Each vial contains 170,000 Normal Human Umbilical Vein Endothelial Cells (HUVEC), pooled from multiple donors. Prior to cryopreservation, the parental HUVEC are lentivirally infected to stably express CytoLight Green (Lenti, CMV) driven off of a CMV promoter. This results in a >90% transduction efficiency of the HUVEC population as measured by flow cytometry analysis. Upon thawing, the HUVEC CytoLight Green are guaranteed to be ≥ 70% viable. Normal human cells have a limited life span in vitro. When cultured according to protocol, these HUVEC CytoLight Green can achieve several population doublings.