Development of biomaterial porous scaffolds for dendritic cell modulation and mRNA delivery

Thesis (Ph.D.)--University of Washington, 2017-07mRNA has emerged as a potential candidate for vaccine applications in recent years as a versatile, safe, and cost-effective alternative to traditional therapeutics. Efficient delivery to antigen presenting cells and protection against rapid in vivo degradation are the two greatest challenges for mRNA vaccine development. Scaffold based platforms represent a novel and promising approach to improve mRNA vaccine efficacy through cell enrichment, modulation and prolonged local release. This dissertation describes the development of biomaterial porous scaffolds as a platform for dendritic cell modulation and local delivery of mRNA vaccines. First, DCs maturation within scaffolds and the effects of materials and pore sizes were investigated. A series of poly (2-hydroxyethyl methacrylate) (pHEMA) and poly (dimethyl siloxane) (PDMS) were fabricated using the sphere-templating method that generated uniform and interconnected pores with controllable pore size. Scaffolds with smaller pore sizes consistently induced DCs maturation characterized by secretion of pro-inflammatory cytokines and upregulation of surface maturation markers in both materials in vitro. In vivo study further revealed that scaffolds with smaller pore sizes favor DC accumulation and maturation at implantation site. At the same time, a minimal throat size among pores is crucial for cell infiltration and potentially gaining access to the therapeutics delivered. Second, a range of polymer and lipid based carriers were evaluated for their ability to facilitate intracellular mRNA delivery and effect on cell viability upon transfection. mRNA lipoplexes formed with StemfectTM demonstrated excellent capacity in mediating mRNA transfection in a range of cell lines and primary cells with minimal cytotoxicity. Lastly, these lipoplexes with optimized formulation were integrated in HEMA scaffolds through surface adsorption. Scaffold mediated mRNA delivery and expression was demonstrated in vitro and in vivo. Compared to unformulated mRNA and/or mRNA delivered via subcutaneous bolus injection, formulated mRNA adsorbed on scaffolds lead to prolonged local release, improved mRNA uptake by cells and enhanced transgene expression. Overall, these findings demonstrate the potential of porous biomaterial scaffolds as a platform for dendritic cell modulation and improving the delivery efficiency of mRNA therapeutics