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Mouse Models of Renal Allograft Transplant Rejection: Methods to Investigate Chemokine–GAG Interaction and Therapeutic Blockade
Abstract
Chemokine–glycosaminoglycan (GAG) interactions direct immune cell activation and invasion, e.g., directing immune cells to sites of infection or injury, and are central to initiating immune responses. Acute innate and also adaptive or antibody-mediated immune cell responses both drive damage to kidney transplants. These immune responses are central to allograft rejection and transplant failure. While treatment for acute rejection has advanced greatly, ongoing or chronic immune damage from inflammation and antibody-mediated rejection remains a significant problem, leading to transplant loss. There are limited numbers of organs available for transplant, and preventing chronic graft damage will allow for longer graft stability and function, reducing the need for repeat transplantation. Chemokine–GAG interactions are the basis for initial immune responses, forming directional gradients that allow immune cells to traverse the vascular endothelium and enter engrafted organs. Targeting chemokine–GAG interactions thus has the potential to reduce immune damage to transplanted kidneys. Mouse models for renal transplant are available, but are complex and require extensive microsurgery expertise. Here we describe simplified subcapsular and subcutaneous renal allograft transplant models, for rapid assessment of the roles of chemokine–GAG interactions during allograft surgery and rejection. These models are described, together with treatment using a unique chemokine modulating protein (CMP) M-T7 that disrupts chemokine–GAG interactions.
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Immune cell invasion after the transplantation of solid organs is directed by chemokines binding to glycosaminoglycans (GAGs), creating gradients that guide immune cell infiltration. Renal transplant is the preferred treatment for end stage renal failure, but organ supply is limited and allografts are often injured during transport, surgery or by cytokine storm in deceased donors. While treatment for adaptive immune responses during rejection is excellent, treatment for early inflammatory damage is less effective. Viruses have developed highly active chemokine inhibitors as a means to evade host responses. The myxoma virus-derived M-T7 protein blocks chemokine: GAG binding. We have investigated M-T7 and also antisense (ASO) as pre-treatments to modify chemokine: GAG interactions to reduce donor organ damage. Immediate pre-treatment of donor kidneys with M-T7 to block chemokine: GAG binding significantly reduced the inflammation and scarring in subcapsular and subcutaneous allografts. Antisense to N-deacetylase N-sulfotransferase1 (ASONdst1) that modifies heparan sulfate, was less effective with immediate pre-treatment, but reduced scarring and C4d staining with donor pre-treatment for 7 days before transplantation. Grafts with conditional Ndst1 deficiency had reduced inflammation. Local inhibition of chemokine: GAG binding in donor organs immediately prior to transplant provides a new approach to reduce transplant damage and graft loss.
The damage of the endothelial glycocalyx as a consequence of ischemia and/or reperfusion injury (IRI) following kidney transplantation has come at the spotlight of research due to potential associations with delayed graft function, acute rejection as well as long-term allograft dysfunction. The disintegration of the endothelial glycocalyx induced by IRI is the crucial event which exposes the denuded endothelial cells to further inflammatory and oxidative damage. The aim of our review is to present the currently available data regarding complex links between shedding of the glycocalyx components, like syndecan-1, hyaluronan, heparan sulphate, and CD44 with the activation of intricate immune system responses, including toll-like receptors, cytokines and pro-inflammatory transcription factors. Evidence on modes of protection of the endothelial glycocalyx and subsequently maintenance of endothelial permeability as well as novel nephroprotective molecules such as sphingosine-1 phosphate (S1P), are also depicted. Although advances in technology are making the visualization and the analysis of the endothelial glycocalyx possible, currently available evidence is mostly experimental. Ongoing progress in understanding the complex impact of IRI on the endothelial glycocalyx, opens up a new era of research in the field of organ transplantation and clinical studies are of utmost importance for the future.
