Prognostic tools to assess candidacy for and efficacy of antibody-removal therapy.

Currently, the ability to predict or monitor the efficacy of HLA antibody-removal therapies is deficient. We previously reported that titration studies are a consistent and accurate means of assessing antibody strength. To test whether titration studies can also predict which patients are better candidates for desensitization, we studied 38 patients from 3 centers (29 receiving plasmapheresis/low-dose intravenous immunoglobulin [IVIg]; 9 patients receiving high-dose IVIg). For patients undergoing plasmapheresis/low-dose IVIg, antibody titer reduction correlated with number of treatment cycles for both class I and II antibodies but only up to approximately 4 cycles. Reduction in titer slowed with additional cycles, suggesting a limit to the efficacy of this approach. Furthermore, initial titer (predesensitization) can guide the selection of candidates for successful antibody-removal treatment. In our experience, patients with antibodies at an initial titer >1:512 could not be reduced to the goal of a negative lymphocyte crossmatch, corresponding to a 1:16 titer, despite a significant increase in the number of treatment cycles. Change in mean fluorescence intensity (MFI) value did not correlate with success of treatment if initial MFI values were >10 000, likely due to single antigen bead saturation. Overall, we present a potential prognostic tool to predict candidacy and a monitoring tool to assess efficacy of desensitization treatment.

Safety, pharmacokinetics, and pharmacodynamic activity of obinutuzumab, a type 2 anti-CD20 monoclonal antibody for the desensitization of candidates for renal transplant.

The limited effectiveness of rituximab plus intravenous immunoglobulin (IVIG) in desensitization may be due to incomplete B cell depletion. Obinutuzumab is a type 2 anti-CD20 antibody that induces increased B cell depletion relative to rituximab and may therefore be more effective for desensitization. This open-label phase 1b study assessed the safety, pharmacokinetics, and pharmacodynamics of obinutuzumab in highly sensitized patients with end-stage renal disease. Patients received 1 (day 1, n = 5) or 2 (days 1 and 15; n = 20) infusions of 1000-mg obinutuzumab followed by 2 doses of IVIG on days 22 and 43. Eleven patients received additional obinutuzumab doses at the time of transplant and/or at week 24. The median follow-up duration was 9.4 months. Obinutuzumab was well tolerated, and most adverse events were grade 1-2 in severity. There were 11 serious adverse events (SAEs) in 9 patients (36%); 10 of these SAEs were infections and 4 occurred after kidney transplant. Obinutuzumab plus IVIG resulted in profound peripheral B cell depletion and appeared to reduce B cells in retroperitoneal lymph nodes. Reductions in anti-HLA antibodies, number of unacceptable antigens, and the calculated panel reactive antibody score as centrally assessed using single-antigen bead assay were limited and not clinically meaningful for most patients (NCT02586051).

Desensitization for solid organ and hematopoietic stem cell transplantation.

Desensitization protocols are being used worldwide to enable kidney transplantation across immunologic barriers, i.e. antibody to donor HLA or ABO antigens, which were once thought to be absolute contraindications to transplantation. Desensitization protocols are also being applied to permit transplantation of HLA mismatched hematopoietic stem cells to patients with antibody to donor HLA, to enhance the opportunity for transplantation of non-renal organs, and to treat antibody-mediated rejection. Although desensitization for organ transplantation carries an increased risk of antibody-mediated rejection, ultimately these transplants extend and enhance the quality of life for solid organ recipients, and desensitization that permits transplantation of hematopoietic stem cells is life saving for patients with limited donor options. Complex patient factors and variability in treatment protocols have made it difficult to identify, precisely, the mechanisms underlying the downregulation of donor-specific antibodies. The mechanisms underlying desensitization may differ among the various protocols in use, although there are likely to be some common features. However, it is likely that desensitization achieves a sort of immune detente by first reducing the immunologic barrier and then by creating an environment in which an autoregulatory process restricts the immune response to the allograft.

Clinically relevant interpretation of solid phase assays for HLA antibody.

