiting CD8 CTL Activity

T cells play an essential role in driving humoral autoimmunity in lupus. Molecules such as TRAIL exhibit strong T cell modulatory effects and are up-regulated in lupus, raising the possibility that they may influence disease severity. To address this possibility, we examined the role of TRAIL expression on pathogenic T cells in an induced model of murine lupus, the parent-into-F(1) (P-->F(1)) model of chronic graft-vs-host disease (GVHD), using wild-type or TRAIL-deficient donor T cells. Results were compared with mice undergoing suppressive acute GVHD. Although chronic GVHD mice exhibited less donor T cell TRAIL up-regulation and IFN-alpha-inducible gene expression than acute GVHD mice, donor CD4(+) T cell TRAIL expression in chronic GVHD was essential for sustaining effector CD4(+) Th cell numbers, for sustaining help to B cells, and for more severe lupus-like renal disease development. Conversely, TRAIL expression on donor CD8(+) T cells had a milder, but significant down-regulatory effect on CTL effector function, affecting the perforin/granzyme pathway and not the Fas ligand pathway. These results indicate that, in this model, T cell-expressed TRAIL exacerbates lupus by the following: 1) positively regulating CD4(+) Th cell numbers, thereby sustaining T cell help for B cells, and 2) to a lesser degree by negatively regulating perforin-mediated CD8(+) CTL killing that could potentially eliminate activated autoreactive B cells.

Apoptotic Cells Induce Tolerance by Generating Helpless CD8+ T Cells That Produce TRAIL

The decision to generate a productive immune response or immune tolerance following pathogenic insult often depends on the context in which T cells first encounter Ag. The presence of apoptotic cells favors the induction of tolerance, whereas immune responses generated with necrotic cells promote immunity. We have examined the tolerance induced by injection of apoptotic cells, a system in which cross-presentation of Ag associated with the dead cells induces CD8+ regulatory (or suppressor) T cells. We observed that haptenated apoptotic cells induced CD8+ suppressor T cells without priming CD4+ T cells for immunity. These CD8+ T cells transferred unresponsiveness to naive recipients. In contrast, haptenated necrotic cells stimulated immunity, but induced CD8+ suppressor T cells when CD4+ T cells were absent. We further found that CD8+ T cells induced by these treatments displayed a "helpless CTL" phenotype and suppress the immune response by producing TRAIL. Animals deficient in TRAIL were resistant to tolerance induction by apoptotic cells. Thus, the outcome of an immune response taking place in the presence of cell death can be determined by the presence of CD4+-mediated Th cell function.

Mcl-1L cleavage is involved in TRAIL-R1– and TRAIL-R2–mediated apoptosis induced by HGS-ETR1 and HGS-ETR2 human mAbs in myeloma cells

We evaluated the ability of 2 human mAbs directed against TRAILR1 (HGS-ETR1) and TRAILR2 (HGS-ETR2) to kill human myeloma cells. HGS-ETR1 and HGS-ETR2 mAbs killed 15 and 9 human myeloma cell lines (HMCLs; n = 22), respectively. IL-6, the major survival and growth factor for these HMCLs, did not prevent their killing. Killing induced by either HGS-ETR1 or HGS-ETR2 was correlated with the cleavage of Mcl-1L, a major molecule for myeloma survival. Mcl-1L cleavage and anti-TRAILR HMCL killing were dependent on caspase activation. Kinetic studies showed that Mcl-1L cleavage occurred very early (less than 1 hour) and became drastic once caspase 3 was activated. Our data showed that both the extrinsic (caspase 8, Bid) and the intrinsic (caspase 9) pathways are activated by anti–TRAIL mAb. Finally, we showed that the HGS-ETR1 and, to a lesser extent, the HGS-ETR2 mAbs were able to induce the killing of primary myeloma cells. Of note, HGS-ETR1 mAb was able to induce the death of medullary and extramedullary myeloma cells collected from patients at relapse. Taken together, our data clearly encourage clinical trials of anti–TRAILR1 mAb in multiple myeloma, especially for patients whose disease is in relapse, at the time of drug resistance.

