Transfer learning in a biomaterial fibrosis model identifies in vivo senescence heterogeneity and contributions to vascularization and matrix production across species and diverse pathologies

Cellular senescence is a state of permanent growth arrest that plays an important role in wound healing, tissue fibrosis, and tumor suppression. Despite senescent cells' (SnCs) pathological role and therapeutic interest, their phenotype in vivo remains poorly defined. Here, we developed an in vivo-derived senescence signature (SenSig) using a foreign body response-driven fibrosis model in a p16-CreERT2;Ai14 reporter mouse. We identified pericytes and "cartilage-like" fibroblasts as senescent and defined cell type-specific senescence-associated secretory phenotypes (SASPs). Transfer learning and senescence scoring identified these two SnC populations along with endothelial and epithelial SnCs in new and publicly available murine and human data single-cell RNA sequencing (scRNAseq) datasets from diverse pathologies. Signaling analysis uncovered crosstalk between SnCs and myeloid cells via an IL34-CSF1R-TGFβR signaling axis, contributing to tissue balance of vascularization and matrix production. Overall, our study provides a senescence signature and a computational approach that may be broadly applied to identify SnC transcriptional profiles and SASP factors in wound healing, aging, and other pathologies.

Helminth egg derivatives as proregenerative immunotherapies

The immune system is increasingly recognized as an important regulator of tissue repair. We developed a regenerative immunotherapy from the helminth Schistosoma mansoni soluble egg antigen (SEA) to stimulate production of interleukin (IL)-4 and other type 2-associated cytokines without negative infection-related sequelae. The regenerative SEA (rSEA) applied to a murine muscle injury induced accumulation of IL-4-expressing T helper cells, eosinophils, and regulatory T cells and decreased expression of IL-17A in gamma delta (γδ) T cells, resulting in improved repair and decreased fibrosis. Encapsulation and controlled release of rSEA in a hydrogel further enhanced type 2 immunity and larger volumes of tissue repair. The broad regenerative capacity of rSEA was validated in articular joint and corneal injury models. These results introduce a regenerative immunotherapy approach using natural helminth derivatives.

Spatial delivery of immune cues to lymph nodes to define therapeutic outcomes in cancer vaccination

Recently approved cancer immunotherapies - including CAR-T cells and cancer vaccination, - show great promise. However, these technologies are hindered by the complexity and cost of isolating and engineering patient cells ex vivo. Lymph nodes (LNs) are key tissues that integrate immune signals to coordinate adaptive immunity. Directly controlling the signals and local environment in LNs could enable potent and safe immunotherapies without cell isolation, engineering, and reinfusion. Here we employ intra-LN (i.LN.) injection of immune signal-loaded biomaterial depots to directly control cancer vaccine deposition, revealing how the combination and geographic distribution of signals in and between LNs impact anti-tumor response. We show in healthy and diseased mice that relative proximity of antigen and adjuvant in LNs - and to tumors - defines unique local and systemic characteristics of innate and adaptive response. These factors ultimately control survival in mouse models of lymphoma and melanoma. Of note, with appropriate geographic signal distributions, a single i.LN. vaccine treatment confers near-complete survival to tumor challenge and re-challenge 100 days later, without additional treatments. These data inform design criteria for immunotherapies that leverage biomaterials for loco-regional LN therapy to generate responses that are systemic and specific, without systemically exposing patients to potent or immunotoxic drugs.

Computational reconstruction of the signalling networks surrounding implanted biomaterials from single-cell transcriptomics

The understanding of the foreign-body responses to implanted biomaterials would benefit from the reconstruction of intracellular and intercellular signalling networks in the microenvironment surrounding the implant. Here, by leveraging single-cell RNA-sequencing data from 42,156 cells collected from the site of implantation of either polycaprolactone or an extracellular-matrix-derived scaffold in a mouse model of volumetric muscle loss, we report a computational analysis of intercellular signalling networks reconstructed from predictions of transcription-factor activation. We found that intercellular signalling networks can be clustered into modules associated with specific cell subsets, and that biomaterial-specific responses can be characterized by interactions between signalling modules for immune, fibroblast and tissue-specific cells. In a Il17ra^-/- mouse model, we validated that predicted interleukin-17-linked transcriptional targets led to concomitant changes in gene expression. Moreover, we identified cell subsets that had not been implicated in the responses to implanted biomaterials. Single-cell atlases of the cellular responses to implanted biomaterials will facilitate the design of implantable biomaterials and the understanding of the ensuing cellular responses.

