CTLA4-Ig immunosuppressive activity at the level of dendritic cell/T cell crosstalk

Localized cytotoxic T cell-associated antigen 4 and antioxidant islet encapsulation alters macrophage signaling and induces regulatory and anergic T cells to enhance allograft survival

The loss of functional β-cell mass is a hallmark of type 1 diabetes. Islet transplantation represents a promising alternative approach, but immune-mediated graft destruction remains a major challenge. We sought to use islet encapsulation technologies to improve graft survival and function without systemic immunosuppression. We hypothesized islet encapsulation with nanothin coatings consisting of tannic acid (TA), an antioxidant; poly(N-vinylpyrrolidone) (PVPON), a biocompatible polymer; and cytotoxic T cell-associated antigen 4 immunoglobulin (CTLA-4-Ig), an inhibitory immune receptor, will elicit localized immunosuppression to prolong islet allograft function and suppress effector T cell responses. In the absence of systemic immunosuppression, we demonstrated (PVPON/TA/CTLA-4-Ig)-encapsulated NOD.Rag islet grafts maintain function significantly longer than control IgG-containing (PVPON/TA/IgG) and nonencapsulated controls after transplantation into diabetic C57BL/6 mice. This protection coincided with diminished proinflammatory macrophage responses mediated by signal transducer and activator of transcription 1 signaling, decreased proinflammatory T cell effector responses, and CTLA-4-Ig-specific concomitant increases in anergic CD4+ T cells and regulatory T cells. Our results provide evidence that conjugation of CTLA-4-Ig to (PVPON/TA) coatings can suppress T cell activation, enhance regulatory T cell populations, prolong islet allograft survival, and induce localized immunosuppression after transplantation.

Tolerogenic Nanovaccine for Prevention and Treatment of Autoimmune Encephalomyelitis

Herein, a tolerogenic nanovaccine is developed and tested on an animal model of multiple sclerosis. The nanovaccine is constructed to deliver the self-antigen, myelin oligodendrocyte glycoprotein (MOG) peptide, and dexamethasone on an abatacept-modified polydopamine core nanoparticle (AbaLDPN-MOG). AbaLDPN-MOG can target dendritic cells and undergo endocytosis followed by trafficking to lysosomes. AbaLDPN-MOG blocks the interaction between CD80/CD86 and CD28 in antigen-presenting cells and T cells, leading to decreased interferon gamma secretion. The subcutaneous administration of AbaLDPN-MOG to mice yields significant biodistribution to lymph nodes and, in experimental-autoimmune encephalomyelitis (EAE) model mice, increases the integrity of the myelin basic sheath and minimizes the infiltration of immune cells. EAE mice are treated with AbaLDPN-MOG before or after injection of the autoantigen, MOG. Preimmunization of AbaLDPN-MOG before the injection of MOG completely blocks the development of clinical symptoms. Early treatment with AbaLDPN-MOG at three days after injection of MOG also completely blocks the development of symptoms. Notably, treatment of EAE symptom-developed mice with AbaLDPN-MOG significantly alleviates the symptoms, indicating that the nanovaccine has therapeutic effects. Although AbaLDPN is used for MOG peptide delivery in the EAE model, the concept of AbaLDPN can be widely applied for the prevention and alleviation of other autoimmune diseases.

Accurate treatment of small cell lung cancer: Current progress, new challenges and expectations

Small cell lung cancer (SCLC) is a deadly disease with poor prognosis. Fast growing speed, inclination to metastasis, enrichment in cancer stem cells altogether constitute its aggressive nature. In stark contrast to non-small cell lung cancer (NSCLC) that strides vigorously on the road to precision oncology, SCLC has been on the embryonic path to achieve effective personalized treatments. The survival of patients with SCLC have not been improved greatly, which could be possibly due to our inadequate understanding of genetic alterations of SCLC. Recently, encouraging effects have been observed in patients with SCLC undergoing immunotherapy. However, exciting results have only been observed in a small fraction of patients with SCLC, warranting biomarkers predictive of responses as well as novel therapeutic strategies. In addition, SCLC has previously been viewed to be homogeneous. However, perspectives have been changed thanks to the advances in sequencing techniques and platforms, which unfolds the complex heterogeneity of SCLC both genetically and non-genetically, rendering the treatment of SCLC a further step forward into the precision era. To outline the road of SCLC towards precision oncology, we summarize the progresses and achievements made in precision treatment in SCLC in genomic, transcriptomic, epigenetic, proteomic and metabolic dimensions. Moreover, we conclude relevant therapeutic vulnerabilities in SCLC. Clinically tested drugs and clinical trials have also been demonstrated. Ultimately, we look into the opportunities and challenges ahead to advance the individualized treatment in pursuit of improved survival for patients with SCLC.

