Basic concepts in transplant immunology

Basic Understanding of Liver Transplant Immunology

The liver is a specialized organ and plays an important role in our immune system. The liver constitutes parenchymal cells which are hepatocytes and cholangiocytes (60-80%) and non-parenchymal cells like liver sinusoidal endothelial cells (LSECs), hepatic satellite/Ito cells, Kupffer cells, neutrophils, mononuclear cells, T and B lymphocytes (conventional and non-conventional), natural killer cells, and natural killer T (NKT) cells. The liver mounts a rapid and strong immune response, under unfavorable conditions and acts as an immune tolerance to a variety of non-pathogenic antigens. This delicate and dynamic interaction between different kinds of immune cells in the liver maintains a balance between immune screening and immune tolerance. The liver allografts are privileged immunologically; however, allograft rejection is not uncommon and is classified as cell or antibody-mediated. Advancements in transplant immunology help in the prevention of allografts rejection by immune reactions of the host thus leading to better graft and host survival. Fewer patients may not require immunosuppression due to systemic donor-specific T-cell tolerance. The liver tolerance mechanism is poorly studied, and LSEC and unconventional lymphocytes play an important role that dampens T cell response either by inducing apoptosis of cells or inhibiting co-stimulatory pathways. Newer cell-based therapy based on Treg, dendritic cells, and mesenchymal stromal cells will probably change the future of immunosuppression. Various invasive and non-invasive biomarkers and artificial intelligence have also been investigated to predict graft survival, post-transplant complications, and immunotolerance in the future.

Immunosuppressive Drugs in Liver Transplant: An Insight

Liver transplantation (LT) is the standard of care for end-stage liver failure and hepatocellular carcinoma. Over the years, immunosuppression regimens have improved, resulting in enhanced graft and patient survival. At present, the side effects of immunosuppressive agents are a significant threat to post-LT quality of life and long-term outcome. The role of personalized immunosuppression is to reach a delicate balance between optimal immunosuppression and minimal side effects. Today, immunosuppression in LT is more of an art than a science. There are no validated markers for overimmunosuppression and underimmunosuppression, only a few drugs have therapeutic drug monitoring and immunosuppression regimens vary from center to center. The immunosuppressive agents are broadly classified into biological agents and pharmacological agents. Most regimens use multiple agents with different modes of action to reduce the dosage and minimize the toxicities. The calcineurin inhibitor (CNI)-related toxicities are reduced by antibody induction or using mTOR inhibitor/antimetabolites as CNI sparing or CNI minimization strategies. Post-liver transplant immunosuppression has an intensive phase in the first three months when alloreactivity is high, followed by a maintenance phase when immunosuppression minimization protocols are implemented. Over time some patients achieve "tolerance," defined as the successful stopping of immunosuppression with good graft function and no indication of rejection. Cell-based therapy using immune cells with tolerogenic potential is the future and may permit complete withdrawal of immunosuppressive agents.

Current Evidence on the Clinical Relevance of Donor-specific Antibodies in Paediatric Liver Transplantation

ABSTRACT

The clinical impact of donor-specific antibodies (DSA) occurring before or after liver transplantation (LT) against donor-human leucocyte antigen (HLA) on graft outcome is still unclear. We aim to present the current consensus based on recent paediatric LT case series. Compared to kidney transplantation, the liver seems to be less susceptible to antibody-mediated graft damage, which is likely due to protective Kupffer cell activity. The incidence of DSA after liver transplantation is higher in children than in adults. DSA directed against HLA class II molecules, mainly DQ, occur more often. The presence of such anti-class II DSA (DQ/DR), especially of the complement-binding IgG3 subclass, may be associated with endothelial injury, T-cell-mediated rejection (TCMR), inflammation, and fibrosis. Regular DSA-posttransplant monitoring cannot as yet be recommended in routine practice but may be useful in selected cases.

Identification of Novel and Noninvasive Biomarkers of Acute Cellular Rejection After Liver Transplantation by Protein Microarray

Background

Acute cellular rejection (ACR) is one of the main factors in transplanted organ failure in liver transplantation. A precise marker for diagnosing or predicting rejection is not currently available; therefore, invasive liver biopsy is standard procedure. To develop a noninvasive method for precise diagnosis of ACR, we evaluated autoantibodies from patient sera as potential biomarkers using protein microarrays (seromics).

Methods

Sera from hepatitis C virus–positive ACR patients were compared to three hepatitis C virus cirrhosis control groups and healthy volunteers. The control groups consisted of 2 no-ACR groups obtained on postoperative day 28 and 1 year after transplantation and a preoperative group obtained 1 day before transplantation. For validation, we evaluated whether the candidate antibodies can distinguish ACR from other types of liver dysfunction after liver transplantation using enzyme-linked immunosorbent assay.

