Rapid reduction in donor-specific anti-human leukocyte antigen antibodies and reversal of antibody-mediated rejection with bortezomib in pediatric heart transplant patients

Bortezomib for refractory autoimmunity in pediatrics

Therapy of refractory autoimmunity remains challenging. In this study, we evaluated the therapeutic effect of bortezomib, a proteasome inhibitor, by targeting plasma cells in 7 patients (median age, 9.9 years). Four doses of bortezomib were administered at a dose of 1.3 mg/m(2) intravenously (n = 6) or subcutaneously (n = 1) every 72 hours. Bortezomib was administered at a median of 120 days from laboratory confirmation of autoantibodies. All patients had failed 2 or more standard therapies. Rituximab was administered on the first day if B cells were present, and all patients received plasmapheresis 2 hours before bortezomib administration. Six patients experienced resolution of cytopenias. Two of 6 patients experienced recurrence of cytopenias after initial response. Adverse effects include nausea (n = 1), thrombocytopenia (n = 2), Clostridium difficile colitis (n = 1)), febrile neutropenia (n = 1), and cellulitis at the subcutaneous injection site (n = 1). Our experience suggests that bortezomib may be beneficial in the treatment of refractory autoimmunity in children.

Transplanting the highly sensitized patient: trials and tribulations

PURPOSE OF REVIEW

Humoral sensitization to antigens of the human leukocyte antigen and ABO systems remains one of the largest barriers to further expansion in renal transplantation. This barrier translates into prolonged waiting time and a greater likelihood of death. The number of highly sensitized patients on the renal transplant waiting list continues to increase. This review focuses on the options available to these patients and speculates on future directions for incompatible transplantation.

RECENT FINDINGS

Desensitization protocols (to remove antibodies), kidney-paired donation (to circumvent antibodies) or a hybrid technique involving a combination of both have broadened the access to transplantation for patients disadvantaged by immunologic barriers. However, the risk of antibody-mediated rejection may be increased and warrants caution. Technical advances in antibody characterization using sensitive bead immunoassays and the C1q assay and therapeutic modalities such as complement inhibitors and proteasome inhibitors have been used to avoid or confront these antibody incompatibilities.

SUMMARY

A growing body of knowledge and literature indicates that these diagnostic and therapeutic modalities can facilitate a safer and more successful treatment course for these difficult-to-treat patients. Rigorous investigations into newer interventions will help in broadening the options for these patients and also expand the living donor pool.

Coincidence of cellular and antibody mediated rejection in heart transplant recipients - preliminary report

Antibody mediated rejection (AMR) can significantly influence the results of orthotopic heart transplantation (OHT). However, AMR and cellular rejection (CR) coexistence is poorly described. Therefore we performed a prospective pilot study to assess AMR/CR concomitance in endomyocardial biopsies (EMBs) obtained electively in 27 OHT recipients (21 M/6 F, 45.4 ± 14.4 y/o). Biopsy samples were paraffin embedded and processed typically with hematoxylin/eosin staining to assess CR, and, if a sufficient amount of material remained, treated with immunohistochemical methods to localize particles C3d and C4d as markers of antibody dependent complement activation. With this approach 80 EMBs, including 41 (51%) harvested within the first month after OHT, were qualified for the study. Among them 14 (18%) were C3d+, 37 (46%) were C4d+, and 12 (15%) were both C3d and C4d positive. At least one C3d+, C4d+, and C3d/C4d+ EMB was found in 10 (37%), 17 (63%), and 8 (30%) patients, respectively. Among 37 CR0 EMBs C3d was observed in 4 (11%), C4d in 17 (46%), and both C3d/C4d in 3 (8%) cases. Among 28 CR1 EMBs C3d was observed in 3 (11%), C4d in 11 (39%), and C3d/C4d in 3 (11%) cases. Among 15 CR2 EMBs C3d was observed in 7 (47%), C4d in 9 (60%), and C3d/C4d in 6 (40%) cases. Differences in C3d and C3d/C4d occurrence between grouped CR0-1 EMBs and CR2 EMBs (7/65 – 11% vs. 7/15 – 47%; 6/65 – 9% vs. 6/15 – 40%) were significant (p = 0.0035 and p = 0.0091, respectively, χ² test). In conclusion, apparently frequent CR and AMR coexistence demonstrated in this preliminary study warrants further investigation in this field.

