Induction of tolerance using Fas ligand: a double-edged immunomodulator

Immunology demystified: A guide for transplant hepatologists

Liver transplantation has become standard practice for treating end-stage liver disease. The success of the procedure relies on effective immunosuppressive medications to control the host's immune response. Despite the liver's inherent capacity to foster tolerance, the early post-transplant period is marked by significant immune reactivity. To ensure favorable outcomes, it is imperative to identify and manage various rejection types, encompassing T-cell-mediated, antibody-mediated, and chronic rejection. However, the approach to prescribing immunosuppressants relies heavily on clinical judgment rather than evidence-based criteria. Given that the majority of patients will require lifelong immuno suppression as the mechanisms underlying operational tolerance are still being investigated, healthcare providers must possess an understanding of immune responses, rejection mechanisms, and the pathways targeted by immunosuppressive drugs. This knowledge enables customization of treatments and improved patient care, even though a consensus on an optimal immunosuppressive regimen remains elusive.

Grafted Sertoli cells prevent neuronal cell death and memory loss induced by seizures

Epilepsy significantly reduces the patient's quality of life, and we still need to develop new therapeutic approaches to control it. Transplantation of cells such as Sertoli cells (SCs), having a potent ability to release a variety of growth and immunoprotective substances, have made them a potential candidate to deal with neurological diseases like epilepsy. Hence, this study aims to evaluate whether SCs transplant effectively protects the hippocampus astrocytes and neurons to oppose seizure damage. For this purpose, the effects of bilateral intrahippocampal transplantation of SCs were investigated on the rats with the pentylenetetrazol (PTZ) induced seizure. After one-month, post-graft analysis was performed regarding behavior, immunohistopathology, and the distribution of the hippocampal cells. Our findings showed SCs transplantation reduced astrogliosis, astrocytes process length, the number of branches, and intersections distal to the soma of the hippocampus in the seizure group. In rats with grafted SCs, there was a drop in the hippocampal caspase-3 expression. Moreover, the SCs showed another protective impact, as shown by an improvement in pyramidal neurons' number and spatial distribution. The findings suggested that SCs transplantation can potently modify astrocytes' reactivation and inflammatory responses.

Immune dysregulation and inflammation causing hypopigmentation in post kala-azar dermal leishmaniasis: partners in crime?

Post kala-azar dermal leishmaniasis (PKDL), a heterogeneous dermal sequela of visceral leishmaniasis (VL), is challenging in terms of its etiopathogenesis. Hypopigmentation is a consistent clinical feature in PKDL, but mechanisms contributing to the loss of melanocytes remains poorly defined. Like other hypopigmentary dermatoses - for example, vitiligo, psoriasis, and leprosy - the destruction of melanocytes is likely a multifactorial phenomenon, key players being immune dysregulation and inflammation. This review focuses on immunological mechanisms responsible for the 'murder' of melanocytes, prime suspects at the lesional sites being CD8+ T cells and keratinocytes and their criminal tools being proinflammatory cytokines, for example, IFN-γ, IL-6, and TNF-α. Collectively, these may cause decreased secretion of melanocyte growth factors, loss/attenuation of cell adhesion molecules and inflammasome activation, culminating in melanocyte death.

Combinatorial islet protective therapeutic approaches in β-cell transplantation: Rationally designed solutions using a target product profile

While progress has been made in the development of islet cell transplantation (ICT) as a viable alternative to the use of exogenous insulin therapy in the treatment of type 1 diabetes, it has not yet achieved its full potential in clinical studies. Ideally, ICT would enable lifelong maintenance of euglycemia without the need for exogenous insulin, blood glucose monitoring or systemic immune suppression. To achieve such an optimal result, therapeutic approaches should simultaneously promote long-term islet viability, functionality, and localized immune protection. In practice, however, these factors are typically tackled individually. Furthermore, while the requirements of optimal ICT are implicitly acknowledged across numerous publications, the literature contains few comprehensive articulations of the target product profile (TPP) for an optimal ICT product, including key characteristics of safety and efficacy. This review aims to provide a novel TPP for ICT and presents promising tried and untried combinatorial approaches that could be used to achieve the target product profile. We also highlight regulatory barriers to the development and adoption of ICT, particularly in the United States, where ICT is only approved for use in academic clinical trials and is not reimbursed by insurance carriers. Overall, this review argues that the clear definition of a TPP in addition to the use of combinatorial approaches could help to overcome the clinical barriers to the widespread adoption of ICT for the treatment of type 1 diabetes.

Nanomaterials for antigen-specific immune tolerance therapy

Impairment of immune tolerance might cause autologous tissue damage or overactive immune response against non-pathogenic molecules. Although autoimmune disease and allergy have complicated pathologies, the current strategies have mainly focused on symptom amelioration or systemic immunosuppression which can lead to fatal adverse events. The induction of antigen-specific immune tolerance may provide therapeutic benefits to autoimmune disease and allergic response, while reducing nonspecific immune adverse responses. Diverse nanomaterials have been studied to induce antigen-specific immune tolerance therapy. This review will cover the immunological background of antigen-specific tolerance, clinical importance of antigen-specific immune tolerance, and nanomaterials designed for autoimmune and allergic diseases. As nanomaterials for modulating immune tolerances, lipid-based nanoparticles, polymeric nanoparticles, and biological carriers have been covered. Strategies to provide antigen-specific immune tolerance have been addressed. Finally, current challenges and perspectives of nanomaterials for antigen-specific immune tolerance therapy will be discussed.

CD40- and CD95-specific antibody single chain-Baff fusion proteins display BaffR-, TACI- and BCMA-restricted agonism

Antibodies that target a clinically relevant group of receptors within the tumor necrosis factor receptor superfamily (TNFRSF), including CD40 and CD95 (Fas/Apo-1), also require binding to Fc gamma receptors (FcγRs) to elicit a strong agonistic activity. This FcγR dependency largely relies on the mere cellular anchoring through the antibody’s Fc domain and does not involve the engagement of FcγR signaling. The aim of this study was to elicit agonistic activity from αCD40 and αCD95 antibodies in a myeloma cell anchoring-controlled FcγR-independent manner. For this purpose, various antibody variants (IgG1, IgG1_N297A, Fab₂) against the TNFRSF members CD40 and CD95 were genetically fused to a single-chain-encoded B-cell activating factor (scBaff) trimer as a C-terminal myeloma-specific anchoring domain substituting for Fc domain-mediated FcγR binding. The antibody-scBaff fusion proteins were evaluated in binding studies and functional assays using tumor cell lines expressing one or more of the three receptors of Baff: BaffR, transmembrane activator and CAML interactor (TACI) and B-cell maturation antigen (BCMA). Cellular binding studies showed that the binding properties of the different domains within the fusion proteins remained fully intact in the antibody-scBaff fusion proteins. In co-culture assays of CD40- and CD95-responsive cells with BaffR, BCMA or TACI expressing anchoring cells, the antibody fusion proteins displayed strong agonism while only minor receptor stimulation was observed in co-cultures with cells without expression of Baff-interacting receptors. Thus, our CD40 and CD95 antibody fusion proteins display myeloma cell-dependent activity and promise reduced systemic side effects compared to conventional CD40 and CD95 agonists.

