Transplanting the highly sensitized patient: The emory algorithm

A Comparative Effectiveness Analysis of Early Steroid Withdrawal in Black Kidney Transplant Recipients

BACKGROUND AND OBJECTIVES

There is continued debate whether early steroid withdrawal is safe to use in high-immunologic risk patients, such as blacks. The goal of this study was to use comparative effectiveness methodology to elucidate the safety of early steroid withdrawal in blacks with kidney transplants.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Our cohort study used United Network of Organ Sharing data including all adult black kidney transplant recipients from 2000 to 2009 followed through 2014. Propensity score matching was used to equalize baseline risk between continued steroid and early steroid withdrawal groups. Interaction terms were used to assess if the effect of early steroid withdrawal on outcomes varied by baseline and post-transplant factors. Of 26,582 eligible black patients with kidney transplants (5825 [21.9%] with early steroid withdrawal), 5565 patients with early steroid withdrawal were matched to 5565 blacks on continued steroid use.

RESULTS

Black patients with early steroid withdrawal had similar risk of graft loss (hazard ratio, 0.98; 95% confidence interval, 0.92 to 1.04; P=0.42) and lower risk of death (hazard ratio, 0.91; 95% confidence interval, 0.84 to 0.99; P=0.02), primarily driven by a late mortality advantage (>4 years post-transplant). Delayed graft function, cytolytic induction, tacrolimus, and mycophenolate significantly modified the effect of early steroid withdrawal on outcomes (P<0.05). Acute rejection rates were slightly higher in the continued steroid group (13.0% versus 11.3%, respectively; P<0.01), but this was not associated with graft or patient survival.

CONCLUSIONS

Overall, early steroid withdrawal in black kidney transplant recipients was not associated with graft loss but seemed to be associated with better long-term patient survival. Early steroid withdrawal in blacks not receiving cytolytic induction, tacrolimus, and mycophenolate or those with delayed graft function was associated with higher risk of graft loss and death.

Kidney Transplantation Results in Very Highly Sensitized Patients Included in a Virtual Crossmatch Program: Analysis of Kidney Pairs

BACKGROUND

Kidney transplantation in highly-sensitized (HS) patients can improve with organ-exchange strategies based on virtual crossmatch (V-XM). Experience in very-HS patients is limited.

METHODS

In June 2012, Andalusia started a V-XM protocol for very-HS patients (calculated panel reactive antibodies ≥95%). After organ allocation a cytotoxic-XM performed immediately before transplantation had to be negative for surgery to proceed. We analyzed results up until December 2015. Whenever possible we also compared the course of the recipient (non-HS) of the other kidney from the same donor.

RESULTS

Of the 57 grafts, 52 kidney transplantations were performed (the pretransplantation cytotoxic-XM was positive in 5; predictive value 91.3%). Five patients (9.6%) experienced acute rejection (4 antibody-mediated rejections [AMRs]; 7.6%). Donor-specific antibodies developed in 10 patients. No patient died. One-year graft survival was 98%. We compared the course of the non-HS recipient of the other kidney, excluding cases with no pair (n = 5), pairs who were children recipients (n = 3), pancreas-kidney recipients (n = 5), or pairs already included in the V-XM protocol (n = 4). Finally, 35 pairs were studied. More HS-patients developed donor-specific antibodies (P = .016). No significant differences were seen in acute rejection, but AMR was more common (P = .057). No deaths occurred in either group, and there were no differences in graft survival or renal function.

CONCLUSIONS

Although a few patients still developed AMR, our V-XM based protocol with a final pretransplantation cytotoxic-XM achieved very satisfactory results. Although the number of patients was limited, the initial survival of these high-risk recipients was comparable to the controls.

Donor-Specific Antibody Monitoring: Where Is the Beef?

This review paper discusses the impact of de novo donor-specific antibodies (DSA) to donor HLA antigens in kidney transplantation and summarizes the benefits and challenges that exist with DSA monitoring. Post-transplant DSA is associated with worse allograft outcomes and its detection may precede or coincide with clinical, biochemical, and histologic allograft dysfunction. There are no absolute features of DSA testing results that perfectly discriminate between states of disease and health. In a state of antibody-associated graft dysfunction, removal or reduction in DSA may only provide clinical benefit for some. Furthermore, various factors influence test results, and detection of HLA antibodies must be interpreted within the appropriate clinical and laboratory context. The utility of DSA monitoring is further affected by the limited effectiveness of treatment for antibody-mediated rejection. Although DSA monitoring is potentially beneficial in some circumstances, the optimal screening and treatment strategies are still to be defined.

Current status on the evaluation and management of the highly sensitized kidney transplant recipient

PURPOSE OF REVIEW

In light of the recent changes to the kidney allocation system (KAS) and the observed increase in the rate of transplantation of the highly sensitized kidney transplant candidate, the evaluation and care of this population is a timely topic.

RECENT FINDINGS

In its first year, the new KAS has already realized one goal of improving the chances of transplanting the most highly sensitized patients in the waiting list. This has brought to the forefront the need for recipient readiness in this special population, as well as the need for histocompatibility labs and kidney transplant programs to align themselves with each other, and also with the requirements of the United Network for Organ Sharing, and increase proficiency in testing and data interpretation. This manuscript is a review of the literature as well as practice patterns as they relate to the changes in KAS and the observed outcome since the activation of the new KAS, with the ultimate goal of aiding in the development of a more unified approach in the care of this specialized population which will allow for interdisciplinary and cross centre dialogue to optimize long term care and outcomes.

SUMMARY

Here we will review the changes to the KAS as they affect the highly sensitized kidney transplant recipient, and additional considerations in the evaluation and management of these patients.

