Impact of donor mismatches at individual HLA-A, -B, -C, -DR, and -DQ loci on the development of HLA-specific antibodies in patients listed for repeat renal transplantation

Impact of HLA Eplet Mismatch on De Novo Donor Specific Antibody Formation After Kidney Transplantation

BACKGROUND

HLA eplet mismatching is an alternative approach to assess the risk of developing de novo donor-specific antibodies (dnDSA) in kidney transplantation. This strategy may offer more precise risk stratification than conventional approaches. This study aimed to find the association between HLA eplet mismatches and dnDSA formation in Thai kidney transplant recipients.

METHODS

A retrospective cohort study of kidney transplant recipients transplanted between 2000 and 2021 at Ramathibodi Hospital was performed. Recipients with pretransplant panel reactive antibody >0% or without DSA testing post-transplant were excluded. One hundred fifty recipients were included in the final study. High-resolution HLA typing was imputed by the HaploStat application. HLA eplet mismatch analysis was conducted using HLAMatchmaker. The association between the number of eplet mismatches and the risk of dnDSA formation was assessed by Cox regression analysis.

RESULTS

Of 150 recipients, 43 were dnDSA-positive, and 107 were dnDSA-negative patients. Compared with the dnDSA-negative group, patients with class II dnDSA had significantly more HLA-DR/DQ antibody (Ab)-verified eplet mismatches (6 [IQR 4-8] vs 4 [IQR 1-7], P = .045). The receiver operating characteristics analysis showed that the HLA-DQ Ab-verified eplet mismatches ≥2 were the best predictive of HLA class II dnDSA development. The number of HLA-DQ Ab-verified eplet mismatches ≥2 had the highest hazard rate of HLA class II dnDSA occurrence (adjusted HR, 3.74; 95%CI, 1.24-11.24, P = .019).

CONCLUSIONS

HLA-DQ Ab-verified eplet mismatches are significantly associated with class II dnDSA development. Our data supports the utility of HLA eplet mismatching for donor-recipient risk assessment.

Antibody verification of HLA class I and class II eplets by human monoclonal HLA antibodies

In solid organ transplantation, formation of de novo donor-specific HLA antibodies is induced by mismatched eplets on donor HLA molecules. While several studies have shown a strong correlation between the number of eplet mismatches and inferior outcomes, not every eplet mismatch is immunogenic. Eplets are theoretically defined entities, necessitating formal proof that they can be recognised and bound by antibodies. This antibody verification is pivotal to ensure that clinically relevant eplets are considered in studies on molecular matching. Recombinant human HLA-specific monoclonal antibodies (mAbs) were generated from HLA-reactive B cell clones isolated from HLA immunised individuals using recombinant HLA molecules. Subsequently, the reactivity patterns of the mAbs obtained from single antigen bead assay were analysed using HLA-EMMA software to identify single or configurations of solvent accessible amino acids uniquely present on the reactive HLA alleles and were mapped to eplets. Two HLA class I and seven HLA class II-specific human mAbs were generated from four individuals. Extensive mAb reactivity analysis, led to antibody verification of three HLA-DR-specific eplets, and conversion of five eplets (one HLA-A, one HLA-B, two HLA-DR, and one HLA-DP), from provisionally verified to truly antibody-verified. Finally, one HLA-DQ-specific eplet was upgraded from level A2 to level A1 verification evidence. The generation of recombinant human HLA-specific mAbs with different specificities contributes significantly to the antibody verification of eplets and therefore is instrumental for implementation of eplet matching in the clinical setting.

Role of Complement-dependent Cytotoxicity Crossmatch and HLA Typing in Solid Organ Transplant

BACKGROUND

Solid organ transplantation is a life-saving medical operation that has progressed greatly because of developments in diagnostic tools and histocompatibility tests. Crossmatching for complement-dependent cytotoxicity (CDC) and human leukocyte antigen (HLA) typing are two important methods for checking graft compatibility and reducing the risk of graft rejection. HLA typing and CDC crossmatching are critical in kidney, heart, lung, liver, pancreas, intestine, and multi-organ transplantation.

METHODS

A systematic literature search was conducted on the internet, using PubMed, Scopus, and Google Scholar databases, to identify peer-reviewed publications about solid organ transplants, HLA typing, and CDC crossmatching.

CONCLUSION

Recent advances in HLA typing have allowed for high-resolution evaluation, epitope matching, and personalized therapy methods. Genomic profiling, next-generation sequencing, and artificial intelligence have improved HLA typing precision, resulting in better patient outcomes. Artificial intelligence (AI) driven virtual crossmatching and predictive algorithms have eliminated the requirement for physical crossmatching in the context of CDC crossmatching, boosting organ allocation and transplant efficiency. This review elaborates on the importance of HLA typing and CDC crossmatching in solid organ transplantation.

Dialysis after kidney transplant failure: how to deal with this daunting task?

The best treatment for patients with end-stage kidney disease is kidney transplantation, which, if successful provides both a reduction in mortality and a better quality of life compared to dialysis. Although there has been significant improvement in short-term outcomes after kidney transplantation, long-term graft survival still remains insufficient. As a result, there has been an increase in the number of individuals who need dialysis again after kidney transplant failure, and increasingly contribute to kidney transplant waiting lists. Starting dialysis after graft failure is a difficult task not only for the patients, but also for the nephrologists and the care team. Furthermore, recommendations for management of dialysis after kidney graft loss are lacking. Aim of this narrative review is to provide a perspective on the role of dialysis in the management of patients with failed kidney allograft. Although numerous studies have reported higher mortality in patients undergoing dialysis following kidney allograft failure, reports are contrasting. A patient-centered, individualized approach should drive the choices of initiating dialysis, dialysis modality, maintenance of immunosuppressive drugs and vascular access.

Molecular HLA mismatching for prediction of primary humoral alloimmunity and graft function deterioration in paediatric kidney transplantation

Introduction

Rejection remains the main cause of allograft failure in paediatric kidney transplantation and is driven by donor-recipient HLA mismatching. Modern computational algorithms enable assessment of HLA mismatch immunogenicity at the molecular level (molecular-mismatch, molMM). Whilst molMM has been shown to correlate with alloimmune outcomes, evidence demonstrating improved prediction performance against traditional antigen mismatching (antMM) is lacking.

Methods

We analysed 177 patients from the CERTAIN registry (median follow-up 4.5 years). molMM scores included Amino-Acid-Mismatch-Score (AAMS), Electrostatic-Mismatch-Score (EMS3D) and netMHCIIpan (netMHC1k: peptide binding affinity ≤1000 nM; netMHC: binding affinity ≤500 nM plus rank <2%). We stratified patients into high/low-risk groups based on risk models of DSA development.

