Noninvasive Cell Tracking Research Articles

226.10: Establishment of a noninvasive cell tracking system for visualizing the fate of human amniotic epithelial cells in immunocompetent mice.

226.10: Establishment of a noninvasive cell tracking system for visualizing the fate of human amniotic epithelial cells in immunocompetent mice.

Enabling Non-invasive Tracking of Vascular Endothelial Cells Derived from Induced Pluripotent Stem Cells Using Nuclear Imaging.

The absence of clinically applicable imaging techniques for continuous monitoring of transplanted cells poses a significant obstacle to the clinical translation of stem cell-based therapies for vascular regeneration. This study aims to optimize a clinically applicable, non-invasive imaging technique to longitudinally monitor vascular endothelial cells (ECs) for vascular regeneration in peripheral artery disease (PAD). Human induced pluripotent stem cells (HiPSCs) were employed to generate ECs (HiPSC-ECs). Lentiviral vectors encoding human sodium iodide symporter (hNIS) and enhanced green fluorescent protein (eGFP) genes were introduced to HiPSCs and HiPSC-ECs at varying multiplicities of infection (MOI). Through a combination of fluorescence microscopy and flow cytometry, an optimized transduction technique for introducing hNIS-eGFP into HiPSC-ECs was established. Subsequently, single-photon emission computed tomography (SPECT) was utilized for imaging of the transduced cells in vitro and in vivo after transplantation into the gastrocnemius muscle of nude mice. Lentiviral transduction resulted in sustained co-expression of hNIS and eGFP in HiPSC-ECs when transduced post-endothelial differentiation. An optimal MOI of five yielded over 90% hNIS-eGFP expression efficiency without compromising cell viability. hNIS-eGFP+ HiPSC-ECs exhibited 99mTc uptake and were detectable through SPECT in vitro. Additionally, intramuscular injection of hNIS-eGFP+ HiPSC-ECs with MatrigelTM into the hindlimbs of nude mice enabled real-time SPECT/CT tracking, from which a reduction in signal exceeding 80% was observed within 7days. This study establishes an optimized cell modification and imaging protocol for tracking transplanted cells. Future efforts will focus on enhancing cell survival and integration via improved delivery systems, thereby advancing the potential of cell-based therapies for PAD.

Phototruncation cell tracking with near-infrared photoimmunotherapy using heptamethine cyanine dye to visualise migratory dynamics of immune cells

Noninvasive invivo cell tracking is valuable in understanding the mechanisms that enhance anti-cancer immunity. We have recently developed a new method called phototruncation-assisted cell tracking (PACT), that uses photoconvertible cell tracking technology to detect invivo cell migration. This method has the advantages of not requiring genetic engineering of cells and employing tissue-penetrant near-infrared light. We applied PACT to monitor the migration of immune cells between a tumour and its tumour-draining lymph node (TDLN) after near-infrared photoimmunotherapy (NIR-PIT). PACT showed a significant increase in the migration of dendritic cells (DCs) and macrophages from the tumour to the TDLN immediately after NIR-PIT. This migration by NIR-PIT was abrogated by inhibiting the sphingosine-1-phosphate pathway or Gαi signaling. These results were corroborated by intranodal immune cell profiles at two days post-treatment; NIR-PIT significantly induced DC maturation and increased and activated the CD8+ T cell population in the TDLN. Furthermore, PACT revealed that NIR-PIT significantly enhanced the migration of CD8+ T cells from the TDLN to the tumour four days post-treatment, which was consistent with the immunohistochemical assessment of tumour-infiltrating lymphocytes and tumour regression. Immune cells dramatically migrated between the tumour and TDLN following NIR-PIT, indicating its potential as an immune-stimulating therapy. Also, PACT is potentially applicable to a wide range of immunological research. This work was supported by the Intramural Research Program of the National Institutes of Health, National Cancer Institute, Centre for Cancer Research (grant number: ZIA BC011513 and ZIA BC011506).