Racial and ethnic disparities in outcomes after heart transplantation: A systematic review of contributing factors and future directions to close the outcomes gap

The demographics of patients undergoing heart transplantation in the United States have shifted over the last 10 years, with an increasing number of racial and ethnic minorities undergoing heart transplant. Multiple studies have shown that survival of African American patients after heart transplantation is lower compared with other ethnic groups. We review the data supporting the presence of this outcome disparity and examine the multiple mechanisms that contribute. With an increasingly diverse population in the United States, knowledge of these disparities, their mechanisms, and ways to improve outcomes is essential.

Transplanting Sensitized Kidney Transplant Patients With Equivalent Outcomes Utilizing Stringent HLA Crossmatching

OBJECIVES

Elevated panel reactive antibody levels have been traditionally associated with increased acute rejection rate and decreased long-term graft survival after kidney transplant. In this study, our objective was to determine patient and allograft outcomes in sensitized kidney transplant recipients with advanced HLA antibody detection and stringent protein sequence epitope analyses.

MATERIALS AND METHODS

This was a subanalysis of a prospective, risk-stratified randomized controlled trial that compared interleukin 2 receptor antagonist to rabbit antithymocyte globulin induction in 200 kidney transplant recipients, examining outcomes based on panel reactive antibody levels of < 20% (low) versus ≥ 20% (high, sensitized). The study was conducted between February 2009 and July 2011. All patients underwent solid-phase single antigen bead assays to detect HLA antibodies and stringent HLA epitope analyses with protein sequence alignment for virtual crossmatching. Delayed graft function, acute rejection rates, and graft loss were the main outcomes measured.

RESULTS

Both the low (134 patients) and high (66 patients) panel reactive antibody level cohorts had equivalent induction and maintenance immunosuppression. Patients in the high-level group were more likely to be female (P < .001), African American (P < .001), and received a kidney from a deceased donor (P = .004). Acute rejection rates were similar between the low (rate of 8%) and high (rate of 9%) panel reactive antibody groups (P = .783). Delayed graft function, borderline rejection, graft loss, and death were not different between groups. Multivariate analyses demonstrated delayed graft function to be the strongest predictor of acute rejection (odds ratio, 5.7; P = .005); panel reactive antibody level, as a continuous variable, had no significant correlation with acute rejection (C statistic, 0.48; P = .771).

CONCLUSIONS

Appropriate biologic matching with single antigen bead assays and stringent epitope analyses provided excellent outcomes in sensitized patients regardless of the induction therapy choice.

Renal Transplantation With Final Allocation Based on the Virtual Crossmatch

Solid phase immunoassays (SPI) are now routinely used to detect HLA antibodies. However, the flow cytometric crossmatch (FCXM) remains the established method for assessing final donor-recipient compatibility. Since 2005 we have followed a protocol whereby the final allocation decision for renal transplantation is based on SPI (not the FCXM). Here we report long-term graft outcomes for 508 consecutive kidney transplants using this protocol. All recipients were negative for donor-specific antibody by SPI. Primary outcomes are graft survival and incidence of acute rejection within 1 year (AR <1 year) for FCXM+ (n = 54) and FCXM- (n = 454) recipients. Median follow-up is 7.1 years. FCXM+ recipients were significantly different from FCXM- recipients for the following risk factors: living donor (24% vs. 39%, p = 0.03), duration of dialysis (31.0 months vs. 13.5 months, p = 0.008), retransplants (17% vs. 7.3%, p = 0.04), % sensitized (63% vs. 19%, p = 0.001), and PRA >80% (20% vs. 4.8%, p = 0.001). Despite these differences, 5-year actual graft survival rates are 87% and 84%, respectively. AR <1 year occurred in 13% FCXM+ and 12% FCXM- recipients. Crossmatch status was not associated with graft outcomes in any univariate or multivariate model. Renal transplantation can be performed successfully, using SPI as the definitive test for donor-recipient compatibility.

Single antigen flow beads for identification of human leukocyte antigen antibody specificities in hypersensitized patients with chronic renal failure

Aims of this study

Aims of this study were to identify class I and class II antibodies in highly sensitized patients by flow cytometry single antigen bead (FC-SAB) assay and to evaluate according to donor HLA type in order to increase their kidney transplantation chance.

Material and methods

We analyzed 60 hypersensitive patients of 351 individuals, who applied to our laboratory for PRA test in November 2013-December 2014. Flow cytometric PRA screening and single antigen bead commercial kits were used for these analyses.

Results

In our study group, 19 (31.7%) of these patients were male while 41 (68.3%) patients were female. The most common acceptable antigens were A*02 (10.11%), HLA-A*23 (10.11%), HLA-B*38 (8.79%) and HLA-DRB1*03 (7.83%) in hypersensitive patients. The highest antibody reactivity on SAB was observed against HLA-A*25, HLA-B*45, HLA-DRB1*04 and HLA-DRB1*08 antigens.

Conclusions

The determination of these acceptable and unacceptable antigens may increase their transplantation chance. Pre-transplant HLA antibody identifications provide prognostic information with respect to the determination of patients who are at increased risk of graft loss.

