T cells require TRAIL for optimal graft-versus-tumor activity

TNF-Related Apoptosis-Inducing Ligand: Non-Apoptotic Signalling

TNF-related apoptosis-inducing ligand (TRAIL or Apo2 or TNFSF10) belongs to the TNF superfamily. When bound to its agonistic receptors, TRAIL can induce apoptosis in tumour cells, while sparing healthy cells. Over the last three decades, this tumour selectivity has prompted many studies aiming at evaluating the anti-tumoral potential of TRAIL or its derivatives. Although most of these attempts have failed, so far, novel formulations are still being evaluated. However, emerging evidence indicates that TRAIL can also trigger a non-canonical signal transduction pathway that is likely to be detrimental for its use in oncology. Likewise, an increasing number of studies suggest that in some circumstances TRAIL can induce, via Death receptor 5 (DR5), tumour cell motility, potentially leading to and contributing to tumour metastasis. While the pro-apoptotic signal transduction machinery of TRAIL is well known from a mechanistic point of view, that of the non-canonical pathway is less understood. In this study, we the current state of knowledge of TRAIL non-canonical signalling.

Hepatitis B Virus (HBV) Upregulates TRAIL-R3 Expression in Hepatocytes Resulting in Escape From Both Cell Apoptosis and Suppression of HBV Replication by TRAIL

BACKGROUND

Hepatitis B virus (HBV) evades host immunity by regulating intracellular signals. To clarify this immune tolerance mechanism, we performed gene expression analysis using HBV-infected humanized mouse livers.

METHODS

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 3 (TRAIL-R3) was significantly upregulated in livers of HBV-infected human hepatocyte transplanted mice by cDNA microarray and next-generation sequencing. We analyzed the significance of TRAIL-R3 upregulation in HBV infection using human hepatocyte transplanted mice and HepG2 cell lines.

RESULTS

TRAIL-R3 induction by HBV infection was verified by in vitro and in vivo HBV replication models, and induction was inhibited by antiviral nucleot(s)ide analogue treatment. TRAIL-R3 transcription was regulated by the TRAIL-R3 promoter at -969 to -479 nucleotides upstream from the transcription start site, and by hepatitis B x (HBx) via activation of nuclear factor-κB (NF-κB) signal. TRAIL not only induced cell apoptosis but also inhibited HBV replication. TRAIL-R3 upregulation could inhibit both TRAIL-dependent apoptosis in HBV-infected hepatocytes and TRAIL-mediated suppression of HBV replication.

CONCLUSIONS

These results suggest a mechanism by which HBV persists by escaping host immunity through upregulation of TRAIL-R3. Development of novel drugs to inhibit this escape system might lead to complete HBV elimination from human hepatocytes.

Immunology of Canine Melanoma

Malignant melanoma is one of the most important tumors in dogs and is highly metastatic and aggressive disease. In recent years, molecular knowledge regarding canine melanoma has increased, and some chromosomal imbalances and tyrosine kinase pathways have been identified to be dysregulated. Mxoreover, canine melanoma is an immunogenic tumor that provides opportunities to administer immunotherapy to the patient. Podoplanin and chondroitin sulfate proteoglycan-4 (CSPG4) are markers against which monoclonal antibodies have been developed and tested in dogs in vivo with promising results. Owing to the importance of canine melanoma in the veterinary oncology field, this chapter reviews the most important aspects related to immunological involvement in the prognosis and treatment of canine melanoma.

Impact of KIR-ligand mismatch on pediatric T-cell acute lymphoblastic leukemia in unrelated cord blood transplantation

BACKGROUND

Currently, allogeneic hematopoietic stem cell transplantation (allo-HSCT) is considered to be indicated for children and adolescents with high-risk or relapsed T-cell acute lymphoblastic leukemia (T-ALL); however, the outcomes are unsatisfactory. Killer cell immunoglobulin-like receptors (KIRs) are the main receptors on natural killer (NK) cells that play an important role in the graft-versus-leukemia effect after allo-HSCT. In allo-HSCT, when the recipient lacks a donor KIR-ligand (KIR-ligand mismatch in the graft-versus-host [GVH] direction), donor NK cells will be activated against recipient cells. KIR-ligand mismatch in the GVH direction improves outcomes after unrelated cord blood transplantation (UCBT) with acute myeloid leukemia, but the effect in T-ALL is unclear.

OBJECTIVE

We evaluated the impact of KIR-ligand mismatch in the GVH direction on the transplant outcomes of children and adolescents with T-ALL who received UCBT.

STUDY DESIGN

We conducted a retrospective study using a nationwide registry of the Japanese Society for Transplantation and Cellular Therapy. Patients diagnosed with T-ALL, aged 0-19 years, and underwent first UCBT between 1999 and 2017 were included.

RESULTS

A total of 91 patients were included in this study. In all, 23 (25.3%) percent of patients had KIR-ligand mismatch in the GVH direction. The 5-year leukemia-free survival (LFS) and overall survival (OS) rates after UCBT were 65.8% and 69.6%, respectively. In a multivariate analysis, KIR-ligand mismatch in the GVH direction was associated with a significant reduction in the relapse rate (hazard ratio [HR], 0.19; P = 0.002), resulting in better LFS (HR, 0.18; P = 0.010) and OS (HR, 0.26; P = 0.048) without increasing non-relapse mortality (NRM; HR, 1.90; P = 0.264). The cumulative incidence of GVH disease (GVHD) did not differ between patients with and without KIR-ligand mismatch (grade II-IV acute GVHD, 39.1% versus 36.8%, P = 0.648, grade III-IV acute GVHD, 13.0% versus 11.8%, P = 0.857, and chronic GVHD, 26.1% versus 22.9%, P = 0.736, respectively). Furthermore, acute and chronic GVHD were not associated with good patient outcomes. Notably, no relapse was observed in patients who received KIR-ligand mismatched UCBT in complete remission.

CONCLUSION

KIR-ligand mismatch in the GVH direction improved LFS and decreased relapse rates without increasing NRM in children and adolescents with T-ALL who received UCBT, which was not mediated by GVHD.

Modeling acute graft-versus-host disease (aGVHD) in murine bone marrow transplantation (BMT) models with MHC disparity

For more than 50years, hematopoietic stem cell transplantation (HSCT) has been the major curative therapy for hematological malignancies and genetic disorders, but its success is limited by the development of graft-versus-host disease (GVHD). GVHD represents a post-transplantation disorder representing the immune-mediated attack of transplant-derived T cells against recipient tissue finally leading to increased morbidity and mortality of the recipient. GVHD develops if donor and recipient are disparate in major or minor histocompatibility antigens (MHC, miHA). Most of the initial knowledge about the biology of GVHD is derived from murine bone marrow transplantation (BMT) models. Of course, GVHD mouse models do not reflect one to one the human situation, but they contribute significantly to our understanding how conditioning and danger signals activate the immune system, enlighten the role of individual molecules, e.g., cytokines, chemokines, death-inducing ligands, define the function of lymphocytes subpopulations for GVHD development and have significant impact on establishing new treatment and prevention strategies used in clinical HSCT. This chapter describes in detail the procedure of allogeneic BMT and the development of GVHD in two commonly used allogeneic murine BMT models (B6→B6.bm1, B6→B6D2F1) with different MHC disparities, which can be used as a basis for advanced studies of GVHD pathology or the development of new treatment strategies.

