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.

Extracellular vesicles as potential diagnostic markers for kidney allograft rejection.

Kidney transplantation is a highly effective treatment for end-stage kidney disease. However, allograft rejection remains a significant clinical challenge in kidney transplant patients. Although kidney allograft biopsy is the gold-standard diagnostic method, it is an invasive procedure. Since the current monitoring methods, including screening of serum creatinine and urinary protein, are not of sufficient sensitivity, there is a need for effective post-transplant monitoring to detect allograft rejection at an early stage. Extracellular vesicles are vesicles with a lipid bilayer that originate from different cell types in pathological and physiological conditions. The content of extracellular vesicles reflects the status of cells at the time of their production. This review comprehensively summarizes clinical, in vivo, and in vitro reports that highlight the potential of extracellular vesicles as diagnostic biomarkers for kidney allograft rejection. Clarification would facilitate differentiation between rejection and non-rejection and identification of the mechanisms involved in the allograft rejection. Despite increasing evidence, further research is necessary to establish the clinical utility of extracellular vesicles in the diagnosis and monitoring of allograft rejection in kidney transplant recipients. Using extracellular vesicles as non-invasive biomarkers for diagnosis of kidney allograft rejection could have tremendous benefits in improving patient outcomes and reduce the need for invasive procedures.

Histopathology, mRNA expression profile, and donor-derived cell-free DNA for assessment of rejection in pediatric heart transplantation.

BACKGROUND: The relationship between histopathologic and molecular ("MMDx"®) assessments of endomyocardial biopsy (EMB) and serum donor-derived cell-free DNA (ddcfDNA) in acute rejection (AR) assessment following pediatric heart transplantation (HT) is unknown. METHODS: EMB sent for MMDx and histopathology from November 2021 to September 2022 were reviewed. MMDx and histopathology results were compared. DdcfDNA obtained ≤1 week prior to EMB were compared with histopathology and MMDx results. The discrimination of ddcfDNA for AR was assessed using receiver-operating curves. FINDINGS: In this study, 177 EMBs were obtained for histopathology and MMDx, 101 had time-matched ddcfDNA values. MMDx and Histopathology displayed moderate agreement for T-cell-mediated rejection (TCMR, Kappa = 0.52, p < .001) and antibody-mediated rejection (ABMR, Kappa = 0.41, p < .001). Discordant results occurred in 24% of cases, most often with ABMR. Compared with no AR, ddcfDNA values were elevated in cases of AR diagnosed by both histopathology and MMDx (p < .01 for all). Additionally, ddcfDNA values were elevated in injury patterns on MMDx, even when AR was not present (p = .01). DdcfDNA displayed excellent discrimination (AUC 0.83) for AR by MMDx and/or histopathology. Using a threshold of ≥0.135%, ddcfDNA had a sensitivity of 90%, specificity of 63%, PPV of 52%, and NPV of 94%. CONCLUSIONS: Histopathology and MMDx displayed moderate agreement in diagnosing AR following pediatric HT, with most discrepancies noted in the presence of ABMR. DdcfDNA is elevated with AR, with excellent discrimination and high NPV particularly when utilizing MMDx. A combination of all three tests may be necessary in some cases.

PCR testing for herpesviruses in aqueous humor samples from patients with and without clinical corneal endothelial graft rejection.

To compare prevalence of positive PCR tests for herpesviruses between patients with and without a history of clinical corneal endothelial allograft rejection (AGR). Retrospective cross-sectional study with two-group comparison. A total of 307 aqueous humor (AH) samples from 235 Patients and 244 eyes who underwent penetrating keratoplasty or Descemet membrane endothelial keratoplasty or had a diagnostic AH aspiration due to clinical AGR between 2019 and 2023 were tested for DNA of herpes simplex virus (HSV), varicella-zoster virus (VZV), cytomegalovirus (CMV), and Epstein-Barr virus (EBV). PCR test results were compared between the two groups (with/without AGR). Another sub-analysis examined the results of patients without a history of herpetic keratitis. A total of 8% of eyes with clinical AGR (9/108) had a positive PCR result for one of the herpesviruses (HSV:3, CMV:3, EBV:2, VZV:1). All patients in the group without AGR had negative PCR results for all previous viruses (0/136). The difference was statistically significant (p < 0.001). The sub-analysis of eyes without a history of herpetic keratitis also revealed significantly more positive herpes PCR results (7/87) in eyes with AGR than in eyes without AGR (0/42, p = 0.005). Clinical AGR after keratoplasty shows a significant correlation to viral replication. Herpetic infection and AGR could occur simultaneously and act synergistically. Timely differentiation between active herpetic infection and/or AGR is pivotal for proper treatment and graft preservation.

