Magnetic resonance and near-infrared imaging using a novel dual-modality nano-probe for dendritic cell tracking in vivo

Background aims. The effect of cellular-based immunotherapy is highly correlated with the success of dendritic cells (DCs) homing to the draining lymph nodes (LNs) and interacting with antigen-specific CD4(+) T cells. In this study, a novel magneto-fluorescent nano-probe was used to track the in vivo migration of DCs to the draining LNs. Methods. A dualmodality nano-probe composed of superparamagnetic iron oxide (SPIO) and near-infrared fluorescent (NIRF) dye (NIR797) was developed, and its magnetic and optical contrasting properties were characterized. DCs generated from mouse bone marrow were co-cultured with the probe at a lower concentration of 10 mu g/mL. The cell phenotype and function of DCs were also investigated by fluorescence-activated cell sorting analysis and mixed leukocyte reactivity assay. Labeled DCs were injected into the footpad of C57BL16 mice. Afterward, magnetic resonance imaging, NIRF imaging, Perls staining and CD11c immunofluorescence were used to observe the migration of the labeled DCs into draining LNs. Results. The synthetic SPIO-NIR797 nano-probe had a desirable superparamagnedc and near-infrared behavior. Perls staining showed perfect labeling efficiency. The cell phenotypes, including CD1 1 c, CD80, CD86 and major histocompatibility complex class II, as well as the T-cell activation potential of the mature DCs were insignificantly affected after incubation (P > 0.05). Labeled DCs migrating into LNs could be detected by both magnetic resonance imaging and NIRF imaging simultaneously, which was further confirmed by Perls staining and immunofluorescence. Conclusions. The novel dual-modality SPIO-NIR797 nano-probe has highly biocompatible characteristics for labeling and tracking DCs, which can be used to evaluate cancer immunotherapy in clinical applications.