Epigenetic Modification of Death Receptor Genes for TRAIL and TRAIL Resistance in Childhood B-Cell Precursor Acute Lymphoblastic Leukemia

Immunotherapies specific for B-cell precursor acute lymphoblastic leukemia (BCP-ALL), such as anti-CD19 chimeric antigen receptor (CAR) T-cells and blinatumomab, have dramatically improved the therapeutic outcome in refractory cases. In the anti-leukemic activity of those immunotherapies, TNF-related apoptosis-inducing ligand (TRAIL) on cytotoxic T-cells plays an essential role by inducing apoptosis of the target leukemia cells through its death receptors (DR4 and DR5). Since there are CpG islands in the promoter regions, hypermethylation of the DR4 and DR5 genes may be involved in resistance of leukemia cells to immunotherapies due to TRAIL-resistance. We analyzed the DR4 and DR5 methylation status in 32 BCP-ALL cell lines by sequencing their bisulfite PCR products with a next-generation sequencer. The DR4 and DR5 methylation status was significantly associated with the gene and cell-surface expression levels and the TRAIL-sensitivities. In the clinical samples at diagnosis (459 cases in the NOPHO study), both DR4 and DR5 genes were unmethylated in the majority of cases, whereas methylated in several cases with dic(9;20), MLL-rearrangement, and hypodiploidy, suggesting that evaluation of methylation status of the DR4 and DR5 genes might be clinically informative to predict efficacy of immunotherapy in certain cases with such unfavorable karyotypes. These observations provide an epigenetic rational for clinical efficacy of immunotherapy in the vast majority of BCP-ALL cases.

Immunological Mechanism and Clinical Application of PAMP Adjuvants

BACKGROUND

The host innate immune system can recognize Pathogen-Associated Molecular Patterns (PAMPs) through Pattern Recognition Receptors (PRRs), thereby initiating innate immune responses and subsequent adaptive immune responses. PAMPs can be developed as a vaccine adjuvant for modulating and optimizing antigen-specific immune responses, especially in combating viral infections and tumor therapy. Although several PAMP adjuvants have been successfully developed they are still lacking in general, and many of them are in the preclinical exploration stage.

OBJECTIVE

This review summarizes the research progress and development direction of PAMP adjuvants, focusing on their immune mechanisms and clinical applications.

METHODS

PubMed, Scopus, and Google Scholar were screened for this information. We highlight the immune mechanisms and clinical applications of PAMP adjuvants.

RESULTS

Because of the differences in receptor positions, specific immune cells targets, and signaling pathways, the detailed molecular mechanism and pharmacokinetic properties of one agonist cannot be fully generalized to another agonist, and each PAMP should be studied separately. In addition, combination therapy and effective integration of different adjuvants can increase the additional efficacy of innate and adaptive immune responses.

CONCLUSION

The mechanisms by which PAMPs exert adjuvant functions are diverse. With continuous discovery in the future, constant adjustments should be made to build new understandings. At present, the goal of therapeutic vaccination is to induce T cells that can specifically recognize and eliminate tumor cells and establish long-term immune memory. Following immune checkpoint modulation therapy, cancer treatment vaccines may be an option worthy of clinical testing.

Summary and comparison of the perforin in teleosts and mammals: A review

Perforin, a pore-forming glycoprotein, has been demonstrated to play key roles in clearing virus-infected cells and tumour cells due to its ability of forming 'pores' on the cell membranes. Additionally, perforin is also found to be associated with human diseases such as tumours, virus infections, immune rejection and some autoimmune diseases. Until now, plenty of perforin genes have been identified in vertebrates, especially the mammals and teleost fish. Conversely, vertebrate homologue of perforin gene was not identified in the invertebrates. Although recently there have been several reviews focusing on perforin and granzymes in mammals, no one highlighted the current advances of perforin in the other vertebrates. Here, in addition to mammalian perforin, the structure, evolution, tissue distribution and function of perforin in bony fish are summarized, respectively, which will allow us to gain more insights into the perforin in lower animals and the evolution of this important pore-forming protein across vertebrates.

T cell-derived interferon-γ programs stem cell death in immune-mediated intestinal damage

Despite the importance of intestinal stem cells (ISCs) for epithelial maintenance, there is limited understanding of how immune-mediated damage affects ISCs and their niche. We found that stem cell compartment injury is a shared feature of both alloreactive and autoreactive intestinal immunopathology, reducing ISCs and impairing their recovery in T cell-mediated injury models. Although imaging revealed few T cells near the stem cell compartment in healthy mice, donor T cells infiltrating the intestinal mucosa after allogeneic bone marrow transplantation (BMT) primarily localized to the crypt region lamina propria. Further modeling with ex vivo epithelial cultures indicated ISC depletion and impaired human as well as murine organoid survival upon coculture with activated T cells, and screening of effector pathways identified interferon-γ (IFNγ) as a principal mediator of ISC compartment damage. IFNγ induced JAK1- and STAT1-dependent toxicity, initiating a proapoptotic gene expression program and stem cell death. BMT with IFNγ-deficient donor T cells, with recipients lacking the IFNγ receptor (IFNγR) specifically in the intestinal epithelium, and with pharmacologic inhibition of JAK signaling all resulted in protection of the stem cell compartment. In addition, epithelial cultures with Paneth cell-deficient organoids, IFNγR-deficient Paneth cells, IFNγR-deficient ISCs, and purified stem cell colonies all indicated direct targeting of the ISCs that was not dependent on injury to the Paneth cell niche. Dysregulated T cell activation and IFNγ production are thus potent mediators of ISC injury, and blockade of JAK/STAT signaling within target tissue stem cells can prevent this T cell-mediated pathology.

Cell death in drug-induced liver injury

Drug-induced liver injury (DILI) is an important cause of liver toxicity which can have varying clinical presentations, the most severe of which being acute liver failure. Hepatocyte death as a cause of drug toxicity is a feature of DILI. There are multiple cell death subroutines; some, like apoptosis, necroptosis, autophagy, and necrosis have been extensively studied, while others such as pyroptosis and ferroptosis have been more recently described. The mode of cell death in DILI depends on the culprit drug, as it largely dictates the mechanism and extent of injury. The main cell death subroutines in DILI are apoptosis and necrosis, with mitochondrial involvement being pivotal for the execution of both. A few drugs such as acetaminophen (APAP) can cause direct, dose-dependent toxicity, while the majority of drugs cause idiosyncratic DILI (IDILI). IDILI is an unpredictable form of liver injury that is not dose dependent, occurs in individuals with a genetic predisposition, and presents with variable latency. APAP-induced programmed necrosis has been extensively studied. However, the mechanisms and pathogenesis of cell death from drugs causing IDILI are harder to elucidate due to the complex and multifactorial nature of the disease. Cell death in IDILI is likely death receptor-mediated apoptosis and the result of an activated innate and adaptive immune system, compounded by other host factors such as genetics, gender, age, and capacity for immune tolerance. This chapter will review the different modes of cell death, namely apoptosis, necrosis, necroptosis, autophagy, pyroptosis, and ferroptosis and their pertinence to DILI.

