Cell-cycling analysis of memory p14 T cells in vitro and in vivo. CFSE-labeled naive (4 × 10⁶) (A) and memory p14 splenocytes (4 × 10⁶) (B) were restimulated in vitro with irradiated gp33-pulsed splenocytes in the presence of 5 μM imatinib or DMSO as a solvent control. Four days later, CFSE dilution of Vα2⁺CD8⁺ was assessed by flow cytometry. (C-D) CFSE-labeled memory p14 splenocytes (5.1 × 10⁶) containing 3.3 × 10⁵ gp33-specific memory CD8⁺ T cells (Vα2⁺CD45.1^–) were injected intravenously into imatinib-treated (high-dose 50/100 regimen) and nontreated CD45.1⁺ recipients. Sixteen hours later, the mice were infected intravenously with 1200 pfu LCMV. CFSE dilution of specific T cells (Vα2⁺CD8⁺CD45.1^–CFSE⁺) was assessed by flow cytometry 4 days after infection. (C) Percentage of proliferating specific T cells in imatinib-treated and nontreated mice. (D) Absolute number of gp33-specific T cells in imatinib-treated and nontreated mice per spleen. (Inset) Percentage of annexin V⁺ cells within Va2⁺CD8⁺CD45.1^– cells in imatinib-treated and nontreated mice. One representative histogram of 4 to 6 samples per group is shown.