Non-invasive imaging of dendritic cell migration in vivo

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.

Intranasal Antifungal Vaccination Using DNA-Transfected Dendritic Cells

Dendritic cells are the most potent antigen-presenting cells, and are critical for the generation of an antigen-specific immune response and protective immunity. These unique features have been applied to dendritic cell-based immunization in a number of disease conditions. Our published results have demonstrated that the immunity induced by intranasal immunization with DNA-transfected dendritic cells results in reduced fungal burden, and alleviated lung tissue damage in a mouse model of pulmonary fungal infection. In this article, approaches for the preparation and characterization of DNA-transfected dendritic cells and intranasal immunization in mice are described.

Migration of dendritic cells to the lymph nodes and its enhancement to drive anti-tumor responses

Better prognoses associated with increased T cell infiltration of tumors, as seen with chimeric antigen receptor (CAR) T cell therapies and immune checkpoint inhibitors, portray the importance and potential of the immune system in controlling tumors. This has rejuvenated the field of cancer immunotherapy leading to an increasing number of immunotherapies developed for cancer patients. Dendritic Cells (DCs) vaccines represent an appealing option for cancer immunotherapy since DCs have the ability to circumvent tolerance to tumors by its adjuvant properties and to induce memory T cells that can become persistent after initial tumor clearance to engage potential metastatic tumors. In the past, DC-based cancer vaccines have elicited only poor clinical response in cancer patients, which can be attributed to complex and a multitude of issues associated with generation, implementing, delivery of DC vaccine and their potential interaction with effector cells. The current review mainly focuses on migration/trafficking of DCs, as one of the key issues that affect the success of DC-based cancer vaccines, and discusses strategies to enhance it for cancer immunotherapy. Additionally, impact of maturation, route of DC delivery and negative effects of tumor microenvironment (TME) on DC homing to LN are reviewed. Moreover, strategies to increase the expression of genes involved in Lymph node homing, preconditioning of the vaccination site, enhancing lymph node ability to attract and receive DCs, while limiting negative impact of TME on DC migration are discussed.

Magnetic Enrichment of Dendritic Cell Vaccine in Lymph Node with Fluorescent-Magnetic Nanoparticles Enhanced Cancer Immunotherapy

Dendritic cell (DC) migration to the lymph node is a key component of DC-based immunotherapy. However, the DC homing rate to the lymphoid tissues is poor, thus hindering the DC-mediated activation of antigen-specific T cells. Here, we developed a system using fluorescent magnetic nanoparticles (α-AP-fmNPs; loaded with antigen peptide, iron oxide nanoparticles, and indocyanine green) in combination with magnetic pull force (MPF) to successfully manipulate DC migration in vitro and in vivo. α-AP-fmNPs endowed DCs with MPF-responsiveness, antigen presentation, and simultaneous optical and magnetic resonance imaging detectability. We showed for the first time that α-AP-fmNP-loaded DCs were sensitive to MPF, and their migration efficiency could be dramatically improved both in vitro and in vivo through MPF treatment. Due to the enhanced migration of DCs, MPF treatment significantly augmented antitumor efficacy of the nanoparticle-loaded DCs. Therefore, we have developed a biocompatible approach with which to improve the homing efficiency of DCs and subsequent anti-tumor efficacy, and track their migration by multi-modality imaging, with great potential applications for DC-based cancer immunotherapy.

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.

In vivo tracking and immunological properties of pulsed porcine monocyte-derived dendritic cells

