Immunological tolerance and liver transplantation

Nanoparticle-Based Interventions for Liver Transplantation

Liver transplantation is the only treatment for hepatic insufficiency as a result of acute and chronic liver injuries/pathologies that fail to recover. Unfortunately, there remains an enormous and growing gap between organ supply and demand. Although recipients on the liver transplantation waitlist have significantly higher mortality, livers are often not allocated because they are (i) classified as extended criteria or marginal livers and (ii) subjected to longer cold preservation time (>6 h) with a direct correlation of poor outcomes with longer cold ischemia. Downregulating the recipient's innate immune response to successfully tolerate a graft having longer cold ischemia times or ischemia-reperfusion injury through induction of immune tolerance in the graft and the host would significantly improve organ utilization and post-transplant outcomes. Broadly, technologies proposed for development aim to extend the life of the transplanted liver through post-transplant or recipient conditioning. In this review, we focus on the potential benefits of nanotechnology to provide unique pre-transplant grafting and recipient conditioning of extended criteria donor livers using immune tolerance induction and hyperthermic pre-conditioning.

Strategies to Improve Immune Suppression Post-Liver Transplantation: A Review

Since the first liver transplantation operation (LT) in 1967 by Thomas Starzl, efforts to increase survival and prevent rejection have taken place. The development of calcineurin inhibitors (CNIs) in the 1980s led to a surge in survival post-transplantation, and since then, strategies to prevent graft loss and preserve long-term graft function have been prioritized. Allograft rejection is mediated by the host immune response to donor antigens. Prevention of rejection can be achieved through either immunosuppression or induction of tolerance. This leads to a clinical dilemma, as the choice of an immunosuppressive agent is not an easy task, with considerable patient and graft-related morbidities. On the other hand, the induction of graft tolerance remains a challenge. Despite the fact that the liver exhibits less rejection than any other transplanted organs, spontaneous graft tolerance is rare. Most immunosuppressive medications have been incriminated in renal, cardiovascular, and neurological complications, relapse of viral hepatitis, and recurrence of HCC and other cancers. Efforts to minimize immunosuppression are directed toward decreasing medication side effects, increasing cost effectiveness, and decreasing economic burden without increasing the risk of rejection. In this article, we will discuss recent advances in strategies for improving immunosuppression following liver transplantation.

TCL1A, B Cell Regulation and Tolerance in Renal Transplantation

Despite much progress in the management of kidney transplantation, the need for life-long immunosuppressive therapies remains a major issue representing many risks for patients. Operational tolerance, defined as allograft acceptance without immunosuppression, has logically been subject to many investigations with the aim of a better understanding of post-transplantation mechanisms and potentially how it would be induced in patients. Among proposed biomarkers, T-cell Leukemia/Lymphoma protein 1A (TCL1A) has been observed as overexpressed in the peripheral blood of operational tolerant patients in several studies. TCL1A expression is restricted to early B cells, also increased in the blood of tolerant patients, and showing regulatory properties, notably through IL-10 secretion for some subsets. TCL1A has first been identified as an oncogene, overexpression of which is associated to the development of T and B cell cancer. TCL1A acts as a coactivator of the serine threonine kinase Akt and through other interactions favoring cell survival, growth, and proliferation. It has also been identified as interacting with others major actors involved in B cells differentiation and regulation, including IL-10 production. Herein, we reviewed known interactions and functions of TCL1A in B cells which could involve its potential role in the set up and maintenance of renal allograft tolerance.

The role of Kupffer cells in hepatic diseases

Kupffer cells (KCs) constitute 80-90% of the tissue macrophages present in the body. Essential to innate and adaptive immunity, KCs are responsible for the swift containment and clearance of exogenous particulates and immunoreactive materials which are perceived as foreign and harmful to the body. Similar to other macrophages, KCs also sense endogenous molecular signals that may result from perturbed homeostasis of the host. KCs have been implicated in host defense and the pathogenesis of various hepatic diseases, including endotoxin tolerance, liver transplantation, nonalcoholic fatty liver disease, and alcoholic liver disease. In this review, we summarized some novel findings associated with the role of KCs in hepatic diseases, such as the origin and mechanisms KCs polarization, molecular basis for caspase-1 activation called "non-canonical inflammasome pathway" involving the cleavage of Gsdmd by caspase-11, the important role of microRNA in liver transplantation, and so on. A better understanding of KCs biological characteristics and immunologic function in liver homeostasis and pathology may pave the way to investigate new diagnostic and therapeutic approaches for hepatic diseases.

