CD20 antigen imaging with ¹²⁴I-rituximab PET/CT in patients with rheumatoid arthritis

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.

ImmunoPET: harnessing antibodies for imaging immune cells

Dramatic, but uneven, progress in the development of immunotherapies for cancer has created a need for better diagnostic technologies including innovative non-invasive imaging approaches. This review discusses challenges and opportunities for molecular imaging in immuno-oncology and focuses on the unique role that antibodies can fill. ImmunoPET has been implemented for detection of immune cell subsets, activation and inhibitory biomarkers, tracking adoptively transferred cellular therapeutics, and many additional applications in preclinical models. Parallel progress in radionuclide availability and infrastructure supporting biopharmaceutical manufacturing has accelerated clinical translation. ImmunoPET is poised to provide key information on prognosis, patient selection, and monitoring immune responses to therapy in cancer and beyond.

Molecular Imaging of Inflammatory Disease

Inflammatory diseases include a wide variety of highly prevalent conditions with high mortality rates in severe cases ranging from cardiovascular disease, to rheumatoid arthritis, to chronic obstructive pulmonary disease, to graft vs. host disease, to a number of gastrointestinal disorders. Many diseases that are not considered inflammatory per se are associated with varying levels of inflammation. Imaging of the immune system and inflammatory response is of interest as it can give insight into disease progression and severity. Clinical imaging technologies such as computed tomography (CT) and magnetic resonance imaging (MRI) are traditionally limited to the visualization of anatomical information; then, the presence or absence of an inflammatory state must be inferred from the structural abnormalities. Improvement in available contrast agents has made it possible to obtain functional information as well as anatomical. In vivo imaging of inflammation ultimately facilitates an improved accuracy of diagnostics and monitoring of patients to allow for better patient care. Highly specific molecular imaging of inflammatory biomarkers allows for earlier diagnosis to prevent irreversible damage. Advancements in imaging instruments, targeted tracers, and contrast agents represent a rapidly growing area of preclinical research with the hopes of quick translation to the clinic.

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.

Rituximab levels are associated with the B cell homeostasis but not with the clinical response in patients with rheumatoid arthritis

Objective

To study the levels of rituximab (RTX) and anti-RTX antibodies (ARAs) in patients with rheumatoid arthritis (RA) at 30, 90, and 180 days after the first infusion, in relation to clinical and serological parameters and B cell homeostasis.

Methods

Thirty-four patients with RA who failed to respond to anti-tumor necrosis factor therapy received RTX. At baseline, 4, 12, and 24 weeks after the first infusion of RTX, we performed a clinical assessment and determined the levels of RTX, ARAs, B cells, rheumatoid factors, anti-cyclic citrullinated peptide antibodies, immunoglobulins, and complements.

Results

RTX levels varied widely among patients. No ARAs were detected during the follow-up. Patients with lower levels of RTX presented with higher decreases in erythrocyte sedimentation rate, immunoglobulins, and complement 6 months after the first infusion. Patients with higher levels of RTX showed a higher B cell depletion at 90 days but an earlier B cell recovery than those with lower levels of RTX. No differences in clinical response were observed between the two groups at 6 months after starting the treatment.

Conclusion

Our findings suggest that RTX levels in the serum of patients with RA are related to B cell homeostasis and the severity of immunological parameters but not to the clinical response at 6 months.

Zirconium-89-labelled rituximab PET-CT in orbital inflammatory disease

Background

Orbital inflammatory diseases are a heterogenic group of conditions that often entail a difficult diagnostic process and many patients are treatment resistant. Inflammatory diseases can be visualized by Zirconium-89-labelled rituximab PET-CT (⁸⁹Zr-rituximab PET/CT). In this study, we describe our experience and possible potential of the ⁸⁹Zr-rituximab PET/CT for diagnostic and therapeutic management of refractory orbital inflammation.

Results

Retrospectively, ⁸⁹Zr-rituximab uptake was assessed and related to clinical data. The main outcome measures were the characteristics of the scan and the clinical relation of uptake with the diagnostic process and treatment effectivity. Twelve patients with thyroid eye disease (TED) and suspected idiopathic orbital inflammation (IOI) were scanned. Six patients had a strong ⁸⁹Zr-rituximab uptake and showed a focal distribution within the lesion. Four patients (one TED, three IOI) responded well to rituximab treatment after a positive scan. ⁸⁹Zr-rituximab PET/CT was essential to the diagnosis of optic nerve meningioma in one patient.