Results

Seromic analysis by weighted average difference (WAD) ranking and Mann-Whitney U test revealed a significant increase of 57 autoantibodies in the sera of ACR patients with liver dysfunction. Among the 57 candidates, autoantibodies to charged multivesicular body protein 2B, potassium channel tetramerization domain containing 14, voltage gated subfamily A regulatory beta subunit 3, and triosephosphate isomerase 1 were regarded as potential biomarkers of ACR after liver transplantation. Using 20 ACR patients with variable backgrounds for validation, the autoantibodies to charged multivesicular body protein 2B and triosephosphate isomerase 1 were significantly increased in ACR patients compared to other control groups.

Conclusions

A panel of autoantibodies identified by seromics as potential noninvasive biomarkers was clinically useful for diagnosing ACR after liver transplantation.

Advantage of tacrolimus/mycophenolate mofetil regimen for cytotoxic T cell-mediated defence and its inhibition by additive steroid administration in high-risk liver transplant recipients

Our previous work revealed that the recipients with the highest pre-existing numbers of CD8(+) effector T cells (TE ) [hyperparathyroidism (HPT)E recipients] occupied approximately 30% of adult transplant recipients performed in our hospital. HPTE recipients demonstrated very poor clinical outcome compared with the remaining 70% of recipients with the lowest pre-existing TE (LPTE recipient). This study aimed to clarify the best combined immunosuppressive regimen related to function of cytotoxic T lymphocytes (CTLs) for HPTE recipients. Eighty-one HPTE recipients were classified into three types, according to the immunosuppressive regimens: type 1, tacrolimus (Tac)/glucocorticoid (GC); type 2, Tac/mycophenolate mofetil (MMF)/GC; and type 3, Tac/MMF. Frequencies of severe infection, rejection and hospital death were the highest in types 1 and 2, whereas the lowest occurred in type 3. The survival rate in type 3 was the highest (100%) during follow-up until post-operative day 2000. Regarding the immunological mechanism, in type 1 TE perforin and interferon (IFN)-γ were generated through the self-renewal of CD8(+) central memory T cells (TCM ), but decreased in the early post-transplant period due to marked down-regulation of interleukin (IL)-12 receptor beta-1 of TCM. In type 2, the self-renewal TCM did not develop, and the effector function could not be increased. In type 3, in contrast, the effectors and cytotoxicity were correlated inversely with IL-12Rβ1(+) TCM levels, and increased at the highest level around the pre-transplant levels of IL-12Rβ1(+) TCM . However, the immunological advantage of Tac/MMF therapy was inhibited strongly by additive steroid administration.

Early coupled up-regulation of interleukin-12 receptor beta-1 in CD8+ central memory and effector T cells for better clinical outcomes in liver transplant recipients

This study aimed to investigate the role of initial priming of interleukin (IL)-12 receptor beta-1 in CD8(+) central memory T cells (initial IL-12RTCM priming) and CCR7-negative subsets (CNS) in effector cell expansion and clinical outcome after living donor liver transplantation (LDLT). One hundred and six patients who underwent LDLT were classified into the following three groups according to hierarchical clustering of CD8(+) CD45 isoforms before LDLT: I, naive-dominant; II, effector memory-dominant; and III, effector-dominant. The pre-existing CD8(+) effector cells (TE ) and activated immune status increased progressively from group I to group II to group III. Groups I, II and III received tacrolimus (Tac)/glucocorticoid (GC) regimens. Eighteen group III recipients received Tac/mycophenolate mofetil (MMF) and were defined as group IV. Initial IL-12RTCM priming was slightly, moderately and markedly decreased in droups I, II, and III, respectively. Initial priming of IL-12Rβ1 in CNS was decreased markedly in the three groups with marked decreases of TE , perforin and interferon (IFN)-γ; all parameters were restored by up-regulation of IL-12Rβ1(+) TCM through the self-renewal of TCM . The lag time required until coupled up-regulation of IL-12Rβ1 of TCM and CNS to above baseline was 12, 20 and 32 days in groups I, II and III, respectively. Inferior clinical outcomes were associated with increasing lag time. In contrast, the initial priming of IL-12Rβ1 in TCM and CNS remained above baseline in group IV due to MMF-mediated increase of IL-12Rβ1. Early coupled up-regulation of TCM and CNS leads to efficient TE differentiation and optimal clinical outcomes.