Cytotoxic Pathways in Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (allo-HCT) is a potentially curative treatment for hematologic malignancies, and other hematologic and immunologic diseases. Donor-derived immune cells identify and attack cancer cells in the patient producing a unique graft-vs.-tumor (GVT) effect. This beneficial response renders allo-HCT one of the most effective forms of tumor immunotherapy. However, alloreactive donor T cells can damage normal host cells thereby causing graft-vs.-host disease (GVHD), which results in substantial morbidity and mortality. To date, GVHD remains as the major obstacle for more successful application of allo-HCT. Of special significance in this context are a number of cytotoxic pathways that are involved in GVHD and GVT response as well as donor cell engraftment. In this review, we summarize progress in the investigation of these cytotoxic pathways, including Fas/Fas ligand (FasL), perforin/granzyme, and cytokine pathways. Many studies have delineated their distinct operating mechanisms and how they are involved in the complex cellular interactions amongst donor, host, tumor, and infectious pathogens. Driven by progressing elucidation of their contributions in immune reconstitution and regulation, various interventional strategies targeting these pathways have entered translational stages with aims to improve the effectiveness of allo-HCT.

Donor CD19 CAR T cells exert potent graft-versus-lymphoma activity with diminished graft-versus-host activity

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative therapy for hematological malignancies. However, graft-versus-host disease (GVHD) and relapse after allo-HSCT remain major impediments to the success of allo-HSCT. Chimeric antigen receptors (CARs) direct tumor cell recognition of adoptively transferred T cells. CD19 is an attractive CAR target, which is expressed in most B cell malignancies, as well as in healthy B cells. Clinical trials using autologous CD19-targeted T cells have shown remarkable promise in various B cell malignancies. However, the use of allogeneic CAR T cells poses a concern in that it may increase risk of the occurrence of GVHD, although this has not been reported in selected patients infused with donor-derived CD19 CAR T cells after allo-HSCT. To understand the mechanism whereby allogeneic CD19 CAR T cells may mediate anti-lymphoma activity without causing a significant increase in the incidence of GVHD, we studied donor-derived CD19 CAR T cells in allo-HSCT and lymphoma models in mice. We demonstrate that alloreactive T cells expressing CD28-costimulated CD19 CARs experience enhanced stimulation, resulting in the progressive loss of both their effector function and proliferative potential, clonal deletion, and significantly decreased occurrence of GVHD. Concurrently, the other CAR T cells that were present in bulk donor T cell populations retained their anti-lymphoma activity in accordance with the requirement that both the T cell receptor (TCR) and CAR be engaged to accelerate T cell exhaustion. In contrast, first-generation and 4-1BB-costimulated CAR T cells increased the occurrence of GVHD. These findings could explain the reduced risk of GVHD occurring with cumulative TCR and CAR signaling.

Genetic variants in the tumor necrosis factor-related apoptosis-inducing ligand and death receptor genes contribute to susceptibility to bladder cancer

AIM

The aim of this study was to evaluate the role of polymorphisms of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and death receptor (DR4) genes in bladder cancer susceptibility in a Turkish population.

MATERIALS AND METHODS

The study group included 91 bladder cancer patients, while the control group comprised 139 individuals with no evidence of malignancy. Gene polymorphisms of TRAIL C1595T (rs1131580) and DR4 C626G (rs4871857) were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis.

RESULTS

The frequency of the TRAIL 1595 TT genotype was significantly lower in patients with bladder cancer compared to controls (p<0.001; odds ratios [OR]=0.143; 95% confidence interval [CI]=0.045-0.454). A significantly increased risk for developing bladder cancer was found for the group bearing a C allele for TRAIL C1595T polymorphism (p<0.001; OR=1.256; 95% CI=1.138-1.386). The observed genotype and allele frequencies of DR4 626 C/G in all groups were in agreement with the Hardy-Weinberg equilibrium (p=0.540). However, the frequency of DR4 GG genotype was found to be 2.1-fold increased in the bladder cancer patients with high-grade tumor, when compared to those having low-grade tumor (p=0.036). Additionally, combined genotype analysis showed that the frequency of TRAILCT-DR4GG was significantly higher in patients with bladder cancer in comparison with those of controls (p=0.037; OR=2.240; 95% CI=1.138-1.386).

CONCLUSIONS

Our study provides new evidence that TRAIL 1595 C allele may be used as a low-penetrant risk factor for bladder cancer development in a Turkish population. Otherwise, gene-gene interaction analysis revealed that the DR4GG genotype may have a predominant effect on the increased risk of bladder cancer over the TRAIL CT genotype.

[(18)F]FHBG PET/CT Imaging of CD34-TK75 Transduced Donor T Cells in Relapsed Allogeneic Stem Cell Transplant Patients: Safety and Feasibility

Described herein is a first-in-man attempt to both genetically modify T cells with an imagable suicide gene and track these transduced donor T cells in allogeneic stem cell transplantation recipients using noninvasive positron emission tomography/computerized tomography (PET/CT) imaging. A suicide gene encoding a human CD34-Herpes Simplex Virus-1-thymidine kinase (CD34-TK75) fusion enabled enrichment of retrovirally transduced T cells (TdT), control of graft-versus-host disease and imaging of TdT migration and expansion in vivo in mice and man. Analysis confirmed that CD34-TK75-enriched TdT contained no replication competent γ-retrovirus, were sensitive to ganciclovir, and displayed characteristic retroviral insertion sites (by targeted sequencing). Affinity-purified CD34-TK75(+)-selected donor T cells (1.0-13 × 10(5))/kg were infused into eight patients who relapsed after allogeneic stem cell transplantation. Six patients also were administered 9-[4-((18)F)fluoro-3-hydroxymethyl-butyl]guanine ([(18)F]FHBG) to specifically track the genetically modified donor T cells by PET/CT at several time points after infusion. All patients were assessed for graft-versus-host disease, response to ganciclovir, circulating TdT cells (using both quantitative polymerase chain reaction and [(18)F]FHBG PET/CT imaging), TdT cell clonal expansion, and immune response to the TdT. This phase 1 trial demonstrated that genetically modified T cells and [(18)F]FHBG can be safely infused in patients with relapsed hematologic malignancies after allogeneic stem cell transplantation.

Genetically engineered donor T cells to optimize graft-versus-tumor effects across MHC barriers

Hematopoietic stem cell transplantation has been used for more than 50 years to combat hematologic malignancies. In addition to being the first stem cell therapy, transplantation has provided evidence for the potent anti-tumor effects of T cells. Facilitating T-cell-based immunity against malignancies requires a careful balancing act between generating a robust response and avoiding off-target killing of healthy tissues, which is difficult to accomplish using bulk donor T cells. To address these issues, several approaches have been developed, drawing on basic T-cell biology, to potentiate graft-versus-tumor activity while avoiding graft-versus-host disease. Current strategies for anti-tumor cell therapies include: (i) selecting optimal T cells for transfer; (ii) engineering T cells to possess enhanced effector functions; and (iii) generating T-cell precursors that complete development after adoptive transfer. In this review, we assess the current state of the art in T-lineage cell therapy to treat malignancies in the context of allogeneic hematopoietic stem cell transplantation.

