Prognostic Biomarkers in Kidney Transplantation: A Systematic Review and Critical Appraisal.

SIGNIFICANCE STATEMENT: Why are there so few biomarkers accepted by health authorities and implemented in clinical practice, despite the high and growing number of biomaker studies in medical research ? In this meta-epidemiological study, including 804 studies that were critically appraised by expert reviewers, the authors have identified all prognostic kidney transplant biomarkers and showed overall suboptimal study designs, methods, results, interpretation, reproducible research standards, and transparency. The authors also demonstrated for the first time that the limited number of studies challenged the added value of their candidate biomarkers against standard-of-care routine patient monitoring parameters. Most biomarker studies tended to be single-center, retrospective studies with a small number of patients and clinical events. Less than 5% of the studies performed an external validation. The authors also showed the poor transparency reporting and identified a data beautification phenomenon. These findings suggest that there is much wasted research effort in transplant biomarker medical research and highlight the need to produce more rigorous studies so that more biomarkers may be validated and successfully implemented in clinical practice. BACKGROUND: Despite the increasing number of biomarker studies published in the transplant literature over the past 20 years, demonstrations of their clinical benefit and their implementation in routine clinical practice are lacking. We hypothesized that suboptimal design, data, methodology, and reporting might contribute to this phenomenon. METHODS: We formed a consortium of experts in systematic reviews, nephrologists, methodologists, and epidemiologists. A systematic literature search was performed in PubMed, Embase, Scopus, Web of Science, and Cochrane Library between January 1, 2005, and November 12, 2022 (PROSPERO ID: CRD42020154747). All English language, original studies investigating the association between a biomarker and kidney allograft outcome were included. The final set of publications was assessed by expert reviewers. After data collection, two independent reviewers randomly evaluated the inconsistencies for 30% of the references for each reviewer. If more than 5% of inconsistencies were observed for one given reviewer, a re-evaluation was conducted for all the references of the reviewer. The biomarkers were categorized according to their type and the biological milieu from which they were measured. The study characteristics related to the design, methods, results, and their interpretation were assessed, as well as reproducible research practices and transparency indicators. RESULTS: A total of 7372 publications were screened and 804 studies met the inclusion criteria. A total of 1143 biomarkers were assessed among the included studies from blood ( n =821, 71.8%), intragraft ( n =169, 14.8%), or urine ( n =81, 7.1%) compartments. The number of studies significantly increased, with a median, yearly number of 31.5 studies (interquartile range [IQR], 23.8-35.5) between 2005 and 2012 and 57.5 (IQR, 53.3-59.8) between 2013 and 2022 ( P < 0.001). A total of 655 studies (81.5%) were retrospective, while 595 (74.0%) used data from a single center. The median number of patients included was 232 (IQR, 96-629) with a median follow-up post-transplant of 4.8 years (IQR, 3.0-6.2). Only 4.7% of studies were externally validated. A total of 346 studies (43.0%) did not adjust their biomarker for key prognostic factors, while only 3.1% of studies adjusted the biomarker for standard-of-care patient monitoring factors. Data sharing, code sharing, and registration occurred in 8.8%, 1.1%, and 4.6% of studies, respectively. A total of 158 studies (20.0%) emphasized the clinical relevance of the biomarker, despite the reported nonsignificant association of the biomarker with the outcome measure. A total of 288 studies assessed rejection as an outcome. We showed that these rejection studies shared the same characteristics as other studies. CONCLUSIONS: Biomarker studies in kidney transplantation lack validation, rigorous design and methodology, accurate interpretation, and transparency. Higher standards are needed in biomarker research to prove the clinical utility and support clinical use.

High-dimensional profiling of immune responses to kidney transplant reveals heterogeneous T helper 1 and B cell effectors associated with rejection.