Exploiting the unique regenerative capacity of the liver to underpin cell and gene therapy strategies for genetic and acquired liver disease

The number of genetic or acquired diseases of the liver treatable by organ transplantation is ever-increasing as transplantation techniques improve placing additional demands on an already limited organ supply. While cell and gene therapies are distinctly different modalities, they offer a synergistic alternative to organ transplant due to distinct architectural and physiological properties of the liver. The hepatic blood supply and fenestrated endothelial system affords relatively facile accessibility for cell and/or gene delivery. More importantly, however, the remarkable capacity of hepatocytes to proliferate and repopulate the liver creates opportunities for new treatments based on emerging technologies. This review will summarise current understanding of liver regeneration, describe clinical and experimental cell and gene therapeutic modalities and discuss critical challenges to translate these new technologies to wider clinical utility. This article is part of a Directed Issue entitled: "Regenerative Medicine: the challenge of translation".

Current status of immunosuppression in liver transplantation

With advancements in immunosuppressive strategies and availability of better immunosuppressive agents, survival rate following liver transplantation has improved significantly in the recent times. Besides improvements in surgical techniques, the most important factor that has contributed to this better outcome is the progress made in the field of immunosuppression. Over the last several years, the trend has changed to tailored immunosuppression with the aim of achieving optimal graft function while avoiding its undesirable side effects. Induction agents are no longer used routinely and the aim is to provide minimal immunosuppression in the maintenance phase. The present review discusses the various types of immunosuppressive agents, their mechanism of action, clinical utility, advantages and disadvantages, and their side effects in short and long-term. It also discusses about tailoring immunosuppression in presence of various situations such as renal dysfunction, metabolic syndrome, hepatitis C recurrence, cytomegalovirus infections and so on. The issue of chronic kidney disease and the available renal sparing immunosuppressive strategies has been particularly stressed upon. Finally, it discusses about the practical aspects of various immunosuppression regimens including drug monitoring.

The association between cytokine gene polymorphisms and graft rejection in liver transplantation: a systematic review and meta-analysis

We investigated the contribution of polymorphisms in cytokine genes (TNFa-308, IL10-1082 and -592, TGFb1-c10 and c25, and IFNg+874) on the risk of graft rejection in liver transplantation. We performed a systematic review by identifying relevant studies and applied meta-analysis to pool gene effects. In total, 12 studies were eligible and included in the study. Data extraction and assessments for risk of bias were independently performed by two reviewers. Data for allele frequencies, allelic, and genotypic effects were pooled. Heterogeneity and publication bias were assessed. Pooled minor allele frequencies for TNFa-308, IL10-1082, TGFb1-c10, TGFb1-c25, IFNg+874, and IL10-592 were 0.140 (95% CI: 0.083, 0.198), 0.432 (95% CI: 0.392, 0.472), 0.387 (95% CI: 0.307, 0.467), 0.090 (95% CI: 0.056, 0.123), 0.460 (95% CI: 0.392, 0.528), and 0.224 (95% CI: 0.178, 0.269), respectively. OnlyTNFa-308 and IL10-1082 polymorphisms were significantly associated with graft rejection. Patients who carried minor homozygous genotypes for these two polymorphisms were at 3.5 and 1.69 times higher risk of graft rejections than patients who carried major homozygous genotypes. The estimated lambdas were 0.41 and 0.47, suggesting an additive mode of effect was most likely. However, we could not detect the associations of TGFb1at c10 and c25, INFg+874, and IL10-592 polymorphisms and graft rejection. In summary, our systematic review has demonstrated that TNFa-308 and IL10-1082 are potential risk factors of poor outcomes in liver transplantation. Future updated meta-analysis studies to confirm the power of these genotypes in association with allograft rejection are needed.

Single-stranded DNA oligonucleotides inhibit TLR3-mediated responses in human monocyte-derived dendritic cells and in vivo in cynomolgus macaques

TLR3 is a key receptor for recognition of double-stranded RNA and initiation of immune responses against viral infections. However, hyperactive responses can have adverse effects, such as virus-induced asthma. Strategies to prevent TLR3-mediated pathology are therefore desired. We investigated the effect of single-stranded DNA oligonucleotides (ssDNA-ODNs) on TLR3 activation. Human monocyte-derived dendritic cells up-regulate maturation markers and secrete proinflammatory cytokines on treatment with the synthetic TLR3 ligand polyinosine-polycytidylic acid (poly I:C). These events were inhibited in cultures with ssDNA-ODNs. Poly I:C activation of nonhematopoietic cells was also inhibited by ssDNA-ODNs. The uptake of poly I:C into cells was reduced in the presence of ssDNA-ODNs, preventing TLR3 engagement from occurring. To confirm this inhibition in vivo, we administered ssDNA-ODNs and poly I:C, alone or in combination, via the intranasal route in cynomolgus macaques. Proinflammatory cytokines were detected in nasal secretions in the poly I:C group, while the levels were reduced in the groups receiving ssDNA-ODNs or both substances. Our results demonstrate that TLR3-triggered immune activation can be modulated by ssDNA-ODNs and provide evidence of dampening proinflammatory cytokine release in the airways of cynomolgus macaques. These findings may open novel perspectives for clinical strategies to prevent or treat inflammatory conditions exacerbated by TLR3 signaling.

