Clinical Outcomes After a Biopsy Diagnosis of Antibody-mediated Rejection in Pediatric Heart Transplant Recipients.

BACKGROUND: Extending graft survival after heart transplant (HT) is of paramount importance to achieve survival well into adulthood for childhood recipients. Acute rejection is a significant adverse event, and biopsy remains the most specific means for diagnosing acute cellular rejection (ACR) versus antibody-mediated rejection (AMR). METHODS: All children in the Pediatric Heart Transplant Society (PHTS) Registry who underwent HT between 1/2015 and 6/2022 and had ≥1 episode of treated rejection were included. Survival after rejection was compared between those with AMR and those with ACR-only. Secondary outcomes of infection, malignancy, and cardiac allograft vasculopathy (CAV) were assessed. Risk factors for graft loss after AMR were identified using Cox proportional hazard modeling. RESULTS: Among 906 children treated for rejection during follow-up through 12/2022, 697 (77%) with complete biopsy information were included. AMR was present on biopsy in 261 (37%) patients; ACR-only was present in 436 (63%) patients. Time to treated rejection was earlier in those with AMR, median time from HT to rejection 0.11 versus 0.29 years, p=0.0006. When rejection occurred within the 1st year, survival after AMR was lower than survival after ACR-only. Predictors of graft loss after AMR were younger age at HT, diagnosis of congenital heart disease, and rejection with hemodynamic compromise. There was no difference in time to CAV, infection, or malignancy after treated rejection between groups. CONCLUSIONS: The largest analysis of pediatric HT recipients treated for rejection with biopsy data to identify AMR underscores the continued importance of AMR on survival. AMR is associated with higher graft loss versus ACR when occurring in the first-year post HT. Predictors of graft loss after AMR identify patients who may benefit from increased surveillance, more aggressive rejection treatment, or augmented maintenance immunosuppression.

Long-term isoagglutinin monitoring after ABO-incompatible kidney transplantation.

OBJECTIVES: This study aimed to evaluate whether a 2-week period of daily isoagglutinin titer testing after ABO-incompatible kidney transplantation (ABOi-KT) is sufficient to ensure successful engraftment and to advocate for an extension of the monitoring duration in specific situations. METHODS: We reviewed patients from January 2022 to December 2023 at Asan Medical Center who underwent therapeutic plasma exchange (TPE) due to elevated ABO antibody titers and suspected acute antibody-mediated rejection (AMR) after ABOi-KT. Data collected included pre- and posttransplantation laboratory results, clinical and procedural information, imaging studies, and needle biopsy results of the renal graft. RESULTS: We encountered 3 cases of acute AMR 2 weeks after transplantation. All cases exhibited simultaneous increases in anti-ABO antibody isoagglutinin titers, creatinine, and C-reactive protein levels. Clinical signs, including fever, suggested possible infection, and renal graft biopsy, confirmed AMR in all cases. Two cases underwent graftectomy, while the third recovered renal function after conservative treatment, including TPE. CONCLUSIONS: Our findings suggest that a 2-week monitoring period for isoagglutinin titers after ABOi-KT may not be sufficient to detect late AMR. Extending the monitoring duration and considering lifelong fresh-frozen plasma transfusion with graft-compatible blood types, along with periodic isoagglutinin titer testing in cases of suspected AMR, may improve long-term graft outcomes.

Polymorphisms in genes involved in regulating follicular helper T cell differentiation predict de novo donor-specific antibody formation after liver transplantation.

BACKGROUND: De novo donor-specific antibodies (dnDSAs) significantly affect the long-term outcomes of liver transplantation (LT), highlighting the importance of risk prediction. Follicular helper T (Tfh) cells have been implicated in dnDSA formation after transplantation. Considering the influence of immune response gene polymorphisms on transplantation outcomes, we investigated the association between polymorphisms in Tfh cell-related genes and dnDSA formation after LT. METHODS: Fifty-three living-donor LT patients were included in this study. Single nucleotide polymorphisms (SNPs) were identified in six Tfh cell-related genes crucial for differentiation and maturation (BCL6, CXCR5, CXCL13, ICOS, CD40L, and IL-21); their association with the development of dnDSA after LT was evaluated. RESULTS: Among the 53 recipients, 9 developed dnDSAs. BCL6 and IL-21 SNPs showed potential associations with dnDSA formation, enabling risk stratification. CONCLUSIONS: Variations in Tfh cell-related genes may predispose individuals to dnDSA formation after LT, emphasizing the importance of genetic factors for predicting post-transplant complications.

