Investigating the Use of Ultra-Small Iron Oxide Nanoparticles as a Subunit Vaccine Delivery Platform with Adjuvant-Like Properties

Abstract

Highly engineered vaccines such as subunit vaccines, nucleic acid vaccines, and self-assembling virus-like particles often display improved safety profiles in comparison to their whole-cell vaccine counterparts. While these vaccines have reduced reactogenicity and are safer for immunosuppressed populations such as the elderly, pregnant women, or the immunocompromised, they often lack in immunogenicity and long-term effectiveness. In order to improve upon these vital qualities, adjuvants are frequently added to subunit vaccine formulations. Inorganic nanoparticle delivery systems with built-in adjuvant properties have the potential increase subunit vaccine immunogenicity without the need for additional adjuvants to be added to vaccine formulations. Previous research in our lab indicates that functionalized iron-oxide nanoparticles possess adjuvant-like properties and are internalized by bone marrow-derived dendritic cells (BMDCs). Iron oxide nanoparticles (IO NPs) have been repeatedly demonstrated to be safe in current clinical applications, and are inexpensive, highly reproducible and can be lyophilized and multiplexed – qualities that are vital for the development of effective vaccines that are practical for global distribution. This project aimed to further elucidate, in vitro and in vivo, the extent of adjuvant-like activities of IO NPs, with a focus on dendritic cells (DCs) at the innate-adaptive immune interface. We evaluated 10nm, 20nm and 30nm IO NPs for their ability to activate bone marrow-derived dendritic cells (BMDCs) in vitro, the uptake efficiency and intracellular localization of IO NPs in vitro and in vivo dissemination following subcutaneous (SC) injection, and the ability of IO NPs to enhance vaccine immunogenicity of a recombinant spike protein (SP) SARS-CoV-2 vaccine. We also aimed to identify if correlations existed in IO NP-induced innate immune modulation and performance of IO NPs as a subunit vaccine delivery system. We found that 10nm IO NPs were superior to 20nm and 30nm IO NPs in their ability to induce activation of CD11c+ BMDC maturation and cytokine and chemokine production. 10nm IO NPs were also internalized more efficiently by BMDCs. IO NPs were largely found to utilize clathrin-mediated endocytosis and macropinosytosis for entry into BMDCs. Following SC injection, IO NPs drained to local lymph nodes for uptake by CD11c+ DCs within 24 hours, followed by presence in CD11c+ DCs in the spleen at 48 and 96 hours post injection. SP-IO vaccine was able to induce vaccine titers similar to SP administered with ISA51 following a three-dose regimen. 10nm IO NPs induced the more uniform antibody titers, leading us to conclude that the innate immune signature induced by 10nm IO NPS on DCs impacts adaptive immune responses when used as a subunit vaccine delivery platform. These studies add to the library of information available to researchers regarding potential delivery systems and adjuvants for the rational design of subunit vaccines.