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.     

A novel CD154 monoclonal antibody in acute and chronic rat vascularized cardiac allograft rejection

BACKGROUND: The CD40-CD154 interaction is critically important in the cell-mediated immune responses. Blockade of this costimulatory pathway has been shown to prevent acute allograft rejection in murine, as well as nonhuman primate models. However, the role of the CD40-CD154 pathway in the development of chronic rejection and the effects of CD154 targeting on progression of chronic rejection have not been evaluated. METHODS: We examined the effect of AH.F5, a new hamster anti-rat CD154 monoclonal antibody, in a fully allogeneic acute(u) into Lewis [LEW] (RT11) and chronic [WF.1L (RT1l) into LEW (RT1l)] vascularized cardiac allograft rejection model. In the chronic model, the antibody was evaluated for prevention (starting day of transplant) and interruption of progression (starting day 30 or 60 after transplant) of chronic vasculopathy. Graft survival, morphology, and immunohistology were evaluated. RESULTS: In the acute rejection model, anti-CD154 therapy alone prevented acute allograft rejection and resulted in 50% long-term allograft survival (>200 days) and donor-specific tolerance. In recipients treated with anti-CD154 monoclonal antibody in combination with a short course of cyclosporine, 100% of allografts survived long-term and all recipients achieved donor-specific tolerance. In the chronic rejection model, allografts from animals treated with the anti-CD154 antibody had a statistically significant lower score of graft arteriosclerosis and fibrosis in both the prevention and 30-day interruption groups when compared with control allografts. In addition, immunohistochemistry showed a decrease in intragraft mononuclear cell infiltration and activation. CONCLUSION: A new anti-CD154 antibody not only prevents acute allograft rejection, but also inhibits and interrupts the development of chronic rejection. In the acute rejection model cyclosporine acts synergistically with anti-CD154 therapy to prolong allograft survival and induce tolerance. In the chronic rejection model relatively early initiation of therapy is essential to prevent progression of chronic allograft vasculopathy and fibrosis.     

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.     

Long-term limb allograft survival using a short course of anti-CD45RB monoclonal antibody, LF 15-0195, and rapamycin in a mouse model

BACKGROUND: The purpose of this study was to determine if a short course of monoclonal antibody (mAb) against CD45RB, LF 15-0195, and rapamycin would achieve long-term survival by inducing tolerance in a mouse limb transplant model. METHODS: Group 1 (n=9) consisted of nine isogenic (C57BL/6) transplants. Group 2 (n=3) included C57BL/6-to-BALB/c transplants receiving no drug therapy. Group 3 mice (n=4) were treated with mAb (3 mg/kg) and LF (2 mg/kg), and Group 4 (n=13) was treated with mAb, LF, and rapamycin (2 mg/kg). Both treatment groups received drug treatment for only 14 days posttransplantation. Animals were sacrificed if they displayed evidence of rejection or when deemed to be tolerant (defined as >day 100). RESULTS: All isografts had normal histology and graft function on day 100. Untreated C57BL/6-to-BALB/c allografts developed acute rejection within 10 days. The combination of mAb and LF prolonged allograft survival to a mean of 39+/-7 days. In Group 4, two animals had to be sacrificed at days 28 and 76 due to acute urinary retention. Transplant tolerance was achieved in 8 of the remaining 11 animals with a mean survival time of 100+/-12 days. Donor specific tolerance was demonstrated through permanent acceptance of skin grafts from the donor strain and rejection of skin grafts from C3H mice. Three Group 4 animals showed clinical and histological signs of mild, chronic rejection. Dendritic cells isolated from tolerant recipients exerted a suppressive effect in mixed lymphocyte reaction. CONCLUSION: A short course of anti-CD45RB mAb and LF 15-0195 prolonged limb allograft survival. The addition of rapamycin induced limb allograft tolerance which is associated with the generation of tolerogenic dendritic cells that suppressed T-cell proliferation.     