Myeloid and Mesenchymal Stem Cell Therapies for Solid Organ Transplant Tolerance

Transplantation is now performed globally as a routine procedure. However, the increased demand for donor organs and consequent expansion of donor criteria has created an imperative to maximize the quality of these gains. The goal is to balance preservation of allograft function against patient quality-of-life, despite exposure to long-term immunosuppression. Elimination of immunosuppressive therapy to avoid drug toxicity, with concurrent acceptance of the allograft-so-called operational tolerance-has proven elusive. The lack of recent advances in immunomodulatory drug development, together with advances in immunotherapy in oncology, has prompted interest in cell-based therapies to control the alloimmune response. Extensive experimental work in animals has characterized regulatory immune cell populations that can induce and maintain tolerance, demonstrating that their adoptive transfer can promote donor-specific tolerance. An extension of this large body of work has resulted in protocols for manufacture, as well as early-phase safety and feasibility trials for many regulatory cell types. Despite the excitement generated by early clinical trials in autoimmune diseases and organ transplantation, there is as yet no clinically validated, approved regulatory cell therapy for transplantation. In this review, we summarize recent advances in this field, with a focus on myeloid and mesenchymal cell therapies, including current understanding of the mechanisms of action of regulatory immune cells, and clinical trials in organ transplantation using these cells as therapeutics.

Vasculitis: From Target Molecules to Novel Therapeutic Approaches

Systemic vasculitis is a group of diverse diseases characterized by immune-mediated inflammation of blood vessels. Current treatments for vasculitis, such as glucocorticoids and alkylating agents, are associated with significant side effects. In addition, the management of both small and large vessel vasculitis is challenging due to a lack of robust markers of disease activity. Recent research has advanced our understanding of the pathogenesis of both small and large vessel vasculitis, and this has led to the development of novel biologic therapies capable of targeting key cytokine and cellular effectors of the inflammatory cascade. It is anticipated that these novel treatments will lead to more effective and less toxic treatment regimens for patients with systemic vasculitis.

In Vivo Imaging of Local Inflammation: Monitoring LPS-Induced CD80/CD86 Upregulation by PET

PURPOSE

The co-stimulatory molecules CD80 and CD86 are upregulated on activated antigen-presenting cells (APC). We investigated whether local APC activation, induced by subcutaneous (s.c.) inoculation of lipopolysaccharides (LPS), can be imaged by positron emission tomography (PET) with CD80/CD86-targeting 64Cu-labelled abatacept.

PROCEDURES

Mice were inoculated s.c. with extracellular-matrix gel containing either LPS or vehicle (PBS). Immune cell populations were analysed by flow cytometry and marker expression by RT-qPCR. 64Cu-NODAGA-abatacept distribution was analysed using PET/CT and ex vivo biodistribution.

RESULTS

The number of CD80+ and CD86+ immune cells at the LPS inoculation site significantly increased a few days after inoculation. CD68 and CD86 expression were higher at the LPS than the PBS inoculation site, and CD80 was only increased at the LPS inoculation site. CTLA-4 was highest 10 days after LPS inoculation, when CD80/CD86 decreased again. A few days after inoculation, 64Cu-NODAGA-abatacept distribution to the inoculation site was significantly higher for LPS than PBS (4.2-fold). Co-administration of unlabelled abatacept or human immunoglobulin reduced tracer uptake. The latter reduced the number of CD86+ immune cells at the LPS inoculation site.

CONCLUSIONS

CD80 and CD86 are upregulated in an LPS-induced local inflammation, indicating invasion of activated APCs. 64Cu-NODAGA-abatacept PET allowed following APC activation over time.

