Is an AIDS Vaccine Possible?

• Author: Esparza, Jose
• Position: Brief Article

In the early eighties, when human immunodeficiency virus (HIV) was established as the cause of acquired immune deficiency syndrome (AIDS), there was considerable expectation that a vaccine would soon be developed. However, the scientific community quickly found out that it was confronting an unusually difficult adversary. Although much has been learned about HIV and AIDS, the quest for an effective HIV vaccine is being challenged by a couple of scientific stumbling blocks: we still need to identify the best ways of utilizing vaccines to teach the immune system to fight HIV and AIDS, and at the same time explore ways of addressing the extreme genetic variability of the virus.

People infected with HIV develop antibodies and other immune responses against the virus, but these are not sufficient to eliminate the infection or prevent progression to disease. Consequently, an HIV vaccine will have to "improve on nature", perhaps inducing protective immune responses that would otherwise not take place in someone infected with HIV. The genetic variability of the virus has resulted in different "sub-types" (known by the letters A to J) that are geographically distinct. For instance, sub-type B viruses are commonly found in the Americas and Western Europe, while C and A are more prevalent in Africa. Presently, we do not have sufficient information to know whether a vaccine based on North American viruses would work in Africa, or whether we need to develop a separate vaccine for each HIV sub-type. Despite these inherent challenges, there are several reasons for optimism. Different types of experimental vaccines have been shown to partially protect monkeys and chimpanzees against challenges w ith pathogenic viruses, although we still do not know how relevant these animal experiments are in terms of vaccine-induced protection in humans. This question can only be answered following vaccine trials conducted in healthy human volunteers.

The first such HIV-vaccine trial was conducted in 1987 in the United States. Since then, over 30 prospective vaccines have been tested in human volunteers in small-scale trials (Phase I/II trials). Over 6,000 volunteers have lent their participation to these efforts--most of these have been conducted in the United States and Europe, and the rest in Brazil, China, Cuba, Thailand and Uganda. Phase I/II trials have shown that candidate vaccines are safe and that at least some of them induce immune responses that could protect...