Branching of new vessels is enhanced by MSC- and SB623 cell-secreted factors. Following suppression of endogenous outgrowth, rat aortic rings were plated in gels with either OptiMEM (“Control”) or OptiMEM conditioned by MSCs or SB623 cells. After 7–10 days, there were more vessels with conditioned medium and significantly more branching points in SB623 CM versus OptiMEM only (*p < 0.05). Representative images of aortic rings after 7 days in culture with OptiMEM only, or MSC-conditoned medium, or SB623-conditioned medium. Mean ± SEM.