Mitigating the Prozone-Like Effect in HLA Antibody Testing: A Case Report of Therapeutic Plasma Exchange for Antibody-Mediated Rejection Post-Heart Transplantation.

Therapeutic plasma exchange (TPE) is a cornerstone treatment for antibody-mediated rejection (AMR) post-organ transplantation, aiming to eliminate pathogenic donor-specific HLA antibodies (DSA). However, limitations in HLA antibody interpretation due to the prozone-like effect (PLE) can lead to inaccurate assessment of treatment efficacy. We present a case of a heart transplant recipient with suspected AMR, where an unexpected increase in DSA levels post-TPE prompted investigation into PLE. Solid-phase Luminex assays were employed to detect HLA antibodies. Serum was run neat as well as after treatment with ethylenediaminetetraacetic acid (EDTA). Nephelometry was used to detect complement levels. Laboratory analysis of pre-TPE serum revealed higher DSA levels with EDTA treatment, characteristic of PLE. Complement measurements supported complement-mediated interference in the pre-TPE sample. This case underscores the importance of being aware that PLE can occur in HLA testing and can impact the interpretation of TPE efficacy for AMR.

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.

Sensitization in transplantation: Assessment of Risk 2022 Working Group Meeting Report.

The Sensitization in Transplantation: Assessment of Risk workgroup is a collaborative effort of the American Society of Transplantation and the American Society of Histocompatibility and Immunogenetics that aims at providing recommendations for clinical testing, highlights gaps in current knowledge, and proposes areas for further research to enhance histocompatibility testing in support of solid organ transplantation. This report provides updates on topics discussed by the previous Sensitization in Transplantation: Assessment of Risk working groups and introduces 2 areas of exploration: non-human leukocyte antigen antibodies and utilization of human leukocyte antigen antibody testing measurement to evaluate the efficacy of antibody-removal therapies.

Loss of heterozygosity leading to incorrect HLA typing for platelet-transfusion refractory patient.

BACKGROUND: Management of platelet-transfusion refractory (PR) patients due to anti-HLA antibodies includes the provision of HLA-matched (HLAm) platelets (PLT) or PLTs that are negative for HLA antigens corresponding to the recipient antibodies. Obtaining HLAm PLTs is predicated on accurate HLA antigen typing of the recipient and donor. Here, we present the clinical implications of a case involving loss of heterozygosity (LOH) in a patient presented for PR workup. STUDY DESIGN AND METHODS: HLA typing was performed by three methods: (1) Real-time PCR; (2) Sequence-specific oligonucleotide (SSO) typing test; and (3) Next-Generation Sequencing (NGS). Cytogenomic SNP microarray was utilized to assess LOH. RESULTS: A 30-year-old female with newly diagnosed acute myelogenous leukemia was found to be PR secondary to HLA sensitization. A peripheral blood (PB) sample, containing 93% myeloid blast cells, was sent for HLA typing for the provision of HLAm PLTs. HLA typing revealed homozygosity at the HLA-A locus but was heterozygous at the -B and -C loci. After chemotherapy, HLA typing on a new PB sample, devoid of blast cells, identified HLA-A locus heterozygosity, which was subsequently confirmed by real-time PCR and NGS. Cytogenomic SNP microarray analysis demonstrated LOH of the HLA-A locus on chromosome 6p in the pretreatment sample but not in the posttreatment sample. CONCLUSION: In hematologic patients with high tumor burden, HLA homozygosity should be viewed with suspicion for potential LOH. Therefore, HLA testing should be repeated, preferably with a non-hematological source (e.g., buccal swab) or following successful reduction of the tumor burden.

ABO-adjusted calculated panel reactive antibody (cPRA): A unified metric for immunologic compatibility in kidney transplantation.