Issues in solid-organ transplantation in children: translational research from bench to bedside

In this review, we identify important challenges facing physicians responsible for renal and cardiac transplantation in children based on a review of the contemporary medical literature. Regarding pediatric renal transplantation, we discuss the challenge of antibody-mediated rejection, focusing on both acute and chronic antibody-mediated rejection. We review new diagnostic approaches to antibody-mediated rejection, such as panel-reactive antibodies, donor-specific cross-matching, antibody assays, risk assessment and diagnosis of antibody-mediated rejection, the pathology of antibody-mediated rejection, the issue of ABO incompatibility in renal transplantation, new therapies for antibody-mediated rejection, inhibiting of residual antibodies, the suppression or depletion of B-cells, genetic approaches to treating acute antibody-mediated rejection, and identifying future translational research directions in kidney transplantation in children. Regarding pediatric cardiac transplantation, we discuss the mechanisms of cardiac transplant rejection, including the role of endomyocardial biopsy in detecting graft rejection and the role of biomarkers in detecting cardiac graft rejection, including biomarkers of inflammation, cardiomyocyte injury, or stress. We review cardiac allograft vasculopathy. We also address the role of genetic analyses, including genome-wide association studies, gene expression profiling using entities such as AlloMap®, and adenosine triphosphate release as a measure of immune function using the Cylex® ImmuKnow™ cell function assay. Finally, we identify future translational research directions in heart transplantation in children.

New immunosuppressive agents in pediatric transplantation

Immunosuppressive therapy in pediatrics continues to evolve. Over the past decade, newer immunosuppressive agents have been introduced into adult and pediatric transplant patients with the goal of improving patient and allograft survival. Unfortunately, large-scale randomized clinical trials are not commonly performed in children. The purpose of this review is to discuss the newer immunosuppressive agents available for induction therapy, maintenance immunosuppression, and the treatment of rejection.

Acute antibody-mediated rejection in pediatric kidney transplants: a single center experience

aAMR is a potentially devastating complication of kidney transplantation. The incidence of aAMR in children, while thought to be rare, is not well defined, and there is a paucity of data on treatment regimens in children. We retrospectively reviewed the outcomes of our pediatric patients that were treated for aAMR between 2007 and 2009. Three adolescent Hispanic males were found to have aAMR. All three received deceased donor transplants, and all three verbalized non-adherence. Treatment consisted of rituximab, solumedrol, PE, and IVIgG in one patient, and PE, IVIgG, and bortezomib in two patients. The only side effect of therapy noted was mild hypotension with rituximab that resolved after decreasing the infusion rate. There were no reported infections two yr after treatment, and all of the viral monitoring in these patients remained negative.

Increased levels of anti-non-Gal IgG following pig-to-baboon bone marrow transplantation correlate with failure of engraftment

BACKGROUND

The development of genetically modified pigs, which lack the expression of alpha 1-3 galactosyl transferase, (GalT-KO pigs) has facilitated the xenogeneic transplantation of porcine organs and tissues into primates by avoiding hyperacute rejection due to pre-existing antibodies against the Gal epitope. However, antibodies against other antigens (anti-non-Gal antibodies), are found at varying levels in the pre-transplant sera of most primates. We have previously found that baboons with high levels of pre-transplant anti-non-Gal IgG, conditioned with a non-myeloablative conditioning regimen, failed to engraft following pig-to-baboon bone marrow transplantation (Xenotransplantation, 17, 2010 and 300). Two baboons with low levels of pre-transplant anti-non-Gal IgG, conditioned with the same regimen, showed porcine bone marrow progenitors at 28 days following transplantation, suggesting engraftment. These baboons also showed evidence of donor-specific hyporesponsiveness. This observation led us to investigate the hypothesis that selecting for baboon recipients with low pre-transplant anti-non-Gal IgG levels might improve engraftment levels following GalT-KO pig-to-baboon bone marrow transplantation.

