Human blood outgrowth endothelial cells (hBOEC) may be useful delivery-cells for gene therapy. hBOEC have high expansion capacity and stable phenotype. If incorporated into blood vessels, hBOEC could release therapeutic agents directly into the blood stream. However, little is known about lodging and homing of hBOEC in vivo. We examined the homing patterns of hBOEC in mice, and explored extending cell-based FVIII gene therapy from mice to larger animals. hBOEC were injected into NOD/SCID mice to determine where they localize, how localization changes over time and if there were toxic effects on host organs. The presence of hBOEC in mouse organs was determined by qPCR and immunofluorescence microscopy. hBOEC lodged most notably in mouse lungs at 3 h, but by 24 h there were no differences between 9 organs. hBOEC longevity was assessed up to 7 months in vivo. hBOEC expanded well and then plateaued in vivo. hBOEC from older cultures expanded equally well in vivo as younger. hBOEC caused no noticeable organ toxicity up to 3 days post-injection. When mice were pretreated with antibodies to E-selectin, P-selectin or anti-α4 integrin prior to hBOEC injection, the number of hBOEC in lungs at 3h was inhibited. Preliminary studies infusing hemophilic dogs with autologous canine BOEC over-expressing FVIII (B-domain deleted) showed improvement in whole blood clotting times (WBCT). In conclusion, the survivability, expandability and lack of toxicity of BOEC in vivo indicate that they may be valuable host cells for gene therapy