TRAIL activates acid sphingomyelinase via a redox mechanism and releases ceramide to trigger apoptosis

We have previously shown that activation of the acid sphingomyelinase (ASM), the release of ceramide and the formation of ceramide-enriched membrane domains are central for the induction of apoptosis by CD95. Here, we demonstrate that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and CD95 activate the ASM via a redox mechanism resulting in release of ceramide and formation of ceramide-enriched membrane platforms. Ceramide-enriched membrane platforms serve to cluster DR5 upon stimulation. Antioxidants prevent TRAIL-mediated stimulation of ASM, the release of ceramide, the formation of ceramide-enriched membrane platforms and the induction of apoptosis by TRAIL. Further, ASM-deficient splenocytes fail to cluster DR5 in ceramide-enriched membrane domains upon TRAIL stimulation and resist TRAIL-induced apoptosis, events that were restored by addition of natural C(16)-ceramide. A dose-response analysis indicates that ceramide-enriched membrane platforms greatly sensitized tumor cells to TRAIL-induced apoptosis. Our data indicate that ceramide-enriched membrane platforms are required for the signaling of TRAIL-DR5 complexes under physiological conditions.

The endoplasmic reticulum is a key component of the plasma cell death pathway

Plasma cells (PC) are the effector cells of the humoral Ab response. Unlike other dedicated secretory cells, they exist as two populations with opposite cell fates: short-lived and long-lived PC. Upon transformation they lead to an incurable neoplasia called multiple myeloma. In this study we have explored the molecular mechanism of PC death. Our data show that their apoptotic pathway is unique among other hemopoietic cells inasmuch as neither the death receptors nor the mitochondria play the central role. PC apoptosis is initiated by activation of Bax at the endoplasmic reticulum membrane and subsequent activation of the endoplasmic reticulum-associated caspase-4 before the release of mitochondrial apoptogenic factors. Together, our observations indicate that the cardinal function of PC (i.e., Ig secretion) is also the cause of their death.

A role of TRAIL in killing osteoblasts by myeloma cells

In multiple myeloma (MM), neoplastic plasma cells accumulate in the bone marrow where their survival, proliferation, and apoptosis are controlled at multiple levels by interaction with the bone marrow microenvironment. Myeloma cells actively control these interactions by activating stromal and endothelial cells for production of survival factors, such as interleukin-6, and suppressing other cell types such as erythroblasts, normal B cell progenitors, and T-cells. In the present study, we identified primary osteoblasts as additional potential targets for myeloma cell-mediated suppression which was partly dependent on the death receptor ligand TRAIL. Besides killing of osteoblasts, myeloma cell lines sensitized osteoblasts to cell death mediated by recombinant TRAIL, whereas primary osteoblasts protected myeloma cells from TRAIL-mediated apoptosis that was mediated by osteoprotegerin (OPG). Besides increase of osteoclastogenesis and osteoclast activity, suppression of bone-forming cells by myeloma cells might contribute to bone loss in MM patients. In addition, clinical development of recombinant TRAIL as anti-myeloma therapy should include evaluation of potential side effects on viability of normal bone cells.

Biology of plasma cells

Multiple myeloma, the second most common haematopoietic cancer, represents a collection of plasma-cell neoplasms that invariably become fatal when self-renewing myeloma cells begin unrestrained proliferation. Myeloma cells are arrested as intermediates in plasma-cell differentiation as a consequence of transformation. Unlike normal plasma cells, myeloma cells retain the self-renewing potential. Although impaired apoptosis accounts for the accumulation of myeloma cells in the bone marrow during the plateau phase of the disease, cell-cycle deregulation underlies unrestrained proliferation of self-renewing myeloma cells in aggressive myelomas and during relapse. The mechanism that governs deregulated cell-cycle re-entry and progression in multiple myeloma is unknown, and the relationship between myeloma cells and their normal counterparts is undefined. Plasma-cell differentiation is a complex multi-step process. This chapter will address recent advances in the mechanism of normal plasma-cell differentiation and our current understanding of the relationship between plasma-cell differentiation and myeloma pathogenesis.

Molecular cloning, expression analysis and assignment of the porcine tumor necrosis factor superfamily member 10 gene (TNFSF10) to SSC13q34-->q36 by fluorescence in situ hybridization and radiation hybrid mapping

