The impact of pre-transplant donor specific antibodies on the outcome of kidney transplantation – Data from the Swiss transplant cohort study

The Impact of HLA-DQαβ Heterodimer Mismatch on Living Donor Kidney Allograft Outcomes

BACKGROUND

HLA-DQ mismatch has been identified as a predictor of de novo donor-specific HLA antibody formation and antibody-mediated rejection. There are insufficient data to guide the incorporation of DQ mismatch into organ allocation decisions.

METHODS

We used a retrospective longitudinal cohort of adult living donor kidney transplant recipients from 11 centers across the United States for whom high-resolution class II typing was available. HLA-DQαβ heterodimer allele mismatch was quantified for all donor-recipient pairs, and outcome data were obtained through linkage with the Scientific Registry of Transplant Recipients.

RESULTS

We studied 3916 donor-recipient pairs. Recipient characteristics were notable for a median age of 51 (38-61) y, primarily unsensitized, with 74.5% of the cohort having 0% calculated panel-reactive antibody, and 60.4% with private insurance, for a median follow-up time of 5.86 y. We found that the HLA-DQαβ allele and HLA-DR antigen mismatch were each individually associated with an increased hazard of all-cause graft failure (adjusted hazard ratio [aHR] DQ = 1.03 1.14 1.28; aHR DR = 1.03 1.15 1.328), death-censored graft failure (aHR DQ =1.01 1.19 1.40; aHR DR = 0.099 1.18 1.39), and rejection. Having 2 HLA-DQαβ allele mismatches further increased the hazard of rejection even when controlling for HLA-DR mismatch (aHR 1.03 1.68 2.74).

CONCLUSIONS

HLA-DQαβ allele mismatch predicted allograft rejection even when controlling for HLA-DR antigen mismatch and were both independently associated with increased risk of graft failure or rejection in adult living kidney transplant recipients. Given the strong burden of disease arising from the HLA-DQ antibody formation, we suggest that HLA-DQαβ should be prioritized over HLA-DR in donor selection.

Risk Stratification Before Living Donor Kidney Transplantation in Patients With Preformed Donor-specific Antibodies by Different Crossmatch Methods

Background

Preformed donor-specific HLA antibodies (DSA) are a well-known risk factor in kidney transplantation. There is still considerable debate, however, about the optimal risk stratification among patients with preformed DSA. Additionally, data on the prognostic value of different crossmatch assays in DSA-positive patients are scarce.

Methods

DSA-positive living kidney transplant recipients were selected from a multicenter study examining 4233 consecutive renal transplants. An additional 7 patients from 2 further centers were included. Flow cytometric crossmatches (FXM), Luminex-based crossmatches, and virtual crossmatches based on C1q- and C3d-binding antibodies (C1qXM and C3dXM) were performed retrospectively using pretransplant sera and lymphocytes isolated from fresh samples. These samples were obtained from 44 donor and recipient pairs from 12 centers. Clinical outcome data and the control group without DSA were compiled from the previous study and were supplemented by data on 10-y death-censored graft survival (10yGS).

Results

Between 19% (C3dXM) and 46% (FXM) of crossmatches were positive. Crossmatch-positive patients showed high incidences of antibody-mediated rejection (AMR) within 6 mo (up to 60% in B-cell FXM+ patients). The incidence of AMR in crossmatch-negative patients ranged between 5% (FXM-) and 13% (C1qXM-). 10yGS was significantly impaired in patients with positive T-cell FXM and total FXM compared with both patients without DSA and those with DSA with negative FXM.

Conclusions

Especially FXM are useful for risk stratification, as the outcome of DSA-positive, FXM-negative patients is similar to that of DSA-negative patients, whereas FXM-positive patients have both more AMR and decreased 10yGS. Because of their lower sensitivity, the significance of Luminex-based crossmatches, C1qXM, and C3dXM would have to be examined in patients with stronger DSA.