PURPOSE OF REVIEW: Accurate and timely detection and characterization of human leukocyte antigen (HLA) antibodies are critical for pre-transplant and post-transplant immunological risk assessment. Solid phase immunoassays have provided increased sensitivity and specificity, but test interpretation is not always straightforward. This review will discuss the result interpretation considering technical limitations; assessment of relative antibody strength; and the integration of data for risk stratification from complementary testing and the patient's immunological history. RECENT FINDINGS: Laboratory and clinical studies have provided insight into causes of test failures - false positive reactions because of antibodies to denatured HLA antigens and false negative reactions resulting from test interference and/or loss of native epitopes. Test modifications permit detection of complement-binding antibodies and determination of the IgG subclasses. The high degree of specificity of single antigen solid phase immunoassays has revealed the complexity and clinical relevance of antibodies to HLA-C, HLA-DQ, and HLA-DP antigens. Determination of antibody specificity for HLA epitopes enables identification of incompatible antigens not included in test kits. SUMMARY: Detection and characterization of HLA antibodies with solid phase immunoassays has led to increased understanding of the role of those antibodies in graft rejection, improved treatment of antibody-mediated rejection, and increased opportunities for transplantation. However, realization of these benefits requires careful and accurate interpretation of test results.

A closer look at rituximab induction on HLA antibody rebound following HLA-incompatible kidney transplantation.

Rituximab has been used to increase the efficacy of desensitization protocols for human leukocyte antigen (HLA)-incompatible kidney transplantation; however, controlled comparisons have not been reported. Here we examined 256 post-transplant HLA antibody levels in 25 recipients desensitized with and 25 without rituximab induction, to determine the impact of B-cell depletion. We found significantly less HLA antibody rebound in the rituximab-treated patients (7% of donor-specific antibodies (DSAs) and 33% of non-DSAs) compared with a control cohort desensitized and transplanted without rituximab (32% DSAs and 55% non-DSAs). The magnitude of the increase was significantly larger among patients who did not receive rituximab. Interestingly, in rituximab-treated patients, of the 39 HLA antibodies that increased post transplant, 34 were specific for HLA mismatches present in previous allografts or pregnancies, implying limited efficacy in memory B-cell depletion. Compared with controls, rituximab-treated patients had a significantly greater mean reduction in DSA (-2505 vs. -292 mean fluorescence intensity), but a similar rate of DSA persistence (52% in rituximab treated-and 40% in non-treated recipients). Thus, rituximab induction in HLA-incompatible recipients reduced the incidence and magnitude of HLA antibody rebound, but did not affect DSA elimination, antibody-mediated rejection, or 5-year allograft survival when compared with recipients desensitized and transplanted without rituximab.

Incidence and early outcomes associated with pre-transplant antivimentin antibodies in the cardiac transplantation population.

BACKGROUND: In cardiac transplant recipients, the development of antibodies to the endothelial intermediate filament protein vimentin (antivimentin antibodies, AVA) has been associated with rejection and poor outcomes. However, the incidence of these antibodies prior to transplantation and their association with early rejection has not been investigated. METHODS: Pre-transplant serum was analyzed from 50 patients who underwent de novo cardiac transplant at Johns Hopkins Hospital from 2004 to 2012. Demographic, one-yr rejection, and survival data were obtained from the transplant database. RESULTS: The incidence of pre-transplant AVA was 34%. AVA-positive patients were younger (p = 0.03), and there was an a trend toward incidence in females (p = 0.08). Demographic data were similar among both groups. AVA positivity did not predict rejection in the first year post-transplant. There was no difference in rejection-free graft survival (53 vs. 52%, p = 0.85) at one yr. Similarly, there was no difference in graft survival at one yr (82 vs. 88%, p = 0.56) or graft survival at a median follow-up of 23 and 26 months, respectively (76 vs. 85%, p = 0.41). CONCLUSIONS: AVA is common in the cardiac pre-transplant population with a higher incidence in the young. The presence of detectable AVA did not correlate with early post-transplant rejection or graft survival.

Desensitization in HLA-incompatible kidney recipients and survival.

