Acquired immune tolerance to cadaveric renal allografts. A study of three patients treated with total lymphoid irradiation

Tolerance and chimerism after renal and hematopoietic-cell transplantation

We describe a recipient of combined kidney and hematopoietic-cell transplants from an HLA-matched donor. A post-transplantation conditioning regimen of total lymphoid irradiation and antithymocyte globulin allowed engraftment of the donor's hematopoietic cells. The patient had persistent mixed chimerism, and the function of the kidney allograft has been normal for more than 28 months since discontinuation of all immunosuppressive drugs. Adverse events requiring hospitalization were limited to a 2-day episode of fever with neutropenia. The patient has had neither rejection episodes nor clinical manifestations of graft-versus-host disease.

Protective conditioning against GVHD and graft rejection after combined organ and hematopoietic cell transplantation

We have performed combined organ and hematopoietic cell transplantation using a similar conditioning regimen in mice and humans. In the mouse model of MHC-mismatched combined heart and marrow transplantation, we compared conditioning of BALB/c hosts with total lymphoid irradiation (TLI: 10 doses of 240 cGy each) targeted to the spleen, lymph nodes and thymus to conditioning with a single dose of sublethal total body irradiation (TBI; 450 cGy). Conditioning also included three injections of anti-thymocyte serum (ATS), in both groups. C57BL/6 heart grafts, marrow cells and blood mononuclear cells were transplanted 24 h after the completion of irradiation. Blood mononuclear cells were added to the marrow cells to engender severe graft versus host disease (GVHD) that is present after combined organ and hematopoietic cell transplantation in humans given non-myeloablative conditioning. Both TLI and TBI conditioned groups accepted the organ grafts and became stable chimeras. However, the TBI group all died of GVHD during the 100-day observation period. The TLI group survived during the same period without clinical signs of GVHD. These hosts were tolerized to the donor organ grafts, since third party grafts were rejected rapidly when transplanted after 100 days. When NK T-cell-deficient CD1d(-/-) BALB/c hosts were used instead of wild-type hosts in the TLI/ATS conditioned group, then all hosts survived but all rejected the organ grafts and almost all failed to develop stable chimerism. None developed GVHD. Since host NK T cells were required for graft acceptance and NK T cells are activated after recognition of CD1d on antigen presenting cells, we compared heart and marrow graft survival from wild-type versus CD1d(-/-) donors after transplantation to TLI and ATS conditioned wild-type hosts. Whereas marrow and heart grafts from wild-type donors were accepted, almost all grafts from CD1d donors were rejected. Grafts from control Jalpha18(-/-) donors that were NK T cell deficient but expressed CD1d were all accepted. The results indicate that host NK T cells facilitate graft acceptance by recognizing CD1d on donor cells. We applied the TLI conditioning regimen using 10 doses of 80 cGy each and 5 doses of rabbit ATG to human recipients of HLA-matched G-CSF "mobilized" blood mononuclear cell transplants for the treatment of leukemia and lymphoma [R. Lowsky, T. Takahashi, Y.P. Liu, et al., Protective conditioning for acute graft-versus-host disease. N. Engl. J. Med. 353 (2005) 1321-1331.]. Currently more than 100 transplants have been performed, and the incidence of acute GVHD has been about 4% when both MRD and MUD transplants are combined. Almost all recipients became complete chimeras after receiving grafts that contained 2-3x10(8) CD3(+) T cells/kg. In further studies, we applied the same TLI and ATG conditioning regimen to combined kidney and G-CSF "mobilized" blood stem cell transplantation from HLA-matched sibling donors. The hematopoietic grafts in the latter protocol were selected CD34(+) cells with 1x10(6) CD3(+) T cells/kg added back to the hematopoietic cells. Preliminary results indicate that stable mixed chimerism can be achieved using this protocol allowing for complete immunosuppressive drug withdrawal without GVHD or subsequent rejection episodes. Thus, conditioning with TLI based regimens can simultaneously protect against organ graft rejection and GVHD. Levels of chimerism are dependent upon the content of donor T cells in the hematopoietic graft.

Immune tolerance: mechanisms and application in clinical transplantation

The achievement of immune tolerance, a state of specific unresponsiveness to the donor graft, has the potential to overcome the current major limitations to progress in organ transplantation, namely late graft loss, organ shortage and the toxicities of chronic nonspecific immumnosuppressive therapy. Advances in our understanding of immunological processes, mechanisms of rejection and tolerance have led to encouraging developments in animal models, which are just beginning to be translated into clinical pilot studies. These advances are reviewed here and the appropriate timing for clinical trials is discussed.

