In vivo imaging of a diabetogenic CD8+ T cell response during type 1 diabetes progression

Advances of functional nanomaterials for magnetic resonance imaging and biomedical engineering applications

Functional nanomaterials have been widely used in biomedical fields due to their good biocompatibility, excellent physicochemical properties, easy surface modification, and easy regulation of size and morphology. Functional nanomaterials for magnetic resonance imaging (MRI) can target specific sites in vivo and more easily detect disease-related specific biomarkers at the molecular and cellular levels than traditional contrast agents, achieving a broad application prospect in MRI. This review focuses on the basic principles of MRI, the classification, synthesis and surface modification methods of contrast agents, and their clinical applications to provide guidance for designing novel contrast agents and optimizing the contrast effect. Furthermore, the latest biomedical advances of functional nanomaterials in medical diagnosis and disease detection, disease treatment, the combination of diagnosis and treatment (theranostics), multi-model imaging and nanozyme are also summarized and discussed. Finally, the bright application prospects of functional nanomaterials in biomedicine are emphasized and the urgent need to achieve significant breakthroughs in the industrial transformation and the clinical translation is proposed. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Correcting for imaging gradients-related bias of T2 relaxation times at high-resolution MRI

Purpose

High‐resolution animal imaging is an integral part of preclinical drug development and the investigation of diseases' pathophysiology. Quantitative mapping of T₂ relaxation times (qT₂) is a valuable tool for both preclinical and research applications, providing high sensitivity to subtle tissue pathologies. High‐resolution T₂ mapping, however, suffers from severe underestimation of T₂ values due to molecular diffusion. This affects both single‐echo and multi‐echo spin echo (SSE and MESE), on top of the well‐known contamination of MESE signals by stimulated echoes, and especially on high‐field and preclinical scanners in which high imaging gradients are used in comparison to clinical scanners.

Methods

Diffusion bias due to imaging gradients was analyzed by quantifying the effective b‐value for each coherence pathway in SSE and MESE protocols, and incorporating this information in a joint T₂‐diffusion reconstruction algorithm. Validation was done on phantoms and in vivo mouse brain using a 9.4T and a 7T MRI scanner.

Results

Underestimation of T₂ values due to strong imaging gradients can reach up to 70%, depending on scan parameters and on the sample's diffusion coefficient. The algorithm presented here produced T₂ values that agreed with reference spectroscopic measurements, were reproducible across scan settings, and reduced the average bias of T₂ values from −33.5 ± 20.5% to −0.1 ± 3.6%.

Conclusions

A new joint T₂‐diffusion reconstruction algorithm is able to negate imaging gradient–related underestimation of T₂ values, leading to reliable mapping of T₂ values at high resolutions.

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Nanoparticle-based autoimmune disease therapy

The goal of immunotherapy against autoimmunity is to block pathogenic inflammation without impairing immunity against infections and tumours. Regulatory T-cells (Tregs) play a central role in maintaining immune homeostasis, and autoimmune inflammation is frequently associated with decreased numbers and/or function of these T-cells. Therapies harnessing Tregs to treat autoimmune inflammation remain under-developed with caveats ranging from the lack of antigenic and disease specificity to the potential phenotypic and functional instability of in vitro-expanded Treg cells in vivo. Here, we review nanotechnology-based approaches designed to promote immune tolerance through various mechanisms, ranging from systemic or local suppression of antigen-presenting cells and deletion of antigen-specific T-cells, to the systemic expansion of antigen- and disease-specific Treg cells in vivo.

Nanomedicine in autoimmunity

The application of nanotechnology to the diagnosis and therapy of human diseases is already a reality and is causing a real revolution in how we design new therapies and vaccines. In this review we focus on the applications of nanotechnology in the field of autoimmunity. First, we review scenarios in which iron oxide nanoparticles have been used in the diagnosis of autoimmune diseases, mostly through magnetic resonance imaging (MRI), both in animal models and patients. Second, we discuss the potential of nanoparticles as an immunotherapeutic platform for autoimmune diseases, for now exclusively in pre-clinical models. Finally, we discuss the potential of this field to generate the 'perfect drug' with the capacity to report on its therapeutic efficacy in real time, that is, the birth of theranostics in autoimmunity.

