Depicting adoptive immunotherapy for prostate cancer in an animal model with magnetic resonance imaging

Tracking adoptive natural killer cells via ultrasound imaging assisted with nanobubbles

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

A primer on in vivo cell tracking using MRI

Cell tracking by in vivo magnetic resonance imaging (MRI) offers a collection of multiple advantages over other imaging modalities, including high spatial resolution, unlimited depth penetration, 3D visualization, lack of ionizing radiation, and the potential for long-term cell monitoring. Three decades of innovation in both contrast agent chemistry and imaging physics have built an expansive array of probes and methods to track cells non-invasively across a diverse range of applications. In this review, we describe both established and emerging MRI cell tracking approaches and the variety of mechanisms available for contrast generation. Emphasis is given to the advantages, practical limitations, and persistent challenges of each approach, incorporating quantitative comparisons where possible. Toward the end of this review, we take a deeper dive into three key application areas - tracking cancer metastasis, immunotherapy for cancer, and stem cell regeneration - and discuss the cell tracking techniques most suitable to each.

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.

Advances in NK cell therapy for brain tumors

Despite advances in treatment regimens that comprise surgery, chemotherapy, and radiation, outcome of many brain tumors remains dismal, more so when they recur. The proximity of brain tumors to delicate neural structures often precludes complete surgical resection. Toxicity and long-term side effects of systemic therapy remain a concern. Novel therapies are warranted. The field of NK cell-based cancer therapy has grown exponentially and currently constitutes a major area of immunotherapy innovation. This provides a new avenue for the treatment of cancerous lesions in the brain. In this review, we explore the mechanisms by which the brain tumor microenvironment suppresses NK cell mediated tumor control, and the methods being used to create NK cell products that subvert immune suppression. We discuss the pre-clinical studies evaluating NK cell-based immunotherapies that target several neuro-malignancies and highlight advances in molecular imaging of NK cells that allow monitoring of NK cell-based therapeutics. We review current and ongoing NK cell based clinical trials in neuro-oncology.

How to stop using gadolinium chelates for magnetic resonance imaging: clinical-translational experiences with ferumoxytol

Gadolinium chelates have been used as standard contrast agents for clinical MRI for several decades. However, several investigators recently reported that rare Earth metals such as gadolinium are deposited in the brain for months or years. This is particularly concerning for children, whose developing brain is more vulnerable to exogenous toxins compared to adults. Therefore, a search is under way for alternative MR imaging biomarkers. The United States Food and Drug Administration (FDA)-approved iron supplement ferumoxytol can solve this unmet clinical need: ferumoxytol consists of iron oxide nanoparticles that can be detected with MRI and provide significant T1- and T2-signal enhancement of vessels and soft tissues. Several investigators including our research group have started to use ferumoxytol off-label as a new contrast agent for MRI. This article reviews the existing literature on the biodistribution of ferumoxytol in children and compares the diagnostic accuracy of ferumoxytol- and gadolinium-chelate-enhanced MRI. Iron oxide nanoparticles represent a promising new class of contrast agents for pediatric MRI that can be metabolized and are not deposited in the brain.

Preclinical studies of chimeric antigen receptor-modified natural killer cells in cancer immunotherapy: a review

INTRODUCTION

As one of the most efficacious methods of cancer immunotherapy, chimeric antigen receptor-modified immune cells have recently drawn enormous attention. After the great success achieved with CAR-T-cells in cancer treatment both in preclinical setting and in the clinic, other types of immune cells, including natural killer (NK)-cells and macrophages, have been evaluated for their anti-cancer effects along with their potential superiority against CAR-T-cells, especially in terms of safety. First introduced by Tran et al. almost 26 years ago, CAR-NK-cells are now being considered as efficient immunotherapeutic modalities in various types of cancers, not only in preclinical setting but also in numerous phase I and II clinical studies.

AREAS COVERED

In this review, we aim to provide a comprehensive survey of the preclinical studies on CAR-NK-cells' development, with an evolutional approach on CAR structures and their associated signaling moieties. Current NK-cell sources and modes of gene transfer are also reviewed.

EXPERT OPINION

CAR-NK-cells have appeared as safe and effective immunotherapeutic tools in preclinical settings; however, designing CAR structures with an eye on their specific biology, along with choosing the optimal cell source and gene transfer method require further investigation to support clinical studies.

Chimeric antigen receptor-engineered natural killer cells for cancer immunotherapy

Natural killer (NK) cells are a critical component of the innate immune system. Chimeric antigen receptors (CARs) re-direct NK cells toward tumor cells carrying corresponding antigens, creating major opportunities in the fight against cancer. CAR NK cells have the potential for use as universal CAR cells without the need for human leukocyte antigen matching or prior exposure to tumor-associated antigens. Exciting data from recent clinical trials have renewed interest in the field of cancer immunotherapy due to the potential of CAR NK cells in the production of "off-the-shelf" anti-cancer immunotherapeutic products. Here, we provide an up-to-date comprehensive overview of the recent advancements in key areas of CAR NK cell research and identify under-investigated research areas. We summarize improvements in CAR design and structure, advantages and disadvantages of using CAR NK cells as an alternative to CAR T cell therapy, and list sources to obtain NK cells. In addition, we provide a list of tumor-associated antigens targeted by CAR NK cells and detail challenges in expanding and transducing NK cells for CAR production. We additionally discuss barriers to effective treatment and suggest solutions to improve CAR NK cell function, proliferation, persistence, therapeutic effectiveness, and safety in solid and liquid tumors.

