Hexamerization: explaining the original sin of IgG-mediated complement activation in acute lung injury.

Although antibody-mediated lung damage is a major factor in transfusion-related acute lung injury (ALI), autoimmune lung disease (for example, coatomer subunit α [COPA] syndrome), and primary graft dysfunction following lung transplantation, the mechanism by which antigen-antibody complexes activate complement to induce lung damage remains unclear. In this issue of the JCI, Cleary and colleagues utilized several approaches to demonstrate that IgG forms hexamers with MHC class I alloantibodies. This hexamerization served as a key pathophysiological mechanism in alloimmune lung injury models and was mediated through the classical pathway of complement activation. Additionally, the authors provided avenues for exploring therapeutics for this currently hard-to-treat clinical entity that has several etiologies but a potentially focused mechanism.

Tacrolimus's Time Below Therapeutic Range Is Associated With Acute Pancreatic Graft Rejection and the Development of De Novo Donor-specific Antibodies.

Tacrolimus is pivotal in pancreas transplants but poses challenges in maintaining optimal levels due to recipient differences. This study aimed to explore the utility of time spent below the therapeutic range and intrapatient variability in predicting rejection and de novo donor-specific antibody (dnDSA) development in pancreas graft recipients. This retrospective unicentric study included adult pancreas transplant recipients between January 2006 and July 2020. Recorded variables included demographics, immunosuppression details, HLA matching, biopsy results, dnDSA development, and clinical parameters. Statistical analysis included ROC curves, sensitivity, specificity, and predictive values. A total of 131 patients were included. Those with biopsy-proven acute rejection (BPAR, 12.2%) had more time (39.9% ± 24% vs. 25.72% ± 21.57%, p = 0.016) and tests (41.95% ± 13.57% vs. 29.96% ± 17.33%, p = 0.009) below therapeutic range. Specific cutoffs of 31.5% for time and 34% for tests below the therapeutic range showed a high negative predictive value for BPAR (93.98% and 93.1%, respectively). Similarly, patients with more than 34% of tests below the therapeutic range were associated with dnDSA appearance (38.9% vs. 9.4%, p = 0.012; OR 6.135, 1.346-27.78). In pancreas transplantation, maintaining optimal tacrolimus levels is crucial. Suboptimal test percentages below the therapeutic range prove valuable in identifying acute graft rejection risk.

Bortezomib for antibody-mediated rejection of kidney transplant in youth: Associations with donor-specific antibody.

BACKGROUND: Antibody-mediated rejection is one of the most significant risk factors for allograft dysfunction and failure in children and adolescents with kidney transplants, yet optimal treatment remains unidentified. To date, there are mixed findings regarding the use of Bortezomib, a plasma cell apoptosis inducer, as an adjunct therapy in the treatment of antibody-mediated rejection. METHODS: In a retrospective single center study, we reviewed the efficacy and tolerability of bortezomib as adjunct therapy for treatment-refractory antibody-mediated rejection. RESULTS: Six patients with a median age of 14.6 years (range 6.9-20.1 years) received bortezomib at a mean of 71 months (range 15-83 months) post-kidney transplant. Four patients experienced decline in estimated glomerular filtration rate (eGFR) from 4% to 42%. One patient started bortezomib while on hemodialysis and did not recover graft function, and another patient progressed to hemodialysis 6 months after receiving bortezomib. Although DSA did not completely resolve, there was a statistically significant decline in DSA MFI pre and 12-months post-BZ (p = .012, paired t-test) for the subjects who were not on dialysis at the time of bortezomib. Chronic Allograft Damage Index (CADI) score of ≥3 was seen in all six subjects at their biopsy prior to therapy. No adverse effects were reported. CONCLUSIONS: Bortezomib was well tolerated and resulted in improvements in MFI of DSA among four pediatric subjects without allograft failure, although no effects were observed on eGFR trajectory. Further studies are needed to clarify whether earlier intervention with bortezomib could prevent renal failure progression.

