The role of costimulatory molecules as targets for new immunosuppressives in transplantation

Stem cells versus donor specific transfusions for tolerance induction in living donor renal transplantation: a single-center experience

BACKGROUND

We undertook this study to define the role of stem cell transplantation (SCT) versus donor-specific transfusion (DST) in tolerance induction and sustenance in living donor renal transplantation (LDRT).

METHODS

In this prospective three-armed trial in LDRT with 13 patients each in demographically well-balanced groups, tolerance induction protocol (TIP) was used with SCT in group 1, DST in group 2, and no induction in group 3. Tolerance induction protocol consisted of SCT/DST under conditioning with bortezomib, methylprednisone, rituximab, and rabbit antithymocyte globulin. Transplantation was performed with prednisone in groups 1 and 2 and with triple immunosuppression in group 3, if lymphocyte/flow crossmatch was negative; and if donor-specific antibodies (DSAs) were absent in the first 2 groups. Posttransplant monitoring included serum creatinine (SCr), peripheral T-regulatory cells (pTregs)(127/CD4+/25), and DSA for groups 1 and 2; DSA was eliminated in group 3. Rescue IS was started with rise of SCr/DSA/ rejection.

RESULTS

Tolerance induction protocol was safe. Over a mean follow-up of 2 years, no patient/graft was lost in groups 1 and 2. One patient of group 3 lost graft to noncompliance. Protocol biopsies were unremarkable. Rejections were noted in six patients of group 1, five of group 2, and seven of group 3. Donor-specific antibodies were elevated in three patients of both groups. Mean SCr of all groups was similar; however, pTregs were increased posttransplant in groups 1 and 2 versus group 3. Group 1 had sustained rise in pTregs.

CONCLUSION

Stem cell transplantation and DST are useful for immunosuppression minimization in LDRT with sustained generation of pTregs with SCT.

Small-molecule inhibitors of IL-2/IL-2R: lessons learned and applied

The IL-2:IL-2R protein-protein interaction is of central importance to both healthy and diseased immune responses, and is one of the earliest examples of successful small-molecule inhibitor discovery against this target class. Drug-like inhibitors of IL-2 have been identified through a combination of fragment discovery, structure-based design, and medicinal chemistry; this discovery approach illustrates the importance of using a diverse range of complementary screening methods and analytical tools to achieve a comprehensive understanding of molecular recognition. The IL-2 story also provides insight into the dynamic nature of protein-protein interaction surfaces, their potential druggability, and the physical and chemical properties of effective small-molecule ligands. These lessons, from IL-2 and similar discovery programs, underscore an increasing awareness of the principles governing the development of drugs for protein-protein interactions.

Dendritic cell-based therapy in Type 1 diabetes mellitus

Dendritic cell (DC) immunotherapy is a clinical reality. Despite two decades of considerable data demonstrating the feasibility of using DCs to prolong transplant allograft survival and to prevent autoimmunity, only now are these cells entering clinical trials in humans. Type 1 diabetes is the first autoimmune disorder to be targeted for treatment in humans using autologous-engineered DCs. This review will highlight the role of DCs in autoimmunity and the manner in which they have been engineered to treat these disorders in rodent models, either via the induction of immune hyporesponsiveness, which may be cell- and/or antigen-specific, or indirectly by upregulation of other immune cell networks.

Rapamycin modulates the maturation of rat bone marrow-derived dendritic cells

The purpose of the study was to observe the effect of rapamycin (RAPA) on the differentiation and maturation of rat bone marrow-derived dendritic cells (BMDCs) in vitro. BMDCs from Wistar rats were cultured with granulocyte-macrophage colony-stimulating factor plus interleukin-4 in the presence or absence of RAPA (20 ng/mL), and stimulated with lipopolysaccharide (LPS) for 24 h before cells and supernatants were collected. Surface phenotype of BMDCs was flow-cytometrically detected to determine the expression of maturation markers, MHC class II and CD86. Supernatants were analyzed for the production of IL-12 and IFN-gamma cytokines by using ELISA. BMDCs were co-cultured with T cells from Lewis rats and mixed lymphocyte reaction was assessed by MTT method. The morphology of BMDCs stimulated with LPS remained immature after RAPA pretreatment. RAPA significantly decreased the CD86 expression, impaired the IL-12 and IFN-gamma production of BMDCs stimulated with LPS, and inhibited the proliferation of allogeneic T cells. In conclusion, RAPA can inhibit the maturation of BMDCs stimulated with LPS in terms of the morphology, surface phenotype, cytokine production, and ability of BMDCs to stimulate the proliferation of allogeneic T cells in vitro.

