In vivotracking of adenoviral-transduced iron oxide-labeled bone marrow-derived dendritic cells using magnetic particle imaging

Abstract

ABSTRACTBackgroundDespite widespread study of dendritic cell (DC)-based cancer immunotherapies, thein vivopost-injection fate of DC remains largely unknown. Due in part to a lack of quantifiable imaging modalities, this is troubling as the amount of DC migration to secondary lymphoid organs correlates with therapeutic efficacy. Preliminary studies have identified magnetic particle imaging (MPI) as a suitable modality to quantifyin vivomigration of superparamagnetic iron oxide-(SPIO)-labeled DC. Herein, we describe a lymph node- (LN)-focused MPI scan to quantify DCin vivomigration accurately and consistently.MethodsBoth adenovirus (Ad)-transduced SPIO+(Ad SPIO+) and SPIO+C57BL/6 bone marrow-derived DC were generated and assessed for viability and phenotype using flow cytometry. Ad SPIO+and SPIO+DC were fluorescently-labeled and injected into C57BL/6 mouse hind footpads (n=6). Two days later,in vivoDC migration was quantified using whole animal, popliteal LN- (pLN)-focused, andex vivopLN MPI scans.ResultsNo significant differences in viability, phenotype andin vivopLN migration were noted for Ad SPIO+and SPIO+DC. Day 2 pLN-focused MPI successfully quantified DC migration in all instances while whole animal MPI only quantified pLN migration in 75% of cases.Ex vivoMPI and fluorescence microscopy confirmed MPI signal was pLN-localized and due to originally-injected Ad SPIO+and SPIO+DC.ConclusionsWe overcame a reported limitation of MPI by using a pLN-focused MPI scan to quantify pLN-migrated Ad SPIO+and SPIO+DC in 100% of cases. With this improved method, we detected as few as 1000 DC (4.4 ng Fe)in vivo. MPI is a suitable pre-clinical imaging modality to assess DC-based cancer immunotherapeutic efficacy.