CD9 expression conditions homing in the testis in vivo. (A) Workflow. REH or NALM6 cells were injected into 4-week-old NSG mice. The mice were killed 4 weeks after xenografting and their testes were collected. After removal of the tunica albuginea, pieces of the testes were dissociated by incubation in 0.25% trypsin and 1 µg/mL collagenase for 30 minutes at 37°C. The cell suspension was filtered through a nylon mesh, labeled with antibodies against CD19, CD10, and CD9, and analyzed by flow cytometry. (B) REH CD9^high, CD9^medium, and CD9^low cells were transplanted into NSG mice. The graph shows the percentage of CD9⁺ cells among REH cells initially injected and REH population found in the testis after xenografting. n is the number of mice undergoing transplantation: REH CD9^low, n = 3; REH CD9^medium, n = 4; REH CD9^high, n = 2. (C) NALM6 cells in which CD9 was stably downregulated or control cells were injected into NSG mice. Three weeks after injection, the contents of the BM and testes were analyzed. The graph shows the results obtained for 6 mice for each set of conditions. **P < .01 in a Mann-Whitney test.