Tolerance In Organ Transplantation Research Articles

Microchimerism in promoting graft acceptance in clinical transplantation

Infusions of bone marrow-derived cells together with 'space making' continue to be tested in clinical organ transplant tolerance protocols. These trials are based on the hypothesis that this might produce initial multilineage chimerism. There is some evidence that this in turn induces regulatory cells that control alloimmunity. Although a wealth of knowledge is available from animal models, this review deals with what we know or can speculate about donor bone marrow cells and chimerism in human organ transplantation. Calcineurin inhibitors are employed in most of these protocols to blunt the initial immune response. One protocol also has a stepwise regulatory cell generating treatment with sirolimus before total withdrawal. A number of donor chimeric lineages including stem cells, dendritic cells, myeloid precursors, and various lymphoid subpopulations have been described. Currently, it is recognized that the nature of cells that make up the chimerism could influence graft rejection versus acceptance. Tolerogenic donor chimeric cells may also generate regulatory subsets, thus controlling alloimmunity on two fronts. It might be speculated that prolonged and sustained regulation or possible anergy induced by chimerism may eventually lead to clonal deletion, thereby bringing about classical immunologic tolerance.

A Novel Monoclonal Antibody against Human CD80 and its Immune Protection in a Mouse Lupus-like Disease

Blockade of the interactions between CD28/CTLA-4 and their ligands, CD80 (B7, B7.1)/CD86 (B70, B7.2), is an attractive means to induce antigen-specific peripheral tolerance in autoimmune disease and organ transplantation. In this study, we generated and characterized a monoclonal antibody (Clone 4E5) against human CD80. 4E5 could recognize both human and mouse CD80 and suppress mixed lymphocyte reaction in vitro. To investigate their potency for clinical use, we further administrated 4E5 to a mouse lupus-like disease model (C57BL/J6) induced by Pristane. 4E5 could inhibit the immune response and attenuate the severity of lupus-like disease. The data showed 4E5 function and suggested that blockade of CD80/CD28 co-stimulatory signal pathway with 4E5 is a promising strategy to decelerate the progression of lupus-like disease and other autoimmune diseases.

The Search for Immunosuppressive Therapies to Induce Tolerance in Organ Transplantation

Organ transplantation has become a major therapeutic option for patients with irreversible organ diseases. Immunosuppressive agents are usually required to prevent allograft rejection in patients who undergo an organ transplantation. Such drugs suppress both specific and nonspecific immunity, and render the recipient more susceptible to both infection and malignancy. Therefore, the development of more effective and less toxic immunosuppressive agents could improve the clinical outcomes of organ transplant recipients. Since the early days of clinical and experimental liver transplantation, it has been known that the liver is less likely to be rejected in comparison to other organs and may be tolerogenic even across a fully allogeneic MHC barrier in some specific cases. Spontaneous acceptance of liver allografts has been observed in several species. Orthotopic liver transplantation (OLT) in certain rat strains is accepted without immunosuppressive agents and serum from post-OLT recipients displays immunosuppressive activity. Attempts have been made to identify the immunosuppressive factors that are present in post-OLT serum to elucidate the mechanism of immunological tolerance and to discover novel immunosuppressive agents for potential use in organ transplantation. In this review we will focus on established and recent findings in the identification of immunosuppressive factors in a rat tolerogenic OLT model. The most recent therapeutic methods in organ transplantation and future prospects will be discussed.

Operational Tolerance in Living-Related Renal Transplantation: A Single-Center Experience

