Early Antibody-mediated Rejection Research Articles

#1130 Biopsy-based transcript diagnostics identify early antibody-mediated rejection phenotypes in biopsies with subclinical donor-specific antibodies

Abstract Background and Aims Biopsy based transcript diagnostics using the molecular microscope diagnostic system (MMDx) have the potential to add diagnostic clarification in the antibody mediated rejection (AMR) continuum. While de novo donor specific antibody (dnDSA) or preformed DSA accompanied by allograft function deterioration are accepted indications for allograft biopsy with therapeutic implications, management strategy for subclinical DSA lacks consensus. MMDx might show clinical utility in this controverse scenario by helping with therapeutic decisions. Method In this single-center cohort of 326 indication kidney transplant biopsies assessed by histology and MMDx at the University Hospital Zurich, we analyzed 58 cases with subclinical DSA as biopsy indication. Cases with (n = 44) and without (n = 14) histopathologic features of AMR according to Banff 2022 were compared for molecular AMR rejection transcripts. Results When biopsied for subclinical DSA, all 14 cases without histopathologic features of AMR showed absence of molecular AMR. In contrast, molecular AMR was detected in 6/19 (32%) cases with histopathologic diagnosis of AMR and 2/25 (8%) with probable AMR (p = 0.059), Fig. 1. Microvascular inflammation below threshold with C4d negativity was significantly associated with absence of molecular AMR (p < 0.0001). Higher number of calculated epitope mismatch load for HLA class II as measured by PIRCHE II Score was significantly associated with molecular AMR (p = 0.01). In cases with molecular AMR, early AMR scores predominated (R4 vs R6, 0.0002 and R4 vs R5 0.051). Conclusion No molecular AMR was observed in absence of histopathologic AMR. Yet, in cases with histopathologic features of AMR, only 8/44 showed molecular AMR. Predominance of early AMR rejection phenotype in cases with molecular AMR transcripts allows hope for MMDx to identify treatment amenable cases with subclinical DSA. Discrepant cases call for re-biopsy to guide therapeutic decisions.

Sequential administration of anti-complement component C5 eculizumab and type-2 anti-CD20 obinutuzumab for the treatment of early antibody-mediated rejection after kidney transplantation: A proof of concept

Kidney transplant (KT) candidates with donor-specific antibodies (DSA) exhibit exceedingly high antibody-mediated rejection (ABMR) and allograft loss rates. Currently, treatment of ABMR remains an unmet clinical need. We report the use of the anti-C5 eculizumab and the type-2 anti-CD20 obinutuzumab in two patients with early ABMR. Eculizumab (900 mg IV) led to complete inhibition of the terminal complement cascade (unremarkable AP50 and CH50 activity) and prompt stoppage of complement-dependent antibody-mediated allograft injury (clearance of intra-graft C4d and C5b-9 deposition). Despite complement inhibition, obinutuzumab (1000 mg IV) determined full and long-lasting peripheral B-cell depletion, with significant reduction in all DSA. Graft function improved, remaining stable up to three years of follow-up. No signs of active ABMR and rebound DSA were detected. Obinutuzumab B-cell depletion and inhibition of DSA production were not affected by complement blockage. Further studies are needed to confirm the potential benefit of obinutuzumab in association with complement inhibitors.

Abstract 16245: Prevalence and Time Course of Adverse Events After a Biopsy Diagnosis of Antibody-Mediated Rejection in Pediatric Heart Transplant Recipients