Protocol liver biopsy predicts graft survival after liver transplantation.

BACKGROUND: The use of protocol liver biopsy to monitor liver allograft status remains controversial. There is limited data from modern transplantation populations that includes protocol biopsies to evaluate its value in predicting clinical outcomes. METHODS: All protocol liver biopsies were identified from 875 patients who underwent liver transplantation at Helsinki University Hospital between 2000 and 2019. Each histologic component was analyzed for its ability to predict long-term outcomes, especially graft survival. We determined the frequency of significant biopsy findings based on the Banff working group definition. Liver function tests (LFTs) and clinical markers were evaluated for their ability to predict significant biopsy findings. RESULTS: In total, 867 protocol liver biopsies were analyzed. Significant findings were identified in 20.1% of the biopsies. In the first protocol biopsy, steatohepatitis (hazard ratio [HR] 3.504, p = .03) and moderate or severe congestion (HR 3.338, p = .04) predicted graft loss. The presence of cholangitis (HR 2.563, p = .04), necrosis (HR 7.635, p < .001), mild congestion (HR 4.291, p = .009), and significant biopsy finding (HR 2.540, p = .02) predicted inferior death-censored graft survival. While the degree of elevation of LFTs was positively associated with significant biopsy findings, the discrimination was poor (AUC .572-.622). Combined LFTs and clinical risk factors remained suboptimal for discriminating significant biopsy findings (AUC .696). CONCLUSIONS: Our findings support the use of protocol liver biopsies after liver transplantation since they frequently revealed changes associated with long-term outcomes, even when LFTs were normal.

Routine screening for HLA Antibodies in Heart Transplant patients-Does it affect clinical decision making?

BACKGROUND: We aimed to assess outcomes in patients with and without donor specific antibodies (DSA) and to evaluate the relationship between DSA presence and graft function, cardiac allograft vasculopathy (CAV), and mortality. METHODS: The study population comprises 193 consecutive long-term heart transplanted (HTx) patients who underwent DSA surveillance between 2016 and 2022. The patients were prospectively screened for CAV through serial coronary angiograms, graft function impairment through serial echocardiograms, and cardiac biomarkers. The patients were followed from the first DSA measurement until death, 5 years follow-up or right censuring on the 30th of June 2023. RESULTS: DSAs were detected in 50 patients using a cut-off at MFI ≥1000 and 45 patients using a cut-off at ≥2000 MFI. The median time since HTx was 9.0 years [3.0-14.4]. DSA positive patients had poorer graft function and higher values of NT-proBNP and troponin T, and more prevalent CAV than DSA negative patients. In total, 25 patients underwent endomyocardial biopsies due to DSA presence while another eight patients underwent endomyocardial biopsies for other reasons. Histological antibody mediated rejection (AMR) signs were seen in three biopsies. During a median follow-up of five years [4.7-5], a total of 41 patients died. Mortality rates did not differ between DSA positive and DSA negative patients (HR 1.2, 95% CI .6-2.4). DSA positive patients were more likely to experience CAV progression than DSA negative patients (HR 2.7, 95% CI 1.5-4.8) CONCLUSIONS: Routine screening reveals DSA in approximately 25% of long-term HTx patients but is rarely related to histopathological AMR signs. DSA presence was associated with poorer graft function and more prevalent and progressive CAV. However, DSA positive patients had similar survival rates to DSA negative patients.

Failing to Make the Grade: Conventional Cardiac Allograft Rejection Grading Criteria Are Inadequate for Predicting Rejection Severity.