Effectual Labeling of Natural Killer Cells with Upconverting Nanoparticles by Electroporation for In Vivo Tracking and Biodistribution Assessment

Natural killer (NK) cells, which are cytotoxic lymphocytes of the innate immune system and recognize cancer cells via various immune receptors, are promising agents in cell immunotherapy. To utilize NK cells as a therapeutic agent, their biodistribution and pharmacokinetics need to be evaluated following systemic administration. Therefore, in vivo imaging and tracking with efficient labeling and quantitative analysis of NK cells are required. However, the lack of the phagocytic capacity of NK cells makes it difficult to establish breakthroughs in cell labeling and subsequent in vivo studies. Herein, an effective labeling of upconverting nanoparticles (UCNPs) in NK cells is proposed using electroporation with high sensitivity and stability. The labeling performance of UCNPs functionalized with carboxy-polyethylene glycol (PEG) is better than with methoxy-PEG or with amine-PEG. The labeling efficiency becomes higher, but cell damage is greater as electric field increases; thus, there is an optimum electroporation condition for internalization of UCNPs into NK cells. The tracking and biodistribution imaging analyses of intravenously injected NK cells show that the labeled NK cells are initially distributed primarily in lungs and then spread to the liver and spleen. These advances will accelerate the application of NK cells as key components of immunotherapy against cancer.

Chimeric antigen receptor T-cell therapies: Optimising the dose

Lymphocytes such as T-cells can be genetically transduced to express a synthetic chimeric antigen receptor (CAR) that re-directs their cytotoxic activity against a tumour-expressed antigen of choice. Autologous (patient-derived) CAR T-cells have been licensed to treat certain relapsed and refractory B-cell malignancies, and numerous CAR T-cell products are in clinical development. As living gene-modified cells, CAR T-cells exhibit unique pharmacokinetics, typically proliferating within the recipient during the first 14 days after administration before contracting in number, and sometimes exhibiting long-term persistence. The relationship between CAR T-cell dose and exposure is highly variable, and may be influenced by CAR design, patient immune function at the time of T-cell harvest, phenotype of the CAR T-cell product, disease burden, lymphodepleting chemotherapy and subsequent immunomodulatory therapies. Recommended CAR T-cell doses are typically established for a specific product and indication, although for some products, stratification of dose based on disease burden may mitigate toxicity while maintaining efficacy. Re-evaluation of CAR T-cell dosing may be necessary following changes to the lymphodepleting regimen, for different disease indications, and following significant manufacturing changes, if product comparability cannot be demonstrated. Dose escalation trials have typically employed 3 + 3 designs, although this approach has limitations, and alternative phase I trial designs may facilitate the identification of CAR T-cell doses that strike an optimal balance of safety, efficacy and manufacturing feasibility.

Improving Tumor Retention of Effector Cells in Adoptive Cell Transfer Therapies by Magnetic Targeting

Adoptive cell transfer therapy is a promising anti-tumor immunotherapy in which effector immune cells are transferred to patients to treat tumors. However, one of its main limitations is the inefficient trafficking of inoculated effector cells to the tumor site and the small percentage of effector cells that remain activated when reaching the tumor. Multiple strategies have been attempted to improve the entry of effector cells into the tumor environment, often based on tumor types. It would be, however, interesting to develop a more general approach, to improve and facilitate the migration of specific activated effector lymphoid cells to any tumor type. We and others have recently demonstrated the potential for adoptive cell transfer therapy of the combined use of magnetic nanoparticle-loaded lymphoid effector cells together with the application of an external magnetic field to promote the accumulation and retention of lymphoid cells in specific body locations. The aim of this review is to summarize and highlight the recent findings in the field of magnetic accumulation and retention of effector cells in tumors after adoptive transfer, and to discuss the possibility of using this approach for tumor targeting with chimeric antigen receptor (CAR) T-cells.

Application of In Vivo Imaging Techniques for Monitoring Natural Killer Cell Migration and Tumor Infiltration

In recent years, the use of natural killer (NK) cell-based immunotherapy has shown promise against various cancer types. To some extent therapeutic potential of NK cell-based immunotherapy depends on migration of NK cells towards tumors in animal models or human subjects and subsequent infiltration. Constant improvement in the pharmacological and therapeutic properties of NK cells is driving the performance and use of NK cell-based immunotherapies. In this review, we summarize the molecular imaging techniques used in monitoring the migration and infiltration of NK cells in vivo at preclinical and clinical levels. A review of pros and cons of each molecular imaging modality is done. Finally, we provide our perception of the usefulness of molecular imaging approaches for in vivo monitoring of NK cells in preclinical and clinical scenarios.

