Allocation to highly sensitized patients based on acceptable mismatches results in low rejection rates comparable to nonsensitized patients

Canadian Highly Sensitized Patient Program Report: A 1000 Kidney Transplants Story

Purpose

Highly sensitized patients (HSPs) with kidney failure have limited access to kidney transplantation and poorer post-transplant outcomes. Prioritizing HSPs in kidney allocation systems and expanding the pool of deceased donors available to them has helped to reduce their wait times for transplant and enhanced post-transplant outcomes. The Canadian HSP Program was established by Canadian Blood Services in collaboration with provincial organ donation and transplantation programs throughout the country to increase transplant opportunities for transplant candidates needing very specific matches from deceased kidney donors. Highly sensitized patients in the Canadian Program are defined by a calculated panel-reactive antibody (cPRA) ≥95%. In this report, we describe the evolution and trajectory of the Canadian HSP Program and evaluate the national impact on the first 1000 kidney transplant cases.

Source of Information

To allocate deceased donor kidney organs nationally to HSPs and report on the Canadian HSP Program's performance, Canadian Blood Services developed a national database registry known as the Canadian Transplant Registry (CTR) and an online reporting tool known as the Canadian HSP Program Data Dashboard.

Methods

The CTR, which collects HSPs' data for the purpose of matching potential donors to HSPs and as part of required national quality, safety, and efficiency performance measurements, was retrospectively reviewed. Due to the nature of using deidentified aggregate registry data, a patient consent form was not required. A Research Ethical Board (REB) application was also waived.

Key Findings

In this article, we describe the historical development, initial deployment, and evolution of the Canadian HSP Program with a primary aim to increase the rate of deceased donor kidney transplantation. A secondary aim was to evaluate the national impact of the Canadian HSP Program on the first 1000 kidney transplant cases. Transplant candidates who have participated in the Canadian HSP Program and recipients who received transplants were predominantly females (average age 50 years, female 62%) with blood group O (47% of candidates, 42% of transplants). Seventy percent of all active transplant candidates enrolled in the HSP Program were in the hardest to match group (cPRA ≥99%), and only 22% of the transplant candidates with cPRA of 100% have received a transplant to date through the Program. The average times from first participation in the Canadian HSP Program to transplantation for cPRA ≥99% transplant recipients were significantly longer than for cPRA 95% to 98% recipients averaging 22 months versus 6 months, respectively. By the end of June 2024, the Canadian HSP Program had facilitated 1000 transplants, 613 of which were from interprovincial matches. The average (SD) cold ischemic time (CIT) was 14.5 (5.9) hours, with interprovincial transplants exhibiting significantly longer CITs compared with intraprovincial transplants, averaging an additional 4.7 hours.

Limitations

Our study limitations include first that it is a retrospective registry data analysis with no available short- and long-term clinical outcomes data at this point (patient and graft survival). Second, given the nature of registry data, not all relevant data may have been captured and reporting may not be complete for all patients.

Implications

Examination of CTR registry data showed the Canadian HSP Program had a meaningful impact in enabling 1000 HSPs to access transplantation opportunities that may otherwise be unavailable to them.

Potential of new 250-nautical mile concentric circle allocation system for improving the donor/recipient HLA matching: Development of new matching algorithm

BACKGROUND

High-resolution typing of human leukocyte antigen (HLA) may revolutionize the field of kidney transplantation by selection of low immunogenic grafts. The new 250-nautical mile circle allocation system offers a unique opportunity to find low HLA immunogenic donors for eligible recipients.

METHODS

501 transplant candidates from the University of Toledo Medical Center (UTMC) between 2015 and 2019, registered at the Scientific Registry of Transplant Recipients (SRTR) were virtually matched to 4812 donors procured within 250-nautical miles using an in-house-developed simulation algorithm. Immunogenicity of HMS (hydrophobic mismatch score) ≤10 was measured based on imputed high-resolution HLAs. Simulated "optimal" matches with a KDPI≤50 % were compared with the transplant cohort between 2000 and 2010 with their kidney allograft survivals.

RESULTS

Out of 501 recipients 500 (99.8 %) were matched with donors ≤10 HMS and KDPI ≤50 %. The average HMS value for simulated transplants was 1.4 (range 0-10) versus 6.3 (range 0-75) in the retrospective cohort (p < 0.001). The simulated model had a median mismatch number of 3/6, while the reference cohort 4/6 among HLA-A/B/DR antigens (p < 0.001). The estimated median graft survival was 18.2 years for the simulated cohort vs. 13.4 years in the real-life cohort (p < 0.001), gaining 4.9 years per transplant and 2450 survival years for all patients. For year 2014, out of 98 patients and 659 donors, each recipient had a median number of 141 donors (HMS < 10; range 8-378). Similar values were found for patients between 2015 and 2019.

CONCLUSION

Donors within 250-nautical miles proffers excellent and multiple options for finding well-matched low immunogenic HLA kidney donors for UTMC patients, thus significantly improving their chances for long-term allograft survival.

Improving long-term kidney allograft survival by rethinking HLA compatibility: from molecular matching to non-HLA genes

Optimizing immunologic compatibility in organ transplantation extends beyond the conventional approach of Human Leukocyte Antigen (HLA) antigen matching, which exhibits significant limitations. A broader comprehension of the roles of classical and non-classical HLA genes in transplantation is imperative for enhancing long-term graft survival. High-resolution molecular HLA genotyping, despite its inherent challenges, has emerged as the cornerstone for precise patient-donor compatibility assessment. Leveraging understanding of eplet biology and indirect immune activation, eplet mismatch calculators and the PIRCHE-II algorithm surpass traditional methods in predicting allograft rejection. Understanding minor histocompatibility antigens may also present an opportunity to personalize the compatibility process. While the application of molecular matching in deceased donor organ allocation presents multiple technical, logistical, and conceptual barriers, rendering it premature for mainstream use, several other areas of donor-recipient matching and post-transplant management are ready to incorporate molecular matching. Provision of molecular mismatch scores to physicians during potential organ offer evaluations could potentially amplify long-term outcomes. The implementation of molecular matching in living organ donation and kidney paired exchange programs is similarly viable. This article will explore the current understanding of immunologic matching in transplantation and the potential applications of epitope and non-epitope molecular biology and genetics in clinical transplantation.

