Noninvasive imaging of dendritic cell migration into lymph nodes using near-infrared fluorescent semiconductor nanocrystals

Dendritic Cell-Based Immunotherapy: The Importance of Dendritic Cell Migration

Dendritic cells (DCs) are specialized antigen-presenting cells that are crucial for maintaining self-tolerance, initiating immune responses against pathogens, and patrolling body compartments. Despite promising aspects, DC-based immunotherapy faces challenges that include limited availability, immune escape in tumors, immunosuppression in the tumor microenvironment, and the need for effective combination therapies. A further limitation in DC-based immunotherapy is the low population of migratory DC (around 5%-10%) that migrate to lymph nodes (LNs) through afferent lymphatics depending on the LN draining site. By increasing the population of migratory DCs, DC-based immunotherapy could enhance immunotherapeutic effects on target diseases. This paper reviews the importance of DC migration and current research progress in the context of DC-based immunotherapy.

A lysosome-targeted triazole near-infrared cyanine fluorescent probe for in vivo long-term cell tracking

In vivo visualization of cell migration and engraftment in small animals provides crucial information for the development and clinical translation of cell-based therapies. Therefore, a good quality near-infrared (NIR) fluorescent probe with high optical properties and excellent cellular retention ability is desired for in vivo cell tracking. Herein, we designed and synthesized a lysosome-targeted triazole NIR cyanine fluorescent probe, named IR780-NT-NH2, for in vivo long-term cell tracking. For the design, the heptamethine cyanine dye IR780 was used as the NIR fluorescent skeleton to ensure that the absorption and emission wavelengths fall within the NIR window. The substituent N-triazole group endowed the probe with high photostability and brightness. It has a quantum yield of 17.3% and the brightness remained above 85% after continuous illumination for 30 min. Due to the primary amine docking group, IR780-NT-NH2 has excellent lysosomal targeting and retention abilities as it becomes protonated in an acidic environment. The strong signal strength of IR780-NT-NH2 was maintained in well-shaped cells after an additional 12 h incubation. Moreover, this NIR probe exhibited ideal cellular permeability and biosafety. Finally, we realized long-term cell tracking with IR780-NT-NH2 labeled PC-3 cells using a NIR imaging system. The present study provides evidence that IR780-NT-NH2 exhibits ideal optical properties, excellent cellular permeation and retention, and good biosafety, which are useful for in vivo long-term observation of cells, and thus it shows promising potential for visualization in cell-based therapy.

Molecular Imaging of Innate Immunity and Immunotherapy

The innate immune system plays a key role as the first line of defense in various human diseases including cancer, cardiovascular and inflammatory diseases. In contrast to tissue biopsies and blood biopsies, in vivo imaging of the innate immune system can provide whole body measurements of immune cell location and function and changes in response to disease progression and therapy. Rationally developed molecular imaging strategies can be used in evaluating the status and spatio-temporal distributions of the innate immune cells in near real-time, mapping the biodistribution of novel innate immunotherapies, monitoring their efficacy and potential toxicities, and eventually for stratifying patients that are likely to benefit from these immunotherapies. In this review, we will highlight the current state-of-the-art in noninvasive imaging techniques for preclinical imaging of the innate immune system particularly focusing on cell trafficking, biodistribution, as well as pharmacokinetics and dynamics of promising immunotherapies in cancer and other diseases; discuss the unmet needs and current challenges in integrating imaging modalities and immunology and suggest potential solutions to overcome these barriers.

Evaluation of different 89Zr-labeled synthons for direct labeling and tracking of white blood cells and stem cells in healthy athymic mice

Cell based therapies are evolving as an effective new approach to treat various diseases. To understand the safety, efficacy, and mechanism of action of cell-based therapies, it is imperative to follow their biodistribution noninvasively. Positron-emission-tomography (PET)-based non-invasive imaging of cell trafficking offers such a potential. Herein, we evaluated and compared three different ready-to-use direct cell radiolabeling synthons, [⁸⁹Zr]Zr-DFO-Bn-NCS, [⁸⁹Zr]Zr-Hy₃ADA⁵-NCS, and [⁸⁹Zr]Zr-Hy₃ADA⁵-SA for PET imaging-based trafficking of white blood cells (WBCs) and stem cells (SCs) up to 7 days in athymic nude mice. We compared the degree of ⁸⁹Zr complexation and percentage of cell radiolabeling efficiencies with each. All three synthons, [⁸⁹Zr]Zr-DFO-Bn-NCS, [⁸⁹Zr]Zr-Hy₃ADA⁵-NCS, and [⁸⁹Zr]Zr-Hy₃ADA⁵-SA, were successfully prepared, and used for radiolabeling of WBCs and SCs. The highest cell radiolabeling yield was found for [⁸⁹Zr]Zr-DFO-Bn-NCS, followed by [⁸⁹Zr]Zr-Hy₃ADA⁵-NCS, and [⁸⁹Zr]Zr-Hy₃ADA⁵-SA. In terms of biodistribution, WBCs radiolabeled with [⁸⁹Zr]Zr-DFO-Bn-NCS or [⁸⁹Zr]Zr-Hy₃ADA⁵-NCS, were primarily accumulated in liver and spleen, whereas SCs radiolabeled with [⁸⁹Zr]Zr-DFO-Bn-NCS or [⁸⁹Zr]Zr-Hy₃ADA⁵-NCS were found in lung, liver and spleen. A high bone uptake was observed for both WBCs and SCs radiolabeled with [⁸⁹Zr]Zr-Hy₃ADA⁵-SA, suggesting in-vivo instability of [⁸⁹Zr]Zr-Hy₃ADA⁵-SA synthon. This study offers an appropriate selection of ready-to-use radiolabeling synthons for noninvasive trafficking of WBCs, SCs and other cell-based therapies.