Nano-immunoimaging

Immunoimaging is a rapidly growing field stoked in large part by the intriguing triumphs of immunotherapy. On the heels of immunotherapy's successes, there exists a growing need to evaluate tumor response to therapy particularly immunotherapy, stratify patients into responders vs. non-responders, identify inflammation, and better understand the fundamental roles of immune system components to improve both immunoimaging and immunotherapy. Innovative nanomaterials have begun to provide novel opportunities for immunoimaging, in part due to their sensitivity, modularity, capacity for many potentially varied ligands (high avidity), and potential for multifunctionality/multimodality imaging. This review strives to comprehensively summarize the integration of nanotechnology and immunoimaging, and the field's potential for clinical applications.

Magnetic Nanoparticles Attached to the NK Cell Surface for Tumor Targeting in Adoptive Transfer Therapies Does Not Affect Cellular Effector Functions

Adoptive cell transfer therapy is currently one of the most promising approaches for cancer treatment. This therapy has some limitations, however, such as the dispersion of in vivo-administered cells, causing only a small proportion to reach the tumor. Nanotechnological approaches could offer a solution for this drawback, as they can increase cell retention and accumulation in a region of interest. In particular, strategies employing magnetic nanoparticles (MNPs) to improve targeting of adoptively transferred T or NK cells have been explored in mice. In vivo magnetic retention is reported using the human NK cell line NK-92MI transfected with MNPs. Primary NK cells are nonetheless highly resistant to transfection, and thus we explore in here the possibility of attaching the MNPs to the NK cell surface to overcome this issue, and examine whether this association would affect NK effector functions. We assessed the attachment of MNPs coated with different polymers to the NK cell surface, and found that APS-MNP attached more efficiently to the NK-92MI cell surface. In association with MNPs, these cells preserved their main functions, exhibiting a continued capacity to degranulate, conjugate with and lyse target cells, produce IFN-γ, and respond to chemotactic signals. MNP-loaded NK-92MI cells were also retained in an in vitro capillary flow system by applying an EMF. A similar analysis was carried out in primary NK cells, isolated from mice, and expanded in vitro. These primary murine NK cells also maintained their functionality intact after MNP treatment and were successfully retained in vitro. This work therefore provides further support for using MNPs in combination with EMFs to favor specific retention of functional NK cells in a region of interest, which may prove beneficial to adoptive cell-therapy protocols.

Magnetic targeting of adoptively transferred tumour-specific nanoparticle-loaded CD8+ T cells does not improve their tumour infiltration in a mouse model of cancer but promotes the retention of these cells in tumour-draining lymph nodes

Background

Adoptive T cell-transfer (ATC) therapy is a highly promising cancer-treatment approach. However, in vivo-administered T cells tend to disperse, with only a small proportion reaching the tumour. To remedy this, magnetic targeting of T cells has been recently explored. Magnetic nanoparticles (MNPs) functionalised with antibodies were attached to effector T cells and magnetically recruited to tumour sites under MRI guidance. In this study, we investigated whether 3-aminopropyl-triethoxysilane (APS)-coated MNPs directly attached to CD8⁺ T cell membranes could also magnetically target and accumulate tumour-specific CD8⁺ T cells in solid tumours using an external magnetic field (EMF). As it has been shown that T cells associated with APS-coated MNPs are retained in lymph nodes (LNs), and tumour-draining LNs are the most common sites of solid-tumour metastases, we further evaluated whether magnetic targeting of APS-MNP-loaded CD8⁺ T cells could cause them to accumulate in tumour-draining LNs.

Results

First, we show that antigen-specific CD8⁺ T cells preserve their antitumor activity in vitro when associated with APS-MNPs. Next, we demonstrate that the application of a magnetic field enhanced the retention of APS-MNP-loaded OT-I CD8⁺ T cells under flow conditions in vitro. Using a syngeneic mouse model, we found similar numbers of APS-MNP-loaded OT-I CD8⁺ T cells and OT-I CD8⁺ T cells infiltrating the tumour 14 days after cell transfer. However, when a magnet was placed near the tumour during the transfer of tumour-specific APS-MNP-loaded CD8⁺ T cells to improve tumour infiltration, a reduced percentage of tumour-specific T cells was found infiltrating the tumour 14 days after cell transfer, which was reflected in a smaller reduction in tumour size compared to tumour-specific CD8⁺ T cells transferred with or without MNPs in the absence of a magnetic field. Nonetheless, magnet placement near the tumour site during cell transfer induced infiltration of activated tumour-specific CD8⁺ T cells in tumour-draining LNs, which remained 14 days after cell transfer.

Conclusions

The use of an EMF to improve targeting of tumour-specific T cells modified with APS-MNPs reduced the percentage of these cells infiltrating the tumour, but promoted the retention and the persistence of these cells in the tumour-draining LNs.