Conclusion

⁸⁹Zr-rituximab PET/CT has the potential to be a powerful tool for the detection of B cell-mediated disease within the orbit and ocular adnexa. This technique can be a valuable addition for diagnosing diseases around the eye and can potentially predict rituximab treatment response in patients with refractory inflammation.

Immuno-Imaging to Predict Treatment Response in Infection, Inflammation and Oncology

Background: Molecular nuclear medicine plays a pivotal role for diagnosis in a preclinical phase, in genetically susceptible patients, for radio-guided surgery, for disease relapse evaluation, and for therapy decision-making and follow-up. This is possible thanks to the development of new radiopharmaceuticals to target specific biomarkers of infection, inflammation and tumour immunology. Methods: In this review, we describe the use of specific radiopharmaceuticals for infectious and inflammatory diseases with the aim of fast and accurate diagnosis and treatment follow-up. Furthermore, we focus on specific oncological indications with an emphasis on tumour immunology and visualizing the tumour environment. Results: Molecular nuclear medicine imaging techniques get a foothold in the diagnosis of a variety of infectious and inflammatory diseases, such as bacterial and fungal infections, rheumatoid arthritis, and large vessel vasculitis, but also for treatment response in cancer immunotherapy. Conclusion: Several specific radiopharmaceuticals can be used to improve diagnosis and staging, but also for therapy decision-making and follow-up in infectious, inflammatory and oncological diseases where immune cells are involved. The identification of these cell subpopulations by nuclear medicine techniques would provide personalized medicine for these patients, avoiding side effects and improving therapeutic approaches.

TSPO PET Imaging: From Microglial Activation to Peripheral Sterile Inflammatory Diseases?

Peripheral sterile inflammatory diseases (PSIDs) are a heterogeneous group of disorders that gathers several chronic insults involving the cardiovascular, respiratory, gastrointestinal, or musculoskeletal system and wherein inflammation is the cornerstone of the pathophysiology. In PSID, timely characterization and localization of inflammatory foci are crucial for an adequate care for patients. In brain diseases, in vivo positron emission tomography (PET) exploration of inflammation has matured over the last 20 years, through the development of radiopharmaceuticals targeting the translocator protein-18 kDa (TSPO) as molecular biomarkers of activated microglia. Recently, TSPO has been introduced as a possible molecular target for PSIDs PET imaging, making this protein a potential biomarker to address disease heterogeneity, to assist in patient stratification, and to contribute to predicting treatment response. In this review, we summarized the major research advances recently made in the field of TSPO PET imaging in PSIDs. Promising preliminary results have been reported in bowel, cardiovascular, and rheumatic inflammatory diseases, consolidated by preclinical studies. Limitations of TSPO PET imaging in PSIDs, regarding both its large expression in healthy peripheral tissues, unlike in central nervous system, and the production of peripheral radiolabeled metabolites, are also discussed, regarding their possible consequences on TSPO PET signal's quantification.

Does B lymphocyte-mediated autoimmunity contribute to post-stroke dementia?

Post-stroke cognitive decline and dementia pose a significant public health problem, with 30% of stroke survivors suffering from dementia. The reason for this high prevalence is not well understood. Pathogenic B cell responses to the damaged CNS are one possible contributing factor. B-lymphocytes and antibodies are present in and around the stroke core of some human subjects who die with stroke and dementia, and mice that develop delayed cognitive dysfunction after stroke have clusters of B-lymphocytes in the stroke lesion, and antibody infiltration in the stroked hemisphere. The ablation of B-lymphocytes prevents post-stroke cognitive impairment in mice. Multiple drugs that target B cells are FDA approved, and so if pathogenic B cell responses are occurring in a subset of stroke patients, this is potentially treatable. However, it has also been demonstrated that regulatory B cells can be beneficial in mouse models of stroke. Consequently, it is important to understand the relative contribution of B-lymphocytes to recovery versus pathogenicity, and if this balance is heterogeneous in different individuals. Therefore, the purpose of this review is to summarize the current state of knowledge with regard to the role of B-lymphocytes in the etiology of post-stroke dementia.

