Cytokine-Functionalized Synthetic Dendritic Cells for T Cell Targeted Immunotherapies

Interleukin-12 decorated nanosized semiflexible Immunofilaments enable directed targeting and augmented IFNγ responses of natural killer cells

Immunotherapies are a powerful strategy to treat cancer by modulating the immune system to raise an anti-tumor immune response. A prime example of immunotherapies are cytokines - small immunomodulatory molecules that are widely used to stimulate immune cells. Undirected administration of cytokines, however, can cause severe side effects, preventing the use of potent cytokines, such as Interleukin (IL)-12, which induces IFNγ responses by cytotoxic effector lymphocytes, including NK cells. Biomaterials, like nanoparticles, can encapsulate IL-12 and accumulate at the tumor site to alleviate side effects. Yet, the released IL-12 might not be directly targeted to extracellular IL-12 receptors on the specific effector cells, thereby potentially compromising the cytokine's therapeutic efficacy. Here, we develop a polymer-based platform to target NK cells, which we call immunofilaments. Immunofilaments are nanosized linear polymers that present an anti-CD16 antibody and IL-12 effectively to NK cells and lead to synergistic NK cell activation as highlighted by an increase in TNFα and IFNγ production and upregulation of multiple activation markers, including CD25, CD69, and degranulation marker CD107a. NK cell proliferation is enhanced in the presence of both anti-CD16 antibody and IL-12 compared to giving IL-12 separately. Finally, we demonstrate that the IF platform is suitable for in vivo applications, as immunofilaments readily activate human NK cells upon administration to mice. STATEMENT OF SIGNIFICANCE: IL-12 is a potent cytokine that stimulates IFNγ responses in NK cells, which supports an anti-tumor immune response. Due to its high potency, the delivery of IL-12 needs to be highly controlled to prevent severe adverse side effects, which can be achieved by using biomaterials. This study shows that nanosized polymers termed Immunofilaments can be used to immobilize IL-12 and effectively target and activate NK cells by co-conjugation of anti-CD16 antibodies. This work is a prime example of careful engineering of innovative biomaterials to improve immunotherapy.

Biomaterial-Based Sustained-Release Drug Formulations for Localized Cancer Immunotherapy

Cancer immunotherapy has revolutionized clinical cancer treatments by taking advantage of the immune system to selectively and effectively target and kill cancer cells. However, clinical cancer immunotherapy treatments often have limited efficacy and/or present severe adverse effects associated primarily with their systemic administration. Localized immunotherapy has emerged to overcome these limitations by directly targeting accessible tumors via local administration, reducing potential systemic drug distribution that hampers drug efficacy and safety. Sustained-release formulations can prolong drug activity at target sites, which maximizes the benefits of localized immunotherapy to increase the therapeutic window using smaller dosages than those used for systemic injection, avoiding complications of frequent dosing. The performance of sustained-release formulations for localized cancer immunotherapy has been validated preclinically using various implantable and injectable scaffold platforms. This review introduces the sustained-release formulations developed for localized cancer immunotherapy and highlights their biomaterial-based platforms for representative classes, including inorganic scaffolds, natural hydrogels, synthetic hydrogels, and microneedle patches. The design rationale and other considerations are summarized for further development of biomaterials for the construction of optimal sustained-release formulations.

Immunofilaments Are Well Tolerated after Local or Systemic Administration in Mice

The invention of nanosized biomaterials has paved the way for novel therapeutics that can manipulate cells on a nanoscale. Nanosized immunofilaments (IFs) are synthetic filamentous polymers consisting out of polyisocyanopeptides, which have been recently established as a powerful platform to activate specific immune cells in vivo such that they raise an antitumor immune response. However, toxicological effects or immunogenicity toward the IFs have not yet been investigated. In this study, we evaluated potential toxic or immunogenic effects in C57BL/6 mice upon intravenous or subcutaneous injection of nonfunctionalized IFs or immunostimulatory IFs over 30 days. We here present a detailed analysis of the gross pathology, hematological parameters, blood biochemistry, histology, and antibody-response against the IF backbone. Our results demonstrate that IFs do not induce severe acute or chronic toxicity in mice. After 30 days, we only found elevated IgG-titers in intravenously injected but not subcutaneously injected mice. In summary, we demonstrate that IFs can be administered into a living organism without adverse side effects, thereby establishing the safety of IFs as a therapeutic intervention.

