Earlier analyses of the results of that trial, known as RV144, suggested that antibodies to sites within a part of the HIV envelope called V1V2 correlated with reduced risk of HIV infection. These antibodies belong to a class called immunoglobulin G, or IgG.
The new studies by two independent laboratories both found that only one subclass of V1V2-directed IgG antibodies—the IgG3 subclass—is associated with antiviral responses linked to the reduced risk of HIV infection seen in RV144. The experiments were led by Georgia D. Tomaras, PhD, of the Duke Human Vaccine Institute, and Galit Alter, PhD, of the Ragon Institute, with funding in part from the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health.
In the study led by Tomaras, scientists found that V1V2-specific IgG3 antibodies correlated with a decreased risk of infection in RV144 vaccinees and were linked to HIV-eliminating activity. The researchers also discovered that the level of V1V2-specific IgG3 antibodies in vaccinees' blood waned rapidly, as did the efficacy of the investigational vaccines tested in the RV144 trial (from 60% efficacy at 12 months post-vaccination to 31.2% efficacy at 42 months).
The study led by Dr. Alter demonstrated that RV144 vaccination induced antibodies able to direct multiple, coordinated HIV-eliminating activities, and that these activities were conducted primarily by V1V2-specific IgG3 antibodies.
The finding has been published in the journal Science Translational Medicine.