Immune rejection after pancreatic islet cell transplantation: in vivo dual contrast-enhanced MR imaging in a mouse model

PURPOSE

To detect adoptively transferred immune attack in a mouse model of islet cell transplantation by using a long-circulating paramagnetic T1 contrast agent, a protected graft copolymer (PGC) that is covalently linked to gadolinium-diethylenetriaminepentaacetic acid with fluorescein isothiocyanate (Gd-DTPA-F), which accumulates in the sites of inflammation that are characterized by vascular disruption.

MATERIALS AND METHODS

All animal experiments were performed in compliance with institutional guidelines and approved by the subcommittee on research animal care. Six nonobese diabetic severe combined immunodeficiency mice received transplanted human islet cells under the kidney capsule and adoptively transferred 5 × 10(6) splenocytes from 6-week-old nonobese diabetic mice. These mice also served as control subjects for comparison of pre- and postadoptive transfer MR imaging results. Mice that received phosphate-buffered saline solution only were included as nonadoptive-transfer control subjects (n = 2). In vivo magnetic resonance (MR) imaging was performed before and 17 hours after intravenous injections of PGC-Gd-DTPA-F, followed by histologic examination. Statistical differences were analyzed by means of a paired Student t test and repeated two-way analysis of variance.

RESULTS

MR imaging results showed significantly greater accumulation of PGC-Gd-DTPA-F in the graft area after immune attack initiated by adoptive transfer of splenocytes compared with that of the same area before the transfer (T1, 137.2 msec ± 39.3 and 239.5 msec ± 17.6, respectively; P < .001). These results were confirmed at histologic examination, which showed considerable leakage of the contrast agent into the islet cell interstitium.

CONCLUSION

PGC-Gd-DTPA-F-enhanced MR imaging allows for the in vivo assessment of vascular damage of the graft T cell challenge.

Theranostic magnetic resonance imaging of type 1 diabetes and pancreatic islet transplantation

Type 1 diabetes mellitus results in impaired insulin production by pancreatic islets due to autoimmunity. Islet transplantation has recently emerged as a promising treatment for this disease. To visualize and monitor endogenous and transplanted islets, non-invasive strategies are currently being developed. These include strategies for in vivo magnetic resonance imaging of microvascular changes during diabetes development, tracking the recruitment of diabetogenic T cells to the pancreas, and imaging of endogenous and transplanted islet mass. The combination of MR imaging agents with therapy is a novel state-of-the-art theranostic approach that has a tremendous potential for type 1 diabetes management. Though still in its infancy, theranostic MR imaging has shown certain encouraging progress. Here we provide an overview of the latest accomplishments in this area as it applies to changes in islet vasculature during diabetes development, monitoring autoimmune attack mediated by T cells, and imaging of transplanted islets. Future challenges and opportunities in the area of theranostic MRI are discussed as well.

Immune biomarkers in immunotherapeutic trials for type 1 diabetes: cui prodest?

Decades of research efforts aimed at upgrading type 1 diabetes (T1DM) treatment did not harvest much success besides improving insulin therapy, which remains the standard of care since 1922. Immunological strategies targeting autoimmune mechanisms, rather than their metabolic consequences, are highly demanded. A dealt of preclinical studies in animal models offered some promises, which were however not maintained once translated into human. All these immune intervention trials evaluated metabolic and clinical endpoints, namely C-peptide secretion, HbA(1c) and insulin requirements. While critical, we argue that these endpoints are insufficient and should be complemented with immune surrogate endpoints, i.e. biomarkers reflecting the immune modifications induced by such treatments. This is even more critical when clinical expectations are not met, in order to sort out the reasons of such failure, i.e. whether immune changes are not accomplished or whether, despite being accomplished, they are insufficient to translate into clinical benefits. Furthermore, these ancillary analyses may give precious indications to design further trials, i.e. to enroll patients with the best odds to respond to therapy and to follow-up their response.

