Preliminary results of [99mTc]OKT3 scintigraphy to evaluate acute rejection in renal transplants

Present status and future trends in molecular imaging of lymphocytes

Immune system is emerging as a crucial protagonist in a huge variety of oncologic and non-oncologic conditions including response to vaccines and viral infections (such as SARS-CoV-2). The increasing knowledge of molecular biology underlying these diseases allowed the identification of specific targets and the possibility to use tailored therapies against them. Immunotherapies and vaccines are, indeed, more and more used nowadays for treating infections, cancer and autoimmune diseases and, therefore, there is the need to identify, quantify and monitor immune cell trafficking before and after treatment. This approach will provide crucial information for therapy decision-making. Imaging of B and T-lymphocytes trafficking by using tailored radiopharmaceuticals proved to be a successful nuclear medicine tool. In this review, we will provide an overview of the state of art and future trends for "in vivo" imaging of lymphocyte trafficking and homing by mean of specific receptor-tailored radiopharmaceuticals.

Non-invasive molecular imaging of kidney diseases

In nephrology, differential diagnosis or assessment of disease activity largely relies on the analysis of glomerular filtration rate, urinary sediment, proteinuria and tissue obtained through invasive kidney biopsies. However, currently available non-invasive functional parameters, and most serum and urine biomarkers, cannot capture intrarenal molecular disease processes specifically. Moreover, although histopathological analyses of kidney biopsy samples enable the visualization of pathological morphological and molecular alterations, they only provide information about a small part of the kidney and do not allow longitudinal monitoring. These limitations not only hinder understanding of the dynamics of specific disease processes in the kidney, but also limit the targeting of treatments to active phases of disease and the development of novel targeted therapies. Molecular imaging enables non-invasive and quantitative assessment of physiological or pathological processes by combining imaging technologies with specific molecular probes. Here, we discuss current preclinical and clinical molecular imaging approaches in nephrology. Non-invasive visualization of the kidneys through molecular imaging can be used to detect and longitudinally monitor disease activity and can therefore provide companion diagnostics to guide clinical trials, as well as the safe and effective use of drugs.

Non-invasive imaging for the diagnosis of acute rejection in transplantation: The next frontier

Acute rejection is a leading cause of organ transplant failure and the most common indication for re-transplantation. Clinically, suspicion of acute rejection is often dependent upon serum laboratory values which may only manifest after organ injury. The gold standard for diagnosis requires an invasive biopsy which can carry serious clinical risks including bleeding and graft loss as well as the possibility of sampling error. The use of noninvasive imaging modalities to monitor transplanted organs is of great clinical value, particularly as a tool for early detection of graft dysfunction or acute rejection. Herein, we provide an overview of the existing literature evaluating noninvasive imaging modalities of solid organ and cellular allografts after transplantation, including both preclinical and clinical studies.

Basic principles and new advances in kidney imaging

Over the past few years, clinical renal imaging has seen great advances, allowing assessments of kidney structure and morphology, perfusion, function and metabolism, and oxygenation, as well as microstructure and the interstitium. Medical imaging is becoming increasingly important in the evaluation of kidney physiology and pathophysiology, showing promise in management of patients with renal disease, in particular with regard to diagnosis, classification, and prediction of disease development and progression, monitoring response to therapy, detection of drug toxicity, and patient selection for clinical trials. A variety of imaging modalities, ranging from routine to advanced tools, are currently available to probe the kidney both spatially and temporally, particularly ultrasonography, computed tomography, positron emission tomography, renal scintigraphy, and multiparametric magnetic resonance imaging. Given that the range is broad and varied, kidney imaging techniques should be chosen based on the clinical question and the specific underlying pathologic mechanism, taking into account contraindications and possible adverse effects. Integration of various modalities providing complementary information will likely provide the greatest insight into renal pathophysiology. This review aims to highlight major recent advances in key tools that are currently available or potentially relevant for clinical kidney imaging, with a focus on non-oncological applications. The review also outlines the context of use, limitations, and advantages of various techniques, and highlights gaps to be filled with future development and clinical adoption.