Results

Donor-specific HLA antibodies (DSA) predominantly targeted the highest scoring molMM donor antigen within each HLA locus. MolMM scores offered superior discrimination versus antMM in predicting de novo DSA for all HLA loci; the EMS3D algorithm had particularly consistent performance (area under the receiver operating characteristic curve (AUC) >0.7 for all HLA loci vs. 0.52-0.70 for antMM). ABMR (but not TCMR) was associated with HLA-DQ molMM scores (AAMS, EMS3D and netMHC). Patients with high-risk HLA-DQ molMM had increased risk of graft function deterioration (50% reduction in baseline eGFR (eGFR50), adjusted HR: 3.5, 95% CI 1.6-8.2 high vs. low EMS3D). Multivariable modelling of the eGFR50 outcome using EMS3D HLA-DQ stratification showed better discrimination (AUC EMS3D vs. antMM at 2 years: 0.81 vs. 0.77, at 4.5 years: 0.72 vs. 0.64) and stratified more patients into the low-risk group, compared to traditional antMM.

Conclusion

Molecular mismatching was superior to antigen mismatching in predicting humoral alloimmunity. Molecular HLA-DQ mismatching appears to be a significant prognostic factor for graft function deterioration in paediatric kidney transplantation.

The HLA-DRB1*04:357 allele first identified in a Chinese transplant recipient

HLA-DRB1*04:357 differs from HLA-DRB1*04:17:02 by two nucleotides in exon 2.

Matching for HLA-DR excluding diabetogenic HLA-DR3 and HLA-DR4 predicts insulin independence after pancreatic islet transplantation

Introduction

In pancreatic islet transplantation, the exact contribution of human leukocyte antigen (HLA) matching to graft survival remains unclear. Islets may be exposed to allogenic rejection but also the recurrence of type 1 diabetes (T1D). We evaluated the HLA-DR matching, including the impact of diabetogenic HLA-DR3 or HLA-DR4 matches.

Methods

We retrospectively examined the HLA profile in 965 transplant recipients and 2327 islet donors. The study population was obtained from patients enrolled in the Collaborative Islet Transplant Registry. We then identified 87 recipients who received a single-islet infusion. Islet-kidney recipients, 2nd islet infusion, and patients with missing data were excluded from the analysis (n=878).

Results

HLA-DR3 and HLA-DR4 were present in 29.7% and 32.6% of T1D recipients and 11.6% and 15.8% of the donors, respectively. We identified 52 T1D islet recipients mismatched for HLA-DR (group A), 11 with 1 or 2 HLA-DR-matches but excluding HLA-DR3 and HLA- DR4 (group B), and 24 matched for HLA-DR3 or HLA-DR4 (group C). Insulin-independence was maintained in a significantly higher percentage of group B recipients from year one through five post-transplantation (p<0.01). At five-year post-transplantation, 78% of group B was insulin-independent compared to 24% (group A) and 35% (group C). Insulin-independence correlated with significantly better glycemic control (HbA1c <7%), fasting blood glucose, and reduced severe hypoglycemic events. Matching HLA-A-B-DR (≥3) independently of HLA- DR3 or HLA-DR4 matching did not improve graft survival.

Conclusion

This study suggests that matching HLA-DR but excluding the diabetogenic HLA-DR3 and/or 4 is a significant predictor for long-term islet survival.

HLA-DQ Mismatches Lead to More Unacceptable Antigens, Greater Sensitization, and Increased Disparities in Repeat Transplant Candidates

BACKGROUND

In single-center studies, HLA-DQ mismatches stimulate the most pathogenic donor-specific antibodies. However, because of limitations of transplant registries, this cannot be directly confirmed with registry-based analyses.

METHODS

We evaluated patients in the Scientific Registry of Transplant Recipients who were relisted after renal graft failure with new, unacceptable antigens corresponding to the HLA typing of their previous donor (UA-PD) as a proxy for donor-specific antibodies. Linear regression was applied to estimate the effects of HLA mismatches on UA-PD and the effects of UA-PD on calculated panel reactive antibody (cPRA) values for 4867 kidney recipients from 2010 to 2021.

RESULTS

Each additional HLA-DQ mismatch increased the probability of UA-PD by 25.2% among deceased donor transplant recipients and by 28.9% among living donor transplant recipients, significantly more than all other HLA loci (P<0.05). HLA-DQ UA-PD increased cPRA by 29.0% in living donor transplant recipients and by 23.5% in deceased donor transplant recipients, significantly more than all loci except for HLA-A in deceased donor transplant recipients (23.1%). African American deceased donor transplant recipients were significantly more likely than Hispanic and White recipients to develop HLA-DQ UA-PD; among living donor transplant recipients, African American or Hispanic recipients were significantly more likely to do so compared with White recipients. Models evaluating interactions between HLA-DR/DQ mismatches revealed largely independent effects of HLA-DQ mismatches on HLA-DQ UA-PD.

CONCLUSIONS

HLA-DQ mismatches had the strongest associations with UA-PD, an effect that was greatest in African American and Hispanic recipients. cPRA increases with HLA-DQ UA-PD were equivalent or larger than any other HLA locus. This suggests a need to consider the effects of HLA-DQ in kidney allocation.

Challenges in the Management of the Patient with a Failing Kidney Graft: A Narrative Review

Patients with a failed kidney allograft have steadily increase in recent years and returning to dialysis after graft loss is one of the most difficult transitions for chronic kidney disease patients and their assistant physicians. The management of these patients is complex and encompasses the treatment of chronic kidney disease complications, dialysis restart and access planning, immunosuppression withdrawal, graft nephrectomy, and evaluation for a potential retransplant. In recent years, several groups have focused on the management of the patient with a failing renal graft and expert recommendations are arising. A review of Pubmed, ScienceDirect and the Cochrane Library was performed focusing on the specific care of these patients, from the management of low clearance complications to concerns with a subsequent kidney transplant. Conclusion: There is a growing interest in the failing renal graft and new approaches to improve these patients' outcomes are being defined including specific multidisciplinary programs, individualized immunosuppression withdrawal schemes, and strategies to prevent HLA sensitization and increase retransplant rates.

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.

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.

Significance of HLA-DQ in kidney transplantation: time to reevaluate human leukocyte antigen matching priorities to improve transplant outcomes? An expert review and recommendations

The weight of human leukocyte antigen (HLA) matching in kidney allocation algorithms, especially in the United States, has been devalued in a stepwise manner, supported by the introduction of modern immunosuppression. The intent was further to reduce the observed ethnic/racial disparity, as data emerged associating HLA matching with decreased access to transplantation for African American patients. In recent years, it has been increasingly recognized that a leading cause of graft loss is chronic antibody-mediated rejection, attributed to the development of de novo antibodies against mismatched donor HLA expressed on the graft. These antibodies are most frequently against donor HLA-DQ molecules. Beyond their impact on graft survival, generation of de novo donor-specific HLA antibodies also leads to increased sensitization, as measured by panel-reactive antibody metrics. Consequently, access to transplantation for patients returning to the waitlist in need of a second transplant is compromised. Herein, we address the implications of reduced HLA matching policies in kidney allocation. We highlight the observed diminished outcome data, the significant financial burden, the long-term health consequences, and, more important, the unintended consequences. We further provide recommendations to examine the impact of donor-recipient HLA class II and specifically HLA-DQα₁β₁ mismatching, focusing on collection of appropriate data, application of creative simulation approaches, and reconsideration of best practices to reduce inequalities while optimizing patient outcomes.