METHODS

Five baboons, with low pre-transplant anti-non-Gal IgG levels, received transplantation of bone marrow cells (1-5 × 10(9) /kg of recipient weight) from GalT-KO pigs. They received a non-myeloablative conditioning regimen consisting of low-dose total body irradiation (TBI) (150 cGy), thymic irradiation (700 cGy), anti-thymocyte globulin (ATG), and tacrolimus. In addition, two baboons received Rituximab and Bortezomib (Velcade) treatment as well as extra-corporeal immunoadsorption using GalT-KO pig livers. Bone marrow engraftment was assessed by porcine-specific PCR on colony forming units (CFU) of day 28 bone marrow aspirates. Anti-non-Gal antibody levels were assessed by serum binding toward GalT-KO PBMC using flow cytometry (FACS). Peripheral macro-chimerism was measured by FACS using pig and baboon-specific antibodies and baboon anti-pig cellular responses were assessed by mixed lymphocyte reactions (MLR).

RESULTS

As previously reported, two of five baboons demonstrated detectable bone marrow engraftment at 4 weeks after transplantation. Engraftment was associated with lack of an increase in anti-non-Gal IgG levels as well as cellular hyporesponsiveness toward pig. Three subsequent baboons with similarly low levels of pre-existing anti-non-Gal IgG showed no engraftment and an increase in anti-non-Gal IgG antibody levels following transplantation. Peripheral macrochimerism was only seen for a few days following transplantation regardless of antibody development.

CONCLUSIONS

Selecting for baboon recipients with low levels of pre-transplant anti-non-Gal IgG did not ensure bone marrow engraftment. Failure to engraft was associated with an increase in anti-non-Gal IgG levels following transplantation. These results suggest that anti-non-Gal-IgG is likely involved in early bone marrow rejection and that successful strategies for combating anti-non-Gal IgG development may allow better engraftment. Since engraftment was only low and transient regardless of antibody development, innate immune, or species compatibility mechanisms will likely also need to be addressed to achieve long term engraftment.

Minimal effect of bortezomib in reducing anti-pig antibodies in human leukocyte antigen-sensitized patients: a pilot study

BACKGROUND

Bortezomib, a proteasome inhibitor used to treat multiple myeloma, has been administered (± plasma exchange ± intravenous immunoglobulin [IVIg]) in attempts to reduce antibodies against human leukocyte antigens (HLA) in sensitized patients undergoing organ transplantation. To our knowledge, bortezomib has not been investigated for its effect on natural anti-pig antibodies. If bortezomib could reduce the production of anti-pig antibodies, this would likely be beneficial to the outcome of pig organ grafts in primates.

METHODS

Nine patients received bortezomib either to reduce anti-HLA antibody levels before organ allotransplantation or to treat antibody-mediated rejection. Patients at the Mayo Clinic (Group 1; n = 4) received bortezomib alone, whereas at the UPMC (Group 2; n = 5), this was combined with plasmaphereses ± IVIg in some cases. Anti-pig IgM and IgG levels against wild-type (WT) and α1,3-galactosyltransferase gene knockout (GTKO) pig aortic endothelial cells (flow cytometry-relative mean fluorescence intensity) and anti-Gal IgM and IgG (ELISA-OD480 nm ) were measured pre- and post-bortezomib therapy.

