The failure of Merck's HIV vaccine caused havoc in the field as the NIH pulled back and tried to find out what went wrong. Now French researchers led by Eric Kremer of the University of Montpellier in France believe they can explain why the crucial Merck HIV vaccine trial had to be stopped last fall after it raised the risk of HIV infection. Injecting an adenovirus 5-based vaccine into people with adenovirus 5 antibodies evidently activated T cells, which are targeted for infection by HIV. And that response--in which the immune system became more receptive to the virus rather than attacking it--created a "target-rich environment favoring successful HIV transmission."
"I think that it outlines a very interesting hypothesis that might explain some of the STEP data," says Larry Corey, leader of the HIV Vaccine Trials Network, which conducted the STEP trial. But he cautions, "One should recognize that the data presented are still largely in vitro and that further experiments to define whether this occurred among vaccines in STEP need to be done."
"They're building on a series of reasonable hypotheses, but there are lots of alternative ways this could be happening," says Jeffrey Ravetch of the Rockefeller University in New York.