Altered intragraft immune responses and improved renal function in MHC class II-deficient mouse kidney allografts

Artificial Urinary Biomarkers for Early Diagnosis of Acute Renal Allograft Rejection

Acute renal allograft rejection (ARAR) after kidney transplantation associated with reduced graft survival and eventual graft failure is poorly diagnosed in hospitals. Here, we report the development of Artificial bioMarker Probes (AMPros) for sensitive urinalysis of ARAR in murine models. AMPros spontaneously go to the kidneys after systemic administration, specifically react with the prodromal immune biomarkers to activate their near-infrared fluorescence signals to report cell-mediated rejection, and efficiently undergo renal excretion into urine. Thus, AMPros enable convenient optical urinalysis that detects ARAR prior to histological manifestation of rejection, which is also earlier than current diagnostic methods measuring proinflammatory cytokines and peripheral blood lymphocyte mRNAs. Due to the high kidney specificity, AMPros-based urinalysis discriminates allograft rejection against other non-alloimmune specific diseases, which is unattainable by measurement of serological biomarkers. Such a noninvasive and sensitive urine test holds great promise in continuous monitoring of renal allograft conditions at low resource settings for timely clinical interventions.

Application of modified small bladder patch-to-bladder double-layer sutures to improve renal transplantation in mice

Background

This study aimed to introduce an improved surgical procedure to reduce the incidence of urinary tract complications after renal transplantation in mice using a modified bladder patch-to-bladder anastomosis technique.

Methods

Renal isotransplantation was performed in 28 male C57BL/6 mice. The urinary tract was reconstructed with a ureteral anastomosis between the donor’s small bladder patch and the recipient’s bladder. The bladder patch was secured through a cystotomy in the recipient’s bladder mucosa and seromuscular layers, which were sutured in a double-layer manner. The food intake and survival of mice were recorded for 100 days in addition to monitoring appearance, weight, and symptoms of pain. On post-transplantation day 7, the native kidney in the recipients was removed and the transplanted kidney assessed visually. Urine leakage from the transplanted graft was monitored by assessing the degree of ascites.

Results

The success rate of renal transplantation was 82 % (23 of 28 cases). Arterial thrombosis at the site of anastomosis occurred in 3 cases (11 %) and hemorrhagic shock in 2 cases (7 %). The mean ± SD time of the operation in recipients was 81 ± 5 min. No complications were noted in the successfully transplanted animals.

Conclusions

The modified procedure of a small bladder patch-to-bladder with double-layer suturing minimizes complications after renal transplantation in mice while requiring the same operating time as other approaches such as ureter to bladder anastomosis, which are associated with more complications.

Autophagy and immune response in kidneys

Autophagy is a ubiquitous intracellular catabolic process that contributes to homeostatic maintenance and regulates the balance between health and disease. Emerging evidence from both the immunology and renal literature suggests that important relationships exist between the immune system and renal autophagy that may have significant implications for our understanding of the pathogenesis of kidney diseases. Autophagic flux in renal parenchymal cells can protect against acute and chronic kidney injury and can be stimulated via activation of innate immune receptors, cytokine secretion, and/or direct contact by immune cells. Conversely, modulation of autophagy in renal cells may influence both adaptive and innate immune cell responses. Autophagy can promote the ability of renal epithelial cells, which can act as antigen-presenting cells, to process and present self-antigen to immune cells. In addition, autophagic control of inflammasome function can modify the intrarenal inflammatory milieu, thereby preventing immune cell infiltration. Because autophagy and immune responses may promote or protect against kidney injury, further research is needed to better understand how interactions between renal parenchymal cells and the immune system are altered by autophagy. Novel agents are being developed that promote or inhibit various steps of the autophagy pathway, and it is likely that whether such agents are beneficial or harmful in the context of kidney disease will depend, at least in part, on whether and how they influence the relationship between autophagy and the immune response in the kidney.

Systematic review of mouse kidney transplantation

A mouse model of kidney transplantation was first described in 1973 by Skoskiewicz et al. Although the mouse model is technically difficult, it is attractive for several reasons: the mouse genome has been characterized and in many aspects is similar to man and there is a greater diversity of experimental reagents and techniques available for mouse studies than other experimental models. We reviewed the literature on all studies of mouse kidney transplantation to report the donor and recipient strain combinations that have been investigated and the resultant survival and histological outcomes. Some models of kidney transplantation have used the transplanted kidney as a life-supporting organ, however, in many studies the recipient mouse's native kidney has been left in situ. Several different combinations of inbred mouse strains have been reported, with varying degrees of injury, survival or tolerance because of haplotype differences. This model has been exceptionally useful as an investigational tool to understand multiple aspects of transplantation including acute rejection, cellular and humoral rejection mechanisms and their treatment. Furthermore, this model has been used to investigate disease mechanisms beyond transplant rejection including intrinsic renal disease and infection-associated pathology.