Frontiers in nephrology: immune tolerance to allografts in humans

Vascularized allografts are rejected unless some indefinite modification to the recipient's immune system is made. This modification is typically achieved through the long-term administration of immunosuppressive drugs. Patients thus trade their end-stage organ failure for dependence on daily drug therapy and the accompanying chronic condition of immunodeficiency. However, it is clear from studies in experimental animals that rejection can be prevented through the use of several therapeutic approaches, including donor hematopoietic cell infusion, chimerism, T cell depletion, and/or co-stimulation blockade. Successfully treated animals avoid rejection beyond the period of therapy without a phenotype of chronic immunosuppression and are thus considered to be tolerant of their grafts. Although intriguing, this success in animals has yet to be reproducibly translated to the clinic, and human transplant recipients remain tethered to immunosuppressive drugs with rare exceptions. This article provides an overview of the existing, largely anecdotal, clinical experience with organ allograft tolerance. It reviews the various approaches that are being applied in pilot human trials and suggests avenues for future clinical investigation.

Clinical transplantation tolerance: many rivers to cross

Modern immunosuppressive regimens for organ transplantation have resulted in excellent short-term results but less dramatic improvements in long-term outcomes. Moreover, they are associated with significant deleterious effects. One solution that should avoid the adverse drug effects and result in improved graft and patient longevity as well as positively impacting on the organ shortage is the establishment of transplantation tolerance. Ever since the original description of transplantation tolerance in rodent allografts, there have been significant efforts made to translate tolerance-promoting strategies to the clinical arena. However, >50 years later, we are still faced with significant barriers that are preventing such a goal from being widely attained. Nonetheless, pilot clinical tolerance protocols are underway in selected transplant recipients. In this review, we discuss the scientific and nonscientific issues that must be overcome for successful transplantation tolerance to become a clinical reality.

New reagents on the horizon for immune tolerance

Recent advances in immunology and a growing arsenal of new drugs are bringing the focus of tolerance research from animal models into the clinical setting. The conceptual framework for therapeutic tolerance induction has shifted from a "sledgehammer" approach that relies solely on cellular depletion and cytokine targeting, to a strategy directed toward restoring a functional balance across the immune system, namely the different populations of naive cells, effector and memory cells, and regulatory cells. Unlocking the key to tolerance induction in the future will likely depend on our ability to harness the functions of T regulatory cells. Also, dendritic cells are strategically positioned at the interface between innate and adaptive immunity and may be subject to deliberate medical intervention in a way that can control a chronic inflammatory response. Many reagents with tolerance-inducing potential are currently undergoing clinical testing in transplantation, autoimmune diseases, and allergic diseases, and even more that are on the horizon promise to offer enormous benefits to human health.

From current immunosuppressive strategies to clinical tolerance of allografts

In order to prevent allograft rejection, most current immunosuppressive drugs nonspecifically target T-cell activation, clonal expansion or differentiation into effector cells. Experimental models have shown that it is possible to exploit the central and peripheral mechanisms that normally maintain immune homeostasis and tolerance to self-antigens, in order to induce tolerance to alloantigens. Central tolerance results from intrathymic deletion of T cells with high avidity for thymically expressed antigens. Peripheral tolerance to nonself-molecules can be achieved by various mechanisms including deletion of activated/effector T cells, anergy induction and active regulation of effector T cells. In this article, we briefly discuss the pathways of allorecognition and their relevance to current immunosuppressive strategies and to the induction of transplantation tolerance (through haematopoietic mixed chimerism, depleting protocols, costimulatory blockade and regulatory T cells). We then review the prospect of clinical applicability of these protocols in solid organ transplantation.

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.

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.

Is tolerance induction the answer to adolescent non-adherence?

By definition, tolerance will eliminate the problem of adolescent medication non-adherence. Although adolescents' propensity toward non-adherence makes them at first glance to be particularly attractive candidates for tolerance trials, there are also immunologic, psychosocial and ethical barriers that temper enthusiasm for their inclusion at present. Limits in emotional and cognitive maturity are combined during the teenage years with adult-like immunologic maturity to lessen the potential for successful implementation of tolerance and near tolerance strategies. Alternatively, an interval step to tolerance in adolescents is to eliminate the medications most likely contributing to non-adherence through harsh side effects such as steroids and calcineurin inhibitors. This manuscript will review the general topic of transplantation tolerance with specific attention given to the application of pro-tolerant therapies in adolescent recipients.

Transplantation tolerance in pediatric recipients: lessons and challenges

Clinical transplantation tolerance has remained an elusive goal in the 50 yr since it was first described in experimental animals. Greater understanding of the molecular mechanisms responsible for allorecognition have allowed for the development of promising immunosuppressive strategies that may bring us closer to reproducible induction of tolerance; consideration of past successes and failures from both clinical and basic science is required to define future challenges facing this field. This article reviews mechanisms of self and transplantation tolerance, translation of basic science research to clinical protocols in animals and human beings, the changing role of immunosuppression, complications following tolerance induction and controversies surrounding the choice of patients for tolerance trials with a focus on issues relevant to pediatric patients. The role of the Immune Tolerance Network is discussed along with realistic goals for tolerance induction in human beings over the next decade.