Cellular therapies using immune cells and in particular dendritic cells (DCs) are being increasingly applied in clinical trials and vaccines. Their success partially depends on accurate delivery of cells to target organs or migration to lymph nodes. Delivery and subsequent migration of cells to regional lymph nodes is essential for effective stimulation of the immune system. Thus, the design of an optimal DC therapy would be improved by optimizing technologies for monitoring DC trafficking. Magnetic resonance imaging (MRI) represents a powerful tool for non-invasive imaging of DC migration in vivo. Domestic pigs share similarities with humans and represent an excellent animal model for immunological studies. The aim of this study was to investigate the possibility using pigs as models for DC tracking in vivo. Porcine monocyte derived DC (MoDC) culture with superparamagnetic iron oxide (SPIO) particles was standardized on the basis of SPIO concentration and culture viability. Phenotype, cytokine production and mixed lymphocyte reaction assay confirmed that porcine SPIO-MoDC culture were similar to mock MoDCs and fully functional in vivo. Alike, similar patterns were obtained in human MoDCs. After subcutaneous inoculation in pigs, porcine SPIO-MoDC migration to regional lymph nodes was detected by MRI and confirmed by Perls staining of draining lymph nodes. Moreover, after one dose of virus-like particles-pulsed MoDCs specific local and systemic responses were confirmed using ELISPOT IFN-γ in pigs. In summary, the results in this work showed that after one single subcutaneous dose of pulsed MoDCs, pigs were able to elicit specific local and systemic immune responses. Additionally, the dynamic imaging of MRI-based DC tracking was shown using SPIO particles. This proof-of-principle study shows the potential of using pigs as a suitable animal model to test DC trafficking with the aim of improving cellular therapies.

Bioluminescence imaging: basics and practical limitations

Over the last three decades, imaging has been a thriving field with continuous egression of more reliable and highly sophisticated tools and techniques allowing better understanding of biological processes in living organisms. This field continues to expand and its applications broaden to encompass limitless applications in various biomedical research areas. It is however, of utmost importance to understand the capabilities and limitations of this technique as new challenges and hurdles continue to arise. This chapter describes the general properties of bioluminescence imaging and commonly used reporters while underlining the challenges and limitations with these modalities.

Tracking and evaluation of dendritic cell migration by cellular magnetic resonance imaging

Cellular magnetic resonance imaging (MRI) is a means by which cells labeled ex vivo with a contrast agent can be detected and tracked over time in vivo. This technology provides a noninvasive method with which to assess cell-based therapies in vivo. Dendritic cell (DC)-based vaccines are a promising cancer immunotherapy, but its success is highly dependent on the injected DC migrating to a secondary lymphoid organ such as a nearby lymph node. There the DC can interact with T cells to elicit a tumor-specific immune response. It is important to verify DC migration in vivo using a noninvasive imaging modality, such as cellular MRI, so that important information regarding the anatomical location and persistence of the injected DC in a targeted lymph node can be provided. An understanding of DC biology is critical in ascertaining how to label DC with sufficient contrast agent to render them detectable by MRI. While iron oxide nanoparticles provide the best sensitivity for detection of DC in vivo, a clinical grade iron oxide agent is not currently available. A clinical grade (19) Fluorine-based perfluorcarbon nanoemulsion is available but is less sensitive, and its utility to detect DC migration in humans remains to be demonstrated using clinical scanners presently available. The ability to quantitatively track DC migration in vivo can provide important information as to whether different DC maturation and activation protocols result in improved DC migration efficiency which will determine the vaccine's immunogenicity and ultimately the tumor immunotherapy's outcome in humans.

Experimental models to investigate the function of dendritic cell subsets: challenges and implications

The dendritic cell (DC) lineage is remarkably heterogeneous. It has been postulated that specialized DC subsets have evolved in order to select and support the multitude of possible T cell differentiation pathways. However, defining the function of individual DC subsets has proven remarkably difficult, and DC subset control of key T cell fates such as tolerance, T helper cell commitment and regulatory T cell induction is still not well understood. While the difficulty in assigning unique functions to particular DC subsets may be due to sharing of functions, it may also reflect a lack of appropriate physiological in-vivo models for studying DC function. In this paper we review the limitations associated with many of the current DC models and highlight some of the underlying difficulties involved in studying the function of murine DC subsets.

Brain dendritic cells: biology and pathology

Dendritic cells (DC) are the professional antigen-presenting cells of the immune system. In their quiescent and mature form, the presentation of self-antigens by DC leads to tolerance; whereas, antigen presentation by mature DC, after stimulation by pathogen-associated molecular patterns, leads to the onset of antigen-specific immunity. DC have been found in many of the major organs in mammals (e.g. skin, heart, lungs, intestines and spleen); while the brain has long been considered devoid of DC in the absence of neuroinflammation. Consequently, microglia, the resident immune cell of the brain, have been charged with many functional attributes commonly ascribed to DC. Recent evidence has challenged the notion that DC are either absent or minimal players in brain immune surveillance. This review will discuss the recent literature examining DC involvement within both the young and aged steady-state brain. We will also examine DC contributions during various forms of neuroinflammation resulting from neurodegenerative autoimmune disease, injury, and CNS infections. This review also touches upon DC trafficking between the central nervous system and peripheral immune compartments during viral infections, the new molecular technologies that could be employed to enhance our current understanding of brain DC ontogeny, and some potential therapeutic uses of DC within the CNS.