Nanoparticle-based approaches to target the lymphatic system for antitumor treatment

Immunotherapies have been established as safe and efficient modalities for numerous tumor treatments. The lymphatic system, which is an important system, can modulate the immune system via a complex network, which includes lymph nodes, vessels, and lymphocytes. With the deepening understanding of tumor immunology, a plethora of immunotherapies, which include vaccines, photothermal therapy, and photodynamic therapy, have been established for antitumor treatments. However, the deleterious off-target effects and nonspecific targeting of therapeutic agents result in low efficacy of immunotherapy. Fortunately, nanoparticle-based approaches for targeting the lymphatic system afford a unique opportunity to manufacture drugs that can simultaneously tackle both aspects, thereby improving tumor treatments. Over the past decades, great strides have been made in the development of DC vaccines and nanomedicine as antitumor treatments in the field of lymphatic therapeutics and diagnosis. In this review, we summarize the current strategies through which nanoparticle technology has been designed to target the lymphatic system and describe applications of lymphatic imaging for the diagnosis and image-guided surgery of tumor metastasis. Moreover, improvements in the tumor specificity of nanovaccines and medicines, which have been realized through targeting or stimulating the lymphatic system, can provide amplified antitumor immune responses and reduce side effects, thereby promoting the paradigm of antitumor treatment into the clinic to benefit patients.

Preclinical models and technologies to advance nanovaccine development

The remarkable success of targeted immunotherapies is revolutionizing cancer treatment. However, tumor heterogeneity and low immunogenicity, in addition to several tumor-associated immunosuppression mechanisms are among the major factors that have precluded the success of cancer vaccines as targeted cancer immunotherapies. The exciting outcomes obtained in patients upon the injection of tumor-specific antigens and adjuvants intratumorally, reinvigorated interest in the use of nanotechnology to foster the delivery of vaccines to address cancer unmet needs. Thus, bridging nano-based vaccine platform development and predicted clinical outcomes the selection of the proper preclinical model will be fundamental. Preclinical models have revealed promising outcomes for cancer vaccines. However, only few cases were associated with clinical responses. This review addresses the major challenges related to the translation of cancer nano-based vaccines to the clinic, discussing the requirements for ex vivo and in vivo models of cancer to ensure the translation of preclinical success to patients.

Near-infrared fluorescence imaging in immunotherapy

Near-infrared (NIR) light possesses many suitable optophysical properties for medical imaging including low autofluorescence, deep tissue penetration, and minimal light scattering, which together allow for high-resolution imaging of biological tissue. NIR imaging has proven to be a noninvasive and effective real-time imaging methodology that provides a high signal-to-background ratio compared to other potential optical imaging modalities. In response to this, the use of NIR imaging has been extensively explored in the field of immunotherapy. To date, NIR fluorescence imaging has successfully offered reliable monitoring of the localization, dynamics, and function of immune responses, which are vital in assessing not only the efficacy but also the safety of treatments to design immunotherapies optimally. This review aims to provide an overview of the current research on NIR imaging of the immune response. We expect that the use of NIR imaging will expand further in response to the recent success in cancer immunotherapy. We will also offer our insights on how this technology will meet rapidly growing expectations in the future.

CRISPR/Cas9 mediated GFP-human dentin matrix protein 1 (DMP1) promoter knock-in at the ROSA26 locus in mesenchymal stem cell for monitoring osteoblast differentiation

BACKGROUND

Dentin matrix protein 1 (DMP1) is highly expressed in mineralized tooth and bone, playing a critical role in mineralization and phosphate metabolism. One important role for the expression of DMP1 in the nucleus of preosteoblasts is the up-regulation of osteoblast-specific genes such as osteocalcin and alkaline phosphatase¹ . The present study aimed to investigate the potential application of human DMP1 promoter as an indicator marker of osteoblastic differentiation.

METHODS

In the present study, we developed DMP1 promoter-DsRed-GFP knock-in mesenchymal stem cell (MSCs) via the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system that enabled automatic detection of osteoblast differentiation. With the application of a homology-directed knock-in strategy, a 2-kb fragment of DMP1 promoter, which was inserted upstream of the GFP and DsRed reporter cassette, was integrated into the human ROSA locus to generate double fluorescent cells. We further differentiated MSCs under osteogenic media to monitor the fate of MSCs. First, cells were transfected using CRISPR/Cas9 plasmids, which culminated in MSCs with a green fluorescence intensity, then GFP-positive cells were selected using puromycin. Second, the GFP-positive MSCs were differentiated toward osteoblasts, which demonstrated an increased red fluorescence intensity. The osteoblast differentiation of MSCs was also verified by performing alkaline phosphatase and Alizarin Red assays.

RESULTS

We have exploited the DMP1 promoter as a predictive marker of MSC differentiation toward osteoblasts. Using the CRISPR/Cas9 technology, we have identified a distinctive change in the fluorescence intensities of GFP knock-in (green) and osteoblast differentiated MSCs ² .

CONCLUSIONS

The data show that DMP1-DsRed-GFP knock-in MSCs through CRISPR/Cas9 technology provide a valuable indicator for osteoblast differentiation. Moreover, The DMP1 promoter might be used as a predictive marker of MSCs differentiated toward osteoblasts.

Multiscale fluorescent tracking of immune cells in the liver with a highly biocompatible far-red emitting polymer probe

The development of innovative immune cell therapies relies on efficient cell tracking strategies. For this, multiscale fluorescence-based analyses of transferred cells into the host with complementary techniques, including flow cytometry for high-throughput cell analysis and two-photon microscopy for deep tissue imaging would be highly beneficial. Ideally, cells should be labelled with a single fluorescent probe combining all the properties required for these different techniques. Due to the intrinsic autofluorescence of most tissues and especially the liver, far-red emission is also an important asset. However, the development of far-red emitting probes suitable for two-photon microscopy and compatible with clearing methods to track labelled immune cells in thick samples, remains challenging. A newly-designed water-soluble far-red emitting polymer probe, 19K-6H, with a large Stokes shift, was thus evaluated for the tracking of primary immune CD8 T cells. These cells, prepared from mouse spleen, were efficiently labelled with the 19K-6H probe, which was internalized via endocytosis and was highly biocompatible at concentrations up to 20 μM. Labelled primary CD8 T cells were detectable in culture by both confocal and two-photon microscopy as well as flow cytometry, even after 3 days of active proliferation. Finally, 19K-6H-labelled primary CD8 T cells were injected to mice in a classical model of immune mediated hepatitis. The efficient tracking of the transferred cells in the liver by flow cytometry (on purified non-parenchymal cells) and by two-photon microscopy on 800 μm thick cleared sections, demonstrated the versatility of the 19K-6H probe.