Characteristics of Early Antibody Mediated Rejection in Antibody Incompatible Living Donor Kidney Transplantation

Antibody incompatible transplantation (AIT) may be an only option for highly sensitized patients. Severe form of early antibody mediated rejection (AMR) adversely affects graft survival after AIT. The aim of this study was to identify individuals at risk of AMR. We analyzed 213 living donor AITs performed at our center. Among 120 ABOi, 58 HLAi and 35 DSA + FCXM-negative cases, the rates of early AMR were 6%, 31%, and 9%, respectively (p < 0.001). On multivariate analysis for graft loss, early AMR had a HR of 3.28 (p < 0.001). The HLAi group had worse death-censored graft survival (p = 0.003). In the HLAi group, Patients with aggressive variant AMR (AAMR) had greater percentage of C3d complement fixing DSA, higher baseline class I and total DSA MFI levels and B-cell FCXM RMF. C1q and C3d complement fixing DSA and strong positivity of baseline B- or T-cell FXCM as predictors of AAMR had 100% sensitivity. Early AMR is of significant clinical concern in AIT as it results in poor graft survival and is not well described in literature. An aggressive variant is characterized by massive rise in DSA levels at rejection. Baseline DSA, C1q, and C3d and baseline FCXM values can be used to risk-stratify candidates for AIT.

Long-Term Graft and Patient Survival After Re-Transplantation

BACKGROUND Kidney transplant recipients have higher life expectancy but may require subsequent transplantations, raising ethical concerns regarding organ allocation. We assessed the safety of multiple kidney transplants through long-term follow-up. MATERIAL AND METHODS A retrospective cohort study was conducted at a single center, categorizing patients based on the number of kidney transplantations received. The primary outcome was the composite of death-censored graft failure and overall mortality. The secondary outcome was death-censored graft failure. RESULTS Between 2000 and 2019, our center performed 2152 kidney transplantations. Patients were divided into 3 groups: A (1 transplant; n=1850), B (2 transplants; n=285), and C (3 or more transplants; n=75). Group C patients were younger, had fewer comorbidities, and received more aggressive induction therapy. The primary outcomes, including death-censored graft loss and overall mortality, showed similar rates across groups (A: 21.3%, B: 25.2%, C: 21.7%, p=0.068). However, the secondary outcome of death-censored graft failure alone was significantly lower in group A compared to the other groups. No significant difference was observed between groups B and C (8% vs 16% and 13%, respectively, p=0.001, p=0.845). Multivariate analysis identified having a living donor as the strongest predictor of patient and graft survival in all study groups. CONCLUSIONS Graft and patient survival rates were similar between first and multiple transplant recipients. Multiple transplant recipients had lower death-censored graft failure risk compared to first transplant recipients. However, the risk did not differ among second and subsequent transplant recipients. Younger patients, especially those with a living donor, should be considered for repeat kidney transplantation.

Positive Long-Term Outcome of Kidney Allocation via Acceptable Mismatch Program in Highly Sensitized Patients

Introduction

Eurotransplant established the acceptable mismatch (AM) program to facilitate timely kidney transplantations of highly sensitized patients, but long-term granular clinical and immunological outcomes regarding overall graft survival and de novo DSA (dnDSA) formation are still intensively researched. The right choice of induction therapy in patients with differing immunological risk is not conclusively determined, as well as the impact of human leukocyte antigen (HLA) epitope matching on dnDSA formation.

Methods

This monocentric, retrospective study analyzed 94 patients transplanted within the AM program between 2000 and 2019 compared to case-control matched cohorts of non- (PRA 0-5%; PRA-0) and intermediately sensitized (PRA 6-84%; PRA-6/84) patients transplanted through Eurotransplant Kidney Allocation System.

Results

Estimated 10-year overall graft survival between the PRA-0 and AM cohorts was similar, whereas PRA-6/84 was significantly disadvantageous compared to PRA-0. Estimated 10-year incidence of antibody-mediated rejection rates was significantly lower in the PRA-0 group compared to AM and PRA-6/84 groups. Compared to the AM group, estimated incidence of de novo donor-specific antibody (dnDSA) was significantly lower in PRA-0 patients, with no differences between the AM and PRA-6/84 cohorts. The PRA-6/84 cohort was the only subgroup in which interleukin-2 receptor antagonist (IL2RA) induction was associated with longer overall graft survival, patient survival, and graft survival compared to depleting induction (ATG or OKT3). Broad HLA-A, -B, -DR mismatches (mmABDR) and HLA epitope mismatches determined by Eplets and PIRCHE-II were predictive for dnDSA formation in the total cohort, and the AM subgroup.

Discussion

The high efforts expended on AM patients are justified to allow timely organ transplantation with acceptable risk profile and non-inferior outcomes. IL2RA induction in intermediately sensitized patients is associated with superior overall graft survival, patient survival, and graft survival compared to ATG/OKT3 induction, without negative effects on rejection episodes or dnDSA formation. In silico epitope matching might further help reduce dnDSA formation, particularly in high-risk AM patients.

Influence of HLA-A, B, and -DRB1 genes and panel-reactive antibodies on the waitlist time for kidney transplantation in the state of Sao Paulo-Brazil

BACKGROUND

Brazil ranks second in the absolute number of transplants. However, the supply remains insufficient to meet the demands, resulting in a lengthy waitlist. This study aimed to analyze whether the frequency of human leukocyte antigen (HLA) and the value of calculated panel reactive antibody (cPRA) would influence the waiting time for kidney transplantation.

METHODS

The HLA-A, B, and -DRB1 frequencies and the cPRA value were analyzed in 11,186 kidney transplant candidates included in the waitlist from 2006 to 2016.

RESULTS

The most frequent alleles were HLA-A*02, HLA-B*35, and HLA-DRB1*13. The overall mean length of stay on the list was 986 ± 1001 days. The mean waiting time for the three most frequent alleles of the HLA-A and B loci showed no significant difference when compared with the least frequent alleles; however, for the HLA-DRB1 locus, the most frequent alleles showed a shorter waiting time. In the association between HLA and PRA, the average length of stay on the list increased according to the candidate's degree of sensitization, regardless of the analyzed HLA frequency.

CONCLUSION

The length of stay on the waitlist is influenced by the frequency of the HLA alleles of the DRB1 locus and the degree of sensitization.

Improving the Access of Highly Sensitized Patients to Kidney Transplantation From Deceased Donors: The Spanish PATHI Program With Allocation Based on the Virtual Crossmatch

BACKGROUND

In 2015, the Spanish National Transplant Organization developed a prioritization system (Program for Access to Transplantation for Highly Sensitized Patients [PATHI]) to increase transplant options for patients with calculated panel-reactive antibodies (cPRAs) ≥98%, based on virtual crossmatch. We describe the experience with the implementation of PATHI and assess its efficacy.