The biology of graft-versus-host disease: experimental systems instructing clinical practice

The last 6 decades have seen major advances in the understanding of immunologic diseases, driven by preclinical animal models. Indeed, bone marrow transplantation (BMT) has its genesis in rodent models dating back to the 1950s. Allogeneic BMT and its major complication, graft-versus-host disease (GVHD), represent a paradigm for the translation of preclinical concepts into clinical practice. The appreciation that GVHD can be thought of as a stepwise escalation in immune activation characterized by eventual massive target tissue apoptosis has allowed the design of rational approaches to better manage patients. Here, we describe the pathophysiology of GVHD as defined in preclinical models, focusing on the successes and failures of this research to instruct and translate clinical practice. We also provide a commentary on the limitations of these models so that they may be better appreciated and addressed in future studies. Notable preclinical successes include the definition of modern immune suppression, reductions in conditioning intensity, posttransplant cyclophosphamide, and the promotion of regulatory T-cell reconstitution. New strategies including naïve T-cell depletion, focused cytokine and chemokine inhibition, and the blockade of costimulation now also appear highly promising and very likely to translate into patients in the near future.

Rejection of leukemic cells requires antigen-specific T cells with high functional avidity

In a context where injection of antigen (Ag)-specific T cells probably represents the future of leukemia immunotherapy, identification of optimal target Ags is crucial. We therefore sought to discover a reliable marker for selection of the most potent Ags. To this end, (1) we immunized mice against 8 individual Ags: 4 minor histocompatibility Ags (miHAs) and 4 leukemia-associated Ags (LAAs) that were overexpressed on leukemic relative to normal thymocytes; (2) we assessed their ability to reject EL4 leukemic cells; and (3) we correlated the properties of our Ags (and their cognate T cells) with their ability to induce protective antileukemic responses. Overall, individual miHAs instigated more potent antileukemic responses than LAAs. Three features had no influence on the ability of primed T cells to reject leukemic cells: (1) MHC-peptide affinity; (2) the stability of MHC-peptide complexes; and (3) epitope density at the surface of leukemic cells, as assessed using mass spectrometry. The cardinal feature of successful Ags is that they were recognized by high-avidity CD8 T cells that proliferated extensively in vivo. Our work suggests that in vitro evaluation of functional avidity represents the best criterion for selection of Ags, which should be prioritized in clinical trials of leukemia immunotherapy.

Acute graft-versus-host disease: are we close to bringing the bench to the bedside?

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplant (AHSCT) associated with significant morbidity and mortality. This review focuses on the pathophysiology, prevention, and treatment of acute GVHD. Specifically, we explain how new discoveries in immunology have expanded our understanding of GVHD, in which tissue damage from chemotherapy or radiation results in cytokine release, activating T cells, resulting in proliferation and differentiation, trafficking to target organs, and tissue destruction and inflammation. Insights into the mechanisms of this disease relate directly to the development of preventive strategies and therapies, such as immunosuppression, calcineurin inhibitors, T-cell depletion, CCR5 antagonists, gut decontamination, extracorporeal photopheresis, and more. Understanding the immunobiology of GVHD and developing effective preventions and treatments are critical to the continuing success of AHSCT.

Targeting of the tumor necrosis factor receptor superfamily for cancer immunotherapy

The tumor necrosis factor (TNF) ligand and cognate TNF receptor superfamilies constitute an important regulatory axis that is pivotal for immune homeostasis and correct execution of immune responses. TNF ligands and receptors are involved in diverse biological processes ranging from the selective induction of cell death in potentially dangerous and superfluous cells to providing costimulatory signals that help mount an effective immune response. This diverse and important regulatory role in immunity has sparked great interest in the development of TNFL/TNFR-targeted cancer immunotherapeutics. In this review, I will discuss the biology of the most prominent proapoptotic and co-stimulatory TNF ligands and review their current status in cancer immunotherapy.

Blazing a new TRAIL in hematopoietic cell transplantation

There is a ying/yang to most biological therapies, and the balance of efficacy versus toxicity is delicate and sometimes difficult to achieve in favor of the patients. When the therapeutic window is wide, these therapies can be used in the majority of patients, but when the therapeutic window is narrow, the decision to proceed must be carefully balanced with a thoughtful risk-benefit analysis. In this issue of the JCI, Ghosh et al. tackle one of the major obstacles in hematopoietic cell transplantation (HCT) technology: balancing the beneficial antitumor effect with the harmful anti-host effect.

Adoptively transferred TRAIL+ T cells suppress GVHD and augment antitumor activity

Current strategies to suppress graft-versus-host disease (GVHD) also compromise graft-versus-tumor (GVT) responses. Furthermore, most experimental strategies to separate GVHD and GVT responses merely spare GVT function without actually enhancing it. We have previously shown that endogenously expressed TNF-related apoptosis-inducing ligand (TRAIL) is required for optimal GVT activity against certain malignancies in recipients of allogeneic hematopoietic stem cell transplantation (allo-HSCT). In order to model a donor-derived cellular therapy, we genetically engineered T cells to overexpress TRAIL and adoptively transferred donor-type unsorted TRAIL+ T cells into mouse models of allo-HSCT. We found that murine TRAIL+ T cells induced apoptosis of alloreactive T cells, thereby reducing GVHD in a DR5-dependent manner. Furthermore, murine TRAIL+ T cells mediated enhanced in vitro and in vivo antilymphoma GVT response. Moreover, human TRAIL+ T cells mediated enhanced in vitro cytotoxicity against both human leukemia cell lines and against freshly isolated chronic lymphocytic leukemia (CLL) cells. Finally, as a model of off-the-shelf, donor-unrestricted antitumor cellular therapy, in vitro-generated TRAIL+ precursor T cells from third-party donors also mediated enhanced GVT response in the absence of GVHD. These data indicate that TRAIL-overexpressing donor T cells could potentially enhance the curative potential of allo-HSCT by increasing GVT response and suppressing GVHD.

Real-time detection of cellular death receptor-4 activation by fluorescence resonance energy transfer

Targeted therapy involving the activation of death receptors DR4 and/or DR5 by its ligand, TRAIL, can selectively induce apoptosis in certain tumor cells. In order to profile the dynamic activation or trimerization of TRAIL-DR4 in live cells in real-time, the development of an apoptosis reporter cell line is essential. Fluorescence resonance energy transfer (FRET) technology via a FRET pair, cyan fluorescence protein (CFP) and yellow fluorescence protein (YFP), was used in this study. DR4-CFP and DR4-YFP were stably expressed in human lung cancer PC9 cells. Flow cytometer sorting and limited dilution coupled with fluorescence microscopy were used to select a monoclonal reporter cell line with high and compatible expression levels of DR4-CFP and DR4-YFP. FRET experiments were conducted and FRET efficiencies were monitored according to the Siegel's YFP photobleaching FRET protocol. Upon TRAIL induction a significant increase in FRET efficiencies from 5% to 9% demonstrated the ability of the DR4-CFP/YFP reporter cell line in monitoring the dynamic activation of TRAIL pathways. 3D reconstructed confocal images of DR4-CFP/YFP reporter cells exhibited a colocalized expression of DR4-CFP and DR4-YFP mainly on cell membranes. FRET results obtained during this study complements the use of epi-fluorescence microscopy for FRET analysis. The real-time FRET analysis allows the dynamic profiling of the activation of TRAIL pathways by using the time-lapse fluorescence microscopy. Therefore, DR4-CFP/YFP PC9 reporter cells along with FRET technology can be used as a tool for anti-cancer drug screening to identify compounds that are capable of activating TRAIL pathways.

