T-cell activation and transplantation tolerance

Human PD-L1 overexpression decreases xenogeneic human T-cell immune responses towards porcine kidneys

Xenotransplantation offers a promising alternative to circumvent the lack of donated human organs available for transplantation. Different attempts to improve the survival of xenografts led to the generation of transgenic pigs expressing various combinations of human protective genes or knocked out for specific antigens. Currently, testing the efficiency of porcine organs carrying different genetic modifications in preventing xenogeneic immune responses completely relies on in vitro assays, humanized mouse models, or non-human primate transplantation models. However, these tests are often associated with major concerns due to reproducibility and generation of insufficient data as well as they raise ethical, logistical, and economic issues. In this study, we investigated the feasibility of specifically assessing the strength of human T-cell responses towards the kidneys of wild-type (WT) or transgenic pigs overexpressing human programmed death-1 ligand 1 (hPD-L1) during ex vivo kidney perfusion (EVKP). Human T cells were shown to adhere to the endothelium and transmigrate into WT and hPD-L1 kidneys. However, transcript levels of TNF-a and IFN-y as well as cytotoxic molecules such as granzyme B and perforin secreted by human T cells were significantly decreased in the tissue of hPD-L1 kidneys in comparison to WT kidneys. These results were confirmed via in vitro assays using renal endothelial cells (ECs) isolated from WT and hPD-L1 transgenic pigs. Both CD4+ and CD8+ T cells showed significantly lower proliferation rates after exposure to hPD-L1 porcine renal ECs in comparison to WT ECs. In addition, the secretion of pro-inflammatory cytokines was significantly reduced in cultures using hPD-L1 ECs in comparison to WT ECs. Remarkably, hPD-L1 EC survival was significantly increased in cytotoxic assays. This study demonstrates the feasibility of evaluating the human response of specific immune subsets such as human T cells towards the whole xenograft during EVKP. This may represent a robust strategy to assess the potency of different genetic modifications to prevent xenogeneic immune responses and thereby predict the risk of immune rejection of new genetically engineered xenografts.

Immune-checkpoint expression in antigen-presenting cells (APCs) of cytomegaloviruses infection after transplantation: as a diagnostic biomarker

Cytomegalovirus (CMV), a member of the Herpesviridae family, mostly causes only slight feverish symptoms or can be asymptomatic in immunocompetent individuals. However, it is known to be particularly a significant cause of morbidity in immunocompromised patients, including transplant recipients, whose immune system has been weakened due to the consumption of immunosuppressor drugs. Therefore, the diagnosis of CMV infection after transplantation is crucial. New diagnostic methods for the quick detection of CMV have been developed as a result of understanding the clinical importance of invasive CMV. Antigen-presenting cells (APCs) and T cells are important components of the immune system and it may be possible to diagnose viral infections using immunological markers, such as lymphocytosis, cytotoxic T lymphocytes (CTL), and serum cytokine levels. Moreover, PD-1, CTLA 4, and TIGIT, which are expressed on certain T cells and antigen-presenting cells, are over-expressed during the infection. The assessment of CMV infection based on T cell and APC activity, and the expression of immunological checkpoints, can be helpful for the diagnosis of transplant patients at risk for CMV infection. In this review, we will investigate how immune checkpoints affect immune cells and how they impair organ transplantation after CMV infection.

Synergistic potential of immune checkpoint inhibitors and therapeutic cancer vaccines

Cancer vaccines and immune checkpoint inhibitors (ICIs) function at different stages of the cancer immune cycle due to their distinct mechanisms of action. Therapeutic cancer vaccines enhance the activation and infiltration of cytotoxic immune cells into the tumor microenvironment (TME), while ICIs, prevent and/or reverse the dysfunction of these immune cells. The efficacy of both classes of immunotherapy has been evaluated in monotherapy, but they have been met with several challenges. Although therapeutic cancer vaccines can activate anti-tumor immune responses, these responses are susceptible to attenuation by immunoregulatory molecules. Similarly, ICIs are ineffective in the absence of tumor-infiltrating lymphocytes (TILs). Further, ICIs are often associated with immune-related adverse effects that may limit quality of life and compliance. However, the combination of the improved immunogenicity afforded by cancer vaccines and restrained immunosuppression provided by immune checkpoint inhibitors may provide a suitable platform for therapeutic synergism. In this review, we revisit the history and various classifications of therapeutic cancer vaccines. We also provide a summary of the currently approved ICIs. Finally, we provide mechanistic insights into the synergism between ICIs and cancer vaccines.

