Utility of HLA Antibody Testing in Kidney Transplantation

Biomarkers in Kidney Transplantation

Currently in the United States, there are more than 250,000 patients with a functioning kidney allograft and over 100,000 waitlisted patients awaiting kidney transplant, with a burgeoning number added to the kidney transplant wait list every year. Although early post-transplant care is delivered at the transplant center, the increasing number of kidney transplant recipients requires general nephrologists to actively participate in the long-term care of these patients. Serum creatinine and proteinuria are imperfect traditional biomarkers of allograft dysfunction and lag behind subclinical allograft injury. This manuscript reviews the various clinically available biomarkers in the field of kidney transplantation for a general nephrologist with a focus on the utility of donor-derived cell-free DNA, as a marker of early allograft injury. Blood gene expression profiling, initially studied in the context of early identification of subclinical rejection, awaits validation in larger multicentric trials. Urinary cellular messenger ribonucleic acid and chemokine CXCL10 hold promising potential for early diagnosis of both subclinical and acute rejection. Torque tenovirus, a ubiquitous DNA virus is emerging as a biomarker of immunosuppression exposure as peripheral blood torque tenovirus copy numbers might mirror the intensity of host immunosuppression. Although high-quality evidence is still being generated, evidence and recommendations are provided to aid the general nephrologist in implementation of novel biomarkers in their clinical practice.

Anti-HLA Class II Antibodies Are the Most Resistant to Desensitization in Crossmatch-positive Living-donor Kidney Transplantations: A Patient Series

Background

In HLA-incompatible kidney transplantation, the efficacy of desensitization in terms of anti-HLA antibody kinetics is not well characterized. We present an overview of the course of anti-HLA antibodies throughout plasma exchange (PE) desensitization in a series of crossmatch-positive patients.

Methods

All consecutive candidates in the Dutch HLA-incompatible kidney transplantation program between November 2012 and January 2022 were included. The eligibility criteria were a positive crossmatch with a living kidney donor and no options for compatible transplantation. Desensitization consisted of 5-10 PE with low-dose IVIg.

Results

A total of 16 patient-donor pairs were included. Patients had median virtual panel-reactive antibody of 99.58%. Cumulative donor-specific anti-HLA antibody (cumDSA) mean fluorescence intensity (MFI) was 31 399 median, and immunodominant DSA (iDSA) MFI was 18 677 for class I and 21 893 for class II. Median anti-HLA antibody MFI response to desensitization was worse in class II as compared with class I (P < 0.001), particularly for HLA-DQ. Class I cumDSA MFI decreased 68% after 4 PE versus 53% in class II. The decrease between the fifth and the 10th PE sessions was modest with 21% in class I versus 9% in class II. Antibody-mediated rejection occurred in 85% of patients, with the iDSA directed to the same mismatched HLA as before desensitization, except for 3 patients, of whom 2 had vigorous rebound of antibodies to repeated mismatches (RMMs). Rebound was highest (86%) in RMM-DSA with prior grafts removed (transplantectomy n = 7), lower (39%) in non-RMM-DSA (n = 30), and lowest (11%) for RMM-DSA with in situ grafts (n = 5; P = 0.018 for RMM-DSA transplantectomy versus RMM-DSA graft in situ). With a median follow-up of 59 mo, 1 patient had died resulting in a death-censored graft survival of 73%.

Conclusions

Patients with class II DSA, and particularly those directed against HLA-DQ locus, were difficult to desensitize.

Biomarkers in Kidney Transplantation: A Rapidly Evolving Landscape

The last decade has seen an explosion in clinical research focusing on the use of noninvasive biomarkers in kidney transplantation. Much of the published literature focuses on donor-derived cell-free DNA (dd-cfDNA). Although initially studied as a noninvasive means of identifying acute rejection, it is now clear that dd-cfDNA is more appropriately described as a marker of severe injury and irrespective of the etiology, elevated dd-cfDNA ≥0.5% portends worse graft outcomes. Blood gene expression profiling is also commercially available and has mostly been studied in the context of early identification of subclinical rejection, although additional data is needed to validate these findings. Torque teno virus, a ubiquitous DNA virus, has emerged as a biomarker of immunosuppression exposure as peripheral blood Torque teno virus copy numbers might mirror the intensity of host immunosuppression. Urinary chemokine tests including C-X-C motif chemokine ligand 9 and C-X-C motif chemokine ligand 10 have recently been assessed in large clinical trials and hold promising potential for early diagnosis of both subclinical and acute rejection, as well as, for long-term prognosis. Urinary cellular messenger RNA and exosome vesicular RNA based studies require additional validation. Although current data does not lend itself to conclusion, future studies on multimodality testing may reveal the utility of serial surveillance for individualization of immunosuppression and identify windows of opportunity to intervene early and before the irreversible allograft injury sets in.

Pre-transplant crossmatch-negative donor-specific anti-HLA antibody predicts acute antibody-mediated rejection but not long-term outcomes in kidney transplantation: an analysis of the Korean Organ Transplantation Registry

Background

Pre-transplant donor-specific anti-human leukocyte antigen antibody (HLA-DSA) is a recognized risk factor for acute antibody-mediated rejection (ABMR) and allograft failure. However, the clinical relevance of pre-transplant crossmatch (XM)-negative HLA-DSA remains unclear.

Methods

We investigated the effect of XM-negative HLA-DSA on post-transplant clinical outcomes using data from the Korean Organ Transplantation Registry (KOTRY). This study included 2019 living donor kidney transplant recipients from 40 transplant centers in South Korea: 237 with HLA-DSA and 1782 without HLA-DSA.

Results

ABMR developed more frequently in patients with HLA-DSA than in those without (5.5% vs. 1.5%, p<0.0001). Multivariable analysis identified HLA-DSA as a significant risk factor for ABMR (odds ratio = 3.912, 95% confidence interval = 1.831-8.360; p<0.0001). Furthermore, the presence of multiple HLA-DSAs, carrying both class I and II HLA-DSAs, or having strong HLA-DSA were associated with an increased incidence of ABMR. However, HLA-DSA did not affect long-term clinical outcomes, such as allograft function and allograft survival, patient survival, and infection-free survival.

Conclusion

Pre-transplant XM-negative HLA-DSA increased the risk of ABMR but did not affect long-term allograft outcomes. HLA-incompatible kidney transplantation in the context of XM-negative HLA-DSA appears to be feasible with careful monitoring and ensuring appropriate management of any occurrence of ABMR. Furthermore, considering the characteristics of pre-transplant XM-negative HLA-DSA, the development of a more detailed and standardized desensitization protocol is warranted.

HLA Genotype Imputation Results in Largely Accurate Epitope Mismatch Risk Categorization Across Racial Groups

Background

Biomarkers that predict posttransplant alloimmunity could lead to improved long-term graft survival. Evaluation of the number of mismatched epitopes between donor and recipient HLA proteins, termed molecular mismatch analysis, has emerged as an approach to classify transplant recipients as having high, intermediate, or low risk of graft rejection. When high-resolution genotypes are unavailable, molecular mismatch analysis requires algorithmic assignment, or imputation, of a high-resolution genotyping. Although imputation introduces inaccuracies in molecular mismatch analyses, it is unclear whether these inaccuracies would impact the clinical risk assessment for graft rejection.

Methods

Using renal transplant patients and donors from our center, we constructed cohorts of surrogate donor-recipient pairs with high-resolution and low-resolution HLA genotyping that were racially concordant or discordant. We systemically assessed the impact of imputation on molecular mismatch analysis for cohorts of 180-200 donor-recipient pairs for each of 4 major racial groups. We also evaluated the effect of imputation for a racially diverse validation cohort of 35 real-world renal transplant pairs.

Results

In the surrogate donor-recipient cohorts, imputation preserved the molecular mismatch risk category for 90.5%-99.6% of racially concordant donor-recipient pairs and 92.5%-100% of racially discordant pairs. In the validation cohort, which comprised 72% racially discordant pairs, we found that imputation preserved the molecular mismatch risk category for 97.1% of pairs.

Conclusions

Overall, these data demonstrate that imputation preserves the molecular mismatch risk assessment in the vast majority of cases and provides evidence supporting imputation in the performance of molecular mismatch analysis for clinical assessment.