Interleukin 17 and senescent cells regulate the foreign body response to synthetic material implants in mice and humans

Medical devices and implants made of synthetic materials can induce an immune-mediated process when implanted in the body called the foreign body response, which results in formation of a fibrous capsule around the implant. To explore the immune and stromal connections underpinning the foreign body response, we analyzed fibrotic capsules surrounding surgically excised human breast implants from 12 individuals. We found increased numbers of interleukin 17 (IL17)-producing γδ⁺ T cells and CD4⁺ T helper 17 (T_H17) cells as well as senescent stromal cells in the fibrotic capsules. Further analysis in a murine model demonstrated an early innate IL17 response to implanted synthetic material (polycaprolactone) particles that was mediated by innate lymphoid cells and γδ⁺ T cells. This was followed by a chronic adaptive CD4⁺ T_H17 cell response that was antigen dependent. Synthetic materials with varying chemical and physical properties implanted either in injured muscle or subcutaneously induced similar IL17 responses in mice. Mice deficient in IL17 signaling established that IL17 was required for the fibrotic response to implanted synthetic materials and the development of p16^INK4a senescent cells. IL6 produced by senescent cells was sufficient for the induction of IL17 expression in T cells. Treatment with a senolytic agent (navitoclax) that killed senescent cells reduced IL17 expression and fibrosis in the mouse implant model. Discovery of a feed-forward loop between the T_H17 immune response and the senescence response to implanted synthetic materials introduces new targets for therapeutic intervention in the foreign body response.

Type 2 immunity induced by bladder extracellular matrix enhances corneal wound healing

The avascular nature of cornea tissue limits its regenerative potential, which may lead to incomplete healing and formation of scars when damaged. Here, we applied micro- and ultrafine porcine urinary bladder matrix (UBM) particulate to promote type 2 immune responses in cornea wounds. Results demonstrated that UBM particulate substantially reduced corneal haze formation as compared to the saline-treated group. Flow cytometry and gene expression analysis showed that UBM particulate suppressed the differentiation of corneal stromal cells into α-smooth muscle actin-positive (αSMA⁺) myofibroblasts. UBM treatments up-regulated interleukin-4 (IL-4) produced primarily by eosinophils in the wounded corneas and CD4⁺ T cells in draining lymph nodes, suggesting a cross-talk between local and peripheral immunity. Gata1^-/- mice lacking eosinophils did not respond to UBM treatment and had impaired wound healing. In summary, stimulating type 2 immune responses in the wounded cornea can promote proregenerative environments that lead to improved wound healing for vision restoration.

Extracting microtentacle dynamics of tumor cells in a non-adherent environment

During metastasis, tumor cells dynamically change their cytoskeleton to traverse through a variety of non-adherent microenvironments, including the vasculature or lymphatics. Due to the challenges of imaging drift in non-adhered tumor cells, the dynamic cytoskeletal phenotypes are poorly understood. We present a new approach to analyze the dynamic cytoskeletal phenotypes of non-adhered cells that support microtentacles (McTNs), which are cell surface projections implicated in metastatic reattachment. Combining a recently-developed cell tethering method with a novel image analysis framework allowed McTN attribute extraction. Full cell outlines, number of McTNs, and distance of McTN tips from the cell body boundary were calculated by integrating a rotating anisotropic filtering method for identifying thin features with retinal segmentation and active contour algorithms. Tethered cells behave like free-floating cells; however tethering reduces cell drift and improves the accuracy of McTN measurements. Tethering cells does not significantly alter McTN number, but rather allows better visualization of existing McTNs. In drug treatment experiments, stabilizing tubulin with paclitaxel significantly increases McTN length, while destabilizing tubulin with colchicine significantly decreases McTN length. Finally, we quantify McTN dynamics by computing the time delay autocorrelations of 2 composite phenotype metrics (cumulative McTN tip distance, cell perimeter:cell body ratio). Our automated analysis demonstrates that treatment with paclitaxel increases total McTN amount and colchicine reduces total McTN amount, while paclitaxel also reduces McTN dynamics. This analysis method enables rapid quantitative measurement of tumor cell drug responses within non-adherent microenvironments, using the small numbers of tumor cells that would be available from patient samples.