Diagnostic Biomarkers and Immune Infiltration in Patients With T Cell-Mediated Rejection After Kidney Transplantation

T cell-mediated rejection (TCMR) is an important rejection type in kidney transplantation, characterized by T cells and macrophages infiltration. The application of bioinformatic analysis in genomic research has been widely used. In the present study, Microarray data was analyzed to identify the potential diagnostic markers of TCMR in kidney transplantation. Cell-type identification by estimating relative subsets of RNA transcript (CIBERSORT) was performed to determine the distribution of immune cell infiltration in the pathology. Totally 129 upregulated differently expressed genes (DEGs) and 378 downregulated DEGs were identified. The GO and KEGG results demonstrated that DEGs were mainly associated with pathways and diseases involved in immune response. The intersection of the two algorithms (PPI network and LASSO) contains three overlapping genes (CXCR6, CXCL13 and FCGR1A). After verification in GSE69677, only CXCR6 and CXCL13 were selected. Immune cells Infiltration analysis demonstrated that CXCR6 and CXCL13 were positively correlated with gamma delta T cells (p < 0.001), CD4⁺ memory activated T cells (p < 0.001), CD8⁺ T cells (p < 0.001) and M1 macrophages (p = 0.006), and negatively correlated with M2 macrophages (p < 0.001) and regulatory T cells (p < 0.001). Immunohistochemical staining and image analysis confirmed the overexpression of CXCR6 and CXCL13 in human allograft TCMR samples. CXCR6 and CXCL13 could be diagnostic biomarkers of TCMR and potential targets for immunotherapy in patients with TCMR.

Bioactive compounds in green tea may improve transplant tolerance: A computational systems biology analysis

BACKGROUND

Green tea (Camellia sinensis) has bioactive compounds that have been shown to possess nutritive effects on various biomolecular processes such as immunomodulation. This research explores the immunomodulatory effects of green tea in reducing transplant rejection.

METHOD

The study employs computational systems biology: 1) to identify biomolecular mechanisms of immunomodulation in transplant rejection; 2) to identify the bioactive compounds of green tea and their specific effects on mechanisms of immunomodulation in transplant rejection; and, 3) to predict the quantitative effects of those bioactive compounds on immunomodulation in transplant rejection.

RESULTS

Three bioactive compounds of green tea - epicatechin (EC), gallic acid (GA), and epigallocatechin gallate (EGCG), were identified for their potential effects on immunomodulation of transplant rejection. Of the three, EGCG was the only one determined to enhance anti-inflammatory activity by: 1) upregulating synthesis of HO-1 that is known to promote Treg and Th2 phenotypes associated with enabling transplant tolerance; and, 2) downregulating pro-inflammatory cytokines IL-2, IL-17, IFN-γ, TNF-α, NO, IL-6, and IL-1β that are known to promote Th1 and Th17 phenotypes associated with transplant rejection.

CONCLUSIONS

To the best of our knowledge, this study provides the first molecular mechanistic understanding the clinical nutritive value of green tea, specifically the bioactive compound EGCG, in enabling transplant tolerance.

Trimetazidine an emerging paradigm in renal therapeutics: Preclinical and clinical insights

Trimetazidine (TMZ) is a well-known anti-ischemic agent used for the treatment of angina pectoris. In the past decades, the efficacy of this drug has been tested in a wide range of kidney injuries, including drug-induced nephrotoxicity (DIN), radio-contrast agent-induced nephropathy, and surgically induced renal ischemic injury. TMZhas renoprotective effects by attenuating oxidative stress, inflammatory cytokine release, maintaining oxygen and energy balance. Moreover, TMZ administration prevented kidney graft rejection in the porcine model by suppressing the infiltration of mononuclear cells, preserving mitochondrial functions, and maintaining Ca+ homeostasis. In DIN and diabetic kidney diseases,TMZ treatment prevents renal injury by inactivating immune cells, attenuating renal fibrosis, inflammation, apoptosis, and histological abnormalities. Interestingly, the clinical therapeutic efficacy of TMZ has also been documented in pre-existing kidney disease patients undergoing contrast exposure for diagnostic intervention. However, the mechanistic insights into the TMZ mediated renoprotective effects in other forms of renal injuries, including type-2 diabetes, drug-induced nephrotoxicity, and hypertension-induced chronic kidney diseases, remain uninvestigated and incomplete. Moreover, the clinical utility of TMZ as a renoprotective agent in radio-contrast-induced nephrotoxicity needs to be tested in a large patient population. Nevertheless, the available pieces of evidence suggest that TMZ is a promising and emerging renal therapy for the treatment and management of kidney diseases of variable etiologies. This review discusses the various pre-clinical and clinical findings and provides mechanistic insights into the TMZ mediated beneficial effects in various kidney diseases.