Working towards an ERAS Protocol for Pancreatic Transplantation: A Narrative Review

Enhanced recovery after surgery (ERAS) initially started in the early 2000s as a series of protocols to improve the perioperative care of surgical patients. They aimed to increase patient satisfaction while reducing postoperative complications and postoperative length of stay. Despite these protocols being widely adopted in many fields of surgery, they are yet to be adopted in pancreatic transplantation: a high-risk surgery with often prolonged length of postoperative stay and high rate of complications. We have analysed the literature in pancreatic and transplantation surgery to identify the necessary preoperative, intra-operative and postoperative components of an ERAS pathway in pancreas transplantation.

What happens after graft loss? A large, long-term, single-center observation

The number of patients returning to dialysis after graft failure increases. Surprisingly, little is known about the clinical and immunological outcomes of this cohort. We retrospectively analyzed 254 patients after kidney allograft loss between 1997 and 2017 and report clinical outcomes such as mortality, relisting, retransplantations, transplant nephrectomies, and immunization status. Of the 254 patients, 49% had died 5 years after graft loss, while 27% were relisted, 14% were on dialysis and not relisted, and only 11% were retransplanted 5 years after graft loss. In the complete observational period, 111/254 (43.7%) patients were relisted. Of these, 72.1% of patients were under 55 years of age at time of graft loss and only 13.5% of patients were ≥65 years. Age at graft loss was associated with relisting in a logistic regression analysis. In the complete observational period, 42 patients (16.5%) were retransplanted. Only 4 of those (9.5%) were ≥65 years at time of graft loss. Nephrectomy had no impact on survival, relisting, or development of dnDSA. Patients after allograft loss have a high overall mortality. Immunization contributes to long waiting times. Only a very limited number of patients are retransplanted especially when ≥65 years at time of graft loss.

Long-term outcomes after kidney transplant failure and variables related to risk of death and probability of retransplant: Results from a single-center cohort study in Brazil

Background

Returning to dialysis after kidney graft loss (GL) is associated with a high risk of mortality, mainly in the first 3–6 months. The follow-up of patients with GL should be extended to better understand crude patient outcomes, mainly in emerging countries, where the transplantation activity has increased.

Methods

This is a historical single-center cohort study conducted in an emerging country (Brazil) that included 115 transplant patients with kidney allograft failure who were followed for 44.1 (21.4; 72.6) months after GL. The outcomes were death or retransplantation after GL calculated by Kaplan-Meier and log-rank tests. Proportional hazard ratios for death and retransplantation were assessed by Cox regression.

Results

The 5-year probability of retransplantation was 38.7% (95% CI: 26.1%-51.2%) and that of death was 37.7% (95% CI: 24.9%-50.5%); OR = 1.03 (95% CI: 0.71–1.70) and P = 0.66. The likelihood of retransplantation was higher in patients who resumed dialysis with higher levels of hemoglobin (HR = 1.22; 95% CI = 1.04–1.43; P = 0.01) and lower in blood type O patients (HR = 0.48; 95% CI = 0.25–0.93; P = 0.03), which was associated with a lower frequency of retransplantation with a subsequent living-donor kidney. On the other hand, the risk of death was significantly associated with Charlson comorbidity index (HR for each point = 1.37; 95% CI 1.19–1.50; P<0.001), and residual eGFR at the time when patients had resumed to dialysis (HR for each mL = 1.14; 95% CI = 1.05–1.25; P = 0.002). The trend toward a lower risk of death when patients had resumed to dialysis using AV fistula access was observed (HR = 0.50; 95% CI 0.25–1.02; P = 0.06), while a higher risk seems to be associated with the number of previous engraftment (HR = 2.01; 95% CI 0.99–4.07; P = 0.05).

Conclusions

The 5-year probability of retransplantation was not less than that of death. Variables related to the probability of retransplantation were hemoglobin level before resuming dialysis and ABO blood type, while the risk of death was associated with comorbidities and residual eGFR.

Clinical relevance of donor-specific antibodies directed at HLA-C: A long road to acceptance

In solid organ transplantation (SOT), the clinical relevance of donor-specific antibodies (DSA) directed at anti-HLA-A, -B, -DR and -DQ antigens is largely recognized while it is still a matter of debate for DSA directed at HLA-C. In this review, we summarize the peculiarities of HLA-C among class I HLA antigens as well as their immunogenicity, which underlie the clinical relevance of HLA-C locus and anti-HLA-C DSA in SOT. Many factors, both intrinsic and extrinsic to the HLA-C gene and HLA-C protein, explain its lower expression in comparison with HLA-A and -B. This lower expression can explain the apparent lower immunogenicity of HLA-C leading to a lower prevalence and strength of anti-HLA-C antibodies. Nevertheless, HLA-C antigens are truly immunogenic and preformed anti-HLA-C DSA are clinically relevant. Indeed, anti-HLA-C DSA are able to bind donor cells and to activate the complement pathway both ex vivo and in vivo. In line with this, numerous clinical studies now show that preformed DSA directed at native HLA-C molecules induce poorer graft outcomes. We then plead for the inclusion of HLA-C in all transplant allocation systems and we propose a strategy to cope with anti-HLA-C DSA in SOT. Beyond SOT, anti-HLA-C antibodies generate a growing interest in the allo-HCT, transfusion and obstetrics fields, while new concepts such as the role of the "missing-self" in solid organ rejection places HLA-C as an inescapable actor in transplant tolerance.

The association between human leukocyte antigen eplet mismatches, de novo donor-specific antibodies, and the risk of acute rejection in pediatric kidney transplant recipients

BACKGROUND

The longitudinal relationship between HLA class I and II eplet mismatches, de novo donor-specific antibodies (dnDSA) development, and acute rejection after transplantation in childhood is unknown.

METHODS

Eplet mismatches at HLA class I and II loci were calculated retrospectively for each donor/recipient pair transplanted between 2005 and 2015 at a single Australian center. Logistic regression analyses were conducted to determine the association between the number of eplet mismatches, dnDSA, and acute rejection.