CPRA for allocation of kidneys in the US: More candidates ≥98% CPRA, lower positive crossmatch rates and improved transplant rates for sensitized patients

In 2009 calculated panel reactive antibody (CPRA) replaced PRA as the metric for HLA sensitization in the US kidney allocation system. During the next four years, registrants with at least one unacceptable antigen increased (34-40%) and registrants with ≥98% PRA/CPRA increased from 7% to 9% of the waitlist. These changes were accompanied by a reduction in kidney offers refused for positive crossmatch: 14,137 (1.7%) in 2009 and 3,310 in 2013 (0.4%). Registrants with ≥98% PRA/CPRA had highest rates of refusal but also showed substantial improvement (20% in 2009 vs 8% in 2013). For registrants with ≥98% PRA/CPRA, 45% of accepted offers in 2009 were not transplanted into the intended recipient compared to 11% in 2013. Transplant rates remained low for these patients (∼50/1000 active patient-years), but rates improved for patients with 80-97% PRA/CPRA (223/1000 active patient-years in 2009 vs 354/1000 in 2013). In 2013, 40% regraft candidates had CPRA ≥98% compared to 4% of primary graft candidates. More females than males were ≥98% CPRA (14% vs 7%) and more females had CPRA above 0 (50% vs 28%). In the CPRA era, listing of unacceptable antigens increased, positive crossmatches were diminished and transplant rates for sensitized patients improved.

Allocating Deceased Donor Kidneys to Candidates with High Panel-Reactive Antibodies

BACKGROUND AND OBJECTIVES

In December of 2014, the Organ Procurement and Transplant Network implemented a new Kidney Allocation System (KAS) for deceased donor transplant, with increased priority for highly sensitized candidates (calculated panel-reactive antibody [cPRA] >99%). We used a modified version of the new KAS to address issues of access and equity for these candidates.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a simulation, 10,988 deceased donor kidneys transplanted into waitlisted recipients in 2010 were instead allocated to candidates with cPRA≥80% (n=18,004). Each candidate's unacceptable donor HLA antigens had been entered into the allocation system by the transplant center. In simulated match runs, kidneys were allocated sequentially to adult ABO identical or permissible candidates with cPRA 100%, 99%, 98%, etc. to 80%. Allocations were restricted to donor/recipient pairs with negative virtual crossmatches.

RESULTS

The simulation indicated that 2111 of 10,988 kidneys (19.2%) would have been allocated to patients with cPRA 100% versus 74 of 10,988 (0.7%) that were actually transplanted. Of cPRA 100% candidates, 74% were predicted to be compatible with an average of six deceased donors; the remaining 26% seemed to be incompatible with every deceased donor organ that entered the system. Of kidneys actually allocated to cPRA 100% candidates in 2010, 66% (49 of 74) were six-antigen HLA matched/zero-antigen mismatched (HLA-A, -B, and -DR) with their recipients versus only 11% (237 of 2111) in the simulation. The simulation predicted that 10,356 of 14,433 (72%) candidates with cPRA 90%-100% could be allocated an organ compared with 7.3% who actually underwent transplant.

CONCLUSIONS

Data in this simulation are consistent with early results of the new KAS; specifically, nearly 20% of deceased donor kidneys were (virtually) compatible with cPRA 100% candidates. Although most of these candidates were predicted to be compatible with multiple donors, approximately one-quarter are unlikely to receive a single offer.

Four years of experience with the Australian kidney paired donation programme

New approaches to increase kidney transplantation rates through expansion of live donor kidney transplantation have become necessary due to ongoing shortage of deceased donor organs. These strategies include desensitization in antibody-incompatible transplants to overcome the barrier of blood group incompatibility or human leucocyte antigen antibodies between recipient and donor and kidney paired donation (KPD) programmes. In KPD, a kidney transplant candidate with an incompatible live donor joins a registry of other incompatible pairs in order to find potentially compatible transplant solutions. To match the largest possible number of donor-recipient pairs while minimizing immunologic risk, KPD programmes use sophisticated algorithms to identify suitable matches with simultaneous two-way or more complex multi-way exchanges as well as including non-directed anonymous donors to start a chain of compatible transplantations. Because of the significant immunologic barriers when fewer donor options are available, the optimal solution for difficult-to-match, highly sensitized patients is access to more potential donors using large multi-centre or national KPD registries. This review focuses on the first 4 years of experience with the Australian multi-centre KPD programme that was established in October 2010.

Peak panel reactive antibody, cancer, graft, and patient outcomes in kidney transplant recipients

BACKGROUND

High levels of pretransplant panel reactive antibodies (PRA) are known to be associated with detrimental effects on graft outcomes, but the association between pretransplant PRA levels and long-term patient outcomes is unclear.

METHODS

Using the Australian and New Zealand Dialysis and Transplant Registry (ANZDATA), we assessed the risk of rejection, graft failure, mortality and cancer in kidney transplant recipients with varying peak PRA levels.

RESULTS

In 7,118 kidney transplant recipients between 1997 and 2009, there were a total of 3,171 (44.6%), 3,306 (46.4%), 323 (4.5%), and 318 (4.5%) recipients with peak PRA levels of 0%, 1% to 50%, 51% to 80%, and greater than 80%, respectively. Compared to recipients with 0% peak PRA level, recipients with peak PRA levels greater than 80% were at increased risk of acute rejection (odds ratio, 1.81, 95% confidence interval [95% CI], 1.30-2.35; P < 0.001), death censored graft failure (hazard ratio [HR], 2.06; 95% CI, 1.46-2.91; P < 0.001), all-cause mortality (HR, 1.56; 95% CI, 1.15-2.11; P < 0.001) and cancer (HR, 1.94; 95% CI, 1.26-2.97; P = 0.002) in the adjusted models independent of human leukocyte antigen mismatches and initial immunosuppression.

CONCLUSION

Highly sensitized kidney transplant recipients with peak PRA greater than 80% had a greater risk of rejection, graft failure, cancer and death independent of age and time on dialysis. Strategies to reduce transplant waiting time and avoidance of sensitization in all potential transplant candidates are imperative to improve the overall graft and patient survival.