Noninvasive Photoacoustic Imaging of Dendritic Cell Stimulated with Tumor Cell-Derived Exosome

PURPOSE

The tools to trigger dendritic cell (DC) activation and to verify DC migration in vivo are important for directing DC immunotherapy toward successful treatment. We evaluated whether tumor cell-derived exosome (TEX)-stimulated DC migration into lymph node (LN) in mouse could be tracked using gold nanoparticle (GN)-labeling and ultrasound (US)-guided photoacoustic imaging (PAI).

PROCEDURES

GFP-transduced DC2.4 cells were used. RFP-tagged TEXs were purified from a stable 4T1 cell line overexpressing the exosomal CD63-RFP fusion protein. The TEX uptake by DCs was visualized using confocal laser scanning microscopy. GNs with surface plasmon resonance at 808 nm were used for DC-labeling. DCs that migrated into axillary LN were longitudinally monitored by US-guided PAI and analyzed by silver staining and immunohistochemistry.

RESULTS

TEXs were easily internalized in DCs, increased proliferation and migration capacities, and upregulated co-stimulatory molecules, CCR7 and TNF-α without cytotoxicity. The GN-labeling exerted no adverse effects on the biological functions of DCs. US-guided PAI and DC-labeling allowed for sensitive and longitudinal monitoring of TEX-stimulated DC migration toaxillary LN.

CONCLUSIONS

TEXs efficiently activated DCs and GN-labeled DC migration into LN was successfully monitored using US-guided PAI, suggesting that TEXs are a good source for DC activation and US-guided PAI is a cost-effective and easy-to-use imaging modality for noninvasive tracking of DCs.

The silencing of indoleamine 2,3-dioxygenase 1 (IDO1) in dendritic cells by siRNA-loaded lipid nanoparticles enhances cell-based cancer immunotherapy

Cell-based therapy using dendritic cells (DC) represents a potent cancer immunotherapy. However, activated DC express indoleamine 2,3-dioxygenase 1 (IDO1), a counter-regulatory and tolerogenic molecule, leading to the inhibition of T cell activation and the promotion of T cell differentiation into regulatory T cells. Silencing the IDO1 gene in DC by small interfering RNA (siRNA) represents a potent therapeutic strategy. We report on the successful and efficient introduction of a siRNA targeting IDO1 into mouse DCs by a means of a multifunctional envelope-type nanodevice (MEND) containing a YSK12-C4 (YSK12-MEND). The YSK12-C4 has both fusogenic and cationic properties. The YSK12-MEND induced an effective level of gene silencing of IDO1 at siRNA doses in the range of 1–20 nM, a concentration that commercially available transfection reagents are not able to silence. The YSK12-MEND mediated IDO1 silencing had no effect on the characteristic determinants of DC phenotype such as CD11c, CD80 and MHC class II. The silencing of IDO1 in DC by the YSK12-MEND significantly enhanced the antitumor effect against E.G7-OVA tumor. Moreover, a decrease in the numbers of regulatory T cells in the tumor was observed in mice that were treated with the IDO1-silenced DC. The YSK12-MEND appears to be a potent delivery system for IDO1-silenced DC based cancer immunotherapy.

The Immunoimaging Toolbox

The recent clinical success of cancer immunotherapy has renewed interest in the development of tools to image the immune system. In general, immunotherapies attempt to enable the body's own immune cells to seek out and destroy malignant disease. Molecular imaging of the cells and molecules that regulate immunity could provide unique insight into the mechanisms of action, and failure, of immunotherapies. In this article, we will provide a comprehensive overview of the current state-of-the-art immunoimaging toolbox with a focus on imaging strategies and their applications toward immunotherapy.

Tracking dendritic cell migration into lymph nodes by using a novel PET probe 18F-tetrafluoroborate for sodium/iodide symporter

BACKGROUND

Recently, ¹⁸F-tetrafluoroborate (TFB) was used as a substrate for the human sodium/iodide symporter (hNIS) reporter gene. This study evaluated the feasibility of performing molecular-genetic imaging by using the new radiotracer (¹⁸F-TFB) for the hNIS gene, to track dendritic cell (DC) migration in live mice. A murine dendritic cell line (DC2.4) co-expressing the hNIS and effluc genes (DC/NF) was established. To confirm the functional cellular expression of both effluc and NIS in the inoculated DC/NF cells by bio-medical imaging, combined bioluminescence imaging (BLI) and ¹⁸F-TFB positron emission tomography/computed tomography (PET/CT) imaging was performed after intramuscular injection with parental DCs and DC/NF cells. For DC-tracking, parental DCs or DC/NF cells were injected in the left or right mouse footpad, respectively, and ¹⁸F-TFB PET/CT and BLI were performed to monitor these cells in live mice.

RESULTS

In vivo PET/CT and BLI showed a clear signal in DC/NF injection sites but not in parental DC injection sites. The signal intensity in DC/NF cells was correlated with time. In vivo ¹⁸F-TFB PET/CT imaging showed higher radiotracer activity in the draining popliteal lymph nodes (DPLNs) in DC/NF injection sites than those in DC injection sites on day 2. BLI also showed DC/NF cell migration to the DPLNs on day 2 after the injection.

CONCLUSIONS

Migration of DCs to the lymph nodes was successfully monitored using ¹⁸F-TFB PET/CT imaging of the NIS gene and optical imaging of the effluc gene in live mice. These data support the feasibility of using ¹⁸F-TFB as a substrate for hNIS reporter gene imaging to track the migration of DCs to the lymph nodes in live animals. The use of ¹⁸F-TFB may facilitate enhanced PET imaging of the hNIS reporter gene in small animals and humans in future studies.