BACKGROUND: Cardiac allograft rejection is the leading cause of early graft failure and is a major focus of postheart transplant patient care. While histological grading of endomyocardial biopsy samples remains the diagnostic standard for acute rejection, this standard has limited diagnostic accuracy. Discordance between biopsy rejection grade and patient clinical trajectory frequently leads to both overtreatment of indolent processes and delayed treatment of aggressive ones, spurring the need to investigate the adequacy of the current histological criteria for assessing clinically important rejection outcomes. METHODS: N=2900 endomyocardial biopsy images were assigned a rejection grade label (high versus low grade) and a clinical trajectory label (evident versus silent rejection). Using an image analysis approach, n=370 quantitative morphology features describing the lymphocytes and stroma were extracted from each slide. Two models were constructed to compare the subset of features associated with rejection grades versus those associated with clinical trajectories. A proof-of-principle machine learning pipeline-the cardiac allograft rejection evaluator-was then developed to test the feasibility of identifying the clinical severity of a rejection event. RESULTS: The histopathologic findings associated with conventional rejection grades differ substantially from those associated with clinically evident allograft injury. Quantitative assessment of a small set of well-defined morphological features can be leveraged to more accurately reflect the severity of rejection compared with that achieved by the International Society of Heart and Lung Transplantation grades. CONCLUSIONS: Conventional endomyocardial samples contain morphological information that enables accurate identification of clinically evident rejection events, and this information is incompletely captured by the current, guideline-endorsed, rejection grading criteria.

Biopsy-based transcriptomics in the diagnosis of kidney transplant rejection.

PURPOSE OF REVIEW: The last year has seen considerable progress in translational research exploring the clinical utility of biopsy-based transcriptomics of kidney transplant biopsies to enhance the diagnosis of rejection. This review will summarize recent findings with a focus on different platforms, potential clinical applications, and barriers to clinical adoption. RECENT FINDINGS: Recent literature has focussed on using biopsy-based transcriptomics to improve diagnosis of rejection, in particular antibody-mediated rejection. Different techniques of gene expression analysis (reverse transcriptase quantitative PCR, microarrays, probe-based techniques) have been used either on separate samples with ideally preserved RNA, or on left over tissue from routine biopsy processing. Despite remarkable consistency in overall patterns of gene expression, there is no consensus on acceptable indications, or whether biopsy-based transcriptomics adds significant value at reasonable cost to current diagnostic practice. SUMMARY: Access to biopsy-based transcriptomics will widen as regulatory approvals for platforms and gene expression models develop. Clinicians need more evidence and guidance to inform decisions on how to use precious biopsy samples for biopsy-based transcriptomics, and how to integrate results with standard histology-based diagnosis.

Immunology Status of Patients During Kidney Transplant.

OBJECTIVES: The immunology status of a patient has a crucial role in kidney transplant. We investigated the effectiveness of a desensitization protocol, guided by the immunology status of patients, for kidney transplant candidates. MATERIALS AND METHODS: Antibody screening for human leukocyte antigens was conducted with the Luminex single-antigen microsphere bead assay method for 34 patients from June 2021 to June 2022. Donor human leukocyte antigen genotypes at 8 loci (A*, B*, С*, DRB1*, DQA1*, DQB1*, DPA1*, and DPB1*) were determined, to correlate the specificities of recipient human leukocyte antigen antibodies with donor antigens and identify unacceptable donor antigen combinations. Specialized immunology studies measured panel reactive antibody levels and human leukocyte antigen class I and class II antibodies. A crossmatch compatibility test using complementdependent cytotoxicity was conducted. RESULTS: Of the 34 patients, 10 completed all 3 stages of the desensitization therapy. Most patients experienced decreased sensitization to human leukocyte antigen class I and class II antibodies. Two patients achieved complete clearance of A1 and DQ5 antibodies, respectively, whereas 1 patient exhibited an increase in donor-specific antibody mean fluorescence intensity. Prior to desensitization therapy, the crossmatch compatibility test yielded positive results with T and B lymphocytes. After completing the therapy, the crossmatch test showed negative results in 4 cases with T lymphocytes and positive results with B lymphocytes. Plasmapheresis sessions effectively reduced circulating antibodies. However, the combination of rituximab and plasmapheresis alone did not achieve a negative crossmatch test required for kidney transplant. CONCLUSIONS: It is crucial to assess the reduction of donor-specific antibody quantity, considering both the percentage and the mean fluorescence intensity. To avoid false-positive results in crossmatch analysis, drug half-life must be considered. Laboratories should have various crossmatch techniques, such as flow cytometry and single-antigen microsphere bead assay technology, available for research and urgent cases that require crossmatch analysis.

