Elevated urinary sVCAM-1, IL6, sIL6R and TNFR1 concentrations indicate acute kidney transplant rejection in the first 2weeks after transplantation

Contemporary Biomarkers for Renal Transplantation: A Narrative Overview

Renal transplantation (RT) is the preferred treatment for end-stage renal disease. However, clinical challenges persist, i.e., early detection of graft dysfunction, timely identification of rejection episodes, personalization of immunosuppressive therapy, and prediction of long-term graft survival. Biomarkers have emerged as valuable tools to address these challenges and revolutionize RT patient care. Our review synthesizes the existing scientific literature to highlight promising biomarkers, their biological characteristics, and their potential roles in enhancing clinical decision-making and patient outcomes. Emerging non-invasive biomarkers seemingly provide valuable insights into the immunopathology of nephron injury and allograft rejection. Moreover, we analyzed biomarkers with intra-nephron specificities, i.e., glomerular vs. tubular (proximal vs. distal), which can localize an injury in different nephron areas. Additionally, this paper provides a comprehensive analysis of the potential clinical applications of biomarkers in the prediction, detection, differential diagnosis and assessment of post-RT non-surgical allograft complications. Lastly, we focus on the pursuit of immune tolerance biomarkers, which aims to reclassify transplant recipients based on immune risk thresholds, guide personalized immunosuppression strategies, and ultimately identify patients for whom immunosuppression may safely be reduced. Further research, validation, standardization, and prospective studies are necessary to fully harness the clinical utility of RT biomarkers and guide the development of targeted therapies.

Impact of interleukin-6 on T cells in kidney transplant recipients

Interleukin-6 (IL-6), a multifunctional proinflammatory cytokine, plays a key role in T cell activation, survival, and differentiation. Acting as a switch that induces the differentiation of naïve T cells into Th17 cells and inhibits their development into regulatory T cells, IL-6 promotes rejection and abrogates tolerance. Therapies that target IL-6 signaling include antibodies to IL-6 and the IL-6 receptor and inhibitors of janus kinases; several of these therapeutics have demonstrated robust clinical efficacy in autoimmune and inflammatory diseases. Clinical trials of IL-6 inhibition in kidney transplantation have focused primarily on its effects on B cells, plasma cells, and HLA antibodies. In this review, we summarize the impact of IL-6 on T cells in experimental models of transplant and describe the effects of IL-6 inhibition on the T cell compartment in kidney transplant recipients.

Association Between Graft Function and Urine CXCL10 and Acylcarnitines Levels in Kidney Transplant Recipients

OBJECTIVE

To evaluate post-transplantation graft functions noninvasively by using urine C-X-C motif chemokine 10 (CXCL10) and metabolome analysis.

METHODS

The 65 living-donor kidney-transplant recipients in our cohort underwent renal biopsy to investigate possible graft dysfunction. The patients were divided into 2 groups, according to pathology reports: chronic allograft dysfunction (CAD; n = 18) and antibody-mediated/humoral allograft rejection (AMR; n = 16). The control group was composed of renal transplant recipients with stable health (n = 33). We performed serum creatinine, blood urea nitrogen (BUN), cystatin C, urine protein, CXCL10, and metabolome analyses on specimens from the patients.

RESULTS

BUN, creatinine, cystatin C, urine protein, leucine + isoleucine, citrulline, and free/acetyl/propionyl carnitine levels were significantly higher in patients with CAD and AMR, compared with the control individuals. CXCL10 levels were significantly elevated in patients with AMR, compared with patients with CAD and controls. CXCL10 (AUC = 0.771) and cystatin C (AUC = 0.746) were significantly higher in the AMR group, compared with the CAD group (P<.02).

CONCLUSIONS

CXCL10 and metabolome analyzes are useful for evaluation of graft functions. Also, CXCL10 might be useful as a supplementary noninvasive screening test for diagnosis of allograft rejection.

TNF, IL-6, and IL-10 cytokines levels and their polymorphisms in renal function and time after transplantation

