In utero blockade of c-Kit and CD47 increases Gr-1⁺cells and prevents early engraftment of Gr-1 cells, in addition to causing transient anemia and permanent fur whitening. (A) Survival to birth after in utero injection of PBS, ACK2, or ACK2 + CD47 at various concentrations. PBS, n = 128; ACK2 (2.5 μg), n = 94; ACK2 (2.5 μg) + MIAP410 (2.5 μg), n = 122; ACK2 (2.5 μg) + MIAP410 (5 μg), n = 154. **P < .01, χ² test. Hemoglobin levels in blood of P0 mice (B) and E18 mice (C) after in utero HSC depletion. (D) Numbers of Gr-1⁺ cells in the spleens of P0 mice. Lineage distribution of host-derived (E) and donor-derived (F) cells in blood from 4-week-old mice. Lineage distribution of host-derived (G) and donor-derived (H) cells in blood of 12-week-old mice. (I) Hypopigmentation in mice after undergoing in utero HSC depletion. In panels B-F,I, *P < .05, **P < .01, ***P < .001, ****P < .0001, ANOVA with the Tukey multiple-comparison test.