Non-HLA Antibodies Impact on C4d Staining, Stellate Cell Activation and Fibrosis in Liver Allografts

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

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

Chronic lung allograft dysfunction is associated with an increased number of non-HLA antibodies

BACKGROUND

Chronic lung allograft dysfunction (CLAD) is the major cause of adverse outcomes in lung transplant recipients. Multiple factors, such as infection, alloimmunity, and autoimmunity, may lead to CLAD. Here, we aim to examine the role of non-human leukocytes antigen (HLA) antibodies in CLAD in a large retrospective cohort.

METHODS

We analyzed non-HLA antibodies in the pre- and post-transplant sera of 226 (100 CLAD, 126 stable) lung transplant recipients from 5 centers, and we used a separate cohort to confirm our findings.

RESULTS

A panel of 18 non-HLA antibodies was selected for analysis based on their significantly higher positive rates in CLAD vs stable groups. The panel-18 non-HLA antibodies (n > 3) may be positive pre- or post-transplant; the risk for CLAD is higher in the latter. The presence of both non-HLA antibody and HLA donor-specific antibody (DSA) was associated with an augmented risk of CLAD (HR=25.09 [5.52-14.04], p < 0.001), which was higher than that for single-positive patients. In the independent confirmatory cohort of 61 (20 CLAD, 41 stable) lung transplant recipients, the risk for CLAD remained elevated in double-positive patients (HR=10.67 [0.98-115.68], p = 0.052). After adjusting for nonstandard immunosuppression, patients with double-positive DSA/Non-HLA antibodies had an elevated risk for graft loss (HR=2.53 [1.29-4.96], p = 0.007).

CONCLUSIONS

Circulating non-HLA antibodies (n > 3) were independently associated with a higher risk for CLAD. Furthermore, when non-HLA antibodies and DSA were detected concomitantly, the risk for CLAD and graft loss was significantly increased. These results show that humoral immunity to HLA and non-HLA antigens may contribute to CLAD development.

Improving liver transplant outcomes with transplant-omics and network biology

PURPOSE OF REVIEW

Molecular omics data is increasingly ubiquitous throughout medicine. In organ transplantation, recent large-scale research efforts are generating the 'transplant-ome' - the entire set of molecular omics data, including the genome, transcriptome, proteome, and metabolome. Importantly, early studies in anesthesiology have demonstrated how perioperative interventions alter molecular profiles in various patient populations. The next step for anesthesiologists and intensivists will be to tailor perioperative care to the transplant-ome of individual liver transplant patients.

RECENT FINDINGS

In liver transplant patients, elements of the transplant-ome predict complications and point to novel interventions. Importantly, molecular profiles of both the donor organ and recipient contribute to this risk, and interventions like normothermic machine perfusion influence these profiles. As we can now measure various omics molecules simultaneously, we can begin to understand how these molecules interact to form molecular networks and emerging technologies offer noninvasive and continuous ways to measure these networks throughout the perioperative period. Molecules that regulate these networks are likely mediators of complications and actionable clinical targets throughout the perioperative period.

SUMMARY

The transplant-ome can be used to tailor perioperative care to the individual liver transplant patient. Monitoring molecular networks continuously and noninvasively would provide new opportunities to optimize perioperative management.

Angiotensin II type 1 receptor antibodies and native kidney function in pediatric liver and intestinal transplant recipients

BACKGROUND

Angiotensin II type-1 receptor antibody (AT1R-Ab) has been associated with vascular injury and kidney dysfunction in pediatric kidney transplant recipients. The role of AT1R-Ab in the development of chronic kidney disease in pediatric liver and intestinal transplant recipients has not been explored.

METHODS

Twenty-five pediatric intestinal transplant recipients and 79 pediatric liver transplant recipients had AT1R-Ab levels measured at varying time points in the post-transplant period. Estimated glomerular filtration rate (eGFR) was determined using creatinine based CKiD U25 equation and measured at time of AT1R-Ab measurement, at 1 year post-AT1R-Ab measurement, at 5 years post-AT1R-Ab measurement, and at the most recent routine clinic visit. The prevalence of hypertension and antihypertensive medication use were also evaluated.

RESULTS

Younger age at time of AT1R-Ab measurement was associated with AT1R-Ab positivity in liver transplant recipients. There was no association between AT1R-Ab status and change in eGFR, prevalence of hypertension, or use of antihypertensive medications at the described time points.

CONCLUSIONS

AT1R-Ab positivity was not associated with a decline in eGFR or hypertension in pediatric liver and intestinal transplant recipients. Further studies are needed using other markers of kidney function, such as cystatin C, to validate this finding. A higher resolution version of the Graphical abstract is available as Supplementary information.

Impact of everolimus plus calcineurin inhibitor on formation of non-HLA antibodies and graft outcomes in kidney transplant recipients: 12-month results from the ATHENA substudy

Background

Non-human leukocyte antigen (non-HLA) antibodies including antibodies targeting Angiotensin II type 1 (AT1R) and Endothelin-1 type A (ETAR) receptors represent a topic of interest in kidney transplantation (KTx). This exploratory substudy evaluated the impact of everolimus (EVR) or mycophenolic acid (MPA) in combination with tacrolimus (TAC) or cyclosporine A (CsA) in patients with preformed non-HLA antibodies, potentially associated rejections and/or their impact on renal function over 1 year.

Methods

All eligible patients were randomized (1:1:1) before transplantation to receive either EVR/TAC, EVR/CsA, or MPA/TAC regimen. The effect of these regimens on the formation of non-HLA antibodies within one year post de novo KTx and the association with clinical events was evaluated descriptively in randomized (n = 268) population.

Results

At Month 12, in EVR/TAC group, higher incidence of patients negative for AT1R- and ETAR-antibodies (82.2% and 76.7%, respectively) was noted, whereas the incidence of AT1R- and ETAR-antibodies positivity (28.1% and 34.7%, respectively) was higher in the MPA/TAC group. Non-HLA antibodies had no influence on clinical outcomes in any treatment group and no graft loss or death was reported.

Conclusions

The studied combinations of immunosuppressants were safe with no influence on clinical outcomes and suggested minimal exposure of calcineurin inhibitors for better patient management.

Clinical Trial Registration

https://clinicaltrials.gov/ (NCT01843348; EudraCT number: 2011-005238-21).

