Relative contribution of direct and indirect allorecognition in developing tolerance after liver transplantation

Non-invasive molecular biomarkers for monitoring solid organ transplantation: A comprehensive overview

Solid organ transplantation is a life-saving intervention for individuals with end-stage organ failure. Despite the effectiveness of immunosuppressive therapy, the risk of graft rejection persists in all viable transplants between individuals. The risk of rejection may vary depending on the degree of compatibility between the donor and recipient for both human leucocyte antigen (HLA) and non-HLA gene-encoded products. Monitoring the status of the allograft is a critical aspect of post-transplant management, with invasive biopsies being the standard of care for detecting rejection. Non-invasive biomarkers are increasingly being recognized as valuable tools for aiding in the detection of graft rejection, monitoring graft status and evaluating the efficacy of immunosuppressive therapy. Here, we focus on the importance of molecular biomarkers in solid organ transplantation and their potential role in clinical practice. Conventional molecular biomarkers used in transplantation include HLA typing, detection of anti-HLA antibodies, killer cell immunoglobulin-like receptor genotypes, and anti-MHC class 1-related chain A antibodies, which are important for assessing the compatibility of the donor and recipient. Emerging molecular biomarkers include the detection of donor-derived cell-free DNA, microRNAs (regulation of gene expression), exosomes (small vesicles secreted by cells), and kidney solid organ response test, in the recipient's blood for early signs of rejection. This review highlights the strengths and limitations of these molecular biomarkers and their potential role in improving transplant outcomes.

Induction of a different immune response in non-titanized compared to titanized polypropylene meshes

It is well known that pelvic organ prolapse (POP) significantly reduces the quality of life of affected women and in many cases requires corrective surgery. Aim of the study was to compare the immune response against titanized versus non-titanized meshes, especially macrophage polarization and immune checkpoint association. For this, we analyzed 644 POP surgeries, which were performed between 2017 and 2022, in our department. Four of them needed revision surgery caused by erosion. We analyzed the influx of CD68 & CD163 positive macrophages and the expression of immune checkpoint molecules PD-L1 and PD1 in these 4 patients. We identified a large number of CD68 and CD163 positive macrophages and additionally a PD-L1 expression of these cells. Based on the in-vivo results, we isolated monocytes and co-cultivated monocytes with different mesh material covered with or without fibroblasts. We identified a significantly enhanced macrophage activation and PD-L1 expression in macrophages surrounding non-titanized polypropylene mesh material. Encapsulation of the material by fibroblasts was crucial for that. Specifically, CD68-positive macrophages are upregulated (p < 0.001), co-expressing PD-L1 (p < 0.001) in monocytes co-cultivated with non-titanized polypropylene meshes. Monocytes co-cultivated with titanized polypropylene meshes showed significantly lower expression of CD163 (p = 0.027) and PD-L1 (p = 0.022). In conclusion, our in vitro data suggest that the titanium coating leads to a decreased polarization of macrophages and to a decreased immune response compared to non-titanized meshes. This could be an indication for the increased incidence of erosion of the non-titanized meshes, which is a severe complication of this procedure and requires revision surgery. STATEMENT OF SIGNIFICANCE: Pelvic organ prolapse is a well-known problem for women and often requires corrective surgery. Polypropylene meshes are often used, which differ in their coating (titanized vs. non-titanized). A severe side effect of these surgeries is mesh erosion, due to onset of inflammation, which requires revision surgery. We examined all erosion cases (4 of 644 patients) with implanted nontitanium-coated meshes by immunohistochemistry and found upregulation of macrophage polarization (as markers CD68 and CD163) and increased expression of the immune checkpoint molecules PD-L1 and PD1. This suggests inflammatory processes and an enhanced immune response. In addition, we set up an in vitro experiment to investigate whether coating plays a role. Here, we demonstrated that the non-titanized meshes elicited a significantly higher immune response in comparison to titanized meshes, which could lead to the higher erosion rate of the non-titanized meshes. Our results highlight the benefit of titanized meshes, which should lead to a lower revision surgery rate and thus improved patient outcome.

