BK Polyomavirus in Pediatric Renal Transplantation-What We Know and What We Do Not.

BK polyomavirus (BKPyV) is still a real threat in the management of kidney transplantation. Immunosuppressive treatment disrupts the equilibrium between virus replication and immune response, and uncontrolled BKPyV replication leads to nephropathy (BKPyV nephropathy). The first evidence of BKPyV reactivation in transplant recipients is the detection of viral shedding in urine, which appears in 20% to 60% of patients, followed by BKPyV viremia in 10-20% of kidney transplant recipients. BKPyV nephropathy eventually occurs in 1-10% of this population, mainly within the first 2 years post-transplantation, causing graft loss in about half of those patients. Few data exist regarding the pediatric population and we focus on them. In this paper, we review the existing diagnostic methods and summarize the evidence on the role of BKPyV humoral and cellular immunity in modulating the clinical course of BKPyV infection and as potential predictors of the outcome. We look at the known risk factors for BKPyV nephropathy in the immunosuppressed patient. Finally, we propose a sensible clinical attitude in order to screen and manage BKPyV infection in kidney transplant children.

Fine-tuning tumor- and allo-immunity: advances in the use of immune checkpoint inhibitors in kidney transplant recipients.

Cancer is a common complication after kidney transplantation. Kidney transplant recipients (KTR) have a 2- to 4-fold higher risk of developing cancer compared to the general population and post-transplant malignancy is the third most common cause of death in KTR. Moreover, it is well known that certain cancer types are overrepresented after transplantation, especially non-melanoma skin cancer. Immune checkpoint inhibitors (ICI) have revolutionized the treatment of cancer, with remarkable survival benefit in a subgroup of patients. ICI are monoclonal antibodies that block the binding of specific co-inhibitory signaling molecules. Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), programmed cell death protein 1 (PD-1), and its ligand programmed cell death ligand 1 (PD-L1) are the main targets of ICI. Solid organ transplant recipients (SOTR) have been excluded from clinical trials owing to concerns about tumor response, allo-immunity, and risk of transplant rejection. Indeed, graft rejection has been estimated as high as 48% and represents an emerging problem. The underlying mechanisms of organ rejection in the context of treatment with ICI are poorly understood. The search for restricted antitumoral responses without graft rejection is of paramount importance. This review summarizes the current knowledge of the use of ICI in KTR, the potential mechanisms involved in kidney graft rejection during ICI treatment, potential biomarkers of rejection, and how to deal with rejection in clinical practice.

Hybrid Immunity Overcomes Defective Immune Response to COVID-19 Vaccination in Kidney Transplant Recipients.

Introduction: Comorbidities and immunosuppressive therapies are associated with reduced immune responses to primary COVID-19 mRNA vaccination in kidney transplant recipients (KTRs). In healthy individuals, prior SARS-COV-2 infection is associated with increased vaccine responses, a phenotype called hybrid immunity. In this study, we explored the potential influence of immune suppression on hybrid immunity in KTRs. Methods: Eighty-two KTRs, including 59 SARS-CoV-2-naïve (naïve KTRs [N-KTRs]) and 23 SARS-CoV-2-experienced (experienced KTRs [E-KTRs]) patients, were prospectively studied and compared to 106 healthy controls (HCs), including 40 SARS-CoV-2-naïve (N-HCs) and 66 SARS-CoV-2-experienced (E-HCs) subjects. Polyfunctional antibody and T cell responses were measured following 2 doses of BNT162b2 mRNA vaccine. Associations between vaccine responses and clinical characteristics were studied by univariate and multivariate analyses. Results: In naïve KTRs, vaccine responses were markedly lower than in HCs and were correlated with older age, more recent transplantation, kidney retransplantation after graft failure, arterial hypertension, and treatment with mycophenolate mofetil (MMF). In contrast, vaccine responses of E-KTRs were similar to those of HCs and were associated with time between transplantation and vaccination, but not with the other risk factors associated with low vaccine responses in naïve KTRs. Conclusion: In conclusion, hybrid immunity overcomes immune suppression and provides potent humoral and cellular immunity to SARS-CoV-2 in KTRs.

Humoral and cellular immune correlates of protection against COVID-19 in kidney transplant recipients.

