LICs lacking the cytokine receptor γ_C exhibit increased sensitivity to dasatinib therapy in vivo. (A) Mice infused with the indicated numbers of γ_C-positive LICs (i) or γ_C-null LICs (ii-iv) were imaged for vector luciferase activity 10 days later. Matched exposures document relative levels of fluorescence radiance indicated at the right. (B) Cohorts of mice receiving 2 × 10⁵ γ_C -positive LICs (Ai) or 2 × 10⁶ γ_C -null LICs (Aiii) were left untreated or were treated once daily 5 days per week with vehicle or dasatinib (10 mg/kg body weight) and euthanized when moribund. Despite their more significant leukemia burden at day 10 (Aiii vs Ai), mice receiving γ_C-null LICs exhibited a better response to dasatinib therapy. Statistics for pairwise comparisons: untreated vs vehicle (whether γ_C WT or null groups) are not significant; γ_C WT, vehicle vs dasatinib, P < .001; γ_C null, vehicle vs dasatinib, P < .001; dasatinib-treated γ_C WT vs dasatinib-treated γ_C null, P = .014. Rx, treatment; WT, wild-type.