Concise review: acute graft-versus-host disease: immunobiology, prevention, and treatment

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplant (AHSCT) associated with significant morbidity and mortality. This review focuses on the pathophysiology, clinical features, prevention, and treatment of acute GVHD. Specifically, we explain how new discoveries in immunology have expanded our understanding of GVHD, in which tissue damage from chemotherapy or radiation results in cytokine release, which activates T cells, resulting in proliferation and differentiation, trafficking to target organs, and tissue destruction and inflammation. Insights into the mechanisms of this disease relate directly to the development of preventive strategies and therapies, such as immunosuppression, T-cell depletion, calcineurin inhibitors, CCR5 antagonists, gut decontamination, extracorporeal photopheresis, and more. We also discuss how GVHD affects the gut, liver, and skin, as well as diagnosis, grading, and scoring. We end by examining future directions of treatment, including new immunomodulators and biomarkers. Understanding the immunobiology of GVHD and developing effective preventions and treatments are critical to the continuing success of AHSCT.

Recombinant CD95-Fc (APG101) prevents graft-versus-host disease in mice without disabling antitumor cytotoxicity and T-cell functions

Graft-versus-host disease (GVHD) induced by transplant-derived T cells represents a major complication after allogeneic bone marrow transplantation (BMT). However, these T cells support engraftment, early T-cell immunity, and mediate the graft-versus-tumor (GVT) effect. Cytotoxic effector functions by transplanted T cells are predominantly mediated by the perforin/granzyme and the CD95/CD95L system. APG101, a novel recombinant human fusion protein consisting of the extracellular domain of CD95 and the Fc domain of an IgG1 antibody inhibited CD95L-induced apoptosis without interfering with T-cell function in vitro and was therefore tested for its ability to prevent GVHD in murine BMT models across minor or major histocompatibility barriers. Starting APG101 treatment either 1 day before or 6 days after transplantation effectively reduced clinical GVHD and rescued survival between 60% and 100% if GVHD was CD95L mediated. APG101 did not interfere with the GVT effect, because P815 mastocytoma and most importantly primary Bcr-Abl-transformed B-cell leukemias were completely eradicated by the alloantigen-specific T cells. Phenotype and homing of alloantigen-specific T cells or their perforin/granzyme-mediated cytotoxicity and proliferative capacity were not affected by APG101 treatment suggesting that APG101 therapy might be useful in GVHD prophylaxis without impairing T-cell function and most importantly preserving GVT activity.

BCR-ABL regulates death receptor expression for TNF-related apoptosis-inducing ligand (TRAIL) in Philadelphia chromosome-positive leukemia

Allogeneic stem cell transplantation (allo-SCT) is a potentially curative therapy for chronic myeloid leukemia and Philadelphia chromosome-positive (Ph(+)) acute lymphoblastic leukemia, and the graft-vs-leukemia (GVL) effect can eradicate residual leukemia after allo-SCT. Ph(+) leukemia cells frequently express death-inducing receptors (DR4 and DR5) for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which is one of the cytotoxic ligands expressed on cytotoxic T cells and natural killer cells mediating the GVL effect. Here we demonstrate that imatinib specifically downregulated DR4 and DR5 expression in cell lines and clinical samples of Ph(+) leukemia. Second-generation tyrosine kinase inhibitors (dasatinib and nilotinib) and short hairpin RNA against bcr-abl also downregulated DR4 and DR5 expression in Ph(+) leukemia cells, and transfection of bcr-abl into a Ph(-) leukemia cell line induced DR4 and DR5 expression, which was abrogated by imatinib treatment. Accordingly, Ph(+) leukemia cells that had been pretreated with imatinib showed resistance to the pro-apoptotic activity of recombinant human soluble TRAIL. These observations demonstrate that BCR-ABL is critically involved in the leukemia-specific expression of DR4 and DR5 and in the susceptibility of Ph(+) leukemia to TRAIL-mediated anti-leukemic activity, providing new insight into the mechanisms of the tumor-specific cytotoxic activities of TRAIL.

Oncogenic fusion E2A-HLF sensitizes t(17;19)-positive acute lymphoblastic leukemia to TRAIL-mediated apoptosis by upregulating the expression of death receptors

t(17;19)-acute lymphoblastic leukemia (ALL) shows extremely poor prognosis. E2A-HLF derived from t(17;19) blocks apoptosis induced by the intrinsic mitochondrial pathway and has a central role in leukemogenesis and chemoresistance. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is expressed on cytotoxic T cells and natural killer cells and binds with death receptors (DR4/DR5), inducing apoptosis by dual activation of intrinsic and extrinsic pathways, and TRAIL mediates the graft-versus-leukemia (GVL) effect after allogeneic stem cell transplantation (allo-SCT). We found that cell lines and patients' samples of t(17;19)-ALL expressed death receptors for TRAIL, and recombinant soluble TRAIL immediately induced apoptosis into t(17;19)-ALL cell lines. E2A-HLF induced gene expression of DR4/DR5, which was dependent on the DNA-binding and transactivation activities of E2A-HLF through the 5' upstream region of the start site at least in the DR4 gene. Introduction of E2A-HLF into non-t(17;19)-ALL cell line upregulated DR4 and DR5 expression, and sensitized to proapoptotic activity of recombinant soluble TRAIL. Finally, a newly diagnosed t(17;19)-ALL patient underwent allo-SCT immediately after induction of first complete remission, and the patient has survived without relapse for over 3-1/2 years after allo-SCT. These findings suggest that E2A-HLF sensitizes t(17;19)-ALL to the GVL effect by upregulating death receptors for TRAIL.

Resistance of MLL-AFF1-positive acute lymphoblastic leukemia to tumor necrosis factor-alpha is mediated by S100A6 upregulation

Mixed-lineage leukemia (MLL)-AFF1 (MLL-AF4)-positive acute lymphoblastic leukemia (ALL) is associated with poor prognosis, even after allogeneic hematopoietic stem cell transplantation (allo-HSCT). The resistance to graft-versus-leukemia (GVL) effects may be responsible for the poor effect of allo-HSCT on MLL-AFF1-positive ALL. Cytotoxic effector mechanisms mediated by tumor necrosis factor-alpha (TNF-α) was reported to contribute to the GVL effect. We showed that MLL-AFF1-positive ALL cell lines are resistant to TNF-α. To examine the mechanism of resistance to TNF-α of MLL-AFF1-positive leukemia, we focused on S100A6 as a possible factor. Upregulation of S100A6 expression and inhibition of the p53-caspase 8-caspase 3 pathway were observed only in MLL-AFF1-positive ALL cell lines in the presence of TNF-α. The effect of S100A6 on resistance to TNF-α by inhibition of the p53-caspase 8-caspase 3 pathway of MLL-AFF1-positive ALL cell lines were also confirmed by analysis using small interfering RNA against S100A6. This pathway was also confirmed in previously established MLL-AFF1 transgenic mice. These results suggest that MLL-AFF1-positive ALL escapes from TNF-α-mediated apoptosis by upregulation of S100A6 expression, followed by interfering with p53-caspase 8-caspase 3 pathway. These results suggest that S100A6 may be a promising therapeutic target for MLL-AFF1-positive ALL in combination with allo-HSCT.

