EGF promotes HSC recovery in vivo in a DNA-PKcs–dependent manner. (A) Schematic design. C57BL/6 mice were irradiated with 500-cGy TBI, followed by daily injections of saline, EGF, NU7441, or EGF + NU7441 for 10 days. BM cells were collected at +4 hours for Comet assay and at day +10 for annexin V apoptosis assay and competitive repopulation assays. (B) Representative images of a Comet assay of BM KSL cells collected at +4 hours following 500-cGy TBI and treatment with EGF with or without NU7441 (scale bars, 100 µm). Measurements of tail moments in KSL cells in each condition (n = 6-7 fields per group [range 110-137 cells per field], mean ± SEM, Student t test) (right panel). (C) Representative flow cytometric analysis of annexin V and 7-AAD staining in BM KSL cells at day +10 from mice described in A (left panel). Percentage of annexin V⁺ KSL cells in each condition (n = 3 or 4 per group, 1-way ANOVA) (right panel). (D) Numbers of CFCs in BM at day +10 from the mice described in A (n = 6 per group, mean ± SEM, 2-way ANOVA). (E) Flow cytometric analysis of BM CD150⁺CD48⁻CD41⁻ KSL cells at day +10 from mice described in A (left panel). Percentage of CD150⁺CD48⁻CD41⁻ cells within the KSL population in each group (n = 7 or 8 per group, 1-way ANOVA). (F) Percentages of donor CD45.2⁺ cells in the BM of primary recipient mice at 16 weeks following transplant of BM cells collected at day +10 from the mice in A (n = 6 per group, 2-way ANOVA). (G) Percentages of donor CD45.2⁺ cells in the BM of secondary mice at 16 weeks posttransplant. Secondary mice were transplanted with 5 × 10⁶ BM cells collected from primary mice at 16 weeks posttransplant, along with 2 × 10⁵ competitor BM (CD45.1⁺) cells (n = 6 per group, 2-way ANOVA). (H) Percentages of CD45.2⁺Mac1/Gr1⁺ (myeloid) cells (left panel), CD45.2⁺B220⁺ B cells (middle panel), and CD45.2⁺CD3⁺ T cells (right panel) in the BM of secondary recipients at 16 weeks posttransplant (n = 6 per group, 2-way ANOVA). (I-J) C57BL/6 mice were injected with 1 dose of doxorubicin as chemotherapy, followed by EGF or saline treatment. (I) PB WBCs, neutrophils (NEU), lymphocytes (LYMPH), and platelets (PLT) in mice at +10 days postdoxorubicin (n = 4 or 5, Student t test). (J) Number of KSL cells per mouse at +10 days postdoxorubicin (n = 5 per group, Student t test) (left panel). Percentages of CD150⁺CD48⁻CD41⁻ cells within the KSL cell population at day +10 postdoxorubicin (n = 5 per group, Student t test) (right panel). *P < .05, **P < .01, ***P < .001, ****P < .0001.