The role of CD154 in organ transplant rejection and acceptance

Vitamin D3 combined with antibody agents suppresses alloreactive memory T-cell responses to induce heart allograft long-term survival

BACKGROUND

The pre-stored memory T cells in organ transplant patient carry a high risk of allograft rejection. The current study aimed to determine whether the allogenic response of adoptively transferred memory T cells in mice was suppressed by vitamin D3 monotherapy alone or in combination with monoclonal antibody treatment.

METHODS

Prior to vascularized heterotopic heart transplantation, naïve C57BL/6 mice were primed with memory T cells. Recipient mice were administered vitamin D3 alone or in combination with monoclonal antibodies (anti-CD40L/ anti-LFA-1). Memory T cells and CD4⁺ forkhead box P3⁺ T cells in recipient spleens were measured using flow cytometry. Additionally, the expression of cytokines was measured by ELISA and quantitative PCR. Inflammatory factors in the grafts were identified by hematoxylin and eosin staining.

RESULTS

Vitamin D3 in conjunction with anti-CD40L/ anti-LFA-1 antibodies were administered according to the median survival time from 6.5 to 80 days. The results revealed that grafts were protected through the prevention of inflammatory cell infiltration. Combined treatment decreased the mRNA levels of IL-2, IFN-γ and IL-10 and increased the mRNA levels of IL-4, Foxp3 and TGF-β in the allograft. Rejection was suppressed by a reduction of CD4⁺CD44^high CD62L⁺ and CD8⁺ CD44^high CD62L⁺ memory T cells, the induction of regulatory T cells in the recipient spleen and a reduction of serum IL-2, IFN-γ and IL-10 levels.

CONCLUSION

Vitamin D3 efficiently protected allografts from memory T-cell allo-responses when combined with anti-CD40L/anti-LFA-1 antibodies therapy.

Identification of peripheral CD154+ T cells and HLA-DRB1 as biomarkers of acute cellular rejection in adult liver transplant recipients

Decreasing graft rejection and increasing graft and patient survival are great challenges facing liver transplantation (LT). Different T cell subsets participate in the acute cellular rejection (ACR) of the allograft. Cell-mediated immunity markers of the recipient could help to understand the mechanisms underlying acute rejection. This study aimed to analyse different surface antigens on T cells in a cohort of adult liver patients undergoing LT to determine the influence on ACR using multi-parametric flow cytometry functional assay. Thirty patients were monitored at baseline and during 1 year post-transplant. Two groups were established, with (ACR) and without (NACR) acute cellular rejection. Leukocyte, total lymphocyte, percentages of CD4+ CD154+ and CD8+ CD154+ T cells, human leukocyte antigen (HLA) mismatch between recipient-donor and their relation with ACR as well as the acute rejection frequencies were analysed. T cells were stimulated with concanavalin A (Con-A) and surface antigens were analysed by fluorescence activated cell sorter (FACS) analysis. A high percentage of CD4+ CD154+ T cells (P = 0·001) and a low percentage of CD8+ CD154+ T cells (P = 0·002) at baseline were statistically significant in ACR. A receiver operating characteristic analysis determined the cut-off values capable to stratify patients at high risk of ACR with high sensitivity and specificity for CD4+ CD154+ (P = 0·001) and CD8+ CD154+ T cells (P = 0·002). In logistic regression analysis, CD4+ CD154+ , CD8+ CD154+ and HLA mismatch were confirmed as independent risk factors to ACR. Post-transplant percentages of both T cell subsets were significantly higher in ACR, despite variations compared to pretransplant. These findings support the selection of candidates for LT based on the pretransplant percentages of CD4+ CD154+ and CD8+ CD154+ T cells in parallel with other transplant factors.

Corneal xenotransplantation: Where are we standing?

The search for alternatives to allotransplants is driven by the shortage of corneal donors and is demanding because of the limitations of the alternatives. Indeed, current progress in genetically engineered (GE) pigs, the introduction of gene-editing technology by clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9, and advanced immunosuppressants have made xenotransplantation a possible option for a human trial. Porcine corneal xenotransplantation is considered applicable because the eye is regarded as an immune-privileged site. Furthermore, recent non-human primate studies have shown long-term survival of porcine xenotransplants in keratoplasty. Herein, corneal immune privilege is briefly introduced, and xenogeneic reactions are compared with allogeneic reactions in corneal transplantation. This review describes the current knowledge on special issues of xenotransplantation, xenogeneic rejection mechanisms, current immunosuppressive regimens of corneal xenotransplantation, preclinical efficacy and safety data of corneal xenotransplantation, and updates of the regulatory framework to conduct a clinical trial on corneal xenotransplantation. We also discuss barriers that might prevent xenotransplantation from becoming common practice, such as ethical dilemmas, public concerns on xenotransplantation, and the possible risk of xenozoonosis. Given that the legal definition of decellularized porcine cornea (DPC) lies somewhere between a medical device and a xenotransplant, the preclinical efficacy and clinical trial data using DPC are included. The review finally provides perspectives on the current standpoint of corneal xenotransplantation in the fields of regenerative medicine.

Thalidomide with blockade of co-stimulatory molecules prolongs the survival of alloantigen-primed mice with cardiac allografts

Background

Miscellaneous memory cell populations that exist before organ transplantation are crucial barriers to transplantation. In the present study, we used a skin-primed heart transplantation model in mouse to evaluate the abilities of Thalidomide (TD), alone or in combination with co-stimulatory blockade, using monoclonal antibodies (mAbs) against memory T cells and alloantibodies to prolong the second cardiac survival.

Results

In the skin-primed heart transplantation model, TD combined with mAbs significantly prolonged the second cardiac survival, accompanied by inhibition of memory CD8⁺ T cells. This combined treatment enhanced the CD4⁺Foxp3⁺ regulatory T cells ratio in the spleen, restrained the infiltration of lymphocytes into the allograft, and suppressed the allo-response of spleen T cells in the recipient. The levels of allo-antibodies also decreased in the recipient serum. In addition, we detected low levels of the constitutions of the lytic machinery of cytotoxic cells, which cause allograft damage.

Conclusions

Our study indicated a potential synergistic action of TD in combination with with mAbs to suppress the function of memory T cells and increase the survival of second allografts in alloantigen-primed mice.

The past, present, and future of costimulation blockade in organ transplantation

PURPOSE OF REVIEW

Manipulating costimulatory signals has been shown to alter T cell responses and prolong graft survival in solid organ transplantation. Our understanding of and ability to target various costimulation pathways continues to evolve.

