title: Baculovirus as an ideal radionuclide reporter gene vector: a new strategy for monitoring the fate of human stem cells in vivo.
abstract: OBJECTIVE
  Radionuclide reporter gene imaging holds promise for non-invasive monitoring of transplanted stem cells. Thus, the feasibility of utilizing recombinant baculoviruses carrying the sodium iodide symporter (NIS) reporter gene in monitoring stem cell therapy by radionuclide imaging was explored in this study.
  
  
  METHODS
  Recombinant baculoviruses carrying NIS and green fluorescent protein (GFP) reporter genes (Bac-NIS and Bac-GFP) were constructed and used to infect human induced pluripotent stem cells (hiPSCs), human embryonic stem cells (hESCs) and human umbilical cord blood mesenchymal stem cells (hUCB-MSCs). Infection efficiency, total fluorescence intensity and duration of transgene expression were determined by flow cytometry. Cytotoxicity/proliferative effects of baculovirus on hUCB-MSCs were assessed using CCK-8 assays. ¹²⁵I uptake and perchlorate inhibition assays were performed on Bac-NIS-infected hUCB-MSCs. Radionuclide imaging of mice transplanted with Bac-NIS-infected hUCB-MSCs was performed by NanoSPECT/CT imaging.
  
  
  RESULTS
  Infection efficiencies of recombinant baculovirus in hESCs, hiPSCs and hUCB-MSCs increased with increasing MOIs (27.3%, 35.8% and 95.6%, respectively, at MOI = 800). Almost no cytotoxicity and only slight effects on hUCB-MSCs proliferation were observed. Obvious GFP expression (40.6%) remained at 8 days post-infection. The radioiodide was functionally accumulated by NIS gene products and specifically inhibited by perchlorate (ClO₄⁻). Radioiodide uptake, peaking at 30 min and gradually decreasing over time, significantly correlated with hUCB-MSCs cell number (R² = 0.994). Finally, radionuclide imaging showed Bac-NIS-infected hUCB-MSCs effectively accumulated radioiodide in vivo, which gradually weakened over time.
  
  
  CONCLUSIONS
  Baculovirus as transgenic vector of radionuclide reporter gene imaging technology is a promising strategy for monitoring stem cell transplantation therapy.
authors.affiliation: Department of Nuclear Medicine, Ruijin Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Pan
authors.forename: Shuai
authors.initials: S
authors.lastname: Liu
authors.forename: Haifei
authors.initials: H
authors.lastname: Wu
authors.forename: Jing
authors.initials: J
authors.lastname: Lv
authors.forename: Xiaoqian
authors.initials: X
authors.lastname: Xu
authors.forename: Yifan
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000818:Animals; D016367:Baculoviridae / Q000235:genetics*; D002460:Cell Line; D049109:Cell Proliferation; D002470:Cell Survival; D058948:Cell Tracking / Q000379:methods*; D053595:Embryonic Stem Cells / Q000378:metabolism; D015870:Gene Expression; D017930:Genes, Reporter; D005822:Genetic Vectors / Q000235:genetics*; D006801:Humans; D057026:Induced Pluripotent Stem Cells / Q000378:metabolism; D008297:Male; D059630:Mesenchymal Stem Cells / Q000378:metabolism; D051379:Mice; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D011868:Radioisotopes / Q000378:metabolism*; D033581:Stem Cell Transplantation; D013234:Stem Cells / Q000378:metabolism*; D027981:Symporters / Q000235:genetics / Q000378:metabolism; D014057:Tomography, X-Ray Computed; D014161:Transduction, Genetic; D000099209:Sodium-Iodide Symporters
chemical_list: D011868:Radioisotopes; D027981:Symporters; D000099209:Sodium-Iodide Symporters