Research Progress of Nanomaterials Acting on NK Cells in Tumor Immunotherapy and Imaging.

The prognosis for cancer patients has declined dramatically in recent years due to the challenges in treating malignant tumors. Tumor immunotherapy, which includes immune target inhibition and chimeric antigen receptor cell treatment, is currently evolving quickly. Among them, natural killer (NK) cells are gradually becoming another preferred cell immunotherapy after T cell immunotherapy due to their unique killing effects in innate and adaptive immunity. NK cell therapy has shown encouraging outcomes in clinical studies; however, there are still some problems, including limited efficacy in solid tumors, inadequate NK cell penetration, and expensive treatment expenses. Noteworthy benefits of nanomaterials include their chemical specificity, biocompatibility, and ease of manufacturing; these make them promising instruments for enhancing NK cell anti-tumor immune responses. Nanomaterials can promote NK cell homing and infiltration, participate in NK cell modification and non-invasive cell tracking and imaging modes, and greatly increase the effectiveness of NK cell immunotherapy. The introduction of NK cell-based immunotherapy research and a more detailed discussion of nanomaterial research in NK cell-based immunotherapy and molecular imaging will be the main topics of this review.

Tracking adoptive natural killer cells via ultrasound imaging assisted with nanobubbles.

The recent years has witnessed an exponential growth in the field of natural killer (NK) cell-based immunotherapy for cancer treatment. As a prerequisite to precise evaluations and on-demand interventions, the noninvasive tracking of adoptive NK cells plays a crucial role not only in post-treatment monitoring, but also in offering opportunities for preclinical studies on therapy optimizations. Here, we describe an NK cell tracking strategy for cancer immunotherapy based on ultrasound imaging modality. Nanosized ultrasound contrast agents, gas vesicles (GVs), were surface-functionalized to label NK cells. Unlike traditional microbubble contrast agents, nanosized GVs with their unique thermodynamical stability enable the detection of labeled NK cells under nonlinear contrast-enhanced ultrasound (nCEUS), without a noticeable impact on cellular viability or migration. By such labeling, we were able to monitor the trafficking of systematically infused NK cells to a subcutaneous tumor model. Upon co-treatment with interleukin (IL)-2, we observed a rapid enhancement in NK cell trafficking at the tumor site as early as 3h post-infusion. Altogether, we show that the proposed ultrasound-based tracking strategy is able to capture the dynamical changes of cell trafficking in NK cell-based immunotherapy, providing referencing information for early-phase monotherapy evaluation, as well as understanding the effects of modulatory co-treatment. STATEMENT OF SIGNIFICANCE: In cellular immunotherapies, the post-infusion monitoring of the living therapeutics has been challenging. Several popular imaging modalities have been explored the monitoring of the adoptive immune cells, evaluating their trafficking and accumulation in the tumor. Here we demonstrated, for the first time, the ultrasound imaging-based immune cell tracking strategy. We showed that the acoustic labeling of adoptive immune cells was feasible with nanosized ultrasound contrast agents, overcoming the size and stability limitations of traditional microbubbles, enabling dynamical tracking of adoptive natural killer cells in both monotherapy and synergic treatment with cytokines. This article introduced the cost-effective and ubiquitous ultrasound imaging modality into the field of cellular immunotherapies, with broad prospectives in early assessment and on-demand image-guided interventions.

Non-Invasive Tracking of Nanobubble Tagged Natural Killer Cells Using Clinical Ultrasound

Non-Invasive Tracking of Nanobubble Tagged Natural Killer Cells Using Clinical Ultrasound

IMMU-41. VERSATILE MRNA-NANOPARTICLE PLATFORM TO REPROGRAM THE BRAIN TUMOR MICROENVIRONMENT AND PREDICT TREATMENT OUTCOME