Subsequent kidney transplant after pediatric heart transplant: Prevalence and risk factors

Pediatric heart failure and transplantation carry associated risks for kidney failure and potential need for kidney transplant following pediatric heart transplantation (KT/pHT). This retrospective, United Network of Organ Sharing study of 10,030 pediatric heart transplants (pHTs) from 1987 to 2020 aimed to determine the incidence of waitlisting for and completion of KT/pHT, risk factors for KT/pHT, and risk factors for nonreceipt of a KT/pHT. Among pHT recipients, 3.4% were waitlisted for KT/pHT (median time of 14 years after pHT). Among those waitlisted, 70% received a KT/pHT, and 18% died on the waitlist at a median time of 0.8 years from KT/pHT waitlisting (median age of 20 years). Moderate-high sensitization at KT/pHT waitlisting (calculated panel reactive antibody, ≥ 20%) was associated with a lower likelihood of KT/pHT (adjusted hazard ratio, 0.67; 95% confidence interval, 0.47-0.95). Waitlisting for heart transplantation simultaneously with kidney transplant (adjusted hazard ratio, 3.73; 95% confidence interval, 2.01-6.92) was associated with increased risk of death on the KT/pHT waitlist. While the prevalence of KT/pHT is low, there is substantial mortality among those waitlisted for KT/pHT. These findings suggest a need to consider novel risk factors for nonreceipt of KT/pHT and death on the waitlist in prioritizing criteria/guidelines for simultaneous heart-kidney transplantation.

Selective Elimination and Rationalization of Cell-based Assays in Deceased Donor Kidney Transplant Crossmatching

Background

While there is increasing reliance on a negative virtual crossmatch to proceed with deceased donor kidney transplantation, a flow cytometry crossmatch (FCXM) is still usually performed after the transplant has already occurred. Our center has eliminated pretransplant physical crossmatches for most patients, and since 2018, we have eliminated the systematic performance of posttransplant FCXMs.

Methods

We studied all deceased donor kidney transplants in our program between June 1, 2018, and March 31, 2021, to evaluate the impact of eliminating retrospective FCXMs on resource utilization and graft outcomes (ie, the occurrence of antibody-mediated rejection [AMR] in the first 3-mo posttransplant).

Results

A total of 358 kidney transplants occurred during the study period, and approximately 70% of these transplants proceeded without the performance of any FCXM. Incidence rates of AMR were low (9.63 per 1000 person-months), which compared favorably with the incidence rate of AMR during the 3-y period preceding the policy (4.82 per 1000 person-months, P = 0.21).

Conclusions

Our results suggest that moving away from retrospective FCXM and relying exclusively on the virtual crossmatch is safe and efficient for kidney allocation.

Interferon-γ and its response are determinants of antibody-mediated rejection and clinical outcomes in patients after renal transplantation

Interferon-γ (IFN-γ) is an important cytokine in tissue homeostasis and immune response, while studies about it in antibody-mediated rejection (ABMR) are very limited. This study aims to comprehensively elucidate the role of IFN-γ in ABMR after renal transplantation. In six renal transplantation cohorts, the IFN-γ responses (IFNGR) biological process was consistently top up-regulated in ABMR compared to stable renal function or even T cell-mediated rejection in both allografts and peripheral blood. According to single-cell analysis, IFNGR levels were found to be broadly elevated in most cell types in allografts and peripheral blood with ABMR. In allografts with ABMR, M1 macrophages had the highest IFNGR levels and were heavily infiltrated, while kidney resident M2 macrophages were nearly absent. In peripheral blood, CD14+ monocytes had the top IFNGR level and were significantly increased in ABMR. Immunofluorescence assay showed that levels of IFN-γ and M1 macrophages were sharply elevated in allografts with ABMR than non-rejection. Importantly, the IFNGR level in allografts was identified as a strong risk factor for long-term renal graft survival. Together, this study systematically analyzed multi-omics from thirteen independent cohorts and identified IFN-γ and IFNGR as determinants of ABMR and clinical outcomes in patients after renal transplantation.

The impact of pretransplant suspected HLA antibody on the long-term outcome of the graft kidney: A retrospective cohort study

INTRODUCTION

The preoperative examination of kidney transplantation includes HLA antibody screening to initially determine the presence of preexisting donor-specific antibody (DSA) that mediates hyperacute rejection. Recipients with positive HLA antibodies require further HLA specificity analysis to type the antigen and determine the antigen mismatches between the donor and recipient. However, recipients with suspected antibodies would have no further HLA specificity analysis. It is unclear whether suspected HLA antibodies would affect renal graft function. This study aimed to explore the impact of pretransplant suspected HLA antibody on the long-term outcome of the graft kidney and thus determine the necessity of routinely performing the HLA specificity analysis in recipients with suspected HLA antibodies preoperatively.

METHODS

This is a single-center retrospective cohort study. 179 kidney transplant recipients (KTRs) were included and further divided into HLA antibody-negative group (Group 1) and HLA antibody-suspected groups (Group 2) based on the result of the pretransplant HLA antibody screen test. And the antibody-suspected group was further divided into a low-mismatched group (Group A) and a high-mismatched group (Group B) according to the HLA specificity analysis. We tracked the renal function indexes, biochemical indexes, and posttransplant adverse events within 5 years after transplantation and explored the necessity of further HLA specificity analysis in recipients with pretransplant suspected HLA antibodies.

RESULTS

There was no statistically significant difference in demographics between HLA antibody-negative group and HLA antibody-suspected groups. At 5 years of follow-up, the KTRs in HLA antibody-negative group had significantly higher eGFR levels, lower serum creatinine levels, and less urinary protein compared to those in antibody-suspected group. Meanwhile, the KTRs in low-mismatched group also had significantly higher eGFR levels, lower serum creatinine levels, and less proteinuria compared to those in high-mismatched group. Correlation analysis showed that the age of KTRs, urinary protein levels and the load capacity of HLA mismatches were associated with eGFR levels of KTRs at 5 year posttransplant.

CONCLUSION

KTRs with suspected HLA antibodies before kidney transplantation have worse graft function than the preoperative HLA antibody-negative recipients in the long-term posttransplant follow-up. The specific load capacity of HLA mismatches, the age of the recipient and the urinary protein was found to be negatively correlated with long-term posttransplant renal outcomes. It is necessary to undergo further HLA specificity analysis for recipients with suspected HLA antibodies in HLA antibody screen test to explicit HLA mismatches and improve long-term posttransplant outcomes.

HLA-B*51 Frequency in Transplant Patients and Donors

OBJECTIVES

HLA molecules play a crucial role in transplantation. The best treatment modality in patients with end-stage renal disease is renal transplant. HLA mismatches between patients and donors can prolong time for renal transplant therapy, reduce graft survival, and increase mortality. HLA region is the most polymorphic genetic region and is essential for antigen presentation. The main target of the recipient's immune system is HLA molecules on the surface of donor cells. HLA-B*51 is associated with Behcet disease, a rare multisystemic disease characterized by autoimmunity and inflammatory processes. In transplant recipients, inflammation and vasculitis are immunologic mechanisms that are responsible for damage of graft tissue. In this retrospective study, we aimed to investigate the frequency of HLA-B*51 in patients diagnosed with end-stage renal disease and in controls and to investigate correlations with rejection episodes.

MATERIALS AND METHODS

Patients who applied to Baskent University Adana Dr. Turgut Noyan Research and Medical Center (between 2010 and 2022) with end-stage renal disease (n = 1732) and a control group (n = 5277) received HLA typing for class I (HLA-A, HLA-B). Sequence-specific primers or sequencespecific oligonucleotides were used. Among patients diagnosed with end-stage renal disease, 321 had kidney transplant.

RESULTS

Frequency of HLA-B*51 was 25.92% in patients and 25.22% in controls. No significant differences were found between patients and controls in the frequency of HLA-B*51. Among kidney transplant recipients with HLA-B*51 (n = 72), 38.89% had rejection episodes and 61.11% had no rejection. No significant association was found between HLA-B*51 allele positivity and rejection.

CONCLUSIONS

No significant relationship was shown between patients diagnosed with end-stage renal disease and HLA-B*51 positivity. Previous studies support frequency of the HLA-B*51 allele in the control group. Although Behçet disease is known to cause renal vasculitis, HLA-B*51 positivity alone was not associated with vasculitis or inflammation.

Crossmatch assays in transplantation: Physical or virtual?: A review

The value of the crossmatch test in assessing pretransplant immunological risk is vital for clinical decisions, ranging from the indication of the transplant to the guidance of induction protocols and treatment with immunosuppressants. The crossmatch tests in transplantation can be physical or virtual, each with its advantages and limitations. Currently, the virtual crossmatch stands out for its sensitivity and specificity compared to the physical tests. Additionally, the virtual crossmatch can be performed in less time, allowing for a reduction in cold ischemia time. It shows a good correlation with the results of physical tests and does not negatively impact graft survival. Proper communication between clinicians and the transplant immunology laboratory will lead to a deeper understanding of each patient's immunological profile, better donor-recipient selection, and improved graft survival.