A Comprehensive Review of Liver Allograft Fibrosis and Steatosis: From Cause to Diagnosis

Despite advances in posttransplant care, long-term outcomes for liver transplant recipients remain unchanged. Approximately 25% of recipients will advance to graft cirrhosis and require retransplantation. Graft fibrosis progresses in the context of de novo or recurrent disease. Recurrent hepatitis C virus infection was previously the most important cause of graft failure but is now curable in the majority of patients. However, with an increasing prevalence of obesity and diabetes and nonalcoholic fatty liver disease as the most rapidly increasing indication for liver transplantation, metabolic dysfunction-associated liver injury is anticipated to become an important cause of graft fibrosis alongside alloimmune hepatitis and alcoholic liver disease. To better understand the landscape of the graft fibrosis literature, we summarize the associated epidemiology, cause, potential mechanisms, diagnosis, and complications. We additionally highlight the need for better noninvasive methods to ameliorate the management of graft fibrosis. Some examples include leveraging the microbiome, genetic, and machine learning methods to address these limitations. Overall, graft fibrosis is routinely seen by transplant clinicians, but it requires a better understanding of its underlying biology and contributors that can help inform diagnostic and therapeutic practices.

Detailed Analysis of Simultaneous Renal and Liver Allografts in the Presence of DSA

Liver allografts protect renal allografts from the same donor from some, but not all, preformed donor specific alloantibodies (DSA). However, the precise mechanisms of protection and the potential for more subtle alterations/injuries within the grafts resulting from DSA interactions require further study.

Methods

We reevaluated allograft biopsies from simultaneous liver-kidney transplant recipients who had both allografts biopsied within 60 d of one another and within 30 d of DSA being positive in serum (positive: mean florescence intensity ≥5000). Routine histology, C4d staining, and specialized immunohistochemistry for Kupffer cells (KCs; CD163) and a C4d receptor immunoglobulin-like transcript-4 were carried out in 4 patients with 6 paired biopsies.

Results

Overt antibody-mediated rejection was found in 3 of 4 renal and liver allografts. One patient had biopsy-confirmed renal and liver allograft antibody-mediated rejection despite serum clearance of DSA. All biopsies showed KC hypertrophy (minimal: 1; mild: 2; moderate: 1; severe: 2) and cytoplasmic C4d KC staining was easily detected in 2 biopsies from 2 patients; minimal and negative in 2 biopsies each. Implications of which are discussed. Control 1-y protocol liver allograft biopsies from DSA- recipients showed neither KC hypertrophy nor KC C4d staining (n = 6).

Conclusions

Partial renal allograft protection by a liver allograft from the same donor may be partially mediated by phagocytosis/elimination of antibody and complement split products by KCs, as shown decades ago in controlled sensitized experimental animal experiments.

Evidence for Alloimmune Sinusoidal Injury in De Novo Nodular Regenerative Hyperplasia After Liver Transplantation

Posttransplant nodular regenerative hyperplasia (NRH) mostly remains unexplained. Microvascular injury due to antibody-mediated rejection (AMR) is suspected, but lack of donor specific antibody (DSA) testing makes it difficult to prove. Centered around a 1-year period of routine DSA testing, concomitant protocol, and indicated posttransplant liver biopsies (LB), recipients with NRH (n = 18) were compared with a matched control group (n = 36). All index, previous, and subsequent LB were reviewed. Both groups were similar in terms of demographics, timing of index LB, and DSA. In the index LB, the NRH group had higher sinusoidal C4d positivity (p = 0.029) and perisinusoidal fibrosis (p = 0.034), both independently associated with NRH (p = 0.038 and 0.050, respectively). Features of "possible" chronic AMR were detected in 28.5% of the NRH group without a known cause and 0% of the control group (p = 0.009). The NRH group had more preceding indicated LB with increased incidence of rejection and biliary obstruction pattern. In the follow-up histology, overall, sinusoidal and portal C4d positivity, sinusoidal microvasculitis, and perisinusoidal fibrosis were also higher (all p < 0.050). In conclusion, we provide evidence towards the hypothesis that some cases of posttransplant NRH are related to preceding active and persistent AMR. Large multicenter studies with protocol DSA testing are required to confirm.

Ixazomib for Desensitization (IXADES) in Highly Sensitized Kidney Transplant Candidates: A Phase II Clinical Trial

Key Points

Ixazomib treatment resulted in decreases in B-cell subsets and bone marrow lymphocytes. Ixazomib treatment resulted in modest decreases in certain anti-HLA antibody specificities. Ixazomib treatment was tolerated, with modest adverse events.

Background

Ixazomib is a second-generation oral proteasome inhibitor approved for treatment of refractory multiple myeloma. We conducted an open-label phase II trial, IXAzomib for DESensitization (IXADES), testing the safety of ixazomib treatment as an approach to decreasing the level and diversity of specificities of anti-HLA antibodies in subjects awaiting kidney transplantation. The trial (NCT03213158 ) enrolled highly sensitized kidney transplant candidates, defined as subjects with calculated panel reactive antibodies (cPRA) >80%, awaiting kidney transplantation >24 months. The subjects were treated with 12 monthly cycles of ixazomib 3 mg+dexamethasone 20 mg. Efficacy was defined as a decrease of cPRA >20% or kidney transplantation. The safety end point was tolerability.

Methods

In ten enrolled subjects, no grade IV, five grade III, 11 grade II, and 43 grade I adverse events were noted. The adverse events included infection, transient paresthesia, nausea, vomiting, and diarrhea. The IXADES regimen was not associated with significant change in levels or diversity of anti-HLA antibodies (cPRA).

Results

Although the IXADES regimen did not exhibit a clear impact on levels and diversity of anti-HLA antibodies in this small cohort, the prolonged half-life of IgG could necessitate a longer duration of treatment for accurate evaluation of efficacy.

Conclusions

In conclusion, treatment with ixazomib/dexamethasone engendered mild-to-moderate toxicity. The impact on anti-HLA was modest and paradoxical in the case of anti-HLA-DR. Clinical trials combining ixazomib with other immunosuppressive agents may be more effective in addressing antibody-mediated processes in kidney transplantation.