Association of HLA B- and T-cell molecular mismatches with HLA antibodies, rejection, and graft survival in pediatric kidney transplantation.

BACKGROUND: Optimizing graft survival and diminishing human leukocyte antigen (HLA) sensitization are essential for pediatric kidney transplant recipients. More precise HLA matching predicting epitope mismatches could reduce alloreactivity. We investigated the association of predicted HLA B- and T-cell molecular mismatches with the formation of de novo donor-specific antibodies, HLA antibodies, rejection, and graft survival. METHODS: Forty-nine pediatric kidney transplant recipients transplanted from 2009 to 2020 were retrospectively studied. Donors and recipients were high-resolution HLA typed, and recipients were screened for HLA antibodies posttransplant. HLA-EMMA (HLA Epitope MisMatch Algorithm) and PIRCHE-II (Predicted Indirectly ReCognizable HLA Epitopes) predicted the molecular mismatches. The association of molecular mismatches and the end-points was explored with logistic regression. RESULTS: Five recipients (11%) developed de novo donor-specific antibodies. All five had de novo donor-specific antibodies against HLA class II, with four having HLA-DQ antibodies. We found no associations between PIRCHE-II or HLA-EMMA with de novo donor-specific antibodies, HLA sensitization, graft loss, or rejection. However, we did see a tendency towards an increased odds ratio in PIRCHE-II predicting de novo donor-specific antibodies formation, with an odds ratio of 1.12 (95% CI: 0.99; 1.28) on HLA class II. CONCLUSION: While the study revealed no significant associations between the number of molecular mismatches and outcomes, a notable trend was observed - indicating a reduced risk of dnDSA formation with improved molecular match. It is important to acknowledge, however, that the modest population size and limited observed outcomes preclude us from making definitive conclusions.

Late graft failure of pig-to-rhesus renal xenografts has features of glomerulopathy and recipients have anti-swine leukocyte antigen class I and class II antibodies.

Prolonged survival in preclinical renal xenotransplantation demonstrates that early antibody mediated rejection (AMR) can be overcome. It is now critical to evaluate and understand the pathobiology of late graft failure and devise new means to improve post xenograft outcomes. In renal allotransplantation the most common cause of late renal graft failure is transplant glomerulopathy-largely due to anti-donor MHC antibodies, particularly anti-HLA DQ antibodies. We evaluated the pig renal xenograft pathology of four long-surviving (>300 days) rhesus monkeys. We also evaluated the terminal serum for the presence of anti-SLA class I and specifically anti-SLA DQ antibodies. All four recipients had transplant glomerulopathy and expressed anti-SLA DQ antibodies. In one recipient tested for anti-SLA I antibodies, the recipient had antibodies specifically reacting with two of three SLA I alleles tested. These results suggest that similar to allotransplantation, anti-MHC antibodies, particularly anti-SLA DQ, may be a barrier to improved long-term xenograft outcomes.

Successful management of maternal anti-PP1Pk alloimmunization in pregnancy with therapeutic plasma exchange and intravenous immunoglobulin.