Vascularized composite allograft-specific characteristics of immune responses

Vascularized composite allograft (VCA) transplantation, or reconstructive transplantation, has revolutionized the treatment of complex tissue and functional defects. Despite arriving during an age in which the immunology of solid organ transplant rejection has been investigated in much detail, these transplants have offered new perspectives from which to explore the immunobiology of transplantation. VCAs have a number of unique molecular, cellular, and architectural features which alter the character and intensity of the rejection response. While much is yet to be clarified, an understanding of these distinct mechanisms affords new possibilities for the control of immune responses in an effort to improve outcomes after VCA transplantation.

Fingerprints of transplant tolerance suggest opportunities for immunosuppression minimization

HLA incompatible organ transplant tolerance is the holy grail of transplantation. Stable engraftment of an HLA mismatched allograft and life-long tolerance induction, though feasible in highly selected cohorts with depletional protocols, is not ready for generalized application to the entire transplant recipient pool. It has thus been important to harness biomarkers that can uncover mechanisms and tools for monitoring HLA mismatched recipients that develop a state of operational tolerance, during accidental immunosuppression withdrawal secondary to problems of over-immunosuppression (infection or malignancy) or toxicity (mostly cosmetic or cardiovascular). A restricted and unpredictable group of patients can demonstrate a clinical state of operational tolerance, manifested by state of stable graft function of a graft with HLA mismatches between recipient and donor, intact immune responses to third party antigens and no measurable immunosuppression. These patients have served as the basis for the discovery of clinically correlative biomarkers, in distal biofluids (mainly blood), that can define the existing state of operational clinical tolerance. Operationally tolerant patients are rare, as withdrawal of immunosuppression most often results in rejection and graft loss. Nevertheless, operationally tolerant kidney, liver and heart allograft recipients have been reported. The presence of similar biomarker signature profiles in HLA mismatched transplant recipients on immunosuppression, suggests the feasibility of utilizing these biomarkers for educated immunosuppression minimization with a view to retaining immunological quiescence, while reducing the maintenance immunosuppression burden to a "safe" alloimmune threshold. Though clinical operational tolerance is rare, as immunosuppression cessation most often results in increased alloimmunity and rejection, the biomarker profile studies that have harnessed whole genome profiling suggest that the frequency of this state may be ~8% in kidney allograft recipients, and even more frequent in pediatric recipients and in liver transplantation: 25% in adult liver allograft recipients and ~60% in pediatric liver allograft recipients. In this review we discuss putative molecular mechanisms, cellular players and correlative biomarkers that have been developed through clinically associative studies of tolerant and non-tolerant patients. Through mechanisms of carefully constructed and monitored randomized, prospective clinical trials, the transplant community stands at the cusp of improved quality of recipient life through educated immunosuppression minimization.

CD39 deficiency in murine liver allografts promotes inflammatory injury and immune-mediated rejection

Adenosine triphosphate (ATP), an essential metabolic energy source, is released following cell apoptosis or necrosis. It acts as a damage-associated molecule pattern to stimulate innate immune cells. The ectonucleotidase CD39 regulates immune activation by hydrolysis of extracellular ATP. We have shown previously that CD39 expression by donor livers helps protect syngeneic grafts with extended (24 hr) cold preservation time from ischemia reperfusion injury. Given its immune regulatory properties, we hypothesized that CD39 expression in donor livers might modulate transplant tolerance that occurs following mouse allogeneic liver transplantation (LTx). Livers from C57BL/6 (B6) wild-type (WT) or CD39 KO mice were transplanted into normal C3H recipients with minimal (approximately 1 hr) cold ischemia. Serum alanine aminotransferase levels at day 4 post LTx were significantly higher in animals given CD39KO compared with WT livers. Moreover, IFN-γ production by liver-infiltrating CD8⁺ T cells at day 4 was significantly higher in CD39KO than in WT grafts. Furthermore, splenic T cells from CD39KO liver recipients exhibited greater proliferative responses to donor alloantigens than those from mice given WT grafts. By contrast, there was a concomitant significant reduction in the frequency of regulatory T cells (Treg) in CD39KO than in WT livers. Whereas WT liver allografts survived > 100 days, no CD39KO grafts survived beyond 40 days (median survival time [MST]: WT: >100 days vs CD39KO: 8 days; p<0.01). In addition, soluble CD39 administration significantly prolonged CD39KO liver allograft survival (MST: 27.5 days). These novel data suggest that CD39 expression in liver allografts modulates tissue injury, inflammation, anti-donor effector T cell responses and Treg infiltration and can suppress transplant rejection.