Endothelial Injury Syndromes after Allogeneic Hematopoietic Stem Cell Transplantation: Angiopetin-2 as a Novel Predictor of the Outcome and the Role of Functional Autoantibodies against Angiotensin II Type 1 and Endothelin A Receptor

Transplant-associated thrombotic microangiopathy (TMA) occurs in a significant percentage of patients after allogeneic stem cell transplantation (allo-SCT) and is associated with significant morbidity and mortality. The aim of the present study was to examine the association of serum angiopoetin-2 (Ang2) levels and the presence of antibodies against angiotensin II type 1 (AT1R) and ndothelin A Recreptor (ETAR) with the outcome of patients with TMA and/or graft-versus-host disease (GVHD) after allo-SCT. Analysis of our data showed that elevated serum Ang2 levels at the time of TMA diagnosis are significantly associated with increased non-relapse mortality and decreased overall survival. To our knowledge, this is the first study demonstrating an association between raised Ang2 levels and poor outcomes in patients with TMA. Antibodies against AT1R (AT1R-Abs) and ETAR (ETAR-Abs) were detected in 27% and 23% of the patients, respectively, but there was no association between the presence of autoantibodies and the outcome of patients with TMA. However, a significant finding was the strong positive correlation between the presence of AT1R-Abs with the occurrence of chronic fibrotic GVHD, such as scleroderma and cryptogenic organizing pneumonia, raising the possibility of the contribution of autoantibodies in the pathogenesis of fibrotic GVHD manifestations.

Loss of anti-AT1R reactivity in ELISA post-adsorption - False reactivity or interference in the assay?

Autoantibodies to Angiotensin II type 1 receptor (AT1R) are associated with detrimental outcomes in organ transplants. However, reports showed that adsorption with latex beads reduced positive anti-AT1R antibodies, suggesting possible false reactivity. To investigate this conundrum, we studied 11 samples positive for AT1R antibodies with an ELISA kit before and after adsorption. Adsorption significantly reduced the measurable level of AT1R antibodies (28.3 ± 9.8 vs. 6.3 ± 3.0 U/ml, p < 0.001). AT1R antibodies were lower when post-adsorption serum was added back at 1:1 ratio to the neat serum compared to the diluent control (8.6 ± 4.2 vs. 18.1 ± 10.3 U/ml, p = 0.02). Sham adsorption with the buffer from Adsorb Out™ kit without beads also suppressed the detection of anti-AT1R antibodies (32.7 ± 9.1 vs. 8.1 ± 3.9 U/ml, p < 0.001). Thus, rather than actively removing nonspecific antibodies by the beads, the adsorption process introduces soluble factors that interfere with the detection of anti-AT1R antibodies with the ELISA kit.

Positive autoantibodies in living liver donors

BACKGROUND

There is a nationwide shortage of organs available for liver transplantation. Living donors help meet this growing demand. Not uncommonly, donors will have positive autoantibodies. However, it is unclear whether donor positive autoantibodies are correlated with worse outcomes following living liver donor transplantations.

AIM

To analyze the significance of positive autoantibodies in donors on post-transplant outcomes in recipients.

METHODS

We performed a retrospective review of living liver donors who had undergone liver transplantation between January 1, 2012 and August 31, 2021. Demographic characteristics and pre-transplant data including antinuclear antibodies (ANA) and anti-smooth muscle antibody titers were collected in donors. Outcomes of interest were post-transplantation complications including mortality, biliary strictures, biliary leaks, infection, and rejection. Pediatric recipients and donors without measured pre-transplant autoantibody serologies were excluded from this study.

RESULTS

172 living donor liver transplantations were performed during the study period, of which 115 patients met inclusion criteria. 37 (32%) living donors were autoantibody-positive with a median ANA titer of 1:160 (range 1:80 to 1:1280) and median anti-SMA titer of 1:40 (range 1:20 to 1:160). There were no significant differences in baseline demographics between the autoantibody positive and negative donors. Post-transplantation rates of death (P value = 1), infections (P value = 0.66), and overall rates of complications (P value = 0.52) were similar between the autoantibody positive and negative groups. Higher incidences of anastomotic strictures and rejection were observed in the autoantibody positive group; however, these differences were not statistically significant (P value = 0.07 and P value = 0.30 respectively).

CONCLUSION

Isolated pre-transplant autoantibody positivity is not correlated to worse post-transplant outcomes in living liver donor transplants.

Antigen and Cell-Based Assays for the Detection of Non-HLA Antibodies

To date, human leukocyte antigens (HLA) have been the major focus in the approach to acute and chronic antibody-mediated rejection (AMBR) in solid-organ transplantation. However, evidence from the clinic and published studies has shown that non-HLA antibodies, particularly anti-endothelial cell antibodies (AECAs), are found either in the context of AMBR or synergistically in the presence of donor-specific anti-HLA antibodies (DSA). Numerous studies have explored the influence of AECAs on clinical outcomes, yet the determination of the exact clinical relevance of non-HLA antibodies in organ transplantation is not fully established. This is due to highly heterogeneous study designs including differences in testing methods and outcome measures. Efforts to develop reliable and sensitive diagnostic non-HLA antibody tests are continuously made. This is essential considering the technical difficulties of non-HLA antibody assays and the large variation in reported incidences of antibodies. In addition, it is important to take donor specificity into account in order to draw clinically relevant conclusions from non-HLA antibody assays. Here, we provide an overview of non-HLA solid-phase and cell-based crossmatch assays for use in solid-organ transplantation that are currently available, either in a research setting or commercially.

Antibodies against Angiotensin II Type 1 and Endothelin 1 Type A Receptors in Cardiovascular Pathologies

Angiotensin II receptor type 1 (AT1R) and endothelin-1 receptor type A (ETAR) are G-protein-coupled receptors (GPCRs) expressed on the surface of a great variety of cells: immune cells, vascular smooth cells, endothelial cells, and fibroblasts express ETAR and AT1R, which are activated by endothelin 1 (ET1) and angiotensin II (AngII), respectively. Certain autoantibodies are specific for these receptors and can regulate their function, thus being known as functional autoantibodies. The function of these antibodies is similar to that of natural ligands, and it involves not only vasoconstriction, but also the secretion of proinflammatory cytokines (such as interleukin-6 (IL6), IL8 and TNF-α), collagen production by fibroblasts, and reactive oxygen species (ROS) release by fibroblasts and neutrophils. The role of autoantibodies against AT1R and ETAR (AT1R-AAs and ETAR-AAs, respectively) is well described in the pathogenesis of many medical conditions (e.g., systemic sclerosis (SSc) and SSc-associated pulmonary hypertension, cystic fibrosis, and allograft dysfunction), but their implications in cardiovascular diseases are still unclear. This review summarizes the current evidence regarding the effects of AT1R-AAs and ETAR-AAs in cardiovascular pathologies, highlighting their roles in heart transplantation and mechanical circulatory support, preeclampsia, and acute coronary syndromes.

