Development Of Chronic Allograft Vasculopathy Research Articles

Donor-Derived Factors Influence NK Cell Effector Activity in a Model of Antibody-Mediated Chronic Rejection

Purpose Natural killer (NK) cells are key components of the innate immune system that contribute to acute and chronic allograft rejection. Previous studies have shown that donor-specific antibodies (DSA) in concert with NK cells can be sufficient to inflict chronic allograft vasculopathy (CAV) in an Fc dependent manner. However, it has been observed clinically that detectable DSA does not always correlate with demonstrable injury. The modern understanding of NK cell triggering suggests that the transition from quiescence to activation is mediated by a network of activating and inhibitory receptors; it is the integration of the sum of these signals that determines the final NK cell response. Our study aimed to investigate if donor-derived factors can alter the balance of the NK cell effector response. Methods We utilized a murine model of cardiac transplant with C3H/HeJ (C3H, H-2k), BALB/cByJ (BALB/c, H-2d), or C3HxBALB/c F1 (F1) generation donors engrafted into C57Bl/6.rag-/- (B6.rag) recipients. Recipients had no functional T or B cells, but an intact innate immune system. Experimental animals received monoclonal IgG2a Class I DSA (anti-H2k or anti-H2d). Allografts were subsequently recovered and examined after 60 days for the presence of CAV (defined by calculation of the neointimal index). Results Initial studies verified that NK cells alone could not cause significant vascular injury. When C3H mice were used as donors (n=7), administration of Class I DSA resulted in marked neointimal changes consistent with CAV. However, when BALB/c mice were used as donors (n=6), administration of Class I DSA did not result in development of CAV, despite the fact that this donor strain also represented a fully allogeneic mismatch from the recipient. When F1 mice were utilized as donors (allografts expressed both H-2k and H-2d MHC molecules), neither administration of anti-H2k (n=7) nor anti-H2d (n=6) Class I DSA resulted in development of CAV. Conclusion Donor strain determines if the activating signal provided to NK cells by binding to Class I DSA, coupled with the lack of inhibition from “missing self,” is sufficient to result in NK cell triggering with initial results suggesting that certain donor / recipient MHC combinations demonstrate a permissive phenotype towards NK cell quiescence.

Hyperlipidemia and Allograft Rejection.

Advances in the development of immunosuppressive drug regimens have led to impressive survival rates in the year following organ transplantation. However rates of long-term graft dysfunction remain undesirably high. Recently it has been shown that co-morbidities in the patient population may affect graft survival. In mouse models, hyperlipidemia, a co-morbidity present in the majority of cardiac transplant patients, can significantly alter T cell responses to cardiac and skin allografts, and accelerate graft rejection. Here we review recent advances in our understanding of how alterations in lipids affect immune function and graft survival. Recent work in humans has highlighted the importance of controlling low density lipoprotein (LDL) levels in transplant recipients to reduce the development of chronic allograft vasculopathy (CAV). High serum levels of cholesterol containing particles leads to extensive immune system changes to T cell proliferation, differentiation and suppression. Changes in B cell subsets, and the ability of antigen presenting cells to stimulate T cells in hyperlipidemic animals may also contribute to increased organ allograft rejection. Cholesterol metabolism is a critical cellular pathway for proper control of immune cell homeostasis and activation. Increasing evidence in both human, and in mouse models shows that elevated levels of serum cholesterol can have profound impact on the immune system. Hyperlipidemia has been shown to increase T cell activation, alter the development of T helper subsets, increase the inflammatory capacity of antigen presenting cells (APC) and significantly accelerate graft rejection in several models.

Innovations in cardiac transplantation.

As the number of people living with heart failure continues to grow, future treatments will focus on efficient donor organ donation and ensuring safe and durable outcomes. This review will focus on organ procurement, graft surveillance and emerging therapies. Preliminary studies into donation after cardiac death have indicated that this may be an effective means to increase the donor pool. Novel preservation techniques that include ex-vivo perfusion to improve donor metabolic stabilization prior to implantation may also expand the donor pool. Biomarkers, including circulating-free DNA, are emerging that could replace the endomyocardial biopsy for acute graft rejection, but we lack a risk predictive biomarker in heart transplantation. Novel immune suppressants are being investigated. Emerging therapeutics to reduce the development of chronic allograft vasculopathy are yet to be found. This review highlights the most recent studies and future possible therapies that will improve outcomes in cardiac transplantation. Larger clinical trials are currently taking place and will be needed in the future to develop and sustain current trends toward better survival rates with cardiac transplantation.

