Thrombalexin: Use of a Cytotopic Anticoagulant to Reduce Thrombotic Microangiopathy in a Highly Sensitized Model of Kidney Transplantation.

Early activation of coagulation is an important factor in the initiation of innate immunity, as characterized by thrombotic microangiopathy (TMA). In transplantation, systemic anticoagulation is difficult due to bleeding. A novel "cytotopic" agent, thrombalexin (TLN), combines a cell-membrane-bound (myristoyl tail) anti-thrombin (hirudin-like peptide [HLL]), which can be perfused directly to the donor organ or cells. Thromboelastography was used to measure time to clot formation (r-time) in both rhesus and human blood, comparing TLN versus HLL (without cytotopic tail) versus negative control. Both TLN- and HLL-treated rhesus or human whole blood result in significantly prolonged r-time compared to kaolin controls. Only TLN-treated human endothelial cells and neonatal porcine islets prolonged time to clot formation. Detection of membrane-bound TLN was confirmed by immunohistochemistry and fluorescence activated cell sorter. In vivo, perfusion of a nonhuman primate kidney TLN-supplemented preservation solution in a sensitized model of transplantation demonstrated no evidence of TLN systemically. Histologically, TLN was shown to be present up to 4 days after transplantation. There was no platelet deposition, and TMA severity, as well as microvascular injury scores (glomerulitis + peritubular capillaritis), were less in the TLN-treated animals. Despite promising evidence of localized efficacy, no survival benefit was demonstrated.

One Size Does Not Fit All--Regional Variation in the Impact of the Share 35 Liver Allocation Policy.

Allocation policies for liver transplantation underwent significant changes in June 2013 with the introduction of Share 35. We aimed to examine the effect of Share 35 on regional variation in posttransplant outcomes. We examined two patient groups from the United Network for Organ Sharing dataset; a pre-Share 35 group composed of patients transplanted between June 17, 2012, and June 17, 2013 (n = 5523), and a post-Share group composed of patients transplanted between June 18, 2013, and June 18, 2014 (n = 5815). We used Kaplan-Meier and Cox multivariable analyses to compare survival. There were significant increases in allocation Model for End-stage Liver Disease (MELD) scores, laboratory MELD scores, and proportions of patients in the intensive care unit and on mechanical, ventilated, or organ-perfusion support at transplant post-Share 35. We also observed a significant increase in donor risk index in this group. We found no difference on a national level in survival between patients transplanted pre-Share 35 and post-Share 35 (p = 0.987). Regionally, however, posttransplantation survival was significantly worse in the post-Share 35 patients in regions 4 and 10 (p = 0.008 and p = 0.04), with no significant differences in the remaining regions. These results suggest that Share 35 has been associated with transplanting "sicker patients" with higher MELD scores, and although no difference in survival is observed on a national level, outcomes appear to be concerning in some regions.

Antibody-Mediated Rejection in Sensitized Nonhuman Primates: Modeling Human Biology.

We have established a model of sensitization in nonhuman primates and tested two immunosuppressive regimens. Animals underwent fully mismatched skin transplantation, and donor-specific antibody (DSA) response was monitored by flow cross-match. Sensitized animals subsequently underwent kidney transplantation from their skin donor. Immunosuppression included tacrolimus, mycophenolate, and methylprednisolone. Three animals received basiliximab induction; compared with nonsensitized animals, they showed a shorter mean survival time (4.7 ± 3.1 vs. 187 ± 88 days). Six animals were treated with T cell depletion (anti-CD4/CD8 mAbs), which prolonged survival (mean survival time 21.6 ± 19.0 days). All presensitized animals showed antibody-mediated rejection (AMR). In two of three basiliximab-injected animals, cellular rejection (ACR) was prominent. After T cell depletion, three of six monkeys experienced early acute rejection within 8 days with histological evidence of thrombotic microangiopathy and AMR. The remaining three monkeys survived 27-44 days, with mixed AMR and ACR. Most T cell-depleted animals experienced a rebound of DSA that correlated with deteriorating kidney function. We also found an increase in proliferating memory B cells (CD20(+) CD27(+) IgD(-) Ki67(+) ), lymph node follicular helper T cells (ICOS(+) PD-1(hi) CXCR5(+) CD4(+) ), and germinal center (GC) response. Depletion controlled cell-mediated rejection in sensitized nonhuman primates better than basiliximab, yet grafts were rejected with concomitant DSA rise. This model provides an opportunity to test novel desensitization strategies.