Making the most of major histocompatibility complex molecule multimers: applications in type 1 diabetes

Classical major histocompatibility complex (MHC) class I and II molecules present peptides to cognate T-cell receptors on the surface of T lymphocytes. The specificity with which T cells recognize peptide-MHC (pMHC) complexes has allowed for the utilization of recombinant, multimeric pMHC ligands for the study of minute antigen-specific T-cell populations. In type 1 diabetes (T1D), CD8+ cytotoxic T lymphocytes, in conjunction with CD4+ T helper cells, destroy the insulin-producing β cells within the pancreatic islets of Langerhans. Due to the importance of T cells in the progression of T1D, the ability to monitor and therapeutically target diabetogenic clonotypes of T cells provides a critical tool that could result in the amelioration of the disease. By administering pMHC multimers coupled to fluorophores, nanoparticles, or toxic moieties, researchers have demonstrated the ability to enumerate, track, and delete diabetogenic T-cell clonotypes that are, at least in part, responsible for insulitis; some studies even delay or prevent diabetes onset in the murine model of T1D. This paper will provide a brief overview of pMHC multimer usage in defining the role T-cell subsets play in T1D etiology and the therapeutic potential of pMHC for antigen-specific identification and modulation of diabetogenic T cells.

The use of peptide-major-histocompatibility-complex multimers in type 1 diabetes mellitus

Major histocompatibility complex (MHC) class I and MHC class II molecules present short peptides that are derived from endogenous and exogenous proteins, respectively, to cognate T-cell receptors (TCRs) on the surface of T cells. The exquisite specificity with which T cells recognize particular peptide-major-histocompatibility-complex (pMHC) combinations has permitted development of soluble pMHC multimers that bind exclusively to selected T-cell populations. Because the pathogenesis of type 1 diabetes mellitus (T1DM) is driven largely by islet-reactive T-cell activity that causes β-cell death, these reagents are useful tools for studying and, potentially, for treating this disease. When coupled to fluorophores or paramagnetic nanoparticles, pMHC multimers have been used to visualize the expansion and islet invasion of T-cell effectors during diabetogenesis. Administration of pMHC multimers to mice has been shown to modulate T-cell responses by signaling through the TCR or by delivering a toxic moiety that deletes the targeted T cell. In the nonobese diabetic mouse model of T1DM, a pMHC-I tetramer coupled to a potent ribosome-inactivating toxin caused long-term elimination of a specific diabetogenic cluster of differentiation 8+ T-cell population from the pancreatic islets and delayed the onset of diabetes. This review will provide an overview of the development and use of pMHC multimers, particularly in T1DM, and describe the therapeutic promise these reagents have as an antigen-specific means of ameliorating deleterious T-cell responses in this autoimmune disease.

Labeling of multiple cell lines using a new iron oxide agent for cell tracking by MRI

Stem cells, cancer cells and immune cells were labeled by co-incubation with a new ultra-small iron oxide nanoparticle called Molday ION Rhodamine-B (MIRB). Iron staining, fluorescence imaging, transmission electron microscopy and flow cytometry were used to assess cell viability, function and labeling efficiency. This study has shown that MIRB can be used to label both adherent and nonadherent cell lines, with high viability and loading levels sufficient for their detection in vivo by MRI at 3 T.

Detection of β cell death in diabetes using differentially methylated circulating DNA

In diabetes mellitus, β cell destruction is largely silent and can be detected only after significant loss of insulin secretion capacity. We have developed a method for detecting β cell death in vivo by amplifying and measuring the proportion of insulin 1 DNA from β cells in the serum. By using primers that are specific for DNA methylation patterns in β cells, we have detected circulating copies of β cell-derived demethylated DNA in serum of mice by quantitative PCR. Accordingly, we have identified a relative increase of β cell-derived DNA after induction of diabetes with streptozotocin and during development of diabetes in nonobese diabetic mice. We have extended the use of this assay to measure β cell-derived insulin DNA in human tissues and serum. We found increased levels of demethylated insulin DNA in subjects with new-onset type 1 diabetes compared with age-matched control subjects. Our method provides a noninvasive approach for detecting β cell death in vivo that may be used to track the progression of diabetes and guide its treatment.

The use of cellular magnetic resonance imaging to track the fate of iron-labeled multipotent stromal cells after direct transplantation in a mouse model of spinal cord injury

PURPOSE

The objective of this study was to track the fate of iron-labeled, multipotent stromal cells (MSC) after their direct transplantation into mice with spinal cord injuries using magnetic resonance imaging (MRI).