BACKGROUND: More than 20,000 candidates for kidney transplantation in the United States are sensitized to HLA and may have a prolonged wait for a transplant, with a reduced transplantation rate and an increased rate of death. One solution is to perform live-donor renal transplantation after the depletion of donor-specific anti-HLA antibodies. Whether such antibody depletion results in a survival benefit as compared with waiting for an HLA-compatible kidney is unknown. METHODS: We used a protocol that included plasmapheresis and the administration of low-dose intravenous immune globulin to desensitize 211 HLA-sensitized patients who subsequently underwent renal transplantation (treatment group). We compared rates of death between the group undergoing desensitization treatment and two carefully matched control groups of patients on a waiting list for kidney transplantation who continued to undergo dialysis (dialysis-only group) or who underwent either dialysis or HLA-compatible transplantation (dialysis-or-transplantation group). RESULTS: In the treatment group, Kaplan-Meier estimates of patient survival were 90.6% at 1 year, 85.7% at 3 years, 80.6% at 5 years, and 80.6% at 8 years, as compared with rates of 91.1%, 67.2%, 51.5%, and 30.5%, respectively, for patients in the dialysis-only group and rates of 93.1%, 77.0%, 65.6%, and 49.1%, respectively, for patients in the dialysis-or-transplantation group (P<0.001 for both comparisons). CONCLUSIONS: Live-donor transplantation after desensitization provided a significant survival benefit for patients with HLA sensitization, as compared with waiting for a compatible organ. By 8 years, this survival advantage more than doubled. These data provide evidence that desensitization protocols may help overcome incompatibility barriers in live-donor renal transplantation. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases and the Charles T. Bauer Foundation.).

Partially mismatched transplantation and human leukocyte antigen donor-specific antibodies.

The presence of donor human leukocyte antigen (HLA)-specific antibodies (DSA) increases engraftment failure risk in partially HLA-mismatched, or HLA-haploidentical, allogeneic marrow (alloBMT) transplantation. As pre-existing sensitization to HLA antigens is not well characterized among candidates for HLA-haploidentical alloBMT, we retrospectively evaluated both the incidence and relative strength of DSA in this patient population. Based on correlations of solid-phase antibody assays on the Luminex (Luminex, Austin, TX) platform with actual crossmatch tests, DSA were characterized as weak for results that were consistent with negative flow cytometric crossmatch results or as moderate-to-strong for results consistent with positive flow cytometric or cytotoxicity crossmatches. We evaluated 296 alloBMT candidates; 111 (37.5%) were female. DSA were detected in 43 (14.5%) candidates, mostly among female candidates (42.9% female versus 12.5% male). Moderate-to-strong DSA strength was more frequently encountered when directed against haploidentical donors as compared with mismatched unrelated donors. DSA were most commonly detected in female patients directed against their children. Because the presence of DSA has been considered prohibitive for HLA-mismatched alloBMT, we additionally report a desensitization methodology used to reduce DSA to negative or weak levels, ie, levels well below those detectable in a flow cytometric crossmatch. Nine patients without other available donors underwent desensitization. Eight who reduced their DSA to negative or weak levels proceeded to alloBMT and achieved full donor engraftment. These data support routine DSA evaluation in all patients considered for mismatched alloBMT; however, for patients with no other viable options, desensitization to weak or negative DSA levels may afford the opportunity for successful transplantation.

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.

A GPS for finding the route to transplantation for the sensitized patient.

PURPOSE OF REVIEW: To identify factors that affect the choice of route to renal transplantation for the sensitized patient. The evolution of protocols for transplanting sensitized patients has been desensitization (DES), paired donation, and most recently, paired donation combined with DES. Use of these protocols has revealed various factors that influence which route is the most likely to work for a given patient. RECENT FINDINGS: The data indicate that patient blood type and HLA sensitization have the dominant influence on what route is best for a patient but numerous other factors, particularly the number, HLA type, and ABO type of donors a patient brings to a program will also affect the likelihood of transplantation. The distribution of these factors among patients transplanted or unable to find a compatible donor can be used to calculate the probability of transplantation via paired donation. SUMMARY: Kidney paired donation with or without DES provides benefits that cannot be achieved with DES alone. However, DES may provide the fastest route to transplantation.

HLA incompatible renal transplantation.

