Superparamagnetic iron-oxide nanoparticles (SPIO) have been extensively studied as magnetic resonance imaging (MRI) contrast agents and have been used for contrast enhanced imaging of tumors, organs, and tracking of single cells after labeling with SPIO. An unexplored application for SPIO is vaccine delivery to antigen presenting cells (APCs) in vitro via SPIO-antigen complexes. Several characteristics of SPIO are advantageous for vaccine delivery. Nanoparticles possess inherent adjuvant-like properties, enabling the complexed antigen to be more efficiently internalized into cells by solid-phase phagocytosis as opposed to fluid phase pinocytosis of soluble antigen. In addition, SPIO may be synthesized with precise size control and surface chemistry to optimize size and surface effects for cellular uptake. Finally, SPIO possess the unique ability to label cells for MRI detection in vivo after delivery of the APCs.

In this study, we have synthesized SPIO and modified the surface with amine-functionalized silica to covalently crosslink ovalbumin (OVA) as a proof-of-concept antigen. Splenocytes were harvested from OVA23-3 TCR transgenic mice that possess a T-cell receptor for a peptide of OVA (OVA 323-339). The ex vivo splenocytes were cultured with OVA and OVA-SPIO to assess the efficiency of antigen uptake and cross-presentation using SPIO as a vaccine delivery agent. Bovine serum albumin (BSA) and BSA-SPIO were used as a control antigen and antigen-SPIO complex. Splenocyte proliferation, as measured by tritiated thymidine uptake, was increased by 100% for cells co-cultured with OVA-SPIO compared to OVA. In addition, production of IFN-γ was increased by 200% for cells co-cultured with OVA-SPIO compared to OVA. The increased production of IFN-γ indicates increased cross-presentation of the OVA 323-339 peptide by APCs to TH1 cells. Cells co-cultured with BSA and BSA-SPIO did not demonstrate increased proliferation or production of IFN-γ.

Based on the experimental results, the authors conclude that SPIO represents an effective vaccine delivery agent with added functionality as an MRI contrast agent. The authors will present detailed methods of SPIO synthesis and functionalization and in vitro experimentation, and detailed results using OVA-SPIO in vitro.