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 dual-modality 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 μg/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 C57BL/6 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 superparamagnetic and near-infrared behavior. Perls staining showed perfect labeling efficiency. The cell phenotypes, including CD11c, 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.