In vivo Imaging Technologies to Monitor the Immune System

The past two decades have brought impressive advancements in immune modulation, particularly with the advent of both cancer immunotherapy and biologic therapeutics for inflammatory conditions. However, the dynamic nature of the immune response often complicates the assessment of therapeutic outcomes. Innovative imaging technologies are designed to bridge this gap and allow non-invasive visualization of immune cell presence and/or function in real time. A variety of anatomical and molecular imaging modalities have been applied for this purpose, with each option providing specific advantages and drawbacks. Anatomical methods including magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound provide sharp tissue resolution, which can be further enhanced with contrast agents, including super paramagnetic ions (for MRI) or nanobubbles (for ultrasound). Conjugation of the contrast material to an antibody allows for specific targeting of a cell population or protein of interest. Protein platforms including antibodies, cytokines, and receptor ligands are also popular choices as molecular imaging agents for positron emission tomography (PET), single-photon emission computerized tomography (SPECT), scintigraphy, and optical imaging. These tracers are tagged with either a radioisotope or fluorescent molecule for detection of the target. During the design process for immune-monitoring imaging tracers, it is important to consider any potential downstream physiologic impact. Antibodies may deplete the target cell population, trigger or inhibit receptor signaling, or neutralize the normal function(s) of soluble proteins. Alternatively, the use of cytokines or other ligands as tracers may stimulate their respective signaling pathways, even in low concentrations. As in vivo immune imaging is still in its infancy, this review aims to describe the modalities and immunologic targets that have thus far been explored, with the goal of promoting and guiding the future development and application of novel imaging technologies.

Ferumoxytol Is Not Retained in Kidney Allografts in Patients Undergoing Acute Rejection

PURPOSE

To evaluate whether ultrasmall superparamagnetic iron oxide nanoparticle (USPIO)-enhanced magnetic resonance imaging (MRI) can detect allograft rejection in pediatric kidney transplant patients.

PROCEDURES

The USPIO ferumoxytol has a long blood half-life and is phagocytosed by macrophages. In an IRB-approved single-center prospective clinical trial, 26 pediatric patients and adolescents (age 10-26 years) with acute allograft rejection (n = 5), non-rejecting allografts (n = 13), and normal native kidneys (n = 8) underwent multi-echo T2* fast spoiled gradient-echo (FSPGR) MRI after intravenous injection (p.i.) of 5 mg Fe/kg ferumoxytol. T2* relaxation times at 4 h p.i. (perfusion phase) and more than 20 h p.i. (macrophage phase) were compared with biopsy results. The presence of rejection was assessed using the Banff criteria, and the prevalence of macrophages on CD163 immunostains was determined based on a semi-quantitative scoring system. MRI and histology data were compared among patient groups using t tests, analysis of variance, and regression analyses with a significance threshold of p < 0.05.

RESULTS

At 4 h p.i., mean T2* values were 6.6 ± 1.5 ms for native kidneys and 3.9 ms for one allograft undergoing acute immune rejection. Surprisingly, at 20-24 h p.i., one rejecting allograft showed significantly prolonged T2* relaxation times (37.0 ms) compared to native kidneys (6.3 ± 1.7 ms) and non-rejecting allografts (7.6 ± 0.1 ms). Likewise, three additional rejecting allografts showed significantly prolonged T2* relaxation times compared to non-rejecting allografts at later post-contrast time points, 25-97 h p.i. (p = 0.008). Histological analysis revealed edema and compressed microvessels in biopsies of rejecting allografts. Allografts with and without rejection showed insignificant differences in macrophage content on histopathology (p = 0.44).

CONCLUSION

After ferumoxytol administration, renal allografts undergoing acute rejection show prolonged T2* values compared to non-rejecting allografts. Since histology revealed no significant differences in macrophage content, the increasing T2* value is likely due to the combined effect of reduced perfusion and increased edema in rejecting allografts.

The nasal delivery of nanoencapsulated statins - an approach for brain delivery

Purpose

Along with their cholesterol-lowering effect, statins have shown a wide range of pleiotropic effects potentially beneficial to neurodegenerative diseases. However, such effects are extremely elusive via the conventional oral administration. The purpose of the present study was to prepare and characterize the physicochemical properties and the in vivo biodistribution of simvastatin-loaded lecithin/chitosan nanoparticles (SVT-LCNs) suitable for nasal administration in view of an improved delivery of the statins to the brain.

Materials and methods

Chitosan, lecithin, and different oil excipients were used to prepare nanocapsules loaded with simvastatin. Particle size distribution, surface charge, structure, simvastatin loading and release, and interaction with mucus of nanoparticles were determined. The nanoparticle nasal toxicity was evaluated in vitro using RPMI 2651 nasal cell lines. Finally, in vivo biodistribution was assessed by gamma scintigraphy via Tc99m labeling of the particles.