Receptor heterodimerization: a new mechanism for platelet-derived growth factor induced resistance to anti-epidermal growth factor receptor therapy for bladder cancer

PURPOSE

Human bladder cancer cells resistant to anti-epidermal growth factor receptor therapy often co-express platelet-derived growth factor receptor-β. We determined whether there is functional crosstalk between epidermal growth factor receptor and platelet-derived growth factor receptor-β, and how this regulates biological functions in bladder cancer cases.

MATERIALS AND METHODS

We determined heterodimerization and co-localization of epidermal growth factor receptor and platelet-derived growth factor receptor-β by immunoprecipitation and confocal microscopy, respectively. We tested the antiproliferative effects of specific inhibitory monoclonal antibodies to each receptor by (3)H-thymidine uptake assay. We transfected the nonplatelet-derived growth factor receptor-β expressing bladder cancer cell line UMUC5 with the platelet-derived growth factor receptor-β gene. These cells were analyzed in vitro by (3)H-thymidine uptake and by Matrigel™ invasion assay, and in vivo for tumorigenicity, metastatic potential and orthotopic growth. In a treatment study nude mice were inoculated with orthotopic tumors and treated with the inhibitory antibodies alone and in combination.

RESULTS

Immunoprecipitation revealed epidermal growth factor receptor/platelet-derived growth factor receptor-β heterodimers in all platelet-derived growth factor receptor-β expressing cell lines. Forced expression of platelet-derived growth factor receptor-β in epidermal growth factor receptor sensitive UMUC5 cells (50% inhibitory concentration less than 10 nM) significantly decreased responsiveness to epidermal growth factor receptor inhibition (50% inhibitory concentration greater than 100 nM) and increased invasive potential 3-fold as well as tumorigenicity. Increased invasiveness was associated with epidermal growth factor triggered platelet-derived growth factor receptor-β transactivation, increased mitogen activated protein kinase and glycogen synthase kinase-3β phosphorylation, and decreased E-cadherin. Inhibition of epidermal growth factor receptor and platelet-derived growth factor receptor-β receptors blocked cell invasion, decreased cell proliferation, reduced xenograft tumor growth and increased E-cadherin expression.

CONCLUSIONS

In epidermal growth factor receptor expressing bladder cancer co-expression of platelet-derived growth factor receptor-β has implications for tumor biology. Thus, it should be further evaluated as a strategy involving dual receptor targeting.

In vivo trafficking and immunostimulatory potential of an intranasally-administered primary dendritic cell-based vaccine

BACKGROUND

Coccidioidomycosis or Valley fever is caused by a highly virulent fungal pathogen: Coccidioides posadasii or immitis. Vaccine development against Coccidioides is of contemporary interest because a large number of relapses and clinical failures are reported with antifungal agents. An efficient Th1 response engenders protection. Thus, we have focused on developing a dendritic cell (DC)-based vaccine for coccidioidomycosis. In this study, we investigated the immunostimulatory characteristics of an intranasal primary DC-vaccine in BALB/c mouse strain that is most susceptible to coccidioidomycosis. The DCs were transfected nonvirally with Coccidioides-Ag2/PRA-cDNA. Expression of DC-markers, Ag2/PRA and cytokines were studied by flow cytometry, dot-immunoblotting and cytometric bead array methods, respectively. The T cell activation was studied by assessing the upregulation of activation markers in a DC-T cell co-culture assay. For trafficking, the DCs were co-transfected with a plasmid DNA encoding HSV1 thymidine kinase (TK) and administered intranasally into syngeneic mice. The trafficking and homing of TK-expressing DCs were monitored with positron emission tomography (PET) using 18F-FIAU probe. Based on the PET-probe accumulation in vaccinated mice, selected tissues were studied for antigen-specific response and T cell phenotypes using ELISPOT and flow cytometry, respectively.