Macrophages in transplant rejection

Transplant rejection is one of the primary factors leading to loss of allograft function, and macrophages are involved in allograft rejection. Macrophages polarize into different phenotypes according to stimulation by different external factors. Different types of macrophages play distinct roles in inflammation, tumors, and autoimmune diseases and are involved in transplant rejection. In this review, we introduce the origin and migration of macrophages, outline the classification of macrophages and their polarization mechanisms, and review the currently understood mechanisms of their involvement in transplant rejection. Finally, we discuss the regulation of macrophage polarization and miRNA expression with respect to transplant rejection, which is important for the development of new anti-rejection therapies.

Changes in DNA Methylation of Glucocorticoid-Induced Tumor Necrosis Factor Receptor and Its Ligand in Liver Transplantation

Liver transplantation (LT) is the criterion standard of care in patients with end-stage liver disease and those with tumors of hepatic origin in the setting of liver dysfunction. Chronic immune rejection of the liver transplant can lead to bad prognosis for patients. Glucocorticoid-induced tumor necrosis factor receptor (GITR) play a key role in dominant immunologic self-tolerance maintained by CD25+/CD4+ regulatory T cells. Here, we investigated the DNA methylation variations of GITR and GITR ligand (GITRL) using pyrosequencing by analyzing blood DNA samples of patients after LT. Our results showed that the methylation level of certain CpGs, such as CpG_13, in GITRL was significantly reduced after LT. Furthermore, we found that the GITRL methylation statuses of cohorts with no chronic immune rejection were significantly lower compared with cohorts with chronic immune rejection after LT treatment. However, the methylation statuses of GITR were less varied. Using linear regression analysis, we further found that factors such as upper gastrointestinal hemorrhage, splenectomy, and creatinine might affect DNA methylation patterns in chronic immune rejection cohorts. These findings provide novel insights into the pivotal role of GITRL as a potential molecular biomarker for the triage of liver transplantation.

Nanodelivery Systems as New Tools for Immunostimulant or Vaccine Administration: Targeting the Fish Immune System

Fish disease treatments have progressed significantly over the last few years and have moved from the massive use of antibiotics to the development of vaccines mainly based on inactivated bacteria. Today, the incorporation of immunostimulants and antigens into nanomaterials provide us with new tools to enhance the performance of immunostimulation. Nanoparticles are dispersions or solid particles designed with specific physical properties (size, surface charge, or loading capacity), which allow controlled delivery and therefore improved targeting and stimulation of the immune system. The use of these nanodelivery platforms in fish is in the initial steps of development. Here we review the advances in the application of nanoparticles to fish disease prevention including: the type of biomaterial, the type of immunostimulant or vaccine loaded into the nanoparticles, and how they target the fish immune system.

Minimization of immunosuppression in adult liver transplantation: new strategies and tools

PURPOSE OF REVIEW

To describe most relevant data regarding strategies to achieve immunosuppression minimization and/or complete withdrawal in liver transplantation and to discuss the development of tolerance biomarkers to predict the success of immunosuppression weaning.

RECENT FINDINGS

In clinical organ transplantation allograft tolerance has been attained through two different pathways: (1) tolerance or immunosuppression minimization has been attempted by administering induction therapies with or without infusion of donor hematopoietic cells; and (2) the availability of spontaneously tolerant liver and kidney recipients has been exploited to develop biomarkers of allograft tolerance. The use of transcriptional profiling is the most promising approach. Recent publications have identified a gene expression signature in tolerant patients.

SUMMARY

Current immunosuppressive regimens reduce acute rejection episodes but promote a number of complications that have a negative impact on patient morbidity, mortality and quality of life. In this setting, achievement of tolerance is a major goal. Although there are no reliable markers to identify tolerant patients, recent studies have found that tolerant liver recipients exhibit unique peripheral blood transcriptional patterns. The difference in expression patterns is related to the immune response and could constitute the basis of a future diagnostic test of tolerance.

Relevance of regulatory T cell promotion of donor-specific tolerance in solid organ transplantation

