Insights in the host response towards biomaterial-based scaffolds for cancer therapy.

Immunotherapeutic strategies have shown promising results in the treatment of cancer. However, not all patients respond, and treatments can have severe side-effects. Adoptive cell therapy (ACT) has shown remarkable therapeutic efficacy across different leukaemia and lymphoma types. But the treatment of solid tumours remains a challenge due to limited persistence and tumour infiltration. We believe that biomaterial-based scaffolds are promising new tools and may address several of the challenges associated with cancer vaccination and ACT. In particular, biomaterial-based scaffold implants allow for controlled delivery of activating signals and/or functional T cells at specific sites. One of the main challenges for their application forms the host response against these scaffolds, which includes unwanted myeloid cell infiltration and the formation of a fibrotic capsule around the scaffold, thereby limiting cell traffic. In this review we provide an overview of several of the biomaterial-based scaffolds designed for cancer therapy to date. We will discuss the host responses observed and we will highlight design parameters that influence this response and their potential impact on therapeutic outcome.

Direct In Vivo Activation of T Cells with Nanosized Immunofilaments Inhibits Tumor Growth and Metastasis.

Adoptive T cell therapy has successfully been implemented for the treatment of cancer. Nevertheless, ex vivo expansion of T cells by artificial antigen-presenting cells (aAPCs) remains cumbersome and can compromise T cell functionality, thereby limiting their therapeutic potential. We propose a radically different approach aimed at direct expansion of T cells in vivo, thereby omitting the need for large-scale ex vivo T cell production. We engineered nanosized immunofilaments (IFs), with a soluble semiflexible polyisocyanopeptide backbone that presents peptide-loaded major histocompatibility complexes and costimulatory molecules multivalently. IFs readily activated and expanded antigen-specific T cells like natural APCs, as evidenced by transcriptomic analyses of T cells. Upon intravenous injection, IFs reach the spleen and lymph nodes and induce antigen-specific T cell responses in vivo. Moreover, IFs display strong antitumor efficacy resulting in inhibition of the formation of melanoma metastases and reduction of primary tumor growth in synergy with immune checkpoint blockade. In conclusion, nanosized IFs represent a powerful modular platform for direct activation and expansion of antigen-specific T cells in vivo, which can greatly contribute to cancer immunotherapy.

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.

Robust Antigen-Specific T Cell Activation within Injectable 3D Synthetic Nanovaccine Depots.

Synthetic cancer vaccines may boost anticancer immune responses by co-delivering tumor antigens and adjuvants to dendritic cells (DCs). The accessibility of cancer vaccines to DCs and thereby the delivery efficiency of antigenic material greatly depends on the vaccine platform that is used. Three-dimensional scaffolds have been developed to deliver antigens and adjuvants locally in an immunostimulatory environment to DCs to enable sustained availability. However, current systems have little control over the release profiles of the cargo that is incorporated and are often characterized by an initial high-burst release. Here, an alternative system is designed that co-delivers antigens and adjuvants to DCs through cargo-loaded nanoparticles (NPs) incorporated within biomaterial-based scaffolds. This creates a programmable system with the potential for controlled delivery of their cargo to DCs. Cargo-loaded poly(d,l-lactic-co-glycolic acid) NPs are entrapped within the polymer walls of alginate cryogels with high efficiency while retaining the favorable physical properties of cryogels, including syringe injection. DCs cultured within these NP-loaded scaffolds acquire strong antigen-specific T cell-activating capabilities. These findings demonstrate that introduction of NPs into the walls of macroporous alginate cryogels creates a fully synthetic immunostimulatory niche that stimulates DCs and evokes strong antigen-specific T cell responses.

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.

Small-molecule screen reveals synergy of cell cycle checkpoint kinase inhibitors with DNA-damaging chemotherapies in medulloblastoma.

Medulloblastoma (MB) consists of four core molecular subgroups with distinct clinical features and prognoses. Treatment consists of surgery, followed by radiotherapy and cytotoxic chemotherapy. Despite this intensive approach, outcome remains dismal for patients with certain subtypes of MB, namely, MYC-amplified Group 3 and TP53-mutated SHH. Using high-throughput assays, six human MB cell lines were screened against a library of 3208 unique compounds. We identified 45 effective compounds from the screen and found that cell cycle checkpoint kinase (CHK1/2) inhibition synergistically enhanced the cytotoxic activity of clinically used chemotherapeutics cyclophosphamide, cisplatin, and gemcitabine. To identify the best-in-class inhibitor, multiple CHK1/2 inhibitors were assessed in mice bearing intracranial MB. When combined with DNA-damaging chemotherapeutics, CHK1/2 inhibition reduced tumor burden and increased survival of animals with high-risk MB, across multiple different models. In total, we tested 14 different models, representing distinct MB subgroups, and data were validated in three independent laboratories. Pharmacodynamics studies confirmed central nervous system penetration. In mice, combination treatment significantly increased DNA damage and apoptosis compared to chemotherapy alone, and studies with cultured cells showed that CHK inhibition disrupted chemotherapy-induced cell cycle arrest. Our findings indicated CHK1/2 inhibition, specifically with LY2606368 (prexasertib), has strong chemosensitizing activity in MB that warrants further clinical investigation. Moreover, these data demonstrated that we developed a robust and collaborative preclinical assessment platform that can be used to identify potentially effective new therapies for clinical evaluation for pediatric MB.

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.

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.