RECENT FINDINGS

Since the approval of belatacept in kidney transplantation, many additional biologics have been developed targeting clinically relevant costimulation signaling axes including CD40-CD40L, inducible costimulator-inducible costimulator ligand (ICOS-ICOSL), and OX40-OX40L. Currently, the effects of costimulation blockade on posttransplant humoral responses, tolerance induction, and xenotransplantation are under active investigation. Here, we will discuss these pathways as well as preclinical and clinical outcomes of biologics targeting these pathways in organ transplantation.

SUMMARY

Targeting costimultion is a promising approach for not only controlling T cell but also B cell responses. Consequently, costimulation blockade shows considerable potential for improving outcomes in antibody-mediated rejection and xenotransplantation.

Development of transplant immunosuppressive agents - considerations in the use of animal models

INTRODUCTION

The development of all immunosuppressant agents to date has involved the experimental use of large and small animal models. Over the last half-century, immunosuppressive drugs have extended the lives of transplant patients worldwide. However, the use of animal models in the development of these drugs is not perfect, and this has brought to light a number of issues including idiosyncratic reactions that are found in animal models but not in humans. The 2006 highly publicized case of the 'elephant man' TGN 1412 drug trial highlights the importance of being cogent of the limitations of animal models. Areas covered: This review covers the utility and limitations of the use of animal models for the development of immunosuppressant agents. This includes both large and small animal models, particularly rodent models in the transplant setting. Expert opinion: The use of animal models represents a critical stage in the development of immunosuppressive drugs. Limitations include physiological differences to humans; this is especially true of immunologically naïve lab rodents with small memory cell populations. Toxic drug levels may differ widely between species. Animal models are also costly and raise ethical concerns. However, there is currently no way to recreate the complex environment of the human immune system purely in vitro.

Correlation Between Percentage of Immuncompetent CD4+ and CD4+CD25+ Cells and Compatibility in the HLA System and Selected Parameters Assessing Transplanted Kidney Function

BACKGROUND

Long-term kidney allograft survival is affected by many coexisting immunologic factors. Currently, only two basic immunologic parameters-HLA compatibility and panel reactive antibodies-are routinely used in kidney transplantation management. At the same time, there is a great need for immunologic biomarkers that will help inrease understanding of kidney transplant immunology and improve clinical care of kidney recipients. T regulatory cells (Tregs) represent one of the major targets of this approach. The aim of this study was to investigate possible simple associations between Tregs count in recipients' blood and other routinely assessed or easily accessible laboratory parameters.

METHODS

Laboratory outcomes from medical files of transplant outpatient clinic in combination with flow cytometry analyses of particular immunocompetent cells populations were used. Flow cytometry was used to calculate Tregs recognized as TCD4⁺CD25^high. The Spearman rank correlation test was used to verify particular associations.

RESULTS

A negative correlation was found beween HLA compatibility and Tregs count as well as between platelets count and Tregs count.

CONCLUSIONS

Whereas the negative correlation between Tregs and platelets counts may possibly mirror some recent findings in basic research, a negative correlation between HLA compatibility and Tregs points the direction of further research to factors triggering post-transplant immune tolerance.

The utility of animal models in developing immunosuppressive agents

The immune system comprises an integrated network of cellular interactions. Some responses are predictable, while others are more stochastic. While in vitro the outcome of stimulating a single type of cell may be stereotyped and reproducible, in vivo this is often not the case. This phenomenon often merits the use of animal models in predicting the impact of immunosuppressant drugs. A heavy burden of responsibility lies on the shoulders of the investigator when using animal models to study immunosuppressive agents. The principles of the three R׳s: refine (less suffering,), reduce (lower animal numbers) and replace (alternative in vitro assays) must be applied, as described elsewhere in this issue. Well designed animal model experiments have allowed us to develop all the immunosuppressive agents currently available for treating autoimmune disease and transplant recipients. In this review, we examine the common animal models used in developing immunosuppressive agents, focusing on drugs used in transplant surgery. Autoimmune diseases, such as multiple sclerosis, are covered elsewhere in this issue. We look at the utility and limitations of small and large animal models in measuring potency and toxicity of immunosuppressive therapies.

Selected hemostatic parameters in patients with pancreatic tumors

INTRODUCTION

Recent experimental studies have suggested that various coagulation-related molecules may be important players in the development and progression of pancreatic cancer. However, these findings have not yet been verified in a clinical setting.

METHODS

In this study, we comprehensively examined the levels of multiple hemostatic substances, including prothrombin, antithrombin, plasminogen, thrombin-anti-thrombin (TAT) and plasmin-anti-plasmin (PAP) complexes, as well as, soluble CD40 (sCD40) in patients diagnosed with pancreatic cancer (n = 37) or other tumors (neuroendocrine neoplasms - NEN [n = 7] or solid pseudopapillary tumors-SPT [n = 3]), and healthy individuals (n = 31).

RESULTS

We found significantly higher anti-thrombin, PAP and sCD40 levels in patients with pancreatic cancer compared to healthy controls and patients diagnosed with other types of pancreatic tumors (for all, at least p < 0.05). Cancer patients had lower plasminogen concentrations than individuals from the other analyzed groups (for both, p < 0.05). None of the examined coagulation-related parameters was significantly associated with neither systemic sCD40 concentrations nor clinical staging of malignancy. Levels of analyzed molecules were comparable between pancreatic cancer patients presenting with early and advanced disease. Moreover, our study identified a potential diagnostic value of prothrombin/TAT and anti-thrombin/TAT coefficients in detection of pancreatic cancer in humans. However, both of these were inferior to currently used marker-CA19.9.

CONCLUSIONS

Subclinical hemostatic alterations (mainly in plasmin-related molecules) i) appear as soon as during the earliest stages of the pancreatic adenocarcinoma development in humans, ii) do not seem to alter within progression of the disease nor are associated with clinical staging, iii) are not observed in patients with other types of pancreatic tumors, as well as, iv) do not seem to be associated with elevated sCD40 concentrations in pancreatic cancer patients. Moreover, examined thrombin- and plasmin-related substances do not appear to possess a sufficient diagnostic value to serve as makers of pancreatic adenocarcinoma in humans.

Synergic silencing of costimulatory molecules prevents cardiac allograft rejection

Background

While substantial progress has been made in blocking acute transplant rejection with the advent of immune suppressive drugs, chronic rejection, mediated primarily by recipient antigen presentation, remains a formidable problem in clinical transplantation. We hypothesized that blocking co-stimulatory pathways in the recipient by induction of RNA interference using small interference RNA (siRNA) expression vectors can prolong allogeneic heart graft survival.