Molecular Imaging of Inflammation: Current Status

The ability to image inflammation in vivo can improve our understanding of the pathophysiology underlying various disease etiologies, including cancer, atherosclerosis, and neurodegeneration. A great wealth of preclinical and translational research has been and is currently being developed to decipher the involvement of the immune system in disease pathophysiology, quantify the course of a disease, and visualize the potential detrimental effects of excessive inflammation. Down the road, the ultimate goal is to have clinical noninvasive in vivo imaging biomarkers of inflammation that will help diagnose disease, establish prognosis, and gauge response to preventative and therapeutic strategies.

Radiation Dosimetry Study of [(89)Zr]rituximab Tracer for Clinical Translation of B cell NHL Imaging using Positron Emission Tomography

PURPOSE

We evaluated the dosimetry of [(89)Zr]rituximab, an anti-CD20 immunoPET tracer to image B cell non-Hodgkin's lymphoma (NHL) using a humanized transgenic mouse model that expresses human CD20 transgenic mice (huCD20TM).

PROCEDURES

Rituximab was conjugated to desferrioxamine (Df) for radiolabeling of Zirconium-89. [(89)Zr]rituximab (2.8 ± 0.2 MBq) was tail vein-injected into huCD20T mice. Positron emission tomography (PET)/CT imaging was performed on the two groups of mice (blocking = 2 mg/kg pre-dose of rituximab and non-blocking; n = 5) at eight time points (1, 4, 24, 48, 72, 96, 120, and 168 h) post injection.

RESULTS

The novel [(89)Zr]rituximab PET tracer had good immunoreactivity, was stable in human serum, and was able to specifically target human CD20 in mice. The human equivalents of highest dose (mean ± SD) organs with and without pre-dose are liver (345 ± 284 μSv/MBq) and spleen (1165 ± 149 μSv/MBq), respectively.

CONCLUSIONS

Dosimetry of the human patient whole-body dose was found to be 145 MBq per annum, and the patient dose-limiting organ will be the liver (with rituximab pre-dose blocking) and spleen for non-blocking. The [(89)Zr]rituximab (t½ = 78.4 h) imaging of B cell NHL patients could permit the observation of targeting lesions in NHL patients over an extended period due to longer half-life as compared to the [(64)Cu] rituximab (t½ = 12.7 h).

Development, optimization, and validation of novel anti-TEM1/CD248 affinity agent for optical imaging in cancer

Tumor Endothelial Marker-1 (TEM1/CD248) is a tumor vascular marker with high therapeutic and diagnostic potentials. Immuno-imaging with TEM1-specific antibodies can help to detect cancerous lesions, monitor tumor responses, and select patients that are most likely to benefit from TEM1-targeted therapies. In particular, near infrared(NIR) optical imaging with biomarker-specific antibodies can provide real-time, tomographic information without exposing the subjects to radioactivity. To maximize the theranostic potential of TEM1, we developed a panel of all human, multivalent Fc-fusion proteins based on a previously identified single chain antibody (scFv78) that recognizes both human and mouse TEM1. By characterizing avidity, stability, and pharmacokinectics, we identified one fusion protein, 78Fc, with desirable characteristics for immuno-imaging applications. The biodistribution of radiolabeled 78Fc showed that this antibody had minimal binding to normal organs, which have low expression of TEM1. Next, we developed a 78Fc-based tracer and tested its performance in different TEM1-expressing mouse models. The NIR imaging and tomography results suggest that the 78Fc-NIR tracer performs well in distinguishing mouse- or human-TEM1 expressing tumor grafts from normal organs and control grafts in vivo. From these results we conclude that further development and optimization of 78Fc as a TEM1-targeted imaging agent for use in clinical settings is warranted.

Recognition of Immune Response for the Early Diagnosis and Treatment of Osteoarthritis

Osteoarthritis is a common and debilitating joint disease that affects up to 30 million Americans, leading to significant disability, reduction in quality of life, and costing the United States tens of billions of dollars annually. Classically, osteoarthritis has been characterized as a degenerative, wear-and-tear disease, but recent research has identified it as an immunopathological disease on a spectrum between healthy condition and rheumatoid arthritis. A systematic literature review demonstrates that the disease pathogenesis is driven by an early innate immune response which progressively catalyzes degenerative changes that ultimately lead to an altered joint microenvironment. It is feasible to detect this infiltration of cells in the early, and presumably asymptomatic, phase of the disease through noninvasive imaging techniques. This screening can serve to aid clinicians in potentially identifying high-risk patients, hopefully leading to early effective management, vast improvements in quality of life, and significant reductions in disability, morbidity, and cost related to osteoarthritis. Although the diagnosis and treatment of osteoarthritis routinely utilize both invasive and non-invasive strategies, imaging techniques specific to inflammatory cells are not commonly employed for these purposes. This review discusses this paradigm and aims to shift the focus of future osteoarthritis-related research towards early diagnosis of the disease process.