The relative benefits and costs of solid phase bead technology to detect preformed donor specific antihuman leukocyte antigen antibodies in determining suitability for kidney transplantation

BACKGROUND

Screening for donor-specific anti-HLA antibodies (DSA) using bead-based multiplex assays to determine transplant suitability is standard practice in many countries. We compared the health benefits and costs of screening preformed DSA using bead-based assay as an add-on test to complement-dependent cytotoxicity (CDC) crossmatch with CDC crossmatch alone, and determined the optimal threshold to determine transplant suitability.

METHODS

Three probabilistic Markov models were developed to compare bead-based assay with CDC and CDC alone. The model assumed a hypothetical cohort of 10,000 patients who received only a single kidney transplant and terminated when all patients were deceased.

RESULTS

Assuming transplantation was permitted for recipients with no DSA or with a DSA mean fluorescence intensity (MFI) value of 500 or less, screening by bead-based assay and CDC saved 6.5 grafts and U.S. $1,192,303 per 100 transplants compared with CDC alone. If the thresholds were increased to an MFI of 2000 or less and 5000 or less, an extra 6.4 and 6.1 grafts would be saved, with cost savings of U.S. $867,203 and U.S. $830,664 per 100 transplants compared with CDC alone. The total number of kidney transplants performed would have increased by 8 and 9, respectively, but at the expense of an extra 0.1 and 0.4 graft lost per 100 transplants after 5 years.

CONCLUSIONS

Screening using bead-based assay is cost-saving and improves graft outcomes. The greatest benefits and cost-savings are achieved if transplantation occurs at a threshold of MFI of 500 or less or in those without preformed DSA. Increasing the threshold to an MFI of 2000 or less may provide an acceptable balance for improving transplant eligibility without compromising longer-term outcomes.

Tacrolimus to Belatacept Conversion Following Hand Transplantation: A Case Report

Vascularized composite allotransplantation (VCA) has emerged as a viable limb replacement strategy for selected patients with upper limb amputation. However, allograft rejection has been seen in essentially all reported VCA recipients indicating a requirement for substantial immunosuppressive therapy. Calcineurin inhibitors have served as the centerpiece agent in all reported cases, and CNI-associated complications associated with the broad therapeutic effects and side effects of calcineurin inhibitors have been similarly common. Recently, belatacept has been approved as a calcineurin inhibitor replacement in kidney transplantation, but to date, its use in VCA has not been reported. Herein, we report on the case of a hand transplant recipient who developed recurrent acute rejection with alloantibody formation and concomitant calcineurin inhibitor nephrotoxicity, all of which resolved upon conversion from a maintenance regimen of tacrolimus, mycophenolate mofetil and steroids to belatacept and sirolimus. This case indicates that belatacept may be a reasonable maintenance immunosuppressive alternative for use in VCA, providing sufficient prophylaxis from rejection with a reduced side effect profile, the latter being particularly relevant for nonlife threatening conditions typically treated by VCA.

Kidney paired donation: principles, protocols and programs

Due to the ongoing shortage of deceased-donor organs, novel strategies to augment kidney transplantation rates through expanded living donation strategies have become essential. These include desensitization in antibody-incompatible transplants and kidney paired donation (KPD) programs. KPD enables kidney transplant candidates with willing but incompatible living donors to join a registry of other incompatible pairs in order to find potentially compatible transplant solutions. Given the significant immunologic barriers with fewer donor options, single-center or small KPD programs may be less successful in transplanting the more sensitized patients; the optimal solution for the difficult-to-match patient is access to more potential donors and large multicenter or national registries are essential. Multicenter KPD programs have become common in the last decade, and now represent one of the most promising opportunities to improve transplant rates. To maximize donor-recipient matching, and minimize immunologic risk, these multicenter KPD programs use sophisticated algorithms to identify optimal match potential, with simultaneous two-, three- or more complex multiway exchanges. The article focuses on the recent progresses in KPD and it also reviews some of the differences and commonalities across four different national KPD programs.

Utility of HLA Antibody Testing in Kidney Transplantation

HLA antigens are polymorphic proteins expressed on donor kidney allograft endothelium and are critical targets for recipient immune recognition. HLA antibodies are risk factors for acute and chronic rejection and allograft loss. Solid-phase immunoassays for HLA antibody detection represent a major advance in sensitivity and specificity over cell-based methods and are widely used in organ allocation and pretransplant risk assessment. Post-transplant, development of de novo donor-specific HLA antibodies and/or increase in donor-specific antibodies from pretransplant levels are associated with adverse outcomes. Although single antigen bead assays have allowed sensitive detection of recipient HLA antibodies and their specificities, a number of interpretive considerations must be appreciated to understand test results in clinical and research contexts. This review, which is especially relevant for clinicians caring for transplant patients, discusses the technical aspects of single antigen bead assays, emphasizes their quantitative limitations, and explores the utility of HLA antibody testing in identifying and managing important pre- and post-transplant clinical outcomes.

Denatured class I human leukocyte antigen antibodies in sensitized kidney recipients: prevalence, relevance, and impact on organ allocation

BACKGROUND

Single antigen flow beads assays may overestimate sensitization because of the detection of supposedly irrelevant antibodies recognizing denatured class I human leukocyte antigens (HLAs).