Background/aim
Diabetes mellitus (DM) is a serious, chronic and epidemic disease. Its effective therapy with exogenous insulin places an overwhelming burden on the patient's lifestyle. Moreover, pancreatic islet transplantation is limited by the scarceness of donors and the need for chronic immunosuppression. Cell-based therapy is considered an alternative source of insulin-producing cells (IPCs); encapsulating such cellular grafts in immunoisolating devices would protect the graft from immune attack without the need for immunosuppression. Herein, we investigate the ability of TheraCyte capsule as an immunoisolating device to promote the maturation of differentiated rat bone marrow derived mesenchymal stem cells (BM-MSCs), transplanted subcutaneously to treat diabetic rats in comparison with intratesticular transplantation.
Main methods
Rat BM-MSC were differentiated into IPCs, and either encapsulated in TheraCyte capsules for subcutaneous transplantation or transplanted intratesticular into diabetic rats. Serum insulin, C-peptide & blood glucose levels of transplanted animals were monitored. Retrieved cells were further characterized by immunofluorescence staining and gene expression analysis.
Key findings
Differentiated rat BM-MSC were able to produce insulin in vitro, ameliorate hyperglycemia in vivo and survive for 6 months post transplantation. Transplanted cells induced higher levels of insulin and C-peptide, lower levels of blood glucose in the cured animals of both experimental groups. Gene expression revealed a further in vivo maturation of the implanted cells.
Significance
These data suggest that TheraCyte encapsulation of allogeneic differentiated stem cells are capable of reversing hyperglycemia, which holds a great promise as a new cell based, clinically applicable therapies for diabetes.
Leukocyte migration into tissues depends on the activity of chemokines that form concentration gradients to guide leukocytes to a specific site. Interaction of chemokines with their specific G protein-coupled receptors (GPCRs) on leukocytes induces leukocyte adhesion to the endothelial cells, followed by extravasation of the leukocytes and subsequent directed migration along the chemotactic gradient. Interaction of chemokines with glycosaminoglycans (GAGs) is crucial for extravasation in vivo. Chemokines need to interact with GAGs on endothelial cells and in the extracellular matrix in tissues in order to be presented on the endothelium of blood vessels and to create a concentration gradient. Local chemokine retention establishes a chemokine gradient and prevents diffusion and degradation. During the last two decades, research aiming at reducing chemokine activity mainly focused on the identification of inhibitors of the interaction between chemokines and their cognate GPCRs. This approach only resulted in limited success. However, an alternative strategy, targeting chemokine-GAG interactions, may be a promising approach to inhibit chemokine activity and inflammation. On this line, proteins derived from viruses and parasites that bind chemokines or GAGs may have the potential to interfere with chemokine-GAG interactions. Alternatively, chemokine mimetics, including truncated chemokines and mutant chemokines, can compete with chemokines for binding to GAGs. Such truncated or mutated chemokines are characterized by a strong binding affinity for GAGs and abrogated binding to their chemokine receptors. Finally, Spiegelmers that mask the GAG-binding site on chemokines, thereby preventing chemokine-GAG interactions, were developed. In this review, the importance of GAGs for chemokine activity in vivo and strategies that could be employed to target chemokine-GAG interactions will be discussed in the context of inflammation.
Kidney transplantation is considered the favored treatment for patients suffering from end-stage renal disease, since successful transplantation is associated with longer survival and improved quality of life compared to dialysis. Alloreactive immune responses against the donor kidney may lead to acute rejection of the transplant. The current diagnosis of renal allograft rejection mainly relies on clinical monitoring, including serum creatinine, proteinuria, and confirmation by histopathologic assessment in the kidney transplant biopsy. These parameters have their limitations. Identification and validation of biomarkers, which correlate with or predict the presence of acute rejection, and which could improve therapeutic decision making, are priorities for the transplantation community. There is a need for alternative, less invasive but sensitive markers to diagnose acute graft rejection. Here, we provide an overview of the current status on research of biomarkers of acute kidney transplant rejection in blood and urine. We specifically discuss relatively novel research strategies in biomarker research, including transcriptomics and proteomics, and elaborate on donor-derived cell-free DNA as a potential biomarker.
