Fig. 4: PfCyRPA virosomes elicited polyclonal IgG antibodies with in vitro and in vivo parasite growth-inhibitory activity.

a Synchronised P. falciparum 3D7 blood-stage parasites were cultivated in vitro for 48 h in the presence of different concentrations of purified total serum IgG antibodies from individual rabbits that received two (orange symbols) or three (blue symbols) doses of PfCyRPA virosomes. Purified IgG antibodies from non-immune rabbit sera were used as negative controls. Two independent experiments yielded comparable results; representative data of a single assay performed in triplicate is shown as mean ± standard deviation. b In vitro [³H]-hypoxanthine incorporation assay to calculate the IC₅₀ values for total IgG from individual rabbits that received three doses of PfCyRPA virosomes. Two independent experiments yielded comparable results; data shown as mean of duplicate wells of a single assay is representative for the two independent assays. c Passive immunisations of P. falciparum infected NSG mice. Humanised NSG mice received either two different doses of purified total serum IgG antibodies formulated in PBS from individual rabbits that received three doses of PfCyRPA virosomes, purified IgG antibodies from non-immune rabbit sera, growth-inhibitory anti-PfCyRPA mAb c12 or PBS. Mice were infected with P. falciparum and parasitaemia in peripheral blood was monitored by flow cytometry. d Percent parasite growth inhibition six days after infection was calculated against the parasitemia of PBS control mice. Shown are mean values ± standard deviation of two mice per group. The observed parasite growth-inhibitory activities of the anti-PfCyRPA antibodies were confirmed in an independent passive immunoprotection experiment.