Prolonged survival of mouse skin allografts after transplantation of fetal liver cells transduced with hIL-10 gene

INTRODUCTION

Interleukin-10 (IL-10) is a cytokine with a moleculary weight of 18 kDa, that was first identified as being produced by Th2 cells. It appears to have anti-inflammatory action by diminishing the production of pro-inflammatory cytokines produced by Th1 cells. IL-10 also regulates the differentiation and proliferation of several immune cells such as T cells, B cells, natural killer cells, antigen-presenting cells, mast cells and granulocytes. Recent data suggest, however, that IL-10 also has immunostimulatory properties with important consequences on the prognosis of disease. In this study, we demonstrate the importance of injection of hematopoietic fetal liver cells transduced with the human IL-10 (hIL-10) gene into an allogenic recipient subsequently transplanted with allogenic skin grafts. The immaturity of stem cells and precursor cells from fetal liver and their transient survival in the host, due to the production of hIL-10, may afford 'prope' tolerance. It also explains the lack of graft-vs.-host reaction (GvHR) and the delay in rejection of the specific donor skin grafts after virtual disappearance of donor hematopoietic cells.

OBJECTIVES

Transduction of CBA hematopoietic fetal cells with the human IL-10 gene was used with the aim of inducing tolerance to donor antigen in recipient BALB/c mice. The observed effects were prolonged IL-10 production, donor cell chimerism in the host and delayed rejection of skin grafts from the specific donor strain.

MATERIALS AND METHODS

To prevent or delay rejection of highly incompatible skin allografts, we used IL-10 gene transfer to establish chimerism with donor hematopoietic cells. Fetal liver cells from CBA mice were transduced with the human IL-10 gene and injected into BALB/c mice.

RESULTS

Human IL-10, which is active in mice but does not cross-react with murine IL-10 in ELISA, was produced in vivo for 3 weeks. Donor cells were identified in the recipients during the same time period, on the basis of presence of the H-2 k gene and human IL-10 intracellular protein. Skin allografts from CBA or C57BL/6 mice survived for a mean of 9.5 days in recipient mice injected with non-transduced cells. In contrast, survival of CBA allograft was extended to 18.9+/-1.8 days in recipients injected with hIL-10-transduced fetal liver cells from CBA mice. Human IL-10 alone, without donor hematopoietic cell engraftment, did not prolong graft survival (9.6+/-1.2 days).

CONCLUSIONS

IL-10 transduction of donor hematopoietic stem cells resulted in production of IL-10, cell engraftment and chimerism. Although full tolerance was not obtained at this level of donor cell development in the host, a specific and highly significant (P<0.001) prolongation of the survival of donor skin allografts was observed.

Correlation between human leukocyte antigen antibody production and serum creatinine in patients receiving sirolimus monotherapy after Campath-1H induction

BACKGROUND

In this study, we determined whether Campath-1H induction followed by sirolimus monotherapy inhibited alloantibody production in renal transplantation. Second, we evaluated the correlation between human leukocyte antigen (HLA) antibody production and serum creatinine levels.

METHODS

Sera were taken 1 to 24 months after transplantation from 24 patients treated with Campath-1H and sirolimus and tested for serum creatinine and HLA-specific antibody by using flow cytometry and enzyme-linked immunosorbent assay.

RESULTS

Ten (42%) of the 24 patients treated with Campath-1H and sirolimus produced HLA antibodies. Six of these 10 developed both donor-specific antibodies (DSAs) and non-donor-specific antibodies (NDSAs), whereas only NDSAs were detected in the other four patients. In patients with biopsy-diagnosed humoral rejection (C4d+), serum levels of both DSA and NDSA significantly correlated with patient serum creatinine levels. Rejection treatment successfully reduced both DSAs and NDSAs and reversed humoral rejection.

CONCLUSIONS

The numeric relationship between serum creatinine and DSA levels suggests a causal relationship between alloantibody and transplant rejection.