Anti-CD45RB Monoclonal Antibody Prolongs Renal Allograft Survival in Cynomolgus Monkeys

Previously, an anti-CD45RB monoclonal antibody (mAb) has been shown to induce murine allograft tolerance. The present study was performed to assess the ability of an anti-human CD45RB mAb to prevent rejection in a monkey MHC-mismatched kidney transplant model. The recipients were allocated into the following treatment groups: (1) isotype control IgG; (2) mouse anti-human CD45RB IgG1 (6G3); (3) human-mouse chimeric anti-CD45RB-IgG1 (C6G3-IgG1); (4) human-mouse chimeric anti-CD45RB-IgG2 (C6G3-IgG2); (5) tacrolimus at a subtherapeutic dose and (6) tacrolimus and C6G3-IgG1 in combination. Monotherapy with anti-CD45RB mAb significantly prolonged renal allograft survival to a median survival of 21 days. Adding a subtherapeutic dose of tacrolimus improved the efficacy of the anti-CD45RB mAb, achieving a median survival of 85 days, whereas a subtherapeutic dose of tacrolimus alone only moderately prolonged survival to 27 days. Treatment with anti-CD45RB mAb resulted in an alteration of the CD45RB(hi) : CD45RB(lo) cell ratio in the peripheral blood. We have, for the first time, demonstrated that an anti-human CD45RB mAb (6G3) can prolong graft survival. Induction with an anti-CD45RB mAb improves the efficacy of tacrolimus in the prevention of rejection. These encouraging results indicate that an anti-CD45RB mAb may be valuable in future clinical transplantation.     

Changes in expression of T-cell activation-related molecules and cytokines during tolerance induction in an allogeneic skin transplantation murine model

Bone marrow transplantation after treatment with busulfan and costimulatory blockade with monoclonal antibodies (mAb) cytotoxic T lymphocyte antigen 4 (CTLA4)-Ig and anti-CD154 mAb or two-signal blockade using anti-CD45RB and anti-CD154 mAb are nonmyeloablative treatment regimens for allogeneic transplantation. There may be differences in the mechanisms of donor cell engraftment and reactive cell deletion by which these regimens induce donor-specific tolerance. Therefore, this study was performed to investigate changes in T cells and cytokines during tolerance induction toward allogeneic skin grafts. BALB/c and C57BL/6 mice were used as donors and recipients, respectively. Skin and bone marrow transplantations were performed and busulfan was administered. Three groups were treated with mAb as follows: group 1, anti-CD154 mAb; group 2, anti-CD154 plus anti-CD45RB mAb; and group 3, anti-CD154 mAb plus CTLA4-Ig. The proportions of CD4+ or CD8+ T cells and the expression of CD45RB isoforms on splenocytes were measured using flow cytometry and the production of cytokines by CD4+ T cells using enzyme-linked immunosorbent assay. Group 2 showed a significant reduction in the proportions of CD8+ T cells and CD45RB high isoforms compared with groups 1 and 3. The levels of interleukin (IL)-2 and IL-4 in group 2 were lower and higher than those of groups 1 and 3, respectively. In conclusion, the combined use of anti-CD154 and anti-CD45RB mAb decreases the CD8+ T-cell population and the expression of CD45RB, resulting in a Th2 cytokine profile, which may be a characteristic mechanism leading to donor cell engraftment and reactive cell deletion for donor-specific tolerance.     

Combined treatment with CD40 costimulation blockade, T-cell depletion, low-dose irradiation, and donor bone marrow transfusion in limb allograft survival

To determine the efficacy of a regimen based on CD40 costimulation blockade and donor bone marrow in the limb allograft model, C57Bl/6 mice received limb allografts from Balb/c mice and either no treatment or a combination of MR1 (anti-CD40 ligand monoclonal antibody), CD4+ and CD8+ T-cell-depleting antibodies, low-dose irradiation, and bone marrow transfusion from Balb/c donors for 1 or 2 weeks. Recipients treated for 1 week showed rejection at 38.2 +/- 5.4 (mean +/- SEM) days, while those treated for 2 weeks had allograft survival of 56.5 +/- 9.9, with a range up to 91 days. Histology demonstrated rejection which was less cell-mediated and suggestive of transplant vasculopathy. Differential rejection of skin occurred first. Thus, a combined regimen based on CD40 costimulatory blockade and donor marrow significantly prolonged allograft survival. However, tolerance was not achieved, and histology suggests chronic rejection as a possible cause of allograft loss.     