Reduction of chronic rejection of renal allografts by anti-transforming growth factor-β antibody therapy in a rat model

There is no effective treatment for chronic rejection (CR) that largely limits long-term survival of kidney transplants. Transforming growth factor (TGF)-β is a fibrogenic factor for tissue fibrosis. This study was to test the efficacy of an anti-TGF-β antibody in preventing the CR of renal allografts in a preclinical model. Male Lewis rats (RT1¹) were orthotopically transplanted with donor kidneys from male Fischer 344 (RT11v1) rats and were treated with either anti-TGF-β or a control antibody. The CR of renal allografts was assessed by semiquantitative histological analyses, and intragraft cytokines and fibrosis-related genes ware examined by PCR arrays. Compared with the control antibody, anti-TGF-β antibody treatment significantly reduced recipients' proteinuria (P = 0.0002), and CR in renal transplants, which was indicated by the fewer injured renal tubules, glomeruli, and interlobular arterioles or arteries, and by less mononuclear cell infiltration and interstitial fibrosis in the anti-TGF-β antibody-treated group (P < 0.05), but not significantly attenuate the ratios of different infiltrating leukocytes. These pathological changes were associated with downregulation of TGF-β1, TGF-β2, and proinflammatory cytokines, or with upregulation of anti-fibrotic HGF, BMP5, and BMP7. The therapeutic effect of the anti-TGF-β antibody was further confirmed by its prevention of graft dysfunction, indicated by lower levels of serum creatinine and blood urea nitrogen or higher creatinine clearance in anti-TGF-β antibody-treated recipients compared with those in control recipients (P < 0.05). In conclusion, the anti-TGF-β antibody (1D11) treatment significantly reduces CR of renal allografts in rats, suggesting the therapeutic potential of this antibody therapy for treating CR of kidney transplants in patients.

Contributing factors to complications and surgical success in mouse kidney transplantation

PURPOSE

Mouse kidney transplantation is a challenging technique for novice microsurgeons. Factors that affect transplant outcomes for a clinical surgeon starting microsurgery have not yet been investigated.

MATERIALS AND METHODS

110 consecutive mouse kidney transplants were performed over a 9-month period. Data were recorded, and surgical results and complication were analyzed.

RESULTS

Three and thirty day survival rates improved from 0 (0/6) to 92.3 % (12/13) between months 1 and 9. Bleeding, arterial thrombosis, kidney failure and hydronephrosis were the most common causes of transplant failure. From month 1 to month 7, using the same surgical technique, practice significantly decreased the incidence of bleeding and increased the 3-day survival rate; however, it didn't significantly decrease the incidence of thrombosis, kidney failure, but improved the 30-day survival rate. From month 8, when surgical technique used on artery anastomosis switched from continuous suture to interrupted suture, surgical survival rate at 3 and 30 days improved significantly. Interestingly, ischemia time was not a significant factor determining the success of transplantation in this study.

CONCLUSIONS

Practice is essential for novice microsurgeons, and the choice of surgical techniques significantly affects surgical results. The use of interrupted arterial sutures can significantly improve mouse kidney transplantation outcomes compared with continuous sutures. Ischemic time was not a factor in determining successful of kidney transplantation in mice in this study.

A reproducible mouse model of chronic allograft nephropathy with vasculopathy

While short-term outcomes in kidney transplantation have improved dramatically, long-term survival remains a major challenge. A key component of long-term, chronic allograft injury in solid organ transplants is arteriosclerosis characterized by vascular neointimal hyperplasia and inflammation. Establishing a model of this disorder would provide a unique tool, not only to identify mechanisms of disease, but also test potential therapeutics for late graft injury. To this end, we utilized a mouse orthotopic renal transplant model in which C57BL/6J (H-2b) recipients were given either a kidney allograft from a completely mismatched Balb/cJ mouse (H-2d), or an isograft from a littermate. A unilateral nephrectomy was performed at the time of transplant followed by a contralateral nephrectomy on post-transplant day seven. Recipients were treated with daily cyclosporine subcutaneously for 14 days and then studied 8 and 12 weeks post transplantation. Renal function was significantly worse in allograft compared to isograft recipients. Moreover, the allografts had significantly more advanced tubulointerstitial fibrosis and profound vascular disease characterized by perivascular leukocytic infiltration and neointimal hyperplasia affecting the intrarenal blood vessels. Thus, we describe a feasible and reproducible murine model of intrarenal transplant arteriosclerosis useful to study allograft vasculopathy.