Introduction Various methods have been tried to induce operational tolerance in organ transplantation. We present a single-center experience using 6 tolerance induction protocols (TIP) in living-related renal transplantation. Methods We evaluated 6 TIP protocols: (1) peripheral blood stem cells employed ( n = 38); (2) midified the protocol by portal infusion ( n = 292); (3) the second protocol plus TIP+DST+BM+intrathymic and intramarrow infusion plus low-dose, nonmyeloablative conditioning employed ( n = 174), (4) the third protocol of TIP plus cultured hematopoietic stem cells (HSC) with target-specific irradiation ( n = 290); (5) TIP 4 plus thymus, intramarrow infusion, and target-specific irradiation converted to total lymphoid irradiation (TLI) ( n = 366); and (6) TIP 5 plus bortzomib–TLI ( n = 165). Patient/donor demographics were comparable. Results We evaluated patient and graft survival, rejection episodes, recurrence, drug toxicity, and chimerism revealed; groups 4 and 5 showed better survival, graft function, chimerism, and decreased rejection episodes compared with previous protocols. Serum creatinine (mg/dL) at 1 year was 1.5, 1.39, 1.5, 1.51, 1.46, and 1.41, and at 5 years, 1.69, 1.72, 1.82 and 1.59, in groups 1–6, respectively. Chronic rejection episodes were 10.5%, 14.1%, 10.4%, 9.3%, 3.5%, 1.7%, and 1.8% respectively. Patient survival of groups 1, 2, and 3 at 1, 5, and 10 years was 86.5%, 56.8%, and 40.1%; 89.4%, 69.1%, and 56.4%; and 89.6%, 67.7%, and 64.6%, respectively; of group 4 for 1 and 5 years was 92.4% and 81.8%; for groups 5 and 6 for 1 year was 94% and 96.3%, respectively. The death-censored graft survival of groups 1, 2, and 3 at 1, 5, and 10 years was 91.9%, 70.3%, and 64.7%; 89%, 66%, and 57.6%; and 86.7%, 67%, and 42.5%, respectively. In group 4 for 1 and 5 years was 87.9% and 74.7%; and for groups 5 and 6 for 1 year was 94% and 96.5%, respectively. Conclusion TIP results showed improved graft/patient survivals, minimum immunosuppression, and fewer rejection episodes and recurrence.

Harnessing the diversity of the human T-cell repertoire: A monitoring tool for transplantation tolerance?

There is significant diversity in the TCR repertoire in heterologous and allogeneic immunity. A paper in this issue of the European Journal of Immunology shows that changes in the TCR repertoire can be correlated with outcomes of renal transplantation. This indicates that the diversity of the TCR repertoire could be utilized to monitor clinical phenotypes, such as chronic humoral rejection and operational tolerance in organ transplantation. However, prior to the clinical use of monitoring changes in the TCR repertoire as a biomarker to monitor clinical status after organ transplantation, many questions regarding time dependency, triggering factors and specificity need to be addressed. A causative role for TCR repertoire disruption in organ transplantation will need to be proven by interventional trials that can demonstrate that the TCR repertoire is modifiable and predictive of graft outcome. In this Commentary, we discuss the strengths and opportunities of TCR repertoire monitoring, and point towards yet unanswered questions that will become important if the Vβ CDR3-length distribution assay will be clinically applied.

Clinical and immunologic aspects of egg donation pregnancies: a systematic review

Egg donation (ED) makes it possible for subfertile women to conceive. Pregnancies achieved using ED with unrelated donors are unique, since the entire fetal genome is allogeneic to the mother. The aims of this review were to evaluate the consequences of ED pregnancies and to place them in the special context of their atypical immunologic relationships. This review comprised an online search of English language publications listed in Pubmed/Medline, up to 29 January 2010. Seventy-nine papers met inclusion criteria. Using the literature and the authors' own experience, the relevant data on pregnancy outcome and complications, placental pathology and immunology were evaluated. Multiple studies document that ED pregnancies are associated with a higher incidence of pregnancy-induced hypertension and placental pathology. The incidence of other perinatal complications, such as intrauterine growth restriction, prematurity and congenital malformations, is comparable to conventional IVF. During pregnancy, both local and systemic immunologic changes occur and in ED pregnancies these changes are more pronounced. There is almost no information in the literature on the long-term complications of ED pregnancies for the mother. ED pregnancies have a higher risk of maternal morbidity. Owing to the high degree of antigenic dissimilarity, ED pregnancies represent an interesting model to study complex immunologic interactions, as the fully allogeneic fetus is not rejected but tolerated by the pregnant woman. Knowledge of the immune system in ED pregnancies has broader significance, as it may also give insight into immunologic aspects of tolerance in solid organ transplantation.

The role of indoleamine 2,3 dioxygenase in the induction of immune tolerance in organ transplantation

The aim of this review is to present current information on transplantation research regarding the role of indoleamine 2,3 dioxygenase in immune regulation. We present the basic mechanisms by which the enzyme is expressed, followed by tryptophan catabolism that leads to midg1 phase arrest and apoptosis. Other effects proposed, although not yet completely proven and generally accepted, include T-cell development suppression, secretion of regulatory cytokines such as IL10, and generation of new T regulatory cells. Clinical studies are being performed worldwide; thus, our goal is to focus on the clinical potential relevance of the enzyme rather than a presentation on a molecular basis so that health care providers concerning transplantation are aware of this promising field in immunology and therapeutics. We do emphasize the fact that information regarding the role of indoleamine 2,3 dioxygenase in human beings is still scarce.