Antibody-mediated rejection diagnosed in early protocol biopsies in high immunological risk kidney transplant recipients.

BACKGROUND: Renal transplant recipients with donor-specific anti-HLA antibodies are at an increased risk of antibody-mediated rejection (AMR). Early protocolized renal biopsies may serve as a strategy to improve diagnosis in this patient population. METHODS: We evaluated 155 highly sensitized renal transplant recipients with cPRA class I + II > 90% pre-transplant from 2015 to 2022. Patients with protocol biopsies within the first two weeks post-transplant were included. RESULTS: A total of 122 patients were included in the study. Of these, 13 (10.6%) were diagnosed with very early antibody-mediated rejection (veABMR) within the first two weeks post-transplant. This corresponds to 52% (13/25 patients) of all ABMR cases reported during the follow-up of this population. The graft survival rates at one and three years were significantly lower in patients with veABMR (p < 0.001) compared to patients without rejection in the early protocol biopsy. In terms of severity, the veABMR cohort exhibited a hazard ratio (HR) of 10.33 (95% CI 3.23-33.06; p < 0.001) for graft failure. The presence of donor-specific antibodies (DSA) class II on the day of transplantation and a higher percentage of eplet mismatch (EpMM), particularly EpMM DQA1, correlated with the development of veABMR. CONCLUSION: Early protocol biopsies play a pivotal role in the early detection of veABMR in high-risk immunological patients. Patients with veABMR face significant risks of graft loss, despite early treatment of rejection.

Biomarkers in Kidney Transplantation.

Currently in the United States, there are more than 250,000 patients with a functioning kidney allograft and over 100,000 waitlisted patients awaiting kidney transplant, with a burgeoning number added to the kidney transplant wait list every year. Although early post-transplant care is delivered at the transplant center, the increasing number of kidney transplant recipients requires general nephrologists to actively participate in the long-term care of these patients. Serum creatinine and proteinuria are imperfect traditional biomarkers of allograft dysfunction and lag behind subclinical allograft injury. This manuscript reviews the various clinically available biomarkers in the field of kidney transplantation for a general nephrologist with a focus on the utility of donor-derived cell-free DNA, as a marker of early allograft injury. Blood gene expression profiling, initially studied in the context of early identification of subclinical rejection, awaits validation in larger multicentric trials. Urinary cellular messenger ribonucleic acid and chemokine CXCL10 hold promising potential for early diagnosis of both subclinical and acute rejection. Torque tenovirus, a ubiquitous DNA virus is emerging as a biomarker of immunosuppression exposure as peripheral blood torque tenovirus copy numbers might mirror the intensity of host immunosuppression. Although high-quality evidence is still being generated, evidence and recommendations are provided to aid the general nephrologist in implementation of novel biomarkers in their clinical practice.

Heart Transplant Rejection: From the Endomyocardial Biopsy to Gene Expression Profiling.

Heart transplant prolongs life for patients with end-stage heart failure but rejection remains a complication that reduces long-term survival. The aim is to provide a comprehensive overview of the current status in HT rejection. EMB is an invasive diagnostic tool, consisting in the sampling of a fragment of myocardial tissue from the right ventricular septum using fluoroscopic guidance. This tissue can later be subjected to histopathological, immunohistochemical or molecular analysis, providing valuable information for cardiac allograft rejection, but this procedure is not without complications. To increase the accuracy of the rejection diagnosis, EMB requires a systematic evaluation of endocardium, myocardium, interstitium and intramural vessels. There are three types of rejection: hyperacute, acute or chronic, diagnosed by the histopathological evaluation of EMB as well as by new diagnostic methods such as DSA, ddcfDNA and gene expression profiling, the last having a high negative predictive value. More than 50 years after the introduction of EMB in medical practice, it still remains the "gold standard" in monitoring rejection in HT recipients but other new, less invasive diagnostic methods reduce the number of EMBs required.

Local intragraft humoral immune responses in chronic lung allograft dysfunction.