Reprogramming the Local Lymph Node Microenvironment Promotes Tolerance that Is Systemic and Antigen Specific

Many experimental therapies for autoimmune diseases, such as multiple sclerosis (MS), aim to bias T cells toward tolerogenic phenotypes without broad suppression. However, the link between local signal integration in lymph nodes (LNs) and the specificity of systemic tolerance is not well understood. We used intra-LN injection of polymer particles to study tolerance as a function of signals in the LN microenvironment. In a mouse MS model, intra-LN introduction of encapsulated myelin self-antigen and a regulatory signal (rapamycin) permanently reversed paralysis after one treatment during peak disease. Therapeutic effects were myelin specific, required antigen encapsulation, and were less potent without rapamycin. This efficacy was accompanied by local LN reorganization, reduced inflammation, systemic expansion of regulatory T cells, and reduced T cell infiltration to the CNS. Our findings suggest that local control over signaling in distinct LNs can promote cell types and functions that drive tolerance that is systemic but antigen specific.

Engineering Immunological Tolerance Using Quantum Dots to Tune the Density of Self-Antigen Display

Treatments for autoimmunity - diseases where the immune system mistakenly attacks self-molecules - are not curative and leave patients immunocompromised. New studies aimed at more specific treatments reveal development of inflammation or tolerance is influenced by the form self-antigens are presented. Using a mouse model of multiple sclerosis (MS), we show for the first time that quantum dots (QDs) can be used to generate immunological tolerance by controlling the density of self-antigen on QDs. These assemblies display dense arrangements of myelin self-peptide associated with disease in MS, are uniform in size (<20 nm), and allow direct visualization in immune tissues. Peptide-QDs rapidly concentrate in draining lymph nodes, co-localizing with macrophages expressing scavenger receptors involved in tolerance. Treatment with peptide-QDs reduces disease incidence 10-fold. Strikingly, the degree of tolerance - and the underlying expansion of regulatory T cells - correlates with the density of myelin molecules presented on QDs. A key discovery is that higher numbers of tolerogenic particles displaying lower levels of self-peptide are more effective for inducing tolerance than fewer particles each displaying higher densities of peptide. QDs conjugated with self-antigens could serve as a new platform to induce tolerance, while visualizing QD therapeutics in tolerogenic tissue domains.

Designing biomaterials with immunomodulatory properties for tissue engineering and regenerative medicine

Recent research in the vaccine and immunotherapy fields has revealed that biomaterials have the ability to activate immune pathways, even in the absence of other immune-stimulating signals. Intriguingly, new studies reveal these responses are influenced by the physicochemical properties of the material. Nearly all of this work has been done in the vaccine and immunotherapy fields, but there is tremendous opportunity to apply this same knowledge to tissue engineering and regenerative medicine. This review discusses recent findings that reveal how material properties-size, shape, chemical functionality-impact immune response, and links these changes to emerging opportunities in tissue engineering and regenerative medicine. We begin by discussing what has been learned from studies conducted in the contexts of vaccines and immunotherapies. Next, research is highlighted that elucidates the properties of materials that polarize innate immune cells, including macrophages and dendritic cells, toward either inflammatory or wound healing phenotypes. We also discuss recent studies demonstrating that scaffolds used in tissue engineering applications can influence cells of the adaptive immune system-B and T cell lymphocytes-to promote regenerative tissue microenvironments. Through greater study of the intrinsic immunogenic features of implantable materials and scaffolds, new translational opportunities will arise to better control tissue engineering and regenerative medicine applications.