Cytotoxic T Lymphocytes (CTLs) and Kidney Transplantation: An Overview

Involvement of T lymphocytes in kidney transplantation is a well-developed topic; however, most of the scientific interest focused on the different type of CD4+ lymphocyte subpopulations. Few authors, instead, investigated the role of CD8+ T cells in renal transplantation and how deleterious they can be to long-term allograft survival. Recently, there has been a renewed interest in the CD8+ T cells involvement in the transplantation field with the aim to investigate the immunological mechanisms underlying the infiltration of CD8+ T cells and their biological functions in human kidney allografts. The purpose of the present review is to highlight the role of allo-reactive cytotoxic T lymphocytes (CTLs) CD8⁺ subset in allograft kidney recipients and their related clinical complications.

Up-Regulation of Donor Dendritic Cell PD-L1 Expression Reduced Recipient Lymphocyte Activation and Proliferation In Vitro

OBJECTIVE

To observe the effects of dendritic cells (DC) in donor C57BL/6 (H-2^b) micetransfected with recombinant adenovirus vector Ad-PD-L1 on proliferation and activation of lymphocytes in recipient DBA/2 (H-2^d) mice.

METHODS

The pSport 1-mSD274 plasmid containing the full-length PD-L1 cDNA of the mouse was digested and subcloned to the shuttle plasmid pShuttle-GFP-CMV(-), and then the adenovirus skeleton plasmid pAdxsi-GFP-CMV-PD-L1 was constructed by enzymolysis and ligation, transformed into DH5α sensitive bacteria, and screened for positive clones. After enzyme digestion, sequencing, and identification, 293 cells were transfected with liposome after linearization for packaging and amplification, and the virus was purified by cesium chloride density gradient centrifugation. DC of donor C57BL/6 mice were isolated, cultured, and divided into the following 3 groups: group A, adenovirus vector Ad-PD-L1 transfection group; group B, empty vector transfection group; and group C, control group. Western blot was used to detect the expression of PD-L1 in each group of cells after transfection. Isolate lymphocytes from recipient DBA/2 mice were labeled with carboxyfluorescein diacetate succinimidyl ester (CFSE) and mixed with DC of donor C57BL/6 mice with lymphocytes of recipient DBA/2 mice. Flow cytometry was performed to observe the proliferation of lymphocytes.

RESULTS

Digestion and sequencing confirmed that the recombinant adenovirus vector Ad-PD-L1 containing PD-L1 was successfully constructed. After transfection with DC of donor C57BL/6 mice, the expression of PD-L1 increased by 37% (P < .05), and the PD-L1 transfected DC and recipient DBA/2. Mouse lymphocytes were cocultured. Compared with the control group, the increased expression of PD-L1 significantly inhibited the proliferation and activation of lymphocytes. The lymphocyte proliferation of DBA/2 mice decreased by 41% (P < .01).

CONCLUSION

The recombinant adenovirus vector Ad-PD-L1 containing the mouse PD-L1 gene was successfully constructed. After transfection with dendritic cells of donor C57BL/6 mice, PD-1/PD-L1 inhibited lymphocytes proliferation and activation of recipient DBA/2 mice through costimulatory pathway.

