Science Spotlight: A late-acting antimalarial turns infection into vaccination 

A chemovaccination strategy published in Science by Merck & Co. Inc. (NYSE:MRK), in collaboration with a team led by Justin Boddey at the Walter and Eliza Hall Institute of Medical Research, combines low-dose malarial infection with a compound that kills the parasite in its antigenically diverse late liver stage, thus generating durable, sterilizing immunity in hosts.

The authors used dual inhibitors of the parasite proteases plasmepsin IX and X — enzymes that are required for a parasite to mature, burst out of liver cells and invade red blood cells, but not for the earlier steps of liver-stage growth — to turn pathogenic sporozoites into chemo-attenuated liver merozoites (CALM). The sporozoites were allowed to replicate fully inside liver cells, maximizing the antigens they produced, but were blocked from progressing to the blood stage of infection that causes disease...