Comparison of immunomodulatory effects of placenta mesenchymal stem cells with bone marrow and adipose mesenchymal stem cells

Mesenchymal stem cells (MSCs) are powerful sources for cell therapy in regenerative medicine because they can be isolated from various tissues, expanded, and induced into multiple-lineages. Of note, their immunomodulatory effects maximize the therapeutic effects of stem cells engrafted on host, making them an especially attractive choice. Recently, several varieties of placenta-derived stem cells (PDSCs) including chorionic plate-derived MSCs (CP-MSCs) have been suggested as alternative sources of stem cells. However, comparative studies of immunomodulatory effects for CP-MSCs among various MSCs are largely lacking. We examined and compared immunomodulatory function of CP-MSCs with that of BM-MSCs and AD-MSCs using co-culture system with activated T-cells derived from human umbilical cord blood (UCB) exposed to anti-CD3 and anti-CD28 which are T-cell activating monoclonal antibodies. All MSCs expressed markers of stem cells and three germ layers by RT-PCR. These cells also exhibited comparable immunomodulatory effects when they were co-cultured with activated T-cells in dose-dependent manner. However, expression of HLA-ABC and HLA-G was highly positive in CP-MSCs compared to other MSCs, and higher levels of cytokines of IL-2, IL-4, IL-13, and GM-CSF were detected in dose-dependent manner in CP-MSCs. Taken together, the results of the present study suggest that while CP-MSCs, BM-MSCs, and AD-MSCs all have immunomodulatory effects, CP-MSCs may have additional advantage over the other MSCs in terms of immunomodulation. In conjunction with other previous studies, CP-MSCs are suggested to be a useful stem cell source in cell therapy.

The significance of plasma cell infiltrate in acute cellular rejection of liver allografts

Acute cellular rejections of higher grades of histologic severity are associated with increased risk of graft failure and death after liver transplantation. Plasma cell-rich infiltrates are associated with adverse clinical outcomes in acute renal allograft rejection and in liver allografts without rejection, but there are limited data on plasma cell-rich infiltrates in acute liver allograft rejection. In this study, 59 biopsies of acute liver allograft rejection were confirmed histologically and clinically, independently graded, and the percentage of plasma cells in portal inflammatory infiltrate was objectively assessed using a standardized protocol. Plasma cell infiltrates were observed in 32 (54%) of the specimens, the mean percentage of plasma cells in the infiltrates being 2.97%. Infiltrates with any plasma cells were significantly more common in groups with higher histologic severity of rejection (75% and 100% versus 31% and 48%, P = .006). The mean percentage of plasma cells in the portal infiltrate was also significantly higher in groups with higher histologic severity of rejection (4.95% and 17.82% versus 0.37 and 0.82%, P = .0002). All the biopsies with more than 30% plasma cells in the infiltrate were found to have severe rejection, whereas all with more than 10% plasma cells had either moderate or severe rejection. The association of plasma cell-rich infiltrates with histologic severity of rejection suggests that plasma cell-rich infiltrates could potentially be useful as a marker of severe rejection.

Present state of immunosuppressive therapy in liver transplant recipients

1. Our increasing understanding of the signaling pathways and cellular interactions in transplant immunobiology has facilitated targeted strategies using novel immunosuppressive agents. 2. The pattern of immunosuppressive drug use in the United States continues to change, and the changes include the use of antibody induction therapy and the agents used in maintenance therapy. 3. The driving forces behind the development of new immunosuppressive regimens are the long-term complications of current immunosuppressive regimens (particularly renal dysfunction and metabolic disturbances).

KIR and HLA-C interactions promote differential dendritic cell maturation and is a major determinant of graft failure following kidney transplantation

BACKGROUND

HLA-C is an important ligand for killer immunoglobulin like receptors (KIR) that regulate natural killer (NK) cell function. Based on KIR specificity HLA-C molecules are allocated into two groups, HLA-C1 or HLA-C2; HLA-C2 is more inhibiting to NK cell function than HLA-C1. We studied the clinical importance of HLA-C genotypes on the long-term graft survival of 760 kidney transplants performed at our centre utilising a population based genetic study and cell culture model to define putative mechanisms.

METHODS AND FINDINGS

Genotyping was performed using conventional DNA PCR techniques and correlations made to clinical outcomes. We found that transplant recipients with HLA-C2 had significantly better long-term graft survival than transplant recipients with HLA-C1 (66% versus 44% at 10 years, log-rank p = 0.002, HR = 1.51, 95%CI = 1.16-1.97). In in-vitro NK and dendritic cell (DC) co-culture model we made several key observations that correlated with the population based genetic study. We observed that donor derived NK cells, on activation with IL-15, promoted differential HLA-C genotype dependent DC maturation. In NK-DC co-culture, the possession of HLA-C2 by DC was associated with anti-inflammatory cytokine production (IL-1RA/IL-6), diminished DC maturation (CD86, HLA-DR), and absent CCR7 expression. Conversely, possession of HLA-C1 by DC was associated with pro-inflammatory cytokine synthesis (TNF-α, IL-12p40/p70), enhanced DC maturation and up-regulation of CCR7 expression. By immunohistochemistry the presence of donor NK cells was confirmed in pre-transplant kidneys.

