Efficacy of HSC depletion and clearance of ACK2 antibody after in utero treatment in mice. Fetuses were treated with isotype control/PBS or varying doses of ACK2 at E13.5 to E14.5 and blood and BM were harvested 7 days later. (A) Gating strategy to detect KLS cells (Lin⁻c-Kit⁺Sca-1⁺) in neonatal pups following in utero ACK2 treatment after first gating on live leukocytes. (B) Total number of BM KLS cells within long bones 7 days after ACK2 treatment. Control, n = 14; 2.5 µg, n = 8; 5 µg, n = 17; 10 µg, n = 5; 20 µg, n = 4. (C) Serum concentrations of ACK2 7 days after in utero isotype control/PBS or ACK2 injections. N ≥ 3 in each group. Data presented as mean ± SEM. ***P < .001 by ANOVA with Tukey’s multiple comparison test.