Electronic supplementary material

The online version of this article (10.1186/s12951-019-0520-0) contains supplementary material, which is available to authorized users.

State of the Art of Natural Killer Cell Imaging: A Systematic Review

Natural killer (NK) cell therapy is a promising alternative to conventional T cell-based treatments, although there is a lack of diagnostic tools to predict and evaluate therapeutic outcomes. Molecular imaging can offer several approaches to non-invasively address this issue. In this study, we systematically reviewed the literature to evaluate the state of the art of NK cell imaging and its translational potential. PubMed and Scopus databases were searched for published articles on the imaging of NK cells in humans and preclinical models. Study quality was evaluated following Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) criteria. We pooled studies as follows: Optical, magnetic resonance imaging (MRI) and nuclear medicine imaging with a total of 21 studies (n = 5, n = 8 and n = 8, respectively). Considering the limitation of comparing different imaging modalities, it appears that optical imaging (OI) of NK cells is very useful in a preclinical setting, but has the least translational potential. MRI provides high quality images without ionizing radiations with lower sensitivity. Nuclear medicine is the only imaging technique that has been applied in humans (four papers), but results were not outstanding due to a limited number of enrolled patients. At present, no technique emerged as superior over the others and more standardization is required in conducting human and animal studies.

The Molecular Imaging of Natural Killer Cells

The recent success of autologous T cell-based therapies in hematological malignancies has spurred interest in applying similar immunotherapy strategies to the treatment of solid tumors. Identified nearly 4 decades ago, natural killer (NK) cells represent an arguably better cell type for immunotherapy development. Natural killer cells are cytotoxic lymphocytes that mediate the direct killing of transformed cells with reduced or absent major histocompatibility complex (MHC) and are the effector cells in antibody-dependent cell-mediated cytotoxicity. Unlike T cells, they do not require human leukocyte antigen (HLA) matching allowing for the adoptive transfer of allogeneic NK cells in the clinic. The development of NK cell-based therapies for solid tumors is complicated by the presence of an immunosuppressive tumor microenvironment that can potentially disarm NK cells rendering them inactive. The molecular imaging of NK cells in vivo will be crucial for the development of new therapies allowing for the immediate assessment of therapeutic response and off-target effects. A number of groups have investigated methods for detecting NK cells by optical, nuclear, and magnetic resonance imaging. In this review, we will provide an overview of the advances made in imaging NK cells in both preclinical and clinical studies.

Natural Killer Cells and Current Applications of Chimeric Antigen Receptor-Modified NK-92 Cells in Tumor Immunotherapy

Natural killer (NK) cells are innate immune cells that can be activated rapidly to target abnormal and virus-infected cells without prior sensitization. With significant advancements in cell biology technologies, many NK cell lines have been established. Among these cell lines, NK-92 cells are not only the most widely used but have also been approved for clinical applications. Additionally, chimeric antigen receptor-modified NK-92 cells (CAR-NK-92 cells) have shown strong antitumor effects. In this review, we summarize established human NK cell lines and their biological characteristics, and highlight the applications of NK-92 cells and CAR-NK-92 cells in tumor immunotherapy.

Combination Therapy with EpCAM-CAR-NK-92 Cells and Regorafenib against Human Colorectal Cancer Models

Adoptive chimeric antigen receptor-modified T or NK cells (CAR-T or CAR-NK) offer new options for cancer treatment. CAR-T therapy has achieved encouraging breakthroughs in the treatment of hematological malignancies. However, their therapeutic efficacy against solid tumors is limited. New regimens, including combinations with chemical drugs, need to be studied to enhance the therapeutic efficacy of CAR-T or NK cells for solid tumors. An epithelial cell adhesion molecule- (EpCAM-) specific second-generation CAR was constructed and transduced into NK-92 cells by lentiviral vectors. Immune effects, including cytokine release and cytotoxicity of the CAR-NK-92 cells against EpCAM-positive colon cancer cells, were evaluated in vitro. Synergistic effects of regorafenib and CAR-NK-92 cells were analyzed in a mouse model with human colorectal cancer xenografts. The CAR-NK-92 cells can specifically recognize EpCAM-positive colorectal cancer cells and release cytokines, including IFN-γ, perforin, and granzyme B, and show specific cytotoxicity in vitro. The growth suppression efficacy of combination therapy with regorafenib and CAR-NK-92 cells on established EpCAM-positive tumor xenografts was more significant than that of monotherapy with CAR-NK-92 cells or regorafenib. Our results provided a novel strategy to treat colorectal cancer and enhance the therapeutic efficacy of CAR-modified immune effector cells for solid tumors.

HIF-1α induces immune escape of prostate cancer by regulating NCR1/NKp46 signaling through miR-224

BACKGROUND

Metastasis of prostate cancer (PCa) is largely affected by natural killer (NK) cells. This study aimed to clarify the mechanisms underlying tumor cells escaping from NK cells mediated by HIF-1α.