Implementation of the kidney allocation system in 2014 greatly reduced access disparity due to human leukocyte antigen (HLA) sensitization. To address persistent disparity related to candidate ABO blood groups, herein we propose a novel metric termed "ABO-adjusted cPRA," which simultaneously considers the impact of candidate HLA and ABO sensitization on the same scale. An ethnic-weighted ABO-adjusted cPRA value was computed for 190 467 candidates on the kidney waitlist by combining candidate's conventional HLA cPRA with the remaining fraction of HLA-compatible donors that are ABO-incompatible. Consideration of ABO sensitization resulted in higher ABO-adjusted cPRA relative to conventional cPRA by HLA alone, except for AB candidates since they are not ABO-sensitized. Within cPRA Point Group = 99%, 43% of the candidates moved up to ABO-adjusted cPRA Point Group = 100%, though this proportion varied substantially by candidate blood group. Nearly all O and most B candidates would have elevated ABO-adjusted cPRA values above this policy threshold for allocation priority, but relatively few A candidates displayed this shift. Overall, ABO-adjusted cPRA more accurately measures the proportion of immune-compatible donors compared with conventional HLA cPRA, especially for highly sensitized candidates. Implementation of this novel metric could enable the development of allocation policies permitting more ABO-compatible transplants without compromising equity.

Delayed Kinetics of IgG, but Not IgA, Antispike Antibodies in Transplant Recipients following SARS-CoV-2 Infection.

BACKGROUND: Kidney transplant recipients are at increased risk of severe outcomes during COVID-19. Antibodies against the virus are thought to offer protection, but a thorough characterization of anti-SARS-CoV-2 immune globulin isotypes in kidney transplant recipients following SARS-CoV-2 infection has not been reported. METHODS: We performed a cross-sectional study of 49 kidney transplant recipients and 42 immunocompetent controls at early (≤14 days) or late (>14 days) time points after documented SARS-CoV-2 infection. Using a validated semiquantitative Luminex-based multiplex assay, we determined the abundances of IgM, IgG, IgG1-4, and IgA antibodies against five distinct viral epitopes. RESULTS: Kidney transplant recipients showed lower levels of total IgG antitrimeric spike (S), S1, S2, and receptor binding domain (RBD) but not nucleocapsid (NC) at early versus late time points after SARS-CoV-2 infection. Early levels of IgG antispike protein epitopes were also lower than in immunocompetent controls. Anti-SARS-CoV-2 antibodies were predominantly IgG1 and IgG3, with modest class switching to IgG2 or IgG4 in either cohort. Later levels of IgG antispike, S1, S2, RBD, and NC did not significantly differ between cohorts. There was no significant difference in the kinetics of either IgM or IgA antispike, S1, RBD, or S2 on the basis of timing after diagnosis or transplant status. CONCLUSIONS: Kidney transplant recipients mount early anti-SARS-CoV-2 IgA and IgM responses, whereas IgG responses are delayed compared with immunocompetent individuals. These findings might explain the poor outcomes in transplant recipients with COVID-19. PODCAST: This article contains a podcast at https://www.asn-online.org/media/podcast/JASN/2021_11_23_briggsgriffin112321.mp3.

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

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

The impact of belatacept on third-party HLA alloantibodies in highly sensitized kidney transplant recipients.

Recent evidence suggests that belatacept reduces the durability of preexisting antibodies to class I and class II human leukocyte antigens (HLAs). In this case series of 163 highly sensitized kidney transplant candidates whose calculated panel-reactive antibody (cPRA) activity was ≥98% to 100%, the impact of belatacept on preexisting HLA antibodies was assessed. Of the 163 candidates, 72 underwent transplantation between December 4, 2014 and April 15, 2017; 60 of these transplanted patients remained on belatacept consecutively for at least 6 months. We observed a decrease in the breadth and/or strength of HLA class I antibodies as assessed by FlowPRA in belatacept-treated patients compared to controls who did not receive belatacept. Specifically, significant HLA antibody reduction was evident for class I (P < .0009). Posttransplant belatacept-treated patients also had a clinically significant reduction in their cPRA compared to controls (P < .01). Collectively, these findings suggest belatacept can reduce HLA class I antibodies in a significant proportion of highly sensitized recipients and could be an option to improve pretransplant compatibility with organ donors.

