Analysis of primate renal allografts after T-cell depletion with anti-CD3-CRM9

Comparison of CD3e Antibody and CD3e-sZAP Immunotoxin Treatment in Mice Identifies sZAP as the Main Driver of Vascular Leakage

Anti-CD3-epsilon (CD3e) monoclonal antibodies (mAbs) and CD3e immunotoxins (ITs) are promising targeted therapy options for various T-cell disorders. Despite significant advances in mAb and IT engineering, vascular leakage syndrome (VLS) remains a major dose-limiting toxicity for ITs and has been poorly characterized for recent "engineered" mAbs. This study undertakes a direct comparison of non-mitogenic CD3e-mAb (145-2C11 with Fc-silentTM murine IgG1: S-CD3e-mAb) and a new murine-version CD3e-IT (saporin-streptavidin (sZAP) conjugated with S-CD3e-mAb: S-CD3e-IT) and identifies their distinct toxicity profiles in mice. As expected, the two agents showed different modes of action on T cells, with S-CD3e-mAb inducing nearly complete modulation of CD3e on the cell surface, while S-CD3e-IT depleted the cells. S-CD3e-IT significantly increased the infiltration of polymorphonuclear leukocytes (PMNs) into the tissue parenchyma of the spleen and lungs, a sign of increased vascular permeability. By contrast, S-CD3e-mAbs-treated mice showed no notable signs of vascular leakage. Treatment with control ITs (sZAP conjugated with Fc-silent isotype antibodies) induced significant vascular leakage without causing T-cell deaths. These results demonstrate that the toxin portion of S-CD3e-IT, not the CD3e-binding portion (S-CD3e-mAb), is the main driver of vascular leakage, thus clarifying the molecular target for improving safety profiles in CD3e-IT therapy.

Experimental modeling of desensitization: What have we learned about preventing AMR?

During the past 5 decades, short-term outcomes in kidney transplant have significantly improved, in large part due to reduced rates and severity of acute rejection. Development of better immunosuppressive maintenance agents, as well as new induction therapies, helped make these advances. Nonhuman primate models provided a rigorous testing platform to evaluate candidate biologics during this process. However, antibody-mediated rejection remains a major cause of late failure of kidney allografts despite advances made in pharmacologic immunosuppression and strategies developed to facilitate improved donor-recipient matching. Our laboratory has been actively working to develop strategies to prevent and treat antibody-mediated rejection and immunologic sensitization in organ transplant, relying largely on a nonhuman primate model of kidney transplant. In this review, we will cover outcomes achieved by managing antibody-mediated rejection or sensitization in nonhuman primate models and discuss promises, limitations, and future directions for this model.

Nonhuman primate models of transplant tolerance: closer to the holy grail

PURPOSE OF REVIEW

Transplantation tolerance, successful acceptance of an organ without the perils of immunosuppression, has been a central goal of transplant research. Many strategies to achieve this tolerance have been examined over the past three decades, culminating in several human trials of transplant tolerance. This progression from the 'benchtop to the clinic' has depended on the successful implementation of these tolerance strategies in nonhuman primates. This review will examine the described methods of transplant tolerance induction in nonhuman primates.

RECENT FINDINGS

Although costimulatory blockade and mixed chimerism have an established record of achieving transplant tolerance in nonhuman primates, some of the most innovative recent techniques of tolerance induction have relied on cellular transfer. This review will fully examine the role of regulatory T-cell transfer and the use of mesenchymal stem/stromal cells to promote tolerance of organ allografts in nonhuman primates.

SUMMARY

Use of translational nonhuman primate transplant models is a vital intermediate step to advance new approaches of transplant tolerance induction from the lab to the clinic. This review will explore numerous techniques of tolerance induction that have been piloted in primates, including depletional techniques, induction of mixed hematopoietic chimerism, costimulation blockade, and adoptive transfer of tolerogenic cell populations.

