CD40 ligand (CD154) triggers a short-term CD4(+) T cell activation response that results in secretion of immunomodulatory cytokines and apoptosis

Single-cell RNA sequencing in ovarian cancer: Current progress and future prospects

Ovarian cancer is one of the most prevalent gynaecological malignancies. The rapid development of single-cell RNA sequencing (scRNA-seq) has allowed scientists to use this technique to study ovarian cancer development, heterogeneity, and tumour environment. Although multiple original research articles have reported the use of scRNA-seq in understanding ovarian cancer and how therapy resistance occurs, there is a lack of a comprehensive review that could summarize the findings from multiple studies. Therefore, this review aimed to fill this gap by comparing and summarizing the results from different studies that have used scRNA-seq in understanding ovarian cancer development, heterogeneity, tumour microenvironment, and treatment resistance. This review will begin with an overview of scRNA-seq workflow, followed by a discussion of various applications of scRNA-seq in studying ovarian cancer. Next, the limitations and future directions of scRNA-seq in ovarian cancer research will be presented.

Machine learning-derived prognostic signature integrating programmed cell death and mitochondrial function in renal clear cell carcinoma: identification of PIF1 as a novel target

BACKGROUND

The pathogenesis and progression of renal cell carcinoma (RCC) involve complex programmed cell death (PCD) processes. As the powerhouse of the cell, mitochondria can influence cell death mechanisms. However, the prognostic significance of the interplay between mitochondrial function (MF) and PCD remains unclear.

METHODS

We collected sets of genes related to PCD and MF. Using a powerful machine learning algorithm framework, we investigated the relationship between MF and PCD in different cohorts of patients and developed a machine learning-derived prognostic signature (mpMLDPS) related to MF and PCD. Finally, the most appropriate prognostic markers for RCC were screened by survival analysis and clinical correlation analysis, and the effects on renal cancer cells were analysed in vitro.

RESULTS

mpMLDPS was significantly correlated with the prognosis of RCC patients, and the prognosis was worse in the high mpMLDPS group, and this result was also validated in external independent cohorts. There were associations between mpMLDPS and immune checkpoints, tumour microenvironment, somatic mutations, and drug sensitivity. Finally, a novel RCC prognostic marker PIF1 was identified in model genes. The knockdown of PIF1 in vitro inhibited the progression of renal carcinoma cells.

CONCLUSION

mpMLDPS has great potential to serve as a reliable clinical signature to improve the accuracy and reliability of prognostic assessment in RCC patients, thereby choosing the appropriate therapeutic regimen in clinical practice. PIF1 is also expected to be a novel target for the clinical treatment of RCC.

VISTA nonredundantly regulates proliferation and CD69low γδ T cell accumulation in the intestine in murine sepsis

Sepsis is a dysregulated systemic immune response to infection i.e. responsible for ∼35% of in-hospital deaths at a significant fiscal healthcare cost. Our laboratory, among others, has demonstrated the efficacy of targeting negative checkpoint regulators (NCRs) to improve survival in a murine model of sepsis, cecal ligation and puncture (CLP). B7-CD28 superfamily member, V-domain immunoglobulin suppressor of T cell activation (VISTA), is an ideal candidate for strategic targeting in sepsis. VISTA is a 35 to 45 kDa type 1 transmembrane protein with unique biology that sets it apart from all other NCRs. We recently reported that VISTA-/- mice had a significant survival deficit post-CLP, which was rescued upon adoptive transfer of a VISTA-expressing pMSCV-mouse Foxp3-EF1α-GFP-T2A-puro stable Jurkat cell line (Jurkatfoxp3 T cells). Based on our prior study, we investigated the effector cell target of Jurkatfoxp3 T cells in VISTA-/- mice. γδ T cells are a powerful lymphoid subpopulation that require regulatory fine-tuning by regulatory T cells to prevent overt inflammation/pathology. In this study, we hypothesized that Jurkatfoxp3 T cells nonredundantly modulate the γδ T cell population post-CLP. We found that VISTA-/- mice have an increased accumulation of intestinal CD69low γδ T cells, which are not protective in murine sepsis. Adoptive transfer of Jurkatfoxp3 T cells decreased the intestinal γδ T cell population, suppressed proliferation, skewed remaining γδ T cells toward a CD69high phenotype, and increased soluble CD40L in VISTA-/- mice post-CLP. These results support a potential regulatory mechanism by which VISTA skews intestinal γδ T cell lineage representation in murine sepsis.

T cell activation and deficits in T regulatory cells are associated with major depressive disorder and severity of depression

Major depressive disorder (MDD) is associated with T cell activation, but no studies have examined the combined effects of T cell activation and deficits in T regulatory (Treg) cells on the severity of acute phase MDD. Using flow cytometry, we determined the percentage and median fluorescence intensity of CD69, CD71, CD40L, and HLADR-bearing CD3+, CD4+, and CD8+ cells, and cannabinoid type 1 receptor (CB1), CD152 and GARP (glycoprotein A repetitions predominant)-bearing CD25+ FoxP3 T regulatory (Treg) cells in 30 MDD patients and 20 healthy controls in unstimulated and stimulated (anti-CD3/CD28) conditions. Based on cytokine levels, we assessed M1 macrophage, T helper (Th)-1 cell, immune-inflammatory response system (IRS), T cell growth, and neurotoxicity immune profiles. We found that the immune profiles (including IRS and neurotoxicity) were significantly predicted by decreased numbers of CD152 or GARP-bearing CD25+ FoxP3 cells or CD152 and GARP expression in combination with increases in activated T cells (especially CD8+ CD40L+ percentage and expression). MDD patients showed significantly increased numbers of CD3+ CD71+, CD3+ CD40L+, CD4+ CD71+, CD4+ CD40L+, CD4+ HLADR+, and CD8+ HLADR+ T cells, increased CD3+ CD71+, CD4+ CD71+ and CD4+ HLADR+ expression, and lowered CD25+ FoxP3 expression and CD25+ FoxP+ CB1+ numbers as compared with controls. The Hamilton Depression Rating Scale score was strongly predicted (between 30 and 40% of its variance) by a lower number of CB1 or GARP-bearing Treg cells and one or more activated T cell subtypes (especially CD8+ CD40L+). In conclusion, increased T helper and cytotoxic cell activation along with decreased Treg homeostatic defenses are important parts of MDD that lead to enhanced immune responses and, as a result, neuroimmunotoxicity.

CD40L modulates CD4+ T-cell activation through receptor for activated C kinase 1

Inhibition of the co-stimulatory ligand CD40L has shown beneficial effects in many experimental models of autoimmune disease and inflammation. Here, we show that CD40L deficiency in T cells in mice causes a reduction of CD4+ T-cell activation and specifically a strong reduction in IFN-γ-producing Th1 cells. In vitro, we could not reproduce this antigen presenting cell-dependent effects, but found that T-cell CD40L affects cell death and proliferation. We identified receptor of activated C kinase, the canonical PKC binding partner and known to drive proliferation and apoptosis, as a mediator of CD40L reverse signaling. Furthermore, we found that CD40L clustering stabilizes IFN-γ mediated Th1 polarization through STAT1, a known binding partner of receptor of activated C kinase. Together this highlights the importance of both CD40L forward and reverse signaling.

