ACK2 and CD47 blockade results in KLS cell depletion in the bone marrow and improved engraftment of donor HSCs after congenic transplantation. (A) Representative gating strategy for identifying KLS cells. (B) Frequency of KLS cells within all live bone marrow cells harvested from bilateral femurs and tibias of P0 pups 7 days after treatment. (C) Rate of engraftment (number of animals with >1% chimerism/number of transplanted mice) at 4 weeks. PBS, n = 19; ACK2 (2.5 μg), n = 9; ACK2 (2.5 μg) + MIAP410 (2.5 μg), n = 18; ACK2 (2.5 μg) + MIAP410 (5 μg), n = 16. (D) Levels of donor CD45 chimerism in chimeric mice over the course of the study. The treatment group that received ACK2 (2.5 μg) + MIAP410 (5 μg) was found to have significantly higher chimerism compared with all other groups. The groups that received ACK2 alone and ACK2 + MIAP410 (2.5 μg) were found to be significantly more chimeric than PBS controls (P < .01 and P < .0001, respectively). PBS, n = 16; ACK2 (2.5 μg), n = 9; ACK2 (2.5 μg) + MIAP410 (2.5 μg), n = 18; ACK2 (2.5 μg) + MIAP410 (5 μg), n = 15. (E) Bone marrow chimerism of KLS cells at age ≥ 24 weeks. (F) Bone marrow KLS chimerism correlates with blood chimerism on linear regression. **P < .01, ****P < .0001, ANOVA with the Tukey multiple-comparison test.