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Background The standard-of-care protocol, based on plasma exchanges, high-dose intravenous immunoglobulin and optimization of maintenance immunosuppression, can slow down the evolution of antibody-mediated rejection (AMR), but with high interindividual variability. Identification of a reliable predictive tool of the response to AMR treatment is a mandatory step for personalization of the follow-up strategy and to guide second-line therapies. Methods Interrogation of the electronic databases of 2 French university hospitals (Lyon and Strasbourg) retrospectively identified 81 renal transplant recipients diagnosed with AMR without chronic lesions (cg score ≤1) at diagnosis and for whom a follow-up biopsy had been performed 3–6 months after initiation of therapy. Results The evolution of humoral lesions on follow-up biopsy (disappearance versus persistence versus progression) correlated with the risk for allograft loss (logrank test, P = .001). Patients with disappearance of humoral lesions had ∼80% graft survival at 10 years. The hazard ratio for graft loss in multivariate analysis was 3.91 (P = .04) and 5.15 (P = .02) for patients with persistence and progression of lesions, respectively. The non-invasive parameters classically used to follow the intensity of humoral alloimmune response (evolution of immunodominant DSA mean fluorescence intensity) and the decline of renal graft function (estimated glomerular filtration rate decrease and persistent proteinuria) showed little clinical value to predict the histological response to AMR therapy. Conclusion We conclude that invasive monitoring of the evolution of humoral lesions by the mean of follow-up biopsy performed 3–6 months after the initiation of therapy is an interesting tool to predict long-term outcome after AMR treatment.

Detection of mismatched human leukocyte antigens by adaptive immune cells is considered as the main cause of transplant rejection, leading to either T-cell mediated rejection or antibody-mediated rejection. This canonical view guided the successful development of immunosuppressive therapies and shaped the diagnostic Banff classification for kidney transplant rejection that is used in clinics worldwide. However, several observations have recently emerged that question this dichotomization between T-cell mediated rejection and antibody-mediated rejection, related to heterogeneity in the serology, histology, and prognosis of the rejection phenotypes. In parallel, novel insights were obtained concerning the dynamics of donor-specific anti-human leukocyte antigen antibodies, the immunogenicity of donor-recipient non-human leukocyte antigen mismatches, and the autoreactivity against self-antigens. Moreover, the potential of innate allorecognition was uncovered, as exemplified by natural killer cell-mediated microvascular inflammation through missing self, and by the emerging evidence on monocyte-driven allorecognition. In this review, we highlight the gaps in the current classification of rejection, provide an overview of the expanding insights into the mechanisms of allorecognition, and critically appraise how these could improve our understanding and clinical approach to kidney transplant rejection. We argue that consideration of the complex interplay of various allorecognition mechanisms can foster a more integrated view of kidney transplant rejection and can lead to improved risk stratification, targeted therapies, and better outcome after kidney transplantation. ispartof: KIDNEY INTERNATIONAL vol:101 issue:4 pages:692-710 ispartof: location:United States status: published

The generation of antibodies against donor-specific major histocompatibility complex (MHC) antigens, a type of donor-specific antibodies (DSAs), after transplantation requires that recipient’s allospecific B cells receive help from T cells. The current dogma holds that this help is exclusively provided by the recipient’s CD4+T cells that recognize complexes of recipient’s MHC II molecules and peptides derived from donor-specific MHC alloantigens, a process called indirect allorecognition. Here, we demonstrated that, after allogeneic heart transplantation, CD3ε knockout recipient mice lacking T cells generate a rapid, transient wave of switched alloantibodies, predominantly directed against MHC I molecules. This is due to the presence of donor CD4+T cells within the graft that recognize intact recipient’s MHC II molecules expressed by B cell receptor–activated allospecific B cells. Indirect evidence suggests that this inverted direct pathway is also operant in patients after transplantation. Resident memory donor CD4+T cells were observed in perfusion liquids of human renal and lung grafts and acquired B cell helper functions upon in vitro stimulation. Furthermore, T follicular helper cells, specialized in helping B cells, were abundant in mucosa-associated lymphoid tissue of lung and intestinal grafts. In the latter, more graft-derived passenger T cells correlated with the detection of donor T cells in recipient’s circulation; this, in turn, was associated with an early transient anti–MHC I DSA response and worse transplantation outcomes. We conclude that this inverted direct allorecognition is a possible explanation for the early transient anti-MHC DSA responses frequently observed after lung or intestinal transplantations.