Cell surface delivery of TRAIL strongly augments the tumoricidal activity of T cells

PURPOSE

Adoptive T-cell therapy generally fails to induce meaningful anticancer responses in patients with solid tumors. Here, we present a novel strategy designed to selectively enhance the tumoricidal activity of T cells by targeted delivery of TNF-related apoptosis-inducing ligand (TRAIL) to the T-cell surface.

EXPERIMENTAL DESIGN

We constructed two recombinant fusion proteins, anti-CD3:TRAIL and K12:TRAIL. Tumoricidal activity of T cells in the presence of these fusion proteins was assessed in solid tumor cell lines, primary patient-derived malignant cells, and in a murine xenograft model.

RESULTS

When added to T cells, K12:TRAIL and anti-CD3:TRAIL selectively bind to the T-cell surface antigens CD3 and CD7, respectively, leading to cell surface accretion of TRAIL. Subsequently, anti-CD3:TRAIL and K12:TRAIL increased the tumoricidal activity of T cells toward cancer cell lines and primary patient-derived malignant cells by more than 500-fold. Furthermore, T-cell surface delivery of TRAIL strongly inhibited tumor growth and increased survival time of xenografted mice more than 6-fold.

CONCLUSIONS

Targeted delivery of TRAIL to cell surface antigens of T cells potently enhances the tumoricidal activity of T cells. This approach may be generally applicable to enhance the efficacy of adoptive T-cell therapy.

In vitro-established alloantigen-specific CD8+ CTLs mediate graft-versus-tumor activity in the absence of graft-versus-host disease

Mature donor-derived T cells in allogeneic bone marrow (BM) transplants mediate the graft-versus-tumor (GVT) effect by recognizing alloantigens on leukemic cells. However, alloantigen reactivity towards non-malignant tissues also induces graft-versus-host disease (GVHD). Defining T-cell subpopulations that mediate the GVT effect in the absence of GVHD induction remains a major challenge in allogeneic BM transplantation. In this study, we show that in vitro-generated alloantigen-specific CD8(+) cytotoxic T cells (CTLs) established by weekly stimulation with alloantigen-expressing antigen-presenting cells did not induce GVHD in two major histocompatibility complex-mismatched BM transplantation models, where induction of lethal GVHD is dependent on the presence of either CD4(+) or CD8(+) T cells. Despite their strong alloantigen specificity, transplantation of CTLs did not induce the expression of GVHD-associated cytokines IFN-γ and TNF-α or clinical or histological signs of GVHD, and lead to a survival rate of above 90%. However, transplantation of unstimulated CD8(+) T cells, which were not primed by the alloantigen in vitro, induced GVHD in both the transplantation models. Although CTLs were impaired in GVHD induction, they efficiently eradicated Bcr-Abl-transformed B-cell leukemias or mastocytomas. Thus, in vitro-derived CTLs might be useful for optimizing anti-tumor therapy in the absence of GVHD induction.

TRAIL receptor signaling regulation of chemosensitivity in vivo but not in vitro

Background

Signaling by Tumor Necrosis Factor-Related Apoptosis Inducing Ligand (TRAIL) and Fas ligand (FasL) has been proposed to contribute to the chemosensitivity of tumor cells treated with various other anti-cancer agents. However, the importance of these effects and whether there are differences in vitro and in vivo is unclear.

Methodology/Principal Findings

To assess the relative contribution of death receptor pathways to this sensitivity and to determine whether these effects are intrinsic to the tumor cells, we compared the chemosensitivity of isogenic BJAB human lymphoma cells where Fas and TRAIL receptors or just TRAIL receptors were inhibited using mutants of the adaptor protein FADD or by altering the expression of the homeobox transcription factor Six1. Inhibition of TRAIL receptors did not affect in vitro tumor cell killing by various anti-cancer agents indicating that chemosensitivity is not significantly affected by the tumor cell-intrinsic activation of death receptor signaling. However, selective inhibition of TRAIL receptor signaling caused reduced tumor regression and clearance in vivo when tested in a NOD/SCID mouse model.

Conclusions

These data show that TRAIL receptor signaling in tumor cells can determine chemosensitivity in vivo but not in vitro and thus imply that TRAIL resistance makes tumors less susceptible to conventional cytotoxic anti-cancer drugs as well as drugs that directly target the TRAIL receptors.

HDAC inhibition and graft versus host disease

Histone deacetylase (HDAC) inhibitors are currently used clinically as anticancer drugs. Recent data have demonstrated that some of these drugs have potent antiinflammatory or immunomodulatory effects at noncytotoxic doses. The immunomodulatory effects have shown potential for therapeutic benefit after allogeneic bone marrow transplantation in several experimental models of graft versus host disease (GVHD). These effects, at least in part, result from the ability of HDAC inhibitors (HDACi) to suppress the function of host antigen presenting cells such as dendritic cells (DC). HDACi reduce the dendritic cell (DC) responses, in part, by enhancing the expression of indoleamine 2,3-dioxygenase (IDO) in a signal transducer and activator of transcription-3 (STAT-3) dependent manner. They also alter the function of other immune cells such as T regulatory cells and natural killer (NK) cells, which also play important roles in the biology of GVHD. Based on these observations, a clinical trial has been launched to evaluate the impact of HDAC inhibitors on clinical GVHD. The experimental, mechanistic studies along with the brief preliminary observations from the ongoing clinical trial are discussed in this review.

BCR-ABL-mediated upregulation of PRAME is responsible for knocking down TRAIL in CML patients

Tumor necrosis factor-related apoptosis-inducing ligand-TNFSF10 (TRAIL), a member of the TNF-α family and a death receptor ligand, was shown to selectively kill tumor cells. Not surprisingly, TRAIL is downregulated in a variety of tumor cells, including BCR-ABL-positive leukemia. Although we know much about the molecular basis of TRAIL-mediated cell killing, the mechanism responsible for TRAIL inhibition in tumors remains elusive because (a) TRAIL can be regulated by retinoic acid (RA); (b) the tumor antigen preferentially expressed antigen of melanoma (PRAME) was shown to inhibit transcription of RA receptor target genes through the polycomb protein, enhancer of zeste homolog 2 (EZH2); and (c) we have found that TRAIL is inversely correlated with BCR-ABL in chronic myeloid leukemia (CML) patients. Thus, we decided to investigate the association of PRAME, EZH2 and TRAIL in BCR-ABL-positive leukemia. Here, we demonstrate that PRAME, but not EZH2, is upregulated in BCR-ABL cells and is associated with the progression of disease in CML patients. There is a positive correlation between PRAME and BCR-ABL and an inverse correlation between PRAME and TRAIL in these patients. Importantly, knocking down PRAME or EZH2 by RNA interference in a BCR-ABL-positive cell line restores TRAIL expression. Moreover, there is an enrichment of EZH2 binding on the promoter region of TRAIL in a CML cell line. This binding is lost after PRAME knockdown. Finally, knocking down PRAME or EZH2, and consequently induction of TRAIL expression, enhances Imatinib sensibility. Taken together, our data reveal a novel regulatory mechanism responsible for lowering TRAIL expression and provide the basis of alternative targets for combined therapeutic strategies for CML.

Combining naturally occurring polyphenols with TNF-related apoptosis-inducing ligand: a promising approach to kill resistant cancer cells?

