Metastable tolerance in nonhuman primates and humans

Transplant research in nonhuman primates to evaluate clinically relevant immune strategies in organ transplantation

Research in transplant immunology using non-human primate (NHP) species to evaluate immunologic strategies to prevent rejection and prolong allograft survival has yielded results that have translated successfully into human organ transplant patient management. Other therapies have not proceeded to human translation due to failure in NHP testing, arguably sparing humans the futility and risk of such testing. The NHP transplant models are ethically necessary for drug development in this field and provide the closest analogue to human transplant patients available. The refinement of this resource with respect to colony MHC typing, reagent and assay development, and availability to the research community has greatly enhanced knowledge about transplant immunology and drug development.

Reciprocal interaction between intestinal microbiota and mucosal lymphocyte in cynomolgus monkeys after alemtuzumab treatment

It has been known that the gut microbiota plays a central role in shaping normal mucosal immunity, however, little information is available whether the variability of mucosal lymphocytes impacts the commensal flora. Here, we applied a cynomolgus monkey model to characterize the structure and composition of the gut microbiota in response to lymphocyte depletion and to determine their potential association. Molecular profiling of 16S rDNA showed that the intestinal microbiota composition was perturbed after the depletion of mucosal lymphocytes and were recovered following the repopulation. Some specific bacteria from the orders Lactobacillales, Enterobacteriales and Clostridiales, and the genus Prevotella and Faecalibacterium, were primarily responsible for the variations of the gut microbiota after lymphocyte depletion. Interestingly, the species richness of the ileal mucosal microbiota was associated the proportions of TCRαβ+ or TCRγδ+ T cells (p<0.01). We demonstrate for the first time the feature of intestinal microbiota composition after lymphocyte depletion and provide novel evidence that the perturbation of gut microbiota is associated with lymphocyte depletion. It may contribute to understand the relationship between gut commensal microbiota and mucosal immune system. Study results provide insight into biological activity of alemtuzumab in intestinal barrier in organ transplantation.

The Tor Vergata weaning of immunosuppression protocols in stable hepatitis C virus liver transplant patients: the 10-year follow-up

We report herein the 10-year outcome of the Tor Vergata weaning off immunosuppression protocol in hepatitis C virus (HCV) liver transplant patients. Thirty-four patients who had received a liver graft for HCV-related cirrhosis were enrolled in a prospective study in which they were progressively weaned off immunosuppression. The primary endpoints were feasibility and safety of the weaning; the second aim was to assess fibrosis progression. At the 10-year follow-up, of the eight original tolerant patients, six remained IS-free. Of the 26 individuals who could not be weaned, 22 were alive. When the baseline biopsies were compared with the 10-year biopsies, the tolerant group showed no differences in staging, whereas the nontolerant group showed a significant increase in staging. The fibrosis progression rates calculated for the tolerant and the nontolerant groups were -0.06 ± 0.12 and 0.1 ± 0.2, respectively (P = 0.04). Furthermore, with the last taken biopsies, nine nontolerant patients were showing frank cirrhosis versus no cirrhosis among the tolerant patients. After a 10-year follow-up of a Tor Vergata weaning protocol, 6/34 patients completed follow-up without reinstitution of immunosuppression and this appeared beneficial regarding a reduction in fibrosis progression.

Vascularized composite allograft rejection is delayed by intrajejunal treatment with donor splenocytes without concomitant immunosuppressants

Background. Mucosal or oral tolerance, an established method for inducing low-risk antigen-specific hyporesponsiveness, has not been investigated in vascularized composite allograft (VCA) research. We studied its effects on recipient immune responses and VCA rejection. Methods. Lewis rats (n = 12; TREATED) received seven daily intrajejunal treatments of 5 × 10⁷ splenocytes from semiallogeneic Lewis-Brown-Norway rats (LBN) or vehicle (n = 11; SHAM). Recipients' immune responses were assessed by mixed lymphocyte reaction (MLR) against donor antigen and controls. Other Lewis (n = 8; TREATED/VCA) received LBN hindlimb VCA and daily intrajejunal treatments of 5 × 10⁷ LBN splenocytes, or LBN VCA without treatment (n = 5; SHAM/VCA), until VCAs rejected. Recipients' immune responses were characterised and VCAs biopsied for histopathology. Immunosuppressants were not used. Results. LBN-specific hyporesponsiveness was induced only in treated Lewis recipients. Treatment significantly reduced MLR alloreactivity, significantly reduced VCA rejection on histopathology, and significantly delayed clinical VCA rejection (P < 0.0005; TREATED/VCA mean 9.6 versus 6.0 days for SHAM/VCA). Treatment significantly increased immunosuppressive IL-10/IL-4/TGF-β production and significantly decreased proinflammatory IFN-γ/TNF-α. Conclusion. Jejunal exposure to antigen conferred donor specific hyporesponsiveness that delayed VCA rejection. This method may offer a low-risk adjunctive treatment option to help protect VCAs from rejection.

