HSC exhaustion does not occur in Ndn-deficient mice. Response of Ndn^+m/−p mice to sequential 5-FU treatment demonstrates a normal sensitivity to repetitive myelotoxic stress. Mice were intraperitoneally injected with 5-FU (150 mg/kg) weekly, and survival was monitored daily. Survival data were analyzed by a log-rank nonparametric test and shown as Kaplan-Meier survival curves (P = .71, n = 10).