Belatacept: is there BENEFIT for liver transplantation too?

The results of the multicenter belatacept liver transplant trial disappoint with respect to safety and efficacy, and new approaches will be required before this agent plays a role in liver transplant immunosuppression. See article by Klintmalm et al on page 1817.

Costimulation blockade alters germinal center responses and prevents antibody-mediated rejection.

De novo donor-specific antibody (DSA) after organ transplantation promotes antibody-mediated rejection (AMR) and causes late graft loss. Previously, we demonstrated that depletion using anti-CD3 immunotoxin combined with tacrolimus and alefacept (AMR regimen) reliably induced early DSA production with AMR in a nonhuman primate kidney transplant model. Five animals were assigned as positive AMR controls, four received additional belatacept and four received additional anti-CD40 mAb (2C10R4). Notably, production of early de novo DSA was completely attenuated with additional belatacept or 2C10R4 treatment. In accordance with this, while positive controls experienced a decrease in peripheral IgM(+) B cells, bela- and 2C10R4-added groups maintained a predominant population of IgM(+) B cells, potentially indicating decreased isotype switching. Central memory T cells (CD4(+) CD28(+) CD95(+)) as well as PD-1(hi) CD4(+) T cells were decreased in both bela-added and 2C10R4-added groups. In analyzing germinal center (GC) reactions in situ, lymph nodes further revealed a reduction of B cell clonal expansion, GC-follicular helper T (Tfh) cells, and IL-21 production inside GCs with additional belatacept or 2C10R4 treatment. Here we provide evidence that belatacept and 2C10R4 selectively suppresses the humoral response via regulating Tfh cells and prevents AMR in this nonhuman primate model.

The role of donor-specific HLA alloantibodies in liver transplantation.

The impact of donor-specific HLA alloantibodies (DSA) on short- and long-term liver transplant outcome is not clearly defined. While it is clear that not all levels of allosensitization produce overt clinical injury, and that liver allografts possess some degree of alloantibody resistance, alloantibody-mediated adverse consequences are increasingly being recognized. To better define the current state of this topic, we assembled experts to provide insights, explore controversies and develop recommendations for future research on the consequences of DSA in liver transplantation. This article summarizes the proceedings of this inaugural meeting. Several insights emerged. Acute antibody-mediated rejection (AMR), although rarely diagnosed, is increasingly understood to overlap with T cell-mediated rejection. Isolated liver allograft recipients are at increased risk of early allograft immunologic injury when preformed DSA are high titer and persist posttransplantation. Persons who undergo simultaneous liver-kidney transplantation are at risk of renal AMR when Class II DSA persist posttransplantation. Other under-appreciated DSA associations include ductopenia and fibrosis, plasma cell hepatitis, biliary strictures and accelerated fibrosis associated with recurrent liver disease. Standardized DSA testing and diagnostic criteria for both acute and chronic AMR are needed to distil existing associations into etiological processes in order to develop responsive therapeutic strategies.

Anti-CD40 ligand monoclonal antibody delays the progression of murine autoimmune cholangitis.

While there have been significant advances in our understanding of the autoimmune responses and the molecular nature of the target autoantigens in primary biliary cirrhosis (PBC), unfortunately these data have yet to be translated into new therapeutic agents. We have taken advantage of a unique murine model of autoimmune cholangitis in which mice expressing a dominant negative form of transforming growth factor ß receptor II (dnTGFßRII), under the control of the CD4 promoter, develop an intense autoimmune cholangitis associated with serological features similar to human PBC. CD40-CD40 ligand (CD40L) is a major receptor-ligand pair that provides key signals between cells of the adaptive immune system, prompting us to determine the therapeutic potential of treating autoimmune cholangitis with anti-CD40L antibody (anti-CD40L; MR-1). Four-week-old dnTGFßRII mice were injected intraperitoneally with either anti-CD40L or control immunoglobulin (Ig)G at days 0, 2, 4 and 7 and then weekly until 12 or 24 weeks of age and monitored for the progress of serological and histological features of PBC, including rigorous definition of liver cellular infiltrates and cytokine production. Administration of anti-CD40L reduced liver inflammation significantly to 12 weeks of age. In addition, anti-CD40L initially lowered the levels of anti-mitochondrial autoantibodies (AMA), but these reductions were not sustained. These data indicate that anti-CD40L delays autoimmune cholangitis, but the effect wanes over time. Further dissection of the mechanisms involved, and defining the events that lead to the reduction in therapeutic effectiveness will be critical to determining whether such efforts can be applied to PBC.