The Challenge of Preoperative Panel Reactive Antibody Positivity in Parathyroid Transplantation.

OBJECTIVES: Identifying suitable recipient criteria and matching recipients with appropriate donors are required to increase survival for parathyroid transplant. This study was undertaken to evaluate transplant survival rates while comparing preoperative panel reactive antibody positivity. MATERIALS AND METHODS: The study included 14 hypoparathyroidism patients who presented to our clinic for parathyroid transplant. Preoperative ABO compatibility and negative cross-match tests were prioritized for recipient-donor matching, and panel reactive antibody screening tests were performed. During the 24-month follow-up, we evaluated medication use and serum calcium, phosphorus, and parathormone levels of patients. RESULTS: Preoperative panel reactive antibody positivity was assessed in 3 groups. The HLA class I-positive group (mean fluorescence intensity range, 179-1770) showed decreased medication use and stability in serum calcium levels. The HLA class IIpositive (mean fluorescence intensity range, 85-3959) showed decreased medication use by 25% to 50% and returned to their former prescription doses after 12 months. An opposite pattern was observed in 2 patients with panel reactive antibody positivity for both HLA classes (mean fluorescence intensity range, 462-2289), with 1 patient requiring medication for continuing symptoms and the other patient occasionally taking additional magnesium supplementation, despite decreased medication doses after 12 months. Serum calcium levels remained normal, and parathormone and phosphorus levels were elevated. CONCLUSIONS: Improving patient symptoms and having no requirement for intravenous calcium replacement are priorities, and monitoring serum levels is the next important step. Varied panel reactive antibody positivities and survival rates indicate a requirement, and each HLA class could require a proper limitation for the mean fluorescence intensity. Preoperative mean fluorescence intensity cut-off value should be <900. Higher mean fluorescence intensity values in panel reactive antibody screenings could increase risk of short-term graft survival after parathyroid transplant. Further studies should include immunological risk assessments by individualizing the outcome with donor-specific antibodies.

Superiority of Single-Antigen Bead Study in Donor-Specific Antibodies: Determination in Highly Sensitized Patients.

OBJECTIVES: The presence of donor-specific antibodies against HLA before kidney transplant has been variably associated with decreased long-term graft survival. Data on the association between pretransplant donor-specific antibodies and rejection and cause of graft failure in recipients of donor kidneys are scarce. MATERIALS AND METHODS: For this study of HLA antibody levels, we analyzed serum samples from 76 patients (48 women and 28 men) who were prepared for kidney transplant at the Baskent University Istanbul Hospital between 2017 and 2022. Levels were determined by using Lifecodes panel reactive antibody class I and II identification kits and Lifecodes LSA class I and II identification kits by the Luminex assay method. RESULTS: Multiple antigen tests showed more than 70% sensitization detected against both class I and class II antigens in our patient group. When some samples were reevaluated with the single-antigen bead method, desensitization values were shown to be considerably reduced compared with values from multiple antigen methods. CONCLUSIONS: The single-antigen-coated bead method can be useful in determining the risk of donor-specific antibodies in highly sensitized patients.

Management of Tacrolimus-Induced Toxicity With Normal Serum Levels After Liver Transplant.