A modeling approach for mean fluorescence intensity value harmonization and cutoff prediction for luminex single antigen bead assays of two different vendors

Luminex single antigen bead (SAB) kits from One Lambda (OL) and Lifecodes (LC) are widely used for HLA antibody detection but have substantial differences in design and assay protocol resulting in different mean fluorescence intensity (MFI) values. Here, we present a non-linear modeling approach to accurately convert MFI values between two vendors and to establish user-independent MFI cutoffs when analyzing big datasets. HLA antibody data from a total of 47 EDTA-treated sera tested using both OL and LC SAB kits were analyzed. MFI comparisons were made for the common 84 HLA class I and 63 class II beads. In the exploration set (n = 24), a non-linear hyperbola model on raw MFI corrected by locus-specific highest self MFI subtraction yielded the highest correlation (class I r2 : 0.946, class II r2 : 0.898). Performance of the model was verified in an independent validation set (n = 12) (class I r2 : 0.952, class II r2 : 0.911). Furthermore, in an independent cohort of post-transplant serum samples (n = 11) using the vendor-specific MFI cutoffs dictated by the current model, we found 94% accuracy in bead-specific reactivity assignments by the two vendors. We recommend using the non-linear hyperbola modeling approach with self HLA correction and locus-specific analyzes to harmonize MFI values between two vendors in particular research datasets. As there are considerable variations between the two assays, using MFI conversion for individual patient samples is not recommended.

Complement-activating donor-specific anti-HLA antibodies in solid organ transplantation: systematic review, meta-analysis, and critical appraisal

Introduction

Several studies have investigated the impact of circulating complement-activating anti-human leukocyte antigen donor-specific antibodies (anti-HLA DSAs) on organ transplant outcomes. However, a critical appraisal of these studies and a demonstration of the prognostic value of complement-activating status over anti-HLA DSA mean fluorescence intensity (MFI) level are lacking.

Methods

We conducted a systematic review, meta-analysis and critical appraisal evaluating the role of complement-activating anti-HLA DSAs on allograft outcomes in different solid organ transplants. We included studies through Medline, Cochrane, Scopus, and Embase since inception of databases till May 05, 2023. We evaluated allograft loss as the primary outcome, and allograft rejection as the secondary outcome. We used the Newcastle-Ottawa Scale and funnel plots to assess risk of bias and used bias adjustment methods when appropriate. We performed multiple subgroup analyses to account for sources of heterogeneity and studied the added value of complement assays over anti-HLA DSA MFI level.

Results

In total, 52 studies were included in the final meta-analysis (11,035 patients). Complement-activating anti-HLA DSAs were associated with an increased risk of allograft loss (HR 2.77; 95% CI 2.33-3.29, p<0.001; I²=46.2%), and allograft rejection (HR 4.98; 95% CI 2.96-8.36, p<0.01; I²=70.9%). These results remained significant after adjustment for potential sources of bias and across multiple subgroup analyses. After adjusting on pan-IgG anti-HLA DSA defined by the MFI levels, complement-activating anti-HLA DSAs were significantly and independently associated with an increased risk of allograft loss.

Discussion

We demonstrated in this systematic review, meta-analysis and critical appraisal the significant deleterious impact and the independent prognostic value of circulating complement-activating anti-HLA DSAs on solid organ transplant risk of allograft loss and rejection.

The correlation of results of panel reactive antibody, identification, and single antigen beads in detection of anti-HLA antibodies: Istanbul Faculty of Medicine, tissue typing laboratory experience

BACKGROUND

We have performed a retrospective analysis of anti-HLA class I MHC and class II MHC antibodies measured using a single antigen bead (SAB) assay and a panel reactive antibody (PRA) assay.

MATERIAL AND METHODS

A group of 256 patients with end-stage renal disease (ESRD) was tested for anti-HLA antibodies in the tissue typing laboratory between 2017 and 2020. In the cohort, the serum samples of patients waiting for transplantation were tested. Both the PRA and SAB tests of these patients were analyzed using the Luminex (Immucor) method. The threshold of positivity was accepted as median fluorescence intensities (MFI) ≥1000 for PRA screening and MFI ≥750 for SAB screening.

RESULTS

Overall, antibodies to HLA antigens were detected in 202 (78.9%) out of 256 patients in the PRA study. Antibodies against both class I/II antigens were detected only in 15.6% of these patients, whereas antibodies against only against class I HLA in 31.3% and only against class II HLA in 32.0%. By comparison, the SAB study found that 66.8% of patients were positive for HLA antigens. Furthermore, donor-specific antibodies (DSA) were detected in 52.0% of PRA-positive patients and 52.6% of SAB-positive patients. It was shown that 168 patients (83.2%) out of 202 PRA-positive patients were found to be SAB-positive. In addition, 51 patients negative in the SAB assay (94.4%) were also negative in the PRA assay. Statistical analysis established a significant correlation between the PRA and SAB positivity (p > 0.001). It was also shown that MFI ≥3000 PRA positivity for class I HLA antigens (p = 0.049) and MFI ≥5000 PRA positivity for class II antigens (p < 0.001) correlated with the SAB positivity in patients.

CONCLUSION

Our results showed the importance of both PRA and SAB assays to define the status of sensitization in patients.

HLA-DQ antibodies in alloimmunity, what makes them different?

PURPOSE OF REVIEW

De novo HLA-DQ antibodies are the most frequently observed after solid-organ allotransplantation; and are associated with the worse adverse graft outcomes compared with all other HLA antibodies. However, the biological explanation for this observation is not yet known. Herein, we examine unique characteristics of alloimmunity directed specifically against HLA-DQ molecules.

RECENT FINDINGS

While investigators attempted to decipher functional properties of HLA class II antigens that may explain their immunogenicity and pathogenicity, most early studies focused on the more expressed molecule - HLA-DR. We here summarize up-to-date literature documenting specific features of HLA-DQ, as compared to other class II HLA antigens. Structural and cell-surface expression differences have been noted on various cell types. Some evidence suggests variations in antigen-presenting function and intracellular activation pathways after antigen/antibody interaction.

SUMMARY

The clinical effects of donor-recipient incompatibility at HLA-DQ, the risk of generating de novo antibodies leading to rejection, and the inferior graft outcomes indicate increased immunogenicity and pathogenicity that is unique to this HLA antigen. Clearly, knowledge generated for HLA-DR cannot be applied interchangeably. Deeper understanding of features unique to HLA-DQ may support the generation of targeted preventive-therapeutic strategies and ultimately improve solid-organ transplant outcomes.

Prospective assessment of pre-existing and de novo anti-HLA IgE in kidney, liver, lung and heart transplantation

Introduction

Antibody mediated rejection (ABMR) is a major factor limiting outcome after organ transplantation. Anti-HLA donor-specific antibodies (DSA) of the IgG isotype are mainly responsible for ABMR. Recently DSA of the IgE isotype were demonstrated in murine models as well as in a small cohort of sensitized transplant recipients. In the present study, we aimed to determine the frequency of pre-existing and de novo anti-HLA IgE antibodies in a cohort of 105 solid organ transplant recipients.

Methods

We prospectively measured anti-HLA IgE antibodies in a cohort of kidney (n=60), liver, heart and lung (n=15 each) transplant recipients before and within one-year after transplantation, employing a single-antigen bead assay for HLA class I and class II antigens. Functional activity of anti-HLA IgE antibodies was assessed by an in vitro mediator release assay. Antibodies of the IgG1-4 subclasses and Th1 and Th2 cytokines were measured in anti-HLA IgE positive patients.

Results

Pre-existing anti-HLA IgE antibodies were detected in 10% of renal recipients (including 3.3% IgE-DSA) and in 4.4% of non-renal solid organ transplant recipients (heart, liver and lung cohort). Anti-HLA IgE occurred only in patients that were positive for anti-HLA IgG, and most IgE positive patients had had a previous transplant. Only a small fraction of patients developed de novo anti-HLA IgE antibodies (1.7% of kidney recipients and 4.4% of non-renal recipients), whereas no de novo IgE-DSA was detected. IgG subclass antibodies showed a distinct pattern in patients who were positive for anti-HLA IgE. Moreover, patients with anti-HLA IgE showed elevated Th2 and also Th1 cytokine levels. Serum from IgE positive recipients led to degranulation of basophils in vitro, demonstrating functionality of anti-HLA IgE.

