Hematopoietic radioprotection deficiency in CXCR4^–/– FL cells. Lethally irradiated recipient mice received transplants of 4 limiting dilutions of E14.5 CXCR4^+/+ and CXCR4^–/– FL cells: 2 × 10⁶ (A), 10⁶ (B), 0.5 × 10⁶ (C), and 0.25 × 10⁶ (D) cells injected per mouse; n = 5 mice per cell dose and per genotype. Recipients were monitored daily during the first 2 weeks and weekly until week 4 after transplantation. Survival data were analyzed using a log-rank nonparametric test and the results are expressed as Kaplan-Meier survival curves.