Abstract RNA vaccines have shown great promise as activators of immune responses against viral pathogens but their efficacy in cancer is unclear. Here, we describe a versatile, personalized mRNA-nanoparticle (RNA-NP) platform that can be customized to produce powerful anti-tumor immune activation, reprogram the brain tumor microenvironment, and predict vaccine efficacy just two days after treatment. Lipid mixtures (i.e. DOTAP, Cholesterol) with or without iron oxide nanoparticle-cores were complexed with mRNA encoding tumor antigens. Intravenous administration of RNA-NPs induced robust activation of innate immune cells resulting in prolonged survival in murine models of subcutaneous and intracranial melanoma. Inclusion of cholesterol in the lipid backbone enabled delivery of nucleic acids across the blood brain barrier and into tumor-associated myeloid cells in intracranial GL261 and KR158b tumors. These cholesterol-bearing liposomes not only activated innate immune cells in the tumor microenvironment (i.e. increased expression of CD80 and MHCII), but also enabled further manipulation of this compartment. Use of RNA-NPs to deliver siRNA targeting PD-L1 resulted in significant reduction in PD-L1 expression among tumor associated myeloid cells, leading to 37% long term survivorship in combination with systemic checkpoint blockade in an otherwise fatal model of GL261. We have also shown that IONPs incorporated into the cores of these particles enable non-invasive tracking of dendritic cells by MRI, enabling creation of a theranostic approach to: 1) enhance immunologic effects; 2) facilitate translocation across the blood-brain barrier; and 3) enable non-invasive imaging to predict response to RNA-NPs.

Far-Red Fluorescent Murine Glioma Model for Accurate Assessment of Brain Tumor Progression.

Simple SummaryThe creation of stable fluorescent glioma cell lines opens prospects for the detailed characterization of the molecular mechanisms of glioma origin and pathogenesis, and the development of breakthrough therapeutic approaches to achieve maximum glioma destruction and minimize the risk of future metastases. Herein, we generated and characterized a novel fluorescent glioma GL261-kat cell line stably expressing a far-red fluorescent protein, TurboFP635 (Katushka). Using the orthotopic mouse glioma model and epi-fluorescence imaging, we demonstrate the detection of fluorescent glioma GL261-kat cells in mice, and observe an increase in the fluorescence signal during glioma progression, which is accompanied by a gradual development of neurological deficit and behavioral alterations in mice. We show that GL261-kat cells can be a useful tool for studying glioma biology, because they can accurately and non-invasively monitor the characteristics of glioma growth in brain tissue in orthotopic mouse models.Glioma is the most common brain tumor, for which no significant improvement in life expectancy and quality of life is yet possible. The creation of stable fluorescent glioma cell lines is a promising tool for in-depth studies of the molecular mechanisms of glioma initialization and pathogenesis, as well as for the development of new anti-cancer strategies. Herein, a new fluorescent glioma GL261-kat cell line stably expressing a far-red fluorescent protein (TurboFP635; Katushka) was generated and characterized, and then validated in a mouse orthotopic glioma model. By using epi-fluorescence imaging, we detect the fluorescent glioma GL261-kat cells in mice starting from day 14 after the inoculation of glioma cells, and the fluorescence signal intensity increases as the glioma progresses. Tumor growth is confirmed by magnetic resonance imaging and histology. A gradual development of neurological deficit and behavioral alterations in mice is observed during glioma progression. In conclusion, our results demonstrate the significance and feasibility of using the novel glioma GL261-kat cell line as a model of glioma biology, which can be used to study the initialization of glioma and monitor its growth by lifetime non-invasive tracking of glioma cells, with the prospect of monitoring the response to anti-cancer therapy.

Hyperspectral CARS microscopy and quantitative unsupervised analysis of deuterated and non-deuterated fatty acid storage in human cells.