The bidirectional immune crosstalk in metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is an unabated risk factor for end-stage liver diseases with no available therapies. Dysregulated immune responses are critical culprits of MASLD pathogenesis. Independent contributions from either the innate or adaptive arms of the immune system or their unidirectional interplay are commonly studied in MASLD. However, the bidirectional communication between innate and adaptive immune systems and its impact on MASLD remain insufficiently understood. Given that both innate and adaptive immune cells are indispensable for the development and progression of inflammation in MASLD, elucidating pathogenic contributions stemming from the bidirectional interplay between these two arms holds potential for development of novel therapeutics for MASLD. Here, we review the immune cell types and bidirectional pathways that influence the pathogenesis of MASLD and highlight potential pharmacologic approaches to combat MASLD based on current knowledge of this bidirectional crosstalk.

Vaccine plus microbicide effective in preventing vaginal SIV transmission in macaques

The human immunodeficiency virus epidemic continues in sub-Saharan Africa, and particularly affects adolescent girls and women who have limited access to antiretroviral therapy. Here we report that the risk of vaginal simian immunodeficiency virus (SIV)mac251 acquisition is reduced by more than 90% using a combination of a vaccine comprising V1-deleted (V2 enhanced) SIV envelope immunogens with topical treatment of the zinc-finger inhibitor SAMT-247. Following 14 weekly intravaginal exposures to the highly pathogenic SIVmac251, 80% of a cohort of 20 macaques vaccinated and treated with SAMT-247 remained uninfected. In an arm of 18 vaccinated-only animals without microbicide, 40% of macaques remained uninfected. The combined SAMT-247/vaccine regimen was significantly more effective than vaccination alone. By analysing immune correlates of protection, we show that, by increasing zinc availability, SAMT-247 increases natural killer cytotoxicity and monocyte efferocytosis, and decreases T-cell activation to augment vaccine-induced protection.

Preclinical development of a first-in-class vaccine encoding HER2, Brachyury and CD40L for antibody enhanced tumor eradication

The induction of antiviral innate immunity by systemic immunization with live virus can be employed to positively impact the response to therapeutic vaccination. We previously demonstrated that systemic immunization with a non-replicating MVA encoding CD40 ligand (CD40L) enhances innate immune cell activation and function, and triggers potent antitumor CD8⁺ T cell responses in different murine tumor models. Antitumor efficacy was increased when combined with tumor targeting antibodies. Here we report the development of TAEK-VAC-HerBy (TVH), a first-in-class human tumor antibody enhanced killing (TAEK) vaccine based on the non-replicating MVA-BN viral vector. It encodes the membrane bound form of human CD40L, HER2 and the transcription factor Brachyury. TVH is designed for therapeutic use in HER2- or Brachyury-expressing cancer patients in combination with tumor targeting antibodies. To preclude possible oncogenic activities in infected cells and to prevent binding of vaccine-encoded HER2 by monoclonal antibodies trastuzumab and pertuzumab, genetic modifications of HER2 were introduced in the vaccine. Brachyury was genetically modified to prevent nuclear localization of the protein thereby inhibiting its transcriptional activity. CD40L encoded in TVH enhanced human leukocyte activation and cytokine secretion in vitro. Lastly, TVH intravenous administration to non-human primates was proven immunogenic and safe in a repeat-dose toxicity study. Nonclinical data presented here highlight TVH as a first-in-class immunotherapeutic vaccine platform currently under clinical investigation.

Interactions between Platelets and Tumor Microenvironment Components in Ovarian Cancer and Their Implications for Treatment and Clinical Outcomes

Platelets, the primary operatives of hemostasis that contribute to blood coagulation and wound healing after blood vessel injury, are also involved in pathological conditions, including cancer. Malignancy-associated thrombosis is common in ovarian cancer patients and is associated with poor clinical outcomes. Platelets extravasate into the tumor microenvironment in ovarian cancer and interact with cancer cells and non-cancerous elements. Ovarian cancer cells also activate platelets. The communication between activated platelets, cancer cells, and the tumor microenvironment is via various platelet membrane proteins or mediators released through degranulation or the secretion of microvesicles from platelets. These interactions trigger signaling cascades in tumors that promote ovarian cancer progression, metastasis, and neoangiogenesis. This review discusses how interactions between platelets, cancer cells, cancer stem cells, stromal cells, and the extracellular matrix in the tumor microenvironment influence ovarian cancer progression. It also presents novel potential therapeutic approaches toward this gynecological cancer.

Novel Functions of Integrins as Receptors of CD154: Their Role in Inflammation and Apoptosis

CD154, an inflammatory mediator also known as CD40 ligand, has been identified as a novel binding partner for some members of the integrin family. The αIIbβ3, specifically expressed on platelets, was the first integrin to be described as a receptor for CD154 after CD40. Its interaction with soluble CD154 (sCD154) highly contributes to thrombus formation and stability. Identifying αIIbβ3 opened the door for investigating other integrins as partners of CD154. The αMβ2 expressed on myeloid cells was shown capable of binding CD154 and contributing as such to cell activation, adhesion, and release of proinflammatory mediators. In parallel, α5β1 communicates with sCD154, inducing pro-inflammatory responses. Additional pathogenic effects involving apoptosis-preventing functions were exhibited by the CD154–α5β1 dyad in T cells, conferring a role for such interaction in the survival of malignant cells, as well as the persistence of autoreactive T cells. More recently, CD154 receptors integrated two new integrin members, αvβ3 and α4β1, with little known as to their biological significance in this context. This article provides an overview of the novel role of integrins as receptors of CD154 and as critical players in pro-inflammatory and apoptotic responses.

Superagonistic CD28 stimulation induces IFN-γ release from mouse T helper 1 cells in vitro and in vivo

Like human Th1 cells, mouse Th1 cells also secrete IFN-γ upon stimulation with a superagonistic anti-CD28 monoclonal antibody (CD28-SA). Crosslinking of the CD28-SA via FcR and CD40-CD40L interactions greatly increased IFN-γ release. Our data stress the utility of the mouse as a model organism for immune responses in humans.

Proinflammatory cytokines and ARDS pulmonary edema fluid induce CD40 on human mesenchymal stromal cells-A potential mechanism for immune modulation

Human mesenchymal stem/stromal cells (hMSCs) are a promising therapy for acute respiratory distress syndrome (ARDS) and other inflammatory conditions. While considerable research has focused on paracrine effects and mitochondrial transfer that improve lung fluid balance, hMSCs are well known to have immunomodulatory properties as well. Some of these immunomodulatory properties have been related to previously reported paracrine effectors such as indoleamine-2,3-dioxygenase (IDO), but these effects cannot fully account for cell-contact dependent immunomodulation. Here, we report that CD40 is upregulated on hMSCs under the same conditions previously reported to induce IDO. Further, CD40 transcription is also upregulated on hMSCs by ARDS pulmonary edema fluid but not by hydrostatic pulmonary edema fluid. Transcription of CD40, as well as paracrine effectors TSG6 and PTGS2 remained significantly upregulated for at least 12 hours after withdrawal of cytokine stimulation. Finally, induction of this immune phenotype altered the transdifferentiation of hMSCs, one of their hallmark properties. CD40 may play an important role in the immunomodulatory effects of hMSCs in ARDS and inflammation.