Rejection is a primary cause of allograft dysfunction after kidney transplantation. The diversity of immune subpopulations involved in the different endotypes of rejection remains to be delineated at single-cell resolution. In a cohort of 76 kidney transplant recipients, we conducted high-dimensional immune phenotyping of blood CD4 T and B cells, single-cell RNA and T/B cell receptor sequencing, and plasma cytokine profiling. Phenotypic, transcriptional, and clonal states of CD4T and B cells could significantly distinguish stable allograft states from rejection. Patients undergoing T cell-mediated rejection displayed accumulation of clonally expanded cytotoxic T helper (Th)1 cells and Th17-like cells, associated with predominant naive B cell responses. In contrast, antibody-mediated rejection was characterized by clonal expansion of Th1-polarized T follicular helper cells and effector T-bet+ memory B cells, both of which strongly expressed interleukin 12 and tumor necrosis factor-signaling pathways. Plasma cytokine analysis confirmed mixed Th1/Th17 and Th1/T follicular helper cell-driven inflammatory profiles distinguishing T cell-mediated rejection and antibody-mediated rejection, respectively. CD4T and B cell subpopulations and signatures were validated using bulk RNA-seq analysis of matched kidney allografts and using an independent single-cell RNA-seq data set. These data improve mechanistic understanding of the immune pathogenesis of rejection and support the development of more specific immunosuppressive therapies to treat allograft rejection.

Kidney Transplantation in Patients With AA Amyloidosis: Outcomes in a French Multicenter Cohort.

RATIONALE & OBJECTIVE: Outcomes of kidney transplantation for patients with renal AA amyloidosis are uncertain, with reports of poor survival and high rates of disease recurrence. However, the data are inconclusive and mostly based on studies from the early 2000s and earlier. STUDY DESIGN: Retrospective multicenter cohort study. SETTING & PARTICIPANTS: We searched the French national transplant database to identify all patients with renal AA amyloidosis who underwent kidney transplantation between 2008 and 2018. EXPOSURES: Age, cause of amyloidosis, use of biotherapies, and C-reactive protein levels. OUTCOMES: Outcomes were all-cause mortality and allograft loss. We also reported amyloidosis allograft recurrence, occurrence of acute rejection episodes, as well as infectious, cardiovascular, and neoplastic disease events. ANALYTICAL APPROACH: Kaplan-Meier estimator for mortality and cumulative incidence function method for allograft loss. Factors associated with patient and allograft survival were investigated using a Cox proportional hazards model and a cause-specific hazards model, respectively. RESULTS: 86 patients who received kidney transplants for AA amyloidosis at 26 French centers were included. The median age was 49.4 years (IQR, 39.7-61.1). The main cause of amyloidosis was familial Mediterranean fever (37 cases; 43%). 16 (18.6%) patients received biotherapy after transplantation. Patient survival rates were 94.0% (95% CI, 89.1-99.2) at 1 year and 85.5% (77.8-94.0) at 5 years after transplantation. Cumulative incidences of allograft loss were 10.5% (4.0-17.0) at 1 year and 13.0% (5.8-20.1) at 5 years after transplantation. Histologically proven AA amyloidosis recurrence occurred in 5 transplants (5.8%). An infection requiring hospitalization developed in 55.8% of cases, and there was a 27.9% incidence of acute allograft rejection. Multivariable analysis showed that C-reactive protein concentration at the time of transplantation was associated with patient survival (HR, 1.01; 95% CI, 1.00-1.02; P=0.01) and allograft survival (HR, 1.68; 95% CI, 1.10-2.57; P=0.02). LIMITATIONS: The study lacked a control group, and the effect of biotherapies on transplantation outcomes could not be explored. CONCLUSIONS: This relatively contemporary cohort of patients who received a kidney transplant for AA amyloidosis experienced favorable rates of survival and lower recurrence rates than previously reported. These data support the practice of treating these patients with kidney transplantation for end-stage kidney disease. PLAIN-LANGUAGE SUMMARY: AA amyloidosis is a severe and rare disease. Kidney involvement is frequent and leads to end-stage kidney disease. Because of the involvement of other organs, these patients are often frail, which has raised concerns about their suitability for kidney transplantation. We reviewed all patients with AA amyloidosis nephropathy who underwent kidney transplantation in France in the recent era (2008-2018) and found that the outcomes after kidney transplantation were favorable, with 85.5% of patients still alive 5 years after transplantation, a survival rate that is comparable to the outcomes of patients receiving a transplant for other forms of kidney diseases. Recurrence of amyloidosis in the transplanted kidney was infrequent (5.8%). These data support the practice of kidney transplantation for patients with AA amyloidosis who experience kidney failure.