Coherent anti-Stokes Raman scattering (CARS) implemented as a vibrational micro-spectroscopy modality eradicates the need for potentially perturbative fluorescent labeling while still providing high-resolution, chemically specific images of biological samples. Isotopic substitution of hydrogen atoms with deuterium introduces minimal change to molecular structures and can be coupled with CARS microscopy to increase chemical contrast. Here, we investigate HeLa cells incubated with non-deuterated or deuterium-labeled fatty acids, using an in-house-developed hyperspectral CARS microscope coupled with an unsupervised quantitative data analysis algorithm, to retrieve Raman susceptibility spectra and concentration maps of chemical components in physically meaningful units. We demonstrate that our unsupervised analysis retrieves the susceptibility spectra of the specific fatty acids, both deuterated and non-deuterated, in good agreement with reference Raman spectra measured in pure lipids. Our analysis, using the cell-silent spectral region, achieved excellent chemical specificity despite having no prior knowledge and considering the complex intracellular environment inside cells. The quantitative capabilities of the analysis allowed us to measure the concentration of deuterated and non-deuterated fatty acids stored within cytosolic lipid droplets over a 24 h period. Finally, we explored the potential use of deuterium-labeled lipid droplets for non-invasive cell tracking, demonstrating an effective application of the technique for distinguishing between cells in a mixed population over a 16 h period. These results further demonstrate the chemically specific capabilities of hyperspectral CARS microscopy to characterize and distinguish specific lipid types inside cells using an unbiased quantitative data analysis methodology.

Noninvasive Tracking of Natural Killer Cells Using Gold Nanoparticles.

Natural killer (NK)-cell-based immunotherapy is emerging as an attractive approach for cancer treatment. However, to facilitate and expedite clinical implementation, important questions must be answered regarding the in vivo functionality and trafficking patterns of the transferred cells. We have recently developed a noninvasive cell-tracking technique, based on gold nanoparticles (GNPs) as cell-labeling and contrast agents for whole-body computed tomography (CT) imaging. Herein, we report the implementation of this technique for longitudinal and quantitative tracking of NK cell kinetics, the migration and biodistribution in tumor-bearing mice. NK cells were successfully labeled with GNPs, without impairing their biological function, as assessed both in vitro, by cytokine release and cytotoxicity assays, and in vivo, using a xenograft model of human tumors. Using CT, we longitudinally tracked the migration of intravenously injected NK cells and observed an accumulation of effector cell clusters at the tumor site, up to 72 h. Fluorescence imaging of the cells over time correlated with ex vivo quantitative analysis of gold content in the tumor, validating the accuracy and reliability of our technique. Our cell-tracking approach thus offers a valuable tool for preclinical studies, as well as for clinical applications, to elucidate the fate of NK cells and promote the implementation of NK-cell-based immunotherapy.

In Vivo Cell Tracking Using PET: Opportunities and Challenges for Clinical Translation in Oncology.

Simple SummaryTracking therapeutic cells with non-invasive imaging methods has the potential to provide important information on the efficacy of cell therapies. In oncology, for example, monitoring the spatial distribution of chimeric antigen receptor (CAR) T-cells or tumour-infiltrating lymphocytes (TILs) could be used to monitor the efficiency of cellular trafficking to target sites within a patient. This review covers different cell labelling approaches for the non-invasive detection of therapeutic cells using positron emission tomography (PET). The potential for the clinical translation of these approaches and first-in-human studies is examined, as well as the translational challenges involved and how imaging can help overcome some of these challenges.Cell therapy is a rapidly evolving field involving a wide spectrum of therapeutic cells for personalised medicine in cancer. In vivo imaging and tracking of cells can provide useful information for improving the accuracy, efficacy, and safety of cell therapies. This review focuses on radiopharmaceuticals for the non-invasive detection and tracking of therapeutic cells using positron emission tomography (PET). A range of approaches for imaging therapeutic cells is discussed: Direct ex vivo labelling of cells, in vivo indirect labelling of cells by utilising gene reporters, and detection of specific antigens expressed on the target cells using antibody-based radiopharmaceuticals (immuno-PET). This review examines the evaluation of PET imaging methods for therapeutic cell tracking in preclinical cancer models, their role in the translation into patients, first-in-human studies, as well as the translational challenges involved and how they can be overcome.