Current clinical strategies to control the alloimmune response after transplantation do not fully prevent induction of the immunological processes which lead to acute and chronic immune-mediated graft rejection, and as such the survival of a solid organ allograft is limited. Experimental research on naturally occurring CD4⁺CD25^highFoxP3⁺ Regulatory T cells (Tregs) has indicated their potential to establish stable long-term graft acceptance, with the promise of providing a more effective therapy for transplant recipients. Current approaches for clinical use are based on the infusion of freshly isolated or ex vivo polyclonally expanded Tregs into graft recipients with an aim to redress the in vivo balance of T effector cells to Tregs. However mounting evidence suggests that regulation of donor-specific immunity may be central to achieving immunological tolerance. Therefore, the next stages in optimizing translation of Tregs to organ transplantation will be through the refinement and development of donor alloantigen-specific Treg therapy. The altering kinetics and intensity of alloantigen presentation pathways and alloimmune priming following transplantation may indeed influence the specificity of the Treg required and the timing or frequency at which it needs to be administered. Here we review and discuss the relevance of antigen-specific regulation of alloreactivity by Tregs in experimental and clinical studies of tolerance and explore the concept of delivering an optimal Treg for the induction and maintenance phases of achieving transplantation tolerance.

Butyrate interferes with the differentiation and function of human monocyte-derived dendritic cells

Dendritic cells (DCs) are specialized antigen-presenting cells that are uniquely capable of either inducing immune responses or maintaining a state of self-tolerance, depending on their stage of maturation. In the present study, we describe a way to interfere with DCs maturation. The compound butyrate can affect the differentiation of DCs generated from human monocytes and can inhibit T cell proliferation. We demonstrate that butyrate substantially down-regulates the expression of CD80, CD83, and MHC class II molecules; increases endocytic capability; reduces allostimulatory abilities; promote interleukin-10 (IL-10) production; and inhibits interleukin-12 (IL-12) and interferon-γ (IFN-γ) production. These results demonstrate a specific immune suppression property of butyrate and supports further investigation for butyrate as a new immunotherapeutic agent.

Postischemic inflammatory response in an auxiliary liver graft predicts renal graft outcome in sensitized patients

BACKGROUND

The liver is considered a tolerogenic organ that favors the induction of peripheral tolerance and protects other organs from the same donor from rejection. This has been exploited in combined auxiliary liver-kidney transplantation, where a renal graft is transplanted against a positive crossmatch under the protection of a liver transplanted from the same donor.

METHODS

To elucidate mechanisms behind the liver protective effect, we studied early transcriptional changes of inflammatory mediators in the grafts during combined auxiliary liver-kidney transplantation using microarrays and real-time polymerase chain reaction. The results were correlated to clinical data.

RESULTS

Liver and kidney grafts both exhibited an upregulation of the leukocyte-recruiting chemokines CCL2, CCL3, and CCL4. Notably, liver grafts strongly upregulated CCL20, a dendritic cell, and T-cell recruiting chemokine. By comparing the gene expression in liver grafts with the clinical outcome, we found that 14 of 45 investigated inflammatory genes were expressed significantly higher in patients without early rejection when compared with those with early rejections. This included the above-mentioned chemokines and the T-cell-recruiting CX3CL1, NFKB1, and the tolerance-inducing gene indoleamine 2,3-dioxygenase.

CONCLUSIONS

In this study, the protective role of the liver was associated with a proinflammatory reaction within this organ after ischemia-reperfusion. In particular, we found an increased expression of leukocyte-recruiting chemokines in patients without rejection, indicating a protective role of host inflammatory cells infiltrating the auxiliary liver graft in presensitized patients. Second, gene expression profiling of transplant biopsies shortly after reperfusion predicted the risk of early rejection in these patients.

Enhanced stimulation of anti-ovarian cancer CD8(+) T cells by dendritic cells loaded with nanoparticle encapsulated tumor antigen

PROBLEM

Dendritic cell (DC)-based cancer therapies are favored approaches to stimulate anti-tumor T-cell responses. Unfortunately, tolerance to tumor antigens is difficult to overcome. Biodegradable poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NP) are effective reagents in the delivery of drugs and tumor-associated antigens (TAA). In this study, we assessed the capacity of a PLGA NP-based delivery system to augment CD8 T-cell responses to ovarian cancer TAA.

METHOD OF STUDY

Human DC were generated from blood monocytes by conventional in vitro differentiation and loaded with either soluble tumor lysate or NP/lysate conjugates (NPL). These antigen-loaded DC were then used to stimulate autologous CD8(+) T cells. Cytokine production and activation markers were evaluated in the CD8(+) T cells.

RESULTS

DC loading with NPL increased cytokine production by stimulated CD8 T cells and induced T-cell expression of cell surface co-stimulatory molecules, typical of anti-tumor immune responses. In contrast, delivery of naked tumor lysate antigens preferentially induced a T-cell profile characteristic of tolerization/exhaustion.

