Fig. 5: PfCSP mRNA-LNP induced responses in mice and protection against sporozoite challenge after four immunizations.

Mice (N = 5 per group) immunized with 3 μg, 10 μg, 30 μg PfCSP mRNA-LNPs, or co-immunized with 10 μg of both Pfs25 and PfCSP mRNA-LNPs (as per Fig. 1a) were challenged with PbPfCSP-GFPLuc sporozoites and progression of infection was monitored by microscope examination of giemsa-stained blood smears for 11 days following challenge. Pfs25 immunized mice were used as negative controls. a Kaplan–Meier survival curves represent the percent of mice without detectable parasitemia following sporozoite challenge. Mice were considered completely protected if no parasitemia was detected by day 11. Statistical analysis was performed using log rank (Mantel-Cox) test (*p < 0.05; **p < 0.01). Antibodies from sera, collected one-week prior to the second challenge, bleed B4 in Fig. 1a, were characterized for antibody isotype (b) by ELISA using IgG1, IgG2a, IgG2b and IgG3 specific secondary antibodies. The optical densities (OD) of each isotype were normalized to the OD of total anti-mouse IgG. c Avidity was characterized by antibody-antigen dissociation curves resulting from treatment with different concentrations of NaSCN from sera collected from the Bleeds, B3 and B4, in Fig. 1a. The avidity index was calculated as the concentration (M) of NaSCN that resulted in 50% dissociation of bound antibodies.