18F]FDG-labelled stem cell PET imaging in different route of administrations and multiple animal species

Stem cell therapy holds great promise for tissue regeneration and cancer treatment, although its efficacy is still inconclusive and requires further understanding and optimization of the procedures. Non-invasive cell tracking can provide an important opportunity to monitor in vivo cell distribution in living subjects. Here, using a combination of positron emission tomography (PET) and in vitro 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) direct cell labelling, the feasibility of engrafted stem cell monitoring was tested in multiple animal species. Human mesenchymal stem cells (MSCs) were incubated with phosphate-buffered saline containing [18F]FDG for in vitro cell radiolabelling. The pre-labelled MSCs were administrated via peripheral vein in a mouse (n = 1), rats (n = 4), rabbits (n = 4) and non-human primates (n = 3), via carotid artery in rats (n = 4) and non-human primates (n = 3), and via intra-myocardial injection in rats (n = 5). PET imaging was started 10 min after cell administration using a dedicated small animal PET system for a mouse and rats. A clinical PET system was used for the imaging of rabbits and non-human primates. After MSC administration via peripheral vein, PET imaging revealed intense radiotracer signal from the lung in all tested animal species including mouse, rat, rabbit, and non-human primate, suggesting administrated MSCs were trapped in the lung tissue. Furthermore, the distribution of the PET signal significantly differed based on the route of cell administration. Administration via carotid artery showed the highest activity in the head, and intra-myocardial injection increased signal from the heart. In vitro [18F]FDG MSC pre-labelling for PET imaging is feasible and allows non-invasive visualization of initial cell distribution after different routes of cell administration in multiple animal models. Those results highlight the potential use of that imaging approach for the understanding and optimization of stem cell therapy in translational research.

Advances in surface‐enhanced Raman scattering bioprobes for cancer imaging

AbstractSurface‐enhanced Raman scattering (SERS) technology with feature of high sensitivity, selective enhancement, in situ detection, nondestructive, label free, and fingerprint spectrum has been widely utilized in various practical applications, especially for bioanalysis. Cancer diagnosis and therapy based on SERS bioimaging has been reported as a promising approach in recent decades, and various types of material‐based SERS bioprobes are rapidly designed continuously. SERS bioimaging has been successfully employed in cancer screening, diagnosis, and componential analysis in both in vitro and in vivo cancer tissue samples, which simultaneously provides visual morphology and biochemical information. Precise tumor tissue excision, real‐time monitoring of cellular uptake process, and noninvasive cell tracking and labeling are realized due to the effective Raman image bioprobes, satisfying the requirements of precision medicine. Here, an overview of SERS bioprobes based on noble metals, metal oxides, and composite materials is presented by highlighting their respective, unique advantages and recent achievements in cancer imaging realm. This review also offers a distinctive perspective on designing multifunctional micro–nanoparticles with remarkable SERS activity, and proposing novel strategies for establishing high‐performance sensors and imaging bioprobes derived from the deep insight of enhancement mechanism for different types of SERS substrates.

Non-radioactive and sensitive tracking of neutrophils towards inflammation using antibody functionalized magnetic particle imaging tracers.

White blood cells (WBCs) are a key component of the mammalian immune system and play an essential role in surveillance, defense, and adaptation against foreign pathogens. Apart from their roles in the active combat of infection and the development of adaptive immunity, immune cells are also involved in tumor development and metastasis. Antibody-based therapeutics have been developed to regulate (i.e. selectively activate or inhibit immune function) and harness immune cells to fight malignancy. Alternatively, non-invasive tracking of WBC distribution can diagnose inflammation, infection, fevers of unknown origin (FUOs), and cancer. Magnetic Particle Imaging (MPI) is a non-invasive, non-radioactive, and sensitive medical imaging technique that uses safe superparamagnetic iron oxide nanoparticles (SPIOs) as tracers. MPI has previously been shown to track therapeutic stem cells for over 87 days with a ~200 cell detection limit. In the current work, we utilized antibody-conjugated SPIOs specific to neutrophils for in situ labeling, and non-invasive and radiation-free tracking of these inflammatory cells to sites of infection and inflammation in an in vivo murine model of lipopolysaccharide-induced myositis. MPI showed sensitive detection of inflammation with a contrast-to-noise ratio of ~8-13.