PURPOSE OF REVIEW: Human leukocyte antigen (HLA) sensitization is a major public health problem that limits access to renal transplantation for 30% of the patients awaiting a kidney transplant. This review describes the transplantation modalities available to the sensitized patient and discusses aspects of the donor/recipient phenotypes that determine the most suitable option for a particular patient. RECENT FINDINGS: Patients, who undergo desensitization have a significant survival benefit compared with similar patients, who either remain on dialysis or wait for a compatible donor. The initial donor-specific antibody (DSA) strength is the best predictor of outcome and cost of desensitization. In small, uncontrolled single center trials, complement inhibitors, proteasome inhibitors and anti-CD20 have been used to both prevent and reverse antibody-mediated rejection (AMR). SUMMARY: With new agents being introduced into the armamentarium, which have not undergone rigorous investigation, it is important to emphasize that plasmapheresis, intravenous immunoglobulin, increased sharing, and kidney-paired donation are very effective strategies for transplanting sensitized patients. However, a significant population of patients will not benefit from either kidney-paired donation or desensitization and will require a hybrid technique in which the goal of matching is to reduce the strength of the DSA to facilitate desensitization.

Antiallograft antibodies: relevance, detection, and monitoring.

PURPOSE OF REVIEW: Solid-phase immunoassays increase the accuracy of assessing pretransplant immunologic risk and facilitate posttransplant prediction and diagnosis of antibody-mediated rejection (AMR). This review will describe methods available for antibody analyses, discuss the types of targets of AMR and the characteristics of pathogenic alloantibodies, and provide guidelines for the application of antibody tests in the prediction of rejection risk and diagnosis of rejection. RECENT FINDINGS: The presence of human leukocyte antigen-specific antibodies increases the risk of AMR, but the clinical relevance of low antibody levels is questioned with reports of stable graft function in their presence. Posttransplant monitoring has been shown to provide early diagnosis of AMR permitting preemptive intervention. Antibodies to other alloantigens and autoantigens are being implicated as potential targets for both acute and chronic AMR. Certain limitations and interfering factors have also been recognized that should be recognized in the interpretation of solid-phase antibody assay results. SUMMARY: Contemporary technology is clearly advancing the detection of various antibodies that can contribute to AMR, but continued work is needed to elucidate the relevance of very low levels of human leukocyte antigen-specific antibody and the importance of antibodies to other alloantigens and autoantigens.

Donor ethnicity influences outcomes following deceased-donor kidney transplantation in black recipients.

Although the majority of deceased-donor kidneys are donated after brain death, increased recovery of kidneys donated after cardiac death could reduce the organ shortage and is now a national priority. Racial disparities in donations after brain death have been well described for renal transplantation, but it is unknown whether similar disparities occur in donations after cardiac death. In this study, outcomes of adult deceased-donor renal transplant recipients included in the United Network for Organ Sharing database (1993 through 2006) were analyzed. Among black recipients of kidneys obtained after cardiac death, those who received kidneys from black donors had better long-term graft and patient survival than those who received kidneys from white donors. In addition, compared with standard-criteria kidneys from white donors after brain death, kidneys from black donors after cardiac death conferred a 70% reduction in the risk for graft loss (adjusted hazard ratio 0.30; 95% confidence interval 0.14 to 0.65; P = 0.002) and a 59% reduction in risk for death (adjusted hazard ratio 0.41; 95% confidence interval 0.2 to 0.87; P = 0.02) among black recipients. These findings suggest that kidneys obtained from black donors after cardiac death may afford the best long-term survival for black recipients.

The role of the histocompatibility laboratory in desensitization for transplantation.