Discussion

These data demonstrate that anti-HLA IgE antibodies occur at low frequency in kidney, liver, heart and lung transplant recipients. Anti-HLA IgE development is associated with sensitization at the IgG level, in particular through previous transplants and distinct IgG subclasses. Taken together, HLA specific IgE sensitization is a new phenomenon in solid organ transplant recipients whose potential relevance for allograft injury requires further investigation.

Clinical Outcome of Kidney Transplant Recipients with C1q-Binding De Novo Donor Specific Antibodies: A Single-Center Experience

Complement activation by HLA antibodies is a key component of immune-mediated graft injury. We examined the clinical outcomes of kidney transplant recipients with complement-fixing de novo donor-specific antibodies (dnDSA) who were followed in our center. The C1q-binding ability was retrospectively assessed in 69 patients with dnDSA and mean fluorescence intensity (MFI) values > 2000 out of the 1325 kidney transplant recipients who were screened for DSA between 2015 and 2019. Luminex IgG single antigen beads (SAB)and C1q-SAB assays (One Lambda) were used. C1q-binding dnDSA was identified in 32/69 (46.4%) of the patients. Significantly higher MFI values were observed in C1q-positive DSA (18,978 versus 5840, p < 0.001). Renal graft biopsies were performed in 43 of the kidney transplant recipients (62.3%) with allograft dysfunction. Antibody-mediated rejection (ABMR) was detected in 29/43 (67.4%) of the patients. The incidence of ABMR was similar among patients with C1q-binding and non-C1q-binding DSA (51.7% vs. 48.3%, p = 0.523). Graft loss occurred in 30/69 (43.5%) of the patients at a median time of 82.5 months (IQR 45-135) from DSA detection. C1q-binding DSA was present in more patients who experienced graft loss (53.1% vs. 35.1%, p = 0.152). Higher MFI values and inferior clinical outcomes occurred in most of the kidney transplant recipients with C1q-binding dnDSA.

Microfluidic antibody affinity profiling of alloantibody-HLA interactions in human serum

Antibody profiling is a fundamental component of understanding the humoral response in a wide range of disease areas. Most currently used approaches operate by capturing antibodies onto functionalised surfaces. Such measurements of surface binding are governed by an overall antibody titre, while the two fundamental molecular parameters, antibody affinity and antibody concentration, are challenging to determine individually from such approaches. Here, by applying microfluidic diffusional sizing (MDS), we show how we can overcome this challenge and demonstrate reliable quantification of alloantibody binding affinity and concentration of alloantibodies binding to Human Leukocyte Antigens (HLA), an extensively used clinical biomarker in organ transplantation, both in buffer and in crude human serum. Capitalising on the ability to vary both serum and HLA concentrations during MDS, we show that both affinity and concentration of HLA-specific antibodies can be determined directly in serum when neither of these parameters is known. Finally, we provide proof of principle in clinical transplant patient sera that our assay enables differentiation of alloantibody reactivity against HLA proteins of highly similar structure, providing information not attainable through currently available techniques. These results outline a path towards detection and in-depth profiling of humoral immunity and may enable further insights into the clinical relevance of antibody reactivity in clinical transplantation and beyond.

Impact of Resolved Preformed, Persistent Preformed, and De Novo Anti-HLA Donor-Specific Antibodies in Kidney Transplant Recipients on Long-Term Renal Graft Outcomes

The post-transplant evolution of antihuman leukocyte antigen donor-specific antibodies (anti-HLA DSAs) includes three clinical patterns: resolved preformed DSAs, persistent preformed DSAs, and de novo DSAs. The aim of this retrospective study was to analyze the impact of resolved preformed, persistent preformed, and de novo anti-HLA-A, -B, and -DR DSAs in kidney transplant recipients on long-term renal allograft outcomes. This is a post hoc analysis of the study conducted in our transplant center. One hundred eight kidney transplant recipients were included in the study. Patients were followed for a minimum of 24 months after allograft biopsy, which was performed 3 to 24 months after kidney transplantation. The identification of persistent preformed DSAs at the time of biopsy was the most significant predictor of the combined endpoint of the study (>30% decline in estimated glomerular filtration rate or death-censored graft loss; HR = 5.96, 95% CI 2.041-17.431, p = 0.0011), followed by the occurrence of de novo DSAs (HR = 4.48, 95% CI 1.483-13.520, p = 0.0079). No increased risk was observed in patients with resolved preformed DSAs (HR = 1.10, 95% CI 0.139-8.676, p = 0.9305). Patients with resolved preformed DSAs have similar graft prognoses as patients without DSAs, therefore, the persistence of preformed DSAs and development of de novo DSAs are associated with inferior long-term allograft outcomes.

Donor specific antibody surveillance among pediatric kidney transplant programs: A report from the improving renal outcome collaborative

BACKGROUND

Kidney transplantation (KT) is the preferred treatment for children with end-stage kidney disease. Recent advances in immunosuppression and advances in donor specific antibody (DSA) testing have resulted in prolonged allograft survival; however, standardized approaches for surveillance DSA monitoring and management of de novo (dn) DSA are widely variable among pediatric KT programs.

METHODS

Pediatric transplant nephrologists in the multi-center Improving Renal Outcomes Collaborative (IROC) participated in a voluntary, web-based survey between 2019 and 2020. Centers provided information pertaining to frequency and timing of routine DSA surveillance and theoretical management of dnDSA development in the setting of stable graft function.

RESULTS

29/30 IROC centers responded to the survey. Among the participating centers, screening for DSA occurs, on average, every 3 months for the first 12 months post-transplant. Antibody mean fluorescent intensity and trend most frequently directed changes in patient management. Increased creatinine above baseline was reported by all centers as an indication for DSA assessment outside of routine surveillance testing. 24/29 centers would continue to monitor DSA and/or intensify immunosuppression after detection of antibodies in the setting of stable graft function. In addition to enhanced monitoring, 10/29 centers reported performing an allograft biopsy upon detection of dnDSA, even in the setting of stable graft function.

CONCLUSIONS

This descriptive report is the largest reported survey of pediatric transplant nephrologist practice patterns on this topic and provides a reference for monitoring dnDSA in the pediatric kidney transplant population.

Three patients highlighting potential pitfalls in platelet refractory testing

BACKGROUND

Platelet-transfusion refractory (PR) patients do not achieve expected post-transfusion platelet counts. We investigate suspected PR patients with post-transfusion platelet counts, indirect platelet antibody screens (ind-PAS), Class I HLA antibody tests (HLA-Scr), and physical platelet crossmatch (PXM) studies.

STUDY DESIGN AND METHODS

The three following cases describe possible pitfalls of laboratory tests used in PR workup and management.

RESULTS

Case #1: Antibody testing detected antibodies to only HLA-B13, corresponding to a 4% calculated panel reactive antibodies (CPRA; 96% predicted donor compatibility). However, PXM showed the patient compatible with 11/14 (79%) donors; two of the PXM-incompatible units were ABO-incompatible. Case #2: PXM revealed compatibility with 1/14 screened donors; however, the patient did not respond to the product from the compatible donor. The patient did respond to HLA-matched product. Dilution studies provided evidence of the prozone effect, which caused negative PXM despite clinically relevant antibodies. Case #3: There was a discrepancy between the ind-PAS and HLA-Scr. Ind-PAS was negative for HLA antibodies, while HLA-Scr was positive and specificity testing corresponded to 38% CPRA. Per the package insert, the sensitivity of ind-PAS is ~85% compared to HLA-Scr.

DISCUSSION

These cases highlight the importance of investigating incongruent results. Cases #1 and #2 demonstrate PXM pitfalls: ABO incompatibility can result in positive PXM and false-negative PXM can occur in the setting of the prozone effect. Case #3 reveals the importance of knowing a test's sensitivity. Centers that only perform ind-PAS may fail to detect HLA antibodies.

Virtual crossmatch for deceased donor kidney transplantation in the United States: A survey of histocompatibility lab directors and transplant surgeons

Virtual crossmatch (VXM) is used as an alternative to or in conjunction with a cell-based physical crossmatch (PXM) for assessing HLA (human leukocyte antigen) compatibility prior to deceased donor kidney transplantation (DDKT). Data on practice patterns and perceptions regarding VXM use in the US are limited. We performed a survey of US HLA directors and transplant surgeons regarding HLA testing and crossmatch strategies. 53 (56 %) HLA directors and 68 surgeons (representing ∼ 23 % of US transplant centers) completed the survey. Both groups agreed that VXM could reduce cold ischemia time (CIT), costs and improve allocation efficiency. VXM use increased following the 2021 kidney allocation change. Reducing CIT was the primary reason for favoring VXM over PXM. Preference for VXM reduced as candidates' panel reactive antibodies increased. Regulations, program policies and limitations of HLA technology were cited as important reasons for preferring PXM over VXM. Surgeons reported similar perceptions, but findings are limited by the low response rate. Finally, half the labs reported lacking specific protocols for VXM use. In conclusion, improved HLA technology and protocols along with changes to institutional procedures and policy regulations are needed for safer expansion of VXM in DDKT.