Monitoring the operationally tolerant liver allograft recipient

A fundamental goal in transplantation is the establishment of allograft function without ongoing immunosuppression. Robust allograft tolerance has been established in experimental transplantation models, whereas clinical operational tolerance has been described most frequently following human liver transplantation. Clinical assessment of tolerance has been limited to laboratory evaluation of organ function. Additional tools include graft monitoring through biopsy and blood sampling for biomarker analysis. Current biomarkers under assessment in recent years include dendritic cell subsets, regulatory T cells, antidonor antibodies, and gene polymorphisms. Emerging microarray analysis that is being prospectively validated will also be reviewed. A further tool in the characterization of the tolerant patient will be the accurate enrollment of such patients into a multicenter registry that will prospectively follow the natural history of the patient withdrawn from immunosuppression and help facilitate the entry of interested patients to mechanistic and immune monitoring trials. The International Solid Organ Transplant Tolerance Registry (www.transplant-tolerance.org) will be briefly described. Effective biomarker characterization of the operationally tolerant liver allograft recipient would allow earlier, well tolerated, prospective drug withdrawal with the goal of extending the potential benefits of drug minimization to an increasing number of patients in a more predictable fashion.

Rapamycin in combination with donor-specific CD4 +CD25 +Treg cells amplified in vitro might be realize the immune tolerance in clinical organ transplantation

It is an urgent need to induce and keep the donor-specific immune tolerance without affecting the function of normal immune defense and immune surveillance in clinical organ transplantation. Large number of studies showed that both the establishment of donor-recipient chimerism and the application of antibodies or drugs could obtain the donor-specific immune tolerance in animal transplantation model. However, the former as treatment of clinical practice has a poor feasibility, the latter has a very low success rate in clinical organ transplantation. There is a group of naturally occurring CD4 +CD25 + regulatory T cells (Tregs) that mediate immune tolerance by suppressing alloreactive T cells in vivo. These cells are unable to curb the occurrence of allograft rejection owing their low content. And donor-specific Tregs amplified in vitro alone can not induce donor-specific immune tolerance for recipient. Rapamycin (RPM) as a proliferation signal inhibitor, studies have shown it can effectively inhibit allograft rejection and maybe contribute to induction of immune tolerance. But there exist still many dose-dependent adverse reactions which could prevent the establishment of immune tolerance and reduce the life quality of recipients in the clinical application of RPM. Therefore, we speculate a small amount of RPM combined with donor-specific Tregs amplified in vitro may be not only induce the achievement of donor-specific tolerance, but also reduce or eliminate the side effects of RPM in clinical organ transplantation.

Noninvasive methods to assess the risk of kidney transplant rejection

In current clinical practice, immune reactivity of kidney transplant recipients is estimated by monitoring the levels of immunosuppressive drugs, and by functional and/or histological evaluation of the allograft. The availability of assays that could directly quantify the extent of the recipient’s immune response towards the allograft would help clinicians to customize the prescription of immunosuppressive drugs to individual patients. Importantly, these assays might provide a more in-depth understanding of the complex mechanisms of acute rejection, chronic injury, and tolerance in organ transplantation, allowing the design of new and potentially more effective strategies for the minimization of immunosuppression, or even for the induction of immunological tolerance. The purpose of this review is to summarize results from recent studies in this field.

A Human Anti-CD40 Monoclonal Antibody, 4D11, for Kidney Transplantation in Cynomolgus Monkeys: Induction and Maintenance Therapy

Blockade of CD40-CD154 signaling pathway is an attractive strategy to induce potent immunosuppression and tolerance in organ transplantation. Due to its strong immunosuppressive effect shown in nonhuman primate experiments, anti-CD154 monoclonal antibodies (mAbs) have been tried in clinical settings, but it was interrupted by unexpected thromboembolic complications. Thus, inhibition of the counter molecule, CD40, has remained an alternative approach. In the previous preliminary study, we have shown that 4D11, a novel fully human anti-CD40 mAb, has a fairly potent immunosuppressive effect on kidney allograft in nonhuman primates. In this study, we aimed to confirm the efficacy and untoward events of the 2-week induction and 180-day maintenance 4D11 treatments. In both, 4D11 significantly suppressed T-cell-mediated alloimmune responses and prolonged allograft survival. Addition of weekly 4D11 administration after the induction treatment further enhanced graft survival. Complete inhibition of both donor-specific Ab and anti-4D11 Ab productions was obtained only with higher-dose maintenance therapy. No serious side effect including thromboembolic complications was noted except for a transient reduction of hematocrit in one animal, and decrease of peripheral B-cell counts in all. These results indicate that the 4D11 appears to be a promising candidate for immunosuppression in clinical organ transplantation.