Regulation of skin and islet allograft survival in mice treated with costimulation blockade is mediated by different CD4+ cell subsets and different mechanisms

BACKGROUND: Donor-specific transfusion (DST) and a brief course of anti-CD154 monoclonal antibody (mAb) induces permanent islet and prolonged skin allograft survival in mice. Induction of skin allograft survival requires the presence of CD4 cells and deletion of alloreactive CD8 cells. The specific roles of CD4 and CD4CD25 cells and the mechanism(s) by which they act are not fully understood. METHODS: We used skin and islet allografts, a CD8 T cell receptor (TCR) transgenic model system, and in vivo depleting antibodies to analyze the role of CD4 cell subsets in regulating allograft survival in mice treated with DST and anti-CD154 mAb. RESULTS: Deletion of CD4 or CD25 cells during costimulation blockade induced rapid rejection of skin but only minimally shortened islet allograft survival. Deletion of CD4 or CD25 cells had no effect upon survival of healed-in islet allografts, and CD25 cell deletion had no effect upon healed-in skin allograft survival. In the TCR transgenic model, DST plus anti-CD154 mAb treatment deleted alloreactive CD8 T cells, and anti-CD4 mAb treatment prevented that deletion. In contrast, injection of anti-CD25 mAb did not prevent alloreactive CD8 T cell deletion. CONCLUSIONS: These data document that (1) both CD4CD25 and CD4CD25 cells are required for induction of skin allograft survival, (2) CD4CD25 T cells are not required for alloreactive CD8 T cell deletion, and (3) CD4CD25 regulatory cells are not critical for islet allograft tolerance. It appears that skin and islet transplantation tolerance are mediated by different CD4 cell subsets and different mechanisms.     

Multiple Combination Therapies Involving Blockade of ICOS/B7RP-1 Costimulation Facilitate Long-Term Islet Allograft Survival

In recent years a series of novel costimulatory molecules have been identified, including inducible costimulator (ICOS). In a fully major histocompatibility complex (MHC)-mismatched mouse model of islet transplantation, we demonstrate that while monotherapy with CTLA4-Ig, CD40 ligand monoclonal antibody (CD40L mAb) or rapamycin each improves islet allograft survival, graft rejection eventually develops. Immunohistologic analysis of rejected grafts revealed increased ICOS expression, suggesting a role for this costimulatory molecule as an alternate pathway for T-cell activation. The combination of a blocking anti-ICOS mAb with each of the above therapies resulted in significantly improved islet allograft survival, confirming the importance of ICOS signaling in islet allograft rejection. Mechanistic studies conducted in mice treated with anti-ICOS mAb and rapamycin demonstrated a lack of donor-specific immunological tolerance and an absence of regulatory T-cell activity. However, a dramatic effect was seen on acute anti-donor responses whereby anti-ICOS mAb and rapamycin significantly reduced the initial expansion and function of alloreactive T cells. These data demonstrate that blockade of the ICOS/B7RP-1 pathway has potential therapeutic benefit given its role in enhancing islet allograft survival and regulating acute alloresponses in vivo.     