The real unmet need: A multifactorial approach for identifying sensitized kidney candidates with low access to transplant

BACKGROUND

At the start of 2020, the kidney waiting list consisted of 2526 candidates with a calculated panel reactive antibody (CPRA) of 99.9% or greater, a cohort demonstrated in published research to have meaningfully lower than average access to transplantation even under the revised kidney allocation system (KAS).

METHODS

This was a retrospective analysis of US kidney registrations using data from the OPTN [Reference (https://optn.transplant.hrsa.gov/data/about-data/)]. The period-prevalent study cohort consisted of US kidney-alone registrations who waited at least 1 day between April 1, 2016, when HLA DQ-Alpha and DP-Beta unacceptable antigen data became available in OPTN data collection, to December 31, 2019. Poisson rate regression was used to model deceased donor kidney transplant rates per active year waiting and using an offset term to account for differential at-risk periods. Median time to transplant was estimated for each IRR group using the Kaplan-Meier method. Sensitivity analyses were included to address geographic variation in supply-to-demand ratios and differences in dialysis time or waiting time.

RESULTS

In this study, we found 1597 additional sensitized (CPRA 50-<99.9%) candidates with meaningfully lower than average access to transplant when simultaneously taking into account CPRA and other factors. In combination with CPRA, candidate blood type, Estimated Post-Transplant Survival Score (EPTS), and presence of other antibody specificities beyond those in the current, 5-locus CPRA were found to influence the likelihood of transplant.

CONCLUSION

In total, this suggests approximately 4100 sensitized candidates are on the waiting list who represent a community of disadvantaged patients who may benefit from progressive therapies and interventions to facilitate incompatible transplantation. Though associated with higher risks, such interventions may nevertheless be more attractive than remaining on dialysis with the associated accumulation of mortality risk over time.

Impact of pre-transplant donor specific antibodies detected by Luminex with negative microlymphocytotoxicity assay and flow crossmatch in live-related renal transplant recipients

INTRODUCTION/AIM

The Luminex assay, where beads are coated with a single HLA antigen, has been shown to detect HLA antibodies with more sensitivity and specificity as compared to microlymphocytotoxicity (CDC) assay and flow cross match (FCXM). We report the impact of low Mean Flourescence intensity (MFI) pre-transplant DSA by Luminex with negative CDC and FCXM on acute rejection, graft function, and survival.

METHODS

In this retrospective study between January 2015 to December 2021, 45 recipients had pre-transplant anti-HLA donor-specific antibodies (DSAs) detected by Luminex. Two control groups of 45 patients each matched for age and gender, first with non-DSA HLA antibodies and second with no antibodies by Luminex were selected to compare outcomes with DSA group.

RESULTS

In the DSA group of 45, 22 (48.8%) had class I (MFI mean 4043 ± 1909, range: 1096-7111), 20 (44.4%) class II (MFI mean 3601 ± 2310, range: 1031-9259), and 3 (6.6%) both class I (MFI mean 4746 ± 1922) and class II (MFI mean 3940 ± 2312) antibodies. Acute rejection episodes were reported in 15.6%, DSA group, 17.8% in non-DSA, and 24.4% in no antibody group (p = .538). Death censored graft survival at 1 and 5 years was 98% and 93% in DSA group, 100% and 95% in non-DSA and 93% and 85% in the no antibody group (p = .254).

CONCLUSIONS

Patients with low MFI DSA pre-transplant, with a negative CDC and FCXM under ATG induction, have similar graft outcomes at 1 and 5 years when compared to non-DSA and no antibody groups.

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.

Clinical recommendations for posttransplant assessment of anti-HLA (Human Leukocyte Antigen) donor-specific antibodies: A Sensitization in Transplantation: Assessment of Risk consensus document

Although anti-HLA (Human Leukocyte Antigen) donor-specific antibodies (DSAs) are commonly measured in clinical practice and their relationship with transplant outcome is well established, clinical recommendations for anti-HLA antibody assessment are sparse. Supported by a careful and critical review of the current literature performed by the Sensitization in Transplantation: Assessment of Risk 2022 working group, this consensus report provides clinical practice recommendations in kidney, heart, lung, and liver transplantation based on expert assessment of quality and strength of evidence. The recommendations address 3 major clinical problems in transplantation and include guidance regarding posttransplant DSA assessment and application to diagnostics, prognostics, and therapeutics: (1) the clinical implications of positive posttransplant DSA detection according to DSA status (ie, preformed or de novo), (2) the relevance of posttransplant DSA assessment for precision diagnosis of antibody-mediated rejection and for treatment management, and (3) the relevance of posttransplant DSA for allograft prognosis and risk stratification. This consensus report also highlights gaps in current knowledge and provides directions for clinical investigations and trials in the future that will further refine the clinical utility of posttransplant DSA assessment, leading to improved transplant management and patient care.

Relevance of Anti-HLA Antibody Strength Underestimation in Single Antigen Bead Assay for Shared Eplets

BACKGROUND

HLAs contain combinations of multiple eplets, sometimes shared between numerous HLA alleles. Some authors suggested that single antigen bead (SAB) assays may underestimate the signal of anti-HLA antibodies (Ab) when several beads share the targeted eplet. However, this assumption has not yet been validated experimentally.

METHODS

We selected 5 eplets shared by 1-24 beads of the routine SAB kits: the eplet 163LS/G; the 3 eplets 127K, 62GE, and 62GRN thereafter called cross-reactive group 2C; the 82LR eplet, well-known as Bw4; the locally called QB2A5 eplet associated with the DQA1*05:01/DQB1*02:01 combination; and the 40GR DQ eplet. We selected a dozen of sera for each eplet with Ab mean fluorescence intensity (MFI) between 1000 and 15 000 for the beads carrying the targeted eplet. We tested them with the classical SAB panel (SABp), with an isolated bead carrying the eplet (isolated SAB [SABi]) and with a mixture of both (SABp+i).

RESULTS

No significant difference in MFI was detected among SABi, SABp, and SABp+i conditions for all the eplets.

CONCLUSIONS

We noticed only a nonsignificant difference in the Ab MFI signal due to eplet sharing on the SAB assay. We, therefore, conclude that this phenomenon should no longer be considered as a significant risk factor during patient follow-up pre- or posttransplantation.

Entering the Third Decade After Kidney Transplantation: Excellent Graft Function Refers to Superior Graft but Not Patient Survival

Kidney transplant recipients (KTRs) with ultralong-term survival represent a growing, yet insufficiently studied patient cohort. In this single-center retrospective study, we analyzed 248 ultralong-term survivors (≥20 years). KTRs were classified into those with superior graft function (defined as eGFR ≥45 ml/min + proteinuria ≤300 mg/day + eGFR-slope ≤ 2 ml/min/1.73 m2/year) and inferior graft function regarding the risk of CKD progression. 20 years post-transplant, median eGFR was 54 ml/min (11-114), proteinuria 200 mg/24 h (0-7,620), eGFR decline 0.45 ml/min/1.73 m2/year (11.7 6.5) and DSA had been detected in 19.7% of KTRs. We identified 96 KTRs (38.7%) with superior (group 1) and 152 KTRs (61.3%) with inferior graft function (group 2). Donation after cardiac death, female sex, glomerulonephritis as primary disease, and early TCMR were independently associated with inferior graft function. Graft survival was significantly better in group 1 compared to group 2 (LogRank, p < 0.001). Besides group affiliation (HR 20.515, p = 0.003), multivariable analysis identified DSA development (HR 3.081, p = 0.023) and donor age (HR 1.032, p = 0.024) as independent factors. Interestingly, there was no significant difference in patient survival (LogRank, p = 0.350). In ultralong-term survivors, excellent graft function refers to superior graft survival but does not extend ultimate patient survival. DSA-formation should be taken seriously even in the ultralong-term.

