Complete attenuation of Plasmodium falciparum sporozoites by atovaquone–proguanil

To develop a Plasmodium falciparum (Pf) vaccine that precludes replication inside the host for improved vaccine safety, we tested chemo-attenuation (CVac) of sporozoites (SPZ) with atovaquone-proguanil (AP). In mice, P. berghei sporozoites administered with AP invaded hepatocytes, arrested early, and induced robust protection, which correlated with parasite-specific effector-memory CD8+ T cell responses. In a clinical trial of PfSPZ-CVac (AP), in which three doses of 5.12 × 10⁴ or 1.5 × 10⁵ PfSPZ were administered by direct venous inoculation combined with oral single-dose AP (1000/400 mg), blood stage infections were fully prevented during immunisation. 2/8 and 2/10 of vaccinees, respectively, were protected when challenged with 3.2 × 10³ PfSPZ 10 weeks later, inferior to PfSPZ-CVac (chloroquine/CQ) that allows in-host replication. Comparative analysis of responses to 228 Pf proteins revealed that protection with PfSPZ-CVac (CQ) was associated with antibodies to two liver-stage antigens (LISP2, LSA1) and a multi-stage antigen (PfMSP5), but not to the major surface protein PfCSP. The complete arrest of high numbers of Pf sporozoites by single-dose AP should allow a significant dose-frequency reduction of the current daily AP malaria chemoprophylaxis regimen.