Particle-Based Artificial Antigen-Presenting Cell Systems for T Cell Activation in Adoptive T Cell Therapy

T cell-based adoptive cell therapy (ACT) has emerged as a promising treatment for various diseases, particularly cancers. Unlike other immunotherapy modalities, ACT involves directly transferring engineered T cells into patients to eradicate diseased cells; hence, it necessitates methods for effectively activating and expanding T cells in vitro. Artificial antigen-presenting cells (aAPCs) have been widely developed based on biomaterials, particularly micro- and nanoparticles, and functionalized with T cell stimulatory antibodies to closely mimic the natural T cell-APC interactions. Due to their vast clinical utility, aAPCs have been employed as an off-the-shelf technology for T cell activation in FDA-approved ACTs, and the development of aAPCs is constantly advancing with the emergence of aAPCs with more sophisticated designs and additional functionalities. Here, we review the recent advancements in particle-based aAPCs for T cell activation in ACTs. Following a brief introduction, we first describe the manufacturing processes of ACT products. Next, the design and synthetic strategies for micro- and nanoparticle-based aAPCs are discussed separately to emphasize their features, advantages, and limitations. Then, the impact of design parameters of aAPCs, such as size, shape, ligand density/mobility, and stiffness, on their functionality and biomedical performance is explored to provide deeper insights into the design concepts and principles for more efficient and safer aAPCs. The review concludes by discussing current challenges and proposing future perspectives for the development of more advanced aAPCs.

Growth Factor Immobilization to Synthetic Hydrogels: Bioactive bFGF-Functionalized Polyisocyanide Hydrogels

With its involvement in cell proliferation, migration and differentiation basic fibroblast growth factor (bFGF) has great potential for tissue engineering purposes. So far, however, clinical translation of soluble bFGF-based therapies is unsuccessful, because the required effective doses are often supraphysiological, which may cause adverse effects. An effective solution is growth factor immobilization, whereby bFGF retains its bioactivity at increased efficacy. Studied carriers include films, solid scaffolds, and particles, as well as natural and synthetic hydrogels. However, these synthetic hydrogels poorly resemble the characteristics of the native extracellular matrix (ECM). In this work, bFGF is covalently conjugated to the synthetic, but highly biocompatible, polyisocyanide-based hydrogel (PIC-bFGF), which closely mimics the architecture and mechanical properties of the ECM. The growth factor conjugation protocol is straightforward and readily extrapolated to other growth factors or proteins. The PIC-bFGF hydrogel shows a prolonged bioactivity up to 4 weeks although no clear effects on the ECM metabolism are observed. Beyond the future potential of the PIC-bFGF hydrogel toward various tissue engineering applications, this work underlines that simple biological conjugation procedures are a powerful strategy to induce additional bioactivity in 3D synthetic cell culture matrices.

Artificial Antigen-Presenting Cell Topology Dictates T Cell Activation

Nanosized artificial antigen-presenting cells (aAPCs), synthetic immune cell mimics that aim to activate T cells ex or in vivo, offer an effective alternative to cellular immunotherapies. However, comprehensive studies that delineate the effect of nano-aAPC topology, including nanoparticle morphology and ligand density, are lacking. Here, we systematically studied the topological effects of polymersome-based aAPCs on T cell activation. We employed an aAPC library created from biodegradable poly(ethylene glycol)-block-poly(d,l-lactide) (PEG-PDLLA) polymersomes with spherical or tubular shape and variable sizes, which were functionalized with αCD3 and αCD28 antibodies at controlled densities. Our results indicate that high ligand density leads to enhancement in T cell activation, which can be further augmented by employing polymersomes with larger size. At low ligand density, the effect of both polymersome shape and size was more pronounced, showing that large elongated polymersomes better activate T cells compared to their spherical or smaller counterparts. This study demonstrates the capacity of polymersomes as aAPCs and highlights the role of topology for their rational design.

Cell-matrix reciprocity in 3D culture models with nonlinear elasticity

Three-dimensional (3D) matrix models using hydrogels are powerful tools to understand and predict cell behavior. The interactions between the cell and its matrix, however is highly complex: the matrix has a profound effect on basic cell functions but simultaneously, cells are able to actively manipulate the matrix properties. This (mechano)reciprocity between cells and the extracellular matrix (ECM) is central in regulating tissue functions and it is fundamentally important to broadly consider the biomechanical properties of the in vivo ECM when designing in vitro matrix models. This manuscript discusses two commonly used biopolymer networks, i.e. collagen and fibrin gels, and one synthetic polymer network, polyisocyanide gel (PIC), which all possess the characteristic nonlinear mechanics in the biological stress regime. We start from the structure of the materials, then address the uses, advantages, and limitations of each material, to provide a guideline for tissue engineers and biophysicists in utilizing current materials and also designing new materials for 3D cell culture purposes.