The Summarized Assessment of Endothelin A Receptor Expression in Renal Transplant Compartments Associated with Antibody-Mediated Rejection

The occurrence of anti-endothelin A receptor antibodies may be useful in diagnosis of transplant damage. We noticed that the presence of the endothelin A receptor (ETA receptor) in biopsy compartments is yet to be defined. We decided therefore to analysed the presence and relevance of the ETA receptor in biopsy to define the cause. Our study aims to evaluate the expression of ETA receptors in renal recipients after a biopsy due to the worsening of transplant function.

METHODS

The expression of ETA receptors was analyzed in renal transplant biopsies using the immunohistochemical method. The evaluation of ETA receptors was performed on paraffin sections. ETA receptor expression was analyzed in four compartments of renal transplant biopsies: glomeruli; vessels; tubular epithelium; and interstitium. The assessment was presented using a three-step scale (0: lack of expression; 1: mild to moderate immunoreactivity; 2: high expression). The results of each compartment from a single biopsy were summarized and assessed in the context of antibody-mediated rejection (AMR).

RESULTS

We analyzed 156 patients who had a renal allograft biopsy after renal transplantation. For each patient, we created a summarized ETA receptor expression score. The summarized ETA receptor expression score analysis showed statistically significant differences in patients with and without AMR. In addition, we noticed that patients with AMR had a significantly higher mean summarized expression of ETA receptor score of 3.28 ± 1.56 compared to patients who had a biopsy for other reasons with a mean summarized ETA receptor expression score of 1.47 ± 1.35 (p < 0.000001). ROC analysis of the ETA receptor expression score for detecting AMR status showed that the most appropriate cut-off for the test of the chosen binary classifier is between 2 and 3 of the summarized ETA receptor expression score.

CONCLUSIONS

The expression of endothelin A receptors in renal transplant compartments may be associated with antibody-mediated rejection. The positive ETA receptor staining might be a vital feature in the diagnosis of damage in AMR. The summarized ETA receptor expression score seems to be an exciting diagnostic tool in transplant injury assessment.

The role of endothelin II type A receptor (ETAR) in transplant injury

PURPOSE OF REVIEW

Antibody-mediated rejection is the leading cause of deterioration of graft function and graft loss after kidney transplantation. Recent studies have reported an increasing role of non-HLA antibodies in the humoral injury after kidney transplantation. We decided to present the influence of non-HLA antibodies - anti-endothelin II type A receptor (ETAR) on a transplanted kidney and characterize the significance of their receptor.

RECENT FINDINGS

The role of non-HLA antibodies is still uncertain. Many studies suggest that the presence of non-HLA antibodies, including anti-ETAR antibodies, is among the risk factors for antibody-mediated rejection, graft injury, and graft loss. The discovery of new antigen targets and antibodies, which participate in the humoral response, has provided a significantly better understanding of the mechanism of antibody-mediated rejection after organ transplantation.

SUMMARY

Endothelin and its receptors play an important role in physiology and pathophysiology after solid organ transplantation. ETAR and antibodies against ETAR may participate in humoral rejection and graft damage. The measurement of anti-ETAR antibodies may identify patients with an increased risk of rejection and even loss of a transplanted organ. Expression of ETAR detected in biopsy of transplant could become an additional tool used to better understand humoral activity. More research is needed to address many questions about non-HLA directed rejection and graft damage.

A Comprehensive Overview of the Clinical Relevance and Treatment Options for Antibody-mediated Rejection Associated With Non-HLA Antibodies

Although solid organ transplant results have improved significantly in recent decades, a pivotal cause of impaired long-term outcome is the development of antibody-mediated rejection (AMR), a condition characterized by the presence of donor-specific antibodies to HLA or non-HLA antigens. Highly HLA-sensitized recipients are treated with desensitization protocols to rescue the transplantation. These and other therapies are also applied for the treatment of AMR. Therapeutic protocols include removal of antibodies, depletion of plasma and B cells, inhibition of the complement cascade, and suppression of the T-cell-dependent antibody response. As mounting evidence illustrates the importance of non-HLA antibodies in transplant outcome, there is a need to evaluate the efficacy of treatment protocols on non-HLA antibody levels and graft function. Many reviews have been recently published that provide an overview of the literature describing the association of non-HLA antibodies with rejection in transplantation, whereas an overview of the treatment options for non-HLA AMR is still lacking. In this review, we will therefore provide such an overview. Most reports showed positive effects of non-HLA antibody clearance on graft function. However, monitoring non-HLA antibody levels after treatment along with standardization of therapies is needed to optimally treat solid organ transplant recipients.

The emerging field of non-human leukocyte antigen antibodies in transplant medicine and beyond

The major medical advances in our knowledge of the human leukocyte antigen (HLA) system have allowed us to uncover several gaps in our understanding of alloimmunity. Although the non-HLA system has long sparked the interest of the transplant community, recognition of the role of immunity to non-HLA antigenic targets has only emerged recently. In this review, we will provide a comprehensive summary of the paradigm-changing concept of immunity to the non-HLA angiotensin II type 1 receptor (AT1R), discovered by Duška Dragun et al., that began from careful bedside clinical observations, to validated detection of anti-AT1R antibodies and lead to clinical intervention. This scientific approach has also allowed the recognition of broader pathogenicity of anti-AT1R antibodies across multiple organ transplants and in other human diseases, the integration of both non-HLA and HLA systems to understand their immunologic effects on organ allografts, and the identification of future directions for therapeutic intervention to modulate immunity to AT1R. Rationally designed successful interventions to target AT1R system provide an exemplar for other non-HLA antibodies to cross borders between medical specialties, will generate new avenues in translational research beyond transplantation, and will foster the development of new and reliable tools to improve our understanding of non-HLA immunity and ultimately allow us to improve patient care.