Transplant recipients, who receive therapeutic immunosuppression to prevent graft rejection, are characterized by high coronavirus disease 2019 (COVID-19)–related mortality and defective response to vaccines. We observed that previous infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but not the standard two-dose regimen of vaccination, provided protection against symptomatic COVID-19 in kidney transplant recipients. We therefore compared the cellular and humoral immune responses of these two groups of patients. Neutralizing anti–receptor-binding domain (RBD) immunoglobulin G (IgG) antibodies were identified as the primary correlate of protection for transplant recipients. Analysis of virus-specific B and T cell responses suggested that the generation of neutralizing anti-RBD IgG may have depended on cognate T-B cell interactions that took place in germinal center, potentially acting as a limiting checkpoint. High-dose mycophenolate mofetil, an immunosuppressive drug, was associated with fewer antigen-specific B and T follicular helper (TFH) cells after vaccination; this was not observed in patients recently infected with SARS-CoV-2. Last, we observed that, in two independent prospective cohorts, administration of a third dose of SARS-CoV-2 mRNA vaccine restored neutralizing titers of anti-RBD IgG in about 40% of individuals who had not previously responded to two doses of vaccine. Together, these findings suggest that a third dose of SARS-CoV-2 mRNA vaccine improves the RBD-specific responses of transplant patients treated with immunosuppressive drugs.

International audience

International audience; End stage kidney disease increase the risk of COVID-19 related death but how the kidney replacement strategy should be adapted during the pandemic is unknown. Chronic hemodialysis makes social distancing difficult to achieve. Alternatively, kidney transplantation could increase the severity of COVID-19 due to therapeutic immunosuppression and contribute to saturation of intensive care units. For these reasons, kidney transplantation was suspended in France during the first epidemic wave. Here, we retrospectively evaluated this strategy by comparing the overall and COVID-19 related mortality in kidney transplant recipients and candidates over the last three years. Cross-interrogation of two national registries for the period 1 March and 1 June 2020, identified 275 deaths among the 42812 kidney transplant recipients and 144 deaths among the 16210 candidates. This represents an excess of deaths for both populations, as compared with the same period the two previous years (mean of two previous years: 253 in recipients and 112 in candidates). This difference was integrally explained by COVID-19, which accounted for 44% (122) and 42% (60) of the deaths in recipients and candidates, respectively. Taking into account the size of the two populations and the geographical heterogeneity of virus circulation, we found that the excess of risk of death due to COVID-19 was similar for recipients and candidates in high viral risk area but four-fold higher for candidates in the low viral risk area. Thus, in case of a second epidemic wave, kidney transplantation should be suspended in high viral risk areas but maintained outside those areas, both to reduce the excess of deaths of candidates and avoid wasting precious resources.

BACKGROUND: Circulating anti-HLA donor-specific antibodies (HLA-DSA) are often absent in kidney transplant recipients with microvascular inflammation (MVI). Missing self, the inability of donor endothelial cells to provide HLA I-mediated signals to inhibitory killer cell Ig-like receptors (KIRs) on recipient natural killer cells, can cause endothelial damage in vitro, and has been associated with HLA-DSA-negative MVI. However, missing self's clinical importance as a nonhumoral trigger of allograft rejection remains unclear. METHODS: In a population-based study of 924 consecutive kidney transplantations between March 2004 and February 2013, we performed high-resolution donor and recipient HLA typing and recipient KIR genotyping. Missing self was defined as the absence of A3/A11, Bw4, C1, or C2 donor genotype, with the presence of the corresponding educated recipient inhibitory KIR gene. RESULTS: We identified missing self in 399 of 924 transplantations. Co-occurrence of missing self types had an additive effect in increasing MVI risk, with a threshold at two concurrent types (hazard ratio [HR], 1.78; 95% confidence interval [95% CI], 1.26 to 2.53), independent of HLA-DSA (HR, 5.65; 95% CI, 4.01 to 7.96). Missing self and lesions of cellular rejection were not associated. No HLA-DSAs were detectable in 146 of 222 recipients with MVI; 28 of the 146 had at least two missing self types. Missing self associated with transplant glomerulopathy after MVI (HR, 2.51; 95% CI, 1.12 to 5.62), although allograft survival was better than with HLA-DSA-associated MVI. CONCLUSION: Missing self specifically and cumulatively increases MVI risk after kidney transplantation, independent of HLA-DSA. Systematic evaluation of missing self improves understanding of HLA-DSA-negative MVI and might be relevant for improved diagnostic classification and patient risk stratification. ispartof: pages:8-8 ispartof: JOURNAL OF THE AMERICAN SOCIETY OF NEPHROLOGY vol:32 issue:8 pages:2070-2082 ispartof: location:United States status: published

