Para- and Transcellular Transport Kinetics of Nanoparticles across Lymphatic Endothelial Cells.

Lymphatic vessels have received significant attention as drug delivery targets, as they shuttle materials from peripheral tissues to the lymph nodes, where adaptive immunity is formed. Delivery of immune modulatory materials to the lymph nodes via lymphatic vessels has been shown to enhance their efficacy and also improve the bioavailability of drugs when delivered to intestinal lymphatic vessels. In this study, we generated a three-compartment model of a lymphatic vessel with a set of kinematic differential equations to describe the transport of nanoparticles from the surrounding tissues into lymphatic vessels. We used previously published data and collected additional experimental parameters, including the transport efficiency of nanoparticles over time, and also examined how nanoparticle formulation affected the cellular transport mechanisms using small molecule inhibitors. These experimental data were incorporated into a system of kinematic differential equations, and nonlinear, least-squares curve fitting algorithms were employed to extrapolate transport coefficients within our model. The subsequent computational framework produced some of the first parameters to describe transport kinetics across lymphatic endothelial cells and allowed for the quantitative analysis of the driving mechanisms of transport into lymphatic vessels. Our model indicates that transcellular mechanisms, such as micro- and macropinocytosis, drive transport into lymphatics. This information is crucial to further design strategies that will modulate lymphatic transport for drug delivery, particularly in diseases like lymphedema, where normal lymphatic functions are impaired.

Mechanical Dissociation of Tissues for Single Cell Analysis Using a Motorized Device.

Being able to isolate and prepare single cells for the analysis of tissue samples has rapidly become crucial for new biomedical discoveries and research. Manual protocols for single-cell isolations are highly time-consuming and prone to user variability. Automated mechanical protocols are able to reduce processing time and sample variability but aren't easily accessible or cost-effective in lower-resourced research settings. The device described here was designed for semi-automated tissue dissociation using commercially available materials as a low-cost alternative for academic laboratories. Instructions to fabricate, assemble, and operate the device design have been provided. The dissociation protocol reliably produces single-cell suspensions with comparable cell yields and sample viability to manual preparations across multiple mouse tissues. The protocol provides the ability to process up to 12 tissue samples simultaneously per device, making studies requiring large sample sizes more manageable. The accompanying software also allows for customization of the device protocol to accommodate varying tissues and experimental constraints.

Mechanisms of Nanoparticle Transport across Intestinal Tissue: An Oral Delivery Perspective.

Oral drug administration has been a popular choice due to patient compliance and limited clinical resources. Orally delivered drugs must circumvent the harsh gastrointestinal (GI) environment to effectively enter the systemic circulation. The GI tract has a number of structural and physiological barriers that limit drug bioavailability including mucus, the tightly regulated epithelial layer, immune cells, and associated vasculature. Nanoparticles have been used to enhance oral bioavailability of drugs, as they can act as a shield to the harsh GI environment and prevent early degradation while also increasing uptake and transport of drugs across the intestinal epithelium. Evidence suggests that different nanoparticle formulations may be transported via different intracellular mechanisms to cross the intestinal epithelium. Despite the existence of a significant body of work on intestinal transport of nanoparticles, many key questions remain: What causes the poor bioavailability of the oral drugs? What factors contribute to the ability of a nanoparticle to cross different intestinal barriers? Do nanoparticle properties such as size and charge influence the type of endocytic pathways taken? In this Review, we summarize the different components of intestinal barriers and the types of nanoparticles developed for oral delivery. In particular, we focus on the various intracellular pathways used in nanoparticle internalization and nanoparticle or cargo translocation across the epithelium. Understanding the gut barrier, nanoparticle characteristics, and transport pathways may lead to the development of more therapeutically useful nanoparticles as drug carriers.

Biomaterials for intranasal and inhaled vaccine delivery.

Delivery of vaccines by nasal sprays may enable more robust, protective mucosal immune responses against infectious diseases, such as COVID-19, compared with intramuscular injection. In this Comment, we highlight how biomaterials can be designed to allow intranasal and inhaled vaccination.

Nanotechnologies for Physiology-Informed Drug Delivery to the Lymphatic System.

