Using magnetic resonance imaging to evaluate dendritic cell-based vaccination

Durable lymph-node expansion is associated with the efficacy of therapeutic vaccination

Following immunization, lymph nodes dynamically expand and contract. The mechanical and cellular changes enabling the early-stage expansion of lymph nodes have been characterized, yet the durability of such responses and their implications for adaptive immunity and vaccine efficacy are unknown. Here, by leveraging high-frequency ultrasound imaging of the lymph nodes of mice, we report more potent and persistent lymph-node expansion for animals immunized with a mesoporous silica vaccine incorporating a model antigen than for animals given bolus immunization or standard vaccine formulations such as alum, and that durable and robust lymph-node expansion was associated with vaccine efficacy and adaptive immunity for 100 days post-vaccination in a mouse model of melanoma. Immunization altered the mechanical and extracellular-matrix properties of the lymph nodes, drove antigen-dependent proliferation of immune and stromal cells, and altered the transcriptional features of dendritic cells and inflammatory monocytes. Strategies that robustly maintain lymph-node expansion may result in enhanced vaccination outcomes.

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.

Magnetic Particle Imaging Is a Sensitive In Vivo Imaging Modality for the Detection of Dendritic Cell Migration

PURPOSE

The purpose of this study was to evaluate magnetic particle imaging (MPI) as a method for the in vivo tracking of dendritic cells (DC). DC are used in cancer immunotherapy and must migrate from the site of implantation to lymph nodes to be effective. The magnitude of the ensuing T cell response is proportional to the number of lymph node-migrated DC. With current protocols, less than 10% of DC are expected to reach target nodes. Therefore, imaging techniques for studying DC migration must be sensitive and quantitative. Here, we describe the first study using MPI to detect and track DC injected into the footpads of C57BL/6 mice migrating to the popliteal lymph nodes (pLNs).

PROCEDURES

DC were labelled with Synomag-D™ and injected into each hind footpad of C57BL/6 mice (n = 6). In vivo MPI was conducted immediately and repeated 48 h later. The MPI signal was measured from images and related to the signal from a known number of cells to calculate iron content. DC numbers were estimated by dividing iron content in the image by the iron per cell measured from a separate cell sample. The presence of SPIO-labeled DC in nodes was validated by ex vivo MPI, histology, and fluorescence microscopy.

RESULTS

Day 2 imaging showed a decrease in MPI signal in the footpads and an increase in signal at the pLNs, indicating DC migration. MPI signal was detected in the left pLN in four of the six mice and two of the six mice showed MPI signal in the right pLN. Ex vivo imaging detected signal in 11/12 nodes. We report a sensitivity of approximately 4000 cells (0.015 µg Fe) in vivo and 2000 cells (0.007 µg Fe) ex vivo.

CONCLUSIONS

Here, we describe the first study to use MPI to detect and track DC in a migration model with immunotherapeutic applications. We also bring attention to the issue of resolving unequal signals within close proximity, a challenge for any pre-clinical study using a highly concentrated tracer bolus that shadows nearby lower signals.

In Vivo MRI Tracking of Tumor Vaccination and Antigen Presentation by Dendritic Cells

Cancer vaccination using tumor antigen-primed dendritic cells (DCs) was introduced in the clinic some 25 years ago, but the overall outcome has not lived up to initial expectations. In addition to the complexity of the immune response, there are many factors that determine the efficacy of DC therapy. These include accurate administration of DCs in the target tissue site without unwanted cell dispersion/backflow, sufficient numbers of tumor antigen-primed DCs homing to lymph nodes (LNs), and proper timing of immunoadjuvant administration. To address these uncertainties, proton (1H) and fluorine (19F) magnetic resonance imaging (MRI) tracking of ex vivo pre-labeled DCs can now be used to non-invasively determine the accuracy of therapeutic DC injection, initial DC dispersion, systemic DC distribution, and DC migration to and within LNs. Magnetovaccination is an alternative approach that tracks in vivo labeled DCs that simultaneously capture tumor antigen and MR contrast agent in situ, enabling an accurate quantification of antigen presentation to T cells in LNs. The ultimate clinical premise of MRI DC tracking would be to use changes in LN MRI signal as an early imaging biomarker to predict the efficacy of tumor vaccination and anti-tumor response long before treatment outcome becomes apparent, which may aid clinicians with interim treatment management.