METHODS

Sera of 323 HLA-sensitized kidney transplant candidates positive with a class I HLA single antigen flow beads assay were retested after acid treatment of the beads. Denatured HLA antibodies were identified according to ratio between the measured fluorescence intensity for treated and nontreated beads. T-lymphocyte flow cytometry crossmatches were performed to characterize the ability of these antibodies to recognize HLA on normal cells as a surrogate of their potential clinical relevance. Their impact on organ allocation was evaluated through a calculated panel reactive antibody. The utility of single antigen flow beads largely devoid of denatured HLA (iBeads) was also evaluated.

RESULTS

Denatured HLA antibodies were detected in 39% of the patients. They provided much less positive flow cytometry crossmatches than anti-native HLA antibodies (16% vs. 83%, P<0.0001). Removing the HLA-A and HLA-B antigens targeted by denatured HLA antibodies from unacceptable antigens lowered the calculated panel reactive antibody for 90 patients, sometimes dramatically. The iBeads assay demonstrated nearly the same ability to predict crossmatch results than the acid treatment assay.

CONCLUSION

Denatured class I HLA antibodies are common, but the antigens they target should not be considered as unacceptable in most cases, because they negatively impact access to a transplant while predominantly providing negative sensitive crossmatches. The iBeads assay seems to be a valuable alternative to better define unacceptable antigens.

HLA antibody detection with solid phase assays: great expectations or expectations too great?

Alloantibodies directed against HLA antigens, are a barrier to long-term solid organ allograft survival. The clinical impact of preformed, donor-directed HLA alloantibodies range from acceptable risk to unequivocal contraindication for organ transplantation. HLA antibodies are key factors that limit patient access to donor organs. Serological methods were once the only approach to identify HLA antigens and antibodies. Limitations in these technologies led to the development of solid phase approaches. In the early 1990s, the development of the polymerase chain reaction enabled DNA-based HLA antigen testing to be performed. By the mid-1990s, microparticle-based technology that utilized flow cytometry for analysis was developed to detect both classes I and II HLA antibodies. These methodologies revolutionized clinical histocompatibility testing. The strengths and weaknesses of these assays are described in detail in this review.

Detection of donor-specific antibodies in kidney transplantation

INTRODUCTION

Precise and timely detection of human leukocyte antigen (HLA) donor-specific antibodies (DSAs) is vital for evaluating humoral immune status of patients pre- and post-transplantation.

SOURCE OF DATA

Clinically relevant articles on theory, development, methodology and application of HLA-DSA testing in kidney transplantation.

AREAS OF AGREEMENT AND CONTROVERSY

The availability of solid phase HLA-antibody testing revolutionized our ability to detect HLA-DSA and to appreciate their significance in kidney transplant outcome. The best approach to determine the strength, immunogenicity and pathogenicity of HLA antibodies still remains controversial.

GROWING POINTS

Assays to identify complement-binding antibodies were developed. Their clinical utilization, pre- and post-transplantation, is currently under investigation. Appreciation of the complexity of HLA-DQ antibodies should lead to better assignment of unacceptable antibodies and cPRA calculation.

AREAS TIMELY FOR DEVELOPING RESEARCH

Characterization of HLA-antibody epitopes, and utilization of epitope matching to better define compatible donors could contribute to better transplant outcomes.

Allosensitization in heart transplantation: an overview

Transplant candidates might manifest circulating antibodies against human leukocyte antigens and nonhuman leukocyte antigens, a condition termed allosensitization. The presence of these antibodies decreases a given candidate's possible donor pool, thereby prolonging the time to transplantation. They are also associated with poorer posttransplant outcomes including increased morbidity and mortality. With the increasing use of ventricular assist devices as a bridge to transplantation, the prevalence of allosensitized transplant candidates has increased. This has implications for transplant programs in terms of donor-recipient matching and managing transplant-related complications, which are more common in this high risk cohort. Controversy exists as to the best approach in managing sensitized patients, before and after transplantation. Transplant centres have used various strategies to reduce antibody loads with mixed results being reported; moreover, it remains unclear as to whether attempts at desensitization translate into better posttransplant outcomes. As an alternative management approach, some centres participate in large organ sharing strategies and allocate organs based on the probability of finding a successful donor-recipient match. In this article, the immunological basis of allosensitization, its causes, implications, and therapeutic strategies to manage sensitized patients are reviewed. The literature in relation to desensitization therapies in heart transplant candidates is also reviewed.

An update on the impact of pre-transplant transfusions and allosensitization on time to renal transplant and on allograft survival

Background

Blood transfusions have the potential to improve graft survival, induce sensitization, and transmit infections. Current clinical practice is to minimize transfusions in renal transplantation candidates, but it is unclear if the evidence continues to support pre-transplant transfusion avoidance. Changes in the Medicare prospective payment system may increase transfusion rates. Thus there is a need to re-evaluate the literature to improve the management options for renal transplant candidates.

Methods

A review applying a systematic approach and conducted using MEDLINE^®, Embase^®, and the Cochrane Library for English-language publications (timeframe: 01/1984–03/2011) captured 180 studies and data from publically available registries and assessed the impact of transfusions on allosensitization and graft survival, and the impact of allosensitization on graft survival and wait time.

Results

Blood transfusions continued to be a major cause of allosensitization, with allosensitization associated with increased rejection and graft loss, and longer wait times to transplantation. Although older studies showed a beneficial effect of transfusion on graft survival, this benefit has largely disappeared in the post-cyclosporine era due to improved graft outcomes with current practice. Recent data suggested that it may be the donor-specific antibody component of allosensitization that carried the risk to graft outcomes.

Conclusions

Results of this review indicated that avoiding transfusions whenever possible is a sound management option that could prevent detrimental effects in patients awaiting kidney transplantation.