Early damage to transplanted organs initiates excess inflammation that can cause ongoing injury, a leading cause for late graft loss. The endothelial glycocalyx modulates immune reactions and chemokine-mediated haptotaxis, potentially driving graft loss. In prior work, conditional deficiency of the glycocalyx-modifying enzyme N-deacetylase-N-sulfotransferase-1 (Ndst1f/f TekCre+) reduced aortic allograft inflammation. Here we investigated modification of heparan sulfate (HS) and chemokine interactions in whole-organ renal allografts. Conditional donor allograft Ndst1 deficiency (Ndst1−/−; C57Bl/6 background) was compared to systemic treatment with M-T7, a broad-spectrum chemokine-glycosaminoglycan (GAG) inhibitor. Early rejection was significantly reduced in Ndst1−/− kidneys engrafted into wildtype BALB/c mice (Ndst1+/+) and comparable to M-T7 treatment in C57Bl/6 allografts (P < 0.0081). M-T7 lost activity in Ndst1−/− allografts, while M-T7 point mutants with modified GAG-chemokine binding displayed a range of anti-rejection activity. CD3+ T cells (P < 0.0001), HS (P < 0.005) and CXC chemokine staining (P < 0.012), gene expression in NFκB and JAK/STAT pathways, and HS and CS disaccharide content were significantly altered with reduced rejection. Transplant of donor allografts with conditional Ndst1 deficiency exhibit significantly reduced acute rejection, comparable to systemic chemokine-GAG inhibition. Modified disaccharides in engrafted organs correlate with reduced rejection. Altered disaccharides in engrafted organs provide markers for rejection with potential to guide new therapeutic approaches in allograft rejection.
The Banff Classification of Allograft Pathology is an international consensus classification for the reporting of biopsies from solid organ transplants. Since its initial conception in 1991 for renal transplants, it has undergone review every 2 years, with attendant updated publications. The rapid expansion of knowledge in the field has led to numerous revisions of the classification. The resultant dispersal of relevant content makes it difficult for novices and experienced pathologists to faithfully apply the classification in routine diagnostic work and in clinical trials.This review shall provide a complete and simple illustrated reference guide of the Banff Classification of Kidney Allograft Pathology based on all publications including the 2017 update. It is intended as a concise desktop reference for pathologists and clinicians, providing definitions, Banff Lesion Scores and Banff Diagnostic Categories. An online website reference guide hosted by the Banff Foundation for Allograft Pathology (www.banfffoundation.org) is being developed, which will be updated with future refinement of the Banff Classification from 2019 onwards.This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.
Kidney transplantation entails a high likelihood of endothelial injury. The endothelium is a target of choice for injury by ischemia-reperfusion, alloantibodies, and autoantibodies. A certain degree of ischemia-reperfusion injury inevitably occurs in the immediate posttransplant setting and can manifest as delayed graft function. Acute rejection episodes, whether T-cell or antibody-mediated, can involve the graft micro- and macrovasculature, leading to endothelial injury and adverse long-term consequences on graft function and survival. In turn, caspase-3 activation in injured and dying endothelial cells favors the release of extracellular vesicles (apoptotic bodies and apoptotic exosome-like vesicles) that further enhance autoantibody production, complement deposition, and microvascular rarefaction. In this review, we present the evidence for endothelial injury, its causes and long-term consequences on graft outcomes in the field of kidney transplantation.