CONCLUSIONS

We propose that after kidney transplantation IL-15 activated donor derived NK cells interact with recipient DC with less activation of indirect allo-reactivity in HLA-C2 positive recipients than HLA-C1 positive recipients; this has implications for long-term graft survival. Early events following kidney transplantation involving NK-DC interaction via KIR and HLA-C immune synapse may have a central role in long-term kidney transplant outcomes.

Suppression of histone deacetylase 11 promotes expression of IL-10 in Kupffer cells and induces tolerance following orthotopic liver transplantation in rats

BACKGROUND

Suppression of histone deacetylase 11 (HDAC11) can promote IL-10 expression in mouse macrophages RAW264.7 and induce immune tolerance. This study is to further investigate the role of HDAC11 in tolerance induction via Kupffer cells (KCs) following orthotopic liver transplantation (OLT) in rats.

MATERIALS AND METHODS

KCs isolated from BALB/c mice were divided into pHDAC11, adHDAC11, and pCV group (treated with HADC11-shRNA, adenovirus encoding HDAC11, and control vector, respectively). IL-10 expression was determined after lipopolysaccharide treatment. The expression of MHC-II and co-stimulatory molecules on KCs surface was evaluated by flow cytometry. T cell proliferation was measured by [(3)H]-thymidine incorporation after culturing with aforementioned three groups, treated KCs, respectively. OLT was performed in rats after Ad-HDAC11 and pHDAC11 treatment. Blood samples were collected for biochemical studies, and postoperative survival was examined.

RESULTS

IL-10 expression was inhibited and promoted by Ad-HDAC11 and HDAC11-shRNA in KCs, respectively. MHC-II and co-stimulatory molecules on KCs surface as well as T cell proliferation were significantly inhibited and induced in pHDAC11 and Ad-HDAC11 compared with pCV, respectively. Serum IL-2, TNF-α, and IFN-γ levels were significantly lower in pHDAC11 and higher in Ad-HDAC11 compared with pCV, respectively, while IL-4 and IL-10 were the reverse. Postoperative survival, liver function, and histology were different among the three groups.

CONCLUSIONS

Suppression of HDAC11 can promote IL-10 expression in KCs and induce tolerance following OLT in rats. Consequently, HDAC11 may be a key component of this immune regulation system and a promising target for development of novel drugs of gene therapy for inducing tolerance in clinical liver transplantation.

Identification of the rat NKG2D ligands, RAE1L and RRLT, and their role in allograft rejection

NKG2D is a receptor expressed by NK cells and subsets of T lymphocytes. On NK cells, NKG2D functions as a stimulatory receptor that induces effector functions. We cloned and expressed two rat NKG2D ligands, both members of the RAE1 family, RAE1L and RRLT, and demonstrate that these ligands can induce IFN-gamma secretion and cytotoxicity by rat NK cells. To examine changes in expression of NKG2D and the NKG2D ligands RAE1L and RRLT after transplantation, we used a Dark Agouti (DA)-->Lewis rat model of liver transplantation. NKG2D expression was significantly increased in allogeneic liver grafts by day 7 post-transplant. Ligands of NKG2D, absent in normal liver, were readily detected in both syngeneic and allogeneic liver grafts by day 1 post-transplant. By day 7 post-transplant, hepatocyte RAE1L and RRLT expression was significantly and specifically increased in liver allografts. In contrast to acute rejection that develops in the DA-->Lewis model, transplantation of Lewis livers into DA recipients (Lewis-->DA) results in spontaneous tolerance. Interestingly, expression of RAE1L and RRLT is low in Lewis-->DA liver allografts, but significantly increased in DA-->Lewis liver allografts undergoing rejection. In conclusion, our results suggest that expression of NKG2D ligands may be important in allograft rejection.

