Potent Immune Stimulation from Nanoparticle Carriers Relies on the Interplay of Adjuvant Surface Density and Adjuvant Mass Distribution

Development of novel adjuvant delivery approaches which provide safe and effective immune stimulation are critical for prophylactic and therapeutic advances in a wide range of diseases. Toll-like receptor agonists (TLRas) have been identified as potent stimulators of antigen presenting cells (APCs) and are capable of inducing proinflammatory immune responses desirable for vaccine and immunostimulatory applications. Although TLRas have been successfully incorporated into nanoparticle platforms, minimal work has been done to evaluate the direct role of the adjuvant incorporation in these formulations in directing the immune response. Here, we developed a series of nanoparticle carriers with controlled surface densities of two TLRas, lipopolysaccharide (LPS), corresponding to TLR-4, and CpG oligodeoxynucleotide, corresponding to TLR-9. The proinflammatory cytokine production and expression of costimulatory molecules on APCs were evaluated following a 24 h particle incubation period in vitro using bone marrow derived macrophages and in vivo following particle instillation in the airway of mice. Results demonstrate that proinflammatory cytokine production is predominantly driven by the distribution of the adjuvant dose to a maximal number of cells, whereas the upregulation of costimulatory molecules needed to drive APC maturation and promote adaptive responses indicate the requirement of an optimal density of TLRa on the particle surface. These results indicate that adjuvant surface density is an important parameter for tight control of immune stimulation and provide a foundation for pathogen mimicking particle (PMP) vaccines and immunostimulatory therapeutics.