Human pluripotent stem cell (hPSC)-derived kidney organoids may facilitate disease modeling and the generation of tissue for renal replacement. Long-term application, however, will require transferability between hPSC lines and significant improvements in organ maturation. A key question is whether time or a patent vasculature is required for ongoing morphogenesis. Here, we show that hPSC-derived kidney organoids, derived in fully defined medium conditions and in the absence of any exogenous vascular endothelial growth factor, develop host-derived vascularization. In vivo imaging of organoids under the kidney capsule confirms functional glomerular perfusion as well as connection to pre-existing vascular networks in the organoids. Wide-field electron microscopy demonstrates that transplantation results in formation of a glomerular basement membrane, fenestrated endothelial cells, and podocyte foot processes. Furthermore, compared with non-transplanted organoids, polarization and segmental specialization of tubular epithelium are observed. These data demonstrate that functional vascularization is required for progressive morphogenesis of human kidney organoids.
Purpose of Review
We will review the recent developments of cell sheet technology as a feasible tissue engineering approach. Specifically, we will focus on the technological advancement for engineering functional liver tissue using cell sheet technology, and the associated therapeutic effect of cell sheets for liver diseases, highlighting hemophilia.
Recent Findings
Cell-based therapies using hepatocytes have recently been explored as a new therapeutic modality for patients with many forms of liver disease. We have developed a cell sheet technology, which allows cells to be harvested in a monolithic layer format. We have succeeded in fabricating functional liver tissues in mice by stacking the cell sheets composed of primary hepatocytes. As a curative measure for hemophilia, we have also succeeded in treating hemophilia mice by transplanting of cells sheets composed of genetically modified autologous cells.
Summary
Tissue engineering using cell sheet technology provides the opportunity to create new therapeutic options for patients with various types of liver diseases.
The skin is a complex organ that, in addition to providing a strong barrier against external insults, serves as an arena for a wide variety of inflammatory processes, including immunity against infections, tumor immunity, autoimmunity, and allergy. A variety of cells collaborate to mount functional immune responses, which are initiated by resident populations and evolve through the recruitment of additional cell populations to the skin. Inflammatory responses are quite diverse, resulting in a wide range of signs and symptoms that depend on the initiating signals, characteristics of the infiltrating cell populations, and cytokines that are produced (cytokines are secreted protein that allows for cell-cell communication; usually refers to communication between immune-immune cells or stromal-immune cells). In this work, we will review the skin architecture and resident and recruited cell populations and discuss how these populations contribute to inflammation using human diseases and treatments when possible to illustrate their importance within a clinical context.
Copyright © 2014 Cold Spring Harbor Laboratory Press; all rights reserved.
Oxidative stress is a major and recurring cause of damage during inflammation, especially following organ transplantation. Initial ischaemia-reperfusion injury causes the production of many reactive oxygen and nitrogen species, and subsequent recruitment and activation of inflammatory cells can lead to further oxidative stress. This stress is well known to cause damage at the cellular level, for example by induction of senescence leading to the production of a characteristic senescence associated secretory phenotype (SASP). Chemokines are an important component of the SASP, recruiting further leukocytes and reinforcing the stress and senescence responses. As well as inducing the production of proteins, including chemokines, oxidative stress can alter proteins themselves, both directly and by induction of enzymes capable of modification. These alterations can lead to important modifications to their biological activity and also alter detection by some antibodies, potentially limiting the biological relevance of some immunochemical and proteomic biomarkers. Peroxynitrite, a reactive nitrogen species generated during inflammation and ischaemia, can cause such modifications by nitrating chemokines. Matrix metalloproteinases, released by many stressed cells, can cleave chemokines, altering function, whilst peptidylarginine deiminases can inactivate certain chemokines by citrullination. This review discusses the relationship between inflammation and post-translational modification, focussing on the functional modulation of transplant-relevant pro-inflammatory chemokines. This article is protected by copyright. All rights reserved.
Brain death is associated with dramatic and serious pathophysiologic changes that adversely affect both the quantity and quality of organs available for transplant. To fully optimise the donor pool necessitates a more complete understanding of the underlying pathophysiology of organ dysfunction associated with transplantation. These injurious processes are initially triggered by catastrophic brain injury and are further enhanced during both brain death and graft transplantation. The activated inflammatory systems then contribute to graft dysfunction in the recipient. Inflammatory mediators drive this process in concert with the innate and adaptive immune systems. Activation of deleterious immunological pathways in organ grafts occurs, priming them for further inflammation after engraftment. Finally, posttransplantation ischaemia reperfusion injury leads to further generation of inflammatory mediators and consequent activation of the recipient's immune system. Ongoing research has identified key mediators that contribute to the inflammatory milieu inherent in brain dead organ donation. This has seen the development of novel therapies that directly target the inflammatory cascade.
