Isolation and in vitro progenitor activity of purified ALDH^hiCD133^-Lin^- and ALDH^hiCD133⁺Lin^- cell populations. (A) Lin^- cells incubated with Aldefluor substrate were used to select ALDH^hi cells (R1, 55.8% ± 3.5%). (B) Staining for CD133 expression revealed the ALDH^hiCD133^-Lin^- (R2 = 33.7% ± 1.7%) and ALDH^hiCD133⁺Lin^- (R3 = 50.4% ± 2.5%) purified populations. (C-D) Isolated ALDH^hiCD133^-Lin^- and ALDHhiCD133⁺Lin^- sorted cells were analyzed for CD34 and CD38 expression. Purified ALDH^hiCD133⁺Lin^- cells were enriched for repopulating CD34⁺CD38^- cells (^**P < .01) and included primitive CD34^-CD38^- cells. Data represent the mean ± SEM for cells isolated from 10 UCB samples. (E) Purified ALDH^hiCD133^-Lin^-, ALDHhiCD133⁺Lin^-, or ALDHhiLin^- cells were cultured in methylcellulose media and erythrocyte, mixed, and granulocyte/macrophage colonies (BFU-E, Mix, CFU-GM) were enumerated after 14 to 17 days of in vitro culture. Data represent the number of individual colonies produced per 1000 cells plated from each population. Data are expressed as mean ± SEM for cells isolated from 4 to 6 UCB Lin^- samples (^*P < .05; ^**P < .01).