Accurate measurement of ABO antibodies is essential for safe ABO-incompatible (ABOi) heart transplantation. Traditional hemagglutination titers lack standardization and reproducibility; moreover, hemagglutination detects antibodies irrelevant to the heart graft. A novel multiplexed immunoassay, similar to human leukocyte antigen antibody assessment assays, enables accurate measurement of IgG and IgM antibodies with specificities to ABO glycan subtypes expressed in donor cardiac tissue, improving precision over titer methods. Recent policy changes in the United States allow ABO-incompatible (ABOi) transplants for pediatric patients, expanding the donor pool. We report here 2 pediatric cases demonstrating the clinical utility of the multiplexed assay: in 1 infant, the assay enabled successful ABOi transplantation despite borderline high conventional titers; in another, unexpectedly high titers post-transplant were shown by the multiplexed assay to be clinically irrelevant, avoiding unnecessary treatment. This new assay supports better candidate eligibility assessment and post-transplant monitoring. Incorporating this technology can safely expand ABOi transplantation and improve immunologic risk assessment.

Patients require immunosuppression after heart transplantation. Conditions such as Crohn's disease can impact tacrolimus absorption and pharmacokinetics. Subtherapeutic tacrolimus levels can lead to rejection and development of donor-specific antibodies (DSA), resulting in the development of cardiac allograft vasculopathy. We present a boy who underwent an ABO blood groupincompatible heart transplant at 10 months of age, and developed diarrhea and subtherapeutic tacrolimus levels with subsequent development of de novo DSA, and then acute cellular and antibody-mediated rejection. He was diagnosed with Crohn's disease, which required vedolizumab for control. Despite aggressive reduction of his DSA, he developed rapidly progressive cardiac allograft vasculopathy and required retransplant, with a high prevalence of plasma cells in the explanted heart. Donor-directed blood group antibodies remained negative. This case demonstrates the importance of early consideration of inflammatory bowel disease for patients with diarrhea and subtherapeutic tacrolimus levels, as prompt diagnosis and treatment may prevent secondary graft injury.

We test the performance of the multiplexed liquid glycan array (LiGA) technology in serological assays. Specifically, we use LiGA to detect ABO blood group antibodies in human serum. This LiGA, which we name ABO-LiGA, contains ABO blood group trisaccharide glycans with an ethylazido aglycone conjugated to groups of ten multi-barcoded M13 particles carrying dibenzocyclooctyne (DBCO) on p8 proteins. ELISA clonal binding assays to anti-A/B antibodies confirmed the functional performance of ABO-clones and aligned with next-generation sequencing (NGS) of the mixed clones. Multiple DNA-barcoded technical replicates in LiGA allow for quantification of reproducibility and robustness as determined by the Z'-score using NGS. We then tested ABO-LiGA for specific detection of IgG and IgM anti-A and anti-B IgG and IgM antibodies in human serum samples. Comparison of antibody binding responses in sera from 31 healthy donors to ABO-LiGA with an ABO-Luminex-based method revealed consistent responses to LiGA-ABO but also minor deficiencies of ABO-LiGA such as low robustness of the current assay format and a limited ability to detect low intensity antibody responses. Some results point to undesired interactions of serum antibodies with small-footprint glycans conjugated to phage via the bulky DBCO moiety. This report illuminates the path for future development of LiGA-based serological assays and suggests the need to develop alternative methods for conjugating glycans to phage to avoid liabilities of the hydrophobic DBCO moiety.