Clinical relevance of human leukocyte antigen antibodies in liver, heart, lung and intestine transplantation

PURPOSE OF REVIEW

Solid phase assays identify human leukocyte antigen (HLA) antibodies with a great sensitivity. Whether to accept or decline an organ if the virtual crossmatch is positive, when to monitor and whether to treat de-novo donor-specific antibody (DSA) posttransplant remain challenging issues for the transplant clinician.

RECENT FINDINGS

Technologies that can differentiate which antibodies pose the greatest risk for antibody-mediated rejection (AMR) are evolving. Complement fixing luminex assays have been used to predict high-risk antibodies, but using these assays alone will miss some preformed antibodies. How these technologies fit into the laboratory's testing algorithm will likely need to be individualized. Posttransplant de-novo DSAs are associated with inferior outcomes. In hearts, similar to renal transplantation, acute rejection is a risk factor for developing de-novo DSA. Further data are needed to determine whether other risk factors are similar to those reported for renal transplants. Antibodies to self-antigens are increasingly recognized posttransplant and how the alloimmune response contributes to altered autoregulation is a current research focus.

SUMMARY

Identification of DSA enables the clinician to make informed decisions regarding whether or not to accept an organ and if augmented immunosuppression is indicated. Monitoring for DSA posttransplant identifies recipients at a greater risk for AMR and can guide management. However, the best approach to dealing with de-novo DSA remains unclear.

Technical aspects of HLA antibody testing

PURPOSE OF REVIEW

Since the landmark studies of Patel and Terasaki, pretransplant identification of donor-directed HLA alloantibodies (DSAs) has been a critical prelude to renal allograft transplantation. Pretransplant, DSAs may be an acceptable risk or an unconditional contraindication to transplantation depending on the particular donor : recipient combination. Posttransplant, DSAs are associated with episodes of acute rejection, chronic rejection, and graft loss. Thus, monitoring for such antibodies is an important aspect of patient care.

RECENT FINDINGS

The development of solid-phase antibody detection assays significantly enhanced our ability to identify HLA antibodies, taking virtual crossmatching from concept to reality. At the root of these detection assays are two questions that have been asked for almost 50 years: are donor-directed HLA antibodies present and, if so, are they clinically relevant? While the technology related to solid-phase antibody detection has seemingly allowed the first question to be answered with exquisite sensitivity and specificity, can the same be said for question 2?

SUMMARY

Solid-phase antibody detection assays have clear benefits over historical approaches to antibody identification, but are not flawless. In fact, the limitations of these assays are frequently ignored. Herein, the strengths and weaknesses of solid-phase antibody detection are highlighted.

Comprehensive assessment and standardization of solid phase multiplex-bead arrays for the detection of antibodies to HLA

Solid phase multiplex-bead arrays for the detection and characterization of HLA antibodies provide increased sensitivity and specificity compared to conventional lymphocyte-based assays. Assay variability due to inconsistencies in commercial kits and differences in standard operating procedures (SOP) hamper comparison of results between laboratories. The Clinical Trials in Organ Transplantation Antibody Core Laboratories investigated sources of assay variation and determined if reproducibility improved through utilization of SOP, common reagents and normalization algorithms. Ten commercial kits from two manufacturers were assessed in each of seven laboratories using 20 HLA reference sera. Implementation of a standardized (vs. a nonstandardized) operating procedure greatly reduced MFI variation from 62% to 25%. Although laboratory agreements exceeded 90% (R(2) ), small systematic differences were observed suggesting center specific factors still contribute to variation. MFI varied according to manufacturer, kit, bead type and lot. ROC analyses showed excellent consistency in antibody assignments between manufacturers (AUC > 0.9) and suggested optimal cutoffs from 1000 to 1500 MFI. Global normalization further reduced MFI variation to levels near 20%. Standardization and normalization of solid phase HLA antibody tests will enable comparison of data across laboratories for clinical trials and diagnostic testing.

Poor kidney allograft survival associated with positive B cell - Only flow cytometry cross matches: a ten year single center study

The presence of donor specific antibody (DSA) to class 1 or class 2 HLA as detected respectively in T cell or B cell - only flow cytometry cross matches (FCXMs) are risk factors for renal allograft survival, though the comparative risk of these XMs has not been definitively established. Allograft survival and FCXM data in 624 microcytotoxicity (CDC) XM negative kidney transplants were evaluated. Short and long term allograft survival was significantly less in recipients with T(-) B(+) FCXMs (1 year, 74%, 10 year, 58%) compared to T(+) B(+) FCXMs (1 year, 84%, 10 year, 68%) and to T(-) B(-) FCXM (1 year, 90%, 10 year, 85%). Risk factors were positive FCXM, deceased donor (DD) transplantation and donor age, but not race, gender, recipient age or previous transplant. Recipients with T(-) B(+) and T(+) B(+) FCXMs were at 4.5 and 2.5 fold greater risk, respectively, of DD allograft failure compared to patients with T(-) B(-) FCXMs. The quantitative value of FCXM did not correlate with the duration of graft survival. We conclude that patients with DSA to class 2 HLA have a greater risk of early and late allograft failure compared to patients with DSA to class 1 HLA.

The use of the calculated panel-reactive antibody and virtual crossmatch in heart transplantation

PURPOSE OF REVIEW

Alloantibodies to human leukocyte antigens (HLAs) in patients awaiting heart transplantation are associated with prolonged wait time to transplant, increased risk of posttransplant rejection and cardiac allograft vasculopathy, and decreased survival. Solid-phase assays to determine antibody presence have allowed for the development of a calculated panel-reactive antibody to denote unacceptable antigens. The virtual crossmatch allows for the comparison of recipient HLA antibodies to prospective donor HLA antigens to safely match a patient to an appropriate donor without a prospective crossmatch.