Imaging dendritic cell functions

Dendritic cells (DCs) are crucial for the appropriate initiation of adaptive immune responses. During inflammation, DCs capture antigens, mature, and migrate to lymphoid tissues to present foreign material to naïve T cells. These cells get activated and differentiate either into pathogen-specific cytotoxic CD8⁺ T cells that destroy infected cells or into CD4⁺ T helper cells that, among other effector functions, orchestrate antibody production by B cells. DC-mediated antigen presentation is equally important in non-inflammatory conditions. Here, DCs mediate induction of tolerance by presenting self-antigens or harmless environmental antigens and induce differentiation of regulatory T cells or inactivation of self-reactive immune cells. Detailed insights into the biology of DCs are, therefore, crucial for the development of novel vaccines as well as the prevention of autoimmune diseases. As in many other life science areas, our understanding of DC biology would be extremely restricted without bioimaging, a compilation of methods that visualize biological processes. Spatiotemporal tracking of DCs relies on various imaging tools, which not only enable insights into their positioning and migration within tissues or entire organs but also allow visualization of subcellular and molecular processes. This review aims to provide an overview of the imaging toolbox and to provide examples of diverse imaging techniques used to obtain fundamental insights into DC biology.

Predictive Markers of Immunogenicity and Efficacy for Human Vaccines

Vaccines represent one of the major advances of modern medicine. Despite the many successes of vaccination, continuous efforts to design new vaccines are needed to fight "old" pandemics, such as tuberculosis and malaria, as well as emerging pathogens, such as Zika virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Vaccination aims at reaching sterilizing immunity, however assessing vaccine efficacy is still challenging and underscores the need for a better understanding of immune protective responses. Identifying reliable predictive markers of immunogenicity can help to select and develop promising vaccine candidates during early preclinical studies and can lead to improved, personalized, vaccination strategies. A systems biology approach is increasingly being adopted to address these major challenges using multiple high-dimensional technologies combined with in silico models. Although the goal is to develop predictive models of vaccine efficacy in humans, applying this approach to animal models empowers basic and translational vaccine research. In this review, we provide an overview of vaccine immune signatures in preclinical models, as well as in target human populations. We also discuss high-throughput technologies used to probe vaccine-induced responses, along with data analysis and computational methodologies applied to the predictive modeling of vaccine efficacy.

In vivo Imaging Technologies to Monitor the Immune System

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

Ligation of the CD44 Glycoform HCELL on Culture-Expanded Human Monocyte-Derived Dendritic Cells Programs Transendothelial Migration

The success of dendritic cell (DC)-based immunotherapeutics critically hinges on the capacity of the vascularly administered cells to enter tissues. Transendothelial migration (TEM) is dictated by an ordered cascade of receptor/ligand interactions. In this study, we examined the key molecular effectors of TEM of human monocyte-derived DCs (mo-DCs) generated by clinically relevant methods: CD14 selection (CD14-S) and plastic adherence selection (PA-S). Without chemokine input, CD14-S cells undergo greater TEM than PA-S cells over TNF-α-stimulated HUVECs. TEM of CD14-S mo-DCs is E-selectin/very late Ag-4 (VLA-4) dependent, and engagement of E-selectin ligands activates VLA-4 on CD14-S mo-DCs but not on PA-S mo-DCs. E-selectin binding glycoforms of P-selectin glycoprotein ligand-1 (PSGL-1) (i.e., cutaneous lymphocyte Ag [CLA]) and CD44 (i.e., hematopoietic cell E-selectin/L-selectin ligand [HCELL]) are both expressed on CD14-S mo-DCs, but only CLA is expressed on PA-S mo-DCs. To elucidate the effect of CD44 or PSGL-1 engagement, mo-DCs were pretreated with their ligands. Ligation of CD44 on CD14-S mo-DCs triggers VLA-4 activation and TEM, whereas PSGL-1 ligation does not. HCELL expression on CD14-S mo-DC can be enforced by cell surface exofucosylation, yielding increased TEM in vitro and enhanced extravasation into bone marrow in vivo. These findings highlight structural and functional pleiotropism of CD44 in priming TEM of mo-DCs and suggest that strategies to enforce HCELL expression may boost TEM of systemically administered CD14-S mo-DCs.

Image-guided dendritic cell-based vaccine immunotherapy in murine carcinoma models

In recent decades, immunotherapy has undergone extensive developments for oncologic therapy applications. Dendritic cells (DCs) plays a fundamental role in cell-based vaccination immunotherapy against various types of cancer. It involves stimulating innate and adaptive immunity, in particular cytotoxic T-cell mediated antitumor effects, against targeted tumors and has been studied in both preclinical and clinical settings. Nevertheless, clinical outcomes have been unsatisfying. The antitumor response requires sufficient migration of viable DCs from primary administration site to targeted tumors through related lymphatics. The dynamics and mechanisms of the DCs migration still need further investigation. Here, we briefly introduce the current clinically applicable methods for manufacturing DC-based cancer vaccines and their most commonly used non-invasive, real-time tracking approaches. Furthermore, we propose a hypothesis that intraperitoneal injection may improve the efficiency of DC-based cancer vaccine.