Interleukin-21 promotes Type-1 activation and cytotoxicity of CD56dimCD16bright natural killer cells during kidney allograft antibody-mediated rejection showing a new link between adaptive and innate humoral allo-immunity.

The role of Natural killer (NK) cells during kidney allograft antibody-mediated rejection (ABMR) is increasingly recognized, but an in-depth characterization of mechanisms that contribute to such immune response is still under investigation. Here, we characterized phenotypic, functional, and transcriptomic profiles of peripheral blood circulating and allograft infiltrating CD56dimCD16bright NK cells during anti-HLA donor-specific antibody (DSA)+ ABMR. Cross-sectional analyses performed in 71 kidney transplant recipients identified a unique phenotypic circulating CD56dimCD16bright NK cell cluster expanded in DSA+ ABMR. This cluster co-expressed high levels of the interleukin-21 Receptor (IL-21R); Type-1 transcription factors T-bet and EOMES, CD160 and natural killer group 2D cytotoxic and activating co-stimulatory receptors. CD160+ IL-21R+ NK cells correlated with elevated plasma IL-21, Ki-67+ ICOS+ (CD278) IL-21-producing circulating T follicular helper cells, enhanced Type-1 pro-inflammatory cytokines, NK cell cytotoxicity, worse microvascular inflammation and graft loss. Single-cell transcriptomic analysis of circulating NK cells delineated an expanded cluster in DSA+ ABMR characterized by elevated pro-inflammatory/cytotoxic pathways, IL-21/STAT3 signaling, and leukocyte trans-endothelial migration pathways. Infiltration of CD160+ IL-21R+ NK cells with similar transcriptomic profile was detected in DSA+ ABMR allograft biopsies, potentially contributing to allograft injury. Thus, the IL-21/IL-21R axis, linking adaptive and innate humoral allo-immunity, or NK cells may represent appealing immunotherapy targets in DSA+ ABMR.

Clinical recommendations for posttransplant assessment of anti-HLA (Human Leukocyte Antigen) donor-specific antibodies: A Sensitization in Transplantation: Assessment of Risk consensus document.

Although anti-HLA (Human Leukocyte Antigen) donor-specific antibodies (DSAs) are commonly measured in clinical practice and their relationship with transplant outcome is well established, clinical recommendations for anti-HLA antibody assessment are sparse. Supported by a careful and critical review of the current literature performed by the Sensitization in Transplantation: Assessment of Risk 2022 working group, this consensus report provides clinical practice recommendations in kidney, heart, lung, and liver transplantation based on expert assessment of quality and strength of evidence. The recommendations address 3 major clinical problems in transplantation and include guidance regarding posttransplant DSA assessment and application to diagnostics, prognostics, and therapeutics: (1) the clinical implications of positive posttransplant DSA detection according to DSA status (ie, preformed or de novo), (2) the relevance of posttransplant DSA assessment for precision diagnosis of antibody-mediated rejection and for treatment management, and (3) the relevance of posttransplant DSA for allograft prognosis and risk stratification. This consensus report also highlights gaps in current knowledge and provides directions for clinical investigations and trials in the future that will further refine the clinical utility of posttransplant DSA assessment, leading to improved transplant management and patient care.

Distinct association between chronic Epstein-Barr virus infection and T cell compartments from pediatric heart, kidney, and liver transplant recipients.