RESULTS

The cohort comprised 59 children (aged 0-18 years) who received their first kidney allograft and were followed for median (interquartile range) 4.5 (± 2.6) years. Overall, 32% (19/59) developed dnDSA (class I 3% (2/59), class II 14% (8/59), 15% class I and II (9/59)), and 24% (14/59) developed biopsy-proven acute rejection. Every unit increase in class I and II eplet mismatches corresponded to an increase in risk of class I (odds ratio (OR) 1.22, 95% CI 1.07-1.39, p < 0.01) and class II (OR 1.06, 95% CI 1.01-1.11, p = 0.02) dnDSA development. Compared with recipients without dnDSA, class I and II dnDSA were associated with direction of effect towards increased risk of acute cellular rejection (class I: OR 5.87, 95% CI 0.99-34.94, p = 0.05; class II: OR 12.00, 95% CI 1.25-115.36, p = 0.03) and acute antibody-mediated rejection (class I: OR 25.67, 95% CI 3.54-186.10, p < 0.01; class II: OR 9.71, 95% CI 1.64-57.72, p = 0.01).

CONCLUSIONS

Increasing numbers of HLA class I or II eplet mismatches were associated with the development of dnDSA. Children who developed dnDSA were also more likely to develop acute rejection compared with children without dnDSA.

HLA-EMMA: A user-friendly tool to analyse HLA class I and class II compatibility on the amino acid level

In renal transplantation, polymorphic amino acids on mismatched donor HLA molecules can lead to the induction of de novo donor‐specific antibodies (DSA), which are associated with inferior graft survival. To ultimately prevent de novo DSA formation without unnecessarily precluding transplants it is essential to define which polymorphic amino acid mismatches can actually induce an antibody response. To facilitate this, we developed a user‐friendly software program that establishes HLA class I and class II compatibility between donor and recipient on the amino acid level. HLA epitope mismatch algorithm (HLA‐EMMA) is a software program that compares simultaneously the HLA class I and class II amino acid sequences of the donor with the HLA amino acid sequences of the recipient and determines the polymorphic solvent accessible amino acid mismatches that are likely to be accessible to B cell receptors. Analysis can be performed for a large number of donor‐recipient pairs at once. As proof of principle, a previously described study cohort of 191 lymphocyte immunotherapy recipients was analysed with HLA‐EMMA and showed a higher frequency of DSA formation with higher number of solvent accessible amino acids mismatches. Overall, HLA‐EMMA can be used to analyse compatibility on amino acid level between donor and recipient HLA class I and class II simultaneously for large cohorts to ultimately determine the most immunogenic amino acid mismatches.

Allograft and Patient Outcomes Between Indigenous and Nonindigenous Kidney Transplant Recipients

BACKGROUND

Kidney transplant outcomes of indigenous Australians are poorer compared with nonindigenous Australians, but it is unknown whether the type of acute rejection differs between these patient groups or whether rejection mediates the effect between ethnicity, death-censored graft failure (DCGF), and death with a functioning graft (DWFG).

METHODS

Biopsy-proven acute rejection (BPAR) rates and types were compared between indigenous and nonindigenous recipients. The associations between ethnicity, BPAR, DCGF, and DWFG were examined using adjusted competing risk analyses, and mediation analysis was conducted to determine whether BPAR mediated the adverse effects between ethnicity and outcomes.

RESULTS

Fifty-seven (9.3%) of 616 patients who have received kidney-only transplants between 2000 and 2010 in Western Australia were indigenous. Compared with nonindigenous recipients, BPAR rates were higher in indigenous recipients (42 versus 74 episodes/100 recipients, P < 0.01), with an excess of antibody-mediated rejections. During a median follow-up of 8 years, indigenous recipients were more likely to experience BPAR, DCGF, and DWFG compared with nonindigenous recipients, with adjusted subdistribution hazard ratio of 1.94 (1.39-2.70), 1.53 (0.85-2.76; P = 0.159), and 2.14 (1.13-4.06; P = 0.020), respectively. Although 70% of the effect between ethnicity and DCGF was mediated by BPAR, no similar association was found for DWFG.

CONCLUSIONS

Indigenous recipients experienced poorer allograft and patient outcomes compared with nonindigenous recipients, with BPAR an important determinant for DCGF. Future research identifying other risk factors and mediators associated with patient survival in indigenous recipients should be considered a priority.

Prolonged Cold Ischemia Time Offsets the Benefit of Human Leukocyte Antigen Matching in Deceased Donor Kidney Transplant

BACKGROUND

The consequences of prolonging cold ischemia time (CIT) to facilitate HLA matching in kidney transplantation are not known.

METHODS

Patients with a history of kidney transplant in the United States (2000-2016) with 0 HLA mismatch (MM) were categorized based on CIT (< 10; 10 to < 15; 15 to < 20; 20 to < 25; 25 to < 30; and ≥ 30 hours). Time to graft loss was compared for each CIT category to a reference group of individuals with > 0 HLA MM and short CIT (< 10 hours) using a multivariable Cox proportional hazards model.

RESULTS

The adjusted risk of graft failure was significantly lower for 0 HLA MM with the shortest CIT compared to the reference group (hazard ratio, 0.82; 95% confidence interval, 0.72-0.94), and this survival advantage persisted to a threshold of < 20 hours of CIT. No survival advantage was observed for the 0 HLA MM group once CIT was > 20 hours. This trend persisted after excluding highly sensitized recipients (panel reactive antibody > 98%) where shipping of organs occurs to achieve more equitable access to organs rather than optimize HLA match.

CONCLUSIONS

CIT > 20 hours offsets the benefit of 0 HLA MM in kidney transplantation. This may have implications in organ shipping to facilitate immunologic match.

Donor-specific antibodies detected by single antigen beads alone can help risk stratify patients undergoing retransplantation across a repeat HLA mismatch

Whether reexposure to mismatched HLA antigens (RMM) in the setting of a negative crossmatch is associated with increased immunological risk remains an area of uncertainty. This is due to evidence derived predominantly from registry data, which lacks comprehensive information on alloantibody and rejection. In this study, we analyze the impact of low-level preformed donor-specific antibodies (DSA) against an RMM on transplant outcomes. From 1988 consecutive renal transplant recipients, we analyzed 179 patients undergoing retransplantation, of whom 55 had a RMM. All patients were crossmatch negative and preformed DSA were detected by single antigen beads alone. Multivariate analysis revealed that patients with preformed DSA against an RMM were independently at risk of antibody-mediated rejection (HR 8.70 [3.42-22.10], P < .0001) and death-censored allograft loss (HR 3.08 [1.17-8.14], P = .023). In addition, prior transplant nephrectomy (HR 2.04 [1.00-4.17], P = .0495) was also associated with allograft failure, whereas receiving a retransplant that was matched at HLA class II was associated with a favorable outcome (HR 0.37 [0.14-0.99], P = .047). In the absence of preformed DSA, an RMM was not associated with de novo DSA development, rejection, or allograft loss. In conclusion, an RMM portends increased immunological risk only in the presence of a preformed DSA in patients undergoing retransplantation.

