Table 1.
Sterile protection in BALB/c mice immunized with attenuated sporozoites
| Immunogen | Immunizing dose (×103) | Immunization route (days between 2 boosts) | Challenge route | Challenge dose (days after last immunization) | No. protected/no. challenged | Protection (%) (mean ± SD) |
|---|---|---|---|---|---|---|
| PBS | 75/20/20/20/20 | i.v. (14), i.d. (14), s.c. (14) | i.v., i.d. or mb | 5000 (7) | 0/15, 0/15, 0/15 | 0, 0, 0 |
| 75/20/20/20/20 | i.v. (14) | i.v., i.d. or mb | 5000 (7) | 29/30, 29/30, 29/30 | 97 ± 6, 97 ± 6, 97 ± 6 | |
| 75/20/20/20/20 | i.d. (14) | i.v., i.d. or mb | 5000 (7) | 5/30, 4/30, 4/30 | 17 ± 6, 13 ± 6, 13 ± 6 | |
| 75/20/20/20/20 | s.c. (14) | i.v., i.d. or mb | 5000 (7) | 5/30, 5/30, 6/30 | 17 ± 6, 17 ± 6, 20 ± 0 | |
| γ-spz | 100/100/100 | i.v. (7), i.d. (7), s.c. (7) | i.v., i.d. or mb | 5000 (7) | 15/15, 15/15, 15/15 | 100, 100, 100 |
| 100/100/100 | i.v. (7), i.d. (7), s.c. (7) | i.v., i.d. or mb | 5000 (180) | 15/15, 15/15, 15/15 | 100, 100, 100 | |
| 100/100/100 | i.v. (7), i.d. (7), s.c. (7) | i.v., i.d. or mb | 5000 (7 + 180) | 15/15, 15/15, 15/15 | 100, 100, 100 | |
| 100 | i.v., i.d., s.c | i.d. | 5000 (7) | 15/15, 0/15, 0/15 | 100, 0, 0 | |
| 100/100 | i.v. (7), i.d. (7), s.c. (7) | i.d. | 5000 (7) | 15/15, 0/15, 0/15 | 100, 0, 0 | |
| 200/200 | i.v. (7), i.d. (7), s.c. (7) | i.d. | 5000 (7) | 15/15, 9/15, 15/15 | 100, 60 ± 0, 100 | |
| 600 | i.v., i.d., s.c | i.d. | 5000 (7) | 15/15, 12/15, 15/15 | 100, 80 ± 0, 100 |
Attenuated sporozoites (γ-spz) were obtained by exposure to 80 Gy of γ-radiation from a 137Cesium source. Mice were challenged with 5 × 103 PyWT (P. yoelii 265BY). Each immunization group had a naïve control group of five mice (n = 5) immunized with PBS. All control mice became patent on days 4 or 5 after PyWT challenge. Blood-stage patency was monitored three times a week by evaluation of Giemsa-stained blood smears from day 4 to day 14 post sporozoites infection. Results expressed as mean ± standard deviation (SD). All experiments were repeated three times (n = 3) with 5 or 10 mice in each group. mb, mosquito bite; i.d., intradermal; i.v., intravenous; s.c., subcutaneous.