Expression of CD40L by the ALVAC-Simian Immunodeficiency Virus Vector Abrogates T Cell Responses in Macaques

Immunization with recombinant ALVAC/gp120 alum vaccine provided modest protection from human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) acquisition in humans and macaques. Vaccine-mediated protection was associated with the elicitation of IgG against the envelope V2 loop and of envelope-specific CD4+ T cell responses. We hypothesized that the simultaneous expression of the costimulatory molecule CD40L (CD154) by the ALVAC-HIV vector could increase both protective humoral and cellular responses. We engineered an ALVAC-SIV coexpressing CD40L with SIVmac251 (ALVAC-SIV/CD40L) gag, pol, and env genes. We compared its immunogenicity in macaques with that of a canonical ALVAC-SIV, with both given as a vector-prime/gp120 in alum boost strategy. The ALVAC-SIV/CD40L was superior to the ALVAC-SIV regimen in inducing binding and tier 1 neutralizing antibodies against the gp120. The increase in humoral responses was associated with the expression of the membrane-bound form of the CD40L by CD4+ T cells in lymph nodes. Unexpectedly, the ALVAC-SIV/CD40L vector had a blunting effect on CD4+ Th1 helper responses and instead favored the induction of myeloid-derived suppressor cells, the immune-suppressive interleukin-10 (IL-10) cytokine, and the down-modulatory tryptophan catabolism. Ultimately, this strategy failed to protect macaques from SIV acquisition. Taken together, these results underlie the importance of balanced vaccine-induced activating versus suppressive immune responses in affording protection from HIV.IMPORTANCE CD40-CD40 ligand (CD40L) interaction is crucial for inducing effective cytotoxic and humoral responses against pathogens. Because of its immunomodulatory function, CD40L has been used to enhance immune responses to vaccines, including candidate vaccines for HIV. The only successful vaccine ever tested in humans utilized a strategy combining canarypox virus-based vector (ALVAC) together with an envelope protein (gp120) adjuvanted in alum. This strategy showed limited efficacy in preventing HIV-1/SIV acquisition in humans and macaques. In both species, protection was associated with vaccine-induced antibodies against the HIV envelope and CD4+ T cell responses, including type 1 antiviral responses. In this study, we tested whether augmenting CD40L expression by coexpressing it with the ALVAC vector could increase the protective immune responses. Although coexpression of CD40L did increase humoral responses, it blunted type 1 CD4+ T cell responses against the SIV envelope protein and failed to protect macaques from viral infection.

Long-term tolerance of islet allografts in nonhuman primates induced by apoptotic donor leukocytes

Immune tolerance to allografts has been pursued for decades as an important goal in transplantation. Administration of apoptotic donor splenocytes effectively induces antigen-specific tolerance to allografts in murine studies. Here we show that two peritransplant infusions of apoptotic donor leukocytes under short-term immunotherapy with antagonistic anti-CD40 antibody 2C10R4, rapamycin, soluble tumor necrosis factor receptor and anti-interleukin 6 receptor antibody induce long-term (≥1 year) tolerance to islet allografts in 5 of 5 nonsensitized, MHC class I-disparate, and one MHC class II DRB allele-matched rhesus macaques. Tolerance in our preclinical model is associated with a regulatory network, involving antigen-specific Tr1 cells exhibiting a distinct transcriptome and indirect specificity for matched MHC class II and mismatched class I peptides. Apoptotic donor leukocyte infusions warrant continued investigation as a cellular, nonchimeric and translatable method for inducing antigen-specific tolerance in transplantation.

Injection of donor apoptotic cells induces graft tolerance in mice. Here the authors combine this approach with short immunosuppressive therapy to achieve long-term tolerance to allogeneic islets and restoration of normoglycemia in diabetic nonhuman primates, and delineate cellular and molecular correlates of tolerance induction.

UVB-induced depletion of donor-derived dendritic cells prevents allograft rejection of immune-privileged hair follicles in humanized mice

Dendritic cells (DCs) are key targets for immunity and tolerance induction; they present donor antigens to recipient T cells by donor- and recipient-derived pathways. Donor-derived DCs, which are critical during the acute posttransplant period, can be depleted in graft tissue by forced migration via ultraviolet B light (UVB) irradiation. Here, we investigated the tolerogenic potential of donor-derived DC depletion through in vivo and ex vivo UVB preirradiation (UV) combined with the injection of anti-CD154 antibody (Ab) into recipients in an MHC-mismatched hair follicle (HF) allograft model in humanized mice. Surprisingly, human HF allografts achieved long-term survival with newly growing pigmented hair shafts in both Ab-treated groups (Ab-only and UV plus Ab) and in the UV-only group, whereas the control mice rejected all HF allografts with no hair regrowth. Perifollicular human CD3⁺ T cell and MHC class II⁺ cell infiltration was significantly diminished in the presence of UV and/or Ab treatment. HF allografts in the UV-only group showed stable maintenance of the immune privilege in the HF epithelium without evidence of antigen-specific T cell tolerance, which is likely promoted by normal HFs in vivo. This immunomodulatory strategy targeting the donor tissue exhibited novel biological relevance for clinical allogeneic transplantation without generalized immunosuppression.

CD154 Costimulation Shifts the Local T-Cell Receptor Repertoire Not Only During Thymic Selection but Also During Peripheral T-Dependent Humoral Immune Responses

CD154 is a transmembrane cytokine expressed transiently on activated CD4 T cells upon T-cell receptor (TCR) stimulation that interacts with CD40 on antigen-presenting cells. The signaling via CD154:CD40 is essential for B-cell maturation and germinal center formation and also for the final differentiation of CD4 T cells during T-dependent humoral immune responses. Recent data demonstrate that CD154 is critically involved in the selection of T-cell clones during the negative selection process in the thymus. Whether CD154 signaling influences the TCR repertoire during peripheral T-dependent humoral immune responses has not yet been elucidated. To find out, we used CD154-deficient mice and assessed the global TCRβ repertoire in T-cell zones (TCZ) of spleens by high-throughput sequencing after induction of a Th2 response to the multiepitopic antigen sheep red blood cells. Qualitative and quantitative comparison of the splenic TCZ-specific TCRβ repertoires revealed that CD154 deficiency shifts the distribution of Vβ-Jβ genes after antigen exposure. This data led to the conclusion that costimulation via CD154:CD40 during the interaction of T cells with CD40-matured B cells contributes to the recruitment of T-cell clones into the immune response and thereby shapes the peripheral TCR repertoire.

The CD40-CD40L Dyad in Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis

The CD40-CD40L dyad is an immune checkpoint regulator that promotes both innate and adaptive immune responses and has therefore an essential role in the development of inflammatory diseases, including multiple sclerosis (MS). In MS, CD40 and CD40L are expressed on immune cells present in blood and lymphoid organs, affected resident central nervous system (CNS) cells, and inflammatory cells that have infiltrated the CNS. CD40-CD40L interactions fuel the inflammatory response underlying MS, and both genetic deficiency and antibody-mediated inhibition of the CD40-CD40L dyad reduce disease severity in experimental autoimmune encephalomyelitis (EAE). Both proteins are therefore attractive therapeutic candidates to modulate aberrant inflammatory responses in MS. Here, we discuss the genetic, experimental and clinical studies on the role of CD40 and CD40L interactions in EAE and MS and we explore novel approaches to therapeutically target this dyad to combat neuroinflammatory diseases.