Effect of Cold Preservation on Chronic Rejection in a Rat Hindlimb Transplantation Model.

Previous studies on solid organ transplantation have shown that cold ischemia contributes to the development of chronic allograft vasculopathy. The authors evaluated the effect of cold ischemia on the development of chronic rejection in vascularized composite allotransplantation. Thirty rat hindlimbs were transplanted and divided into two experimental groups: immediate transplantation and transplantation after 7 hours of cold ischemia. The animals received daily low-dose immunosuppression with cyclosporine A for 2 months. Intimal proliferation, arterial permeability rate, leukocyte infiltration, and tissue fibrosis were assessed. The CD3, CD4, CD8, CD20, and CD68 cells per microscopic field (200×) were counted, and C4d deposition was investigated. Cytokine RNA analysis was performed to measure tumor necrosis factor-α, interleukin-6, and interleukin-10 levels. Significant differences were found in the intimal proliferation and arterial permeability rate between the two groups (p = 0.004). The arterial permeability rate worsened in the most distal and small vessels (p = 0.047). The numbers of CD3, CD8, CD20, and CD68 were also statistically higher in the cold ischemia group (p < 0.05, all levels). A trend toward significance was observed with C4d deposition (p = 0.059). No differences were found in the RNA of cytokines. An association between cold ischemia and chronic rejection was observed in experimental vascularized composite allotransplantation. Chronic rejection intensity and distal progression were significantly related with cold ischemia. The leukocyte infiltrates in vascularized composite allotransplantation components were a rejection marker; however, their exact implication in monitoring and their relation with cold ischemia are yet to be clarified.

SDF-1/CXCR4/CXCR7 is pivotal for vascular smooth muscle cell proliferation and chronic allograft vasculopathy.

Chronic rejection remains a major obstacle in transplant medicine. Recent studies suggest a crucial role of the chemokine SDF-1 on neointima formation after injury. Here, we investigate the potential therapeutic effect of inhibiting the SDF-1/CXCR4/CXCR7 axis with an anti-SDF-1 Spiegelmer (NOX-A12) on the development of chronic allograft vasculopathy. Heterotopic heart transplants from H-2bm12 to B6 mice and aortic transplants from Balb/c to B6 were performed. Mice were treated with NOX-A12. Control animals received a nonfunctional Spiegelmer (revNOX-A12). Samples were retrieved at different time points and analysed by histology, RT-PCR and proliferation assay. Blockade of SDF-1 caused a significant decrease in neointima formation as measured by intima/media ratio (1.0±0.1 vs. 1.8±0.1, P<0.001 AoTx; 0.35±0.05 vs. 1.13±0.27, P<0.05 HTx). In vitro treatment of primary vascular smooth muscle cells with NOX-A12 showed a significant reduction in proliferation (0.42±0.04 vs. 0.24±0.03, P<0.05). TGF-β, TNF-α and IL-6 levels were significantly reduced under SDF-1 inhibition (3.42±0.37 vs. 1.67±0.33, P<0.05; 2.18±0.37 vs. 1.0±0.39, P<0.05; 2.18±0.26 vs. 1.6±0.1, P<0.05). SDF-1/CXCR4/CXCR7 plays a critical role in the development of chronic allograft vasculopathy (CAV). Therefore, pharmacological inhibition of SDF-1 with NOX-A12 may represent a therapeutic option to ameliorate chronic rejection changes.