Cytokine polymorphisms can influence their plasma levels and thus affect the immune response in renal transplantation. A total of 146 renal transplant recipients (RTR) were classified into groups according to the estimated glomerular filtration rate (R1: < 60 and R2: ≥ 60 mL/min/1.73 m²) and time after transplantation (T1: 1 to 24, T2: 25 to 60, T3: 61 to 120, and T4: > 120 months after transplantation). The polymorphisms were genotyped by single specific primer-polymerase chain reaction. IL-10 was measured by ELISA and IL-6, and TNF levels were determined using Miliplex®. A higher frequency of the - 308G allele and the - 308G/G genotype, low-producer, was observed in the R1 group compared with R2. In addition, a higher frequency of the - 308A carriers, high-producer, was found in the R2 group. However, no significant difference was observed in cytokine levels when both groups were compared. Higher levels of IL-6 were observed in T1 compared with T2 and T4 groups. Lower IL-6 levels were found in T2 compared with T3 group. Lower levels of IL-10 were also found in T1 group in relation to T2, while higher levels of this cytokine were observed in T2 group compared with T3. The results suggest that the - 308G > A polymorphism in the TNF gene is associated with filtration function after renal transplantation, and IL-6 and IL-10 levels change according to the time after transplantation. Thus, the joint evaluation of - 308G > A polymorphism in TNF gene and IL-6 and IL-10 levels would provide a broader and effective view on the clinical monitoring of RTR.

Expression Pattern of Tumor Necrosis Factor-α-Induced Protein 8-Like 2 in Acute Rejection of Cardiac Allograft

BACKGROUND

Tumor necrosis factor-α-induced protein-8 like-2 (TIPE2) is a negative regulator of innate immunity and cellular immunity, yet the expression pattern of TIPE2 in acute rejection of cardiac allograft remain enigmatic.

METHODS

We developed cardiac transplantation models and divided into 3 groups: a naive group, a syngeneic group, and an allogeneic group. Then, we detected the messenger RNA and protein of TIPE2 in cardiac allografts. Real-time polymerase chain reaction showed expression of CD4 and CD8 in the donor heart, and immunofluorescence assay revealed the association between T cells and TIPE2.

RESULTS

In our study, we first found that the expression of TIPE2 in cardiac allografts is upregulated compared with the syngeneic control, and increases in a time-dependent manner. The immunocytochemistry of heart grafts revealed a strong expression of TIPE2 in the inflammatory cells, but not in the cardiomyocytes. Finally, we proved that CD4⁺ and CD8⁺ T cells infiltrated cardiac allografts abundantly, which express ample TIPE2.

CONCLUSIONS

The upregulated expression of TIPE2 in cardiac allografts, mainly came from T cells, which infiltrated the donor heart. This finding indicates that there may be an association between TIPE2 and acute cardiac allograft rejection.

Urinary transcriptomics reveals patterns associated with subclinical injury of the renal allograft

AIM

Subclinical pathological features in renal allograft biopsies predict poor outcomes, and noninvasive biomarkers are wanted. RNA quantification in urine predicts overt rejection. We hypothesized that a whole transcriptome analysis would be informative, even for discrete injury.

PATIENTS & METHODS

We performed an mRNA microarray with an optimized normalization method on 26 urinary cell pellets to study renal partial epithelial to mesenchymal transition (pEMT) in stable kidney allografts.

RESULTS & CONCLUSION

Unbiased pathway analysis revealed immune response as the main underlying biological process. In a subgroup of pristine biopsies, isolated pEMT was associated with reduced metabolic functions. Thus, pEMT translates into specific urinary mRNA patterns, in other words, increased inflammation and decreased metabolic functions. Deposited in Gene Expression Omnibus (GSE89652).

Multicolor Flow Cytometry and Cytokine Analysis Provides Enhanced Information on Kidney Transplant Biopsies

Introduction

Current processing of renal biopsy samples provides limited information about immune mechanisms causing kidney injury and disease activity. We used flow cytometry with transplanted kidney biopsy samples to provide more information on the immune status of the kidney.

Methods

To enhance the information available from a biopsy, we developed a technique for reducing a fraction of a renal biopsy sample to single cells for multicolor flow cytometry and quantitation of secreted cytokines present within the biopsy sample. As proof of concept, we used our technique with transplant kidney biopsy samples to provide examples of clinically relevant immune information obtainable with cytometry.

Results

A ratio of CD8⁺ to CD4⁺ lymphocytes greater than or equal to 1.2 in transplanted allografts is associated with rejection, even before it is apparent by microscopy. Elevated numbers of CD45 leukocytes and higher levels of interleukin (IL)−6, IL-8, and IL-10 indicate more severe injury. Antibody binding to renal microvascular endothelial cells can be measured and corresponds to antibody-mediated forms of allograft rejection. Eculizumab binding to endothelial cells suggests complement activation, which may be independent of bound antibody. We compared intrarenal leukocyte subsets and activation states to those of peripheral blood from the same donor at the time of biopsy and found significant differences; thus the need for new techniques to evaluate immune responses within the kidney.