Autoantibodies to LG3 are associated with poor long-term survival after liver retransplantation

Autoantibodies are detrimental to the survival of organ transplantation. We demonstrated that Angiotensin II Type I Receptor agonistic autoantibodies (AT1R-AA) were associated with poor outcomes after liver retransplantation. To examine the effect of other autoantibodies, we studied a retrospective cohort of 93 patients who received a second liver transplant. Pre-retransplant sera were tested with Luminex-based solid-phase assays. Among 33 tested autoantibodies, 15 were significantly higher in 48 patients who lost their regrafts than 45 patients whose regrafts were still functioning. Specifically, patients with autoantibodies to the C-terminal laminin-like globular domain of Perlecan (LG3) experienced significantly worse regraft survival (p = .002) than those with negative LG3 autoantibodies (LG3-A). In multivariate analysis, LG3-A (HR = 2.35 [1.11-4.98], p = .027) and AT1R-AA (HR = 2.09 [1.07-4.10], p = .032) remained significant predictors of regraft loss after adjusting for recipient age and sex. There were synergistic deleterious effects on regraft survival in patients who were double-positive for LG3-A and donor-specific antibody (DSA) (HR = 5.26 [2.15-12.88], p = .001), or LG3-A and AT1R-AA (HR = 3.23 [1.37-7.66], p = .008). All six double-positive patients lost their liver regrafts. In conclusion, LG3-A is associated with inferior long-term outcomes of a second liver transplant. Screening anti-HLA antibodies and autoantibodies such as LG3-A/AT1R-AA identifies patients with a higher risk for liver transplantation.

Non-HLA AT1R antibodies are highly prevalent after pediatric intestinal transplantation

The role of angiotensin II type-1 receptor (AT1R) antibodies in intestinal transplantation (ITx) is unclear. The aims were 1) to identify the prevalence of AT1R antibodies in pediatric ITx, compared to pediatric intestinal failure (IF), and 2) to determine whether AT1R antibodies were associated with graft dysfunction. 46 serum samples from 25 ITx patients (3 isolated ITx, 22 liver-inclusive ITx) were collected during routine visits >6 months apart and during episodes of graft dysfunction as a result of infectious enteritis or rejection. For comparison, samples were collected from 7 IF control patients. AT1R antibodies were considered positive for levels >17 U/mL. The median (range) AT1R antibody level for ITx patients was 40.0 U/mL (7.2-40.0), compared to 7.0 U/mL (5.7-40.0) for IF patients (p = .02). There was a trend toward higher prevalence of AT1R antibodies in ITx compared with IF patients (68% versus 29%, p = .09). Among ITx patients, the prevalence of AT1R antibodies was not different between periods of active graft dysfunction and normal health (83% versus 67%, p = .31). For 16 patients with >2 samples, AT1R antibodies remained positive in 67% cases, developed in 14% cases, disappeared in 10% cases, and remained negative in 10% cases. The changes in AT1R antibodies did not correlate with de/sensitizing events. This is the first study of AT1R antibodies in pediatric ITx. AT1R antibodies are highly prevalent after ITx and may be triggered by immune activation associated with the transplant. However, their pathogenicity and clinical utility remain in question.

Non-HLA Autoantibodies at 1 Year Negatively Affect 5-Year Native Renal Function in Liver Transplant Recipients

BACKGROUND

Angiotensin II type-1 receptor (AT₁R) and endothelin-1 type A receptor (ET_AR) autoantibodies, in addition to allograft injury, can bind native endothelial cells and cause vascular vasoconstriction and fibrosis progression in nontransplanted organs. Therefore, we investigated long-term native renal function in liver transplant (LT) recipients with and without anti-AT₁R-Abs and/or anti-ET_AR-Abs present in serum.

METHODS

Primary LT recipients at our single center from January 2000 to April 2009 had their prospectively collected pre-LT (1269 patients) and year 1 post-LT (795 patients) serum tested retrospectively for anti-AT₁R-Abs and/or anti-ET_AR-Abs. Anti-AT₁R-Abs and anti-ET_AR-Abs testing was accomplished with a standardized solid phase assay in which >10 U was considered positive.

RESULTS

Pretransplant anti-AT₁R-Abs and/or anti-ET_AR-Abs did not change the median delta creatinine from pretransplant to 1 year post-transplant. In multivariable analysis controlling for diabetes (DM) and calcineurin inhibitor (CNI) use, anti-AT₁R-Abs and/or anti-ET_AR-Abs at 1-year remained statistically significantly associated with a decline in GFR (measured by Modification of Diet in Renal Disease-6) from years 1-5 post-LT (P = .04). In diabetic patients the association with a decline in renal function was more pronounced with (-9.29 mL/min) vs without (-2.28 mL/min) anti-AT₁R-Abs and/or anti-ET_AR-Abs at year 1, respectively (P = .004).

CONCLUSION

At 1-year post-LT, the autoantibodies anti-AT₁R-Abs and/or anti-ET_AR-Abs are associated in multivariable analysis with an increased risk of native renal function decline especially in diabetic patients.

Angiotensin II Type-1 Receptor Antibodies Are Associated With Active Allograft Dysfunction Following Pediatric Liver Transplantation

BACKGROUND

Angiotensin II type-1 receptor (AT1R) antibodies have been associated with rejection and allograft loss in solid organ transplantation and may act synergistically with HLA donor-specific antibodies (DSA). Our aims were to assess the prevalence of AT1R antibodies and determine if they were associated with allograft dysfunction in pediatric liver transplant recipients.

METHODS

We performed a retrospective, cross-sectional study of HLA DSA and AT1R antibodies in 2 cohorts of pediatric liver transplant recipients: a stable control cohort with normal allograft function (n = 70) who consented to have serum samples collected for research purposes during a routine clinic visit and a cohort with active allograft dysfunction (n = 9) whose serum samples were collected as part of clinical care.

RESULTS

AT1R antibodies >17 U/mL were detected in 29% of stable control patients and 89% of patients with active allograft dysfunction (P = 0.001). In stable control patients, AT1R antibodies were associated with younger age at transplant (P = 0.010), younger age at time of sample collection (P < 0.001), shorter interval since transplant (P = 0.090), and presence of HLA DSA (P = 0.003). AT1R antibodies in stable control patients were not associated with rejection or allograft loss. However, AT1R antibodies combined with HLA DSA in patients with active allograft dysfunction were associated with rejection and allograft loss.