Probing changes to local and systemic immunity following intranodal injection

Polymeric vaccine carriers protect and control delivery of encapsulated immune cues to target organs such as lymph nodes (LNs), tissues that coordinate adaptive immunity. Our lab recently established a non-surgical intranodal injection (i.LN.) technique allowing for control of the dose and combination of signals that reach inguinal LNs of mice. We discovered that after treating both inguinal LNs with a model antigen (Ovalbumin) and polymeric particles encapsulating a TLR3 agonist PolyIC (PolyIC MP), strikingly large increases to the percentage and number of activated dendritic cells and macrophages led to increases in B and T cells after 7 days. This treatment generated antigen-specific CD8+ T cells within the treated LNs (~3%) and blood (~13%) leading to memory phenotypes 28 days after vaccination. We used this system as a tool to study how local vaccine exposure and persistence impact systemic immunity by priming of one or more immune sites. Matching vaccine doses were deposited via i.LN. injection into one LN, two LNs, or with the antigen and adjuvant split into separate LNs. LNs receiving PolyIC MPs increased dendritic cell activation. Within the treated LNs, the highest percentage of antigen-specific CD8+ T cells occurred after treating one LN while treating two LNs resulted in half as many antigen-specific cells per LN. Interesting, while all treatments increased blood antigen-specific responses, the response to treating two LNs was double that of one LN treatment and six-fold higher than splitting the signals. These results indicate that the localization and kinetics of immune signals influences the magnitude of systemic immunity and could inform the design of future vaccine strategies to mount robust, antigen-specific responses.

Impact of molecular weight on the intrinsic immunogenic activity of poly(beta amino esters)

Polymeric carriers are ubiquitously studied in vaccine and drug delivery to control the encapsulation, kinetics, and targeting of cargo. Recent research reveals many polymers can cause immunostimulatory and inflammatory responses, even in the absence of other immune signals. However, the extent to which this intrinsic immunogenicity evolves during degradation is understudied. Here we synthesized a small library of poly(beta amino esters) (PBAEs) that exhibit different starting molecular weights (MWs), but with similar and rapid degradation rates. Primary dendritic cells (DCs) treated with free PBAEs, either intact or degraded to form low MW fragments, were not activated. In contrast particles formed from PBAEs at different extents of degradation caused differential expression of classical DC activation markers (for example, CD40, CD80, CD86, MHCII), as well as antigen presentation. During degradation, activation levels changed with changing physicochemical properties (for example, MW, concentration, size, charge). Of note, irrespective of starting MW, immunogenicity peaked when the MW of degrading PBAEs decreased to a range of ∼1500-3000 Da. These findings could help inform design of future carriers that exploit the dynamic interactions with the immune system as materials degrade, leading to carriers that deliver cargo but also help direct the immune responses to vaccine or immunotherapy cargo. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1219-1229, 2017.

Lipid tethering of breast tumor cells enables real-time imaging of free-floating cell dynamics and drug response

Free-floating tumor cells located in the blood of cancer patients, known as circulating tumor cells (CTCs), have become key targets for studying metastasis. However, effective strategies to study the free-floating behavior of tumor cells in vitro have been a major barrier limiting the understanding of the functional properties of CTCs. Upon extracellular-matrix (ECM) detachment, breast tumor cells form tubulin-based protrusions known as microtentacles (McTNs) that play a role in the aggregation and re-attachment of tumor cells to increase their metastatic efficiency. In this study, we have designed a strategy to spatially immobilize ECM-detached tumor cells while maintaining their free-floating character. We use polyelectrolyte multilayers deposited on microfluidic substrates to prevent tumor cell adhesion and the addition of lipid moieties to tether tumor cells to these surfaces through interactions with the cell membranes. This coating remains optically clear, allowing capture of high-resolution images and videos of McTNs on viable free-floating cells. In addition, we show that tethering allows for the real-time analysis of McTN dynamics on individual tumor cells and in response to tubulin-targeting drugs. The ability to image detached tumor cells can vastly enhance our understanding of CTCs under conditions that better recapitulate the microenvironments they encounter during metastasis.