Elevated Concentrations of Soluble Fas and FasL in Multiple Sclerosis Patients with Antinuclear Antibodies

Antinuclear antibodies (ANA) are currently considered as an epiphenomenon of apoptotic processes, possibly in control of autoreactivity in patients with multiple sclerosis (MS). Apoptosis of reactive lymphocytes by the Fas/FasL system is described as an effective control mechanism for autoreactivity in MS. We aimed to provide a context to the potential link between ANA and peripheral lymphocyte apoptosis in MS. The presence of ANA was detected in sera by immunofluorescence assay, and concentrations of sFas and sFasL were determined in the sera of 44 and cerebrospinal fluid (CSF) of 11 relapsing-remitting (RR) MS patients using cytometric bead-based array, and their association with the disease characteristics was determined. ANA were detected in the sera of 43.2% of RRMS patients, and their frequency was the highest in patients with disease duration of less than one year (88,89%). In addition, the number of experienced relapses was lower in ANA-positive patients. Concentrations of sFasL were inversely associated with patients' expanded disability status scale (EDSS) scores. Low concentrations of both soluble factors strongly discriminated patients with moderate to severe disability, from patients with mild or absent disability only in a group of patients with prolonged disease duration (>10 years). Both soluble mediators were significantly higher in ANA-positive patients. FasL concentrations were inversely associated with the number of relapses. There is a potential link between the presence of ANA and peripheral lymphocyte apoptosis mediated by Fas/FasL system in MS, whose precise role and significance needs to be determined by future mechanistic studies.

Responsiveness to i.v. immunoglobulin therapy in patients with toxic epidermal necrolysis: A novel pharmaco-immunogenetic concept

Toxic epidermal necrolysis (TEN) represents a rare drug-induced autoimmune reaction with delayed-type hypersensitivity that initiates the process of developing massive keratinocyte apoptosis, dominantly in the dermoepidermal junction. Although the etiopathophysiology has not yet been fully elucidated, the binding of Fas ligand (FasL, CD95L) to the Fas receptor (CD95) was shown to play a key role in the induction of apoptosis in this syndrome. The knowledge of the role of immunoglobulin G (IgG) in inhibition of Fas-mediated apoptosis contributed to the introduction of i.v. Ig (IVIg) in the therapy of TEN patients. Despite great enthusiasm for this therapy at the end of the 1990s, subsequent studies in various populations and meta-analyses could not unequivocally confirm the efficacy of the IVIg-based treatment concept. Today, therefore, we are faced with the dilemmas of how to adjust therapy of TEN patients most effectively, which patients could benefit from IVIg therapy and what dose of the preparation should be administrated. The ground-breaking question is: do the host genetic profiles influence the responsiveness and side-effects of IVIg therapy in TEN patients? Based on recent pharmacological, immunological and genetic findings, we suggest that the variability of IVIg therapy outcomes in TEN patients may be related to functional variants in Fas, FasL and Fc-γ receptor genes. This novel concept could lead to improved quality of care for patients with TEN, facilitating personalized therapy to reduce mortality.

Inflammatory Responses Induced by the Rupture of Intracranial Aneurysms Are Modulated by miRNAs

Influence of an intracranial aneurysm (IA) rupture on the expression of miRNAs and the potential significance of the resulting changes remains poorly understood. We aimed to characterize the response to the IA rupture through the analysis of miRNAs in peripheral blood cells. Expression of small RNAs was investigated using deep transcriptome sequencing in patients in the acute phase of an IA rupture (first 72 h), in the chronic phase (3–15 months), and controls. A functional analysis and the potential interactions between miRNAs and target genes were investigated. We also measured the levels of proteins that were influenced by regulated miRNAs. We found that 106 mature miRNAs and 90 miRNA precursors were differentially expressed among the groups. The regulated miRNAs were involved in a variety of pathways, and the top pathway involved cytokine-cytokine receptor interactions. The identified miRNAs targeted the inflammatory factors HMGB1 and FASLG. Changes in their expression were detected at the mRNA and protein levels. IA rupture strongly influences the transcription profiles in peripheral blood cells. The regulated miRNAs were involved in the control of immune cell homeostasis. In summary, these results may aid in the elucidation of the molecular mechanisms that orchestrate the inflammatory response to IA rupture.

IL-6-driven FasL promotes NF-κBp65/PUMA-mediated apoptosis in portal hypertensive gastropathy

Mucosal epithelial apoptosis with non-specific inflammation is an essential pathological characteristic in portal hypertensive gastropathy (PHG). However, whether a coordinated crosstalk between myeloid cells and epithelial cells involved in PHG remains unclear. IL-6, which is induced in the mucosa of PHG patients and mice, promotes FasL production via enhancing NF-κBp65 activation in myeloid cells, while blockage of IL-6 signaling by Tocilizumab or deletion of NF-κBp65 in myeloid cells attenuates the inflammatory response and Fas/FasL-mediated epithelial apoptosis in PHG. IL-6-driven FasL from myeloid cells combines with epithelial Fas receptor to encourage NF-κBp65/PUMA-mediated epithelial apoptosis in PHG, and inhibition of NF-κBp65 or knockout of PUMA alleviates Fas/FasL-mediated epithelial apoptosis in PHG. These results indicate that IL-6 drives FasL generation via NF-κBp65 in myeloid cells to promote Fas/NF-κBp65/PUMA-mediated epithelial apoptosis in PHG, and this coordinated crosstalk between myeloid cells and epithelial cells may provide a potential therapeutic target for PHG.

Rapid On-Demand Extracellular Vesicle Augmentation with Versatile Oligonucleotide Tethers

Exosomes show potential as ideal vehicles for drug delivery because of their natural role in transferring biological cargo between cells. However, current methods to engineer exosomes without negatively impacting their function remain challenging. Manipulating exosome-secreting cells is complex and time-consuming, while direct functionalization of exosome surface proteins suffers from low specificity and low efficiency. We demonstrate a rapid, versatile, and scalable method with oligonucleotide tethers to enable diverse surface functionalization on both human and murine exosomes. These exosome surface modifiers, which range from reactive functional groups and small molecules to aptamers and large proteins, can readily and efficiently enhance native exosome properties. We show that cellular uptake of exosomes can be specifically altered with a tethered AS1411 aptamer, and targeting specificity can be altered with a tethered protein. We functionalize exosomes with an immunomodulatory protein, FasL, and demonstrate their biological activity both in vitro and in vivo. FasL-functionalized exosomes, when bioprinted on a collagen matrix, allows spatial induction of apoptosis in tumor cells and, when injected in mice, suppresses proliferation of alloreactive T cells. This oligonucleotide tethering strategy is independent of the exosome source and further circumvents the need to genetically modify exosome-secreting cells.