The impact of belatacept on the phenotypic heterogeneity of renal T cell-mediated alloimmune response: The critical role of maintenance treatment and inflammatory load

Belatacept offers superior long-term outcome relative to calcineurin inhibitor (CNI)-based immunosuppression. However, the higher frequency of early T cell-mediated rejection (TCMR) in belatacept-treated patients hampered the widespread adoption of costimulation blockade. Here, we applied gene expression analysis and whole-slide inflammatory cell quantification to assess the impact of belatacept on intragraft immune signature. We studied formalin-fixed, paraffin-embedded renal biopsies from 92 patients stratified by histopathologic diagnosis (TCMR, borderline changes, or normal) and immunosuppression regimen (belatacept, CNI). An interaction model was built to explore maintenance treatment-dependent expression level changes of immune response-related genes across diagnostic categories of normal, borderline changes, and TCMR. Ninety-one percent of genes overexpressed in TCMR showed significant correlation with whole section inflammatory load. There were 27 genes that had a positive association with belatacept treatment. These were mostly related to myeloid cells and innate immunity. Genes negatively associated with costimulation blockade (n = 14) could be linked to B-cell differentiation and proliferation. We concluded that expression levels of genes characteristic of TCMR are strongly interconnected with quantitative changes of the biopsy inflammatory load. Our results might suggest differential involvement of the innate immune system, and an altered B-cell engagement during TCMR in belatacept-treated patients relative to CNI-treated referents.

Regulatory T cells in paracoccidioidomycosis

This review addresses the role of regulatory T cells (Tregs), which are essential for maintaining peripheral tolerance and controlling pathogen immunity, in the host response against Paracoccidioides brasiliensis, a primary fungal pathogen. A brief introduction on the general features of Treg cells summarizes their main functions, subpopulations, mechanisms of suppression and plasticity. The main aspects of immunity in the diverse forms of the P. brasiliensis infection are presented, as are the few extant studies on the relevance of Treg cells in the control of severity of the human disease. Finally, the influence of Toll-like receptors, Dectin-1, NOD-like receptor P3 (NLRP3), Myeloid differentiation factor-88 (MyD88), as well as the enzyme indoleamine 2,3 dioxygenase (IDO) on the expansion and function of Treg cells in a murine model of pulmonary paracoccidioidomycosis (PCM) is also discussed. It is demonstrated that some of these components are involved in the negative control of Treg cell expansion, whereas others positively trigger the proliferation and activity of these cells. Finally, the studies here summarized highlight the dual role of Treg cells in PCM, which can be protective by controlling excessive immunity and tissue pathology but also deleterious by inhibiting the anti-fungal immunity necessary to control fungal growth and dissemination.

Current Status on Immunological Therapies for Type 1 Diabetes Mellitus

PURPOSE OF REVIEW

Type 1 diabetes (T1D) occurs when there is destruction of beta cells within the islets of Langerhans in the pancreas due to autoimmunity. It is considered a complex disease, and different complications can surface and worsen the condition if T1D is not managed well. Since it is an incurable disease, numerous treatments and therapies have been postulated in order to control T1D by balancing hyperglycemia control while minimizing hypoglycemic episodes. The purpose of this review is to primarily look into the current state of the available immunological therapies and their advantages for the treatment of T1D.

RECENT FINDINGS

Over the years, immunological therapy has become the center of attraction to treat T1D. Immunomodulatory approaches on non-antigens involving agents such as cyclosporine A, mycophenolate mofetil, anti-CD20, cytotoxic T cells, anti-TNF, anti-CD3, and anti-thymocyte globulin as well as immunomodulative approaches on antigens such as insulin, glutamic acid decarboxylase, and heat shock protein 60 have been studied. Aside from these two approaches, studies and trials have also been conducted on regulatory T cells, dendritic cells, interleukin 2, interleukin 4, M2 macrophages, and rapamycin/interleukin 2 combination therapy to test their effects on patients with T1D. Many of these agents have successfully suppressed T1D in non-obese diabetic (NOD) mice and in human trials. However, some have shown negative results. To date, the insights into the management of the immune system have been increasing rapidly to search for potential therapies and treatments for T1D. Nevertheless, some of the challenges are still inevitable. A lot of work and effort need to be put into the investigation on T1D through immunological therapy, particularly to reduce complications to improve and enhance clinical outcomes.