Accompanying the increasing translational impact of immunotherapeutic strategies to treat and prevent disease has been a broadening interest across both bioscience and bioengineering in the lymphatic system. Herein, the lymphatic system physiology, ranging from its tissue structures to immune functions and effects, is described. Design principles and engineering approaches to analyze and manipulate this tissue system in nanoparticle-based drug delivery applications are also elaborated.

Inhaled CpG increases survival and synergizes with checkpoint inhibition in lymphangioleiomyomatosis.

Rationale: Lymphangioleiomyomatosis (LAM) is a devastating disease primarily found in women of reproductive age that leads to cancer-like cystic destruction of the lungs. Recent work has shown that LAM causes immunosuppression and that checkpoint inhibitors can be used as LAM treatment. IN lung cancer, TLR agonist, in particular TLR9 agonist CpG has been shown to be effective. Objectives: Here we investigate the use of TLR9 agonist CpG as LAM immunotherapy in combination with checkpoint inhibitor, anti-PD1 and assess induced changes in anti-LAM immunity. Methods: We used a murine model of metastatic LAM to determine survival after intranasal treatment with TLR9 agonist CpG at two doses and in combination the checkpoint inhibitor immunotherapy, anti-PD-1. We used histology and flow cytometry to assess overall inflammation as well as changes in the immune response upon treatment. Measurements and Main Results: We found that local administration of CpG enhances survival in a murine model of LAM and that a lower dose more effectively balanced the inflammation induced by CpG with the anti-LAM therapeutic benefits. We also found that CpG reduces regulatory T cell infiltration in LAM lungs and that CD4 helper T cells are skewed toward pro-inflammatory phenotypes. We also found that CpG treatment is effective in both early stage and progressive disease and that CpG is synergistic with previously tested anti-PD1 therapy. Conclusions: We have found that TLR9 agonist CpG can be used as LAM immunotherapy and effectively synergizes with anti-PD1 therapy in LAM.

In Vitro Models of Blood and Lymphatic Vessels-Connecting Tissues and Immunity.

Blood and lymphatic vessels are regulators of physiological processes, including oxygenation and fluid transport. Both vessels are ubiquitous throughout the body and are critical for sustaining tissue homeostasis. The complexity of each vessel's processes has limited the understanding of exactly how the vessels maintain their functions. Both vessels have been shown to be involved in the pathogenesis of many diseases, including cancer metastasis, and it is crucial to probe further specific mechanisms involved. In vitro models are developed to better understand blood and lymphatic physiological functions and their mechanisms. In this review, blood and lymphatic in vitro model systems, including 2D and 3D designs made using Transwells, microfluidic devices, organoid cultures, and various other methods, are described. Models studying endothelial cell-extracellular matrix interactions, endothelial barrier properties, transendothelial transport and cell migration, lymph/angiogenesis, vascular inflammation, and endothelial-cancer cell interactions are particularly focused. While the field has made significant progress in modeling and understanding lymphatic and blood vasculature, more models that include coculture of multiple cell types, complex extracellular matrix, and 3D morphologies, particularly for models mimicking disease states, will help further the understanding of the role of blood and lymphatic vasculature in health and disease.

Multiple particle tracking (MPT) using PEGylated nanoparticles reveals heterogeneity within murine lymph nodes and between lymph nodes at different locations.

Lymph nodes (LNs) are highly structured lymphoid organs that compartmentalize B and T cells in the outer cortex and inner paracortex, respectively, and are supported by a collagen-rich reticular network. Tissue material properties like viscoelasticity and diffusion of materials within extracellular spaces and their implications on cellular behavior and therapeutic delivery have been a recent topic of investigation. Here, we developed a nanoparticle system to investigate the rheological properties, including pore size and viscoelasticity, through multiple particle tracking (MPT) combined with LN slice cultures. Dense coatings with polyethylene glycol (PEG) allow nanoparticles to diffuse within the LN extracellular spaces. Despite differences in function in B and T cell zones, we found that extracellular tissue properties and mesh spacing do not change significantly in the cortex and paracortex, though nanoparticle diffusion was slightly reduced in B cell zones. Interestingly, our data suggest that LN pore sizes are smaller than the previously predicted 10-20 µm, with pore sizes ranging from 500 nm-1.5 µm. Our studies also confirm that LNs exhibit viscoelastic properties, with an initial solid-like response followed by stress-relaxation at higher frequencies. Finally, we found that nanoparticle diffusion is dependent on LN location, with nanoparticles in skin draining LNs exhibiting a higher diffusion coefficient and pore size compared to mesenteric LNs. Our data shed new light onto LN interstitial tissue properties, pore size, and define surface chemistry parameters required for nanoparticles to diffuse within LN interstitium. Our studies also provide both a tool for studying LN interstitium and developing design criteria for nanoparticles targeting LN interstitial spaces.

