Polymer-based synthetic dendritic cells for tailoring robust and multifunctional T cell responses.

Dendritic cells (DCs) are antigen-presenting cells that play an essential role in T cell activation. Recent efforts in cancer immunotherapy have been directed at the development of artificial antigen presenting cells (aAPCs) loaded with tumor antigens. These aAPCs are designed to mimic DCs with the goal of triggering an efficient and specific T cell response directed against the tumor. We have designed a novel synthetic dendritic cell (sDC) that possesses the essential features of natural DCs. Our sDC is based on a semiflexible poly(isocyano peptide) polymer and carries anti-CD3 antibodies (αCD3) for triggering the T cell receptor/CD3 complex as well as anti-CD28 antibodies (αCD28) as a co-stimulatory signal. Multiple copies of both antibodies facilitate multivalent binding similar to natural DCs. The high mobility of these polymer-bound antibodies, reminiscent of protein motility in a natural plasma membrane, enables receptor rearrangements to occur during T cell activation. We show that our bifunctional αCD3/αCD28-sDC triggers T cell activation at significantly lower antibody concentrations than freely soluble antibodies. This superior performance is further demonstrated in comparison to a mixture of monofunctional αCD3-sDC and αCD28-sDC. The presence of both antibodies on the same polymer not only reduces the threshold for T cell activation but, more importantly, critically shapes the specificity of the T cell response. αCD3/αCD28-sDC is a far more efficient activator of multifunctional killer cells. These findings demonstrate the potential of multifunctional polymers for mimicking natural DCs, paving the way for their exploitation in immunotherapeutic strategies.

Responsive biomimetic networks from polyisocyanopeptide hydrogels.

Mechanical responsiveness is essential to all biological systems down to the level of tissues and cells. The intra- and extracellular mechanics of such systems are governed by a series of proteins, such as microtubules, actin, intermediate filaments and collagen. As a general design motif, these proteins self-assemble into helical structures and superstructures that differ in diameter and persistence length to cover the full mechanical spectrum. Gels of cytoskeletal proteins display particular mechanical responses (stress stiffening) that until now have been absent in synthetic polymeric and low-molar-mass gels. Here we present synthetic gels that mimic in nearly all aspects gels prepared from intermediate filaments. They are prepared from polyisocyanopeptides grafted with oligo(ethylene glycol) side chains. These responsive polymers possess a stiff and helical architecture, and show a tunable thermal transition where the chains bundle together to generate transparent gels at extremely low concentrations. Using characterization techniques operating at different length scales (for example, macroscopic rheology, atomic force microscopy and molecular force spectroscopy) combined with an appropriate theoretical network model, we establish the hierarchical relationship between the bulk mechanical properties and the single-molecule parameters. Our results show that to develop artificial cytoskeletal or extracellular matrix mimics, the essential design parameters are not only the molecular stiffness, but also the extent of bundling. In contrast to the peptidic materials, our polyisocyanide polymers are readily modified, giving a starting point for functional biomimetic hydrogels with potentially a wide variety of applications, in particular in the biomedical field.