Tolerance induction in clinical transplantation

Introduction of modern immunosuppressive agents has led to great success of allotransplantation in humans, and survival rates for all solid organs have been dramatically improved. However, a constant proportion of organs is lost every year due to chronic allograft rejection and immunosuppressive drug toxicity. This has led to a situation where, despite the of donor organ shortage, about one third of the patients on the kidney transplant waiting list are listed for a retransplant. The induction of donor-specific tolerance has the potential of at least partially resolving this problem, since it might prevent chronic rejection and drug toxicity at the same time. For a variety of protocols, successful tolerance induction has been demonstrated in rodent models. However, translation of such protocols to large animal models and on clinical trials has turned out to be very difficult. This review briefly describes mechanisms and barriers to transplantation tolerance, and then focuses on pre-clinical and clinical studies in non-human primates and humans. We have divided the strategies into two groups, based on the principle mechanisms of tolerance induction: the first group are protocols not using hematopoietic stem cell transplantation (HCT) as part of there regimen. They rely mainly on intensive T cell depletion (either by total body irradiation, total lymphoid irradiation or treatment with T cell-depleting agents such as anti-thymocyte globulin, anti-CD52 antibody or CD3 immunotoxin), which have been combined with costimulatory blockade, signaling blockade or donor antigen infusion. The second group are HCT-based protocols combining HCT with T cell-depleting agents and cytoreductive treatment. So far, only two protocols (one with total lymphoid irradiation and anti-thymocyte globulin, but no HCT; one with HCT, cyclophosphamide, anti-thymocyte globulin and thymic irradiation) have been translated into successful human studies. We summarize and discuss the results of these trials and suggest goals for further studies for the development tolerance protocols applicable for a broad population of allograft recipients.

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.

Clinical trials: where are we now?

Clinical trials in transplantation have focused on improving outcomes and minimizing side effects associated with renal transplantation. Although immunologic tolerance, which means complete freedom from immunosuppressive drugs and maintenance of excellent long-term graft function, has seldom been achieved, in rare cases, this has been accomplished. Most current clinical trials focus on minimization of steroid use and calcineurin inhibitor use as a step toward tolerance, sometimes termed prope tolerance. Alternatively, new immunosuppressive agents are studied to assess their efficacy in preventing graft rejection with the anticipation of lesser toxicity. This review is organized in a case presentation style with actual cases from the University of Wisconsin kidney transplant experience presented as illustrations of actual scenarios in clinical trials. Lessons learned from these particular patients are then summarized with reference to the literature associated with the case. Using this format, some of the important lessons learned from clinical trials are outlined and directions for future study are noted. Clinical trials have permitted a dramatic improvement in graft survival and lowering of infectious and malignant side effects over the past 30-40 years. Nevertheless, we remain far from achieving true tolerance in patients for a variety of reasons.

Clinical transplantation tolerance: The promise and challenges

Organ transplantation is now well established as a preferred option for the treatment of end-stage organ failure. However, there is a severe shortage of donor organs and continued loss of a significant number of organ grafts due to chronic allograft dysfunction. Induction of tolerance of a transplant recipient toward their foreign organ graft, therefore, remains the "Holy Grail" of transplantation immunobiologists. Recently, clinical trials to explore pilot tolerance protocols in humans have been initiated. Defining the ideal strategy(ies) and the role of immunosuppressive drugs, developing tolerance assay(s), and enhancing cooperation between transplant professionals, industry, and the government are some of the challenges to achieving clinical transplantation tolerance. This article reviews the promise and the challenges of achieving clinical transplantation tolerance in human organ transplant recipients.

Approaches to transplantation tolerance in humans

Although transplantation tolerance to organ allografts has been achieved using a wide variety of immunologic interventions in laboratory animals, few tolerance induction protocols with complete immunosuppressive drug withdrawal have been tested in humans. Preclinical and clinical studies of the use of total lymphoid irradiation for the induction of chimeric and nonchimeric tolerance are summarized here.

Comprehensive examination of gene expression associated with long-term stable graft acceptance by renal transplant recipients

Expression levels of mRNA in peripheral blood mononuclear cells from five renal transplant recipients and five non-transplanted controls were analyzed with GeneChips (GeneChip Instrument system, Affymetrix, Santa Clara, CA, USA). All recipients had retained a well-functioning kidney graft for more than 15 yr on low-dose maintenance immunosuppression. Among a total of 12630 transcripts examined, significant differential expression was observed for 599 genes, whereby 470 genes were up-regulated and 129 down-regulated in the transplant recipients compared with controls. Of these, 192 up-regulated and 46 down-regulated genes showing a change greater than twofold were divided into eight functional categories as follows (numbers of genes, up/down): immune system (12/14), cell proliferation (17/3), oncology (15/3), transporter/receptor/binding protein (16/5), transcription factors (8/2), enzymes (17/4), expressed sequence tags (91/9), and others (16/6). Predictably, expression of immune-associated genes was decreased in the recipients. Significant reduction of expression levels of CD3, ICAM-1, and B7.2, which are critical molecules for interactions between antigen presenting cells and T cells, were observed. In T cell signal transduction, the Ras pathway was likely to be suppressed by activation of hVH-5. The present data help to elucidate the immunological status in long-term kidney graft recipients and may provide insights for future regimens to establish donor-specific hyporesponsiveness.

Detection of regulatory cells as an assay for allograft tolerance in miniature swine

BACKGROUND

There is currently a great need for an in vitro assay to assess the presence of tolerance following allotransplantation to determine whether immunosuppressive medications can be discontinued. Our laboratory has recently developed an assay involving coculture inhibition of cell-mediated lympholysis that correlates with tolerance to allografts in swine leukocyte antigen (SLA) Class I-mismatched miniature swine. The potential for clinical application of this assay may depend on 2 important factors: (1) whether the assay can be used in the presence of immunosuppression; and (2) whether frozen-stored naive responder cells can be utilized.