Tolerogenic therapies in transplantation

Since the concept of immunologic tolerance was discovered in the 1940s, the pursuit of tolerance induction in human transplantation has led to a rapid development of pharmacologic and biologic agents. Short-term graft survival remains an all-time high, but successful withdrawal of immunosuppression to achieve operational tolerance rarely occurs outside of liver transplantation. Collaborative efforts through the NIH sponsored Immune Tolerance Network and the European Commission sponsored Reprogramming the Immune System for Establishment of Tolerance consortia have afforded researchers opportunity to evaluate the safety and efficacy of tolerogenic strategies, investigate mechanisms of tolerance, and identify molecular and genetic markers that distinguish the tolerance phenotype. In this article, we review traditional and novel approaches to inducing tolerance for organ transplantation, with an emphasis on their translation into clinical trials.

Lymphocyte depletion and repopulation in peripheral blood and small intestine of cynomolgus monkeys after alemtuzumab treatment

BACKGROUND

Alemtuzumab has been used as an induction agent in organ transplantation over 10 years, but the effect of alemtuzumab on lymphocytes in small intestine was not clear. We investigate lymphocyte depletion and repopulation phenomena both in peripheral blood and small intestine of cynomolgus monkeys, to assess the model using in preclinical transplantation.

MATERIALS AND METHODS

Monkeys without CD52 antigen on erythrocytes were selected. Lymphocyte depletion and repopulation was documented by flow cytometry. Sections of ileum were obtained for isolation of intestinal intraepithelial lymphocytes (IEL) and lamina propria lymphocytes (LPL), and also for immunofluorescence examination.

RESULTS

Powerful depletion of lymphocytes (>80%) from blood followed by gradual repopulation was observed. CD20(+) B cells, CD8(+) T cells, CD4(+) T cells returned to pretreatment levels by d 21, 35, 56. IEL, LPL reduced by 70%, 72% on d 9, recovered to 59%, 57% of pretreatment levels by d 35, and were completed by d 56. Depletion and repopulation of IEL and LPL were confirmed by immunofluorescence.

CONCLUSIONS

Depletion of lymphocytes in peripheral blood was less powerful and repopulation occurred faster than in patients. The lymphocyte depletion and repopulation occurred in small intestine. This model can be used in preclinical transplantation.

The mosaic of KIR haplotypes in rhesus macaques

To further refine and improve biomedical research in rhesus macaques, it is necessary to increase our knowledge concerning both the degree of allelic variation (polymorphism) and diversity (gene copy number variation) in the killer cell immunoglobulin-like receptor (KIR) gene cluster. Pedigreed animals in particular should be studied, as segregation data will provide clues to the linkage of particular KIR genes/alleles segregating on a haplotype and to its gene content as well. A dual strategy allowed us to screen the presence and absence of genes and the corresponding transcripts, as well as to track differences in transcription levels. On the basis of this approach, 14 diverse KIR haplotypes have been described. These haplotypes consist of multiple inhibitory and activating Mamu-KIR genes, and any gene present on one haplotype may be absent on another. This suggests that the cost of accelerated evolution by recombination may be the loss of certain framework genes on a haplotype.

Biochemical aspects of inflammation

This review considers biochemical aspects of inflammation. The international literature until December 2006 has been analyzed, with the principal attention paid to the most dynamic problems: enzymology of inflammation, its regulation by hormones and signal transducers, and negative feedbacks, which underlie intensive current studies on pathogenesis, diagnostics, and therapy of inflammation. Such achievements as discoveries of defensins, toll-like receptors, interconnections of inflammation and iron metabolism, the roles of oxidative stress and antioxidant defense, lipoxins, inflammatory components of "non-inflammatory" diseases, and action mechanisms of effective drugs are discussed.