Generating an In Vitro Gut Model with Physiologically Relevant Biophysical Mucus Properties.

Introduction: Gastrointestinal (GI) in vitro models have received lasting attention as an effective tool to model drug and nutrient absorption, study GI diseases, and design new drug delivery vehicles. A complete model of the GI epithelium should at a minimum include the two key functional components of the GI tract: mucus and the underlying epithelium. Mucus plays a key role in protecting and lubricating the GI tract, poses a barrier to orally administered therapies and pathogens, and serves as the microenvironment for the GI microbiome. These functions are reliant on the biophysical material properties of the mucus produced, including viscosity and pore size. Methods: In this study, we generated in vitro models containing Caco-2 enterocyte-like cells and HT29-MTX goblet-like cells and determined the effects of coculture and mucus layer on epithelial permeability and biophysical properties of mucus using multiple particle tracking (MPT). Results: We found that mucus height increased as the amount of HT29-MTX goblet-like cells increased. Additionally, we found that increasing the amount of HT29-MTX goblet-like cells within culture corresponded to an increase in mucus pore size and mucus microviscosity, measured using MPT. When compared to ex vivo mucus samples from mice and pigs, we found that a 90:10 ratio of Caco-2:HT29-MTX coculture displayed similar mucus pore size to porcine jejunum and that the mucus produced from 90:10 and 80:20 ratios of cells shared mechanical properties to porcine jejunum and ileum mucus. Conclusions: GI coculture models are valuable tools in simulating the mucus barrier and can be utilized for a variety of applications including the study of GI diseases, food absorption, or therapeutic development.

Targeting Lymphatics for Nanoparticle Drug Delivery.

The lymphatics transport material from peripheral tissues to lymph nodes, where immune responses are formed, before being transported into systemic circulation. With key roles in transport and fluid homeostasis, lymphatic dysregulation is linked to diseases, including lymphedema. Fluid within the interstitium passes into initial lymphatic vessels where a valve system prevents fluid backflow. Additionally, lymphatic endothelial cells produce key chemokines, such as CCL21, that direct the migration of dendritic cells and lymphocytes. As a result, lymphatics are an attractive delivery route for transporting immune modulatory treatments to lymph nodes where immunotherapies are potentiated in addition to being an alternative method of reaching systemic circulation. In this review, we discuss the physiology of lymphatic vessels and mechanisms used in the transport of materials from peripheral tissues to lymph nodes. We then summarize nanomaterial-based strategies to take advantage of lymphatic transport functions for delivering therapeutics to lymph nodes or systemic circulation. We also describe opportunities for targeting lymphatic endothelial cells to modulate transport and immune functions.

Nanoparticles with dense poly(ethylene glycol) coatings with near neutral charge are maximally transported across lymphatics and to the lymph nodes.