Anti-PP1PK alloimmunization is rare given ubiquitous P1PK expression. Prevention of recurrent miscarriages and hemolytic disease of the fetus and newborn (HDFN) in pregnant individuals with anti-PP1PK antibodies has relied upon individual reports. Here, we demonstrate the successful management of maternal anti-PP1PK alloimmunization in a 23-year-old, G2P0010, with therapeutic plasma exchange (TPE), intravenous immunoglobulin (IVIG), and monitoring of anti-PP1Pk titers. Twice-weekly TPE (1.5 plasma volume [PV], 5% albumin replacement) with weekly titers and IVIG (1 g/kg) was initiated at 9 weeks of gestation (WG). The threshold titer was ≥16. Weekly middle cerebral artery-peak systolic velocities (MCA-PSV) for fetal anemia monitoring was initiated at 16 WG. PVs were adjusted throughout pregnancy based on treatment schedule, titers, and available albumin. Antigen-negative, ABO-compatible RBCs were obtained through the rare donor program and directed donation. An autologous blood autotransfusion system was reserved for delivery. Titers decreased from 128 to 8 by 10 WG. MCA-PSV remained stable. At 24 WG, TPE decreased to once weekly. After titers increased to 32, twice-weekly TPE resumed at 27 WG. Induction of labor was scheduled at 38 WG. Vaginal delivery of a 2950 g neonate (APGAR score: 9, 9) occurred without complication (Cord blood: 1+ IgG DAT; Anti-PP1Pk eluted). Newborn hemoglobin and bilirubin were unremarkable. Discharge occurred postpartum day 2. Anti-PP1Pk alloimmunization is rare but associated with recurrent miscarriages and HDFN. With multidisciplinary care, a successful pregnancy is possible with IVIG and TPE adjusted to PV and titers. We also propose a patient registry and comprehensive management plan.

Kidney transplant candidates' perspectives on the implementation of a Canadian Willingness to Cross program: A strategy to increase access to kidney transplantation for highly sensitized patients.

BACKGROUND: Kidney transplantation is the optimal treatment for end-stage renal disease. However, highly sensitized patients (HSPs) have reduced access to transplantation, leading to increased morbidity and mortality on the waiting list. The Canadian Willingness to Cross (WTC) program proposes allowing transplantation across preformed donor specific antibodies (DSA) determined to be at a low risk of rejection under the adaptive design framework. This study collected patients' perspectives on the development of this program. METHODS: Forty-one individual interviews were conducted with kidney transplant candidates from three Canadian transplant centers in 2022. The interviews were digitally recorded and transcribed for subsequent analyses. RESULTS: Despite limited familiarity with the adaptive design, participants demonstrated trust in the researchers. They perceived the WTC program as a pathway for HSPs to access transplantation while mitigating transplant-related risks. HSPs saw the WTC program as a source of hope and an opportunity to leave dialysis, despite acknowledging inherent uncertainties. Some non-HSPs expressed concerns about fairness, anticipating increased waiting times and potential compromise in kidney graft longevity due to higher rejection risks. Participants recommended essential strategies for implementing the WTC program, including organizing informational meetings and highlighting the necessity for psychosocial support. CONCLUSION: The WTC program emerges as a promising strategy to enhance HSPs' access to kidney transplantation. While HSPs perceived this program as a source of hope, non-HSPs voiced concerns about distributive justice issues. These results will help develop a WTC program that is ethically sound for transplant candidates.

Neonatal and Obstetrical Outcomes of Pregnancies Complicated by Alloimmunization.

BACKGROUND AND OBJECTIVES: Despite advances in the prevention of rhesus (Rh)(D) alloimmunization, alloantibodies to Rh(D) and non-Rh(D) red blood cell antigens continue to be detected in ∼4% of US pregnancies and can result in hemolytic disease of the fetus and newborn (HDFN). Recent reports on HDFN lack granularity and are unable to provide antibody-specific outcomes. The objective of this study was to calculate the frequency of alloimmunization in our large hospital system and summarize the outcomes based on antibody specificity, titer, and other clinical factors. METHODS: We identified all births in a 6-year period after a positive red blood cell antibody screen result during pregnancy and summarized their characteristics and outcomes. RESULTS: A total of 707 neonates were born after a positive maternal antibody screen result (3.0/1000 live births). In 31 (4%), the positive screen result was due to rhesus immune globulin alone. Of the 676 neonates exposed to alloantibodies, the direct antibody test (DAT) result was positive, showing antigen-positivity and evidence of HDFN in 37% of those tested. Neonatal disease was most severe with DAT-positive anti-Rh antibodies (c, C, D, e, E). All neonatal red blood cell transfusions (15) and exchange transfusions (6) were due to anti-Rh alloimmunization. No neonates born to mothers with anti-M, anti-S, anti-Duffy, anti-Kidd A, or anti-Lewis required NICU admission for hyperbilirubinemia or transfusion. CONCLUSIONS: Alloimmunization to Rh-group antibodies continues to cause a majority of the severe HDFN cases in our hospital system. In neonates born to alloimmunized mothers, a positive DAT result revealing antigen-positivity is the best predictor of anemia and hyperbilirubinemia.