Method

Vectors expressing siRNA specifically targeting CD40 and CD80 were prepared. Recipients (BALB/c mice) were treated with CD40 and/or CD80 siRNA expression vectors via hydrodynamic injection. Control groups were injected with a scrambled siRNA vector and sham treatment (PBS). After treatment, a fully MHC-mismatched (BALB/c to C57/BL6) heart transplantation was performed.

Result

Allogeneic heart graft survival (>100 days) was approximately 70% in the mice treated simultaneously with CD40 and CD80 siRNA expression vectors with overall reduction in lymphocyte interstitium infiltration, vascular obstruction, and edema. Hearts transplanted into CD40 or CD80 siRNA vector-treated recipients had an increased graft survival time compared to negative control groups, but did not survive longer than 40 days. In contrast, allogenic hearts transplanted into recipients treated with scrambled siRNA vector and PBS stopped beating within 10–16 days. Real-time PCR (RT-PCR) and flow cytometric analysis showed an upregulation of FoxP3 expression in spleen lymphocytes and a concurrent downregulation of CD40 and CD80 expression in splenic dendritic cells of siRNA-treated mice. Functional suppressive activity of splenic dendritic cells (DCs) isolated from tolerant recipients was demonstrated in a mixed lymphocyte reaction (MLR). Furthermore, DCs isolated from CD40- and CD80-treated recipients promoted CD4 + CD25 + FoxP3+ regulatory T cell differentiation in vitro.

Conclusion

This study demonstrates that the simultaneous silencing of CD40 and CD80 genes has synergistic effects in preventing allograft rejection, and may therefore have therapeutic potential in clinical transplantation.

CD154 blockade modulates the ratio of Treg to Th1 cells and prolongs the survival of allogeneic corneal grafts in mice

Administration of anti-CD154 monoclonal antibody (mAb) may prolong the survival of an allograft; however, the associated therapeutic mechanisms remain poorly understood. This study aimed to evaluate the effects of anti-CD154 mAb on T-cell responses in a mouse model of corneal allograft transplantation. BALB/c mice were transplanted with corneal grafts from C57BL/6 mice and treated intraperitoneally with 250 μg anti-CD154 mAb or isotype IgG on days 0, 3 and 6 post surgery. The transparency of the corneal grafts was evaluated for potential rejection signs by slit-lamp biomicroscopy and histopathology. The percentages of CD4⁺ T, Tim-3⁺CD4⁺ T helper (Th) 1 and CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) in the spleen, ipsilateral draining lymph nodes and corneal grafts, and the frequency of splenic IFN-γ⁺ and IL-10⁺ expression in CD4⁺ T cells were determined by flow cytometry. Moreover, the ratio of Tregs to Th1 cells was calculated and the suppressive activity of splenic Tregs was measured. Anti-CD154 neutralization significantly prolonged the survival of the corneal allograft (P=0.0012) and reduced the numbers of inflammatory infiltrates in the corneal graft. In the spleen and lymph nodes, anti-CD154 treatment reduced the frequency of CD4⁺ T cells, Tregs and particularly Th1 cells. In the corneal allografts, anti-CD154 treatment downregulated graft-infiltrated CD4⁺ T cells and Th1 cells, but increased graft-infiltrated Tregs. Furthermore, anti-CD154 treatment increased the frequency of splenic IL-10⁺CD4⁺ T cells and decreased the concentration of splenic IFN-γ⁺CD4⁺ T cells. As a result, the ratio of Tregs to Th1 cells in the anti-CD154-treated recipients increased. Anti-CD154 treatment did not enhance the suppressive activity of Tregs in the recipients. The results indicate that the therapeutic effects of anti-CD154 mAb on prolonging the survival of the corneal allograft may be associated with an increased ratio of Tregs to Th1 cells in mice.

Platelet-derived CD154: ultrastructural localization and clinical correlation in organ transplantation

CD154 is an immunostimulatory ligand for CD40 that markedly influences alloimmunity. Its presence in platelets suggests that its release and subsequent immune effects are driven by trauma and thus could be relevant following organ transplantation. However, the release of platelet derived CD154 and its consequences have not been investigated in a clinical transplant setting. To better characterize the relationship between platelet activation and CD154 release, we investigated CD154 release by platelets obtained from normal individuals, and patients with two genetic defects that influence platelet granule development. Using these unique patient populations and immune-electron microscopy, we confirmed that CD154 was an alpha granule and not a cell surface protein, and thereafter optimized the methods for its in vivo measurement in humans. We then investigated plasma CD154 levels in kidney and liver transplant recipients and found no evidence that CD154 levels fluctuated systemically as a result of kidney or liver transplant procedures. Paradoxically, we found that kidney transplant patients had significantly lower systemic CD154 levels during episodes of rejection. These data suggest that the immune effects of CD154 are likely mediated through local and not systemic mechanisms, and discourage the use of CD154 as a peripheral biomarker in organ transplantation.

T cells interact with T cells via CD40-CD154 to promote autoimmunity in type 1 diabetes

We have investigated the role of CD40 signaling in islet-reactive, diabetogenic CD4(+) Th1 T-cell clones. Using multispectral flow cytometry, we showed that CD40 and CD154 are co-expressed and form complexes on the surface of activated T cells. We also demonstrate that activated Tcells can transactivate CD4(+) CD40(+) T cells through the CD40-CD154 pathway. To investigate the role of CD40 signaling on Th1 cells, we used the diabetogenic clone BDC-5.2.9 retrovirally transduced with a truncated form of the CD40 molecule to produce a CD40 dominant-negative T-cell clone. Upon challenge with antigen in vitro, the production of IFN-&#x003B3; by BDC-5.2.9 CD40DN was greatly reduced and, in vivo, the dominant-negative variant was unable to induce diabetes. Transduction with the CD40DN vector was also effective in preventing transfer of disease by primary NOD CD4(+) T cells. Ex vivo analysis of pancreatic infiltrates after transfer of BDC-5.2.9 CD40DN cells revealed an overall reduction of cell numbers and cytokine production by both T cells and macrophages. These data indicate that CD40 is an important signaling molecule on autoreactive CD4(+) T cells and contributes to their pathogenic effector function.

Blockade of CD27/CD70 pathway to reduce the generation of memory T cells and markedly prolong the survival of heart allografts in presensitized mice

BACKGROUND

Alloreactive memory T cells are a major obstacle to transplantation acceptance due to their capacity for accelerated rejection.

