Flow cytometric detection of HLA antibodies using a spectrum of microbeads

ASTCT Consensus Recommendations on Testing and Treatment of Patients with Donor-specific Anti-HLA Antibodies

Donor-specific anti-HLA antibodies (DSA) are an important cause of engraftment failure and may negatively impact survival outcomes of patients receiving allogeneic hematopoietic stem cell transplantation (HSCT) using an HLA-mismatched allograft. The incidence of DSA varies across studies, depending on individual factors, detection or identification methods and thresholds considered clinically relevant. Although DSA testing by multiplex bead arrays remains semiquantitative, it has been widely adopted as a standard test in most transplant centers. Additional testing to determine risk of allograft rejection may include assays with HLA antigens in natural conformation, such as flow cytometric crossmatch, and/or antibody binding assays, such as C1q testing. Patients with low level of DSA (<2,000 mean fluorescence intensity; MFI) may not require treatment, while others with very high level of DSA (>20,000 MFI) may be at very high-risk for engraftment failure despite current therapies. By contrast, in patients with moderate or high level of DSA, desensitization therapy can successfully mitigate DSA levels and improve donor cell engraftment rate, with comparable outcomes to patients without DSA. Treatment is largely empirical and multimodal, involving the removal, neutralization, and blocking of antibodies, as well as inhibition of antibody production to prevent activation of the complement cascade. Desensitization protocols are based on accumulated multicenter experience, while prospective multicenter studies remain lacking. Most patients require a full intensity protocol that includes plasma exchange, while protocols relying only on rituximab and intravenous immunoglobulin may be sufficient for patients with lower DSA levels and negative C1q and/or flow cytometric crossmatch. Monitoring DSA levels before and after HSCT could guide preemptive treatment when high levels persist after stem cell infusion. This paper aims to standardize current evidence-based practice and formulate future directions to improve upon current knowledge and advance treatment for this relatively rare, but potentially serious complication in allogeneic HSCT recipients.

Allosensitisation in NHP results in cross-reactive anti-SLA antibodies not detected by a lymphocyte-based flow cytometry crossmatch

Xenotransplantation is a potential option for individuals for whom an acceptable human allograft is unavailable. Individuals with broadly reactive HLA antibodies due to prior exposure to foreign HLA are potential candidates for a clinical xenotransplant trial. It remains controversial if allosensitisation results in the development of cross-reactive antibodies against SLA. This may require increased histocompatibility scrutiny for highly sensitised individuals prior to enrollment in a clinical trial. Serum samples were obtained from non-human primates sensitised via serial skin transplantation from maximally MHC-mismatched donor, as reported. Sera from pre- and post-allosensitisation timepoints were assessed in a flow crossmatch (FXM) for IgM and IgG binding to pig splenocytes with or without red blood cell adsorption. Xenoreactive antibodies were eluted from pig splenocytes and screened on a single antigen HLA bead assay. A MHC Matchmaker algorithm was developed to predict potential conserved amino acid motifs among the pig, NHP, and human. Our sensitised NHP model was used to demonstrate that allosensitisation does not result in an appreciable difference in xenoreactive antibody binding in a cell-based FXM. However, antibody elution and screening on single antigen HLA beads suggest the existence of potential cross-reactive antibodies against SLA. The cross-reactive IgG after allosensitisation were predicted by comparing the recipient Mamu alleles against its previous allograft donor Mamu alleles and the donor pig SLA alleles. Our study suggests that allosensitisation could elevate cross-reactive antibodies, but a more sensitive assay than a cell-based FXM is required to detect them. The MHC Matchmaker algorithm was developed as a potential tool to help determine amino acid motif conservation and reactivity pattern.

Modes of assay interference and the effectiveness of serum pretreatment approaches in detection of anti-HLA antibodies

AIMS

Several modes of assay interference common to immunoassays affect solid-phase single-antigen bead-based immunoassays (SAB) used to detect antibodies against human leucocyte antigens (HLA). Best practice recommendations include methods to address assay interference, though the clinical impact and optimal approaches are undefined. We sought to evaluate assay interference in HLA SAB to identify an efficient approach for avoiding erroneous results.

METHODS

Retrospective analysis of 14 059 patient samples tested for anti-HLA antibodies was performed. This included 4685 samples tested prior to implementation of serum pretreatment with EDTA and 4982 samples tested with routine EDTA treatment using the same testing algorithm. An algorithm for efficiently identifying and processing samples with suspected interference was evaluated in a separate cohort of 4392 EDTA-treated samples.

RESULTS

EDTA serum pretreatment reduced assay interference, but did not eliminate all modes of interference. A protocol for identification and testing of samples with suspected interference facilitated efficient detection of interference while reducing the amount of additional testing required.

CONCLUSIONS

Our data indicate that a single-method approach is insufficient to address all sources of interference in HLA SAB. A multimodal approach with a proactive screening is a more effective way to minimise risk of erroneous results.

Development of a calculated panel reactive antibody calculator for the United Arab Emirates: a proof of concept study

Calculated panel reactive antibody (CPRA) is used to help increase sensitized patient's access to transplantation. United Arab Emirates (UAE) has a diverse resident population hence we developed a UAE-CPRA calculator based on HLA antigen frequencies of the different ethnic groups that represent the UAE population. HLA antigen frequencies at serological split antigen level for HLA-A, -B, -C, -DRB1 and -DQB1 of 1002 healthy unrelated donors were performed. We subsequently compared the performance of the UAE CPRA calculator with the Organ Procurement and Transplantation Network (OPTN) and the Canadian CPRA calculators in 110 Kidney Transplant waitlist patients from January 2016 to December 2018. Lin's concordance correlation coefficient showed a moderate agreement between the UAE and OPTN calculator (Rc = 0.949, 95% CI 0.929-0.963) and the UAE and Canadian calculators (Rc = 0.952, 95% CI 0.932-0.965). While there continued to be a moderate agreement (Rc = 0.937, UAE versus OPTN calculator) in the lower sensitized group, a poor agreement (Rc = 0.555, UAE versus OPTN calculator) was observed in the higher sensitized group. In this study, we provide a template for countries to develop their own population-specific CPRA calculator. Implementation of the CPRA algorithm based on HLA frequencies of the multi-ethnic UAE population will be more fitting to increase access to transplantation and improve transplant outcomes. Our study demonstrates that the CPRA calculators developed using the data from the western population had poor correlation in our higher sensitized patients disadvantaging them in potential organ allocations systems. We plan to further refine this calculator by using high resolution HLA typing to address the problem of a genetically diverse population.