Background: Antibody-mediated rejection (AMR) is of great relevance when assessing therapies to improve survival for pediatric heart transplant (HT). Biopsy (EMB) is the most specific means for diagnosing AMR. This study explores the impact on survival and adverse events after treated rejection (TRej) in children with AMR on EMB (any pAMR 1h or i, 2, or 3) vs acute cellular rejection (ACR). Methods: Children in the Pediatric HT Study transplanted between 1/2015-6/2022 who survived ≥2 weeks and had at least 1 TRej with EMB data were included. Survival was compared after 1st TRej with any AMR to pure ACR. Secondary outcomes of infection, malignancy, and cardiac allograft vasculopathy (CAV) after 1st TRej were assessed. Risk factors for mortality after AMR were identified using Cox proportional hazard modeling. Results: Among 3172 HT recipients, 906 (29%) had at least 1 TRej. Of these, 697 (77%) had EMB data to determine the presence of AMR. At the 1st TRej episode, 261 (37%) children had features of AMR. Median time to 1st Trej was earlier in those with AMR vs ACR, 0.11 vs 0.29 yrs. p=0.001. Survival after 1st TRej with AMR was worse than ACR in the 1st yr post HT (A); however, survival was similar when 1st TRej occurred after year 1 (B) (Figure 1 A, B). The AMR group had higher panel reactive antibody at HT, more congenital heart disease (CHD), and more had ABO incompatible HT (all p<0.05). There was no difference in time to 1st infection, malignancy, or CAV between those with treated AMR vs ACR. Multivariate predictors of graft loss after AMR were younger age, CHD, and ECMO at HT, and hemodynamic compromise at TRej (all p<0.048). Neither AMR grade nor concomitant ACR was associated with graft loss after AMR. Conclusion: This is the largest analysis of contemporary outcomes of EMB-confirmed AMR in pediatric HT. Findings underscore the impact of early AMR on graft loss and the need for tailored therapies. Similar time to infection after AMR vs ACR is notable since immune targets of therapy often differ.

A modified perioperative regimen for deceased donor kidney transplantation in presensitized recipients without prior desensitization therapy.

Renal transplantation in HLA-presensitized recipients entails an increased risk of antibody-mediated rejection (AMR) and graft loss. There is currently no accepted standard treatment protocol that can help transplant surgeons safely perform deceased donor (DD) kidney transplantation in presensitized patients without pretransplant desensitization. Fifty-one panel-reactive antibody (PRA)-positive recipients and 62 PRA-negative retransplant recipients (control) who received DD renal transplantation were included. Patients in the presensitized group (donor-specific antibody [DSA]-positive, n=25; DSA-negative, n=26) without desensitization received a modified perioperative treatment starting on day 0 or -1 with rituximab, thymoglobulin, and low daily doses of intravenous immunoglobulin (IVIG, 10-20 g/d, for 14 days). Plasmapheresis was performed once before surgery in DSA-positive recipients. The median follow-up time was 51 months in the presensitized group and 41 months in the control group. The incidence of early acute rejection (AR) and AMR (including mixed rejection) was 35.3% and 13.7% in the presensitized group, respectively, significantly higher than in the control group (14.5% and 1.6%, respectively). Within the presensitized group, the DSA-positive subgroup had more AMR than the DSA-negative subgroup (24.0% vs. 3.8%), but the incidence of T cell-mediated rejection was comparable (20.0% vs. 23.4%). In the presensitized group, all rejections were successfully reversed, and graft function remained stable during follow-up. The 1-year and 3-year survival rates of the grafts and recipients in this group were 98.0%. With a modified IVIG-based perioperative regimen, excellent intermediate-term graft and recipient survival outcomes can be achieved in presensitized patients who received DD kidney transplantation without prior desensitization.

Early Versus Late Acute AMR in Kidney Transplant Recipients-A Comparison of Treatment Approaches and Outcomes From the ANZDATA Registry.

Antibody-mediated rejection (AMR) is a major cause of kidney allograft failure and demonstrates different properties depending on whether it occurs early (<6 mo) or late (>6 mo) posttransplantation. We aimed to compare graft survival and treatment approaches for early and late AMR in Australia and New Zealand. Transplant characteristics were obtained for patients with an AMR episode reported to the Australia and New Zealand Dialysis and Transplant Registry from January 2003 to December 2019. The primary outcome of time to graft loss from AMR diagnosis, with death considered a competing risk, was compared between early and late AMR using flexible parametric survival models. Secondary outcomes included treatments used, response to treatment, and time from AMR diagnosis to death. After adjustment for other explanatory factors, late AMR was associated with twice the risk of graft loss relative to early AMR. The risk was nonproportional over time, with early AMR having an increased early risk. Late AMR was also associated with an increased risk of death. Early AMR was treated more aggressively than late with more frequent use of plasma exchange and monoclonal/polyclonal antibodies. There was substantial variation in treatments used by transplant centers. Early AMR was reported to be more responsive to treatment than late. Late AMR is associated with an increased risk of graft loss and death compared with early AMR. The marked heterogeneity in the treatment of AMR highlights the need for effective, new therapeutic options for these conditions.

Impact of ABO incompatibility and early antibody-mediated rejection on chronic antibody-mediated rejection in kidney transplant patients.