Toward a cure for type 1 diabetes mellitus: diabetes-suppressive dendritic cells and beyond

Insulin has been the gold standard therapy for diabetes since its discovery and commercial availability. It remains the only pharmacologic therapy for type 1 diabetes (T1D), an autoimmune disease in which autoreactive T cells specifically kill the insulin-producing beta cells. Nevertheless, not even molecularly produced insulin administered four or five times per day can provide a physiologic regulation able to prevent the complications that account for the morbidity and mortality of diabetic patients. Also, insulin does not eliminate the T1D hallmark: beta-cell-specific autoimmunity. In other words, insulin is not a 'cure'. A successful cure must meet the following criteria: (i) it must either replace or maintain the functional integrity of the natural, insulin-producing tissue, the endocrine islets of Langerhans' and, more specifically, the insulin-producing beta cells; (ii) it must, at least, control the autoimmunity or eliminate it altogether; and (iii) it must be easy to apply to a large number of patients. Criterion 1 has been partially realized by allogeneic islet transplantation. Criterion 2 has been partially realized using monoclonal antibodies specific for T-cell surface proteins. Criterion 3 has yet to be realized, given that most of the novel therapies are currently quasi-patient-specific. Herein, we outline the current status of non-insulin-based therapies for T1D, with a focus on cell-based immunomodulation which we propose can achieve all three criteria illustrated above.

Immunoregulatory dendritic cells to prevent and reverse new-onset Type 1 diabetes mellitus

Herein, the authors provide an overview of where dendritic cells lie in the immunopathology of autoimmune Type 1 diabetes mellitus and how dendritic cell-based therapy may be usefully translated to treat and reverse the disease. The immunopathology of Type 1 diabetes mellitus offers a number of windows at which immunotherapy can be applied to delay, stop and even reverse the autoimmune processes, especially in light of the recent antibody-based accomplishment of improvement in residual beta-cell mass function. As in almost all cell-specific inflammatory processes, dendritic cells are central regulators of diabetes onset and progression. This realisation, along with accumulating data confirming a role for dendritic cells in maintaining and inducing tolerance in multiple therapeutic settings, has prompted a line of investigation to identify the most effective embodiments of dendritic cells for diabetes immunotherapy.

New aspect of immunosuppressive treatment in liver transplantation. How could you induce tolerance in liver transplantation?

New immunosuppressive strategies have improved short- and long-term graft survival. The current aim is to decrease the intensity of the immunosuppressive regimen, in an attempt to limit side effects and the direct toxicity of calcineurin inhibitor (CNI) for kidney function. We describe here current experience in liver and liver-kidney transplantation, the mechanism of tolerance and the immunosuppressive strategy used in liver transplantation.

Immunosuppressants in advanced clinical development for organ transplantation and selected autoimmune diseases

Immunosuppressants dampen the immune response or restore balance among immune system components. They are primarily used to prevent allograft rejection after organ transplantation and to prevent or treat disease flares in autoimmune diseases. Immunosuppressants available at present include the calcineurin inhibitors (cyclosporin, tacrolimus), antimetabolites (azathioprine, leflunomide, methotrexate, mycophenolate mofetil), antiproliferatives (sirolimus), monoclonal antibodies to T lymphocyte (basiliximab, daclizumab, muromonab-CD3) and anticytokines (anakinra, etanercept, infliximab). The immunosuppressive market grows at a rate of > 10% yearly, with total sales in 2001 of US$2.7 billion. Immunotherapy in transplantation and autoimmune diseases is tending towards the use of multi-drug regimens tailored for the individual patient. At least 23 new immunosuppressants are currently in advanced clinical testing or preregistration, and can be divided into three groups. First, emerging drugs targeting intracellular ligands in immune cells are primarily analogues of currently-marketed agents, which attempt to provide improved pharmaceutical or safety profiles compared with the prototype compound. They are largely being developed in organ transplantation. Second, emerging drugs targeting cell surface ligands on immune cells attempt to antagonise novel molecular sites to interfere with immune cell activation via costimulatory signals, immune cell adhesion to tissues or the vasculature and immune cell trafficking. These agents are being primarily developed in rheumatoid arthritis, psoriasis and/or multiple sclerosis. Finally, emerging drugs acting as anticytokines, which largely follow on from the success of those on the market, by antagonising the function of tumour necrosis factor or a narrow selection of interleukins. All are being assessed in rheumatoid arthritis. Drug development of immunosuppressants is increasingly attempting to intervene in disease progression over the long term. These efforts bring with them trial design and regulatory issues, such as what markers can be used as trial outcome measures, over what duration do trials need to be conducted and what labelling claims are allowed. With the intensive activity in this field, it is likely that several new drugs will reach the market in the coming decade. One caveat, however, is that emerging immunosuppressants that are likely to capture a reasonable share of this increasingly-fragmented market must demonstrate the ability to achieve disease remission or long-term slowing of disease progression.