RECENT FINDINGS

Expansion of the donor pool and decreased waiting time for heart transplant may be impacted by further assessment of the functional status of alloantibodies and novel means for desensitization. Sensitized patients who receive left ventricular assist device (LVAD) as a bridge to cardiac transplant appear to have similar postoperative 1-year outcomes compared with nonsensitized patients.

SUMMARY

Antibody sensitization poses an additional hurdle to patients awaiting heart transplantation. Functional antibody assessment, placement of a LVAD as bridge to cardiac transplant, and novel means of desensitization may impact a sensitized patient's ability to safely undergo heart transplantation.

Consensus guidelines on the testing and clinical management issues associated with HLA and non-HLA antibodies in transplantation

BACKGROUND

The introduction of solid-phase immunoassay (SPI) technology for the detection and characterization of human leukocyte antigen (HLA) antibodies in transplantation while providing greater sensitivity than was obtainable by complement-dependent lymphocytotoxicity (CDC) assays has resulted in a new paradigm with respect to the interpretation of donor-specific antibodies (DSA). Although the SPI assay performed on the Luminex instrument (hereafter referred to as the Luminex assay), in particular, has permitted the detection of antibodies not detectable by CDC, the clinical significance of these antibodies is incompletely understood. Nevertheless, the detection of these antibodies has led to changes in the clinical management of sensitized patients. In addition, SPI testing raises technical issues that require resolution and careful consideration when interpreting antibody results.

METHODS

With this background, The Transplantation Society convened a group of laboratory and clinical experts in the field of transplantation to prepare a consensus report and make recommendations on the use of this new technology based on both published evidence and expert opinion. Three working groups were formed to address (a) the technical issues with respect to the use of this technology, (b) the interpretation of pretransplantation antibody testing in the context of various clinical settings and organ transplant types (kidney, heart, lung, liver, pancreas, intestinal, and islet cells), and (c) the application of antibody testing in the posttransplantation setting. The three groups were established in November 2011 and convened for a "Consensus Conference on Antibodies in Transplantation" in Rome, Italy, in May 2012. The deliberations of the three groups meeting independently and then together are the bases for this report.

RESULTS

A comprehensive list of recommendations was prepared by each group. A summary of the key recommendations follows. Technical Group: (a) SPI must be used for the detection of pretransplantation HLA antibodies in solid organ transplant recipients and, in particular, the use of the single-antigen bead assay to detect antibodies to HLA loci, such as Cw, DQA, DPA, and DPB, which are not readily detected by other methods. (b) The use of SPI for antibody detection should be supplemented with cell-based assays to examine the correlations between the two types of assays and to establish the likelihood of a positive crossmatch (XM). (c) There must be an awareness of the technical factors that can influence the results and their clinical interpretation when using the Luminex bead technology, such as variation in antigen density and the presence of denatured antigen on the beads. Pretransplantation Group: (a) Risk categories should be established based on the antibody and the XM results obtained. (b) DSA detected by CDC and a positive XM should be avoided due to their strong association with antibody-mediated rejection and graft loss. (c) A renal transplantation can be performed in the absence of a prospective XM if single-antigen bead screening for antibodies to all class I and II HLA loci is negative. This decision, however, needs to be taken in agreement with local clinical programs and the relevant regulatory bodies. (d) The presence of DSA HLA antibodies should be avoided in heart and lung transplantation and considered a risk factor for liver, intestinal, and islet cell transplantation. Posttransplantation Group: (a) High-risk patients (i.e., desensitized or DSA positive/XM negative) should be monitored by measurement of DSA and protocol biopsies in the first 3 months after transplantation. (b) Intermediate-risk patients (history of DSA but currently negative) should be monitored for DSA within the first month. If DSA is present, a biopsy should be performed. (c) Low-risk patients (nonsensitized first transplantation) should be screened for DSA at least once 3 to 12 months after transplantation. If DSA is detected, a biopsy should be performed. In all three categories, the recommendations for subsequent treatment are based on the biopsy results.

CONCLUSIONS

A comprehensive list of recommendations is provided covering the technical and pretransplantation and posttransplantation monitoring of HLA antibodies in solid organ transplantation. The recommendations are intended to provide state-of-the-art guidance in the use and clinical application of recently developed methods for HLA antibody detection when used in conjunction with traditional methods.

Precision diagnostics in transplantation: from bench to bedside

The Canadian and American Societies of Transplantation held a symposium on February 22, 2012 in Quebec City focused on discovery, validation and translation of new diagnostic tools into clinical transplantation. The symposium focused on antibody testing, transplantation pathology, molecular diagnostics and laboratory support for the incompatible patient. There is an unmet need for more precise diagnostic approaches in transplantation. Significant potential for increasing the diagnostic precision in transplantation was recognized through the integration of conventional histopathology, molecular technologies and sensitive antibody testing into one enhanced diagnostic system.