Repeated human leukocyte antigens eplets, importance of typing the partner.

INTRODUCTION: Antibody-mediated rejection (AMR) is the most common cause of immune-mediated allograft failure after kidney transplant and impacts allograft survival. Previous sensitization is a major risk factor for development of donor specific antibodies (DSA). AMR can have a wide range of clinical features such as impaired kidney function, proteinuria/hypertension or can be subclinical. HLA molecules have specific regions of antigens binding antibodies called epitopes and eplets are considered essential components responsible for immune recognition. We present a patient with subclinical AMR 1 week post transplantation. CASE REPORT: A 48-year-old, caucasian woman with end-stage kidney disease (ESKD) secondary to autosomal dominant polycystic kidney disease (ADPKD) on peritoneal dialysis was registered in deceased donor waitlist. She was a hypersensitized patient from 3 prior pregnancies with a calculated panel reactive antibody of 93,48%. She was transplanted through kidney paired exchange donation with no evidence of DSA pre transplantation. Surgery and post-op were unremarkable with excellent and immediate graft function. Per protocol DSA levels on the 5th day was DR1 of 3300 MFI, with an increase in MFI by day 13 with 7820 MFI and a new B41 1979MFI. Allograft kidney biopsy findings were diagnostic of AMR and she was treated with immunoglobulin and plasmapheresis. As early onset AMR post transplantation was observed an anamnestic response was hypothesized from a previous exposure to allo-HLA. We decided to type her husband, her son's father, which was presented with DSA. Mismatch eplet analysis revealed a shared 41 T and 67LQ eplets between the donor and husband, responsible for the reactivity and new HLA class I B41 and HLA class II DR1 DSA, respectively. DISCUSSION: Shared eplets between the patient husband and donor was responsible for the alloimmune response and early development of DSAs. This case highlights the importance of early monitoring DSA levels in highly sensitized patients after transplant in order to promptly address and lower inflammatory damage. Mismatch eplet analysis can provide a thorough and precise evaluation of immune compatibility providing a useful technique to immune risk stratification, donor selection and post-transplant immunosuppressive therapy and monitoring.

Impact of donor-specific antibody with low mean fluorescence intensity on allograft outcomes in kidney transplant.

BACKGROUND: Immune-mediated rejection is the most common cause of allograft failure in kidney transplant (KT) patients. Exposure to alloantigen, including human leukocyte antigen (HLA), results in the production of donor-specific antibodies (DSA). There are limited data about low levels of mean fluorescence intensity (MFI) DSA, especially post-transplantation. This study evaluated allograft outcomes in KT patients with low MFI DSA. METHODS: From January 2007 to December 2021, KT patients who were tested for post-transplant DSA at Ramathibodi Hospital, Bangkok, Thailand, with the DSA MFI ≤ 1000 were evaluated. These KT patients were categorized into two groups: very low DSA (VLL; MFI = 1-500) and low DSA (LL; MFI = 501-1000). All KT patients were evaluated for the primary outcomes, such as the incidence of acute rejection, serum creatinine levels at one and five years after transplantation as well as allograft and patient survivals. RESULTS: Among 36 KT patients 25 were included as those with VLL and 11 as those with LL. The LL group had significantly higher T-cell mediated allograft rejection (TCMR) than the VLL group (45% vs. 12%, P = 0.04). In addition, 10 patients, 5 in the VLL group and 5 in the LL group developed antibody-mediated allograft rejection (ABMR). Both TCMR and ABMR were confirmed by biopsy results. There was a trend toward higher MFI in KT patients with ABMR than without ABMR (P = 0.22). At 5 post-transplant years, serum creatinine, allograft and patient survivals were comparable between these two groups. Furthermore, the univariate and multivariate analyzes revealed that the LL group was a high risk for rejection. CONCLUSION: Low MFI DSA values after transplantation may be associated with a higher incidence of rejection, but this finding did not show differences in allograft and patient survival in this study's analysis.