METHODS

Long-term tolerant MGH miniature swine that had accepted SLA Class I-mismatched kidney transplants after a 12-day course of cyclosporine or tacrolimus were studied. Two long-term tolerant and 2 naive control animals were treated with a clinically relevant dose of cyclosporine for 2 weeks (trough level 100 to 400 ng/ml) to simulate the ongoing "chronic" immunosuppression used in human recipients of allografts. Cells from tolerant or naive, recipient-matched animals were stimulated for 6 days with donor or third-party SLA. These primed cells were then cocultured with naive unstimulated recipient major histocompatibility complex (MHC)-matched responders and irradiated stimulators. Responder cells were tested both fresh and frozen.

RESULTS

Suppression of cytotoxic responses of naive responder cells was observed in all coculture assays using cells from tolerant animals primed against donor antigen in vitro, but not in assays using similarly primed cells from naive animals. Responder cells from tolerant animals receiving immunosuppression had a suppressive activity similar to that from cells of the same animals not receiving immunosuppression. Similar suppression was also observed in coculture assays using either fresh or frozen naive responder cells.

CONCLUSIONS

This coculture assay appears to correlate with the presence of tolerance under conditions applicable to the clinical setting. The assay appears to identify peripheral regulatory mechanisms of tolerance in allogeneic transplant recipients, and therefore may provide an approach for determining an appropriate timepoint at which to test withdrawal of immunosuppressive medications.

Campath-1H induction plus rapamycin monotherapy for renal transplantation: results of a pilot study

Campath-1H, an anti-CD52 monoclonal antibody, was used as induction therapy (40 mg i.v. total dose) in 29 primary human renal transplants, and the patients were maintained on rapamycin monotherapy (levels 8-15 ng/mL) post-transplant. Campath-1H profoundly depletes lymphocytes long-term and more transiently depletes B cells and monocytes. All patients are alive and well at 3-29 months of follow up. One graft was lost because of rejection. There have been no systemic infections and no malignancies. Eight of 29 patients have experienced rejection, which was successfully treated in seven of eight patients. Five of these patients had pathological evidence of a humoral component of their rejection. Seven of the 29 patients were converted to standard triple therapy on account of rejection. Rapamycin was generally well tolerated in that there were no significant wound-healing problems; two lymphoceles required surgical drainage; and most patients were treated with a lipid-lowering agent. Flow crossmatch testing post-transplant revealed evidence of alloantibody in two patients tested with previous combined cellular and humoral rejection. Biopsies have shown no chronic allograft nephropathy to date. In view of the relatively high incidence of early humoral rejection, we plan to modify the immunosuppressive regimen in subsequent pilot studies. This clinical trial provides insight into the use of Campath-1H induction in combination with rapamycin maintenance monotherapy.

A role for indirect allorecognition in lung transplant recipients with obliterative bronchiolitis

Obliterative bronchiolitis (OB) occurs in 50% of patients 2 years after lung transplantation. Although a correlation between OB and indirect recognition of donor peptides has been reported, the relative roles of direct vs. indirect recognition have not been investigated. Limiting dilution analysis was used to determine the frequencies of recipient T-helper cells recognizing donor and third-party alloantigens in 19 patients (8 OB positive, 11 OB negative). The assays were designed to distinguish between indirect and direct presentation. In three patients the direct and indirect assay were performed on the same blood sample. Six out of seven patients with OB were hyperresponsive in the indirect pathway to donor antigens compared to third-party, the corresponding figure for OB negative patients being 2/7. In contrast, 5/7 patients were hyporesponsive in the direct pathway; hyporesponsiveness in the direct pathway did not correlate with freedom from OB. The patients in whom the assays were performed from the same blood sample confirmed that donor specific hyperresponsiveness in the indirect route can coexist with donor-specific hyporesponsiveness in the direct route. In conclusion, lung allograft recipients, like recipients of other organ allografts, become hyporesponsive in the direct route but sensitization via the indirect pathway is associated with chronic rejection.

Induction of kidney allograft tolerance after transient lymphohematopoietic chimerism in patients with multiple myeloma and end-stage renal disease

BACKGROUND

Two patients with end-stage renal disease secondary to multiple myelomas were treated with combined kidney and bone marrow transplantation in an effort to achieve donor-specific allotolerance through the induction of mixed lymphohematopoietic chimerism.