Multimodality Imaging of Bone Marrow-Derived Dendritic Cell Migration and Antitumor Immunity

Here, we sought to monitor bone marrow-derived dendritic cell (BMDC) migration and antitumor effects using a multimodal reporter imaging strategy in living mice. BMDCs were transduced with retroviral vector harboring human sodium iodide symporter (hNIS, nuclear imaging reporter), firefly luc2 (optical imaging reporter), and thy1.1 (surrogate marker of NIS and luc2) genes (BMDC/NF cells). No significant differences in biological functions, including cell proliferation, antigen uptake, phenotype expression, and migration ability, were observed between BMDC and BMDC/NF cells. Combined bioluminescence imaging and I-124 positron emission tomography/computed tomography clearly revealed the migration of BMDC/NF cells to draining popliteal lymph nodes at day 7 postinjection. Interestingly, marked tumor protection was observed in mice immunized with TC-1 lysate-pulsed BMDC/NF cells. Our findings suggested that multimodal reporter gene imaging of NIS and luciferase could provide insights into the biological behaviors of dendritic cells in living organisms and could be a useful tool for the optimization of DC-based immunotherapy protocols.

Advances in Molecular Imaging Strategies for In Vivo Tracking of Immune Cells

Tracking of immune cells in vivo is a crucial tool for development and optimization of cell-based therapy. Techniques for tracking immune cells have been applied widely for understanding the intrinsic behavior of immune cells and include non-radiation-based techniques such as optical imaging and magnetic resonance imaging (MRI), radiation-based techniques such as computerized tomography (CT), and nuclear imaging including single photon emission computerized tomography (SPECT) and positron emission tomography (PET). Each modality has its own strengths and limitations. To overcome the limitations of each modality, multimodal imaging techniques involving two or more imaging modalities are actively applied. Multimodal techniques allow integration of the strengths of individual modalities. In this review, we discuss the strengths and limitations of currently available preclinical in vivo immune cell tracking techniques and summarize the value of immune cell tracking in the development and optimization of immune cell therapy for various diseases.

Harnessing the potential of noninvasive in vivo preclinical imaging of the immune system: challenges and prospects

Preclinical imaging has become a powerful method for investigation of in vivo processes such as pharmacokinetics of therapeutic substances and visualization of physiologic and pathophysiological mechanisms. These are important aspects to understand diseases and develop strategies to modify their progression with pharmacologic interventions. One promising intervention is the application of specifically tailored nanoscale particles that modulate the immune system to generate a tumor targeting immune response. In this complex interaction between immunomodulatory therapies, the immune system and malignant disease, imaging methods are expected to play a key role on the way to generate new therapeutic strategies. Here, we summarize examples which demonstrate the current potential of imaging methods and develop a perspective on the future value of preclinical imaging of the immune system.

Meta-analysis of cellular toxicity for cadmium-containing quantum dots

Understanding the relationships between the physicochemical properties of engineered nanomaterials and their toxicity is critical for environmental and health risk analysis. However, this task is confounded by material diversity, heterogeneity of published data and limited sampling within individual studies. Here, we present an approach for analysing and extracting pertinent knowledge from published studies focusing on the cellular toxicity of cadmium-containing semiconductor quantum dots. From 307 publications, we obtain 1,741 cell viability-related data samples, each with 24 qualitative and quantitative attributes describing the material properties and experimental conditions. Using random forest regression models to analyse the data, we show that toxicity is closely correlated with quantum dot surface properties (including shell, ligand and surface modifications), diameter, assay type and exposure time. Our approach of integrating quantitative and categorical data provides a roadmap for interrogating the wide-ranging toxicity data in the literature and suggests that meta-analysis can help develop methods for predicting the toxicity of engineered nanomaterials.

Improving cell-based therapies by nanomodification

Cell-based therapies are emerging as a promising approach for various diseases. Their therapeutic efficacy depends on rational control and regulation of the functions and behaviors of cells during their treatments. Different from conventional regulatory strategy by chemical adjuvants or genetic engineering, which is restricted by limited synergistic regulatory efficiency or uncertain safety problems, a novel approach based on nanoscale artificial materials can be applied to modify living cells to endow them with novel functions and unique properties. Inspired by natural "nano shell" and "nano compass" structures, cell nanomodification can be developed through both external and internal pathways. In this review, some novel cell surface engineering and intracellular nanoconjugation strategies are summarized. Their potential applications are also discussed, including cell protection, cell labeling, targeted delivery and in situ regulation. It is believed that these novel cell-material complexes can have great potentials for biomedical applications.

A short-wavelength infrared emitting multimodal probe for non-invasive visualization of phagocyte cell migration in living mice

For the non-invasive visualization of cell migration in deep tissues, we synthesized a short-wavelength infrared (SWIR) emitting multimodal probe that contains PbS/CdS quantum dots, rhodamine 6G and iron oxide nanoparticles. This probe enables multimodal (SWIR fluorescence/magnetic resonance) imaging of phagocyte cell migration in living mice.

Tracking of dendritic cell migration into lymph nodes using molecular imaging with sodium iodide symporter and enhanced firefly luciferase genes

We sought to evaluate the feasibility of molecular imaging using the human sodium iodide symporter (hNIS) gene as a reporter, in addition to the enhanced firefly luciferase (effluc) gene, for tracking dendritic cell (DCs) migration in living mice. A murine dendritic cell line (DC2.4) co-expressing hNIS and effluc genes (DC/NF) was established. For the DC-tracking study, mice received either parental DCs or DC/NF cells in the left or right footpad, respectively, and combined I-124 PET/CT and bioluminescence imaging (BLI) were performed. In vivo PET/CT imaging with I-124 revealed higher activity of the radiotracer in the draining popliteal lymph nodes (DPLN) of the DC/NF injection site at day 1 than DC injection site (p < 0.05). The uptake value further increased at day 4 (p < 0.005). BLI also demonstrated migration of DC/NF cells to the DPLNs at day 1 post-injection, and signals at the DPLNs were much higher at day 4. These data support the feasibility of hNIS reporter gene imaging in the tracking of DC migration to lymphoid organs in living mice. DCs expressing the NIS reporter gene could be a useful tool to optimize various strategies of cell-based immunotherapy.