CONCLUSION

These findings indicate that delivery of TAA in NP enables DC to efficiently activate anti-tumor CD8(+) T cells. PLGA NP encapsulation of tumor-derived lysate protein antigens is an encouraging new preparative methodology for DC-based vaccination meriting clinical testing.

T-cell alloimmunity and chronic allograft dysfunction

Solid organ transplantation is the standard treatment to improve both the quality of life and survival in patients with various end-stage organ diseases. The primary barrier against successful transplantation is recipient alloimmunity and the need to be maintained on immunosuppressive therapies with associated side effects. Despite such treatments in renal transplantation, after death with a functioning graft, chronic allograft dysfunction (CAD) is the most common cause of late allograft loss. Recipient recognition of donor histocompatibility antigens, via direct, indirect, and semidirect pathways, is critically dependent on the antigen-presenting cell (APC) and elicits effector responses dominated by recipient T cells. In allograft rejection, the engagement of recipient and donor cells results in recruitment of T-helper (Th) cells of the Th1 and Th17 lineage to the graft. In cases in which the alloresponse is dominated by regulatory T cells (Tregs), rejection can be prevented and the allograft tolerated with minimum or no immunosuppression. Here, we review the pathways of allorecognition that underlie CAD and the T-cell effector phenotypes elicited as part of the alloresponse. Future therapies including depletion of donor-reactive lymphocytes, costimulation blockade, negative vaccination using dendritic cell subtypes, and Treg therapy are inferred from an understanding of these mechanisms of allograft rejection.

Isolation and phenotyping of normal mouse liver dendritic cells by an improved method

INTRODUCTION

Dendritic cells (DCs) are bone marrow-derived cells, which migrate to lymphoid and non-lymphoid organs via blood. Liver DCs are believed to play an important role in the regulation of hepatic allograft acceptance. However, because of inherent difficulties in isolating adequate numbers of DCs from liver, limited information is available on the phenotype and functions of liver DCs. To address this issue, we isolated DCs from normal C57BL/6 mouse liver using a modified procedure and described their immunophenotypic characteristics.

MATERIALS AND METHODS

Non-parenchymal cells (NPCs) were obtained by collagenase digestion of perfused liver fragments and density gradient centrifugation (14.5% nycodenz column). After overnight (18 hr) incubation of the NPCs, enrichment for transiently adherent, low- density cells on 13% nycodenz gradients permitted the recovery of low numbers of cells (approximately 1.2-1.5 x 10(5) per liver), many of which displayed distinct DCs morphology (abundant cytoplasm with prominent projections and irregularly shaped nuclei).

RESULTS

Flowcytometric analysis revealed that most of these cells were recognized by anti-CD11c (60-70%). The results obtained from double staining with PE and FITC conjugated monoclonal antibodies indicated that these cells were CD11c(+)/MHC-II(+) (53%), CD11c(+)/CD86(+) (53.5%), CD11c(+)/ CD8α(+) (36%) and CD11c(+)/CD11b(+) (45%).

CONCLUSION

These findings indicate that the purity of DCs isolated by nycodenz gradient is higher than other reported methods. Considering the similar ratio of lymphoid (CD11c(+)/CD8α(+)) and myeloid (CD11c(+)/CD11b(+)) DCs in the liver, and the known role of lymphoid DCs in tolerance induction, it seems that this subpopulation of DCs is not the main reason of liver tolerogenecity. Therefore, other factors such as the immaturity of liver DCs or the effect of liver microenvironment on these cells, etc. may explain the acceptance of hepatic allograft.

In vitro-derived alternatively activated macrophages reduce colonic inflammation in mice

BACKGROUND & AIMS

Infection with the rat tapeworm Hymenolepis diminuta reduces the severity of dinitrobenzene sulfonic acid (DNBS)-induced colitis in mice. Infection with H. diminuta increases colonic expression of arginase-1 and found in inflammatory zone 1 (FIZZ1), markers of alternatively activated macrophages (AAMs). We investigated whether AAMs have anticolitic effects.

METHODS

Normal or macrophage-depleted Balb/c mice were infected with H. diminuta; some mice were given DNBS, and the severity of colitis was assessed by disease activity scores, myeloperoxidase activity, and histologic examination. AAMs were also differentiated in vitro, given to mice by intraperitoneal or intravenous injection, and the effects on DNBS-induced colitis were determined. Numbers of AAMs were assessed in biopsy specimens from patients with Crohn's disease.