Evidence of Chronic Allograft Injury in Liver Biopsies From Long-term Pediatric Recipients of Liver Transplants.

BACKGROUND & AIMS: A substantial proportion of pediatric liver transplant recipients develop subclinical chronic allograft injury. We studied whether there are distinct patterns of injury based on histopathologic features and identified associated immunologic profiles. METHODS: We conducted a cross-sectional study of 157 stable, long-term pediatric recipients of transplanted livers (70 boys; > 6 years old at time of transplantation; mean, 8.9 ± 3.46 years after liver transplantation) who underwent liver biopsy analysis from August 13, 2012, through May 1, 2014. Participants had received livers from a living or deceased donor and had consistently normal results from liver tests. Liver biopsy specimens were scored by a central pathologist; an unsupervised hierarchical cluster analysis of histologic features was used to sort biopsy samples into 3 clusters. We conducted transcriptional and cytometric analyses of liver tissue samples and performed a systems biology analysis that incorporated clinical, serologic, histologic, and transcriptional data. RESULTS: The mean level of alanine aminotransferase in participants was 27.6 ± 14.57 U/L, and the mean level of γ-glutamyl transferase was 17.4 ± 7.93 U/L. Cluster 1 was characterized by interface activity (n = 34), cluster 2 was characterized by periportal or perivenular fibrosis without interface activity (n = 45), and cluster 3 had neither feature (n = 78). We identified a module of genes whose expression correlated with levels of alanine aminotransferase, class II donor-specific antibody, portal inflammation, interface activity, perivenular inflammation, portal and perivenular fibrosis, and cluster assignment. The module was enriched in genes that regulate T-cell-mediated rejection (TCMR) of liver and other transplanted organs. Functional pathway analysis showed overrepresentation of TCMR gene sets for cluster 1 but not clusters 2 or 3. CONCLUSION: In an analysis of biopsies from an apparently homogeneous group of stable, long-term pediatric liver transplant recipients with consistently normal liver test results, we found evidence of chronic graft injury (inflammation and/or fibrosis). Biopsy samples with interface activity had a gene expression pattern associated with TCMR.

A diagnostic 'C' saw: the ups and downs of C1q testing.

PURPOSE OF REVIEW: The present review will focus on recently published data of solid organ allograft recipients reporting that patients with de-novo donor-specific HLA antibodies (DSA) that fix complement in vitro have a significantly higher risk for antibody-mediated rejection (AMR) and/or graft loss compared to patients whose de-novo DSA do not fix complement or patients who present with preexisting complement fixing DSA. RECENT FINDINGS: HLA DSAs that fix complement in vitro appear to be a key indicator for rejection and failure of kidney, heart, and lung allografts from studies performed around the world. The majority of these studies are population based and retrospective in nature. Although these studies seemingly indicate that in-vitro complement activating DSAs represent a higher clinical risk than noncomplement fixing DSAs, the majority have not accounted for false-negative reactions attributable to the so-called prozone/interference phenomenon. In the limited number of published studies addressing that concern, high mean fluorescence intensity (MFI) value noncomplement fixing DSAs correlate as well as complement fixing DSAs with AMR and graft loss. Combined with the cost of additional testing, these observations bring into question whether there is sufficient clinical applicability to warrant routine testing for complement fixing antibodies. SUMMARY: Complement fixing DSAs are clearly associated with AMR and/or loss of transplanted allografts. However, under appropriate testing conditions, complement fixing capability typically correlates with MFI values of the DSAs. As such, the routine implementation of in-vitro assays to determine whether DSAs fix complement is of questionable value especially when considering additional issues such as cost of testing, logistics, and whether the test results factor into individualized patient care.

Comparison of de novo IgM and IgG anti-HLA DSAs between belatacept- and calcineurin-treated patients: An analysis of the BENEFIT and BENEFIT-EXT trial cohorts.

