Important note: Information in this article was accurate in February 1999. The state of the art may have changed since the publication date.AIDSWEEKLY Plus; Monday, February 15, 1999
Daniel J. DeNoon, Senior Editor
The most difficult problem facing AIDS vaccine researchers is that they don't know what protective immunity to HIV looks like. Studies of highly exposed, uninfected individuals and of people who remain healthy despite long-standing HIV infection indicate that cell- mediated - and not antibody-mediated- immune responses are desirable.
Now a monkey study shows that antibodies can indeed protect against HIV infection and disease.
"An HIV vaccine that induces neutralizing antibodies should have a protective effect against HIV infection and disease," said Walter Reed Army Institute researcher J. Mascola.
Mascola discussed the study in a presentation to the 6th Conference on Retroviruses and Opportunistic Infections, held January 31-February 4, 1999, in Chicago, Illinois.
The study used the SHIV/macaque model of HIV infection. SHIV is a hybrid virus that has the HIV envelope (and external antigens) and the SIV core. The SHIV[89.6PD] strain is highly pathogenic.
In order to examine the role of antibodies in protection against HIV, Mascola and colleagues used passively transferred macaques with HIV hyperimmune serum (HIVIG) and/or the HIV neutralizing monoclonal antibodies (MAbs) F5 and 2G12.
Three of six animals that received all three types of neutralizing antibodies were protected against intravenous challenge infection with SHIV[89.6PD]. The three animals that became infected did not develop disease.
Animals treated with single or double antibody preparations all became infected. Some treated with double antibody transfers had transient protection against disease.
"Sterile protection can be attained, but it requires very high levels of potent neutralizing antibodies," Mascola said. "It may be difficult for a neutralizing-antibody vaccine to induce a potent enough effect to protect against infection. But it may be possible to induce enough neutralizing antibody to protect against disease."
The researchers, who are developing HIV vaccines in collaboration with NABI, Boca Raton, Florida, next plan to see whether passively transferred antibody can protect against vaginal infection with SHIV.
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