Recombinant anti-monkey CD3 immunotoxin depletes peripheral lymph node T lymphocytes more effectively than rabbit anti-thymocyte globulin in naïve baboons

T cell depletion is an important procedure for both experimental and therapeutic immune modulation. Rabbit anti-thymocyte globulin (ATG), which is a commonly used T cell depletion antibody in clinical organ and cell transplantation protocols, is effective in temporarily depleting peripheral blood T lymphocytes but only moderately effective in depleting peripheral lymph node T cells which comprise the majority of T lymphocytes. A recombinant anti-CD3 immunotoxin, A-dmDT390-scfbDb (C207), has been developed and shown in an initial study to retain the lymph node depleting properties of conjugated CD3 immunotoxin. This agent could potentially be used synergistically with or as a replacement for rabbit ATG in preclinical primate models of transplantation. We directly compared the peripheral blood and lymph node depleting abilities of this recombinant anti-CD3 immunotoxin and rabbit ATG in naïve animals at clinically tolerated doses. Baboons were treated with a full course of either rabbit ATG (n=2) or CD3 immunotoxin (n=3). Peripheral blood and lymph node T lymphocytes were measured before and following treatment. Peripheral blood CD3+ cells fell below 100cells/μL in every animal. In the two animals receiving ATG, CD3+ cells represented 53% and 68% of lymph node cells two days following a full course of rabbit ATG. In contrast, CD3+ cells represented 3%, 5%, and 38% in lymph nodes following a full course of CD3-IT. Thus, recombinant anti-monkey CD3 immunotoxin showed improved peripheral lymph node T lymphocyte depletion to rabbit ATG and spared other immune cells.

Primate models in organ transplantation

Large animal models have long served as the proving grounds for advances in transplantation, bridging the gap between inbred mouse experimentation and human clinical trials. Although a variety of species have been and continue to be used, the emergence of highly targeted biologic- and antibody-based therapies has required models to have a high degree of homology with humans. Thus, the nonhuman primate has become the model of choice in many settings. This article will provide an overview of nonhuman primate models of transplantation. Issues of primate genetics and care will be introduced, and a brief overview of technical aspects for various transplant models will be discussed. Finally, several prominent immunosuppressive and tolerance strategies used in primates will be reviewed.

In vivo depletion of leukocytes and platelets following injection of T cell-specific antibodies into mice

In vivo T cell depletion experiments are widely used to establish the role of these cells in a variety of immunological processes. Different clones of monoclonal antibody targeting the CD3 molecular complex (mainly 145-2C11 and 17A2) have been successfully used for T cell depletion. In the present work, we assessed the specificity of monoclonal antibody-mediated CD3 T cell depletion in mouse peripheral blood. We showed that treatment of BALB/C mice with monoclonal antibodies (clones 145-2C11 and 17A2) not only efficiently depletes T cells in vivo, but also leads to a substantial reduction in B cell, granulocyte and platelet counts. In contrast, T cell depletion using a combination of anti-CD4 and anti-CD8 antibodies was efficient and produced less deleterious effects on other blood cell populations. Therefore, the results obtained from T cell depletion experiments using anti-CD3 antibodies must be interpreted with caution prior to draw definitive conclusions on the role of T cells in a given immunological process.

Towards the identification of biomarkers of transplantation tolerance

Although transplantation has been a standard medical practice for decades, the marked morbidity from the use of immunosuppressive drugs and poor long-term graft survival remain important limitations in the field. Achieving tolerance to transplanted organs should solve both problems, but has been an elusive goal. Recent advances in the human immunological toolbox have rekindled interest in studying the small number of transplant recipients who become tolerant to their grafts over time. The development of biomarkers of transplantation tolerance holds promise to improve the care of organ allograft recipients, to provide surrogate end points of tolerance induction strategies and to advance our understanding of the human immune response to both self and foreign antigens.