METHODS

MiR-224 expression in lymphocytes and HIF-1α protein level in NK cells were determined by qRT-PCR and western blot, respectively. The amount of NKp46⁺ NK cells was detected with flow cytometry. The IFN-γ level was examined by enzyme linked immunosorbent assay (ELISA). NK cells were tested for cytolytic activity with a Non-Radioactive Cytotoxicity Assay, and treated with oxygenglucose deprivation (OGD) for hypoxia simulation. Interaction between miR-224 and NCR1 was evaluated with dual luciferase reporter assay.

RESULTS

MiR-224 was down-regulated in lymphocytes isolated from prostate cancer tissues (n = 10). Overexpression of miR-224 protected prostate cancer from NK cells. HIF-1α increased miR-224 to inhibit the killing capability of NK cells on prostate cancer. MiR-224 controlled the expression of NCR1. Overexpression of miR-224 protected prostate cancer from NK cells through NCR1/NKp46 signaling. Suppression of HIF-1α enhanced the cytotoxicity of NK cells on prostate cancer via miR-224/NCR1 pathway.

CONCLUSION

HIF-1α inhibits NCR1/NKp46 pathway through up-regulating miR-224, which affects the killing capability of NK cells on prostate cancer, thus inducing immune escape of tumor cells.

MRI-guided interventional natural killer cell delivery for liver tumor treatment

While natural killer (NK) cell‐based adoptive transfer immunotherapy (ATI) provides only modest clinical success in cancer patients. This study was hypothesized that MRI‐guided transcatheter intra‐hepatic arterial (IHA) infusion permits local delivery to liver tumors to improve outcomes during NK‐based ATI in a rat model of hepatocellular carcinoma (HCC). Mouse NK cells were labeled with clinically applicable iron nanocomplexes. Twenty rat HCC models were assigned to three groups: transcatheter IHA saline infusion as the control group, transcatheter IHA NK infusion group, and intravenous (IV) NK infusion group. MRI studies were performed at baseline and at 24 h, 48 h, and 8 days postinfusion. There was a significant difference in tumor R2* values between baseline and 24 h following the selective transcatheter IHA NK delivery to the tumors (P = 0.039) when compared to IV NK infusion (P = 0.803). At 8 days postinfusion, there were significant differences in tumor volumes between the control, IV, and IHA NK infusion groups (control vs. IV, P = 0.196; control vs. IHA, P < 0.001; and IV vs. IHA, P = 0.001). Moreover, there was a strong correlation between tumor R2* value change (∆R2*) at 24 h postinfusion and tumor volume change (∆volume) at 8 days in IHA group (R² = 0.704, P < 0.001). Clinically applicable labeled NK cells with 12‐h labeling time can be tracked by MRI. Transcatheter IHA infusion improves NK cell homing efficacy and immunotherapeutic efficiency. The change in tumor R2* value 24 h postinfusion is an important early biomarker for prediction of longitudinal response.

Molecular Imaging: A Useful Tool for the Development of Natural Killer Cell-Based Immunotherapies

Molecular imaging is a relatively new discipline that allows visualization, characterization, and measurement of the biological processes in living subjects, including humans, at a cellular and molecular level. The interaction between cancer cells and natural killer (NK) cells is complex and incompletely understood. Despite our limited knowledge, progress in the search for immune cell therapies against cancer could be significantly improved by dynamic and non-invasive visualization and tracking of immune cells and by visualization of the response of cancer cells to therapies in preclinical and clinical studies. Molecular imaging is an essential tool for these studies, and a multimodal molecular imaging approach can be applied to monitor immune cells in vivo, for instance, to visualize therapeutic effects. In this review, we discuss the usefulness of NK cells in cancer therapies and the preclinical and clinical usefulness of molecular imaging in NK cell-based therapies. Furthermore, we discuss different molecular imaging modalities for use with NK cell-based therapies, and their preclinical and clinical applications in animal and human subjects. Molecular imaging has contributed to the development of NK cell-based therapies against cancers in animal models and to the refinement of current cell-based cancer immunotherapies. Developing sensitive and reproducible non-invasive molecular imaging technologies for in vivo NK cell monitoring and for real-time assessment of therapeutic effects will accelerate the development of NK cell therapies.

Current Perspective on In Vivo Molecular Imaging of Immune Cells

Contemporaneous development of improved immune cell-based therapies, and powerful imaging tools, has prompted growth in technologies for immune cell tracking in vivo. Over the past couple of decades, imaging tools such as magnetic resonance imaging (MRI) and optical imaging have successfully monitored the trafficking patterns of therapeutic immune cells and assisted the evaluation of the success or failure of immunotherapy. Recent advancements in imaging technology have made imaging an indispensable module of immune cell-based therapies. In this review, emerging applications of non-radiation imaging modalities for the tracking of a range of immune cells are discussed. Applications of MRI, NIR, and other imaging tools have demonstrated the potential of non-invasively surveying the fate of both phagocytic and non-phagocytic immune cells in vivo.