Introduction L’Orf est une zoonose due a un Parapoxvirus, involuant generalement de maniere spontanee en quelques semaines chez les patients immunocompetents. Chez les patients immunodeprimes, l’Orf peut etre persistant et difficile a traiter. Nous rapportons, a notre connaissance, le premier cas d’Orf traite par injections intralesionnelles de cidofovir apres echec des autres therapeutiques. Materiel et methodes Un homme de 40 ans a consulte en aout 2020 pour une lesion du 5e doigt de la main gauche, apparue 10 jours apres la fete de l’Aid, et 1 jour apres sa transplantation renale pour nephropathie indeterminee. Son traitement immunosuppresseur (TIS) comportait prednisolone10 mg/j, mycophenolate mofetil 2000 mg/j et tacrolius 12 mg/j. Le diagnostic d’Orf a ete confirme histologiquement. Deux seances de cryotherapie puis un traitement par imiquimod topique se sont averes inefficaces. Une exerese chirurgicale avec reconstruction de la perte de substance par greffe de peau totale a alors ete realisee avec reprise du traitement par imiquimod en preventif des l’ablation des fils. Une recidive de l’Orf 3 semaines apres l’operation a ete constatee, avec a nouveau une lesion a croissance tres rapide. Nous avons alors decide de realiser des injections intra-lesionnelles de cidofovir (disponible en ATU), a la dose de 3,75 mg, toutes les 2 semaines, sous anesthesie locale. Une guerison complete a ete obtenue en 4 injections. Il a ete observe par la suite 2 nouvelles lesions, auto-inoculees, sur l’hemilevre blanche superieure droite puis sur l’index droit, respectivement 3 et 8 semaines apres le debut du traitement, egalement efficacement traitees par injections intra-lesionnelles de cidofovir. La tolerance clinique et biologique etait bonne. En parallele, une modification de son TIS (remplacement du mycophenolate par un inhibiteur de mTOR) a ete effectuee. Aucune recidive n’a ete notee a 3 mois. Discussion Plusieurs cas d’Orf avec evolution rapide et echec des traitements classiques chez des patients greffes d’organe ont ete decrits. Les traitements rapportes dans ces cas sont la cryotherapie, l’imiquimod topique et la chirurgie, associes a une baisse du TIS. Le cidofovir a egalement ete rapporte efficace dans l’Orf par voie topique (mais la penetration transcutanee aurait ete limitee sur la volumineuse lesion de notre patient), et par voie systemique (mais avec un risque d’effets secondaires, notamment de toxicite renale). Nous avons donc choisi d’effectuer des injections intra-lesionnelles, en se referant au protocole utilise dans les papillomatoses laryngees. Le cidofovir intra-lesionnel, associe a une revision du TIS, peut etre une alternative therapeutique efficace en cas d’Orf d’evolution rapide, resistant aux traitements classiques, chez un patient greffe d’organe.

The current transplant immunology dogma defends that allograft rejection is initiated by recipient's adaptive immune system. In this prevalent model, innate immune cells in general, and NK cells in particular, are merely considered as downstream effectors which participate in the destruction of the graft only upon recruitment by adaptive effectors: alloreactive T cells or donor-specific antibodies (DSA). Challenging this vision, recent data demonstrated that recipients' NK cells are capable of a form of allorecognition because they can sense the absence of self HLA class I molecules on the surface of graft endothelial cells. Missing-self triggers mTORC1-dependent activation of NK cells, which in turn promote the development of graft microvascular inflammation and detrimentally impact graft survival. The fact that some patients develop chronic vascular rejection in absence of DSA or genetically-predicted missing self suggest that other molecular mechanisms could underly NK cell allorecognition. This review provides an overview of these proven and putative molecular mechanisms and discusses future research directions in this emerging field in organ transplant immunology. This article is protected by copyright. All rights reserved.

The analysis of immune cell signaling is critical for the understanding of the biology and pathology of the immune system, and thus a mandatory step for the development of efficient biomarkers and targeted therapies. Phosflow, which has progressively replaced the traditional western blot approach, relies on flow cytometry to analyze various signaling pathways at a single-cell level. This technique however suffers a lack of sensitivity largely due to the low signal/noise ratio that characterizes cell signaling analysis. In this study, we describe a new technique, which combines the use of biofunctionalized nanospheres (i.e., synthetic particulate antigens, SPAg) to stimulate the immune cells in suspension and imaging flow cytometry to identify homogenously-stimulated cells and quantify the activity of the chosen signaling pathway in selected subcellular regions of interest. Using BCR signaling as model, we demonstrate that SIBERIAN (SPAg-assIsted suB-cEllulaR sIgnaling ANalysis) allows assessing immune cell signaling with unprecedented sensitivity and specificity.