Reduction of chronic allograft nephropathy by inhibition of extracellular signal-regulated kinase 1 and 2 signaling

Chronic allograft nephropathy (CAN), the most common cause of late kidney allograft failure, is not effectively prevented by immunosuppressive regimens. Activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) via MEK mediates actions of various growth factors, including transforming growth factor (TGF)-beta1, which plays a key role in CAN. Hence, we tested the therapeutic potential of MEK-ERK1/2 signaling disruption to prevent CAN. Kidneys from C57BL/6J (H-2(b)) mice were transplanted to bilaterally nephrectomized BALB/c (H-2(d)) mice. At 14 days after transplantation, the recipients were subjected to 28 days of treatment with the MEK inhibitor CI-1040. All six CI-1040-treated allografts survived, while two of seven grafts in the vehicle-treated group were lost. At the end of the experiment, the function and structure of grafts in the CI-1040-treated group were significantly preserved, as indicated by lower levels of serum creatinine or blood urea nitrogen than in the vehicle-treated group [30 +/- 6 vs. 94 +/- 39 microM creatinine (P = 0.0015) and 22 +/- 8 vs. 56 +/- 25 mM BUN (P = 0.0054)] and reduced CAN in the CI-1040-treated group compared with vehicle controls (CAN score = 4.2 vs. 10.3, P = 0.0119). The beneficial effects induced by CI-1040 were associated with reduction of ERK1/2 phosphorylation and TGFbeta1 levels in grafts. Also, CI-1040 potently suppressed not only TGFbeta biosynthesis in kidney cell cultures but also antiallograft immune responses in vitro and in vivo. Our data suggest that interference of MEK-ERK1/2 signaling with a pharmacological agent (e.g., CI-1040) has therapeutic potential to prevent CAN in kidney transplantation.

Late kidney allograft loss: what we know about it, and what we can do about it

Despite dramatic improvements in immunosuppression, late graft loss after kidney transplantation remains a common and difficult problem. Histologic evaluation may reveal changes related to BK polyomavirus infection, hypertension, or calcineurin inhibitor toxicity, which can help to guide therapy. The designation chronic allograft nephropathy should thus be reserved for biopsies with tubular atrophy and interstitial fibrosis without an apparent cause. Although the cause clearly includes both antigen-dependent and antigen-independent events, the approach remains largely to exclude immune mechanisms. Although this review discusses the potential contribution of antibody to chronic injury, it focuses on the basic elements of kidney injury, the role of parenchymal cells in promoting injury, and the proliferative and inflammatory responses that accompanying injury. Strategies to manage these recipients include close attention to accompanying hypertension, diabetes, and hyperlipidemia, as well as consideration for altering immunosuppression; however, therapies that limit epithelial-to-mesenchymal transition or directly block fibrosis pathways may reduce chronic allograft fibrosis and may prove to be useful. Understanding the basic pathogenesis sufficiently to allow early intervention may finally benefit patients who are at high risk for tubular atrophy and interstitial fibrosis and promote their long-term graft function.

Connective tissue growth factor is a biomarker and mediator of kidney allograft fibrosis

Chronic allograft nephropathy (CAN) is a leading cause of kidney graft failure following transplantation. Its causes are complex and include both immunological and nonimmunological factors. Here we have studied the development of CAN in a mouse model of kidney transplantation comparing isografts and allografts. Unlike the normal histology and normal serum creatinine of the uninephrectomized, nonrejecting isografted mice (0.219 +/- 0.024 mg/dL), allografted mice demonstrated severe renal dysfunction (mean serum creatinine 0.519 +/- 0.061 mg/dL; p < 0.005) with progressive inflammation and fibrosis of the kidney. These animals also showed an increased expression of connective tissue growth factor (CTGF), both systemically and within the graft. CTGF was highly expressed in tubuloepithelial cells of allografts, along with alpha-smooth muscle actin, a marker of myofibroblasts, and transcriptionally associated with other markers of fibrosis. In vitro studies of tubular epithelium indicate that CTGF is capable of inducing EMT, independent of TGF-beta. Finally, in human transplant recipients, serum and urine CTGF levels are significantly elevated compared to naïve individuals. Urinary levels correlated with the histological presence of CAN. These studies suggest a critical role of CTGF in graft fibrogenesis, for both mouse and man. Thus, CTGF has potential as a biomarker of CAN, and also a therapeutic target in managing graft fibrosis.