As solid organ transplant recipients are at high risk of severe COVID-19 and respond poorly to primary SARS-CoV-2 mRNA vaccination, they have been prioritized for booster vaccination. However, an immunological correlate of protection has not been identified in this vulnerable population. We conducted a prospective monocentric cohort study of 65 kidney transplant recipients who received 3 doses of BNT162b2 mRNA vaccine. Associations among breakthrough infection (BTI), vaccine responses, and patient characteristics were explored in 54 patients. Symptomatic COVID-19 was diagnosed in 32% of kidney transplant recipients during a period of 6 months after booster vaccination. During this period, SARS-CoV-2 delta and omicron were the dominant variants in the general population. Univariate Analyses identified the avidity of SARS-CoV-2 receptor binding domain binding IgG, neutralizing antibodies, and SARS-CoV-2 S2-specific interferon gamma responses as correlates of protection against BTI. No demographic or clinical parameter correlated with the risk of BTI. In multivariate analysis, the risk of BTI was best predicted by neutralizing antibody and S2-specific interferon gamma responses. In conclusion, T cell responses may help compensate for the suboptimal antibody response to booster vaccination in kidney transplant recipients. Further studies are needed to confirm these findings.

Afucosylation of HLA-specific IgG1 as a potential predictor of antibody pathogenicity in kidney transplantation.

Antibody-mediated rejection (AMR) is the leading cause of graft failure. While donor-specific antibodies (DSAs) are associated with a higher risk of AMR, not all patients with DSAs develop rejection, suggesting that the characteristics of alloantibodies determining their pathogenicity remain undefined. Using human leukocyte antigen (HLA)-A2-specific antibodies as a model, we apply systems serology tools to investigate qualitative features of immunoglobulin G (IgG) alloantibodies including Fc-glycosylation patterns and FcγR-binding properties. Levels of afucosylated anti-A2 antibodies are elevated in seropositive patients, especially those with AMR, suggesting potential cytotoxicity via FcγRIII-mediated mechanisms. Afucosylation of both glycoengineered monoclonal and naturally glycovariant polyclonal serum IgG specific to HLA-A2 drives potentiated binding to, slower dissociation from, and enhanced signaling through FcγRIII, a receptor widely expressed on innate effector cells, and greater cytotoxicity against HLA-A2+ cells mediated by natural killer (NK) cells. Collectively, these results suggest that afucosylated DSA may be a biomarker of AMR and contribute to pathogenesis.

Does kidney transplantation with a standard or expanded criteria donor improve patient survival? Results from a Belgian cohort.

BACKGROUND: Changes in recipient and donor factors have reopened the question of survival benefits of kidney transplantation versus dialysis. METHODS: We analysed survival among 3808 adult Belgian patients waitlisted for a first deceased donor kidney transplant from 2000 to 2012. The primary outcome was mortality during the median waiting time plus 3 years of follow-up after transplantation or with continued dialysis. Outcomes were analysed separately for standard criteria donor (SCD) and expanded criteria donor (ECD) kidney transplants. We adjusted survival analyses for recipient age (20-44, 45-64 and ≥65 years), sex and diabetes as the primary renal disease. RESULTS: Among patients ≥65 years of age, only SCD transplantation provided a significant survival benefit compared with dialysis, with a mortality of 16.3% [95% confidence interval (CI) 13.2-19.9] with SCD transplantation, 20.5% (95% CI 16.1-24.6) with ECD transplantation and 24.6% (95% CI 19.4-29.5) with continued dialysis. Relative mortality risk was increased in the first months after transplantation compared with dialysis, with equivalent risk levels reached earlier with SCD than ECD transplantation in all age groups. CONCLUSIONS: The results of this study suggest that older patients might gain a survival benefit with SCD transplantation versus dialysis, but any survival benefit with ECD transplantation versus dialysis may be small.

The mononuclear phagocyte system contributes to fibrosis in post-transplant obliterans bronchiolitis.