CD28 gene polymorphisms and acute cellular rejection after liver transplantation

The co-stimulatory molecule CD28 plays an important role in T-cell-mediated immune response like acute cellular liver transplant rejection. The aim of the retrospective case- control study was to examine whether the single nucleotide polymorphisms (SNPs) rs3116487, rs3116494, and rs3116496 of the CD28 gene are associated with acute cellular liver transplant rejection. The mentioned SNPs were genotyped in 147 liver transplant recipients without acute cellular rejection and 144 liver transplant recipients with acute cellular rejection by real-time endpoint genotyping. The genotype and allele frequencies of the SNPs did not show any significant differences between both groups. Haplotype analyzes of the SNPs also showed no association. Our data suggest that the analyzed SNPs are not major contributors to the susceptibility of acute cellular liver transplant rejection.

Manipulation of Regulatory Dendritic Cells for Induction Transplantation Tolerance

Current organ transplantation therapy is life-saving but accompanied by well-recognized side effects due to post-transplantation systematic immunosuppressive treatment. Dendritic cells (DCs) are central instigators and regulators of transplantation immunity and are responsible for balancing allograft rejection and tolerance. They are derived from monocyte-macrophage DC progenitors originating in the bone marrow and are classified into different subsets based on their developmental, phenotypical, and functional criteria. Functionally, DCs instigate allograft immunity by presenting donor antigens to alloreactive T cells via direct, indirect, and semidirect recognition pathways and provide essential signaling for alloreactive T cell activation via costimulatory molecules and pro-inflammatory cytokines. Regulatory DCs (DCregs) are characterized by a relatively low expression of major histocompatibility complex, costimulatory molecules, and altered cytokine production and exert their regulatory function through T cell anergy, T cell deletion, and regulatory T cell induction. In rodent transplantation studies, DCreg-based therapy, by in situ targeting or infusion of ex vivo generated DCregs, exhibits promising potential as a natural, well-tolerated, organ-specific therapeutic strategy for promoting lasting organ-specific transplantation tolerance. Recent early-phase studies of DCregs have begun to examine the safety and efficacy of DCreg-induced allograft tolerance in living-donor renal or liver transplantations. The present review summarizes the basic characteristics, function, and translation of DCregs in transplantation tolerance induction.

Clinical Pharmacology and Interplay of Immune Checkpoint Agents: A Yin-Yang Balance

T cells have a central role in immune system balance. When activated, they may lead to autoimmune diseases. When too anergic, they contribute to infection spread and cancer proliferation. Immune checkpoint proteins regulate T cell function, including cytotoxic T lymphocyte antigen-4 (CTLA-4) and programmed cell death-1 (PD-1) and its ligand (PD-L1). These nodes of self-tolerance may be exploited pharmacologically to downregulate (CTLA-4 agonists) and activate [CTLA-4 and PD-1/PD-L1 antagonists, also called immune checkpoint inhibitors (ICIs)] the immune system.CTLA-4 agonists are used to treat rheumatologic immune disorders and graft rejection. CTLA-4, PD-1, and PD-L1 antagonists are approved for multiple cancer types and are being investigated for chronic viral infections. Notably, ICIs may be associated with immune-related adverse events (irAEs), which can be highly morbid or fatal. CTLA-4 agonism has been a promising method to reverse such life-threatening irAEs. Herein, we review the clinical pharmacology of these immune checkpoint agents with a focus on their interplay in human diseases.

Bendamustine with total body irradiation conditioning yields tolerant T-cells while preserving T-cell-dependent graft-versus-leukemia

Graft-versus-host disease (GvHD) remains a significant impediment to allogeneic hematopoietic cell transplantation (HCT) success, necessitating studies focused on alleviating GvHD, while preserving the graft-versus-leukemia (GvL) effect. Based on our previous studies showing bendamustine with total body irradiation (BEN-TBI) conditioning reduces GvHD compared to the current clinical standard of care cyclophosphamide (CY)-TBI in a murine MHC-mismatched bone marrow transplantation (BMT) model, this study aimed to evaluate the role and fate of donor T-cells following BEN-TBI conditioning. We demonstrate that BEN-TBI reduces GvHD compared to CY-TBI independently of T regulatory cells (Tregs). BEN-TBI conditioned mice have a smaller proportion and less activated donor T-cells, with lower CD47 expression, early post-transplant, but no sustained phenotypic differences in T-cells. In BEN-TBI conditioned mice, donor T-cells gain tolerance specific to host MHC antigens. Though these T-cells are tolerant to host antigens, we demonstrate that BEN-TBI preserves a T-cell-dependent GvL effect. These findings indicate that BEN-TBI conditioning reduces GvHD without compromising GvL, warranting its further investigation as a potentially safer and more efficacious clinical alternative to CY-TBI.