Future Therapeutics for the Induction of Peripheral Immune Tolerance in Autoimmune Disease and Organ Transplantation

Rodent models of transplantation and autoimmune disease have demonstrated that it is possible to induce lifelong and specific immunological tolerance to both self and graft antigens in the absence of any continued immunosuppression. If this situation could be achieved clinically, it would avoid many of the longer-term complications of immunosuppression, such as the increased risk of infection, cancer and other side effects, such as nephrotoxicity. In this review, we shall consider the interplay between regulatory T cells, dendritic cells and the tissue itself, and the resulting local protective mechanisms that are coordinated to maintain the tolerant state and an acquired local immune privilege. The current status of attempts to apply tolerogenic approaches to the clinical treatment of autoimmune diseases and to induce either tolerance to organ grafts or sufficient immune regulation so that conventional immunosuppression can be minimized will also be considered.

Human transplant acceptance-inducing cells suppress mitogen-stimulated T cell proliferation

The Transplant Acceptance-inducing Cell (TAIC) is a form of immunoregulatory macrophage which appears to be capable of establishing a state of alloantigen-specific partial tolerance of solid organ transplants in renal transplant recipients. This report establishes that human TAICs do not elicit a proliferative response from co-cultured allogeneic T cells. More significantly, it has been shown that TAICs are able to suppress proliferation of allogeneic CD4 + and CD8 + T cells after mitogenic stimulation. This suppressive activity can be attributed to the deletion of activated T cells by TAICs and to the secretion of a soluble inhibitor of T cell proliferation. It is further shown that the acquisition of T cell-suppressive properties by human TAICs depends upon an unidentified component of human serum.

Operational tolerance after liver transplantation

The achievement of an immunosuppression (IS)-free state after transplantation represents the ultimate goal of any immunosuppressive regimen. While clinical operational tolerance (COT) remains the exception after other types of solid organ transplantation, several cases of COT have been described after liver transplantation (LT). Overall, the experience gained so far worldwide demonstrates that COT can be achieved safely in one quarter of selected individuals, irrespective of the immunological background of donor and recipient, patient age, indication for LT, study endpoint, length of the weaning period and of pre/post-weaning follow-up, presence or not of chimerism. However, most transplant physicians still believe that the achievement of COT is still out of reach for the majority of LT recipients because of the potential risk for transplant survival, the non-randomized nature of most of the studies reported so far, and the selective nature of the patients enrolled in such studies, making them non-representative of the whole population of LT recipients. Despite these concerns, the present article demonstrates that this attitude is potentially no longer justified, given the growing evidence that a permanent and stable IS-free state can be achieved in a proportion of individuals who have received a LT for non-immune mediated liver diseases.

Immunoglobulin-like transcript 3: A crucial regulator of dendritic cell function

Dendritic cells (DC) are key components of the immune system, which actively participate in innate and adaptive immune responses. They are traditionally viewed as the immunologic centerpiece that is able to prime CD4 + helper and CD8 + cytotoxic T-cell effector populations. However, accumulated evidence highlights the functional plasticity of DC, which are shown to also be able to display a tolerogenic function eliciting the differentiation of T suppressor (Ts) and regulatory (Treg) cells. This tolerogenic state of DC is characterized by low costimulatory potential and high expression of inhibitory receptors. Conspicuously among the latter is the immunoglobulin-like transcript 3 (ILT3), which independently prevents the activation of both DC and T cells. DC overexpressing ILT3 display lower phosphorylation levels of NF-κB and fail to stimulate the full program of Th proliferation and maturation eliciting instead the differentiation of CD8 + T S and CD4 + Treg. In contrast, ILT3-knockdown DC have robust cytokine and chemokine production, and are able to trigger stronger T-cell responses to viral antigens or alloantigens. Understanding and manipulating the functional immunogenic/tolerogenic dichotomy of DC has important clinical applications for achieving tolerance in organ transplantation, stemming autoimmune diseases or, conversely, generating efficient immunogenic vaccines for immunotherapy in cancer and chronic viral diseases.

Induction of Tolerance in Solid Organ Transplantation: The Rationale to Develop Clinical Protocols in Liver Transplantation

Minimization or withdrawal of immunosuppressive treatments after organ transplantation represents a major objective for improving quality of life and long-term survival of grafted patients. Such a goal may be reached under some clinical conditions, particularly in liver transplantation, making these patients good candidates for tolerance trials. In this context in liver transplantation, the central questions are (1) how to promote the natural propensity of the liver graft to be accepted, (2) which type of immunosuppressive drug should be used for induction and maintenance, and (3) which biomarkers could be used to discriminate tolerant patients from those requiring long-term immunosuppression. Induction therapies using aggressive T-cell–depleting agents may favor graft acceptance. However, persistent and/or rapidly reemerging cell lines, such as memory-type cells or CD8 + T cells, could represent a significant barrier for induction of tolerance. The type of maintenance drugs also remains questionable. Calcineurin inhibitors may be eventually deleterious in the context of tolerance protocols, through inhibitory effects on regulatory T cells, that are not observed with rapamycin. In conclusion, significant efforts must be made to achieve reliable strategies for immunosuppression minimization or withdrawal after organ transplantation into the clinics.