METHODS

PATHI registry was used to collect characteristics of donors and patients between June 15, 2015, and March 1, 2018. One-year graft and patient survival and acute rejection were also measured. A Cox model was used to identify factors related to patient death and graft loss and logistical regression for those associated with rejection.

RESULTS

One thousand eighty-nine patients were included, and 272 (25%) were transplanted. Transplant rate by cPRA was 54.9%, 40.5%, and 12.8% in patients with cPRA98%, cPRA99%, and cPRA100%, respectively. One-year patient survival was 92.5%. Recipient age ≥60, time under dialysis >7 y, and delayed graft function were mortality risk factors. One-year graft survival was 88.7%. The factor related to graft loss was delayed graft function. The rejection rate was 22%. Factors related to rejection were sex, older recipients, and posttransplant donor-specific antibodies.

CONCLUSIONS

A prioritization approach increases transplant options for highly sensitized patients with appropriate short-term postransplant outcomes. Along with other programs, PATHI may inspire other countries to adopt strategies to meet transplant needs of these patients.

PIRCHE-II Risk and Acceptable Mismatch Profile Analysis in Solid Organ Transplantation

To optimize outcomes in solid organ transplantation, the HLA genes are regularly compared and matched between the donor and recipient. However, in many cases a transplant cannot be fully matched, due to widespread variation across populations and the hyperpolymorphism of HLA alleles. Mismatches of the HLA molecules in transplanted tissue can be recognized by immune cells of the recipient, leading to immune response and possibly organ rejection. These adverse outcomes are reduced by analysis using epitope-focused models that consider the immune relevance of the mismatched HLA.PIRCHE, an acronym for Predicted Indirectly ReCognizable HLA Epitopes, aims to categorize and quantify HLA mismatches in a patient-donor pair by predicting HLA-derived T cell epitopes. Specifically, the algorithm predicts and counts the HLA-derived peptides that can be presented by the host HLA, known as indirectly-presented T cell epitopes. Looking at the immune-relevant epitopes within HLA allows a more biologically relevant understanding of immune response, and provides an expanded donor pool for a more refined matching strategy compared with allele-level matching. This PIRCHE algorithm is available for analysis of single transplantations, as well as bulk analysis for population studies and statistical analysis for comparison of probability of organ availability and risk profiles.

Equity matrix for kidney transplant allocation

There is a general agreement that the distribution of kidneys for transplantation should balance utility criteria with justice. Moreover, a kidney allocation system must be based on transparent policies and seen as an ongoing process. This study aims to present an allocation system grounded on an equity matrix that balances the criteria of utility and justice. Synthetic data for a waiting list with 2000 transplant candidates and a pool of 280 donors were generated. A color priority system, the Eurotransplant (ET) kidney allocation system, and the proposed Equity Matrix (EQM) allocation system were compared after 1000 iterations of kidney allocations. Distributions of variables like the age difference, Human Leukocyte Antigens (HLA) mismatches (mmHLA), recipients' time on dialysis, cPRA, and a transplant score obtained by different allocation models were compared graphically and with Cohen's d effect size. For the analyzed variables, when we compare only the selected recipients from ET with the selected recipients from the EQM neutral model, we can conclude that the former model selects more hypersensitized recipients, a higher number of 65+ years' old recipients with 65+ years' old donors and higher number of recipients with 0 mmHLA. While recipients from EQM neutral are slightly older, have a lower age difference with their donors, have a lower number of mmHLA, are less likely to have 6 mmHLA with their donors, and have more time on dialysis. The proposed EQM model attempts to provide a simple, transparent, and equitable response to a complex question with results that outperform established practices.

Adding epitope compatibility to deceased donor kidney allocation criteria: recommendations from a pan-Canadian online public deliberation

BACKGROUND

The widening supply-demand imbalance for kidneys necessitates finding ways to reduce rejection and improve transplant outcomes. Human leukocyte antigen (HLA) epitope compatibility between donor and recipient may minimize premature graft loss and prolong survival, but incorporating this strategy to deceased donor allocation criteria prioritizes transplant outcomes over wait times. An online public deliberation was held to identify acceptable trade-offs when implementing epitope compatibility to guide Canadian policymakers and health professionals in deciding how best to allocate kidneys fairly.

METHODS

Invitations were mailed to 35,000 randomly-selected Canadian households, with over-sampling of rural/remote locations. Participants were selected for socio-demographic diversity and geographic representation. Five two-hour online sessions were held from November-December 2021. Participants received an information booklet and heard from expert speakers prior to deliberating on how to fairly implement epitope compatibility for transplant candidates and governance issues. Participants collectively generated and voted on recommendations. In the final session, kidney donation and allocation policymakers engaged with participants. Sessions were recorded and transcribed.

RESULTS

Thirty-two individuals participated and generated nine recommendations. There was consensus on adding epitope compatibility to the existing deceased donor kidney allocation criteria. However, participants recommended including safeguards/flexibility around this (e.g., mitigating declining health). They called for a transition period to epitope compatibility, including an ongoing comprehensive public education program. Participants unanimously recommended regular monitoring and public sharing of epitope-based transplant outcomes.

CONCLUSIONS

Participants supported adding epitope compatibility to kidney allocation criteria, but advised safeguards and flexibility around implementation. These recommendations provide guidance to policymakers about incorporating epitope-based deceased donor allocation criteria.

Steroid Sparing Maintenance Immunosuppression in Highly Sensitised Patients Receiving Alemtuzumab Induction

This analysis reports on the outcomes of two different steroid sparing immunosuppression protocols used in the management of 120 highly sensitised patients (HSPs) with cRF>85% receiving Alemtuzumab induction, 53 maintained on tacrolimus (FK) monotherapy and 67 tacrolimus plus mycophenolate mofetil (FK + MMF). There was no difference in the median cRF or mode of sensitisation between the two groups, although the FK + MMF cohort received more poorly matched grafts. There was no difference in one-year patient or allograft survival, however rejection free survival was inferior with FK monotherapy compared with FK + MMF at 65.4% and 91.4% respectively, p < 0.01. DSA-free survival was comparable. Whilst there was no difference in rates of BK between the cohorts, CMV-free survival was inferior in the FK + MMF group at 86.0% compared with 98.1% in the FK group, p = 0.026. One-year post-transplant diabetes free survival was 89.6% and 100.0% in the FK and FK + MMF group respectively, p = 0.027, the difference attributed to the use of prednisolone to treat rejection in the FK cohort, p = 0.006. We report good outcomes in HSPs utilising a steroid sparing protocol with Alemtuzumab induction and FK + MMF maintenance and provide granular data on immunological and infectious complications to inform steroid avoidance in these patient groups.