RESULTS

We found that the primary DCs transfected with Coccidioides-Ag2/PRA-cDNA were of immature immunophenotype, expressed Ag2/PRA and activated naïve T cells. In PET images and subsequent biodistribution, intranasally-administered DCs were found to migrate in blood, lung and thymus; lymphocytes showed generation of T effector memory cell population (T(EM)) and IFN-γ release.

CONCLUSIONS

In conclusion, our results demonstrate that the intranasally-administered primary DC vaccine is capable of inducing Ag2/PRA-specific T cell response. Unique approaches utilized in our study represent an attractive and novel means of producing and evaluating an autologous DC-based vaccine.

Migration of dendritic cells from murine skeletal muscle

To better understand the role of dendritic cells (DCs) in skeletal muscle, we investigated the migration of DCs from murine skeletal muscle and compared that to previously studied footpad (FP) DC trafficking. We adoptively transferred carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled mature DCs to syngeneic mice and followed them in various lymphatic tissues at different time points. Injection of DCs into the tibialis anterior muscle resulted in the peak number of CFSE(+) DCs recovered in spleen at 12h, not at 24h, when the largest number of these cells appeared in the draining lymph nodes. Interestingly, this result for adoptive transfer of DCs to skeletal muscle differs with what is previously reported for adoptive transfer to the FP, a result that we also confirmed in parallel studies. These findings could have a significant impact on (1) understanding muscle diseases with immunological complications such as muscular dystrophies and (2) the immunologic effects of treatments for muscle diseases.

Ultrasound biomicroscopy: a powerful tool probing murine lymph node size in vivo

Invasive cell-counting in lymph node (LN) is the current reference to assess LN changes due to inflammation, immunodeficiency and cancer in murine models. This work evaluates whether ultrasound biomicroscopy (UBM) can measure LN size alterations noninvasively for a large range of sizes (0.1 mm3 to 22 mm3). Correlation was assessed (rho = 0.91, p < 0.0001) between invasive cell count and LN volume estimated with UBM (24, 2 to 28-week-old, C57BL/6 mice; 13 same-strain, transgenic mice presenting LN hyperplasia). UBM LN modification screening was applied in a skin-graft rejection model and compared with cell-counting (15 mice). UBM LN-size follow-up with fine temporal sampling was demonstrated from 9 d of age (minimum area 0.13 mm2). Reliability (intraclass correlation coefficient [ICC] > 0.84) and variability of UBM evaluations compared favourably with invasive cell count. UBM provides a noninvasive alternative to cell-counting in mice for early detection and longitudinal screening of LN modifications. This can enable significant reduction in the number of mice and exploration of LNs that would be too small to dissect for cell count.

Lymphoid-tissue-specific homing of bone-marrow-derived dendritic cells

Because of their potent immunoregulatory capacity, dendritic cells (DCs) have been exploited as therapeutic tools to boost immune responses against tumors or pathogens, or dampen autoimmune or allergic responses. Murine bone marrow-derived DCs (BM-DCs) are the closest known equivalent of the blood monocyte-derived DCs that have been used for human therapy. Current imaging methods have proven unable to properly address the migration of injected DCs to small and deep tissues in mice and humans. This study presents the first extensive analysis of BM-DC homing to lymph nodes (and other selected tissues) after intravenous and intraperitoneal inoculation. After intravenous delivery, DCs accumulated in the spleen, and preferentially in the pancreatic and lung-draining lymph nodes. In contrast, DCs injected intraperitoneally were found predominantly in peritoneal lymph nodes (pancreatic in particular), and in omentum-associated lymphoid tissue. This uneven distribution of BM-DCs, independent of the mouse strain and also observed within pancreatic lymph nodes, resulted in the uneven induction of immune response in different lymphoid tissues. These data have important implications for the design of systemic cellular therapy with DCs, and in particular underlie a previously unsuspected potential for specific treatment of diseases such as autoimmune diabetes and pancreatic cancer.