Enhanced de novo alloantibody and antibody-mediated injury in rhesus macaques.

Chronic allograft rejection is a major impediment to long-term transplant success. Humoral immune responses to alloantigens are a growing clinical problem in transplantation, with mounting evidence associating alloantibodies with the development of chronic rejection. Nearly a third of transplant recipients develop de novo antibodies, for which no established therapies are effective at preventing or eliminating, highlighting the need for a nonhuman primate model of antibody-mediated rejection. In this report, we demonstrate that depletion using anti-CD3 immunotoxin (IT) combined with maintenance immunosuppression that included tacrolimus with or without alefacept reliably prolonged renal allograft survival in rhesus monkeys. In these animals, a preferential skewing toward CD4 repopulation and proliferation was observed, particularly with the addition of alefacept. Furthermore, alefacept-treated animals demonstrated increased alloantibody production (100%) and morphologic features of antibody-mediated injury. In vitro, alefacept was found to enhance CD4 effector memory T cell proliferation. In conclusion, alefacept administration after depletion and with tacrolimus promotes a CD4+memory T cell and alloantibody response, with morphologic changes reflecting antibody-mediated allograft injury. Early and consistent de novo alloantibody production with associated histological changes makes this nonhuman primate model an attractive candidate for evaluating targeted therapeutics.

Patterns of de novo allo B cells and antibody formation in chronic cardiac allograft rejection after alemtuzumab treatment.

Even though the etiology of chronic rejection (CR) is multifactorial, donor specific antibody (DSA) is considered to have a causal effect on CR development. Currently the antibody-mediated mechanisms during CR are poorly understood due to lack of proper animal models and tools. In a clinical setting, we previously demonstrated that induction therapy by lymphocyte depletion, using alemtuzumab (anti-human CD52), is associated with an increased incidence of serum alloantibody, C4d deposition and antibody-mediated rejection in human patients. In this study, the effects of T cell depletion in the development of antibody-mediated rejection were examined using human CD52 transgenic (CD52Tg) mice treated with alemtuzumab. Fully mismatched cardiac allografts were transplanted into alemtuzumab treated CD52Tg mice and showed no acute rejection while untreated recipients acutely rejected their grafts. However, approximately half of long-term recipients showed increased degree of vasculopathy, fibrosis and perivascular C3d depositions at posttransplant day 100. The development of CR correlated with DSA and C3d deposition in the graft. Using novel tracking tools to monitor donor-specific B cells, alloreactive B cells were shown to increase in accordance with DSA detection. The current animal model could provide a means of testing strategies to understand mechanisms and developing therapeutic approaches to prevent chronic rejection.

Donor-directed MHC class I antibody is preferentially cleared from sensitized recipients of combined liver/kidney transplants.

For patients with chronic renal and liver diseases, simultaneous liver and kidney transplantation (SLKT) is the best therapeutic option. The role of a pretransplant donor-specific antibody (DSA) in SLKT is unclear. We report the results of a retrospective review from 7/08 to 10/09 of SLKT at our institution. Monitoring of DSA was performed using single antigen bead assay. Between 7/08 and 10/09, there were six SLKT who had preformed DSA and positive XM (four class I and II DSA, one class I DSA only, one class II only). One-year patient and renal graft survival was 83%. Death-censored liver allograft survival was 100%. Acute humoral rejection (AHR) of the kidney occurred in 66% (three with both class I and II DSA and one with only class II DSA) of patients. In those with AHR, class I antibodies were rapidly cleared (p < 0.01) while class II antibodies persisted (p = 0.25). All patients who had humoral rejection of their kidney had preformed anticlass II antibodies. Liver allografts may not be fully protective of the renal allograft, especially with pre-existing MHC class II DSA. Long-term and careful follow-up will be critical to determine the impact of DSA on both allografts.

Treatment with humanized monoclonal antibody against CD154 prevents acute renal allograft rejection in nonhuman primates.