Lymphatic vessels have recently been shown to effectively deliver immune modulatory therapies to the lymph nodes, which enhances their therapeutic efficacy. Prior work has shown that lymphatics transport 10-250 nm nanoparticles from peripheral tissues to the lymph node. However, the surface chemistry required to maximize this transport is poorly understood. Here, we determined the effect of surface poly(ethylene glycol) (PEG) density and size on nanoparticle transport across lymphatic endothelial cells (LECs) by differentially PEGylated model polystyrene nanoparticles. Using an established in-vitro lymphatic transport model, we found PEGylation improved the transport of 100 and 40 nm nanoparticles across LECs 50-fold compared to the unmodified nanoparticles and that transport is maximized when the PEG is in a dense brush conformation or high grafting density (Rf/D = 4.9). We also determined that these trends are not size-dependent. PEGylating 40 nm nanoparticles improved transport efficiency across LECs 68-fold compared to unmodified nanoparticles. We also found that PEGylated 100 nm and 40 nm nanoparticles accumulate in lymph nodes within 4 h after intradermal injection, while unmodified nanoparticles accumulated minimally. Densely PEGylated nanoparticles traveled the furthest distance from the injection site and densely PEGylated 40 nm nanoparticles had maximum accumulation in the lymph nodes compared to low density PEGylated and unmodified nanoparticles. Finally, we determined that nanoparticles are transported via both paracellular and transcellular mechanisms, and that PEG conformation modulates the cellular transport mechanisms. Our results suggest that PEG conformation is crucial to maximize nanoparticle transport across LECs and into lymphatic vessels, making PEG density a crucial design. Optimizing PEG density on nanoparticle formulations has the potential to enhance immunotherapeutic and vaccine outcomes. STATEMENT OF SIGNIFICANCE: Lymphatic vessels are an emerging target for drug delivery both in the context of modulating immune responses and enhancing bioavailability by avoiding first pass hepatic metabolism after oral delivery. Lymphatic vessels are the natural conduits from peripheral tissues to the lymph nodes, where the adaptive immune response is shaped, and eventually to systemic circulation via the thoracic duct. Lymphatics can be targeted via nanoparticles, but the surface chemistry required to maximize nanoparticle transport by lymphatics vessels remains poorly understood. Here, we demonstrate that coating nanoparticles with hydrophilic polyethylene glycol (PEG) effectively enhances their transport across lymphatic endothelial cells in vitro and in vivo and that both paracellular and micropinocytosis mechanisms underly this transport. We found that dense PEG coatings maximize lymphatic transport of nanoparticles, thus providing new material design criteria for lymphatic targeted drug delivery.

Lung lymphatic thrombosis and dysfunction caused by cigarette smoke exposure precedes emphysema in mice.

The lymphatic vasculature is critical for lung function, but defects in lymphatic function in the pathogenesis of lung disease is understudied. In mice, lymphatic dysfunction alone is sufficient to cause lung injury that resembles human emphysema. Whether lymphatic function is disrupted in cigarette smoke (CS)-induced emphysema is unknown. In this study, we investigated the effect of CS on lung lymphatic function. Analysis of human lung tissue revealed significant lung lymphatic thrombosis in patients with emphysema compared to control smokers that increased with disease severity. In a mouse model, CS exposure led to lung lymphatic thrombosis, decreased lymphatic drainage, and impaired leukocyte trafficking that all preceded the development of emphysema. Proteomic analysis demonstrated an increased abundance of coagulation factors in the lymph draining from the lungs of CS-exposed mice compared to control mice. In addition, in vitro assays demonstrated a direct effect of CS on lymphatic endothelial cell integrity. These data show that CS exposure results in lung lymphatic dysfunction and a shift in thoracic lymph towards a prothrombic state. Furthermore, our data suggest that lymphatic dysfunction is due to effects of CS on the lymphatic vasculature that precede emphysema. These studies demonstrate a novel component of CS-induced lung injury that occurs early in the pathogenesis of emphysema.

Targeting the Gut Mucosal Immune System Using Nanomaterials.

The gastrointestinal (GI) tract is one the biggest mucosal surface in the body and one of the primary targets for the delivery of therapeutics, including immunotherapies. GI diseases, including, e.g., inflammatory bowel disease and intestinal infections such as cholera, pose a significant public health burden and are on the rise. Many of these diseases involve inflammatory processes that can be targeted by immune modulatory therapeutics. However, nonspecific targeting of inflammation systemically can lead to significant side effects. This can be avoided by locally targeting therapeutics to the GI tract and its mucosal immune system. In this review, we discuss nanomaterial-based strategies targeting the GI mucosal immune system, including gut-associated lymphoid tissues, tissue resident immune cells, as well as GI lymph nodes, to modulate GI inflammation and disease outcomes, as well as take advantage of some of the primary mechanisms of GI immunity such as oral tolerance.

Microfluidic systems to study tissue barriers to immunotherapy.

