Extended protection capabilities of an immature dendritic-cell targeting malaria sporozoite vaccine

Mouse studies evaluating candidate malaria vaccines have typically examined protective efficacy over the relatively short time frames of several weeks after the final of multiple immunizations. The current study examines the protective ability in a mouse model system of a novel protein vaccine construct in which the adjuvant polyinosinic polycytidilic acid (poly(I:C)) is used in combination with a vaccine in which the immature dendritic cell targeting chemokine, macrophage inflammatory protein 3 alpha (MIP3α), is fused to the circumsporozoite protein (CSP) of Plasmodium falciparum (P. falciparum). Two vaccinations, three weeks apart, elicited extraordinarily high, MIP3α-dependent antibody responses. MIP3α was able to target the vaccine to the CCR6 receptor found predominantly on immature dendritic cells and significantly enhanced the cellular influx at the vaccination site. At three and 23 weeks after the final of two immunizations, mice were challenged by intravenous injection of 5 × 10³ transgenic Plasmodium berghei sporozoites expressing P. falciparum CSP, a challenge dose approximately one order of magnitude greater than that which is encountered after mosquito bite in the clinical setting. A ninety-seven percent reduction in liver sporozoite load was observed at both time points, 23 weeks being the last time point tested.