Effect of Alemtuzumab (CAMPATH 1-H) in patients with inclusion-body myositis

Sporadic inclusion-body myositis (sIBM) is the most common disabling, adult-onset, inflammatory myopathy histologically characterized by intense inflammation and vacuolar degeneration. In spite of T cell-mediated cytotoxicity and persistent, clonally expanded and antigen-driven endomysial T cells, the disease is resistant to immunotherapies. Alemtuzumab is a humanized monoclonal antibody that causes an immediate depletion or severe reduction of peripheral blood lymphocytes, lasting at least 6 months. We designed a proof-of-principle study to examine if one series of Alemtuzumab infusions in sIBM patients depletes not only peripheral blood lymphocytes but also endomysial T cells and alters the natural course of the disease. Thirteen sIBM patients with established 12-month natural history data received 0.3 mg/kg/day Alemtuzumab for 4 days. The study was powered to capture > or =10% increase strength 6 months after treatment. The primary end-point was disease stabilization compared to natural history, assessed by bi-monthly Quantitative Muscle Strength Testing and Medical Research Council strength measurements. Lymphocytes and T cell subsets were monitored concurrently in the blood and the repeated muscle biopsies. Alterations in the mRNA expression of inflammatory, stressor and degeneration-associated molecules were examined in the repeated biopsies. During a 12-month observation period, the patients' total strength had declined by a mean of 14.9% based on Quantitative Muscle Strength Testing. Six months after therapy, the overall decline was only 1.9% (P < 0.002), corresponding to a 13% differential gain. Among those patients, four improved by a mean of 10% and six reported improved performance of daily activities. The benefit was more evident by the Medical Research Council scales, which demonstrated a decline in the total scores by 13.8% during the observation period but an improvement by 11.4% (P < 0.001) after 6 months, reaching the level of strength recorded 12 months earlier. Depletion of peripheral blood lymphocytes, including the naive and memory CD8+ cells, was noted 2 weeks after treatment and persisted up to 6 months. The effector CD45RA(+)CD62L(-) cells, however, started to increase 2 months after therapy and peaked by the 4th month. Repeated muscle biopsies showed reduction of CD3 lymphocytes by a mean of 50% (P < 0.008), most prominent in the improved patients, and reduced mRNA expression of stressor molecules Fas, Mip-1a and alphaB-crystallin; the mRNA of desmin, a regeneration-associated molecule, increased. This proof-of-principle study provides insights into the pathogenesis of inclusion-body myositis and concludes that in sIBM one series of Alemtuzumab infusions can slow down disease progression up to 6 months, improve the strength of some patients, and reduce endomysial inflammation and stressor molecules. These encouraging results, the first in sIBM, warrant a future study with repeated infusions

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.

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.

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.

T cell tolerance induced by therapeutic antibodies

Ever since the discovery of Medawar, over 50 years ago, that immunological tolerance was an acquired phenomenon that could be manipulated in neonatal mice, the ability to induce therapeutic tolerance against autoantigens, allergens and organ grafts has been a major driving force in immunology. Within the last 20 years we have found that a brief treatment with monoclonal antibodies that block certain functional molecules on the surface of the T cell is able to reprogramme the established immune repertoire of the adult mouse, allowing indefinite acceptance of allografts or effective curing of autoimmune diseases. We are only now just beginning to define many of the regulatory mechanisms that induce and maintain the tolerant state with the aim of being able to safely and reliably apply these technologies to human clinical situations.

Organ transplantation—how much of the promise has been realized?

Since the introduction of organ transplantation into medical practice, progress and optimism have been abundant. Improvements in immunosuppressive drugs and ancillary care have led to outstanding short-term (1--3-year) patient and graft survival rates. This success is mitigated by several problems, including poor long-term (>5-year) graft survival rates, the need for continual immunosuppressive medication and the discrepancy between the demand for organs and the supply. Developing methods to induce transplant tolerance, as a means to improve graft outcomes and eliminate the requirement for immunosuppression, and expanding the pool of organs for transplantation are the major challenges of the field.

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 road to tolerance: renal transplant tolerance induction in nonhuman primate studies and clinical trials

Organ transplantation has become a standard life-saving therapy for many causes of end stage organ failure. Although valuable, it remains hampered by the requirement for, and complications of, immunosuppression to prevent immune rejection of the transplanted organ. It is now clear that rejection can be avoided in some experimental systems without a requirement of immunosuppressive medication, and these experimental concepts are now making their way into the clinic in the form of early transplantation tolerance trials. This manuscript will discuss the most promising techniques for tolerance induction, namely, costimulation blockade, lymphocyte depletion, and mixed chimerism. Seminal preclinical studies will be cited and the results of initial clinical trials will be reviewed. The data to date indicate that while tolerance remains elusive, immunosuppression minimization is a feasible near-term alternative.

Crossing the bridge: large animal models in translational transplantation research

Many methods for reducing the immunosuppressive requirements of allotransplantation have been proposed based on a growing understanding of physiological and allospecific immunity. As these regimens are developed for clinical application, they require validation in models that are reasonably predictive of their performance in humans. This article provides an overview of the large animal models commonly used to test immunomodulatory organ transplant protocols. The rationale for the use of large animals and the effects of common immunosuppressants in the dog, pig, and non-human primate are reviewed. Promising methods for the induction of allospecific tolerance are surveyed with references to early human trials where appropriate.