Early antibody-mediated rejection has been reported to increase chronic antibody-mediated rejection and decrease graft survival in kidney transplantation. However, the impact of early antibody-mediated rejection in ABO-incompatible kidney transplantation remains unclear. We retrospectively analyzed living-donor kidney transplantation patients from two Korean centers. Patients were categorized based on ABO compatibility and early antibody-mediated rejection within 1 year. The primary outcome was chronic antibody-mediated rejection. The secondary outcomes were production of de novo donor-specific antibody and composite kidney outcome, defined as graft loss or a decline in estimated glomerular filtration rate to below 30mL/min/1.73 m2. A total of 1639 patients were analyzed, including 1292 patients who underwent ABO-compatible kidney transplantation and 347 patients who underwent ABO-incompatible kidney transplantation. ABO-incompatible kidney transplantation had a lower risk of de novo donor-specific antibody production (hazard ratio [HR] 0.68, 95% confidence interval [CI] 0.48-0.95) and chronic antibody-mediated rejection (HR 0.33, 95% CI 0.12-0.92) with a comparable risk of the composite kidney outcome (HR 1.06, 95% CI 0.71-1.59) compared to ABO-compatible kidney transplantation. When outcomes of ABO-incompatible kidney transplantation were analyzed according to early antibody-mediated rejection, ABO-incompatible kidney transplantation without antibody-mediated rejection had a lower risk of de novo donor-specific antibody production (HR 0.60, 95% CI 0.41-0.88) and chronic antibody-mediated rejection (HR 0.28, 95% CI 0.09-0.91) than ABO-compatible kidney transplantation without antibody-mediated rejection. However, ABO-incompatible kidney transplantation with antibody-mediated rejection showed a higher risk of de novo donor-specific antibody production and similar risk of chronic antibody-mediated rejection compared to ABO-compatible kidney transplantation without antibody-mediated rejection. ABO-incompatible kidney transplantation showed a lower risk of de novo donor-specific antibody production and chronic antibody-mediated rejection compared to ABO-compatible kidney transplantation; however, early antibody-mediated rejection abrogated these beneficial effects of ABO-incompatible kidney transplantation.

(1106) The Molecular Microscope Diagnostic System (MMDx) Fails to Detect Early Antibody Mediated Rejection after Flow Crossmatch Positive Pediatric Heart Transplantation

(1106) The Molecular Microscope Diagnostic System (MMDx) Fails to Detect Early Antibody Mediated Rejection after Flow Crossmatch Positive Pediatric Heart Transplantation

Impact of ABO-Incompatibility and Early Antibody-Mediated Rejection on Kidney Allograft Outcomes

Impact of ABO-Incompatibility and Early Antibody-Mediated Rejection on Kidney Allograft Outcomes

Assessing the Relationship Between Molecular Rejection and Parenchymal Injury in Heart Transplant Biopsies.

The INTERHEART study (ClinicalTrials.gov #NCT02670408) used genome-wide microarrays to detect rejection in endomyocardial biopsies; however, many heart transplants with no rejection have late dysfunction and impaired survival. We used the microarray measurements to develop a molecular classification of parenchymal injury. In 1320 endomyocardial biopsies from 645 patients previously studied for rejection-associated transcripts, we measured the expression of 10 injury-induced transcript sets: 5 induced by recent injury; 2 reflecting macrophage infiltration; 2 normal heart transcript sets; and immunoglobulin transcripts, which correlate with time. We used archetypal clustering to assign injury groups. Injury transcript sets correlated with impaired function. Archetypal clustering based on the expression of injury transcript sets assigned each biopsy to 1 of 5 injury groups: 87 Severe-injury, 221 Late-injury, and 3 with lesser degrees of injury, 376 No-injury, 526 Mild-injury, and 110 Moderate-injury. Severe-injury had extensive loss of normal transcripts (dedifferentiation) and increase in macrophage and injury-induced transcripts. Late-injury was characterized by high immunoglobulin transcript expression. In Severe- and Late-injury, function was depressed, and short-term graft failure was increased, even in hearts with no rejection. T cell-mediated rejection almost always had parenchymal injury, and 85% had Severe- or Late-injury. In contrast, early antibody-mediated rejection (AMR) had little injury, but late AMR often had the Late-injury state. Characterizing heart transplants for their injury state provides new understanding of dysfunction and outcomes and demonstrates the differential impact of T cell-mediated rejection versus AMR on the parenchyma. Slow deterioration from AMR emerges as a major contributor to late dysfunction.