Impact of dose, route, and composition on the immunogenicity of immune polyelectrolyte multilayers delivered on gold templates

Biomaterial vaccines offer new capabilities that can be exploited for both infectious disease and cancer. We recently developed a novel vaccine platform based on self‐assembly of immune signals into immune polyelectrolyte multilayers (iPEMs). These iPEM vaccines are electrostatically assembled from peptide antigens and nucleic acid‐based toll‐like receptor agonists (TLRas) that serve as molecular adjuvants. Gold nanoparticles (AuNPs) coated with iPEMs stimulate effector cytokine secretion in vitro and expand antigen‐specific T cells in mice. Here we investigated how the dose, injection route, and choice of molecular adjuvant impacts the ability of iPEMs to generate T cell immunity and anti‐tumor response in mice. Three injection routes—intradermal, subcutaneous, and intramuscular—and three iPEM dosing levels were employed. Intradermal injection induced the most potent antigen‐specific T cell responses and, for all routes, the level of response was dose‐dependent. We further discovered that these vaccines generate durable memory, indicated by potent, antigen‐specific CD8⁺ T cell recall responses in mice challenged with vaccine 49 days after a prime‐boost immunization regimen. In a common exogenous antigen melanoma model, iPEM vaccines slowed or stopped tumor growth more effectively than equivalent ad‐mixed formulations. Further, iPEMs containing CpG—a TLR9a—were more potent compared with iPEMs containing polyIC, a TLR3a. These findings demonstrate the ability of iPEMs to enhance response to several different classes of vaccine cargos, supporting iPEMs as a simple vaccine platform that mimics attractive features of other nanoparticles using immune signals that can be self‐assembled or coated on substrates. Biotechnol. Bioeng. 2017;114: 423–431. © 2016 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

Polyplexes assembled from self-peptides and regulatory nucleic acids blunt toll-like receptor signaling to combat autoimmunity

Autoimmune diseases occur when the immune system incorrectly recognizes self-molecules as foreign; in the case of multiple sclerosis (MS), myelin is attacked. Intriguingly, new studies reveal toll-like receptors (TLRs), pathways usually involved in generating immune responses against pathogens, play a significant role in driving autoimmune disease in both humans and animal models. We reasoned polyplexes formed from myelin self-antigen and regulatory TLR antagonists might limit TLR signaling during differentiation of myelin-specific T cells, inducing tolerance by biasing T cells away from inflammatory phenotypes. Complexes were formed by modifying myelin peptide with cationic amino acids to create peptides able to condense the anionic nucleic-acid based TLR antagonist. These immunological polyplexes eliminate synthetic polymers commonly used to condense polyplexes and do not rely on gene expression; however, the complexes mimic key features of traditional polyplexes such as tunable loading and co-delivery. Using these materials and classic polyplex analysis techniques, we demonstrate condensation of both immune signals, protection from enzymatic degradation, and tunable physicochemical properties. We show polyplexes reduce TLR signaling, and in primary dendritic cell and T cell co-culture, reduce myelin-driven inflammation. During mouse models of MS, these tolerogenic polyplexes improve the progression, severity, and incidence of disease.