Expression of CTLA-4 in nonhuman primate lymphocytes and its use as a potential target for specific immunotoxin-mediated apoptosis: results of in vitro studies

T-cell-mediated immunoregulation is one of the main mechanisms implicated in induction and maintenance of transplantation tolerance. In this regard, deletion or modulation of xeno/alloantigen-specific T cells, as well as blocking of their interactions with other cell populations, are currently being pursued for tolerance induction in humans as well as nonhuman primates. In order to investigate whether cytotoxic T-lymphocyte antigen-4 (CTLA-4) may represent a suitable target for a T cell depletion approach in nonhuman primate models, we analysed CTLA-4 expression in peripheral blood mononuclear cells (PBMCs) from nonhuman primates and the potential role of two anti-CTLA-4 saporin-conjugated immunotoxins. The analysis was performed in PBMCs from 8 cynomolgus monkeys from Philippines and from Mauritius both at protein level by flow cytometry and at transcriptional level by RT-PCR. In addition, the apoptotic role of the immunotoxins was investigated. The results showed that CTLA-4 was expressed at variable levels depending on the origin of the cynomolgus monkeys and the resting or activated cell condition. CTLA-4 was not expressed on resting Mauritius PBMCs and showed a lower up-regulation upon PMA/PHA activation compared to the Philippines PBMCs that expressed CTLA-4 also before activation. Two CTLA-4 RNA transcripts (672 and 550 bp) were detected with levels variations after cell stimulation. Two anti-CTLA-4 immunotoxins induced in vitro apoptosis of activated PBMCs from both sources of cynomolgus monkeys. This is the first report that documents CTLA-4 expression both at protein and transcriptional level by nonhuman primate PBMCs and provides novel perspectives of xeno/allograft rejection immunotherapy based on CTLA-4 targeting.

Piceatannol in combination with low doses of cyclosporine A prolongs kidney allograft survival in a stringent rat transplantation model

BACKGROUND

The discovery of new immunosuppressive agents has enhanced short-term graft survival. However, current immunosuppressants often induce toxicities that limit their clinical use. Thus, there is a need for new immunosuppressants for use in clinical transplantation. Piceatannol blocks Syk and ZAP-70, tyrosine kinases involved in immune cell activation. We examined whether piceatannol prolongs kidney allograft survival in the stringent ACI-to-Lewis rat model.

METHODS

Kidney recipients were divided into four groups. Group 1 (n=8) received piceatannol 30 mg/kg per day intravenously and cyclosporine A (CsA) 2 mg/kg per day intramuscularly from day -3 to day 7 after transplantation. At day 8, piceatannol was reduced to 10 mg/kg per day and the combined treatment continued until day 60. Group 2 (n=9) received 2 mg/kg per day CsA alone from day -3 to day 60. Group 3 (n=4) received piceatannol alone as in group 1. Group 4 (n=2) received only the vehicle dimethyl sulfoxide from day -3 to day 60. Graft rejection was defined as either a serum creatinine level more than 2 mg/dL or animal death.

RESULTS

Group 1 animals survived for at least 115 days (n=8, P<0.05), with several animals maintaining their grafts for more than 200 days. In contrast, 8 of 9 animals in group 2 rejected their grafts within 10 days of transplantation; one animal survived for 71 days. Excellent graft function was maintained in group 1 animals despite withdrawal of immunosuppression.

CONCLUSIONS

These results are the first to show that piceatannol, when combined with subtherapeutic dosages of CsA, prevents graft rejection, suggesting that targeting Syk and Zap could be useful for preventing graft rejection.

Immunotherapy as a means to induce transplantation tolerance

There have been several recent advances in the use of immunotherapy to induce transplantation tolerance. These include newer and safer protocols to create hematopoietic chimerism, the development of more-powerful T cell depleting antibodies, the identification of additional costimlulatory pathways as molecular targets and the identification of a role for suppressor cells in transplant tolerance.

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.