Current knowledge of immunomodulation strategies for chronic skin wound repair

In orchestrating the wound healing process, the immune system plays a critical role. Hence, controlling the immune system to repair skin defects is an attractive approach. The highly complex immune system includes the coordinated actions of several immune cells, which can produce various inflammatory and antiinflammatory cytokines and affect the healing of skin wounds. This process can be optimized using biomaterials, bioactive molecules, and cell delivery. The present review discusses various immunomodulation strategies for supporting the healing of chronic wounds. In this regard, following the evolution of the immune system and its role in the wound healing mechanism, the interaction between the extracellular mechanism and immune cells for acceleration wound healing will be firstly investigated. Consequently, the immune-based chronic wounds will be briefly examined and the mechanism of progression, and conventional methods of their treatment are evaluated. In the following, various biomaterials-based immunomodulation strategies are introduced to stimulate and control the immune system to treat and regenerate skin defects. Other effective methods of controlling the immune system in wound healing which is the release of bioactive agents (such as antiinflammatory, antigens, and immunomodulators) and stem cell therapy at the site of injury are reviewed.

Semiflexible Immunobrushes Induce Enhanced T Cell Activation and Expansion

A variety of bioactive materials developed to expand T cells for adoptive transfer into cancer patients are currently evaluated in the clinic. In most cases, T cell activating biomolecules are attached to rigid surfaces or matrices and form a static interface between materials and the signaling receptors on the T cells. We hypothesized that a T cell activating polymer brush interface might better mimic the cell surface of a natural antigen-presenting cell, facilitating receptor movement and concomitant advantageous mechanical forces to provide enhanced T cell activating capacities. Here, as a proof of concept, we synthesized semiflexible polyisocyanopeptide (PIC) polymer-based immunobrushes equipped with T cell activating agonistic anti-CD3 (αCD3) and αCD28 antibodies placed on magnetic microbeads. We demonstrated enhanced efficiency of ex vivo expansion of activated primary human T cells even at very low numbers of stimulating antibodies compared to rigid beads. Importantly, the immunobrush architecture appeared crucial for this improved T cell activating capacity. Immunobrushes outperform current benchmarks by producing higher numbers of T cells exhibiting a combination of beneficial phenotypic characteristics, such as reduced exhaustion marker expression, high cytokine production, and robust expression of cytotoxic hallmarks. This study indicates that semiflexible immunobrushes have great potential in making T cell-based immunotherapies more effective.

Chemically Engineered Immune Cell-Derived Microrobots and Biomimetic Nanoparticles: Emerging Biodiagnostic and Therapeutic Tools

Over the past decades, considerable attention has been dedicated to the exploitation of diverse immune cells as therapeutic and/or diagnostic cell-based microrobots for hard-to-treat disorders. To date, a plethora of therapeutics based on alive immune cells, surface-engineered immune cells, immunocytes' cell membranes, leukocyte-derived extracellular vesicles or exosomes, and artificial immune cells have been investigated and a few have been introduced into the market. These systems take advantage of the unique characteristics and functions of immune cells, including their presence in circulating blood and various tissues, complex crosstalk properties, high affinity to different self and foreign markers, unique potential of their on-demand navigation and activity, production of a variety of chemokines/cytokines, as well as being cytotoxic in particular conditions. Here, the latest progress in the development of engineered therapeutics and diagnostics inspired by immune cells to ameliorate cancer, inflammatory conditions, autoimmune diseases, neurodegenerative disorders, cardiovascular complications, and infectious diseases is reviewed, and finally, the perspective for their clinical application is delineated.

Multivalent Sgc8c-aptamer decorated polymer scaffolds for leukemia targeting

T-cell acute lymphoblastic leukemia causes a disproportional amount of immature white blood cells in the patients' bone marrow. The significant undesired side effects associated with traditional chemotherapy treatment prompted us to study a more effective treatment strategy. We decorated polyisocyanopeptide scaffolds with the selective leukemia cell binding aptamer sgc8c and found that the polymers inhibit proliferation by G0/G1-phase arrest, serving as an opportunity for future therapeutic strategies.

Semiflexible polymer scaffolds: an overview of conjugation strategies

Semiflexible polymers are excellent scaffolds for the presentation of a wide variety of (bio)molecules. This manuscript reviews advantages and challenges of the most common conjugation strategies for the major classes of semiflexible polymers.

Materials for Immunotherapy

Breakthroughs in materials engineering have accelerated the progress of immunotherapy in preclinical studies. The interplay of chemistry and materials has resulted in improved loading, targeting, and release of immunomodulatory agents. An overview of the materials that are used to enable or improve the success of immunotherapies in preclinical studies is presented, from immunosuppressive to proinflammatory strategies, with particular emphasis on technologies poised for clinical translation. The materials are organized based on their characteristic length scale, whereby the enabling feature of each technology is organized by the structure of that material. For example, the mechanisms by which i) nanoscale materials can improve targeting and infiltration of immunomodulatory payloads into tissues and cells, ii) microscale materials can facilitate cell-mediated transport and serve as artificial antigen-presenting cells, and iii) macroscale materials can form the basis of artificial microenvironments to promote cell infiltration and reprogramming are discussed. As a step toward establishing a set of design rules for future immunotherapies, materials that intrinsically activate or suppress the immune system are reviewed. Finally, a brief outlook on the trajectory of these systems and how they may be improved to address unsolved challenges in cancer, infectious diseases, and autoimmunity is presented.