METHODS

C57BL/6 mice that had rejected BALB/c skin grafts 4 weeks earlier were used as recipients. The recipient mice were treated with anti-CD154/LFA-1 with or without anti-CD70 during the primary skin transplantation and anti-CD154/LFA-1 or not during the secondary transplantation of BALB/c heart. We evaluated the impact of combinations of antibody-mediated blockade on the generation of memory T cells and graft survival after fully MHC-mismatched transplantations.

RESULTS

One month after the primary skin transplantation, the proportions of CD4(+) memory T cells/CD4(+) T cells and CD8(+)memory T cells/CD8(+) T cells in the anti-CD154/LFA-1 combination group were 47.32±4.28% and 23.18±2.77%, respectively. In the group that included anti-CD70 treatment, the proportions were reduced to 34.10±2.71% and 12.19±3.52% (P<0.05 when comparing the proportion of memory T cells between the two groups). The addition of anti-CD70 to the treatment regimen prolonged the mean survival time following secondary heart transplantation from 10days to more than 90days (P<0.001). Furthermore, allogenic proliferation of recipient splenic T cells and graft-infiltrating lymphocytes were significantly decreased. Meanwhile, the proportion of regulatory T cells was increased to 9.46±1.48% on day 100 post-transplantation (P<0.05).

CONCLUSIONS

The addition of anti-CD70 to the anti-CD154/LFA-1 combination given during the primary transplantation reduced the generation of memory T cells. This therapy regimen provided a potential means to alleviate the accelerated rejection mediated by memory T cells during secondary heart transplantation and markedly prolong the survival of heart allografts.

Monoclonal antibody treatment to prolong the secondary cardiac allograft survival in alloantigen-primed mice

We have previously shown that costimulation blockade using a combination of monoclonal antibodies (mAbs) - CTLA4Ig, antibodies to CD154, LFA-1, and OX40L - can induce tolerance of cardiac allografts in mice with adoptively transferred CD4(+) memory T cells [1]. However, the effect of costimulatory blockade in secondary allograft rejection has not been studied. B6 mice that rejected BALB/c skin grafts for more than 4 weeks (defined as alloantigen-primed mice) were used as recipients. The recipient mice were treated with the mAbs to CD154, LFA-1, OX40L, and CD122 on days 0, 2, 4, and 6 after the secondary transplantation of BALB/c heart. The mean survival time (MST) of secondary cardiac allografts in rats treated with antibodies to CD154 and LFA-1 (2-antibodies approach) and those treated with antibodies to CD154, LFA-1, OX40L, and CD122 (4-antibodies approach) was greater than that of the controls (MST = 6.7 days, 22.2 days, and 3.2 days, respectively). The 4-antibodies approach prevented lymphocytic infiltration in the grafts, inhibited memory T-cells proliferation in the spleen, increased IL-10 secretion in the serum, and enhanced the expression of CD4(+) Foxp3(+) regulatory T cells (Tregs) in spleen. Expression levels of alloreactive antibodies were high in the recipient mice of experimental and control groups. Inhibiting the memory T cells by costimulation blockade extended allograft survival in secondary transplant models but could not induce tolerance of graft. Alloreactive antibodies may participate in alloresponse and play an important role in secondary cardiac allograft rejection.

Oligonucleotide based-strategies for allergy with special reference to siRNA

BACKGROUND

Allergic diseases are a significant global health care problem. Current pharmacological approaches address symptoms but do not alter the underlying immune dysregulation. Current allergen-specific immunotherapy has several drawbacks. Therefore, approaches that attenuate allergic responses safely and effectively at the level of upstream causative events are desirable. Oligonuleotide-based therapies [CpG DNA, antisense oligonucleotides, and small interfering RNA (siRNA)] are promising approaches.

OBJECTIVE/METHODS

We review developments in oligonucleotide-based therapies and the potential of siRNA for treating allergy.

RESULTS/CONCLUSIONS

Strategies with oligonucleotides basically aim to reduce T helper type 2 (Th2) responses. It is controversial whether the reduction of Th2 responses does, in fact, attenuate allergic diseases. Increased understanding of allergic mechanisms will enhance the efficacy of oligonucleotide-based therapy.

OX40 costimulation prevents allograft acceptance induced by CD40-CD40L blockade

Disrupting the CD40-CD40L costimulation pathway promotes allograft acceptance in many settings. Herein, we demonstrate that stimulating OX40 overrides cardiac allograft acceptance induced by disrupting CD40-CD40L interactions. This effect of OX40 stimulation was dependent on CD4(+) T cells, which in turn provided help for CD8(+) T cells and B cells. Allograft rejection was associated with donor-reactive Th1 and Th2 responses and an unconventional granulocytic infiltrate and thrombosis of the arteries. Interestingly, OX40 stimulation induced a donor-reactive IgG class switch in the absence of CD40-CD40L interactions, and the timing of OX40 stimulation relative to transplantation affected the isotype of donor-reactive Ab produced. Inductive OX40 stimulation induced acute graft rejection, which correlated with both IgG1 and IgG2a deposition within the graft. Once graft acceptance was established following CD40-CD40L blockade, delayed OX40 stimulation did not induce acute allograft rejection despite priming of graft-reactive Th1 and Th2. Rather, chronic rejection was induced, which was characterized by IgG1 but not IgG2a deposition within the graft. These studies reveal both redundancy and key differences in function among costimulatory molecules that manifest in distinct pathologies of allograft rejection. These findings may help guide development of therapeutics aimed at promoting graft acceptance in transplant recipients.

Platelets influence vascularized organ transplants from start to finish

This review relates the basic functions of platelets to specific aspects of organ allograft rejection. Platelet activation can occur in the donor or recipient before transplantation as well as during antibody- and cell-mediated rejection. Biopsies taken during organ procurement from cadaver donors have documented that activated platelets are attached to vascular endothelial cells or leukocytes. In addition, many patients waiting for transplants have activated platelets due to the diseases that lead to organ failure or as a result of interventions used to support patients before and during transplantation. The contribution of platelets to hyperacute rejection of both allografts and xenografts is well recognized. Intravascular aggregates of platelets can also be prominent in experimental and clinical transplants that undergo acute antibody or cell-mediated rejection. In acute rejection, platelets can recruit mononuclear cells by secretion of chemokines. After contact, monocytes, macrophages and T cells interact with platelets through receptor/ligand pairs, including P-selectin/PSGL-1 and CD40/CD154. There is a potential for therapy to inhibit platelet mediated immune stimulation, but it is counterbalanced by the need to maintain coagulation in the perioperative period.