A simple predictor for donor-specific anti-HLA antibody desensitisation in haploidentical haematopoietic stem cell transplantation

Donor-specific HLA antibody (DSA) has been recognised as an independent risk factor for graft failure in patients undergoing haploidentical haematopoietic stem cell transplantation (HID HSCT). Therapeutic plasma exchange (TPE), as a first-line strategy for DSA desensitisation, can promptly reduce serum DSA levels. This study aimed to investigate DSA characteristics and identify a biomarker predicting the efficacy of DSA desensitisation in patients proceeding to HID HSCT. We retrospectively enrolled 32 patients with DSA from April 2021 to January 2024, and analysed the mean fluorescence intensity (MFI) value of DSA at the different time points of desensitisation treatment. Compared with baseline DSA level before TPE, the median MFI of HLA class I DSA was reduced from 8178.6 to 795.3 (p < 0.001), and HLA class II DSA decreased from 6210.9 to 808.8 (p < 0.001) after TPE. The DSA level in 1:16 diluted pre-TPE serum correlated well with DSA value in post-TPE serum (class I, r = 0.85, p < 0.0001; class II, r = 0.94, p < 0.0001), predicting TPE efficacy in 84.4% of patients. Based on the degree of DSA reduction after TPE, patients were divided into complete responders (decreased by >70%), partial responders (decreased by 30 to 70%) and non-responders (decreased by <30%) and the percentages were 43.8%, 25% and 31.2%, respectively. Non-responders receiving aggressive immunotherapy had longer overall survival compared to those receiving standard strategies (p < 0.05). The 1:16 diluted pre-TPE serum may predict the efficacy of TPE and allow for more rational immunotherapy strategy for patients with DSA proceeding to HID HSCT.

Sensitive HLA antibody testing and the risk of antibody-mediated rejection and graft failure

Solid phase detection and identification of HLA antibodies in kidney transplantation currently relies on single antigen bead (Luminex®) assays, which is more sensitive than the previously used enzyme-linked immunosorbent assays (ELISA). To evaluate the impact of more sensitive HLA testing on antibody-mediated rejection (AMR) occurrence and allograft survival, we analysed 1818 renal allograft recipients transplanted between March 2004 and May 2021. In 2008, solid phase testing switched from ELISA to Luminex. We included 393 (21.6%) transplantations before and 1425 (78.4%) transplantations after transition from ELISA- to Luminex-based testing. For this study, bio-banked ELISA era samples were tested retrospectively with Luminex. Significantly less pretransplant DSA were found in patients transplanted with pre-existing HLA antibodies in the Luminex (109/387) versus the ELISA period (43/90) (28% vs. 48%, p < 0.01). Throughout histological follow-up, 169 of 1818 (9.3%) patients developed AMR. After implementing Luminex-based testing, the rate of AMR significantly decreased (p = 0.003). However, incidence of graft failure did not significantly differ between both eras. In conclusion, less patients with pretransplant DSA were transplanted since the implementation of Luminex HLA testing. Transition from ELISA- to Luminex-based HLA testing was associated with a significant decrease in AMR occurrence post-transplantation. Since the decline of AMR did not translate into improved graft survival, Luminex-based testing has the added value of preventing low-risk AMR cases. Therefore, Luminex' high sensitivity must be balanced against waiting time for a suitable organ.

Detection of donor-derived cell-free DNA in the setting of multiple kidney transplantations

Background

The routine use of donor-derived cell-free DNA (dd-cfDNA) assays to monitor graft damage in patients after kidney transplantation is being implemented in many transplant centers worldwide. The interpretation of the results can be complicated in the setting of multiple sequential kidney transplantations where accurate donor assignment of the detected dd-cfDNA can be methodologically challenging.

Methods

We investigated the ability of a new next-generation sequencing (NGS)-based dd-cfDNA assay to accurately identify the source of the detected dd-cfDNA in artificially generated samples as well as clinical samples from 31 patients who had undergone two sequential kidney transplantations.

Results

The assay showed a high accuracy in quantifying and correctly assigning dd-cfDNA in our artificially generated chimeric sample experiments over a clinically meaningful quantitative range. In our clinical samples, we were able to detect dd-cfDNA from the first transplanted (nonfunctioning) graft in 20% of the analyzed patients. The amount of dd-cfDNA detected from the first graft was consistently in the range of 0.1%-0.6% and showed a fluctuation over time in patients where we analyzed sequential samples.