Control of the Antitumor Immune Response by Cancer Metabolism

The metabolic reprogramming of tumor cells and immune escape are two major hallmarks of cancer cells. The metabolic changes that occur during tumorigenesis, enabling survival and proliferation, are described for both solid and hematological malignancies. Concurrently, tumor cells have deployed mechanisms to escape immune cell recognition and destruction. Additionally, therapeutic blocking of tumor-mediated immunosuppression has proven to have an unprecedented positive impact in clinical oncology. Increased evidence suggests that cancer metabolism not only plays a crucial role in cancer signaling for sustaining tumorigenesis and survival, but also has wider implications in the regulation of antitumor immune signaling through both the release of signaling molecules and the expression of immune membrane ligands. Here, we review these molecular events to highlight the contribution of cancer cell metabolic reprogramming on the shaping of the antitumor immune response.

CD28 between tolerance and autoimmunity: the side effects of animal models

Regulation of immune responses is critical for ensuring pathogen clearance and for preventing reaction against self-antigens. Failure or breakdown of immunological tolerance results in autoimmunity. CD28 is an important co-stimulatory receptor expressed on T cells that, upon specific ligand binding, delivers signals essential for full T-cell activation and for the development and homeostasis of suppressive regulatory T cells. Many in vivo mouse models have been used for understanding the role of CD28 in the maintenance of immune homeostasis, thus leading to the development of CD28 signaling modulators that have been approved for the treatment of some autoimmune diseases. Despite all of this progress, a deeper understanding of the differences between the mouse and human receptor is required to allow a safe translation of pre-clinical studies in efficient therapies. In this review, we discuss the role of CD28 in tolerance and autoimmunity and the clinical efficacy of drugs that block or enhance CD28 signaling, by highlighting the success and failure of pre-clinical studies, when translated to humans.

CD28 Blockade Ex Vivo Induces Alloantigen-Specific Immune Tolerance but Preserves T-Cell Pathogen Reactivity

Donor T-cells contribute to reconstitution of protective immunity after allogeneic hematopoietic stem cell transplantation (HSCT) but must acquire specific tolerance against recipient alloantigens to avoid life-threatening graft-versus-host disease (GvHD). Systemic immunosuppressive drugs may abrogate severe GvHD, but this also impedes memory responses to invading pathogens. Here, we tested whether ex vivo blockade of CD28 co-stimulation can enable selective T-cell tolerization to alloantigens by facilitating CD80/86-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) signaling. Treatment of human allogeneic dendritic cell/T-cell co-cultures with a human CD28 blocking antibody fragment (α-huCD28) significantly abrogated subsequent allospecific immune responses, seen by decreased T-cell proliferation and of type 1 cytokine (IFN-γ and IL-2) expression. Allo-tolerization persisted after discontinuation of CD28 blockade and secondary alloantigen stimulation, as confirmed by enhanced CTLA-4 and PD-1 immune checkpoint signaling. However, T-cells retained reactivity to pathogens, supported by clonotyping of neo-primed and cross-reactive T-cells specific for Candida albicans or third-party antigens using deep sequencing analysis. In an MHC-mismatched murine model, we tolerized C57BL/6 T-cells by ex vivo exposure to a murine single chain Fv specific for CD28 (α-muCD28). Infusion of these cells, after α-muCD28 washout, into bone marrow-transplanted BALB/c mice caused allo-tolerance and did not induce GvHD-associated hepatic pathology. We conclude that selective CD28 blockade ex vivo can allow the generation of stably allo-tolerized T-cells that in turn do not induce graft-versus-host reactions while maintaining pathogen reactivity. Hence, CD28 co-stimulation blockade of donor T-cells may be a useful therapeutic approach to support the immune system after HSCT.

Belatacept Does Not Inhibit Follicular T Cell-Dependent B-Cell Differentiation in Kidney Transplantation