Although ABO-incompatible (ABOi) living donor kidney transplantation is currently performed on a routine basis, it remains a procedure with a high immunologic risk requiring both immunosuppression aimed at diminishing antibody production and removal of circulating antibodies from the recipient's blood. We describe two cases of kidney transplant recipients (KTR) who experienced hyperacute antibody-mediated rejection after ABOi transplantation and further testing was performed on their sera using a novel bead-based ABO antibody assay to understand the cause of such unfortunate outcomes. Both patients were ABO-O recipients who received ABO-A grafts; neither had donor-specific anti-HLA antibodies (DSA). Both received rituximab >4 weeks and standard immunosuppression according to the Swiss ABOi protocol, starting 10–25 days before transplantation; basiliximab was used for induction at time of transplant. Immunoadsorption was performed before transplant with a nonselective Therasorb column; immunoadsorption effectiveness was analyzed by measuring the anti-A-IgG titer and anti-A-IgM titer by gel column agglutination technique. Case 1: Transplantation was performed after 17 immunoadsorption runs (prolonged due to postponed date of surgery for non-immunological reasons); post-adsorption anti-A titres were negative IgG and <1:8 IgM. After an initial diuresis, the patient became anuric within 24 hours. Biopsy histology revealed hyperacute rejection. Graft nephrectomy was performed two days post-transplant. Case 2: transplantation was performed after 11 immunoadsorption runs; post-adsorption anti-A titres were negative IgG and 1:1 IgM. After an initial diuresis urine output decreased within hours. Biopsy histology showed hyperacute rejection. Plasmapheresis was started empirically approximately 15 hours after transplant despite negative anti-A titer and no anti-HLA DSA, and treatment with high dose steroids, IVIG and eculizumab was administered. Graft nephrectomy was performed seven days post-transplant. Analysis of the original sera with a novel single antigen bead assay for anti-A subtype-specific antibodies showed an initial drop in MFIs of IgG and IgM for both patients. However, at time of transplant, despite acceptable anti-A titers with our standard hemagglutination methods, patient 1 and 2 MFI were still 17200 and 9300, respectively for anti-A-IgG isotype antibodies (II, III and IV averaged) and 3300 and 3800 for anti-A-IgM isotype IgM (II, III and IV averaged). Analysis of sera from the days immediately after transplantation showed a rebound for these subtype-specific anti-A antibodies in Case 1, with an MFI up to 26000 (anti-A-IgG) and 5000 (anti-A-IgM). In Case 2 (where samples were drawn after plasmapheresis) the MFIs of the anti-A-II/III/IV further dropped to 2100 (IgG) and 1200 (IgM). Refer to Fig. 1 for antibody data. Hyperacute AMR in these two ABO-A-incompatible kidney transplant cases was likely due to insufficient removal of anti-A antibodies. Whether this is due to insufficient removal of anti-A antibodies by the nonselective Therasorb column needs to be further investigated. These results suggest that for such an immunological high-risk procedure, a switch from titer-based diagnostics to single bead Luminex diagnostics should be considered. Of further note, transcriptome diagnostics might support the histology, but it is not yet established in ABOi graft biopsies.

Kidney transplantation from ABO-A2 donors into ABO-O and ABO-B recipients can alleviate inequitable transplant access created by ABO demographics. ABO-A2-incompatible (ABO-A2i) eligibility is determined by anti-A hemagglutination titers. However, titers do not distinguish antibodies specific for A-II glycans, the sole A-antigen subtype in vascular endothelium, from other anti-A antibodies. We examined whether reliance on anti-A titers unnecessarily limited ABO-A2i transplants for candidates with low anti-A-II levels. We created a single-antigen bead immunoassay for ABO antibodies, confirmed the specificity and reproducibility, and demonstrated the ability to detect anti-A and anti-B glycan subtype-specific antibodies in healthy control sera. We then measured subtype-specific anti-A antibodies in original sera from ABO-B and ABO-O candidates who had been previously evaluated for ABO-A2i eligibility. Anti-A-II levels in candidates who had been deemed ineligible (anti-A titers >4) were compared to eligible candidates (anti-A titers ≤4) who had subsequently received ABO-A2i kidneys. Of 141 candidates, 75 (53%) were ineligible; 66 (47%) were eligible and received ABO-A2 kidneys. Retesting original sera, 55% (41/75) of ineligible candidates had anti-A-II levels comparable to eligible candidates. Anti-A titers did not reflect anti-A-II levels. Our ABO antibody assay reproducibly measures graft-specific anti-A-II antibodies, providing information beyond anti-A titers that may increase transplant access for ABO-B and ABO-O candidates.