Oxygen-Generating Scaffolds for Cardiac Tissue Engineering Applications

Homogeneous vascularization of implanted tissue constructs can extend to 5 weeks, during which cell death can occur due to inadequate availability of oxygen. Researchers are engineering biomaterials that generate and release oxygen in a regulated manner, in an effort to overcome this hurdle. A main limitation of the existing oxygen-generating biomaterials is the uncontrolled release of oxygen, which is ultimately detrimental to the cells. This study demonstrates the incorporation of calcium peroxide (CaO2) within a hydrophobic polymer, polycaprolactone (PCL), to yield composite scaffolds with controlled oxygen release kinetics sustained over 5 weeks. Oxygen-generating microparticles coencapsulated with cardiomyocytes in a gelatin-based hydrogel matrix can serve as model systems for cardiac tissue engineering. Specifically, the results reveal that the oxygen-generating microspheres significantly improve the scaffold mechanical strength ranging from 5 kPa to 35 kPa, have an average scaffold pore size of 50-100 μm, swelling ratios of 33.3-29.8%, and degradation with 10-49% remaining mass at the end of a 48 h accelerated enzymatic degradation. The oxygen-generating scaffolds demonstrate improvement in cell viability, proliferation, and metabolic activity compared to the negative control group when cultured under hypoxia. Additionally, the optimized oxygen-generating constructs display no cytotoxicity or apoptosis. These oxygen-generating scaffolds can possibly assist the in vivo translation of cardiac tissue constructs.

Alloimmune risk assessment for antibody-mediated rejection in kidney transplantation: A practical proposal

Kidney transplantation is the treatment of choice for patients with end-stage renal disease. Although an improvement in graft survival has been observed in the last decades with the use of different immunosuppressive drugs, this is still limited in time with antibody-mediated rejection being a main cause of graft-loss. Immune monitoring and risk assessment of antibody-mediated rejection before and after kidney transplantation with useful biomarkers is key to tailoring treatments to achieve the best outcomes. Here, we provide a review of the rationale and several accessible tools for immune monitoring, from the most classic to the modern ones. Finally, we end up discussing a practical proposal for alloimmune risk assessment in kidney transplantation, including histocompatibility leukocyte antigen (HLA) and non-HLA antibodies, HLA molecular mismatch analysis and characterization of peripheral blood immune cells.

Seeking Standardized Definitions for HLA-incompatible Kidney Transplants: A Systematic Review

BACKGROUND

There is no standard definition for "HLA incompatible" transplants. For the first time, we systematically assessed how HLA incompatibility was defined in contemporary peer-reviewed publications and its prognostic implication to transplant outcomes.

METHODS

We combined 2 independent searches of MEDLINE, EMBASE, and the Cochrane Library from 2015 to 2019. Content-expert reviewers screened for original research on outcomes of HLA-incompatible transplants (defined as allele or molecular mismatch and solid-phase or cell-based assays). We ascertained the completeness of reporting on a predefined set of variables assessing HLA incompatibility, therapies, and outcomes. Given significant heterogeneity, we conducted narrative synthesis and assessed risk of bias in studies examining the association between death-censored graft failure and HLA incompatibility.

RESULTS

Of 6656 screened articles, 163 evaluated transplant outcomes by HLA incompatibility. Most articles reported on cytotoxic/flow T-cell crossmatches (n = 98). Molecular genotypes were reported for selected loci at the allele-group level. Sixteen articles reported on epitope compatibility. Pretransplant donor-specific HLA antibodies were often considered (n = 143); yet there was heterogeneity in sample handling, assay procedure, and incomplete reporting on donor-specific HLA antibodies assignment. Induction (n = 129) and maintenance immunosuppression (n = 140) were frequently mentioned but less so rejection treatment (n = 72) and desensitization (n = 70). Studies assessing death-censored graft failure risk by HLA incompatibility were vulnerable to bias in the participant, predictor, and analysis domains.

CONCLUSIONS

Optimization of transplant outcomes and personalized care depends on accurate HLA compatibility assessment. Reporting on a standard set of variables will help assess generalizability of research, allow knowledge synthesis, and facilitate international collaboration in clinical trials.

Dissecting the impact of molecular T-cell HLA mismatches in kidney transplant failure: A retrospective cohort study

Introduction

Kidney transplantation is the optimal treatment in end-stage kidney disease, but de-novo donor specific antibody development continues to negatively impact patients undergoing kidney transplantation. One of the recent advances in solid organ transplantation has been the definition of molecular mismatching between donors and recipients' Human Leukocyte Antigens (HLA). While not fully integrated in standard clinical care, cumulative molecular mismatch at the level of eplets (EMM) as well as the PIRCHE-II score have shown promise in predicting transplant outcomes. In this manuscript, we sought to study whether certain T-cell molecular mismatches (TcEMM) were highly predictive of death-censored graft failure (DCGF).

Methods

We studied a retrospective cohort of kidney donor:recipient pairs from the Scientific Registry of Transplant Recipients (2000-2015). Allele level HLA-A, B, C, DRB1 and DQB1 types were imputed from serologic types using the NMDP algorithm. TcEMMs were then estimated using the PIRCHE-II algorithm. Multivariable Accelerated Failure Time (AFT) models assessed the association between each TcEMM and DCGF. To discriminate between TcEMMs most predictive of DCGF, we fit multivariable Lasso penalized regression models. We identified co-expressed TcEMMs using weighted correlation network analysis (WGCNA). Finally, we conducted sensitivity analyses to address PIRCHE and IMGT/HLA version updates.

Results

A total of 118,309 donor:recipient pairs meeting the eligibility criteria were studied. When applying the PIRCHE-II algorithm, we identified 1,935 distinct TcEMMs at the population level. A total of 218 of the observed TcEMM were independently associated with DCGF by AFT models. The Lasso penalized regression model with post selection inference identified a smaller subset of 86 TcEMMs (56 and 30 TcEMM derived from HLA Class I and II, respectively) to be highly predictive of DCGF. Of the observed TcEMM, 38.14% appeared as profiles of highly co-expressed TcEMMs. In addition, sensitivity analyses identified that the selected TcEMM were congruent across IMGT/HLA versions.

Conclusion

In this study, we identified subsets of TcEMMs highly predictive of DCGF and profiles of co-expressed mismatches. Experimental verification of these TcEMMs determining immune responses and how they may interact with EMM as predictors of transplant outcomes would justify their consideration in organ allocation schemes and for modifying immunosuppression regimens.