Impact of Transient and Persistent Donor-Specific Antibodies in Lung Transplantation.

Lung transplantation (LuTx) is an established treatment for patients with end-stage lung diseases, however, outcomes are limited by acute and chronic rejection. One aspect that has received increasing attention is the role of the host's humoral alloresponse, particularly the formation of de novo donor-specific antibodies (dnDSAs). The aim of this study was to investigate the clinical significance of transient and persistent dnDSAs and to understand their impact on outcomes after LuTx. A retrospective analysis was conducted using DSA screening data from LuTx recipients obtained at the Medical University of Vienna between February 2016 and March 2021. Of the 405 LuTx recipients analyzed, 205 patients developed dnDSA during the follow-up period. Among these, 167 (81%) had transient dnDSA and 38 (19%) persistent dnDSA. Persistent but not transient dnDSAs were associated with chronic lung allograft dysfunction (CLAD) and antibody-mediated rejection (AMR) (p < 0.001 and p = 0.006, respectively). CLAD-free survival rates for persistent dnDSAs at 1-, 3-, and 5-year post-transplantation were significantly lower than for transient dnDSAs (89%, 59%, 56% vs. 91%, 79%, 77%; p = 0.004). Temporal dynamics of dnDSAs after LuTx have a substantial effect on patient outcomes. This study underlines that the persistence of dnDSAs poses a significant risk to graft and patient survival.

Antenatal RHD screening to guide antenatal anti-D immunoprophylaxis in non-immunized D- pregnant women.

In pregnancy, D- pregnant women may be at risk of becoming immunized against D when carrying a D+ fetus, which may eventually lead to hemolytic disease of the fetus and newborn. Administrating antenatal and postnatal anti-D immunoglobulin prophylaxis decreases the risk of immunization substantially. Noninvasive fetal RHD genotyping, based on testing cell-free DNA extracted from maternal plasma, offers a reliable tool to predict the fetal RhD phenotype during pregnancy. Used as a screening program, antenatal RHD screening can guide the administration of antenatal prophylaxis in non-immunized D- pregnant women so that unnecessary prophylaxis is avoided in those women who carry a D- fetus. In Europe, antenatal RHD screening programs have been running since 2009, demonstrating high test accuracies and program feasibility. In this review, an overview is provided of current state-of-the-art antenatal RHD screening, which includes discussions on the rationale for its implementation, methodology, detection strategies, and test performance. The performance of antenatal RHD screening in a routine setting is characterized by high accuracy, with a high diagnostic sensitivity of ≥99.9 percent. The result of using antenatal RHD screening is that 97-99 percent of the women who carry a D- fetus avoid unnecessary prophylaxis. As such, this activity contributes to avoiding unnecessary treatment and saves valuable anti-D immunoglobulin, which has a shortage worldwide. The main challenges for a reliable noninvasive fetal RHD genotyping assay are low cell-free DNA levels, the genetics of the Rh blood group system, and choosing an appropriate detection strategy for an admixed population. In many parts of the world, however, the main challenge is to improve the basic care for D- pregnant women.

Severe neonatal thrombocytopenia due to anti-HPA-4b alloantibodies: Third report described in a Caucasian mother.