Preventing conversion of donor-specific anti-HLA antibodies (DSAs) from an IgM-to-IgG could a way to prevent chronic rejection. We evaluated whether belatacept-treated patients (belatacept less-intensive [LI] or more-intensive [MI] regimens) have a lower rate of conversion than do cyclosporine A (CsA)-treated patients. We included 330 HLA-mismatched patients from 2 phase 3 trials with either (a) complete donor/recipient HLA-A, -B, -DR, and -DQ loci typing or (b) incomplete HLA typing with IgG DSAs detected pretransplant or posttransplant. IgM and IgG DSAs were tested with single antigen beads at 0, 6, 12, 24, and 36 months posttransplant. The overall (preexisting or de novo) rates of IgM- and IgG-positive DSAs were 29% and 34%, respectively. The pretransplant IgM and IgG DSA-positive frequencies were similar between treatment groups. The IgG-positive dnDSA rate was significantly higher in the CsA-treated group (34%) compared with the belatacept-LI (8%) and belatacept-MI (11%) (P < .001) groups. In IgM-positive dnDSA patients, the IgG-positive dnDSA rate of conversion was 2.8 times higher in the CsA group than in the combined belatacept groups (P = .006). However, the observed association between belatacept treatment and more limited conversion of IgM-to-IgG dnDSAs was based on a limited number of patients and requires further validation.

Sensitization in Transplantation: Assessment of Risk (STAR) 2017 Working Group Meeting Report.

The presence of preexisting (memory) or de novo donor-specific HLA antibodies (DSAs) is a known barrier to successful long-term organ transplantation. Yet, despite the fact that laboratory tools and our understanding of histocompatibility have advanced significantly in recent years, the criteria to define presence of a DSA and assign a level of risk for a given DSA vary markedly between centers. A collaborative effort between the American Society for Histocompatibility and Immunogenetics and the American Society of Transplantation provided the logistical support for generating a dedicated multidisciplinary working group, which included experts in histocompatibility as well as kidney, liver, heart, and lung transplantation. The goals were to perform a critical review of biologically driven, state-of-the-art, clinical diagnostics literature and to provide clinical practice recommendations based on expert assessment of quality and strength of evidence. The results of the Sensitization in Transplantation: Assessment of Risk (STAR) meeting are summarized here, providing recommendations on the definition and utilization of HLA diagnostic testing, and a framework for clinical assessment of risk for a memory or a primary alloimmune response. The definitions, recommendations, risk framework, and highlighted gaps in knowledge are intended to spur research that will inform the next STAR Working Group meeting in 2019.

Stability of anti-A blood group titers among blood group B renal transplant candidates.

BACKGROUND: As deceased donor kidney allocation is based in part on blood type compatibility, group B candidates are disadvantaged due to their disproportionate representation on the wait list compared to the group B donor pool. To mitigate this discrepancy, group B candidates can receive group A2 or A2 B donor kidneys if their anti-A titers are below a predetermined cutoff. Currently, eligibility is reverified quarterly to UNet based on individual center protocols, which can vary due to a lack of set guidelines for monitoring ABO titers in these patients. Our goal was to assess the stability of anti-A titers in blood group B renal transplant candidates over time to provide data that could aid in the development of standardized ABO titer protocols. STUDY DESIGN AND METHODS: Titers performed between January 2011 and December 2015 were assessed for 191 group B patients with two or more documented titers. RESULTS: Fifty patients (26%) were ineligible, as the first titer exceeded the cutoff of 8. Of the remaining 141 patients, 19 (13%) became ineligible as the second titer exceeded 8. Thirty-nine patients (28%) had no change in titer between samples, while 71 (50%) had a titer change that never exceeded 8. Only 12 patients (8.5% of total) experienced a titer change that affected eligibility after the second test. CONCLUSION: Although patients experience some variability in anti-A titers over time, in most cases, stability did not affect candidate eligibility. Our results indicate that regular testing beyond the second titer may be unnecessary and represent test overutilization.

De novo DQ donor-specific antibodies are associated with worse outcomes compared to non-DQ de novo donor-specific antibodies following heart transplantation.

