Intravenous immune globulin treatment inhibits crossmatch positivity and allows for successful transplantation of incompatible organs in living-donor and cadaver recipients

Extending options for highly sensitized patients to receive a suitable kidney graft

Highly sensitized patients (anti-HLA) on the kidney waiting list wait longer for a suitable crossmatch negative organ. At the moment there are two strategies to enhance transplantation of these patients. One approach is the determination of acceptable HLA mismatches and application of this knowledge for the selection of crossmatch negative donors, and the second is the desensitization of patients with intravenous immunoglobulin-based protocols to enable transplantation of an organ from a donor towards which antibodies were originally present. Both approaches have advantages and disadvantages and are only successful in a proportion of the patients. The optimal solution is an integrated strategy whereby desensitization is used for those patients for whom the acceptable mismatch approach is not successful.

Antibody-mediated organ-allograft rejection

Recent studies show that alloantibodies mediate a substantial proportion of graft-rejection episodes, contributing to both early and late graft loss. Rejection that is caused by antibody is mediated by different mechanisms from rejection that is caused by T cells, thereby requiring other approaches to treatment and prevention. Antibody induces rejection acutely through the fixation of complement, resulting in tissue injury and coagulation. In addition, complement activation recruits macrophages and neutrophils, causing additional endothelial injury. Antibody and complement also induce gene expression by endothelial cells, which is thought to remodel arteries and basement membranes, leading to fixed and irreversible anatomical lesions that permanently compromise graft function.

The Dutch national living donor kidney exchange program

The wait time for deceased-donor kidney transplantation has increased to 4-5 years in the Netherlands. Strategies to expand the donor pool include a living donor kidney exchange program. This makes it possible that patients who cannot directly receive a kidney from their intended living donor, due to ABO blood type incompatibility or a positive cross match, exchange donors in order to receive a compatible kidney. All Dutch kidney transplantation centers agreed on a common protocol. An independent organization is responsible for the allocation, cross matches are centrally performed and exchange takes place on an anonymous basis. Donors travel to the recipient centers. Surgical procedures are scheduled simultaneously. Sixty pairs participated within 1 year. For 9 of 29 ABO blood type incompatible and 17 of 31 cross match positive combinations, a compatible pair was found. Five times a cross match positive couple was matched to a blood type incompatible one, where the recipients were of blood type O. The living donor kidney exchange program is a successful approach that does not harm any of the candidates on the deceased donor kidney waitlist. For optimal results, both ABO blood type incompatible and cross match positive pairs should participate.

Current approaches to treatment of antibody-mediated rejection

Antibody-mediated rejection (AMR) has recently been recognized as a significant and unique form of rejection that is not amenable to treatment with standard immunosuppressive medications aimed at modification of T-cell function. Recent interest in AMR and the role of B cells in rejection has been aided by the concomitant discovery that C4d staining of renal biopsy tissue is strongly associated with AMR and a poor prognosis, and the emergence of desensitization protocols for treatment of highly human leukocyte antigen (HLA)-sensitized patients. Treatment options include: (i) the use of high-dose intravenous immunoglobulin (IVIG) which works by blocking anti-HLA antibody activity and through complement inhibition, (ii) the use of Rituxan (anti-CD20 chimeric antibody) to deplete B cells and interfere with antigen-presenting cell (APC) activity of B cells subsequently decreasing T-cell activation, and (iii) the use of plasmapheresis (PE) + anti-cytomegalovirus (CMV) immunoglobulin G (IgG) or IVIG in lower doses. This protocol removes deleterious anti-HLA antibodies and may also allow complexing of anti-HLA with anti-idiotypes in the anti-CMV IgG. Although early, data support the efficacy of all three approaches. Many centers are now designing protocols that utilize a combination of all three agents. In summary, recent advances in the diagnosis and treatment of AMR has allowed for significant improvements in outcomes of a condition usually associated with rapid graft failure. However, much work needs to be done to better understand the immunologic processes leading to AMR and how current therapies can be best used to effectively prevent and treat it.

Peritransplant immunoadsorption: a strategy enabling transplantation in highly sensitized crossmatch-positive cadaveric kidney allograft recipients

BACKGROUND

Kidney transplant recipients with a current positive complement-dependent cytotoxicity crossmatch (CDCXM) are at high risk for hyperacute rejection and graft loss. Immunoadsorption (IA) represents an efficient strategy to remove donor-specific alloantibodies. In this analysis, we evaluated effectiveness of peritransplant IA as an anti-humoral strategy to overcome a current positive CDCXM in presensitized renal allograft recipients.

