In vivo migration of dendritic cells labeled with synthetic superparamagnetic iron oxide

Yongbin Mou¹, Yayi Hou², Baoan Chen³, Zichun Hua⁴, Yu Zhang⁵, Hao Xie², Guohua Xia³, Zhiyong Wang¹, Xiaofeng Huang¹, Wei Han¹, Yanhong Ni¹, Qingang Hu^1,6
1Central Laboratory of Stomatology, Stomatological Hospital Affiliated Medical School, Nanjing University, Nanjing, People's Republic of China; ²Immunology and Reproductive Biology Laboratory, Medical School, Nanjing University, Nanjing, People's Republic of China; ³Department of Hematology, Zhongda Hospital, Medical School, Southeast University, Nanjing, People's Republic of China; ⁴Jiangsu Key Laboratory of Molecular Medicine, Nanjing University, Nanjing, People's Republic of China; ⁵State Key Laboratory of Bioelectronics, Jiangsu Key Laboratory for Biomaterials and Devices, Southeast University, Nanjing, People's Republic of China; ⁶Leeds Dental Institute, Faculty of Medicine and Health, University of Leeds, Leeds, UK

Background: Successful treatment of cancer with dendritic cell tumor vaccine is highly dependent on how effectively the vaccine migrates into lymph nodes and activates T cells. In this study, a simple method was developed to trace migration of dendritic cells to lymph nodes.
Methods: Superparamagnetic iron oxide (SPIO) of γ-Fe₂O₃ nanoparticles were prepared to label dendritic cells generated from bone marrow of enhanced green fluorescent protein (EGFP) transgenic mice, to explore the fluorescence intensity of EGFP influenced by the SPIO, and to make images of labeled dendritic cells with the help of magnetic resonance imaging in vitro. The SPIO-EGFP-labeled dendritic cells were injected into the footpads of five mice. After 48 hours, magnetic resonance imaging, optical imaging, confocal imaging, and Prussian blue staining were used to confirm migration of the SPIO-EGFP-labeled dendritic cells into draining lymph nodes.
Results: The synthetic SPIO nanoparticles had a spherical shape and desirable superparamagnetism, and confocal imaging and Prussian blue staining showed perfect labeling efficiency as well. Furthermore, the dendritic cells dual-labeled by SPIO and EGFP could migrate into lymph nodes after footpad injection, and could be detected by both magnetic resonance imaging and optical imaging simultaneously, which was further confirmed by immunohistochemistry and Prussian blue staining. The percentage of dendritic cells migrated to the draining lymph nodes was about 4%.
Conclusion: Synthetic SPIO nanoparticles are strong contrast agents with good biocompatibility, and EGFP transgenic dendritic cells can be labeled efficiently by SPIO, which are suitable for further study of the migratory behavior and biodistribution of dendritic cells in vivo.

Keywords: magnetic resonance imaging, optical imaging, dendritic cell, superparamagnetic iron oxide, cell tracking