We have cloned the complete coding region of the porcine TNFSF10 gene. The porcine TNFSF10 cDNA has an ORF of 870 nucleotides and shares 85% identity with human TNFSF10, and 75% and 72% identity with rat and mouse Tnfsf10 coding sequences, respectively. The deduced porcine TNFSF10 protein consists of 289 amino acids with the calculated molecular mass of 33.5 kDa and a predicted pI of 8.15. The amino acid sequence similarities correspond to 86, 72 and 70% when compared with human, rat and mouse sequences, respectively. Northern blot analysis detected TNFSF10-specific transcripts (approximately 1.7 kb) in various organs of a 10-week-old pig, suggesting ubiquitous expression. Real-time RT-PCR studies of various organs from fetal (days 73 and 98) and postnatal stages (two weeks, eight months) demonstrated developmental and tissue-specific regulation of TNFSF10 mRNA abundance. The chromosomal location of the porcine TNFSF10 gene was determined by FISH of a specific BAC clone to metaphase chromosomes. This TNFSF10 BAC clone has been assigned to SSC13q34-->q36. Additionally, the localization of the TNFSF10 gene was verified by RH mapping on the porcine IMpRH panel.

Increased Expression and a Potential Anti-Inflammatory Role of TRAIL in Atopic Dermatitis

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis of many transformed but also of non-transformed cells. In addition, TRAIL receptor activation has been reported to activate non-apoptotic signaling pathways. Here, we report an increased expression of TRAIL in peripheral blood T cells and monocytes from patients with atopic dermatitis (AD) compared with control individuals. High TRAIL expression was also observed in skin-infiltrating T cells of AD patients. Topical tacrolimus treatment reduced the total number of T cells in the skin, but the relative proportion of TRAIL-positive cells within both CD4+ and CD8+ cell populations did not change. TRAIL was demonstrated to induce the expression of interleukin-1 receptor antagonist (IL-1Ra) in keratinocytes in a caspase-independent manner in vitro. Moreover, increased expression of IL-1Ra was observed in keratinocytes of AD lesional skin. These data suggest that TRAIL-expressing inflammatory skin cells may contribute to the epidermal activation of the IL-1Ra gene in AD.

Expression of Biologically Active Human TRAIL in Transgenic Pigs

BACKGROUND

Xenotransplantation of porcine organs into human recipients is a potential option for overcoming the dramatic shortage of suitable donor organs. To date, transgenic modification of pig organs has achieved partial or temporal reduction of xenograft rejection by inhibition of hyperacute rejection. Expression of human tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) in transgenic pigs might be a strategy for controlling posthyperacute rejection mechanisms mediated by cellular components of the immune system. The objective of this study was generation of a transgenic pig model to evaluate the potential of this strategy for xenotransplantation.

METHODS

Transgenic pigs were generated by microinjection of an expression vector for human TRAIL under control of the murine H-2K promoter. Expression of the transgene was analyzed by Western blot and immunohistochemistry. Biologic activity of TRAIL on transgenic porcine lymphocytes was evaluated in co-culture experiments using Jurkat and Hut 78.2 cells as targets.

RESULTS

In three lines of transgenic pigs, human TRAIL protein was detected in the membrane fractions of various tissues. Highest expression levels were observed in spleen and lung. Human TRAIL expression on porcine lymphocytes was augmented on activation of cells. Transgenic pig lymphoblasts induced apoptosis in Jurkat and Hut 78.2 cells, which was inhibited by neutralizing anti-TRAIL antibodies, demonstrating a TRAIL-specific effect.

CONCLUSIONS

Ubiquitous expression of human TRAIL was achieved in transgenic pigs without detrimental side effects. Pigs expressing biologically active human TRAIL will be used for future xenotransplantation experiments to modulate primate anti-pig cellular immune responses.

Depsipeptide (FR901228) Enhances the Cytotoxic Activity of TRAIL by Redistributing TRAIL Receptor to Membrane Lipid Rafts

TRAIL (TNF-related apoptosis-inducing ligand) induces apoptosis in various tumor cell types and is under investigation as a cancer therapeutic. The development of a recombinant adenovirus encoding the full-length human TRAIL gene (Ad5-TRAIL) replaces the need for large quantities of soluble TRAIL protein in tumor suppressive therapies. However, the full potential of Ad5-TRAIL has not yet been maximized. Recent investigation of a histone deacetylase inhibitor, depsipeptide (FR901228), has demonstrated that it increases cellular susceptibility to adenovirus infection and augments adenoviral transgene expression. Thus, studies were initiated to evaluate the ability of depsipeptide to enhance the cytotoxic activity of Ad5-TRAIL against human prostate tumor cells. In vitro, depsipeptide increased expression of coxsackie-adenovirus receptor, leading to increased adenoviral infection and transgene expression. Additionally, tumor cell killing by Ad5-TRAIL was higher following depsipeptide pretreatment. More surprisingly, depsipeptide also increased prostate tumor cell sensitivity to TRAIL-induced apoptosis. Investigation into the mechanism responsible for increased TRAIL responsiveness revealed increased levels of TRAIL-R1 and -R2 in membrane lipid rafts following depsipeptide treatment. These results indicate that depsipeptide is a potent agent for enhancing the activity of Ad5-TRAIL by multiple mechanisms, allowing for a more efficient use of Ad5-TRAIL as an antitumor therapy.