Stratifying the humoral risk of candidates to a solid organ transplantation: a proposal of the ENGAGE working group

Detection of circulating antibodies directed against human leukocyte antigen (HLA) molecules, which corresponds to the current definition of 'sensitized patient', has been shown to have a severe impact on both access to transplantation and, if the anti-HLA antibodies are specific to the selected donor, survival of the graft. However, not all donor-specific antibodies (DSA) are equally harmful to the graft and progress in the understanding of humoral memory has led to the conclusion that absence of DSA at transplantation does not rule out the possibility that the patient has a preformed cellular humoral memory against the graft (thereby defining a category of DSA-negative sensitized recipients). Technological progress has led to the generation of new assays that offer unprecedented precision in exploring the different layers (serological and cellular) of alloimmune humoral memory. Based on this recent knowledge, the EuropeaN Guidelines for the mAnagement of Graft rEcipients (ENGAGE) working group to propose an updated definition of sensitization in candidates for solid organ transplantation - one that moves away from the current binary division towards a definition based on homogenous strata with similar humoral risk.

KDIGO Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation

The 2020 Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guideline on the Evaluation and Management of Candidates for Kidney Transplantation is intended to assist health care professionals worldwide who evaluate and manage potential candidates for deceased or living donor kidney transplantation. This guideline addresses general candidacy issues such as access to transplantation, patient demographic and health status factors, and immunological and psychosocial assessment. The roles of various risk factors and comorbid conditions governing an individual's suitability for transplantation such as adherence, tobacco use, diabetes, obesity, perioperative issues, causes of kidney failure, infections, malignancy, pulmonary disease, cardiac and peripheral arterial disease, neurologic disease, gastrointestinal and liver disease, hematologic disease, and bone and mineral disorder are also addressed. This guideline provides recommendations for evaluation of individual aspects of a candidate's profile such that each risk factor and comorbidity are considered separately. The goal is to assist the clinical team to assimilate all data relevant to an individual, consider this within their local health context, and make an overall judgment on candidacy for transplantation. The guideline development process followed the Grades of Recommendation Assessment, Development, and Evaluation (GRADE) approach. Guideline recommendations are primarily based on systematic reviews of relevant studies and our assessment of the quality of that evidence, and the strengths of recommendations are provided. Limitations of the evidence are discussed with differences from previous guidelines noted and suggestions for future research are also provided.

Incidence and impact of allele-specific anti-HLA antibodies and high-resolution HLA genotyping on assessing immunologic compatibility

The ability to identify specific HLA molecules against which a patient has alloantibodies has revolutionized assessment of immunologic compatibility. Anti-HLA antibodies are typically evaluated as reactive against well-defined serologic antigen groups. Thus, donor HLA genotyping is aimed at defining HLA at the serologic split-antigen level to avoid incompatible antigen-antibody combinations. However, anti-HLA antibodies can have reactivities not accurately described by well-defined serologic antigens. While existence of these antibodies is acknowledged, their precise impact on clinical practice is not clear. We performed a single-center review of 2 years of pre-and post-transplant anti-HLA antibody testing data combined with high-resolution HLA genotyping data for living and deceased organ donors to evaluate the clinical impact of anti-HLA antibodies with reactivities outside of commonly defined serologic antigen groups. We find approximately 15% of patients awaiting transplantation have alloantibodies with differential reactivity for HLA proteins encoded by specific alleles within a serologic antigen group. Allele-specific antibodies are associated with positive cellular crossmatches not accurately predicted by standard donor HLA genotyping and can manifest as post-transplant donor-specific antibodies. Our data highlights the importance of evaluating anti-HLA antibodies at the allele-level and provides evidence supporting utility for high-resolution HLA genotyping in solid organ transplantation.

Tailored immunosuppression after kidney transplantation - a single center real-life experience

Background

Kidney allograft survival continuously improved with introduction of novel immunosuppressants. However, also immunologically challenging transplants (blood group incompatibility and sensitized recipients) increase. Between 2006 and 2008, a new tailored immunosuppression scheme for kidney transplantation was implemented at the University Hospital in Zurich, together with an ABO-incompatible transplant program and systematic pre- and posttransplant anti-human leukocyte antigen (HLA) antibody screening by Luminex technology. This study retrospectively evaluated the results of this tailored immunosuppression approach with a particular focus on immunologically higher risk transplants.

Methods

A total of 204 consecutive kidney transplantations were analyzed, of whom 14 were ABO-incompatible and 35 recipients were donor-specific anti-HLA antibodies (DSA) positive, but complement-dependent cytotoxicity crossmatch (CDC-XM) negative. We analyzed patient and graft survival, acute rejection rates and infectious complications in ABO-compatible versus -incompatible and in DSA positive versus negative patients and compared those with a historical control group.

Results

Overall patient, death-censored allograft survival and non-death-censored allograft survival at 4 years were 92, 91 and 87%, respectively. We found that (1) there were no differences between ABO-compatible and -incompatible and between DSA positive and DSA negative patients concerning acute rejection rate and graft survival; (2) compared with the historical control group there was a significant decrease of acute rejection rates in sensitized patients who received an induction with thymoglobulin; (3) there was no increased rate of infection among the patients who received induction with thymoglobulin compared to no induction therapy.

Conclusions

We observed excellent overall mid-term patient and graft survival rates with our tailored immunosuppression approach. Induction with thymoglobulin was efficient and safe in keeping rejection rates low in DSA positive patients with a negative CDC-XM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-020-02137-5.

Identification of a tumor-specific allo-HLA-restricted γδTCR

γδT cells are key players in cancer immune surveillance because of their ability to recognize malignant transformed cells, which makes them promising therapeutic tools in the treatment of cancer. However, the biological mechanisms of how γδT-cell receptors (TCRs) interact with their ligands are poorly understood. Within this context, we describe the novel allo-HLA-restricted and CD8α-dependent Vγ5Vδ1TCR. In contrast to the previous assumption of the general allo-HLA reactivity of a minor fraction of γδTCRs, we show that classic anti-HLA-directed, γδTCR-mediated reactivity can selectively act on hematological and solid tumor cells, while not harming healthy tissues in vitro and in vivo. We identified the molecular interface with proximity to the peptide-binding groove of HLA-A*24:02 as the essential determinant for recognition and describe the critical role of CD8 as a coreceptor. We conclude that alloreactive γδT-cell repertoires provide therapeutic opportunities, either within the context of haplotransplantation or as individual γδTCRs for genetic engineering of tumor-reactive T cells.