Effects of IL-10- and FasL-overexpressing dendritic cells on liver transplantation tolerance in a heterotopic liver transplantation rat model

Acute rejection is the major determinant for the long-term survival of donor liver after liver transplantation (LT). The aim of this study was to examine the therapeutic potential of interleukin (IL)-10-FasL-overexpressing immature dendritic cells (imDCs) to induce local immunosuppression in liver grafts. imDCs derived from donors were transduced by lentiviral vectors expressing human IL-10 and/or Fas ligand (FasL) gene(s), and the expression of surface molecules and the ability to induce T-cell proliferation were measured. imDCs were intraperitoneally injected into recipient rats as a model of LT to examine the rejection grade [Banff rejection activity index (RAI)], liver functions [Alanine aminotransferase, Aspartate aminotransferase (AST) and total bilirubin (TBIL)] and post-transplant survival. IL-10 and FasL co-transduction of imDCs induced a greater reduction in CD80, CD86 and major histocompatibility complex class II (MHC II) expression, as well as T-cell proliferation, but increased levels of IL-10 and FasL in culture supernatants compared with mono-transduced or untransduced imDCs (P < 0.05). The infusion of co-transduced imDCs in LT recipients reduced RAI scores, decreased plasma AST and TBIL, and prolonged survival compared with mono-transduced or untransduced imDC-treated liver allografts. These findings demonstrated that the transfusion of IL-10-FasL/imDCs enhanced immune tolerance and prolonged the survival of liver allografts after LT. The immunomodulatory activity of IL-10- and FasL-modified imDCs might be a new therapeutic approach to prevent organ rejection in clinical transplantation.

Fas, FasL and Foxp3 gene expression in post-liver transplant autoimmune hepatitis patients with and without acute rejection

Aim of the study

In this study we investigated Fas, FasL and Foxp3 expression in relation to liver graft rejection and its severity in autoimmune hepatitis (AIH) patients.

Material and methods

Twenty-three AIH patients including five post-transplant patients with acute rejection (AR) and 18 patients without AR (non-AR) were studied for Fas, FasL and Foxp3 gene expression in peripheral blood mononuclear cells on days 1, 3 and 7 after transplantation by real-time PCR. The relationships between gene expression and clinical features were determined.

Results

Real-time PCR showed various Fas gene expression levels with no significant difference between the days in AR patients (p = 0.52). In non-AR patients, Fas level increased from 0.98 ±0.24 fold on the first day to 1.89 ±0.42 fold on day 3 after transplantation (p < 0.01). In this group of patients, we also found a significant increase in FasL expression on day 7 (29.91 ±6.89 fold) compared to day 1 (13.50 ±7.44 fold, p < 0.05). Foxp3 gene expression in both groups showed decreased levels during the first week after transplantation. The decreased Foxp3 expression in AR patients was correlated with rejection activity index (r = 0.86, p < 0.0001).

Conclusions

Increased Fas and FasL gene expression levels in non-AR patients and decreased Foxp3 gene expression in both groups suggested the important role of these molecules in the alloreactive response after liver transplantation in AIH patients. Foxp3 expression might be useful for monitoring rejection severity.

Fas receptor induces apoptosis of synovial bone and cartilage progenitor populations and promotes bone loss in antigen-induced arthritis

Rheumatoid arthritis (RA) is an inflammatory joint disease that eventually leads to permanent bone and cartilage destruction. Fas has already been established as the regulator of inflammation in RA, but its role in bone formation under arthritic conditions is not completely defined. The aim of this study was to assess the effect of Fas inactivation on the bone damage during murine antigen-induced arthritis. Subchondral bone of wild-type (WT) and Fas-knockout (Fas^-/-) mice was evaluated by histomorphometry and microcomputerized tomography. Proportions of synovial bone and cartilage progenitors were assessed by flow cytometry. Synovial bone and cartilage progenitors were purified by fluorescence-activated cell sorting and expression of Fas and Fas-induced apoptosis were analyzed in vitro. Results showed that Fas^-/- mice developed attenuated arthritis characterized by preserved epiphyseal bone and cartilage. A proportion of the earliest CD200⁺ bone and cartilage progenitors was reduced in WT mice with arthritis and was unaltered in Fas^-/- mice. During osteoblastic differentiation in vitro, CD200⁺ cells express the highest levels of Fas and are removed by Fas ligation. These results suggest that Fas-induced apoptosis of early CD200⁺ osteoprogenitor population represents potential mechanism underlying the impaired bone formation in arthritis, so their preservation may represent the bone-protective mechanism during arthritis.-Lazić Mosler, E., Lukač, N., Flegar, D., Fadljević, M., Radanović, I., Cvija, H., Kelava, T., Ivčević, S., Šućur, A., Markotić, A., Katavić, V., Marušić, A., Grčević, D., Kovačić, N. Fas receptor induces apoptosis of synovial bone and cartilage progenitor populations and promotes bone loss in antigen-induced arthritis.

Neutralization Versus Reinforcement of Proinflammatory Cytokines to Arrest Autoimmunity in Type 1 Diabetes

As physiological pathways of intercellular communication produced by all cells, cytokines are involved in the pathogenesis of inflammatory insulitis as well as pivotal mediators of immune homeostasis. Proinflammatory cytokines including interleukins, interferons, transforming growth factor-β, tumor necrosis factor-α, and nitric oxide promote destructive insulitis in type 1 diabetes through amplification of the autoimmune reaction, direct toxicity to β-cells, and sensitization of islets to apoptosis. The concept that neutralization of cytokines may be of therapeutic benefit has been tested in few clinical studies, which fell short of inducing sustained remission or achieving disease arrest. Therapeutic failure is explained by the redundant activities of individual cytokines and their combinations, which are rather dispensable in the process of destructive insulitis because other cytolytic pathways efficiently compensate their deficiency. Proinflammatory cytokines are less redundant in regulation of the inflammatory reaction, displaying protective effects through restriction of effector cell activity, reinforcement of suppressor cell function, and participation in islet recovery from injury. Our analysis suggests that the role of cytokines in immune homeostasis overrides their contribution to β-cell death and may be used as potent immunomodulatory agents for therapeutic purposes rather than neutralized.

Tea Polyphenol Inhibits Allostimulation in Mixed Lymphocyte Culture

Green tea polyphenols are known to protect allogenic donor tissues from acute rejection by their recipients. This immunosuppressive effect may be generated by a unique chemical property of the major component, epigallocatechin-o-gallate (EGCG), which can block specific cell surface molecules of the donor tissues. To test this hypothesis, we examined the effects of EGCG on the murine mixed lymphocyte reactions. EGCG treatment of stimulator cells significantly attenuated the proliferation of responder T cells. The proliferation did not recover upon the secondary stimulations by fresh untreated cells or exogenous IL-2. Flow cytometric analyses showed that EGCG treatment decreased the staining intensities of various cell surface molecules including MHC II, which plays a major role in antigen presentation, and B7.1, B7.2, and their ligand, CD28, which are required for costimulatory signals in T-cell activation. These results suggest that an anergic state of alloreactive T cells may be induced by either weakening of antigen signaling or blockage of costimulatory signals with EGCG. Other possible mechanisms behind the immunosuppressive effect and a potential use of EGCG treatment of donor tissues in transplantation medicine are discussed.