From bench to bedside: reversing established antibody responses and desensitization.

Basic transplant immunology has primarily focused on the definition of mechanisms, but an often-stated aspirational goal is to translate basic mechanistic research into future therapy. Pretransplant donor-specific antibodies (DSA) mediate hyperacute as well as early antibody-mediated rejection (AMR), whereas DSA developing late posttransplantation may additionally mediate chronic rejection. Although contemporary immunosuppression effectively prevents early cellular rejection after transplant in nonsensitized patients, it is less effective at controlling preexisting HLA antibody responses or reversing DSA once established, thus underscoring a need for better therapies. We here review the development of a bench-to-bedside approach involving transient proteasome inhibition to deplete plasma cells, combined with maintenance co-stimulation blockade, with CTLA-4Ig or belatacept, to prevent the generation of new antibody-secreting cells (ASCs). This review discusses how this treatment regimen, which was rationally designed and validated to reverse established DSA responses in mouse models, translated into reversing active AMR in the clinic, as well as desensitizing highly sensitized patients on the transplant waitlist.

Misidentification of preformed anti-HLA-DP antibodies leads to antibody-mediated kidney transplant rejection: a case report

BackgroundPatients who are HLA-sensitized are at high risk for early antibody-mediated rejection (AMR) and worse outcomes. Therefore, it is crucial to detect the presence of donor-specific antibodies (DSAs) using pretransplant antibody identification and crossmatch assays. An error in antibody identification can lead to disastrous clinical outcomes. We present a case of acute AMR associated with preformed HLA-DPα and HLA-DPβ DSAs that were not identified before transplantation.Case presentationA 27-year-old woman received a second kidney transplant from a deceased donor. Her pretransplant panel-reactive antibody level was 94%. The complement-dependent cytotoxicity crossmatch was negative for T and B cells at the time of transplantation. She experienced early acute AMR proven by a kidney biopsy. Single antigen bead testing of the patient’s serum at the time of rejection as well as the pre-second transplant serum revealed strong antibodies against the DPA1*01:03 and DPB1*02:01 alleles in the second donor. These antibodies were not identified by phenotypic bead assay during the patient’s time on the waiting list. The patient was treated with plasmapheresis and anti-thymocyte globulin. However, she experienced abdominal pain on day 37 post-transplantation. Surgical exploration revealed a laceration on the transplanted kidney, which was then repaired. Subsequently, infected hematoma was suspected and the transplanted kidney was removed.ConclusionThe present case highlights the clinical significance of preformed HLA-DPα and HLA-DPβ DSAs. Accuracy in determination of HLA antibodies before transplantattion is critical for transplant outcome. HLA-DP typing and single antigen bead testing are recommended for a precise antibody interpretation, especially in highly sensitized patients. Careful interpretation of antibody testing results is essential for the success of organ transplantation.

Glomerular C4d Immunoperoxidase in Chronic Antibody-Mediated Rejection and Transplant Glomerulopathy

IntroductionThe diagnosis of late antibody-mediated rejection (AMR) is compromised by frequent absence of C4d in peritubular capillaries (C4dptc), termed “C4d-negative” AMR. We hypothesized that glomerular capillary C4d (C4dglom) reflected endothelial interaction with antibody and could improve immunologic classification of transplant glomerulopathy (TG).MethodsWe evaluated C4d using immunoperoxidase in 3524 consecutive, kidney transplant biopsies from a single center.ResultsC4dglom was detected in 16.5% and C4dptc in 9.9% of biopsies. C4dglom occurred in 60.3% of TG (n = 174) and was absent in normal glomeruli. Epidemiologic risk factors for C4dglom were younger, female, living-donor recipients with early AMR, prior treated rejection, and late presentation using multivariable analysis. Semiquantitative C4dglom score correlated with donor specific antibody (DSA) level, C4dptc, microvascular inflammation (MVI), Banff cg scores, renal dysfunction, and proteinuria. Principal component analysis colocalized C4dglom with histologic AMR. Multivariable analysis of TG found DSA, C4dptc, and post-transplant time associated with C4dglom. Addition of C4dglom into Banff chronic AMR schema improved its diagnostic sensitivity for TG (verified by electron microscopy [EM]) from 22.2% to 82.4% and accuracy from 59.6% to 93.9%, compared with Banff 2019 using only C4dptc. Tissue C4dglom and chronic AMR diagnosis incorporating C4dglom were associated with death-censored allograft failure in TG (P < 0.001), independent of the severity of glomerulopathy and chronic interstitial fibrosis.ConclusionC4dglom is a promising diagnostic biomarker of endothelial interaction with antibody which substantially improved test performance of the Banff schema to correctly classify TG by pathophysiology and prognosticate graft loss. We recommend routine C4d immunoperoxidase to minimize underdiagnosis of late AMR in TG.