Humoral alloreactivity has been recognized as a common cause of kidney transplant dysfunction. B-cell activation, differentiation, and antibody production are dependent on IL-21⁺CXCR5⁺follicular T-helper (Tfh) cells. Here, we studied whether belatacept, an inhibitor of the costimulatory CD28-CD80/86-pathway, interrupts the crosstalk between Tfh- and B-cells more efficiently than the calcineurin inhibitor tacrolimus. The suppressive effects of belatacept and tacrolimus on donor antigen-driven Tfh-B-cell interaction were functionally studied in peripheral blood mononuclear cells from 40 kidney transplant patients randomized to a belatacept- or tacrolimus-based immunosuppressive regimen. No significant differences in uncultured cells or donor antigen-stimulated cells were found between belatacept- and tacrolimus-treated patients in the CXCR5⁺Tfh cell generation and activation (upregulation of PD-1). Belatacept and tacrolimus in vitro minimally inhibited Tfh-cell generation (by ~6-7%) and partially prevented Tfh-cell activation (by ~30-50%). The proportion of IL-21⁺-activated Tfh-cells was partially decreased by in vitro addition of belatacept or tacrolimus (by ~60%). Baseline expressions and proportions of activated CD86⁺ B-cells, plasmablasts, and transitional B-cells after donor antigen stimulation did not differ between belatacept- and tacrolimus-treated patients. Donor antigen-driven CD86 upregulation on memory B-cells was not fully prevented by adding belatacept in vitro (~35%), even in supratherapeutic doses. In contrast to tacrolimus, belatacept failed to inhibit donor antigen-driven plasmablast formation (~50% inhibition vs. no inhibition, respectively, p < 0.0001). In summary, donor antigen-driven Tfh-B-cell crosstalk is similar in cells obtained from belatacept- and tacrolimus-treated patients. Belatacept is, however, less potent in vitro than tacrolimus in inhibiting Tfh-cell-dependent plasmablast formation.

IDO1: An important immunotherapy target in cancer treatment

Indoleamine 2,3-dioxigenase 1 (IDO1) acts in pathogenic inflammatory processes and engender immune tolerance to tumor antigens. IDO1 can decrease the tryptophan and produce a series of toxic kynurenine metabolites to promote the immune toleration via GCN2 pathway, mTOR pathway, toxic effect of kynurenine and favoring differentiation of Tregs. IDO1 can be induced in most human cells, especially APCs and cancer cells through canonical and non-canonical NF-κB and Jak/STAT pathways, as well as PKC and TGF-β signaling pathways. A series of human cancers over-express IDO1 in a constitutive way. Thus, IDO1 is likely to be an attractive target for developing inhibitors of tumor treatments. Many preclinical and clinical trials have been underway and suggest that IDO1 inhibitor maybe an effective tool against a wide range of cancers. However, the IDO1 inhibitor alone had been verified that to be disappointment in achieving effective antitumor efficacy. Concentrating on its molecular mechanism in immune toleration and complex environments of cancer, IDO1 inhibitor could cooperate with chemotherapies and other immune target inhibitors to lessen the tumor.

The soluble cytoplasmic tail of CD45 (ct-CD45) in human plasma contributes to keep T cells in a quiescent state

The cytoplasmic tail of CD45 (ct‐CD45) is proteolytically cleaved and released upon activation of human phagocytes. It acts on T cells as an inhibitory, cytokine‐like factor in vitro. Here, we show that ct‐CD45 is abundant in human peripheral blood plasma from healthy adults compared with plasma derived from umbilical cord blood and plasma from patients with rheumatoid arthritis or systemic lupus erythematosus. Plasma depleted of ct‐CD45 enhanced T‐cell proliferation, while addition of exogenous ct‐CD45 protein inhibited proliferation and reduced cytokine production of human T lymphocytes in response to TCR signaling. Inhibition of T‐cell proliferation by ct‐CD45 was overcome by costimulation via CD28. T‐cell activation in the presence of ct‐CD45 was associated with an upregulation of the quiescence factors Schlafen family member 12 (SLFN12) and Krueppel‐like factor 2 (KLF2) as well as of the cyclin‐dependent kinase (CDK) inhibitor p27kip1. In contrast, positive regulators of the cell cycle such as cyclin D2 and D3 as well as CDK2 and CDK4 were found to be downregulated in response to ct‐CD45. In summary, we demonstrate that ct‐CD45 is present in human plasma and sets the threshold of T‐cell activation.