RESULTS

Mean anti-pig IgM levels were 11.2 (WT) and 1.9 (GTKO) pre-bortezomib treatment and 9.4 (WT: P = 0.02) and 1.7 (GTKO: P = 0.33) post-bortezomib treatment, respectively. Mean anti-pig IgG levels were 4.3 (WT) and 1.5 (GTKO) pre-bortezomib treatment and 3.6 (WT: P = 0.21) and 1.4 (GTKO: P = 0.20) post-bortezomib treatment, respectively. Mean anti-Gal IgM and IgG levels were 0.7 and 1.1, respectively, pre-treatment, and 0.6 (P = 0.03) and 1.1 (NS), respectively, post-treatment. When the data were analyzed in Groups 1 and 2 separately, there were no significant differences between the pre- and post-bortezomib levels of anti-pig, anti-non-Gal, or anti-Gal IgM or IgG.

CONCLUSIONS

From this limited study, we conclude that bortezomib might reduce anti-Gal IgM levels in primates, but, in this respect alone, is unlikely to have any significant effect on the outcome of GTKO pig organ transplantation.

Reversing endogenous alloreactive B cell GC responses with anti-CD154 or CTLA-4Ig

Alloantibodies mediate acute antibody-mediated rejection as well as chronic allograft rejection in clinical transplantation. To better understand the cellular dynamics driving antibody production, we focused on the activation and differentiation of alloreactive B cells in the draining lymph nodes and spleen following sensitization to allogeneic cells or hearts. We used a modified staining approach with a single MHC Class I tetramer (K(d)) bound to two different fluorochromes to discriminate between the Class I-binding and fluorochrome-streptavidin-binding B cells with a high degree of specificity and binding efficiency. By Day 7-8 postsensitization, there was a 1.5- to 3.2-fold increase in the total numbers of K(d) -binding B cells. Within this K(d) -binding B cell population, approximately half were IgD(low) , MHC Class II(high) and CD86(+), 30-45% expressed a germinal center (Fas(+) GL7(+)) phenotype and 3-12% were IRF4(hi) plasma cells. Remarkably, blockade with anti-CD40 or CTLA-4Ig, starting on Day 7 postimmunization for 1 or 4 weeks, completely dissolved established GCs and halted further development of the alloantibody response. Thus MHC Class I tetramers can specifically track the in vivo fate of endogenous, Class I-specific B cells and was used to demonstrate the ability of delayed treatment with anti-CD154 or CTLA-4Ig to halt established allo-B cell responses.

Quantification, identification, and relevance of anti-human leukocyte antigen antibodies formed in association with the berlin heart ventricular assist device in children

BACKGROUND

Ventricular assist devices (VADs) are increasingly being used in pediatric patients to provide long-term cardiac support. One potential complication of VAD therapy is the development of antibodies directed against human leukocyte antigens (HLA). This phenomenon has not been well described with the Berlin Heart EXCOR VAD, the most commonly used VAD in pediatric patients.

METHODS

The records of all pediatric patients undergoing VAD support using the Berlin Heart device at our institution between April 2005 and August 2011 were reviewed retrospectively. Demographic and clinical data regarding the VAD course were collected. Assessment of anti-HLA antibodies was performed using Luminex, and antibodies were quantified using mean fluorescence intensity (MFI). Assessment for anti-HLA antibodies was performed before VAD implantation and in serial fashion after VAD implantation. Clinically significant anti-HLA antibodies (sensitization) were defined by an MFI of more than 1000.

RESULTS

Thirty-six patients were supported with the Berlin Heart VAD; 13 met inclusion criteria. The majority (85%) carried the diagnosis of dilated cardiomyopathy. Evidence of sensitization pre-VAD was found in 69%; new-onset sensitization (the development of new antibodies on VAD) occurred in 69%. All patients survived to transplantation. In two patients, the retrospective crossmatch was positive, but only in one patient was the crossmatch positive for antibodies formed while on VAD.

CONCLUSIONS

Using Luminex and MFI quantification, anti-HLA antibodies are common before VAD implantation in pediatric patients. While on VAD support, new anti-HLA antibodies formed in a majority, but the immediate impact of these antibodies appears to be limited.