CONCLUSIONS

Our results suggest that AT1R antibodies are more common in patients with active allograft dysfunction and may be a risk factor for worse outcomes. Further research is needed to longitudinally assess the clinical impact of HLA DSA and AT1R antibodies.

What Makes Antibodies Against G Protein-Coupled Receptors so Special? A Novel Concept to Understand Chronic Diseases

Expressions of G protein-coupled receptors (GPCR) on immune and tissue resident cells are the consequence of the cellular environment, which is highly variable. As discussed here, antibodies directed to GPCR (GPCR abs), their levels and correlations to other abs, serve as biomarkers for various diseases. They also could reflect the individual interplay between the environment and the immune system. Thus, GPCR abs could display pathogenic chronic conditions and could help to identify disease-related pathways. Moreover, by acting as ligands to their corresponding receptors, GPCR abs modulate autoimmune as well as non-autoimmune diseases. This article introduces GPCR abs as drivers for diseases by their capability to induce a specific signaling and by determining immune cell homeostasis. The identification of the individual GPCR ab function is challenging but might be pivotal in the comprehension of the aetiology of diseases. This, hopefully, will lead to the identification of novel therapeutic strategies. This article provides an overview about concepts and recent developments in research. Accordingly, GPCR abs could represent ideal candidates for precision medicine. Here, we introduce the term antibodiom to cover the network of abs with GPCR abs as prominent players.

DSA Are Associated With More Graft Injury, More Fibrosis, and Upregulation of Rejection-associated Transcripts in Subclinical Rejection

BACKGROUND

Subclinical T cell-mediated rejection (subTCMR) is commonly found after liver transplantation and has a good short-term prognosis, even when it is left untreated. Donor-specific antibodies (DSA) are putatively associated with a worse prognosis for recipient and graft after liver transplantation.

METHODS

To assess the immune regulation in subTCMR grafts, gene expression of 93 transcripts for graft injury, tolerance, and immune regulation was analyzed in 77 biopsies with "no histologic rejection" (NHR; n = 25), "clinical TCMR" (cTMCR; n = 16), and subTCMR (n = 36). In addition, all available subTCMR biopsies (n = 71) were tested for DSA with bead assays.

RESULTS

SubTCMR showed heterogeneous and intermediate expression profiles of transcripts that were upregulated in cTCMR. Graft gene expression suggested a lower activation of effector lymphocytes and a higher activation of regulatory T cells in grafts with subTCMR compared to cTCMR. DSA positivity in subTCMR was associated with histological evidence of more severe graft inflammation and fibrosis. This more severe DSA+ associated graft injury in subTCMR was converged with an upregulation of cTCMR-associated transcripts. In nonsupervised analysis, DSA positive subTCMR mostly clustered together with cTCMR, while DSA negative subTCMR clustered together with NHR.

CONCLUSIONS

T cell-mediated rejection seems to form a continuum of alloimmune activation. Although subTCMR exhibited less expression of TCMR-associated transcript, DSA positivity in subTCMR was associated with an upregulation of rejection-associated transcripts. The identification of DSA positive subclinical rejection might help to define patients with more inflammation in the graft and development of fibrosis.

Endothelin Type A Receptor Antibodies Are Associated With Angiotensin II Type 1 Receptor Antibodies, Vascular Inflammation, and Decline in Renal Function in Pediatric Kidney Transplantation

Introduction

Autoantibody to angiotensin II type 1 receptor (AT1R-Ab) has been recognized as a non-human leukocyte antigen (HLA) antibody relevant in transplantation. Endothelin type A receptor antibody (ETAR-Ab) has been strongly associated with AT1R-Ab, but the data in kidney transplantation are scarce.

Methods

We examined the relationship of ETAR-Ab and AT1R-Ab with clinical outcomes, biopsy findings, inflammatory cytokines, and HLA donor-specific antibody (DSA) in a cohort of pediatric renal transplant recipients. Sixty-five patients were longitudinally monitored for ETAR-Ab, AT1R-Ab, HLA DSA, interleukin (IL)-8, tumor necrosis factor-α, IL-1β, interferon-γ, IL-17, IL-6, renal dysfunction, hypertension, rejection, and allograft loss during the first 2 years post-transplant.

Results

Fifteen patients (23%) had AT1R-Ab alone, 1 (2%) had ETAR-Ab alone, 23 (35%) had both ETAR-Ab and AT1R-Ab, and 26 (40%) were negative for both antibodies at all timepoints. Having both ETAR-Ab and AT1R-Ab was associated with >30% decline in estimated glomerular filtration rate (P = 0.024), arteritis (P = 0.016), and elevated IL-8 levels (P = 0.010), but not rejection, HLA DSA, or allograft loss. Having both antibodies resulted in greater increases in IL-8 compared with AT1R-Ab alone, even when controlled for additional clinical factors, including HLA DSA (P = 0.012).

Conclusion

Our study demonstrates that, in pediatric kidney transplantation, ETAR-Ab is highly associated with AT1R-Ab, but there are a subset of patients with AT1R-Ab alone. Having both antibodies is significantly associated with arteritis, elevated IL-8, and decline in renal function, and our results suggest possible interaction effects. Better understanding of this interaction may be informative in developing protocols for testing, treatment, and prevention of allograft injury.

Non-invasive screening for subclinical liver graft injury in adults via donor-specific anti-HLA antibodies

The majority of liver grafts exhibit abnormal histological findings late after transplantation, even when liver enzymes are normal. Such subclinical graft injuries were associated with rejection and fibrosis progression in recent studies. The identification of non-invasive biomarkers for subclinical graft injury might help to individualize immunosuppression. Therefore, graft injury was assessed in 133 liver biopsies with normal/near normal liver enzymes from a prospective liver biopsy program. Cytokeratin-18 cell death marker (M65) and donor specific anti-HLA antibodies (DSA) were measured as non-invasive markers in paired plasma samples in addition to routine parameters. M65 was associated with subclinical graft injury but this association was too weak for reasonable clinical application. DSA positivity was associated with more graft inflammation (OR = 5.4) and more fibrosis (OR = 4.2). Absence of DSA excluded fibrosis in 87–89%, while presence of DSA excluded histological criteria for immunosuppression minimization attempts in 92–97%. While CK18 cell death marker had no diagnostic value for the detection of subclinical liver graft injury, DSA testing can help to preselect patients for immunosuppression reduction in case of DSA negativity, while DSA positivity should prompt elastography or liver biopsy for the assessment of subclinical graft injury.