Conclusion

This is the first report on the use of a dd-cfDNA assay to detect dd-cfDNA from multiple kidney transplants. Our data show that a clinically relevant fraction of the transplanted patients have detectable dd-cfDNA from the first donor graft and that the amount of detected dd-cfDNA is in a range where it could influence clinical decision-making.

Advancing precision in histocompatibility and immunogenetics: a comprehensive review of the UCLA exchange program

Precise typing of human leukocyte antigens (HLA) is crucial for clinical hematopoietic stem cell and solid organ transplantations, transfusion medicine, HLA-related disease association, and drug hypersensitivity analysis. The UCLA Cell Exchange program has played a vital role in providing educational and proficiency testing surveys to HLA laboratories worldwide for the past 5 decades. This article highlights the significant contribution of the UCLA Cell and DNA Exchange Programs in advancing HLA antibody testing, genotyping, crossmatches, and, more recently, virtual crossmatches. Additionally, we discuss future directions of the UCLA Cell Exchange program to support histocompatibility testing to adapt to the fast-evolving field of immunotherapy, tolerance and xenotransplantation.

Pre-transplant donor specific antibodies in ABO incompatible kidney transplantation - data from the Swiss transplant cohort study

Background

Living donor (LD) kidney transplantation in the setting of ABO blood group incompatibility (ABOi) has been previously reported to be associated with increased risk for antibody-mediated rejection (ABMR). It is however unclear if the presence of pre-transplant donor specific antibodies (DSA) works as an additive risk factor in the setting of ABOi and if DSA positive ABOi transplants have a significantly worse long-term outcome as compared with ABO compatible (ABOc) DSA positive transplants.

Methods

We investigated the effect of pre-transplant DSA in the ABOi and ABOc setting on the risk of antibody-mediated rejection (ABMR) and graft loss in a cohort of 952 LD kidney transplants.

Results

We found a higher incidence of ABMR in ABOi transplants as compared to ABOc transplants but this did not significantly affect graft survival or overall survival which was similar in both groups. The presence of pre-transplant DSA was associated with a significantly increased risk of ABMR and graft loss both in the ABOi and ABOc setting. We could not detect an additional risk of DSA in the ABOi setting and outcomes were comparable between DSA positive ABOi and ABOc recipients. Furthermore, a combination of DSA directed at both Class I and Class II, as well as DSA with a high mean fluorescence intensity (MFI) showed the strongest relation to ABMR development and graft loss.

Conclusion

The presence of pre-transplant DSA was associated with a significantly worse long-term outcome in both ABOi and ABOc LD kidney transplants and our results suggests that the risk associated with pre-transplant DSA is perhaps not augmented in the ABOi setting. Our study is the first to investigate the long-term effects of DSA in the ABOi setting and argues that pre-transplant DSA risk could potentially be evaluated similarly regardless of ABO compatibility status.

HLA class I peptide polymorphisms contribute to class II DQβ0603:DQα0103 antibody specificity

Antibodies reactive to human leukocyte antigens (HLA) represent a barrier for patients awaiting transplantation. Based on reactivity patterns in single-antigen bead (SAB) assays, various epitope matching algorithms have been proposed to improve transplant outcomes. However, some antibody reactivities cannot be explained by amino acid motifs, leading to uncertainty about their clinical relevance. Antibodies against the HLA class II molecule, DQβ0603:DQα0103, present in some candidates, represent one such example. Here, we show that peptides derived from amino acids 119-148 of the HLA class I heavy chain are bound to DQβ0603:DQα0103 proteins and contribute to antibody reactivity through an HLA-DM-dependent process. Moreover, antibody reactivity is impacted by the specific amino acid sequence presented. In summary, we demonstrate that polymorphic HLA class I peptides, bound to HLA class II proteins, can directly or indirectly be part of the antibody binding epitope. Our findings have potential important implications for the field of transplant immunology and for our understanding of adaptive immunity.

