Controlled Human Malaria Infection (CHMI) differentially affects cell-mediated and antibody responses to CSP and AMA1 induced by adenovirus vaccines with and without DNA-priming

Abstract

We have previously shown that a DNA-prime followed by an adenovirus-5 boost vaccine containing CSP and AMA1 (DNA/Ad) successfully protected 4 of 15 subjects to controlled human malaria infection (CHMI). However, the adenovirus-5 vaccine alone (AdCA) failed to induce protection despite eliciting cellular responses that were often higher than those induced by DNA/Ad. Here we determined the effect of CHMI on pre-CHMI cellular and antibody responses against CSP and AMA1 expressed as fold-changes in activities. Generally, in the DNA/Ad trial, CHMI caused pre-CHMI ELISpot IFN-γ and CD8+ T cell IFN-γ responses of the protected subjects to fall but among non-protected subjects, CHMI caused rises of pre-CHMI ELISpot IFN-γ but falls of CD8+ T cell IFN-γ responses. In contrast in the AdCA trial, CHMI caused both pre-CHMI ELISpot IFN-γ and CD8+ T cell IFN-γ responses of the AdCA subjects to fall. We suggest that the falls in activities are due to migration of peripheral CD8+ T cells to the liver in response to developing liver stage parasites, and this fall, in the DNA/Ad trial, is masked in ELISpot responses of the non-protected subjects by rises in other immune cell types. In addition, CHMI caused falls in antibody activities of protected subjects, but rises in non-protected subjects in both trials to CSP, and dramatically in the AdCA trial to AMA1, reaching 380 μg/ml that is probably due to boosting by transient blood stage infection before chloroquine treatment. Taken together, these results further define differences in cellular responses between DNA/Ad and AdCA trials, and suggest that natural transmission may boost responses induced by these malaria vaccines especially when protection is not achieved.

Trial registration: ClinicalTrials.gov NCT00392015 NCT00870987.

Keywords: AMA1; CHMI; CSP; DNA -prime; T cells; adenovirus-boost; antibody; efficacy; malaria; vaccine.

Figure 1.

Ex vivo ELISpot IFN-γ activities of infectivity controls. Five infectivity controls from the DNA/Ad trial and 4 infectivity controls from the AdCA trial were used. The associations of fold-changes of pre-CHMI and post-CHMI activities with pre-CHMI activities are shown as log-transformed values, and the dotted line represents no-change. The shaded box shows ±1.5 range (log ±0.18)-. (A) CSP: the fold change was ≤1.5, except one outlier, and all 9 subjects remained negative after CHMI. (B) AMA1: the fold change of all subjects was <1.5, and 6/9 subjects remained negative after CHMI, but 3/9 subjects developed positive activities after CHMI each to a single AMA1 peptide pool (not shown).

Figure 2.

DNA/Ad trial: ex vivo ELISpot IFN-γ activities to CSP and AMA1. The associations of fold-changes of pre-CHMI and post-CHMI activities with pre-CHMI activities are shown as log-transformed values, and the dotted line represents no-change. The shaded box shows ±1.5 range. (A) CSP: there was a significant relationship between fold-change and pre-CHMI activities; the fold changes of 2 protected (v11, v18) and 3 non-protected subjects were greater than ±1.5 (shaded box). (B) AMA1: there was a significant relationship between fold-change and pre-CHMI activities; the fold changes of theAMA1 immunodominant pools of v10 (Ap8), v11 (Ap10) and v18 (Ap8) were used as they represented most of the total summed activities. The fold changes of 3 protected subjects (v10, v11, v18) and 9 non-protected subjects were greater than ±1.5 (shaded box).

Figure 3.

DNA/Ad trial: CD8+ T cell IFN-γ activities to CSP and AMA1. The associations of fold-changes of pre-CHMI and post-CHMI activities with pre-CHMI activities are shown as log-transformed values, and the dotted line represents no-change. The shaded box shows ±1.5 range. (A) CSP: there was a significant relationship between fold-change and pre-CHMI activities; the fold changes of 2 protected (v11, v18) and 3 non-protected subjects were greater than ±1.5 (shaded box). (B) AMA1: there was no significant relationship between fold-change and pre-CHMI activities; the fold changes of 3 protected (v10, v11, v18) and 4 non-protected subjects were greater than −1.5 (shaded box).

Figure 4.

AdCA trial: ex vivo ELISpot IFN-γ activities to CSP and AMA1. The associations of fold-changes of pre-CHMI and post-CHMI activities with pre-CHMI activities are shown as log-transformed values, and the dotted line represents no-change. The shaded box shows ±1.5 range. (A) CSP: there was a significant negative association between fold-change and pre-CHMI activities; activities of all 13/17 positive before CHMI fell after CHMI. (B) AMA1: although activities of all 17/17 subjects that were positive pre-CHMI all fell after CHMI, there was no relationship between fold-change and pre-CHMI activities as only 10/17 were greater than −1.5.

Figure 5.

AdCA trial: CD8+ T cell IFN-γ activities to CSP and AMA1. The associations of fold-changes of pre-CHMI and post-CHMI activities with pre-CHMI activities are shown as log-transformed values, and the dotted line represents no-change. The shaded box shows ±1.5 range. (A) CSP: there was no significant relationship between fold-change and pre-CHMI activities, although activities fell in 5/15 subjects. (B) AMA1: There was a significant relationship between fold-change and pre-CHMI and activities fell in 9/15 subjects.

Figure 6.

DNA/Ad and AdCA trials: association of fold changes of antibody responses to CSP and AMA1 with pre-CHMI activities. The associations of fold-changes of pre-CHMI and post-CHMI activities with pre-CHMI activities are shown as log-transformed values, and the dotted line represents no-change. (A) DNA-Ad trial: AMA1: there was no relationship between fold change after CHMI and pre-CHMI activities. (B) AdCA trial: CSP: there was a significant relationship between fold change after CHMI and pre-CHMI activities. (C): AdCA trial: AMA1: there was a stronger significant relationship than CSP between fold change and pre-CHMI activities. In the AdCA trial, CHMI had a greater effect on lower than higher pre-CHMI activities, and for AMA1, CHMI greatly increased pre-CHMI activities.