Significance of the intraindividual variability of HLA IgG antibodies in renal disease patients observed with different beadsets monitored with two different secondary antibodies on a Luminex platform

The accurate measurement of anti-HLA alloantibodies in transplant candidates is required for determining the degree of sensitization and for the listing of unacceptable antigens for organ allocation. Both the configuration of the HLA molecules coated on the beads and the nature of detection antibodies may impede assessment of the presence and strength of anti-HLA IgG- with the Luminex single-antigen-bead assay. Sera antibodies of the end-stage renal disease patients were compared using LIFECODES (LC) and LABScreen (LS) beadsets monitored with polyclonal-Fab (IgHPolyFab) and monoclonal-IgG (FcMonoIgG) second antibodies. Positive results at mean fluorescence intensity (MFI) > 500 (at serum dilution 1/10) were used to calculate panel reactive antibody (cPRA) levels. LS-beadsets are coated with monomeric variants in addition to intact HLA antigens with or without peptides, while LC-beadsets are devoid of monomeric variants and with lesser levels of peptide-free heterodimers. Consequently, IgG antibodies against both classes of HLA were reactive to more antigens with LS than with LC-beadsets. For both classes, MFIs were also frequently higher with LS than with LC. For HLA-I, MFIs were higher with IgHPolyFab than with FcMonoIgG with the exception of sera with MFIs > 5000 where they were comparable. For HLA-II, the reverse occurred, with significantly higher levels with FcMonoIgG regardless of the beadsets. The intraindividual variability observed between beadsets with two detection antibodies elucidates that antigens found as acceptable with one beadset may end up unacceptable with the other beadsets, with the possibility of denying potentially compatible transplants to candidates.

Sensitization in Heart Transplantation: Emerging Knowledge: A Scientific Statement From the American Heart Association

Sensitization, defined as the presence of circulating antibodies, presents challenges for heart transplant recipients and physicians. When present, sensitization can limit a transplantation candidate’s access to organs, prolong wait time, and, in some cases, exclude the candidate from heart transplantation altogether. The management of sensitization is not yet standardized, and current therapies have not yielded consistent results. Although current strategies involve antibody suppression and removal with intravenous immunoglobulin, plasmapheresis, and antibody therapy, newer strategies with more specific targets are being investigated.

Swine Leukocyte Antigen Class II Is a Xenoantigen

BACKGROUND

Over 130 000 patients in the United States alone need a lifesaving organ transplant. Genetically modified porcine organs could resolve the donor organ shortage, but human xenoreactive antibodies destroy pig cells and are the major barrier to clinical application of xenotransplantation. The objective of this study was to determine whether waitlisted patients possess preformed antibodies to swine leukocyte antigen (SLA) class II, homologs of the class II HLA.

METHODS

Sera from people currently awaiting solid organ transplant were tested for IgG binding to class II SLA proteins when expressed on mammalian cells. Pig fibroblasts were made positive by transfection with the class II transactivator. As a second expression system, transgenes encoding the alpha and beta chains of class II SLA were transfected into human embryonic kidney cells.

RESULTS

Human sera containing IgG specific for class II HLA molecules exhibited greater binding to class II SLA positive cells than to SLA negative cells. Sera lacking antibodies against class II HLA showed no change in binding regardless of the presence of class II SLA. These antibodies could recognize either SLA-DR or SLA-DQ complexes.

CONCLUSIONS

Class II SLA proteins may behave as xenoantigens for people with humoral immunity toward class II HLA molecules.

Posttransplant reduction in preexisting donor-specific antibody levels after belatacept- versus cyclosporine-based immunosuppression: Post hoc analyses of BENEFIT and BENEFIT-EXT

BENEFIT and BENEFIT-EXT were phase III studies of cytotoxic T-cell crossmatch-negative kidney transplant recipients randomized to belatacept more intense (MI)-based, belatacept less intense (LI)-based, or cyclosporine-based immunosuppression. Following study completion, presence/absence of HLA-specific antibodies was determined centrally via solid-phase flow cytometry screening. Stored sera from anti-HLA-positive patients were further tested with a single-antigen bead assay to determine antibody specificities, presence/absence of donor-specific antibodies (DSAs), and mean fluorescent intensity (MFI) of any DSAs present. The effect of belatacept-based and cyclosporine-based immunosuppression on MFI was explored post hoc in patients with preexisting DSAs enrolled to BENEFIT and BENEFIT-EXT. In BENEFIT, preexisting DSAs were detected in 4.6%, 4.9%, and 6.3% of belatacept MI-treated, belatacept LI-treated, and cyclosporine-treated patients, respectively. The corresponding values in BENEFIT-EXT were 6.0%, 5.7%, and 9.2%. In both studies, most preexisting DSAs were of class I specificity. Over the first 24 months posttransplant, a greater proportion of preexisting DSAs in belatacept-treated versus cyclosporine-treated patients exhibited decreases or no change in MFI. MFI decline was more apparent with belatacept MI-based versus belatacept LI-based immunosuppression in both studies and more pronounced in BENEFIT-EXT versus BENEFIT. Although derived post hoc, these data suggest that belatacept-based immunosuppression decreases preexisting DSAs more effectively than cyclosporine-based immunosuppression.

The European Society for Blood and Marrow Transplantation (EBMT) Consensus Guidelines for the Detection and Treatment of Donor-specific Anti-HLA Antibodies (DSA) in Haploidentical Hematopoietic Cell Transplantation

Haploidentical donors are now increasingly considered for transplantation in the absence of HLA-matched donors or when an urgent transplant is needed. Donor-specific anti-HLA antibodies (DSA) have been recently recognized as an important barrier against successful engraftment of donor cells, which can affect transplant survival. DSA appear more prevalent in this type of transplant due to higher likelihood of alloimmunization of multiparous females against offspring's HLA antigens, and the degree of mismatch. Here we summarize the evidence for the role of DSA in the development of primary graft failure in haploidentical transplantation and provide consensus recommendations from the European Society for Blood and Marrow Transplant Group on testing, monitoring, and treatment of patients with DSA receiving haploidentical hematopoietic progenitor cell transplantation.

Graft immunologic events in deceased donor kidney transplant recipients with preformed HLA-donor specific antibodies

INTRODUCTION

Pretransplant donor-specific HLA alloantibodies detected with the Single Antigen Bead (SAB) assay reflect an increased risk for acute antibody-mediated rejection (AMR). We herein report the incidence of both acute AMR and acute cellular rejection (ACR) during the first year posttransplantation, in a cohort of kidney transplant recipients (KTR) of deceased donor (DD) grafts, according to their DSA status. Pretransplant DSA do not preclude DD-KT in negative CDC-XM recipients at our center.