Bronchiolitis obliterans syndrome (BOS) is a fibrotic disease that is heavily responsible for the high mortality rates after lung transplantation. Myofibroblasts are primary effectors of this fibrotic process, but their origin is still debated. The purpose of this work was to identify the precursors of mesenchymal cells responsible for post-transplant airway fibro-obliteration.Lineage-tracing tools were used to track or deplete potential sources of myofibroblasts in the heterotopic tracheal transplantation model. Allografts were analysed by histology, confocal microscopy, flow cytometry or single-cell transcriptomic analysis. BOS explants were evaluated by histology and confocal microscopy.Myofibroblasts in the allografts were recipient-derived. When recipient mice were treated with tacrolimus, we observed rare epithelial-to-mesenchymal transition phenomena and an overall increase in donor-derived myofibroblasts (p=0.0467), but the proportion of these cells remained low (7%). Haematopoietic cells, and specifically the mononuclear phagocyte system, gave rise to the majority of myofibroblasts found in occluded airways. Ablation of Cx3cR1+ cells decreased fibro-obliteration (p=0.0151) and myofibroblast accumulation (p=0.0020). Single-cell RNA sequencing revealed similarities between myeloid-derived cells from allografts and both murine and human samples of lung fibrosis. Finally, myofibroblasts expressing the macrophage marker CD68 were increased in BOS explants when compared to controls (14.4% versus 8.5%, p=0.0249).Recipient-derived myeloid progenitors represent a clinically relevant source of mesenchymal cells infiltrating the airways after allogeneic transplantation. Therapies targeting the mononuclear phagocyte system could improve long-term outcomes after lung transplantation.

Heme oxygenase-1 orchestrates the immunosuppressive program of tumor-associated macrophages.

Tumor-associated macrophages (TAMs) contribute to the maintenance of a strong immunosuppressive environment, supporting tumor progression and resistance to treatment. To date, the mechanisms that drive acquisition of these immunosuppressive features are still poorly defined. Heme oxygenase-1 (HO-1) is the rate-limiting enzyme that catabolizes free heme. It displays important cytoprotective, antiinflammatory, and antioxidant properties. A growing body of evidence suggests that HO-1 may also promote tumor development. Herein, we show that HO-1 is highly expressed in monocytic cells in the tumor microenvironment (TME) once they differentiate into TAMs. Deletion of HO-1 in the myeloid compartment enhances the beneficial effects of a therapeutic antitumor vaccine by restoring CD8+ T cell proliferation and cytotoxicity. We further show that induction of HO-1 plays a major role in monocyte education by tumor cells by modulating their transcriptional and epigenetic programs. These results identify HO-1 as a valuable therapeutic target to reprogram the TME and synergize with current cancer therapies to facilitate antitumor response.

Donor-Derived Myeloid Heme Oxygenase-1 Controls the Development of Graft-Versus-Host Disease.

Graft-versus-host disease (GVHD) remains a major clinical drawback of allogeneic hematopoietic stem cell transplantation (HSCT). Here, we investigated how the stress responsive heme catabolizing enzyme heme oxygenase-1 (HO-1, encoded by HMOX1) regulates GVHD in response to allogeneic hematopoietic stem cell transplantation in mice and humans. We found that deletion of the Hmox1 allele, specifically in the myeloid compartment of mouse donor bone marrow, promotes the development of aggressive GVHD after allogeneic transplantation. The mechanism driving GVHD in mice transplanted with allogeneic bone marrow lacking HO-1 expression in the myeloid compartment involves enhanced T cell alloreactivity. The clinical relevance of these observations was validated in two independent cohorts of HSCT patients. Individuals transplanted with hematopoietic stem cells from donors carrying a long homozygous (GT)n repeat polymorphism (L/L) in the HMOX1 promoter, which is associated with lower HO-1 expression, were at higher risk of developing severe acute GVHD as compared to donors carrying a short (GT)n repeat (S/L or S/S) polymorphism associated with higher HO-1 expression. In this study, we showed the unique importance of donor-derived myeloid HO-1 in the prevention of lethal experimental GVHD and we corroborated this observation by demonstrating the association between human HMOX1 (GT)n microsatellite polymorphisms and the incidence of severe acute GVHD in two independent HSCT patient cohorts. Donor-derived myeloid HO-1 constitutes a potential therapeutic target for HSCT patients and large-scale prospective studies in HSCT patients are necessary to validate the HO-1 L/L genotype as an independent risk factor for developing severe acute GVHD.