Immune regulation by non-lymphoid cells in transplantation.

Regulatory cells play a crucial role in the induction and maintenance of tolerance by controlling T cell as well as B and natural killer (NK) cell-mediated immunity. In transplantation, CD4+CD25+forkhead box P3+ T regulatory cells are instrumental in the maintenance of immunological tolerance, as are several other T cell subsets such as NK T cells, double negative CD3+ T cells, gammadelta T cells, interleukin-10-producing regulatory type 1 cells, transforming growth factor-beta-producing T helper type 3 cells and CD8+CD28(-) cells. However, not only T cells have immunosuppressive properties, as it is becoming increasingly clear that both T and non-T regulatory cells co-operate and form a network of cellular interactions controlling immune responses. Non-T regulatory cells include tolerogenic dendritic cells, plasmacytoid dendritic cells, mesenchymal stem cells, different types of stem cells, various types of alternatively activated macrophages and myeloid-derived suppressor cells. Here, we review the mechanism of action of these non-lymphoid regulatory cells as they relate to the induction or maintenance of tolerance in organ transplantation.

Can Proliferation Signal Inhibitor-Induced Tregs Really Reflect Transplantation Tolerance in Clinical Solid Organ Transplantation?

Exploring new immunosuppressive strategies inducing donor-specific hyporesponsiveness is a great challenge in transplantation. For this purpose, monitoring the alloimmune response is a critical step to carrying out protolerogenic immunosuppressive protocols. Regulatory T cells (Tregs), known as controlling various immune responses, were found to play an important part in allograft transplant tolerance. It is said that Rapamycin (RAPA), one of the proliferation signal inhibitors (PSIs), could achieve true tolerance through the induction of Tregs in clinical trials. Can PSI-induced Tregs in peripheral blood mononuclear cells (PBMC) really reflect transplantation tolerance in clinical solid organ transplantation?

Depleting T-cell subpopulations in organ transplantation

T-cell depletion strategies are an efficient therapy for the treatment of acute rejection after organ transplantation and have been successfully used as induction regimens. Although eliminating whole T cells blocks alloreactivity, this therapy challenges the development of regulatory mechanisms because it depletes regulatory cells and modifies the profile of T cells after homeostatic repopulation. Targeting T-cell subpopulations or selectively activated T cells, without modifying Treg cells, could constitute a pro-tolerogenic approach. However, the perfect molecular target that would be totally specific probably still needs to be identified. In this study, we have reviewed the biological activities of broad or specific T-cell depletion strategies as these contribute to the induction of regulatory cells and tolerance in organ transplantation.

Prolongation of cardiac allograft survival by syngeneic Hematopoietic stem/progenitor cell transplantation in mice

Organ transplantation is a rapidly developing field, being the only effective treatment for end-stage organ disease. However, the associated immunosuppressant therapy has numerous direct and indirect adverse effects. Hematopoietic stem cell transplantation (HSCT), via immune reconstitution, offers an alternative method of treatment. In this study, we determined the cardiac allograft survival in mice treated with syngeneic HSCT or hematopoietic progenitor cell transplantation (HPCT). BALB/c and C57BL/6 mice were randomly divided into three groups. Mice in Group A (n=7) were untreated while those in Group B (n=8) and C (n=7) were treated with HPCT and HSCT, respectively. Cervical heterotopic cardiac transplantation models were established in all groups and cardiac grafts were observed throughout. Regulatory T (Treg) cell expression in peripheral blood was analyzed by flow cytometry. We recorded the cardiac allograft survival time and constructed Kaplan-Meier survival curves. The number of Treg cells in Group B was significantly higher than that in Group C (P<0.05). The survival time of mice from each group differed significantly according to Kaplan-Meier/log-rank analysis (P<0.01). A total of 62.5% of the grafts in Group B showed long-term survival (>100 days); all the mice in Group A died within 9 days, compared with 59 days in Group C. We conclude that syngeneic HSCT and HPCT can prolong cardiac allograft survival in mice. These two methods could be promising ways to induce immune tolerance in future organ transplantation.