Design of Polyelectrolyte Multilayers to Promote Immunological Tolerance

Recent studies demonstrate that excess signaling through inflammatory pathways (e.g., toll-like receptors, TLRs) contributes to the pathogenesis of human autoimmune diseases, including lupus, diabetes, and multiple sclerosis (MS). We hypothesized that codelivery of a regulatory ligand of TLR9, GpG oligonucleotide, along with myelin-the "self" molecule attacked in MS-might restrain the pro-inflammatory signaling typically present during myelin presentation, redirecting T cell differentiation away from inflammatory populations and toward tolerogenic phenotypes such as regulatory T cells. Here we show that myelin peptide and GpG can be used as modular building blocks for co-assembly into immune polyelectrolyte multilayers (iPEMs). These nanostructured capsules mimic attractive features of biomaterials, including tunable cargo loading and codelivery, but eliminate all carriers and synthetic polymers, components that often exhibit intrinsic inflammatory properties that could exacerbate autoimmune disease. In vitro, iPEMs assembled from myelin and GpG oligonucleotide, but not myelin and a control oligonucleotide, restrain TLR9 signaling, reduce dendritic cell activation, and polarize myelin-specific T cells toward tolerogenic phenotype and function. In mice, iPEMs blunt myelin-triggered inflammatory responses, expand regulatory T cells, and eliminate disease in a common model of MS. Finally, in samples from human MS patients, iPEMs bias myelin-triggered immune cell function toward tolerance. This work represents a unique opportunity to use PEMs to regulate immune function and promote tolerance, supporting iPEMs as a carrier-free platform to alter TLR function to reduce inflammation and combat autoimmunity.

Assembly and Immunological Processing of Polyelectrolyte Multilayers Composed of Antigens and Adjuvants

While biomaterials provide a platform to control the delivery of vaccines, the recently discovered intrinsic inflammatory characteristics of many polymeric carriers can also complicate rational design because the carrier itself can alter the response to other vaccine components. To address this challenge, we recently developed immune-polyelectrolyte multilayer (iPEMs) capsules electrostatically assembled entirely from peptide antigen and molecular adjuvants. Here, we use iPEMs built from SIINFEKL model antigen and polyIC, a stimulatory toll-like receptor agonist, to investigate the impact of pH on iPEM assembly, the processing and interactions of each iPEM component with primary immune cells, and the role of these interactions during antigen-specific T cell responses in coculture and mice. We discovered that iPEM assembly is pH dependent with respect to both the antigen and adjuvant component. Controlling the pH also allows tuning of the relative loading of SIINFEKL and polyIC in iPEM capsules. During in vitro studies with primary dendritic cells (DCs), iPEM capsules ensure that greater than 95% of cells containing at least one signal (i.e., antigen, adjuvant) also contained the other signal. This codelivery leads to DC maturation and SIINFEKL presentation via the MHC-I antigen presentation pathway, resulting in antigen-specific T cell proliferation and pro-inflammatory cytokine secretion. In mice, iPEM capsules potently expand antigen-specific T cells compared with equivalent admixed formulations. Of note, these enhancements become more pronounced with successive booster injections, suggesting that iPEMs functionally improve memory recall response. Together our results reveal some of the features that can be tuned to modulate the properties of iPEM capsules, and how these modular vaccine structures can be used to enhance interactions with immune cells in vitro and in mice.

Intrinsic immunogenicity of rapidly-degradable polymers evolves during degradation

Recent studies reveal many biomaterial vaccine carriers are able to activate immunostimulatory pathways, even in the absence of other immune signals. How the changing properties of polymers during biodegradation impact this intrinsic immunogenicity is not well studied, yet this information could contribute to rational design of degradable vaccine carriers that help direct immune response. We use degradable poly(beta-amino esters) (PBAEs) to explore intrinsic immunogenicity as a function of the degree of polymer degradation and polymer form (e.g., soluble, particles). PBAE particles condensed by electrostatic interaction to mimic a common vaccine approach strongly activate dendritic cells, drive antigen presentation, and enhance T cell proliferation in the presence of antigen. Polymer molecular weight strongly influences these effects, with maximum stimulation at short degradation times--corresponding to high molecular weight--and waning levels as degradation continues. In contrast, free polymer is immunologically inert. In mice, PBAE particles increase the numbers and activation state of cells in lymph nodes. Mechanistic studies reveal that this evolving immunogenicity occurs as the physicochemical properties and concentration of particles change during polymer degradation. This work confirms the immunological profile of degradable, synthetic polymers can evolve over time and creates an opportunity to leverage this feature in new vaccines.