Quantum dots: bright and versatile in vitro and in vivo fluorescence imaging biosensors

Colourful cells and tissues: semiconductor quantum dots and their versatile applications in multiplexed bioimaging research.

Magnetic resonance and near-infrared imaging using a novel dual-modality nano-probe for dendritic cell tracking in vivo

BACKGROUND AIMS

The effect of cellular-based immunotherapy is highly correlated with the success of dendritic cells (DCs) homing to the draining lymph nodes (LNs) and interacting with antigen-specific CD4(+) T cells. In this study, a novel magneto-fluorescent nano-probe was used to track the in vivo migration of DCs to the draining LNs.

METHODS

A dual-modality nano-probe composed of superparamagnetic iron oxide (SPIO) and near-infrared fluorescent (NIRF) dye (NIR797) was developed, and its magnetic and optical contrasting properties were characterized. DCs generated from mouse bone marrow were co-cultured with the probe at a lower concentration of 10 μg/mL. The cell phenotype and function of DCs were also investigated by fluorescence-activated cell sorting analysis and mixed leukocyte reactivity assay. Labeled DCs were injected into the footpad of C57BL/6 mice. Afterward, magnetic resonance imaging, NIRF imaging, Perls staining and CD11c immunofluorescence were used to observe the migration of the labeled DCs into draining LNs.

RESULTS

The synthetic SPIO-NIR797 nano-probe had a desirable superparamagnetic and near-infrared behavior. Perls staining showed perfect labeling efficiency. The cell phenotypes, including CD11c, CD80, CD86 and major histocompatibility complex class II, as well as the T-cell activation potential of the mature DCs were insignificantly affected after incubation (P > 0.05). Labeled DCs migrating into LNs could be detected by both magnetic resonance imaging and NIRF imaging simultaneously, which was further confirmed by Perls staining and immunofluorescence.

CONCLUSIONS

The novel dual-modality SPIO-NIR797 nano-probe has highly biocompatible characteristics for labeling and tracking DCs, which can be used to evaluate cancer immunotherapy in clinical applications.

Quantum dots: heralding a brighter future for clinical diagnostics

Quantum dots (QDs) are semiconductor nanocrystals that possess unique optical properties including broad-range excitation, size-tunable narrow emission spectra and high photostability, giving them considerable value in various biomedical applications. The size and composition of QDs can be varied to obtain the desired emission properties and make them amenable to simultaneous detection of multiple targets. Furthermore, numerous surface functionalizations can be used to adapt QDs to the needed application. The successful use of QDs has been reported in the areas of in vitro diagnostics and imaging. There is also potential for multimodal applications for simultaneous imaging. Toxicity issues are still a prime concern with regards to in vivo applications on account of the toxic constituents of QDs.

Dendritic cell-based vaccination for renal cell carcinoma: challenges in clinical trials

After decades of research, dendritic cell (DC)-based vaccines for renal cell carcinoma have progressed from preclinical rodent models and safety assessments to Phase I/II clinical trials. DC vaccines represent a promising therapy that has produced measurable immunological responses and prolonged survival rates. However, there is still much room to improve in terms of therapeutic efficacy. The key issues that affect the efficiency and reliability of DC therapy include the selection of patients who will respond best to treatment, the proper preparation and administration of DC vaccines, and a combination of DC vaccination with other immune-enhancing therapies (e.g., removal of Tregs, CTLA-4 blockade and lymphodepletion). Additional antiangiogenic agents will hopefully lead to greater survival benefits for patients in early disease stages. This review focuses on the different approaches of DC-based vaccination against renal cell carcinoma and potential strategies to enhance the efficacy of DC vaccination.

PGI₂ signaling inhibits antigen uptake and increases migration of immature dendritic cells

PGI₂ signaling through IP inhibits allergen-induced inflammatory responses in mice. We reported previously that PGI₂ analogs decreased proinflammatory cytokine and chemokine production by mature BMDCs. However, whether PGI₂ modulates the function of immature DCs has not been investigated. We hypothesized that PGI2 negatively regulates immature DC function and investigated the effect of PGI2 analogs on immature BMDC antigen uptake and migration in vitro and in vivo. Immature BMDCs were obtained from WT and IPKO mice, both on a C57BL/6 background. The PGI2 analog cicaprost decreased FITC-OVA uptake by immature BMDCs. In addition, cicaprost increased immature BMDC podosome dissolution, pro-MMP-9 production, cell surface CCR7 expression, and chemotactic migration toward CCL19 and CCL21, as well as chemokinesis, in an IP-specific fashion. These in vitro results suggested that cicaprost promotes migration of immature DCs from mucosal surface to draining LNs. This concept was supported by the finding that migration of immature GFP⁺ BMDCs to draining LNs was enhanced by pretreatment with cicaprost. Further, migration of immature lung DCs labeled with PKH26 was enhanced by intranasal cicaprost administration. Our results suggest PGI2-IP signaling increases immature DC migration to the draining LNs and may represent a novel mechanism by which this eicosanoid inhibits immune responses.

Potential applications of quantum dots in mapping sentinel lymph node and detection of micrometastases in breast carcinoma

Breast cancer cure aims at complete elimination of malignant cells and essentially requires detection and treatment of any micrometastases. Here, we present a review of the current methods in use and the potential role of the quantum dots (QDs) in detection and visualization of sentinel lymph node and micrometastases in breast cancer patients. The traditional histopathological, immunohistochemical, and reverse transcriptase polymerase chain reaction procedures being used for micrometastases detection had serious drawbacks of high false negativity, specificity variations and false positivity of the results. Photon emission fluorescence multiplexing characteristics of the quantum dots make them potentially ideal probes for studying the dynamics of cellular processes over time such as continuous tracking of cell migration, differentiation, and metastases. In breast cancer, QDs based molecular and genomic detections had an unparallel high sensitivity and specificity.