The understanding of circulating antibodies and their relationship to antibody-mediated rejection (AMR) has yet to be fully elucidated in heart transplantation. Circulating antibodies are important in both pretransplant and post-transplant. In the pretransplant period, the more antibodies detected in a patient awaiting heart transplantation often significantly reduces the chance of obtaining a compatible donor heart. In the post-transplant period, de novo antibody development against the donor heart remains a challenge to manage. In both pre- and post-transplant scenarios, it is not known what approach is optimal for treating these patients with circulating antibodies. To address these unmet needs, a consensus conference was organized on April 18, 2023, endorsed by the International Society for Heart and Lung Transplantation. The conference represented a collaborative multidisciplinary effort by experts in cardiothoracic transplantation from across the world to understand and discuss the optimum approach and treatment of circulating antibodies and AMR in heart transplant candidates and recipients. The conference served as a forum to better understand antibodies and AMR and their impact on transplant patients. The nature of this consensus is to prepare a platform and pave the way for further detailed studies. The findings and consensus statements are hereby presented.

Purpose of the Conference: The 2022 Banff-Canadian Society of Transplantation Meeting in Banff, Alberta, brought together transplant professionals to review new developments across various aspects of solid organ transplantation (SOT) in Canada. Sources of Information: Presentations included consensus recommendations from expert-led forums; experiences with new procedures and legislation; reports from public health data repositories; original clinical and laboratory research; and industry updates regarding novel technologies. Speakers referenced articles and reports published in peer-reviewed journals and online, and unpublished data and preliminary findings. Methods: All authors attended presentations in-person or virtually. Recordings of select presentations were available for later review. Summaries emphasize concepts indicated by speakers as new and clinically relevant. Key Findings: The COVID-19 pandemic disproportionately affected solid organ transplant recipients (SOTRs), who experience worse outcomes of COVID-19 infection than the general population. Vaccinations demonstrate an attenuated immunological response in SOTRs yet provide meaningful protection. Monoclonal antibodies are effective for both passive immunization and treatment of COVID-19 in SOTRs. Infection control protocols have driven the development of virtual methods for clinical research, such as using home blood draws and virtual follow-up to evaluate vaccine efficacy in SOTRs; and patient care delivery, such as employing telerehabilitation post transplant. Access to living kidney donation is limited by various disincentives experienced by potential donors, which may be overcome by more efficient evaluations including a One-Day Living Kidney Donor Assessment Clinic. The International Donation and Transplantation Legislative and Policy Forum provided a means of establishing consensus guidance for organ donation and transplantation (ODT) program policy to standardize delivery across jurisdictions. The implementation of a deemed consent model for organ and tissue donation in Nova Scotia may provide insight as to whether this model indeed improves access to organs. Canada’s Indigenous population experiences unique barriers to transplantation, prompting efforts for more inclusive ODT policy-making. The Pan-Canadian ODT Data and Performance Reporting System Project has defined performance quality indicators, of which iTransplant and other point-of-care software solutions may facilitate collection; however, these endeavors ultimately require information technology infrastructure that exceeds the capabilities of the existing Canadian Organ Replacement Register and Canadian Transplant Registry. Pig-to-human xenotransplantation requires genetic modification of pigs and xenoantibody testing in recipients but may yet prove viable. Serum cell-free DNA, urine biomarkers, and genetic markers offer an alternative to routine biopsy for identifying subclinical rejection. Modified perfusion temperatures and perfusion solutions with hydrogen sulfide donor compounds may improve organ preservation. Molecular compatibility tools provide another means of improving SOTR outcomes, and the Genome Canada Transplant Consortium has been examining important considerations of their implementation. Limitations: We were unable to capture all presentations and topics at the meeting due to the sizable quantity and variety. Topics ultimately excluded from this summary include those in pathology including Banff Classification updates; those unique to extra-renal SOT; as well as numerous abstract and poster presentations, allied health provider forums, and business meetings. A portion of the material was presented by speakers prior to peer-review or publication. Implications: The various conference presentations summarized in this report identify methods by which individual clinicians and provincial ODT programs may improve access, delivery, and quality of SOT care in Canada, while additionally identifying gaps in the literature that investigators are encouraged to pursue.