Pharmacokinetics, Pharmacodynamics, Safety, and Tolerability of ASP2408, a Potent Selective T-Cell Costimulation Modulator After Single and Multiple Ascending Doses in Healthy Volunteers and RA Patients

ASP2408 is a next-generation anti-cytotoxic T lymphocyte antigen-4 fusion protein engineered for improved CD86 binding affinity as a treatment for rheumatoid arthritis (RA). In 72 healthy subjects (n = 6/treatment), ASP2408 was administered as single ascending doses intravenously at 0.003 to 10.0 mg/kg or subcutaneously at 0.3 to 3.0 mg/kg. It showed decreased clearance and prolonged half-life with increasing doses, consistent with target-mediated disposition. The apparent bioavailability was 36.3%-56.7% across single subcutaneous doses. Sixteen RA patients (n = 8/treatment) on stable methotrexate received 3 × 3.0 mg/kg subcutaneously every 4 weeks or every 2 weeks. Similar to single-dose treatment, ASP2408 concentrations peaked 2 to 3 days postdose, with a median t1/2 of approximately 8 days. Using CD86 receptor occupancy (RO) as a mechanistic biomarker, ASP2408 demonstrated dose-dependent binding to its target. ASP2408 3.0 mg/kg subcutaneously every 4 weeks and every 2 weeks led to a mean %CD86 RO ≥ 74.7% and ≥ 81.5%, respectively, within each dosing interval. ASP2408 was well tolerated across studies with no evidence of dose-limiting toxicity or clinically significant changes in clinical laboratory test results, vital signs, or 12-lead electrocardiograms. ASP2408 elicited antidrug antibodies in the majority of patients, but with no clinical sequelae.

Ubiquitous LEA29Y Expression Blocks T Cell Co-Stimulation but Permits Sexual Reproduction in Genetically Modified Pigs

We have successfully established and characterized a genetically modified pig line with ubiquitous expression of LEA29Y, a human CTLA4-Ig derivate. LEA29Y binds human B7.1/CD80 and B7.2/CD86 with high affinity and is thus a potent inhibitor of T cell co-stimulation via this pathway. We have characterized the expression pattern and the biological function of the transgene as well as its impact on the porcine immune system and have evaluated the potential of these transgenic pigs to propagate via assisted breeding methods. The analysis of LEA29Y expression in serum and multiple organs of CAG-LEA transgenic pigs revealed that these animals produce a biologically active transgenic product at a considerable level. They present with an immune system affected by transgene expression, but can be maintained until sexual maturity and propagated by assisted reproduction techniques. Based on previous experience with pancreatic islets expressing LEA29Y, tissues from CAG-LEA29Y transgenic pigs should be protected against rejection by human T cells. Furthermore, their immune-compromised phenotype makes CAG-LEA29Y transgenic pigs an interesting large animal model for testing human cell therapies and will provide an important tool for further clarifying the LEA29Y mode of action.

Tolerogenic Dendritic Cells on Transplantation: Immunotherapy Based on Second Signal Blockage

Dendritic cells (DCs), the most important professional antigen-presenting cells (APC), play crucial role in both immunity and tolerance. It is well known that DCs are able to mount immune responses against foreign antigens and simultaneously tolerate self-antigens. Since DCs can be modulated depending on the surrounding microenvironment, they can act as a bridge between innate and adaptive immunity. However, the mechanisms that support this dual role are not entirely clear. Recent studies have shown that DCs can be manipulated ex vivo in order to trigger their tolerogenic profile, what can be a tool to be used in clinical trials aiming the treatment of various diseases and the prevention of transplant rejection. In this sense, the blockage of costimulatory molecules on DC, in the attempt of inhibiting the second signal in the immunological synapse, can be considered as one of the main strategies under development. This review brings an update on current therapies using tolerogenic dendritic cells modulated with costimulatory blockers with the aim of reducing transplant rejection. However, although there are current clinical trials using tolerogenic DC to treat allograft rejection, the actual challenge is to modulate these cells in order to maintain a permanent tolerogenic profile.

IDO expressing dendritic cells suppress allograft rejection of small bowel transplantation in mice by expansion of Foxp3+ regulatory T cells

BACKGROUND

Indoleamine 2,3-dioxygenase (IDO), the enzyme that catalyzes the first and rate-limiting step of tryptophan catabolism, suppresses T-cell responses by tryptophan depletion and accumulation of kynurenine metabolites. IDO prevents allograft rejection in various transplantations.

METHODS

Dendritic cells (DC) highly expressing IDO (IDO(+) DC) were cultured through transduction of adenovirus vectors carrying the IDO sequence. IDO(+) DC were incubated with CD4(+) CD25(-) T cells to detect T cell proliferation. The effects of IDO(+) DC and 3-Hydroxyanthranilic acid (3-HAA) were verified in an allogeneic murine small bowel transplantation (SBT) model. Foxp3(+) Treg cells of recipient mice were detected by flow cytometry and cytokines in plasma were determined by ELISA.