CD8+ Th17 mediate costimulation blockade-resistant allograft rejection in T-bet-deficient mice

While studying Th responses induced by cardiac transplantation, we observed that mice deficient in the Th1 transcription factor T-bet (T-bet(-/-)) mount both Th1 and Th17 responses, whereas wild-type recipients mount only Th1 responses. Cells producing both IFN-gamma and IL-17 were readily detectable within the rejecting graft of T-bet(-/-) recipients, but were absent from the spleen, indicating that the in vivo microenvironment influences Th function. In addition, disrupting CD40-CD40L costimulatory interactions was highly effective at prolonging allograft survival in WT mice, but ineffective in T-bet(-/-) recipients. In this study, we report that CD8(+) Th17 mediate costimulation blockade-resistant rejection in T-bet(-/-) allograft recipients. Depleting CD8(+) cells or neutralizing IL-17 or the Th17-inducing cytokine IL-6 ablated the Th17 response and reversed costimulation blockade-resistant graft rejection. Neutralizing IL-4 in IFN-gamma(-/-) allograft recipients did not induce Th17, suggesting that T-bet, rather than IL-4 and IFN-gamma (known inhibitors of Th17), plays a critical role in negatively regulating Th17 in the transplant setting.

Transplant acceptance following anti-CD4 versus anti-CD40L therapy: evidence for differential maintenance of graft-reactive T cells

Inductive therapy with anti-CD4 or anti-CD40L monoclonal antibodies (mAb) leads to long-term allograft acceptance but the immune parameters responsible for graft maintenance are not well understood. This study employed an adoptive transfer system in which cells from mice bearing long-term cardiac allografts following inductive anti-CD4 or anti-CD40L therapy were transferred into severe combined immunodeficiency (SCID) allograft recipients. SCID recipients of cells from anti-CD4-treated mice (anti-CD4 cells) did not reject allografts while those receiving cells from anti-CD40L-treated mice (anti-CD40L cells) did reject allografts. Carboxyfluorescein succinimidyl ester (CFSE) labeling of transferred cells revealed that this difference was not associated with differential proliferative capacities of these cells in SCID recipients. Like cells from naïve mice, anti-CD40L cells mounted a Th1 response following transfer while anti-CD4 cells mounted a dominant Th2 response. Early (day 10) T-cell priming was detectable in both groups of primary allograft recipients but persisted to day 30 only in recipients treated with anti-CD4 mAb. Thus, anti-CD40L therapy appears to result in graft-reactive T cells with a naïve phenotype while anti-CD4 therapy allows progression to an altered state of differentiation. Additional data herein support the notion that anti-CD40L mAb targets activated, but not memory, cells for removal or functional silencing.

Novel vaccination for allergy through gene silencing of CD40 using small interfering RNA

Small interfering RNA (siRNA) is a potent means of inducing gene-specific silencing. Gene silencing strategies using siRNA have demonstrated therapeutic benefits in animal models of various diseases, and are currently in clinical trials. However, the utility of gene silencing as a treatment for allergic diseases has not yet been reported. In this study, we report a novel therapy for allergy through gene silencing of CD40, a critical costimulatory molecule and a key factor in allergic immune responses. Silencing CD40 resulted in generation of immunoregulatory dendritic cells (DCs). Administration of CD40 siRNA remarkably reduced nasal allergic symptoms and local eosinophil accumulation in the OVA-induced allergic mice. The OVA-specific T cell response was inhibited after the CD40 siRNA treatment. Additionally, anti-OVA specific IgE and production of IL-4 and IL-5 of T cells stimulated by OVA were significantly decreased in CD40 siRNA-treated mice. Furthermore, we demonstrated that the therapeutic effects by CD40 siRNA were associated with impaired Ag-presenting functions of DCs and B cells, and generation of regulatory T cells. The present study highlights a therapeutic potential of siRNA-based treatment for allergic diseases.

Mechanisms underlying B-cell tolerance induction by antigen-immunoglobulin G gene transfer

Previous studies on the mechanisms underlying tolerance induction in diabetes have mainly focused on T cells, however B cells also have an important role in diabetes. Based on our previous studies that splenocytes, transduced with glutamic acid decarboxylase (GAD) 65 fused to immunoglobulin (Ig) G carrier, reduced antibody-mediated response in non-obese diabetic (NOD) mice, here we examined the mechanisms underlying B-cell tolerance in this system. We found that GAD-IgG-transduced splenocytes did not reduce CD40 expression on B-cells in NOD mice, but they did downregulate CD40 ligand (CD40L) expression. Furthermore, anti-CD40L injection reduced autoantibody levels in NOD mice and in vitro experiments demonstrated that CD40L blockade reduced the antigenpresenting capability of B-cells. In conclusion, the results of this study suggest that downregulation of CD40L may be one mechanism underlying the induction of B-cell tolerance in GAD-IgG-treated NOD mice.

Recent Progress in Tolerance Induction through Mixed Chimerism

Organ transplant recipients require life-long treatment with immunosuppressive drugs. Currently available immunosuppression is associated with substantial morbidity and mortality, and is ineffective in inhibiting chronic rejection and graft loss. Therefore, a permanent state of donor-specific tolerance remains a primary goal for transplantation research. The induction of mixed hematopoietic chimerism is an attractive concept in this regard. Hematopoietic chimerism modulates the immunologic repertoire by extending the mechanisms of self-tolerance to donor-specific allotolerance. Despite recent progress in developing nontoxic bone marrow transplantation protocols for rodents, translation to large animals has remained difficult. Here, we outline the concept of tolerance via mixed chimerism, and review recent progress and remaining challenges in bringing this approach to the clinical setting.

Long-term n-3 polyunsaturated fatty acids administration ameliorates arteriosclerosis by modulating T-cell activity in a rat model of small intestine transplantation

BACKGROUND

Fish oil, rich in n-3 polyunsaturated fatty acids (n-3 PUFAs), has been found to reduce graft rejection and increase allografts survival. But these studies mainly focused on acute rejection. We imitated long-term fish oil administration to investigate the effects of n-3 PUFAs on graft arteriosclerosis, and T cells in a rat model of small intestine transplantation.

METHODS

From 2 weeks pre-transplantation to the 60th day post-transplantation, the Lewis rats were supplemented by gavage with phosphate buffer saline, corn oil and fish oil respectively. Total small intestine was heterotopically transplanted from F344 to Lewis rat. Graft arteriosclerosis was assessed by histological grading of intimal thickening. The expression of CD25 and CD154, IL-2 level, and NF-kappaB activation in T cells were analyzed by western blotting, ELISA, and electrophoretic mobility shift assay respectively.