Obliterative bronchiolitis, characterized histopathologically by airway inflammation and occlusion of small airways by vascularized fibrous tissue, constitutes an important threat to the long-term survival of lung and heart-lung transplant recipients. The pathogenesis of obliterative bronchiolitis is poorly understood, and successful preventative or treatment strategies are not available. We sought to develop a preclinical model system of obliterative bronchiolitis by transplanting murine airway grafts, consisting of tracheas and main bronchi, into the subcutaneous tissue of allogeneically mismatched recipient animals. By 10 days after transplantation, allografts demonstrated subepithelial and/or peritracheal inflammation, epithelial necrosis, and early fibroproliferation. Grafts harvested 21 days after transplantation demonstrated fibroproliferation in the airway wall or lumen in nine of 10 allografts versus 0 of 10 isografts (P = 0.0001). In addition, abnormal epithelium (ie, nonciliated cuboidal, squamous, or absent) was seen in all allografts, while nine of nine isografts demonstrated normal respiratory epithelium (P = 0.0003). Although differences exist between this model and the chronic rejection process in human lung transplant recipients, these findings reproduce the characteristic features of obliterative bronchiolitis and demonstrate that this lesion can result from allograft rejection. This model will be useful for studying the pathogenesis, prevention, and treatment of obliterative bronchiolitis after lung transplantation.
Solid tissue transplant is a growing medical need that is further complicated by a limited donor organ supply. Acute and chronic rejection occurs in nearly all transplants and reduces long-term graft survival, thus increasing the need for repeat transplantation. Viruses have evolved highly adapted responses designed to evade the host’s immune defenses. Immunomodulatory proteins derived from viruses represent a novel class of potential therapeutics that are under investigation as biologics to attenuate immune-mediated rejection and damage. These immune-modulating proteins have the potential to reduce the need for traditional posttransplant immune suppressants and improve graft survival. The myxoma virus-derived protein M-T7 is a promising biologic that targets chemokine and glycosaminoglycan pathways central to kidney transplant rejection. Orthotopic transplantations in mice are prohibitively difficult and costly and require a highly trained microsurgeon to successfully perform the procedure. Here we describe a kidney-to-kidney subcapsular transplant model as a practical and simple method for studying transplant rejection, a model that requires fewer mice. One kidney can be used as a donor for transplants into six or more recipient mice. Using this model there is lower morbidity, pain, and mortality for the mice. Subcapsular kidney transplantation provides a first step approach to testing virus-derived proteins as new potential immune-modulating therapeutics to reduce transplant rejection and inflammation.