Objective: To provide the largest single-center analysis of islet (ITx) and pancreas (PTx) transplantation. Summary Background Data: Studies describing long-term outcomes with ITx and PTx are scarce. Methods: We included adults undergoing ITx (n=266) and PTx (n=146) at the University of Alberta from January 1999 to October 2019. Outcomes include patient and graft survival, insulin independence, glycemic control, procedure-related complications, and hospital readmissions. Data are presented as medians (interquartile ranges, IQR) and absolute numbers (percentages, %) and compared using Mann-Whitney and χ 2 tests. Kaplan-Meier estimates, Cox proportional hazard models and mixed main effects models were implemented. Results: Crude mortality was 9.4% and 14.4% after ITx and PTx, respectively (P=0.141). Sex-adjusted and age-adjusted hazard-ratio for mortality was 2.08 (95% CI, 1.04–4.17, P=0.038) for PTx versus ITx. Insulin independence occurred in 78.6% and 92.5% in ITx and PTx recipients, respectively (P=0.0003), while the total duration of insulin independence was 2.1 (IQR 0.8–4.6) and 6.7 (IQR 2.9–12.4) year for ITx and PTx, respectively (P=2.2×10-22). Graft failure ensued in 34.2% and 19.9% after ITx and PTx, respectively (P=0.002). Glycemic control improved for up to 20-years post-transplant, particularly for PTx recipients (group, P=7.4×10-7, time, P=4.8×10-6, group*time, P=1.2×10-7). Procedure-related complications and hospital readmissions were higher after PTx (P=2.5×10-32 and P=6.4×10-112, respectively). Conclusions: PTx shows higher sex-adjusted and age-adjusted mortality, procedure-related complications and readmissions compared with ITx. Conversely, insulin independence, graft survival and glycemic control are better with PTx. This study provides data to balance risks and benefits with ITx and PTx, which could improve shared decision-making.

ABO‐incompatible heart transplantation (HTx) has become a standard procedure for children below 2 years of age due to an immunologically immature immune system and associated low isohemagglutinin titers.

Background. ABO-incompatible transplantation has improved accessibility of kidney, heart, and liver transplantation. Pancreatic islet transplantation continues to be ABO-matched, yet ABH antigen expression within isolated human islets or novel human embryonic stem cell (hESC)-derived islets remain uncharacterized. Methods. We evaluated ABH glycans within human pancreata, isolated islets, hESC-derived pancreatic progenitors, and the ensuing in vivo mature islets following kidney subcapsular transplantation in rats. Analyses include fluorescence immunohistochemistry and single-cell analysis using flow cytometry. Results. Within the pancreas, endocrine and ductal cells do not express ABH antigens. Conversely, pancreatic acinar tissues strongly express these antigens. Acinar tissues are present in a substantial portion of cells within islet preparations obtained for clinical transplantation. The hESC-derived pancreatic progenitors and their ensuing in vivo-matured islet-like clusters do not express ABH antigens. Conclusions. Clinical pancreatic islet transplantation should remain ABO-matched because of contaminant acinar tissue within islet preparations that express ABH glycans. Alternatively, hESC-derived pancreatic progenitors and the resulting in vivo-matured hESC-derived islets do not express ABH antigens. These findings introduce the potential for ABO-incompatible cell replacement treatment and offer evidence to support scalability of hESC-derived cell therapies in type 1 diabetes.