RESULTS

Compared with corn oil, graft arteriosclerosis was ameliorated by fish oil significantly. The expression of CD25 and CD154, IL-2 level, and NF-kappaB activation were markedly reduced by fish oil.

CONCLUSIONS

Long-term n-3 PUFAs administration pre- and post-transplantation could inhibit T-cell activity by reducing CD154 expression and NF-kappaB activation, which might contribute to amelioration of graft arteriosclerosis.

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

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

The impact of memory T cells on rejection and the induction of tolerance

Accumulating evidence suggests that alloreactive memory T cells (Tm) may be generated in transplant recipients that have not previously been exposed to alloantigen through mechanisms such as cross-reactivity and homeostatic proliferation. The presence of Tm correlates with both acute and chronic rejection episodes and, furthermore, may be responsible for the failure to induce tolerance in large animal and clinical settings. A clearer understanding of how Tm function and their requirements to mount an effective response to alloantigen will be key to further attempts to translate tolerance induction protocols from the experimental setting to the clinic.

Short-Term Anti-CD40 Ligand Costimulatory Blockade Induces Tolerance to Peripheral Nerve Allografts, Resulting in Improved Skeletal Muscle Function

BACKGROUND

Reconstruction of long or multiple peripheral nerve defects with peripheral nerve autografts may not be possible due to insufficient quantities of donor nerve. There are promising preliminary data that nerve allografting has the potential to improve functional outcome and quality of life after devastating nerve injuries or large tumor resections. The authors previously demonstrated that blockade of the CD40/CD40 ligand costimulatory pathway, via anti-CD40 ligand monoclonal antibody (MR1) therapy, induces tolerance to peripheral nerve allografts in mice. In this study, the authors sought to correlate the immunomodulatory effects of MR1 treatment with functional muscle recovery after peripheral nerve allografting in the murine model.

METHODS

In the mouse hindlimb model, peroneal nerve isografts (C57BL/6 into C57BL/6) and allografts (BALB/c into C57BL/6) were utilized to reconstruct 0.8-cm peroneal nerve gaps. MR1 versus vehicle was administered on days 0, 1, and 2. At 60 days after transplantation, splenocyte production of interferon-gamma and interleukins 2, 4, and 5 were quantified using ELISPOT analysis, and in vitro maximum tetanic isometric force of the extensor digitorum longus muscle was measured.

RESULTS

At 60 days after transplantation, immunomodulation persisted in MR1-treated, allografted animals, as evidenced by significantly muted interferon-gamma, interleukin 4, and interleukin 2 splenocyte production. Functional extensor digitorum longus muscle recovery after nerve allografting and MR1 administration was improved due to the tolerance induced by MR1 compared with untreated allograft recipients.

CONCLUSIONS

Three-day inductive therapy with MR1 produces 60-day immunologic tolerance to peripheral nerve allografts, as evidenced by dramatic decreases in interferon-gamma, interleukin 4, and interleukin 2 production, and results in increased muscle force recovery. This work emphasizes the potential promise of CD40-CD40 ligand costimulatory blockade in reducing or eliminating peripheral nerve allograft rejection.

Platelet-derived or soluble CD154 induces vascularized allograft rejection independent of cell-bound CD154

CD154 is a cell surface molecule expressed on activated T cells that binds to CD40, an activating molecule on APCs. Its blockade has been shown to prevent allograft rejection, presumably by interrupting interactions between T cells and APCs. It is known that activated human platelets express and shed CD154 and can induce APC activation and other immune processes in vitro. Here we show that platelet-derived CD154 is sufficient to initiate cardiac allograft rejection independent of any cellular source of this molecule. CD154-KO mice reject cardiac allografts after receiving CD154-expressing human platelets or recombinant CD154 (rCD154) trimers. Treatment with the human CD154-specific mAb 5c8 specifically prevents this induced rejection. Soluble trimers, but not platelets, induce rejection when infused temporally remote from the surgical procedure, suggesting that surgically induced platelet activation is required for CD154 release. Allograft rejection can thus be instigated by activated platelets through CD154. These data implicate platelets as a proximal component of acquired alloimmunity, providing insight into the mechanisms of allograft rejection and the physiological response to trauma in general.

IDEC-131 (anti-CD154), sirolimus and donor-specific transfusion facilitate operational tolerance in non-human primates

CD154-specific antibody therapy prevents allograft rejection in many experimental transplant models. However, initial clinical transplant trials with anti-CD154 have been disappointing suggesting the need for as of yet undetermined adjuvant therapy. In rodents, donor antigen (e.g., a donor blood transfusion), or mTOR inhibition (e.g., sirolimus), enhances anti-CD154's efficacy. We performed renal transplants in major histocompatibility complex-(MHC) mismatched rhesus monkeys and treated recipients with combinations of the CD154-specific antibody IDEC-131, and/or sirolimus, and/or a pre-transplant donor-specific transfusion (DST). Therapy was withdrawn after 3 months. Triple therapy prevented rejection during therapy in all animals and led to operational tolerance in three of five animals including donor-specific skin graft acceptance in the two animals tested. IDEC-131, sirolimus and DST are highly effective in preventing renal allograft rejection in primates. This apparently clinically applicable regimen is promising for human renal transplant trials.

Development of a Chimeric Anti-CD40 Monoclonal Antibody That Synergizes with LEA29Y to Prolong Islet Allograft Survival

In recent years, reagents have been developed that specifically target signals critical for effective T cell activation and function. Manipulation of the CD28/CD80/86 and CD40/CD154 pathways has exhibited extraordinary efficacy, particularly when the pathways are blocked simultaneously. Despite the reported efficacy of anti-CD154 in rodents and higher models, its future clinical use is uncertain due to reported thromboembolic events in clinical trials. To circumvent this potential complication, we developed and evaluated a chimeric Ab targeting CD40 (Chi220, BMS-224819) as an alternative to CD154. Although Chi220 blocks CD154 binding, it also possesses partial agonist properties and weak stimulatory potential. The anti-CD40 was tested alone and in combination with a rationally designed, high affinity variant of CTLA4-Ig, LEA29Y (belatacept), in a nonhuman primate model of islet transplantation. Although either agent alone only modestly prolonged islet survival (Chi220 alone: 14, 16, and 84 days; LEA29Y alone: 58 and 60 days), their combination (LEA29Y and Chi220) dramatically facilitated long term survival (237, 237, 220, >185, and 172 days). We found that the effects of Chi220 treatment were not mediated solely through deletion of CD20-bearing cells and that the combined therapy did not significantly impair established antiviral immunity.