Introduction Le rejet cellulaire (TCMR) est caracterise par des lesions histologiques des compartiments tubulaires et interstitiels du greffon renal. Alors qu’elles expriment les molecules du CMH du donneur et qu’elles interagissent etroitement avec les lymphocytes T CD8+ cytotoxiques (LTc) alloreactifs, les cellules endotheliales (CE) du greffon semblent relativement epargnees au cours du TCMR. Description claire et complete de l’experience Les mecanismes qui sous-tendent cette observation ne sont pas connus. Methodes Une analyse transcriptomique « single cell » et la quantification de la transition endotheliale-mesenchymateuse (associee aux dommages endotheliaux) sur des biopsie de greffons nous ont permis de confirmer que les CE sont moins impactees que les cellules tubulaires epitheliales (CTE) au cours du TCMR. Pourtant nos experiences de cocultures ont montre que les CE mouraient avec la meme cinetique que les CTE lorsqu’elles etaient mises en contact avec des LTc alloreactifs, ecartant la possibilite d’un “privilege immunitaire” intrinseque. Resultats L’utilisation de techniques de microscopie intravitale dans un modele murin de transplantation renale a revele que la duree des interactions entre les LTc alloreactifs et les CE etait plus courte qu’avec les CTE du greffon, une observation validee dans des biopsies humaines. Cette difference dans la qualite des interactions semble due au fait que les LTc exposes a un gradient de chimiokine (comme c’est le cas lors de leur migration de la circulation vers les CTE du greffon) semblent repondre en priorite a ce signal au detriment de la mise en place d’une synapse cytotoxique. Une hypothese originale, que nous avons validee dans un modele in vitro. Conclusion Les CE sont relativement epargnees au cours du TCMR du fait des gradients chimiotactiques, qui detournent l’action cytotoxique les LTc alloreactifs au detriment des cellules epitheliales tubulaires. Ce privilege immunologique « extrinseque », a des implications majeures dans la reponse immunitaire physiologique, qui doit preserver la vascularisation des tissus.

BACKGROUND: Binding of donor-specific antibodies (DSAs) to kidney allograft endothelial cells that does not activate the classic complement cascade can trigger the recruitment of innate immune effectors, including NK cells. Activated NK cells contribute to microvascular inflammation leading to chronic antibody-mediated rejection (AMR). Recipient NK cells can also trigger antibody-independent microvascular inflammation by sensing the absence of self HLA class I molecules ("missing self") on allograft endothelial cells. This translational study investigated whether the condition of missing self amplifies DSA-dependent NK cell activation to worsen chronic AMR. METHODS AND RESULTS: Among 1682 kidney transplant recipients who underwent an allograft biopsy at Lyon University Hospital between 2004 and 2017, 135 fulfilled the diagnostic criteria for AMR and were enrolled in the study. Patients with complement-fixing DSAs identified by a positive C3d binding assay (n=73, 54%) had a higher risk of transplant failure (P=0.002). Among the remaining patients with complement-independent chronic AMR (n=62, 46%), those in whom missing self was identified through donor and recipient genotyping exhibited worse allograft survival (P=0.02). In multivariable analysis, only proteinuria (HR: 7.24; P=0.01) and the presence of missing self (HR: 3.57; P=0.04) were independent predictors for transplant failure following diagnosis of chronic AMR. Cocultures of human NK cells and endothelial cells confirmed that addition of missing self to DSA-induced NK cell activation increased endothelial damage. CONCLUSIONS: The assessment of missing self at the time of diagnosis of chronic AMR identifies patients at higher risk for kidney transplant failure. ispartof: JOURNAL OF THE AMERICAN SOCIETY OF NEPHROLOGY vol:32 issue:2 pages:479-494 ispartof: location:United States status: published

Background Circulating donor-specific anti-HLA antibodies (HLA-DSAs) are often absent in serum of kidney allograft recipients whose biopsy specimens demonstrate histology of antibody-mediated rejection (ABMR). It is unclear whether cases involving ABMR histology without detectable HLA-DSAs represent a distinct clinical and molecular phenotype. Methods In this multicenter cohort study, we integrated allograft microarray analysis with extensive clinical and histologic phenotyping from 224 kidney transplant recipients between 2011 and 2017. We used the term ABMR histology for biopsy specimens that fulfill the first two Banff 2017 criteria for ABMR, irrespective of HLA-DSA status. Results Of 224 biopsy specimens, 56 had ABMR histology; 26 of these (46.4%) lacked detectable serum HLA-DSAs. Biopsy specimens with ABMR histology showed overexpression of transcripts mostly related to IFNγ-induced pathways and activation of natural killer cells and endothelial cells. HLA-DSA-positive and HLA-DSA-negative biopsy specimens with ABMR histology displayed similar upregulation of pathways and enrichment of infiltrating leukocytes. Transcriptional heterogeneity observed in biopsy specimens with ABMR histology was not associated with HLA-DSA status but was caused by concomitant T cell-mediated rejection. Compared with cases lacking ABMR histology, those with ABMR histology and HLA-DSA had higher allograft failure risk (hazard ratio [HR], 7.24; 95% confidence interval [95% CI], 3.04 to 17.20) than cases without HLA-DSA (HR, 2.33; 95% CI, 0.85 to 6.33), despite the absence of transcriptional differences. Conclusions ABMR histology corresponds to a robust intragraft transcriptional signature, irrespective of HLA-DSA status. Outcome after ABMR histology is not solely determined by the histomolecular presentation but is predicted by the underlying etiologic factor. It is important to consider this heterogeneity in further research and in treatment decisions for patients with ABMR histology.

