The current objective of most HIV vaccines, the absence of any infection of a human by the AIDS virus, is at the present time not possible according to a pioneer HIV/AIDS researcher at the University of California, San Francisco.
In an opinion piece published in January 20th issue of The Lancet, Jay Levy, MD, UCSF professor of medicine and one of the first to discover HIV, further asserts that an HIV vaccine with a more limited aim can be developed and could play a decisive role in preventing and controlling HIV disease. The title of his article is "What Can Be Achieved with an HIV Vaccine."
Levy, the director of the Laboratory for Tumor and AIDS Virus Research at UCSF, explains why sterilizing immunity--the absence of any infection of a human host cell by a virus--will not be achievable in the near future. He points to the fact that virtually no vaccine has ever succeeded in giving complete protection from a virus. Re-infection occurs in a person who has been immunized, but the infection is eliminated both by the individual's immune response and the self-limiting nature of most of the viruses for which we have a vaccine. Additionally, these viruses kill the cells they infect; they do not set up a reservoir in the host.
HIV is a different kind of virus. When HIV infects a cell, it is able to incorporate its genetic material into the cell without necessarily killing it. Unlike other viruses for which there is a vaccine, these HIV infected cells then become a persistent reservoir and a source of transmission. Also, since almost all existing antiviral vaccine strategies involve some replication of the target virus, replicating HIV would almost certainly lead to HIV establishing itself in the cells of a vaccinated individual. And presently, once individuals are infected with HIV, they are infected for the rest of their life.
Levy makes the case that a more achievable objective should be set for an HIV vaccine. A vaccine could be developed that prevented the virus from reaching a level of replication that made a person contagious, he says. The goal of this vaccine would be to maintain such low levels of virus in blood and genital fluids that transmission to others is unlikely. Low HIV levels in blood have been shown to correlate with reduced risk of HIV transmission. With HIV transmission reduced, the exponential growth rates of new infections could be halted, and the virus could then become suppressed worldwide, he explains.
In addition, Levy sees a goal of this vaccine being able to stimulate the immune system sufficiently to allow an individual's immune system to maintain control of the virus in the same manner as long-term non-progressors. These people have been infected with HIV for quite some time, some as long as twenty years, without any symptoms and without any treatments. As Levy reported in a study published in 1997, these patients are able to mount an immune system response that succeeds in blocking the replication of HIV.
While Levy believes that sterilizing immunity remains the primary goal of vaccine research, a vaccine that delayed disease development and sustained low levels of virus in blood and genital fluids by blocking replication of HIV would be able to fulfill the primary goal of a preventive vaccine, protecting a population from the massive spread of an infectious agent, and, thus, could end the global epidemic.
Journal
The Lancet