Mitochondrial Activity - a Novel Strategy for Prevention and Reversion of Transplant Vasculopathy

Background: This study aimed at investigating the efficacy of dichloracetate (DCA) to prevent the development and progression of chronic allograft vasculopathy (CAV) by regulating the mitochondrial metabolism of aberrant proliferating smooth muscle cells. Methods: Orthotopic aortic transplantations were performed in the PVG-to-ACI rat model and followed over 120 days. Immunosuppression with DCA (0.75mg/L) or everolimus+clopidogrel (4 mg/kg and 1mg/kg per os, respectively) was either started early or delayed when CAV was already present. Through levels were monitored. Aortic luminal obliteration was quantified using computer morphometry and confocal microscopy. Donor-reactive antibodies were quantified by flow cytometry. Results: Untreated animals developed CAV with luminal obliteration of 40.1±24.2% after 120 days. Continuous immunosuppression with DCA or everolimus/clopidogrel effectively prevented the development of vasculopathy (7.9±4 and 8.1±12.9, respectively; p< 0.001 vs. no treatment). When the start of the immunosuppressive regimen was delayed until postoperative day 80, DCA and everolimus/clopidogrel inhibited a progression of established CAV (6.6±8 and 5.3±4.6; p< 0.001 vs. no treatment). Even more importantly, both treatment regimens did also reverse the luminal obliteration (p< 0.001). Interestingly, delayed treatment of DCA induced apoptosis resulting in shrinking hyperplasia area and inhibition of aberrant SMC proliferation. A stable elevation of donor-reactive IgG-antibody levels was found over 120 days in the absence of treatment. DCA was very well tolerated. Conclusions: DCA prevents the development of CAV and not only inhibits a progression of established disease, but also reverses the established disease by inducing apoptosis. It shows a similar efficacy but a safer drug profile when compared to everolimus/clopidogrel, since only aberrant SMC are affected.

Human Amniotic Fluid Stem Cells Reduce Neointimal Formation and Inflammation in a Model of Aortic Allograft Vasculopathy

Introduction: Chronic allograft vasculopathy (CAV) is a major limiting factor of long-term allograft survival. Although some mechanisms involved in CAV have already been identified, there is no specific treatment for this clinical condition. Considering the immune-inflammatory events involved in the development of CAV, therapeutic approaches to target this process are of relevance. In this context, human amniotic fluid derived stem cells (hAFSC), a class of fetal, pluripotent stem cells with intermediate characteristics between embryonic and adult stem cells, may represent an alternative strategy. hAFSC display immunomodulatory properties, express mesenchymal and embryonic markers, show high proliferation rates, but do not induce tumor formation and their use does not raise ethical issues. Based on these observations, we sought to investigate the effect of hAFSC on CAV in a model of aorta transplantation. Methods: Experimental aorta transplantation was performed using Fisher (F344) rats as donors and Lewis rats as recipients. The abdominal aorta segment, obtained from the emergency of renal arteries until its bifurcation, was orthotopically anastomosed in syngeneic or allogeneic recipients. hAFSC were isolated from amniotic fluid of 16-20 weeks pregnant women, who underwent amniocentesis due to advanced maternal age. Briefly, these cells were cultivated in Dulbecco's modified Eagle's medium-low glucose (DMEM-low) supplemented with 10% fetal bovine serum. hAFSC were purified using their characteristic to adhere to plastic culture dishes, characterized by flow cytometry, and characterized by their potential osteogenic, adipogenic, and chondrogenic differentiation. In addition, RT-PCR experiments demonstrated that these hAFSC express OCT-4 4/5 and NANOG. Rats were divided into 3 groups: syngeneic (SYNG), untreated F344 receiving syngeneic aorta from F344 (n=8); allogeneic (ALLO), Lewis rats receiving allogeneic aorta from F344 (n=8); and ALLO+hAFSC, ALLO rats treated with hAFSC (106 cells) (n=8). Histological analysis and immunohistochemistry were performed 30 days post transplantation. Results: Neointima formation was not observed in the SYNG group. However, the intimal thickness was dramatically increased in the ALLO group accompanied by a high number of ED1+ and CD43+ cells, and enhanced expression of α-SMA in the neointima. Treatment with hAFSC attenuated neointimal thickness and induced a significant decrease of ED1+, CD43+ cells as well as α-SMA expression in the neointima. Table 1: Effects of hAFSC in experimental aortic allograft vasculopathy.Table: No Caption available.Conclusion: These preliminary results showed that hAFSC suppressed inflammation and myofibroblast migration in the intima, possibly through immunomodulatory properties, which may have contributed to ameliorate vascular lesions in CAV.