RESULTS

Depletion of intestinal macrophages using clodronate-liposomes prevented the anticolitic effect of infection with H. diminuta. Injection of AAMs, but not classically activated macrophages, significantly reduced the severity of DNBS-induced colitis. The AAM-induced, anticolitic effect was accompanied by increased interleukin (IL)-10 production from mitogen-stimulated spleen cells; in vivo neutralization of IL-10 partially reduced the effects of AAM transfer. Patients with active CD had reduced numbers of CD68(+)CD206(+) macrophages (which indicate AAM), whereas biopsy specimens from patients with inactive CD had increased numbers of these cells.

CONCLUSIONS

Analysis of the H. diminuta-murine DNBS system identified the AAM, which, when administered to mice, significantly reduced DNBS-induced colitis. The ability to derive AAMs from patients' blood suggests that adoptive transfer of these cells could be a novel approach to inflammatory bowel disease.

Donor IL-4-treatment induces alternatively activated liver macrophages and IDO-expressing NK cells and promotes rat liver allograft acceptance

Most approaches to transplant tolerance involve treatment of the recipient to prevent rejection. This study investigates donor treatment with IL-4 for its effect on subsequent rat liver allograft survival. Rat orthotopic liver transplants were performed in rejecting (PVG donor to Lewis recipient) or spontaneously tolerant (PVG to DA) strain combinations. Donors were untreated or injected intraperitoneally with IL-4 (30,000U/day) for 5days. Tissue infiltrates and gene expression were examined by immunohistochemistry and real-time quantitative PCR. IL-4 induced a marked leukocyte infiltrate in donor livers prior to transplant. Macrophages comprised the major population, although B cells, T cells and natural killer (NK) cells also increased. IL-4-induced liver macrophages had an alternatively activated phenotype with increased expression of mannose receptor but not inducible nitric oxide synthase (NOS2). IL-4 also induced IDO and IFN-gamma expression by NK cells. Donor IL-4-treatment converted rejection to acceptance in the majority of Lewis recipients (median survival time >96days) and did not prevent acceptance in DA recipients. Acceptance in Lewis recipients was associated with increased donor cell migration to recipient spleens and increased splenic IL-2, IFN-gamma and IDO expression 24h after transplantation. Donor IL-4-treatment increased leukocytes in the donor liver including potentially immunosuppressive populations of alternatively activated macrophages and IDO-expressing NK cells. Donor treatment led to long-term acceptance of most livers in association with early immune activation in recipient lymphoid tissues.

The importance of the indirect pathway of allorecognition in clinical transplantation

The immune system mounts a response to non-self transplanted tissue through a number of mechanisms. The indirect pathway of allorecognition, in which cells of the adaptive immune system recognize MHC alloantigen-derived peptide on self-MHC molecules, has emerged as a potent inducer of allograft rejection. In particular, recent evidence convincingly connects the indirect pathway with chronic rejection, including antibody-mediated and CD8(+) T cell-mediated rejection. However, the indirect pathway can also promote the generation of regulatory T cells, which have emerged as crucial suppressors of the alloresponse, and hold much promise in the quest for clinical tolerance. An improved understanding of the indirect pathway is likely to bring important benefits to transplant recipients.

Transplantation immunology: what the clinician needs to know for immunotherapy

The liver is unique among transplanted organs with respect to its interaction with the host immune system. There is evidence, both anecdotal and documented, that some liver recipients who cease taking immunosuppressive drugs maintain allograft function, suggesting robust tolerance is in place. Moreover, recipients of human liver allografts require less immunosuppression than do other organ recipients, and liver transplants confer protection on other organ grafts from the same donor. Hence, the liver shows features of immune privilege. Still, the liver can display destructive immunologic processes such as rejection in approximately one quarter of patients. The understanding of the cellular and molecular mechanisms operant in tolerance vs allograft rejection is important for developing new agents to improve long-term outcome, minimize infectious complications (including recurrence of hepatotropic viruses), and deliver immunosuppression without long-term toxicity. This review describes the unique aspects of the hepatic immune response, the pathways involved in T-cell activation and alloantigen recognition, effector cells and pathways mediating liver allograft rejection, the role of regulatory T cells, and targets of current and future immunosuppressive agents.