STATEMENT OF SIGNIFICANCE

Degradable polymers are increasingly important in vaccination, but how the inherent immunogenicity of polymers changes during degradation is poorly understood. Using common rapidly-degradable vaccine carriers, we show that the activation of immune cells--even in the absence of other adjuvants--depends on polymer form (e.g., free, particulate) and the extent of degradation. These changing characteristics alter the physicochemical properties (e.g., charge, size, molecular weight) of polymer particles, driving changes in immunogenicity. Our results are important as many common biomaterials (e.g., PLGA) are now known to exhibit immune activity that alters how vaccines are processed. Thus, the results of this study could contribute to more rational design of biomaterial carriers that also actively direct the properties of responses generated by vaccines.

Modular Vaccine Design Using Carrier-Free Capsules Assembled from Polyionic Immune Signals

New vaccine adjuvants that direct immune cells toward specific fates could support more potent and selective options for diseases spanning infection to cancer. However, the empirical nature of vaccines and the complexity of many formulations has hindered design of well-defined and easily characterized vaccines. We hypothesized that nanostructured capsules assembled entirely from polyionic immune signals might support a platform for simple, modular vaccines. These immune-polyelectrolyte (iPEM) capsules offer a high signal density, selectively expand T cells in mice, and drive functional responses during tumor challenge. iPEMs incorporating clinically relevant antigens could improve vaccine definition and support more programmable control over immunity.

Harnessing biomaterials to engineer the lymph node microenvironment for immunity or tolerance

Nanoparticles, microparticles, and other biomaterials are advantageous in vaccination because these materials provide opportunities to modulate specific characteristics of immune responses. This idea of “tuning” immune responses has recently been used to combat infectious diseases and cancer, and to induce tolerance during organ transplants or autoimmune disease. Lymph nodes and other secondary lymphoid organs such as the spleen play crucial roles in determining if and how these responses develop following vaccination or immunotherapy. Thus, by manipulating the local microenvironments within these immunological command centers, the nature of systemic immune response can be controlled. This review provides recent examples that harness the interactions between biomaterials and lymph nodes or other secondary lymphoid organs to generate immunity or promote tolerance. These strategies draw on mechanical properties, surface chemistry, stability, and targeting to alter the interactions of cells, signals, and vaccine components in lymph nodes. While there are still many unanswered questions surrounding how best to design biomaterial-based vaccines to promote specific structures or functions in lymph nodes, features such as controlled release and targeting will help pave the way for the next generation of vaccines and immunotherapies that generate immune responses tuned for specific applications.

Intra-lymph node injection of biodegradable polymer particles

Generation of adaptive immune response relies on efficient drainage or trafficking of antigen to lymph nodes for processing and presentation of these foreign molecules to T and B lymphocytes. Lymph nodes have thus become critical targets for new vaccines and immunotherapies. A recent strategy for targeting these tissues is direct lymph node injection of soluble vaccine components, and clinical trials involving this technique have been promising. Several biomaterial strategies have also been investigated to improve lymph node targeting, for example, tuning particle size for optimal drainage of biomaterial vaccine particles. In this paper we present a new method that combines direct lymph node injection with biodegradable polymer particles that can be laden with antigen, adjuvant, or other vaccine components. In this method polymeric microparticles or nanoparticles are synthesized by a modified double emulsion protocol incorporating lipid stabilizers. Particle properties (e.g. size, cargo loading) are confirmed by laser diffraction and fluorescent microscopy, respectively. Mouse lymph nodes are then identified by peripheral injection of a nontoxic tracer dye that allows visualization of the target injection site and subsequent deposition of polymer particles in lymph nodes. This technique allows direct control over the doses and combinations of biomaterials and vaccine components delivered to lymph nodes and could be harnessed in the development of new biomaterial-based vaccines.