BACKGROUND: Fetal and Neonatal Alloimmune Thrombocytopenia (FNAIT) results from maternal platelet alloimmunization against paternal antigens inherited by the fetus, most often due to the Human Platelet Antigen (HPA)-1 system in Caucasians. We investigated in 2023, a 30-year-old Caucasian woman Gravida 2 Para 1 who gave birth at 35 weeks of gestation to a male (body weight 2210 g) without signs of bleeding. A severe thrombocytopenia (platelet count at 3 G/L) was discovered incidentally a few hours after delivery in the context of the management of a respiratory distress. The newborn recovered after one platelet concentrate transfusion and normalized his platelet count at Day 5. STUDY DESIGN AND METHODS: FNAIT investigation was performed according to guideline recommendations. Platelet genotyping was carried out by multiplex PCR. Maternal serological investigation included Monoclonal Antibody-specific Immobilization of Platelet Antigens method (MAIPA) and Luminex technology. RESULTS: Parental and newborn genotyping pointed out an HPA-4 incompatibility between the mother and the newborn and the father. Serological investigation revealed an anti-HPA-4b alloantibody confirming the diagnosis of neonatal alloimmune thrombocytopenia. CONCLUSION: We described the third case of anti-HPA-4b alloantibody discovered in a Caucasian mother. This case strengthens the need for reference laboratory to genotype a panel of HPA alleles reflecting local genetic population diversity and for crossmatch of maternal serum with fresh paternal platelets in clinical suspected cases of neonatal alloimmune thrombocytopenia.

Bridge-to-transplant temporary mechanical circulatory support and risk of allosensitization.

INTRODUCTION: Since the 2018 change in the US adult heart allocation policy, more patients are bridged-to-transplant on temporary mechanical circulatory support (tMCS). Previous studies indicate that durable left ventricular assist devices (LVAD) may lead to allosensitization. The goal of this study was to assess whether tMCS implantation is associated with changes in sensitization. METHODS: We included patients evaluated for heart transplants between 2015 and 2022 who had alloantibody measured before and after MCS implantation. Allosensitization was defined as development of new alloantibodies after tMCS implant. RESULTS: A total of 41 patients received tMCS before transplant. Nine (22.0%) patients developed alloantibodies following tMCS implantation: 3 (12.0%) in the intra-aortic balloon pump group (n = 25), 2 (28.6%) in the microaxial percutaneous LVAD group (n = 7), and 4 (44.4%) in the veno-arterial extra-corporeal membrane oxygenation group (n = 9)-p = .039. Sensitized patients were younger (44.7 ± 11.6 years vs. 54.3 ± 12.5 years, p = .044), were more likely to be sensitized at baseline - 3 of 9 (33.3%) compared to 2 out of 32 (6.3%) (p = .028) and received more transfusions with red blood cells (6 (66.6%) vs. 8 (25%), p = .02) and platelets (6 (66.6%) vs. 5 (15.6%), p = .002). There was no significant difference in tMCS median duration of support (4 [3,15] days vs. 8.5 [5,14.5] days, p = .57). Importantly, out of the 11 patients who received a durable LVAD after tMCS, 5 (45.5%) became sensitized, compared to 4 out of 30 patients (13.3%) who only had tMCS-p = .028. CONCLUSIONS: Our findings suggest that patients bridged-to-transplant with tMCS, without significant blood product transfusions and a subsequent durable LVAD implant, have a low risk of allosensitization. Further studies are needed to confirm our findings and determine whether risk of sensitization varies by type of tMCS and duration of support.

Using single antigen specificity magnetic beads for the isolation of specific antibodies against HLA antigens.