Novel Technology Has Made It Possible To Diagnose A New Clinical Phenotype Of Rejection called Early Antibody Mediated Rejection, With Significant Therapeutic Implications For Renal Allograft Survival

Novel technology in transplant, specifically, the Molecular Microscope Diagnostic System, has made it possible to diagnose a new clinical phenotype of rejection called "early antibody-mediated rejection." Here, we present 2 kidney transplant recipients who had normal serum creatinine levels but elevated donor-derived cell-free DNA. Allograft biopsies did not show antibody-mediated rejection, but the Molecular Microscope Diagnostic System reported early antibody -mediated rejection. Once considered as an isolated incident occurring after kidney transplant, antibody-mediated rejection is now recognized to be a progressive condition that waxes and wanes over time and may ultimately lead to chronic allograft damage and allograft loss. Hence, if it can be diagnosed early before causing allograft injury, the early diagnosis can represent a paradigm shift in the management of antibody-mediated rejection in kidney transplant recipients, with better treatment outcomes and prolonged allograft survival.

Increased Levels of sCD30 Have No Impact on the Incidence of Early ABMR and Long-Term Outcome in Intermediate-Risk Renal Transplant Patients With Preformed DSA.

Background: It is still incompletely understood why some patients with preformed donor-specific anti-HLA antibodies (DSA) have reduced kidney allograft survival secondary to antibody-mediated rejection (ABMR), whereas many DSA-positive patients have favorable long-term outcomes. Elevated levels of soluble CD30 (sCD30) have emerged as a promising biomarker indicating deleterious T-cell help in conjunction with DSA in immunologically high-risk patients. We hypothesized that this would also be true in intermediate-risk patients.Methods: We retrospectively analyzed pre-transplant sera from 287 CDC-crossmatch negative patients treated with basiliximab induction and tacrolimus-based maintenance therapy for the presence of DSA and sCD30. The incidence of ABMR according to the Banff 2019 classification and death-censored allograft survival were determined.Results: During a median follow-up of 7.4 years, allograft survival was significantly lower in DSA-positive as compared to DSA-negative patients (p < 0.001). In DSA-positive patients, most pronounced in those with strong DSA (MFI > 5,000), increased levels of sCD30 were associated with accelerated graft loss compared to patients with low sCD30 (3-year allograft survival 75 vs. 95%). Long-term survival, however, was comparable in DSA-positive patients irrespective of sCD30 status. Likewise, the incidence of early ABMR and lesion score characteristics were comparable between sCD30-positive and sCD30-negative patients with DSA. Finally, increased sCD30 levels were not predictive for early persistence of DSA.Conclusion: Preformed DSA are associated with an increased risk for ABMR and long-term graft loss independent of sCD30 levels in intermediate-risk kidney transplant patients.

TNFRSF13B genotypes control immune-mediated pathology by regulating the functions of innate B cells.

Host genes define the severity of inflammation and immunity but specific loci doing so are unknown. Here we show that TNF receptor superfamily member 13B (TNFRSF13B) variants, which enhance defense against certain pathogens, also control immune-mediated injury of transplants, by regulating innate B cells’ functions. Analysis of TNFRSF13B in human kidney transplant recipients revealed that 33% of those with antibody-mediated rejection (AMR) but fewer than 6% of those with stable graft function had TNFRSF13B missense mutations. To explore mechanisms underlying aggressive immune responses, we investigated alloimmunity and rejection in mice. Cardiac allografts in Tnfrsf13b-mutant mice underwent early and severe AMR. The dominance and precocity of AMR in Tnfrsf13b-deficient mice were not caused by increased alloantibodies. Rather, Tnfrsf13b mutations decreased “natural” IgM and compromised complement regulation, leading to complement deposition in allografted hearts and autogenous kidneys. Thus, WT TNFRSF13B and Tnfrsf13b support innate B cell functions that limit complement-associated inflammation; in contrast, common variants of these genes intensify inflammatory responses that help clear microbial infections but allow inadvertent tissue injury to ensue. The wide variation in inflammatory reactions associated with TNFRSF13B diversity suggests polymorphisms could underlie variation in host defense and explosive inflammatory responses that sometimes enhance morbidity associated with immune responses.