Chronic Epstein-Barr virus (EBV) infection after pediatric organ transplantation (Tx) accounts for significant morbidity and mortality. The risk of complications, such as posttransplant lymphoproliferative disorders, in high viral load (HVL) carriers is the highest in heart Tx recipients. However, the immunologic signatures of such a risk have been insufficiently defined. Here, we assessed the phenotypic, functional, and transcriptomic profiles of peripheral blood CD8+/CD4+ T cells, including EBV-specific T cells, in 77 pediatric heart, kidney, and liver Tx recipients and established the relationship between memory differentiation and progression toward exhaustion. Unlike kidney and liver HVL carriers, heart HVL carriers displayed distinct CD8+ T cells with (1) up-regulation of interleukin-21R, (2) decreased naive phenotype and altered memory differentiation, (3) accumulation of terminally exhausted (TEX PD-1+T-bet-Eomes+) and decrease of functional precursors of exhausted (TPEX PD-1intT-bet+) effector subsets, and (4) transcriptomic signatures supporting the phenotypic changes. In addition, CD4+ T cells from heart HVL carriers displayed similar changes in naive and memory subsets, elevated Th1 follicular helper cells, and plasma interleukin-21, suggesting an alternative inflammatory mechanism that governs T cell responses in heart Tx recipients. These results may explain the different incidences of EBV complications and may help improve the risk stratification and clinical management of different types of Tx recipients.

Sensitization in transplantation: Assessment of Risk 2022 Working Group Meeting Report.

The Sensitization in Transplantation: Assessment of Risk workgroup is a collaborative effort of the American Society of Transplantation and the American Society of Histocompatibility and Immunogenetics that aims at providing recommendations for clinical testing, highlights gaps in current knowledge, and proposes areas for further research to enhance histocompatibility testing in support of solid organ transplantation. This report provides updates on topics discussed by the previous Sensitization in Transplantation: Assessment of Risk working groups and introduces 2 areas of exploration: non-human leukocyte antigen antibodies and utilization of human leukocyte antigen antibody testing measurement to evaluate the efficacy of antibody-removal therapies.

mTOR signaling cascade: novel clinical implications in HLA and non-HLA antibody-mediated vasculopathies?

Antibodies targeting endothelial antigens represent major threats to the integrity of endothelial vasculature, contributing to development of organ transplant rejection and vasculopathies. In this issue, Catar et al. present the mechanisms by which non-human leukocyte antigen angiotensin II type 1 receptor and endothelin-1 type A receptor antibodies mediate impairment of endothelial repair via ß2-arrestin link to the mammalian target of rapamycin pathway. This commentary discusses the mechanisms of human leukocyte antigen and non-human leukocyte antigen antibody-endothelium interactions, and the clinical implications and challenges of the use of mammalian target of rapamycin signaling activation as biomarker and therapeutic target in vasculopathies.

Concomitant loss of regulatory T and B cells is a distinguishing immune feature of antibody-mediated rejection in kidney transplantation.

Although considerable advances have been made in understanding the cellular effector mechanisms responsible for donor-specific antibody generation leading to antibody-mediated rejection (ABMR), the identification of cellular regulators of such immune responses is lacking. To clarify this, we used high dimensional flow cytometry to concomitantly profile and track the two major subsets of regulatory lymphocytes in blood: T regulatory (TREG) and transitional B cells in a cohort of 96 kidney transplant recipients. Additionally, we established co-culture assays to address their respective capacity to suppress antibody responses in vitro. TREG and transitional B cells were found to be potent suppressors of T follicular helper-mediated B-cell differentiation into plasmablast and antibody generation. TREG and transitional B cells were both durably expanded in patients who did not develop donor-specific antibody post-transplant. However, patients who manifested donor-specific antibody and progressed to ABMR displayed a marked and persistent numerical reduction in TREG and transitional B cells. Strikingly, specific cell clusters expressing the transcription factor T-bet were selectively depleted in both TREG and transitional B-cell compartments in patients with ABMR. Importantly, the coordinated loss of these T-bet+CXCR5+TREG and T-bet+CD21- transitional B-cell clusters was correlated with increased and inflammatory donor specific antibody responses, more extensive microvascular inflammation and a higher rate of kidney allograft loss. Thus, our study identified coordinated and persistent defects in regulatory T- and B-cell responses in patients undergoing ABMR, which may contribute to their loss of humoral immune regulation, and warrant timely therapeutic interventions to replenish and sustain TREG and transitional B cells in these patients.

DSA in solid organ transplantation: is it a matter of specificity, amount, or functional characteristics?