Pathway analysis to identify genetic variants associated with efficacy of adalimumab in rheumatoid arthritis

AIM

About 30% of rheumatoid arthritis patients have no clinical benefit from TNF inhibitors. Genome-wide association (GWA) and candidate gene studies tested several putative genetic variants for TNF inhibitor efficacy with inconclusive results. Therefore, this study applied a systematic pathway analysis.

PATIENTS & METHODS

A total of 325 rheumatoid arthritis patients treated with adalimumab were genotyped for 223 SNPs. We tested the association between SNPs and European League Against Rheumatism response and remission at 14 weeks under the additive genetic model using logistic regression.

RESULTS

A total of 3 SNPs located in CD40LG (rs1126535), TANK (rs1267067) and VEGFA (rs25648) showed association with both end points. TNFAIP3 (rs2230926) had the strongest effect related to European League Against Rheumatism response.

CONCLUSION

This exploratory study suggests that TNFAIP3, CD40LG, TANK and VEGFA play a role in the response to adalimumab treatment.

Potential importance of B cells in aging and aging-associated neurodegenerative diseases

Our understanding of B cells as merely antibody producers is slowly changing. Alone or in concert with antibody, they control outcomes of seemingly different diseases such as cancer, rheumatoid arthritis, diabetes, and multiple sclerosis. While their role in activation of effector immune cells is beneficial in cancer but bad in autoimmune diseases, their immunosuppressive and regulatory subsets (Bregs) inhibit autoimmune and anticancer responses. These pathogenic and suppressive functions are not static and appear to be regulated by the nature and strength of inflammation. Although aging increases inflammation and changes the composition and function of B cells, surprisingly, little is known whether the change affects aging-associated neurodegenerative disease, such as Alzheimer's disease (AD). Here, by analyzing B cells in cancer and autoimmune and neuroinflammatory diseases, we elucidate their potential importance in AD and other aging-associated neuroinflammatory diseases.

LPS, dsRNA and the interferon bridge to adaptive immune responses: Trif, Tram, and other TIR adaptor proteins

Toll-like receptors (TLRs) expressed on antigen-presenting cells (APCs), form a critical link between innate and the adaptive immune responses. Activation of TLRs by LPS and dsRNA results in up-regulation of co-stimulatory molecules (UCM) essential for the generation of robust T-cell responses. It is now evident that type I interferons (IFNs) play an important role in UCM and in the subsequent maturation of APCs. The recently identified adaptor molecules Trif and Tram, unlike their counterparts MyD88 and MAL/Tirap, induce type I IFN via the TLR4 signaling pathway, whereas Trif appears to be the sole adaptor molecule involved in TLR3 signaling, resulting in subsequent production of type I IFN. Here, we discuss how Trif and type I IFN are involved in the optimization of APC-T cell interaction in response not only to viral but also bacterial stimuli.

Intratumoral injection of Ad-ISF35 (Chimeric CD154) breaks tolerance and induces lymphoma tumor regression

Ad-ISF35, an adenovirus vector encoding a membrane-bound engineered CD154 chimeric protein (ISF35), induces complete A20 lymphoma tumor regression in mice after intratumoral direct injection (IDI). Ad-ISF35 induced durable local and systemic antitumor responses associated with a rapid tumor infiltration of macrophages and neutrophils as well as increased levels of proinflammatory cytokines in the tumor microenvironment. Ad-ISF35 IDI transduced preferentially fibroblasts and macrophages present in the tumor microenvironment, and ISF35 protein expression was observed in only 0.25% of cells present in the tumor. Moreover, Ad-ISF35 IDI induced upregulation of CD40 in tumor and immune regulatory cells, including those that did not express ISF35, suggesting the presence of a strong bystander effect. These responses resulted in the generation of IFN-γ-secreting cytotoxic lymphocytes and the production of specific cytotoxic antibodies against lymphoma cells. Overall, cellular immune therapy based on ISF35 induced phenotypic changes in the tumor cells and tumor microenvironment that were associated with a break in tumor immune tolerance and a curative antitumor effect in this lymphoma mouse model. Our data highlight the potential activity that modulation of costimulatory signaling has in cancer therapy.

Rapamycin and CTLA4Ig synergize to induce stable mixed chimerism without the need for CD40 blockade

The mixed chimerism approach achieves donor-specific tolerance in organ transplantation, but clinical use is inhibited by the toxicities of current bone marrow (BM) transplantation (BMT) protocols. Blocking the CD40:CD154 pathway with anti-CD154 monoclonal antibodies (mAbs) is exceptionally potent in inducing mixed chimerism, but these mAbs are clinically not available. Defining the roles of donor and recipient CD40 in a murine allogeneic BMT model, we show that CD4 or CD8 activation through an intact direct or CD4 T cell activation through the indirect pathway is sufficient to trigger BM rejection despite CTLA4Ig treatment. In the absence of CD4 T cells, CD8 T cell activation via the direct pathway, in contrast, leads to a state of split tolerance. Interruption of the CD40 signals in both the direct and indirect pathway of allorecognition or lack of recipient CD154 is required for the induction of chimerism and tolerance. We developed a novel BMT protocol that induces mixed chimerism and donor-specific tolerance to fully mismatched cardiac allografts relying on CD28 costimulation blockade and mTOR inhibition without targeting the CD40 pathway. Notably, MHC-mismatched/minor antigen-matched skin grafts survive indefinitely whereas fully mismatched grafts are rejected, suggesting that non-MHC antigens cause graft rejection and split tolerance.

Interaction of CD154 with different receptors and its role in bidirectional signals

In addition to its classical receptor, CD40, it is now well established that CD154 also binds αIIbβ3, α5β1, and αMβ2 integrins. Although these integrins are all members of the same family, they bind CD154 differently. The current investigation aims to analyze the interaction of CD154 with α5β1 and αMβ2 and investigate its role in bidirectional signals in various human cell lines. Results obtained herein indicate that the CD154 residues involved in the interaction with α5β1 are N151 and Q166, whereas those involved in αMβ2 binding are common to residues required for CD40, namely Y145 and R203. Soluble CD40/CD154 or αMβ2/CD154 complexes do not interfere with the binding of CD154 to α5β1-positive cells, but inhibit the binding of CD154 to CD40- or αMβ2-positive cells, respectively. Ligation of CD154 on CD154-positive cells with soluble CD40, αIIbβ3, α5β1, or αMβ2 stimulates intracellular signaling, including MAPK phosphorylation. Given that CD154 exists as a trimer, our data strongly suggest that CD154 may bind concomitantly to two receptors of the same or different family, and biologically activate cells expressing both receptors. The characterization of CD154/receptor interactions helps the identification of new therapeutic targets for the prevention and/or treatment of CD154-associated autoimmune and inflammatory diseases.