TNF-related apoptosis-inducing ligand (TRAIL) and its receptors are attractive targets for anticancer therapy owing to their ability to trigger apoptosis selectively in cancer cells but not in normal cells. To date, many combinatorial strategies, such as chemotherapy or radiotherapy, have given encouraging results for overcoming TRAIL resistance in preclinical models. In this review, we provide an overview of the molecular mechanisms underlying sensitization to TRAIL-induced apoptosis by polyphenols. These naturally occurring compounds can restore tumor cell sensitivity to TRAIL-induced cell death with no apparent toxicity towards normal cells. Both extrinsic and intrinsic pathways can be modulated by polyphenols, the activation of which largely depends on the cell type, the particular polyphenolic compound, and the conditions of treatment. The large variety of polyphenol cellular targets could prove useful in circumventing TRAIL resistance. The relevance of these combined treatments for cancer therapy is discussed in the light of recent preclinical studies.

Resistance of T-cell acute lymphoblastic leukemia to tumor necrosis factor--related apoptosis-inducing ligand-mediated apoptosis

OBJECTIVE

Cytotoxic ligands are involved in tumor immunity and graft-vs.-leukemia effect after allogeneic stem cell transplantation for leukemia. To clarify the susceptibility of T-cell acute lymphoblastic leukemia (T-ALL) to tumor immunity, sensitivity to recombinant human soluble Fas ligand (rhsFasL) and tumor necrosis factor-related apoptosis-inducing ligand (rhsTRAIL) was determined.

MATERIALS AND METHODS

Sensitivity to rhsFasL and rhsTRAIL and cell surface expression of their receptors were tested in T-ALL cell lines (n = 7) and patients' samples (n = 17) and compared with those in B-precursor ALL cell lines (n = 30). Expression of components of the death-inducing signaling complex and the TRAIL receptor genes (DR4/DR5), and the methylation status and promoter activity of the DR4/DR5 gene were tested in T-ALL cell lines.

RESULTS

T-ALL cell lines showed higher level of Fas expression and higher sensitivity to rhsFasL than did B-precursor ALL cell lines. Despite comparable expression of components of death-inducing signaling complex, cell lines and patients' samples of T-ALL showed TRAIL-resistance associated with low cell surface expression of DR4/DR5. Gene expression of DR4/DR5 in T-ALL cell lines was significantly lower than that in B-precursor ALL cell lines, and the methylation status of the gene promoter in T-ALL cell lines was associated with the gene expression level at least for DR4. The demethylating agent, 5-aza 2'deoxycytidine, upregulated the gene expression of DR4/DR5, but was insufficient for their surface expression due to low basal promoter activity.

CONCLUSIONS

In contrast to higher sensitivity to FasL, T-ALL showed resistance to TRAIL, which might be responsible for resistance to TRAIL-mediated cellular immunity.

Regulatory functions of TRAIL in hematopoietic progenitors: human umbilical cord blood and murine bone marrow transplantation

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) signaling pathway has selective toxicity to malignant cells. The TRAIL receptors DR4 and DR5 are expressed at low levels in human umbilical cord blood cells (3-15%) and are upregulated by incubation with the cognate ligand, triggering apoptosis in 70-80% of receptor-positive cells (P<0.001). Apoptosis is not induced in hematopoietic progenitors, as determined from sustained severe combined immunodeficiency reconstituting potential and clonogenic activity. Furthermore, elimination of dead cells after incubation with TRAIL for 72 h results in a threefold enrichment in myeloid progenitors. Exposure to TRAIL in semisolid cultures showed synergistic activity of DR4 and granulocyte/macrophage colony-stimulating factor in recruiting lineage-negative (lin(-)) and CD34(+) progenitors and in promoting the formation of large colonies. In murine bone marrow, approximately 30% of lin(-) cells express TRAIL-R2 (the only murine receptor), and the receptor is upregulated after transplantation in cycling and differentiating donor cells that home to the host marrow. However, this receptor is almost ubiquitously expressed in the most primitive (lin(-)SCA-1(+)c-kit(+)) progenitors, and stimulates the clonogenic activity of lin(-) cells (P<0.001), suggesting a tropic function after transplantation. It is concluded that TRAIL does not trigger apoptosis in hematopoietic progenitors, and upregulation of its cognate receptors under stress conditions mediates tropic signaling that supports recovery from hypoplasia.

Perforin: more than just a pore-forming protein

Cellular apoptosis induced by T cells is mainly mediated by two pathways. One, granule exocytosis utilizes perforin/granzymes. The other involves signaling through death receptors of the TNF-alpha R super-family, especially FasL. Perforin plays a central role in apoptosis induced by granzymes. However, the mechanisms of perforin-mediated cytotoxicity are still not elucidated completely. Perforin is not only a pore-forming protein, but also performs multiple biological functions or perforin performs one biological function (cytolysis), but has multiple biological implications in the cellular immune responses, including regulation of proliferation of CD8+ CTLs.

Immune reconstitution after allogeneic transplantation and expanding options for immunomodulation: an update

Allogeneic hematopoietic stem cell transplantation (HSCT) has advanced to a common procedure for treating also older patients with malignancies and immunodeficiency disorders by redirecting the immune system. Unfortunately, cure is often hampered by relapse of the underlying disease, graft-versus-host disease, or severe opportunistic infections, which account for the majority of deaths after HSCT. Enhancing immune reconstitution is therefore an area of intensive research. An increasing variety of approaches has been explored preclinically and clinically: the application of cytokines, keratinocyte growth factor, growth hormone, cytotoxic lymphocytes, and mesenchymal stem cells or the blockade of sex hormones. New developments of allogeneic HSCT, for example, umbilical cord blood or haploidentical graft preparations leading to prolonged immunodeficiency, have further increased the need to improve immune reconstitution. Although a slow T-cell reconstitution is regarded as primarily responsible for deleterious infections with viruses and fungi, graft-versus-host disease, and relapse, the importance of innate immune cells for disease and infection control is currently being reevaluated. The groundwork has been prepared for the creation of individualized therapy partially based on genetic features of the underlying disease. We provide an update on selected issues of development in this fast evolving field; however, we do not claim completeness.

Proteasome inhibition and allogeneic hematopoietic stem cell transplantation: a review

The proteasome and its associated ubiquitin protein modification system have proved to be an important therapeutic target in the treatment of multiple myeloma and other cancers. In addition to direct antitumor effects, proteasome inhibition also exerts strong effects on nonneoplastic immune cells. This indicates that proteasome inhibition, through the use of agents like bortezomib, could be used therapeutically to modulate immune responses. In this review we explore the emerging data, both preclinical and clinical, highlighting the importance of proteasome targeting of immunologic responses, primarily in the context of allogeneic hematopoietic stem cell transplantation (HSCT), both for the control of transplant-related toxicities like acute and chronic graft-versus-host disease (aGVHD, cGHVHD), and for improved malignant disease control after allogeneic HSCT.

Emerging apoptosis agonists for bladder cancer

Bladder cancer is a very common and aggressive tumor entity. Unfortunately, common chemotherapy is not able to cure advanced bladder cancer. Therefore, several attempts have been made to improve the response to chemotherapy. Because changes in apoptotic pathways are frequent events in the development of chemoresistance of malignancies, pro-apoptotic treatment seems promising for the improvement of bladder cancer prognosis. Preclinical data show potential ways for a successful combination of apoptosis agonists with conventional chemotherapy. None of these principles has so far successfully been translated into clinical trials for bladder cancer. This review describes actual studies and future perspectives for apoptotic agonists in bladder cancer.