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.

Administration of antisense oligodeoxyribonucleotides targeting NF-kappaB prolongs allograft survival via suppression of cytotoxicity

Presentation of alloantigens by antigen-presenting cells (APC) deficient in expression of costimulatory molecules (CM) induces alloantigen-specific hyporesponsiveness or tolerance. NF-kappaB has been shown to be a crucial transcription factor that regulates CM expression on the surface of APC. We designed an antisense phosphorothioate oligodeoxynucleotide (ODN) to specifically inhibit mRNA of mouse NF-kappaB, resulting in a deficiency in CM expression on APC that may prolong organ allograft survival. Anti-NF-kappaB ODN was delivered systemically by an osmotic pump implanted in the abdominal cavity of recipients following transplantation of vascularized heart allografts. The animals in control groups were given scrambled control ODN or were left untreated. Normal C3H (H2(k)) recipients rejected B10 (H2(b)) heart allografts at a median survival time (MST) of 15 days. A 14-day administration of 12.5 mg/kg/day anti-NF-kappaB ODN prolonged the survival of cardiac allografts to an MST of 25 days (P <0.05). In contrast, a scrambled control ODN was not effective (MST 17 days, P >0.05 compared to untreated controls). To investigate the underlying mechanisms of the immunosuppressive effect of anti-NF-kappaB ODN administration, graft infiltrating cells, spleen cells, and serum were collected from animals on day 7 posttransplant. Freshly isolated graft-infiltrating cells from anti-NF-kappaB ODN-treated recipients exhibited significantly decreased donor-specific CTL activity. Generation of CTL activity of spleen T cells from anti-NF-kappaB ODN-treated recipients was also impaired compared with untreated animals. Administration of anti-NF-kappaB ODN did not influence the titers of complement-dependent cytotoxic antibodies. These data suggest that treatment with anti-NF-kappaB ODN markedly inhibits the cellular response of allograft recipients, resulting in significant prolongation of allograft survival. Antisense ODN therapy targeting NF-kappacB may be a novel strategy for future immunosuppressive therapy.

New insights into the interactions between T-cell costimulatory blockade and conventional immunosuppressive drugs

OBJECTIVE

To determine the precise in vivo interaction between T-cell costimulatory blockade and conventional immunosuppression in transplantation.

SUMMARY BACKGROUND DATA

Blocking B7 or CD154 T-cell costimulatory activation pathways prevents allograft rejection in small and large animal transplant models and is considered a promising strategy for clinical organ transplantation.

METHODS

A fully MHC-mismatched vascularized mouse cardiac allograft model was used to test the interactions between anti-CD154 or CTLA4Ig monotherapy and conventional immunosuppressive drugs in promoting long-term graft acceptance. The frequency of alloreactive T cell was measured by ELISPOT. Chronic rejection was examined by histology.

RESULTS

Cyclosporine, tacrolimus, and anti-IL-2R monoclonal antibody therapy abrogated the effect of a single-dose protocol of anti-CD154 therapy. In contrast, rapamycin acted synergistically with anti-CD154 therapy in promoting long-term allograft survival. The addition of calcineurin inhibitors did not abolish this synergistic effect. Intense CD154-CD40 blockade by a multiple-dose schedule of anti-CD154 resulted in long-term graft survival and profound alloreactive T-cell unresponsiveness and overcame the opposite effects of calcineurin inhibitors. CTLA4Ig induced long-term graft survival, and the effect was not affected by the concomitant use of any immunosuppressive drugs.

CONCLUSIONS

The widespread view that calcineurin inhibitors abrogate the effects of T-cell costimulatory blockade should be revisited. Sufficient costimulatory blockade and synergy induced by CD154 blockade and rapamycin promote allograft tolerance and prevent chronic rejection.