Successful conversion from conventional immunosuppression to anti-CD154 monoclonal antibody costimulatory molecule blockade in rhesus renal allograft recipients

BACKGROUND

Several conventional forms of immunosuppression have been shown to antagonize the efficacy of anti-CD154 monoclonal antibody- (mAb) based costimulatory molecule blockade immunotherapy. Our objective was to determine if allograft recipients treated with a conventional immunosuppressive regimen could be sequentially converted to anti-CD154 mAb monotherapy without compromising graft survival.

METHODS

Outbred juvenile rhesus monkeys underwent renal allotransplantation from MHC-disparate donors. After a 60-day course of triple therapy immunosuppression with steroids, cyclosporine, and mycophenolate mofetil, monkeys were treated with: (1) cessation of all immunosuppression (control); (2) seven monthly doses of 20 mg/kg hu5C8 (maintenance), or; (3) 20 mg/kg hu5C8 on posttransplant days 60, 61, 64, 71, 79, and 88 followed by five monthly doses (induction+maintenance). Graft rejection was defined by elevation in serum creatinine>1.5 mg/dl combined with histologic evidence of rejection.

RESULTS

Graft survival for the three groups were as follows: group 1 (control): 70, 75, >279 days; group 2 (maintenance): 83, 349, >293 days, and; group 3 (induction+maintenance): 355, >377, >314 days. Acute rejection developing in two of four monkeys after treatment with conventional immunosuppression was successfully reversed with intensive hu5C8 monotherapy.

CONCLUSIONS

Renal allograft recipients can be successfully converted to CD154 blockade monotherapy after 60 days of conventional immunosuppression. An induction phase of anti-CD154 mAb appears to be necessary for optimal conversion. Therefore, although concurrent administration of conventional immunosuppressive agents including steroids and calcineurin inhibitors has been shown to inhibit the efficacy of CD154 blockade, sequential conversion from these agents to CD154 blockade appears to be effective.

Immunotoxin FN18-CRM9 induces stronger T cell signaling than unconjugated monoclonal antibody FN18

BACKGROUND

The T-cell receptor (TCR)/CD3 complex is the target of therapeutic strategies aimed at prolonging allograft survival. The immunotoxin FN18-CRM9, composed of the anti-CD3 monoclonal antibody FN18 and the mutated diphtheria toxin CRM9, is useful for prolonging allograft survival in preclinical models of transplantation. To explore the influence of conjugation of the mutated diphtheria toxin on functional activation of the TCR/CD3 complex, we compared the effects of FN18-CRM9 and unconjugated FN18 on protein tyrosine phosphorylation and ligand/receptor internalization in purified monkey peripheral blood T cells.

METHODS

Purified normal rhesus monkey T cells were incubated with unconjugated FN18 or conjugated FN18-CRM9 and examined for differences in antibody binding, tyrosine phosphorylation, and CD3 internalization.

RESULTS

Binding cross-inhibition studies demonstrated that both compounds were able to inhibit fluorescein isothiocyanate-FN18 binding to CD3 with similar efficacy and potency. However, FN18-CRM9 was more potent than FN18 in triggering the phosphorylation of several proteins on tyrosine residues and in inducing CD3 internalization. The tyrosine kinase inhibitor genistein blocked FN18-CRM9-induced protein tyrosine phosphorylation and CD3 internalization, suggesting that tyrosine phosphorylation is involved in the internalization of the immunotoxin. Interestingly, in FN18-CRM9- but not FN18-treated cells, there was a gradual decrease in cellular CD3 protein levels within 24 and 48 hr; such a decrease was not observed with the control protein Csk.

CONCLUSIONS

Our findings suggest that the conjugation of the mutated diphtheria toxin CRM9 to FN18 modulates the monoclonal antibody-mediated cross-linking of the TCR/CD3 complex, leading to a stronger protein tyrosine phosphorylation and CD3 internalization. This may in turn contribute to the greater efficacy of the immunotoxin in prolonging allograft survival.

LONG-TERM ALLOGRAFT ACCEPTANCE INDUCED BY SINGLE DOSE ANTI-LEUKOCYTE COMMON ANTIGEN (RT7) ANTIBODY IN THE RAT1

BACKGROUND

In clinical organ transplantation monoclonal antibodies (mAb) to different surface molecules of immunocompetent cells become integral parts of the immunosuppressive therapy. In this study, a mAb against the rat leukocyte common antigen CD45 (RT7) was tested for its immunosuppressive potency after a single perioperative injection.