The signaling role of CD40 ligand in platelet biology and in platelet component transfusion

The CD40 ligand (CD40L) is a transmembrane molecule of crucial interest in cell signaling in innate and adaptive immunity. It is expressed by a variety of cells, but mainly by activated T-lymphocytes and platelets. CD40L may be cleaved into a soluble form (sCD40L) that has a cytokine-like activity. Both forms bind to several receptors, including CD40. This interaction is necessary for the antigen specific immune response. Furthermore, CD40L and sCD40L are involved in inflammation and a panoply of immune related and vascular pathologies. Soluble CD40L is primarily produced by platelets after activation, degranulation and cleavage, which may present a problem for transfusion. Soluble CD40L is involved in adverse transfusion events including transfusion related acute lung injury (TRALI). Although platelet storage designed for transfusion occurs in sterile conditions, platelets are activated and release sCD40L without known agonists. Recently, proteomic studies identified signaling pathways activated in platelet concentrates. Soluble CD40L is a good candidate for platelet activation in an auto-amplification loop. In this review, we describe the immunomodulatory role of CD40L in physiological and pathological conditions. We will focus on the main signaling pathways activated by CD40L after binding to its different receptors.

With(out) a little help from my friends: an IL-12/CD40L-mediated feed-forward loop between CD8+ T cells and DCs

CD40-CD40L interactions are important for both antigen-dependent B-cell differentiation and effector and memory T-cell formation. The prevailing view is that CD40L is expressed on activated CD4(+) T cells, which enables them to provide help to high-affinity B cells in GCs and to license DCs for efficient induction of CD8(+) T-cell responses. Interestingly, CD8(+) T cells themselves can also express CD40L and, in this issue of the European Journal of Immunology, Thiel and colleagues [Eur. J. Immunol. 2013. 43: 1511-1517] show that CD40L expression on these cells can be part of a self-sustaining feed-forward loop, in which expression of CD40L is induced by IL-12 and TCR signaling. This provides a paradigm shift in our thinking about the requirements of effector CD8(+) T-cell development and the role herein of CD4(+) T cells to provide help in this process.

Costimulation blockade: current perspectives and implications for therapy

T cells must be activated before they can elicit damage to allografts, through interaction of their T cell receptor (TCR) with peptide-MHC complex and through accessory molecules. Signaling through accessory molecules or costimulatory molecules is a critical way for the immune system to fine tune T cell activation. An emerging therapeutic strategy is to target selective molecules involved in the process of T cell activation using biologic agents, which do not impact TCR signaling, thus only manipulating the T cells, which recognize alloantigen. Costimulatory receptors and their ligands are attractive targets for this strategy and could be used both to prevent acute graft rejection as well as for maintenance immunosuppression. Therapeutic agents targeting costimulatory molecules, notably belatacept, have made the progression from the bench, through nonhuman primate studies and into the clinic. This overview describes some of the most common costimulatory molecules, their role in T cell activation, and the development of reagents, which target these pathways and their efficacy in transplantation.

Gene transfer of human CD40Ig does not prevent rejection in a non-human primate kidney allotransplantation model

BACKGROUND

Blockade of costimulation signaling required for immune response, such as CD40/CD40L and CD28/B7, is a reasonable strategy to prevent rejection and in defined combinations may allow donor specific tolerance. Indeed, in rodents, costimulation blockade with CD28/B7 antagonists or with CD40Ig was able to induce regulatory T cells and transplant tolerance whereas in primates, anti-CD40 antibodies, anti-CD40L antibodies or CTLA4Ig, used as monotherapy, significantly delayed graft rejection.

METHODS

Using an adeno-associated virus (AAV) vector mediated gene transfer of a human CD40Ig fusion protein (hCD40Ig) in primates, we evaluated the capacity of this costimulation blockade molecule interfering with CD40/CD40L signaling in prolonging kidney transplants in cynomolgus monkeys.

RESULTS

This gene transfer strategy allowed for maintaining a plateau of hCD40Ig production within two months and avoided a high-scale production phase of this molecule. Although the hCD40Ig was able to bind efficiently to human and macaque CD40L and high (>200 μg/ml) transgene expression was obtained, no effect on graft survival was observed. In addition, there was no inhibition of humoral response to vaccination. In vitro, hCD40Ig strongly increased mixed lymphocyte reaction, and when compared to the anti-CD40L antibody h5C8, was not as potent to induce complement-dependent cytotoxicity.

CONCLUSION

These data suggest that CD40/CD40L blockade using a non-depleting CD40Ig fusion protein, a therapeutic strategy that showed efficacy in rodents, is not able to modulate the immune response in primates. These data highlight important biological differences between rodent and primate models to evaluate therapeutic strategies at the preclinical level.

Hyper-immunoglobulin M syndrome type 3 with normal CD40 cell surface expression

Mutations of the CD40 gene have been found in patients with autosomal recessive hyper-immunoglobulin M (HIGM) syndrome type 3. Five patients from four unrelated families with CD40 mutation have been reported so far. Clinical manifestations include recurrent sinopulmonary infections, Pneumocystis carinii pneumonia and Cryptosporidium parvum infection. Affected patients typically have very low levels of IgG and IgA and normal or high levels of IgM. Flow cytometry analysis of these five patients demonstrated that peripheral blood B lymphocytes lacked expression of surface CD40. Herein, we present two siblings from second-degree consanguineous Turkish parents with homozygous CD40 deletion of four nucleotides including the stop codon resulting presumably to a longer protein. Clinical and immunological profile of these patients is similar to the already reported HIGM3 patients except normal CD40 expression on B lymphocytes. This observation emphasizes the requirement of CD40 mutation analysis for definite diagnosis of HIGM3 despite normal flow cytometric expression of CD40, particularly if the immunological and clinical profile is suggestive for HIGM3.

Requirement of transmembrane domain for CD154 association to lipid rafts and subsequent biological events

Interaction of CD40 with CD154 leads to recruitment of both molecules into lipid rafts, resulting in bi-directional cell activation. The precise mechanism by which CD154 is translocated into lipid rafts and its impact on CD154 signaling remain largely unknown. Our aim is to identify the domain of CD154 facilitating its association to lipid rafts and the impact of such association on signaling events and cytokine production. Thus, we generated Jurkat cell lines expressing truncated CD154 lacking the cytoplasmic domain or chimeric CD154 in which the transmembrane domain was replaced by that of transferrin receptor I, known to be excluded from lipid rafts. Our results show that cell stimulation with soluble CD40 leads to the association of CD154 wild-type and CD154-truncated, but not CD154-chimera, with lipid rafts. This is correlated with failure of CD154-chimera to activate Akt and p38 MAP kinases, known effectors of CD154 signaling. We also found that CD154-chimera lost the ability to promote IL-2 production upon T cell stimulation with anti-CD3/CD28 and soluble CD40. These results demonstrate the implication of the transmembrane domain of CD154 in lipid raft association, and that this association is necessary for CD154-mediated Akt and p38 activation with consequent enhancement of IL-2 production.