Feasibility study of 68Ga-labeled CART cells for in vivo tracking using micro-positron emission tomography imaging.

Clinical tracking of chimeric antigen receptor (CAR) T cells in vivo by positron emission tomography (PET) imaging is an area of intense interest. But the long-livedpositron emitter-labeled CAR T cells stay in the liver and spleen for days or even weeks. Thus, the excessive absorbed effective dose becomes a major biosafety issue leading it difficult for clinical translation. In this study we used68Ga, a commercially available short-livedpositron emitter, to label CAR T cells for noninvasive cell tracking in vivo. CAR T cells could be tracked in vivo by 68Ga-PET imaging for at least 6 h. We showed a significant correlation between the distribution of 89Zr and 68Ga-labeled CAR T cells in the same tissues (lungs, liver, and spleen). The distribution and homing behavior of CAR T cells at the early period is highly correlated with the long-term fate of CAR T cells in vivo. And the effective absorbed dose of 68Ga-labeled CAR T cells is only one twenty-fourth of 89Zr-labeled CAR T cells, which was safe for clinical translation. We conclude the feasibility of 68Ga instead of 89Zr directly labeling CAR T cells for noninvasive tracking of the cells in vivo at an early stage based on PET imaging. This method provides a potential solution to the emerging need for safe and practical PET tracer for cell tracking clinically.

Dual-modal magnetic resonance and photoacoustic tracking and outcome of transplanted tendon stem cells in the rat rotator cuff injury model

Stem cells have been used to promote the repair of rotator cuff injury, but their fate after transplantation is not clear. Therefore, contrast agents with good biocompatibility for labeling cell and a reliable technique to track cell are necessary. Here, we developed a micron-sized PLGA/IO MPs to label tendon stem cells (TSCs) and demonstrated that PLGA/IO MPs were safe and efficient for long-term tracking of TSCs by using dual-modal MR and Photoacoustic (PA) imaging both in vitro and in rat rotator cuff injury. Moreover, TSCs improved the repair of injury and the therapeutic effect was not affected by PLGA/IO MPs labeling. We concluded that PLGA/IO particle was a promising dual-modal MR/PA contrast for noninvasive long-term stem cell tracking.

In vivo stem cell tracking using scintigraphy in a canine model of DMD

One of the main challenges in cell therapy for muscle diseases is to efficiently target the muscle. To address this issue and achieve better understanding of in vivo cell fate, we evaluated the relevance of a non-invasive cell tracking method in the Golden Retriever Muscular Dystrophy (GRMD) model, a well-recognised model of Duchenne Muscular Dystrophy (DMD). Mesoangioblasts were directly labelled with 111In-oxine, and injected through one of the femoral arteries. The scintigraphy images obtained provided the first quantitative mapping of the immediate biodistribution of mesoangioblasts in a large animal model of DMD. The results revealed that cells were trapped by the first capillary filters: the injected limb and the lung. During the days following injection, radioactivity was redistributed to the liver. In vitro studies, performed with the same cells prepared for injecting the animal, revealed prominent cell death and 111In release. In vivo, cell death resulted in 111In release into the vasculature that was taken up by the liver, resulting in a non-specific and non-cell-bound radioactive signal. Indirect labelling methods would be an attractive alternative to track cells on the mid- and long-term.

Noninvasive Tracking of Hematopoietic Stem Cells in a Bone Marrow Transplant Model.