HO-1 mitigates acute kidney injury and subsequent kidney-lung cross-talk.

Ischemia-reperfusion injury (IRI) is a leading cause of acute kidney injury (AKI), which contributes to the development of chronic kidney disease (CKD). IRI-induced AKI releases proinflammatory cytokines (e.g. IL-1ß, TNF-α, IL-6) that induce a systemic inflammatory response, resulting in proinflammatory cells recruitment and remote organ damage. AKI is associated with poor outcomes, particularly when extrarenal complications or distant organ injuries occur. Acute lung injury (ALI) is a major remote organ dysfunction associated with AKI. Hence, kidney-lung cross-talk remains a clinical challenge, especially in critically ill population. The stress-responsive enzyme, heme oxygenase-1 (HO-1) is largely known to protect against renal IRI and may be preventively induced using hemin prior to renal insult. However, the use of hemin-induced HO-1 to prevent AKI-induced ALI remains poorly investigated. Mice received an intraperitoneal injection of hemin or sterile saline 1 day prior to surgery. Twenty-four hours later, mice underwent bilateral renal IRI for 26 min or sham surgery. After 4 or 24 h of reperfusion, mice were sacrificed. Hemin-induced HO-1 improved renal outcomes after IRI (i.e. fewer renal damage, renal inflammation, and oxidative stress). This protective effect was associated with a dampened systemic inflammation (i.e. IL-6 and KC). Subsequently, mitigated lung inflammation was found in hemin-treated mice (i.e. neutrophils influx and lung KC). The present study demonstrates that hemin-induced HO-1 controls the magnitude of renal IRI and the subsequent AKI-induced ALI. Therefore, targeting HO-1 represents a promising approach to prevent the impact of renal IRI on distant organs, such as lung.

Early Acute Microvascular Kidney Transplant Rejection in the Absence of Anti-HLA Antibodies Is Associated with Preformed IgG Antibodies against Diverse Glomerular Endothelial Cell Antigens.

BACKGROUND: Although anti-HLA antibodies (Abs) cause most antibody-mediated rejections of renal allografts, non-anti-HLA Abs have also been postulated to contribute. A better understanding of such Abs in rejection is needed. METHODS: We conducted a nationwide study to identify kidney transplant recipients without anti-HLA donor-specific Abs who experienced acute graft dysfunction within 3 months after transplantation and showed evidence of microvascular injury, called acute microvascular rejection (AMVR). We developed a crossmatch assay to assess serum reactivity to human microvascular endothelial cells, and used a combination of transcriptomic and proteomic approaches to identify non-HLA Abs. RESULTS: We identified a highly selected cohort of 38 patients with early acute AMVR. Biopsy specimens revealed intense microvascular inflammation and the presence of vasculitis (in 60.5%), interstitial hemorrhages (31.6%), or thrombotic microangiopathy (15.8%). Serum samples collected at the time of transplant showed that previously proposed anti-endothelial cell Abs-angiotensin type 1 receptor (AT1R), endothelin-1 type A and natural polyreactive Abs-did not increase significantly among patients with AMVR compared with a control group of stable kidney transplant recipients. However, 26% of the tested AMVR samples were positive for AT1R Abs when a threshold of 10 IU/ml was used. The crossmatch assay identified a common IgG response that was specifically directed against constitutively expressed antigens of microvascular glomerular cells in patients with AMVR. Transcriptomic and proteomic analyses identified new targets of non-HLA Abs, with little redundancy among individuals. CONCLUSIONS: Our findings indicate that preformed IgG Abs targeting non-HLA antigens expressed on glomerular endothelial cells are associated with early AMVR, and that in vitro cell-based assays are needed to improve risk assessments before transplant.

Immune checkpoint blockade for organ transplant patients with advanced cancer: how far can we go?