BACKGROUND: Antibody-mediated rejection (AMR) resulting from de novo donor-specific antibodies (dnDSA) leads to adverse outcomes following heart transplantation (HTx). It remains unclear what role dnDSA to specific HLA antigens play in adverse outcomes. This study compares outcomes in patients developing dnDSA to DQ antigens with those developing non-DQ dnDSA and those free from dnDSA. METHODS: The present study was a single-center, retrospective analysis of 122 consecutive HTx recipients. The primary outcome was a composite of death or graft dysfunction. RESULTS: After 3.3 years of follow-up, 31 (28%) patients developed dnDSA. Mean time to dnDSA was 539 days. Of 31 patients, 19 developed DQ antibodies and 12 developed non-DQ antibodies. Compared to non-DQ dnDSA, DQ antibodies presented with higher MFI values (P=.001) were more likely persistent (P=.001) and appeared later post-HTx (654 vs 359 days, P=.035). In a multivariable analysis, DQ dnDSA was associated with increased risk of the primary endpoint (HR 6.15, 95% CI 2.57-14.75, P=.001), whereas no increased risk was seen with non-DQ dnDSA (P=.749). CONCLUSIONS: dnDSA to DQ antigens following HTx are associated with increased risk of death and graft dysfunction.

Becoming a chef in the human leukocyte antigen kitchen: interpretation and modification of human leukocyte antigen-antibody assays.

PURPOSE OF REVIEW: Fluorescence-based human leukocyte antigen (HLA) antibody detection methods, including flow cytometric crossmatch and single antigen bead assays revolutionized HLA antibody identification and assessment of immunological risk in transplant candidates and patients. Nevertheless, these assays are not flawless and their interpretation can be complex. This review highlights the limitations of the single antigen bead and flow cytometric crossmatch assays and discusses protocol modifications and interpretive approaches to address these issues. RECENT FINDINGS: Several limitations of HLA antibody detection methods have been identified in recent years. Protocol variability, denatured epitopes, and interfering factors can all significantly impact the identification of clinically relevant HLA antibodies. A number of solutions to address these challenges have been developed. These include pretreatment of sera, method standardization, and protocol modifications. In addition, HLA epitope-based analysis approaches to improve interpretation of antibody test results have been introduced. SUMMARY: In the 50 years, since Patel and Terasaki first developed the crossmatch assay there have been remarkable advances in HLA antibody testing methodology. However, with these advances, new problems emerged and solutions had to be developed. As the technology continues to evolve, our methods and ability to interpret results must keep pace to provide transplant patients with the best possible care.

Class I and II HLA antibodies in pediatric patients with thalassemia major.

BACKGROUND: HLA alloimmunization is a potential complication of red blood cell (RBC) transfusion with detrimental consequences for future organ or hematopoietic stem cell transplantation. STUDY DESIGN AND METHODS: The study aimed to determine the prevalence and specificity of HLA antibodies among pediatric patients with thalassemia major (TM) and antibody changes over time while on leukoreduced chronic transfusion therapy. HLA antibodies were measured at two or more time points in children and young adults ages 3 to 21 years with TM. HLA Class I and II antibodies were measured by FlowPRA screening. Positive screening assays were confirmed with LabScreen single-antigen bead assays for antibody specificity. RESULTS: HLA antibodies were detected in 10 of 19 (53%) subjects: seven of 19 (37%) with HLA Class I and II antibodies, two of 19 (11%) with only HLA Class I antibodies, and one of 19 (5%) with only HLA Class II antibodies. Subjects with HLA antibodies were older (14.6 years vs. 7.1 years, p = 0.05), predominantly male (80%), and more likely to have a remote history of nonleukoreduced transfusions (p = 0.057). Median time between testing was 3.7 years. De novo HLA antibodies were detected in two of 11 patients who initially had negative panel-reactive antibody screens, while one subject lost detection of Class II antibody. Two of seven patients with HLA antibodies had antibodies to self-HLA. CONCLUSION: HLA antibodies have a high prevalence in TM patients and may be associated with nonleukoreduced transfusions and older age. For such patients, antibody identification will be useful if subsequent organ or stem cell transplantation is needed.