CD154 Blockade for Induction of Mixed Chimerism and Prolonged Renal Allograft Survival in Nonhuman Primates

Costimulatory blockade with anti-CD154 monoclonal antibody (aCD154) prolongs allograft survival in nonhuman primates, but has not reliably induced tolerance when used alone. In the current studies, we evaluated the effect of adding CD154 blockade to a chimerism inducing nonmyeloablative regimen in primates. We observed a significant improvement of donor bone marrow (DBM) engraftment, which has been associated with a lower incidence of acute rejection and long-term survival of renal allografts without the need for previously required splenectomy. Among the long-term survivors, four never showed evidence of rejection, with the longest survival exceeding 1700 days following discontinuation of immunosuppression. Nevertheless, late chronic rejection was observed in three of eight recipients, indicating the necessity of further modifications of the regimen. Control recipients receiving no DBM or donor splenocytes in place of DBM rejected their allografts. Thus, DBM engraftment with, at least, transient mixed chimerism appears essential for induction of allograft tolerance using this conditioning regimen. Modification of the original mixed chimerism approach, by the addition of costimulatory blockade, has been shown to enhance mixed chimerism and induce renal allograft tolerance with less morbidity in nonhuman primates.     

Impact of both donor and recipient strains on cardiac allograft survival after blockade of the CD40-CD154 costimulatory pathway

BACKGROUND: The effectiveness of anti-CD154 monoclonal antibodies in prolonging the survival of mouse allografts is dependent on the strain combination. In this report, we examined the impact of the donor and the recipient strains on the success of CD40-CD154 blockade. MATERIALS AND METHODS: Cardiac allograft survival was monitored in different donor/recipient strain combinations. Morphometric analyses on the allograft coronary arteries allowed quantification of vessel intimal thickening. RESULTS: Prolonged cardiac allograft survival after the administration of an anti-CD154 monoclonal antibody was found to be dependent on the donor and the recipient strains. The influence of the donor and the recipient strains lay in the ability of CD8 T cells to cause graft rejection despite CD40-CD154 blockade. Elimination of CD8 T cells before transplantation resulted in similar graft prolongation irrespective of the genotype of the donor or the recipient strain. CONCLUSION: These data show that both donor and recipient strains contribute to CD40-CD154-independent CD8 T-cell-mediated rejection.     

Critical Role for CD8+ T Cells in Allograft Acceptance Induced by DST and CD40/CD154 Costimulatory Blockade

Donor-specific transfusion (DST) and CD40/CD154 costimulation blockade is a powerful immunosuppressive strategy which prolongs survival of many allografts. The efficacy of DST and anti-CD154 mAb for prolongation of hepatocellular allograft survival was only realized in C57BL/6 mice that have both CD4- and CD8-dependent pathways available (median survival time, MST, 82 days). Hepatocyte rejection in CD8 KO mice which is CD4-dependent was not suppressed by DST and anti-CD154 mAb treatment (MST, 7 days); unexpectedly DST abrogated the beneficial effects of anti-CD154 mAb for suppression of hepatocyte rejection (MST, 42 days) and on donor-reactive alloantibody production. Hepatocyte rejection in CD4 KO mice which is CD8-dependent was suppressed by treatment with DST and anti-CD154 mAb therapy (MST, 35 days) but did not differ significantly from immunotherapy with anti-CD154 mAb alone (MST, 32 days). Induction of hepatocellular allograft acceptance by DST and anti-CD154 mAb immunotherapy was dependent on host CD8(+) T cells, as demonstrated by CD8 depletion studies in C57BL/6 mice (MST, 14 days) and CD8 reconstitution of CD8 KO mice (MST, 56 days). These studies demonstrate that both CD4(+) and CD8(+) T-cell subsets contribute to induction of hepatocellular allograft acceptance by this immunotherapeutic strategy.     

A major role for host MHC class I antigen presentation for promoting islet allograft survival