Low-MFI (median fluorescence intensity) pre-transplant DSA (donor specific antibodies) leading to anamnestic antibody mediated rejection in live-related donor kidney transplantation

"In solid organ transplantation, the compatibility between recipient and donor relies on testing prior to transplantation as a major determinant for the successful transplant outcomes. This compatibility testing depends on the detection of donor-specific antibodies (DSAs) present in the recipient. Indeed, sensitized transplant candidates are at higher risk of allograft rejection and graft loss compared to non-sensitized individuals. Most of the laboratories in India have adopted test algorithms for the appropriate risk stratification of transplants, namely: 1) donor cell-based flow-cytometric cross-match (FCXM) assay with patient's serum to detect DSAs; 2) HLA-coated beads to detect anti-HLA antibodies; and 3) complement-dependent cytotoxicity crossmatch (CDCXM) with donor cells to detect cytotoxic antibodies. In the risk stratification strategy, laboratories generally accept a DSA median fluorescence index (MFI) of 1000 MFI or lower MFI (low-MFI) as a negative value and clear the patient for the transplant. We present two cases of live-related donor kidney transplants (LDKTs) with low-MFI pre-transplant DSA values who experienced an early acute antibody-mediated rejection (ABMR) as a result of an anamnestic antibody response by DSA against HLA class II antibodies. These results were confirmed by retesting of both pre-transplant and post-transplant archived sera from patients and freshly obtained donor cells. Our examples indicate a possible ABMR in patients with low MFI pre-transplant DSA. Reclassification of low vs. high-risk may be appropriate for sensitized patients with low-MFI DSA."

Impact of Preformed Donor-Specific Anti-HLA-Cw and Anti-HLA-DP Antibodies on Acute Antibody-Mediated Rejection in Kidney Transplantation

Given the risk of rejection, the presence of preformed donor specific antibodies (DSA) contraindicates transplantation in most allocation systems. However, HLA-Cw and -DP DSA escape this censorship. We performed a multicentric observational study, in which the objective was to determinate risk factors of acute antibody-mediated rejection (aABMR) in recipients transplanted with preformed isolated Cw- or DP-DSA. Between 2010 and 2019, 183 patients were transplanted with a preformed isolated Cw- or DP-DSA (92 Cw-DSA; 91 DP-DSA). At 2 years, the incidence of aABMR was 12% in the Cw-DSA group, versus 28% in the DP-DSA group. Using multivariable Cox regression model, the presence of a preformed DP-DSA was associated with an increased risk of aABMR (HR = 2.32 [1.21-4.45 (p = 0.001)]) compared with Cw-DSA. We also observed a significant association between the DSA's MFI on the day of transplant and the risk of aABMR (HR = 1.09 [1.08-1.18], p = 0.032), whatever the DSA was. Interaction term analysis found an increased risk of aABMR in the DP-DSA group compared with Cw-DSA, but only for MFI below 3,000. These results may plead for taking these antibodies into account in the allocation algorithms, in the same way as other DSA.

Impact of HLA eplet mismatch load in immunological outcomes after living donor kidney transplantation

INTRODUCTION

HLA eplets mismatches (eMM) have been associated with negative kidney outcomes after transplantation, such as the development of de novo donor-specific antibody (dnDSA), antibody-mediated rejection (ABMR), and early graft loss. This study aimed to evaluate the clinical effects of the HLA eMM load on dnDSA development, ABMR, renal function, allograft survival and graft loss.

MATERIAL AND METHODS

This retrospective study involved 159 living donor kidney transplant patients categorized into groups based on antigen HLA mismatches assessed traditionally and HLA eMM load. Patients had followed for at least one year. The EpViX online program was used to evaluate the HLA eMM load. Cox models were constructed to assess the risk of graft loss. Kaplan-Meier survival curves were carried out. The analyses had performed using the R program and p < 0.05 was considered significant.

RESULTS

From all 159 patients, 28 (17.6%) lost their allografts. Rejection episodes occurred in 37.1% of patients, 13.6% of whom were ABMR. Patients with rejection episodes had higher HLA-AB (p = 0.032) and HLA-DR (p = 0.008) HLA eMM load, HLA-AB (p = 0.006) and HLA-DR (p = 0.009) antigens mismatches, and higher proportions of the following eMM in the HLA-DR locus: 70R eMM (p = 0.015), 70RE (p = 0.015), 74E (p = 0.015) and 48Q (p = 0.047). In multiple models, the presence of HLA-DR 70qq eMM (HR 3.75, 95% CI 1.47; 9.55) add an increase in creatinine levels at 1-year (HR 3.87, 95% CI 2.30, 6.53) were associated with the risk of graft loss.