PURPOSE OF REVIEW: The present review describes the clinical relevance of human leukocyte antigen (HLA) donor-specific antibodies (HLA-DSAs) as biomarkers of alloimmunity and summarizes recent improvements in their characterization that provide insights into immune risk assessment, precision diagnosis, and prognostication in transplantation. RECENT FINDINGS: Recent studies have addressed the clinical utility of HLA-DSAs as biomarkers for immune risk assessment in pretransplant and peritransplant, diagnosis and treatment evaluation of antibody-mediated rejection, immune monitoring posttransplant, and risk stratification. SUMMARY: HLA-DSAs have proved to be the most advanced immune biomarkers in solid organ transplantation in terms of analytical validity, clinical validity and clinical utility. Recent studies are integrating multiple HLA-DSA characteristics including antibody specificity, HLA class, quantity, immunoglobulin G subclass, and complement-binding capacity to improve risk assessment peritransplant, diagnosis and treatment evaluation of antibody-mediated rejection, immune monitoring posttransplant, and transplant prognosis evaluation. In addition, integration of HLA-DSAs to clinical, functional and histological transplant parameters has further consolidated the utility of HLA-DSAs as robust biomarkers and allows to build new tools for monitoring, precision diagnosis, and risk stratification for individual patients. However, prospective and randomized-controlled studies addressing the clinical benefit and cost-effectiveness of HLA-DSA-based monitoring and patient management strategies are required to demonstrate that the use of HLA-DSAs as biomarkers can improve current clinical practice and transplant outcomes.

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 Duska 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.

Impact of the COVID-19 pandemic on publication dynamics and non-COVID-19 research production.

BACKGROUND: The COVID-19 pandemic has severely affected health systems and medical research worldwide but its impact on the global publication dynamics and non-COVID-19 research has not been measured. We hypothesized that the COVID-19 pandemic may have impacted the scientific production of non-COVID-19 research. METHODS: We conducted a comprehensive meta-research on studies (original articles, research letters and case reports) published between 01/01/2019 and 01/01/2021 in 10 high-impact medical and infectious disease journals (New England Journal of Medicine, Lancet, Journal of the American Medical Association, Nature Medicine, British Medical Journal, Annals of Internal Medicine, Lancet Global Health, Lancet Public Health, Lancet Infectious Disease and Clinical Infectious Disease). For each publication, we recorded publication date, publication type, number of authors, whether the publication was related to COVID-19, whether the publication was based on a case series, and the number of patients included in the study if the publication was based on a case report or a case series. We estimated the publication dynamics with a locally estimated scatterplot smoothing method. A Natural Language Processing algorithm was designed to calculate the number of authors for each publication. We simulated the number of non-COVID-19 studies that could have been published during the pandemic by extrapolating the publication dynamics of 2019 to 2020, and comparing the expected number to the observed number of studies. RESULTS: Among the 22,525 studies assessed, 6319 met the inclusion criteria, of which 1022 (16.2%) were related to COVID-19 research. A dramatic increase in the number of publications in general journals was observed from February to April 2020 from a weekly median number of publications of 4.0 (IQR: 2.8-5.5) to 19.5 (IQR: 15.8-24.8) (p < 0.001), followed afterwards by a pattern of stability with a weekly median number of publications of 10.0 (IQR: 6.0-14.0) until December 2020 (p = 0.045 in comparison with April). Two prototypical editorial strategies were found: 1) journals that maintained the volume of non-COVID-19 publications while integrating COVID-19 research and thus increased their overall scientific production, and 2) journals that decreased the volume of non-COVID-19 publications while integrating COVID-19 publications. We estimated using simulation models that the COVID pandemic was associated with a 18% decrease in the production of non-COVID-19 research. We also found a significant change of the publication type in COVID-19 research as compared with non-COVID-19 research illustrated by a decrease in the number of original articles, (47.9% in COVID-19 publications vs 71.3% in non-COVID-19 publications, p < 0.001). Last, COVID-19 publications showed a higher number of authors, especially for case reports with a median of 9.0 authors (IQR: 6.0-13.0) in COVID-19 publications, compared to a median of 4.0 authors (IQR: 3.0-6.0) in non-COVID-19 publications (p < 0.001). CONCLUSION: In this meta-research gathering publications from high-impact medical journals, we have shown that the dramatic rise in COVID-19 publications was accompanied by a substantial decrease of non-COVID-19 research. META-RESEARCH REGISTRATION: https://osf.io/9vtzp/ .