PURPOSE OF REVIEW: Checkpoint inhibitors (CPIs) provide impressive response rates among immunocompetent patients with various solid tumors. So far, organ transplant recipients have been excluded from clinical studies due to the putative risk of allograft rejection however 48 cases of liver and renal transplant patients treated with CPI were already described in literature. RECENT FINDINGS: Here we discuss 19 cases of liver and 29 cases of renal transplant patients who received CPI for advanced cancer. Disease control rate [stable disease, complete response (CR) and partial response (PR) together] was 35% (21% for liver and 45% for kidney transplant patients). Graft rejection was seen in 37% of liver and 45% and kidney transplant patients. Significantly, our analysis shows that an 'ideal' response occurs in 21% of all patients (antitumor response accompanied with durable graft tolerance). SUMMARY: We believe that transplant patients can be treated with CPI in a controlled setting and for well informed patients. To obtain a durable antitumor immune response while avoiding rejection, to be able to adjust immunosuppression and to have the opportunity to develop biomarkers for tumor response and transplant rejection, these patients should be treated according to a clinical care path or a prospective clinical trial.

Host and microbial factors in kidney transplant recipients with Escherichia coli acute pyelonephritis or asymptomatic bacteriuria: a prospective study using whole-genome sequencing.

BACKGROUND: Urinary tract infection is the most common infection among kidney transplant recipients (KTRs). Many transplant physicians fear that host compromise will allow low-virulence strains to cause pyelonephritis in KTRs, so they often treat asymptomatic bacteriuria with antibiotics. Identification of the host/microbe factors that determine the clinical presentation (i.e. pyelonephritis versus asymptomatic bacteriuria) once an Escherichia coli strain enters a KTRs bladder could inform management decisions. METHODS: We prospectively collected all E. coli isolates causing either pyelonephritis or asymptomatic bacteriuria in KTRs at our institution (December 2012-June 2015). Whole-genome sequencing was used to assess bacterial characteristics (carriage of 48 virulence genes and phylogenetic and clonal background). Host parameters were also collected. RESULTS: We analysed 72 bacteriuria episodes in 54 KTRs (53 pyelonephritis, 19 asymptomatic bacteriuria). The pyelonephritis and asymptomatic bacteriuria isolates exhibited a similar total virulence gene count per isolate [median 18 (range 5-33) and 18 (5-30), respectively; P = 0.57] and for individual virulence genes differed significantly only for the prevalence of the pap operon (pyelonephritis 39%,versus asymptomatic bacteriuria 0%; P = 0.002). No other significant between-group differences were apparent for 86 other bacterial and host variables. CONCLUSIONS: Our findings suggest that bacterial adherence plays a role in the pathogenesis of pyelonephritis in KTRs despite significantly altered host urinary tract anatomy and weakened immunity. Whether KTRs might benefit from targeted therapies (e.g. vaccination or inhibitors of fimbrial adhesion) has yet to be studied.

Dual effect of hemin on renal ischemia-reperfusion injury.

Acute kidney injury (AKI) is a major public health concern, which is contributing to serious hospital complications, chronic kidney disease (CKD) and even death. Renal ischemia-reperfusion injury (IRI) remains a leading cause of AKI. The stress-responsive enzyme, heme oxygenase-1 (HO-1) mediates protection against renal IRI and may be preventively induced using hemin prior to renal insult. This HO-1 induction pathway called hemin preconditioning is largely known to be effective. Therefore, HO-1 might be an interesting therapeutic target in case of predictable AKI (e.g. partial nephrectomy or renal transplantation). However, the use of hemin to mitigate established AKI remains poorly characterized. Mice underwent bilateral renal IRI for 26 min or sham surgery. After surgical procedure, animals were injected either with hemin (5 mg/kg) or vehicle. Twenty-four hours later, mice were sacrificed. Despite strong HO-1 induction, hemin-treated mice exhibited significant renal damage and oxidative stress as compared to vehicle-treated mice. Interestingly, higher dose of hemin is associated with more severe IRI-induced AKI in a dose-dependent relation. To determine whether hemin preconditioning remains efficient to dampen postoperative hemin-amplified IRI-induced AKI, we pretreated mice either with hemin (5 mg/kg) or vehicle 24 h prior to surgical procedure. Then, all mice (hemin- and vehicle-pretreated) received postoperative injection of hemin (5 mg/kg) to amplify IRI-induced AKI. In comparison to vehicle, prior administration of hemin to renal IRI mitigated hemin-amplified IRI-induced AKI as attested by fewer renal damage, inflammation and oxidative stress. In conclusion, hemin may have a dual effect on renal IRI, protective or deleterious, depending on the timing of its administration.