Biocompatibility and immunogenicity of NGD-MNPs. (A) The flow cytometry assay and (B) the apoptosis index of HUVECs after incubation with NGD-MNPs. (C) The cell viability of HUVECs after incubation with NGD-MNPs at various iron concentrations. (D) The cell cycle of HUVECs after incubation with NGD-MNPs. (E) Representative Prussian blue staining of major visceral organs (heart, lungs, liver, spleen and kidneys) harvested from mice at 4 or 12 weeks after injection of NGD-MNPs or PBS (the scale bar is 50 μm). (F) Blood samples were collected from PBS or NGD-MNPs treated groups at different time points, and serum concentrations of AST, (G) ALT and (H) CREAT were analyzed. (I) Splenocytes from the immunized mice were incubated with NGD-MNPs for 2 days and then measured by the MTT assay to calculate the SI. (J) Splenocytes were isolated from immunized mice 10 days after the last immunization and the relative percentages of CD4+ T cells or CD8+ T cells were analyzed by flow cytometry.