352 Role of Mitochondrial Activity in the Development of Chronic Allograft Vasculopathy

This study aimed at investigating the efficacy of dichloracetate (DCA) to prevent the development and progression of chronic allograft vasculopathy (CAV) by regulating the mitochondrial metabolism of aberrant proliferating smooth muscle cells.

Acetylcholine and Chronic Vasculopathy in Rat Renal Allografts

Chronic allograft vasculopathy (CAV) is an important aspect of chronic allograft injury, which limits the long-term success of renal transplantation. The pathogenesis of CAV is ill defined, and no effective therapies exist. Acute rejection episodes are a major risk factor for CAV. Recently, we demonstrated that leukocytes, which strongly accumulate in allograft blood vessels during fatal acute rejection, produce acetylcholine (ACh), which has the potential to provoke CAV. Herein, we test the hypothesis that ACh is also produced by leukocytes during the development of CAV. Kidneys were transplanted in the Fischer 344 to Lewis rat strain combination, an established experimental model for CAV. Isografts were performed in Lewis rats. The capacity of intravascular graft leukocytes to synthesize ACh was investigated during reversible acute rejection on day 9 posttransplantation and during the process of vascular remodeling on day 42. Furthermore, allograft recipients were treated with rivastigmine, which blocks enzymatic degradation of ACh. The protein expression of the high-affinity choline transporter-1 and choline acetyltransferase was increased in leukocytes from allografts on day 9 and 42 posttransplantation. In addition, leukocytes accumulating in the lumina of allograft blood vessels were by far more numerous compared with isografts. In line with our hypothesis, ACh itself was detected by high-pressure liquid chromatography in graft leukocytes but not in leukocytes from untreated kidneys. Treatment with rivastigmine drastically exacerbated CAV compared with placebo. We suggest that endogenous ACh contributes to the pathogenesis of CAV and may be a promising target for novel therapies preventing CAV.

Donor Age Is Associated With Chronic Allograft Vasculopathy After Adult Heart Transplantation: Implications for Donor Allocation

Chronic allograft vasculopathy (CAV) is a major cause of long-term complications and mortality after heart transplantation. Although recipient factors have been implicated, little is known of the role of donor factors in CAV development. We sought to identify donor factors associated with development of CAV after heart transplantation. We reviewed the United Network for Organ Sharing heart transplant database from August 1987 to May 2008. Univariate and multivariate analyses were performed to assess the association between donor variables and the onset of CAV for adult recipients. Donor age was matched to recipient age and analyzed with respect to development of CAV. Of the 39,704 recipients, a total of 11,714 (29.5%) experienced CAV. Multivariate analysis demonstrated seven donor factors as independent predictors of CAV: age, ethnicity, sex, weight, history of diabetes, hypertension, and tobacco use. When matching young donors (0 to 19.9 years) and old donors (> or =50 years) to each recipient age group, older donors (> or =50 years) conferred a higher risk of developing CAV. Further modeling demonstrated that for each recipient group, older donor age (> or =50 years) conferred a higher risk of CAV development compared with younger donor age (0 to 19.9 years; p < 0.0001). Donor factors including sex, hypertension, diabetes, and tobacco use are independently associated with recipient CAV. Older donor age confers a greater risk of CAV development regardless of the age of the recipient. A heightened awareness for the development of CAV is warranted when using older donors in adult cardiac transplantation, in particular with recipients 40 years of age or older.

An Unexpected Counter-Regulatory Role of IL-10 in B-Lymphocyte-Mediated Transplantation Tolerance

Monoclonal antibody against the CD45RB protein induces stable transplantation tolerance to multiple types of allograft. We have previously established that this tolerance protocol relies on the regulatory function of B lymphocytes for its effect. B lymphocytes have also been reported to participate in immune regulation in several other settings. In most of these systems, the regulatory function of B lymphocytes depends on the production of IL-10. Therefore, we investigated the role of IL-10 in the anti-CD45RB model of B-cell-mediated transplantation tolerance. Surprisingly, using antibody-mediated neutralization of IL-10, IL-10-deficient recipients and adoptive transfer of IL-10-deficient B lymphocytes, we found that IL-10 actually counter-regulates tolerance induced by anti-CD45RB. Furthermore, neutralization of IL-10 reduced the development of chronic allograft vasculopathy compared to anti-CD45RB alone and reduced the production of graft reactive alloantibodies. These data suggest that the participation of regulatory B lymphocytes in transplantation tolerance may be distinct from how they operate in other systems. Identifying the specific B lymphocytes that mediate transplantation tolerance and defining their mechanism of action may yield new insights into the complex cellular network through which antigen-specific tolerance is established and maintained.