Which is the best predictor of de novo donor-specific antibodies in a cohort of non-sensitized first kidney transplantation: Antigenic, allelic, epitope, or physiochemical HLA mismatches?

BACKGROUND

Assessment of human leukocyte antigen (HLA) matching by using high-resolution allele typing and knowledge of HLA molecule structure may lead to better prediction of de novo donor-specific antibody (dnDSA) development.

METHODS

We conducted a single-center cohort study among 150 non-sensitized first kidney transplant recipients to compare the association between antigenic (Ag), allelic (Al), eplet (Ep), amino acid (AAMS) HLA matching and electrostatic (EMS) and hydrophobic (HMS) mismatch scores, and the development of dnDSA.

RESULTS

After a mean follow-up time of 49.3 ± 17.7 months, 18 patients (12%) developed dnDSA. The number of HLA mismatches (MM) was significantly associated with the development of dnDSA. The optimal threshold, determined by Harrell's C-index, varied according to the method (5 MM for Ag, P = 0.006; 6 for Al, P = 0.009; 22 for Ep, P = 0.005; 42 for AAMS, P = 0.0007; 45 for EMS, P = 0.009 and 44 for HMS, P = 0.026). C-indices were similar for all matching approaches, suggesting a similar prediction of dnDSA development.

CONCLUSION

In this cohort of low immunological risk transplant patients, the use of Al or Ep matching did not improve the prediction of dnDSA development in comparison with the traditional approach.

Clinical significance of donor-specific anti-HLA-DR51/52/53 antibodies for antibody-mediated rejection in kidney transplant recipients

Background

The presence of donor-specific antibodies (DSAs) to human leukocyte antigen (HLA) increases the risk of antibody-mediated rejection (ABMR) after kidney transplantation (KT). However, the clinical relevance of anti-HLA-DR51/52/53 antibodies remains unclear because of their weak antigen expression. This study evaluated the association between anti-HLA-DR51/52/53 DSAs and ABMR.

Methods

We retrospectively reviewed the single-antigen-bead panel reactive antibody (single PRA) results of 130 patients tested between August 1, 2009 and March 6, 2015, based on clinical necessity after allograft KT. Single PRA analysis was performed using Luminex assay kits (Lifecodes LSA class I and II). We reviewed the clinical course and biopsy results of patients with anti-HLA-DR51/52/53 DSAs.

Results

Post-KT DSAs were identified in 89 of the 130 patients (68.5%), with 26 of 32 class I DSAs and 63 of 66 class II DSAs being immunodominant DSAs. Thirteen patients had anti-HLA-DR51/52/53 DSAs. Three patients with anti-HLA-DR51/52/53 immunodominant DSAs alone were diagnosed with biopsy-proven ABMR. One patient who developed anti-HLA-DR DSA 13 days after KT showed a rapid increase in anti-HLA-DR51 DSA and had biopsy-proven ABMR.

Conclusions

Although the expression of the HLA-DR51/52/53 antigen was weak, anti-HLA-DR51/52/53 DSAs might be correlated with biopsy-proven ABMR. Therefore, anti-HLA-DR51/52/53 DSAs must be evaluated as a cause of ABMR after transplantation.

Management of chronic renal allograft dysfunction and when to re-transplant

Despite the advances in renal transplantation over the last decades, chronic allograft dysfunction remains the largest concern for patients, their families, clinicians and other members of the multi-disciplinary team. Although we have made progress in improving patient and renal allograft survival within the first year after transplantation, the rate of transplant failure with requirement for commencement of dialysis or re-transplantation has essentially remained unchanged. It is important that paediatric and adult nephrologists and transplant surgeons, not only manage their patients and their renal transplants but provide the best chronic kidney disease management during the time of decline of renal allograft function. The gold standard for patients with Stage V chronic kidney disease is to have pre-emptive living donor transplants, where possible and the same is true for healthy renal transplant recipients with declining renal allograft function. The consideration for children and young people as they embark on their end-stage kidney disease journey is the risk-benefit profile of giving the best immunologically matched and good quality renal allografts as they may require multiple renal transplantation operations during their lifetime.

The Impact of Withdrawal of Maintenance Immunosuppression and Graft Nephrectomy on HLA Sensitization and Calculated Chance of Future Transplant

Background

The development of HLA antibodies towards a failing renal allograft is a barrier to retransplantation. This study aimed to compare the formation of HLA donor-specific antibodies (DSA) in patients undergoing graft nephrectomy and in those with a failed graft left in situ who had maintenance immunosuppression (IS) stopped, and assess the relative impact of IS cessation and graft nephrectomy on future relative chance of transplant (R-CoT).

Methods

A single-center retrospective study of patients with failed grafts between 2005 and 2015 was performed. Samples were tested for DSA pre-IS wean, post-IS wean, and post-IS cessation. Nephrectomy patients additionally had samples tested for DSA before and after nephrectomy. Calculated reaction frequency (cRF) was determined at each timepoint and entered into the UK Organ Donation and Transplant R-CoT calculator.

Results

Forty-one patients were included in the study: 24 with nephrectomy and 17 with a failed graft in situ. Patient demographics and duration of IS wean were similar between groups. There was a higher rate of blood transfusion (54% vs 24%) in nephrectomy patients. In patients whose graft remained in situ, cRF rose from 13% pre-IS wean to 40% post-IS wean and 62% after IS cessation. This equated to a reduction in mean R-CoT from 54% to 46% at 5 years. In patients undergoing nephrectomy mean cRF rose from 31% pre-IS wean to 69% post-IS wean and 89% post-IS cessation. Mean R-CoT fell from 54% to 42% at 5 years.

Conclusions

A stepwise increase in cRF with reduced chance of transplant was observed in both groups as IS was withdrawn, with a similar pattern irrespective of graft nephrectomy. Calculated reaction frequency was higher in the nephrectomy group. The risks and benefits of stopping IS need to be carefully considered on an individual basis to maximize chance of future transplant.

Predicting Humoral Alloimmunity from Differences in Donor and Recipient HLA Surface Electrostatic Potential

In transplantation, development of humoral alloimmunity against donor HLA is a major cause of organ transplant failure, but our ability to assess the immunological risk associated with a potential donor–recipient HLA combination is limited. We hypothesized that the capacity of donor HLA to induce a specific alloantibody response depends on their structural and physicochemical dissimilarity compared with recipient HLA. To test this hypothesis, we first developed a novel computational scoring system that enables quantitative assessment of surface electrostatic potential differences between donor and recipient HLA molecules at the tertiary structure level [three-dimensional electrostatic mismatch score (EMS-3D)]. We then examined humoral alloimmune responses in healthy females subjected to a standardized injection of donor lymphocytes from their male partner. This analysis showed a strong association between the EMS-3D of donor HLA and donor-specific alloantibody development; this relationship was strongest for HLA-DQ alloantigens. In the clinical transplantation setting, the immunogenic potential of HLA-DRB1 and -DQ mismatches expressed on donor kidneys, as assessed by their EMS-3D, was an independent predictor of development of donor-specific alloantibody after graft failure. Collectively, these findings demonstrate the translational potential of our approach to improve immunological risk assessment and to decrease the burden of humoral alloimmunity in organ transplantation.

