CD81KO cells exhibit deficiency in homing and engraftment in vivo. (A) Representative images of mouse femurs harvested 3 days postinjection (10 × 10⁶ of Nalm6 cells) in NSG-SM3 mice and stained using anti-human mitochondria antibody to detect the presence of leukemic cells (brown). Scale bar, 100 μm. (B) Individual stained cells were counted in 6 images from each mouse femur in the cohort (n = 2) to quantitate the presence of human cells. Mean ± standard deviation was plotted. *P < .01. (C) For competitive homing assay, equal numbers of WT (VPD450 stained) and CD81KO (CFSE stained) Nalm6 cells were coinjected into mice. After 72 hours, femurs were harvested and flushed (n = 6). Absolute counts of CFSE⁺ CD81KO cells and VPD450⁺ WT Nalm6 cells in each femur were detected by flow cytometry. Connecting lines comparing the absolute counts of each cell type within a single femur indicate paired data. A paired Student t test was calculated. *P < .05. Plots presented in supplemental Figure 5. (D) Peripheral blood monitoring of human CD10⁺ leukemic cells in a separate cohort of NSG-SGM3 mice transplanted with 0.5 × 10⁶ or 5 × 10⁶ cells. (E) Kaplan-Meier survival plot shows NSG-SGM3 mice xenografted with CD81KO Nalm6 cells live significantly (*P < .05) longer than WT cell-transplanted mice.