A Fas Ligand (FasL)-Fused Humanized Antibody Against Tumor-Associated Glycoprotein 72 Selectively Exhibits the Cytotoxic Effect Against Oral Cancer Cells with a Low FasL/Fas Ratio

Altered expression of the Fas ligand (FasL)/Fas ratio exhibits a direct impact on the prognosis of cancer patients, and its impairment in cancer cells may lead to apoptosis resistance. Thus, the development of effective therapies targeting the FasL/Fas system may play an important role in the fight against cancer. In this study, we evaluated whether a fusion protein (hcc49scFv-FasL) comprising of the cytotoxicity domain of the FasL fused to a humanized antibody (CC49) against tumor-associated glycoprotein 72, which is expressed on oral squamous cell carcinoma (OSCC), can selectively kill OSCC cells with different FasL/Fas ratios. In clinical samples, the significantly low FasL and high Fas transcripts were observed in tumors compared with normal tissues. A lower FasL/Fas ratio was correlated with a worse prognosis of OSCC patients and higher proliferative and invasive abilities of OSCC cells. The hcc49scFv-FasL showed a selective cytotoxic effect on OSCC cells (Cal-27 and SAS) but not on normal oral keratinocytes cells (HOK) through apoptosis induction. Moreover, SAS cells harboring a lower FasL/Fas ratio than Cal-27 were more sensitive to the cytotoxic effect of hcc49scFv-FasL. Unlike wild-type FasL, hcc49scFv-FasL was not cleaved by matrix metalloproteinases and did not induce nonapoptotic signaling in SAS cells. In vivo, we found that hcc49scFv-FasL drastically reduced the formation of lymph node metastasis and decreased primary tumor growth in SAS orthotopic and subcutaneous xenograft tumor models. Collectively, our data indicate that a tumor-targeting antibody fused to the FasL can be a powerful tool for OSCC treatment, especially in populations with a low FasL/Fas ratio. Mol Cancer Ther; 16(6); 1102-13. ©2017 AACR.

Diagnostic significance of serum concentrations of soluble Fas ligand (sFasL) in children with autoimmune thyroid disease

INTRODUCTION

The aim of the study was to assess serum levels of sFasL as a marker of thyroid dysfunction in children with autoimmune thyroid disease (AITD).

DESIGN

The group comprised 45 newly diagnosed children with Hashimoto's thyroiditis and Graves' disease versus euthyroid control group: 11 with hypothyroidism (10 girls and 1 boy, aged 12.2 ± 1.9 years), 19 children with hyperthyroidism (15 girls and 4 boys, aged 12.4 ± 4.9 years) and 15 healthy subjects (7 girls and 8 boys, aged 10.5 ± 4.8 years).

METHODS

Thyroid function (TSH, fT4, fT3), autoimmune (ATG, ATPO, TRAb) and anthropometric (weight, height, BMI, BMI-SDS, Cole index) parameters were evaluated. sFasL concentration was measured by ELISA. Nonparametric statistical test and ROC analysis were performed to assess the data.

RESULTS

We found no significant differences in serum concentrations of sFasL between boys and girls in the studied groups. Significantly higher sFasL levels (median 0.26 ng/ml) were identified in children with hypothyroidism compared with the control group (median 0.06 ng/ml, p < 0.001) and in comparison to a group of children with hyperthyroidism (median 0.14 ng/ml, p < 0.05). ROC analysis indicates that sFasL effectively discriminated hypothyroid and healthy children (area under the curve/AUC = 0.897; p < 0,001; sensitivity: 100%, specificity: 73.3%), as well as both clinically opposing states: hyperthyroidism and hypothyroidism among themselves (AUC = 0.833; p= 0,003; sensitivity: 94,7%, specificity: 72.7%).

CONCLUSIONS

Our work shows that sFasL may be useful marker in the assessment of thyroid dysfunction in children with autoimmune thyroid disease.

Interferon-α-inducible Dendritic Cells Matured with OK-432 Exhibit TRAIL and Fas Ligand Pathway-mediated Killer Activity

Active human dendritic cells (DCs), which efficiently induce immune responses through their functions as antigen-presenting cells, exhibit direct anti-tumour killing activity in response to some pathogens and cytokines. These antigen-presenting and tumour killing abilities may provide a breakthrough in cancer immunotherapy. However, the mechanisms underlying this killer DC activity have not been fully proven, despite the establishment of interferon-α (IFN-α)-generated killer DCs (IFN-DCs). Here mature IFN-DCs (mIFN-DCs), generated from IFN-DCs primed with OK-432 (streptococcal preparation), exhibited elevated expression of CD86 and human leukocyte antigen-DR (minimum criteria for DC vaccine clinical trials) as well as antigen-presenting abilities comparable with those of mature IL-4-DCs (mIL-4-DCs). Interestingly, the killing activity of mIFN-DCs, which correlated with the expression of CD56 (natural killer cell marker) and was activated via the tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) and Fas ligand pathway, was stronger than that of IFN-DCs and remarkably stronger than that of mIL-4-DCs. Therefore, mIFN-DCs exhibit great potential as an anti-cancer vaccine that would promote both acquired immunity and direct tumour killing.

Mechanisms of Tolerance Induction by Hematopoietic Chimerism: The Immune Perspective

Hematopoietic chimerism is one of the effective approaches to induce tolerance to donor‐derived tissue and organ grafts without administration of life‐long immunosuppressive therapy. Although experimental efforts to develop such regimens have been ongoing for decades, substantial cumulative toxicity of combined hematopoietic and tissue transplants precludes wide clinical implementation. Tolerance is an active immunological process that includes both peripheral and central mechanisms of mutual education of coresident donor and host immune systems. The major stages include sequential suppression of early alloreactivity, establishment of hematopoietic chimerism and suppressor cells that sustain the state of tolerance, with significant mechanistic and temporal overlap along the tolerization process. Efforts to devise less toxic transplant strategies by reduction of preparatory conditioning focus on modulation rather than deletion of residual host immunity and early reinstitution of regulatory subsets at the central and peripheral levels. Stem Cells Translational Medicine2017;6:700–712

Novel technologies to engineer graft for tolerance induction

PURPOSE OF REVIEW

Conquering allograft rejection remains an elusive goal in spite of recent breakthroughs in the field of immunosuppression. Much of the problem lies in the toxicity and side-effects of long-term use of systemic immunosuppressant drugs, which are sometimes ineffective in controlling rejection, but also hinder establishment of transplant tolerance. In this review, we discuss novel technologies that use grafts engineered with immunomodulatory molecules as a means of inducing tolerance.

