One of the most important factors behind resistance evolution in malaria is the failure to deliver sufficiently high
amounts of drugs to early stages of Plasmodium-infected red blood cells (pRBCs). Despite having been considered
for decades as a promising approach, the delivery of antimalarials encapsulated in immunoliposomes targeted to
pRBCs has not progressed towards clinical applications, whereas in vitro assays rarely reach drug efficacy improvements
above 10-fold. Here we show that encapsulation efficiencies reaching N96% are achieved for the
weak basic drugs chloroquine (CQ) and primaquine using the pH gradient loading method in liposomes containing
neutral saturated phospholipids. Targeting antibodies are best conjugated through their primary amino
groups, adjusting chemical crosslinker concentration to retain significant antigen recognition. Antigens from
non-parasitized RBCs have also been considered as targets for the delivery to the cell of drugs not affecting the
erythrocytic metabolism. Using this strategy, we have achieved unprecedented complete nanocarrier targeting
to early intraerythrocytic stages of the malaria parasite for which there is a lack of specific extracellular molecular
tags. Immunoliposomes studded with monoclonal antibodies raised against the erythrocyte surface protein
glycophorin A were capable of targeting 100% RBCs and pRBCs at the low concentration of 0.5 μM total lipid in
the culture, with N95% of added liposomes retained on cell surfaces. When exposed for only 15 min to Plasmodium
falciparum in vitro cultures of early stages, free CQ had no significant effect on the viability of the parasite up to
200 nM, whereas immunoliposomal 50 nM CQ completely arrested its growth. In vivo assays in mice showed
that immunoliposomes cleared the pathogen below detectable levels at a CQ dose of 0.5 mg/kg, whereas free CQ administered
at 1.75 mg/kg was, at most, 40-fold less efficient. Our data suggest that this significant improvement is in
part due to a prophylactic effect of CQ found by the pathogen in its host cell right at the very moment of invasion.