Orientia tsutsugamushi subverts dendritic cell functions by escaping from autophagy and impairing their migration

Background

Dendritic cells (DCs) are the most potent antigen-presenting cells that link innate and adaptive immune responses, playing a pivotal role in triggering antigen-specific immunity. Antigen uptake by DCs induces maturational changes that include increased surface expression of major histocompatibility complex (MHC) and costimulatory molecules. In addition, DCs actively migrate to regional lymph nodes and activate antigen-specific naive T cells after capturing antigens. We characterize the functional changes of DCs infected with Orientia tsutsugamushi, the causative agent of scrub typhus, since there is limited knowledge of the role played by DCs in O. tsutsugamushi infection.

Methodology/Principal Finding

O. tsutsugamushi efficiently infected bone marrow-derived DCs and induced surface expression of MHC II and costimulatory molecules. In addition, O. tsutsugamushi induced autophagy activation, but actively escaped from this innate defense system. Infected DCs also secreted cytokines and chemokines such as IL-6, IL-12, MCP5, MIP-1α, and RANTES. Furthermore, in vitro migration of DCs in the presence of a CCL19 gradient within a 3D collagen matrix was drastically impaired when infected with O. tsutsugamushi. The infected cells migrated much less efficiently into lymphatic vessels of ear dermis ex vivo when compared to LPS-stimulated DCs. In vivo migration of O. tsutsugamushi-infected DCs to regional lymph nodes was significantly impaired and similar to that of immature DCs. Finally, we found that MAP kinases involved in chemotactic signaling were differentially activated in O. tsutsugamushi-infected DCs.

Conclusion/Significance

These results suggest that O. tsutsugamushi can target DCs to exploit these sentinel cells as replication reservoirs and delay or impair the functional maturation of DCs during the bacterial infection in mammals.

Scrub typhus is an acute febrile illness caused by Orientia tsutsugamushi infection and is one of the main causes of febrile illness in the Asia-Pacific region. If not properly treated with antibiotics, patients often develop severe vasculitis that affects multiple organs, and the mortality rate of untreated patients reaches up to 30%. To understand the pathogenic mechanisms of the infectious disease, we characterized the functional changes of O. tsutsugamushi–infected dendritic cells (DCs), which play a pivotal role in orchestrating innate and adaptive immune responses. The obligate intracellular bacteria efficiently infected bone marrow-derived DCs and activated the cells as measured by induced surface expression of MHC II and costimulatory molecules, secretion of cytokines and chemokines, and autophagy induction. However, the live bacteria actively escaped from host autophagosomes and the migration of infected cells was severely impaired in vitro, ex vivo, and in vivo infection models. Finally, we found that MAP kinases involved in chemotactic signaling were differentially activated in O. tsutsugamushi-infected DCs. These results suggest that O. tsutsugamushi can target DCs to exploit these sentinel cells as replication reservoirs and delay or impair the functional maturation of DCs during the bacterial infection in mammals.

A large-scale (19)F MRI-based cell migration assay to optimize cell therapy

Adoptive transfer of cells for therapeutic purposes requires efficient and precise delivery to the target organ whilst preserving cell function. Therefore, therapeutically applied cells need to migrate and integrate within their target tissues after delivery, e.g. dendritic cells (DCs) need to migrate to lymph nodes to elicit an antigen-specific immune response. Previous studies have shown that inappropriate cell delivery can hinder DC migration and result in insufficient immune induction. As migration can be extremely difficult to study quantitatively in vivo, we propose an in vitro assay that reproduces key in vivo conditions to optimize cell delivery and migration in vivo. Using DC migration along a chemokine gradient, we describe here a novel (19)F MR-based, large-scale, quantitative assay to measure cell migration in a three-dimensional collagen scaffold. Unlike conventional migration assays, this set-up is amenable to both large and small cell numbers, as well as opaque tissue samples and the inclusion of chemokines or other factors. We labeled primary human DCs with a (19)F label suitable for clinical use; (0.5-15) × 10(6) cells in the scaffolds were imaged sequentially, and migration was assessed using two independent methods. We found no migration with larger numbers of cells, but up to 3% with less than one million cells. Hence, we show that the cell density in cell bolus injections has a decisive impact on migration, and this may explain the limited migration observed using large cell numbers in the clinic.

Mechanisms of dendritic cell trafficking across the blood-brain barrier

Although the central nervous system (CNS) is considered to be an immunoprivileged site, it is susceptible to a host of autoimmune as well as neuroinflammatory disorders owing to recruitment of immune cells across the blood-brain barrier into perivascular and parenchymal spaces. Dendritic cells (DCs), which are involved in both primary and secondary immune responses, are the most potent immune cells in terms of antigen uptake and processing as well as presentation to T cells. In light of the emerging importance of DC traficking into the CNS, these cells represent good candidates for targeted immunotherapy against various neuroinflammatory diseases. This review focuses on potential physiological events and receptor interactions between DCs and the microvascular endothelial cells of the brain as they transmigrate into the CNS during degeneration and injury. A clear understanding of the underlying mechanisms involved in DC migration may advance the development of new therapies that manipulate these mechanistic properties via pharmacologic intervention. Furthermore, therapeutic validation should be in concurrence with the molecular imaging techniques that can detect migration of these cells in vivo. Since the use of noninvasive methods to image migration of DCs into CNS has barely been explored, we highlighted potential molecular imaging techniques to achieve this goal. Overall, information provided will bring this important leukocyte population to the forefront as key players in the immune cascade in the light of the emerging contribution of DCs to CNS health and disease.

