The production of certain antibodies could explain the partial success of an HIV-vaccine trial and the failure of another.

In 2009, researchers reported that an experimental HIV vaccine had reduced infection risk by 31%, the only HIV vaccine ever shown to be effective. Two teams have now compared the immune responses of people in that trial, known as RV144, with those of participants in a different trial, VAX003, in which a vaccine did not prevent infection. Georgia Tomaras at Duke University in Durham, North Carolina, and her colleagues found that volunteers in the RV144 trial produced a greater response, in terms of IgG3 antibodies, which recognize a portion of HIV's outer shell, than people in the unsuccessful trial.

Another team, led by Galit Alter at Massachusetts General Hospital, Boston, also found that the differences between the two vaccines may be explained by higher levels of IgG3, and by another antibody called IgG1, in the successful trial. These antibodies might have spurred other immune cells to vanquish cells infected with HIV, both teams conclude.

Sci. Transl. Med. 6, 228ra38; 228ra39 (2014)