CONCLUSION

The HLA eMM load was related to episodes of rejection and allograft loss. The HLA-DR eMM was most strongly associated with a worse immunologic outcome than eMM mismatches for HLA-AB.

The Clinical Utility of Post-Transplant Monitoring of Donor-Specific Antibodies in Stable Renal Transplant Recipients: A Consensus Report With Guideline Statements for Clinical Practice

Solid phase immunoassays improved the detection and determination of the antigen-specificity of donor-specific antibodies (DSA) to human leukocyte antigens (HLA). The widespread use of SPI in kidney transplantation also introduced new clinical dilemmas, such as whether patients should be monitored for DSA pre- or post-transplantation. Pretransplant screening through SPI has become standard practice and DSA are readily determined in case of suspected rejection. However, DSA monitoring in recipients with stable graft function has not been universally established as standard of care. This may be related to uncertainty regarding the clinical utility of DSA monitoring as a screening tool. This consensus report aims to appraise the clinical utility of DSA monitoring in recipients without overt signs of graft dysfunction, using the Wilson & Junger criteria for assessing the validity of a screening practice. To assess the evidence on DSA monitoring, the European Society for Organ Transplantation (ESOT) convened a dedicated workgroup, comprised of experts in transplantation nephrology and immunology, to review relevant literature. Guidelines and statements were developed during a consensus conference by Delphi methodology that took place in person in November 2022 in Prague. The findings and recommendations of the workgroup on subclinical DSA monitoring are presented in this article.

Preformed Donor-Specific Antibodies in Kidney Transplant: A Center Experience

BACKGROUND

The presence of preformed donor-specific alloantibodies (DSAs) at the time of transplantation has been associated with an increased risk of rejection, dysfunction, and shorter survival. Detection and identification of these antibodies have improved with more sensitive assays, but their clinical relevance and influence on long-term outcomes are unclear.

METHODS

We investigate the impact of pretransplant DSAs on the outcomes of kidney transplantation. A retrospective analysis was conducted on all patients who received a deceased donor kidney transplant in our center between January 2017 and December 2021. The study population consisted of 75 kidney transplantations, and DSAs were detected in 15 patients (20%) before transplantation.

RESULTS

There was no significant difference in delayed graft function, serum creatinine level at discharge and the first year after transplant, acute rejection rates, or graft survival in patients with and without preformed DSAs.

CONCLUSIONS

Detecting pretransplant DSAs by highly sensitive assays may not necessarily impact long-term graft outcomes, and the mismatch should be individually evaluated.

Association between PIRCHE-II scores and de novo allosensitization after reduction of immunosuppression during SARS-CoV-2 infection in kidney transplant recipients

BACKGROUND

Before the availability of mRNA vaccines, many transplant centers chose to significantly reduce maintenance immunosuppression in kidney transplant recipients (KTRs) with SARS-CoV-2 infection. The extent to which this increases the risk of allosensitization is unclear.

METHODS

In this observational cohort study, we analyzed 47 KTRs from March 2020 to February 2021 who underwent substantial reduction of maintenance immunosuppression during SARS-CoV-2 infection. KTRs were followed at 6 and 18 months concerning the development of de novo donor-specific anti-HLA (human leukocyte antigen) antibodies (DSA). The HLA-derived epitope mismatches were calculated using the predicted indirectly recognizable HLA-epitopes (PIRCHE-II) algorithm.

RESULTS

In total, 14 of 47 KTRs (30%) developed de novo HLA antibodies after the reduction of maintenance immunosuppression. KTRs with higher total PIRCHE-II scores and higher PIRCHE-II scores for the HLA-DR locus were more likely to develop de novo HLA antibodies (p = .023, p = .009). Furthermore, 4 of the 47 KTRs (9%) developed de novo DSA after reduction of maintenance immunosuppression, which were exclusively directed against HLA-class II antigens and also showed higher PIRCHE-II scores for HLA-class II. The cumulative mean fluorescence intensity of 40 KTRs with preexisting anti-HLA antibodies and 13 KTRs with preexisting DSA at the time of SARS-CoV-2 infection remained stable after the reduction of maintenance immunosuppression (p = .141; p = .529).