Tolerance and chimerism and allogeneic bone marrow/stem cell transplantation in liver transplantation

The liver has particular tolerogenic properties that allow its spontaneous acceptance in some animal species. Liver structure is considered to favor a tolerogenic environment. The peripheral tolerance mechanisms also play a role in spontaneous tolerance to liver graft. In a clinical setting, the main challenge nowadays facing liver transplantation is minimization of immunosuppression with the goal of donor-specific tolerance. Mechanisms involved in tolerance to transplanted organs are complex and partly unknown. A significant mechanism in tolerance induction is chimerism. Chimerism can be induced through transplantation of allogeneic donor bone marrow/stem cells under appropriate host conditioning. This review focuses on the tolerance mechanisms in liver transplantation and highlights the role of chimerism and allogeneic bone marrow/stem cell transplantation in tolerance development.

Ab initio calcineurin inhibitor-based monotherapy immunosuppression after liver transplantation reduces the risk for Pneumocystis jirovecii pneumonia

At the Tor Vergata University of Rome, ab initio calcineurin inhibitor-based monotherapy immunosuppression (IS) is the standard of treatment after liver transplantation (LT). As the net state of IS determines the onset of Pneumocystis jirovecii pneumonia (PCP), we hypothesized that, in the presence of weak impairment of the immune function, as determined by the above-mentioned IS, the host is not overexposed to the risk for PCP and consequently the specific anti-PCP prophylaxis is unnecessary. In a single-cohort descriptive study, we retrospectively investigated the incidence of PCP in 203 LT patients who did not receive anti-PCP prophylaxis because they were under monotherapy IS. The primary endpoint of the study was the incidence of PCP during the first 12 months following LT; secondary endpoints were the incidence of acute rejection requiring additional IS and of CMV infection. No cases of PCP were recorded. The incidence of CMV and acute rejection was 3.9% and 0.9%, respectively. Our data suggest that monotherapy IS after LT may nullify the risk for PCP even in the absence of any specific prophylaxis.

Calcineurin inhibitor minimization in pediatric liver allograft recipients

The use of CNI in pediatric LTx has dramatically improved the outcome for children with end-stage liver disease by significantly reducing the rate of acute and chronic rejection. Long-term concerns about CNI-induced nephrotoxicity and other adverse effects remain an issue, particularly as the emphasis moves from short-term survival to long-term quality of life. This review summarizes lessons learnt from pediatric and adult solid organ transplantation in minimizing CNI use in immunosuppression protocols in children following LTx. There are three models for CNI minimization: dose reduction, withdrawal or avoidance, supplemented by the use of IL-2 receptor blocking antibodies in the peri-transplant period, and early transition to alternate drugs such as MMF or SRL. Prospective studies evaluating reduction or withdrawal protocols in adult and pediatric LTx indicate that rejection rates are comparable with traditional CNI-based immunosuppression and that two and five yr patient and graft survival are similar, with recovery in renal function. There are few studies evaluating complete avoidance of CNI, apart from that in renal transplantation, although the benefits of long-term reduction in cardiovascular, metabolic, and possibly neoplastic side effects may justify this approach. It is not clear yet how CNI minimization will affect the development of tolerance but experimental and preliminary clinical studies indicate that CNI and steroid avoidance or minimization in the peri-operative period may favor the development of long-term graft tolerance. In summary, CNI minimization may be safe and effective in the short term but large-scale pediatric randomized studies are required to evaluate the long-term efficacy of these regimes in the development of chronic rejection, PTLD, and graft tolerance.

FoxP3 in peripheral blood is associated with operational tolerance in liver transplant patients during immunosuppression withdrawal

BACKGROUND

Human liver allografts do sometimes survive in a recipient after withdrawal of immunosuppression (IS), commonly referred to as "operational tolerance." Preliminary clinical data have suggested an increase in the frequency of regulatory T cells (Treg) CD4+CD25 high and FoxP3 expression in operationally tolerant liver transplant recipients (Gr-T). In the context of human liver transplantation, the dynamics of Treg have not been studied. We designed a prospective study to ascertain the profile of the Treg population and FoxP3 expression during IS withdrawal.