PATIENTS AND METHODS

246 KT were performed at our center between 01/2012 and 12/2015 and 100 KTR obtained from a DD were analyzed; 24% harbored DSA by SAB assay, MFI values >500 were considered positive. All recipients received thymoglobulin induction and generic tacrolimus-based maintenance therapy. Graft biopsies were performed by protocol on months 3 and 12 as well as per indication. The incidence of AMR and ACR was correlated with the existence of pretransplant DSA.

RESULTS

Overall, 34% of patients developed an acute rejection episode, 54.2% in the DSA group versus 27.6% in the non-DSA group (p=0.032), and most of these events were detected as subclinical conditions in protocol biopsies. AMR events developed in 33.3% and 19.7% (p=0.176) in the DSA and the non-DSA groups, respectively. ACR events were found in 16.6% and 6.6% (p=0.127) in the DSA and non-DSA groups, respectively. Graft function was similar between groups at the end of the 1st year posttransplant and no immunological graft loss occurred.

CONCLUSION

Despite the use of depleting induction therapy and adequate tacrolimus trough levels along with MMF and steroids, a high rate of rejection events was observed during the first year post-transplantation.

Human Leukocyte Antigen Sensitization in Solid Organ Transplantation: A Primer on Terminology, Testing, and Clinical Significance for the Apheresis Practitioner

The human leukocyte antigen (HLA) system is an important immunologic barrier that must be considered for successful solid organ transplantation. Formation of donor-specific HLA antibodies in solid organ transplantation is an important cause of allograft injury and may contribute to recipient morbidity and mortality. Therapeutic plasma exchange is often requested to lower HLA antibody levels prior to or after transplantation and for management of HLA antibodies in the context of organ rejection. In this review, we summarize the current terminology, laboratory testing, and clinical significance of HLA sensitization in the solid organ transplant population. Furthermore, to illustrate applications of HLA testing in clinical practice, we summarize our own lung and kidney institutional protocols for managing HLA antibodies in the peri-transplant setting.

Histocompatibility and management of the highly sensitized kidney transplant candidate

PURPOSE OF REVIEW

Increasing national participation in kidney paired donation and implementation of new sharing policies via the current kidney allocation system have brought about greater opportunities for the most highly sensitized patients awaiting a kidney transplant. The purpose of this review is to discuss the application of histocompatibility data in the context of the clinical practice of kidney transplantation as pertains to the sensitized candidate.

RECENT FINDINGS

With desensitization techniques, transplantation across virtually any antibody barrier is technically feasible, but long-term outcomes after transplantation are improved when the immunologic match between donor and recipient is optimized. Solid-phase immunoassays have changed the landscape of histocompatibility testing. These sensitive and specific assays for identifying donor-specific antibody not only help determine feasibility of transplantation but have enabled outcomes studies aimed at understanding the spectrum of risk posed by different antibody profiles. This, in turn, has helped guide decision-making in donor selection, in particular for sensitized patients.

SUMMARY

Careful evaluation of donor-specific antibody profiles with individualized, patient-specific determination of unacceptable antigens is necessary to ensure that highly sensitized patients receive every opportunity for transplantation.

Nature and Clonality of the Fluoresceinated Secondary Antibody in Luminex Multiplex Bead Assays Are Critical Factors for Reliable Monitoring of Serum HLA Antibody Levels in Patients for Donor Organ Selection, Desensitization Therapy, and Assessment of the Risk for Graft Loss

Luminex multiplex immunoassays enable simultaneous monitoring of Abs against multiple Ags in autoimmune, inflammatory, and infectious diseases. The assays are used extensively to monitor anti-HLA Abs in transplant patients for donor organ selection, desensitization, and assessing the risk for graft rejection. To monitor IgG Abs, fluoresceinated IgG constant H chain-binding polyclonal F(ab')₂ (IgHPolyFab) is used as the fluoresceinated secondary Ab (2nd-Ab), whereas IgG subclasses are monitored with Fc-specific monoclonal whole IgG (FcMonoIgG). The fluorescent signal from the 2nd-Ab is measured as mean florescence intensity (MFI). When IgHPolyFab is used, the signal is amplified as a result of the binding of multiple polyclonal Fabs to the C region of primary IgH. The reliability of such amplification for Ab measurements was not validated, nor were MFIs compared with 1:1 binding of FcMonoIgG to primary Abs. Comparing the MFIs of anti-HLA Abs obtained with IgHPolyFab and FcMonoIgG against normal human sera, IVIg, and allograft recipients' sera, it was observed that the number of HLA-Abs was notably higher with IgHPolyFab than with FcMonoIgG The MFIs of anti-HLA Abs also remained higher with IgHPolyFab in the normal sera and in IVIg, but the reverse was true when the autologous and allogeneic IgG concentrations were augmented in allograft recipients. Indeed, MFIs of the de novo allo-HLA Abs were markedly higher with FcMonoIgG than with IgHPolyFab. Serum titration established the superiority of FcMonoIgG for monitoring MFIs of de novo allo-HLA Abs in allograft recipients. Avoiding false amplifications of the number and MFIs of anti-HLA IgG with FcMonoIgG may minimize immunosuppressive therapies, maximize the number of donors for patients waiting for allografts, and enable better prediction of graft rejection.

B cell repertoires in HLA-sensitized kidney transplant candidates undergoing desensitization therapy

Background

Kidney transplantation is the most effective treatment for end-stage renal disease. Sensitization refers to pre-existing antibodies against human leukocyte antigen (HLA) protein and remains a major barrier to successful transplantation. Despite implementation of desensitization strategies, many candidates fail to respond. Our objective was to determine whether measuring B cell repertoires could differentiate candidates that respond to desensitization therapy.

Methods

We developed an assay based on high-throughput DNA sequencing of the variable domain of the heavy chain of immunoglobulin genes to measure changes in B cell repertoires in 19 highly HLA-sensitized kidney transplant candidates undergoing desensitization and 7 controls with low to moderate HLA sensitization levels. Responders to desensitization had a decrease of 5% points or greater in cumulated calculated panel reactive antibody (cPRA) levels, and non-responders had no decrease in cPRA.

Results

Dominant B cell clones were not observed in highly sensitized candidates, suggesting that the B cells responsible for sensitization are either not present in peripheral blood or present at comparable levels to other circulating B cells. Candidates that responded to desensitization therapy had pre-treatment repertoires composed of a larger fraction of class-switched (IgG and IgA) isotypes compared to non-responding candidates. After B cell depleting therapy, the proportion of switched isotypes increased and the mutation frequencies of the remaining non-switched isotypes (IgM and IgD) increased in both responders and non-responders, perhaps representing a shift in the repertoire towards memory B cells or plasmablasts. Conversely, after transplantation, non-switched isotypes with fewer mutations increased, suggesting a shift in the repertoire towards naïve B cells.