Introduction La survenue d’un rejet humoral, c’est-a-dire medie par l’apparition d’anticorps specifiques du donneur (DSA), represente desormais la premiere cause de perte de transplant renal. Les protocoles de traitement actuels, associant la plasmapherese et l’administration d’immunoglobulines polyvalentes a une majoration de l’immunosuppression de base permettent uniquement de ralentir la progression inexorable vers l’insuffisance renale terminale, avec une efficacite tres variable selon les individus. Evaluer correctement la reponse au traitement est un element pronostique indispensable de la strategie de surveillance du patient atteint de rejet humoral, et permet de guider l’utilisation des traitements de seconde ligne. Description Quatre-vingt-un patients traites pour un rejet humoral aigu entre 2004 et 2017, avec une biopsie de controle post-traitement disponible, ont ete inclus dans une etude retrospective bicentrique (centre hospitaliers universitaires de Lyon et Strasbourg). Methodes L’evolution apres traitement des parametres de suivi cliniques, histologiques et immunologiques a ete analysee. Resultats L’evolution des lesions de rejet humoral sur la biopsie (disparition, persistance ou progression) correlait avec le risque de perte du transplant renal (Logrank test, p = 0,001). Les patients dont les lesions ont disparu avaient une survie du transplant d’environ 80 % a 10 ans. Les patients qui avaient une persistance ou une progression des lesions histologiques sur la biopsie de controle apres traitement avaient un risque plus eleve de perte du transplant (HR : 3,91, p = 0,04 ; HR : 5,15, p = 0,02 respectivement). Aucun des parametres non invasifs habituellement utilises apres traitement pour surveiller l’intensite de la reponse humorale (evolution de la MFI du DSA immunodominant) ou le declin de la fonction renale (perte de DFG, persistance d’une proteinurie) n’a permis de predire l’evolution des lesions histologiques ( Fig. 1 ). Conclusion La surveillance invasive de l’evolution des lesions humorales par une biopsie de controle quelques mois apres traitement du rejet humoral aigu est un outil fiable pour predire la survie du greffon a long terme.

Current doctrine is that microvascular inflammation (MVI) triggered by a transplant -recipient antibody response against alloantigens (antibody-mediated rejection) is the main cause of graft failure. Here, we show that histological lesions are not mediated by antibodies in approximately half the participants in a cohort of 129 renal recipients with MVI on graft biopsy. Genetic analysis of these patients shows a higher prevalence of mismatches between donor HLA I and recipient inhibitory killer cell immunoglobulin-like receptors (KIRs). Human in vitro models and transplantation of β2-microglobulin-deficient hearts into wild-type mice demonstrates that the inability of graft endothelial cells to provide HLA I-mediated inhibitory signals to recipient circulating NK cells triggers their activation, which in turn promotes endothelial damage. Missing self-induced NK cell activation is mTORC1-dependent and the mTOR inhibitor rapamycin can prevent the development of this type of chronic vascular rejection., ‘Missing self’ is a mode of natural killer (NK) cell activation aimed to detect the lack of HLA-I molecules on infected or neoplastic cells. Here, the authors show that mismatch between donor HLA-I and cognate receptors on recipient NK cells mediates microvascular inflammation-associated graft rejection, a pathology that is preventable by mTOR inhibition.

Despite partial elucidation of the pathophysiology of antibody-mediated rejection (ABMR) after kidney transplantation, it remains largely unclear which of the involved immune cell types determine disease activity and outcome. We used microarray transcriptomic data from a case-control study (n=95) to identify genes that are differentially expressed in ABMR. Given the co-occurrence of ABMR and T-cell-mediated rejection (TCMR), we built a bioinformatics pipeline to distinguish ABMR-specific mRNA markers. Differential expression of 503 unique genes was identified in ABMR, with significant enrichment of natural killer (NK) cell pathways. CIBERSORT (Cell type Identification By Estimating Relative Subsets Of known RNA Transcripts) deconvolution analysis was performed to elucidate the corresponding cell subtypes and showed increased NK cell infiltration in ABMR in comparison to TCMR and normal biopsies. Other leukocyte types (including monocytes/macrophages, CD4 and CD8 T cells, and dendritic cells) were increased in rejection, but could not discriminate ABMR from TCMR. Deconvolution-based estimation of NK cell infiltration was validated using computerized morphometry, and specifically associated with glomerulitis and peritubular capillaritis. In an external data set of kidney transplant biopsies, activated NK cell infiltration best predicted graft failure amongst all immune cell subtypes and even outperformed a histologic diagnosis of acute rejection. These data suggest that NK cells play a central role in the pathophysiology of ABMR and graft failure after kidney transplantation. ispartof: Kidney International vol:95 issue:1 pages:188-198 ispartof: location:United States status: published