CCL19-IgG prevents allograft rejection by impairment of immune cell trafficking

An adaptive immune response is initiated in the T cell area of secondary lymphoid organs, where antigen-presenting dendritic cells may induce proliferation and differentiation in co-localized T cells after T cell receptor engagement. The chemokines CCL19 and CCL21 and their receptor CCR7 are essential in establishing dendritic cell and T cell recruitment and co-localization within this unique microenvironment. It is shown that systemic application of a fusion protein that consists of CCL19 fused to the Fc part of human IgG1 induces effects similar to the phenotype of CCR7-/- animals, like disturbed accumulation of T cells and dendritic cells in secondary lymphoid organs. CCL19-IgG further inhibited their co-localization, which resulted in a marked inhibition of antigen-specific T cell proliferation. The immunosuppressive potency of CCL19-IgG was tested in vivo using murine models for TH1-mediated immune responses (delayed-type hypersensitivity) and for transplantation of different solid organs. In allogeneic kidney transplantation as well as heterotopic allogeneic heart transplantation in different strain combinations, allograft rejection was reduced and organ survival was significantly prolonged by treatment with CCL19-IgG compared with controls. This shows that in contrast to only limited prolongation of graft survival in CCR7 knockout models, the therapeutic application of a CCR7 ligand in a wild-type environment provides a benefit in terms of immunosuppression.

Therapeutic targets in the treatment of allograft fibrosis

The dramatic improvements in short-term graft survival and acute rejection rates could only have been dreamed of 20 years ago. Late graft loss following kidney transplantation is now the critical issue of this decade. Frequently, graft loss is associated with the development of tubular atrophy and interstitial fibrosis within the kidney (i.e. chronic allograft nephropathy; CAN). Major treatment strategies in this disorder are non-specific and the focus of intervention has been on limiting injurious events. Following graft injury is a fibrogenesis phase featuring both proliferative and infiltrative responses mediated by chemokines, cytokines and growth factors. In particular, TGFbeta has been strongly implicated in the pathogenesis of chronic injury and epithelial-mesenchymal transformation (EMT) may be part of this process. The cascade of events results in matrix accumulation, due to either increased production and/or reduced degradation of matrix. Recent investigations into the pathogenesis of tissue fibrosis have suggested a number of new strategies to ameliorate matrix synthesis. While the majority of therapies have focused on TGFbeta, this may not be an ideal maneuver in transplant settings and alternative targets identified in other fibrotic diseases will be discussed. Attacking graft fibrosis should be a new focus in organ transplantation.

Preconditioning Strategies to Limit Graft Immunogenicity and Cold Ischemic Organ Injury

During the transplant process, the graft is exposed to numerous events, which may enhance its immunogenicity. In particular, factors related to brain death, such as hemodynamic instability and systemic release of cytokines, cold preservation on harvesting, and reperfusion injury, are known to accumulate in harm, conveying a proinflammatory state to the graft before transplant. Alloimmune reactivity is initiated when the host immune system detects non–self-antigens in the context of “danger signals.” Eliminating these danger signals by modifying the graft before transplant has the potential to attenuate the alloimmune response. The molecules, which mediate danger signals, have not yet been fully identified. Free oxygen radicals and interferon-γ are important candidates. One of the most important protective mechanisms against oxidative stress is the heme oxygenase 1 system. Up-regulation of heme oxygenase 1 in grafts has been shown to prevent ischemia-reperfusion damage and improve long-term graft survival in various transplant models. The benefit of blocking the action of interferon-γ in kidney transplants is less clear because the compound plays such a complex and pivotal role in the immune response, and experimental data with interferon-γ receptor knockout mice are conflicting. It has recently become clear that catecholamines are important graft-modifying agents. Dopamine is capable of stimulating the induction of protective enzymes like heme oxygenase-1 (HO-1) rendering the organ more resistant to the insult of ischemia/reperfusion and inflammation. Retrospective clinical data suggest that treatment of brain-dead organ donors with catecholamines is associated with less rejection and a better long-term graft survival of kidneys transplanted from these donors. Catecholamines can also modulate cytokine production and prevent cold-induced damage. Other substances, such as proteoglycans and phosphatidylethanolamine-bound hyaluronic acid, may interfere with the actions of interferon-γ. Further studies of these compounds in experimental animal models and in prospective randomized clinical trials will help establish their efficacy in donor pretreatment. It is important to underscore that donor pretreatment will have great advantages for the recipient because an improved long-term graft survival could thus be achieved cost-efficiently and without great effort or side effects.

