Objective To explore the feasibility and efficacy of an MRI-visible,targeted,nano-vector which is synthesized by attaching a targeting ligand,the GD2 single chain antibody (scAb GD2),to the distal ends of PEG-g-PEI-SPION as a carrier for gene delivery into human bone marrow mesenchymal stem cells (hBMSCs) and in vitro cellular MR imaging.Methods scAbGD2-PEG-g-PEI-SPION was synthesized as previously reported.Gel electrophoresis was performed to assess the pDNA condensation ability of scAbGD2-PEG-g-PEI-SPION.The particle size and Zeta potential of scAbGD2-PEG-g-PEI-SPION/pDNA nanocomplexes were observed by dynamic light scattering.Cytotoxicity of scAbGD2-PEG-g-PEI-SPI-ON was evaluated by CCK-8 assay using hBMSCs.Gene transfection efficiency of scAbGD2-PEG-g-PEI-SPION in hBMSCs was quantified by flow cytometry,PEG-g-PEI-SPION,scAbGD2-PEG-g-PEI-SPION,scAbGD2-PEG-g-PEI-SPION+ free AbGD2 and scAbIgG2a-PEG-g-PEI-SPION group was established.The cellular internalization of scAbGD2-PEG-g-PEI-SPION/pDNA nanocomplexes was observed by confocal laser scanning microscopy and Prussian blue staining.MRI of scAbGD2-PEG-g-PEI-SPION was performed by cellular MRI scanning in vitro.Results scAbGD2-PEG-g-PEI-SPION condensed pDNA to form stable nanocomplexes of 80-100 nm in diameter and showed low cytotoxicity to hBMSCs.At the same N/P ratio,the transfection efficiency of scAbGD2-PEG-g-PEI-SPION group was significantly higher than those of other groups (P＜0.001).At the optimal N/P ratio of 20,scAbGD2-PEG-g-PEI-SPION/pDNA obtained the highest transfection efficiency of (59.60 ± 4.50) ％ in hBMSCs.Furthermore,hBMSCs labeled with scAbGD2-PEG-g-PEI-SPION showed sensitive low signal intensity on MRI T2/T2 *-weighted images in vitro.Conclusion scAbGD2-PEG-g-PEI-SPION is an efficient MRL visible targeted nano vector for gene delivery into hBMSCs.