Conclusions

Relative abundance of different B cell isotypes is strongly perturbed by desensitization therapy and transplantation, potentially reflecting changes in the relative abundance of memory and naïve B cell compartments. Candidates that responded to therapy experienced similar changes to those that did not respond. Further studies are required to understand differences between these two groups of highly sensitized kidney transplant candidates.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1118-7) contains supplementary material, which is available to authorized users.

C1Q Assay Results in Complement-Dependent Cytotoxicity Crossmatch Negative Renal Transplant Candidates with Donor-Specific Antibodies: High Specificity but Low Sensitivity When Predicting Flow Crossmatch

The aim of the present study was to describe the association of positive flow cross match (FXM) and C1q-SAB. Methods. In this observational, cross-sectional, and comparative study, patients included had negative AHG-CDC-XM and donor specific antibodies (DSA) and were tested with FXM. All pretransplant sera were tested with C1q-SAB assay. Results. A total of 50 donor/recipient evaluations were conducted; half of them had at least one C1q+ Ab (n = 26, 52%). Ten patients (20.0%) had DSA C1q+ Ab. Twenty-five (50%) FXMs were positive. Factors associated with a positive FXM were the presence of C1q+ Ab (DSA C1q+ Ab: OR 27, 2.80–259.56, P = 0.004, and no DSA C1q+ Ab: OR 5, 1.27–19.68, P = 0.021) and the DSA LABScreen-SAB MFI (OR 1.26, 95% CI 1.06–1.49, P = 0.007). The cutoff point of immunodominant LABScreen SAB DSA-MFI with the greatest sensitivity and specificity to predict FXM was 2,300 (sensitivity: 72% and specificity: 75%). For FXM prediction, DSA C1q+ Ab was the most specific (95.8%, 85–100) and the combination of DSA-MFI > 2,300 and C1q+ Ab was the most sensitive (92.0%, 79.3–100). Conclusions. C1q+ Ab and LABScreen SAB DSA-MFI were significantly associated with FXM. DSA C1q+ Ab was highly specific but with low sensitivity.

Donor-Specific Antibody Monitoring: Where Is the Beef?

This review paper discusses the impact of de novo donor-specific antibodies (DSA) to donor HLA antigens in kidney transplantation and summarizes the benefits and challenges that exist with DSA monitoring. Post-transplant DSA is associated with worse allograft outcomes and its detection may precede or coincide with clinical, biochemical, and histologic allograft dysfunction. There are no absolute features of DSA testing results that perfectly discriminate between states of disease and health. In a state of antibody-associated graft dysfunction, removal or reduction in DSA may only provide clinical benefit for some. Furthermore, various factors influence test results, and detection of HLA antibodies must be interpreted within the appropriate clinical and laboratory context. The utility of DSA monitoring is further affected by the limited effectiveness of treatment for antibody-mediated rejection. Although DSA monitoring is potentially beneficial in some circumstances, the optimal screening and treatment strategies are still to be defined.

Safety and efficacy of cryopreserved autologous platelet concentrates in HLA-alloimmunized patients with hematologic malignancies

BACKGROUND

Curative chemotherapy approaches in patients with malignancies and platelet (PLT) transfusion refractoriness due to alloimmunization may be hampered by the lack of suitable PLT donors. For these patients, transfusion of cryopreserved autologous PLTs is an option, but is time- and resource-consuming. We aimed at further simplifying this process.

STUDY DESIGN AND METHODS

A retrospective single-center analysis was conducted on the transfusion of cryopreserved autologous PLTs in nine female alloimmunized, PLT transfusion-refractory patients treated for acute leukemia (n = 8) and non-Hodgkin's lymphoma (n = 1). No additional processing was used before transfusion, and most notably, washing and centrifugation steps were omitted. Clinical efficacy and safety, as well as a flow cytometric assessment of structural and functional PLT changes, were analyzed.

RESULTS

A total of 40 autologous PLT concentrates were thawed at bedside and transfused a median of 32 (range, 9 to 994) days after cryopreservation. No major bleeds and no severe dimethyl sulfoxide toxicity were observed. The median PLT count increments did not differ 1 and 18 to 24 hours after transfusion and reached 6 × 10⁹ /L (interquartile range [IQR], 3 × 10⁹ -7.5 × 10⁹ /L) and 6 × 10⁹ /L (IQR, 2.5 × 10⁹ -9.5 × 10⁹ /L), respectively. Cryopreservation resulted in partial activation of one-third of the PLTs. In vitro stimulation with strong agonists induced additional full activation of cryopreserved PLTs: median, 55% (IQR, 42%-60%) after thrombin and 39% (IQR, 36%-39%) after convulxin.

CONCLUSION

The transfusion of cryopreserved autologous PLTs is feasible and safe. Despite the cryopreservation process, PLT functionality is partially maintained.

C1q-binding anti-HLA antibodies do not predict platelet transfusion failure in Trial to Reduce Alloimmunization to Platelets study participants

BACKGROUND

In the Trial to Reduce Alloimmunization to Platelets (TRAP) study, 101 of 530 subjects became clinically refractory (CR) to platelets (PLTs) without lymphocytotoxicity assay (LCA)-detectable anti-HLA antibodies. The LCA only detects complement-binding antibodies and is less sensitive than newer assays. Utilizing a more sensitive bead-based assay that does not distinguish between complement-binding versus non-complement-binding antibodies, we have previously shown that while many LCA-negative (LCA-) patients do have anti-HLA antibodies, these low- to moderate-level antibodies do not predict refractoriness. As complement can contribute to PLT rejection, we assessed if previously undetected complement-binding antibodies account for refractoriness among LCA- patients.

STUDY DESIGN AND METHODS

Samples from 169 LCA- (69 CR, 100 non-CR) and 20 LCA-positive (LCA+; 10 CR, 10 non-CR) subjects were selected from the TRAP study serum repository. Anti-Class I HLA immunoglobulin (Ig)G and C1q-binding antibodies were measured in serum or plasma with bead-based detection assays. Levels of C1q-binding antibodies were compared between CR and non-CR subjects and correlated with corrected count increments (CCIs).