Introduction Le rejet medie par les anticorps (AMR) est une cause majeure de perte d’organe en transplantation. Pourtant, certains patients conservent une bonne fonction du greffon au long cours, malgre la presence d’anticorps specifiques du donneur (DSA) dans leur circulation. L’identification des parametres associes a la pathogenicite des DSA est donc aussi importante que la detection de leur presence. Des etudes experimentales recentes ont montre que la teneur en sucre, en particulier l’etat de sialylation du fragment Fc des IgG, est variable. Cela pourrait modifier la capacite des IgG a se lier au recepteur C1q et au recepteur Fc, modulant ainsi les fonctions effectrices des IgG. Dans cette etude, le statut de sialylation des DSA a ete analyse et sa relation avec la physiopathologie de l’AMR evaluee. Methodes Parmi les 938 greffes renaux ayant beneficie d’une biopsie du greffon entre 2004 et 2012 au CHU de Lyon, 69 remplissaient les criteres diagnostiques d’AMR. Les serums collectes au moment de la biopsie ont ete testes pour la presence de DSA par luminex. Le niveau de sialylation des DSA presents dans chaque serum a ete determine par chromatographie avec l’agglutinine de Sambucus nigra. Resultats obtenus ou attendus Tous les patients avaient des niveaux de sialylation des IgG seriques remarquablement similaires (∼ 2 %). Cependant, le statut de sialylation des DSA etait tres variable (mediane = 9 % ; range = 0–100 %), permettant de repartir les patients en deux groupes : DSA fortement sialyles : n = 44 (64 %) et faiblement sialyles : n = 25 (36 %). Les deux groupes ne differaient ni par l’intensite des lesions de rejet (C4d, ptc et g ; p > 0,05), ni par les taux de survie du greffon (Log rank test ; p = 0,99). Ces resultats cliniques ont ete confirmes in vitro dans les tests de cytotoxicite dependante du complement et de l’ADCC ( Fig. 1 ). Conclusion Le statut de sialylation des DSA est tres variable mais ne correle pas avec leur pathogenicite.

International audience; Antibody-mediated rejection is associated with heterogeneous kidney allograft outcomes. Accurate evaluation of risk for graft loss at time of diagnosis is necessary to offer personalized treatment. In contrast with serological and molecular assessment, morpho-histological evaluation of antibody-mediated rejection lesions has not significantly evolved. This relies on Banff classifications designed to be of diagnostic discriminatory power rather than prognostic and face quantitative and qualitative limitations. Here we developed a method of Computer-assisted Analysis of Graft Inflammation (CAGI) to improve the classification of allograft inflammation. Digitization of immunostained biopsy sections, image processing and algorithm-driven analysis allowed quantification of macrophages, T cells, B cells, and granulocytes per unit surface of interstitium, capillaries or glomeruli. CAGI was performed on biopsy specimens of 52 patients with extensively phenotyped antibody-mediated rejection. Macrophage numbers in capillaries and interstitium, but not Banff scores or the amount of other immune cell subsets, correlated with donor-specific antibody (DSA) mean fluorescence intensity and DSA-C3d status. The quantity of macrophages in the interstitium and DSA-C3d status were the only independent predictors for significant allograft loss at the time of antibody-mediated rejection diagnosis (hazard ratio 3.71 and 2.34, respectively). A significant strategy integrating the DSA-C3d assay and the quantification of interstitial macrophages allowed identification of three groups with distinct renal prognosis: DSA-C3d-, DSA-C3d+/macrophages-low and DSAC3d+/macrophages-high. Thus, CAGI brings a missing piece to the antibody-mediated rejection puzzle by identifying morpho-histological processes that bridge in~vitro parameters of DSA pathogenicity and graft loss. Hence, this approach could be useful in future integrated strategies of risk evaluation.