Antibody-mediated rejection: prevention, monitoring and treatment dilemmas

PURPOSE OF REVIEW

Antibody-mediated rejection (AMR) has emerged as the leading cause of late graft loss in kidney transplant recipients. Donor-specific antibodies are an independent risk factor for AMR and graft loss. However, not all donor-specific antibodies are pathogenic. AMR treatment is heterogeneous due to the lack of robust trials to support clinical decisions. This review provides an overview and comments on practical but relevant dilemmas physicians experience in managing kidney transplant recipients with AMR.

RECENT FINDINGS

Active AMR with donor-specific antibodies may be treated with plasmapheresis, intravenous immunoglobulin and corticosteroids with additional therapies considered on a case-by-case basis. On the contrary, no treatment has been shown to be effective against chronic active AMR. Various biomarkers and prediction models to assess the individual risk of graft failure and response to rejection treatment show promise.

SUMMARY

The ability to personalize management for a given kidney transplant recipient and identify treatments that will improve their long-term outcome remains a critical unmet need. Earlier identification of AMR with noninvasive biomarkers and prediction models to assess the individual risk of graft failure should be considered. Enrolling patients with AMR in clinical trials to assess novel therapeutic agents is highly encouraged.

Strategies to Overcome HLA Sensitization and Improve Access to Retransplantation after Kidney Graft Loss

An increasing number of patients waitlisted for kidney transplantation have a previously failed graft. Retransplantation provides a significant improvement in morbidity, mortality, and quality of life when compared to dialysis. However, HLA sensitization is a major barrier to kidney retransplantation and the majority of the highly sensitized patients are waiting for a subsequent kidney transplant. A multidisciplinary team that includes immunogeneticists, transplant nephrologists and surgeons, and adequate allocation policies is fundamental to increase access to a kidney retransplant. A review of Pubmed, ScienceDirect, and the Cochrane Library was performed on the challenges of kidney retransplantation after graft loss, focusing on the HLA barrier and new strategies to overcome sensitization. Conclusion: Technical advances in immunogenetics, new desensitization protocols, and complex allocation programs have emerged in recent years to provide a new hope to kidney recipients with a previously failed graft.

European Guideline for the Management of Kidney Transplant Patients With HLA Antibodies: By the European Society for Organ Transplantation Working Group

This guideline, from a European Society of Organ Transplantation (ESOT) working group, concerns the management of kidney transplant patients with HLA antibodies. Sensitization should be defined using a virtual parameter such as calculated Reaction Frequency (cRF), which assesses HLA antibodies derived from the actual organ donor population. Highly sensitized patients should be prioritized in kidney allocation schemes and linking allocation schemes may increase opportunities. The use of the ENGAGE 5 ((Bestard et al., Transpl Int, 2021, 34: 1005–1018) system and online calculators for assessing risk is recommended. The Eurotransplant Acceptable Mismatch program should be extended. If strategies for finding a compatible kidney are very unlikely to yield a transplant, desensitization may be considered and should be performed with plasma exchange or immunoadsorption, supplemented with IViG and/or anti-CD20 antibody. Newer therapies, such as imlifidase, may offer alternatives. Few studies compare HLA incompatible transplantation with remaining on the waiting list, and comparisons of morbidity or quality of life do not exist. Kidney paired exchange programs (KEP) should be more widely used and should include unspecified and deceased donors, as well as compatible living donor pairs. The use of a KEP is preferred to desensitization, but highly sensitized patients should not be left on a KEP list indefinitely if the option of a direct incompatible transplant exists.

Harnessing the B Cell Response in Kidney Transplantation - Current State and Future Directions

Despite dramatic improvement in kidney transplantation outcomes over the last decades due to advent of modern immunosuppressive agents, long-term outcomes remain poor. Antibody-mediated rejection (ABMR), a B cell driven process, accounts for the majority of chronic graft failures. There are currently no FDA-approved regimens for ABMR; however, several clinical trials are currently on-going. In this review, we present current mechanisms of B cell response in kidney transplantation, the clinical impact of sensitization and ABMR, the B cell response under current immunosuppressive regimens, and ongoing clinical trials for ABMR and desensitization treatment.

Pediatric Kidney Transplantation-Can We Do Better? The Promise and Limitations of Epitope/Eplet Matching

Kidney transplant is the optimal treatment for end-stage kidney disease as it offers significant survival and quality of life advantages over dialysis. While recent advances have significantly improved early graft outcomes, long-term overall graft survival has remained largely unchanged for the last 20 years. Due to the young age at which children receive their first transplant, most children will require multiple transplants during their lifetime. Each subsequent transplant becomes more difficult because of the development of de novo donor specific HLA antibodies (dnDSA), thereby limiting the donor pool and increasing mortality and morbidity due to longer time on dialysis awaiting re-transplantation. Secondary prevention of dnDSA through increased post-transplant immunosuppression in children is constrained by a significant risk for viral and oncologic complications. There are currently no FDA-approved therapies that can meaningfully reduce dnDSA burden or improve long-term allograft outcomes. Therefore, primary prevention strategies aimed at reducing the risk of dnDSA formation would allow for the best possible long-term allograft outcomes without the adverse complications associated with over-immunosuppression. Epitope matching, which provides a more nuanced assessment of immunological compatibility between donor and recipient, offers the potential for improved donor selection. Although epitope matching is promising, it has not yet been readily applied in the clinical setting. Our review will describe current strengths and limitations of epitope matching software, the evidence for and against improved outcomes with epitope matching, discussion of eplet load vs. variable immunogenicity, and conclude with a discussion of the delicate balance of improving matching without disadvantaging certain populations.

How to Deal With Kidney Retransplantation-Second, Third, Fourth, and Beyond

Kidney transplantation is the best health option for patients with end-stage kidney disease. Ideally, a kidney transplant would last for the lifetime of each recipient. However, depending on the age of the recipient and details of the kidney transplant, there may be a need for a second, third, fourth, or even more kidney transplants. In this overview, the outcome of multiple kidney transplants for an individual is presented. Key issues include surgical approach and immunologic concerns. Included in the surgical approach is an analysis of transplant nephrectomy, with indications, timing, and immunologic impact. Allograft thrombosis, whether related to donor or recipient factors merits investigation to prevent it from happening again. Other posttransplant events such as rejection, viral illness (polyomavirus hominis type I), recurrent disease (focal segmental glomerulosclerosis), and posttransplant lymphoproliferative disease may lead to the need for retransplantation. The pediatric recipient is especially likely to need a subsequent kidney transplant. Finally, noncompliance/nonadherence can affect both adults and children. Innovative approaches may reduce the need for retransplantation in the future.