Anti-CD40 Ligand Antibody Permits Regeneration through Peripheral Nerve Allografts in a Nonhuman Primate Model

Systemic immunosuppression is typically required to prevent allograft rejection. Antibody-based therapies that induce immune unresponsiveness represent an appealing alternative to nonspecific immunosuppression, which is often associated with significant morbidity. In mice, successful prevention of nerve allograft rejection has been demonstrated through interference with the CD40/CD40 ligand interaction. This study investigated the effectiveness of anti-CD40 ligand monoclonal antibody as single-agent therapy in preventing rejection and supporting nerve regeneration across long nerve allografts in nonhuman primates. Twelve outbred cynomolgus macaques were arranged into six genetically mismatched pairs, with each animal receiving a 5-cm ulnar nerve allograft in the right arm and a 5-cm autograft in the left arm. Mixed lymphocyte reaction assays were used to assess resulting immune unresponsiveness. Treated animals (n = 10) received anti-CD40 ligand monoclonal antibody 10 mg/kg one time, locally applied, and 20 mg/kg systemically on postoperative days 0, 1, 3, 10, 18, and 28, and then monthly. Untreated animals (n = 2) served as the untreated controls. At 4 or 6 months after transplantation, nerves were harvested for histological analysis. Four treated animals underwent an additional challenge after cessation of anti-CD40 ligand monoclonal antibody therapy and nerve graft harvests. Autogenous and allogeneic skin and nerve inlay grafting was performed to assess the permanence of immune unresponsiveness induced by anti-CD40 ligand monoclonal antibody. Animals that received anti-CD40 ligand monoclonal antibody demonstrated robust regeneration across nerve allografts, similar to that seen in the autograft control in the contralateral arm. The histomorphometric analysis of allografts in the untreated animals demonstrated significantly worse measurements compared with their matched autograft controls. Animals that received anti-CD40 ligand monoclonal antibody with concomitant skin allografts had virtually no evidence of nerve regeneration through allografts. Allogeneic skin and nerve allografts applied 2 to 12 months after withdrawal of anti-CD40 ligand monoclonal antibody therapy were consistently rejected. This study demonstrates that anti-CD40 ligand monoclonal antibody prevents rejection and allows regeneration of peripheral nerve allografts in nonhuman primates. The effect of anti-CD40 ligand monoclonal antibody appears to be transient, however, with restoration of immunocompetence shortly after withdrawal of therapy.

The contribution of Fc effector mechanisms in the efficacy of anti-CD154 immunotherapy depends on the nature of the immune challenge

Blockade of the CD154-CD40 co-stimulatory pathway with anti-CD154 mAbs has shown impressive efficacy in models of autoimmunity and allotransplantation. Clinical benefit was also demonstrated in systemic lupus erythematosus (SLE) and idiopathic thrombocytopenia patients with the humanized anti-CD154 mAb, 5C8 (hu5C8). However, thromboembolic complications that occurred during the course of the hu5C8 clinical trials have proven to be a major setback to the field and safe alternative therapeutics targeting the CD154-CD40 pathway are of great interest. Recently, effector mechanisms have been shown to play a part in anti-CD154 mAb-induced transplant acceptance in murine models, while this issue remains unresolved for humoral-mediated models. Herein, aglycosyl anti-CD154 mAbs with reduced binding to FcgammaR and complement were used as a novel means to test the role of effector mechanisms in non-human primate and murine models not amenable to gene knockout technology. While aglycosyl hu5C8 mAb was relatively ineffective in rhesus renal and islet allotransplantation, it inhibited primary and secondary humoral responses to a protein immunogen in cynomolgus monkeys. Moreover, an aglycosyl, chimeric MR1 mAb (muMR1) prolonged survival and inhibited pathogenic auto-antibody production in a murine model of SLE. Thus, the mechanisms required for efficacy of anti-CD154 mAbs depend on the nature of the immune challenge.

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.

CD40/CD154 interactions at the interface of tolerance and immunity

Development of the acquired immune response is dependent on the signaling of CD40 by its ligand, CD154. These molecules govern both the magnitude and quality of humoral- and cell-mediated immunity. A litany of studies have conclusively documented that blockade of this ligand-receptor pair can prevent, and also intervene in, the progression of antibody- and cell-mediated autoimmune diseases, and can instill long-lived allogeneic and xenogeneic graft tolerance. Many effector mechanisms of inflammation are abolished as a result of CD154 blockade, but we are now beginning to understand that CD154 blockade may, in some instances, engender long-lived, antigen-specific tolerance. In the context of transplantation tolerance, we present a hypothesis that alpha CD154 blockade is most effective at inducing long-lived allospecific tolerance if anergy and regulation can be elicited prior to the onslaught of inflammation that is induced by grafting (preemptive tolerance). This facet of alpha CD154-induced tolerance appears to co-opt the normal processes of peripheral tolerance induced by immature DCs and can be exploited to induce long-lived antigen-specific tolerance. The underlying science and the prospects for inducing long-lived antigen-specific tolerance in a model of allograft tolerance through CD154 blockade are presented and discussed.

Requirement for Donor and Recipient CD40 Expression in Cardiac Allograft Rejection: Induction of Th1 Responses and Influence of Donor-Derived Dendritic Cells

Costimulation through the CD40-CD40 ligand (CD40L) pathway is critical to allograft rejection, in that anti-CD40L mAb therapy prolongs allograft survival. However, the majority of studies exploring CD40-CD40L interactions have targeted CD40L. Less is known about the requirement for donor- and/or host-derived CD40 during rejection. This study assessed the relative contributions of donor and recipient CD40 expression to the rejection process. As the effectiveness of costimulatory blockade may be mouse strain dependent, this study explored the requirement for donor and recipient CD40 expression in BALB/c and C57BL/6 mice. Wild-type (WT) and CD40(-/-) BALB/c recipients readily rejected WT and CD40(-/-) C57BL/6 allografts, and rejection was associated with a prominent Th1 response. In contrast, CD40(-/-) C57BL/6 recipients failed to reject WT or CD40(-/-) BALB/c allografts and did not mount Th1 or Th2 responses. However, injection of donor CD40(-/-) dendritic cells induced both Th1 and Th2 responses and allograft rejection in CD40(-/-) C57BL/6 recipients. Finally, WT C57BL/6 mice rejected CD40(-/-) allografts, but this rejection response was associated with muted Th1 responses. These findings demonstrate that 1) CD40 expression by the recipient or the graft may impact on the immune response following transplantation; 2) the requirement for CD40 is influenced by the mouse strain; and 3) the requirement for CD40 in rejection may be bypassed by donor DC. Further, as CD40 is not required for rejection in BALB/c recipients, but anti-CD40L mAb prolongs graft survival in these mice, these results suggest that anti-CD40L therapy functions at a level beyond disruption of CD40-CD40L interactions.