Ethylenecarbodiimide-fixed donor splenocyte infusions differentially target direct and indirect pathways of allorecognition for induction of transplant tolerance

Strategic exposure to donor Ags prior to transplantation can be an effective way for inducting donor-specific tolerance in allogeneic recipients. We have recently shown that pretransplant infusion of donor splenocytes treated with the chemical cross-linker ethylenecarbodiimide (ECDI-SPs) induces indefinite islet allograft survival in a full MHC-mismatched model without the need for any immunosuppression. Mechanisms of allograft protection by this strategy remain elusive. In this study, we show that the infused donor ECDI-SPs differentially target T cells with indirect versus direct allospecificities. To target indirect allospecific T cells, ECDI-SPs induce upregulation of negative, but not positive, costimulatory molecules on recipient splenic CD11c(+) dendritic cells phagocytosing the injected ECDI-SPs. Indirect allospecific T cells activated by such CD11c(+) dendritic cells undergo robust initial proliferation followed by rapid clonal depletion. The remaining T cells are sequestered in the spleen without homing to the graft site or the graft draining lymph node. In contrast, direct allospecific T cells interacting with intact donor ECDI-SPs not yet phagocytosed undergo limited proliferation and are subsequently anergized. Furthermore, CD4(+)CD25(+)Foxp3(+) T cells are induced in lymphoid organs and at the graft site by ECDI-SPs. We conclude that donor ECDI-SP infusions target host allogeneic responses via a multitude of mechanisms, including clonal depletion, anergy, and immunoregulation, which act in a synergistic fashion to induce robust transplant tolerance. This simple form of negative vaccination has significant potential for clinical translation in human transplantation.

Fates of CD4+ T cells in a tolerant environment depend on timing and place of antigen exposure

In experimental organ transplantation, tolerance is induced by administration of anti-CD40L mAb in conjunction with donor-specific splenocyte transfusion. Multiple, sometimes conflicting mechanisms of action resulting from this treatment have been reported. To resolve these issues, this study assessed the fates of graft reactive cells at different times and locations in the tolerant environment. Alloantigen-specific CD4(+) T cells transferred at time of tolerance induction (7 days before transplantation) became activated, expressed CD69 and CD44, and proliferated. Importantly, a large subset of this population became Foxp3(+) , more so in the lymph nodes than spleen, indicative of differentiation to a regulatory phenotype. In contrast, graft reactive CD4(+) T cells transferred to tolerogen-treated recipients at the time of transplantation failed either to proliferate or to differentiate, and instead were deleted via apoptosis. In untreated rejecting recipients graft reactive CD4(+) T cells became activated, proliferated and differentiated mainly in the spleen, and many of these cells were eventually deleted. These data resolve many apparent contradictions in the literature by showing that the timing of antigen exposure, the immunologic status of the recipients and secondary lymphoid organ location act together as key factors to determine the fate of graft reactive CD4(+) T cells.

Nondepleting anti-CD40-based therapy prolongs allograft survival in nonhuman primates

Costimulation blockade of the CD40/CD154 pathway has been effective at preventing allograft rejection in numerous transplantation models. This strategy has largely depended on mAbs directed against CD154, limiting the potential for translation due to its association with thromboembolic events. Though targeting CD40 as an alternative to CD154 has been successful at preventing allograft rejection in preclinical models, there have been no reports on the effects of CD40-specific agents in human transplant recipients. This delay in clinical translation may in part be explained by the presence of cellular depletion with many CD40-specific mAbs. As such, the optimal biologic properties of CD40-directed immunotherapy remain to be determined. In this report, we have characterized 3A8, a human CD40-specific mAb and evaluated its efficacy in a rhesus macaque model of islet cell transplantation. Despite partially agonistic properties and the inability to block CD40 binding of soluble CD154 (sCD154) in vitro, 3A8-based therapy markedly prolonged islet allograft survival without depleting B cells. Our results indicate that the allograft-protective effects of CD40-directed costimulation blockade do not require sCD154 blockade, complete antagonism or cellular depletion, and serve to support and guide the continued development of CD40-specific agents for clinical translation.

Role of co-stimulation in Leishmaniasis

Leishmania are obligate intracellular parasites that cause a wide spectrum of diseases ranging from cutaneous, mucocutaneous and the visceral kind. Persistence or resolution of leishmaniasis is governed by host immune response. Co-stimulation is an important secondary signal that governs the extent, strength and direction of the immune response that follows. Co-stimulation by CD40, B7 and OX40 family has been shown to influence the outcome following Leishmania infection and manipulation of these pathways has shown promise for use in immune therapy of leishmaniasis. In this review, we discuss the roles of CD40, B7 and OX40 co-stimulatory pathways in regulating immunity to Leishmania and their implications in the treatment of this disease.

Costimulatory pathways in transplantation

Secondary, so-called costimulatory, signals are critically required for the process of T cell activation. Since landmark studies defined that T cells receiving a T cell receptor signal without a costimulatory signal, are tolerized in vitro, the investigation of T cell costimulation has attracted intense interest. Early studies demonstrated that interrupting T cell costimulation allows attenuation of the alloresponse, which is particularly difficult to modulate due to the clone size of alloreactive T cells. The understanding of costimulation has since evolved substantially and now encompasses not only positive signals involved in T cell activation but also negative signals inhibiting T cell activation and promoting T cell tolerance. Costimulation blockade has been used effectively for the induction of tolerance in rodent models of transplantation, but turned out to be less potent in large animals and humans. In this overview we will discuss the evolution of the concept of T cell costimulation, the potential of 'classical' and newly identified costimulation pathways as therapeutic targets for organ transplantation as well as progress towards clinical application of the first costimulation blocking compound.

Co-stimulation blockade as a new strategy in kidney transplantation: benefits and limits

New immunosuppressive drugs have greatly decreased the frequency of graft failure due to acute rejection but have had little impact on long-term graft survival. This is due, at least in part, to the broad non-immune effects of the current immunosuppressive drugs, which are involved in the death of patients and in chronic allograft dysfunction, particularly due to their nephrotoxicity. Recent progress in the development of biologicals, i.e. antibodies and fusion proteins, allows precise targeting of the immune system, preventing the non-immune side effects encountered with current protocols. In particular, targeting of the two most important co-stimulation pathways critical for T-cell activation, i.e. B7/CD28 and CD40/CD40L, has provided excellent results in many experimental models of organ transplantation. This has led to the clinical development of belatacept, a cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin (CTLA4-Ig) fusion protein, which has proved to be efficient in preventing acute rejection in kidney transplant recipients. Its use is associated with improved renal function and a better metabolic profile than calcineurin inhibitors. However, because belatacept does not selectively target alloreactive T lymphocytes and must be combined with classical immunosuppressive drugs, infectious and neoplastic complications may occur, particularly post-transplantation lymphoproliferative disorders. We also address the current development of molecules targeting other co-stimulatory pathways (CD40/CD40L, leukocyte function-associated antigen [LFA]-1/intercellular adhesion molecule [ICAM], CD2/LFA-3). Many unresolved issues regarding the use of co-stimulation blocking agents are also discussed, e.g. their long half-life, which can be problematic in cases of serious adverse events, their long-term safety and efficacy, and the lack of monitoring tools to allow modulation of their use over time.