METHODS

Binding and depleting properties of the anti-RT7 mAb were investigated by flow cytometry. In the fully major histocompatibility complex-disparate heart and skin transplantation models (LEW [RT1l]--> LEW.1W [RT1u]), a single dose of anti-RT7 mAb (10 mg/kg) was administered intravenously (day -1). To characterize the long-term acceptance of heart allografts second set skin transplantation (day 100), mixed lymphocyte reaction studies (day 100) and reverse transcriptase-polymerase chain reaction analysis for intragraft cytokine expression (day 200) were performed.

RESULTS

The anti-RT7 mAb bound to nearly all hematopoietic lineage cells, but particularly T and NK cells, and profoundly depleted these cells in circulation and lymphoid tissues. Anti-RT7 mAb-treated rats showed long-term acceptance of heart allografts (>200 days; n=12), whereas untreated recipients rejected allografts by day 8 (n=6). In contrast to hearts, primary skin allograft survival was only moderately prolonged. Animals with stable heart allograft acceptance showed normal in vitro lymphocyte proliferation responses to donor and third party antigen. These recipients also acutely rejected second set donor-strain skin grafts without inducing rejection of persisting heart allografts. Reverse transcriptase-polymerase chain reaction analysis of intragraft cytokines showed up-regulation of Fas-ligand and IL-4 mRNA in long-surviving heart allografts.

CONCLUSIONS

The findings demonstrate that a single injection of an anti-RT7 mAb in the rat can induce stable long-term acceptance of heart allografts by transient but profound T-cell depletion. Local immunoregulatory mechanisms seem to play a role for maintenance of long-term graft acceptance.

Peritransplant tolerance induction in macaques: early events reflecting the unique synergy between immunotoxin and deoxyspergualin

BACKGROUND

Day of transplant T cell depletion with anti-CD3 immunotoxin or F(Ab)2 immunotoxin induces stable tolerance to renal allografts in rhesus monkeys given 15-deoxyspergualin (DSG), a NF-kappaB inhibitor that suppresses proinflammatory cytokine (PC) production. Because PC and NF-kappaB are involved in dendritic cell (DC) maturation, we asked if impaired DC maturation and Th2-type cytokine deviation might be related to the synergistic effect of DSG in this novel model.

METHODS

Immunosuppression was initiated 4 hr before transplanting a major histocompatibility complex mismatched renal allograft. Some groups received a supplemental 5-day course of cyclosporine A or DSG or a 15-day course of DSG. Peripheral lymph nodes were sequentially examined for presence of mature DC. In vitro effects of DSG on PC-induced maturation of DC were also examined.

RESULTS

Allografts survived without rejection in 87% of recipients given immunotoxin or F(Ab)2 immunotoxin with DSG x 15 days, in 50% with DSG x 5 days, and 0% with cyclosporine A. The longest DSG survivors are >1000 days with normal graft function and tolerance validated, including acceptance of challenge second donor kidneys without treatment. DSG-treated recipients were unique in developing polarized Th2-type plasma cytokines. In DSG recipients, mature DC were significantly reduced in day +5 lymph node biopsies, with complete repopulation by 30 days. In vitro studies verified an inhibitory effect of DSG on DC maturation.

CONCLUSIONS

The study suggests DSG arrests DC maturation. The unusual synergy of immunotoxin and DSG apparently involves coincidental reduction in lymph node T cell mass and mature DC, a transient circumstance favoring development of stable tolerance.

Long-term outcome and alloantibody production in a non-myeloablative regimen for induction of renal allograft tolerance

BACKGROUND

Multilineage chimerism and long-term acceptance of renal allografts has been produced in non-human primates conditioned with a nonmyeloablative regimen. Our study was undertaken to evaluate the immunological and pathological status of long-term survivors and to define the role of splenectomy and of the primarily vascularized kidney in the regimen.

METHOD

Monkeys were treated with the basic regimen, including: total body irradiation, thymic irradiation, antithymocyte globulin, donor bone marrow transplantation, and a 4-week course of cyclosporine after which no further immunosuppression was given. They were divided into four groups according to the timing of kidney transplantation (KTx) and splenectomy as follows; group A (n=13): KTx and splenectomy on the day of donor bone marrow transplantation (day 0); group B (n=3): KTx on day 0 without splenectomy; group C (n=7): splenectomy on day 0 but delayed KTx until 3 to 16 weeks post-donor bone marrow transplantation; group D (n=3): both splenectomy and KTx delayed until day 120 post-donor bone marrow transplantation.