Principles of Virtual Crossmatch Testing for Kidney Transplantation

Human leukocyte antigens (HLAs) are the primary determinants of alloimmunity. A crossmatch test is a test that determines the immunologic risk of a recipient with a potential donor by ensuring that there are no transplant-relevant circulating antibodies in the recipient directed against donor antigens. Physical crossmatch (PXM) tests, such as complement-dependent cytotoxicity crossmatch (CDCXM) and flow cytometry crossmatch (FCXM), require mixing of patient serum and donor cells, are labor intensive, and are logistically challenging. Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests—patient anti-HLA antibody and donor HLA typing. The goal of VXM is pretransplant risk stratification—though there is no consensus on whether such risk assessment involves predicting the PXM result or the posttransplant outcome. Although the concept of VXM is not new, the advent of solid-phase assays for detecting circulating antibodies in the recipient directed against individual HLA and DNA-based methods for typing donor HLA specificities at a higher resolution makes the routine use of VXM a reality. Accordingly, VXM may be applied at different scenarios—both for sensitized and nonsensitized patients. Implementation of VXM-based approach has resulted in statistically significant reduction in cold ischemia time without an increase in hyperacute rejection episodes. Though there are considerable challenges, VXM is expected to be used more often in the future, depending on the transplant center’s tolerance of immunologic risk.

Outcomes at 3 years posttransplant in imlifidase-desensitized kidney transplant patients

Imlifidase is a cysteine proteinase which specifically cleaves IgG, inhibiting Fc-mediated effector function within hours of administration. Imlifidase converts a positive crossmatch to a potential donor (T cell, B cell, or both), to negative, enabling transplantation to occur between previously HLA incompatible donor-recipient pairs. To date, 39 crossmatch positive patients received imlifidase prior to a kidney transplant in four single-arm, open-label, phase 2 studies. At 3 years, for patients who were AMR+ compared to AMR-, death-censored allograft survival was 93% vs 77%, patient survival was 85% vs 94%, and mean eGFR was 49 ml/min/1.73 m² vs 61 ml/min/1.73 m² , respectively. The incidence of AMR was 38% with most episodes occurring within the first month post-transplantation. Sub-analysis of patients deemed highly sensitized with cPRA ≥ 99.9%, and unlikely to be transplanted who received crossmatch-positive, deceased donor transplants had similar rates of patient survival, graft survival, and eGFR but a higher rate of AMR. These data demonstrate that outcomes and safety up to 3 years in recipients of imlifidase-enabled allografts is comparable to outcomes in other highly sensitized patients undergoing HLA-incompatible transplantation. Thus, imlifidase is a potent option to facilitate transplantation among patients who have a significant immunologic barrier to successful kidney transplantation. Clinical Trial: ClinicalTrials.gov (NCT02790437), EudraCT Number: 2016-002064-13.

Highly Sensitized Patients Are Well Served by Receiving a Compatible Organ Offer Based on Acceptable Mismatches

Highly sensitized kidney patients accrue on the transplant waiting list due to their broad immunization against non-self Human Leucocyte Antigens (HLA). Although challenging, the best option for highly sensitized patients is transplantation with a crossmatch negative donor without any additional therapeutic intervention. The Eurotransplant Acceptable Mismatch (AM) program was initiated more than 30 years ago with the intention to increase the chance for highly sensitized patients to be transplanted with such a compatible donor. The AM program allows for enhanced transplantation to this difficult to transplant patient group by allocating deceased donor kidneys on the basis of a match with the recipient’s own HLA antigens in combination with predefined acceptable antigens. Acceptable antigens are those HLA antigens towards which the patients has never formed antibodies, as determined by extensive laboratory testing. By using this extended HLA phenotype for allocation and giving priority whenever a compatible donor organ becomes available, organ offers are made for roughly 80% of patients in this program. Up till now, more than 1700 highly sensitized patients have been transplanted through the AM program. Recent studies have shown that the concept of acceptable mismatches being truly immunologically acceptable holds true for both rejection rates and long-term graft survival. Patients that were transplanted through the AM program had a similar rejection incidence and long-term graft survival rates identical to non-sensitized patients transplanted through regular allocation. However, a subset of patients included in the AM program does not receive an organ offer within a reasonable time frame. As these are often patients with a rare HLA phenotype in comparison to the Eurotransplant donor population, extension of the donor pool for these specific patients through further European collaboration would significantly increase their chances of being transplanted. For those patients that will not benefit from such strategy, desensitization is the ultimate solution.

Donor type and 3-month hospital readmission following kidney transplantation: results from the Netherlands organ transplant registry

BACKGROUND

Hospital readmission after transplantation is common in kidney transplant recipients (KTRs). In this study, we aim to compare the risk of 3-month hospital readmission after kidney transplantation with different donor types in the overall population and in both young (< 65 years) and elderly (≥65 years) KTRs.

METHODS

We included all first-time adult KTRs from 2016 to 2018 in the Netherlands Organ Transplant Registry. Multivariable logistic regression models were used to estimate the effect while adjusting for baseline confounders.

RESULTS

Among 1917 KTRs, 615 (32.1%) had at least one hospital readmission. Living donor kidney transplantation (LDKT) recipients had an adjusted OR of 0.76 (95%CI, 0.61 to 0.96; p = 0.02) for hospital readmission compared to deceased donor kidney transplantation (DDKT) recipients. In the young and elderly, the adjusted ORs were 0.69 (95%CI, 0.52 to 0.90, p = 0.01) and 0.93 (95%CI, 0.62 to 1.39, p = 0.73) and did not differ significantly from each other (p-value for interaction = 0.38). In DDKT, the risk of hospital readmission is similar between recipients with donation after cardiac death (DCD) or brain death (DBD) and the risk was similar between the young and elderly.

CONCLUSION

A lower risk of post-transplant 3-month hospital readmission was found in recipients after LDKT compared to DDKT, and this benefit of LDKT might be less dominant in elderly patients. In DDKT, having either DCD or DBD donors is not associated with post-transplant 3-month hospital readmission, regardless of age. Tailored patient management is needed for recipients with DDKT and elderly KTRs.