METHODS

Two female patients (55 and 50 years of age) with end-stage renal disease secondary to kappa light-chain multiple myelomas received a nonmyeloablative conditioning regimen that consisted of 60 mg/kg cyclophosphamide intravenously (IV) on days -5 and -4; 15 mg/kg equine anti-thymocyte globulin (ATGAM) IV on days -1, +1, and +3; and thymic irradiation (700 cGy) on day -1. On day 0, the recipients underwent kidney transplantation, followed by IV infusion of donor bone marrow (2.7x10(8) and 3.8x10(8) /kg nucleated cells, respectively) obtained from a human leukocyte antigen (HLA)-matched sibling. Cyclosporine A was administered IV at a dose of 5 mg/kg on day -1, then continued orally at 8 to 12 mg/kg per day until days +73 and +77, respectively, after which no further immunosuppression was given. Donor leukocyte infusions (1x10(7) /kg CD3+ T cells) were administered in an attempt to enhance the graft-versus-myeloma effect (days +66 and +112 in the first patient and day +78 in the second patient). Hematopoietic chimerism was monitored weekly by microsatellite assays.

RESULTS

Multilineage lymphohematopoietic chimerism (5%-80% donor CD3+ or CD3- cells, or both) was first detected during the second posttransplant week and was maintained for approximately 12 weeks, after which there was a gradual decline to undetectable levels (<1% donor cells) after day 105 in the first patient and after day 123 in the second patient. In both recipients, the blood urea nitrogen and creatinine levels returned to normal within 3 days. No rejection episodes have occurred. Quantification of urinary kappa light chains revealed a decline from 28 mg/dL to undetectable levels (<2.5 mg/dL) within 29 days in the first case and from 99.8 mg/dL to <10 mg/dL within 50 days in the second case. Both patients continue with normal kidney function and sustained anti-tumor responses, while receiving no immunosuppression for nearly 4 years and 2 years, respectively.

CONCLUSIONS

This nonmyeloablative regimen followed by combined HLA-matched donor bone marrow and renal allotransplantation is the first example of an intentional and clinically applicable approach to inducing renal allograft tolerance and achieving potent and sustained antitumor effects in patients with multiple myeloma.

Mixed chimerism and immunosuppressive drug withdrawal after HLA-mismatched kidney and hematopoietic progenitor transplantation

BACKGROUND

Rodents and dogs conditioned with total-lymphoid irradiation (TLI), with or without antithymocyte globulin (ATG), have been shown to develop mixed chimerism and immune tolerance without graft-versus-host disease (GVHD) after the infusion of major histocompatability complex (MHC)-mismatched donor bone marrow cells given alone or in combination with an organ allograft.

METHODS

Four human leukocyte antigen (HLA)-mismatched recipients of living donor kidney transplants were conditioned with TLI and ATG posttransplantation and infused with cyropreserved donor granulocyte colony-stimulating factor (G-CSF) "mobilized" hematopoietic progenitor (CD34+) cells (3-5x10(6) cells/kg) thereafter. Maintenance prednisone and cyclosporine dosages were tapered, and recipients were monitored for chimerism, GVHD, graft function, T-cell subsets in the blood, and antidonor reactivity in the mixed leukocyte reaction (MLR).

RESULTS

Three of the four patients achieved multilineage macrochimerism, with up to 16% of donor-type cells among blood mononuclear cells without evidence of GVHD. Prolonged depletion of CD4+ T cells was observed in all four patients. Rejection episodes were not observed in the three macrochimeric recipients, and immunosuppressive drugs were withdrawn in the first patient by 12 months. Prednisone was withdrawn from a second patient at 9 months, and cyclosporine was tapered thereafter.

CONCLUSIONS

Multilineage macrochimerism can be achieved without GVHD in HLA-mismatched recipients of combined kidney and hematopoietic progenitor transplants. Conditioning of the host with posttransplant TLI and ATG was nonmyeloablative and was not associated with severe infections. Recipients continue to be studied for the development of immune tolerance.

Loss of direct and maintenance of indirect alloresponses in renal allograft recipients: implications for the pathogenesis of chronic allograft nephropathy

Chronic allograft nephropathy (CAN) is the principal cause of late renal allograft failure. This complex process is multifactorial in origin, and there is good evidence for immune-mediated effects. The immune contribution to this process is directed by CD4(+) T cells, which can be activated by either direct or indirect pathways of allorecognition. For the first time, these pathways have been simultaneously compared in a cohort of 22 longstanding renal allograft recipients (13 with good function and nine with CAN). CD4(+) T cells from all patients reveal donor-specific hyporesponsiveness by the direct pathway according to proliferation or the secretion of the cytokines IL-2, IL-5, and IFN-gamma. Donor-specific cytotoxic T cell responses were also attenuated. In contrast, the frequencies of indirectly alloreactive cells were maintained, patients with CAN having significantly higher frequencies of CD4(+) T cells indirectly activated by allogeneic peptides when compared with controls with good allograft function. An extensive search for alloantibodies has revealed significant titers in only a minority of patients, both with and without CAN. In summary, this study demonstrates widespread donor-specific hyporesponsiveness in directly activated CD4(+) T cells derived from longstanding recipients of renal allografts, whether they have CAN or not. However, patients with CAN have significantly higher frequencies of CD4(+) T cells activated by donor Ags in an indirect manner, a phenomenon resembling split tolerance. These findings provide an insight into the pathogenesis of CAN and also have implications for the development of a clinical tolerance assay.

