3a).
For all constructs, the vector induced T cell responses decreased with time following immunization. Similar results were seen by intracellular cytokine staining assays (data not presented). Responses were primarily mediated by CD8+ T cells, not CD4+ T cells (data not presented). Serum IgG antibody titers induced by immunization with the various AMA1 adenovectors were measured by ELISA and compared against antibodies produced to a recombinant Pichia pastoris produced glycosylated AMA1 protein (residues 25–546) [40] as a reference standard ( Fig. 3b). Antibody Selleckchem GS 1101 responses were observed 2 weeks following the first adenovector administration for all cell surface associated forms of AMA1, and these responses were effectively boosted by a second administration of adenovector. The adenovector that expressed an intracellular form of AMA1, AMA1-IC, did not induce AMA1-specific serum antibody responses. Adenovector-induced antibody responses were also evaluated in rabbits. Two immunizations of adenovector were administered at an 8-week interval and AMA1-specific serum antibodies were measured 4 weeks after the second dose. AMA1-IC was not included in this analysis as it was a poor inducer of antibody responses
in the murine studies. The results with rabbit sera were similar to those from the murine studies. Specifically, the native glycosylated AMA1 and both glycosylation mutants GM1 and GM2 MDV3100 induced comparable levels of
AMA1-specific serum antibody, with the highest responses induced by adenovectors that expressed native AMA1 and the AMA1-GM2 antigens (Fig. 3c). Since ELISA assays do not provide information on the biological function of antibodies, the ability of the adenovectors to induce functional antibodies capable of inhibiting the invasion of erythrocytes by blood stage forms of P. falciparum was evaluated, using a standardized and highly reproducible parasite GIA [41]. Initially, GIA was performed Adenylyl cyclase using a final concentration of 2.5 mg/ml of purified IgG from immunized rabbits. This concentration of IgG is approximately one-quarter of that in human blood. Previous results from other experiments in rabbits, also performed at the GIA Reference Center utilizing the same assay and standardized operating procedures, yielded approximately 90% inhibition of parasite growth following immunization with recombinant AMA1 protein (80 mg) formulated in alum +CpG or ISA720. Very high titers of functional antibodies were induced in rabbits by the adenovectors expressing AMA1. Greater than 99% inhibition was achieved following vaccination with AdAMA1 in this standard assay. The native and GM2 versions of AMA1 induced equally high levels of functional antibodies ( Fig. 4a) and total antibody by ELISA ( Fig. 4b).