Conclusion

Assessment of leukocyte subsets, renal microvascular endothelial properties, and measurement of cytokines within a renal biopsy by flow cytometry enhance understanding of pathogenesis, indicate disease activity, and identify potential targets for therapy.

Drug repurposing: Ibrutinib exhibits immunosuppressive potential in organ transplantation

Long-term administration of classic immunosuppressants can induce severe adverse effects. The development of novel immunosuppressants confronts great challenges and opportunities. Ibrutinib, an approved drug for B-cell lineages and chronic graft versus host disease (cGVHD), exhibits immunosuppressive efficacy in autoimmune diseases. Ibrutinib's potential as an immunosuppressant in organ transplantation has not been investigated to date. In a xeno-artery patch model ex vivo, ibrutinib inhibited the proliferation of PBMCs (POD 14-42), mainly CD3⁺CD4⁺ and CD3⁺CD8⁺ T cells ex vivo. The secretion of cytokines (IL-6, IL-2 and IFN-γ) was suppressed in response to ibrutinib. In allo-skin transplantation models, ibrutinib delayed the rejection of grafted skins. Ibrutinib decreased the amount of T/B cells and lymphocyte infiltration. Altogether, ibrutinib exhibited immunosuppressive potential through cytokine regulation and T cell inhibition ex vivo and in vitro. Repositioning of ibrutinib as an immunosuppressant will greatly facilitate novel immunosuppressant development.

Peri- and Postoperative Treatment with the Interleukin-1 Receptor Antagonist Anakinra Is Safe in Patients Undergoing Renal Transplantation: Case Series and Review of the Literature

In patients undergoing solid organ transplantation, the presence of an interleukin-1 (IL-1) driven disease may require the addition of IL-1 inhibiting drugs to the standard immunosuppressive regimen to protect against inflammation and negative graft outcome. Three patients undergoing renal transplantation were treated perioperatively with the interleukin-1 receptor antagonist anakinra. Kidney function increased rapidly in all three and the only complications seen were minor infections. In vitro studies report associations between serum and urinary levels of IL-1β and IL-1 receptor antagonist and negative graft outcome, and studies in animals and two small human trials illustrate a possible protective effect of anti-IL-1 therapy after solid organ transplantation. Peri- and postoperative use of anakinra is safe and effective in patients undergoing renal transplantation.

The role of midkine in the inflammatory process and its correlation with other inflammatory markers in renal transplant recipients

BACKGROUND

Midkine (MK), which is expressed in the proximal tubular epithelial cells of the kidney, is thought to have a role in the pathophysiology of inflammation-related renal diseases. Both immunological and nonimmunological mechanisms may affect renal functions negatively during the early and late post-transplantation periods. We aimed in our study to evaluate the relationship of MK with clinical findings and inflammatory markers, including high sensitivity C-reactive protein (hs-CRP), interleukin (IL-6) and tumor necrosis factor (TNF-α) in the pretransplant and post-transplant period.

METHODS

Forty-one consecutive patients transplanted from living related donors were included in this prospective observational study. All patients received the same immunosuppressive treatment protocol. MK, hsCRP, IL-6 and TNF-α levels were measured before and 2 months after renal transplantation.

RESULTS

Pretransplant MK levels correlated positively with hsCRP (r = 0.41, p = 0.004) and IL-6 (r = 0.58, p&lt;0.001). The mean post-transplant MK level was found to be higher than the pretransplant level (143 ± 350 pg/mL, 2792 ± 4235 pg/mL respectively, p = &lt;0.001), while the mean hsCRP, IL-6 and TNF-α levels did not change significantly. Post-transplant IL-6 correlated significantly with MK (r = 0.388, p = 0.012), hsCRP (r = 0.41, p = 0.007) and TNF-α (r = 0.348, p = 0.026). There was no significant correlation between clinical findings and inflammatory markers.

CONCLUSIONS

MK may be a good inflammatory marker in renal transplant recipients as in other inflammatory diseases. Moreover, it seems that it is not affected by factors other than inflammation during the post-transplantation period.