Integrated Immunologic Monitoring in Solid Organ Transplantation: The Road Toward Torque Teno Virus-guided Immunosuppression

Potent immunosuppressive drugs have been introduced into clinical care for solid organ transplant recipients. It is now time to guide these drugs on an individual level to optimize their efficacy. An ideal tool simultaneously detects overimmunosuppression and underimmunosuppression, is highly standardized, and is straightforward to implement into routine. Randomized controlled interventional trials are crucial to demonstrate clinical value. To date, proposed assays have mainly focused on the prediction of rejection and were based on the assessment of few immune compartments. Recently, novel tools have been introduced based on a more integrated approach to characterize the immune function and cover a broader spectrum of the immune system. In this respect, the quantification of the plasma load of a highly prevalent and apathogenic virus that might reflect the immune function of its host has been proposed: the torque teno virus (TTV). Although TTV control is driven by T cells, other major immune compartments might contribute to the hosts' response. A standardized in-house polymerase chain reaction and a conformité européenne-certified commercially available polymerase chain reaction are available for TTV quantification. TTV load is associated with rejection and infection in solid organ transplant recipients, and cutoff values for risk stratification of such events have been proposed for lung and kidney transplantation. Test performance of TTV load does not allow for the diagnosis of rejection and infection but is able to define at-risk patients. Hitherto TTV load has not been used in interventional settings, but two interventional randomized controlled trials are currently testing the safety and efficacy of TTV-guided immunosuppression.

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.

Non-HLA Antibodies in Kidney Transplantation: Immunity and Genetic Insights

The polymorphic human leukocyte antigen (HLA) system has been considered the main target for alloimmunity, but the non-HLA antibodies and autoimmunity have gained importance in kidney transplantation (KT). Apart from the endothelial injury, secondary self-antigen exposure and the presence of polymorphic alloantigens, respectively, auto- and allo- non-HLA antibodies shared common steps in their development, such as: antigen recognition via indirect pathway by recipient antigen presenting cells, autoreactive T cell activation, autoreactive B cell activation, T helper 17 cell differentiation, loss of self-tolerance and epitope spreading phenomena. Both alloimmunity and autoimmunity play a synergic role in the formation of non-HLA antibodies, and the emergence of transcriptomics and genome-wide evaluation techniques has led to important progress in understanding the mechanistic features. Among them, non-HLA mismatches between donors and recipients provide valuable information regarding the role of genetics in non-HLA antibody immunity and development.

The Accuracy of Sequence-Specific Oligonucleotide and Real-Time Polymerase Chain Reaction HLA Typing in Determining the Presence of Pre-Transplant Donor-Specific Anti-HLA Antibodies and Total Eplet Mismatches for Deceased Donor Kidney Transplantation

High resolution human leukocyte antigen (HLA) typing is important in establishing eplet compatibility and the specificity of donor-specific anti-HLA antibodies (DSA). In deceased donor kidney transplantation, high resolution donor HLA typing may not be immediately available, leading to inaccuracies during the organ allocation process. We aimed to determine the concordance and agreement of HLA-Class I and II eplet mismatches calculated using population frequency based allelic haplotype association (linkage disequilibrium, LD) from sequence-specific oligonucleotide (SSO) and real-time polymerase chain reaction (rtPCR) donor HLA typing (available at time of donor kidney allocation) compared to high-resolution Next Generation Sequencing (NGS) donor typing. NGS high resolution HLA typing were available for all recipients prior to donor kidney allocation. A cohort of 94 deceased donor-recipient pairs from a single Western Australian center were included (77 individual donors typed, 55 local and 22 interstate). The number of class I (HLA-A+B+C) and class II (HLA-DRB1+DRB3/4/5+DQB1+DQA1+DPB1+DPA1) eplet mismatches were calculated using HLAMatchmaker, comparing LD- and NGS-HLA typing. The accuracy in assigning pre-transplant DSA was compared between methods. The concordance correlation coefficient (95%CI) for HLA-class I and II eplet mismatches were 0.994 (0.992 to 0.996) and 0.991 (0.986 to 0.993), respectively. The 95% limits of agreement for class I were -1.3 (-1.6 to -1.1) to 1.4 (1.2 to 1.7) and -4.8 (-5.7 to -3.9) to 5.0 (4.1 to 5.9) for Class II. Disagreement between the two methods were present for 11 and 37 of the Class I and II donor/recipient pairs. Of which, 5 had a difference of ≥5 class II eplet mismatches. There were 34 (36%) recipients with potential pre-transplant DSA, of which 8 (24% of recipients with DSA) had indeterminate and ultimately false positive DSA assigned by donor LD-typing. While the concordance between NGS- and LD-typing was high, the limits of agreement suggest meaningful differences between these two techniques. The inaccurate assignment of DSA from donor LD-typing may result in associated HLA being considered unacceptable mismatches, inappropriately precluding candidates’ access to transplantation. Accurate imputation of two-field HLA alleles based on LD from SSO and rtPCR HLA typing remains a substantial challenge in clinical practice in-lieu of widely available, rapid, high-resolution methods.

Surrogate Endpoints for Late Kidney Transplantation Failure

In kidney transplant recipients, late graft failure is often multifactorial. In addition, primary endpoints in kidney transplantation studies seek to demonstrate the short-term efficacy and safety of clinical interventions. Although such endpoints might demonstrate short-term improvement in specific aspects of graft function or incidence of rejection, such findings do not automatically translate into meaningful long-term graft survival benefits. Combining many factors into a well-validated model is therefore more likely to predict long-term outcome and better reflect the complexity of late graft failure than using single endpoints. If conditional marketing authorization could be considered for therapies that aim to improve long-term outcomes following kidney transplantation, then the surrogate endpoint for graft failure in clinical trial settings needs clearer definition. This Consensus Report considers the potential benefits and drawbacks of several candidate surrogate endpoints (including estimated glomerular filtration rate, proteinuria, histological lesions, and donor-specific anti-human leukocyte antigen antibodies) and composite scoring systems. The content was created from information prepared by a working group within the European Society for Organ Transplantation (ESOT). The group submitted a Broad Scientific Advice request to the European Medicines Agency (EMA), June 2020: the request focused on clinical trial design and endpoints in kidney transplantation. Following discussion and refinement, the EMA made final recommendations to ESOT in December 2020 regarding the potential to use surrogate endpoints in clinical studies that aim to improving late graft failure.

Presence of Panel-reactive Antibodies after Penetrating Keratoplasty

PURPOSE

To evaluate the relationship between penetrating keratoplasty (PK) and postoperative PRA level and number of unacceptable antigens.

METHODS

A cross-sectionalstudy was performed on patients with history of PK. Patients with prior solid organ transplantation, pregnancy, or blood transfusion were excluded. These findings were combined with a retrospective review. Patients were grouped by single or multiple PKs. The primary outcome was postoperative PRA level.

RESULTS

Incidence of postoperative PRA elevation and mean peak PRA was higher in the multiple PK group (p = .08 and p = .010, respectively). Mean number of unacceptable antigens was elevated in the multiple PK group (p = .024). There was a moderately positive correlation between number of PK grafts and PRA level (r = 0.629, p = .0002).

CONCLUSIONS

PRA level may be influenced by PKs, with higher PRA associated with increased prior PKs. Further studies are necessary to determine the potential prognostic value.Abbreviations: PK: penetrating keratoplasty; PRA: panel reactive antibodies; OSST: ocular surface stem cell transplantation; LSCD: limbal stem cell deficiency.

The Clinical Impact of Anti-HLA Donor Specific Antibody Detection Through First Year Screening on Stable Kidney Transplant Recipients

Anti-HLA Donor Specific Antibody (DSA) detection post kidney transplant has been associated with adverse outcomes, though the impact of early DSA screening on stable patients remain unclear. We analyzed impact of DSA detection through screening in 1st year stable patients (n = 736) on subsequent estimated glomerular filtration rate (eGFR), death censored graft survival (DCGS), and graft failure (graft loss including return to dialysis or re-transplant, patient death, or eGFR < 20 ml/min at last follow up). Patients were grouped using 1st year screening into DSA+ (Class I, II; n = 131) or DSA- (n = 605). DSA+ group were more DR mismatched (p = 0.02), more sensitized (cPRA ≥90%, p = 0.002), less Caucasian (p = 0.04), and had less pre-emptive (p = 0.04) and more deceased donor transplants (p = 0.03). DSA+ patients had similar eGFR (54.8 vs. 53.8 ml/min/1.73 m², p = 0.56), DCGS (91% vs. 94%, p = 0.30), and graft failure free survival (76% vs. 82%, p = 0.11). DSA timing and type did not impact survival. Among those with a protocol biopsy (n = 515), DSA detected on 1st year screening was a predictor for graft failure on multivariate analysis (1.91, 95% CI 1.03-3.55, p = 0.04). Overall, early DSA detection in stable patients was an independent risk factor for graft failure, though only among those who underwent a protocol biopsy.