METHODS

To identify such parameters, we analyzed peripheral blood mononuclear cell populations and FoxP3 mRNA expression in 12 liver allograft recipients under cyclosporine A-based IS, who showed stable function of the allograft for more than 2 years.

RESULTS

An increase was observed in the frequency of CD4+CD25 high cells when the IS was withdrawn in Gr-T patients (n=5). These patients exhibited a 3.5-fold increase for relative mRNA FoxP3 expression before the complete IS withdrawal and this continued when IS therapy was stopped. In patients who suffered rejection (n=7) there was no increase in the CD4+CD25 high cells or FoxP3 expression.

CONCLUSIONS

With the present study, the first evidence is provided that the increase of CD4+CD25 high T cells and FoxP3 transcripts is associated with operational tolerance in liver transplanted patients during IS withdrawal.

Basiliximab versus steroids in double therapy immunosuppression in liver transplantation: a prospective randomized clinical trial

BACKGROUND

: Basiliximab (B), an anti-CD25 monoclonal antibody, may represent an alternative to steroids (S) in immunosuppression after liver transplantation (LTx). The aim of this prospective randomized clinical trial was to compare B with S in a cyclosporin A (CsA)-based immunosuppression regimen in primary LTx.

METHODS

: Forty-seven adult recipients of LTx were randomly assigned to receive B or S. CsA was administered at the initial dose of 10 mg/kg/day and adjusted to the target C2 level of 800 to 1000 ng/mL by day 7. Clinically suspected acute cellular rejection (ACR) was histologically confirmed. Endpoints include ACR, survival, and disease-free survival.

RESULTS

: In group B (26 patients), there were seven biopsy-confirmed ACR with an ACR rate of 15.4%; in group S (21 patients), 8 ACR with an ACR rate of 28.6% (P=n.s.). Cumulative survival at 36 months after transplantation was 84.3% for group B and 61.0% for group S. In hepatitis C virus patients (n=20: 12 in group B, 8 in group S), the ACR rate was 25% in group B and 50% in group S. The incidence of infection and other adverse events was similar in the two treatment groups.

CONCLUSIONS

: B may represent a valid alternative to S in the induction of immunosuppression in LTx. Further studies of basiliximab in a large cohort are needed.

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.

Multiparameter immune profiling of operational tolerance in liver transplantation

Immunosuppressive drugs can be completely withdrawn in up to 20% of liver transplant recipients, commonly referred to as 'operationally' tolerant. Immune characterization of these patients, however, has not been performed in detail, and we lack tests capable of identifying tolerant patients among recipients receiving maintenance immunosuppression. In the current study we have analyzed a variety of biological traits in peripheral blood of operationally tolerant liver recipients in an attempt to define a multiparameter 'fingerprint' of tolerance. Thus, we have performed peripheral blood gene expression profiling and extensive blood cell immunophenotyping on 16 operationally tolerant liver recipients, 16 recipients requiring on-going immunosuppressive therapy, and 10 healthy individuals. Microarray profiling identified a gene expression signature that could discriminate tolerant recipients from immunosuppression-dependent patients with high accuracy. This signature included genes encoding for gammadelta T-cell and NK receptors, and for proteins involved in cell proliferation arrest. In addition, tolerant recipients exhibited significantly greater numbers of circulating potentially regulatory T-cell subsets (CD4+ CD25+ T-cells and Vdelta1+ T cells) than either non-tolerant patients or healthy individuals. Our data provide novel mechanistic insight on liver allograft operational tolerance, and constitute a first step in the search for a non-invasive diagnostic signature capable of predicting tolerance before undergoing drug weaning.

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.