Impact of infection on transplantation tolerance

Allograft tolerance is the ultimate goal of organ transplantation. Current strategies for tolerance induction mainly focus on inhibiting alloreactive T cells while promoting regulatory immune cells. Pathogenic infections may have direct impact on both effector and regulatory cell populations, therefore can alter host susceptibility to transplantation tolerance induction as well as impair the quality and stability of tolerance once induced. In this review, we will discuss existing data demonstrating the effect of infections on transplantation tolerance, with particular emphasis on the role of the stage of infection (acute, chronic, or latent) and the stage of tolerance (induction or maintenance) in this infection-tolerance interaction. While the deleterious effect of acute infection on tolerance is mainly driven by proinflammatory cytokines induced shortly after the infection, chronic infection may generate exhausted T cells that could in fact facilitate transplantation tolerance. In addition to pathogenic infections, commensal intestinal microbiota also has numerous significant immunomodulatory effects that can shape the host alloimmunity following transplantation. A comprehensive understanding of these mechanisms is crucial for the development of therapeutic strategies for robustly inducing and stably maintaining transplantation tolerance while preserving host anti-pathogen immunity in clinically relevant scenarios.

CCR4 expression on host T cells is a driver for alloreactive responses and lung rejection

Despite current immunosuppressive strategies, long-term lung transplant outcomes remain poor due to rapid allogenic responses. Using a stringent mouse model of allo-airway transplantation, we identify the CCR4-ligand axis as a central node driving secondary lymphoid tissue homing and activation of the allogeneic T cells that prevent long-term allograft survival. CCR4 deficiency on transplant recipient T cells diminishes allograft injury and when combined with CTLA4-Ig leads to an unprecedented long-term lung allograft accommodation. Thus, we identify CCR4-ligand interactions as a central mechanism driving allogeneic transplant rejection and suggest it as a potential target to enhance long-term lung transplant survival.

In vivo reprogramming of immune cells: Technologies for induction of antigen-specific tolerance

Technologies that induce antigen-specific immune tolerance by mimicking naturally occurring mechanisms have the potential to revolutionize the treatment of many immune-mediated pathologies such as autoimmunity, allograft rejection, and allergy. The immune system intrinsically has central and peripheral tolerance pathways for eliminating or modulating antigen-specific responses, which are being exploited through emerging technologies. Antigen-specific tolerogenic responses have been achieved through the functional reprogramming of antigen-presenting cells or lymphocytes. Alternatively, immune privileged sites have been mimicked using biomaterial scaffolds to locally suppress immune responses and promote long-term allograft survival. This review describes natural mechanisms of peripheral tolerance induction and the various technologies being developed to achieve antigen-specific immune tolerance in vivo. As currently approved therapies are non-specific and carry significant associated risks, these therapies offer significant progress towards replacing systemic immune suppression with antigen-specific therapies to curb aberrant immune responses.

Interleukin-2 Functionalized Nanocapsules for T Cell-Based Immunotherapy

A major demand on immunotherapy is the direct interference with specific immune cells in vivo. In contrast to antibody-engineered nanoparticles to control dendritic cells function, targeting of T cells for biomedical applications still remains an obstacle as they disclose reduced endocytic activities. Here, by coupling the cytokine interleukin-2 (IL-2) to the surface of hydroxyethyl starch nanocapsules, we demonstrated a direct and specifc T cell targeting in vitro and in vivo by IL-2 receptor-mediated internalization. For this purpose, defined amounts of azide-functionalized IL-2 were linked to alkyne-functionalized hydroxyethyl starch nanocapsules via copper-free click reactions. In combination with validated quantification of the surface-linked IL-2 with anthracen azide, this method allowed for engineering IL-2-functionalized nanocapsules for an efficient targeting of human and murine T cell populations with various IL-2 receptor affinities. This nanocapsule-mediated technique is a promising strategy for T cell-based immunotherapies and may be translated to other cytokine-related targeting systems.

Down-Regulation of Donor Kupffer Cell B7 Expression Reduced Recipient Lymphocyte Activation and Secretion of Interleukin-2 In Vitro

BACKGROUND

Kupffer cell (KC), a kind of important antigen-presenting cell in liver, play an important role in the process of acute rejection after liver transplantation. The aim of this study was to investigate effect of suppression of donor KC B7 expression on recipient lymphocyte activation and secretion of interleukin-2 (IL-2) in vitro.