Identification of a peripheral blood transcriptional biomarker panel associated with operational renal allograft tolerance

Long-term allograft survival generally requires lifelong immunosuppression (IS). Rarely, recipients display spontaneous "operational tolerance" with stable graft function in the absence of IS. The lack of biological markers of this phenomenon precludes identification of potentially tolerant patients in which IS could be tapered and hinders the development of new tolerance-inducing strategies. The objective of this study was to identify minimally invasive blood biomarkers for operational tolerance and use these biomarkers to determine the frequency of this state in immunosuppressed patients with stable graft function. Blood gene expression profiles from 75 renal-transplant patient cohorts (operational tolerance/acute and chronic rejection/stable graft function on IS) and 16 healthy individuals were analyzed. A subset of samples was used for microarray analysis where three-class comparison of the different groups of patients identified a "tolerant footprint" of 49 genes. These biomarkers were applied for prediction of operational tolerance by microarray and real-time PCR in independent test groups. Thirty-three of 49 genes correctly segregated tolerance and chronic rejection phenotypes with 99% and 86% specificity. The signature is shared with 1 of 12 and 5 of 10 stable patients on triple IS and low-dose steroid monotherapy, respectively. The gene signature suggests a pattern of reduced costimulatory signaling, immune quiescence, apoptosis, and memory T cell responses. This study identifies in the blood of kidney recipients a set of genes associated with operational tolerance that may have utility as a minimally invasive monitoring tool for guiding IS titration. Further validation of this tool for safe IS minimization in prospective clinical trials is warranted.

The immunology of composite tissue transplantation

Composite tissue allotransplantation holds great potential for reconstructive surgery. That these procedures can be successful has been clearly demonstrated by the success of hand, face, and larynx transplants around the world. Although the immunology of composite tissue allotransplantation mirrors that of any allogeneic organ transplant, there are several unique aspects to these grafts. This article reviews the immunology of transplantation, histocompatibility testing for composite tissue allotransplantation, graft rejection, immunosuppression, and specific immunologic considerations of composite tissue allotransplantation.

Current concepts and perspectives of immunosuppression in organ transplantation

BACKGROUND

While early surgical success made organ transplantation possible in the 1950s and 1960s, the breakthrough in clinical organ transplantation was achieved through the discovery and invention of modern immunosuppressive agents in the early/mid-1980s. Especially during the 1990 s, a large array of immunosuppressants has expanded the armamentarium used to prevent and treat allograft rejection, resulting in an excellent short-term and an acceptable long-term outcome. However, these drugs have potent but still non-specific immunosuppressive properties and frequently show severe acute and chronic side effects, sometimes questioning the overall success.

CONCEPTS/TRENDS

As the "Holy-Grail" of the transplant community, the induction of "true donor-specific tolerance" has not been achieved yet; current immunosuppressive strategies, in particular in Europe, include "individually tailored immunosuppressive" protocols, mostly based on specific immunologic and non-immunologic risk factors. These protocols allow for optimal immunosuppressive protocols for each patient group according to their needs by choosing the most suitable, well-tolerated combination of agents and the most effective doses to avoid acute rejection episodes (incidence and severity) and minimise drug-related toxicity to reduce long-term drug-related morbidity and mortality. Nevertheless, transplant recipient are still being forced to take a life-long course of chemical immunosuppressive agents to keep their graft, knowing about the possible life-threatening side effects.

SUMMARY

We review current trends of immunosuppressive protocols in liver and kidney transplantation, focusing on calcineurin-inhibitor-sparing protocols, mammalian-target-of-rapamycin (mTOR) inhibitor based-protocols and corticosteroid-avoidance protocols, being aware of the fact, that most of these strategies could be applicable for other transplanted organs, too. Finally, we describe future trends and new developments that are rising on the horizon.

Does our current understanding of the molecular basis of immune tolerance predict new therapies for autoimmune disease?

The creation of specific immune tolerance has often been referred to as the ultimate goal of immunotherapy, because it would allow autoimmune disease to be reversed without the need for nonspecific and potentially harmful immunosuppressive therapy. Studies performed during the past decade have been immensely fruitful in terms of advances in our understanding of the cellular and molecular mechanisms of immune tolerance, and have paved the way for successful exploitation of these mechanisms for therapeutic purposes. Important developments include an increased understanding of central and peripheral tolerance, and treatment strategies that mimic the mechanisms behind deletion of self-reactive cells, the identification of crucial gene products that are involved in the induction of anergy, and the characterization of regulatory T cells and protocols for their induction and expansion for therapeutic applications. These landmarks of immune-tolerance research are summarized and their potential use in the immunotherapy of autoimmune disease discussed.