The purpose of this study was to determine the role for CD8 T cells versus generalized MHC class I-restricted antigen presentation in islet allograft rejection and tolerance. Diabetic C57BI/6 (B6, H-2(b)) controls, C57BI/6 CD8-deficient (CD8 KO), or MHC class I-deficient C57BI/6 (beta 2m KO) recipients were grafted with allogeneic BALB/c (H-2(d)) islets. Islet allografts were acutely rejected in untreated B6, CD8 KO, and in beta 2m KO mice, indicating that neither CD8 T cells nor host MHC class I is required for allograft rejection. We then determined the efficacy of costimulation blockade in these same strains. Costimulation blockade with anti-CD154 therapy facilitated long-term islet allograft survival in both B6 and in CD8 KO recipients. However, anti-CD154 treated beta 2m KO recipients were completely refractory to anti-CD154 therapy; all treated animals acutely rejected islet allografts with or without therapy. Also, anti-NK1.1 treatment of wild-type B6 mice abrogated graft prolongation following anti-CD154 therapy. Taken together, results show a dramatic distinction between two forms of MHC class I-restricted pathways in allograft prolongation. Although anti-CD154-induced allograft survival was CD8 T-cell independent, an intact host MHC class I-restricted (beta 2m-dependent) pathway is nevertheless necessary for allograft survival. This pathway required NK1.1+ cells, implicating NK and/or NKT cells in promoting allograft prolongation in vivo.     

Cigarette smoke exposure hinders long-term allograft survival by suppressing indoleamine 2, 3-dioxygenase expression

Cigarette smoke causes cancer and increases the vulnerability of smokers to infections. Epidemiologic studies have shown that smoking is one of major risk factors for late allograft rejection. Despite statistical data that associate smoking with allograft rejection, no any study has been conducted to prove that cigarette smoke directly causes allograft rejection in a cause-effect manner. In particular, investigation into immunologic mechanisms underlying smoke-related allograft rejection is lacking. Here we found that second hand smoke (SHS) hindered long-term islet allograft survival induced by CD154 costimulatory blockade plus donor-specific splenocyte transfusion (DST), although it failed to alter acute islet allograft rejection. SHS did not directly interfere with vigorously alloreactive T-cell proliferation in vivo and in vitro. Neither naturally occurring nor induced CD4+CD25+ Treg cell numbers were significantly reduced by SHS. However, SHS suppressed mRNA and protein expression of indoleamine 2, 3-dioxygenase (IDO) and its activity upon transplantation while IDO overexpression in islet allografts restored their long-term survival induced by CD154 blockade. Therefore, SHS prevents long-term allograft survival by inhibiting IDO expression and activity. Thus, our study for the first time demonstrates that SHS shortens allograft survival in a cause-effect manner and unveils a novel immunologic mechanism underlying smoking-related allograft rejection.     

CD40 expression on graft infiltrates and parenchymal CD154 (CD40L) induction in human chronic renal allograft rejection

BACKGROUND: CD40-CD154 (CD40L) costimulatory signaling plays a pivotal role in the effector mechanisms of transplant graft rejection. In animal models, CD40-CD154 blockade induces long-term graft acceptance concurrent with an absence of chronic rejection (CR) lesions. Given the critical importance of CD40-CD154 interactions in the development of chronic transplant allograft rejection, the relevance of in situ CD40 and CD154 expression was assessed in human chronic renal allograft rejection. METHODS: The expression of CD40, CD154, CD68, and T-cell receptor (TCR)alpha/beta was analyzed by immunohistochemistry. Serial cryostat sections of snap-frozen core renal allograft biopsies were obtained from 30 renal transplant patients. Biopsy specimens received diagnoses of CR (N = 23) according to the Banff classification and were compared with controls (N = 7) consisting of stable allografts and normal kidney tissue. RESULTS: Striking CD40 staining of graft cellular infiltrates (P = 0.016) was observed in renal allografts with CR compared with controls. The CD40+ cellular infiltrates in CR were predominantly TCR alpha/beta + T cells and some CD68+ macrophages. These findings were contrasted by the low-level CD40 expression detected in glomeruli and tubules of CR and controls. However, glomerular induction of CD154 was observed in CR allografts (P = 0.028) as compared with controls. CD154 immunoreactivity was demonstrated on glomerular endothelial, epithelial, and mesangial cells. Moderate CD154 expression was detected on tubular epithelial cells, and only weak CD154 immunoreactivity was observed on the infiltrates in isolated CR cases. CONCLUSION: In human chronic renal allograft rejection, CD40 is expressed on graft-infiltrating cells of the T cell and macrophage compartments. CD154 expression is induced on glomerular and tubular epithelial cells during CR, demonstrating another novel source of CD154 expression. The data substantiate the potential contributory role of an interaction between CD40+ graft-destructive effector T cells and macrophages with CD154+ renal allograft parenchymal cells in the development of chronic renal allograft rejection.     