Magnetovaccination as a novel method to assess and quantify dendritic cell tumor antigen capture and delivery to lymph nodes

A major parameter limiting immune responses to vaccination is the number of activated antigen-presenting cells (APC) that capture antigen and migrate to draining lymph nodes (LN). Currently, a quantitative noninvasive technique for monitoring in vivo antigen capture and delivery is lacking. The use of cellular magnetic resonance (MR) imaging (MRI) is a promising approach for this purpose; however, cellular imaging currently requires ex vivo prelabeling of cells with contrast agents followed by reintroduction of cells into the subject being monitored. Here, we describe an in vivo labeling method, which relies upon cell-to-cell transfer of superparamagnetic iron oxide (SPIO) from tumor cells to endogenous APCs, in situ, to quantify APC delivery to LNs in a tumor vaccine model. Mice were immunized with a tumor cell-based vaccine that was irradiated and labeled with SPIO. APCs that had captured SPIO were imaged over time as they accumulated in LNs. We show here that MRI is capable of monitoring, in vivo, the trafficking of magnetically labeled APCs inducing a tumor-specific immune response, and that these cells can be magnetically recovered ex vivo. Excellent correlation was observed between in vivo and ex vivo quantification of APCs, with resolution sufficient to detect increased APC trafficking elicited by an adjuvant. This study shows the potential of magnetovaccination and MRI cell tracking to systematically evaluate a key parameter relevant to the optimization of vaccine therapies through noninvasive MRI-based quantification of APC numbers.

Mechanisms and consequences of dendritic cell migration

Dendritic cells (DCs) are critical for adaptive immunity and tolerance. Most DCs are strategically positioned as immune sentinels poised to respond to invading pathogens in tissues throughout the body. Differentiated DCs and their precursors also circulate in blood and can get rapidly recruited to sites of challenge. Within peripheral tissues, DCs collect antigenic material and then traffic to secondary lymphoid organs, where they communicate with lymphocytes to orchestrate adaptive immune responses. Hence, the migration and accurate positioning of DCs is indispensable for immune surveillance. Here, we review the molecular traffic signals that govern the migration of DCs throughout their life cycle.

Assessing siRNA pharmacodynamics in a luciferase-expressing mouse

A significant barrier to the successful general development of small-interfering RNA (siRNA) therapeutics is the ability to deliver them systemically to target organs and cell types. In this study, we have developed a mouse strain that will facilitate the evaluation of the efficacy of siRNA delivery strategies. This strain contains robust ubiquitous expression of firefly luciferase from germ line Cre-mediated recombination of the ROSA26-LSL-Luc allele. We show that luciferase is highly and uniformly expressed in all tissues examined. Using this mouse model, we describe a facile assay that enables the assessment of the pharmacodynamics of a systemically delivered siRNA formulation. These mice can also be used as universal donors, enabling the efficient and sensitive monitoring of cell trafficking or tissue transplantation. The primary advantage of this approach is that siRNA efficacy against a nonessential target can be easily evaluated in any tissue. This strain should generally enhance the ability to rapidly screen, compare and optimize various siRNA formulations for tissue-targeted or -enhanced systemic delivery in a preclinical development setting.

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

Effective tracking of immunotherapeutic cells is essential for monitoring the migration of injected cells to the target tissue. Here we report the use of near-infrared (NIR) -emitting fluorescent semiconductor nanocrystals, called quantum dots (QDs), for noninvasive in vivo tracking of dendritic cell (DC) migration into lymph nodes. The effect of QDs on DC viability and maturation was systematically investigated using MTT assays and FACS analysis. We found that the labeling of DCs with QDs had no effect on DC phenotype or maturation potential. Cytokine and migration assays revealed that there were no significant changes in either cytokine production or chemokine-dependent migration of QD-labeled DCs relative to unlabeled cells; in both labeled and unlabeled cells, cytokine production and migratory capacity was increased by stimulation with lipopolysaccharide. Furthermore, QDs did not influence allogenic naive T cell activation or uptake of exogenous antigens. Notably, we also demonstrated that it was possible to track QD-labeled DCs injected into the footpad into popliteal and inguinal lymph nodes using NIR fluorescence. Taken together, our protocols establish the potential of noninvasive in vivo imaging of NIR-emitting QDs for tracking immunotherapeutic cells.