COVID-19-related medical research: a meta-research and critical appraisal.

BACKGROUND: Since the start of the COVID-19 outbreak, a large number of COVID-19-related papers have been published. However, concerns about the risk of expedited science have been raised. We aimed at reviewing and categorizing COVID-19-related medical research and to critically appraise peer-reviewed original articles. METHODS: The data sources were Pubmed, Cochrane COVID-19 register study, arXiv, medRxiv and bioRxiv, from 01/11/2019 to 01/05/2020. Peer-reviewed and preprints publications related to COVID-19 were included, written in English or Chinese. No limitations were placed on study design. Reviewers screened and categorized studies according to i) publication type, ii) country of publication, and iii) topics covered. Original articles were critically appraised using validated quality assessment tools. RESULTS: Among the 11,452 publications identified, 10,516 met the inclusion criteria, among which 7468 (71.0%) were peer-reviewed articles. Among these, 4190 publications (56.1%) did not include any data or analytics (comprising expert opinion pieces). Overall, the most represented topics were infectious disease (n = 2326, 22.1%), epidemiology (n = 1802, 17.1%), and global health (n = 1602, 15.2%). The top five publishing countries were China (25.8%), United States (22.3%), United Kingdom (8.8%), Italy (8.1%) and India (3.4%). The dynamic of publication showed that the exponential growth of COVID-19 peer-reviewed articles was mainly driven by publications without original data (mean 261.5 articles ± 51.1 per week) as compared with original articles (mean of 69.3 ± 22.3 articles per week). Original articles including patient data accounted for 713 (9.5%) of peer-reviewed studies. A total of 576 original articles (80.8%) showed intermediate to high risk of bias. Last, except for simulation studies that mainly used large-scale open data, the median number of patients enrolled was of 102 (IQR = 37-337). CONCLUSIONS: Since the beginning of the COVID-19 pandemic, the majority of research is composed by publications without original data. Peer-reviewed original articles with data showed a high risk of bias and included a limited number of patients. Together, these findings underscore the urgent need to strike a balance between the velocity and quality of research, and to cautiously consider medical information and clinical applicability in a pressing, pandemic context. SYSTEMATIC REVIEW REGISTRATION: https://osf.io/5zjyx/.

COVID-19 Infection in Kidney Transplant Recipients: Disease Incidence and Clinical Outcomes.

BACKGROUND: COVID-19 has been associated with high morbidity and mortality in kidney transplant recipients. However, risk factors for COVID-19 disease in patients with kidney transplants remain poorly defined. METHODS: We enrolled patients who underwent kidney transplantation and were actively followed up in two hospitals in Paris on March 1st, 2020. Patients were screened for baseline and transplant characteristics, functional parameters, comorbidities, and immunosuppressive therapies. COVID-19 disease was assessed. Patients were followed up during the pandemic until April 30th, 2020 by the COVID-19 SLS KT survey program, including teleconsulting, at-home monitoring for patients with COVID-19, and a dedicated phone hotline platform. RESULTS: Among 1216 patients with kidney transplants enrolled, 66 (5%) patients were identified with COVID-19 disease, which is higher than the incidence observed in the general population in France (0.3%). Their mean age was 56.4±12.5 years, and 37 (56%) patients were men. The following factors were independently associated with COVID-19 disease: non-White ethnicity (adjusted odds ratio [OR], 2.17; 95% confidence interval [95% CI], 1.23 to 3.78; P=0.007), obesity (OR, 2.19; 95% CI, 1.19 to 4.05; P=0.01), asthma and chronic pulmonary disease (OR, 3.09; 95% CI, 1.49 to 6.41; P=0.002), and diabetes (OR, 3.33; 95% CI, 1.92 to 5.77; P<0.001). The mortality rate related to COVID-19 disease was 1% in the overall study population and 24% in COVID-19-positive patients. CONCLUSIONS: Patients with kidney transplants display a high risk of mortality. Non-White ethnicity and comorbidities such as obesity, diabetes, asthma, and chronic pulmonary disease were associated with higher risk of developing COVID-19 disease. It is imperative that policy makers urgently ensure the integration of such risk factors on response operations against COVID-19.

