Uptake and activation profile of murine dendritic cells in response to stimulation with functionalized iron oxide nanoparticles

Abstract

Abstract Subunit vaccines typically have better safety profiles than live attenuated or killed whole-cell vaccines, but are often less immunogenic and less efficacious when deployed alone. Thus, immunological adjuvants are frequently formulated with subunit vaccines to improve efficacy. However, few vaccine adjuvants are FDA-approved; and for many adjuvants their mechanisms of action are poorly understood. We previously explored the use of iron oxide (IO) nanoparticles (NPs) in subunit vaccine delivery and show that the IO NPs also possess adjuvant-like qualities, eliminating the need for additional adjuvants in the vaccine formulation. This study further dissects the mode of action of IO NPs as immunological adjuvants by examining the relationship of particle size and uptake on the activation profile of murine bone marrow derived dendritic cells (BMDCs) in response to in vitro stimulation with functionalized IO NPs. Using IO NPs of sizes ranging 5 – 30 nm, we showed by flow cytometry immunophenotyping that only IOs of 20nm and 30nm could induce an activated BMDC subset. The level of NP uptake by BMDCs, as measured by Prussian Blue staining, also varied with particle size, with IO of 5nm being the most efficiently internalized. Intriguingly, the levels of BMDC activation did not correlate with the level of IO NP uptake. We hypothesize only IO NPs taken up via selective endocytic pathways will activate BMDCs. The production of cytokine/chemokines by these BMDCs as further characterizations of the adjuvant-like profiles of IO NPs in relation to particle size and cellular uptake is currently being examined. These studies begin to dissect the mode of action of IO NPs as a self-adjuvanted vaccine delivery system on the innate-adaptive immune interface.