RESULTS

IDO(+) DC effectively suppressed proliferation of CD4(+) CD25(-) T cells in vitro, and this effect could be enhanced by adding 3-HAA. In the SBT transplantation model, both 3-HAA (P < 0.05) and IDO(+) DC (P < 0.01) prolonged the survival time of transplanted mice. Mice treated with IDO(+) DC achieved longer mean survival time than 3-HAA administrated mice (11.5d vs. 18.5d). Grafts from IDO(+) DC, 3-HAA and combination treatment group showed reduced inflammation and minimal architectural distortion. IFN-γ production was significantly inhibited by IDO(+) DC and 3-HAA (P<0.05). The expression of IL-2 was slightly lower with 3-HAA or IDO(+) DC treatment. However, IL-10 was higher in 3-HAA, IDO(+) DC and combination treatment groups, while TGF-β was elevated in all non-control groups.

CONCLUSIONS

IDO(+) DC plus 3-HAA has an immunoprotective role and represents a potential strategy to suppress acute rejection and prolong survival of grafts in SBT.

The potential of targeting indoleamine 2,3-dioxygenase for cancer treatment

INTRODUCTION

Degradation of the essential amino acid tryptophan via indoleamine 2,3-dioxygenase (IDO1) represents an important antiproliferative strategy of the cellular immune response. Tryptophan shortage and accumulation of kynurenine downstream products also affect T-cell responses, providing a negative feedback control of immune activation. IDO1 activity can promote a regulatory phenotype in both T cells and dendritic cells. These phenomena can support tumor immune escape.

AREAS COVERED

IDO1 activity reflects the course of several malignancies, and determination of kynurenine to tryptophan ratio in serum/plasma can be used to assess immune activation. Moreover, the accelerated breakdown of tryptophan has been correlated with the development of cancer-associated disturbances such as anemia, weight loss and depression. Tumoral IDO1 expression was correlated with a poor prognosis in several types of tumors, which makes it to an interesting target for immunotherapy. In addition, according to recent data, a role of trytptophan 2,3-dioxygenase (TDO) in tumorigenesis cannot be excluded.

EXPERT OPINION

Tryptophan metabolism is critical for cell proliferation, inflammation and immunoregulation. Accelerated tryptophan breakdown favors tumor immune escape. Accordingly, targeting IDO1 by immunotherapy may represent a favorable approach; however, blocking crucial immunoregulatory pathways could also introduce the risk of immune system overactivation, finally leading to unresponsiveness.

CTLA4-Ig preserves thymus-derived T regulatory cells

BACKGROUND

CTLA-4 immunoglobulin fusion proteins (CTLA4-Ig) suppress immune reactions by blocking the T-cell costimulatory CD28-CD80-86 pathway and are used in clinical trials for diseases featuring exaggerated T-cell reactivity including autoimmune diseases and allograft rejection. However, because CTLA4-Ig has been suspected to interfere with T regulatory (Treg) cell homeostasis and function, recently, substantial concerns on CTLA4-Ig's potentially antitolerogenic effects have been raised.

METHODS

We tested immunoregulatory CTLA4-Ig explicitly for its effect on Treg cell numbers, frequencies and function in an in vitro murine major histocompatibility complex mismatched setting using C57BL/6 bone marrow-derived dendritic cells as stimulators of allogeneic Balb/c Foxp3 T cells, which allowed for tracing Treg cells in a straightforward fashion.

RESULTS

The presence of CTLA4-Ig in mixed leukocyte reactions-while dampening the global proliferative response of allostimulated Balb/c T cells-resulted in a relative increase of the frequency of thymus-derived CD4CD25Foxp3 Treg cells with intact suppressive activity. This relative increase was caused by a selective inhibitory effect of CTLA4-Ig on proliferating conventional T cells, whereas the proliferative capacity of Treg cells in cell cultures remained unaffected. Additionally, in the presence of CTLA4-Ig, the frequency of apoptosis was decreased in these cells.

CONCLUSION

Our findings unequivocally demonstrate that CTLA4-Ig does not negatively affect Treg cell frequencies and function in vitro.