Following a TRAIL: update on a ligand and its five receptors

Identification of tumour necrosis factor apoptosis inducing ligand (TRAIL), a TNF family ligand, sparked a torrent of research, following an initial observation that it could kill tumour cells, but spare normal cells. Almost a decade after its discovery, and with five known receptors, the true physiological role of TRAIL is still debated and its anti-tumorigenic properties limited by potential toxicity. This review takes a comprehensive look at the story of this enigmatic ligand, addressing its remaining potential as a therapeutic and providing an overview of the TRAIL receptors themselves.

Apoptosis of multiple myeloma

Multiple myeloma (MM) is a malignancy of terminally differentiated plasma cells. MM cells localize to the bone marrow, where cell adhesion-mediated autocrine or paracrine activation of various cytokines, such as interleukin 6, insulin-like growth factor 1, and interferon alpha, results in their accumulation mainly because of loss of critical apoptotic controls. Resistance to apoptosis, a genetically regulated cell death process, may play a critical role in both pathogenesis and resistance to treatment of MM. Abnormalities in regulation and execution of apoptosis can contribute to tumor initiation, progression, as well as to tumor resistance to various therapeutic agents. Apoptosis is executed via 2 main pathways that lead to activation of caspases: the death receptor (extrinsic) pathway and the mitochondrial (intrinsic) pathway. Ionizing radiation and chemotherapeutic agents act primarily through the intrinsic pathway, in which mitochondria play the central role. Various therapeutic modalities that are effective in MM modulate levels of the proapoptotic and antiapoptotic Bcl-2 family of proteins and of inhibitors of apoptosis, expression of which is primarily regulated by p53, nuclear factor KB, and STAT (signal transducers and activators of transcription) factors. This review focuses on the key concepts and some of the most recent studies of signaling pathways regulated in MM and summarizes what is known about the clinical role of these pathways.

TRAIL and its receptors as targets for cancer therapy

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family of cytokines, which can induce apoptotic cell death in a variety of tumor cells by engaging the death receptors DR4 and DR5, while sparing most normal cells. Preclinical studies in mice and non-human primates have shown the potential utility of recombinant soluble TRAIL and agonistic anti-DR5 or DR4 antibodies for cancer therapy. Moreover, we have recently revealed a vital role for endogenously expressed TRAIL in immunosurveillance of developing and metastatic tumors. In this review, we summarize recent knowledge about TRAIL and its receptors as promising targets for cancer therapy.

Novel targeted deregulation of c-Myc cooperates with Bcl-X(L) to cause plasma cell neoplasms in mice

Deregulated expression of both Myc and Bcl-X(L) are consistent features of human plasma cell neoplasms (PCNs). To investigate whether targeted expression of Myc and Bcl-X(L) in mouse plasma cells might lead to an improved model of human PCN, we generated Myc transgenics by inserting a single-copy histidine-tagged mouse Myc gene, Myc(His), into the mouse Ig heavy-chain Calpha locus. We also generated Bcl-X(L) transgenic mice that contain a multicopy Flag-tagged mouse Bcl-x(Flag) transgene driven by the mouse Ig kappa light-chain 3' enhancer. Single-transgenic Bcl-X(L) mice remained tumor free by 380 days of age, whereas single-transgenic Myc mice developed B cell tumors infrequently (4 of 43, 9.3%). In contrast, double-transgenic Myc/Bcl-X(L) mice developed plasma cell tumors with short onset (135 days on average) and full penetrance (100% tumor incidence). These tumors produced monoclonal Ig, infiltrated the bone marrow, and contained elevated amounts of Myc(His) and Bcl-X(L)(Flag) proteins compared with the plasma cells that accumulated in large numbers in young tumor-free Myc/Bcl-X(L) mice. Our findings demonstrate that the enforced expression of Myc and Bcl-X(L) by Ig enhancers with peak activity in plasma cells generates a mouse model of human PCN that recapitulates some features of human multiple myeloma.