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.

Is clinical tolerance realistic in the next decade?

Tolerance to allografts would mean a better quality of life and prognosis for transplant patients. Despite the first descriptions of tolerance to alloantigens over 50 years ago, deliberately induced tolerance in the clinic on a wide scale remains a goal that is not quite in reach. However, much progress has been made in understanding tolerance in rodent models and in the few reports of induced or spontaneously occurring tolerance in humans. Here, we review this progress made in the quest to achieve clinical tolerance.

Transplant tolerance in non-human primates: progress, current challenges and unmet needs

Given the significant morbidity associated with current post-transplant immunosuppressive regimens, induction of immune tolerance continues to be an important goal of clinical organ transplantation. While many strategies for inducing tolerance have been successfully applied in murine models, significant barriers are faced when translating these approaches to the clinic. This has necessitated pre-clinical studies in the more closely related model system, the non-human primates (NHP). In this review, we will discuss the four most prominent strategies for inducing transplantation tolerance and highlight their relative success and shortcomings in NHP. These strategies are: (1) T-cell costimulation blockade (2) mixed chimerism induction (3) T-cell depletion and (4) tolerance induction through regulatory T-cells. After discussing the progress that has been made with each of these strategies, we will identify this field's most pressing unmet needs and discuss how we may best overcome the resulting barriers to tolerance induction.

Induction of transplantation tolerance in non-human primate preclinical models

Short-term outcomes following organ transplantation have improved considerably since the availability of cyclosporine ushered in the modern era of immunosuppression. In spite of this, many of the current limitations to progress in the field are directly related to the existing practice of relatively non-specific immunosuppression. These include increased risks of opportunistic infection and cancer, and toxicity associated with long-term immunosuppressive drug exposure. In addition, long-term graft loss continues to result in part from a failure to adequately control the anti-donor immune response. The development of a safe and reliable means of inducing tolerance would ameliorate these issues and improve the lives of transplant recipients, yet given the improving clinical standard of care, the translation of new therapies has become appropriately more cautious and dependent on increasingly predictive preclinical models. While convenient and easy to use, rodent tolerance models have not to date been reliably capable of predicting a therapy's potential efficacy in humans. Non-human primates possess an immune system that more closely approximates that found in humans, and have served as a more rigorous preclinical testing ground for novel therapies. Prior to clinical adaptation therefore, tolerance regimens should be vetted in non-human primates to ensure that there is sufficient potential for efficacy to justify the risk of its application.

Development of tolerogenic strategies in the clinic

The study of tolerance in the clinic can be divided into three areas: (i) focused evaluation of existing tolerant transplant recipients as to their mechanism of tolerance; (ii) prospective tolerance trials, such as combined bone marrow and kidney transplantation as well as T cell depletion followed by subsequent weaning of immunosuppression; and (iii) immunologic assays to assess the likelihood of rejection or tolerance. Frankly, a very small number of patients have been transplanted with the intention of removing all immunosuppressive therapy, but several clinical trials with this aim are currently in progress, largely sponsored by the Immune Tolerance Network, a joint venture between the National Institutes of Health and the Juvenile Diabetes Research Foundation. Similarly, a reliable assay to assess tolerance has not yet been developed but a variety of approaches towards assessing rejection, and in some cases tolerance, are being developed. It would be accurate to state that many of the experimental and preclinical approaches to the induction of tolerance have resulted in better immunosuppression for human transplantation, but reliable tolerance strategies in humans have not yet been achieved. Combined bone marrow and kidney transplantation may be considered as one exception to this, but such a strategy is not generally applicable to the vast majority of solid organ transplant recipients. This review will summarize efforts to date, particularly focusing on kidney transplantation.

Beyond Operational Tolerance: Effect of Ischemic Injury on Development of Chronic Damage in Renal Grafts

BACKGROUND

The induction of operational tolerance is the holy grail of clinical transplantation. However, in animal models with operational tolerance, long- term grafts still develop chronic damage. The elucidation of the impact of allogenic versus nonallogeneic factors in such a model is important. This study examined the effect of a clinically relevant combination of warm ischemia and cold preservation in the absence of allogeneic response (isografts) and in the context of operational tolerance.

METHODS

Dark Agouti (DA) rat kidneys were transplanted into DA recipients (isografts) or Albino Surgery recipients (allografts) tolerized by two transfusions of DA blood, under cover of cyclosporin A. Grafts were subjected to minimal cold preservation or to 30 mins warm ischemia followed by 24 hrs cold preservation.