Th1 cytokines, programmed cell death, and alloreactive T cell clone size in transplant tolerance

The Th1 cytokines IL-2 and IFN-gamma, which inhibit T cell proliferation and promote activation induced cell death, may be required to diminish alloreactive T cell numbers and to foster tolerance across full allogeneic barriers. However, we hypothesized that these cytokines might be dispensable when the alloreactive T cell clone size is relatively small, as is seen in recipients of minor-mismatched grafts. We show that alloreactive T cell clone size of C57BL/6 mice against multiple minor-mismatched 129X1/sv mice was approximately 4-9-fold smaller than that against MHC-mismatched BALB/c mice. In the MHC-mismatched combination, CD28-B7 blockade by CTLA4Ig induced long-term graft survival in wild-type recipients, but this treatment was ineffective in IFNgamma(-/-) or IL-2(-/-) recipients. In contrast, in the minor-mismatched combination, CTLA4Ig induced long-term allograft survival in wild-type, IFNgamma(-/-), and IL-2(-/-) recipients. Bcl-x(L) transgenic animals, which are defective in "passive" T cell death, are likewise sensitive to the effects of CTLA4Ig only in the setting of the minor-mismatch grafts. Therefore, the alloreactive T cell clone size is an important determinant affecting the need for Th1 cytokines and T cell death in tolerance induction. These data have implications for the design of tolerance strategies in transplant recipients with varying degrees of MHC mismatching.

Antisense deoxyoligonucleotides or antibodies to murine MD-1 inhibit rejection of allogeneic and xenogeneic skin grafts in C3H mice

BACKGROUND

Altered expression of murine MD-1, a molecule controlling expression of members of the interleukin (IL)-1 receptor family of signaling proteins, regulates antigen-presenting cell-induced alloreactions. We investigated the effect of treatment with antisense deoxyoligonucleotides or antibodies to MD-1 in vivo on allogeneic and xenogeneic skin graft survival and the immune responses in transplanted mice.

METHODS

C3H mice received C57BL/6 or Lewis rat skin grafts, followed by i.v. injections of anti-MD-1 antibody or antisense oligonucleotides or control reagents at 48-hr intervals. Survival was monitored. In separate studies, mice were sacrificed at 5-day intervals. Serum was analyzed for circulating MD-1 antigen, and peritoneal cells for surface expression of MD-1. The proliferative and cytolytic response of lymphocytes harvested from treated animals and restimulated in vitro with allo- or xenogeneic cells, and the cytokines produced, was measured. Graft histology was assessed at 11 days after transplantation.

RESULTS

Treatment with anti-MD-1 oligonucleotides or antibodies suppressed rejection of both xeno- and allogeneic grafts, decreased induction of graft-specific cytotoxic T cells, increased production of type-2 cytokines (IL-4 and IL-10), and decreased production of type-1 cytokines (IL-2 and interferon-gamma). Serum levels of MD-1 were suppressed, as was expression of MD-1 on the surface of antigen-presenting cells. Grafts from MD-1-treated mice showed little lymphocyte infiltration, and no signs of graft necrosis.

CONCLUSION

Our data suggest a critical in vivo role for MD-1 expression in regulating graft rejection, as well as in the concomitant sensitization of T cells and their cytokine production profile, which parallels the rejection response.

Th1 cytokines, programmed cell death, and alloreactive T cell clone size in transplant tolerance

The Th1 cytokines IL-2 and IFN-gamma, which inhibit T cell proliferation and promote activation induced cell death, may be required to diminish alloreactive T cell numbers and to foster tolerance across full allogeneic barriers. However, we hypothesized that these cytokines might be dispensable when the alloreactive T cell clone size is relatively small, as is seen in recipients of minor-mismatched grafts. We show that alloreactive T cell clone size of C57BL/6 mice against multiple minor-mismatched 129X1/sv mice was approximately 4-9-fold smaller than that against MHC-mismatched BALB/c mice. In the MHC-mismatched combination, CD28-B7 blockade by CTLA4Ig induced long-term graft survival in wild-type recipients, but this treatment was ineffective in IFNgamma(-/-) or IL-2(-/-) recipients. In contrast, in the minor-mismatched combination, CTLA4Ig induced long-term allograft survival in wild-type, IFNgamma(-/-), and IL-2(-/-) recipients. Bcl-x(L) transgenic animals, which are defective in "passive" T cell death, are likewise sensitive to the effects of CTLA4Ig only in the setting of the minor-mismatch grafts. Therefore, the alloreactive T cell clone size is an important determinant affecting the need for Th1 cytokines and T cell death in tolerance induction. These data have implications for the design of tolerance strategies in transplant recipients with varying degrees of MHC mismatching.

Cardiac apoptosis: from organ failure to allograft rejection

Cardiac myocyte apoptosis has been extensively studied in the last few years. Increased interest in the field stems from the hope that pharmacological manipulation of apoptosis may become a valuable tool for preventing excessive cell death observed in different pathological conditions. This paper is not intended as a comprehensive overview of current research about life and death in the cardiovascular system, but rather as a concise update on new developments in areas that were highlighted in a recent series of excellent reviews. A short inventory of unsolved issues concerning the significance of cardiac myocyte loss through apoptosis in both physiological and pathological circumstances is addressed.