RECENT FINDINGS

Several recent studies have demonstrated the feasibility of engineering cells, tissues, or solid organ grafts with immunoregulatory biologics to achieve long termgraft survival without the use of chronic immunosuppression. This approach was shown to primarily change the ratio of T effector versus CD4+CD25+FoxP3+ T regulatory cells within the graft microenvironment in favor of attaining localized tolerance induction and maintenance.

SUMMARY

Localized immunomodulation using biologic-engineered allografts represent a new paradigm for achieving long-term graft survival in the absence of chronic use of immunosuppression. The manipulation of the graft, rather than the recipient, not only ensures short- and long-term safety by minimizing the adverse effects of immunosuppression, but also allows retention of immune competency critical for the ability of the recipient to fight infections and cancer.

Susceptibility to oral cancers with CD95 and CD95L promoter SNPs may vary with the site and gender

We investigated risk association of oral cancers (tongue and buccal mucosa cancers) with FAS (-1377G > A and FAS -670 A > G) and FASL (-844 T > C) SNPs, in males and females. A case-control study of 535 oral cancer and 525 control subjects was performed. SNPs were detected in the genomic DNA isolated from peripheral blood using PCR-RFLP. We report FASL -844 T > C SNPs increased risk for buccal mucosa cancer in females but not in males. On the other hand, FAS genotypes did not alter the risk of the cancers in both females and males. However, co-occurrence of FAS -1377 GA and -670 GG, FAS -1377 AA and -670 GG genotypes, and combined genotypes of FAS and FASL (FAS -1377 AA + FAS -670 GG + FASL -844 CC) alter male susceptibility towards tongue cancer. In females, combined genotypes of FAS (-1377GA and -670 AA) were found to be a risk factor of buccal mucosa cancer (OR = 3.27, CI = 1.28-8.36; P ≤ 0.01). FASL variants (GA and AA) increased tongue cancer risk in females who were tobacco users compared to non-tobacco users. In conclusion, SNPs of the FAS and FASL might alter risk of tongue and buccal mucosa cancers differentially, in a gender-dependent manner.

Killer B lymphocytes and their fas ligand positive exosomes as inducers of immune tolerance

Induction of immune tolerance is a key process by which the immune system is educated to modulate reactions against benign stimuli such as self-antigens and commensal microbes. Understanding and harnessing the natural mechanisms of immune tolerance may become an increasingly useful strategy for treating many types of allergic and autoimmune diseases, as well as for improving the acceptance of solid organ transplants. Our laboratory and others have been interested in the natural ability of some B lymphocytes to express the death-inducing molecule Fas ligand (FasL), and their ability to kill T helper (T_H) lymphocytes. We have recently shown that experimental transformation of human B cells by a non-replicative variant of Epstein-Barr virus (EBV) consistently resulted in high expression of functional FasL protein. The production and release of FasL⁺ exosomes that co-expressed major histocompatibility complex (MHC) class II molecules and had the capacity to kill antigen-specific T_H cells was also observed. Several lines of evidence indicate that FasL+ B cells and FasL⁺MHCII⁺ exosomes have important roles in natural immune tolerance and have a great deal of therapeutic potential. Taken together, these findings suggest that EBV-immortalized human B lymphoblastoid cell lines could be used as cellular factories for FasL⁺ exosomes, which would be employed to therapeutically establish and/or regain immune tolerance toward specific antigens. The goals of this review are to summarize current knowledge of the roles of FasL⁺ B cells and exosomes in immune regulation, and to suggest methods of manipulating killer B cells and FasL⁺ exosomes for clinical purposes.

Engineering of bone marrow cells with fas-ligand protein-enhances donor-specific tolerance to solid organs

Effective immunomodulation to induce tolerance to tissue/organ allografts is attained by infusion of donor lymphocytes endowed with killing capacity through ectopic expression of a short-lived Fas-ligand (FasL) protein. The same approach has proven effective in improving hematopoietic stem and progenitor cell engraftment. This study evaluates the possibility of substitution of immune cells for bone marrow cells (BMC) to induce FasL-mediated tolerance to solid organ grafts. Expression of FasL protein on BMC increased the survival of simultaneously grafted vascularized heterotopic cardiac grafts to 90%, as compared to 30% in recipients of naïve BMC. Similar results were obtained for skin allografts implanted into radiation chimeras at 1 week after bone marrow transplantation. Further reduction of preparative conditioning to busulfan resulted in acceptance of donor skin implanted at 2 weeks after transplantation of naïve and FasL-coated BMC, whereas third-party grafts were acutely rejected. The levels of donor chimerism were in the range of 0.7% to 12% at the time of skin grafting, with higher levels in recipients of FasL-coated BMC. It is concluded that FasL-mediated abrogation of alloimmune responses can be effectively attained with BMC. There is no threshold of donor chimerism, but tolerance to solid organs evolves during the process of donor-host mutual acceptance.

Interferon and tumor necrosis factor as humoral mechanisms coupling hematopoietic activity to inflammation and injury

Enhanced hematopoiesis accompanies systemic responses to injury and infection. Tumor necrosis factor (TNF) produced by injured cells and interferons (IFNs) secreted by inflammatory cells is a co-product of the process of clearance of debris and removal of still viable but dysfunctional cells. Concomitantly, these cytokines induce hematopoietic stem and progenitor cell (HSPC) activity as an intrinsic component of the systemic response. The proposed scenario includes induction of HSPC activity by type I (IFNα/β) and II (IFNγ) receptors within the quiescent bone marrow niches rendering progenitors responsive to additional signals. TNFα converges as a non-selective stimulant of HSPC activity and both cytokines synergize with other growth factors in promoting differentiation. These physiological signaling pathways of stress hematopoiesis occur quite frequent and do not cause HSPC extinction. The proposed role of IFNs and TNFs in stress hematopoiesis commends revision of their alleged involvement in bone marrow failure syndromes.

Physiological functions of TNF family receptor/ligand interactions in hematopoiesis and transplantation

Secretion of ligands of the tumor necrosis factor (TNF) superfamily is a conserved response of parenchymal tissues to injury and inflammation that commonly perpetuates elimination of dysfunctional cellular components by apoptosis. The same signals of tissue injury that induce apoptosis in somatic cells activate stem cells and initiate the process of tissue regeneration as a coupling mechanism of injury and recovery. Hematopoietic stem and progenitor cells upregulate the TNF family receptors under stress conditions and are transduced with trophic signals. The progeny gradually acquires sensitivity to receptor-mediated apoptosis along the differentiation process, which becomes the major mechanism of negative regulation of mature proliferating hematopoietic lineages and immune homeostasis. Receptor/ligand interactions of the TNF family are physiological mechanisms transducing the need for repair, which may be harnessed in pathological conditions and transplantation. Because these interactions are physiological mechanisms of injury, neutralization of these pathways has to be carefully considered in disorders that do not involve intrinsic aberrations of excessive susceptibility to apoptosis.