METHODS

Between 1999 and 2003, 40 high risk cadaveric kidney allograft recipients (median CDC panel reactive antibody [PRA] level, 77%; number of retransplants, n = 38) were subjected to peritransplant IA with protein A (one pretransplant IA session followed by a course of repeat posttransplant IA sessions) in addition to preemptive antilymphocyte antibody therapy.

RESULTS

In nine of these patients, a current positive CDCXM was rendered negative by a single pretransplant IA session. Thirty-one recipients had a negative CDCXM already before pretransplant IA. No difference in graft survival was found between CDCXM-positive and CDCXM-negative recipients (3-year graft survival, 78% vs. 71%, P = 0.6). Comparable rates of immunological graft loss at 3 years were observed (11% vs. 13%, P = 0.8). Patient groups did not significantly differ with respect to median serum creatinine at 1 year (1.23 mg/dL [CDCXM-positive] vs. 1.57 mg/dl [CDCXM-negative], P = 0.07) and at the end of follow-up (median 32 months; 1.19 mg/dL vs. 1.63 mg/dL, P = 0.06). Moreover, patient groups showed similar rates of biopsy-proven cellular rejection (11% vs. 20%) or C4d-positive graft dysfunction (33% vs. 32%).

CONCLUSION

Our results demonstrate that peritransplant IA enables successful cadaveric kidney transplantation in the context of a positive CDCXM.

Effect of Delayed Graft Function in Hypersensitized Kidney Transplant Recipients

There is increased evidence about the deleterious effect of delayed graft function (DGF) in both short- and long-term kidney graft outcome. Among the mechanisms involved in the production of DGF, immune factors play a role, especially in the level of hypersensitization. From the 1389 patients transplanted at our hospital until November 2004, it has been found that the presence of moderate and high levels of sensitization, as measured by panel-reactive antibodies, is a risk factor for suffering from DGF. Further, DGF was associated with poor graft survival, and the risk was even higher when DGF was combined with moderate/high panel-reactive antibodies. Recent data demonstrate the usefulness of intravenous immunoglobulins in the management of hypersensitized patients in terms of short-term outcome. It remains to be demonstrated whether this therapy is able to ameliorate the higher ischemic injury that kidneys undergo from these immunologically high-risk patients.

Intravenous Immunoglobulin Induction Treatment in Flow Cytometry Cross-Match—Positive Kidney Transplant Recipients

Many recent studies have demonstrated increased acute humoral, cellular, subclinical, or chronic rejection, and decreased allograft survival in flow cytometry cross-match-positive kidney transplant recipients. The use of newer techniques and more sensitive of enzyme-linked immunosorbent assay (ELISA) or Flow Beads (microparticle based methods), donor-specific anti-human leukocyte antigen (HLA) antibodies have been detected in these immunologically high-risk patients. Intravenous immunoglobulin (IVIG) has immunomodulatory effects and has been demonstrated to downregulate anti-HLA antibodies in highly sensitized dialysis patients awaiting transplantation. Our initial studies demonstrate that IVIG induction treatment is promising in flow cytometry cross-match-positive kidney transplant recipients, and thus, those patients should not be excluded from receiving transplantation despite a positive flow cytometry cross match. Further studies with long-term follow-up are required to determine the effective dose and duration of IVIG treatment, and additional studies are needed to determine the most accurate tests for risk stratification.

Intravenous Immunoglobulin and Plasmapheresis in Acute Humoral Rejection: Experience in Renal Allograft Transplantation

Acute humoral rejection (AHR) in kidney transplantation is associated with higher rates of allograft loss when compared with acute cellular rejection (ACR). Treatment with intravenous immunoglobulin (IVIG) combined with plasmapheresis (PP) has been used recently in many centers. We report the incidence, clinical characteristics, and outcome of patients with AHR treated with IVIG and PP. All patients (n=519) at our institution who underwent kidney transplantation between January 1999 and August 2003 were retrospectively analyzed and classified according to biopsy results into three groups: AHR, ACR, and no rejection. AHR was diagnosed in 23 patients (4.5%) and ACR in 75 patients (15%). Mean follow-up was 844+/-23 days. Female sex, black race, and high panel-reactive antibody were risk factors for AHR. Most AHR patients (22 of 23) were treated with IVIG and PP. Two-year graft survival was numerically worse in patients with AHR versus ACR (78% vs. 85%, p=0.5) but the difference was not statistically significant. Graft survival after AHR treated with IVIG and PP is much better than it has been historically. IVIG in combination with PP is an effective treatment for AHR. Graft survival in this setting is similar to graft survival in patients with ACR.