Migration of allosensitizing donor myeloid dendritic cells into recipients after liver transplantation

It is thought, but there is no evidence, that myeloid dendritic cells (MDCs) of donor origin migrate into the recipient after clinical organ transplantation and sensitize the recipient's immune system by the direct presentation of donor allo-antigens. Here we show prominent MDC chimerism in the recipient's circulation early after clinical liver transplantation (LTx) but not after renal transplantation (RTx). MDCs that detach from human liver grafts produce large amounts of pro-inflammatory [tumor necrosis factor alpha and interleukin 6 (IL-6)] and anti-inflammatory (IL-10) cytokines upon activation with various stimuli, express higher levels of toll-like receptor 4 than blood or splenic MDCs, and are sensitive to stimulation with a physiological concentration of lipopolysaccharide (LPS). Upon stimulation with LPS, MDCs detaching from liver grafts prime allogeneic T cell proliferation and production of interferon gamma but not of IL-10. Soluble factors secreted by liver graft MDCs amplify allogeneic T helper 1 responses. In conclusion, after clinical LTx, but not after RTx, prominent numbers of donor-derived MDCs migrate into the recipient's circulation. MDCs detaching from liver grafts produce pro-inflammatory and anti-inflammatory cytokines and are capable of stimulating allogeneic T helper 1 responses, and this suggests that MDC chimerism after clinical LTx may contribute to liver graft rejection rather than acceptance.

Gene expression profiling of acute cellular rejection in rat liver transplantation using DNA microarrays

Acute cellular rejection (ACR) is still a major problem in organ transplantation, and its genetic and molecular mechanisms remain poorly understood. We used DNA microarrays to investigate the gene expression profiles in ACR. We hypothesized that changes of gene expression in grafts could also be detected in peripheral blood leukocytes. We first compared the gene expression profiles in liver isografts (Lewis to Lewis) and allografts (Dark Agouti to Lewis) harvested from rats at days 1, 3, 5, and 7 after transplantation. Hierarchical clustering analysis indicated that gene expression started to change on day 3, and 89 differentially expressed genes were extracted from allografts in comparison with isografts at day 3. Most of the up-regulated genes were associated with graft-infiltrating leukocytes. We then confirmed the similarity of gene expression changes in peripheral leukocytes by quantitative real-time polymerase chain reaction. We also investigated the gene expression changes in other inflammatory and liver dysfunction models. Two interferon-gamma inducible genes, interferon regulatory factor 1 and guanylate nucleotide binding protein 2, were overexpressed in both the peripheral leukocytes and liver graft during ACR. Although further studies are necessary, these 2 genes in peripheral leukocytes could be potentially useful markers for rejection or immunosuppression.

Using an immune functional assay to differentiate acute cellular rejection from recurrent hepatitis C in liver transplant patients

In transplant recipients transplanted for hepatitis C, presentation of abnormal transaminases can herald the presentation of recurrent hepatitis C, cellular rejection, or both. Given the sometimes ambiguous histology with these 2 entities, the ability to distinguish them is of great importance because misinterpretation can potentially affect graft survival. We used an immune functional assay to help assess the etiology of abnormal liver function test results in liver transplant recipients. Blood samples for the immune functional assay were taken from 42 recipients prospectively at various times post-transplant and compared with clinical and histologic findings. In patients whose liver biopsy showed evidence of cellular rejection, the immune response was noted to be very high, whereas in those with active recurrence of hepatitis C, the immune response was found to be very low. This finding was found to be statistically significant (P < 0.0001). In those patients in whom there was no predominant histologic features suggesting 1 entity over the other, the immune response was higher than in those with aggressive hepatitis C but lower than in those with cellular rejection. In conclusion, these data show the potential utility of the ImmuKnow assay as a means of distinguishing hepatitis C from cellular rejection and its potential usefulness as a marker for outlining the progression of hepatitis C.

Exendin-4 does not promote Beta-cell proliferation or survival during the early post-islet transplant period in mice

Current pancreatic islet transplantation protocols achieve remarkable short-term success, but long-term insulin independence remains elusive. Hypoxic and inflammatory insults cause substantial early posttransplant graft loss while allo/autoimmunity and immunosuppressive drug toxicity threaten long-term graft mass and function. Exendin-4 (Ex4) is a GLP-1 receptor agonist that promotes beta-cell proliferation, survival, and differentiation. To determine whether Ex-4 displays potential as a graft-supportive agent, we transplanted 500 murine islets under the kidney capsule of syngeneic or allogeneic streptozocin-treated recipient mice and immediately initiated daily treatment with vehicle or Ex4. Graft beta-cell proliferation, death, and vascularity were assessed at 1, 3, and 10 days after syngeneic islet transplantation. For allogeneic recipients, blood glucose and body weight were assessed until glycemic deterioration. Ex-4 did not promote graft beta-cell proliferation, reduce beta-cell death, or enhance graft vascularity over the first 10 days after syngeneic islet transplantation. A trend toward prolongation of posttransplant euglycemia was observed with Ex4 treatment in nonimmune-suppressed allograft recipients, but its use in this setting was associated with frequent, severe hypoglycemia over the first 2 posttransplant days. Our findings do not support a beneficial effect of Ex-4 on islet grafts during the critical early posttransplant period, further, they demonstrate a significant hypoglycemic potential of Ex-4 in the first days after islet transplantation in mice. Optimal application of GLP-1 receptor agonists for long-term proliferative and survival benefits in transplantation may require earlier intervention prior to and/or during islet isolation for peri-transplant cytoprotection and administration beyond the period of engraftment.