Antigen-Specific Priming is Dispensable in Depletion of Apoptosis-Sensitive T Cells for GvHD Prophylaxis

Prophylactic approaches to graft versus host disease (GvHD) have employed both phenotypic reduction of T cells and selective elimination of host-primed donor T cells in vitro and in vivo. An additional approach to GvHD prophylaxis by functional depletion of apoptosis-sensitive donor T cells without host-specific sensitization ex vivo showed remarkable reduction in GHD incidence and severity. We address the role and significance of antigen-specific sensitization of donor T cells and discuss the mechanisms of functional T cell purging by apoptosis for GvHD prevention. Host-specific sensitization is dispensable because migration is antigen-independent and donor T cell sensitization is mediated by multiple and redundant mechanisms of presentation of major and minor histocompatibility complex and tissue antigens by donor and host antigen-presenting cells. Our data suggest that potential murine and human GvH effectors reside within subsets of preactivated T cells susceptible to negative regulation by apoptosis prior to encounter of and sensitization to specific antigens.

Posttransplantation systemic immunomodulation with SA-FasL-engineered donor splenocytes has robust efficacy in preventing cardiac allograft rejection in mice

Apoptosis induced by the engagement of FasL with Fas receptor on the surface of lymphocytes is an important immune homeostatic mechanism that ensures tolerance to self-antigens under normal physiologic conditions. As such, FasL has been extensively tested as a tolerogenic molecule with the use of gene therapy in settings of autoimmunity and transplantation with conflicting outcomes. Although the mechanistic basis of these contradictory observations is largely unknown, the use of wild-type FasL and the means by which the gene was expressed may provide an explanation. To overcome these complications, we generated a chimeric FasL protein with streptavidin (SA-FasL) having potent apoptotic activity and displayed this molecule effectively and rapidly on biotinylated biologic membranes for immunomodulation. In the present study, we displayed SA-FasL on the surface of BALB/c splenocytes and injected 5 × 10(6) cells intraperitoneally into C57BL/6 recipients of BALB/c heart grafts on days 1, 3, and 5 after-transplantation. To control initial graft-reactive immune responses and facilitate FasL-mediated apoptosis, rapamycin was used as an immunosuppressant at 0.2 mg/kg daily for a total of 15 doses immediately after heart transplantation. All mice injected with SA-FasL-engineered donor splenocytes accepted their grafts during the 100-day observation period. In marked contrast, immunomodulation with control streptavidin protein-engineered BALB/c splenocytes had minimal effect on graft survival (mean survival, 21.4 ± 1.5 d). Taken together, these results establish posttransplantation systemic immunomodulation with SA-FasL-engineered donor splenocytes under transient cover of rapamycin as an effective regimen in preventing cardiac allograft rejection in rodents with important clinical implications.

Mouse T cells engineered to display on their surface a novel form of FasL protein undergo apoptosis when stimulated with alloantigens: implications for graft-versus-host disease

BACKGROUND

Allogeneic bone marrow transplantation as a therapeutic approach in the clinic suffers from graft-versus- host disease (GVHD) initiated and perpetuated by donor T cells responding to alloantigens in immunocompromised hosts. Although the depletion of mature T cells from bone marrow inoculum overcomes GVHD, this manipulation is associated with engraftment failure and early post-transplant infection complications. Therefore, approaches that specifically purge out alloreactive T cells in the bone marrow inoculum without major effect on alloantigen-nonreactive T cells may be effective in facilitating engraftment without complications of GVHD and infections.

METHODS

Inasmuch as Fas/FasL-induced apoptosis plays a critical role in self-tolerance, we tested whether the direct display of a novel form of FasL (SA-FasL) protein chimeric with streptavidin (SA) on the surface of T cells induces apoptosis in such cells in response to alloantigens. BALB/c and C57BL/6 total lymphocytes or purified T cells were biotinylated under physiologic conditions and engineered with SA-FasL protein taking advantage of the high-affinity interaction between biotin and SA.

RESULTS

All engineered cells displayed SA-FasL protein on their surface as determined by flow cytometry. When used as responders against irradiated, unmodified allogeneic stimulators, the SA-FasL-engineered T cells underwent apoptosis, which resulted in minimal proliferation. This effect was specific to SA-FasL; control SA protein-engineered T cells generated a potent proliferative alloresponse without significant apoptosis.

CONCLUSIONS

Taken together, these results demonstrate the feasibility of purging out alloreactive T cells by the display of SA-FasL protein on their surface with important implications for the prevention of GVHD associated with allogeneic bone marrow transplantation.

Resistance of hematopoietic progenitors to Fas-mediated apoptosis is actively sustained by NFκB with a characteristic transcriptional signature

Umbilical cord blood (UCB) is a good source of hematopoietic progenitors with increasing implementation in the clinical transplant setting. This study evaluates the molecular mechanisms of progenitor resistance to apoptosis triggered by Fas cross-linking. CD34(+) and lineage-negative progenitors survive short-term ex vivo incubation and are not induced into apoptosis by Fas cross-linking. Furthermore, brief exposure of UCB cells to Fas-ligand for 24-48 h does not impair quantitative severe combine immune deficiency (SCID) reconstitution activity and appears to foster myelomonocyte reconstitution. The transcriptome of Fas receptor-positive CD34(+) cells that survived an apoptotic challenge showed significant transcriptional upregulation of caspase-8, mucosa-associated lymphoid tissue lymphoma translocation gene-1 (MALT1), HtrA2, and GSK3β in addition to higher levels of c-FLICE inhibitory protein (FLIP), Bcl-2, and cytosolic inhibitor of apoptosis protein (cIAP) in all Fas-positive cells. Most prominent is the transcriptional upregulation of several key components the NFκB1 pathway including the membrane receptors TGF-β, interleukin-1 (IL-1), and TCR, the associated factor TNF receptor-associated factor-6 (TRAF6), and the converting enzymes TGF-β-activated kinase-1 (TAK1), double-stranded RNA-activated protein kinase (PKR), and α-catalytic subunit of IκB kinase (IKKα), that promote activation and nuclear translocation of this transcription factor. These data indicate that hematopoietic progenitors are not insensitive to apoptosis but are actively shielded from the extrinsic and intrinsic apoptotic pathways. This may occur through inherent transcriptional upregulation of the entire NFκB pathway in the presence of competent apoptotic signaling.