CD154 is the ligand for the receptor CD40. This ligand-receptor pair mediates endothelial and antigen-presenting cell activation, and facilitates the interaction of these cells with T cells and platelets. We demonstrate here that administration of a CD154-specific monoclonal antibody (hu5C8) allows for renal allotransplantation in outbred, MHC-mismatched rhesus monkeys without acute rejection. The effect persisted for more than 10 months after therapy termination, and no additional drug was required to achieve extended graft survival. Indeed, the use of tacrolimus or chronic steroids seemed to antagonize the anti-rejection effect. Monkeys treated with antibody against CD154 remained healthy during and after therapy. The mechanism of action does not require global depletion of T or B cells. Long-term survivors lost their mixed lymphocyte reactivity in a donor-specific manner, but still formed donor-specific antibody and generated T cells that infiltrated the grafted organ without any obvious effect on graft function. Thus, therapy with antibody against CD154 is a promising agent for clinical use in human allotransplantation.

Early and limited use of tacrolimus to avoid rejection in an alemtuzumab and sirolimus regimen for kidney transplantation: clinical results and immune monitoring.

Alemtuzumab induction with 60 days of tacrolimus treatment and continuous sirolimus treatment prevented acute rejection in nine of 10 consecutive renal allograft recipients. All patients are alive with a functioning kidney graft at 27-39 months of follow-up. Extensive immune monitoring was performed in all patients. Alloantibody detection, cytokine kinetics assay (CKA), and trans vivo delayed-type hypersensitivity (DTH) assay were performed every 6 months showing correlation with clinical evolution. Despite alloantibody presence in five patients, eight patients remain without the need for specific treatment and only sirolimus monotherapy in decreasing dosage. Four patients take only 1 mg sirolimus daily with levels of 3-4 ng/mL. One patient showed clinical signs of rejection at month 9 post-transplant, with slow increase in serum creatinine and histological signs of mixed cellular (endarteritis) and humoral rejection (C4d positivity in peritubular capillaries and donor-specific antibody (DSA)). In summary, the addition of tacrolimus therapy for 2 months to a steroid-free, alemtuzumab induction and sirolimus maintenance protocol limited the previously shown acute rejection development. Nevertheless, alloantibody was present in serum and/or C4d present on 1-year biopsy in half the patients. The combination of CKA and DSA monitoring or the performance of transvivo DTH correlated with immune status of the patients.

Calcineurin inhibitor withdrawal after renal transplantation with alemtuzumab: clinical outcomes and effect on T-regulatory cells.

To address the results of calcineurin inhibitor (CNI) withdrawal after alemtuzumab induction relative to CNI continuation, we performed a pilot randomized clinical trial in renal allograft recipients on CNI, a mycophenolic acid derivative and steroids after the first 2 months posttransplantation. Forty patients were randomized to taper off CNI or to maintain it, and followed for at least 1 year. Four patients in the withdrawal group were treated for acute rejection while no patient received antirejection treatment in the control group. Two control patients withdrew CNI due to nephrotoxicity. Estimated GFR was similar in both groups after 1 year. Flow cytometry of CD4(+)CD25(+)CTLA-4(+)FoxP3(+) regulatory T cells (Treg) demonstrated a significant increase in Treg percentages in the peripheral blood of alemtuzumab-treated patients on CNI early postransplant. Furthermore, the increased Treg percentages in the withdrawal cohort were unchanged at month 6 postenrollment, whereas they decreased significantly in those patients maintained on CNI. Patients withdrawn from CNI after alemtuzumab trend toward a higher rejection rate, but most patients can be weaned from a CNI using this regimen. With the exception of maintaining increased Treg levels, the benefits are not appreciable in this short follow-up, and a larger randomized trial is justified.

CD4+ CD25+ FOXP3+ regulatory T cells increase de novo in kidney transplant patients after immunodepletion with Campath-1H.

Campath-1H (Alemtuzumab) is an effective immunodepletion agent used in renal transplantation. To evaluate its influence on T lymphocytes during repletion, we analyzed peripheral blood from Campath-1H-treated renal allograft recipients for the presence of FOXP3(+) regulatory T (Treg) cells. Flow cytometry demonstrated that CD4(+)CD25(+)FOXP3(+) lymphocytes increased significantly within the CD4(+) T-cell population, skewing Treg/Teff (T effector) ratios for up to several years. In contrast, Treg levels in patients treated with anti-CD25 (Basiliximab) and maintained on CsA demonstrated a sustained decrease. The increase in Tregs in Campath-1H treated patients developed independent of maintenance immunosuppression. Importantly, the increase in Tregs was not fully explained by their homeostatic proliferation, increased thymic output, or Treg sparing, suggesting de novo generation/expansion. Consistent with this, in vitro stimulation of PBMCs with Campath-1H, with or without anti-CD3, activation led to an increase in CD4(+)CD25(+)FOXP3(+) cells that had suppressive capabilities. Together, these data suggest that Campath-1H promotes an increase in peripheral Tregs and may act as an intrinsic generator of Tregs in vivo.

