GF-stimulated CD49f⁺cells display a progressive age-related delay in vitro. (A) Design of the culture system used to compare the survival and cell division kinetics of CD49f⁺ cells isolated from differently aged donors over 7 days of culture. (B) Kaplan-Meier curves of CD49f⁺ cell survival in the cultures described in panel A (log-rank test, ∗∗∗P < .001). (C) Weighted dose-response curves describing the completion of a first division of the different sources of CD49f⁺ tested. Curves reflect only CD49f⁺ cells that remained viable past a first division, or until the end of the assay without dividing. Error bars are indicated at the median point of each curve (CB = 57 hours, young adult = 75 hours, aged adult = 90 hours) and indicate the range defined by ± 1 SEM of this estimate (∗∗∗P < .001). Time required for clones to complete a second (D) or third (E) division after completing their previous division (∗∗∗P < .001).