Fas signal promotes the immunosuppressive function of regulatory dendritic cells via the ERK/β-catenin pathway

Dendritic cells (DCs) play important roles in the initiation of immune response and also in the maintenance of immune tolerance. Now, many kinds of regulatory DCs with different phenotypes have been identified to suppress immune response and contribute to the control of autoimmune diseases. However, the mechanisms by which regulatory DCs can be regulated to exert the immunosuppressive function in the immune microenvironment remain to be fully investigated. In addition, how T cells, once activated, can feedback affect the function of regulatory DCs during immune response needs to be further identified. We previously identified a unique subset of CD11b(hi)Ia(low) regulatory DCs, differentiated from mature DCs or hematopoietic stem cells under a stromal microenvironment in spleen and liver, which can negatively regulate immune response in a feedback way. Here, we show that CD11b(hi)Ia(low) regulatory DCs expressed high level of Fas, and endothelial stromal cell-derived TGF-β could induce high expression of Fas on regulatory DCs via ERK activation. Fas ligation could promote regulatory DCs to inhibit CD4(+) T cell proliferation more significantly. Furthermore, Fas ligation preferentially induced regulatory DCs to produce IL-10 and IP-10 via ERK-mediated inactivation of GSK-3 and subsequent up-regulation of β-catenin. Interestingly, activated T cells could promote regulatory DCs to secrete more IL-10 and IP-10 partially through FasL. Therefore, our results demonstrate that Fas signal, at least from the activated T cells, can promote the immunosuppressive function of Fas-expressing regulatory DCs, providing a new manner for the regulatory DCs to regulate adaptive immunity.

Association between FAS A670G polymorphism and susceptibility to cervical cancer: evidence from a meta-analysis

Previous studies published to evaluate the association between FAS A670G polymorphism and susceptibility to cervical cancer provided conflicting findings. A meta-analysis of published case-control studies was performed to get a comprehensive evidence for the possible association. We searched in PubMed and Wanfang databases for eligible studies published before February 10, 2013. The odds ratio (OR) with 95% confidence interval (95% CI) was used to evaluate the association. Ten studies with a total of 4,904 participants were finally included into the meta-analysis. Overall, there was no obvious association between FAS A670G polymorphism and susceptibility to cervical cancer under all four genetic models (G versus A: OR = 0.97, 95% CI 0.84-1.11, P = 0.64; GG versus AA: OR = 0.92, 95% CI 0.69-1.24, P = 0.60; GG/AG versus AA: OR = 0.99, 95% CI 0.77-1.26, P = 0.92; GG versus AA/AG: OR = 0.92; 95% CI 0.68-1.25, P = 0.59). Subgroup analyses by ethnicity further showed that there was no association between FAS A670G polymorphism and susceptibility to cervical cancer in both Caucasians and Asians. There was no risk of publication bias. In summary, the meta-analysis suggests that there is no association between FAS A670G polymorphism and susceptibility to cervical cancer in both Caucasians and Asians.

Kupffer cells potentiate liver sinusoidal endothelial cell injury in sepsis by ligating programmed cell death ligand-1

PD-1 and PD-L1 have been reported to provide peripheral tolerance by inhibiting TCR-mediated activation. We have reported that PD-L1-/- animals are protected from sepsis-induced mortality and immune suppression. Whereas studies indicate that LSECs normally express PD-L1, which is also thought to maintain local immune liver tolerance by ligating the receptor PD-1 on T lymphocytes, the role of PD-L1 in the septic liver remains unknown. Thus, we hypothesized initially that PD-L1 expression on LSECs protects them from sepsis-induced injury. We noted that the increased vascular permeability and pSTAT3 protein expression in whole liver from septic animals were attenuated in the absence of PD-L1. Isolated LSECs taken from septic animals, which exhibited increased cell death, declining cell numbers, reduced cellular proliferation, and VEGFR2 expression (an angiogenesis marker), also showed improved cell numbers, proliferation, and percent VEGFR2(+) levels in the absence of PD-L1. We also observed that sepsis induced an increase of liver F4/80(+)PD-1(+)-expressing KCs and increased PD-L1 expression on LSECs. Interestingly, PD-L1 expression levels on LSECs decreased when PD-1(+)-expressing KCs were depleted with clodronate liposomes. Contrary to our original hypothesis, we document here that increased interactions between PD-1(+) KCs and PD-L1(+) LSECs appear to lead to the decline of normal endothelial function-essential to sustain vascular integrity and prevent ALF. Importantly, we uncover an underappreciated pathological aspect of PD-1:PD-L1 ligation during inflammation that is independent of its normal, immune-suppressive activity.

Enhanced killing activity of regulatory T cells ameliorates inflammation and autoimmunity

Regulatory T cells (Treg) are pivotal suppressor elements in immune homeostasis with potential therapeutic applications in inflammatory and autoimmune disorders. Using Treg as vehicles for targeted immunomodulation, a short-lived Fas-ligand (FasL) chimeric protein (killer Treg) was found efficient in preventing the progression of autoimmune insulitis in NOD mice, and amelioration of chronic colitis and graft versus host disease. The main mechanisms of disease suppression by killer Treg are: a) in the acute phase induction of apoptosis in effector cells at the site of inflammation decreases the pathogenic burden, and b) persistent increase in FoxP3⁺ Treg with variable CD25 co-expression induced by FasL sustains disease suppression over extended periods of time. Reduced sensitivity of Treg to receptor-mediated apoptosis under inflammatory conditions makes them optimal vehicles for targeted immunotherapy using apoptotic agents.

Association between FAS-1377 G/A polymorphism and susceptibility to gastric cancer: evidence from a meta-analysis

Previous studies published to evaluate the association between FAS-1377 G/A polymorphism and susceptibility to gastric cancer provided inconclusive outcomes. To derive a more precise estimation on this association, a meta-analysis of published case-control studies was performed. Eligible studies up to November 13, 2012 were identified from PubMed, Wanfang Medicine database, and Web of Science. Nine studies with a total of 2,086 cases and 2,701 controls were finally included into this meta-analysis. Overall, there was an obvious association between FAS-1377 G/A polymorphism and susceptibility to gastric cancer (for AA versus GG: odds ratio (OR) = 1.38; 95 % confidence interval (CI) 1.00-1.91, P = 0.05; for AA versus

GA/GG

OR = 1.28; 95 %CI 1.07-1.53, P = 0.006). After excluding studies with low quality, there was no between-study heterogeneity, and there was still an obvious association between FAS-1377 G/A polymorphism and susceptibility to gastric cancer (for AA versus GG: OR = 1.25; 95 %CI 1.02-1.52, P = 0.03; for AA versus

GA/GG

OR = 1.27; 95 %CI 1.05-1.53, P = 0.01). Subgroup analyses by ethnicity showed that the association above was still obvious in Asians, but the association was still unclear in Caucasians owing to the limited sample. In summary, this meta-analysis suggests that the FAS-1377 G/A polymorphism is associated with susceptibility to gastric cancer, especially in Asians. More studies from Caucasians are needed to provide further evidence for the possible association in Caucasians.