BACKGROUND: Donor human leukocyte antigen (HLA)-specific antibodies (DSA) and non-HLA antibodies can cause allograft injury, possibly leading to chronic lung allograft dysfunction (CLAD) after lung transplantation. It remains unclear whether these antibodies are produced locally in the graft or derived solely from circulation. We hypothesized that DSA and non-HLA antibodies are produced in CLAD lungs. METHODS: Lung tissue was prospectively collected from 15 CLAD patients undergoing retransplantation or autopsy. 0.3 g of fresh lung tissue was cultured for 4 days without or with lipopolysaccharide or CD40L: lung culture supernatant (LCS) was sampled. Protein eluate was obtained from 0.3 g of frozen lung tissue. The mean fluorescence intensity (MFI) of DSA and non-HLA antibodies was measured by Luminex and antigen microarray, respectively. RESULTS: LCS from all 4 patients who had serum DSA at lung isolation were positive for DSA, with higher levels measured after CD40L stimulation (CD40L+LCS). Of these, only 2 had detectable DSA in lung eluate. MFI of non-HLA antibodies from CD40L+LCS correlated with those from lung eluate but not with those from sera. Flow cytometry showed higher frequencies of activated lung B cells in patients whose CD40L+LCS was positive for DSA (n = 4) or high non-HLA antibodies (n = 6) compared to those with low local antibodies (n = 5). Immunofluorescence staining showed CLAD lung lymphoid aggregates with local antibodies contained larger numbers of IgG+ plasma cells and greater IL-21 expression. CONCLUSIONS: We show that DSA and non-HLA antibodies can be produced within activated B cell-rich lung allografts.

Corrigendum: Pre-transplant crossmatch-negative donor-specific anti-HLA antibody predicts acute antibody-mediated rejection but not long-term outcomes in kidney transplantation: an analysis of the Korean Organ Transplantation Registry.

[This corrects the article DOI: 10.3389/fimmu.2024.1420351.].

Donor-Derived Cell-Free DNA as a Companion Biomarker for AMR Treatment With Daratumumab: Case Series.

Antibody-mediated rejection (AMR) is among the most frequent causes for graft loss after kidney transplantation. While there are no approved therapies, several case reports with daratumumab and the very recent phase 2 trial of felzartamab in AMR have indicated the potential efficacy of therapeutic interventions targeting CD38. Donor-derived cell-free DNA (dd-cfDNA) is an emerging biomarker with injury-specific release and a short half-life, which could facilitate early diagnosis of AMR and monitoring of treatment response. We describe two cases of patients with chronic active AMR, who were treated with monthly daratumumab infusions, and in whom donor-derived cell-free DNA (dd-cfDNA) was measured longitudinally to monitor treatment response. In both patients, daratumumab treatment led to stabilization of kidney function parameters, a strong decline of dd-cfDNA below the previously established threshold for rejection, and partial or complete histologic resolution of AMR activity. Our case series suggests that dd-cfDNA may be a useful companion biomarker for longitudinal monitoring of anti-CD38 treatment in patients with AMR.

Outcomes of Kidney Transplantation in Highly HLA-Sensitized Patients Treated with Intravenous Immuno-Globulin, Plasmapheresis and Rituximab: A Meta-Analysis.

(1) Background: We aimed to investigate the outcomes of human leukocyte antigen (HLA)-incompatible transplantation for patients who received desensitization with intravenous immunoglobulins (IVIg), plasmapheresis, and rituximab. (2) Methods: A comprehensive search of multiple electronic databases to identify studies that utilized desensitization was conducted. The random-effects model was used to calculate the pooled rates and the 95% confidence interval (CI). (3) Results: A total of 1517 studies were initially identified. From these, 16 studies met the inclusion criteria, encompassing 459 patients, with a mean age of 45 years, of whom 40.8% were male. CDC crossmatch was positive in 68.3% (95% CI: 43.5-85.8; I2 87%), and 89.4% (95% CI: 53.4-98.4%; I2 89.8%) underwent living-donor transplantation. The 1-year graft survival pooled rate was 88.9% (95% CI: 84.8-92; I2 0%) and the 5-year graft survival rate was 86.1% (95% CI: 81.2-89.9; I2 0%). The 1-year patient survival rate was 94.2% (95% CI: 91-96.3; I2 0%), and the 5-year patient survival rate was 88.9% (95% CI: 83.5-92.7%; I2 7.7%). The rate of antibody-mediated rejection was 37.7% (95% CI: 25-52.3; I2 80.3%), and the rate of acute cell-mediated rejection was 15.1% (95% CI: 9.1-24; I2 55%). (4) Conclusions: Graft and patient survival are favorable in highly sensitized patients who undergo desensitization using IVIg, plasmapheresis, and rituximab for HLA-incompatible transplantation.

Interchain disulfide engineering enables the efficient production of functional HLA-DQ-Fc fusion proteins.