Terasaki Epitope Mismatch Burden Predicts the Development of De Novo DQ Donor-Specific Antibodies and are Associated With Adverse Allograft Outcomes

BACKGROUND

De novo DQ donor-specific antibody (DSA) are associated with antibody-mediated rejection and allograft loss. Given the lack of effective treatment of de novo DQ DSA, their prevention is vital if there is to be an improvement of long-term allograft survival. Using the HLA Matchmaker program, DQ epitope matching has been shown to be superior to HLA antigen mismatching in predicting de novo DQ DSA development. Whether DQ epitopes determined by Terasaki may more accurately predict de novo DQ development over HLA antigen matching is not known.

METHODS

We retrospectively analyzed the immunogenicity of the different HLA antigens, DQB1 alleles and DQB1 Teraskai epitopes (TerEp) in a large cohort of renal transplant recipients, by comparing patient mismatches with de novo DSA development.

RESULTS

Patients mismatched at a DQB1 allele were at significantly higher risk of developing de novo DSA compared with other mismatched HLA antigens. Patients mismatched at the DQ7 allele appear to be at specific risk. For patients mismatched at a single DQB1 allele, the risk of de novo DQ DSA development increases with the number of TerEp mismatches. However, the immunogenicity of the different DQ TerEps does not appear to be equal. Patients who develop antibodies against TerEps are at increased risk of adverse allograft outcomes, specifically antibody-mediated rejection.

CONCLUSIONS

Epitope mismatch burden, determined by TerEps, helps predict risk of de novo DQ DSA development and offers an alternative approach to predict an alloimmune response.

Management of chronic renal allograft dysfunction and when to re-transplant

Despite the advances in renal transplantation over the last decades, chronic allograft dysfunction remains the largest concern for patients, their families, clinicians and other members of the multi-disciplinary team. Although we have made progress in improving patient and renal allograft survival within the first year after transplantation, the rate of transplant failure with requirement for commencement of dialysis or re-transplantation has essentially remained unchanged. It is important that paediatric and adult nephrologists and transplant surgeons, not only manage their patients and their renal transplants but provide the best chronic kidney disease management during the time of decline of renal allograft function. The gold standard for patients with Stage V chronic kidney disease is to have pre-emptive living donor transplants, where possible and the same is true for healthy renal transplant recipients with declining renal allograft function. The consideration for children and young people as they embark on their end-stage kidney disease journey is the risk-benefit profile of giving the best immunologically matched and good quality renal allografts as they may require multiple renal transplantation operations during their lifetime.

What is the impact of human leukocyte antigen mismatching on graft survival and mortality in renal transplantation? A meta-analysis of 23 cohort studies involving 486,608 recipients

Background

The magnitude effects of human leukocyte antigen (HLA) mismatching on post-transplant outcomes of kidney transplantation remain controversial. We aim to quantitatively assess the associations of HLA mismatching with graft survival and mortality in adult kidney transplantation.

Methods

We searched PubMed, EMBASE and the Cochrane Library from their inception to December, 2016. Priori clinical outcomes were overall graft failure, death-censored graft failure and all-cause mortality.

Results

A total of 23 cohort studies covering 486,608 recipients were selected. HLA per mismatch was significant associated with increased risks of overall graft failure (hazard ratio (HR), 1.06; 95% confidence interval (CI), 1.05–1.07), death-censored graft failure (HR: 1.09; 95% CI 1.06–1.12) and all-cause mortality (HR: 1.04; 95% CI: 1.02–1.07). Besides, HLA-DR mismatches were significant associated with worse overall graft survival (HR: 1.12, 95% CI: 1.05–1.21). For HLA-A locus, the association was insignificant (HR: 1.06; 95% CI: 0.98–1.14). We observed no significant association between HLA-B locus and overall graft failure (HR: 1.01; 95% CI: 0.90–1.15). In subgroup analyses, we found recipient sample size and ethnicity maybe the potential sources of heterogeneity.

Conclusions

HLA mismatching was still a critical prognostic factor that affects graft and recipient survival. HLA-DR mismatching has a substantial impact on recipient’s graft survival. HLA-A mismatching has minor but insignificant impact on graft survival outcomes.

Electronic supplementary material

The online version of this article (10.1186/s12882-018-0908-3) contains supplementary material, which is available to authorized users.

Correlation and agreement between eplet mismatches calculated using serological, low-intermediate and high resolution molecular human leukocyte antigen typing methods

Structural human leukocyte antigen (HLA) matching at the eplet level can be identified by HLAMatchmaker, which requires the entry of four-digit alleles. The aim of this study was to evaluate the agreement between eplet mismatches calculated by serological and two-digit typing methods compared to high-resolution four-digit typing. In a cohort of 264 donor/recipient pairs, the evaluation of measurement error was assessed using intra-class correlation to confirm the absolute agreement between the number of eplet mismatches at class I (HLA-A, -B, C) and II loci (HLA-DQ and -DR) calculated using serological or two-digit molecular typing compared to four-digit molecular typing methods. The proportion of donor/recipient pairs with a difference of >5 eplet mismatches between the HLA typing methods was also determined. Intra-class correlation coefficients between serological and four-digit molecular typing methods were 0.969 (95% confidence intervals [95% CI] 0.960–0.975) and 0.926 (95% CI 0.899–0.944), respectively; and 0.995 (95% CI 0.994–0.996) and 0.993 (95% CI 0.991–0.995), respectively between two-digit and four-digit molecular typing methods. The proportion of donor/recipient pairs with a difference of >5 eplet mismatches at class I and II loci was 4% and 16% for serological versus four-digit molecular typing methods, and 0% and 2% for two-digit versus four-digit molecular typing methods, respectively. In this small predominantly Caucasian population, compared with serology, there is a high level of agreement in the number of eplet mismatches calculated using two-compared to four-digit molecular HLA-typing methods, suggesting that two-digit typing may be sufficient in determining eplet mismatch load in kidney transplantation.

Graft nephrectomy in children

Kidney transplantation is recognised as the gold standard treatment of end-stage renal disease in most children, with excellent graft survival rates. When graft failure occurs, renal transplant recipients (RTRs) have the option of removal of the transplant (graft nephrectomy [GN]), or leaving the failed transplant in situ. The aims of this review are to discuss the indications for GN, surgical techniques, outcomes after GN (including risks of allosensitisation and the impact on subsequent transplants), and the possible role of routine GN in the asymptomatic RTR with a failed renal allograft. Literature in both the pediatric and adult renal transplant fields is reviewed. We also discuss how future research in this area could advance our knowledge of which patients to select for GN, and the most appropriate surgical approach.