PROCEDURES

Mice with spinal cord injuries received a direct transplant of (1) live MSC labeled with micron-sized iron oxide particles (MPIO); (2) dead, MPIO-labeled MSC; (3) unlabeled MSC; or (4) free MPIO and were imaged at 3 T for 6 weeks after transplantation.

RESULTS

Live, iron-labeled MSC appeared as a well-defined region of signal loss in the mouse spinal cord at the site of transplant. However, the MR appearance of dead, iron-labeled MSC and free iron particles was similar and persisted for the 6 weeks of the study.

CONCLUSIONS

Iron-labeled stem cells can be detected and monitored in vivo after direct transplantation into the injured spinal cord of mice. However, the fate of the iron label is not clear. Our investigation indicates that caution should be taken when interpreting MR images after direct transplantation of iron-labeled cells.

Immune intervention in type 1 diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease that results in the specific immune destruction of insulin producing beta cells. Currently there is no cure for T1D and treatment for the disease consists of lifelong administration of insulin. Immunotherapies aimed at preventing beta cell destruction in T1D patients with residual c-peptide or in individuals developing T1D are being evaluated. Networks of researchers such as TrialNet and the Immune Tolerance Network in the U.S. and similar networks in Europe have been established to evaluate such immunotherapies. This review focuses on immune intervention for the prevention and amelioration of human T1D with a focus on potential immune suppressive, antigen specific and environmental therapies.

An update on the use of NOD mice to study autoimmune (Type 1) diabetes

The widely used nonobese diabetic (NOD) mouse model of autoimmune (Type 1) diabetes mellitus shares multiple characteristics with the human disease, and studies employing this model continue to yield clinically relevant and important information. Here, we review some of the recent key findings obtained from NOD mouse investigations that have both advanced our understanding of disease pathogenesis and suggested new therapeutic targets and approaches. Areas discussed include antigen discovery, identification of genes and pathways contributing to disease susceptibility, development of strategies to image islet inflammation and the testing of therapeutics. We also review recent technical advances that, combined with an improved understanding of the NOD mouse model's limitations, should work to ensure its popularity, utility and relevance in the years ahead.

T-cell autoantigens in the non-obese diabetic mouse model of autoimmune diabetes

The non-obese diabetic (NOD) mouse model of autoimmune (type 1) diabetes has contributed greatly to our understanding of disease pathogenesis and has facilitated the development and testing of therapeutic strategies to combat the disease. Although the model is a valuable immunological tool in its own right, it reaches its fullest potential in areas where its findings translate to the human disease. Perhaps the foremost example of this is the field of T-cell antigen discovery, from which diverse benefits can be derived, including the development of antigen-specific disease interventions. The majority of NOD T-cell antigens are also targets of T-cell autoimmunity in patients with type 1 diabetes, and several of these are currently being evaluated in clinical trials. Here we review the journeys of these antigens from bench to bedside. We also discuss several recently identified NOD T-cell autoantigens whose translational potential warrants further investigation.

In vivo tracking of 'color-coded' effector, natural and induced regulatory T cells in the allograft response

Here we present methods to longitudinally track islet allograft-infiltrating T cells in live mice by endoscopic confocal microscopy and to analyze circulating T cells by in vivo flow cytometry. We developed a new reporter mouse whose T cell subsets express distinct, 'color-coded' proteins enabling in vivo detection and identification of effector T cells (T(eff) cells) and discrimination between natural and induced regulatory T cells (nT(reg) and iT(reg) cells). Using these tools, we observed marked differences in the T cell response in recipients receiving tolerance-inducing therapy (CD154-specific monoclonal antibody plus rapamycin) compared to untreated controls. These results establish real-time cell tracking as a powerful means to probe the dynamic cellular interplay mediating immunologic rejection or transplant tolerance.