CONCLUSIONS

Our data show that the HLA-derived epitope mismatch load between donor and recipient influences the risk of de novo DSA development when immunosuppression is temporarily reduced. Our data further suggest that reduction in immunosuppression should be made more cautiously in KTRs with high PIRCHE-II scores for HLA-class II antigens.

Donation type and the effect of pre-transplant donor specific antibodies - Data from the Swiss Transplant Cohort Study

Introduction

The type of donation may affect how susceptible a donor kidney is to injury from pre-existing alloimmunity. Many centers are, therefore, reluctant to perform donor specific antibody (DSA) positive transplantations in the setting of donation after circulatory death (DCD). There are, however, no large studies comparing the impact of pre-transplant DSA stratified on donation type in a cohort with a complete virtual cross-match and long-term follow-up of transplant outcome.

Methods

We investigated the effect of pre-transplant DSA on the risk of rejection, graft loss, and the rate of eGFR decline in 1282 donation after brain death (DBD) transplants and compared it to 130 (DCD) and 803 living donor (LD) transplants.

Results

There was a significant worse outcome associated with pre-transplant DSA in all of the studied donation types. DSA directed against Class II HLA antigens as well as a high cumulative mean fluorescent intensity (MFI) of the detected DSA showed the strongest association with worse transplant outcome. We could not detect a significant additive negative effect of DSA in DCD transplantations in our cohort. Conversely, DSA positive DCD transplants appeared to have a slightly better outcome, possibly in part due to the lower mean fluorescent intensity (MFI) of the pre-transplant DSA. Indeed when DCD transplants were compared to DBD transplants with similar MFI (<6.5k), graft survival was not significantly different.

Discussion

Our results suggest that the negative impact of pre-transplant DSA on graft outcome could be similar between all donation types. This suggests that immunological risk assessment could be performed in a similar way regardless of the type of donor kidney transplantation.

Extended genomic HLA typing identifies previously unrecognized mismatches in living kidney transplantation

Introduction

Antibody mediated rejection (ABMR) is the most common cause of long-term allograft loss in kidney transplantation (KT). Therefore, a low human leukocyte antigen (HLA) mismatch (MM) load is favorable for KT outcomes. Hitherto, serological or low-resolution molecular HLA typing have been adapted in parallel. Here, we aimed to identify previously missed HLA mismatches and corresponding antibodies by high resolution HLA genotyping in a living-donor KT cohort.

Methods

103 donor/recipient pairs transplanted at the University of Leipzig Medical Center between 1998 and 2018 were re-typed using next generation sequencing (NGS) of the HLA loci -A, -B, -C, -DRB1, -DRB345, -DQA1, -DQB1, -DPA1, and -DPB1. Based on these data, we compiled HLA MM counts for each pair and comparatively evaluated genomic HLA-typing with pre-transplant obtained serological/low-resolution HLA (=one-field) typing results. NGS HLA typing (=two-field) data was further used for reclassification of de novo HLA antibodies as "donor-specific".

Results

By two-field HLA re-typing, we were able to identify additional MM in 64.1% (n=66) of cases for HLA loci -A, -B, -C, -DRB1 and -DQB1 that were not observed by one-field HLA typing. In patients with biopsy proven ABMR, two-field calculated MM count was significantly higher than by one-field HLA typing. For additional typed HLA loci -DRB345, -DQA1, -DPA1, and -DPB1 we observed 2, 26, 3, and 23 MM, respectively. In total, 37.3% (69/185) of de novo donor specific antibodies (DSA) formation was directed against these loci (DRB345 ➔ n=33, DQA1 ➔ n=33, DPA1 ➔ n=1, DPB1 ➔ n=10).

Conclusion

Our results indicate that two-field HLA typing is feasible and provides significantly more sensitive HLA MM recognition in living-donor KT. Furthermore, accurate HLA typing plays an important role in graft management as it can improve discrimination between donor and non-donor HLA directed cellular and humoral alloreactivity in the long range. The inclusion of additional HLA loci against which antibodies can be readily detected, HLA-DRB345, -DQA1, -DQB1, -DPA1, and -DPB1, will allow a more precise virtual crossmatch and better prediction of potential DSA. Furthermore, in living KT, two-field HLA typing could contribute to the selection of the immunologically most suitable donors.