pone-0020977-g006: Antibody responses in mice induced by the mono-allelic and bi-allelic PfAMA1 vaccine constructs.6 week old female BALB/c mice (n = 6) were primed with 1×109 vp of each of the adenovirus constructs i) ChAd63-biallelic, ii) AdHu5-biallelic and iii) AdHu5-PfAMA1 (3D7). Groups i) and ii) were boosted at day 56 with 1×107 pfu of MVA-biallelic and group iii) was boosted with the mono-allelic MVA-PfAMA1 (3D7). The total IgG response was measured by ELISA in the serum at day 14, 55 and 70 against both the 3D7 (A) and FVO (B) alleles. The median and the range of the endpoint titer (log 10) are shown in the figure. There were significant differences between the ELISA titres at day 14 by one-way ANOVA: 3D7 PfAMA1 ChAd63-biallelic versus AdHu5-monoallelic P <0.001; FVO PfAMA1 ChAd63-biallelic versus AdHu5-biallelic P <0.05. The MVA boost significantly increased IgG titres against both alleles in all groups (* P <0.05 by Wilcoxon signed rank test).

Mentions: Mice were primed with either i) ChAd63-bi-allelic, ii) AdHu5-bi-allelic or iii) the mono-allelic AdHu5-PfAMA1 (3D7) vectors. Groups i) and ii) were boosted with MVA-bi-allelic and group iii) was boosted with the mono-allelic MVA-PfAMA1 (3D7) vaccine. Total IgG was measured in the serum on days 14, 55 and 70 by ELISA against recombinant 3D7 and FVO PfAMA1. AMA1 specific IgG responses were detected in all the groups to both 3D7 (Figure 6A) and FVO (Figure 6B) recombinant proteins. Although minor, but statistically significant differences were noted between groups by one-way ANOVA analysis at day 14, by day 55 these differences in IgG antibody responses had equalized between the different groups, suggesting that after priming with ChAd63 rather than AdHu5, the antibodies take slightly longer to reach maximal levels. The MVA immunization significantly increased the antibody response against both alleles in all the groups to similar levels by day 70 (P≤0.05). Thus, in agreement with data for the MSP1 antigen [32], the ChAd63 and AdHu5 vectors expressing the bi-allelic PfAMA1 construct primed similar IgG responses, which remained equivalent after a heterologous MVA boost vaccination. However, the immunogenicity of the mono-allelic and bi-allelic AMA1 vaccine constructs was indistinguishable based on the absolute IgG titers.

Biswas S, Dicks MD, Long CA, Remarque EJ, Siani L, Colloca S, Cottingham MG, Holder AA, Gilbert SC, Hill AV, Draper SJ - PLoS ONE (2011)

Bottom Line: This antigen, composed of the 3D7 and FVO alleles of PfAMA1 fused in tandem and with expression driven by a single promoter, was optimized for antigen secretion and transmembrane expression.CD8(+) and CD4(+) T cell responses against epitopes that were both common and unique to the two alleles of PfAMA1 were also measured in mice.Optimized transgene inserts encoding two divergent alleles of the same antigen can be successfully inserted into adeno- and pox-viral vaccine vectors.Adenovirus-MVA immunization leads to the induction of T cell responses common to both alleles, as well as functional antibody responses that are effective against both of the encoded strains of P. falciparum in vitro.

Affiliation: The Jenner Institute, University of Oxford, Oxford, Oxfordshire, United Kingdom. sumi.biswas@ndm.ox.ac.uk

Abstract: Apical membrane antigen 1 (AMA1) is a leading candidate vaccine antigen against blood-stage malaria, although to date numerous clinical trials using mainly protein-in-adjuvant vaccines have shown limited success. Here we describe the pre-clinical development and optimization of recombinant human and simian adenoviral (AdHu5 and ChAd63) and orthopoxviral (MVA) vectors encoding transgene inserts for Plasmodium falciparum AMA1 (PfAMA1).AdHu5-MVA prime-boost vaccination in mice and rabbits using these vectors encoding the 3D7 allele of PfAMA1 induced cellular immune responses as well as high-titer antibodies that showed growth inhibitory activity (GIA) against the homologous but not heterologous parasite strains. In an effort to overcome the issues of PfAMA1 antigenic polymorphism and pre-existing immunity to AdHu5, a simian adenoviral (ChAd63) vector and MVA encoding two alleles of PfAMA1 were developed. This antigen, composed of the 3D7 and FVO alleles of PfAMA1 fused in tandem and with expression driven by a single promoter, was optimized for antigen secretion and transmembrane expression. These bi-allelic PfAMA1 vaccines, when administered to mice and rabbits, demonstrated comparable immunogenicity to the mono-allelic vaccines and purified serum IgG now showed GIA against the two divergent strains of P. falciparum encoded in the vaccine. CD8(+) and CD4(+) T cell responses against epitopes that were both common and unique to the two alleles of PfAMA1 were also measured in mice.Optimized transgene inserts encoding two divergent alleles of the same antigen can be successfully inserted into adeno- and pox-viral vaccine vectors. Adenovirus-MVA immunization leads to the induction of T cell responses common to both alleles, as well as functional antibody responses that are effective against both of the encoded strains of P. falciparum in vitro. These data support the further clinical development of these vaccine candidates in Phase I/IIa clinical trials.