Polymer nanoparticles in malaria: a dual role in targeted drug delivery and in vaccination approaches

Most malaria vaccination strategies rely on antigens present in laboratory-maintained parasite strains. Because of the high clonal variability that Plasmodium exhibits in the wild, when these vaccines reach their clinical application after over a decade of product development and clinical trials, the original antigens might have disappeared from the parasites circulating in the human population. In addition, in each person are found several pathogen strains in a typical malaria infection in high transmission endemic areas, which will dramatically reduce the efficacy of prophylaxis based on only a predetermined set of antigens. These could be some of the reasons why current malaria vaccines in clinical assays do not offer prospects of complete protection. Experimental evidence presented here and elsewhere has shown that malaria parasites are targeted by different sulfated polysaccharides and polyamidoamines, which in turn bind plasmodia from widely diverging malarias. The antiparasitic mechanism of these natural and synthetic polymers operates through inhibition of Plasmodium invasion of red blood cells. The failure of egressed parasites to quickly invade a new host cell will expose the pathogen to the immune system for a longer time, representing a new vaccination concept that requires the existence of an active malaria infection at the time of administration. This strategy is not a classical vaccine because it is not administered before contact with the pathogen, but the resulting prophylactic effect would provide protection against all the Plasmodium strains infecting the patient at the moment of treatment.