METHODS

Liver ex vivo perfusion with collagenase IV and density-gradient centrifugation were used to isolate donor Lewis rat KCs. The interference fragments of the B7 molecule were designed to construct RNA interference vector pSilencer 3.1H1-Neo-B7 that was transfected into KCs of donor rat. Reverse-transcription polymerase chain reaction was used to detect the changes in the expression of B7 molecules in KCs. The transfected KCs were divided into 3 groups: A, control group; B, empty vector group; and C, RNA interference group. The lymphocytes of recipient Brown Norway (BN) rats were isolated and cocultured with the cells in the 3 groups. Enzyme-linked immunosorbent assay was used to detect the content of IL-2 in the culture supernate. Methylthiazolyl tetrazolium assay was used to detect the proliferation of lymphocytes.

RESULTS

The yield rate of KCs was 5 × 10(7), and the cell viability was >98%. RNA interference vector had been successfully constructed and identified by means of enzyme digestion and sequencing. The expression of B7 in KCs decreased by 22% after RNA interference (P < .01). After coculturing with lymphocytes of BN rats, compared with the control group, the decreased expression of B7 significantly inhibited the activation and proliferation of lymphocytes as well as the secretion of IL-2 by lymphocytes. The proliferation of lymphocytes in recipient BN rats decreased by 49% (P < .01), and the secretion of IL-2 in the culture supernate decreased by 67% (P < .01).

CONCLUSIONS

This study successfully constructed a B7 RNA interference vector, and applied it to assessing reduction of B7 expression in donor KCs. RNA interference significantly suppressed the activation of recipient T lymphocytes and secretion of IL-2 via the CD28/B7 costimulatory pathway and may induce immune tolerance in liver transplants.

Interferon-γ, interleukin-10 and interferon-inducible protein 10 (CXCL10) as serum biomarkers for the early allograft dysfunction after liver transplantation

Orthotopic liver transplantation (LTP) is nowadays a standard procedure, and provides the chance of survival of patients with end-stage non-treatable chronic liver disease or acute liver failure. Despite long-term survival with a good quality of life in the majority of patients, about 20% develop early allograft dysfunction (EAD), which leads to death or the need for re-transplantation. Therefore, the early diagnosis of EAD and evaluation of its risk factors are very important. Many primary pathological processes leading to EAD are accompanied by the release of different mediators and by a change of biochemical parameters detectable in the peripheral blood. The aim of this study was to investigate cytokines as well as soluble mediators in the serum of patients with and without EAD from our LTP bank, and to evaluate their predictive and prognostic values for EAD. We demonstrated for the first time that the level of IFNγ during the nearest preoperative period may serve as a predictive parameter for EAD. We additionally found that IL-10 and CXCL10 (IP-10) levels in the early postoperative period can be prognostic for EAD. We believe our data expand the spectrum of predictive and prognostic parameters for EAD in LTP.

PD-1/PD-L1 costimulatory pathway-induced mouse islet transplantation immune tolerance

BACKGROUND

Programmed death-1/PD-1 ligand-1 (PD-1/PD-L1) costimulatory signals may play an important role in T-cell-induced immune response. The aim of this study is to investigate the role of the PD-1/PD-L1 costimulatory pathway on immunotolerance induction in mouse pancreatic islet transplantation.

METHODS

Full-length mouse PD-L1 cDNA was subcloned into pShuttle-GFP-CMV(-) shuttle plasmid. The product was cut by certain restriction endonuclease and ligated with pAdxsi vector. The adenovirus bone plasmid was transformed into DH5α-competent bacteria. After linearization, the recombined adenovirus DNA was transfected into 293 cells for package and amplification. Streptozotocin was injected intraperitoneally into C57BL/6 (H-2(b)) mouse to induce diabetic model recipient. Recipients were randomly divided into 3 groups. Group A was the control. Group B and group C were injected with Ad-EGFP and Ad-PD-L1 through the tail vein, respectively, 1 day before islet transplantation. The 300 to 400 islets of DBA/2 (H-2(d)) were transplanted into the renal subcapsular space of the diabetic model recipient. We monitored and analyzed the blood glucose levels and the survival time of grafts after transplantation.

