HIV presents a challenge to vaccine design because it is always changing. If doctors vaccinate people against one variety of virus, will the antibodies they produce stop the virus that they later encounter?
A recently published report on an experimental HIV vaccineâ€™s limited effectiveness in human volunteers illustrates this ongoing puzzle in the HIV vaccine field.
Paul Spearman, now chief research officer for Childrenâ€™s Healthcare of Atlanta and vice chair for research for Emoryâ€™s Department of Pediatrics, began overseeing the study when he was at Vanderbilt. The report is in the April 15 issue of the Journal of Infectious Diseases.
The vaccine was designed to elicit both antibody and T cell responses against HIV and in particular, to generate broadly neutralizing antibodies. Unfortunately, it didnâ€™t work. Volunteers who received the vaccine made antibodies that could neutralize the virus in the vaccine, but not related viruses thought to be like what participants in a larger study might encounter.
â€œHigh levels of neutralizing antibodies can be raised against HIV, while at the same time, breadth of neutralization has never yet been achieved in a vaccine,â€ Spearman says. â€œThe essential problem is that the antibodies raised have a narrow specificity, while the virus is extremely variable. In contrast, about 20% of HIV-infected individuals will demonstrate neutralization breadth.â€
Last year, scientists demonstrated a method for identifying these broadly neutralizing antibodies in HIV-infected individuals. However, having a vaccine hit that target reliably is still elusive.
Spearman reports that he is in charge of a new trial that will be boosting the same individuals that participated in the previous trial with HIV protein from a clade C virus, starting later this year. Clade C is the predominant HIV subtype in southern Africa, while clade B, used in the published trial, is the predominant subtype in North America and Western Europe.