Overexpression of phospholipase Cε in keratinocytes upregulates cytokine expression and causes dermatitis with acanthosis and T-cell infiltration

Phospholipase Cε (PLCε) is an effector of Ras and Rap small GTPases. We showed previously using PLCε-deficient mice that PLCε plays a critical role in activation of cytokine production in non-immune skin cells in a variety of inflammatory reactions. For further investigation of its role in inflammation, we created transgenic mice overexpressing PLCε in epidermal keratinocytes. The resulting transgenic mice spontaneously developed skin inflammation as characterized by formation of adherent silvery scales, excessive growth of keratinocytes, and aberrant infiltration of immune cells such as T cells and DC. Development of the skin symptoms correlated well with increased expression of factors implicated in human inflammatory skin diseases, such as IL-23, in keratinocytes, and with the accumulation of CD4(+) T cells producing IL-22, a potent inducer of keratinocyte proliferation. Intradermal injection of a blocking antibody against IL-23 as well as treatment with the immunosuppressant FK506 reversed these skin phenotypes, which was accompanied by suppression of the IL-22-producing T-cell infiltration. These results reveal a crucial role of PLCε in the development of skin inflammation and suggest a mechanism in which PLCε induces the production of cytokines including IL-23 from keratinocytes, leading to the activation of IL-22-producing T cells.

CD40·FasL and CTLA-4·FasL fusion proteins induce apoptosis in malignant cell lines by dual signaling

Evolution of apoptosis resistance in both lymphoma and leukemia cells is well documented, and induction of apoptosis in malignant cells is a major goal of cancer therapy. Up-regulation of anti-apoptotic signals is one of the mechanisms whereby resistance to apoptosis emerges. We have previously described the fusion proteins CD40·FasL and CTLA-4·FasL, which are formed from two functional membrane proteins and induce apoptosis of activated T cells. The present study explores the potential use of CD40·FasL and CTLA-4·FasL for the killing of malignant cells of lymphatic origin. Using malignant B and T cell lines that differ in surface expression of costimulatory molecules, we found that CTLA-4·FasL induces effective apoptosis of cells expressing CD95 and activates caspases 3, 8, and 9. Only B7-expressing B cells responded to CTLA-4·FasL with rapid abrogation of cFLIP expression. CD40·FasL effectively killed only the T cells that express high levels of CD40L in addition to CD95. In these cells, CD40·FasL significantly diminished cFLIP expression. Importantly, each of the fusion proteins is more potent than its respective components parts, alone or in combination. Thus, the proteins with their two functional ends deliver a pro-apoptotic signal and, in parallel, inhibit an anti-apoptotic signal, thus optimizing the wanted, death-inducing effect. Therefore, these proteins emerge as promising agents to be used for targeted and specific tumor cell killing.

A given number of effector T cells can only destroy a limited number of target cells in graft rejection

Anti-donor T cells mediate graft rejection and the frequency of anti-donor T cells directly correlates with transplant outcome. It has long been noted that long-term tolerance was occasionally observed in minor mismatched recipients, little is known about the mechanisms underlying this phenomenon. To quantitatively analyze the relationship between anti-donor T cells and target cells, long-term tolerant C57BL/6 mice were established by infusing 3 x 10(7) F1 splenocytes during the neonatal period. The removal of anti-donor T cells in these mice was demonstrated by unresponsiveness in mixed-lymphocyte reaction. A total of 2 x 10(7) or 5 x 10(7) syngenic naive cells were transferred into long-term tolerant mice; the dose of 5 x 10(7) syngenic cells destroyed chimerism and the skin grafts, while the dose of 2 x 10(7) syngenic cells led to loss of chimerism but the survival of the skin grafts. On Day 20 after the transfusion, a portion of 5 x 10(7) syngenic cells still remained in the mice, while no syngenic cells were detected in mice that received a total of 2 x 10(7) syngenic cells suggesting that these cells were completely exhausted. Syngenic CD4+ T cells proliferated and activated in both groups, while syngenic cells in the low-dose group were more susceptible to apoptosis than those in the high-dose group. Our results suggest that a given number of effector T cells could only kill a limited number of target cells. When that limit was reached, the T cells died. This novel concept not only provides a reasonable explanation for long-term tolerance in minor mismatched transplantation but also provides new insight into tolerance induction that depleting alloreactive T cells in recipients by donor cells or agents is a prerequisite for reconstitution of thymus by donor cells, the establishment of central tolerance is the key for successful tolerance induction.

CD40 expression in Wehi-164 cell line

CD40-CD154 interaction is an important process for cellular and humoral immunity regulation and can be effective in the body's defense against tumors. In the present study, we evaluated the expression of CD40 in Wehi-164 cell line. CD40 expressions on the cell surface and in the cytoplasm were assessed by flow cytometry and intracellular staining assay, respectively. Also, the mRNA expression was identified by real time-PCR. The obtained results showed the high mRNA and cytoplasmic protein expression of CD40 but no surface expression. These results suggest that the Wehi-164 cell line down regulates expression of CD40 on the surface for evasion of immune system.

[Novel therapeutic possibilities in systemic lupus erythematosus]

Systemic lupus erythematosus (SLE) is an autoimmune disorder involving different organs and organ systems with consequent characteristic clinical and serologic symptoms. Despite of the improvement in lupus survival, approximately 10-20% of patients do not respond to traditional immune suppressive therapies. Relapses are more frequent; e.g. after cyclophosphamide therapy diffuse proliferative nephritis flares in 1/3 of patients. Different immune competent cells and inflammatory mediators participate in the pathogenesis of SLE involving both the adaptive and innate immunity. Several pathogenic elements and mechanisms may serve as therapeutic targets, consequently. Authors summarize novel therapeutic possibilities and their mechanisms regarding the pathogenesis of SLE. Immune modulation of B and T cells, co-stimulatory pathways, cytokine network, soluble mediators and autologous hemopoietic stem cell transplantation are discussed.

T cell recognition of self-antigen presenting cells by protein transfer assay reveals a high frequency of anti-myelin T cells in multiple sclerosis

Although peripheral blood myelin-autoreactive T cells are thought to play a key role in multiple sclerosis, they are generally considered to have qualitative differences rather than quantitative ones when compared to those found in healthy individuals. Here, we revisited the assessment of myelin-autoreactive T cells in a new approach based on their combined ability to acquire membrane proteins from autologous antigen presenting cells, and to respond to whole myelin extract as the stimulating autoantigen. Using this approach, the myelin-autoreactive T cell frequency in patients with multiple sclerosis was found to be unexpectedly high (n = 22, subtracted values median 2.08%, range 0-6%; background median 1%, range 0-4%) and to exceed that of age/gender-matched healthy individuals significantly (n = 18, subtracted values median 0.1%, range 0-5.3%, P < 0.0001; background median 1.45%, range 0.1-4%). Higher anti-myelin autoreactivity was stable in patients with multiple sclerosis after several months. These data correlated with whole myelin-induced gamma interferon-enzyme-linked immunosorbent spot assay performed under the same conditions, although the values obtained with enzyme-linked immunosorbent spot assay under all conditions were 58 times lower than with this new method. The myelin-autoreactive T cells were memory T cells expressing CD40L with a CD62(low) phenotype, suggesting their ability for homing to tissues. Collectively, these new data show a higher frequency of autoreactive T cells during multiple sclerosis than in age/gender-matched healthy individuals, and support an autoimmune aetiology in multiple sclerosis.