PURPOSE OF REVIEW: The ability of histocompatibility laboratories to define and monitor human leukocyte antigen (HLA)-specific antibodies via highly sensitive immunoassays has been a major contributing factor in the development of desensitization protocols for HLA-incompatible transplants. This review will focus on the laboratory's role in desensitization and the types of tests needed for determining the specificity and strength of antibodies to donor HLA pretransplant, during treatment, and after transplant. RECENT FINDINGS: Increasingly, solid-phase immunoassays that use purified HLA molecules are providing sensitive characterization of HLA-specific antibodies. Assay parameters, such as median fluorescence intensity, can be correlated with cross-match results and clinical outcomes, and subsequently used to monitor antibody status in patients undergoing desensitization. The strength of donor HLA-specific antibody, measured by cross-match and/or solid phase assays, is used to determine the likelihood of successful desensitization, as well as the risk of posttransplant antibody-mediated rejection. SUMMARY: Histocompatibility laboratories are essential components of desensitization programs. Thorough antibody characterization and serial monitoring of changes in antibody status are needed pretreatment, during treatment and after transplant. Because clinical decisions rely heavily on changes in antibody specificity and strength, desensitization should not be undertaken without access to appropriate histocompatibility testing.

The problem of transplanting the sensitized patient: whose problem is it?

Transplantation is the treatment of choice for end-stage renal failure and a life-saving treatment for failure of other major organs. Improvements in surgical techniques, histocompatibility testing, and immunosuppressive drugs have significantly improved both patient and graft survival. However, there are formidable barriers to the successful transplantation of patients who possess HLA-specific antibodies. Sensitized patients wait longer for a transplant and, once transplanted, experience more rejection episodes and have decreased graft survival compared to non-sensitized recipients. Improvements in HLA-specific antibody detection have expanded the donor pool available to sensitized patients and desensitization protocols designed to reduce the breadth and amount of HLA-specific antibody have found increased success during the last decade. Determining the appropriate course of treatment for the sensitized patient requires accurate immunologic characterization and clinical assessment of the patient. Together, the transplant physician and histocompatibility expert must determine what constitutes a compatible donor and assess the patient's risk for a particular transplant. Thus, sensitization to HLA antigens is a problem for the patient, the transplant physician, and the histocompatibility laboratory.

Detecting and monitoring human leukocyte antigen-specific antibodies.

Renewed awareness of the relevance of HLA-specific antibodies to transplantation and the development of protocols to reduce or eliminate sensitization have made monitoring of antibodies and accurate interpretation of test results increasingly important. Here we review the various tests available and provide guidelines for the development of monitoring protocols.

Defining unacceptable HLA antigens.

PURPOSE OF REVIEW: Neither the concept nor the formal application of unacceptable antigens is new. However, identification of unacceptable antigens is now sufficiently accurate to be used as a virtual crossmatch, which can both prevent the unnecessary shipment of organs and increase the access for sensitized patients. RECENT FINDINGS: Desensitization protocols and an increasing array of cell-depleting agents can overcome the immunological barriers to transplantation for some patients, reducing the risk of graft rejection to an acceptable level. Increasingly sensitive and specific assays for identifying HLA antigens and antibodies are providing more accurate definition of incompatibilities. Additionally, tests of various biomarkers may permit characterization of responder types. SUMMARY: The definition of unacceptable antigens is determined by the clinical protocols and the physiological and immunological characteristics of the recipient and donor. These data should be integrated to maximize the opportunity for transplantation. The development of additional tests to assess a patient's capacity for recognizing and responding to a transplant will improve the identification of incompatible donor-recipient pairs.

HLA in transplantation.

The human major histocompatibility complex is a family of genes that encodes HLAs, which have a crucial role in defence against foreign pathogens and immune surveillance of tumours. In the context of transplantation, HLA molecules are polymorphic antigens that comprise an immunodominant alloreactive trigger for the immune response, resulting in rejection. Remarkable advances in knowledge and technology in the field of immunogenetics have considerably enhanced the safety of transplantation. However, access to transplantation among individuals who have become sensitized as a result of previous exposure to alloantigens is reduced proportional to the breadth of their sensitization. New approaches for crossing the HLA barrier in transplantation using plasmapheresis, intravenous immunoglobulin and kidney paired donation have been made possible by the relative ease with which even low levels of anti-HLA antibodies can now be detected and tracked. The development of novel protocols for the induction of tolerance and new approaches to immunomodulation was also facilitated by advances in HLA technology. Here, we review the progress made in understanding HLAs that has enabled organ transplantation to become a life-saving endeavour that is accessible even for sensitized patients. We also discuss novel approaches to desensitization, immunomodulation and tolerance induction that have the potential to further improve transplantation access and outcomes.