B-lymphocyte-mediated delayed cognitive impairment following stroke

Each year, 10 million people worldwide survive the neurologic injury associated with a stroke. Importantly, stroke survivors have more than twice the risk of subsequently developing dementia compared with people who have never had a stroke. The link between stroke and the later development of dementia is not understood. There are reports of oligoclonal bands in the CSF of stroke patients, suggesting that in some people a B-lymphocyte response to stroke may occur in the CNS. Therefore, we tested the hypothesis that a B-lymphocyte response to stroke could contribute to the onset of dementia. We discovered that, in mouse models, activated B-lymphocytes infiltrate infarcted tissue in the weeks after stroke. B-lymphocytes undergo isotype switching, and IgM, IgG, and IgA antibodies are found in the neuropil adjacent to the lesion. Concurrently, mice develop delayed deficits in LTP and cognition. Genetic deficiency, and the pharmacologic ablation of B-lymphocytes using an anti-CD20 antibody, prevents the appearance of delayed cognitive deficits. Furthermore, immunostaining of human postmortem tissue revealed that a B-lymphocyte response to stroke also occurs in the brain of some people with stroke and dementia. These data suggest that some stroke patients may develop a B-lymphocyte response to stroke that contributes to dementia, and is potentially treatable with FDA-approved drugs that target B cells.

Rheumatoid arthritis: Nuclear Medicine state-of-the-art imaging

Rheumatoid arthritis (RA) is an autoimmune disease, which is associated with systemic and chronic inflammation of the joints, resulting in synovitis and pannus formation. For several decades, the assessment of RA has been limited to conventional radiography, assisting in the diagnosis and monitoring of disease. Nevertheless, conventional radiography has poor sensitivity in the detection of the inflammatory process that happens in the initial stages of RA. In the past years, new drugs that significantly decrease the progression of RA have allowed a more efficient treatment. Nuclear Medicine provides functional assessment of physiological processes and therefore has significant potential for timely diagnosis and adequate follow-up of RA. Several single photon emission computed tomography (SPECT) and positron emission tomography (PET) radiopharmaceuticals have been developed and applied in this field. The use of hybrid imaging, which permits computed tomography (CT) and nuclear medicine data to be acquired and fused, has increased even more the diagnostic accuracy of Nuclear Medicine by providing anatomical localization in SPECT/CT and PET/CT studies. More recently, fusion of PET with magnetic resonance imaging (PET/MRI) was introduced in some centers and demonstrated great potential. In this article, we will review studies that have been published using Nuclear Medicine for RA and examine key topics in the area.

Molecular imaging of rheumatoid arthritis: emerging markers, tools, and techniques

Early diagnosis and effective monitoring of rheumatoid arthritis (RA) are important for a positive outcome. Instant treatment often results in faster reduction of inflammation and, as a consequence, less structural damage. Anatomical imaging techniques have been in use for a long time, facilitating diagnosis and monitoring of RA. However, mere imaging of anatomical structures provides little information on the processes preceding changes in synovial tissue, cartilage, and bone. Molecular imaging might facilitate more effective diagnosis and monitoring in addition to providing new information on the disease pathogenesis. A limiting factor in the development of new molecular imaging techniques is the availability of suitable probes. Here, we review which cells and molecules can be targeted in the RA joint and discuss the advances that have been made in imaging of arthritis with a focus on such molecular targets as folate receptor, F4/80, macrophage mannose receptor, E-selectin, intercellular adhesion molecule-1, phosphatidylserine, and matrix metalloproteinases. In addition, we discuss a new tool that is being introduced in the field, namely the use of nanobodies as tracers. Finally, we describe additional molecules displaying specific features in joint inflammation and propose these as potential new molecular imaging targets, more specifically receptor activator of nuclear factor κB and its ligand, chemokine receptors, vascular cell adhesion molecule-1, αVβ₃ integrin, P2X7 receptor, suppression of tumorigenicity 2, dendritic cell-specific transmembrane protein, and osteoclast-stimulatory transmembrane protein.