Augmentation of T-Cell Activation by Oscillatory Forces and Engineered Antigen-Presenting Cells

Activation of T cells by antigen presenting cells (APCs) initiates their proliferation, cytokine production, and killing of infected or cancerous cells. We and others have shown that T-cell receptors require mechanical forces for triggering, and these forces arise during the interaction of T cells with APCs. Efficient activation of T cells in vitro is necessary for clinical applications. In this paper, we studied the impact of combining mechanical, oscillatory movements provided by an orbital shaker with soft, biocompatible, artificial APCs (aAPCs) of various sizes and amounts of antigen. We showed that these aAPCs allow for testing the strength of signal delivered to T cells, and enabled us to confirm that that absolute amounts of antigen engaged by the T cell are more important for activation than the density of antigen. We also found that when our aAPCs interact with T cells in the context of an oscillatory mechanoenvironment, they roughly double antigenic signal strength, compared to conventional, static culture. Combining these effects, our aAPCs significantly outperformed the commonly used Dynabeads. We finally demonstrated that tuning the signal strength down to a submaximal "sweet spot" allows for robust expansion of induced regulatory T cells. In conclusion, augmenting engineered aAPCs with mechanical forces offers a novel approach for tuning of T-cell activation and differentiation.

Synthetic Semiflexible and Bioactive Brushes

Polymer brushes are extensively used for the preparation of bioactive surfaces. They form a platform to attach functional (bio)molecules and control the physicochemical properties of the surface. These brushes are nearly exclusively prepared from flexible polymers, even though much stiffer brushes from semiflexible polymers are frequently found in nature, which exert bioactive functions that are out of reach for flexible brushes. Synthetic semiflexible polymers, however, are very rare. Here, we use polyisocyanopeptides (PICs) to prepare high-density semiflexible brushes on different substrate geometries. For bioconjugation, we developed routes with two orthogonal click reactions, based on the strain-promoted azide-alkyne cycloaddition reaction and the (photoactivated) tetrazole-ene cycloaddition reaction. We found that for high brush densities, multiple bonds between the polymer and the substrate are necessary, which was achieved in a block copolymer strategy. Whether the desired biomolecules are conjugated to the PIC polymer before or after brush formation depends on the dimensions and required densities of the biomolecules and the curvature of the substrate. In either case, we provide mild, aqueous, and highly modular reaction strategies, which make PICs a versatile addition to the toolbox for generating semiflexible bioactive polymer brush surfaces.

Engineering Biomaterials to Direct Innate Immunity

Small alterations during early stages of innate immune response can drive large changes in how adaptive immune cells develop and function during protective immunity or disease. Controlling these events creates exciting potential in development of immune engineered vaccines and therapeutics. This progress report discusses recent biomaterial technologies exploiting innate immunity to dissect immune function and to design new vaccines and immunotherapies for infectious diseases, cancer, and autoimmunity. Across these examples, an important idea is the possibility to co-opt innate immune mechanisms to enhance immunity during infection and cancer. During inflammatory or autoimmune disease, some of these same innate immune mechanisms can be manipulated in different ways to control excess inflammation by promotion of immunological tolerance.

Biomaterial-Based Activation and Expansion of Tumor-Specific T Cells

Traditional tumor vaccination approaches mostly focus on activating dendritic cells (DCs) by providing them with a source of tumor antigens and/or adjuvants, which in turn activate tumor-reactive T cells. Novel biomaterial-based cancer immunotherapeutic strategies focus on directly activating and stimulating T cells through molecular cues presented on synthetic constructs with the aim of improving T cell survival, more precisely steer T cell activation and direct T cell differentiation. Synthetic artificial antigen presenting cells (aAPCs) decorated with T cell-activating ligands are being developed to induce robust tumor-specific T cell responses, essentially bypassing DCs. In this perspective, we approach these promising new technologies from an immunological angle, first by identifying the CD4⁺ and CD8⁺ T cell subtypes that are imperative for robust anti-cancer immunity and subsequently discussing the molecular cues needed to induce these cells types. We will elaborate on how biomaterials can be applied to stimulate T cells in vitro and in vivo to improve their survival, activation and function. Scaffold-based methods can also be used as delivery vehicles for adoptive transfer of T cells, including tumor-infiltrating lymphocytes (TILs) and chimeric antigen receptor expressing (CAR) T cells, while simultaneously stimulating these cells. Finally, we provide suggestions on how these insights could advance the field of biomaterial-based activation and expansion of tumor-specific T cells in the future.