Chimeric Antigen Receptor-Engineered NK-92 Cells: An Off-the-Shelf Cellular Therapeutic for Targeted Elimination of Cancer Cells and Induction of Protective Antitumor Immunity

Significant progress has been made in recent years toward realizing the potential of natural killer (NK) cells for cancer immunotherapy. NK cells can respond rapidly to transformed and stressed cells and have the intrinsic potential to extravasate and reach their targets in almost all body tissues. In addition to donor-derived primary NK cells, also the established NK cell line NK-92 is being developed for adoptive immunotherapy, and general safety of infusion of irradiated NK-92 cells has been established in phase I clinical trials with clinical responses observed in some of the cancer patients treated. To enhance their therapeutic utility, NK-92 cells have been modified to express chimeric antigen receptors (CARs) composed of a tumor-specific single chain fragment variable antibody fragment fused via hinge and transmembrane regions to intracellular signaling moieties such as CD3ζ or composite signaling domains containing a costimulatory protein together with CD3ζ. CAR-mediated activation of NK cells then bypasses inhibitory signals and overcomes NK resistance of tumor cells. In contrast to primary NK cells, CAR-engineered NK-92 cell lines suitable for clinical development can be established from molecularly and functionally well-characterized single cell clones following good manufacturing practice-compliant procedures. In preclinical in vitro and in vivo models, potent antitumor activity of NK-92 variants targeted to differentiation antigens expressed by hematologic malignancies, and overexpressed or mutated self-antigens associated with solid tumors has been found, encouraging further development of CAR-engineered NK-92 cells. Importantly, in syngeneic mouse tumor models, induction of endogenous antitumor immunity after treatment with CAR-expressing NK-92 cells has been demonstrated, resulting in cures and long-lasting immunological memory protecting against tumor rechallenge at distant sites. Here, we summarize the current status and future prospects of CAR-engineered NK-92 cells as off-the-shelf cellular therapeutics, with special emphasis on ErbB2 (HER2)-specific NK-92 cells that are approaching clinical application.

Intraperitoneal immunotherapy with T cells stably and transiently expressing anti-EpCAM CAR in xenograft models of peritoneal carcinomatosis

The epithelial cell adhesion molecule (EpCAM) is overexpressed in a wide variety of tumor types, including peritoneal carcinomatosis (PC) from gastrointestinal and gynecological malignancies. To develop a chimeric antigen receptor T (CART) cell therapy approach to treat patients with end-stage PC, we constructed third generation CARs specific to EpCAM using the 4D5MOC-B single chain variable fragment. CART cells were generated with lentiviral transduction and exhibited specific in vitro killing activity against EpCAM-positive human ovarian and colorectal cancer cells. A single intraperitoneal injection of the CART cells eradicated established ovarian xenografts and resulted in significantly prolonged animal survival. Since EpCAM is also expressed on normal epithelium, anti-EpCAM CART cells were generated by mRNA electroporation that display a controlled cytolytic activity with a limited CAR expression duration. Multiple repeated infusions of these RNA CAR-modified T cells delayed disease progression in immunodeficient mice bearing well-established peritoneal ovarian and colorectal xenografts. Thus, our study demonstrates the effectiveness of using anti-EpCAM CAR-expressing T cells for local treatment of PC in mice. The possibility of using this approach for clinical treatment of EpCAM-positive gastrointestinal and gynecological malignancies warrants further validation.

Cytokine-Mediated Immunopathogenesis of Hepatitis B Virus Infections

Hepatitis B virus (HBV) infection is a worldwide health problem, with approximately one third of populations have been infected, among which 3-5% of adults and more than 90% of children developed to chronic HBV infection. Host immune factors play essential roles in the outcome of HBV infection. Thus, ineffective immune response against HBV may result in persistent virus replications and liver necroinflammations, then lead to chronic HBV infection, liver cirrhosis, and even hepatocellular carcinoma. Cytokine balance was shown to be an important immune characteristic in the development and progression of hepatitis B, as well as in an effective antiviral immunity. Large numbers of cytokines are not only involved in the initiation and regulation of immune responses but also contributing directly or indirectly to the inhibition of virus replication. Besides, cytokines initiate downstream signaling pathway activities by binding to specific receptors expressed on the target cells and play important roles in the responses against viral infections and, therefore, might affect susceptibility to HBV and/or the natural course of the infection. Since cytokines are the primary causes of inflammation and mediates liver injury after HBV infection, we have discussed recent advances on the roles of various cytokines [including T helper type 1 cells (Th1), Th2, Th17, regulatory T cells (Treg)-related cytokines] in different phases of HBV infection and cytokine-related mechanisms for impaired viral control and liver damage during HBV infection. We then focus on experimental therapeutic applications of cytokines to gain a better understanding of this newly emerging aspect of disease pathogenesis.