A comparison of alemtuzumab with basiliximab induction in simultaneous pancreas-kidney transplantation.

Alemtuzumab is a humanized, rat monoclonal antibody directed against the CD52 antigen. After binding, alemtuzumab causes profound and durable depletion and has been successfully used as immune induction therapy for organ transplantation. This was a single center, retrospective review of patients who underwent simultaneous pancreas-kidney transplantation at the University of Wisconsin using alemtuzumab induction therapy compared with historical controls that received induction with basiliximab. There were no differences in donor or recipient demographics, rates of patient survival, renal or pancreas allograft survival, renal allograft delayed graft function, EBV infection, BKV infection, PTLD or sepsis. There was a statistically significant increase in the incidence of cytomegalovirus (CMV) infection in the alemtuzumab-treated group. Given the significantly higher incidence of CMV infections, we have since altered our induction protocol to consist of a single 30 mg dose of alemtuzumab instead of two doses. The long-term effects of this change remain to be seen. Due to the results seen in this study, the low initial cost of the drug and the absence of any severe, short-term side effects, alemtuzumab has been selected as the induction drug of choice at our center for patients undergoing SPK.

Unaltered graft survival and intragraft lymphocytes infiltration in the cardiac allograft of Cxcr3-/- mouse recipients.

Previous studies showed that absence of chemokine receptor Cxcr3 or its blockade prolong mouse cardiac allograft survival. We evaluated the effect of the CXCR3 receptor antagonist MRL-957 on cardiac allograft survival, and also examined the impact of anti-CXCR3 mAb in human CXCR3 knock-in mice. We found only a moderate increase in graft survival (10.5 and 16.6 days, p < 0.05) using either the antagonist or the antibody, respectively, compared to control (8.7 days). We re-evaluated cardiac allograft survival with two different lines of Cxcr3(-/-) mice. Interestingly, in our hands, neither of the independently derived Cxcr3(-/-) lines showed remarkable prolongation, with mean graft survival of 9.5 and 10.8 days, respectively. There was no difference in the number of infiltrating mononuclear cells, expansion of splenic T cells or IFN-gamma production of alloreactive T cells. Mechanistically, an increased other chemokine receptor fraction in the graft infiltrating CD8 T cells in Cxcr3(-/-) recipients compared to wild-type recipients suggested compensatory T-cell trafficking in the absence of Cxcr3. We conclude Cxcr3 may contribute to, but does not govern, leukocyte trafficking in this transplant model.

The impact of donor variables on the outcome of orthotopic liver transplantation for hepatitis C.

Morphologic characteristics of the graft have been proposed as a major contributor to the long-term outcomes in orthotopic liver transplantation (OLT). Our objective was to determine the impact of donor variables, including donor age, donor-recipient HLA match, and type of donation (DCD vs donation after brain death [DBD]), on the outcome of OLT in 192 patients with hepatitis C virus (HCV). Fourteen patients underwent OLT from donation after cardiac death (DCD) donors and 188 from DBD donors. Mean donor age, warm ischemia time at recovery, and cold ischemia time were similar between the groups. Overall graft survival rate at 1 year (55% DCD vs 85% DBD) and 5 years (46% DCD vs 78% DBD) was significantly lower in the DCD group (P = .0003). Similarly, patient survival rate at 1 year (62% DCD vs 93% DBD) and 5 years (62% DCD vs 82% DBD) was significantly lower in the DCD group (P = .0295). Incidences of hepatic artery thrombosis, portal vein thrombosis, and primary nonfunction were similar between the DCD and DBD groups. The incidence of liver abscess with ischemic-type biliary stricture was higher in recipients from DCD as compared with DBD (42% vs 2%). A trend toward lower graft survival was noted in recipients from donors older than 60 years of age in the HCV population (P = .07), with statistically lower patient survival (P = .02). Donor- recipient HLA matching did not appear to correlate with OLT outcome in patients with HCV. DCD donors and donors older than 60 years of age significantly impact patient and graft survival. Lower graft and patient survival in recipients from DCD donors does not appear to be related to early disease recurrence.