Circulating TNF receptors 1 and 2 are associated with the severity of renal interstitial fibrosis in IgA nephropathy

The current study aimed to examine whether the levels of TNF receptors 1 and 2 (TNFR1 and TNFR2) in serum and urine were associated with other markers of kidney injury and renal histological findings, including TNFR expression, in IgA nephropathy (IgAN). The levels of the parameters of interest were measured by immunoassay in 106 biopsy-proven IgAN patients using samples obtained immediately before renal biopsy and in 34 healthy subjects. Renal histological findings were evaluated using immunohistochemistry. The levels of serum TNFRs were higher in IgAN patients than in healthy subjects. The levels of both TNFRs in serum or urine were strongly correlated with each other (r > 0.9). Serum TNFR levels were positively correlated with the urinary protein to creatinine ratio (UPCR) and four markers of tubular damage of interest (N-acetyl-β-D-glucosaminidase [NAG], β2 microglobulin [β2m], liver-type fatty acid-binding protein [L-FABP], and kidney injury molecule-1 [KIM-1]) and negatively correlated with estimated glomerular filtration rate (eGFR). Patients in the highest tertile of serum TNFR levels showed more severe renal interstitial fibrosis than did those in the lowest or second tertiles. The tubulointerstitial TNFR2-, but not TNFR1-, positive area was significantly correlated with the serum levels of TNFRs and eGFR. Stepwise multiple regression analysis revealed that elevated serum TNFR1 or TNFR2 levels were a significant determinant of renal interstitial fibrosis after adjusting for eGFR, UPCR, and other markers of tubular damage. In conclusion, elevated serum TNFR levels were significantly associated with the severity of renal interstitial fibrosis in IgAN patients. However, the source of TNFRs in serum and urine remains unclear.

TNF receptors: signaling pathways and contribution to renal dysfunction

Tumor necrosis factor (TNF), initially reported to induce tumor cell apoptosis and cachexia, is now considered a central mediator of a broad range of biological activities from cell proliferation, cell death and differentiation to induction of inflammation and immune modulation. TNF exerts its biological responses via interaction with two cell surface receptors: TNFR1 and TNFR2. (TNFRs). These receptors trigger shared and distinct signaling pathways upon TNF binding, which in turn result in cellular outputs that may promote tissue injury on one hand but may also induce protective, beneficial responses. Yet the role of TNF and its receptors specifically in renal disease is still not well understood. This review describes the expression of the TNFRs, the signaling pathways induced by them and the biological responses of TNF and its receptors in various animal models of renal diseases, and discusses the current outcomes from use of TNF biologics and TNF biomarkers in renal disorders.

Expression of receptor activator of nuclear factor-kappa B ligand in leukocytes during acute kidney rejection after transplantation in rats

BACKGROUND

Acute cellular rejection of the transplanted kidney is an important cause of impaired graft function. One of the basic characteristics of acute cellular rejection according to the latest Banff classification of renal allograft pathology is the presence of a large number of T lymphocytes in the allografted tissue. Osteoprotegerin, receptor activator of nuclear factor-kappa B (RANK) and RANK ligand (RANKL), three relatively novel members of the tumor necrosis factor superfamily, have crucial roles not only in physiologic and pathologic bone metabolism but also in immunologic processes. The aim of our study was to determine the expression of RANKL and RANK by T lymphocytes and macrophages in acute cellular kidney allograft rejection in rats.

METHODS

The study included 15 male Wistar rats of 3 months old and 250-300 g as recipients and 15 male DA rats donors of 3 months old; and weight 250-300 g. When animals were sacrificed at 3 weeks to extract the transplanted kidney for pathohistologic analysis and immunoflorescence. all samples showed acute cellular rejection. Kidney sections were examined by dual-labeled immunofluorescence to detect CD4, CD8, or CD68 (red) and RANK or RANKL (green) with coexpressing cells as orange.

RESULTS

RANKL-positive expression colocalized with CD4(+) and CD8(+) T lymphocytes in acutely rejected kidney tissue. There was no association between CD4(+) and CD8(+) T cells with RANK expression, which was evident by infiltrating CD68-positive macrophages in the kidney tissue interstitium.

CONCLUSION

RANK and RANKL were expressed by T lymphocytes and macrophages in acute cellular kidney rejection after transplantation in rats.

Tumor necrosis factor receptor 2: its contribution to acute cellular rejection and clear cell renal carcinoma

Tumor necrosis factor receptor 2 (TNFR2) is a type I transmembrane glycoprotein and one of the two receptors that orchestrate the complex biological functions of tumor necrosis factor (TNF, also designed TNF-α). Accumulating experimental evidence suggests that TNFR2 plays an important role in renal disorders associated with acute cellular rejection and clear cell renal carcinoma but its exact role in these settings is still not completely understood. This papers reviews the factors that may mediate TNFR2 induction in acute cellular rejection and clear cell renal carcinoma and its contribution to these conditions and discusses its therapeutic implications. A greater understanding of the function of TNFR2 may lead to the development of new anti-TNF drugs.