Impaired T cell activation and cytokine production by calcitriol-primed human B cells

The biologically active form of vitamin D3 , 1, 25-dihydroxyvitamin D3 (calcitriol), is a potent modulator of the immune response. We have shown previously that calcitriol modulates the immunoglobulin response in vitro and in vivo in mice and humans. To analyse the underlying molecular mechanisms we studied whether calcitriol-primed B cells modulate T cell activation and function. Human B cells were stimulated with anti-CD40 and interleukin (IL)-4 in the presence of increasing concentrations of calcitriol. After removal of calcitriol, primed B cells were co-cultured with autologous CD4(+) T cells; the B cell phenotype T cell activation and their consecutive cytokine production were also assessed. Naive T cells co-cultured with calcitriol-primed naive B cells showed a reduced expansion, nuclear factor of activated T cells, cytoplasmic 2 (NFATc2) expression and cytokine production upon restimulation. CD86 expression on B cells after calcitriol priming was identified as an underlying mechanism, as T cell activation and expansion was rescued by activating anti-CD28 antibodies. Our data indicate that calcitriol-primed B cells display an impaired capacity to activate T cells. Taken together, we identified a novel B cell-dependent vitamin D immune regulatory mechanism, namely by decreased co-stimulation of calcitriol-primed B cells.

Blockade of the activation of T cells around β-cell by the targeted CTLA-4 Ig at the surface of β-cell

Diabetes mellitus affects 347 million people worldwide, and over 80 % of diabetes deaths occur in low- and middle-income countries. Type 1 diabetes (T1D) is characterized by the attacks of the body's own immune system on the pancreatic β-cells. In this work, we present a new CTLA-4 Ig targeting at the surface of β-cell and prepare it from Escherichia coli aiming at clearing activated T cells around β-cells and avoiding all-round decline in systematic immunity. This fusion protein is composed of CTLA-4-Ig part and β-cell-targeting part, with properties of the therapeutic effect of CTLA-4-Ig and selective binding to β-cells. In preliminary biological activity assay, our results verified the feasibility of β-cell-targeting strategy and its activity of CTLA-4-Ig part. The fusion protein recognizes and binds specifically to CD80(+) and CD86(+) cells as well as β-cell, but not to control cells, displaying the potential to be used as a feasible and effective treatment of T1D with lessened side effect.

Regulatory myeloid cells in transplantation

Regulatory myeloid cells (RMC) are emerging as novel targets for immunosuppressive (IS) agents and hold considerable promise as cellular therapeutic agents. Herein, we discuss the ability of regulatory macrophages, regulatory dendritic cells, and myeloid-derived suppressor cells to regulate alloimmunity, their potential as cellular therapeutic agents, and the IS agents that target their function. We consider protocols for the generation of RMC and the selection of donor- or recipient-derived cells for adoptive cell therapy. Additionally, the issues of cell trafficking and antigen (Ag) specificity after RMC transfer are discussed. Improved understanding of the immunobiology of these cells has increased the possibility of moving RMC into the clinic to reduce the burden of current IS agents and to promote Ag-specific tolerance. In the second half of this review, we discuss the influence of established and experimental IS agents on myeloid cell populations. IS agents believed historically to act primarily on T cell activation and proliferation are emerging as important regulators of RMC function. Better insights into the influence of IS agents on RMC will enhance our ability to develop cell therapy protocols to promote the function of these cells. Moreover, novel IS agents may be designed to target RMC in situ to promote Ag-specific immune regulation in transplantation and to usher in a new era of immune modulation exploiting cells of myeloid origin.

A transendocytosis perspective on the CD28/CTLA-4 pathway

T cell activation is a key event in the adaptive immune response and vital to the generation of both cellular and humoral immunity. Activation is required not only for effective CD4 T cell responses but also to provide help for B cells and the generation of cytotoxic T cell responses. Unsurprisingly, impaired T cell activation results in infectious pathology, whereas dysregulated activation can result in autoimmunity. The decision to activate is therefore tightly regulated and the CD28/CTLA-4 pathway represents this apical decision point at the molecular level. In particular, CTLA-4 (CD152) is an essential checkpoint control for autoimmunity; however, the molecular mechanism(s) by which CTLA-4 achieves its regulatory function are not well understood, especially how it functionally intersects with the CD28 pathway. In this chapter, we review the established molecular and cellular concepts relating to CD28 and CTLA-4 biology, and attempt to integrate these by discussing the transendocytosis of ligands as a new model of CTLA-4 function.