Transplantation in autoimmune liver diseases

Liver transplantation remains an effective treatment for those with end-stage disease and with intractable liver-related symptoms. The shortage of organs for transplantation has resulted in the need for rationing. A variety of approaches to selection and allocation have been developed and vary from country to country. The shortage of donors has meant that new approaches have to be adopted to make maximal use of the available organs; these include splitting grafts, use of extended criteria livers, livers from non-heart-beating donors and from living donors. Post transplantation, most patients will need life-long immunosuppression, although a small proportion can have immunosuppression successfully withdrawn. Newer immunosuppressive drugs and different strategies may allow a more targeted approach with a reduction in side-effects and so improve the patient and graft survival. For autoimmune diseases, transplantation is associated with significant improvement in the quality and length of life. Disease may recur after transplantation and may affect patient and graft survival.

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.

Initial steroid bolus injection promotes vigorous CD8+ alloreactive responses toward early graft acceptance immediately after liver transplantation in humans

We have found that steroid bolus withdrawal prior to graft reperfusion increased the incidence of acute cellular rejection (ACR). This study aims to clarify how initial steroid bolus (ISB) injection at reperfusion influences the kinetics of CD8(+) alloreactive immune responses immediately after living donor liver transplantation (LDLT). A total of 49 hepatitis C virus (HCV)-infected recipients were classified into 3 groups according to hierarchical clustering by preoperative CD8(+)CD45 isoforms. The naive T cell proportion was considerably higher in Group I than in Groups II and III, whereas Group II recipients had the highest effector memory (EM) T cells and Group III the highest effector T cells. The frequency of ACR was significantly higher in recipients without ISB than in those with ISB. In particular, the ACR rates were the highest in Group II without ISB. Following ISB, the proportion of effector T cells was promptly upregulated within 6 hours after graft reperfusion, simultaneously with the upregulation of CD27(-)CD28(-) subsets, interferon-gamma (IFN-gamma), tumor necrosis factor-alpha and perforin expression, which significantly correlated with increasing interleukin (IL)-12 receptor beta 1 cells. These were then downregulated to below preoperative levels by tacrolimus (Tac) administered at 24 hours. These changes did not occur in the absence of ISB. In Group II without ISB, the downregulation of IL-12Rbeta1(+) cells was the greatest, consistent with the highest rates of ACR and mortality (60%). In conclusion, ISB must be done in place, especially in Group II with preexisting high EM T cells, to enable the development of early allograft acceptance.

Chronic ductopenic rejection in patients with recurrent hepatitis C virus treated with pegylated interferon alfa-2a and ribavirin

BACKGROUND

Interferon use for post liver transplantation (LT) recurrent hepatitis C (HCV) has not consistently been associated with acute cellular rejection (ACR). We examined the incidence of chronic ductopenic rejection (CR) in patients receiving pegylated interferon alfa-2a and ribavirin (PEG) to treat recurrent HCV.

METHODS

A chart review of 12 patients developing CR while receiving an escalating dose regimen of PEG with protocol liver biopsies every 6 months was conducted. Values are shown as median (range).

RESULTS

Twelve of the 70 patients treated with PEG developed CR. Median age at LT was 53 (37-63) years; immunosuppression consisted of tacrolimus or cyclosporine with prednisone. PEG was started at 3.6 (0.2-13.5) years after LT. Two patients had one episode of ACR before PEG. Four patients had first ACR while receiving PEG. CR was diagnosed after 12 (4-17) months of PEG; by then 8 patients had undetectable HCV-RNA. Tacrolimus and cyclosporine levels (ng/mL) were 7.9 (3.2-18.9) and 76 (71-93) before PEG, and 6.9 (3.7-9.7) and 130 (81-153) at CR. Six patients were treated more than 1 year with PEG; three had undetectable HCV-RNA when CR was diagnosed. Five patients are being treated for CR; one has been listed for LT; two patients were retransplanted. Five patients died as a result of sepsis partially related to CR.

CONCLUSIONS

Treatment with pegylated-interferon alpha-2a and ribavirin may trigger rapidly progressive CR in patients with therapeutic immunosuppressive trough levels, with or without first inducing ACR.

Isolation of Kupffer cells and their suppressive effects on T lymphocyte growth in rat orthotopic liver transplantation

AIM: To develop a practical method for isolation, purification and culture of hepatic Kupffer cells (KCs) and to observe their suppressive effects on the proliferation of alloreactive T cells.

