Physicochemical and immunological assessment of mesoporous silica-templated particles for vaccine delivery applications

Routine vaccination was initiated in the early 20th century and is now considered one of the most beneficial health initiatives of all time. Despite their immense success, vaccines are often associated with safety concerns and there are still no approved vaccines for protection against insidious pathogens such as HIV, malaria, and tuberculosis. Progress in the area of vaccinology has been limited by an incomplete understanding of the immune system and the mechanisms of infection-­ and vaccine-­induced immunity. Therefore, vaccine development has been restricted to empirical approaches throughout the majority of its history. Recently, advances in immunology have given rise to new understanding regarding vaccine-­induced immunity. In addition, advances in biotechnology have enabled the isolation of various immunopotentiating components with molecular definition and high safety profiles. In collaboration with immunologists, materials scientists are now using these tools to rationally develop highly defined systems based on the latest insights in vaccinology. However, our understanding of rational vaccine formulation is still in its infancy. In order to completely shift vaccine design approaches from empirical to rational, systematic studies that delineate the roles of various vaccine design parameters on the immune response are needed to fill the existing gaps in knowledge. The overall aim of this thesis is to systematically evaluate various aspects of vaccine design that are not yet adequately addressed in the current literature. Specifically, the work aims to: (i) understand how interactions between particles and immune cells change as a result of protein adsorption onto the surfaces of particles, (ii) delineate the physicochemical and immunological impacts of protein antigen redox state in particulate systems, and (iii) immunologically assess a novel combination of defined adjuvant molecules codelivered with a model antigen by a particle-­‐based system. These aims are addressed throughout the thesis using single-­‐component, molecularly defined particles fabricated via mesoporous silica templating and covalent crosslinking. Particles comprised of poly(methacrylic acid) (PMA) stablized by disulfide bonds are used to evaluate the effects of protein adsorption in physiological media containing fetal bovine serum. Using a similar fabrication approach, another set of particles is fabricated with a model protein antigen (i.e., ovalbumin) in its native, reduced, or oxidized state and stabilized by amide bonds. The effect of redox state on the immunological properties of the particles is uncovered throughout a series of studies using in vitro, ex vivo, and in vivo mouse models. From the set of particles, the best performer was rationally selected to produce a new series of particles to elegantly delineate the roles of two adjuvant molecules delivered alone or in combination. Overall, the work shown in this thesis uncovers and elaborates on several important links between vaccine properties and induced immune responses with specific emphasis on extrinsic particle surface properties, protein antigen conformation, and combinatorial adjuvant delivery