Utility of Peritransplant and Rescue Intravenous Immunoglobulin and Extracorporeal Immunoadsorption in Lung Transplant Recipients Sensitized to HLA Antigens

The role of anti-human leukocyte antigen (HLA) antibodies in lung transplantation is not fully clear. The presence of pretransplant third-party anti-HLA antibodies or the development of de novo anti-HLA antibodies has been associated with acute posttransplant complications, bronchiolitis obliterans syndrome (BOS), and early mortality in some studies. However, little has been reported regarding the utility of desensitization therapy in sensitized lung transplant recipients. For approximately 3 years, desensitization therapy consisting of intravenous immunoglobulin (IVIG) and, in most instances, extracorporeal immunoadsorption (ECI) has been administered peritransplant to lung transplant recipients at our institution with third-party anti-HLA antibodies or as rescue therapy to those who develop de novo anti-HLA antibodies. Notably, the administration of peritransplant desensitization therapy to these patients has been associated with improvement in several clinical parameters, including acute rejection and BOS. Furthermore, administration of rescue IVIG with or without ECI has been associated with an overall improvement in the rate of pulmonary function decline. Our experience suggests that desensitization therapy may be beneficial for lung transplant recipients with pretransplant or de novo anti-HLA antibodies. We discuss the appropriateness and clinical impact of IVIG and ECI in sensitized lung transplant recipients as well as cellular mechanisms that may contribute.

Post-transplant therapy with high-dose intravenous gammaglobulin: Applications to treatment of antibody-mediated rejection

B-cells and their products (antibodies) are now recognized as important mediators of allograft rejection. This represents a significant departure from previous doctrine where the T-cells were felt to be of paramount importance. Antibody-mediated rejection (AMR) has emerged as a significant and common complication of transplantation. The development of donor-specific (anti-HLA class I and class II) antibodies is known to correlate strongly with the development of AMR. Recognition of the unique features of AMR that were often confused with non-specific acute tubular injury is aided considerably by improvements in monitoring of anti-HLA antibodies and the immunopathologic demonstration of C4d staining in affected capillary beds. Although imperfect, the demonstration of C4d (a complement breakdown product) staining in an allograft, especially accompanied by the presence of anti-HLA antibodies in the recipient sera, strongly suggests a diagnosis of AMR. Thus, AMR is a complement-dependent, antibody-mediated disorder. AMR can occur as a de novo complication of transplantation in individuals not previously recognized to be sensitized to HLA antigens, but more often occurs as a complication of desensitization therapies in highly-HLA sensitized patients. AMR may also constitute a significant portion of what is now referred to as chronic allograft nephropathy (CAN). The prognosis of C4d (+) AMR is poor as current therapies for treatment of AR are directed primarily at the T-cell. Until recently, no therapeutic options existed to address this problem from a primary etiological standpoint. Here we discuss the use of high dose IVIG as an option for treatment of AMR. We have significant experience with this approach which is outlined here. IVIG has many ideal advantages as a therapy for AMR. First, it can down regulate B-cell activation and antibody production, second, it can induce anti-inflammatory cytokines and contains blocking antiidiotyic antibodies to anti-HLA antibodies and third, IVIG has the unique ability to block complement-mediated injury through inhibition of C3 activation. Further clinical trials are necessary to prove efficacy for treatment of AMR.

The efficacy of CD40 ligand blockade in discordant pig-to-rat islet xenotransplantation is correlated with an immunosuppressive effect of immunoglobulin

BACKGROUND

The authors' aim was to evaluate the efficacy of immunosuppression with monoclonal anti-CD40 ligand antibodies (aCD40L) or nonspecific polyclonal intravenous immunoglobulin (IVIG) in the pig-to-rat islet xenotransplantation model.

METHODS

Fetal porcine islet-like cell clusters were transplanted under the kidney capsule of nondiabetic rats. All antibodies were administered alone or in combination with cyclosporine A (CsA). In addition, some animals were administered antibodies plus tacrolimus (TAC) or sirolimus (SIR). Twelve days after transplantation, islet xenograft survival and rejection were evaluated using immunohistochemistry.

