Primary CTL responses in imatinib-treated mice. Imatinib-treated (low-25/25 and high-dose 50/100 regimen) and nontreated naive C57BL/6 mice were infected intravenously with 200 pfu LCMV (A-E) or immunized intraperitoneally with 2 × 10⁶ MC-GP cells (F-H). Eight days after LCMV infection the frequency of gp33-specific CTLs was analyzed in the spleen by intracellular IFNγ staining after in vitro restimulation (A) and by tetramer staining (B). (C-D) To determine CTL activity, splenocytes were isolated 8 days after LCMV infection and analyzed in a ⁵¹Cr-release assay. • indicates imatinib-treated mice; ▪, nontreated mice; and ♦, mice treated with sterile water. Filled symbols represent gp33-pulsed target cells and open symbols represent unpulsed target cells. CTL activity is given as mean ± SEM of 3 to 5 mice per group. (E) Virus titers were measured in the spleen 4, 6, and 8 days after LCMV infection. Virus titers are expressed as log₁₀ plaque-forming units (pfu) of virus per spleen. (F) Nine days after immunization with MC-GP cells, the frequency of gp33-specific CTLs was analyzed by intracellular IFNγ staining after in vitro restimulation. (G-H) Splenocytes of MC-GP–immunized mice were isolated 9 days after immunization and the induction of a CTL response was assessed in a ⁵¹Cr-release assay after 5 days of in vitro restimulation. CTL activity is given as mean ± SEM of 3 to 5 mice per group. One of 2 representative experiments is shown (A-D, F-H).