Human CD45⁺cells show systemic multilineage engraftment with increased engraftment rates following ACK2 treatment. (A) Percentage of human CD45⁺ cells in lymphoid tissues of chimeric mice and peripheral blood. *P < .05, ***P < .001, ****P < .0001 (analysis of variance with Tukey’s honest significance test). (B) Immunohistochemistry of harvested spleen from a T-cell–dominant mouse demonstrating organized lymphoid follicles. (original magnification ×10; immunohistochemical analysis was performed on fixed/paraffin-embedded tissue sections for human CD45⁺, CD3⁺, CD4⁺, CD8⁺, CD20⁺, and CD68⁺ then counterstained with hematoxylin) (C) Effect of ACK2 treatment on the rates of engraftment (the proportion of surviving animals with ≥1% chimerism in any tissue). (D) Overall chimerism levels. (E-H) NSG mice treated with in utero transplantation of human CD34⁺ cells demonstrate populations of human cells, within the lung alveolar and bronchiole tissue (E), small and large bowel (F), female reproductive tract (G), and brain (H) (original magnification ×40; immunohistochemical analysis was performed on fixed/paraffin-embedded tissue sections for human CD45⁺, CD3⁺, CD4⁺, CD8⁺, CD68⁺, and CD20⁺ and counterstained with hematoxylin). BM, bone marrow; LN, lymph nodes; PB, peripheral blood.