The cytolytic molecules Fas ligand and TRAIL are required for murine thymic graft-versus-host disease

Thymic graft-versus-host disease (tGVHD) can contribute to profound T cell deficiency and repertoire restriction after allogeneic BM transplantation (allo-BMT). However, the cellular mechanisms of tGVHD and interactions between donor alloreactive T cells and thymic tissues remain poorly defined. Using clinically relevant murine allo-BMT models, we show here that even minimal numbers of donor alloreactive T cells, which caused mild nonlethal systemic graft-versus-host disease, were sufficient to damage the thymus, delay T lineage reconstitution, and compromise donor peripheral T cell function. Furthermore, to mediate tGVHD, donor alloreactive T cells required trafficking molecules, including CCR9, L selectin, P selectin glycoprotein ligand-1, the integrin subunits alphaE and beta7, CCR2, and CXCR3, and costimulatory/inhibitory molecules, including Ox40 and carcinoembryonic antigen-associated cell adhesion molecule 1. We found that radiation in BMT conditioning regimens upregulated expression of the death receptors Fas and death receptor 5 (DR5) on thymic stromal cells (especially epithelium), while decreasing expression of the antiapoptotic regulator cellular caspase-8-like inhibitory protein. Donor alloreactive T cells used the cognate proteins FasL and TNF-related apoptosis-inducing ligand (TRAIL) (but not TNF or perforin) to mediate tGVHD, thereby damaging thymic stromal cells, cytoarchitecture, and function. Strategies that interfere with Fas/FasL and TRAIL/DR5 interactions may therefore represent a means to attenuate tGVHD and improve T cell reconstitution in allo-BMT recipients.

New perspectives on the biology of acute GVHD

The use of allogeneic hematopoietic cell transplantation (HCT) has increased as new techniques have been developed for transplantation in patients who previously would not have been considered HCT candidates. However, its efficacy continued to be limited by the development of frequent and severe acute GVHD. The complex and intricate pathophysiology of acute GVHD is a consequence of interactions between the donor and host innate and adaptive immune responses. Multiple inflammatory molecules and cell types are implicated in the development of GVHD that can be categorized as: (1) triggers that initiate GVHD by therapy-induced tissue damage and the antigen disparities between host and graft tissue; (2) sensors that detect the triggers, that is, process and present alloantigens; (3) mediators such as T-cell subsets (naive, memory, regulatory, Th17 and natural killer T cells) and (4) the effectors and amplifiers that cause damage of the target organs. These multiple inflammatory molecules and cell types that are implicated in the development of GVHD have been described with models that use stepwise cascades. Herein, we provide a novel perspective on the immunobiology of acute GVHD and briefly discuss some of the outstanding questions and limitations of the model systems.

PKCtheta is required for alloreactivity and GVHD but not for immune responses toward leukemia and infection in mice

When used as therapy for hematopoietic malignancies, allogeneic BM transplantation (BMT) relies on the graft-versus-leukemia (GVL) effect to eradicate residual tumor cells through immunologic mechanisms. However, graft-versus-host disease (GVHD), which is initiated by alloreactive donor T cells that recognize mismatched major and/or minor histocompatibility antigens and cause severe damage to hematopoietic and epithelial tissues, is a potentially lethal complication of allogeneic BMT. To enhance the therapeutic potential of BMT, we sought to find therapeutic targets that could inhibit GVHD while preserving GVL and immune responses to infectious agents. We show here that T cell responses triggered in mice by either Listeria monocytogenes or administration of antigen and adjuvant were relatively well preserved in the absence of PKC isoform theta (PKCtheta), a key regulator of TCR signaling. In contrast, PKCtheta was required for alloreactivity and GVHD induction. Furthermore, absence of PKCtheta raised the threshold for T cell activation, which selectively affected alloresponses. Most importantly, PKCtheta-deficient T cells retained the ability to respond to virus infection and to induce GVL effect after BMT. These findings suggest PKCtheta is a potentially unique therapeutic target required for GVHD induction but not for GVL or protective responses to infectious agents.

G to C transition at position -173 of MIF gene of the recipient is associated with reduced relapse rates after allogeneic stem cell transplantation

Pro-inflammatory and dendritic cell-activating properties of macrophage migration inhibitory factor (MIF) suggest a potentially important role for MIF in alloantigen-specific immune responses after allogeneic stem cell transplantation (allo-SCT). We tested whether MIF -173 G/C gene polymorphism of donor or patient had impacts on the outcomes after allo-SCT. Four hundred and fifty-four donor-patient pairs were genotyped and mortality, relapse, and development of complications were analyzed. Patient but not donor MIF -173 *C allele was associated with improved overall survival (OS) (5 years: 60.8% versus 46.3%, p=0.042) and disease free survival (DFS) (5 years: 55.4% versus 39.5%; p=0.014) due to a reduction in relapse (day 2000: 22.8% versus 42.0% p=0.006) but not due to decreased transplantation-related mortality (TRM) (p=0.44). Multivariate analysis proved patient -173 *C allele as an independent factor for reducing relapse after allo-SCT (p=0.023). Subgroup analysis showed a clear MIF -173 *C allele-related reduction in relapse for those patients who did not receive T cell depleted (TCD) SCT (p=0.01) in contrast to patients receiving TCD SCT (p=0.20). In summary, patient MIF -173 *C allele may be linked to specific, yet unrevealed functions in tumor biology and graft versus leukemia and lymphoma effects and potentially presents a novel prognostic marker for patient-tailored counseling and therapy in allo-SCT.

The TRAIL to targeted therapy of breast cancer

Breast cancers can be classified into those which express the estrogen (ER) and progesterone (PR) receptors, those with HER-2 amplification, and those without expression of ER, PR, or amplified HER-2 (referred to as triple-negative or basal-like breast cancer). Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) activates apoptosis upon binding to its receptors in many tumor types and the ligand and agonist antibodies are currently being studied in patients in clinical phases I and II trials. Cell line studies suggest that many breast cancer cell lines are very resistant to TRAIL-induced apoptosis. However, recent data suggest that a subset of triple-negative/basal-like breast cancer cells is sensitive to TRAIL as a single agent. In addition, many studies have demonstrated that resistance to TRAIL-mediated apoptosis in breast cancer cells can be overcome by combinations of TRAIL with chemotherapy, radiation, and various targeted agents. This chapter will discuss the current understanding of the mechanisms, which control TRAIL-mediated apoptosis in breast cancer cells. The preclinical data supporting the use of TRAIL ligands and agonistic antibodies alone and in combination in breast cancer will also be discussed.

Dissection of effector pathways in the host-versus-graft response to bone marrow transplantation

We have dissected the role of the primary cytotoxic pathways Fas-FasL and perforin-granzyme in host-versus-graft reactions after allogeneic bone marrow transplantation. Sublethally irradiated female recipient mice deficient for FasL (B6.gld) or perforin (B6.prf-/-) were transplanted with bone marrow from B6 male donors. Donor engraftment in B6.prf-/- recipients was higher when compared with B6.gld, particularly when assessed by in vivo killing, demonstrating the importance of the perforin pathway over the Fas-FasL pathway. In the absence of both pathways, however, donor bone marrow engraftment was not fully restored identifying a role for an additional pathway(s) in the host-versus-graft response.