Drug-induced liver injury after liver transplant occurs in 1.7% of patients. Tacrolimus is an effective immunosuppressant that is used to treat acute rejection. Although rare, it can cause toxicity, which is demonstrated by cholestatic liver injury. Here, we present a case of a young male patient who was diagnosed with Wilson disease, had penicillaminechelating therapy, and underwent living related liver transplant. Within 1 month posttransplant, he developed deranged, predominantly cholestatic pattern liver function tests. Laboratory parameters showed total bilirubin of 1.12 mg/ dL, alanine aminotransferase of 553 IU/L, gammaglutamyltransferase of 624 IU/L, and tacrolimus level of 10.2 ng/mL. After thorough evaluation, a liver biopsy was performed. Liver biopsy showed hepatocellular necrosis with centrilobular cholestasis without any evidence of graft rejection. However, with normal level of tacrolimus, the biopsy was suggestive of drug-induced liver injury. Thus, tacrolimus dose was reduced, resulting in improved liver function tests and patient discharge from the hospital. Tacrolimus is an effective immunosuppressant after liver transplant and has the ability to treat early acute rejection. The patient's liver biopsy showed hepatocellular necrosis with centrilobular cholestasis without any evidence of graft rejection. Cholestatic liver injury after tacrolimus usually resolves after dose reduction or by switching to another agent. With demonstrated tacrolimus-induced toxicity in liver transplant recipients, despite normal serum levels, transplant physicians should keep high index of suspicion regarding toxicity in the posttransplant setting.

Economic and humanistic burden in kidney transplant rejection: a literature review.

INTRODUCTION: Antibody-mediated rejection (ABMR) is a major cause of late kidney allograft failure, but its economic and humanistic impacts have not been well-characterized in the literature. AREAS COVERED: We reviewed available literature on economic burden (costs and healthcare resource use) and humanistic burden (health-related quality of life impacts [HRQOL] and utility estimates) in patients diagnosed with kidney transplant rejection; ABMR-specific studies were of particular interest. In total, 21 publications reporting economic and humanistic burden were included in the review; 9 of these reported ABMR-specific outcomes. The reviewed studies consistently showed a greater burden associated with ABMR-related transplant rejection than with non-ABMR transplant rejection. EXPERT OPINION: Evidence suggests greater economic burden and increased HRQOL impairment with ABMR-related kidney transplant rejection relative to non-ABMR, although small sample sizes and missing definitions for ABMR make meaningful comparisons between studies challenging. Because no International Classification of Diseases (ICD)-10 codes currently describe the etiologies of transplant rejection, it is difficult to characterize the burden of distinct types of transplant rejection. The paucity of high-quality data on the burden of ABMR in kidney transplant rejection demonstrates the need for more etiology-centric ICD-10 codes.

Urine CXCL10 as a biomarker in kidney transplantation.

PURPOSE OF REVIEW: Urine CXCL10 is a promising biomarker for posttransplant renal allograft monitoring but is currently not widely used for clinical management. RECENT FINDINGS: Large retrospective studies and data from a prospective randomized trial as well as a prospective cohort study demonstrate that low urine CXCL10 levels are associated with a low risk of rejection and can exclude BK polyomavirus replication with high certainty. Urine CXCL10 can either be used as part of a multiparameter based risk assessment tool, or as an individual biomarker taking relevant confounders into account. A novel Luminex-based CXCL10 assay has been validated in a multicenter study, and proved to be robust, reproducible, and accurate. SUMMARY: Urine CXCL10 is a well characterized inflammation biomarker, which can be used to guide performance of surveillance biopsies. Wide implementation into clinical practice depends on the availability of inexpensive, thoroughly validated assays with approval from regulatory authorities.

"Pre-Histologic" Antibody-Mediated Rejection Detected by Donor-Derived Cell-Free DNA and a Novel Tissue Gene Expression Assay: A Case Report.

BACKGROUND: Despite its well-characterized association with poor long-term graft outcomes, subclinical antibody-mediated rejection (ABMR) in recipients of kidney transplants continues to pose a significant diagnostic and therapeutic challenge. Specifically, its detection currently relies on invasive histologic surveillance, a relatively uncommon practice among US transplant centers. We describe a subclinical, "pre-histologic" antibody-mediated rejection identified and characterized by a combination of novel molecular tools, donor-derived cell-free DNA (dd-cfDNA), and molecular histology. CASE REPORT: A 67-year-old kidney transplant recipient was found to have a marked elevation of dd-cfDNA on routine testing at 3 months post-transplant; other laboratory parameters were stable. A biopsy was performed, demonstrating the absence of rejection by traditional histology, but evidence of rejection was seen when tissue was evaluated using a research use molecular histology assay. Four months later, in the setting of persistently elevated dd-cfDNA, the patient developed graft dysfunction and was found to have C4d-negative ABMR, which was treated with improvement in both graft function and dd-cfDNA. CONCLUSION: This case highlighted the complementary use of dd-cfDNA and molecular histology to aid in the early detection and characterization of graft injury. Hybrid approaches combining these tools may allow more expeditious therapeutic intervention, leading to improved graft and patient outcomes.