RESULTS

In group A, 11 of 13 monkeys developed chimerism and 9 monkeys achieved long-term survival of 4 to 70 months without evidence of chronic vascular rejection. Alloantibodies were detected in only one long-term survivor. In contrast, all three monkeys in group B developed alloantibodies and rejected their allografts. In group C, long-term survival without alloantibody production was observed in two of three monkeys that had developed chimerism. In group D, all three recipients were sensitized and rejected the kidney allografts rapidly after transplantation.

CONCLUSIONS

1) Production of anti-donor antibody was prevented in most recipients that developed mixed chimerism in the regimens with splenectomy at the time of donor bone marrow transplantation. 2) If splenectomy is not included in the initial conditioning regimen, induction of B cell tolerance is less likely and the result is late onset of alloantibody production and allograft rejection. 3) Immediate transplantation of the kidney at the time of recipient conditioning is not essential for induction of donor specific hyporesponsiveness by bone marrow transplantation.

Improved techniques for kidney transplantation in the monkey

Improved microsurgical techniques for kidney transplantation in the monkey are described. The left graft kidney is transplanted to the lower part of abdomen with end-to-side anastomoses of renal artery to aorta without a patch of aorta, renal vein to inferior vena cava, and end-to-end anastomosis of donor and recipient ureter with 8-0 nylon sutures in a bilateral nephrectomized recipient monkey. We recently performed 60 kidney transplantations in Vervet monkeys. None died of surgery or surgical complications. This reproducible model provides a useful tool to test new immunosuppressants and to investigate the mechanism of drug-induced tolerance and xenotransplantation in primates as a support to clinical trial.

Transplantation tolerance-where do we stand?

Our understanding of tolerance mechanisms has progressed to the point that tolerance-induction protocols are being tested in humans for organ transplantation. However, a range of scientific, ethical, logistic and commercial issues have arisen, and must be resolved before tolerance induction for human allograft patients can become a reality.

Tolerance to vascularized organ allografts in large-animal models

Although studies of tolerance induction in large animals remain limited compared with murine studies, a number of encouraging observations have been recently reported - especially in nonhuman primate models. The development of antibodies or proteins binding to costimulatory molecules and of an immunotoxin that is active on T cells have been particularly important advances leading to expanded opportunities for extending strategies for tolerance induction to large animals.

Activation of T lymphocytes for adhesion and cytokine expression by toxin-conjugated anti-CD3 monoclonal antibodies

BACKGROUND

Immunosuppressive drugs that target T cells are useful for prolonging allograft survival. The anti-CD3 immunotoxin FN18-CRM9 has been shown to effectively prolong renal allograft survival in a rhesus monkey model of transplantation. However, immunotoxin-treated monkeys showed increased levels of inflammatory cytokines and produced antibodies to donor proteins. To better understand the role of FN18-CRM9 in the production of cytokines and anti-donor antibodies in the monkey model, we examined whether this immunotoxin elicits functional responses in T cells.

METHODS

Purified normal rhesus monkey T cells (>98% purity) were incubated with immunotoxin FN18-CRM9 or the unconjugated anti-CD3 monoclonal antibodies and then examined for changes in protein tyrosine phosphorylation, adhesion to fibronectin, gene expression, and proliferation in the presence or absence of anti-CD28 monoclonal antibodies (mAb) and interleukin-2.

RESULTS

Immunotoxin treatment of T cells in vitro increased protein tyrosine phosphorylation, cell adhesion to the extracellular matrix, and expression of the inflammatory cytokines interferon-gamma and tumor necrosis factor-alpha. These immunotoxin effects were similar in magnitude to those induced by the unconjugated mAb. In contrast, immunotoxin-induced T cell proliferation was markedly less than that induced by the unconjugated mAb. Interestingly, the mitogenic molecules IL-2 and anti-CD28 mAb did not prevent immunotoxin-induced inhibition of cell proliferation.

CONCLUSIONS

The activation of T cells for protein phosphorylation, adhesion, and cytokine expression strongly suggests that the actions of FN18-CRM9 in vivo are not limited to the inhibition of protein synthesis.