The presence of multiple donor-specific antibodies (DSAs) targeting HLA antigens poses a challenge to transplantation. Various techniques, including the use of recombinant cell lines and crossmatch cells have been developed to isolate DSAs. To simplify the extraction of HLA-specific DSAs from complex sera, we introduced magnetic beads with single HLA specificity (MagSort). Sera were treated with MagSort, allowing HLA-specific antibodies to bind to the beads, and these specific antibodies were subsequently eluted. MagSort beads, coated with 59 different HLA variants, underwent testing through 1329 adsorption/elution processes, demonstrating their effectiveness and specificity in adsorbing and eluting HLA-specific antibodies. The MagSort method proves comparable to the cell method, showing similar isolated antibody binding patterns. The isolated antibody binding patterns from MagSort reveal both known eplets and unknown patterns, suggesting its utility for eplet discovery. Additionally, MagSort proved effective in extracting signals for flow cytometry cross-matching, offering a means to assess the binding capability of isolated antibodies against specific donor cells.

Qualitative, rather than quantitative, differences between HLA-DQ alleles affect HLA-DQ immunogenicity in organ transplantation.

Prolonging the lifespan of transplanted organs is critical to combat the shortage of this life-saving resource. Chronic rejection, with irreversible demise of the allograft, is often caused by the development of donor-specific HLA antibodies. Currently, enumerating molecular (amino acid) mismatches between recipient and donor is promoted to identify patients at higher risk of developing HLA antibodies, for use in organ allocation, and immunosuppression-minimization strategies. We have counseled against the incorporation of such approaches into clinical use and hypothesized that not all molecular mismatches equally contribute to generation of donor-specific immune responses. Herein, we document statistical shortcomings in previous study design: for example, use of individuals who lack the ability to generate donor-specific-antibodies (HLA identical) as part of the negative cohort. We provide experimental evidence, using CRISPR-Cas9-edited cells, to rebut the claim that the HLAMatchmaker eplets represent "functional epitopes." We further used unique sub-cohorts of patients, those receiving an allograft with two HLA-DQ mismatches yet developing antibodies only to one mismatch (2MM1DSA), to interrogate differential immunogenicity. Our results demonstrate that mismatches of DQα05-heterodimers exhibit the highest immunogenicity. Additionally, we demonstrate that the DQα chain critically contributes to the overall qualities of DQ molecules. Lastly, our data proposes that an augmented risk to develop donor-specific HLA-DQ antibodies is dependent on qualitative (evolutionary and functional) divergence between recipient and donor, rather than the mere number of molecular mismatches. Overall, we propose an immunological mechanistic rationale to explain differential HLA-DQ immunogenicity, with potential ramifications for other pathological processes such as autoimmunity and infections.

Memory B-cell derived donor-specific antibodies do not predict outcome in sensitized kidney transplant recipients: a retrospective single-center study.

Background: Repeated exposure to sensitizing events can activate HLA-specific memory B cells, leading to the production of donor-specific memory B cell antibodies (DSAm) that pose a risk for antibody-mediated rejection (ABMR) in kidney transplant recipients (KTRs). This single-center retrospective study aimed to identify DSAm and assess their association with outcomes in a cohort of KTRs with pretransplant serum donor-specific antibodies (DSA). Methods: We polyclonally activated pretransplant peripheral blood mononuclear cells (PBMCs) from 60 KTRs in vitro, isolated and quantified IgG from the culture supernatant using ELISA, and analyzed the HLA antibodies of eluates with single antigen bead (SAB) assays, comparing them to the donor HLA typing for potential DSAm. Biopsies from 41 KTRs were evaluated for rejection based on BANFF 2019 criteria. Results: At transplantation, a total of 37 DSAm were detected in 26 of 60 patients (43%), of which 13 (35%) were found to be undetectable in serum. No significant association was found between pretransplant DSAm and ABMR (P=0.53). Similar results were observed in a Kaplan-Meier analysis for ABMR within the first year posttransplant (P=0.29). Additionally, MFI levels of DSAm showed no significant association with ABMR (P=0.28). Conclusion: This study suggests no significant association between DSAm and biopsy-proven clinical ABMR. Further prospective research is needed to determine whether assessing DSAm could enhance existing immunological risk assessment methods for monitoring KTRs, particularly in non-sensitized KTRs.