Immunotherapies have been heavily explored in the last decade, ranging from new treatments for cancer to allergic diseases. These therapies target the immune system, a complex organ system consisting of tissues with intricate structures and cells with a multitude of functions. To better understand immune functions and develop better therapeutics, many cellular and 2-dimensional (2D) tissue models have been developed. However, research has demonstrated that the 3-dimensional (3D) tissue structure can significantly affect cellular functions, and this is not recapitulated by more traditional 2D models. Microfluidics has been used to design 3D tissue models that allow for intricate arrangements of cells and extracellular spaces, thus allowing for more physiologically relevant in vitro model systems. Here, we summarize the multitude of microfluidic devices designed to study the immune system with the ultimate goal to improve existing and design new immunotherapies. We have included models of the different immune organs, including bone marrow and lymph node (LN), models of immunity in diseases such as cancer and inflammatory bowel disease, and therapeutic models to test or engineer new immune-modulatory treatments. We particularly emphasize research on how microfluidic devices are used to better understand different physiological states and how interactions within the immune microenvironment can influence the efficacy of immunotherapies.

Pro-lymphangiogenic VEGFR-3 signaling modulates memory T cell responses in allergic airway inflammation.

In allergic airway inflammation, VEGFR-3-mediated lymphangiogenesis occurs in humans and mouse models, yet its immunological roles, particularly in adaptive immunity, are poorly understood. Here, we explored how pro-lymphangiogenic signaling affects the allergic response to house dust mite (HDM). In the acute inflammatory phase, the lungs of mice treated with blocking antibodies against VEGFR-3 (mF4-31C1) displayed less inflammation overall, with dramatically reduced innate and T-cell numbers and reduced inflammatory chemokine levels. However, when inflammation was allowed to resolve and memory recall was induced 2 months later, mice treated with mF4-31C1 as well as VEGF-C/-D knockout models showed exacerbated type 2 memory response to HDM, with increased Th2 cells, eosinophils, type 2 chemokines, and pathological inflammation scores. This was associated with lower CCL21 and decreased TRegs in the lymph nodes. Together, our data imply that VEGFR-3 activation in allergic airways helps to both initiate the acute inflammatory response and regulate the adaptive (memory) response, possibly in part by shifting the TReg/Th2 balance. This introduces new immunomodulatory roles for pro-lymphangiogenic VEGFR-3 signaling in allergic airway inflammation and suggests that airway lymphatics may be a novel target for treating allergic responses.

Engineering drug delivery systems to overcome mucosal barriers for immunotherapy and vaccination.

Mucosal surfaces protect our bodies from pathogens and external irritants using a system of biological barriers. Overcoming these barriers is a significant drug delivery challenge, particularly for immunotherapies that aim to modulate the local immune response. Reaching local lymphoid tissues and draining lymph nodes (LNs) requires crossing the mucus mesh, mucosal epithelium, and either targeting M cells covering lymphoid tissues or utilizing lymphatic transport that shuttles molecules and particulates from the periphery to the LN. We first highlight the barrier properties of mucus and mucosal epithelium, and the function of the mucosal immune system. We then dive into existing drug delivery technologies that have been engineered to overcome each of these barriers. We particularly focus on novel strategies for targeting lymphoid tissues, which has been shown to enhance immunotherapies and vaccinations, via directly targeting LNs, lymphatic vessels, and M cells that transport samples of mucosal content to the lymphoid tissues.

Immune Checkpoint Ligand PD-L1 Is Upregulated in Pulmonary Lymphangioleiomyomatosis.

Pulmonary lymphangioleiomyomatosis (LAM) is a slow-progressing metastatic disease that is driven by mutations in the tumor suppressor tuberous sclerosis complex 1/2 (TSC1/2). Rapamycin inhibits LAM cell proliferation and is the only approved treatment, but it cannot cause the regression of existing lesions and can only stabilize the disease. However, in other cancers, immunotherapies such as checkpoint blockade against PD-1 and its ligand PD-L1 have shown promise in causing tumor regression and even curing some patients. Thus, we asked whether PD-L1 has a role in LAM progression. In vitro, PD-L1 expression in murine Tsc2-null cells is unaffected by mTOR inhibition with torin but can be upregulated by IFN-γ. Using immunohistochemistry and single-cell flow cytometry, we found increased PD-L1 expression both in human lung tissue from patients with LAM and in Tsc2-null lesions in a murine model of LAM. In this model, PD-L1 is highly expressed in the lung by antigen-presenting and stromal cells, and activated T cells expressing PD-1 infiltrate the affected lung. In vivo treatment with anti-PD-1 antibody significantly prolongs mouse survival in the model of LAM. Together, these data demonstrate that PD-1/PD-L1-mediated immunosuppression may occur in LAM, and suggest new opportunities for therapeutic targeting that may provide benefits beyond those of rapamycin.