RESULTS

Recombinant adenovirus Ad-PD-L1 had high efficiency expression of PD-L1 in recipient mouse. The blood glucose concentration of mice in the Ad-PD-L1 gene treatment group was obviously lower than that of the control and Ad-EGFP treatment groups and was stable and kept within the normal range at post-transplant 21 days. The survival time of grafts in the Ad-PD-L1 group (27.6 ± 3.5 days) was significantly longer than in the control (7.8 ± 0.33 days) and Ad-EGFP groups (7.6 ± 0.59 days), P < .01. Mixed lymphocyte response showed a specific decrease reaction of recipient lymphocyte vs donor lymphocyte. Flow cytometry detection showed that unsplit cells occupied 90% of recipient mouse lymphocytes, but unsplit cells among normal C57BL/6 mouse lymphocytes without Ad-PD-L1 gene treatment were 51 in the control group. The differences between them were significant (P < .01).

CONCLUSION

Recombinant adenovirus Ad-PD-L1 has been successfully constructed. In mouse pancreatic islet transplantation, it can suppress the activation of recipient T lymphocyte through the PD-1/PD-L1 costimulatory pathway, and significantly prolong the survival time of grafts.

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

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

Chemokine programming dendritic cell antigen response: part II - programming antigen presentation to T lymphocytes by partially maintaining immature dendritic cell phenotype

In a companion article to this study,(1) the successful programming of a JAWSII dendritic cell (DC) line's antigen uptake and processing was demonstrated based on pre-treatment of DCs with a specific 'cocktail' of select chemokines. Chemokine pre-treatment modulated cytokine production before and after DC maturation [by lipopolysaccharide (LPS)]. After DC maturation, it induced an antigen uptake and processing capacity at levels 36% and 82% higher than in immature DCs, respectively. Such programming proffers a potential new approach to enhance vaccine efficiency. Unfortunately, simply enhancing antigen uptake does not guarantee the desired activation and proliferation of lymphocytes, e.g. CD4(+) T cells. In this study, phenotype changes and antigen presentation capacity of chemokine pre-treated murine bone marrow-derived DCs were examined in long-term co-culture with antigen-specific CD4(+) T cells to quantify how chemokine pre-treatment may impact the adaptive immune response. When a model antigen, ovalbumin (OVA), was added after intentional LPS maturation of chemokine-treated DCs, OVA-biased CD4(+) T-cell proliferation was initiated from ~ 100% more undivided naive T cells as compared to DCs treated only with LPS. Secretion of the cytokines interferon-γ, interleukin-1β, interleukin-2 and interleukin-10 in the CD4(+) T cell : DC co-culture (with or without chemokine pre-treatment) were essentially the same. Chemokine programming of DCs with a 7 : 3 ratio of CCL3 : CCL19 followed by LPS treatment maintained partial immature phenotypes of DCs, as indicated by surface marker (CD80 and CD86) expression over time. Results here and in our companion paper suggest that chemokine programming of DCs may provide a novel immunotherapy strategy to obviate the natural endocytosis limit of DC antigen uptake, thus potentially increasing DC-based vaccine efficiency.

CD28 family and chronic rejection: "to belatacept...And beyond!"

Kidneys are one of the most frequently transplanted human organs. Immunosuppressive agents may prevent or reverse most acute rejection episodes; however, the graft may still succumb to chronic rejection. The immunological response involved in the chronic rejection process depends on both innate and adaptive immune response. T lymphocytes have a pivotal role in chronic rejection in adaptive immune response. Meanwhile, we aim to present a general overview on the state-of-the-art knowledge of the strategies used for manipulating the lymphocyte activation mechanisms involved in allografts, with emphasis on T-lymphocyte costimulatory and coinhibitory molecules of the B7-CD28 superfamily. A deeper understanding of the structure and function of these molecules improves both the knowledge of the immune system itself and their potential action as rejection inducers or tolerance promoters. In this context, the central role played by CD28 family, especially the relationship between CD28 and CTLA-4, becomes an interesting target for the development of immune-based therapies aiming to increase the survival rate of allografts and to decrease autoimmune phenomena. Good results obtained by the recent development of abatacept and belatacept with potential clinical use aroused better expectations concerning the outcome of transplanted patients.