RESULTS

While some of the LCA- subjects had detectable C1q-binding anti-Class I HLA antibodies, and some LCA+ subjects did not, levels were significantly higher among LCA+ subjects. C1q-binding anti-Class I HLA antibody levels did not differ significantly between CR and non-CR among either the LCA- or the LCA+ subjects. Furthermore, there was no significant correlation observed between CCIs and either C1q-binding or any anti-HLA IgG antibodies.

CONCLUSIONS

This work confirms that low- to moderate-level anti-Class I antibodies do not drive PLT rejection, suggesting a role for antibody-independent mechanisms.

Multiplex Antibody Detection for Noninvasive Genus-Level Diagnosis of Prosthetic Joint Infection

We developed and evaluated a multiplex antibody detection-based immunoassay for the diagnosis of prosthetic joint infections (PJIs). Sixteen protein antigens from three Staphylococcus species (Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus lugdunensis) (8 antigens), Streptococcus agalactiae (4 antigens), and Propionibacterium acnes (4 antigens) were selected by comparative immunoproteomics using serum samples from PJI cases versus controls. A bead-based multiplex immunoassay that measured serum IgG against purified, recombinant forms of each of the 16 antigens was developed. We conducted a prospective study to evaluate the performance of the assay. A PJI was defined by the presence of a sinus tract and/or positive intraoperative sample cultures (at least one sample yielding a virulent organism or at least two samples yielding the same organism). A total of 455 consecutive patients undergoing revision or resection arthroplasty (hip, 66.3%; knee, 29.7%; shoulder, 4%) at two French reference centers for the management of PJI were included: 176 patients (38.7%) were infected and 279 (61.3%) were not. About 60% of the infections involved at least one of the species targeted by the assay. The sensitivity/specificity values were 72.3%/80.7% for targeted staphylococci, 75%/92.6% for S. agalactiae, and 38.5%/84.8% for P. acnes. The assay was more sensitive for infections occurring >3 months after arthroplasty and for patients with an elevated C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR). However, it detected 64.3% and 58.3% of targeted staphylococcal infections associated with normal CRP and ESR values, respectively. This new multiplex immunoassay approach is a novel noninvasive tool to evaluate patients suspected of having PJIs and provides information complementary to that from inflammatory marker values.

Characteristics of Circulating Donor Human Leukocyte Antigen-specific Immunoglobulin G Antibodies Predictive of Acute Antibody-mediated Rejection and Kidney Allograft Failure

BACKGROUND

Characteristics of pretransplant antibodies directed at donor human leukocyte antigen (HLA) donor-specific antibodies (DSA) associated with adverse outcomes in kidney transplant recipients are being elucidated but uncertainties exist.

METHODS

We prospectively screened pretransplant sera from 543 kidney recipients using single antigen bead assays and identified 154 patients with and 389 without DSA. We investigated the association of DSA features to acute rejection and graft failure.

RESULTS

One-year acute rejection incidence was higher in DSA-positive group (P < 0.001), primarily due to antibody-mediated rejection (AMR, 13% vs. 1.8%, P < 0.001) and not T cell-mediated rejection (ACR, 5% vs.6%, P = 0.65). The sum of mean fluorescence intensity of DSA (DSA MFI-Sum) of 6,000 or higher (OR, 18; 95% CI, 7.0-47; P < 0.001) and the presence of DSA against both HLA class I and II (OR, 39; 95% CI, 14-106; P < 0.0001) predicted 1-year AMR, independent of other covariates. Calculated panel reactive antibody and a positive flow cytometry cross-match result were associated with AMR by bivariate analysis but neither was an independent predictor in a multivariable regression analysis that included DSA-MFI-Sum or HLA DSA class. In multivariable Cox proportional hazards models, the covariate-adjusted hazard ratio for graft failure was 2.03 (95%CI, 1.05-3.92; P = 0.04) for DSA MFI-Sum of 6,000 or higher and 2.23 (95% CI, 1.04-4.80; P = 0.04) for class I and II DSA. Prediction of graft failure was not independent of AMR.

CONCLUSION

Our study suggests that DSA MFI-Sum and HLA class of DSA are characteristics predictive of AMR and graft failure. The elevated risk of graft failure in those with the identified features of DSA is attributable to increased risk of AMR.

Deciphering allogeneic antibody response against native and denatured HLA epitopes in organ transplantation

Anti-HLA donor-specific antibodies are deleterious for organ transplant survival. Class I HLA donor-specific antibodies are identified by using the Luminex single antigen beads (LSAB) assay, which also detects anti-denatured HLA antibodies (anti-dHLAs). Anti-dHLAs are thought to be unable to recognize native HLA (nHLA) on the cell surface and therefore to be clinically irrelevant. Acid denaturation of nHLA on LSAB allows anti-dHLAs to be discriminated from anti-nHLAs. We previously defined a threshold for the ratio between mean fluorescence intensity against acid-treated (D for denaturation) and nontreated (N) LSAB, D ≥ 1.2 N identifying the anti-dHLAs. However, some anti-dHLAs remained able to bind nHLA on lymphocytes in flow cytometry crossmatches, and some anti-nHLAs conserved significant reactivity toward acid-treated LSAB. After depleting serum anti-nHLA reactivity with HLA-typed cells, we analyzed the residual LSAB reactivity toward nontreated and acid-treated LSABs, and then evaluated the ability of antibodies to recognize nHLA alleles individually. We observed that sera can contain mixtures of anti-nHLAs and anti-dHLAs, or anti-nHLAs recognizing acid-resistant epitopes, all possibly targeting the same allele(s). Therefore, the anti-HLA antibody response can be highly complex and subtle, as is the accurate identification of pathogenic anti-HLA antibodies in human serum.

Utility of HLA Antibody Testing in Kidney Transplantation

HLA antigens are polymorphic proteins expressed on donor kidney allograft endothelium and are critical targets for recipient immune recognition. HLA antibodies are risk factors for acute and chronic rejection and allograft loss. Solid-phase immunoassays for HLA antibody detection represent a major advance in sensitivity and specificity over cell-based methods and are widely used in organ allocation and pretransplant risk assessment. Post-transplant, development of de novo donor-specific HLA antibodies and/or increase in donor-specific antibodies from pretransplant levels are associated with adverse outcomes. Although single antigen bead assays have allowed sensitive detection of recipient HLA antibodies and their specificities, a number of interpretive considerations must be appreciated to understand test results in clinical and research contexts. This review, which is especially relevant for clinicians caring for transplant patients, discusses the technical aspects of single antigen bead assays, emphasizes their quantitative limitations, and explores the utility of HLA antibody testing in identifying and managing important pre- and post-transplant clinical outcomes.