Results

Among the different types of nanoparticles produced, the SVT-LCN_MaiLab showed the most ideal physicochemical characteristics, with small diameter (200 nm), positive surface charge (+48 mV) and high encapsulation efficiency (EE; 98%). Size distribution was further confirmed by nanoparticle tracking analysis and electron microscopy. The particles showed a relatively fast release of simvastatin in vitro (35.6%±4.2% in 6 hours) in simulated nasal fluid. Blank nanoparticles did not show cytotoxicity, evidencing that the formulation is safe for nasal administration, while cytotoxicity of simvastatin-loaded nanoparticles (IC₅₀) was found to be three times lower than the drug solution (9.92 vs 3.50 μM). In rats, a significantly higher radioactivity was evidenced in the brain after nasal delivery of simvastatin-loaded nanoparticles in comparison to the administration of a similar dose of simvastatin suspension.

Conclusion

The SVT-LCNs developed presented some of the most desirable characteristics for mucosal delivery, that is, small particle size, positive surface charge, long-term stability, high EE, and mucoadhesion. In addition, they displayed two exciting features: First was their biodegradability by enzymes present in the mucus layer, such as lysozyme. This indicates a new Trojan-horse strategy which may enhance drug release in the proximity of the nasal mucosa. Second was their ability to enhance the nose-to-brain transport as evidenced by preliminary gamma scintigraphy studies.

Imaging-based diagnosis of acute renal allograft rejection

Kidney transplantation is the best available treatment for patients with end stage renal disease. Despite the introduction of effective immunosuppressant drugs, episodes of acute allograft rejection still endanger graft survival. Since efficient treatment of acute rejection is available, rapid diagnosis of this reversible graft injury is essential. For diagnosis of rejection, invasive core needle biopsy of the graft is the “gold-standard”. However, biopsy carries the risk of significant graft injury and is not immediately feasible in patients taking anticoagulants. Therefore, a non-invasive tool assessing the whole organ for specific and fast detection of acute allograft rejection is desirable. We herein review current imaging-based state of the art approaches for non-invasive diagnostics of acute renal transplant rejection. We especially focus on new positron emission tomography-based as well as targeted ultrasound-based methods.

Role of nuclear medicine imaging in evaluation of complications following renal transplant

Evaluation of a failing renal allograft is a complex and challenging diagnostic problem. While ultrasonography with colour Doppler is usually the first approach for evaluation of graft dysfunction, radionuclide imaging is an excellent modality which provides complementary information regarding the perfusion and function of the allograft without any deleterious effect on the precious allograft. In this article, we review the imaging techniques of the nuclear medicine studies most commonly performed after renal transplant, discuss their roles and limitations in different clinical settings and illustrate with cases from our institution. Lastly, we will explore future development in the arena of nuclear imaging for renal transplant related complications.

SPECT- and PET-based approaches for noninvasive diagnosis of acute renal allograft rejection

Molecular imaging techniques such as single photon emission computed tomography (SPECT) or positron emission tomography are promising tools for noninvasive diagnosis of acute allograft rejection (AR). Given the importance of renal transplantation and the limitation of available donors, detailed analysis of factors that affect transplant survival is important. Episodes of acute allograft rejection are a negative prognostic factor for long-term graft survival. Invasive core needle biopsies are still the “goldstandard” in rejection diagnostics. Nevertheless, they are cumbersome to the patient and carry the risk of significant graft injury. Notably, they cannot be performed on patients taking anticoagulant drugs. Therefore, a noninvasive tool assessing the whole organ for specific and fast detection of acute allograft rejection is desirable. We herein review SPECT- and PET-based approaches for noninvasive molecular imaging-based diagnostics of acute transplant rejection.

Microparticles of Aloe vera/vitamin E/chitosan: microscopic, a nuclear imaging and an in vivo test analysis for burn treatment

The use of drug-loaded nanoparticles and microparticles has been increasing, especially for cosmetic and drug delivery purposes. In this work, a new microparticle formulation was developed for use in the healing process of skin burns in a composition of Aloe vera/vitamin E/chitosan. In order to observe the morphological properties, Raman and atomic force microscopy evaluation were performed. The biodistribution studies were analyzed by using a nuclear methodology, labeling the microparticles with Technetium-99m and in vivo test was procedure to analyzed the cicatrization process. The results of AFM analysis show the formation and the adherence property of the microparticles. Raman analyses show the distribution of each component in the microparticle. The nuclear method used shows that the biodistribution of the microparticles remained in the skin. The in vivo cicatrization test showed that the poloxamer gel containing the microparticles make a better cicatrization in relation to the other formulations tested.

(99m)Tc-anti-TNF-α scintigraphy in RA: a comparison pilot study with MRI and clinical examination

OBJECTIVE

To compare the use of radiolabelled human monoclonal anti-TNF-α scintigraphy with clinical examination and MRI of hands and wrists joints in patients with active RA.

