Effects of Cdc42 and Rac1 deletions on in vitro migration and in vivo dissemination of NPM-ALK lymphoma cells. (A) Three independent CreER^T2 lymphoma cell lines for each genotype were transduced with a retrovirus expressing Bcl2 to protect cells from apoptosis as in Figure 5. Cdc42 and Rac1 deletions were induced by treatment with 10 nM 4-hydroxytamoxifen for 4 hours. Cell were then seeded into the upper chamber of transwells (0.8 µm pore size) and allowed to migrate toward a gradient of SDF-1α (100 ng/mL) that was plated in the lower chamber for 4 hours in CO₂ incubator. Migrated cells in the bottom chamber were counted. The histograms indicate means ± SD from 3 independent cell lines for each genotype using triplicate wells for experimental point. The Student t test was used to calculate statistical significance (*P < .001). (B) Immortalized NPM-ALK lymphoma cell lines with the genotypes as in panel A were inoculated i.v. (5 × 10⁶) in NOD scid γ (NSG) mice. After 15 days, mice were euthanized and all organs were isolated and fixed in formalin solution for H&E staining. Figure shows representative histology of spleen, liver, and kidney. NPM-ALK;CreER^T2 (NPM-ALK), NPM-ALK;CreER^T2;Cdc42^fl/fl;Bcl2 (NPM-ALK/Cdc42KO), NPM-ALK;CreER^T2;Rac1^fl/fl;Bcl2 (NPM-ALK/Rac1KO), NPM-ALK;CreER^T2;Cdc42^fl/fl;Rac1^fl/fl;Bcl2 (NPM-ALK/Cdc42/Rac1KO). Scale bar, 1 mm.