Clinically applicable magnetic-labeling of natural killer cells for MRI of transcatheter delivery to liver tumors: preclinical validation for clinical translation

AIM

To test the hypothesis that MRI can monitor intraportal vein (IPV) transcatheter delivery of clinically applicable heparin-protamine-ferumoxytol (HPF) nanocomplex-labeled natural killer (NK) cells to liver tumor.

MATERIALS & METHODS

Liver tumor rat models underwent catheterization for IPV infusion of HPF-labeled NK cells (NK-92MI cell line). MRI measurements within tumor and adjacent liver tissues were compared pre- and post-NK cell infusion. Histology studies were used to identify NK cells in the target tumors.

RESULTS

For first time, we demonstrated that MRI tracks HPF-labeled NK cells migration within liver following IPV delivery.

CONCLUSION

IPV transcatheter infusion permitted selective delivery of NK cells to liver tissues and MRI allowed tracking NK cell biodistributions within the tumors.

(19)F-MRI for monitoring human NK cells in vivo

The availability of clinical-grade cytokines and artificial antigen-presenting cells has accelerated interest in using natural killer (NK) cells as adoptive cellular therapy (ACT) for cancer. One of the technological shortcomings of translating therapies from animal models to clinical application is the inability to effectively and non-invasively track these cells after infusion in patients. We have optimized the nonradioactive isotope fluorine-19 ((19)F) as a means to label and track NK cells in preclinical models using magnetic resonance imaging (MRI). Human NK cells were expanded with interleukin (IL)-2 and labeled in vitro with increasing concentrations of (19)F. Doses as low as 2 mg/mL (19)F were detected by MRI. NK cell viability was only decreased at 8 mg/mL (19)F. No effects on NK cell cytotoxicity against K562 leukemia cells were observed with 2, 4 or 8 mg/mL (19)F. Higher doses of (19)F, 4 mg/mL and 8 mg/mL, led to an improved (19)F signal by MRI with 3 × 10(11) (19)F atoms per NK cell. The 4 mg/mL (19)F labeling had no effect on NK cell function via secretion of granzyme B or interferon gamma (IFNγ), compared to NK cells exposed to vehicle alone. (19)F-labeled NK cells were detectable immediately by MRI after intratumoral injection in NSG mice and up to day 8. When (19)F-labeled NK cells were injected subcutaneously, we observed a loss of signal through time at the site of injection suggesting NK cell migration to distant organs. The (19)F perfluorocarbon is a safe and effective reagent for monitoring the persistence and trafficking of NK cell infusions in vivo, and may have potential for developing novel imaging techniques to monitor ACT for cancer.

In Vivo (19)F-Magnetic Resonance Imaging of Adoptively Transferred NK Cells

In order to assess the biodistribution, homing, and persistence of adoptively transferred natural killer (NK) cell immunotherapies, there is a need for imaging methodology suitable for use in preclinical studies with relevance to clinical translation. Amongst the available approaches, (19)F-MRI is very appealing for in vivo imaging due to the absence of background signal, enabling clear detection of (19)F labeled cells in vivo. Here we describe a methodology for in vivo imaging of adoptively transferred NK cells labeled with (19)F nano-emulsion, using clinically translatable technology of (19)F/(1)H magnetic resonance imaging.

Molecular magnetic resonance imaging in cancer

The ability to identify key biomolecules and molecular changes associated with cancer malignancy and the capacity to monitor the therapeutic outcome against these targets is critically important for cancer treatment. Recent developments in molecular imaging based on magnetic resonance (MR) techniques have provided researchers and clinicians with new tools to improve most facets of cancer care. Molecular imaging is broadly described as imaging techniques used to detect molecular signature at the cellular and gene expression levels. This article reviews both established and emerging molecular MR techniques in oncology and discusses the potential of these techniques in improving the clinical cancer care. It also discusses how molecular MR, in conjunction with other structural and functional MR imaging techniques, paves the way for developing tailored treatment strategies to enhance cancer care.

Near-infrared imaging of adoptive immune cell therapy in breast cancer model using cell membrane labeling

The overall objective of this study is to non-invasively image and assess tumor targeting and retention of directly labeled T-lymphocytes following their adoptive transfer in mice. T-lymphocytes obtained from draining lymph nodes of 4T1 (murine breast cancer cell) sensitized BALB/C mice were activated in-vitro with Bryostatin/Ionomycin for 18 hours, and were grown in the presence of Interleukin-2 for 6 days. T-lymphocytes were then directly labeled with 1,1-dioctadecyltetramethyl indotricarbocyanine Iodide (DiR), a lipophilic near infrared fluorescent dye that labels the cell membrane. Assays for viability, proliferation, and function of labeled T-lymphocytes showed that they were unaffected by DiR labeling. The DiR labeled cells were injected via tail vein in mice bearing 4T1 tumors in the flank. In some cases labeled 4T1 specific T-lymphocytes were injected a week before 4T1 tumor cell implantation. Multi-spectral in vivo fluorescence imaging was done to subtract the autofluorescence and isolate the near infrared signal carried by the T-lymphocytes. In recipient mice with established 4T1 tumors, labeled 4T1 specific T-lymphocytes showed marked tumor retention, which peaked 6 days post infusion and persisted at the tumor site for up to 3 weeks. When 4T1 tumor cells were implanted 1-week post-infusion of labeled T-lymphocytes, T-lymphocytes responded to the immunologic challenge and accumulated at the site of 4T1 cell implantation within two hours and the signal persisted for 2 more weeks. Tumor accumulation of labeled 4T1 specific T-lymphocytes was absent in mice bearing Meth A sarcoma tumors. When lysate of 4T1 specific labeled T-lymphocytes was injected into 4T1 tumor bearing mice the near infrared signal was not detected at the tumor site. In conclusion, our validated results confirm that the near infrared signal detected at the tumor site represents the DiR labeled 4T1 specific viable T-lymphocytes and their response to immunologic challenge can be imaged in vivo.

