title: Stem cell transplantation: the lung barrier.
abstract: BACKGROUND
  Mesenchymal stem cells (MSCs) show differentiation capacity along mesenchymal lineages and have the potential to aid tissue regeneration. MSC transplantation strategies are therefore currently being assessed following injury to various organs. However, potential MSC migration to these organs after intravenous (IV) MSC injection continues to be impeded by cell trapping within the lung.
  
  
  METHODS
  Mouse MSCs were isolated, purified, transfected with firefly luciferase, and labeled with CSFE. Their size was assessed in vitro. To estimate the diameter of mouse pulmonary capillaries, fluorescence-labeled microspheres of different sizes were injected with or without sodium nitroprusside (SN) pretreatment. The lungs were harvested after 30 seconds and mean numbers of trapped microspheres per high-power field (HPF) were calculated. After IV injection of MSC suspensions (with or without SN), their dynamic distribution was monitored by in vivo luciferine imaging as well as by histopathology.
  
  
  RESULTS
  The diameter of suspended MSCs in vitro was 15 to 19 microm. Whereas nearly no 4-microm microspheres could be detected in lung sections, the numbers of trapped 10- and 15-microm microspheres could be significantly decreased by prior SN injection from 19.3 +/- 11.1 to 6.0 +/- 1.6 cells/HPF (P = .004) and from 34.9 +/- 11.9 to 25.6 +/- 8.1 cells/HPF (P = .028), respectively. Within seconds after MSC IV injection, the vast majority of cells was found in the lungs. However, cell trapping in the pulmonary microvasculature was significantly reduced by pre-treatment with SN.
  
  
  CONCLUSIONS
  We demonstrate that cell trapping in lungs can be reduced with IV SN pretreatment, increasing MSC passage through the lung capillaries, and potentially facilitating cell access to injured organs.
authors.affiliation: Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, California, USA. schrepfer@stanford.edu
authors.forename: S
authors.initials: S
authors.lastname: Schrepfer
authors.forename: T
authors.initials: T
authors.lastname: Deuse
authors.forename: H
authors.initials: H
authors.lastname: Reichenspurner
authors.forename: M P
authors.initials: MP
authors.lastname: Fischbein
authors.forename: R C
authors.initials: RC
authors.lastname: Robbins
authors.forename: M P
authors.initials: MP
authors.lastname: Pelletier
mesh_terms: D000818:Animals; D007262:Infusions, Intravenous; D008156:Luciferases / Q000032:analysis / Q000235:genetics; D008168:Lung / Q000503:physiopathology*; D045164:Mesenchymal Stem Cell Transplantation / Q000009:adverse effects*; D051379:Mice; D008807:Mice, Inbred BALB C; D011994:Recombinant Proteins / Q000032:analysis; D014162:Transfection
chemical_list: D011994:Recombinant Proteins; D008156:Luciferases