A study by researchers at the Howard Hughes Medical Institute published in the March 20 issue of the journal Nature shows that HIV's ability to evade antibodies that target the virus is due to its ability to constantly alter the arrangement of molecules on its outer coat. The researchers discovered that the large sugar molecules on the virus's outer envelope are in a nearly constant state of rearrangement, effectively blocking sites that the antibodies would attach to. Lead researcher George Shaw called the changing protein coat a "glycan shield" and said his research team was "surprised at the rapidity and extent to which the replicating virus population in infected patients escaped antibody recognition." Shaw said he hopes the discovery will be useful for researchers attempting to craft HIV vaccines that produce an antibody response to the virus. "The trick will be to understand these [defense] mechanisms more fully and to find the Achilles' heel," he said. "We are not there yet."