The progressive organisation of immune effectors into functional ectopic lymphoid structures, named tertiary lymphoid organs (TLO), has been observed in many conditions in which target antigens fail to be eliminated by the immune system. Not surprisingly, TLO have been recurrently identified in chronically rejected allografts. Although significant progress has been made over the last decades in understanding the molecular mechanisms involved in TLO development (a process named lymphoid neogenesis), the role of intragraft TLO (if any) in chronic rejection remains elusive. The prevailing dogma is that TLO contribute to graft rejection by generating and propagating local humoral and cellular alloimmune responses. However, TLO have been recently observed in long-term accepting allografts, suggesting that they might also be able to regulate alloimmune responses. In this review, we discuss our current understanding of how TLO are induced and propose a unified model in which TLO can play deleterious or regulatory roles and therefore actively modulate the kinetics of chronic rejection.

Introduction Si le rejet humoral (RH) est largement reconnu comme la 1re cause de perte des greffons son pronostic individuel est heterogene, rendant difficile l’evaluation du risque de perte de greffon au moment du diagnostic. Au cours du RH, la fixation des anticorps anti-donneur (DSA) a la surface des vaisseaux du greffon permet le recrutement de cellules de l’immunite innee (en particulier les cellules NK (NK)). Ces dernieres sont capables de leser les cellules endotheliales du greffon par un mecanisme de cytotoxicite dependante des anticorps (ADCC). Les NK interagissent avec le fragment Fc des DSA par un unique recepteur : le FcγR3A (CD16A). Un SNP (Fcγ RIIIa * 559A > C, rs396991) modulant l’affinite du FcγR3A pour le Fc des IgG a ete identifie mais son impact au cours du RH est inconnu. Methodes Parmi les transplantes renaux de notre centre ayant eu une biopsie de leur greffon entre 2004 et 2015, 118 presentaient un RH selon la definition de Banff : presence de i) lesions d’inflammation microvasculaire sur la biopsie, et ii) DSA dans la circulation. Resultats obtenus ou attendus 15,9 % des patients etaient homozygotes pour l’allele associe a une haute affinite du FcγR3A pour les IgG. Ces derniers presentaient une survie reduite du greffon par rapport aux patients ayant un FcγR3A de faible affinite (p = 0,03). Un modele in vitro humain d’ADCC entre des NK et des cellules endotheliales primaires recouvertes d’anticorps anti-HLA a confirme que les NK de donneurs ayant un FcγR3A de haute affinite s’activaient plus fortement et provoquaient davantage de dommages endotheliaux a un niveau equivalent de DSA. Conclusion Notre travail demontre que le polymorphisme du FcγR3A influe sur la severite du RH et suggere que ce parametre pourrait etre utilise comme un biomarqueur genetique de stratification du risque de perte de greffon au moment du diagnostic de RH.

Introduction La transplantation d’organe est le meilleur traitement en cas de defaillance terminale d’un organe vital. Cependant, la survie au long cours des greffon reste limitee par la perte inexorable de fonction, que le dogme immunologique actuel met sur le compte de l’inflammation microvasculaire causee par la reponse humorale allo-immune. Methodes L’analyse de 129 transplantes renaux presentant une inflammation microvasculaire sur la biopsie de greffon a demontre l’absence d’allo et d’auto-anticorps dans la moitie des cas. Chez ces patients, des etudes genetiques ont revele une prevalence plus elevee de « mismatches » entre les molecules HLA de classe I (HLA-I) du donneur et les « Killer-cell immunoglobulin-receptors » (KIR) inhibiteurs des cellules NK du receveur. Resultats obtenus ou attendus Nous avons emis l’hypothese que la nature allogenique de l’endothelium du greffon pouvait parfois creer un « pseudo-missing-self », responsable d’un rejet medie par les cellules NK. Pour demontrer cette hypothese, des co-cultures de cellules endotheliales et de NK humains ont ete realisees. Dans ce modele, l’absence du ligand HLA-I du soi sur la cellule endotheliale conduit a l’activation des NK qui deviennent capables de leser ces cellules endotheliales. Enfin, l’existence des rejets NK induit par le « missing-self » a ete demontree in vivo dans un modele murin de transplantation cardiaque. Conclusion Notre travail identifie un nouveau type de rejet chronique, exclusivement medie par l’immunite innee (les cellules NK), ayant le meme impact deletere sur la survie des greffons que le rejet humoral chronique.

The negative effect of donor-specific antibodies on the success of solid transplant is now clearly established. However, the lack of effective treatment to prevent the development of antibody-mediated lesions deepens the need for clinicians to focus on primary prevention of de novo humoral allosensitization. Among the factors associated with the risk of developing de novo donor-specific antibodies, therapeutic immunosuppression is the most obvious parameter in which improvement is possible. Beyond compliance and the overall depth of immunosuppression, it is likely that the nature of the drugs is also crucial. Here, we provide an overview of the molecular effect of the various immunosuppressive drugs on B cell biology. Clinical data related to the effect of these drugs on de novo humoral allosensitization are also examined, providing a platform from which clinicians can optimize immunosuppression for prevention of de novo donor-specific antibody generation at the individual level.