Quantum dots for labeling live cells

Quantum dots (QDs) are semiconductor nanocrystals with unique photo-physical properties. QDs are brightly fluorescent and photostable, and therefore represent a novel class of fluorescence probes for bio-imaging and cell monitoring. There are different techniques for labeling cells with QDs. Moreover, there is evidence that optical properties of the QD can be changed as a result of interaction with live cells. This manuscript describes a simple method for labeling of rat endothelial progenitor cells using ODs and for characterization of their optical properties.

Nanoparticle-based monitoring of cell therapy

Exogenous cell therapy aims to replace/repair diseased or dysfunctional cells and promises to revolutionize medicine by restoring tissue and organ function. To develop effective cell therapy, the location, distribution and long-term persistence of transplanted cells must be evaluated. Nanoparticle (NP) based imaging technologies have the potential to track transplanted cells non-invasively. Here we summarize the most recent advances in NP-based cell tracking with emphasis on (1) the design criteria for cell tracking NPs, (2) protocols for cell labeling, (3) a comparison of available imaging modalities and their corresponding contrast agents, (4) a summary of preclinical studies on NP-based cell tracking and finally (5) perspectives and future directions.

In vivo migration of dendritic cells labeled with synthetic superparamagnetic iron oxide

BACKGROUND

Successful treatment of cancer with dendritic cell tumor vaccine is highly dependent on how effectively the vaccine migrates into lymph nodes and activates T cells. In this study, a simple method was developed to trace migration of dendritic cells to lymph nodes.

METHODS

Superparamagnetic iron oxide (SPIO) of γ-Fe(2)O(3) nanoparticles were prepared to label dendritic cells generated from bone marrow of enhanced green fluorescent protein (EGFP) transgenic mice, to explore the fluorescence intensity of EGFP influenced by the SPIO, and to make images of labeled dendritic cells with the help of magnetic resonance imaging in vitro. The SPIO-EGFP-labeled dendritic cells were injected into the footpads of five mice. After 48 hours, magnetic resonance imaging, optical imaging, confocal imaging, and Prussian blue staining were used to confirm migration of the SPIO-EGFP-labeled dendritic cells into draining lymph nodes.

RESULTS

The synthetic SPIO nanoparticles had a spherical shape and desirable superparamagnetism, and confocal imaging and Prussian blue staining showed perfect labeling efficiency as well. Furthermore, the dendritic cells dual-labeled by SPIO and EGFP could migrate into lymph nodes after footpad injection, and could be detected by both magnetic resonance imaging and optical imaging simultaneously, which was further confirmed by immunohistochemistry and Prussian blue staining. The percentage of dendritic cells migrated to the draining lymph nodes was about 4%.

CONCLUSION

Synthetic SPIO nanoparticles are strong contrast agents with good biocompatibility, and EGFP transgenic dendritic cells can be labeled efficiently by SPIO, which are suitable for further study of the migratory behavior and biodistribution of dendritic cells in vivo.

Synthesis and high performance of magnetofluorescent polyelectrolyte nanocomposites as MR/near-infrared multimodal cellular imaging nanoprobes

Here, we describe an easy but robust chemical strategy to synthesize high-performance magnetic resonance (MR)/near-infrared (NIR) multimodal imaging nanoprobes. Poly(γ-glutamic acid) was used for the convenient phase transfer of MnFe(2)O(4) nanoparticles dispersed in organic solvents into aqueous solutions and facilitated further ionic gelation with poly(l-lysine). During the gelation process, MnFe(2)O(4) nanoparticulate satellites were encapsulated in the ionic nanocomplex, which induced synergistic magnetism and resulted in huge T(2) relaxivity (r(2)). The positively charged outer surfaces were assembled with other negatively charged NIR emitting fluorescent nanocrystals and enabled the highly efficient delivery of the magnetofluorescent polyelectrolyte nanocomposites (MagFL-PEN) into cancer cells. The enhancement of negative contrast of MagFL-PEN at 2 μg/mL concentration was similar to that of Resovist at 20 μg/mL concentration. The NIR fluorescence microscopy images of the MagFL-PEN-labeled cells even at 12.5 pM were able to be clearly observed. The labeling efficiency of MagFL-PEN was approximately 65-fold higher compared to that of the commercialized fluorescent nanocrystals, only after 3 h incubation period, even at the test concentration (100 pM). Due to the high-performance capabilities both in materials properties and cell labeling efficiency, the MagFL-PEN is expected to be used as a highly efficient MR/NIR dual-modality imaging nanoprobe in the detection of cancer cells and monitoring of therapeutic cells in vivo.

Enhancement of the photostability and retention time of indocyanine green in sentinel lymph node mapping by anionic polyelectrolytes

Sentinel lymph node (SLN) biopsy techniques have been widely used in the diagnosis of cancer metastasis because lymph node metastasis is one of the most important prognostic signs. Indocyanine green (ICG) has potential application as a molecular imaging probe for SLN mapping due to its fluorescent properties emitting in the near-infrared (NIR) region, where light transmission through biological tissue is maximized. However, its low photostability in an aqueous solution at the physiological temperature and its rapid diffusion behavior through SLN into the second lymph node have limited its wide use in real clinical fields. In this study, we developed a new NIR imaging contrast system consisting of ICG and poly (γ-glutamic acid) (γ-PGA) polymers for efficient sentinel lymph node mapping. By a combination of clinically used ICG and the biocompatible anionic polyelectrolyte, γ-PGA, the photostabilities of aqueous ICG solutions at room and body temperatures were drastically enhanced. When the ICG/γ-PGA complex was injected subcutaneously into the front paw of a mouse, it entered the lymphatics and migrated to the axillary sentinel lymph node (SLN) within 2 min. Furthermore, the NIR fluorescent signal intensity and retention time of ICG/γ-PGA complex in lymph node were superior to those of ICG only. In addition, a histofluorescentstudy of the SLN resected under NIR imaging revealed that ICG and γ-PGA were co-localized in the lymph node.Taken together, the experimental results on the enhanced photostability and retention time of the ICG/γ-PGA complex provide strong evidence that it has promising potential for improved sentinel lymph node mapping.