HLA class II donor specific antibodies are associated with graft cirrhosis after liver transplant independent of the mean fluorescence intensity level

Background

The importance of donor-specific antibodies (DSA) after liver transplantation (LT) for graft and patient survival is an ongoing controversy. So far it has not been elucidated when and in how far DSA are harmful for graft and patient survival. Therefore, we had the aim to investigate the association of DSA with complications after LT.

Methods

Data of 430 LT recipients were collected and statistically analyzed. Detection of HLA antibodies (Ab) was performed by Luminex assay.

Results

DSA were detected in 81 patients (18.8%). These were mainly HLA class II Ab (81.5%). HLA class II Ab show a higher MFI (median: 5.300) compared to HLA class I Ab (median: 2.300). There is no association between MFI levels and development of complications after LT. However, cirrhosis occurred significantly more often in DSA positive patients (18%) than in patients without detectable DSA (9%, P = 0.027). All DSA positive patients with cirrhosis of the graft showed HLA class II antibodies (OR: 3.028; 95% CI: 1.51–6.075; P = 0.002).

Conclusion

Occurrence of HLA class II DSA after LT is associated with graft cirrhosis and may indicate a higher risk to develop graft damage independent on MFI and requires an individualized risk management.

Enhancing the Value of Histopathological Assessment of Allograft Biopsy Monitoring

Traditional histopathological allograft biopsy evaluation provides, within hours, diagnoses, prognostic information, and mechanistic insights into disease processes. However, proponents of an array of alternative monitoring platforms, broadly classified as "invasive" or "noninvasive" depending on whether allograft tissue is needed, question the value proposition of tissue histopathology. The authors explore the pros and cons of current analytical methods relative to the value of traditional and illustrate advancements of next-generation histopathological evaluation of tissue biopsies. We describe the continuing value of traditional histopathological tissue assessment and "next-generation pathology (NGP)," broadly defined as staining/labeling techniques coupled with digital imaging and automated image analysis. Noninvasive imaging and fluid (blood and urine) analyses promote low-risk, global organ assessment, and "molecular" data output, respectively; invasive alternatives promote objective, "mechanistic" insights by creating gene lists with variably increased/decreased expression compared with steady state/baseline. Proponents of alternative approaches contrast their preferred methods with traditional histopathology and: (1) fail to cite the main value of traditional and NGP-retention of spatial and inferred temporal context available for innumerable objective analyses and (2) belie an unfamiliarity with the impact of advances in imaging and software-guided analytics on emerging histopathology practices. Illustrative NGP examples demonstrate the value of multidimensional data that preserve tissue-based spatial and temporal contexts. We outline a path forward for clinical NGP implementation where "software-assisted sign-out" will enable pathologists to conduct objective analyses that can be incorporated into their final reports and improve patient care.

Angiotensin II type I receptor agonistic autoantibodies are associated with poor allograft survival in liver retransplantation

Angiotensin II type I receptor (AT1R) agonistic autoantibodies (AT1R-AA) are detrimental to kidney transplantation. Early studies suggested a similar negative effect in primary liver transplantation. Here, we studied AT1R-AA in a retrospective cohort of 94 patients who received a second liver transplant to determine their prevalence and effects. The concentrations of preformed AT1R-AA before transplantation were higher (P = .019) in the 48 patients who lost their liver grafts than in the 46 patients whose grafts survived. About half (48/94, 51.1%) of the patients were positive for AT1R-AA >17 U/mL before the second liver transplantation. In 22 (23.4%) patients, strong positive AT1R-AA (defined as >40 U/mL) were detected, of whom 16 (72.7%) patients lost their grafts. Based on Kaplan-Meier analysis, patients with strong positive AT1R-AA had significantly worse graft survival than those with AT1R-AA <40 U/mL (P = .035). In multivariate Cox models that included confounders such as sex and age, either AT1R-AA >40 U/mL (HR = 1.999 [1.085-3.682], P = .026) or increased concentrations of AT1R-AA (HR = 1.003 [1.001-1.006] per incremental U/mL, P = .019) were significantly associated with elevated risk for graft loss. In conclusion, our data indicate that there is a high prevalence of AT1R-AA in candidates for second liver transplantation and that their presence is associated with inferior long-term outcomes of the second graft.

Antibodies against Angiotensin II Type 1 and Endothelin A Receptors: Relevance and pathogenicity

Antibodies against two G-protein coupled receptors (GPCRs), angiotensin II type 1 receptor (AT1R) and endothelin A receptor (ETAR) are among a growing number of autoantibodies that are found to be associated with allograft dysfunction. AT1R antibodies (AT1Rabs) and ETAR antibodies (ETARabs) have been shown to activate their target receptors and affect signaling pathways. Multiple single center reports have shown an association between presence of these antibodies and acute or chronic rejection and graft loss in kidney, heart, liver, lung and composite tissue transplantations. However, the characteristics of patients that are most likely to develop adverse outcomes, the phenotypes associated with graft damage solely due to these antibodies, and the antibody titer required to cause dysfunction are areas that remain controversial. This review compiles existing knowledge on the effect of antibodies against GPCRs in other diseases in order to bridge the gap in knowledge within transplantation biology. Future areas for research are highlighted and include the need for functional assays and treatment protocols for transplant patients who present with AT1Rabs and ETARabs. Understanding how antibodies that activate GPCRs influence transplantation outcome will have direct clinical implications for preemptive evaluation of transplant candidates as well as the post-transplant care of organ recipients.

Evidence of Chronic Allograft Injury in Liver Biopsies From Long-term Pediatric Recipients of Liver Transplants

BACKGROUND & AIMS

A substantial proportion of pediatric liver transplant recipients develop subclinical chronic allograft injury. We studied whether there are distinct patterns of injury based on histopathologic features and identified associated immunologic profiles.

METHODS

We conducted a cross-sectional study of 157 stable, long-term pediatric recipients of transplanted livers (70 boys; > 6 years old at time of transplantation; mean, 8.9 ± 3.46 years after liver transplantation) who underwent liver biopsy analysis from August 13, 2012, through May 1, 2014. Participants had received livers from a living or deceased donor and had consistently normal results from liver tests. Liver biopsy specimens were scored by a central pathologist; an unsupervised hierarchical cluster analysis of histologic features was used to sort biopsy samples into 3 clusters. We conducted transcriptional and cytometric analyses of liver tissue samples and performed a systems biology analysis that incorporated clinical, serologic, histologic, and transcriptional data.