HLA antibody detection with solid phase assays: great expectations or expectations too great?

Alloantibodies directed against HLA antigens, are a barrier to long-term solid organ allograft survival. The clinical impact of preformed, donor-directed HLA alloantibodies range from acceptable risk to unequivocal contraindication for organ transplantation. HLA antibodies are key factors that limit patient access to donor organs. Serological methods were once the only approach to identify HLA antigens and antibodies. Limitations in these technologies led to the development of solid phase approaches. In the early 1990s, the development of the polymerase chain reaction enabled DNA-based HLA antigen testing to be performed. By the mid-1990s, microparticle-based technology that utilized flow cytometry for analysis was developed to detect both classes I and II HLA antibodies. These methodologies revolutionized clinical histocompatibility testing. The strengths and weaknesses of these assays are described in detail in this review.

HLA-DQ barrier: effects on cPRA calculations

BACKGROUND

Panel-reactive antibody (PRA) testing provides assessment of the breadth of sensitization a patient might have against human leukocyte antigen (HLA) antigens. The evolution of calculated PRA (cPRA) reflects the commitment of the transplant community to increase accessibility and promote equity to all patients awaiting kidney transplantation. Recent data from our center and others, however, suggested that a significant diversity of HLA-DQ antigens is not captured, which may lead to inequity in allocating cPRA points.

METHODS

HLA-DRB1-DQA1-DQB1 typing of 2182 individuals was evaluated for this study using Luminex-based sequence-specific oligonucleotide typing. A total of 3182 haplotypes were confirmed to have the level of resolution required for this study.

RESULTS

The diversity of HLA-DQαβ alleles is greater than what is apparent using the serologic equivalents. The distribution of these alleles within a serologic group varies, with some alleles being more frequent than others; therefore, their representation within the current cPRA system is inaccurate. Three informative examples are given. Haplotypes of DR antigens with DQαβ alleles did not always follow the common published linkage disequilibrium, especially in populations where there is greater genetic diversity.

CONCLUSIONS

The current cPRA system does not take into account the distribution of molecular equivalents within DQ serologic specificities. This can result is inequitable allocation of sensitization points and disadvantaging the more sensitized patients. To ameliorate this situation, the United Network for Organ Sharing system should allow inputting HLA-DQαβ alleles both for donor typing and as antibody specificities, which will lead to better representation of unacceptable DQ alleles and improve organ allocation equity.

A prominent lack of IgG1-Fc fucosylation of platelet alloantibodies in pregnancy

Immunoglobulin G (IgG) formed during pregnancy against human platelet antigens (HPAs) of the fetus mediates fetal or neonatal alloimmune thrombocytopenia (FNAIT). Because antibody titer or isotype does not strictly correlate with disease severity, we investigated by mass spectrometry variations in the glycosylation at Asn297 in the IgG Fc because the composition of this glycan can be highly variable, affecting binding to phagocyte IgG-Fc receptors (FcγR). We found markedly decreased levels of core fucosylation of anti-HPA-1a-specific IgG1 from FNAIT patients (n = 48), but not in total serum IgG1. Antibodies with a low amount of fucose displayed higher binding affinity to FcγRIIIa and FcγRIIIb, but not to FcγRIIa, compared with antibodies with a high amount of Fc fucose. Consequently, these antibodies with a low amount of Fc fucose showed enhanced phagocytosis of platelets using FcγRIIIb(+) polymorphonuclear cells or FcγRIIIa(+) monocytes as effector cells, but not with FcγRIIIa(-) monocytes. In addition, the degree of anti-HPA-1a fucosylation correlated positively with the neonatal platelet counts in FNAIT, and negatively to the clinical disease severity. In contrast to the FNAIT patients, no changes in core fucosylation were observed for anti-HLA antibodies in refractory thrombocytopenia (post platelet transfusion), indicating that the level of fucosylation may be antigen dependent and/or related to the immune milieu defined by pregnancy.

Donor-specific anti-HLA antibodies detected by Luminex: predictive for short-term but not long-term survival after heart transplantation

In heart transplantation, the clinical significance of pretransplant donor-specific antibodies (DSA) detected by solid phase assay (SPA), which is more sensitive than the conventional complement-dependent cytotoxicity (CDC) assays, is unclear. The aim was to evaluate SPA performed on pretransplant sera for survival after heart transplantation. Pretransplant sera of 272 heart transplant recipients were screened for anti-HLA antibodies using CDC and SPA. For determination of pretransplant DSA, a single-antigen bead assay was performed. The presence of anti-HLA antibodies was correlated with survival. Secondary outcome parameters were acute cellular rejection, graft coronary vasculopathy and ejection fraction. In Kaplan-Meier analysis, SPA-screening did not predict survival (P = 0.494), this in contrast to CDC screening (P = 0.002). However, the presence of pretransplant DSA against HLA class I was associated with decreased short-term survival compared to non-DSA (P = 0.038). ROC curve analysis showed a sensitivity of 76% and specificity of 73% at a cutoff of 2000 MFI. In contrast, the presence of anti-HLA antibodies had no influence on long-term survival, rejection incidence, and graft function. Thus, detection of DSA class I in pretransplant serum is a strong predictor of short-term, but not long-term survival and may help in the early management of heart transplant patients.

Systematic comparison of four cell- and Luminex-based methods for assessment of complement-activating HLA antibodies

BACKGROUND

Efforts to increase the specificity and sensitivity of human leukocyte antigen (HLA) antibody detection assays recently led to the establishment of two novel Luminex bead-based assays to detect complement-activating antibodies by the assessment of complement products C1q or C4d. Here, we present a systematic comparison of the four methods, complement-dependent lymphocytotoxicity (CDC) and C1q-, C4d-, and IgG-Luminex, to assess or predict the complement-binding capability of HLA IgG antibodies.

METHODS

Forty-five sera of highly immunized patients have been assessed by in-house modified C1q- and C4d-Luminex assays and compared with standard CDC and IgG-Luminex.

RESULTS

Antibody specificities assigned by the C1q- and C4d-Luminex assay revealed an excellent concordance of 94% and 97% for HLA class I and II, respectively. Complement-fixing HLA class II antibodies were found less frequently among IgG antibodies compared with class I. Both C1q- and C4d-Luminex detected, on average, three times more specificities than CDC. Although we found a high correlation of mean fluorescence intensity values between C1q- and C4d-Luminex assays, IgG mean fluorescence intensity was not a suitable surrogate marker for the prediction of complement binding.