Anti-C5 Antibody Tesidolumab Reduces Early Antibody-mediated Rejection and Prolongs Survival in Renal Xenotransplantation.

Pig-to-primate renal xenotransplantation is plagued by early antibody-mediated graft loss which precludes clinical application of renal xenotransplantation. We evaluated whether temporary complement inhibition with anti-C5 antibody Tesidolumab could minimize the impact of early antibody-mediated rejection in rhesus monkeys receiving pig kidneys receiving costimulatory blockade-based immunosuppression. Double (Gal and Sda) and triple xenoantigen (Gal, Sda, and SLA I) pigs were created using CRISPR/Cas. Kidneys from DKO and TKO pigs were transplanted into rhesus monkeys that had the least reactive crossmatches. Recipients received anti-C5 antibody weekly for 70 days, and T cell depletion, anti-CD154, mycophenolic acid, and steroids as baseline immunosuppression (n = 7). Control recipients did not receive anti-C5 therapy (n = 10). Temporary anti-C5 therapy reduced early graft loss secondary to antibody-mediated rejection and improved graft survival (P < 0.01). Deleting class I MHC (SLA I) in donor pigs did not ameliorate early antibody-mediated rejection (table). Anti-C5 therapy did not allow for the use of tacrolimus instead of anti-CD154 (table), prolonging survival to a maximum of 62 days. Inhibition of the C5 complement subunit prolongs renal xenotransplant survival in a pig to non-human primate model.

Incidence, risk factors, and long-term outcomes associated with antibody-mediated rejection - The long-term Deterioration of Kidney Allograft Function (DeKAF) prospective cohort study.

Major gaps remain in our understanding of antibody-mediated rejection (AMR) after kidney transplant. We examined the incidence, risk factors, response to treatment, and effects on outcomes of AMR at seven transplant programs in the long-term Deterioration of Kidney Allograft Function prospective study cohort. Among 3131 kidney recipients, there were 194 observed AMR cases (6.2%) during (mean±SD) 4.85±1.86years of follow-up. Time to AMR was 0.97±1.17 (median, 0.48) years. Risk factors for AMR included younger recipient age, human leukocyte antigen DR mismatches, panel-reactive antibody >0%, positive T- or B-cell cross-match, and delayed graft function. Compared with no AMR, the adjusted time-dependent hazard ratio for death-censored graft failure is 10.1 (95% confidence interval, 6.5-15.7) for all AMR patients, 4.0 (2.5, 9.1) for early AMR (<90days after transplant), and 24.0 (14.0-41.1) for late AMR (≥90days after transplant). Patients were treated with different therapeutic combinations. Of 194 kidney transplant recipients with AMR, 50 (25.8%) did not respond to treatment, defined as second AMR within 100days or no improvement in estimated glomerular filtration rate by 42days. Long-term outcomes after AMR are poor, regardless of the initial response to treatment. Better prevention and new therapeutic strategies are needed to improve long-term allograft survival.

Single antigen testing to reduce early antibody-mediated rejection risk in female recipients of a spousal donor kidney

Female recipients of a spousal donor kidney transplant are at greater risk of donor-specific pre-immunization, which may increase the risk of acute antibody-mediated rejection (ABMR). We assessed the incidence of early ABMR (within two weeks after transplantation), risk factors for ABMR and graft function in 352 complement-dependent cytotoxicity test-negative LURD transplant recipients, transplanted between 1997 and 2014 at the Leiden University Medical Center in The Netherlands. Risk factors for immunization were retrieved from the health records. As methods to screen for preformed donor-specific antibodies (pDSA) have developed through time, we retrospectively screened those with ABMR for pDSA using pooled-antigen bead (PAB) and single-antigen bead (SAB) assays. The cumulative incidence of rejection in the first six months after transplantation was 18% (TCMR 15%; early ABMR 3%). Early ABMR resulted in inferior graft survival and was more common in women who received a kidney from their spouse (10%) than in other women (2%) and men (<1%). The SAB assay retrospectively identified pDSA in seven of nine cases of early ABMR (78%), while the PAB detected pDSA in only three cases (33%). Seeing that early ABMR occurred in 10% of women who received a kidney from their spouse, a SAB assay should be included in the pre-transplant assessment of this group of women, regardless of the result of the PAB assay.