Coordinated Circulating T Follicular Helper and Activated B Cell Responses Underlie the Onset of Antibody-Mediated Rejection in Kidney Transplantation.

BACKGROUND: Although antibody-mediated rejection (ABMR) has been long recognized as a leading cause of allograft failure after kidney transplantation, the cellular and molecular processes underlying the induction of deleterious donor-specific antibody (DSA) responses remain poorly understood. METHODS: Using high-dimensional flow cytometry, in vitro assays, and RNA sequencing, we concomitantly investigated the role of T follicular helper (TFH) cells and B cells during ABMR in 105 kidney transplant recipients. RESULTS: There were 54 patients without DSAs; of those with DSAs, ABMR emerged in 20 patients, but not in 31 patients. We identified proliferating populations of circulating TFH cells and activated B cells emerging in blood of patients undergoing ABMR. Although these circulating TFH cells comprised heterogeneous phenotypes, they were dominated by activated (ICOS+PD-1+) and early memory precursor (CCR7+CD127+) subsets, and were enriched for the transcription factors IRF4 and c-Maf. These circulating TFH cells produced large amounts of IL-21 upon stimulation with donor antigen and induced B cells to differentiate into antibody-secreting cells that produced DSAs. Combined analysis of the matched circulating TFH cell and activated B cell RNA-sequencing profiles identified highly coordinated transcriptional programs in circulating TFH cells and B cells among patients with ABMR, which markedly differed from those of patients who did not develop DSAs or ABMR. The timing of expansion of the distinctive circulating TFH cells and activated B cells paralleled emergence of DSAs in blood, and their magnitude was predictive of IgG3 DSA generation, more severe allograft injury, and higher rate of allograft loss. CONCLUSIONS: Patients undergoing ABMR may benefit from monitoring and therapeutic targeting of TFH cell-B cell interactions.

Microvasculature partial endothelial mesenchymal transition in early posttransplant biopsy with acute tubular necrosis identifies poor recovery renal allografts.

Acute tubular necrosis (ATN), a frequent histopathological feature in the early post-renal transplant biopsy, affects long-term graft function. Appropriate markers to identify patients at risk of no or incomplete recovery after delayed graft function are lacking. In this study, we first included 41 renal transplant patients whose biopsy for cause during the first month after transplantation showed ATN lesions. Using partial microvasculature endothelial (fascin, vimentin) and tubular epithelial (vimentin) to mesenchymal transition markers, detected by immunohistochemistry, we found a significant association between partial endothelial to mesenchymal transition and poor graft function recovery (Spearman's rho = -0.55, P = .0005). Transforming growth factor-ß1 was strongly expressed in these phenotypic changed endothelial cells. Extent of ATN was also correlated with short- and long-term graft dysfunction. However, the association of extensive ATN with long-term graft dysfunction (24 months posttransplant) was observed only in patients with partial endothelial to mesenchymal transition marker expression in their grafts (Spearman's rho = -0.64, P = .003), but not in those without. The association of partial endothelial to mesenchymal transition with worse renal graft outcome was confirmed on 34 other early biopsies with ATN from a second transplant center. Our results suggest that endothelial cell activation at the early phase of renal transplantation plays a detrimental role.

Markers of graft microvascular endothelial injury may identify harmful donor-specific anti-HLA antibodies and predict kidney allograft loss.

Graft microvasculature is a major target of donor-specific antibodies (DSA) and endothelial damage is direct evidence of antibody-mediated rejection (ABMR). Using immunohistochemistry, we analyzed the expression of three microvascular endothelial activation markers (fascin, vimentin, and hsp47), suggestive of endothelial-to-mesenchymal transition (EndMT) in 351 graft biopsies from 248 kidney recipients, with concomitant screening of circulating antihuman leukocyte antigen (HLA) DSA at the time of the biopsy. The factors associated with EndMT marker expression were DSA and the presence of microvascular inflammation (MI). EndMT expressing grafts had significantly more allograft loss compared to EndMT negative grafts (P < .0001). The expression of EndMT markers positively correlated with anti-HLA DSA class II mean fluorescence intensity (MFI) levels and especially identified DQ and DR antibodies as being more closely associated with microvascular injury. Moreover, only DSA linked to positive EndMT score affected allograft survival, regardless of DSA MFI levels or presence of C4d deposition. Thus, EndMT markers could represent a clinically relevant tool for early identification of ongoing endothelial injury, harmful DSA, and patients at high risk for allograft failure.