RESULTS

The mean level of alanine aminotransferase in participants was 27.6 ± 14.57 U/L, and the mean level of γ-glutamyl transferase was 17.4 ± 7.93 U/L. Cluster 1 was characterized by interface activity (n = 34), cluster 2 was characterized by periportal or perivenular fibrosis without interface activity (n = 45), and cluster 3 had neither feature (n = 78). We identified a module of genes whose expression correlated with levels of alanine aminotransferase, class II donor-specific antibody, portal inflammation, interface activity, perivenular inflammation, portal and perivenular fibrosis, and cluster assignment. The module was enriched in genes that regulate T-cell-mediated rejection (TCMR) of liver and other transplanted organs. Functional pathway analysis showed overrepresentation of TCMR gene sets for cluster 1 but not clusters 2 or 3.

CONCLUSION

In an analysis of biopsies from an apparently homogeneous group of stable, long-term pediatric liver transplant recipients with consistently normal liver test results, we found evidence of chronic graft injury (inflammation and/or fibrosis). Biopsy samples with interface activity had a gene expression pattern associated with TCMR.

Anti-perlecan antibodies and acute humoral rejection in hypersensitized patients without forbidden HLA specificities after kidney transplantation

BACKGROUND

The improvement in the definition of serum anti-HLA antibodies (HLA-Abs) profiles after Luminex-assay implementation in transplant patients follow-up is clear. This success has permitted the development of hypersensitized-recipient allocation and donor-paired exchange programs improving the access to transplantation. However, non-HLA Abs have been described in transplanted patients but their effect in hypersensitized transplanted recipients is unclear.

METHODS

Twenty-seven HLA hypersensitized patients awaiting for kidney transplantation (KT) were studied and 11 of them were followed after KT. The HLA Abs profile was confirmed in serum by Single Antigen Luminex assay and panel reactive of antigens >98% was achieved in all patients. Subsequently, the ability to fix complement by C1q test was also assessed. Serum non-HLA Abs before and 1 month after transplantation were measured in the 11 hypersensitized recipients.

RESULTS

95.2% of the hypersensitized on waiting list had concomitant serum anti-HLA and non-HLA Abs. The more frequent specificity in non-HLA Abs were found against Glutathione S-transferase theta-1 (GSST-1) (in 62%) and C-terminal fragment of perlecan (LG3) (in 52%). Four out of 11 transplanted patients presented early antibody-mediated rejection (ABMR) confirmed by biopsy and had serum anti-LG3 antibodies, two of them with concomitant anti-anti-angiotensin II type I receptor. Only one patient developed de novo-donor specific HLA antibodies.

CONCLUSIONS

The incidence of non-HLA antibodies in patients in the waiting list is largely underestimated. The concomitance anti-HLA and non-HLA Abs in hypersensitized patients is very common and the detection of non-HLA Abs in this population could allow to identify patients with an increased risk of humoral rejection.

Cardiovascular disease after transplantation: an emerging role of the immune system

Cardiovascular disease (CVD) after transplantation remains a major concern. Little is known about what drives the increased cardiovascular risk in transplant recipients apart from traditional risk factors. The immune system is involved in the pathogenesis of hypertension, atherosclerosis, and coronary artery disease in the general population. Recently, inhibition of interleukin 1 - β by canakinumab versus placebo decreased the incidence of cardiovascular events. Emerging evidence points to a role of adaptive cellular immunity in the development of CVD. Especially, expansion of pro-inflammatory and antiapoptotic cytotoxic CD4⁺ CD28^null T cells is closely associated with incident CVD in various study populations including transplant recipients. The association of cytomegalovirus exposure with increased cardiovascular mortality might be explained by its capacity to upregulate these cytotoxic cells. Also, humoral immunity seems to be relevant for cardiovascular outcome in transplant recipients. Panel-reactive antibodies at baseline and donor-specific antibodies are independently associated with poor cardiovascular outcome after kidney transplantation. Cardiovascular effects of immunosuppressive drugs and statins do not only imply indirect positive or negative effects on traditional cardiovascular risk factors but also intrinsic immunological effects. How immunosuppressive drugs modify atherosclerosis largely remains elusive.

Obliterative portal venopathy: A histopathologic finding associated with chronic antibody-mediated rejection in pediatric liver allografts

The significance of post-transplant HLA DSA and chronic AMR in LT is an emerging field of study. Although OPV has previously been described as a histopathologic finding in DSA-positive adult LT recipients, it was not included in the recent Banff criteria for chronic AMR. Our aim was to describe the association between OPV and chronic AMR in pediatric LT recipients. A retrospective review of 67 liver biopsies performed between November 2014 and April 2016 in 45 pediatric LT recipients identified four patients with OPV. Clinical status, liver biochemistry, the presence of DSA, and available non-HLA antibody testing, as well as histopathologic features of chronic AMR, were assessed. All four patients with OPV had class II DSA and histopathologic features of chronic AMR based on the Banff criteria. Two patients were noted to have non-HLA antibodies. Three patients are undergoing treatment with IVIG but have persistent DSA. Two patients have graft failure and are awaiting retransplantation. In conclusion, OPV is a histopathologic finding associated with chronic AMR in pediatric LT recipients. Further studies are needed to elucidate whether OPV is reversible and/or amenable to medical therapy.

Circular RNA in Liver: Health and Diseases

Circular RNA (circRNA) is an important class of noncoding RNA characterized by covalently closed continuous loop structures. In recent years, the various functions of circRNAs have been continuously documented, including effects on cell proliferation and apoptosis and nutrient metabolism. The liver is the largest solid organ in mammals, and it also performs many functions in the body, which is considered to be the busiest organ in the body. At the same time, the liver is vulnerable to multiple pathogenic factors, causing various acute and chronic liver diseases. The pathogenesis of liver disease is still not fully understood. As a rising star for the past few years, circRNAs have been proven involved in the regulation of liver homeostasis and disease. This chapter will explain the role of circRNAs in liver health and diseases and sort out the confusion in the present study.