Background. Subcutaneous pockets provide an extrahepatic transplant site for islet grafting to treat type 1 diabetes. However, a hypoxic environment may cause central ne-crosis to islets and lead to graft failure. Our previous studies focused on a pre-treated subcutaneous site with basic fibroblast growth factor (bFGF) for the formation of vascular bed. In addition to neovascularization, bFGF was also shown to protect islets against oxidative stress and chemical-induced damage in vitro. Accordingly, we propose that subcutaneous islet transplantation with a bFGF-slow releasing device simultaneously can improve islet survival in vivo. Methods. A bFGF-impregnated collagen sheet was implanted in the right back of a streptozotocin-induced diabetic mouse for neovascularization. After 10 days, the sheet was removed and the rat islet-embedding gel within the immune-isolation device was transplanted (2-time operation [OP]). In another group, the diabetic mice received bFGF-impregnated gel with rat islets within the immune-isolation device simultaneously (1-time OP). Results. Diabetic mice in 2-time OP group experienced a decrease in their non-fasting blood glucose level for a period of 10 days, and the glucose levels were lower than those of untreated diabetic mice post-implantation. However, the mice in the 1-time OP group remained hyperglycemic post-operation and showed no improvements in body weight or the area under curve in intraperitoneal glucose tolerance test. Furthermore, mice in the 2-time OP had relatively higher serum insulin levels with improved renal and metabolic biomarkers. Conclusion. Our findings suggest that bFGF had no beneficial effect on a 1-time operation in subcutaneous islet transplantation. P ANCREATIC islet transplantation can be performed using a minimally invasive approach that involves infusing the isolated islets through the portal vein into the liver of the recipient for type 1 diabetes [1]. However, the instant blood-mediated inflammatory reaction is known to kill off more than 50% of infused islets immediately after transplantation. Oxidative stress and proinflammatory cytokines also deteriorate islet survival and function [2]. Many research groups have evaluated other transplant sites such as kidney subcapsular spaces and intramedullary cavities for islet transplantation, although accessibility remains a concern. However, subcutaneous tissue, which provides several advantages, including sufficient capacity, low morbidity rate, easy surgical procedure, minimal
Ischemia-reperfusion injury (IRI) is a clinically important cause of acute kidney injury leading to chronic kidney disease. Furthermore, IRI in renal transplantation still remains a risk factor for delayed graft function.Previous studies on IRI have had some limitations and few of the studied therapies have been clinically applicable. Therefore, a new method for treating renal IRI is needed. We examined the effects of human mesothelial cell (MC) sheets and hepatocyte growth factor (HGF)-transgenic mesothelial cell (HGF-tg MC) sheets transplanted under the renal capsule in an IRI rat model, and compared these two treatments with the intravenous administration of HGF protein and no treatment through serum, histological, and mRNA analyses over 28 days. The MC sheets and HGF-tg MC sheets produced HGF protein and significantly improved acute renal dysfunction, acute tubular necrosis, and survival rate. The improvement in necrosis was likely due to the cell sheets promoting the migration and proliferation of renal tubular cells, as observed in vitro. Expression of alpha smooth muscle actin at day 14 and renal fibrosis at day 28 after IRI were significantly suppressed in the MC sheet and HGF-tg MC sheet treatment groups compared with the other groups, and these effects tended to be reinforced by the HGF-tg MC sheets. These results suggest that the cell sheets locally and continuously affect renal paracrine factors, such as HGF, and support recovery from acute tubular necrosis and improvement of renal fibrosis in chronic disease.
It has become evident that nonlymphoid tissues are populated by distinct subsets of innate and adaptive lymphocytes that are characterized by minimal exchange with recirculating counterparts. Especially at barrier sites, such as the skin, gut, and lung, these tissue-resident lymphocyte populations are ideally positioned to quickly respond to pathogens and other environmental stimuli. The kidney harbors several classes of innate and innate-like lymphocytes that have been described to contribute to this tissue-resident population in other organs, including innate lymphoid cells, natural killer cells, natural killer T cells, mucosal-associated invariant T cells, and γδ T cells. Additionally, a substantial proportion of the adaptive lymphocytes that are found in the kidney displays a surface phenotype suggestive of tissue residency, such as CD69(+)CD4(+) T cells. In this review, we summarize recent advances in the understanding of tissue-resident lymphocyte populations, review the available evidence for the existence of these populations in the kidney, and discuss the potential physiologic and pathophysiologic roles thereof in kidney.