Matchmaker, matchmaker make me a match: Opportunities and challenges in optimizing compatibility of HLA eplets in transplantation

The development of donor-specific antibodies (DSAs) is a major complication in transplantation, which is associated with inferior graft survival, impaired quality of life, and increased healthcare costs. DSA develop upon recognition of nonself HLA by the recipient's immune system. HLA molecules contain epitopes, which are the surface regions of HLA molecules recognized by antibodies. HLAMatchmaker is an algorithm for assessing donor:recipient HLA compatibility at the level of structurally defined HLA targets called eplets. The consideration of eplets, rather than the whole HLA molecule, could offer some advantages when classifying the immune risk associated with particular donor:recipient pairs. Assessing compatibility at the level of HLA eplets could decrease misclassification of post-transplant immune risk by improving specificity, when antibodies are confirmed to be directed against donor eplets missing from the recipient's repertoire of eplets. Consideration of eplets may also increase the sensitivity of immune risk assessment, when identifying mismatched eplets that could give rise to new, not previously detected, donor-specific antibodies post-transplant. Eplet matching can serve as a rational strategy for immune risk mitigation. Herein, we review the evolution of HLA (in) compatibility assessment for organ allocation. We outline challenges in the implementation of eplet-based donor:recipient matching, including unavailability of allele-level donor genotypes for 11 HLA loci at the time of organ allocation and difficulty in assessing the hierarchy of immune risk associated with particular HLA eplet mismatches. Opportunities to address some of the current shortcomings of donor genotyping and HLAMatchmaker are also discussed. While there is a demonstrated benefit in the application of HLAMatchmaker for donor: recipient HLA (in)compatibility assessment, evolving long-read genotyping methods, compilation of large data sets with allele-level genotypes, and standardization of methods to verify eplets as determinants of immune-mediated injuries are required before HLA eplet matching is implemented in organ allocation to improve upon transplant outcomes.

Creating Options for Difficult-to-match Kidney Transplant Candidates

BACKGROUND

Most transplantation centers recognize a small patient population that unsuccessfully participates in all available, both living and deceased donor, transplantation programs for many years: the difficult-to-match patients. This population consists of highly immunized and/or ABO blood group O or B patients.

METHODS

To improve their chances, Computerized Integration of Alternative Transplantation programs (CIAT) were developed to integrate kidney paired donation, altruistic/unspecified donation, and ABO and HLA desensitization. To compare CIAT with reality, a simulation was performed, including all patients, donors, and pairs who participated in our programs in 2015-2016. Criteria for inclusion as difficult-to-match, selected-highly immunized (sHI) patient were as follows: virtual panel reactive antibody >85% and participating for 2 years in Eurotransplant Acceptable Mismatch program. sHI patients were given priority, and ABO blood group incompatible (ABOi) and/or HLA incompatible (HLAi) matching with donor-specific antigen-mean fluorescence intensity (MFI) <8000 were allowed. For long-waiting blood group O or B patients, ABOi matches were allowed.

RESULTS

In reality, 90 alternative program transplantations were carried out: 73 compatible, 16 ABOi, and 1 both ABOi and HLAi combination. Simulation with CIAT resulted in 95 hypothetical transplantations: 83 compatible (including 1 sHI) and 5 ABOi combinations. Eight sHI patients were matched: 1 compatible, 6 HLAi with donor-specific antigen-MFI <8000 (1 also ABOi), and 1 ABOi match. Six/eight combinations for sHI patients were complement-dependent cytotoxicity cross-match negative.

CONCLUSIONS

CIAT led to 8 times more matches for difficult-to-match sHI patients. This offers them better chances because of a more favorable MFI profile against the new donor. Besides, more ABO compatible matches were found for ABOi couples, while total number of transplantations was not hampered. Prioritizing difficult-to-match patients improves their chances without affecting the chances of regular patients.

A Europe wide acceptable mismatch program will enable transplantation of long waiting highly sensitised patients with a compatible donor

Immunisation against Human Leucocyte Antigens (HLA) can be caused by pregnancy, blood transfusion, or organ transplants. The HLA antibody status of a given patient significantly influences their access and waiting time to transplant. For some highly sensitised patients (HSP) there is hardly any suitable donor available in the deceased donor pool of their allocation organisation and therefore they wait a very long time before being offered a kidney for transplant. Especially patients with rare HLA phenotypes in relation to the actual donor pool are waiting extremely long. As HLA phenotypes are different in the various European populations, we hypothesized that extension of the donor pool outside the respective allocation system will increase the chance of receiving a compatible transplant for this subgroup of highly sensitised patients. One of the objectives of the EUROSTAM project, (a Europe-wide Strategy to enhance Transplantation of highly sensitised patients on the basis of Acceptable HLA Mismatches) was to develop a tool to compare the chance of transplanting HSP in different European populations with donor organs from within and outside their own donor pool. Information on the HLA type and ABO blood group of the actual donor population, as well as the acceptable mismatches of long waiting HSP were obtained from the EUROSTAM partner organizations i.e. Eurotransplant (ET), UK National Health Service Blood and Transplant (NHSBT), Barcelona, Prague and Athens. Results from simulations using the newly developed tool shows that 195 (27%) of the 724 long waiting highly sensitised patients registered at each partner organisation have increased chances of transplant in a different European donor pool. This makes a strong case for sharing kidneys between European countries for selected difficult to transplant patients.

Pre-existing Alloreactive T and B Cells and Their Possible Relevance for Pre-transplant Risk Estimation in Kidney Transplant Recipients

In allogeneic transplantation, genetic disparities between patient and donor may lead to cellular and humoral immune responses mediated by both naïve and memory alloreactive cells of the adaptive immune system. This review will focus on alloreactive T and B cells with emphasis on the memory compartment, their role in relation to kidney rejection, and in vitro assays to detect these alloreactive cells. Finally, the potential additional value of utilizing donor-specific memory T and B cell assays supplementary to current routine pre-transplant risk assessment of kidney transplant recipients will be discussed.

What have we learned about how to prevent and treat antibody-mediated rejection in kidney transplantation?

Antibody-mediated rejection (ABMR) in kidney transplantation is a major cause of late graft loss, and despite all efforts to date the "standard of care" remains plasmapheresis, IVIg, and steroids, which itself is based on low quality evidence. This review focuses on the risk factors leading to memory and de novo donor-specific antibody (DSA)-associated ABMR, the optimal prevention strategies for ABMR, and advances in  adjunctive and emerging therapies for ABMR. Because new agents require regulatory approval via a Phase 3 randomized control trial (RCT), an overview of progress in innovative trial design for ABMR is provided. Finally, based on the insights gained in the biology of ABMR, current knowledge gaps are identified for future research that could significantly affect our understanding of how to optimally treat ABMR.

Immunosuppression in sensitized recipients

PURPOSE OF REVIEW

Due to a substantial lack of kidney donor organs and an increasing number of sensitized recipients, a growing number of kidney transplantations has to be performed across human leukocyte antigen (HLA) and ABO barriers. These transplantations carry an inherent risk of antibody-mediated rejection (AMR) with subsequently impaired graft and patient survival. This review focuses on new developments in desensitization strategies and dedicated programs for sensitized allograft recipients.