HLA-DQ molecules drive unwanted alloimmune responses after solid-organ transplants and several autoimmune diseases, including type 1 diabetes and celiac disease. Biologics with HLA molecules as part of the design are emerging therapeutic options for these allo- and autoimmune conditions. However, the soluble α and ß chains of class II HLA molecules do not dimerize efficiently without their transmembrane domains, which hinders their production. In this study, we examined the feasibility of interchain disulfide engineering by introducing paired cysteines to juxtaposed positions in the α and ß chains of HLA-DQ7, encoded by HLA-DQA1∗05:01 and HLA-DQB1∗03:01 respectively. We identified three variant peptide-HLA-DQ7-Fc fusion proteins (DQ7Fc) with increased expression and production yield, namely Y19C-D6C (YCDC), A83C-E5C (ACEC), and A84C-N33C (ACNC). The mutated residues were conserved across all HLA-DQ proteins and had limited solvent exposure. Further characterizations of the YCDC variant showed that the expression of the fusion protein is peptide-dependent; inclusion of a higher-affinity peptide correlated with increased protein expression. However, high-affinity peptide alone was insufficient for stabilizing the DQ7 complex without the engineered disulfide bond. Multiple DQ7Fc variants demonstrated expected binding characteristics with commercial anti-DQ antibodies in two immunoassays and by a cell-based assay. Lastly, DQ7Fc variants demonstrated dose-dependent killing of DQ7-specific B cell hybridomas in a flow cytometric, complement-dependent cytotoxicity assay. These data support inter-chain disulfide engineering as a novel approach to efficiently producing functional HLA-DQ molecules and potentially other class II HLA molecules as candidate therapeutic agents.

Antibody-Mediated Rejection in Lung Transplantation: Diagnosis and Therapeutic Armamentarium in a 21st Century Perspective.

Humoral immunity is a major waypoint towards chronic allograft dysfunction in lung transplantation (LT) recipients. Though allo-immunization and antibody-mediated rejection (AMR) are well-known entities, some diagnostic gaps need to be addressed. Morphological analysis could be enhanced by digital pathology and artificial intelligence-based companion tools. Graft transcriptomics can help to identify graft failure phenotypes or endotypes. Donor-derived cell free DNA is being evaluated for graft-loss risk stratification and tailored surveillance. Preventative therapies should be tailored according to risk. The donor pool can be enlarged for candidates with HLA sensitization, with strategies combining plasma exchange, intravenous immunoglobulin and immune cell depletion, or with emerging or innovative therapies such as imlifidase or immunoadsorption. In cases of insufficient pre-transplant desensitization, the effects of antibodies on the allograft can be prevented by targeting the complement cascade, although evidence for this strategy in LT is limited. In LT recipients with a humoral response, strategies are combined, including depletion of immune cells (plasmapheresis or immunoadsorption), inhibition of immune pathways, or modulation of the inflammatory cascade, which can be achieved with photopheresis. Altogether, these innovative techniques offer promising perspectives for LT recipients and shape the 21st century's armamentarium against AMR.

Perspective for Donor-Derived Cell-Free DNA in Antibody-Mediated Rejection After Kidney Transplantation: Defining Context of Use and Clinical Implications.

Antibody-mediated rejection (AMR) is a major cause of graft failure limiting long-term graft survival after kidney transplantation. Current diagnostic strategy to detect AMR is suboptimal and requires further improvement. Previously suggested treatment regimens for AMR could not demonstrate efficacy, however novel therapeutic agents are currently under investigation. Donor-derived cell-free DNA (dd-cfDNA) is a novel non-invasive biomarker for allograft injury, that has been mainly studied in the context of rejection. Its short-half-life in circulation and injury-dependent release are its key advantages that contribute to its superior diagnostic accuracy, compared to traditional biomarkers. Moreover, previous studies showed that dd-cfDNA-release is well-linked to histological and molecular features of AMR, and thus able to reflect real-time injury. Further observations suggest that dd-cfDNA can be used as a suitable screening tool for early detection of AMR in patients with donor-specific-anti-HLA-antibodies (DSA), as well as for monitoring AMR activity after anti-rejection treatment. The weight of evidence suggests that the integration of dd-cfDNA in the graft surveillance of patients with AMR, or those suspicious of AMR (e.g., due to the presence of donor-specific anti-HLA-antibodies) has an added value and might have a positive impact on outcomes in this specific cohort.

Interstitial Foci Expression of Indoleamine 2,3-Dioxygenase 1: A Potential Biomarker for Kidney Transplant Rejection.