Inadequate (Ax) Transbronchial Lung Transplant Biopsies-Scope and the Potential Contributing Factors.

BACKGROUND: Transbronchial biopsy is the cornerstone for the evaluation of graft function after lung transplant and a standard of care to diagnose acute cellular rejection. However, the yield from these biopsies is variable, with about 15% to 50% of samples being judged as nondiagnostic, leading to additional procedures. The factors contributing to the nondiagnostic sampling have not been delineated, and the discordance in sample assessment between the bronchoscopist and pathologist has not been quantified. METHODS: A retrospective cohort of patients who had bronchoscopies with biopsies for surveillance and graft assessment at a large-volume transplant center was studied. The occurrence of nondiagnostic alveolar sampling was assessed, and the patient demographics and procedural characteristics were compared with the diagnostic group. RESULTS: We included 128 patients in our study and found the inadequacy rate for alveolar tissue sampling to be 15.5%. The median number of passes made by the bronchoscopist was 9, and the number of samples assessed by the bronchoscopist was 8, with a median of 6 adequate samples identified by the pathologist. The frequency of previous biopsies, history of prior inadequate samples, need for a higher number of pass attempts, presence of airway abnormalities, and the use of general anesthesia increased the odds of inadequate sampling. CONCLUSIONS: Patients with the identified factors may be at risk of inadequate sampling on transbronchial biopsies. The bronchoscopist could consider getting additional samples to avoid a nondiagnostic alveolar sample. Further multicenter studies would help to elucidate other contributing factors.

Detrimental impact of early biopsy-proven rejection in liver transplantation.

Existing literature offers conflicting conclusions about whether early acute cellular rejection influences long-term outcomes in liver transplantation. We retrospectively collected donor and recipient data on all adult, first-time liver transplants performed at a single center between 2008 and 2020. We divided this population into two cohorts based on the presence of early biopsy-proven acute cellular rejection (EBPR) within the first 90 days post-transplant and compared outcomes between the groups. There were 896 liver transplants that met inclusion criteria with 112 cases (12.5%) of EBPR. Recipients who developed EBPR had higher biochemical Model for End-Stage Liver Disease scores (28 vs. 24, p < .01), but other donor and recipient characteristics were similar. Recipients with EBPR had similar overall survival compared to patients without EBPR (p = .09) but had decreased graft survival (p < .05). EBPR was also associated with decreased time to first episode of late (> 90 days post-transplant) rejection (p < .0001) and increased vulnerability to bacterial and viral infection (p < .05). In subgroup analysis of recipients with autoimmune indications for liver transplantation, EBPR had a more pronounced association with patient death (hazard ratio [HR] 3.9, p < .05) and graft loss (HR 4.0, p < .01). EBPR after liver transplant is associated with inferior graft survival, increased susceptibility to late rejections, and increased vulnerability to infection.

Evaluation of serial monitoring of donor-specific antibodies in pediatric and adult intestinal/multivisceral transplant recipients.