METHODS

Eight patients with active RA, 28-joint DAS (DAS-28) ≥ 3.2 and a healthy volunteer underwent whole body and hand/wrist scintigraphy after the administration of anti-human TNF-α labelled with technetium-99m ((99m)Tc). One hundred and ninety-eight joints were examined. Patients were also given clinical examinations in addition to MRI of the hands and wrists.

RESULTS

Of the 198 joints examined, signs of inflammation were detected by MRI in 49 (24.7%) and by scintigraphy in 48 (24.2%) joints, with agreement between the two methods in 44 joints. In five joints, MRI was positive and scintigraphy negative. In another four joints, scintigraphy was positive and MRI negative for signs of inflammation. MRI and scintigraphy were in agreement for negative results for 145 joints. The sensitivity and specificity of scintigraphy was 89.8 and 97.3%, respectively. When clinical parameters (presence of swelling and tenderness of joints) were compared with the MRI findings, lower correlation coefficients were observed (sensitivity of 59.2% and 65.3%, respectively).

CONCLUSIONS

Scintigraphy using (99m)Tc-anti-TNF-α showed high correlation with the presence of inflammatory signs detected by MRI in the hands and wrists of patients with active RA, and demonstrated a greater sensitivity than clinical examination. These results can assist in better understanding of anti-cytokine therapy and support the achievement of evidence-based biologic therapy.

Use of 99mTc-anti-CD3 scintigraphy in the differential diagnosis of rheumatic diseases

OBJECTIVES

The aim of this study was to assess the use of anti-CD3, labelled with technetium-99m scintigraphy, for evaluating the joints of patients with RA, juvenile idiopathic arthritis (JIA), OA and gouty arthritis, and to establish the diagnosis parameters for each disease.

METHODS

We evaluated 2044 joints from 77 patients with rheumatic diseases. The clinical evaluation consisted of laboratory assays; examination for joint inflammation (pain and/or oedema); and for patients with RA, the disease activity score of 28 joints. To evaluate the sensitivity and specificity of 99mTc-anti-CD3 in detecting disease activity, patients received an injection of the radiopharmaceutical compound 99mTc-anti-CD3, and underwent a scintigraphy scan 1 h later. Scanning was repeated 3 h later. As a control, after 2 days, the patient was injected with 99mTc-non-specific human immunoglobulins, and scintigraphy scanning performed at 1 and 3 h after the injection. The intensity of uptake and the pattern of activity were defined, and Spearman's correlation and analysis of variance used for statistical evaluation.

RESULTS

Diagnosis criteria were established for 99mTc-anti-CD3 uptake in different diseases. RA and JIA showed joint uptake with progressive increase in late images. Gouty arthritis showed joint uptake with decrease during the late images. Joint uptake was low or absent in patients with OA, although when present the joint uptake decreased during the examination.

CONCLUSION

99mTc-anti-CD3 scintigraphy is a useful method in the differential diagnosis of rheumatic diseases.

Nuclear imaging in the genitourinary tract: recent advances and future directions

For almost three decades, noninvasive radionuclide procedures for the evaluation of renal disease have been important components of nuclear medicine practice. With the introduction of new imaging agents and procedures, these techniques can provide valuable data on perfusion and function of individual kidneys. In general, these procedures are easy to perform and carry a low radiation burden and sedation is not required. Moreover, radionuclide imaging of the genitourinary tract has become an invaluable asset to clinicians in the evaluation of renal parenchyma and urologic abnormalities.

Monitoring rheumatoid arthritis synovitis with 99mTc-anti-CD3

The aim of this study was to investigate the feasibility of using a monoclonal antibody (OKT3) labelled with technetium-99m (99mTc) to monitor disease activity in patients with rheumatoid arthritis. We evaluated 38 patients who were diagnosed with rheumatoid arthritis and classified as Classes II and III after functional assessment (according to the revised criteria specified by the American College of Rheumatology). Two sets of planar anterior images of the patients' wrists, metacarpophalangeal and interphalangeal joints, elbows, shoulders and knees joints were obtained 1 h and 3 h after the injection of 99mTc-OKT3. The scintigraphic findings showed significant correlation (p<0.05) between the radiopharmaceutical accumulation of 99mTc-OKT3 and swollen joints, tender joints and the visual analogue scale. They were able to differentiate patients in remission from patients with active synovitis, according to DAS 28. In contrast, there was no correlation between the radiopharmaceutical accumulation and the patients' age, gender, duration of disease or erythrocyte sedimentation rate. A relatively high disease activity score of 28 joints (4.08+/-1.74) was found in the majority of patients. In conclusion, 99mTc-OKT3 scintigraphy is a reliable and objective method for detecting synovial activity, and can be used to observe disease prognosis.