Anti-CD40 ligand monoclonal antibody induces a permissive state, but not tolerance, for murine peripheral nerve allografts

Anti-CD40 ligand monoclonal antibody prevents the interaction between CD40 and its T-cell-based ligand, thereby resulting in selective inhibition of T cell costimulation without pan-T-cell suppression. This antibody has found application in several animal models of solid organ transplantation. This study investigated use of anti-CD40 ligand antibody to promote acceptance of nerve allografts. In Experiment 1, 40 BALB/cj mice with tibial nerve transplants were administered anti-CD40 ligand antibody, a control antibody, or no treatment. In Experiment 2, 40 BALB/cj mice underwent the same regimen as in Experiment 1, but were later challenged with a second nerve allograft 3 weeks after discontinuation of treatment. Animals treated with anti-CD40 ligand antibody in Experiment 1 exhibited improved functional recovery and greater mean fiber count, fiber density, and percent nerve fiber than animals treated with control antibody or no antibody (P < 0.05). These permissive effects on nerve regeneration were associated with immune unresponsiveness on Elispot assay. The benefit of anti-CD40 ligand therapy did not persist after withdrawal of treatment (Experiment 2). Active blockade of the CD40 costimulatory pathway with murine anti-CD40 ligand antibody therefore induces a permissive state conducive to nerve regeneration across allografts but does not establish long-term tolerance.

Tolerance: is it achievable in pediatric solid organ transplantation?

Significant advances have been made in the understanding of allograft rejection. There is growing awareness that allograft acceptance, or tolerance, is also an active process rather than a passive absence of rejection. Mechanistic awareness of this process has spawned many preclinical strategies for the prevention of allograft rejection without the need for chronic immunosuppression. These therapies are currently entering clinical trials. This article reviews the prevailing therapies that hold promise for future clinical application. In particular, their application in children is discussed, as are biologic aspects of childhood immunity that may play a role in the success or failure of these strategies.

Prevention of allograft rejection by in vitro generated tolerogenic dendritic cells

Achieving immunological tolerance in transplantation has been a long sought-after goal since the 1960s. It is, therefore, interesting that the dendritic cells (DC), which are classically known as the most potent stimulators of T cell activation, are now also considered putative tools for tolerance induction. In line with this, much work has been performed using DC for vaccination and immune stimulation. Recently, great interest has been generated regarding the ability of DC to act as immune regulatory cells. Specific subsets of DC or immature DC (iDC) appear to be responsible for maintaining self-tolerance. In this review we will highlight our efforts at elucidating the contribution of DC in transplant tolerant in mice. Specifically, four strategies will be outlined that are currently being used for the generation of DC that have tolerogenic properties in the prevention of allograft rejection. The present study demonstrates that modulated iDC with blunted T cell stimulatory or antigen presentation abilities can afford transplant tolerance by minimizing T cell activation and proinflammatory cytokine production. Moreover, in an alternate strategy, normally matured DC have also been modulated such that alloreactive T cells are specifically targeted for deletion.

Studies investigating pretransplant donor-specific blood transfusion, rapamycin, and the CD154-specific antibody IDEC-131 in a nonhuman primate model of skin allotransplantation

Anti-CD154 variably prolongs allograft survival in nonhuman primates. Rodent studies suggest that adding pretransplant donor-specific transfusion (DST) and/or rapamycin to anti-CD154 improves survival. The CD154-specific Ab IDEC-131 was tested alone and in combination with rapamycin for its ability to inhibit rhesus MLRs. The ability of the Ab to block endothelial activation was also assessed. IDEC-131 was then tested alone and in combination with DST and/or rapamycin for its ability to prevent rejection of full-thickness, MHC-mismatched rhesus skin allografts. Animals were monitored for donor-specific hyporesponsiveness by MLR and alloantibody determination. IDEC-131 modestly inhibited rhesus MLRs and inhibited CD154-dependent endothelial cell activation. Rapamycin combined with IDEC-131 additively inhibited MLRs. IDEC-131 modestly prolonged allograft survival when compared with no treatment, rapamycin alone, or DST plus rapamycin. Adding DST to IDEC-131 did not prolong survival beyond IDEC-131 alone. IDEC-131 plus rapamycin was effective in prolonging graft survival, although animals had episodes of acute rejection before graft demise. Therapy with IDEC-131, rapamycin, and DST induced long-term allograft survival without intermittent acute rejection. However, no evidence for MLR inhibition was seen, and most animals eventually developed alloantibody. All animals ultimately rejected their grafts after drug withdrawal. IDEC-131 modestly prolongs rhesus skin allograft survival. Rapamycin and rapamycin plus DST improves the efficacy of IDEC-131 in prolonging allograft survival. IDEC-131, rapamycin, and DST are a promising combination for clinical evaluation in allotransplantation.

Combination induction therapy with monoclonal antibodies specific for CD80, CD86, and CD154 in nonhuman primate renal transplantation

BACKGROUND

Antibodies and fusion proteins specific for CD80, CD86, and CD154 have shown promise as agents capable of inducing donor-specific tolerance in rodents. These agents have also been shown to be synergistic with one another in many settings of counter-adaptive immunity. In the nonhuman primate, monoclonal antibodies specific for CD80 and CD86 have prolonged the time to rejection of renal allografts but have not resulted in tolerance. A monoclonal antibody specific for CD154 has resulted in markedly prolonged survival of kidney, islet, cardiac, and skin allografts, but again most animals have eventually developed rejection after prolonged periods of rejection-free survival off therapy.

METHODS

A combination of monoclonal antibodies specific for CD80, CD86, and CD154 were used in a mismatched nonhuman primate renal-allograft model. Doses used were based on optimized treatment protocols for each agent individually.

RESULTS

Treatment of four rhesus macaques with this combination yielded a mean rejection-free survival of 565 days (311-911 days), significantly greater than untreated controls (mean survival=7.0 days, P=0.001) and animals treated with only a combination of anti-CD80 and CD86 (mean survival=191 days, P=0.01). The survival of animals treated with this combination of monoclonal antibodies was not significantly greater than those treated with anti-CD154 alone, but the production of alloantibody was delayed compared with monotherapy anti-CD154.

CONCLUSION

These data suggest that a synergy exists between these agents, particularly with regard to T-dependent B-cell responses, but that they fail to induce durable tolerance in nonhuman primates.

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.