Critical role of lipid rafts in CD154-mediated T cell signaling

Although signal pathways triggered via the CD40 molecule are well characterized, those induced via CD154 are less known. This study demonstrates that engagement of CD154 in Jurkat D1.1 cells with soluble CD40 leads to PKC alpha and delta activation, calcium mobilization, and phosphorylation of the Map kinases ERK1/2 and p38. Such response is accompanied by significant recruitment of CD154 into lipid rafts. Disruption of lipid rafts integrity with nystatin or methyl beta-cyclodextrin abrogated PKCalpha PKCdelta and p38 phosphorylation, but had no effect on ERK1/2 phosphorylation. Inhibition of PKC activation completely abolished p38 phosphorylation but had no effect on ERK1/2 phosphorylation, suggesting that localization of CD154 within lipid rafts is an absolute requirement for CD154-induced PKCalpha- and PKCdelta-dependent p38 phosphorylation. Furthermore, CD154 acts as co-stimulator for the production of IL-2 in an APC-superantigen-T-cell activation model. The results obtained demonstrate for the first time, that lipid rafts are of immunological relevance for CD154-triggered signals, and reinforce the importance of CD154 in T-cell activation.

CCR6 is expressed on an IL-10-producing, autoreactive memory T cell population with context-dependent regulatory function

Interleukin (IL)-10 produced by regulatory T cell subsets is important for the prevention of autoimmunity and immunopathology, but little is known about the phenotype and function of IL-10–producing memory T cells. Human CD4⁺CCR6⁺ memory T cells contained comparable numbers of IL-17– and IL-10–producing cells, and CCR6 was induced under both Th17-promoting conditions and upon tolerogenic T cell priming with transforming growth factor (TGF)–β. In normal human spleens, the majority of CCR6⁺ memory T cells were in the close vicinity of CCR6⁺ myeloid dendritic cells (mDCs), and strikingly, some of them were secreting IL-10 in situ. Furthermore, CCR6⁺ memory T cells produced suppressive IL-10 but not IL-2 upon stimulation with autologous immature mDCs ex vivo, and secreted IL-10 efficiently in response to suboptimal T cell receptor (TCR) stimulation with anti-CD3 antibodies. However, optimal TCR stimulation of CCR6⁺ T cells induced expression of IL-2, interferon-γ, CCL20, and CD40L, and autoreactive CCR6⁺ T cell lines responded to various recall antigens. Notably, we isolated autoreactive CCR6⁺ T cell clones with context-dependent behavior that produced IL-10 with autologous mDCs alone, but that secreted IL-2 and proliferated upon stimulation with tetanus toxoid. We propose the novel concept that a population of memory T cells, which is fully equipped to participate in secondary immune responses upon recognition of a relevant recall antigen, contributes to the maintenance of tolerance under steady-state conditions.

Role of IDO in organ transplantation: promises and difficulties

Induction of donor-antigen-specific immunological tolerance still remains the "holy grail" in organ transplantation. Recently, Indoleamine-2,3 Dioxygenase (IDO)--a tryptophan degrading enzyme--has been shown to be implicated in one of nature's most impressive examples of tolerance, which is maternal acceptance of the semi-allogeneic foetus. Although many experimental findings propose IDO as a key player in induction and maintenance of peripheral tolerance, scepticism exists as to whether IDO represents a promising therapeutic target with clinical relevance. In this review article we will discuss the role of IDO in transplantation and take a critical look at IDO-based therapeutic strategies.

Anti-CD40 monoclonal antibody synergizes with CTLA4-Ig in promoting long-term graft survival in murine models of transplantation

Blockade of the CD40/CD154 signaling pathway using anti-CD154 Abs has shown promise in attenuating the alloimmune response and promoting long-term graft survival in murine model systems, although side effects observed in humans have hampered its progression through clinical trials. Appropriately designed anti-CD40 Abs may provide a suitable alternative. We investigated two isoforms of a novel monoclonal rat anti-mouse CD40 Ab (7E1) for characteristics and effects mirroring those of anti-CD154: 7E1-G1 (an IgG1 isotype); and 7E1-G2b (an IgG2b isotype). In vitro proliferation assays to measure the agonist properties of the two anti-CD40 Abs revealed similar responses when plate bound. However, when present as a soluble stimulus, 7E1-G1 but not 7E1-G2b led to proliferation. 7E1-G2b was as effective as anti-CD154 when administered in vivo in concert with CTLA4-Ig in promoting both allogeneic bone marrow chimerism and skin graft survival, whereas 7E1-G1 was not. The protection observed with 7E1-G2b was not due to depletion of CD40-bearing APCs. These data suggest that an appropriately designed anti-CD40 Ab can promote graft survival as well as anti-CD154, making 7E1-G2b an attractive substitute in mouse models of costimulation blockade-based tolerance regimens.

Translating costimulation blockade to the clinic: lessons learned from three pathways

SUMMARY

As the recognition that costimulatory signals are critical for optimal T-cell activation, proliferation, and differentiation, there has been an explosion in the study of costimulatory molecules and their roles in enhancing anti-donor T-cell responses following transplantation. Here, we focus on the bench-to-beside translation of blocking agents designed to target three critical costimulatory pathways: the CD28/CD80/CD86 pathway, the CD154/CD40 pathway, and the lymphocyte function associated antigen-1/intercellular adhesion molecule pathway. While blockade of each of these pathways proved promising in inhibiting donor-reactive T-cell responses and promoting long-term graft survival in murine models of transplantation, the progression of development of therapeutic agents to block these pathways has each taken a slightly different course. Both logistical and biological pitfalls have accompanied the translation of blockers of all three pathways into clinically applicable therapies, and the development of costimulatory blockade as a substitute for current standard-of-care calcineurin inhibitors has by no means reached completion. Collaboration between both the basic and clinical arenas will further propel the development of costimulation blockers currently in the pipeline, as well as of novel methods to target these critical pathways during transplantation.

New strategies in immune tolerance induction

Induction of tolerance in clinical organ transplantation that will obviate the use of chronic immunosuppression and preserve host immune response to other antigens remains the goal of transplant research. The thymus plays a critical role in the ability of the immune system to discriminate between self- and nonself-antigens or harmful and harmless alloantigens. We now know that multiple factors determine how the immune system responds to a self-antigen or foreign antigen. These determinants include developmental stage of the host, stage of T-cell maturity, site of antigen encounter, type and maturity of antigen-presenting cells, and presence and type of costimulatory molecules. Our understanding of the mechanisms of T-cell interactions with peptide/ major histocompatibility complex in peripheral lymphoid organs has led to experiments that translate into peripheral T-cell tolerance. The induction of high-avidity peripheral alloreactive T cells in the early phase of organ transplantation makes it difficult to achieve long-term alloantigen-specific tolerance without the use of transient perioperative immunosuppression. Therefore, protocols that induce robust tolerance in rodent and nonhuman primate models involve the use of donor antigen combined with a short course of perioperative immunosuppression. These studies suggest that the underlying mechanisms of peripheral tolerance include deletion, anergy, immune deviation, and regulatory T cells. This review focuses on recent advances in tolerance induction in experimental animal models and discusses their relevance to the development of protocols for the induction and maintenance of clinical transplant tolerance.