Treatment with immunotoxin

T-cell depletion prior to or beginning at the time of transplantation has been shown to be a valuable adjunct to the induction of immunological unresponsiveness. Both total lymphoid irradiation and anti-lymphocyte globulin have been used for this purpose in experimental models of transplantation as well as in human organ transplant recipients. However, these methods of T-cell depletion are limited in their ability to deplete T cells selectively due to non-specific targeting and limited efficacy. A new anti-CD3 immunotoxin has been developed with a far more potent ability to deplete T cells selectively as measured by flow cytometry analysis of peripheral blood T lymphocytes as well as lymph node lymphocytes. This immunotoxin is well tolerated by rhesus monkeys when administered in vivo. When administered as a single immunosuppressive agent pretransplant, it substantially promotes allograft survival, inducing tolerance in at least one-third of recipients as measured by subsequent acceptance of donor skin grafts and rejection of third-party skin grafts. When administered on the day of transplant in combination with steroid pretreatment and a brief course of deoxyspergualin or mycophenolate mofetil (4 to 14 days), long-term unresponsiveness is also produced and in a more reliable manner than using immunotoxin alone. A new immunotoxin directed at the human CD3epsilon has been developed with excellent potency in T-cell killing and lacking the Fc portion of the CD3 antibody. This construct may be useful for T-cell depletion in humans and has a potential application in tolerance induction in human organ transplantation. Lessons learned from anti-CD3 immunotoxin in the non-human primate model to date include (i) profound (2-3 log) depletion of T-cells can be accomplished safely without inducing lymphoma or infection, (ii) such depletion is a useful adjunct for tolerance induction to allogeneic organ transplants, and (iii) tolerance to both allogeneic renal transplants and xenogeneic islet transplants has been accomplished using such strategies to date in non-human primates and in pigs. Immunotoxin may be useful for the induction of chimerism using strategies that include donor bone marrow infusion. Successful strategies for tolerance induction have also been developed using immunotoxin without the adjunct of donor bone marrow or stem cell infusion. Clinical application of immunotoxin will use a newly engineered construct with the potential for causing cytokine release, less susceptibility to neutralization by anti-diphtheria antibody and not dependent on chemical conjugation of an antibody and toxin. The usefulness of immunotoxin is directly related to its tremendous potency for depleting T cells. Based on results in nonhuman primates, it is anticipated that it will become a useful agent in tolerance induction in humans.

Analysis of alloreactivity and intragraft cytokine profiles in living donor liver transplant recipients with graft acceptance

Although some previous studies have indicated the possibility of immunosuppression withdrawal in clinical liver transplantation, the mechanism of graft acceptance is not clear. The aim of this study is to elucidate the alloreactivity against the donor and intragraft cytokine profiles in living donor liver transplant (LDLT) recipients with graft acceptance. In October 1999, we had 23 patients who survived without immunosuppression after LDLT with a median drug-free period of 25 months (range: 3-69 months). They consisted of six patients who were electively weaned by an elective weaning protocol and 17 either forcibly or accidentally weaned patients due to various causes but mainly due to infection. We evaluated the alloreactivity against the donor in these patients by a mixed lymphocyte reaction and intragraft cytokine profiles by real-time reverse transcriptase-polymerase chain reaction. The development of donor-specific hyporeactivity was observed in the patients with graft acceptance. The cytokine pattern in the supernatant of the culture medium revealed a down regulation of T helper (Th) 1 cytokine INF gamma against the donor while no significant difference was seen in Th2 cytokine IL-10. Regarding the intragraft cytokine profiles, we could find no amplification of Thl cytokines (IL-2, INF y) and IL-4 while some of the patients revealed a gene expression of IL-10 with no significant difference from that of the normal, untransplanted liver specimen. In addition, no difference was observed in any other cytokines (IL-1beta, IL-8, IL-15, TNFalpha) compared with those of the normal controls. We propose that the down regulation of Th1 cytokine is one possible mechanism of graft acceptance in LDLT recipients.

Knowledge about transplantation tolerance gained in primates

Research in transplantation tolerance relies on application of successful strategies in a nonhuman-primate organ transplant model for preclinical testing. Three principal approaches are being evaluated: hematopoietic chimerism, lymphocyte depletion and costimulation blockade. Interactive work in these three areas has yielded much new information on mechanisms of tolerance and opened the door to pilot clinical trials. Clinical application of xenotransplantation is likely to depend on such strategies.