RESULTS

After an initial peak of renal dysfunction, serum creatinine concentration returned to normal in isografts and nonischemic allografts, but remained significantly elevated in ischemic allografts (P<0.0002) throughout 6 months follow-up. Both allograft groups developed proteinuria. At 6 months, ischemic isografts and nonischemic allografts demonstrated very mild tubular atrophy and interstitial fibrosis. Tubulointerstitial injury was significantly more severe in ischemic allografts (P<0.01 vs. nonischemic allografts) and was associated with increased infiltrating monocyte/macrophages and NK cells (P<0.05). Moderate glomerulosclerosis was a feature of both allograft groups (P<0.05).

CONCLUSIONS

The modified allogeneic response in operationally tolerant recipients acts in synergy with ischemia/reperfusion injury in the development of chronic damage. Strategies to limit or modify the initial ischemia/reperfusion injury may ameliorate chronic tubulointerstitial damage. Progressive glomerular damage and proteinuria in allografts may require other pharmacological intervention.

Microsatellite typing of the rhesus macaque MHC region

To improve the results gained by serotyping rhesus macaque major histocompatibility complex (MHC) antigens, molecular typing techniques have been established for class I and II genes. Like the rhesus macaque Mamu-DRB loci, the Mamu-A and -B are not only polymorphic but also polygenic. As a consequence, sequence-based typing of these genes is time-consuming. Therefore, eight MHC-linked microsatellites, or short tandem repeats (STRs), were evaluated for their use in haplotype characterization. Polymorphism analyses in rhesus macaques of Indian and Chinese origin showed high STR allelic diversity in both populations but different patterns of allele frequency distribution between the groups. Pedigree data for class I and II loci and the eight STRs allowed us to determine extended MHC haplotypes in rhesus macaque breeding groups. STR sequencing and comparisons with the complete rhesus macaque MHC genomic map allowed the exact positioning of the markers. Strong linkage disequilibria were observed between Mamu-DR and -DQ loci and adjacent STRs. Microsatellite typing provides an efficient, robust, and quick method of genotyping and deriving MHC haplotypes for rhesus macaques regardless of their geographical origin. The incorporation of MHC-linked STRs into routine genetic tests will contribute to efforts to improve the genetic characterization of the rhesus macaque for biomedical research and can provide comparative information about the evolution of the MHC region.

What's new--what's hot in basic science: American Transplant Congress 2004

The field of transplantation biology has, in the past year, given rise to several improved models explaining the in vivo phenomena of allograft rejection and acceptance. Although T-cells remain central participants in allorecognition, innate immune cells are increasingly recognized as critical. There is also growing acceptance that T-cell responses can vary widely not only based on their repertoire, but also on their immune experience in general, and their participation in homeostatic proliferation. Additional signaling pathways and molecules, such as the Janus kinase pathway and vascular endothelial growth factor have been added to those recognized as important in pharmacologic immunosuppression, and the concepts of regulation, once polarized between CD8+ and CD4+ camps, have begun to converge upon a recognition that there are many phenotypes of regulatory cells. In addition to improved basic science, several translational fields have accelerated in the past 12 months. Promising and clinically applicable islet transplant regimens have been developed and look appropriate for near-term clinical trials. Significant progress in discordant xenotransplantation is also apparent. This manuscript will review the past year in transplantation science as reported at the 2004 American Transplant Congress.

The concept of “partial” clinical tolerance

The status of "partial" tolerance to organ allografts versus the status of complete tolerance is the main topic of this paper. Progress made in immunosuppression, particularly by use of various lymphocyte depleting agents for "induction therapy", seems to favor the subsequent development of T cells with suppressor/regulatory properties. The effective deletion of alloreactive T helper and cytotoxic cells in conjunction with the expansion of antigen-specific suppressor (CD8 + CD28 - FOXP3+) and regulatory (CD4 + CD25+ FOXP3+) T cells creates a milieu in which the graft is well tolerated under an "umbrella" of low dosage immunosuppression. The most effective induction treatment is Campath-1H, although ATGAM at high dosage is also widely used. Total lymphoid irradiation (TLI) is another very effective pretreatment strategy in spite of the risks which are associated with it. The induction of "partial" tolerance is a step in the right direction for exploring strategies that may lead to the induction of complete tolerance. It is safe for the patients and can prolong significantly the function of the graft, preventing the onset of chronic rejection.