(1) Background: Kidney transplantation is the best therapy for patients with end-stage renal disease, but the risk of rejection complicates it. Indoleamine 2,3-dioxygenase 1 (IDO1), an enzyme involved in immune response modulation, has been suggested to play a role in transplant immunological injury. The aim of the study was to explore the expression of IDO1 in the interstitial foci of transplanted kidneys and its potential association with rejection episodes. (2) Methods: This retrospective study analysed kidney transplant biopsies from 121 patients, focusing on IDO1 expression in interstitial foci. Immunohistochemistry was used to detect IDO1, and patients were categorised based on IDO1 presence (IDO1-IF positive or negative). The incidence of rejection was compared between these groups. (3) Results: Patients with IDO1 expression in interstitial foci (IDO1-IF(+)) exhibited higher incidences of rejection 46/80 (57.5%) vs. 10/41 (24.34%) patients compared to IDO1-IF(-) patients, which was statistically significant with p = 0.0005. The analysis of antibody-mediated rejection showed that IDO1-IF(+) patients developed AMR at 12/80 (15%), while only 1 IDO1-IF(-) negative patient did (2,44%), with p = 0.035. T-cell-mediated rejection was also more common in IDO1-IF(+) patients 43/80 (53.75%) than in IDO1-IF(-) patients 7/41 (17.07%), with p = 0.0001. (4) Conclusions: IDO1 expression in interstitial foci of renal transplant biopsies is associated with a higher incidence of rejection, suggesting that IDO1 could serve as a potential biomarker for transplant rejection. These findings highlight the importance of IDO1 in immune regulation and its potential utility in improving the management of kidney transplant recipients.

Pre-transplant crossmatch-negative donor-specific anti-HLA antibody predicts acute antibody-mediated rejection but not long-term outcomes in kidney transplantation: an analysis of the Korean Organ Transplantation Registry.

Background: Pre-transplant donor-specific anti-human leukocyte antigen antibody (HLA-DSA) is a recognized risk factor for acute antibody-mediated rejection (ABMR) and allograft failure. However, the clinical relevance of pre-transplant crossmatch (XM)-negative HLA-DSA remains unclear. Methods: We investigated the effect of XM-negative HLA-DSA on post-transplant clinical outcomes using data from the Korean Organ Transplantation Registry (KOTRY). This study included 2019 living donor kidney transplant recipients from 40 transplant centers in South Korea: 237 with HLA-DSA and 1782 without HLA-DSA. Results: ABMR developed more frequently in patients with HLA-DSA than in those without (5.5% vs. 1.5%, p<0.0001). Multivariable analysis identified HLA-DSA as a significant risk factor for ABMR (odds ratio = 3.912, 95% confidence interval = 1.831-8.360; p<0.0001). Furthermore, the presence of multiple HLA-DSAs, carrying both class I and II HLA-DSAs, or having strong HLA-DSA were associated with an increased incidence of ABMR. However, HLA-DSA did not affect long-term clinical outcomes, such as allograft function and allograft survival, patient survival, and infection-free survival. Conclusion: Pre-transplant XM-negative HLA-DSA increased the risk of ABMR but did not affect long-term allograft outcomes. HLA-incompatible kidney transplantation in the context of XM-negative HLA-DSA appears to be feasible with careful monitoring and ensuring appropriate management of any occurrence of ABMR. Furthermore, considering the characteristics of pre-transplant XM-negative HLA-DSA, the development of a more detailed and standardized desensitization protocol is warranted.

Correlation of cTfh cells and memory B cells with AMR after renal transplantation.

Renal transplantation is the preferred treatment option for patients with end-stage renal disease (ESRD) in a clinical setting. Antibody mediated rejection (AMR) is one of the leading causes of graft dysfunction. To address the current shortcomings in the early diagnosis and treatment of AMR in clinical practice, this article analyzes the distribution of different circulating T follicular helper (cTfh) cell subtypes and B cell subpopulations in peripheral blood and detects the cytokine levels of chemokine ligand 13 (CXCL13), interleukin-21 (IL-21), and interleukin-4 (IL-4) related to cTfh cells in peripheral blood of kidney transplant recipients. Moreover, we also explore the correlation between cTfh cells, peripheral blood memory B cells, and AMR, their value as early predictive indicators of AMR, and explore potential therapeutic targets for AMR patients. Our results indicate that the proportion of cTfh cells increased at the onset of AMR, which plays an important role in antigen-specific B-cell immune regulation. Activation of cTfh cells in AMR patients correlates with phenotypes of memory B cells and plasma blasts. cTfh cells and memory B cells have promising diagnostic efficacies and predictive values for AMR. The proportion of cTfh cells to CD4+ T cells and the proportion of memory B cells to CD19+ B cells are correlated with serum creatinine levels, indicating that cTfh cells and memory B cells may be involved in the progression of AMR. In addition, the CXCL13, IL-21, and IL-4, which were associated with cTfh cells, may be involved in the onset of AMR.