RESULTS

aCD40L plus CsA had a pronounced inhibitory effect on islet xenograft rejection for up to 12 days after transplantation. Unexpectedly, treatment with a monoclonal control antibody (anti-keyhole limpet hemocyanin [aKLH]) plus CsA had a similar inhibitory effect. Furthermore, a similar inhibition of islet xenograft rejection was observed also in animals administered IVIG plus CsA. Monotherapy with aCD40L, aKLH, IVIG, or CsA had no effect on the rejection process. Also, when aCD40L or aKLH was administered together with TAC, islet xenograft rejection was inhibited. There was no marked difference compared with rats treated with aCD40L or aKLH and CsA. Immunosuppression with aCD40L or aKLH in combination with SIR also inhibited pig-to-rat islet xenograft rejection, but the protective effect was not as pronounced.

CONCLUSIONS

Immunosuppression with high doses of antibodies, monoclonal or polyclonal, in combination with CsA or TAC inhibits pig-to-rat islet xenograft rejection. No specific effect of co-stimulatory blockade with aCD40L could be observed. Instead, the results indicate a nonspecific immunosuppressive effect of high doses of antibodies in this model.

Update on kidney transplantation for the urologist

The incidence of end-stage renal disease (ESRD) in the United States is increasing dramatically and renal transplantation is the best treatment for many of these patients. The results of kidney transplantation also have improved. This has resulted in a significant demand for organs that is not met by the current supply of deceased donors. There now are more living kidney donors than cadaveric donors because the results of living donor renal transplantation are superior and the prolonged wait for a cadaveric kidney transplant can be avoided. Therefore, urologists will have increasing exposure to patients with ESRD and those with renal transplantation.

A renewable source of donor cells for repetitive monitoring of T- and B-cell alloreactivity

A major impediment to repetitive monitoring of alloreactivity or tolerance is the limited supply of donor cells available for assays of host-versus-graft T- and B-cell reactivity. In this paper, we describe the use of CD40L stimulated CD19(+) B cells as targets or stimulators in flow cytometric crossmatching (FXM), mixed lymphocyte reactivity and IFN-gamma ELISPOT assays. Stimulated B cells (sBc) express high levels of MHC class I and II, as well as the costimulatory molecules CD80 and CD86. They can be polyclonally expanded and frozen for later use. We describe the use of sBc in ELISPOT, mixed lymphocyte cultures and FXM. CD4(+) T cells exposed to sBc express a similar cytokine profile as those stimulated with unfractionated PBMC. We further analyzed T- and B-cell responses in 14 patients on the renal transplant waiting list, finding that those with an elevated panel reactive antibody (PRA) (>60%) had higher alloreactive T-cell precursor frequencies as measured by CDFSE MLR and IFN-gamma ELISPOT. We conclude that sBc are a renewable source of donor-specific target/stimulator cells for use in repetitive and coordinate assays of B- and T-cell alloreactivity.

Current and future immunosuppressive strategies in renal transplantation

The past decade has witnessed the introduction of several new immunosuppressive agents. The availability of these new pharmacologic offerings has not diminished the challenge of achieving a balance of adequate graft protection while minimizing the consequences of excessive immunosuppression. For renal transplant recipients, maintenance immunosuppression generally consists of a calcineurin inhibitor in combination with an antiproliferative agent and a corticosteroid; more recently, mammalian target of rapamycin inhibitors have been used. Excellent results have been achieved at many transplant centers with combinations of these agents in a variety of protocols. Regimens designed to limit or eliminate calcineurin inhibitor and/or corticosteroid therapy are actively being pursued in the transplant community. Allograft tolerance and xenotransplantation are being studied, and the knowledge gained from the effort may help in the development of innovative strategies and new immunosuppressive agents.

The case for living kidney sales: rationale, objections and concerns

Currently, potential kidney transplant candidates are dying on the waiting list. One potential solution would be a regulated system of living kidney sales (with safeguards to protect the vendor). Potential objections and practical concerns are discussed.

