Fig. 4

Assessment of sterile protection in Pf rCSP-CAF09-immunized mice against sporozoite infection. a Mice immunized three times with Pf rCSP-CAF09 were challenged with P.b.-P.f. CSP-FL CD8CT chimeric sporozoites delivered by five infectious mosquito bites. Four days after challenge, daily blood smears were taken and analyzed under a microscope until day 14. b Nine out of ten mice (90%) developed sterile immunity when challenged 2 weeks after the last immunization (n = 10). c Five weeks later, the nine mice that were sterilely protected in b were challenged again, with none of the animals developing blood-stage parasitemia. Kaplan–Meier plots show the time to detection of parasites in the blood for each group after the challenge (n = 10 for Naïve group). Data were analyzed for statistical significance using Log-rank (Mantel-Cox) test **P < 0.01; ****P < 0.0001. d Antibody titers against different regions of CSP were evaluated in mice immunized three times with Pf rCSP-CAF09 before and after sporozoite challenge (Test bleed 1 and Test bleed 2, respectively). IgG levels against the N-terminal region, repeat region and C-terminal region of CSP did not change significantly in sterilely protected mice during the 5-week interval. Titers are reported as the corresponding sera dilution at which OD405 was 1.0 and compared for significance using a paired Student’s t-test; n = 9. Abbreviations: ns, not significant; Pf rCSP-CAF09, P. falciparum recombinant circumsporozoite protein in adjuvant CAF09; OD, optical density