CONCLUSIONS

C1q- and C4d-Luminex assays are characterized by an increased sensitivity and specificity compared with CDC, the current standard in detecting complement-fixing HLA antibodies. Pretransplantation risk assessment for transplantation but also posttransplantation monitoring are important applications for both assays to improve overall allograft survival.

The DQ barrier: improving organ allocation equity using HLA-DQ information

BACKGROUND

The United Network for Organ Sharing algorithm for deceased-donor kidney allocation considers only the human leukocyte antigen (HLA)-A, HLA-B, and HLA-DR loci. Although HLA-DQ serologic specificities can be entered as unacceptable antigens, they are assigned only by the identity of the DQβ chain, disregarding the role of the similarly polymorphic α chain. DQα/β combinations result in unique antigenic epitopes, which serve as targets to different antibodies. Therefore, the presence of HLA antibodies to one DQα/β combination should not preclude negative crossmatch (XM) against another combination. In this retrospective analysis, patients were allowed XM against a particular donor if they had antibodies to some, but not all, DQα/β allele combinations with the donor serologic HLA-DQ antigens.

METHODS

HLA antibody signature was obtained using solid-phase Luminex-based antibody analysis. Results were captured at the high-resolution level (as provided by the positive beads). Potential donors were typed to include information on both HLA-DQA and HLA-DQB alleles.

RESULTS

Of the 1130 flow XM assays performed, 147 patients had antibodies to donor serologic HLA-DQ antigens. Thirty-five of those patients had antibodies to an allelic DQα/β combination within the donor serologic DQ specificity that were different from the donor's DQα/β, leading to negative flow XM results (24%). Virtual XM, accounting for donor DQα/β combinations, successfully predicts more than 98% of XM outcomes.

CONCLUSIONS

In patients with allelic DQα/β antibodies, denying the opportunity for XM based on serologically defined unacceptable antigens can disadvantage the patient. Larger cohort studies are required to substantiate our observation. Introducing DQα/β combination information may increase virtual XM accuracy and organ allocation equity.

Consensus guidelines on the testing and clinical management issues associated with HLA and non-HLA antibodies in transplantation

BACKGROUND

The introduction of solid-phase immunoassay (SPI) technology for the detection and characterization of human leukocyte antigen (HLA) antibodies in transplantation while providing greater sensitivity than was obtainable by complement-dependent lymphocytotoxicity (CDC) assays has resulted in a new paradigm with respect to the interpretation of donor-specific antibodies (DSA). Although the SPI assay performed on the Luminex instrument (hereafter referred to as the Luminex assay), in particular, has permitted the detection of antibodies not detectable by CDC, the clinical significance of these antibodies is incompletely understood. Nevertheless, the detection of these antibodies has led to changes in the clinical management of sensitized patients. In addition, SPI testing raises technical issues that require resolution and careful consideration when interpreting antibody results.

METHODS

With this background, The Transplantation Society convened a group of laboratory and clinical experts in the field of transplantation to prepare a consensus report and make recommendations on the use of this new technology based on both published evidence and expert opinion. Three working groups were formed to address (a) the technical issues with respect to the use of this technology, (b) the interpretation of pretransplantation antibody testing in the context of various clinical settings and organ transplant types (kidney, heart, lung, liver, pancreas, intestinal, and islet cells), and (c) the application of antibody testing in the posttransplantation setting. The three groups were established in November 2011 and convened for a "Consensus Conference on Antibodies in Transplantation" in Rome, Italy, in May 2012. The deliberations of the three groups meeting independently and then together are the bases for this report.

RESULTS

A comprehensive list of recommendations was prepared by each group. A summary of the key recommendations follows. Technical Group: (a) SPI must be used for the detection of pretransplantation HLA antibodies in solid organ transplant recipients and, in particular, the use of the single-antigen bead assay to detect antibodies to HLA loci, such as Cw, DQA, DPA, and DPB, which are not readily detected by other methods. (b) The use of SPI for antibody detection should be supplemented with cell-based assays to examine the correlations between the two types of assays and to establish the likelihood of a positive crossmatch (XM). (c) There must be an awareness of the technical factors that can influence the results and their clinical interpretation when using the Luminex bead technology, such as variation in antigen density and the presence of denatured antigen on the beads. Pretransplantation Group: (a) Risk categories should be established based on the antibody and the XM results obtained. (b) DSA detected by CDC and a positive XM should be avoided due to their strong association with antibody-mediated rejection and graft loss. (c) A renal transplantation can be performed in the absence of a prospective XM if single-antigen bead screening for antibodies to all class I and II HLA loci is negative. This decision, however, needs to be taken in agreement with local clinical programs and the relevant regulatory bodies. (d) The presence of DSA HLA antibodies should be avoided in heart and lung transplantation and considered a risk factor for liver, intestinal, and islet cell transplantation. Posttransplantation Group: (a) High-risk patients (i.e., desensitized or DSA positive/XM negative) should be monitored by measurement of DSA and protocol biopsies in the first 3 months after transplantation. (b) Intermediate-risk patients (history of DSA but currently negative) should be monitored for DSA within the first month. If DSA is present, a biopsy should be performed. (c) Low-risk patients (nonsensitized first transplantation) should be screened for DSA at least once 3 to 12 months after transplantation. If DSA is detected, a biopsy should be performed. In all three categories, the recommendations for subsequent treatment are based on the biopsy results.

CONCLUSIONS

A comprehensive list of recommendations is provided covering the technical and pretransplantation and posttransplantation monitoring of HLA antibodies in solid organ transplantation. The recommendations are intended to provide state-of-the-art guidance in the use and clinical application of recently developed methods for HLA antibody detection when used in conjunction with traditional methods.

Low-level HLA antibodies do not predict platelet transfusion failure in TRAP study participants

In the Trial to Reduce Alloimmunization to Platelets (TRAP) study, 101 of 530 participants became refractory to platelet transfusions without evidence of HLA or human platelet antigen (HPA) antibodies. We used a more sensitive bead-based assay to detect and quantify HLA antibodies and a qualitative solid-phase enzyme-linked immunosorbet assay for HPA to determine whether low-level antibodies could predict refractoriness in longitudinal panels from 170 lymphocytotoxicity assay (LCA)(-) and 20 LCA(+) TRAP participants. All TRAP recipients who previously tested LCA(+) were HLA antibody(+), using the bead-based system. Levels of HLA or HPA antibodies did not predict refractoriness among LCA(-) recipients, although higher levels of HLA antibodies were associated with refractoriness among LCA(+) recipients. These data demonstrate that weak to moderate HLA antibody levels detectable by modern binding assays are not associated with platelet refractoriness.