BACKGROUND: The study purpose was to add to limited literature assessing anti-HLA donor-specific antibody (DSA) appearance, clearance, specificity, and impact in intestinal/multivisceral (MV) transplant as well as the value of serial monitoring following an institutional protocol shift implementing serial monitoring. METHODS: This single-center retrospective review included intestinal/MV recipients transplanted 1/1/15-9/31/17 with completed DSA testing. Patients were divided into groups based on DSA presence post-transplant. The primary outcome was biopsy-proven acute rejection (BPAR). Secondary outcomes included graft loss and death. Descriptive analysis of DSA was completed. RESULTS: Of the 35 intestinal/MV recipients (60% pediatric) with DSA testing, 24 patients had post-transplant DSA. Fifteen patients in the DSA(+) group had T-cell-mediated BPAR versus five in the DSA(-) group (63% vs 45%, p = .47). Days to BPAR were 25 [IQR 19-165] (DSA(+) group) versus 232 [IQR 25.5-632.5] (DSA(-) group) (p = .066). There were no differences between groups for graft loss or death. One hundred and five DSA were identified in the DSA(+) group with 63% being class II, and 54% cleared during follow-up. DSA were directed against 50 different HLA alleles, with the most common being directed against HLA- DQ (35%). Time to first DSA and to clearance did not differ between class I and II. CONCLUSION: Findings confirm previous data that suggest post-transplant DSA in this population may lead to increased BPAR or shorter time to BPAR, although not statistically significant. Most DSA were identified within the first month after transplant, and ahead of rejection identification on biopsy. DSA therefore may have utility as an early rejection biomarker and use may be considered in place of early protocol biopsies, particularly in pediatric patients. We identified novel findings of DSA directed against a large breadth of HLA in intestinal/MV patients.

Mimicking Clinical Rejection Patterns in a Rat Osteomyocutaneous Flap Model of Vascularized Composite Allotransplantation.

INTRODUCTION: Graft loss in vascularized composite allotransplantation (VCA) is more often associated with vasculopathy and chronic rejection (CR) than acute cellular rejection (ACR). We present a rat osteomyocutaneous flap model using titrated tacrolimus administration that mimics the graft rejection patterns in our clinical hand transplant program. Comparison of outcomes in these models support a role for ischemia reperfusion injury (IRI) and microvascular changes in CR of skin and large-vessel vasculopathy. The potential of the surgical models for investigating mechanisms of rejection and vasculopathy in VCA and treatment interventions is presented. MATERIALS AND METHODS: Four rodent groups were evaluated: syngeneic controls (Group 1), allogeneic transient immunosuppression (Group 2), allogeneic suboptimal immunosuppression (Group 3), and allogeneic standard immunosuppression (Group 4). Animals were monitored for ACR, vasculopathy, and CR of the skin. RESULTS: Transient immunosuppression resulted in severe ACR within 2 wk of tacrolimus discontinuation. Standard immunosuppression resulted in minimal rejection but subclinical microvascular changes, including capillary thrombosis and luminal narrowing in arterioles in the donor skin. Further reduction in tacrolimus dose led to femoral vasculopathy and CR of the skin. Surprisingly, femoral vasculopathy was also observed in the syngeneic control group. CONCLUSIONS: Titration of tacrolimus in the allogeneic VCA model resulted in presentations of rejection and vasculopathy similar to those in patients and suggests vasculopathy starts at the microvascular level. This adjustable experimental model will allow the study of variables and interventions, such as external trauma or complement blockade, that may initiate or mitigate vasculopathy and CR in VCA.

Center variability in the prognostic value of a cumulative acute cellular rejection "A-score" for long-term lung transplant outcomes.

The acute rejection score (A-score) in lung transplant recipients, calculated as the average of acute cellular rejection A-grades across transbronchial biopsies, summarizes the cumulative burden of rejection over time. We assessed the association between A-score and transplant outcomes in 2 geographically distinct cohorts. The primary cohort included 772 double lung transplant recipients. The analysis was repeated in 300 patients from an independent comparison cohort. Time-dependent multivariable Cox models were constructed to evaluate the association between A-score and chronic lung allograft dysfunction or graft failure. Landmark analyses were performed with A-score calculated at 6 and 12 months posttransplant. In the primary cohort, no association was found between A-score and graft outcome. However, in the comparison cohort, time-dependent A-score was associated with chronic lung allograft dysfunction both as a time-dependent variable (hazard ratio, 1.51; P < .01) and when calculated at 6 months posttransplant (hazard ratio, 1.355; P = .031). The A-score can be a useful predictor of lung transplant outcomes in some settings but is not generalizable across all centers; its utility as a prognostication tool is therefore limited.