Design and development of therapies using chimeric antigen receptor-expressing T cells

Investigators developed chimeric antigen receptors (CARs) for expression on T cells more than 25 years ago. When the CAR is derived from an antibody, the resultant cell should combine the desirable targeting features of an antibody (e.g. lack of requirement for major histocompatibility complex recognition, ability to recognize non-protein antigens) with the persistence, trafficking, and effector functions of a T cell. This article describes how the past two decades have seen a crescendo of research which has now begun to translate these potential benefits into effective treatments for patients with cancer. We describe the basic design of CARs, describe how antigenic targets are selected, and the initial clinical experience with CAR-T cells. Our review then describes our own and other investigators' work aimed at improving the function of CARs and reviews the clinical studies in hematological and solid malignancies that are beginning to exploit these approaches. Finally, we show the value of adding additional engineering features to CAR-T cells, irrespective of their target, to render them better suited to function in the tumor environment, and discuss how the safety of these heavily modified cells may be maintained.

In vivo monitoring of natural killer cell trafficking during tumor immunotherapy

Natural killer (NK) cells are a crucial part of the innate immune system and play critical roles in host anti-viral, anti-microbial, and antitumor responses. The elucidation of NK cell biology and their therapeutic use are actively being pursued with 200 clinical trials currently underway. In this review, we outline the role of NK cells in cancer immunotherapies and summarize current noninvasive imaging technologies used to track NK cells in vivo to investigate mechanisms of action, develop new therapies, and evaluate efficacy of adoptive transfer.

Migration of iron-labeled KHYG-1 natural killer cells to subcutaneous tumors in nude mice, as detected by magnetic resonance imaging

BACKGROUND AIMS

A novel cell line of cytotoxic natural killer (NK) cells, KHYG-1, was examined in vivo for immunotherapy against prostate cancer. The feasibility of using magnetic resonance imaging (MRI) tracking to monitor the fate of injected NK cells following intravenous (i.v.), intraperitoneal (i.p.) and subcutaneous (s.c.) administration was assessed.

METHODS

PC-3M human prostate cancer cells were injected s.c. into the flank of nude mice (day 0). KHYG-1 NK cells were labeled with an iron oxide contrast agent and injected s.c., i.v. or i.p. on day 8. Mice were imaged by MRI on days 7, 9 and 12. Tumor sections were examined with fluorescence microscopy and immunohistologic staining for NK cells.

RESULTS

NK cells were detected in the tumors by histology after all three administration routes. NK cells and fluorescence from the iron label were co-localized. Signal loss was seen in the areas around the tumors and between the tumor lobes in the s.c. group.

CONCLUSIONS

We are the first to label this cell line of NK cells with an iron oxide contrast agent. Accumulation of NK cells was visualized by MRI after s.c. injection but not after i.v. and i.p. injection.

Chimeric antigen receptor (CAR)-engineered lymphocytes for cancer therapy

INTRODUCTION

Chimeric antigen receptors (CARs) usually combine the antigen binding site of a monoclonal antibody with the signal activating machinery of a T cell, freeing antigen recognition from MHC restriction and thus breaking one of the barriers to more widespread application of cellular therapy. Similar to treatment strategies employing monoclonal antibodies, T cells expressing CARs are highly targeted, but additionally offer the potential benefits of active trafficking to tumor sites, in vivo expansion and long-term persistence. Furthermore, gene transfer allows the introduction of countermeasures to tumor immune evasion and of safety mechanisms.

AREAS COVERED

The basic structure of so-called first and later generation CARs and their potential advantages over other immune therapy systems. How these molecules can be grafted into immune cells (including retroviral and non-retroviral transduction methods) and strategies to improve the in vivo persistence and function of immune cells expressing CARs. Examples of tumor-associated antigens that have been targeted in preclinical models and clinical experience with these modified cells. Safety issues surrounding CAR gene transfer into T cells and potential solutions to them.

EXPERT OPINION

Because of recent advances in immunology, genetics and cell processing, CAR-modified T cells will likely play an increasing role in the cellular therapy of cancer, chronic infections and autoimmune disorders.