Combination therapy with anti-ICOS and cyclosporine enhances cardiac but not islet allograft survival

The blockade of costimulatory signals is a powerful strategy to prevent allograft rejection and facilitate transplantation tolerance. In recent years, a series of novel costimulatory molecules have been identified, including an inducible costimulatory molecule (ICOS). To date, little has been uncovered regarding the therapeutic potential of blocking ICOS signaling in the setting of transplantation. In a fully MHC-mismatched mouse model, we studied the effect of blocking ICOS signaling using a specific monoclonal antibody (anti-ICOS mAb) in combination with cyclosporine on cardiac and islet allograft survival. We demonstrated that combined treatment with anti-ICOS mAb and cyclosporine can induce long-term graft acceptance in cardiac but not islet allografts, suggesting that the type of transplanted tissue significantly influences the immunologic patterns of graft acceptance or rejection in this model.     

ICOS-Dependent and -Independent Functions of Memory CD4 T Cells in Allograft Rejection

Donor-reactive memory T cells undermine the survival of transplanted organs through multiple pathways. We have previously reported that memory CD4 T cells resist treatment with anti-CD154 antibody and donor-specific transfusion (DST/MR1) and promote cardiac allograft rejection via generation of effector CD4 T cells and alloantibody. We hypothesized that the helper functions of memory CD4 T cells are independent of T-cell costimulation through CD154 but instead are regulated by alternative costimulatory pathways. This study investigated how blocking ICOS/B7RP-1 interactions affects functions of donor-reactive memory CD4 T cells. Treatment with blocking anti-ICOS mAb synergized with DST/MR1 and prolonged mouse cardiac allograft survival despite the presence of donor-reactive memory CD4 T cells. While blocking ICOS did not diminish the expansion of preexisting memory CD4 T cells or the induction of allospecific effector T cells, it did inhibit recruitment of the activated memory and effector T cells into the graft. In addition, anti-ICOS mAb treatment in combination with DST/MR1 prevented help provided by memory CD4 T cells for production of donor-specific IgG antibody. These results demonstrate the potential efficacy of ICOS blockade in sensitized transplant patients and provide the foundation for rational use of ICOS blockade in combination with other graft-prolonging strategies.     

Prevention of kidney allograft rejection using anti-CD40 and anti-CD86 in primates

BACKGROUND: Costimulation blockade has been proposed to induce allograft tolerance. We combined an antagonist anti-CD40 monoclonal antibody (mAb) with an antagonist anti-CD86 mAb in a rhesus monkey kidney allograft model. We chose this combination because it leaves CD80-CD152 signaling unimpaired, allowing for the down-regulatory effect of CD152 signaling to take place through this pathway. METHODS: Rhesus monkeys underwent transplantation with a major histocompatibility complex-mismatched kidney. One group of animals received anti-CD40 alone, and a second group received the combination of anti-CD40 and anti-CD86, twice weekly for 56 days. RESULTS: Three animals with low levels of anti-CD40 rejected the transplanted kidney while still receiving treatment. Three animals with high levels of anti-CD40 rejected at days 91, 134, and 217 with signs of chronic rejection. Animals treated with the combination of anti-CD40 and anti-CD86 mAbs rejected their kidneys at days 61, 75, and 78, shortly after cessation of treatment. Two animals were killed on days 71 and 116 with a blocked ureter. These animals developed virtually no signs of tubulitis or infiltration during treatment and no donor-specific alloantibodies. CONCLUSIONS: Both treatment protocols prevented rejection for the duration of the treatment in most animals. Blocking costimulation by anti-CD40 or by anti-CD40 plus anti-CD86 may be an effective method to prevent graft rejection and may obviate the need for other immunosuppressive drugs, especially in the immediate posttransplantation period.