Transplanting patients with a positive donor-specific crossmatch: a single center's perspective

An increasing number of individuals with end-stage renal disease have become sensitized to human leukocyte antigens (HLA). Sensitization can have a profound impact on the likelihood of obtaining a requisite negative crossmatch (-XM) with a potential donor. Technologic breakthroughs in our ability to diagnose antibody-mediated rejection (AMR) and monitor anti-HLA antibodies has set the stage for a renascence in the understanding and treatment of individuals who harbor donor-specific antibody (DSA). Promising early results from single institutions that have developed preconditioning protocols allowing successful transplantation of XM (+) patients have encouraged other centers to adopt these protocols. Sensitized patients represent a great challenge for the clinician and there is much that remains unknown about the assessment and treatment of these patients. We have successfully preconditioned and transplanted more than 80 patients over a 5-yr period. As our understanding of these patients has increased, we have progressed from a 'one size fits all' approach to therapy to more rational, individualized treatment plans that take into account the varying immunologic risk that each patient possesses. In this article we have summarized our evolving experience with the assessment, treatment, transplantation, and monitoring of patients who undergo preconditioning for a (+) XM with a live donor.

Acute renal failure and intravenous immune globulin: occurs with sucrose-stabilized, but not with D-sorbitol-stabilized, formulation

OBJECTIVE

To report 2 cases of acute renal failure (ARF) following administration of sucrose-stabilized intravenous immune globulin (IVIG), one of which did not recur following subsequent doses of d-sorbitol-stabilized formulation, and review the relevant literature.

CASE SUMMARIES

A 44-year-old white man awaiting heart transplantation developed ARF requiring hemodialysis following administration of sucrose-stabilized IVIG for high alloreactivity to population human leukocyte antigens. Following a return of renal function to baseline, subsequent doses of d-sorbitol-stabilized IVIG were administered without incident. A 90-year-old white man developed ARF after administration of sucrose-stabilized IVIG for monoclonal gammopathy. Renal function returned to baseline, and no subsequent IVIG doses were administered. An objective causality assessment revealed that sucrose-stabilized IVIG was the probable cause of the adverse drug event for both cases.

DISCUSSION

Several case reports of ARF secondary to IVIG have been published. Recent publications note that sucrose-stabilized IVIG products have a disproportionately high rate of ARF occurrence (approximately 88%) versus non-sucrose-stabilized formulations. Recent market data for IVIG products indicate that sucrose-stabilized products account for approximately 40% of the total IVIG market. When administered intravenously, sucrose is excreted unchanged in the urine. ARF has been reported in patients receiving large doses of intravenous sucrose.

CONCLUSIONS

ARF secondary to IVIG may be more likely to occur with sucrose-stabilized formulations. Before prescribing IVIG, clinicians should consider other nephrotoxic medications, preexisting renal function, age, diabetes mellitus, and rate of infusion. In patients at risk, it may be best to avoid sucrose-stabilized formulations.

Donor kidney exchanges

Kidney transplantation from live donors achieves an excellent outcome regardless of human leukocyte antigen (HLA) mismatch. This development has expanded the opportunity of kidney transplantation from unrelated live donors. Nevertheless, the hazard of hyperacute rejection has usually precluded the transplantation of a kidney from a live donor to a potential recipient who is incompatible by ABO blood type or HLA antibody crossmatch reactivity. Region 1 of the United Network for Organ Sharing (UNOS) has devised an alternative system of kidney transplantation that would enable either a simultaneous exchange between live donors (a paired exchange), or a live donor/deceased donor exchange to incompatible recipients who are waiting on the list (a live donor/list exchange). This Regional system of exchange has derived the benefit of live donation, avoided the risk of ABO or crossmatch incompatibility, and yielded an additional donor source for patients awaiting a deceased donor kidney. Despite the initial disadvantage to the list of patients awaiting an O blood type kidney, as every paired exchange transplant removes a patient from the waiting list, it also avoids the incompatible recipient from eventually having to go on the list. Thus, this approach also increases access to deceased donor kidneys for the remaining candidates on the list.

Isometric Tubular Epithelial Vacuolization in Renal Allograft Biopsy Specimens of Patients Receiving Low-Dose Intravenous Immunoglobulin for a Positive Crossmatch

BACKGROUND

Perioperative treatment with plasmapheresis and intravenous immunoglobulin (IVIG), combined with a tacrolimus-based immunosuppressive regimen, has been used successfully to allow renal transplantations in cross-match-positive recipients. A common finding in biopsy specimens of these allografts is isometric vacuolization of proximal tubular epithelium. This finding presents a diagnostic dilemma because it may occur secondary to IVIG treatment or tacrolimus nephrotoxicity.