PET imaging of inflammation biomarkers

Inflammation plays a significant role in many disease processes. Development in molecular imaging in recent years provides new insight into the diagnosis and treatment evaluation of various inflammatory diseases and diseases involving inflammatory process. Positron emission tomography using (18)F-FDG has been successfully applied in clinical oncology and neurology and in the inflammation realm. In addition to glucose metabolism, a variety of targets for inflammation imaging are being discovered and utilized, some of which are considered superior to FDG for imaging inflammation. This review summarizes the potential inflammation imaging targets and corresponding PET tracers, and the applications of PET in major inflammatory diseases and tumor associated inflammation. Also, the current attempt in differentiating inflammation from tumor using PET is also discussed.

Image guided biodistribution and pharmacokinetic studies of theranostics

Image guided technique is playing an increasingly important role in the investigation of the biodistribution and pharmacokinetics of drugs or drug delivery systems in various diseases, especially cancers. Besides anatomical imaging modalities such as computed tomography (CT), magnetic resonance imaging (MRI), molecular imaging strategy including optical imaging, positron emission tomography (PET) and single-photon emission computed tomography (SPECT) will facilitate the localization and quantization of radioisotope or optical probe labeled nanoparticle delivery systems in the category of theranostics. The quantitative measurement of the bio-distribution and pharmacokinetics of theranostics in the fields of new drug/probe development, diagnosis and treatment process monitoring as well as tracking the brain-blood-barrier (BBB) breaking through by high sensitive imaging method, and the applications of the representative imaging modalities are summarized in this review.

Development of a novel long-lived immunoPET tracer for monitoring lymphoma therapy in a humanized transgenic mouse model

Positron emission tomography (PET) is an attractive imaging tool to localize and quantify tracer biodistribution. ImmunoPET with an intact mAb typically requires two to four days to achieve optimized tumor-to-normal ratios. Thus, a positron emitter with a half-life of two to four days such as zirconium-89 [(89)Zr] (t1/2: 78.4 h) is ideal. We have developed an antibody-based, long-lived immunoPET tracer (89)Zr-Desferrioxamine-p-SCN (Df-Bz-NCS)-rituximab (Zr-iPET) to image tumor for longer durations in a humanized CD20-expressing transgenic mouse model. To optimize the radiolabeling efficiency of (89)Zr with Df-Bz-rituximab, multiple radiolabelings were performed. Radiochemical yield, purity, immunoreactivity, and stability assays were carried out to characterize the Zr-iPET for chemical and biological integrity. This tracer was used to image transgenic mice that express the human CD20 on their B cells (huCD20TM). Each huCD20TM mouse received a 7.4 MBq/dose. One group (n = 3) received a 2 mg/kg predose (blocking) of cold rituximab 2 h prior to (89)Zr-iPET; the other group (n = 3) had no predose (nonblocking). Small animal PET/CT was used to image mice at 1, 4, 24, 48, 72, and 120 h. Quality assurance of the (89)Zr-iPET demonstrated NCS-Bz-Df: antibody ratio (c/a: 1.5 ± 0.31), specific activity (0.44-1.64 TBq/mol), radiochemical yield (>70%), and purity (>98%). The Zr-iPET immunoreactivity was >80%. At 120 h, Zr-iPET uptake (% ID/g) as mean ± STD for blocking and nonblocking groups in spleen was 3.2 ± 0.1% and 83.3 ± 2.0% (p value <0.0013.). Liver uptake was 1.32 ± 0.05% and 0.61 ± 0.001% (p value <0.0128) for blocking and nonblocking, respectively. The small animal PET/CT image shows the spleen specific uptake of Zr-iPET in mice at 120 h after tracer injection. Compared to the liver, the spleen specific uptake of Zr-iPET is very high due to the expression of huCD20. We optimized the radiolabeling efficiency of (89)Zr with Df-Bz-rituximab. These radioimmunoconjugate lots were stable up to 5 days in serum in vitro. The present study showed that (89)Zr is well-suited for mAbs to image cancer over an extended period of time (up to 5 days).