Subcutaneous tissue is a promising site for islet transplantation, due to its large area and accessibility, which allows minimally invasive procedures for transplantation, graft monitoring, and removal of malignancies as needed. However, relative to the conventional intrahepatic transplantation site, the subcutaneous site requires a large number of islets to achieve engraftment success and diabetes reversal, due to hypoxia and low vascularity. We report that the efficiency of subcutaneous islet transplantation in a Lewis rat model is significantly improved by treating recipients with inhaled 50% oxygen, in conjunction with prevascularization of the graft bed by agarose-bFGF. Administration of 50% oxygen increased oxygen tension in the subcutaneous site to 140 mmHg, compared to 45 mmHg under ambient air. In vitro, islets cultured under 140 mmHg oxygen showed reduced central necrosis and increased insulin release, compared to those maintained in 45 mmHg oxygen. Six hundred syngeneic islets subcutaneously transplanted into the prevascularized graft bed reversed diabetes when combined with post-operative 50% oxygen inhalation for 3 days, a number comparable to that required for intrahepatic transplantation; in the absence of oxygen treatment, diabetes was not reversed. Thus, we show oxygen inhalation to be a simple and promising approach to successfully establishing subcutaneous islet transplantation.
Perfecting tissue engineering and cell sheet transplantation is an important step toward realizing regenerative medicine and is a growing area of research. Before being applied to clinical settings, it is important that these approaches are evaluated in vivo. Here we provide a detailed protocol for handling thin cell sheets, for a simple and highly reproducible subcutaneous transplantation of cell sheets into mice, and for the histological examination of regenerated tissues. Various aspects of transplants can be assessed, such as maintenance, differentiation and proliferation. An emphasis is placed on surgical precision and reproducibility. The resulting consistency between surgeries helps minimize artifacts from surgical variation and therefore enables researchers to not only observe and compare the interactions between host tissues but also to compare transplants among different host animals. A single transplantation can be carried out within ∼10 min.
In order to investigate the importance of the transplantation site for the replication of grafted islet cells, we implanted syngeneic mouse pancreatic islets intrasplenically, intraportally and subcapsularly in the kidney. Fourteen days later the alloxan-diabetic mice were killed after an injection of tritiated thymidine, and the graft-bearing organs fixed and processed for autoradiography. The highest labelling indices were recorded for subcapsularly grafted islets, followed by intraportal and intrasplenic islets in that order. In separate experiments some islet-containing kidney sections were immune stained for insulin before the autoradiographic process. The labelling index of the insulin-positive cells was as high as in the entire islet cell population of the sections from the same mice stained with haematoxylin only. This indicates that the B cells of the islets replicate as often as the other islet cell types. The present data also suggest that the renal subcapsular space offers better growth conditions for transplanted islet cells than the liver or spleen.
To determine whether corneal tissue as an allograft displays immune privilege in a nonprivileged site and, if so, whether CD95 ligand expression contributes to the privileged status.
Syngenic and allogeneic corneal tissues deprived of epithelium were transplanted beneath the kidney capsule of normal mice. Syngeneic BALB/c, allogeneic C57BL/6, and allogeneic B6Smn.C3H-gld (CD95 ligand-deficient) mice were used as donors for BALB/c recipients, and syngeneic C3H/HeJ-gld (CD95 ligand-deficient) mice were used for normal C3H/HeJ recipients. Allogeneic conjunctival segments served as positive grafting controls. Graft fate was assessed by visual inspection at 4, 7, 14, and 21 days and was confirmed by histologic study. Viability of graft endothelium was assessed by immunocytochemical analysis.
Syngeneic corneas and C57BL/6 corneas survived almost indefinitely beneath the kidney capsule. Both the stroma and the endothelial layers remained healthy and intact. Allogeneic conjunctiva evoked a strong inflammatory response attended by neovascularization. Similarly, B6-gld corneas deficient in CD95 ligand expression showed acute destruction beneath the kidney capsule. Circumstantial evidence implicates alloimmune rejection as the mechanism.
Epithelium-deprived corneas from normal mice possess inherent immune privilege that protects them from alloimmune rejection even at nonprivileged sites. Constitutive expression of CD95 ligand contributes to the privileged status. It is inferred that the extraordinary success of orthotopic corneal allografts owes as much to the qualities of the graft as an immune-privileged tissue as to the qualities of the eye as an immune-privileged site.