Clinical characteristics of renal transplant recipients who developed de novo donor-specific antigen in Kyoto University Hospital: a case series

Background

The clinical significance of de novo donor-specific antigen (DSA) in renal transplant recipients is not yet fully understood. This study aimed to report the prevalence of de novo DSA detected in antihuman leukocyte antigen (HLA) antibody testing and to evaluate the association between de novo DSA and renal transplant prognosis in living-donor renal transplant recipients at our hospital.

Methods

Of the 110 patients who underwent living-donor renal transplantation from 1980 to 2019, 80 patients who underwent anti-HLA antibody screening tests were retrospectively reviewed for the development of de novo DSA and outcomes regarding graft function.

Results

The mean age at transplantation was 43.2 ± 14.6 years. Of the 80 patients, 43 (53.8%) were men and 68 (85.0%) underwent ABO-compatible transplantation. Anti-HLA antibody was detected in 14 patients (17.5%), including eight (10.0%) with de novo DSA. Graft loss occurred in two (25%) of the eight patients with de novo DSA, none of the six patients with non-DSA anti-HLA antibody and no anti-HLA antibody (P = 0.0419, log-rank test). The mean estimated glomerular filtration rate at the time of the anti-HLA antibody test was 45.1 ± 14.4 mL/min/1.73m2 in the 66 patients with no anti-HLA antibody, while it was 35.0 ± 11.5 mL/min/1.73m2 in the eight patients with de novo DSA (P = 0.0702) and 39.3 ± 15.3 mL/min/1.73m2 in the six patients with non-DSA anti-HLA antibody (P = 0.3921). The mean monthly cyclosporin A trough concentration for the past year from the anti-HLA antibody test was 59.2 ± 24.8 ng/ml in the seven patients with no anti-HLA antibody, while it was 61.9 ± 12.5 ng/ml in the five patients with de novo DSA (P = 0.5670) and 36.3 ± 9.0 ng/ml in a patient with non-DSA anti-HLA antibody (P = 0.3921). The mean monthly tacrolimus trough concentration for the past year from the anti-HLA antibody test was 4.62 ± 1.20 ng/ml in the 55 patients with no anti-HLA antibody, while it was 4.09 ± 1.10 ng/ml in the three patients with de novo DSA (P = 0.0027) and 4.21 ± 1.14 ng/ml in the four patients with non-DSA anti-HLA antibody (P = 0.0722).

Conclusions

The optimal treatment for patients with de novo DSA has not been established, and immunosuppressive management that suppresses the development of de novo DSA is essential.

Predictive Potential of Flow Cytometry Crossmatching in Deceased Donor Kidney Transplant Recipients Subjected to Peritransplant Desensitization

Recipient sensitization is a major risk factor of antibody-mediated rejection (ABMR) and inferior graft survival. The predictive effect of solid-phase human leukocyte antigen antibody testing and flow cytometry crossmatch (FCXM) in the era of peritransplant desensitization remains poorly understood. This observational retrospective single-center study with 108 donor-specific antibody (DSA)-positive deceased donor kidney allograft recipients who had undergone peritransplant desensitization aimed to analyze variables affecting graft outcome. ABMR rates were highest among patients with positive pretransplant FCXM vs. FCXM-negative (76 vs. 18.7%, p < 0.001) and with donor-specific antibody mean fluorescence intensity (DSA MFI) > 5,000 vs. <5,000 (54.5 vs. 28%, p = 0.01) despite desensitization. In univariable Cox regression, FCXM positivity, retransplantation, recipient gender, immunodominant DSA MFI, DSA number, and peak panel reactive antibodies were found to be associated with ABMR occurrence. In multivariable Cox regression adjusted for desensitization treatment (AUC = 0.810), only FCXM positivity (HR = 4.6, p = 0.001) and DSA number (HR = 1.47, p = 0.039) remained significant. In conclusion, our data suggest that pretransplant FCXM and DSA number, but not DSA MFI, are independent predictors of ABMR in patients who received peritransplant desensitization.

HLA Desensitization Based on Results of the Luminex Technique in Kidney Transplant - A Single-center Experience

Background:

There is little experience of human leucocyte antigen (HLA) desensitization in India based on the Luminex single-antigen bead (SAB) testing. We retrospectively analyzed our patients, who underwent HLA desensitization based on Luminex SAB results.

Method:

Between 2014 and 2018, patients with complement-dependent cytotoxicity cross-match (CDC-XM) negativity but flow cytometry crossmatch (FC-XM) positivity were further analyzed with Luminex SAB for donor-specific antibodies (DSAs). A total of 12 patients who had DSA mean fluorescent intensity (MFI) of >1000 and <10,000 were included in the study. Our protocol for desensitization consisted of plasmapheresis (PP) followed by low dose intravenous immunoglobulin (IV IG) 100 mg/kg and induction with antithymocyte globulin (ATG). Patients were taken for transplant when either MFI was <1000 and/or FC-XM was negative.

Results:

All 12 patients were first transplant and 10 had a history of some sensitizing event; pregnancy in 4, blood transfusions in 4, and both in 2 patients. FC-XM was positive for T-cell in 4, B-cell in 6, and both in 2 patients. On evaluation by Luminex SAB, 6 patients had MFI from 1000 to 2000, and 6 had MFI of >2000. All underwent desensitization successfully. Two patients had an increase in posttransplant DSA titers requiring posttransplant PP. The mean follow-up was 26.6 ± 13.9 months. On follow-up, only one patient developed acute T cell-mediated rejection 1 year after transplant, which responded to pulse steroids. There was no graft or patient loss until the last follow-up.

Conclusion:

This study shows that HLA desensitization is feasible and successful in the Indian setting if patients are properly selected.

Crossmatch, Donor-specific Antibody Testing, and Immunosuppression in Simultaneous Liver and Kidney Transplantation: A Review

Since the introduction of simultaneous liver-kidney transplantation (SLKT) in the 1960s, the potential for immunological protection from the liver allograft to a simultaneously transplanted kidney has been recognized. Due to expanded indications and changes in allocation policies, there has been increased utilization of SLKT. Despite growing experience, a lack of consensus exists regarding the extent of the immunological privilege of the liver the role for donor-specific HLA antibody (DSA) and crossmatch testing, and appropriateness of modern immunosuppression protocols in SLKT recipients. This review provides a detailed analysis of SLKT outcomes in the context of these factors, suggesting that although the liver can reduce the incidence of antibody-mediated rejection, attention should be given to liver allograft function, previous failed transplants, and other risk factors in pretransplant risk assessment. Current methods of DSA and crossmatch testing in SLKT are also discussed, and the role of specific DSA (high mean fluorescence intensity antibody, C1q+ binding) and their potential importance in posttransplant risk assessment are examined. Finally, trends in SLKT immunosuppression are discussed, including the use of nondepleting agents for induction and de-escalating use of steroids for maintenance immunosuppression. Ongoing research, including multicenter or randomized trials, will be necessary to optimize immune-related outcomes in SLKT recipients.

Donor-Specific Antibody Is Associated with Increased Expression of Rejection Transcripts in Renal Transplant Biopsies Classified as No Rejection

BACKGROUND

Donor -specific HLA antibody (DSA) is present in many kidney transplant patients whose biopsies are classified as no rejection (NR). We explored whether in some NR kidneys DSA has subtle effects not currently being recognized.

METHODS

We used microarrays to examine the relationship between standard-of-care DSA and rejection-related transcript increases in 1679 kidney transplant indication biopsies in the INTERCOMEX study (ClinicalTrials.gov NCT01299168), focusing on biopsies classified as NR by automatically assigned archetypal clustering. DSA testing results were available for 835 NR biopsies and were positive in 271 (32%).

RESULTS

DSA positivity in NR biopsies was associated with mildly increased expression of antibody-mediated rejection (ABMR)-related transcripts, particularly IFNG-inducible and NK cell transcripts. We developed a machine learning DSA probability (DSA_Prob) classifier based on transcript expression in biopsies from DSA-positive versus DSA-negative patients, assigning scores using 10-fold cross-validation. This DSA_Prob classifier was very similar to a previously described "ABMR probability" classifier trained on histologic ABMR in transcript associations and prediction of molecular or histologic ABMR. Plotting the biopsies using Uniform Manifold Approximation and Projection revealed a gradient of increasing molecular ABMR-like transcript expression in NR biopsies, associated with increased DSA (P<2 × 10^-16). In biopsies with no molecular or histologic rejection, increased DSA_Prob or ABMR probability scores were associated with increased risk of kidney failure over 3 years.