Regulation of the proteasome by ATP: implications for ischemic myocardial injury and donor heart preservation

Several lines of evidence suggest that proteasomes are involved in multiple aspects of myocardial physiology and pathology, including myocardial ischemia-reperfusion injury. It is well established that the 26S proteasome is an ATP-dependent enzyme and that ischemic heart disease is associated with changes in the ATP content of the cardiomyocyte. A functional link between the 26S proteasome, myocardial ATP concentrations, and ischemic cardiac injury, however, has been suggested only recently. This review discusses the currently available data on the pathophysiological role of the cardiac proteasome during ischemia and reperfusion in the context of the cellular ATP content. Depletion of the myocardial ATP content during ischemia appears to activate the 26S proteasome via direct regulatory effects of ATP on 26S proteasome stability and activity. This implies pathological degradation of target proteins by the proteasome and could provide a pathophysiological basis for beneficial effects of proteasome inhibitors in various models of myocardial ischemia. In contrast to that in the ischemic heart, reduced and impaired proteasome activity is detectable in the postischemic heart. The paradoxical findings that proteasome inhibitors showed beneficial effects when administered during reperfusion in some studies could be explained by their anti-inflammatory and immune suppressive actions, leading to reduction of leukocyte-mediated myocardial reperfusion injury. The direct regulatory effects of ATP on the 26S proteasome have implications for the understanding of the contribution of the 26S proteasome to the pathophysiology of the ischemic heart and its possible role as a therapeutic target.

Pediatric heart transplantation for congenital and restrictive cardiomyopathy

BACKGROUND

Recent reports suggest worse outcomes in pediatric orthotopic heart transplantation (OHT) for congenital heart disease (CHD) and restrictive cardiomyopathy (RCM). We examined early outcomes in these diverse groups of patients in comparison with patients with dilatated cardiomyopathy (DCM).

METHODS

From 2000 to 2011, 209 patients were included: 50 with CHD, 23 with RCM, and 136 with DCM. Early survival was studied, as was the occurrence of acute rejection, donor-specific antibodies (DSAs) and nondonor-specific antibodies (NSDAs), incidence of pulmonary hypertension (PHT), right ventricular failure (RVF), and the need for mechanical circulatory support (MCS).

RESULTS

The incidence of preoperative PHT was greatest in the RCM group (χ(2)p = 0.0006); the requirement for mechanical support before OHT was greatest in patients with DCM. Thirty-day survival was 92.0%, 97.1%, and 100% for patients with CHD, DCM, and RCM respectively. The incidence of RVF was highest for patients with RCM (43.5%; versus CHD, 26.0%; versus DCM, 14.7%). One-year survival estimates for patients with CHD, DCM, and RCM were 92.0%, 97.8%, and 82.6%, respectively (log-rank p = 0.165). Multivariable analysis revealed 4 significant risk factors for mortality: age, incidence of acute rejection, preoperative PHT, and the presence of NDSAs. The occurrence of DSAs was similar, although there was a significantly higher incidence of NDSAs in the CHD and RCM groups (36.0% and 30.4%, respectively, versus 14.0% in the DCM group; χ(2)p = 0.0024).

CONCLUSIONS

Equivalent outcomes are achievable in pediatric OHT despite marked heterogeneity in anatomic and physiologic complexity in recipients. Physiologic factors such as PHT are likely to be more important than anatomic complexities in determining survival. The potential relevance of NDSAs warrants further investigation.

Tolerogenic therapies in transplantation

Since the concept of immunologic tolerance was discovered in the 1940s, the pursuit of tolerance induction in human transplantation has led to a rapid development of pharmacologic and biologic agents. Short-term graft survival remains an all-time high, but successful withdrawal of immunosuppression to achieve operational tolerance rarely occurs outside of liver transplantation. Collaborative efforts through the NIH sponsored Immune Tolerance Network and the European Commission sponsored Reprogramming the Immune System for Establishment of Tolerance consortia have afforded researchers opportunity to evaluate the safety and efficacy of tolerogenic strategies, investigate mechanisms of tolerance, and identify molecular and genetic markers that distinguish the tolerance phenotype. In this article, we review traditional and novel approaches to inducing tolerance for organ transplantation, with an emphasis on their translation into clinical trials.