Alteration of innate immunity by donor IL-6 deficiency in a presensitized heart transplant model

Engraftment of IL-6 deficient donor into wild-type recipient could significantly improve allograft survival through T cell lineage particularly regulatory T cells (Tregs) in non-sensitized transplant host. However, its effect on innate immune responses remains uncertain. Our data revealed that donor IL-6 deficiency significantly increased infiltration of two subsets of MDSCs (CD11b+Gr1+myeloid-derived suppressor cells), CD11b+Gr1(-low) and CD11b+Gr1(-int) with strong immunosuppression activity in the transplanted graft. It resulted in a dramatic increase of CD11b+Gr1(-low) frequency and a significant decrease of the frequency of CD11b+Gr1(-high) and CD4-CD8-NK1.1+ cells in the recipient's spleen. Unexpectedly, donor IL-6 deficiency could not significantly reduce macrophage frequency irrespective of in the host's spleen or graft. Taken together, suppression of innate immune effector cells and enhanced activity of regulatory MDSCs contributed to tolerance induction by blockade of IL-6 signaling pathway. The unveiled novel mechanism of targeting IL-6 might shed light on clinical therapeutic application in preventing accelerated allograft rejection for those pre-sensitized transplant recipients.

Urine of patients with acute kidney transplant rejection show high normetanephrine and decreased 2-hydroxyestrogens concentrations

BACKGROUND

A shift from anti- to proinflammatory steroid hormones has been observed in chronic inflammation. We tested the hypothesis that this shift occurs also in kidney transplant rejection together with a rise of urinary catecholamine degradation product concentrations as a consequence of locally produced cytokines, thus further promoting rejection.

METHODS

We examined 8 patients with an early rejection episode in the protocol biopsy ∼2 weeks, 9 with biopsy-proven rejection at 2-3 months, and 18 without rejection, both at 2 weeks and 3 months after transplantation. Metanephrine, normetanephrine, and 2- and 16-hydroxyestrogens concentrations were measured by EIA.

RESULTS

The median urinary concentrations of normetanephrine, but not metanephrine, were significantly higher in acute kidney transplant rejection in the first 2 weeks after transplantation (P < .05). During acute kidney transplant rejection at 2-3 months, but not in the first 2 weeks, after transplantation, 2-, but not 16-hydroxyestrogens, concentrations were significantly decreased (P < .05).

CONCLUSIONS

We demonstrated that the downstream product of noradrenaline conversion normetanephrine was elevated in kidney transplant rejection in the first weeks after transplantation. This change may promote rejection together with an important proinflammatory and mitogenic steroid hormone shift, which becomes increasingly relevant over time.

Lipoxygenase products in the urine correlate with renal function and body temperature but not with acute transplant rejection

Acute transplant rejection is the leading cause of graft loss in the first months after kidney transplantation. Lipoxygenase products mediate pro- and anti-inflammatory actions and thus we aimed to correlate the histological reports of renal transplant biopsies with urinary lipoxygenase products concentrations to evaluate their role as a diagnostic marker. This study included a total of 34 kidney transplant recipients: 17 with an acute transplant rejection and 17 controls. LTE4, LTB4, 12-HETE and 15-HETE concentrations were measured by enzyme immunoassay. Urinary lipoxygenase product concentrations were not significantly changed during an acute allograft rejection. Nevertheless, LTB4 concentrations correlated significantly with the body temperature (P ≤ 0.05) 3 months after transplantation, and 12- and 15-HETE concentrations correlated significantly with renal function (P ≤ 0.05) 2 weeks after transplantation. In conclusion, our data show a correlation for LTB4 with the body temperature 3 months after transplantation and urinary 12- and 15-HETE concentrations correlate positively with elevated serum creatinine concentrations but do not predict acute allograft rejection.

Tumor necrosis factor receptors: biology and therapeutic potential in kidney diseases

The major evolutionary advance represented in the human immune system is a mechanism of antigen-directed immunity in which tumor necrosis factor (TNF)-α and TNF receptors (TNFRs) play essential roles. Binding of TNF-α to the 55-kDa type I TNFR (TNFR1, TNFRSF1A, CD120a, p55) or the 75-kDa type II TNFR (TNFR2, TNFRSF1B, CD120b, p75) activates signaling pathways controlling inflammatory, immune and stress responses, as well as host defense and apoptosis. Multiple studies have investigated the role of TNFRs in the development of early and late renal failure (diabetic nephropathy, nephroangiosclerosis, acute kidney transplant rejection, renal cell carcinoma, glomerulonephritis, sepsis and obstructive renal injury). This article reviews the general characteristics, the analytical aspects and the biology of TNFRs in this domain. In addition, the potential therapeutic application of specific TNFR blockers is discussed.