METHODS: Perfusion in situ in vivo combined with density gradient centrifugation was applied in isolation, purification and culture of hepatic KC. The suppression by KCs on the T cell proliferation in mixed lymphocyte reaction (MLR) was observed.

RESULTS: This method resulted in a satisfactorily high yield of (1.1 ± 0.2) × 10⁷ KCs per liver, (93.5% ± 1.8%) viable cells, over 90% purity and positive for ED-2. After the first 24 h in culture, a great number of KCs which exhibited typical characteristics were observed. Using ³H-TdR incorporation assay, non-irradiated KCs significantly suppressed allo-MLR. The KCs recovered from accepted liver allografts in groups D and E were more effective in suppressing allo-MLR.

CONCLUSION: A standardized procedure for isolation of highly purified rat KCs is proposed and KCs have suppressive effects on the proliferation of alloreactive T cells, especially those derived from accepted liver allografts.

Induction of long-term liver allograft survival by delayed immunosuppression is dependent on interleukin-10

This study aims to investigate the potential role of endogenous interleukin (IL)-10 in long-term liver allograft survival induced by delayed immunosuppression (FK506 days 2-7). Liver transplantation was performed by using Dark Agouti and Lewis rats as donors and recipients, respectively. The delayed immunosuppression protocol induced indefinite allograft survival. A transient upregulation of plasma IL-10 levels was detected in the nontreatment and FK506 treatment groups. Macrophages were found to be one of the major sources of IL-10 produced from the liver allografts. Administration of IL-10-neutralizing antibody shortened the long-term isograft survival and FK506-induced indefinite allograft survival, particularly in the FK506 group. Damaged liver graft histology and increase of plasma alanine aminotransferase levels were detected in the groups with IL-10 antibody treatment. In an ex vivo setting, IL-10 recombinant protein augmented the expression of Foxp3, downregulated the expression of IL-2 and interferon gamma, and induced the generation of CD4(+)CD25(+)Foxp3(+) and CD8(+)CD25(+)Foxp3(+) cells, but this effect was blocked by the administration of IL-10 antibody. Finally, administration of IL-10 recombinant protein after the decline of endogenous IL-10 levels improved allograft survival, and a 100% long-term allograft survival was achieved by the combination of IL-10 with low-dose FK506. In conclusion, the delayed immunosuppression could induce long-term liver allograft survival in the presence of endogenous IL-10 produced by the tissue macrophages. Supplementary exogenous IL-10 administration combined with low-dose immunosuppressive drug may be a useful strategy to induce long-term liver allograft survival.

Acute rejection in HCV-infected liver transplant recipients: The great conundrum

1. In hepatitis C virus (HCV)-infected patients, treatment of acute rejection is associated with worse outcomes (increased risk of allograft cirrhosis and mortality). 2. Whether patients with HCV are at higher risk for rejection remains controversial. 3. The mechanisms mediating acute rejection and recurrence of HCV are distinct, and as such, it should be possible to develop techniques based on these molecular differences that are diagnostically useful. 4. Liver biopsy is considered the gold-standard for diagnosing acute rejection and recurrent HCV; however, given histopathological similarities between the two conditions, discrimination can be extremely difficult. 5. At the present time, there are no reliable, noninvasive tools available to distinguish between HCV recurrence alone and acute rejection plus HCV recurrence. 6. Mild rejection per se is not associated with graft loss and treatment of rejection with steroids and OKT3 is associated with worse outcome in HCV; thus, it seems logical that we should no longer treat mild rejection.

Operational tolerance in clinical liver transplantation: emerging developments

There is still little understanding of the immune events that occur in transplant patients as they develop a relationship with their graft alloantigens. Though, there is an enormous interest and motivation in inducing specific unresponsiveness to organ allografts in order to allow minimization or complete withdrawal of immunosuppression in the recipient, given that life-long immunosuppressive treatment entails a high risk of infectious and metabolic complications, malignancies, and drug-specific toxicity. Clinical tolerance is defined as stable normal graft function in the total absence of a requirement for maintenance immunosuppression. Effective clinical tolerance has been reported more frequently in liver transplant recipients than after transplantation of other organs, as the liver is an immune-privileged organ for several mechanisms, most of which still remain unclear. According to the English medical literature, cautious, carefully supervised weaning of immunosuppressive drugs in controlled trials is not unreasonable, especially when monitored by protocol biopsies. The five centers in which the weaning has been attempted have reported a similar degree of success (1 out of 4 patients) and no harm to the patient over the short-term. Though, long-term follow-up has been lacking and, at present, there are no reliable immunological parameters that enable patients who can be withdrawn from immunosuppressants without the risk of rejection to be identified. To achieve that goal, appropriate collaboration and interaction between clinicians, immunologists and other basic scientists are desirable, as well as the creation of an international, maybe intercontinental, registry for tolerant patients.