Association between the polymorphism of HLA and ESRD in Dalian Han population located in north of China

BACKGROUND

End-stage renal disease (ESRD), the last stage of chronic renal failure, is a global health problem. The number of ESRD patients worldwide is increasing faster than the number of kidneys available per year for renal transplantation. Most of the ESRD patients are awaiting renal transplantation. The immune response to the transplanted kidney is directed mainly against mismatched human leukocyte antigen (HLA) glycoproteins expressed on donor tissues. Thus, the analysis of HLA allele and haplotype polymorphisms is valuable not only for identifying ESRD susceptibility factors but also to improve graft survival.

METHODS

In this study, 163 Han ESRD patients were recruited to participate. The blood samples were genotyped by sequence-specific oligonucleotide method. A group of 14,529 healthy Chinese Han individuals registered at the Dalian Blood Center as bone marrow donors, living in the same region and of the same ethnicity, were used as controls.

RESULTS

We found that only one allele, HLA-DRB1*12, showed a positive association with ESRD (p = 0.004, p_c = 0.028, odds ratio = 1.530, 95% confidence interval = 1.147-2.041); A*02-B*40-DRB1*09, A*02-B*40-DRB1*12, A*24-B*15-DRB1*12, and B*40-DRB1*12 were significantly more frequent in ESRD patients after Bonferroni correction (p_c < 0.05).

CONCLUSION

They were potentially valuable predictors for evaluating the risk of ESRD in the Dalian Han population.

HLA Epitope Matching in Kidney Transplantation: An Overview for the General Nephrologist

Rapid changes in tissue-typing technology, including the widespread availability of highly specific molecular typing methods and solid-phase assays for the detection of allele-specific anti-HLA antibodies, make it increasingly challenging to remain up to date with developments in organ matching. Terms such as epitopes and eplets abound in the transplantation literature, but often it can be difficult to see what they might mean for the patient awaiting transplantation. In this review, we provide the historical context for current practice in tissue typing and explore the potential role of HLA epitopes in kidney transplantation. Despite impressive gains in preventing and managing T-cell-mediated rejection and the associated improvements in graft survival, the challenge of the humoral alloresponse remains largely unmet and is the major cause of late graft loss. Describing HLA antigens as a series of antibody targets, or epitopes, rather than based on broad seroreactivity patterns or precise amino acid sequences may provide a more practical and clinically relevant system to help avoid antibody-mediated rejection, reduce sensitization, and select the most appropriate organs in the setting of pre-existing alloantibodies. We explain the systems proposed to define HLA epitopes, summarize the evidence to date for their role in transplantation, and explore the potential benefits of incorporating HLA epitopes into clinical practice as this field continues to evolve toward everyday practice.

Clinically relevant interpretation of solid phase assays for HLA antibody

Purpose of review

Accurate and timely detection and characterization of human leukocyte antigen (HLA) antibodies are critical for pre-transplant and post-transplant immunological risk assessment. Solid phase immunoassays have provided increased sensitivity and specificity, but test interpretation is not always straightforward. This review will discuss the result interpretation considering technical limitations; assessment of relative antibody strength; and the integration of data for risk stratification from complementary testing and the patient's immunological history.

Recent findings

Laboratory and clinical studies have provided insight into causes of test failures – false positive reactions because of antibodies to denatured HLA antigens and false negative reactions resulting from test interference and/or loss of native epitopes. Test modifications permit detection of complement-binding antibodies and determination of the IgG subclasses. The high degree of specificity of single antigen solid phase immunoassays has revealed the complexity and clinical relevance of antibodies to HLA-C, HLA-DQ, and HLA-DP antigens. Determination of antibody specificity for HLA epitopes enables identification of incompatible antigens not included in test kits.

Summary

Detection and characterization of HLA antibodies with solid phase immunoassays has led to increased understanding of the role of those antibodies in graft rejection, improved treatment of antibody-mediated rejection, and increased opportunities for transplantation. However, realization of these benefits requires careful and accurate interpretation of test results.

Waiting Time Between Failure of First Graft and Second Kidney Transplant and Graft and Patient Survival

BACKGROUND

The number of patients with end-stage renal disease being relisted for a second kidney transplant is increasing worldwide. The aim of this study was to determine the relationship between waiting time for a second transplant and outcomes after that second transplant.

METHODS

Using Australia and New Zealand Dialysis and Transplant registry, patients who have received second kidney transplants between 1997 and 2009 were included. The associations between waiting time, defined as duration of dialysis between first allograft failure and second transplantation, and clinical outcomes including acute rejection, graft and patient survival were examined using adjusted logistic and Cox regression models.

RESULTS

Of the 911 recipients, the median follow-up time was 4.7 years resulting in 4825 person-years of follow-up. Increasing waiting time before second transplants was associated with an increased risk of early acute rejection occurring within the first 6 months after transplant (adjusted odds ratio, 1.11; 95% confidence interval [95% CI], 1.06-1.16; P < 0.001), severe vascular and/or humoral rejection (adjusted odds ratio, 1.06; 95% CI, 1.01-1.11; P = 0.011), overall graft failure (adjusted hazard ratio [HR], 1.06; 95% CI, 1.02-1.10; P = 0.001), all-cause mortality (adjusted HR, 1.13; 95% CI, 1.07-1.19; P < 0.001), and death with a functioning graft (adjusted HR, 1.12; 95% CI, 1.06-1.18; P < 0.001), independent of donor, recipient, and immunological factors.

CONCLUSIONS

Prolonged waiting time for a second transplant was associated with inferior patient and graft outcomes.

Diagnostic Contribution of Donor-Specific Antibody Characteristics to Uncover Late Silent Antibody-Mediated Rejection-Results of a Cross-Sectional Screening Study

BACKGROUND

Circulating donor-specific antibodies (DSA) detected on bead arrays may not inevitably indicate ongoing antibody-mediated rejection (AMR). Here, we investigated whether detection of complement-fixation, in parallel to IgG mean fluorescence intensity (MFI), allows for improved prediction of AMR.

METHODS

Our study included 86 DSA+ kidney transplant recipients subjected to protocol biopsy, who were identified upon cross-sectional antibody screening of 741 recipients with stable graft function at 6 months or longer after transplantation. IgG MFI was analyzed after elimination of prozone effect, and complement-fixation was determined using C1q, C4d, or C3d assays.