BACKGROUND:Ventricular assist devices (VADs) have improved survival to heart transplantation (HTx). However, VADs have been associated with development of antibodies against human leukocyte antigen (HLA-Ab) which may limit the donor pool and decrease survival post-HTx. Since HLA-Ab development after VAD insertion is poorly understood, the purpose of this prospective single-center study was to quantify the incidence of and evaluate risk factors for HLA-Ab development across the age spectrum following VAD implantation. METHODS:Adult and pediatric patients undergoing VAD placement as bridge to transplant or transplant candidacy between 5/2016 and 7/2020 were enrolled. HLA-Ab were assessed pre-VAD and at 1-, 3-, and 12-months post-implant. Factors associated with HLA-Ab development post-VAD implant were explored using univariate and multivariate logistic regression. RESULTS:15/41 (37%) adults and 7/17 (41%) children developed new HLA-Ab post-VAD. The majority of patients (19/22) developed HLA-Ab within two months of implant. New class I HLA-Ab were more common (87% adult, 86% pediatric). Prior pregnancy was strongly associated with HLA-Ab development in adults post-VAD (HR 16.7, 95% CI 1.8-158, p = 0.01). Of the patients who developed new HLA-Ab post-VAD, in 45% (10/22) the HLA-Ab resolved while in 55% (12/22) the HLA-Ab persisted. CONCLUSION:More than one-third of adult and pediatric VAD patients developed new HLA-Ab early after VAD implant with the majority having class I antibodies. Prior pregnancy was strongly associated with post-VAD HLA-Ab development. Further studies are needed to predict regression or persistence of HLA-Ab developed post-VAD, to understand modulation of individuals' immune responses to sensitizing events, and to determine whether transiently detected HLA-Ab post-VAD recur and have long-term clinical impact post-heart transplantation.

Background:In solid organ transplantation, HLA matching between donor and recipient is associated with superior outcomes. In islet transplantation, an intervention for Type 1 diabetes, HLA matching between donor and recipient is not performed as part of allocation. Susceptibility to Type 1 diabetes is associated with the presence of certain HLA types. This study was conducted to determine the impact of these susceptibility antigens on islet allograft survival. Methods:This is a single-centre retrospective cohort study. This cohort of transplant recipients (n = 268) received islets from 661 donor pancreases between March 11th, 1999 and August 29th, 2018 at the University of Alberta Hospital (Edmonton, AB, Canada). The frequency of the Type 1 diabetes susceptibility HLA antigens (HLA-A24, -B39, -DQ8, -DQ2 and-DQ2-DQA1∗05) in recipients and donors were determined. Recipient and donor HLA antigens were examined in relation to time to first C-peptide negative status/graft failure or last observation point. Taking into account multiple transplants per patient, we fitted a Gaussian frailty survival analysis model with baseline hazard function stratified by transplant number, adjusted for cumulative islet dose and other confounders. Findings:Across all transplants recipients of donors positive for HLA-DQ8 had significantly better graft survival (adjusted HRs 0.33 95% CI 0.17-0.66; p = 0.002). At first transplant only, donors positive for HLA-DQ2-DQA1∗05 had inferior graft survival (adjusted HR 1.96 95% CI 1.10-3.46); p = 0.02), although this was not significant in the frailty analysis taking multiple transplants into account (adjusted HR 1.46 95% CI 0.77-2.78; p = 0.25). Other HLA antigens were not associated with graft survival after adjustment for confounders. Interpretation:Our findings suggest islet transplantation from HLA-DQ8 donors is associated with superior graft outcomes. A donor positive for HLA-DQ2-DQA1∗05 at first transplant was associated with inferior graft survival but not when taking into account multiple transplants per recipient. The relevance of HLA-antigens on organ allocation needs further evaluation and inclusion in islet transplant registries and additional observational and interventional studies to evaluate the role of HLA-DQ8 in islet graft survival are required. Funding:None.