Labeling of cell therapies: How can we get it right?

Labeling cells for non-invasive tracking in vivo using magnetic resonance imaging (MRI) is an emerging hot topic garnering ever increasing attention, yet it is fraught with numerous methodological challenges, which merit careful attention. Several of the current procedures used to label cells for tracking by MRI take advantage of the intrinsic phagocytic nature of cells to engulf nanoparticles, though cells with low intrinsic phagocytic capacity are also commonly studied. Before we take the next steps towards administering such cells in vivo, it is essential to understand how the nanolabel is recognized, internalized, trafficked and distributed within the specific host cell. This is even more critical when contemplating labeling of cells that may ultimately be applied in vivo to patients in a therapeutic context.

Lipopeptide-Coated Iron Oxide Nanoparticles as Potential Glycoconjugate-Based Synthetic Anticancer Vaccines

Although iron oxide magnetic nanoparticles (NPs) have been widely utilized in molecular imaging and drug delivery studies, they have not been evaluated as carriers for glycoconjugate-based anticancer vaccines. Tumor-associated carbohydrate antigens (TACAs) are attractive targets for the development of anticancer vaccines. Due to the weak immunogenicity of these antigens, it is highly challenging to elicit strong anti-TACA immune responses. With their high biocompatibilities and large surface areas, magnetic NPs were synthesized for TACA delivery. The magnetic NPs were coated with phospholipid-functionalized TACA glycopeptides through hydrophobic-hydrophobic interactions without the need for any covalent linkages. Multiple copies of glycopeptides were presented on NPs, potentially leading to enhanced interactions with antibody-secreting B cells through multivalent binding. Mice immunized with the NPs generated strong antibody responses, and the glycopeptide structures important for high antibody titers were identified. The antibodies produced were capable of recognizing both mouse and human tumor cells expressing the glycopeptide, resulting in tumor cell death through complement-mediated cytotoxicities. These results demonstrate that magnetic NPs can be a new and simple platform for multivalently displaying TACA and boosting anti-TACA immune responses without the need for a typical protein carrier.

Dendritic cell-based vaccine efficacy: aiming for hot spots

Many approaches for cancer immunotherapy have targeted dendritic cells (DCs), directly or indirectly, for the induction of antitumor immune responses. DC-based vaccines have been developed using a wide variety of ex vivo DC culture conditions, antigen (Ag) source and loading strategies, maturation agents, and routes of vaccination. Adjuvants are used to activate innate immune cells at the vaccine injection site, to promote Ag transport to the draining lymph nodes (LNs) and to model adaptive immune responses. Despite years of effort, the effective induction of strong and durable antitumor T-cell responses in vaccinated patients remains a challenge. The study of vaccine interactions with other immune cells in the LNs and, more recently, in the injection site has opened new doors for understanding antitumor effector T-cell licensing and function. In this review, we will briefly discuss the relevant sites and up-to-date facts regarding possible targets for antitumor vaccine refinement. We will focus on the processes taking place at the injection site, adjuvant combinations and their role in DC-based vaccines, LN homing, and modeling vaccine-induced immune responses capable of controlling tumor growth and generating immune memory.

Dendritic cell vaccination for glioblastoma multiforme: review with focus on predictive factors for treatment response

Glioblastoma multiforme (GBM) is the most common and most aggressive type of primary brain cancer. Since median overall survival with multimodal standard therapy is only 15 months, there is a clear need for additional effective and long-lasting treatments. Dendritic cell (DC) vaccination is an experimental immunotherapy being tested in several Phase I and Phase II clinical trials. In these trials, safety and feasibility have been proven, and promising clinical results have been reported. On the other hand, it is becoming clear that not every GBM patient will benefit from this highly personalized treatment. Defining the subgroup of patients likely to respond to DC vaccination will position this option correctly amongst other new GBM treatment modalities, and pave the way to incorporation in standard therapy. This review provides an overview of GBM treatment options and focuses on the currently known prognostic and predictive factors for response to DC vaccination. In this way, it will provide the clinician with the theoretical background to refer patients who might benefit from this treatment.

Nanomedical research in Australia and New Zealand

Although Australia and New Zealand have a combined population of less than 30 million, they have an active and interlinked community of nanomedical researchers. This report provides a synopsis and update on this network with a view to identifying the main topics of interest and their likely future trajectories. In addition, our report may also serve to alert others to opportunities for joint projects. Australian and New Zealand researchers are engaged in most of the possible nanomedical topics, but the majority of interest is focused on drug and nucleic acid delivery using nanoparticles or nanoporous constructs. There are, however, smaller programs directed at hyperthermal therapy and radiotherapy, various kinds of diagnostic tests and regenerative technologies.