RESULTS

Among DSA+ study patients, 44 recipients (51%) had AMR, 24 of them showing C4d-positive rejection. Although DSA number or HLA class specificity were not different, patients with AMR or C4d + AMR showed significantly higher IgG, C1q, and C3d DSA MFI than nonrejecting or C4d-negative patients, respectively. Overall, the predictive value of DSA characteristics was moderate, whereby the highest accuracy was computed for peak IgG MFI (AMR, 0.73; C4d + AMR, 0.71). Combined analysis of antibody characteristics in multivariate models did not improve AMR prediction.

CONCLUSIONS

We estimate a 50% prevalence of silent AMR in DSA+ long-term recipients and conclude that assessment of IgG MFI may add predictive accuracy, without an independent diagnostic advantage of detecting complement-fixation.

Changing Paradigms in the Management of Rejection in Kidney Transplantation: Evolving From Protocol-Based Care to the Era of P4 Medicine

PURPOSE OF REVIEW

P4 medicine denotes an evolving field of medicine encompassing predictive, preventive, personalized, and participatory medicine. Using the example of kidney allograft rejection because of donor-recipient incompatibility in human leukocyte antigens, this review outlines P4 medicine's relevance to the various stages of the kidney transplant cycle.

SOURCES OF INFORMATION

A search for English articles was conducted in Medline via OvidSP (up to August 18, 2016) using a combination of subject headings (MeSH) and free text in titles, abstracts, and author keywords for the concepts kidney transplantation and P4 medicine. The electronic database search was expanded further on particular subject headings.

FINDINGS

Available histocompatibility methods exemplify current applications of the predictive and preventive domains of P4 medicine in kidney transplant recipients' care. Pharmacogenomics are discussed as means to facilitate personalized immunosuppression regimens and promotion of active patient participation as a means to improve adherence.

LIMITATIONS

For simplicity, this review focuses on rejection. P4 medicine, however, should more broadly address health concerns in kidney transplant recipients, including competing outcomes such as infections, malignancies, and cardiovascular disease. This review highlights how biomarkers to evaluate these competing outcomes warrant validation and standardization prior to their incorporation into clinical practice.

IMPLICATIONS

Consideration of all 4 domains of the P4 medicine framework when caring for and/or studying kidney transplant recipients has the potential of increasing therapeutic efficiency, minimizing adverse effects, decreasing health care costs, and maximizing wellness. Technologies to gauge immune competency, immunosuppression requirements, and early/reversible immune-mediated injuries are required to optimize kidney transplant care.

The Humoral Theory of Transplantation: Epitope Analysis and the Pathogenicity of HLA Antibodies

Central to the humoral theory of transplantation is production of antibodies by the recipient against mismatched HLA antigens in the donor organ. Not all mismatches result in antibody production, however, and not all antibodies are pathogenic. Serologic HLA matching has been the standard for solid organ allocation algorithms in current use. Antibodies do not recognize whole HLA molecules but rather polymorphic residues on the surface, called epitopes, which may be shared by multiple serologic HLA antigens. Data are accumulating that epitope analysis may be a better way to determine organ compatibility as well as the potential immunogenicity of given HLA mismatches. Determination of the pathogenicity of alloantibodies is evolving. Potential features include antibody strength (as assessed by antibody titer or, more commonly and inappropriately, mean fluorescence intensity) and ability to fix complement (in vitro by C1q or C3d assay or by IgG subclass analysis). Technical issues with the use of solid phase assays are also of prime importance, such as denaturation of HLA antigens and manufacturing and laboratory variability. Questions and controversies remain, and here we review new relevant data.

HLA Mismatching Strategies for Solid Organ Transplantation - A Balancing Act

HLA matching provides numerous benefits in organ transplantation including better graft function, fewer rejection episodes, longer graft survival, and the possibility of reduced immunosuppression. Mismatches are attended by more frequent rejection episodes that require increased immunosuppression that, in turn, can increase the risk of infection and malignancy. HLA mismatches also incur the risk of sensitization, which can reduce the opportunity and increase waiting time for a subsequent transplant. However, other factors such as donor age, donor type, and immunosuppression protocol, can affect the benefit derived from matching. Furthermore, finding a well-matched donor may not be possible for all patients and usually prolongs waiting time. Strategies to optimize transplantation for patients without a well-matched donor should take into account the immunologic barrier represented by different mismatches: what are the least immunogenic mismatches considering the patient’s HLA phenotype; should repeated mismatches be avoided; is the patient sensitized to HLA and, if so, what are the strengths of the patient’s antibodies? This information can then be used to define the HLA type of an immunologically optimal donor and the probability of such a donor occurring. A probability that is considered to be too low may require expanding the donor population through paired donation or modifying what is acceptable, which may require employing treatment to overcome immunologic barriers such as increased immunosuppression or desensitization. Thus, transplantation must strike a balance between the risk associated with waiting for the optimal donor and the risk associated with a less than optimal donor.

Advances in Pretransplant Donor-Specific Antibody Testing in Solid Organ Transplantation: From Bench to Bedside

Immunological risk stratification has a central role in determining both the feasibility of solid organ transplantation and the type (and amount) of induction and maintenance immunosuppressive therapy. Currently there is poor consensus on how to exactly estimate the global immunological risk, and most transplant centers adopt complicated internal guidelines for risk stratification. Here we systematically review published evidences that should drive appropriateness in risk stratification, focusing on donor-specific antibodies against HLA and other antigens.

Alloantibody Responses After Renal Transplant Failure Can Be Better Predicted by Donor-Recipient HLA Amino Acid Sequence and Physicochemical Disparities Than Conventional HLA Matching

We have assessed whether HLA immunogenicity as defined by differences in donor-recipient HLA amino-acid sequence (amino-acid mismatch score, AMS; and eplet mismatch score, EpMS) and physicochemical properties (electrostatic mismatch score, EMS) enables prediction of allosensitization to HLA, and also prediction of the risk of an individual donor-recipient HLA mismatch to induce donor-specific antibody (DSA). HLA antibody screening was undertaken using single-antigen beads in 131 kidney transplant recipients returning to the transplant waiting list following first graft failure. The effect of AMS, EpMS, and EMS on the development of allosensitization (calculated reaction frequency [cRF]) and DSA was determined. Multivariate analyses, adjusting for time on the waiting list, maintenance on immunosuppression after transplant failure, and graft nephrectomy, showed that AMS (odds ratio [OR]: 1.44 per 10 units, 95% CI: 1.02-2.10, p = 0.04) and EMS (OR: 1.27 per 10 units, 95% CI: 1.02-1.62, p = 0.04) were independently associated with the risk of developing sensitization to HLA (cRF > 15%). AMS, EpMS, and EMS were independently associated with the development of HLA-DR and HLA-DQ DSA, but only EMS correlated with the risk of HLA-A and -B DSA development. Differences in donor-recipient HLA amino-acid sequence and physicochemical properties enable better assessment of the risk of HLA-specific sensitization than conventional HLA matching.