Transplanting the highly sensitized patient: The emory algorithm

A pig allograft model of antibody-mediated rejection

Allograft rejection caused by antibodies in sensitised individuals remains a real problem in human allotransplantation. There would be value in a simple model of this process to evaluate the mechanisms involved in antibody-mediated damage and the development of accommodation, as well as the impact of potential interventions. We have thus developed a novel large animal model of this process using an allosensitisation system. Two inbred lines of miniature pigs that carry different major histocompatibility antigen haplotypes were used. Pigs of one line were sensitised by the sequential subcutaneous injection of major histocompatibility antigen-mismatched allogeneic peripheral blood mononuclear cells derived from the other inbred line. We demonstrated that this generated high titres of allospecific antibodies. We then transplanted carotid arteries from donors syngeneic to the priming cells into the sensitised animals. After 48 h these vessels showed a profound mononuclear cell inflammatory infiltrate in both intima and media, fibrin deposition, and luminal compromise with thrombus and antibody deposition. The mean endothelial surface affected by this process was 59.2%. No such pathology was seen in any of the controls. This model is technically simple to perform with few post-operative complications. It provides proof-of-principle of a model of antibody-mediated rejection which will be of potential value in elucidating the mechanisms underlying the process and the efficacy of interventions to prevent or treat it.

Donor-specific antibodies by flow single antigen beads in pediatric living donor kidney transplants: single center experience

Flow PRA and SAB are now routinely performed to identify HLA antibodies in the recipient sera. The presence of DSA is considered a risk factor for graft failure. However, this risk is not clearly defined. We reviewed all the pediatric recipients of living donor kidney transplants since Flow PRA and Flow SAB became routinely done at our institution. All children had negative CDC and Flow XMs. Comparison of clinical outcome was done between those with and without pretransplant DSA. Six children had positive DSA by Flow SAB. They received thymoglobulin, steroids, tacrolimus, and MMF. Five had anti-HLA class I antibodies and one anti-HLA class II. Only one child had an AR. Graft survival: 100% at last visit with GFR >70 mL/min/1.73 m(2). A control group without DSA was used for comparison (n = 44). They received our standard protocol: basiliximab, tacrolimus, MMF, and steroids. AR rate was 9%. Both groups had similar follow-up time, and patient and graft survival rates. In our small series, we saw excellent outcome despite the presence of DSA pretransplant. No unequivocal ideal to establish the ideal immunosuppressive regimen for this cohort of patients has been established and the long-term outcome of these recipients has not been delineated.

Alemtuzumab (Campath 1H) induction with tacrolimus monotherapy is safe for high immunological risk renal transplantation

Immunosuppression for immunologically high-risk renal transplant patients usually involves antithymocyte globulin induction with triple drug maintenance therapy. Alemtuzumab, a humanized anti-CD52 antibody, has shown promise in tolerogenic induction protocols, requiring minimal maintenance immunosuppression. In this prospective, open-label, randomized, controlled trial, we enrolled 21 high immunological risk patients (i.e., panel reactive antibody>20% or previous transplant). Patients received either single-dose alemtuzumab given before graft reperfusion, with tacrolimus monotherapy, or four doses of Thymoglobulin with tacrolimus, mycophenolate, and steroids. Median follow-up was 377 days. One patient in the Thymoglobulin group who suffered primary graft nonfunction died. One-year cumulative graft survival was 85.7% for the alemtuzumab group and 87.5% for the Thymoglobulin group. Two alemtuzumab and three Thymoglobulin patients suffered rejection episodes. Infection rates were similar. Early results of this ongoing study indicate that a tolerogenic protocol with alemtuzumab induction and tacrolimus maintenance monotherapy is safe in immunologically high-risk renal transplant patients.

Pretransplant HLA antibodies are associated with reduced graft survival after clinical islet transplantation

Despite significant improvements in islet transplantation, long-term graft function is still not optimal. It is likely that both immune and nonimmune factors are involved in the deterioration of islet function over time. Historically, the pretransplant T-cell crossmatch and antibody screening were done by anti-human globulin--complement-dependent cytotoxicity (AHG-CDC). Class II antibodies were not evaluated. In 2003, we introduced solid-phase antibody screening using flow-based beads and flow crossmatching. We were interested to know whether pretransplant human leukocyte antigen (HLA) antibodies or a positive flow crossmatch impacted islet function post-transplant. A total of 152 islet transplants was performed in 81 patients. Islet function was determined by a positive C-peptide. Results were analyzed by procedure. Class I and class II panel reactive antibody (PRA) > 15% and donor-specific antibodies (DSA) were associated with a reduced C-peptide survival (p<0.0001 and p<0.0001, respectively). A positive T- and or B-cell crossmatch alone was not. Pretransplant HLA antibodies detectable by flow beads are associated with reduced graft survival. This suggests that the sirolimus and low-dose tacrolimus-based immunosuppression may not control the alloimmune response in this presensitized population and individuals with a PRA > 15% may require more aggressive inductive and maintenance immunosuppression, or represent a group that may not benefit from islet transplantation.