Human BM ALDH^hi cells cultured in mesenchymal- or endothelial-supportive conditions form cellular networks in secondary Matrigel cultures. (A) Human BM ALDH^lo and ALDH^hi cells cultured in complete EGM-2 media formed colonies at 9 to 14 days of culture. (B) Only ALDH^hi colonies established proliferative outgrowth. (C) ALDH^hi cells showed an increased frequency of colony formation (1 CFC in 1464 cells) compared with ALDH^lo cells (1 CFC in 4.2 × 10⁵ cells; *P < .05, n = 4). (D-F) HAECs cultured in EGM-2 media, ALDH^hi cells cultured in Amniomax media, and ALDH^hi cells cultured in EGM-2 were tested for spontaneous tubule forming capacity in secondary Matrigel assays. (G) Mature HAECs formed patterned multinucleated tubule networks. (H) ALDH^hi MCFCs grown in Amniomax aggregated into organized cellular networks with elongated tubule-like cellular morphology. (I) ALDH^hi cells grown in EGM-2 media also aggregated into cellular networks forming tubule-like structures with more diffuse cellular connections (n = 3).