Clinical transplantation tolerance twelve years after prospective withdrawal of immunosuppressive drugs: studies of chimerism and anti-donor reactivity

BACKGROUND

Previous studies showed the feasibility of inducing transplantation tolerance to cadaveric renal allografts in patients given pretransplant total lymphoid irradiation (TLI). Microchimerism has been theorized to be an important or necessary factor in long-term graft acceptance and tolerance in humans.

METHODS

A cadaveric renal transplant recipient given pretransplant total lymphoid irradiation and withdrawn from immunosuppressive drugs more than 12 years ago was tested for microchimerism using a sensitive nested polymerase chain reaction technique, and for anti-donor reactivity using the mixed leukocyte reaction and an ELISA screen for anti-HLA antibodies. Donor and recipient were mismatched for all HLA-A, B, and DR antigens.

RESULTS

The "tolerant" recipient had good graft function, no detectable donor-type cells in the blood by polymerase chain reaction analysis, vigorous reactivity to donor stimulator cells in the mixed leukocyte reaction, and no detectable serum anti-HLA antibodies.

CONCLUSIONS

Operational tolerance to HLA-A, B, and DR mismatched organ allografts can be induced prospectively in humans for at least 12 years after withdrawal of immunosuppressive drugs. The allograft can be maintained in the absence of detectable donor microchimerism and in the presence of anti-donor reactivity in the mixed leukocyte reaction, suggesting that neither chimerism nor clonal deletion or anergy of recipient T cells to alloantigens presented by donor Class II HLA molecules is required for persistence of the tolerant state using this total lymphoid irradiation protocol.

Donor blood monocytes but not T or B cells facilitate long-term allograft survival after total lymphoid irradiation

BACKGROUND

Previous studies showed that a combination of posttransplant total lymphoid irradiation (TLI), rabbit antithymocyte globulin (ATG), and a single donor blood transfusion induced tolerance to ACI heart allografts in Lewis rats. All three modalities were required to achieve tolerance. The objective of the current study was to determine the subset(s) of cells in the donor blood that facilitated long-term allograft survival.

METHODS

Lewis hosts received TLI, ATG, and donor cell infusion after heart transplantation. Graft survival, mixed leukocyte reaction (MLR), and intragraft cytokine mRNA were studied.

RESULTS

The intravenous injection of 25 x 10(6) ACI peripheral blood mononuclear cells (PBMC) significantly prolonged graft survival as compared with that of Lewis hosts given TLI and ATG alone. Injection of highly enriched blood T cells or splenic B cells adjusted for the number contained in 25 x 10(6) PBMC failed to induce significant graft prolongation. Unexpectedly, depletion of monocytes (CD11b+ cells) from PBMC resulted in the loss of graft prolongation activity. Enriched populations of monocytes obtained by plastic adherence were more efficient in prolonging graft survival than PBMC on a per cell basis. Hosts with long-term grafts (>100-day survival) showed evidence of immune deviation, because the MLR to ACI stimulator cells was vigorous, but secretion of interferon-gamma in the MLR was markedly reduced. In situ hybridization studies of long-term grafts showed markedly reduced levels of interferon-gamma mRNA as compared with rejecting grafts.

CONCLUSION

Infusion of donor monocytes facilitated graft prolongation via immune deviation.

Endolymphatic irradiation in preparation for renal transplantation: a 26-year's follow-up

OBJECTIVE

The aim of the present study was to analyze the long-term evolution of patients submitted to endolymphatic irradiation as a pre-transplant preparation.

SETTING

Referral center of university hospital.

DESIGN

Case-control study.

MAIN OUTCOMES MEASURES

The study was designed to evaluate the incidence of rejection, kidney loss, leukopenia, infection, and graft survival in the group treated (group 1) prior to surgery, compared to a control group (group 2) composed of patients under identical clinical conditions (sex, age, type of donor, immunosuppressive therapy and time of transplant) that did not undergo treatment preparation.

PATIENTS

Patients were selected from amongst transplantation candidates on a long-term waiting list, some with a high level of antibodies against panel. The control group was chosen from amongst recently transplanted patients. Patients in the treated group received lipoiodine containing 131I with specific activity ranging between 4 and 6 mCu/ml.

RESULTS

A significant difference between the two groups was found with regard to the incidence of rejection crises (21.0% in group 1 and 73.6% in group 2; P = 0.003), and the maintenance dose of azathioprine (smaller in group 1; P < 0.01). As to kidney graft loss due to rejection, a tendency to significance could be identified (10.5% in group 1 and 42.1% in group 2; P = 0.063); however, the difference was not significant between the two groups in terms of reversibility of rejection episodes during the first 60 post-transplant days.

CONCLUSIONS

The authors concluded that this method, besides being relatively innocuous (there was no compromising of either the thyroid gland or of gonad function and there was no increase in tumor incidence), has an extended immunosuppressive effect, and can be indicated for cadaveric renal allograft recipients, especially those showing high panel reactivity.