Overlooked for decades, the humoral alloimmune response is increasingly recognized as a leading cause of graft loss after transplantation. However, improvement in the diagnosis of antibody-mediated rejection has not yet translated into better outcomes for transplanted patients. After an update on B cell physiology and antibody generation, the 2015 Beaune Seminar in Transplant Research challenged the conventional view of antibody-mediated rejection pathophysiology and discussed the latest promising therapeutic approaches.

International audience; Adoptive cell therapy represents a promising approach for several chronic diseases. This study describes an innovative strategy for biofunctionalization of nanoparticles, allowing the generation of synthetic particulate antigens (SPAg). SPAg activate polyclonal B cells and vectorize noncognate proteins into their endosomes, generating highly efficient stimulators for ex vivo expansion of antigen-specific CD4+ T cells. This method also allows harnessing the ability of B cells to polarize CD4+ T cells into effectors or regulators.

Overlooked for decades, antibodies have taken center stage in renal transplantation and are now widely recognized as the first cause of allograft failure. Diagnosis of antibody-mediated rejection has considerably improved with identification of antibody-mediated lesions in graft biopsies and advances made in the detection of circulating donor-specific antibodies. Unfortunately, this progress has not yet translated into better outcomes for patients. Indeed, in the absence of a drug able to suppress antibody generation by plasma cells, available therapies can only slow down graft destruction. This review provides an overview of the current knowledge of antibody-mediated rejection and discusses future interesting research directions.

Introduction La survie renale apres un rejet humoral (RH) est heterogene et difficilement predictible au niveau individuel. Elle depend de la pathogenicite des DSA qui est fortement liee a leur aptitude a activer le complement [1] . Les degâts causes par les DSA sont responsables de l’infiltration du greffon par des cellules inflammatoires. Nous avons emis l’hypothese qu’une strategie integrant un phenotypage quantitatif et qualitatif precis de l‘infiltrat inflammatoire et l’evaluation de la capacite des DSA a activer le complement permettrait d’identifier au mieux les patients a risque de perdre leur greffon au moment d’un RH. Patients et methodes Parmi les 69 patients ayant presente un RH entre 2004 et 2012, 52 avaient suffisamment de materiel histologique pour l’analyse. Apres des marquages immuno-histochimiques, une analyse informatisee a ete utilisee pour quantifier les cellules CD68+ (macrophage), CD3+ (lymphocyte T), CD66b+ (granulocyte), CD20+ (lymphocyte B) ou CD56+ (natural killer) dans l’interstitium, les glomerules et les capillaires. La capacite des DSA a fixer le complement (C3d) au moment du RH a ete evaluee par technique Luminex. Resultats Seul le nombre de cellules CD68+ dans les capillaires et dans l’interstitium permettait d’identifier les patients a risque de perte de greffon (HR = 3,18, p Discussion Le test C3d isole a une excellente valeur predictive negative (89,5 % pour la perte de greffon a 1 an) mais une valeur predictive positive perfectible (52,9 %) [1] . La quantification des monocytes permet de preciser le pronostic des patients dans le groupe C3d+. Conclusion La quantification topographique informatisee des monocytes permet d’ameliorer la stratification du risque de perte de greffon au moment du diagnostic de RH.

Main problem The number of kidney transplant candidates with prosthetic heart valves (PHVs) is increasing. Yet, outcomes of kidney transplantation in these patients are still unclear. This is the first report of post-transplant outcomes in patients with PHVs at time of kidney transplantation. Methods We conducted a matched cohort study among recipients from the multicentric and prospective DIVAT cohort to compare outcomes in patients with left-sided PHVs at time of transplantation and a group of recipients without PHV matched according to age, dialysis time, initial disease, pre-transplant DSA, diabetes and cardiovascular events. Results Of 23018 patients, 92 patients with PHVs were included and compared to 276 patients without PHV. Delayed graft function and post-operative bleeding occurred more frequently in patients with PHVs. Kidney graft survival was similar between groups. 5-year overall survival was 68.5 % in patients with PHV versus 87.9 % in patients without PHV (HR, 2.72[1.57-4.70], p=0.0004). Deaths from infection, endocarditis and bleeding were more frequent in patients with PHV. Mechanical valves, but not bioprosthetic valves, were independent risk factors for mortality (HR, 2.89[1.68-4.97], p=0.0001). Conclusions Patients with PHV have high mortality rates after kidney transplantation. These data suggest that mechanical valves, but not biological valves, increase risks of post-transplant mortality.