Response to treatment and long-term outcomes in kidney transplant recipients with acute T cell-mediated rejection.

The recent recognition of complex and chronic phenotypes of T cell-mediated rejection (TCMR) has fostered the need to better evaluate the response of acute TCMR-a condition previously considered to lack relevant consequences for allograft survival-to the standard of care. In a prospective cohort of kidney recipients (n = 256) with biopsy-proven acute TCMR receiving corticosteroids, we investigated clinical, histological, and immunological phenotypes at the time of acute TCMR diagnosis and 3 months posttreatment. Independent posttreatment determinants of allograft loss included the glomerular filtration rate (GFR) (HR = 0.94; 95% CI = 0.92-0.96; P < .001), proteinuria (HR = 1.40; 95% CI = 1.10-1.79; P = .007), time since transplantation (HR = 1.02; 95% CI = 1.00-1.03; P = .016), peritubular capillaritis (HR = 2.27; 95% CI = 1.13-4.55; P = .022), interstitial inflammation in sclerotic cortical parenchyma (i-IF/TA) (HR = 1.87; 95% CI = 1.08-3.25; P = .025), and donor-specific anti-HLA antibodies (DSAs) (HR = 2.67; 95% CI = 1.46-4.88; P = .001). Prognostic value was improved using a composite evaluation of response to treatment versus clinical parameters only (cNRI = 0.68; 95% CI = 0.41-0.95; P < .001). A classification tree for allograft loss identified five patterns of response to treatment based on the posttreatment GFR, i-IF/TA, and anti-HLA DSAs (cross-validated accuracy = 0.80). Compared with responders (n = 155, 60.5%), nonresponders (n = 101, 39.5%) had a higher incidence of de novo DSAs, antibody-mediated rejection, and allograft loss at 10 years (P < .001 for all comparisons). Thus, clinical, histological, and immunological assessment of response to treatment of acute TCMR revealed different profiles of the response to treatment with distinct outcomes.

T cell-mediated rejection is a major determinant of inflammation in scarred areas in kidney allografts.

Inflammation in fibrosis areas (i-IF/TA) of kidney allografts is associated with allograft loss; however, its diagnostic significance remains to be determined. We investigated the clinicohistologic phenotype and determinants of i-IF/TA in a prospective cohort of 1539 kidney recipients undergoing evaluation of i-IF/TA and tubulitis in atrophic tubules (t-IF/TA) on protocol allograft biopsies performed at 1 year posttransplantation. We considered donor, recipient, and transplant characteristics, immunosuppression, and histological diagnoses in 2260 indication biopsies performed within the first year posttransplantation. Nine hundred forty-six (61.5%) patients presented interstitial fibrosis/tubular atrophy (IF/TA Banff grade > 0) at 1 year posttransplant, among whom 394 (41.6%) showed i-IF/TA. i-IF/TA correlated with concurrent t-IF/TA (P < .001), interstitial inflammation (P < .001), tubulitis (P < .001), total inflammation (P < .001), peritubular capillaritis (P < .001), interstitial fibrosis (P < .001), and tubular atrophy (P = .02). The independent determinants of i-IF/TA were previous T cell-mediated rejection (TCMR) (P < .001), BK virus nephropathy (P = .007), steroid therapy (P = .039), calcineurin inhibitor therapy (P = .011), inosine-5'-monophosphate dehydrogenase inhibitor therapy (P = .011), HLA-B mismatches (P = .012), and HLA-DR mismatches (P = .044). TCMR patients with i-IF/TA on posttreatment biopsy (N = 83/136, 61.0%) exhibited accelerated progression of IF/TA over time (P = .01) and decreased 8-year allograft survival (70.8% vs 83.5%, P = .038) compared to those without posttreatment i-IF/TA. Our results support that i-IF/TA may represent a manifestation of chronic active TCMR.