Daratumumab treatment in six highly sensitised solid organ transplant recipients: A case series and literature review.

We report data on six kidney or heart recipients who were administered daratumumab to treat or prevent antibody-mediated rejection (ABMR). To date, data are scarce concerning the use of daratumumab in solid organ transplantation and most reports show a decrease in donor-specific antigen (DSA) levels and an improvement in ABMR using a multiple myeloma daratumumab administration scheme, that is, with sequential systematic administration. Here, we report on the efficacy of daratumumab 1/ in reducing the histological signs of ABMR, 2/ in reducing the ability of DSA to bind to donor cells in vitro through negativation of flow cytometry crossmatching, 3/ in preferentially being directed towards antibodies sharing epitopes, suggesting that daratumumab may specifically target activated plasma cells, 4/ and when administered as a single dose. This last point suggests, for the first time, that, as for rituximab in auto-immune diseases, the scheme for daratumumab administration could be different for targeting DSA-producing plasma cells than for tumour cells.

European Consensus on the Management of Sensitized Kidney Transplant Recipients: A Delphi Study.

An increasing number of sensitized patients awaiting transplantation face limited options, leading to fatalities during dialysis and higher costs. The absence of established evidence highlights the need for collaborative consensus. Donor-specific antibodies (DSA)-triggered antibody-mediated rejection (AMR) significantly contributes to kidney graft failure, especially in sensitized patients. The European Society for Organ Transplantation (ESOT) launched the ENGAGE initiative, categorizing sensitized candidates by AMR risk to improve patient care. A systematic review assessed induction and maintenance regimens as well as antibody removal strategies, with statements subjected to the Delphi methodology. A Likert-scale survey was distributed to 53 European experts (Nephrologists, Transplant surgeons and Immunologists) with experience in kidney transplant recipient care. A rate ≥75% with the same answer was considered consensus. Consensus was achieved in 95.3% of statements. While most recommendations aligned, two statements related to complement inhibitors for AMR prophylaxis lacked consensus. The ENGAGE consensus presents contemporary recommendations for desensitization and immunomodulation strategies, grounded in predefined risk categories. The adoption of tailored, patient-specific measures is anticipated to streamline the care of sensitized recipients undergoing renal allografts. While this approach holds the promise of enhancing transplant accessibility and fostering long-term success in transplantation outcomes, its efficacy will need to be assessed through dedicated studies.

Antibody-mediated rejection in pediatric kidney transplant recipients: A report from the Pediatric Nephrology Research Consortium.

BACKGROUND: Antibody-mediated rejection (AMR) is a major cause of kidney allograft loss. There is a paucity of large-scale pediatric-specific data regarding AMR treatment outcomes. METHODS: Data were obtained from 14 centers within the Pediatric Nephrology Research Consortium. Kidney transplant recipients aged 1-18 years at transplant with biopsy-proven AMR between 2009 and 2019 and at least 12 months of follow-up were included. The primary outcome was graft failure or an eGFR <20 mL/min/1.73 m2 at 12 months following AMR treatment. AMR treatment choice, histopathology, and DSA class were also examined. RESULTS: We reviewed 123 AMR episodes. Median age at diagnosis was 15 years at a median 22 months post-transplant. The primary outcome developed in 27.6%. eGFR <30 m/min/1.73 m2 at AMR diagnosis was associated with a 5.6-fold higher risk of reaching the composite outcome. There were no significant differences in outcome by treatment modality. Histopathology scores and DSA class at time of AMR diagnosis were not significantly associated with the primary outcome. CONCLUSIONS: In this large cohort of pediatric kidney transplant recipients with AMR, nearly one-third of patients experienced graft failure or significant graft dysfunction within 12 months of diagnosis. Poor graft function at time of diagnosis was associated with higher odds of graft failure.