METHODS

We compared the frequency and severity of isometric tubular vacuolization in renal allograft biopsy specimens obtained during the first 10 days after transplantation in 24 patients who received one or more postoperative treatments with IVIG (100 mg/kg; as part of a desensitization protocol also involving plasmapheresis) with specimens obtained in 91 patients who did not receive IVIG. All patients received tacrolimus. Isometric vacuolization was graded on a 0 to 4 scale based on the fraction of proximal tubules involved: 0, none; 1, less than 10%; 2, 10% to 25%; 3, 26% to 50%; 4, more than 50%.

RESULTS

There was a higher frequency of isometric tubular vacuolization (71 % vs. 31%) and more widespread involvement in patients who received IVIG and tacrolimus versus tacrolimus alone, although mean tacrolimus levels were not significantly different between these groups. In control, but not IVIG, biopsy specimens, there was a significant association between vacuolization score and blood tacrolimus level on the day of biopsy.

CONCLUSIONS

Isometric tubular vacuolization is a common finding in renal transplant biopsy specimens of patients who receive low-dose IVIG and in many cases is likely to be related, at least in part, to IVIG. In these patients, this finding should not necessarily be interpreted as indicative of tacrolimus (or cyclosporine) nephrotoxicity.

Persistence of Low Levels of Alloantibody after Desensitization in Crossmatch-Positive Living-Donor Kidney Transplantation

BACKGROUND

: Desensitization protocols have been developed to allow successful kidney transplantation in sensitized recipients. However, a detailed analysis of the impact of these protocols on alloantibody has not been performed.

METHODS

: We studied 12 living-donor kidney-transplant recipients with positive antihuman globulin-enhanced complement dependent cytotoxicity (AHG-CDC) crossmatches against their donors. Using a variety of crossmatch techniques and single-antigen flowbeads (SAFBs), we characterized the specificity and amount of alloantibody at baseline before desensitization, after desensitization (using plasmapheresis followed by 100 mg/kg intravenous immunoglobulin, and anti-CD20 antibody), and 4 months after transplantation (after splenectomy and on maintenance immunosuppression).

RESULTS

: All 12 patients with a positive baseline AHG-CDC crossmatch were AHG-CDC crossmatch negative at the time of transplant (after desensitization). However, despite desensitization, the majority of patients had low-level donor-specific alloantibodies demonstrable on the day of transplantation by both flow crossmatch (FXM 8/12) and SAFBs (10/11). Four months after transplantation, no patient had a positive AHG-CDC crossmatch, but again the majority had persistent low levels of donor-specific alloantibodies by FXM (6/12) and SAFBs (9/11). No patient experienced hyperacute rejection, and the persistence of low levels of donor-specific alloantibodies did not correlate with the development of humoral rejection in the early posttransplant period.

CONCLUSIONS

: Despite desensitization, a majority of positive crossmatch transplant recipients demonstrate low levels of donor-specific alloantibodies both on the day of transplant and 4 months after transplantation. The impact of these antibodies appears to be minimal early after transplant, but their long-term significance bears further study.

National conference to assess antibody-mediated rejection in solid organ transplantation

The process of humoral rejection is multifaceted and has different manifestations in the various types of organ transplants. Because this process is emerging as a leading cause of graft loss, a conference was held in April 2003 to comprehensively address issues regarding humoral rejection. Though humoral rejection may result from different factors, discussion focused on a paradigm caused by antibodies, typically against donor HLA antigens, leading to the term 'antibody-mediated rejection' (AMR). Conference deliberations were separated into four workgroups: The Profiling Workgroup evaluated strengths and limitations of different methods for detecting HLA reactive antibody, and created risk assessment guidelines for AMR; The Diagnosis Workgroup reviewed clinical, pathologic, and serologic criteria for assessing AMR in renal, heart and lung transplant recipients; The Treatment Workgroup discussed advantages, limitations and possible mechanisms of action for desensitization protocols that may reverse AMR; and The Basic Science Workgroup presented animal and human immunologic models for humoral rejection and proposed potential targets for future intervention. This work represents a comprehensive review with contributions from experts in the fields of Transplantation Surgery, Medicine, Pathology, Histocompatibility, Immunology, and clinical trial design. Immunologic barriers once considered insurmountable are now consistently overcome to enable more patients to undergo organ transplantation.