CONCLUSIONS

Many biopsies currently considered to have no molecular or histologic rejection have mild increases in expression of ABMR-related transcripts, associated with increasing frequency of DSA. Thus, mild molecular ABMR-related pathology is more common than previously realized.

Influence of a low-dose tacrolimus protocol on the appearance of de novo donor-specific antibodies during 7 years of follow-up after renal transplantation

BACKGROUND

Tacrolimus (TAC) is a key immunosuppressant drug for kidney transplantation (KTx). However, the optimal serum trough level of TAC for good long-term outcomes remains unclear. This study aimed to investigate the relationship between the maintenance TAC trough level and the appearance of de novo donor-specific anti-human leukocyte antigen (HLA) antibodies (dnDSAs).

METHODS

A total of 584 KTx recipients were enrolled in this study, of whom 164 developed dnDSAs during the follow-up period and 420 did not.

RESULTS

We found no significant relationship between TAC trough level during the follow-up period and dnDSA incidence. Patients who developed dnDSAs had a significantly greater number of HLA-A/B/DR mismatches (3.4 ± 1.3 versus 2.8 ± 1.5; P < 0.001), were more likely to have preformed DSAs (48.2% versus 27.1%; P < 0.001) and showed poor allograft outcome.

CONCLUSIONS

There was no clear relationship between TAC trough level and dnDSA incidence for KTx recipients whose TAC trough levels were kept within the narrow range of 4-6 ng/mL during the immunosuppression maintenance period.

Long-term outcomes of sensitized lung transplant recipients after peri-operative desensitization

The Toronto Lung Transplant Program has been using a peri-operative desensitization regimen of plasma exchange, intravenous immune globulin, and antithymocyte globulin in order to accept donor-specific antibody (DSA)-positive lung transplants safely since 2008. There are no long-term data on the impact of this practice on allograft survival or the development of chronic lung allograft dysfunction (CLAD). We extended our prior study to include long-term follow-up of 340 patients who received lung transplants between January 1, 2008 and December 31, 2011. We compared allograft survival and CLAD-free survival among patients in three cohorts: DSA-positive, panel reactive antibody (PRA)-positive/DSA-negative, and unsensitized at the time of transplant. The median follow-up time in this extension study was 6.7 years. Among DSA-positive, PRA-positive/DSA-negative, and unsensitized patients, the median allograft survival was 8.4, 7.9, and 5.8 years, respectively (p = .5908), and the median CLAD-free survival was 6.8, 7.3, and 5.7 years, respectively (p = .5448). This follow-up study confirms that long-term allograft survival and CLAD-free survival of patients who undergo DSA-positive lung transplants with the use of our protocol do not differ from other lung transplant recipients. Use of protocols such as ours, therefore, may improve access to transplant for sensitized candidates.

Appearance of new CDC-reactive antibodies in patients waiting for kidney transplantation

BACKGROUND

Patients awaiting kidney transplantation are regularly screened for HLA-antibodies, but there is scarce data about the optimal interval.

METHODS

Results from Complement-dependent cytotoxicity testing (CDC) for waitlisted patients were reviewed for increases in panel reactive antibodies (PRA) by at least 10%-points. Clinical records were screened for historic immunizing events and possible trigger factors preceding the PRA-increase. Additionally, non-pretransplanted men tested negative for HLA antibodies by solid-phase assays (SPA) out of their first two samples on the waiting list ("non-immunized men") were evaluated for detection of HLA antibodies by SPA during their further stay on the waiting list.

RESULTS

15,360 samples from 1928 patients tested by CDC were analyzed for changes in PRA. PRA-increases occurred most frequently in patients waitlisted recently for retransplantation (annual incidence 6%). Removal of previous transplants, severe infections and/or reduced immunosuppression triggered 65% of PRA-increases during the first year after waitlisting. Transfusions accounted for 55% of PRA-increases in later years. Leucocyte-reduced red blood cell units not only boosted historic antibodies, but even induced primary immunization. In the second part of the study, 6780 samples tested by SPA from 703 non-immunized men were evaluated for development of HLA-antibodies. Only 9 men (1.3%) turned HLA antibody-positive (annual incidence 0.4%).

CONCLUSION

A uniform screening interval does not fit all: Frequencies should be highest in patients newly waitlisted for re-transplant and lowest in non-immunized men. Transfused patients should be monitored closely for development of HLA-antibodies even if leukoreduced products are used.

The emerging field of non-human leukocyte antigen antibodies in transplant medicine and beyond

The major medical advances in our knowledge of the human leukocyte antigen (HLA) system have allowed us to uncover several gaps in our understanding of alloimmunity. Although the non-HLA system has long sparked the interest of the transplant community, recognition of the role of immunity to non-HLA antigenic targets has only emerged recently. In this review, we will provide a comprehensive summary of the paradigm-changing concept of immunity to the non-HLA angiotensin II type 1 receptor (AT1R), discovered by Duška Dragun et al., that began from careful bedside clinical observations, to validated detection of anti-AT1R antibodies and lead to clinical intervention. This scientific approach has also allowed the recognition of broader pathogenicity of anti-AT1R antibodies across multiple organ transplants and in other human diseases, the integration of both non-HLA and HLA systems to understand their immunologic effects on organ allografts, and the identification of future directions for therapeutic intervention to modulate immunity to AT1R. Rationally designed successful interventions to target AT1R system provide an exemplar for other non-HLA antibodies to cross borders between medical specialties, will generate new avenues in translational research beyond transplantation, and will foster the development of new and reliable tools to improve our understanding of non-HLA immunity and ultimately allow us to improve patient care.

De novo donor-specific HLA antibodies reduce graft survival rates and increase the risk of kidney transplant rejection: A single-center retrospective study

BACKGROUND

We investigated the impact of de novo donor-specific anti-human leukocyte antigen antibodies (dnDSAs) on long-term death-censored graft survival and renal allograft rejection in kidney transplant recipients.

METHODS

The sample for this retrospective cohort study comprised 121 recipients of kidney transplants with negative complement-dependent cytotoxicity crossmatches to their deceased donors. Recipients were divided into two groups: dnDSAs+ (n = 31) and dnDSAs- (n = 90). We evaluated rejection and long-term graft survival rates in the recipients along with pathologic changes in the transplanted kidneys.

RESULTS

DnDSAs were identified in 31/121 patients (25.6%). The graft survival rate in the dnDSAs+ group was 87.1% (27/31) and that of the dnDSAs- group was 97.8% (88/90). The dnDSAs+ group had lower graft survival rates than patients without dnDSAs (p = 0.007). There was no difference in the graft survival rates between patients with high DSA mean fluorescence intensity (≥4000) and those with low intensity (<4000) (p = 0.669). There was also no difference in the graft survival rates of patients with HLA class I, II, and I + II dnDSAs (p = 0.571). The presence of dnDSA in serum was associated with a higher incidence of antibody- and T-cell-mediated rejection (p < 0.0001). Banff scores for arterial fibrointimal and arteriolar hyalin, thickening as well as C4d deposition differed for the dnDSAs+ and dnDSAs- groups (p < 0.05).

CONCLUSION

DnDSAs were found to be associated with decreased long-term graft survival rates and increased rejection rates, often accompanied by C4d deposition.

Measuring human leukocyte antigen alloantibodies: beyond a binary decision

PURPOSE OF REVIEW

Accurate measurement of human leukocyte antigen antibodies is critical for making clinical decisions treating patients awaiting transplantation or monitoring them post transplantation. Single antigen bead assay results are given as Mean Fluorescence Intensity, falling short of providing the required quantitative measure.

RECENT FINDINGS

Titration studies were shown to circumvent the limitation of target-saturation that affect interpretation of single antigen bead assays especially in highly sensitized patients with strong antibodies. In fact, titration information can serve to measure efficacy of antibody removal during pretransplant desensitization using plasmapheresis/intravenous immunoglobulin (PP/IVIg) approaches. Moreover, recent studies indicate that knowing the donor-specific antibody titer has prognostic value that can guide PP/IVIg desensitization treatments. Newer data demonstrates an additional layer of information obtained by titration studies allowing to stratify patients with very high cPRA (>99%) based on the strength of the antibodies present, rather than the breadth. This data can thereby identify patients that are more likely to benefit from desensitization approaches on the transplant wait-list.

SUMMARY

Titration studies have a prognostic value with regards to quantifying antibody strength. Obtaining this information does not require performing the complete set of dilutions. In fact, performing two to three specific dilutions can provide relevant information while maintaining practical cost.