The hematopoietic stem cell engraftment depends on adequate cell numbers, their homing, and the subsequent short and long-term engraftment of these cells in the niche. We performed a systematic review of the methods employed to track hematopoietic reconstitution using molecular imaging. We searched articles indexed, published prior to January 2020, in PubMed, Cochrane, and Scopus with the following keyword sequences: (Hematopoietic Stem Cell OR Hematopoietic Progenitor Cell) AND (Tracking OR Homing) AND (Transplantation). Of 2191 articles identified, only 21 articles were included in this review, after screening and eligibility assessment. The cell source was in the majority of bone marrow from mice (43%), followed by the umbilical cord from humans (33%). The labeling agent had the follow distribution between the selected studies: 14% nanoparticle, 29% radioisotope, 19% fluorophore, 19% luciferase, and 19% animal transgenic. The type of graft used in the studies was 57% allogeneic, 38% xenogeneic, and 5% autologous, being the HSC receptor: 57% mice, 9% rat, 19% fish, 5% for dog, porcine and salamander. The imaging technique used in the HSC tracking had the following distribution between studies: Positron emission tomography/single-photon emission computed tomography 29%, bioluminescence 33%, fluorescence 19%, magnetic resonance imaging 14%, and near-infrared fluorescence imaging 5%. The efficiency of the graft was evaluated in 61% of the selected studies, and before one month of implantation, the cell renewal was very low (less than 20%), but after three months, the efficiency was more than 50%, mainly in the allogeneic graft. In conclusion, our review showed an increase in using noninvasive imaging techniques in HSC tracking using the bone marrow transplant model. However, successful transplantation depends on the formation of engraftment, and the functionality of cells after the graft, aspects that are poorly explored and that have high relevance for clinical analysis.

How Non-invasive in vivo Cell Tracking Supports the Development and Translation of Cancer Immunotherapies.

Immunotherapy is a relatively new treatment regimen for cancer, and it is based on the modulation of the immune system to battle cancer. Immunotherapies can be classified as either molecular or cell-based immunotherapies, and both types have demonstrated promising results in a growing number of cancers. Indeed, several immunotherapies representing both classes are already approved for clinical use in oncology. While spectacular treatment successes have been reported, particularly for so-called immune checkpoint inhibitors and certain cell-based immunotherapies, they have also been accompanied by a variety of severe, sometimes life-threatening side effects. Furthermore, not all patients respond to immunotherapy. Hence, there is the need for more research to render these promising therapeutics more efficacious, more widely applicable, and safer to use. Whole-body in vivo imaging technologies that can interrogate cancers and/or immunotherapies are highly beneficial tools for immunotherapy development and translation to the clinic. In this review, we explain how in vivo imaging can aid the development of molecular and cell-based anti-cancer immunotherapies. We describe the principles of imaging host T-cells and adoptively transferred therapeutic T-cells as well as the value of traceable cancer cell models in immunotherapy development. Our emphasis is on in vivo cell tracking methodology, including important aspects and caveats specific to immunotherapies. We discuss a variety of associated experimental design aspects including parameters such as cell type, observation times/intervals, and detection sensitivity. The focus is on non-invasive 3D cell tracking on the whole-body level including aspects relevant for both preclinical experimentation and clinical translatability of the underlying methodologies.

Non-invasive Reporter Gene Imaging of Cell Therapies, including T Cells and Stem Cells.

Cell therapies represent a rapidly emerging class of new therapeutics. They are intended and developed for the treatment of some of the most prevalent human diseases, including cancer, diabetes, and for regenerative medicine. Currently, they are largely developed without precise assessment of their invivo distribution, efficacy, or survival either clinically or preclinically. However, it would be highly beneficial for both preclinical cell therapy development and subsequent clinical use to assess these parameters in situ to enable enhancements in efficacy, applicability, and safety. Molecular imaging can be exploited to track cells non-invasively on the whole-body level and can enable monitoring for prolonged periods in a manner compatible with rapidly expanding cell types. In this review, we explain how invivo imaging can aid the development and clinical translation of cell-based therapeutics. We describe the underlying principles governing non-invasive invivo long-term cell tracking in the preclinical and clinical settings, including available imaging technologies, reporter genes, and imaging agents as well as pitfalls related to experimental design. Our emphasis is on adoptively transferred Tcell and stem cell therapies.