Early Antibody-Mediated Rejection in Non-Pre-Sensitized Heart Transplant Recipient

Introduction Antibody-mediated rejection (AMR) is an important cause of allograft dysfunction. It usually occurs after the first month of heart transplant (HT), but an early presentation is possible. We present an unusual case of a female HT recipient who had early AMR with no evidence of pre-sensitization to the donor. Case Report A woman, 45 years old, idiopathic dilated cardiomyopathy, two kids, with previous negative panel reactive antibody (PRA) was submitted to HT with success. The prospective crossmatch was negative and she did not receive blood cells during the surgery. The donor was a woman, 47 years old, who had a hemorrhagic stroke. After the procedure, she needed low doses of vasoactive drugs, received immunosuppression therapy according to institutional protocol and maintained normal ventricular function. On the 5th day, she developed biventricular graft dysfunction (left ventricular ejection fraction of 40%) requiring inotropes. The PRA revealed a donor specific antibody (DSA) not previously detected and the result of endomyocardial biopsy (EMB) confirmed acute AMR (pAMR2). Patient was successfully treated with methylprednisolone, plasmapheresis, immunoglobulin and rituximab. Biventricular function recovered; no DSA was detected and new EMB showed no rejection findings. Summary AMR results from recipient antibodies against donor-HLA antigens, causing complement activation, inflammation and injury to the allograft endothelium. In general, it occurs in the first two months after HT due to a rise in DSA by the contact with donor-HLA antigens. Early AMR, that occurs in the first week, is related to pre-sensitization to donor HLA antigens and associated with graft dysfunction. In this case report, no previous antibody had been detected. Two possibilities could explain such findings: the presence of non-HLA antibodies or the presence of memory B cells with levels of DSA too low to be detected on PRA. This case highlights the importance of monitoring antibodies in HT recipients with early allograft dysfunction even with previous negative PRA.

AT1R-Ab: A New Player in Pediatric Heart Transplant AMR?

<h3>Purpose</h3> Angiotensin II type 1 receptor antibodies (AT1R-Ab) are associated with non-human leukocyte antigen (HLA) mediated antibody mediated rejection (AMR) and graft failure in adult renal transplantation. They can be stimulated by ventricular assist device (VAD) support, but data regarding AT1R-Ab in pediatric heart transplantation (HT) are scarce. The purpose of this study is to describe the incidence of non-HLA mediated AMR and identification of AT1R-Ab in a pediatric HT cohort. <h3>Methods</h3> We performed a single-center retrospective review of children who underwent primary HT from July 2016 to July 2020. AMR was defined by the presence of complement deposition (+C4d) on heart biopsy. Non-HLA mediated AMR was defined by the absence of donor-specific HLA antibodies (HLA-DSA). AT1R-Ab testing was defined as < 10 negative, 10-17 borderline, and > 17 positive (ELISA). <h3>Results</h3> There were 100 patients who underwent primary HT during the study period (median age 4.5 years). There were 19 episodes of AMR in 17 patients. HLA-DSA were present in 12 episodes (63%) and absent in 7 (37%) episodes. Non-HLA mediated AMR occurred earlier post-HT compared to AMR with HLA-DSA (median 7 days vs 244 days, p = 0.04). Four patients with AMR in the absence of HLA-DSA were tested for AT1R-Ab; 3 were positive and 1 was borderline. Of the 3 patients with positive AT1R-Ab, 2 were previously supported on VAD, 2 had symptomatic AMR, 2 subsequently received losartan, and none have had recurrence of AMR (Table). <h3>Conclusion</h3> Non-HLA mediated AMR accounted for 37% of AMR episodes and occurred earlier post-HT compared to AMR with HLA-DSA in a single-center cohort. AT1R-Ab were present in 3 of 4 patients with non-HLA mediated AMR in whom AT1R-Ab testing was performed. In light of the recent data regarding AT1R-Ab in renal transplantation, investigation of the prevalence and clinical significance of AT1R-Ab in pediatric HT, particularly in early non-HLA mediated AMR and in those bridged to HT with VAD, is warranted.