RECENT FINDINGS

Whereas ABO-incompatible kidney transplantation using rituximab-based desensitization achieves long-term survival rates comparable with ABO-compatible kidney transplantation, HLA-incompatible living kidney transplantation shows no definite survival advantage as compared with staying on the waiting list for an HLA-compatible organ. To overcome HLA-incompatibilities dedicated programs for highly sensitized recipients (such as the Eurotransplant Acceptable Mismatch program) have been established. For optimal graft outcome, these programs should be based on proven acceptable mismatches and not just on avoiding unacceptable antigens. Novel desensitizing agents (e.g. complement inhibitors) that specifically inhibit the molecular pathways of AMR have shown promising results in HLA-incompatible kidney transplantation in smaller studies.

SUMMARY

Despite ever more challenging conditions, kidney transplantation in highly sensitized patients can be achieved with the use of dedicated programs, well established desensitizing agents and new drugs that specifically inhibit the molecular processes of AMR.

Novel insights into non-HLA alloimmunity in kidney transplantation

Recognition of non‐self structures on donor cells represents the main immunological barrier in solid organ transplantation. The human leukocyte antigens (HLA) are considered the most important non‐self (allo)antigens in transplantation. Long‐term graft attrition is mainly caused by the formation of alloreactive antibodies that are directed against non‐self structures (i.e., epitopes) on cell surface proteins. Recently published data provided evidence for a similar importance of non‐HLA mismatches between donors and recipients in acute rejection as well as long‐term kidney allograft survival. These data suggest a broader concept of immunological non‐self that goes beyond HLA incompatibility and expands the current concept of polymorphic non‐self epitopes on cell surface molecules from HLA to non‐HLA targets. Amino acid substitutions caused by single nucleotide variants in protein‐coding genes or complete loss of gene expression represent the basis for polymorphic residues in both HLA and non‐HLA molecules. To better understand these novel insights in non‐HLA alloimmunity, we will first review basic principles of the alloimmune response with a focus on the HLA epitope concept in donor‐specific antibody formation before discussing key publications on non‐HLA antibodies.

Epitopes as characterized by antibody-verified eplet mismatches determine risk of kidney transplant loss

To optimize strategies that mitigate the risk of graft loss associated with HLA incompatibility, we evaluated whether sequence defined HLA targets (eplets) that result in donor-specific antibodies are associated with transplant outcomes. To define this, we fit multivariable Cox proportional hazard models in a cohort of 118 382 United States first kidney transplant recipients to assess risk of death-censored graft failure by increments of ten antibody-verified eplet mismatches. To verify robustness of our findings, we conducted sensitivity analysis in this United States cohort and assessed the role of antibody-verified eplet mismatches as autonomous predictors of transplant glomerulopathy in an independent Canadian cohort. Antibody-verified eplet mismatches were found to be independent predictors of death-censored graft failure with hazard ratios of 1.231 [95% confidence interval 1.195, 1. 268], 1.268 [1.231, 1.305] and 1.411 [1.331, 1.495] for Class I (HLA-A, B, and C), -DRB1 and -DQB1 loci, respectively. To address linkage disequilibrium between HLA-DRB1 and -DQB1, we fit models in a subcohort without HLA-DQB1 eplet mismatches and found hazard ratios for death-censored graft failure of 1.384 [1.293, 1.480] for each additional antibody-verified HLA-DRB1 eplet mismatch. In a subcohort without HLA-DRB1 mismatches, the hazard ratio was 1.384 [1.072, 1.791] for each additional HLA-DQB1 mismatch. In the Canadian cohort, antibody-verified eplet mismatches were independent predictors of transplant glomerulopathy with hazard ratios of 5.511 [1.442, 21.080] for HLA-DRB1 and 3.640 [1.574, 8.416] for -DRB1/3/4/5. Thus, donor-recipient matching for specific HLA eplets appears to be a feasible and clinically justifiable strategy to mitigate risk of graft loss.

Allocation to highly sensitized patients based on acceptable mismatches results in low rejection rates comparable to nonsensitized patients

Whereas regular allocation avoids unacceptable mismatches on the donor organ, allocation to highly sensitized patients within the Eurotransplant Acceptable Mismatch (AM) program is based on the patient's HLA phenotype plus acceptable antigens. These are HLA antigens to which the patient never made antibodies, as determined by extensive laboratory testing. AM patients have superior long-term graft survival compared with highly sensitized patients in regular allocation. Here, we questioned whether the AM program also results in lower rejection rates. From the PROCARE cohort, consisting of all Dutch kidney transplants in 1995-2005, we selected deceased donor single transplants with a minimum of 1 HLA mismatch and determined the cumulative 6-month rejection incidence for patients in AM or regular allocation. Additionally, we determined the effect of minimal matching criteria of 1 HLA-B plus 1 HLA-DR, or 2 HLA-DR antigens on rejection incidence. AM patients showed significantly lower rejection rates than highly immunized patients in regular allocation, comparable to nonsensitized patients, independent of other risk factors for rejection. In contrast to highly sensitized patients in regular allocation, minimal matching criteria did not affect rejection rates in AM patients. Allocation based on acceptable antigens leads to relatively low-risk transplants for highly sensitized patients with rejection rates similar to those of nonimmunized individuals.

Parsing the 100% calculated panel reactive antibody kidney transplant candidates: Who gets transplanted?

The new kidney allocation system in the United States has improved deceased donor transplant rates among candidates with high calculated panel reactive antibodies (CPRAs). Probability analysis predicts a very low transplant rate as the CPRA approaches 100%. This study sought to determine if the rate of deceased donor kidney transplant based on the actual CPRA in the cohort of 100% qualifying candidates behaved as predicted by probability analysis. Nine thousand two hundred and twenty eight patients were identified on the waiting list on or after December 2014 that had at least one CPRA greater than or equal to 99.5%. The distribution of the 100% CPRA group was highly skewed toward 100% (Median CPRA 99.98%). The decile group within the 100% CPRA qualifying population was by far the most important factor determining kidney transplantation. The highest two deciles of CPRA had a very low rate of transplantation. Options to improve the prospects of deceased donor transplant include intelligently lowering the CPRA by reducing unacceptable antigens, expanding the donor pool by listing candidates for higher risk donors, or through desensitization. The CPRA calculator should display the non-integer CPRA out to several decimal points so that informed decisions can be made for these candidates regarding their prospects of receiving a deceased donor offer.