Prevention and Inhibition But Not Reversion of Chronic Allograft Vasculopathy by FK778

This study aimed at investigating the efficacy of the novel immunosuppressant FK778 to prevent the development and progression of chronic allograft vasculopathy (CAV). Orthotopic aortic transplantations were performed in the PVG-to-ACI rat model and followed over the course of 120 days. Immunosuppression with FK778 (20 mg/kg) or sirolimus (2 mg/kg) was either started early or delayed when CAV was already present. Trough levels were monitored. Aortic luminal obliteration was quantified using computer morphometry and intragraft cytokine profiles were analyzed with Western Blotting. Donor-reactive antibodies were quantified by flow cytometry. Untreated animals developed CAV with luminal obliteration of 25.2+/-13.6% and 41.4+/-23.3% after 80 and 120 days, respectively. Continuous immunosuppression with FK778 or sirolimus effectively prevented the development of vasculopathy. When the start of the immunosuppressive regimen was delayed until postoperative day 80, FK778 and sirolimus inhibited a progression of established CAV but did not reverse the luminal obliteration. Intragraft tumor growth factor-beta activity increased over the course of time in untreated recipients but was significantly suppressed after continuous immunosuppression with either agent. Expression of platelet-derived growth factor, intercellular adhesion molecule-1, and vascular adhesion molecule-1 also was moderately suppressed. A stable elevation of donor-reactive IgG-antibody levels was found over 120 days in the absence of treatment. With FK778 or sirolimus, antibody levels were effectively decreased. FK778 was very well tolerated and only sirolimus showed side effects with elevation of BUN, cholesterol, triglycerides, and ALT after 120 days. FK778 prevents the development of CAV and inhibits a progression of established disease. It shows a similar efficacy but a safer drug profile when compared to sirolimus.

The emerging role of T cell Ig mucin 1 in alloimmune responses in an experimental mouse transplant model

T cell Ig mucin 1 (TIM-1) plays an important role in regulating immune responses in autoimmune and asthma models, and it is expressed on both Th1 and Th2 cells. Using an antagonistic TIM-1-specific antibody, we studied the role of TIM-1 in alloimmunity. A short course of TIM-1-specific antibody monotherapy prolonged survival of fully MHC-mismatched vascularized mouse cardiac allografts. This prolongation was associated with inhibition of alloreactive Th1 responses and preservation of Th2 responses. TIM-1-specific antibody treatment was more effective in Th1-type cytokine-deficient Stat4(-/-) recipients as compared with Th2-type cytokine-deficient Stat6(-/-) recipients. Subtherapeutic doses of rapamycin plus TIM-1-specific antibody resulted in allograft acceptance and prevented the development of chronic allograft vasculopathy. Allograft survival via this treatment was accompanied by a Th1- to Th2-type cytokine switch. Depletion of natural Tregs abrogated the graft-protecting effect of the TIM-1-specific antibody. Importantly, CD4(+)CD25(+) Tregs obtained from long-term survivors had enhanced regulatory activity as compared with naive CD4(+)CD25(+) Tregs. Consistent with this, TIM-1-specific antibody treatment both preserved Tregs and prevented the expansion of alloreactive effector Th1 cells in an alloreactive TCR transgenic adoptive transfer model. These studies define previously unknown functions of TIM-1 in regulating alloimmune responses in vivo and may provide a novel approach to promoting transplantation tolerance.

