Protection of Kunming mice against
infection. Survival curves of mice immunized with pVAX-CDPK1 (17.3 ± 4.3 days), pVAX-IL-21-IL-15 (12.0 ± 2.0 days), pVAX-CDPK1 + pVAX-IL-21-IL-15 (19.2 ± 5.1 days), pVAX I, PBS and blank controls after lethal challenge with 1 × 103 tachyzoites of virulent T. gondii RH strain 2 weeks after the last immunization. Each group had 15 mice. Three control groups (PBS, pVAX I and blank control) had 0% survival at day 6. The same letter in front of experimental group means no statistically significant difference (P > 0.05) between different experimental groups from the same measurement, while different letter means statistically significant difference (P < 0.05).