Tolerogenic Protocol for Intestinal Transplantation

Transplantation is standard therapy for many patients suffering from kidney, liver, or heart failure. In contrast, transplantation of the intestine remains a high-risk procedure, which is performed in a minority of patients with short bowel syndrome. The difficulty is the strong alloimmune response caused by intestinal grafts and the complications of the profound immunosuppression. We tested a new clinical immunomodulatory protocol using donor-specific blood transfusion, a strategy that was popular before the introduction of cyclosporine and was recently shown to promote development of regulatory cells. Low-dose steroids and low-dose tacrolimus were administered based on previous observations that tolerance requires an intact immune system, that over-immunosuppression is counterproductive, and that high doses of calcineurin inhibitors block development of regulatory cells whereas low doses promote it. Finally, inflammation within the intestinal graft was minimized to reduce the additional stimulants that the innate immunity of the transplanted intestine exert on the adaptive immune response. Under this protocol, freedom from rejection was achieved in four consecutive intestinal transplant recipients using extremely low immunosuppression.

Complete weaning off immunosuppression in HCV liver transplant recipients is feasible and favourably impacts on the progression of disease recurrence

BACKGROUND/AIMS

HCV-related disease recurrence progresses rapidly after liver transplantation. We hypothesised that withdrawal of immunosuppression might favourably impact on disease progression.

METHODS

Weaning off immunosuppression was attempted in 34 HCV-RNA positive patients (mean age 62+/-6.4 years) transplanted 63.5+/-20.1 months earlier, under cyclosporine A monotherapy. Patients were followed for 3 years including yearly protocol liver biopsies. Primary endpoints were feasibility of weaning off immunosuppression and its impact on disease progression. Secondary endpoint was to identify predictors of an immunosuppression-free state and fibrosis progression.

RESULTS

Complete and permanent immunosuppression withdrawal was achieved in 8 patients (23.4%), whereas 14 (41.2%) developed rejection within eight months despite an initial response and 12 (35.2%) rejected during tapering. After a mean follow-up 45.5+/-5.8 months weaned patients showed stabilisation/improvement of histological fibrosis (P<0.01), lower necro-inflammation (P<0.02) and improved liver function (P<0.05) compared to weaning-intolerants. Multiple logistic regression identified low blood cyclosporine A trough levels during the first post-transplant week (P=0.004) and initial steroid-free immunosuppression (P<0.008) as independent predictors of sustained weaning. Achievement of immunosoppression freedom (P=0.02) and baseline staging score (P<0.0001) were independently associated with stabilisation/improvement of histological fibrosis.

CONCLUSIONS

Reconstitution of immune-competence in the host improves the natural history of HCV recurrence in the graft.

Infusion of nonmyeloablative bone marrow alleviates acute rejection reaction in liver allotransplantation

OBJECTIVE

To study the effect and implication of nonmyeloablative donor specific bone marrow (DSBM) infusion on the immunoreaction of liver allotransplantation.

METHODS

Orthotopic liver transplantation model was used in this study. Groups were set as follows: Group I, syngeneic control (Wistar-to-Wistar); Group II, acute rejection (SD-to-Wistar); Group III, acute rejection treated with cyclosporine A (CsA) by intramuscular injection (SD-to-Wistar+CsA); Group IV, bone marrow infusion at 7 d pretransplantation followed by short-term CsA treatment (SD-to-Wistar+DSBM); Another group of short-term CsA treatment preoperatively without bone marrow infusion was also set as control. General characteristics and survival time were observed. Histological grades of rejection were determined by pathological examination. IL-2 and IFN-gamma level in peripheral blood and donor liver were detected respectively by Enzyme-Linked Immuno-Sorbent Assay (ELISA) and Western blot. Chimerism of donor cells was measured by PCR for a male-specific marker (Y-chromosome-specific sequence, Sry).

RESULTS

No signs of rejection were found in Group I. Acute rejection occurred in both Group II and the short-term CsA treated group. All the recipients died at (9-15) d posttransplantation with a median survival time of (10.7+/-0.5) d and (11.2+/-2.4) d, respectively. Only mild rejection could be seen in Group III. In Group IV, 4 out of 6 recipients had long-term survival (>100 d), the histological grade of rejection was significantly lower than that of Group II, so did the expression level of IL-2 and IFN-gamma in both peripheral blood and grafted liver. Y-chromosome-specific sequence (Sry) of male SD rats could be detected in the bone marrow, spleen and thymus of female recipients at 15 d after bone marrow infusion.

CONCLUSION

Mild preconditioning nonmyeloablative donor specific bone marrow infusion can enhance chimerism formation in recipients, alleviate the rejection of liver allotransplantation and prolong survival of liver allotransplantation.