Chemokines and Chronic Heart Allograft Rejection

Early work reported that targeting the CXCR3 and CCR5 could delay, but not prevent, acute allograft rejection (1–6). However, it is unclear how targeting single or multiple chemokine receptors could affect chronic rejection. In this study, we have examined the importance of chemokine receptors in acute and chronic rejection using CCR2, CXCR3, CCR5 knockout mice and CXCR3/CCR5 double knockout mice with heart allografts. Transplanted heart grafts were harvested at or near cessation of palpable contractility or at 60 days for chronic rejection, bisected to create a four-chamber section to visualize the aortic anastomosis, where chronic allograft vasculopathy is most readily identified. The median survival times for B6, CCR2−/−, CCR5−/−, CXCR3−/−, and CXCR3−/− × CCR5−/− recipients of heart allografts from complete major histocompatibility complex mismatch Balb/c donors were 8, 9, 11, 12, and 14 days, respectively. The pathology of acute rejections was similar in all mice with a mononuclear infiltrates and myocyte necrosis, diagnostic of acute cellular rejection (Fig. 1A, D, G, J, and M).FIGURE 1.: Histopathology of acute and chronic rejection. Acute rejection of Balb/c allografts showing mononuclear cell infiltrates with myocyte necrosis (A, D, G, J, and M). Recipients are B6 (A), CCR2−/− (D), CCR5−/− (G) CXCR3−/− (J), and CXCR3−/− × CCR5−/− DKO (M). Histopathology of active chronic rejection of BM12 allograft showing coronary and intraparenchymal arteries infiltrated by mononuclear cells with endothelialitis (B, E, H, K, and N). Recipients are B6 (B), CCR2−/− (E), CCR5−/− (H), CXCR3−/− (K), and CXCR3−/− × CCR5−/− DKO (N). Histopathology of active chronic rejection of BM12 allograft showing donor aortas at the anastomotic site infiltrated by mononuclear cells with endothelialitis (C, F, I, L, and O, and R). Recipients are B6 (C), CCR2−/− (F), CCR5−/− (I), CXCR3−/− (L), and CXCR3−/− × CCR5−/− DKO (O). Hematoxylin/eosin stained slides. Original magnification, 400×.Using a well-established model of chronic rejection (7–9), hearts from donor BM12 mice were transplanted into B6, CCR2−/−, CCR5−/−, CXCR3−/−, and CXCR3−/− × CCR5−/− recipients. In both control and the KO animals, coronary arteries and/or intramural arteries contained intimal and medial mononuclear cell infiltrates with endothelialitis (Fig. 1B, E, H, K, and N) with similar infiltrates in the donor aorta adjacent to the aortic anastomotic site (Fig. 1C, F, I, L, and O). Morphometric analysis failed to identify any quantitative differences among animal groups. In addition, smooth muscle cell loss was present in the donor aortas. These histological findings are diagnostic of an active phase of chronic allograft vasculopathy. Little parenchymal inflammation was present in all chronic rejection recipients. Syngeneic allografts showed no intimal hyperplasia or inflammation in the coronary arteries or at the anastomotic site (data not shown). In this study, there was modest prolongation of acute heart allograft survival in the mice deficient for certain chemokine receptors and there was no effect on chronic rejection. Chemokines control the inflammatory infiltrate so that a modest delay in the recruitment of cells, especially CD4 cells, could have a modest effect on acute cellular rejection and chronic allograft vasculopathy (10–14). Because there is redundancy in the chemokine and chemokine receptor network deleting or targeting a single chemokine or receptor has only marginal effects in acute cellular rejection (15, 16). Additional prolongation observed in the DKO mice suggests that targeting multiple chemokine receptors may further delay rejection. Potent costimulatory blockade or conventional immunosuppressive strategies, which dramatically reduces parenchymal inflammation, is also often unable to reduce chronic rejection (17–21). Likewise in this BM12 model of chronic rejection using B6 and selected chemokine receptor knockout recipients, there is relatively little parenchymal inflammation with ongoing active chronic vasculopathy. Parenchymal infiltration, therefore, is probably not the trigger for the development of chronic allograft vasculopathy, which may come about by an inflammatory pathway distinct from that which recruits parenchymal inflammation. R. Neal Smith Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, MA Takuya Ueno Transplantation Unit, Surgical Services, Massachusetts General Hospital, Transplantation Research Center, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA Toshiro Ito Transplantation Unit, Surgical Services, Massachusetts General Hospital, Harvard Medical School, Boston, MA Katsunori Tanaka Transplantation Research Center, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA Susan P. Shea Transplantation Unit, Surgical Services, Massachusetts General Hospital, Harvard Medical School, Boston, MA Reza Abdi Transplantation Research Center, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA

