FLT1 and lentivirus infection: TRAIL-transduced MSCs (MOI 2) were examined by flow cytometry with the use of a PE-conjugated anti-human TRAIL antibody, which demonstrated that more than 98% of flT-transduced MSCs (MSC-flT) were positive for TRAIL expression, whereas only approximately 1% of control GFP virus-infected cells were positive, which indicated TRAIL expression was not the result of endogenous TRAIL induction after lentivirus infection (Figure 1B).