Inhibition of prolyl-4-hydroxylase ameliorates chronic rejection of mouse kidney allografts

Interstitial fibrosis, glomerulosclerosis and arteriosclerosis are the major components of chronic allograft nephropathy (CAN), the leading cause of late graft failure after transplantation. To investigate the mechanism of collagen deposition in CAN, we studied the effects of prolyl-hydroxylase inhibitor (PHI), an enzyme essential for collagen formation, using a mouse model of kidney transplantation. Kidneys from H-2b mice were transplanted into MHC-incompatible H-2d recipients (allografts) and at 3 weeks post-transplant, received either PHI or vehicle treatment daily for 3 weeks. At 6 weeks post-transplant, GFR was significantly improved in the allografts receiving PHI (3.3 +/- 0.5 mL/min/kg) compared with those receiving vehicle (1.8 +/- 0.5 mL/min/kg, p < 0.05), while renal function was relatively unimpaired in the nonrejecting isografts (6.45 +/- 0.53 mL/min/kg). Allografts had histologic changes of CAN but the severity was significantly reduced with PHI treatment compared with vehicle, with reductions in interstitial inflammation and fibrosis. Furthermore, TGFâ and connective tissue growth factor mRNA expression was enhanced in both allograft groups compared with the isografts. In conclusion, PHI-treated allografts had improved renal function and reduced the severity of renal injury as a result of CAN. Inhibition of matrix synthesis may be a useful adjunct in ameliorating the development of CAN in humans.

Absence of donor MHC antigen expression ameliorates chronic kidney allograft rejection

BACKGROUND

In previous studies, we have demonstrated that a subset of mouse kidney allografts has prolonged survival without any immunosuppressive treatment. Chronic rejection (CR) develops in these long surviving grafts. The pathologic features of CR in this model are similar to CR in human kidney grafts.

METHODS

To explore the role of donor major histocompatibility complex (MHC) antigens in the development of CR, we performed vascularized kidney transplants using kidneys from donor mice that lack expression of both MHC class I and II antigens (MHC-/-).

RESULTS

Survival was significantly improved in recipients of MHC-/- allografts. This enhanced survival was associated with higher glomerular filtration rate (GFR) in MHC-/- allografts (4.92 +/- 0.54 cc/min/kg) compared to controls (2.19 +/- 0.63 cc/min/kg; P = 0.004). The typical histologic features of CR were markedly reduced in MHC-/- allografts. Semiquantitative histopathological scores for MHC-/- grafts (13.3 +/- 2.1) were significantly lower than in control allografts (19.0 +/- 1.0; P = 0.04). Along with this improvement in structural abnormalities, significantly fewer CD4+ T (38.3 cells/mm(2) vs. 75.0 cells/mm(2); P = 0.008), CD8+ T cells (38.7 vs. 96 cells/mm(2), respectively; P = 0.008) and macrophages (60 vs. 134 cells/mm(2), respectively; P = 0.04) infiltrated MHC-/- allografts compared to controls. The levels of intragraft cytokine mRNA expression also were reduced in MHC-/- allografts compared to control allografts. Finally, serum alloantibodies were virtually undetectable in recipients of MHC-/- kidney allografts.

CONCLUSIONS

Cell surface expression of donor MHC antigens promotes the development of CR. Donor antigen expression promotes the accumulation of infiltrating cells in the graft and the development of donor specific alloantibodies. Abrogation of these responses is associated with improved graft survival and reduced CR in MHC-/- grafts.

The role of the class II transactivator (CIITA) in MHC class I and II regulation and graft rejection in kidney

Class II transactivator (CIITA) induces transcription of MHC class II genes, and induces class I in some cell lines. We examined the effect of CIITA deficiency on class I and II expression in mouse kidney. In CIITA knockout (CIITAKO) mice, basal class II was absent, but class I levels were mildly but significantly increased. Allogeneic stimulation or ischemic injury increased class I and II expression in kidneys of control (wild-type, WT) mice but induced only class I in CIITAKO mice. Thus, in kidney, all basal and induced class II expression was CIITA-dependent, but neither basal nor induced class I was CIITA-dependent. Rejecting kidney allografts from CIITAKO mice in CBA hosts manifested intense induction of donor class I but no donor class II expression. Rejecting kidneys from both WT and CIITAKO donors showed predominantly CD8 T-cell infiltration at days 7 and 21, with increasing tubulitis and arteritis at day 21. CIITAKO kidneys showed fewer infiltrating cells than WT kidneys at day 21. Thus CIITA-deficient kidneys have no basal and induced class II expression but display intense induction of class I expression, and evoke typical rejection lesions, although some indices of infiltration are reduced at day 21.