Genetics, pathogenesis and clinical interventions in type 1 diabetes

Type 1 diabetes is an autoimmune disorder afflicting millions of people worldwide. Once diagnosed, patients require lifelong insulin treatment and can experience numerous disease-associated complications. The last decade has seen tremendous advances in elucidating the causes and treatment of the disease based on extensive research both in rodent models of spontaneous diabetes and in humans. Integrating these advances has led to the recognition that the balance between regulatory and effector T cells determines disease risk, timing of disease activation, and disease tempo. Here we describe current progress, the challenges ahead and the new interventions that are being tested to address the unmet need for preventative or curative therapies.

MRI as a tool to monitor islet transplantation

The development of new methods for noninvasive imaging is an area of biotechnology that is of great relevance for the diagnosis and characterization of diabetes mellitus. Noninvasive imaging can be used to study the dynamics of beta-cell mass and function; beta-cell death; vascularity, innervation and autoimmune attack of pancreatic islets; and the efficacy of islet transplantation to remedy beta-cell loss in patients with diabetes mellitus. In this Review, we focus on the application of MRI for monitoring islet transplantation and on the potential causes of islet graft failure, which are still poorly understood. Questions that have been addressed by MRI studies encompass graft longevity, and the effects of immune rejection, glucose toxic effects, and the transplanted islets' purity on graft fate. We also highlight novel technologies for simultaneous imaging and delivery of experimental therapies that aim to extend the lifespan and functionality of islet grafts. On the basis of this evidence, MRI represents a valuable platform for a thorough investigation of beta-cell function in the context of islet transplantation. State-of-the-art multimodality approaches, such as PET-MRI, can extend our current capabilities and help answer the critical questions that currently inhibit the prevention and cure of diabetes mellitus.

Noninvasive imaging of pancreatic beta cells

Noninvasive imaging and quantification of pancreatic, insulin-producing beta cells has been considered a high-priority field of investigation for the past decade. In the first review on this issue, attention was already paid to various agents for labeling beta cells, including 6-(125)I-D-glucose, (65)Zn, (3)H-glibenclamide, (3)H-mitiglinide, an (125)I-labeled mouse monoclonal antibody against beta-cell surface ganglioside(s), D-(U-(14)C)-glucose and 2-deoxy-2-(18)F-D-glucose to label glycogen accumulated in beta cells in response to sustained hyperglycemia, and, last but not least, an analog of D-mannoheptulose. This Review discusses these methods and further contributions. For instance, emphasis is placed on labeling beta cells with (11)C-dihydrotetrabenazine, which is the most advanced method at present. Attention is also drawn to the latest approaches for noninvasive imaging and functional characterization of pancreatic beta cells. None of these procedures is used in clinical practice yet.

Molecular pathway-specific 99mTc-N-(3-bromo-2,4,6-trimethyacetanilide) iminodiacetic acid liver imaging to assess innate immune responses induced by cell transplantation

OBJECTIVES

Inflammatory responses after cell transplantation impair engraftment of transplanted cells. We studied whether perturbations in specific molecular pathways after inflammation in a syngeneic cell transplantation model could be identified by noninvasive imaging.

METHODS

After transplanting hepatocytes into the liver of dipeptidyl peptidase IV-deficient Fischer 344 rats, we imaged hepatobiliary excretion of ppmTc-N-(3-bromo-2,4,6-trimethyacetanilide) iminodiacetic acid (99mTc-mebrofenin). Fractional retention of peak hepatic mebrofenin activity over 60-min periods was correlated with parameters of hepatic inflammation.

RESULTS

In healthy animals, 28+/-6% 99mTc-mebrofenin activity was in the liver after 60 min, whereas cell transplantation dose-dependently inhibited excretion of 99mTc-mebrofenin, P value of less than 0.001. Resolution of this abnormality in 99mTc-mebrofenin transport required 2 weeks in the setting of prolonged activation of Kupffer cells with increased TNF-alpha and IL-6 expression. Hepatic transport of 00mTc-mebrofenin was promptly restored by anti-inflammatory treatments, including inhibition of cyclooxygenase activity, depletion of neutrophils, or blocking of inflammatory cytokines before cell transplantation. Moreover, these treatments improved transplanted cell engraftment.

CONCLUSION

Molecular pathway-based imaging offers appropriate noninvasive means to address activation of innate immune responses. This will help in developing suitable strategies for characterizing and overcoming immune responses for cell and gene therapy.