Successful isolated intestinal transplantation in sensitized recipients with the use of virtual crossmatching

We evaluated virtual crossmatching (VXM) for organ allocation and immunologic risk reduction in sensitized isolated intestinal transplantation recipients. All isolated intestine transplants performed at our institution from 2008 to 2011 were included in this study. Allograft allocation in sensitized recipients was based on the results of a VXM, in which the donor-specific antibody (DSA) was prospectively evaluated with the use of single-antigen assays. A total of 42 isolated intestine transplants (13 pediatric and 29 adult) were performed during this time period, with a median follow-up of 20 months (6-40 months). A sensitized (PRA ≥ 20%) group (n = 15) was compared to a control (PRA < 20%) group (n = 27) to evaluate the efficacy of VXM. With the use of VXM, 80% (12/15) of the sensitized patients were transplanted with a negative or weakly positive flow-cytometry crossmatch and 86.7% (13/15) with zero or only low-titer (≤ 1:16) DSA. Outcomes were comparable between sensitized and control recipients, including 1-year freedom from rejection (53.3% and 66.7% respectively, p = 0.367), 1-year patient survival (73.3% and 88.9% respectively, p = 0.197) and 1-year graft survival (66.7% and 85.2% respectively, p = 0.167). In conclusion, a VXM strategy to optimize organ allocation enables sensitized patients to successfully undergo isolated intestinal transplantation with acceptable short-term outcomes.

Detection of anti-HLA antibodies by solid-phase assay in kidney transplantation: friend or foe?

Pre-formed and de novo anti-human leukocyte antigen (HLA) antibodies induce antibody-mediated rejection and are also involved in mechanisms leading to chronic graft nephropathy. The detection of anti-HLA antibodies by solid-phase assay (SPA) has revolutionized the management of immunized patients before and after kidney transplantation. Characterized by high sensitivity and specificity, the clinical relevance of anti-HLA antibodies by SPA has to be clarified. The presence of donor-specific antibody at the epitope level, their titer, and the use of different crossmatch technologies could help to determine which of the anti-HLA antibodies are friends and which are foes in kidney transplantation. In this review, we summarize the current state of the art on this debated topic, and give clinical guidelines for the management of antibody detection pre- and post-transplantation, based on these evidences and our own clinical expertise.

A possible system for optimal donor kidney exchange in Turkey

The lack of available deceased donors and the immunological incompatibility between the patients and their voluntary donor candidates make kidney exchange among donor-patient pairs a preferable solution performed locally by many organ transplantation centers in Turkey. However, maximum benefit from kidney exchange can only be achieved when the donor patient pool is maximized using a nationwide kidney exchange program. This work discusses kidney exchange practices worldwide to develop a nationwide exchange program in Turkey and related challenges.

Heart transplantation in adults with end-stage congenital heart disease

Residual abnormalities in cardiac structure and function predispose adults with congenital heart disease to late-onset heart failure and its complications. Evaluation of this population requires collaboration between adult congenital and heart failure specialists. In addition to assessing heart transplant eligibility, clinicians must balance the risks of premature listing against progressive heart failure and increased waiting list mortality. Following heart transplantation, adults with congenital heart disease have higher mortality due to an increased risk of bleeding, infection and donor right heart failure secondary to pulmonary hypertension. Concerns relating to increased early mortality should be balanced against superior long-term survival in adult congenital heart disease patients surviving beyond the first year after heart transplantation.

Successful rescue of refractory acute antibody-mediated renal allograft rejection with splenectomy--a case report

Highly sensitized patients receive fewer kidney transplants and have a high risk for severe rejection with increased rates of graft loss. We present a highly sensitized child who after desensitization protocol received a kidney transplant and developed refractory acute antibody-mediated rejection. He failed to respond to standard therapy and needed an urgent splenectomy as rescue therapy. Our patient, an 18-yr-old AA male with ESRD due to obstructive uropathy received a second DD transplant. The allograft functioned immediately with SCr 1.4 mg/dL on day #5. On day #8, he was re-admitted with fever, oligoanuria, and renal failure. He was started on methylprednisolone pulse, thymoglobulin, intravenous immunoglobulin, and PP. The transplant kidney biopsy revealed features suggestive of acute AMR. On day #14, the patient remained dialysis dependent with no response to therapy. He underwent an urgent splenectomy and a slow increase in urine output and GFR was noted. The SCr one month post-splenectomy was 1.1 mg/dL. At one yr post-txp, his GFR remained stable with SCr 0.9 mg/dL on tacrolimus, mycophenolate mofetil, and prednisone. Urgent splenectomy successfully reversed refractory acute AMR, in our highly sensitized patient with second renal transplant.

Application of calculated panel reactive antibody using HLA frequencies in Koreans

Background

Introduction of the Luminex panel reactive antibody (PRA)-single antigen (SA) assay has increased the detection rates of unacceptable antigens in sensitized patients; the calculated PRA (CPRA) level represents the percentage of actual organ donors that express 1 or more of these unacceptable antigens. We developed a CPRA calculator based on the HLA frequencies in Koreans to measure sensitization levels in Korean patients.

Methods

To develop the calculator, we obtained the HLA-A, HLA-B, and HLA-DR phenotypes of 1,622 Koreans, and compared these with previously reported frequencies in Koreans. Sera from patients awaiting kidney transplantation were tested for HLA antibodies by Luminex PRA-screen, PRA-identification (ID), and PRA-SA assays. The measured %PRA from the PRA-screen (N=55) and PRA-ID (N=71) were compared to the %CPRA for the unacceptable antigens obtained from PRA-SA.

Results

Phenotype frequencies used for the CPRA calculator agreed with previously reported data. The concordance rates among the 3 PRA methods for the detection of class I and class II antibodies were 76.1-81.8% (kappa, 0.519-0.636) and 72.7-83.6% (0.463-0.650), respectively. For the detection of broadly sensitized sera (>50% or >80%), the concordance rates were over 80%. In sera with 80-100% CPRA, 91.7% and 94.4% of the samples had concordant results (80-100% PRA) in the PRA-screen and PRA-ID assay, respectively.

Conclusions

Although further clinical studies are required to confirm the benefits of CPRA values, adoption of CPRA analysis based on HLA frequencies in Koreans may be useful for sensitization measurements and organ-allocation algorithms.