Generation and labeling of murine bone marrow-derived dendritic cells with Qdot nanocrystals for tracking studies

Dendritic cells (DCs) are professional antigen presenting cells (APCs) found in peripheral tissues and in immunological organs such as thymus, bone marrow, spleen, lymph nodes and Peyer's patches ^1-3. DCs present in peripheral tissues sample the organism for the presence of antigens, which they take up, process and present in their surface in the context of major histocompatibility molecules (MHC). Then, antigen-loaded DCs migrate to immunological organs where they present the processed antigen to T lymphocytes triggering specific immune responses. One way to evaluate the migratory capabilities of DCs is to label them with fluorescent dyes ⁴.

Herewith we demonstrate the use of Qdot fluorescent nanocrystals to label murine bone marrow-derived DC. The advantage of this labeling is that Qdot nanocrystals possess stable and long lasting fluorescence that make them ideal for detecting labeled cells in recovered tissues. To accomplish this, first cells will be recovered from murine bone marrows and cultured for 8 days in the presence of granulocyte macrophage-colony stimulating factor in order to induce DC differentiation. These cells will be then labeled with fluorescent Qdots by short in vitro incubation. Stained cells can be visualized with a fluorescent microscopy. Cells can be injected into experimental animals at this point or can be into mature cells upon in vitro incubation with inflammatory stimuli. In our hands, DC maturation did not determine loss of fluorescent signal nor does Qdot staining affect the biological properties of DCs. Upon injection, these cells can be identified in immune organs by fluorescent microscopy following typical dissection and fixation procedures.

Labeling Stem Cells with a Near-Infrared Fluorescent Heptamethine Dye for Noninvasive Optical Tracking

Near-infrared (NIR) fluorescent agents hold great promise for noninvasive in vivo imaging. We have recently reported that a NIR fluorescent heptamethine dye, IR-780 iodide, exhibits unique optical properties for biomedical imaging. On the basis of this foregoing work, we further describe here the potential application of IR-780 iodide as a novel NIR agent for stem cell labeling and tracking. The labeling efficiency, subcellular localization, and the effects on cell viability and differentiation of IR-780 iodide were investigated. The in vivo distribution of stem cells after intravenous transplantation was traced by whole-body animal NIR imaging. Our results showed that IR-780 iodide exhibited superior labeling efficiency and biocompatibility with unique optical properties. Following whole-body NIR imaging, the pulmonary passage of stem cells was noninvasively visualized in rats after systemic transplantation of IR-780 iodide-labeled stem cells through intravenous delivery. With this NIR imaging method, we further confirmed that pretreatment with sodium nitroprusside (SNP), a vasodilator agent, significantly reduced the cell trapping in the lung and increased the cell passage through the lung capillaries. Our study suggests that IR-780 iodide may represent an effective NIR fluorophore for stem cell labeling and tracking.

Simultaneous in vivo tracking of dendritic cells and priming of an antigen-specific immune response

We report the fabrication of a one-pot antigen system that delivers antigen to dendritic cells (DCs) and tracks their in vivo migration after injection. Multifunctional polymer nanoparticles containing ovalbumin protein, magnetic resonance imaging contrast agents (iron oxide nanoparticles), and near-infrared fluorophores (indocyanine green, ICG), MPN-OVA, were prepared using a double emulsion method. The MPN-OVA was efficiently taken up by the dendritic cells and subsequently localized in the lysosome. Flow cytometry analysis revealed an increase in the uptake of OVA antigen by MPN-OVA at 37 °C, when compared with soluble OVA protein. We found that MPN-OVA had no effect on DC surface expression of MHC class I, costimulatory (CD80, CD86) or adhesion (CD54) molecules or the ability of DCs to mature in response to LPS. Following the uptake of MPN-OVA, exogenous OVA antigen was delivered to the cytoplasm, and OVA peptides were presented on MHC class I molecules, which enhanced OVA antigen-specific cross-presentation to OT-1 T cells and CD8OVA1.3 T cell hybridoma in vitro. The immunization of mice with MPN-OVA-treated DCs induced OVA-specific CTL activity in draining lymph nodes. The presence of MPN allowed us to monitor the migration of DCs via lymphatic drainage using NIR fluorescence imaging, and the homing of DCs into the lymph nodes was imaged using MRI. This system has potential for use as a delivery system to induce T cell priming and to image DC-based immunotherapies.

Molecular imaging of cell-based cancer immunotherapy

Cell-based cancer immunotherapy represents a new and powerful weapon in the arsenal of anticancer treatments. Non-invasive monitoring of the disposition, migration and destination of therapeutic cells will facilitate the development of cell based therapy. The therapeutic cells can be modified intrinsically by a reporter gene or labeled extrinsically by introducing imaging probes into the cells or on the cell surface before transplant. Various advanced non-invasive molecular imaging techniques are playing important roles in optimizing cellular therapy by tracking cells and monitoring the therapeutic effects of transplanted cells in vivo. This review will summarize the application of multiple molecular imaging modalities in cell-based cancer immunotherapy.

Nanoparticles for cell labeling

Cell based therapeutics are emerging as powerful regimens. To better understand the migration and proliferation mechanisms of implanted cells, a means to track cells in living subjects is essential, and to achieve that, a number of cell labeling techniques have been developed. Nanoparticles, with their superior physical properties, have become the materials of choice in many investigations along this line. Owing to inherent magnetic, optical or acoustic attributes, these nanoparticles can be detected by corresponding imaging modalities in living subjects at a high spatial and temporal resolution. These features allow implanted cells to be separated from host cells; and have advantages over traditional histological methods, as they permit non-invasive, real-time tracking in vivo. This review attempts to give a summary of progress in using nanotechnology to monitor cell trafficking. We will focus on direct cell labeling techniques, in which cells ingest nanoparticles that bear traceable signals, such as iron oxide or quantum dots. Ferritin and MagA reporter genes that can package endogenous iron or iron supplement into iron oxide nanoparticles will also be discussed.