Proliferation signal inhibitors in cardiac transplantation

Standard immunosuppression after cardiac transplantation includes a calcineurin inhibitor in combination with mycophenolate mofetil or azathioprine and corticosteroids. These agents have led to excellent outcomes but have shortcomings in terms of efficacy and toxicity. A new class of immunosuppressants, proliferation signal inhibitors, may meet some of these shortcomings. The efficacy of the available proliferation signal inhibitors - sirolimus and its derivative everolimus - has been compared with azathioprine in three randomized clinical trials. Sirolimus or everolimus use was associated with lower rates of acute rejection and reduced development of chronic allograft vasculopathy. Sirolimus was not found to be superior to mycophenolate mofetil in a randomized trial. Proliferation signal inhibitors have been reported to be effective in refractory recurrent acute rejection. Nonrandomized studies have demonstrated that proliferation signal inhibitor-based immunosuppression enables recovery from renal dysfunction secondary to calcineurin inhibitor treatment. Proliferation signal inhibitor-based treatment is associated with a lower risk of malignancy than calcineurin inhibitor-based regimens. Proliferation signal inhibitors have significant adverse effects that may limit widespread use. Proliferation signal inhibitors are important new immunosuppressive agents that have added considerably to the armamentarium allowing further tailored immunosuppression to individualize patient care after heart transplantation.

CD70 Signaling Is Critical for CD28-Independent CD8+ T Cell-Mediated Alloimmune Responses In Vivo

The inability to reproducibly induce robust and durable transplant tolerance using CD28-B7 pathway blockade is in part related to the persistence of alloreactive effector/memory CD8(+) T cells that are less dependent on this pathway for their cellular activation. We studied the role of the novel T cell costimulatory pathway, CD27-CD70, in alloimmunity in the presence and absence of CD28-B7 signaling. CD70 blockade prolonged survival of fully mismatched vascularized cardiac allografts in wild-type murine recipients, and in CD28-deficient mice induced long-term survival while significantly preventing the development of chronic allograft vasculopathy. CD70 blockade had little effect on CD4(+) T cell function but prevented CD8(+) T cell-mediated rejection, inhibited the proliferation and activation of effector CD8(+) T cells, and diminished the expansion of effector and memory CD8(+) T cells in vivo. Thus, the CD27-CD70 pathway is critical for CD28-independent effector/memory CD8(+) alloreactive T cell activation in vivo. These novel findings have important implications for the development of transplantation tolerance-inducing strategies in primates and humans, in which CD8(+) T cell depletion is currently mandatory.

Neutralization of monokine induced by interferon-γ during the early posttransplantation period prevents development of chronic allograft vasculopathy and graft fibrosis

Immunologic surveillance for rejection detection in human heart transplantation offers many potential advantages. To date, investigative efforts have focused primarily on the acquired immune system, particularly the lymphocyte. Little attention has been given to aspects of innate immune function. We have previously reported that perioperative neutrophil adhesion molecule expression is associated with early rejection episodes after human cardiac transplantation. Herein we have investigated the utility of neutrophil immunosurveillance in human heart transplant recipients at later time points. We recruited patients more than 3 months after transplantation. Neutrophil assessment was performed simultaneously with an endomyocardial biopsy that showed rejection. No significant relationship was seen between neutrophil maturity (P = .622; n = 34), adhesion marker expression (P = .567; n = 34), respiratory burst (P = .604; n = 34), or apoptosis rates (P = .662; n = 34) and contemporary rejection status at >3 months after transplantation. However, interesting relationships were noted between neutrophil adhesion markers at this late stage and historical rejection status. Higher levels of the adhesion protein CD11b observed at this late stage were significantly associated with a history of higher rejection grades in the first postoperative biopsy (Spearman rank coefficient 0.359; R = 0.304; P = .005; n = 62). Other aspects of neutrophil function and persistence were not significantly associated with rejection history. This finding, combined with the previously reported findings, supports a role for an individual phenotype in neutrophil function in early rejection episodes after transplantation.