Alloreactive CD8 T cells rescued from apoptosis during co-stimulation blockade by Toll-like receptor stimulation remain susceptible to Fas-induced cell death

Blockade of co-stimulatory signals to T cells is extremely effective for the induction of transplantation tolerance in immunologically naive rodents. However, infections and inflammation compromise the efficacy of co-stimulation blockade regimens for the induction of tolerance, thereby stimulating the rejection of allografts. Previous studies have shown that stimulation of innate immunity abrogates tolerance induction by preventing the deletion of alloreactive CD8(+) T cells that normally occurs during co-stimulation blockade. Although inflammation prevents the deletion of alloreactive T cells during co-stimulation blockade, it is not known if this resistance to cell death is the result of a mechanism intrinsic to the T cell. Here, we used syngeneic bone marrow chimeric mice that contain a trace population of T-cell receptor transgenic alloreactive CD8(+) T cells to investigate the early apoptotic signature and activation status of alloreactive T cells following exposure to inflammatory signals during co-stimulation blockade with an antibody specific for CD154. Our findings revealed that the presence of bacterial lipopolysaccharide during co-stimulation blockade enhanced the early activation of alloreactive CD8(+) T cells, as indicated by the up-regulation of CD25 and CD69, suppressed Fas ligand expression, and prevented apoptotic cell death. However, alloreactive CD8(+) T cells from lipopolysaccharide-treated mice remained sensitive to Fas-mediated apoptosis in vitro. These findings suggest that alloreactive T cells rescued from deletion during co-stimulation blockade by inflammation are still sensitive to pro-apoptotic signals and that stimulating these apoptotic pathways during co-stimulation blockade may augment the induction of tolerance.

Soluble FAS in the prediction of benefit from cetuximab and irinotecan for patients with advanced colorectal cancer

The FAS/FASL system, comprising membrane-bound (mFAS and mFASL) and soluble forms (sFAS and sFASL), has been related to apoptosis driven by chemotherapy administration. In vitro experiments show chemotherapy upregulating membrane-bound forms, leading to an increase of receptor availability (at 24-72 h) and favoring apoptosis. The regulatory effect of chemotherapy on sFAS in patients has never been explored prospectively in advanced colorectal cancer (ACRC). We performed a pharmacodynamic study to address sFAS/sFASL variation. A prospective phase II translational multicenter study was designed to evaluate progression-free rate (PFR) in patients with ACRC treated with irinotecan and cetuximab in third-line therapy. The effect of sFAS was studied in vitro in colorectal cancer cell lines. Our results showed that statistically significant changes were observed in sFAS at 24-72 h compared to baseline levels in the pharmacodynamic study. Of the 93 patients enrolled in the prospective study in third-line therapy with cetuximab-irinotecan, 85 were evaluated for sFAS/sFASL changes at 48 h. There was no difference in PFR at 4 months between patients with sFAS and sFASL changes. In vitro analysis showed that although LoVo cell lines were sensitive to oxaliplatin and fluorouracil due to modulation of sFAS and FAS, HT29 lines were not. In summary, chemotherapy regulates FAS soluble fractions in vitro and in vivo, but does not predict PFR in ACRC patients undergoing third-line therapy with the combination of cetuximab and irinotecan.

Immune privilege of stem cells

Immune privilege provides protection to vital tissues or cells of the body when foreign antigens are introduced into these sites. The modern concept of relative immune privilege applies to a variety of tissues and anatomical structures, including the hair follicles and mucosal surfaces. Even sites of chronic inflammation and developing tumors may acquire immune privilege by recruiting immunoregulatory effector cells. Adult stem cells are no exception. For their importance and vitality, many adult stem cell populations are believed to be immune privileged. A preimplantation-stage embryo that derives from a totipotent stem cell (i.e., a fertilized oocyte) must be protected from maternal allo-rejection for successful implantation and development to occur. Embryonic stem cells, laboratory-derived cell lines of preimplantation blastocyst-origin, may, therefore, retain some of the immunological properties of the developing embryo. However, embryonic stem cells and their differentiated tissue derivatives transplanted into a recipient do not necessarily have an ability to subvert immune responses to the extent required to exploit their pluripotency for regenerative medicine. In this review, an extended definition of immune privilege is developed and the capacity of adult and embryonic stem cells to display both relative and acquired immune privilege is discussed. Furthermore, we explore how these intrinsic properties of stem cells may one day be harnessed for therapeutic gain.

Attenuation of Murine Graft-Versus-Host Disease by a Tea Polyphenol

Since donor T-cells' allorecognition of host antigens is a prerequisite for the onset of graft-versus-host disease (GVHD), blocking their cellular signaling pathways can decrease the severity of GVHD. We hypothesized that epigallocatechin-3-gallate (EGCG), due to its strong affinity to macromolecules, would adhere to surface molecules of donor T cells, inhibit their allorecognition, and attenuate GVHD in the recipient. We tested the hypothesis by treating donor splenocytes with EGCG in both in vitro and in vivo murine GVHD models. EGCG treatment decreased the proliferation of donor cells in MLR cultures and secretion of IL-2 and INF-γ. It also reduced the epitope detection of CD3∊, CD4, and CD28 but did not downregulate the protein expression of these molecules, suggesting blockage of cell surface stimulatory signals. Similarly, EGCG treatment did not decrease mRNA expression for some of these molecules but decreased mitogen-induced cell proliferation, indicating that EGCG did not interfere the transcription of these genes but affected cell proliferation pathways. Furthermore, EGCG-treated donor splenocytes, when transplanted into immunocompromized recipient mice, decreased of proliferation, and the treatment extended the recipients' survival at least during the early stage of GVHD. These results strongly suggest that EGCG attenuates GVHD by both blocking specific cell surface molecules and affecting the donor T-cell proliferation pathways.

Targeted mutation of Fas ligand gene attenuates brain inflammation in experimental stroke

Inflammation is an important contributing mechanism in ischemic brain injury. The current study elucidates a previously unexplored role of Fas ligand (FasL) in post-stroke inflammatory responses that is independent of its well-known effect in triggering apoptosis. Focal cerebral ischemia was induced for 2 h by right middle cerebral artery occlusion (MCAO) in FasL mutant (gld) and wild-type mice. FasL mutation profoundly reduced brain damage and improved neurological performance from 6 to 72 h after ischemic stroke. The production of inflammatory cytokines in the brain was attenuated in gld mice after ischemia in the absence of dramatic change in inflammatory cell apoptosis. FasL mutation attenuated the recruitment of peripheral inflammatory cells (neutrophil) and inhibited the activation of residential glial cells (microglia and astrocyte). FasL mutation reduced CD8(+) T cells and turned the Th1/Th2 balance towards Th2 in the brain and peripheral blood after cerebral ischemia. In contrast to cerebral ischemia, the molecular and cellular inflammatory changes induced by intracerebroventricular injection of lipopolysaccharide (LPS) were also attenuated in gld mice. Moreover, the soluble FasL (sFasL) and phospho-SAPK/JNK were decreased in gld mice, suggesting that the inflammatory role of FasL in experimental stroke might relate to sFasL and the c-Jun N-terminal kinase (JNK) signaling pathway. Taken together, our data suggest a novel role of FasL in the damaging inflammatory responses associated with cerebral ischemia. Neutralization of FasL may be a novel therapeutic strategy to suppress post-stroke inflammation and improve the long-term outcomes of stroke.